阅读说明：本技术 包括静电夹具的载物台 (Stage comprising an electrostatic clamp ) 是由 J-G·C·范德托恩 J·G·A·胡尹克 H·W·H·赛维特 A·E·库伊克 M·J·C·龙 于 2019-12-16 设计创作，主要内容包括：公开了一种用于保持物体的载物台,该载物台包括：被布置为将物体夹持在载物台上的静电夹具；被布置为中和静电夹具的残余电荷的中和器；被布置为控制中和器的控制单元,其中残余电荷是在没有电压被施加到静电夹具时存在于静电夹具上的静电荷。(An object table for holding an object is disclosed, the object table comprising: an electrostatic clamp arranged to clamp the object on the stage; a neutralizer arranged to neutralize residual charge of the electrostatic chuck; a control unit arranged to control the neutralizer, wherein the residual charge is an electrostatic charge present on the electrostatic clamp when no voltage is applied to the electrostatic clamp.)

1. An object table for holding an object, comprising:

an electrostatic clamp arranged to clamp the object on the stage;

a neutralizer arranged to neutralize residual charge of the electrostatic chuck;

a control unit arranged to control the neutralizer.

2. The object table of claim 1, wherein the control unit is arranged to receive an information signal representing a residual force or the residual charge, wherein the residual force is exerted on the object by the electrostatic clamp during unloading of the object from the electrostatic clamp, wherein the residual charge is an electrostatic charge present on the electrostatic clamp when no voltage is applied to the electrostatic clamp, and wherein the control unit is arranged to control the neutralizer based on the information signal.

3. The object table of claim 2, wherein the information signal comprises at least one of: measurement information, estimation information, and internal signal information.

4. The object table of claim 2, further comprising a measurement unit, wherein the measurement unit comprises a force sensor configured to provide a measurement of the residual force and/or a gap sensor configured to provide a measurement of a gap between the object and the electrostatic clamp.

5. The stage of claim 2, further comprising a further measurement unit, wherein the further measurement unit is configured to determine the information signal indicative of the residual charge of the electrostatic chuck, the one or more electrical characteristics being indicative of the residual charge of the electrostatic chuck, and wherein the further measurement unit is configured to measure one or more voltages of the electrostatic chuck as the one or more electrical characteristics or the further measurement unit is configured to measure one or more currents supplied to the electrostatic chuck as the one or more electrical characteristics.

6. The object table of claim 2, further comprising

A particle beam generator configured to generate a particle beam;

a detector configured to detect the particle beam;

wherein the control unit is configured to control the particle beam generator to impinge the particle beam on a surface of the electrostatic clamp,

wherein the detector is configured to detect a response of the electrostatic clamp, the response being caused by the electrostatic clamp being impacted by the particle beam, and

wherein the control unit is further configured to:

receiving a detector signal from the detector, the detector signal being indicative of the response of the electrostatic clamp, an

Determining the information signal representative of the residual charge on the electrostatic chuck based on the detector signal.

7. The object table of claim 1, wherein the neutralizer comprises a power supply configured to apply a discharge voltage to the electrostatic clamp, and wherein the control unit is arranged to control the discharge voltage to the power supply.

8. The object table of claim 5 or 6, wherein the neutralizer comprises a power supply configured to apply a discharge voltage to the electrostatic clamp, and wherein the control unit is arranged to control the discharge voltage to the power supply based on the information signal representing the residual charge.

9. The object table of claim 1, wherein the neutralizer is an ionizer device arranged to provide an ionized stream of a gas, and wherein the control unit is arranged to control the ionizer device to provide the ionized stream of the gas to the electrostatic clamp.

10. An apparatus comprising the object table of claim 1, wherein the apparatus is one of: particle beam device, electron beam device, scanning electron microscope, electron beam writer, electron beam projection lithography device, electron beam inspection device, electron beam defect verification device, electron beam measurement device, lithography device, and measurement device.

11. A method for unloading an object from an electrostatic chuck, the method comprising:

unloading the object from the electrostatic chuck;

neutralizing a residual charge of the electrostatic chuck before, during, and/or after the unloading step.

12. The method of claim 11, the method comprising:

providing an information signal representing a residual force or the residual charge, wherein the residual force is exerted on the object by the electrostatic clamp during unloading of the object from the electrostatic clamp, wherein the residual charge is present on the electrostatic clamp when no charging voltage is applied to the electrostatic clamp, and wherein the step of neutralizing the residual charge is based on the information signal.

13. The method of claim 11, wherein the information signal comprises at least one of: measurement information, estimation information, and internal signals.

14. The method of claim 11, comprising the step of providing an ionized stream of gas to the electrostatic chuck based on the information signal and/or the step of providing a discharge voltage to the electrostatic chuck based on the information signal.

Technical Field

The present invention relates to an object stage, and more particularly, to an object stage that can be applied to an inspection apparatus such as a particle beam inspection apparatus.

Background

The present invention relates to an object stage, and more particularly, to an object stage that can be applied to an inspection apparatus such as a particle beam inspection apparatus. Such an inspection apparatus may, for example, be used for inspecting an object used in a lithographic process, such as a semiconductor substrate, also referred to as a wafer. Such inspection devices may also be used to inspect patterning devices, also referred to as reticles.

During semiconductor processing, defects may be generated that affect device performance and even lead to device failure. Device yield may thus be affected, resulting in increased cost. In order to control semiconductor process yield, defect monitoring is important. One tool that is useful in defect monitoring is an electron beam inspection system, such as an SEM (scanning electron microscope), that scans a target portion of a sample using one or more electron beams.

The substrate is typically held by a stage during operation of the inspection tool. Inspection tools typically include a substrate positioning apparatus for positioning a stage relative to a particle beam, such as an electron beam, while the substrate is held by the stage, so as to position a target area, i.e. an area to be inspected, on the substrate within the working range of the electron beam. Such a substrate positioning apparatus may, for example, comprise a plurality of actuators and motors to achieve the desired positioning.

The substrate positioning apparatus includes, for example: a stage for supporting a first portion of the substrate, e.g. by the first portion; and a second portion movably supporting the first portion. In this embodiment, the movement of the first part relative to the second part is achieved by placing two linear actuator systems on top of each other. The first actuator system is arranged to provide movement in a first horizontal direction and the second actuator system supported on the first actuator system is arranged to provide movement in a second horizontal direction perpendicular to the first horizontal direction.

The second part supports a short stroke actuator system that allows positioning of the stage supporting the substrate in three degrees of freedom (i.e., vertical and rotation about first and second horizontal directions). Such short stroke positioning systems can level the substrate at the focus of the inspection beam.

The inspection electron beam may be steered in first and second horizontal directions by a deflection unit in the inspection tool. This function can be used to check the fine positioning of the beam relative to the substrate.

To ensure that the object (e.g., substrate) is maintained in a desired position during inspection, the stage is typically configured to exert a clamping force on the object. To achieve this, the stage applied in the inspection apparatus may for example comprise an electrostatic clamp configured to exert a holding or clamping force on the object. Such electrostatic chucks may typically have one or more electrodes embedded in a dielectric material, for example. Furthermore, the stage used in an examination apparatus, such as a particle beam apparatus, may be provided with electrodes (also referred to as high voltage electrodes) configured to generate an appropriate electric field for the particle beam during an object examination. The use of electrostatic clamps to hold an object to be inspected may present problems. In particular, when an electrostatic chuck is used to clamp an object, an electric charge may accumulate on the surface of the chuck, which makes unloading of the clamped object more difficult, i.e., the object tends to stick to the chuck even in the absence of a voltage applied to the chuck.

Furthermore, during the unloading of the object, there is a risk of sparks or discharges being generated to the high voltage electrode or other parts of the object table.

Disclosure of Invention

It is an object of the present invention to provide an object table for an inspection apparatus in which the above problems are at least alleviated. Such an inspection apparatus may, for example, be used for inspecting an object used in a lithographic process, such as a semiconductor substrate, also referred to as a wafer. Such inspection devices may also be used to inspect patterning devices, also referred to as reticles. The inspection apparatus in which the stage according to the invention is applied may also be advantageously applied in process control of a process such as a lithographic process. In such an arrangement, the inspection apparatus may, for example, be used to detect defects on an object (e.g., a substrate) by inspecting the object, or to evaluate process parameters such as illumination settings applied in a lithographic process of the object, applied illumination dose, etc. The determined parameters may then be applied as feedback to adjust the lithographic process.

According to a first aspect of the invention there is provided an object table comprising

-a gripping mechanism for gripping an object;

-a loading/unloading mechanism configured to contact the object to load or unload the object;

an electrical conductor configured to electrically connect the object to a voltage source or to electrical ground to apply a predetermined voltage to the object during at least a part of an unloading sequence of the object,

wherein the electrical conductor is configured to form a low mechanical stiffness connection when the object is held on the stage.

According to a second aspect of the present invention, there is provided an object table for an inspection apparatus, the object table being configured to hold an object such as a substrate and comprising:

-an electrostatic clamp configured to hold an object;

-a measurement unit configured to determine an electrical characteristic of the electrostatic clamp, the electrical characteristic being indicative of a charge state of the electrostatic clamp;

a control unit configured to control a power supply of the electrostatic clamp during unloading of the object based on the determined electrical characteristic.

According to a third aspect of the present invention there is provided an object table for holding an object, the object table comprising:

-an electrostatic clamp arranged to clamp the object on the stage;

-a neutralizer arranged to neutralize residual charge of the electrostatic clamp;

a control unit arranged to control the neutralizer,

wherein the residual charge is an electrostatic charge present on the electrostatic clamp when no voltage is applied to the electrostatic clamp.

According to a fourth aspect of the present invention, there is provided a method for clamping an object to an electrostatic clamp, the method comprising:

i) providing an object on an electrostatic chuck;

ii) increasing the clamping voltage until a clamped state is detected in which the object is clamped on the electrostatic clamp;

iii) determining a first clamping voltage (V)_max) Is a clamping voltage in a clamping state;

iv) providing less than a first clamping voltage (V) to the electrostatic clamp_max) Second clamping voltage (V)_final)。

According to a fifth aspect of the present invention there is provided a method of determining residual charge of a clamping mechanism of a stage, the method comprising:

-impacting a surface of the clamping mechanism with a particle beam;

-detecting a response of the clamping mechanism caused by an impact of the surface, and

-determining a residual charge of the clamping mechanism based on the response.

According to a sixth aspect of the present invention, there is provided a particle beam device comprising:

-a particle beam generator;

-an object table for holding an object, the object table comprising a clamping mechanism for clamping the object to the object table;

-a detector;

-a control unit configured to:

o controlling the particle beam generator to cause the particle beam to impinge on a surface of the clamping mechanism;

-a detector configured to detect a response of the clamping mechanism caused by the clamping mechanism being impacted by the particle beam;

-a control unit further configured to:

o receiving a detector signal from a detector, the detector signal being indicative of a response of the gripper mechanism;

o determining a residual charge on the clamping mechanism based on the detector signal.

According to a seventh aspect of the present invention, there is provided a method of reducing surface charge of a gripping mechanism, the method comprising:

-generating a particle beam configured to have a Secondary Emission Yield (SEY) substantially equal to 1 in a surface of the holding mechanism;

-impacting a surface of the clamping mechanism with a particle beam.

According to an eighth aspect of the present invention, there is provided a particle beam device comprising:

-a particle beam generator;

-an object table for holding an object, the object table comprising a clamping mechanism for clamping the object to the object table;

-a control unit configured to:

controlling a particle beam generator to generate a particle beam configured to have a Secondary Emission Yield (SEY) substantially equal to 1 in a surface of the clamping mechanism;

o controlling the particle beam to impinge on the surface of the clamping mechanism.

According to a ninth aspect of the present invention, there is provided an object table comprising:

-an electrostatic clamp arranged to clamp the object on the stage; and

-a cleaning device;

wherein the cleaning device is arranged to clean the electrostatic clamp.

According to a tenth aspect of the present invention, there is provided an object table comprising:

-an electrostatic clamp arranged to clamp the object on the stage; and

-one or more electrodes arranged to charge an object;

wherein a first set of electrodes of the one or more electrodes is arranged to apply an electrical charge to the object; and a second set of electrodes of the one or more electrodes is arranged to discharge the object.

According to an eleventh aspect of the present invention there is provided an object table for holding an object, the object table comprising:

-an electrostatic clamp arranged to clamp the object on the stage;

-one or more lifting pins arranged to lift the object from the object table; and

-a controller configured to send an actuation signal to the one or more lift pin positioning devices to vibrate at least a portion of the one or more lift pins and/or the object table.

Drawings

The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which:

fig. 1a and 1b are schematic views of an electron beam inspection tool according to an embodiment of the present invention.

Fig. 2 and 3 are schematic diagrams of electron optical systems that can be applied to embodiments of the present invention.

Fig. 4 schematically depicts a possible control architecture of an EBI system according to the present invention.

Figure 5 schematically shows a cross-sectional view of a stage known in the art.

Figure 6 schematically illustrates a cross-sectional view of another stage known in the art.

Fig. 7a and 7b schematically show a first arrangement of electrical conductors that can be applied to the present invention.

Fig. 7c schematically shows another arrangement of electrical conductors that can be applied to the present invention.

Fig. 8 schematically shows a cross-sectional view of a second object table according to the invention.

Fig. 9 schematically shows a second arrangement of electrical conductors that can be applied to the present invention.

Fig. 10 schematically shows a third arrangement of electrical conductors that can be applied to the present invention.

Fig. 11a and 11b schematically show a fourth arrangement of electrical conductors that can be applied to the present invention.

Fig. 12 schematically shows a fifth arrangement of electrical conductors that can be applied to the present invention.

Fig. 13 schematically shows a cross-sectional view of a third object table according to the invention.

Fig. 14 schematically shows a cross-sectional view of a fourth object table according to the invention.

Fig. 15 schematically shows a cross-sectional view of a fifth object table according to the invention.

Fig. 16 schematically shows another embodiment of the object table according to the invention.

Figure 17 schematically presents clamping voltages provided to an electrostatic clamp according to one embodiment of the present invention.

Figure 18 schematically presents clamping voltages provided to an electrostatic clamp according to another embodiment of the present invention.

Figure 19 schematically presents clamping voltages provided to an electrostatic clamp according to yet another embodiment of the invention.

Fig. 20 presents schematically a further embodiment of an object table according to the invention.

Fig. 21 schematically shows a flow chart of a method of determining a residual charge of a clamping mechanism according to the invention.

FIG. 22 schematically shows a particle beam device according to an embodiment of the invention.

Fig. 23 schematically illustrates a flow chart of a method of reducing the surface charge of a clamping mechanism.

FIG. 24 schematically shows a diagram of SEY versus LE.

FIG. 25 schematically shows a particle beam apparatus according to another embodiment of the present invention.

FIG. 26 is a conceptual diagram illustrating an object on a stage according to an embodiment of the ninth aspect of the invention;

fig. 27 is a conceptual diagram showing an object on the stage, a positioning apparatus, and an object unloading device;

fig. 28 is a conceptual diagram illustrating an object on a stage according to an embodiment of the eleventh aspect of the invention.

Fig. 29 is a conceptual diagram illustrating an object on a stage according to an embodiment of the eleventh aspect of the invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and may herein be described in detail. The figures may not be drawn to scale. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.

Detailed Description

Various example embodiments of the present invention will now be described more fully with reference to the accompanying drawings, in which some example embodiments of the invention are shown. In the drawings, the thickness of layers and regions may be exaggerated for clarity.

Detailed illustrative embodiments of the invention are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments of the present invention. This invention may, however, be embodied in many alternate forms and should not be construed as limited to the embodiments set forth herein.

Accordingly, while example embodiments of the invention are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intention to limit example embodiments of the invention to the specific forms disclosed, but on the contrary, example embodiments of the invention are to cover all modifications, equivalents, and alternatives falling within the scope of the invention. Like numbers refer to like elements throughout the description of the figures.

As used herein, the term "sample" generally refers to a wafer or any other sample on which a defect of interest (DOI) may be located. Although the terms "specimen" and "sample" are used interchangeably herein, it should be understood that embodiments described herein with respect to a wafer may be configured and/or used with any other specimen (e.g., reticle, mask, or photomask).

As used herein, the term "wafer" generally refers to a substrate formed of a semiconductor or non-semiconductor material. Examples of such semiconductor or non-semiconductor materials include, but are not limited to, monocrystalline silicon, gallium arsenide, and indium phosphide. Such substrates are typically found and/or processed in a semiconductor manufacturing facility.

The term "crossover" refers to the point at which the electron beam is focused.

The term "virtual source" means that the electron beam emitted from the cathode can be traced back to the "virtual" source.

The inspection tool according to the invention may relate to a charged particle source, in particular an electron beam source which may be applied in an SEM, an electron beam inspection tool or an EBDW. In the art, an electron beam source may also be referred to as an electron gun.

With respect to the figures, it is noted that the figures are not drawn to scale. In particular, the proportions of some of the elements in the figures may be exaggerated strongly to emphasize characteristics of the elements. It should also be noted that the figures are not drawn to the same scale. Elements shown in more than one figure that may be similarly configured have been indicated using the same reference numerals.

In the drawings, the relative sizes of and between each component may be exaggerated for clarity. In the following description of the drawings, the same or similar reference numerals refer to the same or similar components or entities, and only the differences with respect to the individual embodiments are described.

Accordingly, while example embodiments of the invention are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intention to limit example embodiments of the invention to the specific forms disclosed, but on the contrary, example embodiments of the invention are to cover all modifications, equivalents, and alternatives falling within the scope of the invention.

Fig. 1a and 1b schematically depict a top view and a cross-sectional view of an electron beam (e-beam) inspection (EBI) system 100, for example, according to one embodiment of the invention. The illustrated embodiment includes a housing 110, a pair of load ports 120 that serve as an interface to receive objects to be inspected and output objects that have been inspected. The illustrated embodiment also includes an object transport system, referred to as an EFEM device front end module 130, the EFEM 130 configured to process and/or transport objects to and from the load port. In the illustrated embodiment, the EFEM 130 includes a handling robot 140 configured to transport objects between a load port and a load lock 150 of the EBI system 100. The load lock 150 is an interface between atmospheric conditions occurring outside the enclosure 110 and in the EFEM and vacuum conditions occurring in the vacuum chamber 160 of the EBI system 100. In the illustrated embodiment, the vacuum chamber 160 includes an electron optical system 170, the electron optical system 170 being configured to project an electron beam onto an object to be inspected (e.g., a semiconductor substrate or wafer). EBI system 100 further comprises a positioning device 180, positioning device 180 being configured to move object 190 relative to the electron beam generated by electron optical system 170.

In one embodiment, the positioning apparatus may comprise a cascade arrangement of a plurality of positioners, such as an XY stage for positioning the object in a substantially horizontal plane and a Z stage for positioning the object in a vertical direction.

In one embodiment, the positioning device may comprise a combination of a coarse positioner configured to provide a coarse positioning of the object over a relatively large distance and a fine positioner configured to provide a fine positioning of the object over a relatively small distance.

In one embodiment, the positioning apparatus 180 further comprises an object table for holding the object during the inspection process performed by the EBI system 100. In such embodiments, the object 190 may be clamped to the stage by a clamp, such as an electrostatic clamp. Such a fixture may be integrated in the object table.

In one embodiment, the positioning apparatus 180 includes a first positioner for positioning the stage and a second positioner for positioning the first positioner and the stage. Further, the positioning apparatus 180 applied to the electron beam inspection tool 100 may include a heating device configured to generate a heat load in the stage.

Fig. 2 schematically depicts an embodiment of an electron optical system 200 that may be applied to an electron beam inspection tool or system according to the present invention. The electron optical system 200 includes an electron beam source referred to as an electron gun 210 and an imaging system 240.

The electron gun 210 includes an electron source 212, a suppressor 214, an anode 216, a set of apertures 218, and a capacitor 220. The electron source 212 may be a schottky emitter. More specifically, in one embodiment, the electron source 212 includes a ceramic substrate, two electrodes, a tungsten filament, and a tungsten needle. Two electrodes are fixed in parallel to the ceramic substrate, and the other sides of the two electrodes are connected to both ends of the tungsten wire, respectively. The tungsten is slightly bent to form a tip for placing a tungsten needle. Next, ZrO2 was coated on the surface of the tungsten needle, ZrO2 was heated to 1300 ℃ to melt and cover the tungsten needle, but the tip of the tungsten needle was exposed. The melted ZrO2 may lower the work function of tungsten and lower the energy barrier for emitting electrons, thereby effectively emitting the electron beam 202. Then, the electron beam 202 is suppressed by applying negative electricity to the suppressor 214. Therefore, the electron beam having a large divergence angle is suppressed to the primary electron beam 202, thereby improving the brightness of the electron beam 202. The electron beam 202 may be extracted by the positive charge of the anode 216, and the coulomb forcing of the electron beam 202 may then be controlled by using adjustable apertures 218 with different aperture sizes to eliminate unwanted electron beams outside the apertures. To converge the electron beam 202, a condenser 220 is applied to the electron beam 202, which also provides magnification. The condenser 220 shown in fig. 2 may be an electrostatic lens capable of condensing the electron beam 202. Alternatively, the condenser 220 may be a magnetic lens.

The imaging system 240 as shown in fig. 3 includes a blanker 248, a set of apertures 242, a detector 244, four sets of deflectors 250, 252, 254 and 256, a pair of coils 262, a yoke 260, a filter 246 and electrodes 270. The electrode 270 serves to delay and deflect the electron beam 202 and further has an electrostatic lens function due to the combination of the upper pole piece and the specimen 300. Further, the coil 262 and the yoke 260 are configured to the magnetic objective lens.

The electron beam 202 as described above is generated by heating the electron needle and applying an electric field to the anode 216, and therefore, in order to stabilize the electron beam 202, it is necessary to have a long time to heat the electron needle. This is certainly time consuming and inconvenient for the user side. Thus, the blanker 248 is applied to the converging electron beam 202 to temporarily deflect the electron beam 202 away from the sample rather than turning it off.

Deflectors 250 and 256 are used to scan electron beam 202 to a large field of view, and deflectors 252 and 254 are used to scan electron beam 202 to a small field of view. All deflectors 250, 252, 254 and 256 can control the scanning direction of the electron beam 202. Deflectors 250, 252, 254, and 256 may be electrostatic deflectors or magnetic deflectors. The opening of the yoke 260 faces the sample 300 so that the magnetic field is immersed in the sample 300. On the other hand, the electrode 270 is disposed below the opening of the yoke 260, and thus the specimen 300 is not damaged. To correct for chromatic aberrations of the electron beam 202, the retarder 270, the sample 300, and the upper pole piece form a lens to eliminate chromatic aberrations of the electron beam 202.

Furthermore, when the electron beam 202 bombards into the sample 300, secondary electrons will be emitted from the surface of the sample 300. Next, the secondary electrons are directed by the filter 246 to the detector 244.

Fig. 4 schematically depicts a possible control architecture of an EBI system according to the present invention. As shown in fig. 1, the EBI system includes a load lock, a wafer transfer system, a load/lock apparatus, an electro-optical system, and a positioning device, including, for example, a z-stage and an xy-stage. As shown, these various components of the EBI system may be equipped with respective controllers, i.e., a wafer conveyor system controller, a load/lock controller, an electro-optical controller, a detector controller, a stage controller, connected to the wafer conveyor system. These controllers may be communicatively connected to, for example, a system controller computer and an image processing computer, for example, via a communication bus. In the illustrated embodiment, a system controller computer and an image processing computer may be connected to the workstation.

The load port loads the wafer to a wafer transfer system, such as EREM 130, and the wafer transfer system controller controls wafer transfer to transfer the wafer to a load/lock device, such as load lock 150. The load/lock controller controls the loading/locking of the chamber so that an object to be inspected (e.g., a wafer) can be secured to a chuck (e.g., an electrostatic chuck), also referred to as an electronic chuck. Positioning devices (e.g., z-stage and xy-stage) enable the wafer to be moved by a stage controller. In one embodiment, the height of the z-stage may be adjusted, for example, using a piezoelectric element (such as a piezoelectric actuator). The electro-optical controller may control all states of the electro-optical system, and the detector controller may receive an electrical signal from the electro-optical system and convert it into an image signal. The system controller computer sends instructions to the corresponding controller. After receiving the image signal, the image processing computer may process the image signal to identify defects.

As mentioned above, during inspection, the object is held on the stage by a clamp or gripping arrangement. Such a clamp or clamping arrangement may, for example, comprise an electrostatic clamp. Such an electrostatic chuck may, for example, include one or more electrodes configured to generate an electrostatic field that creates an attractive force between an object (e.g., a substrate) and the chuck. Thus, during inspection, the object may be held in a fixed position on the stage while the stage may be displaced relative to the inspection radiation beam.

In general, a process of inspecting an object (such as a substrate) may include the steps of:

in a first step, the object to be examined is brought into the vicinity of the stage. This may be done, for example, using a robot or a carrier. Such a robot or carrier may for example be configured to position an object above the object table, in particular above a supporting/clamping surface of the object table.

In a second step, the object is mounted to the object table, e.g. to a support/clamping surface of the object table. This step can be realized, for example, by a loading/unloading mechanism of the stage. In one embodiment, such a loading/unloading mechanism may include one or more pin-shaped members that may protrude through the object table, support the object and lower the object onto a support surface of the object table.

In a third step, once the object is mounted on the stage, a clamp (e.g., an electrostatic clamp) can be operated to clamp the object to a support surface of the stage.

In a fourth step, an inspection process may be performed, during which the object may be subjected to an inspection beam, such as a particle beam, for example an electron beam, for example. During such inspection, the object table and the held object may be moved relative to the inspection beam, for example by a positioner as described above.

In a fifth step, the object may be released, for example by de-energizing the clamp or clamping arrangement.

In a sixth step, the object may then be removed from the support surface, for example lifted by a load/unload mechanism, to be received by a robot or carrier, which may then remove the inspected substrate from the inspection device.

The inventors have observed that there may be one or more difficulties or problems associated with the above-described processes.

In particular, when a conventional stage is used in the inspection apparatus in the above-described inspection process, the following problems may occur:

the mentioned problem or problems relate in particular to the unloading process of the object after the inspection process has been performed. In particular, it has been observed that when an electrostatic clamp is used to clamp an object, a charge may accumulate on the surface of the electrostatic clamp. Such a build-up of charge may occur gradually, for example during processing of a plurality of objects. As a result of this surface charge, the voltage of the object may increase when the object is lifted from the stage. Such an increase in the object voltage may cause an electrical discharge between the object and the surface of the electrostatic chuck or the surrounding environment, thereby damaging the object, the electrostatic chuck or the surrounding environment, or causing contamination of the space around the object and the electrostatic chuck. This can be a problem, particularly for any vacuum apparatus in which the object and electrostatic chuck are arranged in a vacuum chamber. Before the object is unloaded, the object may be inspected, for example using a particle beam (such as an electron beam). During such an examination, electrodes of the stage (e.g., high voltage electrodes mounted to the stage) may be connected to a voltage source as well as the object itself. When the object needs to be unloaded, the high voltage electrode may for example be grounded and the object is disconnected from the electrode and unloaded by the loading/unloading mechanism, e.g. lifting or lowering the object from the object table. The surface charge remaining on the electrostatic chuck during unloading may also create an attractive force between the object and the electrostatic chuck. The force required by the unloading mechanism to unload the object may increase or even the unloading mechanism may not be able to lift and unload the object.

In known arrangements, the lifting or lowering mechanism of the stage is typically made of an electrically insulating member to ensure that no sparks or electrical discharges occur towards the member during the inspection process. The inventors have observed that an increase in the object voltage that occurs during the unloading of the object may cause an electrical discharge or spark, for example, towards a high voltage electrode that is typically grounded during the unloading process.

An object table that may suffer from the above-mentioned difficulties or problems is schematically illustrated in fig. 5.

Figure 5 schematically shows a cross-sectional view of a stage known in the art. Fig. 5 schematically shows a cross-sectional view of the object table 500, the object table 500 comprising a support member 510. The stage 500 further comprises an electrostatic clamp 530 arranged in a recess of the support member, the electrostatic clamp 530 having a support surface 510.1 for supporting an object 520 (e.g. a semiconductor substrate). Such an electrostatic clamp may be provided with one or more electrodes that may be connected to a voltage source. The object table 500 further comprises an electrode 540, the electrode 540 surrounding a support surface 510.1, the object 520 being mounted to the support surface 510.1 during inspection. In a particle beam inspection apparatus, such electrodes 540 may for example be applied to generate an electric field suitable for inspecting an object. In an electron beam inspection apparatus, the electrodes may be connected to a negative voltage source, for example, during inspection of the object 520. The object table 500 further comprises a loading/unloading mechanism 550, the loading/unloading mechanism 550 comprising a pin-shaped member 550.1. During use, the member 550.1 may be moved in a vertical direction by the actuator 550.2 to enable the object 520 to be lifted from the support surface 510.1 (i.e. to unload the object) or to enable the object 520 to be lowered onto the support surface 510.1 (i.e. to load the object). In the arrangement shown, the actuator 550.2 may be mounted, for example, to a positioning device 560, the positioning device 560 being configured to position the stage 500. Typically, the positioner and actuator 550.2 will be grounded. Since the electrostatic clamp 530 and the electrode 540 may be at relatively high voltages during operation, the pin-shaped member 550.1 is typically made of an electrically insulating material to avoid electrical discharges or sparks. The known stage 500 as schematically shown in fig. 5 may suffer from the above-mentioned problems. This can be illustrated as follows:

during clamping of an object, such as a semiconductor substrate, a gradual accumulation or build-up of charge may occur on the surface of the electrostatic clamp 530. In fig. 5, this accumulated charge (also referred to as surface charge) is represented by the + and-symbols 530.3. In the illustrated arrangement, a surface charge is generated on a surface of the electrostatic clamp 530 facing the bottom surface of the object 520. As a result of this surface charge, a voltage is induced in the object 520 when the object 520 is lifted from the support surface 510.1, i.e. when the object is unloaded. This voltage is caused by the fact that the object is insulated from the electrostatic clamp, i.e. at a floating potential. During unloading, when the object is lifted from the support surface by the insulating pin-shaped member 550.1, a voltage is induced in the object 520 due to the varying capacitance formed by the bottom surface 520.1 of the object 520 and the surface of the electrostatic clamp provided with the surface charge 530.3. As the distance between the two surfaces increases, the capacitance value decreases, resulting in an increase in the voltage on the object 520. This increased voltage on the object may generate a spark 570 from the object 520 to a nearby conductive surface (e.g., to the electrode 540).

To alleviate this sparking problem, it has been proposed to provide an electrical connection between the electrode of the stage and the top or tip of the loading/unloading mechanism. This known arrangement is shown schematically in figure 6.

Figure 6 schematically shows a cross-sectional view of a stage known in the art. Fig. 6 schematically illustrates a cross-sectional view of an object table 600, similar to the object table 500 of fig. 5, the object table 600 including a support member 510 and an electrostatic clamp 530 providing a support surface 510.1 for supporting an object 520 (e.g., a semiconductor substrate). In the illustrated arrangement, the electrostatic clamp 530 is disposed in a recess of the support member 510. In the arrangement shown, the electrostatic clamp is provided with one or more clamping electrodes 530.1, which may be connected to a voltage source (not shown). In the arrangement shown, the object table 600 further comprises an electrode 540 arranged adjacent to the support surface 510.1. During use, the electrode 540 may for example be connected to a voltage source 542, for example a negative voltage source. In the arrangement shown, the voltage source 542 is schematically represented by an output terminal 542.1 via which a suitable voltage may be applied to the electrode 540 via the output terminal 542.1. The electrodes 540 (which may also be referred to as high voltage electrodes 540) may be connected to a suitable voltage during inspection to create a substantially uniform potential around the object 520. The object table 600 further comprises a loading/unloading mechanism 550, the loading/unloading mechanism 550 comprising a pin-shaped member 550.1. During use, the member 550.1 may be moved in a vertical direction, for example by the actuator 550.2, to enable the object 520 to be lifted (i.e., unloaded) from the support surface 510.1 or to enable the object 520 to be lowered (i.e., loaded) onto the support surface 510.1. In the arrangement shown, the actuator 550.2 may be mounted, for example, to a positioning device 560 configured to position the object table 600. In the arrangement shown, the pin-shaped member 550.1 is considered to be made of an electrically insulating material. In the arrangement shown, the stage 600 also includes electrical conductors 580 connecting the top surface of the pin-shaped member 550.1 to the electrodes 540. In particular, in the arrangement shown, the electrical conductor 580 comprises a conductive wire having one end 580.1 electrically connected to the top surface of the pin member 550.1 and the other end 580.2 connected to the electrode 540. By doing so, electrical conductor 580 is held at the same potential as electrode 540. During inspection, pin member 550.1 is in the retracted position such that there is no contact between pin member 550.1 and object 520. When the object needs to be unloaded, the voltage source 542 providing the voltage to the electrode 540 will be off or will output a low voltage, e.g. 0V. In the illustrated embodiment, the same voltage will be applied to the electrical conductor 580. When the object is subsequently unloaded, the pin-shaped member 550.1 will move upwards, causing the top surface of the pin-shaped member 550.1 to contact the bottom surface 520.1 of the object 520. As a result, during unloading, the object 520 will remain at the voltage generated by the voltage source 542 and supplied to the electrode 540, e.g., 0V. By doing so, the risk of sparks being generated, for example, from the object 520 to the electrode 540 may be reduced.

It has been found that the arrangement as schematically shown in fig. 6 suffers from the following disadvantages:

it has been observed that the application of an electrical conductor 580 as schematically shown in fig. 6 may result in the generation of a relatively large electric field in the vicinity of the electrical conductor 580. As a result, undesirable so-called field emission or field electron emission may occur. This risk occurs especially when the voltage applied to the electrode 540 is relatively high. Currently, there is a trend to increase the voltage applied to the electrode 540 during the inspection process to improve the inspection process. Thus, a voltage in the range of-5 kV to-50 kV or higher may be applied. When such a voltage is applied to electrode 540 as shown in fig. 6, application of electrical conductor 580 will result in the field emission described above.

The known arrangement in which the electrical connection 580 is provided between the pin-shaped member 550.1 of the loading/unloading mechanism 550 and the electrode 540 may cause mechanical interference during inspection. As can be seen in fig. 6, the electrical connection 580 results in a permanent mechanical connection between the electrode 540 mounted to the support member 510 and the pin-shaped member 550.1 mounted to the positioning device 560. Such a mechanical short between the positioning device 560 and the support member 510 may result in the transmission of vibrations from the positioning device 560 to the support member 510 supporting the object 520. Such vibration of the support member 510 may adversely affect the inspection process. To accurately locate the object, the positioning device 560 may, for example, comprise a cascaded arrangement of a fine positioning device and a coarse positioning device. The fine positioning device may also be referred to as a short stroke positioning device and the coarse positioning device may also be referred to as a long stroke positioning device. In such embodiments, the support member 510 may be accurately positioned, for example, by a short stroke positioning device (not shown), while the support member 510 along with the short stroke positioning device may be moved over a relatively large distance by the positioning device 560. In such embodiments, 560 may for example refer to a mover of a linear or planar motor, which is configured to move the support member and the short stroke positioning device over a relatively large distance.

It is an object of the present invention to overcome or at least mitigate the above-mentioned disadvantages of the arrangement shown in figure 6.

In particular, according to the first aspect of the present invention, measures are taken to avoid or mitigate the occurrence of field electron emission and/or to avoid or mitigate the transmission of vibration toward a support member that supports an object under inspection.

According to a first aspect of the present invention, there is therefore provided in one embodiment an object table comprising

A clamping mechanism for clamping an object (such as a substrate);

-a loading/unloading mechanism configured to contact a bottom surface of the object to load or unload the object;

-and wherein the object table further comprises an electrical conductor configured to electrically connect the object to a predetermined voltage during at least a part of an unloading sequence of the object.

In one embodiment, the electrical conductor is configured to form a low mechanical stiffness connection when the object is held on the stage. In one embodiment, such a low mechanical stiffness connection may be achieved by appropriately shaping or forming the electrical conductor. With regard to the meaning of "low mechanical stiffness", it may be noted that within the meaning of the present invention, a mechanical stiffness equal to zero is considered as an example of a low mechanical stiffness. In particular, in various embodiments of the present invention, the electrical conductor may be configured to electrically connect the object to a predetermined voltage during at least a portion of an unloading sequence of the object, and may be disconnected, i.e., mechanically disconnected, when the object is held on the stage.

In one embodiment, the electrical conductor may, for example, have a cross-section and the mechanical stiffness of the electrical conductor is lower than the mechanical stiffness of a wire having the same cross-section.

Such an embodiment may be realized, for example, by providing the electrical conductor with a coil-shaped or spiral-shaped portion.

In an embodiment according to the first aspect of the invention, the applied electrical conductor comprises a coil-shaped portion. Examples of such electrical conductors are schematically shown in fig. 7a and 7 b. In the illustrated embodiment, an electrical connector or wire 680 is connected to the electrode 640 during inspection of the object 620. Thus, the wire 680 may be at a relatively high voltage, e.g., negative, during inspection. In the illustrated embodiment, the electrical connector 680 is connected at one end 680.1 to the top of the pin-shaped member 650.1 and at the other end 680.2 to the electrode 640. In the illustrated embodiment, the wires 680 are advantageously arranged in a particular shape to mitigate the electric field generated when the wires are at a higher voltage. In particular, the electrical wire 680 comprises a coil-shaped part 680.3, i.e. a part in which the electrical wire 680 is arranged in a spiral manner. As a result, the maximum electric field generated by the wire when connected to the voltage source is reduced, thereby reducing the risk of so-called field emission or field electron emission. Within the meaning of the present invention, coil-like means having a plurality of windings or turns or being arranged in a spiral manner. It may also be referred to as a spring shape.

As an alternative to using wires as electrical conductors, the use of flexible PCB connectors may also be mentioned. Such a flexible PCB or flex PCB may be described as a sheet of conductive material covered on both sides by insulating layers. In embodiments of the present invention, such a flexible PCB may be easily cut into a coil or spiral shape and used as a flexible conductor.

Fig. 7a and 7b schematically show a possible arrangement of electrical conductors 680 that may be applied to embodiments of the present invention. The electrical conductor 680 may be, for example, a bare, i.e., non-insulated, wire shaped, for example, as shown in fig. 7a and 7 b. A portion of the electrical conductor 680 may also be an electrically insulating or shielded cable arranged between the pin-shaped member 650.1, in particular the top or tip thereof, and the electrode 640 or the flexible PCB. The electrical conductor 680 may also include a first portion comprising a bare, uninsulated wire and a second portion comprising an electrically insulated or shielded electrical cable.

Fig. 7a schematically shows a cross-sectional view of a pin-shaped member 650.1 and an electrical conductor 680 for two different positions of the pin-shaped member. At the top of fig. 7a, the pin 650.1 is in a raised position, contacting the object 620, while at the bottom of fig. 7a, the pin 650.1 is in a retracted position, such that the object 620 is arranged on the object table 610. In the illustrated embodiment, the wires 680 (i.e., the wires forming the electrical conductors 680) are arranged in a spiral fashion around the pin member 650.1 and between the top of the pin member 650.1 and the electrode 640. The electrodes 640 may also be disposed on the stage 610, for example, in a manner similar to the manner in which the electrodes 540 are disposed on the support member 510. By arranging the electric wires 680 in a spiral (i.e., coil-like) manner, the electric field generated around the conductor can be relaxed.

Fig. 7b schematically shows a top view of a possible arrangement of wires 680 between the top 690 of the pin-shaped member and the electrode 640. In the illustrated embodiment, the first portion 680.3 of the wire 680 is arranged in a spiral fashion around the top, and the second portion 680.4 of the wire 680 is arranged in a meandering fashion towards the electrode 640.

In the embodiment shown in fig. 6, 7a and 7b, the electrical conductors 680 are arranged to connect the top surface of the pin-shaped elevation member 650.1 to the electrodes 640 of the object table 600. It will be understood by those skilled in the art that the electrical conductors 680 may also be between the top surface of the pin-shaped lifting member 650.1 and the output of a voltage source (e.g., such as voltage source 542). In such an embodiment, the electrical conductor 680 may include a conductive wire having one end 680.1 connected to the top surface of the pin member 650.1 and another end 680.2 connected to an output terminal (such as output terminal 542.1 of the voltage source 542). By doing so, electrical conductor 680 is held at substantially the same potential as electrode 640.

With regard to this alternative embodiment, it may be noted that the voltage source 542 may be arranged, for example, on the positioner 660. Thus, the electrical conductor 680 will preferably be at least partially a shielded wire or cable extending between the output terminal 542.1 of the voltage source 542 and the pin member 650.1. In such an arrangement, it may be advantageous to have at least one unshielded portion on the electrical connection that has a lower stiffness to mitigate vibration transmission between the positioner 660 and the stage 600.

As an alternative to providing the electrical conductor 680 with a coil-shaped or spiral portion, it is also contemplated to apply a conductive shield in order to mitigate or avoid field electron emission. Such an embodiment is schematically illustrated in fig. 7 c. Fig. 7c schematically shows a cross-sectional view of the pin-shaped member 650.1 and the electrical conductor 680, the pin-shaped member 650.1 being in a raised state, thereby lifting the object 620 above the object table 610. In the illustrated embodiment, one end 780.1 of the wire 780 is disposed to the top of the pin-shaped member 650.1, while the other end 780.2 is disposed to the electrode 640. The electrodes 640 may, for example, be disposed on the stage 610, e.g., in a manner similar to the electrodes 540 disposed on the support member 510. The illustrated embodiment also includes an electrical shield 790 that may, for example, be mounted to the object table 610. In the illustrated embodiment, the electrical shield can be mounted to the stage 610, for example. In the illustrated embodiment, the electrical shield may, for example, have a hemispherical shape and include a first aperture 790.1 that allows the pin-shaped member to protrude and a second aperture 790.2 that allows the wire 780 to pass through. Such an electrical shield 790 may also be capable of mitigating or avoiding field electron emission.

In the illustrated embodiment, wire 780 includes a conductor 780.3 that connects the wire to shield 790, thereby ensuring that the shield is at the same voltage as the wire it shields. Alternatively, the wire 780 may include a first wire connecting the electrode 640 to the shield 790 and a second wire connecting the shield 790 to the pin member 650.1, in particular to the conductive top of the pin member.

Alternatively, the shield may be mechanically connected to the pin-shaped member 650.1 and move with the pin-shaped member. In such embodiments, wire 780 may further include a first wire connecting electrode 640 to shield 790 and a second wire connecting shield 790 to pin member 650.1. Alternatively, the shield may be mechanically connected to the conductive top of the pin-shaped member 650.1. In such embodiments, only electrical wiring between the electrode 640 and the shield 790 is required.

In the embodiment described with reference to fig. 7a and 7b, the application of an electrical conductor having a coil-shaped portion also provides a reduced mechanical stiffness between the pin-shaped member 650.1 and the electrode 640. By arranging at least a portion of the electrical conductor 680 in a spiral or meandering manner, a reduced mechanical stiffness of the conductor may be obtained. As a result, the transmission of vibrations, for example from the pin-shaped member 650.1 to the electrode 640, is reduced. This enables a more accurate inspection process of the object 620.

In one embodiment of the invention, the loading/unloading mechanism comprises one or more lifting members, such as pin-shaped lifters, the contact area of which is configured to contact the object during loading and unloading and which are permanently grounded. In one embodiment, this may be accomplished, for example, by fabricating the lifting member from a conductive material. Alternatively, the conductive wire may be connected between the contact area (e.g., the top surface of the pin-shaped member) and the electrical ground terminal.

It is noted that in such embodiments, to avoid sparking during inspection, it may be desirable to retract the pin-shaped lifting member a greater distance. Depending on the voltage applied to the electrode 640 during inspection, it may be desirable to retract the pin-shaped lift member, for example, a few centimeters below the electrostatic clamp, e.g., 50 mm. In such embodiments, the permanently grounded pin member should be retracted or lowered such that the distance between the pin member and the electrode 640 (i.e., the high voltage electrode of the stage) is large enough to avoid electrical discharge between the pin member and the electrode.

In an alternative embodiment the object table is provided with dedicated pin-shaped members for grounding the object during the unloading or at least part of the unloading sequence of the object. Such an embodiment is schematically illustrated in fig. 8.

In fig. 8, an object table 800 according to an embodiment of the invention is schematically shown, the object table 800 comprising a support member 610 and an electrostatic clamp 630, the electrostatic clamp 630 providing a support surface 610.1 for supporting an object 520 (e.g. a semiconductor substrate). The support member 610 has a support surface 610.1 for supporting an object 620 (e.g., a semiconductor substrate or a reticle). In the illustrated embodiment, the electrostatic clamp 630 is disposed in a recess of the support member 610. The stage also includes an electrode 640 and a loading/unloading mechanism 650. Further details, such as the electrode arrangement of the electrostatic clamp 630 or the voltage source of the electrode 640, are omitted for clarity.

In the illustrated embodiment, the object table 800 further comprises a pin member 810, the pin member 810 being configured to contact the object 620, in particular the bottom surface 620.1 of the object 620. In the illustrated embodiment, the pin member 810 is considered to be made of a conductive material and is permanently grounded. In the illustrated embodiment, the pin member 810 may be moved in the indicated Z direction by an actuator 815. According to the present invention, the permanently grounded pin member 810 may be applied before and/or during the unloading sequence or a portion thereof to ground the object 620 by raising the member 810 to contact the object 620 during the unloading process. As a result of the grounding, no voltage will be induced in the object 620, thereby reducing the risk of the object 620 generating sparks, for example towards the electrodes 640. Also in this embodiment, it is important to ensure that the pin members 810 are configured to retract or lower sufficiently during inspection so that the distance between the pin members 810 and the electrode 640 (i.e., the high voltage electrode of the stage) is large enough to avoid electrical discharge between the pin members and the electrode.

The above-described embodiment in which a pin-shaped member with a permanent ground is applied offers the advantage that there is no wired electrical connection between the pin-shaped member and the high voltage electrode of the object table, which could lead to a transmission of vibrations. It may also be noted that the application of such a dedicated permanent earth pin-shaped member may be relatively simple, since the member only needs to contact the object during unloading. Precise position control of the member is not required to control the position of the object, for example during loading/unloading. In an embodiment of the invention as described above, in which the object table is provided with a high voltage electrode, the discharge towards the high voltage electrode is avoided or mitigated by increasing the distance between the high voltage electrode and the object to be unloaded before the unloading sequence. This may be achieved, for example, by configuring the hv electrode in a retractable manner, e.g. lowered or moved away from the object. In such an embodiment, the high voltage electrode may for example be configured as a retractable high voltage ring, which may for example be lowered before the object is unloaded. Alternatively, the clamping mechanism for holding the object of the stage may be configured to move away from the high voltage electrode prior to the unloading sequence. In such an embodiment, the clamping mechanism holding the object may be elevated relative to the hv electrode. As a result, the distance between the clamping mechanism and the high voltage electrode is increased, thereby reducing the risk of discharge from the object to the high voltage electrode.

In one embodiment, an electrical connector for use with a subject table according to the present invention comprises two members. In such embodiments, the two members of the electrical connector may be configured to form an electrical connection under certain conditions. In particular, two members of the electrical connector may be configured to connect when the loading/unloading mechanism is in a particular position or a particular range. By doing so, it may for example be ensured that no mechanical connection between the two components exists during the inspection process, and that a mechanical connection exists only during at least a part of the unloading sequence. The transmission of vibrations via the electrical connection during the inspection process can thus be avoided. Fig. 9 and 10 schematically show two possible embodiments of such an arrangement. Fig. 9 schematically shows a pin-shaped member 900. the pin-shaped member 900 may be applied to a loading/unloading mechanism as applied to a stage according to the invention. The pin-shaped member 900 is shown in two different positions relative to the support surface 910 and the object 920 may be supported on the support surface 910. The pin-shaped member 900 is schematically shown with an electrically conductive top 900.1. The arrangement shown further comprises an electrical conductor 950, the electrical conductor 950 comprising a first conductor member 950.1, e.g. a flexible, bendable, rod-like electrical conductor, the first conductor member 950.1 being hinged to the top portion 900.1 of the pin-shaped member 900.1. The first conductor member 950.1 is also configured such that the first conductor member 950.1 may pivot or rotate as indicated by arrow 960 when the pin member 900 moves upward. As a result of the pivoting or rotation, the end 950.11 of the first conductor member 950.1 may be brought into contact with the second conductor member 950.2 of the electrical conductor 950. This is schematically shown in the upper part of the right part of fig. 9. In the illustrated arrangement, when the top 900.1 of the pin member 900 contacts the object 920, the end 950.11 contacts the second conductor member 950.2. In the embodiment shown, the second conductor member 950.2 may be connected to electrical ground or ground potential. When the pin-shaped member 900.1 is moved further upwards, as shown in the lower part of the right part of fig. 9, the first conductor member 950.1 may bend while remaining in contact with the second conductor member 950.2. The first conductor member 950.1 may be considered to operate as a cantilever. By a suitable choice of the position of the pivot point 960, it may be arranged that a relatively small displacement of the pin-shaped member 900 results in a relatively large displacement of the end 950.11 of the first conductor member 950.1, thereby ensuring that a sufficiently large gap exists between the end 950.11 and the grounded second conductor member 950.2. Note that instead of the electrical grounding of the second conductor portion or member 950.2, the second conductor member 950.2 may also be connected to an electrode, such as the electrode 640 described above, or to a voltage source 642.

Fig. 10 schematically illustrates an alternative embodiment in which the electrical connectors are configured to provide a connection when the load/unload mechanism is in a particular position or range. In the embodiment shown, the electrical conductor can also be considered to have two components.

In the embodiment shown, the top part 1000.1 of the pin-shaped member 1000 is considered to be electrically conductive, e.g. made of an electrically conductive material or comprising an electrically conductive coating. Such a conductive top may thus be considered as a first conductive member of the electrical conductor. In the illustrated embodiment, the pin member is configured to protrude through the aperture 1010 of the second conductive member 1020 of the electrical connector or connector, wherein when the pin member 1000 protrudes from the aperture 1010, an electrical connection is made between the pin member 1000 and the conductive member 1020, as schematically illustrated, the conductive member 1020 being connected to the electrode 640, which electrode 640 may be connected to a voltage source, for example as described above. The conductive member 1020 may also be directly connected to a voltage source. To ensure electrical contact, the hole may be provided with a plurality of fine conductive elements 1030, e.g. brushes or hair-like wires, the fine conductive elements 1030 may be arranged to at least partially obscure the hole and may be deflected, e.g. as shown in the right part of fig. 10, when the pin-shaped member 1000 protrudes out of the hole 1010. Thus, during at least a portion of the unloading sequence of the object 920 supported on the support surface 910, the object 920 is electrically connected to a predetermined voltage or potential, i.e., the potential applied to the electrodes 640.

In the embodiment shown, the second conductor member 950.2, 1020 is connected directly or indirectly (e.g. by a high voltage electrode) to a potential predefined voltage source. These embodiments thus also ensure that object 920 is connected to the predefined voltage during at least a portion of the unloading sequence of object 920. By so doing, as described above, the voltage of the object can be controlled; an increase in voltage of the object 920, for example due to surface charge of the electrostatic chuck of the stage and reduced capacitance during unloading, may be avoided or mitigated.

In an embodiment of the invention in which the object table comprises a high voltage electrode as described above, the discharge to the high voltage electrode, e.g. during unloading of the object, may be avoided or mitigated by applying an elevated voltage across the high voltage electrode during the above unloading or at least part of the above unloading.

In one embodiment, similar to the embodiment shown in fig. 10, the electrical connections applied are configured in the following manner: this way, during at least part of the unloading sequence of the object, a controlled discharge of any accumulated charge on the object is achieved. By suitable shaping of at least one member of the electrical connector, in particular by shaping it for example as a sharp needle, a controlled electrical discharge can occur between the two conductor members. Such an embodiment is schematically shown in fig. 11a and b.

Fig. 11a may be considered similar to fig. 10, except for the following:

in fig. 11a, the second electrical conductor member 1020 connected to the electrode 640 is provided with one or more needle-shaped electrical conductors 1110 arranged along the circumference of the bore 1010, e.g. pointing inwards. Note that the pin conductor need not block the passage of the pin member 1000 through the bore 1010. When the pin-shaped member 1000 protrudes from the hole 1010, for example to unload the object 920 from the support surface 910, a voltage rise of the object may be prevented, since the electrical connection or connector formed by the conductive top 1000.1 and the second electrical conductor member 1020 provided with the pin-shaped conductor 1110 will discharge 1120 the object during at least a part of the unloading sequence.

Due to the controlled discharge 1120, the voltage of the object will not rise any more during the unloading phase; the risk of sparks or electrical discharges being generated towards the stage (e.g. towards electrodes on the stage) is thus reduced.

It should be understood that alternative arrangements may be devised in which the conductive portions of the pin-shaped member are configured to make electrical connections within a particular range of positions and break connections within another range.

In the illustrated embodiment, the pin conductor 1110 is disposed on the second electrical conductor member 1020. Alternatively, they can also be arranged on the conductive top 1000.1 of the pin-shaped member 1000. In such embodiments, the second electrical conductor member 1020 may be suitably shaped to form an electrical connection over a desired range of positions. Such an embodiment is schematically illustrated in fig. 11 b. In the embodiment shown, the conductive top 1000.1 of the pin-shaped member 1000 is provided with a pin conductor 1110. When the pin-shaped member is raised, as shown on the right side of fig. 11b, the pin-shaped conductor 1110 may interact with the second electrical conductor member 1020 to allow an electrical discharge. It is to be understood that the embodiments of fig. 11a and 11b may also be combined to have a pin conductor 1110 on both the second electrical conductor member 1020 and the conductive top part 1000.1 of the pin-shaped member 1000.

Fig. 12, for example, shows an arrangement in which a first conductor member 1210 of a pin-shaped member 1200 of a loading/unloading mechanism is configured to contact a second conductor member 1220 having a flexible conductive member 1220.1. When the pin-shaped member 1200 is lifted, e.g. to unload the object 920 from the support surface 910, as shown in the right part of fig. 12, the first conductor member 1210 may contact the second conductor member 1220, thereby establishing contact between the object 920 and the predefined voltage, e.g. via a connection with the electrode 640, during at least a part of the unloading sequence of the object 920.

Yet another alternative way of switching the pin-shaped member between the connected state, wherein the top surface of the pin-shaped member is for example connected to ground or to a HV power supply and in the disconnected state, wherein the top surface is for example allowed to adjust its potential, i.e. to have a floating potential, is schematically shown in fig. 13.

In fig. 13, schematically showing an object table 1300 according to an embodiment of the invention, the object table 800 comprises a support member 610 and an electrostatic clamp 630, the electrostatic clamp 630 providing a support surface 610.1 for supporting the object 520 (e.g. a semiconductor substrate or a reticle). In the illustrated embodiment, the electrostatic clamp 630 is disposed in a recess of the support member 610. The stage also includes an electrode 640 and a loading/unloading mechanism 1350 having pin members 1350.1 and 1350.2. Further details, such as the electrode arrangement of the electrostatic clamp 630 or the voltage source of the electrode 640, are omitted for clarity.

In fig. 13, the pin-shaped member 1350.1 may be, for example, a conventional insulating pin-shaped member, for example applied in known loading/unloading arrangements. However, pin member 1350.2 includes a conductive top portion 1350.21, a conductive bottom portion 1350.22 (e.g., configured as a ground), a middle portion 1350.23, the middle portion 1350.23 may be filled with a gas that may be ionized. The intermediate portion 1350.23 may be, for example, a tube having a pair of electrodes for ionizing the gas. In such an arrangement, the conductivity of the pin-shaped members 1350.2 may be controlled; by controlling the voltage supplied to the pair of electrodes, ionized gas may be generated in the intermediate portion 1350.23, thereby making the intermediate portion conductive. By doing so, the top 1350.21 becomes electrically grounded to the bottom 1350.22. In such an embodiment, the pin-shaped members 1350.1 may thus be made electrically conductive when the object is to be loaded or unloaded and may be insulated when the object is to be inspected.

As an alternative to ionizing the gas inside the intermediate portion, one or more pin-shaped members may be configured to receive gas that has been ionized. In such embodiments, rather than ionizing the gas inside the pin members, the conductivity of one or more pin members may be controlled by supplying and exhausting gas to the pin members that has been ionized.

Suitable gases that may be more readily ionized may include, for example, argon or neon.

In the embodiments discussed so far, the object is configured to be connected to a predetermined voltage or voltage source via the loading/unloading mechanism, in particular via the pin-shaped member of the above-mentioned mechanism, during at least a part of the unloading phase. However, alternative arrangements of the electrical connector may also be devised.

As an example, the electrical connection between the object and the predetermined voltage may be achieved by contacting an edge or even an upper surface of the object, e.g. using a movable electrode or an electrical connector. A gripper of a carrier or a transfer robot may be suitable for this. Thus, in an embodiment, the object table according to the invention may be configured, for example, to cooperate with a robotic carrier, for example a robotic carrier comprising end actuator fingers, for example conductive or semi-conductive end actuator fingers, configured to contact an object to be unloaded, for example an edge or a top surface of the object, during at least a part of an unloading sequence of the object. This arrangement also ensures that the object is connected to a predefined voltage or voltage source during at least a portion of the unloading sequence when the end actuator fingers are grounded. As an alternative to applying the end actuator grip to contact the object during at least part of the unloading sequence, the end actuator grip of the robotic carrier may comprise electrodes or contacts, e.g. thin flexible wires, for contacting the object during at least part of the unloading. In one embodiment, during such unloading or during at least a portion of such unloading, the high voltage electrode of the stage may be electrically isolated from the object by a semiconductor end actuator grip interposed between the object and the high voltage electrode.

Alternatively, the flexible conductive contact may be provided during at least a part of the unloading sequence of the object, for example along an edge of the object. Such an embodiment is schematically illustrated in fig. 14. The stage 1400 as schematically shown in fig. 14 comprises a support member 610 and an electrostatic clamp 630, the electrostatic clamp 630 providing a support surface 610.1 for supporting an object 520 (e.g. a semiconductor substrate). The support member 610 has a support surface 610.1 for supporting an object 620 (e.g., a semiconductor substrate or a reticle). In the illustrated embodiment, the electrostatic clamp 630 is disposed in a recess of the support member 610. The stage also includes an electrode 640 and a loading/unloading mechanism 1450 with a pin-shaped member 1450.1. In a preferred embodiment, the loading/unloading mechanism 1450 may, for example, include three pin-shaped members. Further details, such as the electrode arrangement of the electrostatic clamp 630 or the voltage source of the electrode 640, are omitted for clarity. In the illustrated embodiment, object table 1400 further includes a flexible electrical connector or contact 1460 for connecting to an edge or bottom surface of object 620 during at least a portion of an unloading sequence of object 620. As shown, a flexible electrical connector or contact 1460 is connected to the electrode 640, such as by a wire 1460.1. The flexible electrical connector 1460 may, for example, be configured to contact an object in a sliding manner. Alternatively, roller contacts may be provided at the end 1460.2 of the flexible electrical connector 1460, thereby reducing the risk of particle generation. The electrical connector 1460 may be, for example, a leaf spring or leaf spring-like member that may bend downward when the object is loaded and upward during at least a portion of unloading to maintain contact with the object 620.

As an alternative to the arrangement shown in fig. 14, the flexible electrical connector 1460 may be, for example, a spring-type connector mounted below the bottom surface 620.1 of the object (i.e., between the support surface 610.1 and the bottom surface 620.1 of the object). The spring may then be connected to the hv electrode 640 in a manner similar to the connection of the connector 1460 to the electrode.

As an alternative to the electrical connector 1460 shown in fig. 14, the electrical connector applied may comprise an electrically conductive spring or spring-like conductor arranged between the support surface 610.1 and the bottom surface 620.1 of the object to be supported. Such a spring or spring-like conductor may be configured to be compressed when the object 620 is loaded and configured to expand during at least a portion of an unloading sequence of the object to maintain contact with the object 620. It may also be connected to the electrode 640 by a wire.

Another alternative way to provide an electrical connection between the object and a predetermined voltage (e.g., ground potential) is to purge the volume between the object and the electrostatic chuck with an ionized gas. Such a gas may be considered to form an electrical connection between the object and any material in the vicinity (e.g., an electrode surrounding the object, such as the electrode 640 shown above). Within the meaning of the present invention, therefore, an ionized gas can also be considered as an electrical conductor, i.e. a gaseous electrical conductor. It may further be noted that the application of such an ionized flow of gas may also at least partially eliminate or compensate for surface charges generated on the surface of the electrostatic chuck 630.

Thus, in embodiments of the present invention, the volume below the object and/or above the electrostatic chuck is purged with ionized gas, e.g., periodically, to mitigate or avoid the accumulation of surface charges on the surface of the electrostatic chuck 630.

In such embodiments, rather than attempting to mitigate any adverse effects of accumulated surface charge, the surface charge itself is mitigated or removed, for example by grounding the object during unloading.

According to a second aspect of the present invention there is provided an object table configured to hold an object (such as a substrate), the object table comprising:

-an electrostatic chuck configured to hold an object;

-a measurement unit configured to determine an electrical characteristic of the electrostatic clamp, the electrical characteristic being indicative of a charge state of the electrostatic clamp;

-a control unit configured to control a power supply of the electrostatic clamp during unloading of the object based on the determined electrical characteristic.

According to a second aspect of the invention, there is provided an object table capable of controlling a power supply of an electrostatic clamp of the object table prior to and/or during unloading of an object, based on a determined electrical characteristic of the electrostatic clamp, wherein the electrical characteristic is indicative of a state of charge of the electrostatic clamp, in particular a residual charge on the electrostatic clamp when no voltage is applied to the electrostatic clamp.

As described above, with reference to fig. 5, holding an object such as a semiconductor substrate on a stage using an electrostatic chuck may cause surface charges to appear on the surface of the electrostatic chuck. This surface charge creates an attractive force, also referred to as adhesion, between the object and the stage, in particular between the object and an electrostatic clamp of the stage. Those skilled in the art will appreciate that this adhesion must be overcome in order to unload the object from the stage. In other words, unloading the object from the stage would require a force on the object that is at least equal to the adhesion force and that is directed in a direction opposite to the adhesion force. Thus, the greater the adhesion, the greater the unloading force (i.e., the force required to unload the object) is required. Since the unloading force is typically performed using a loading/unloading mechanism comprising one or more pin-shaped members, the unloading force that can be generated may be relatively small. Furthermore, the application of a large unloading force to the object by means of one or more pin-shaped members may damage the object.

In a typical stage, such as described with reference to fig. 5, the electrostatic chuck employed in the stage is not powered during the unloading of the object. However, according to a second aspect of the present invention, it is proposed to control the power supply of the electrostatic clamp, i.e. the power supplied to the electrostatic clamp, during unloading, based on a determined electrical characteristic indicative of the state of charge of the electrostatic clamp. By doing so, as will be explained in more detail below, the charging phase of the electrostatic clamp can be taken into account and appropriate measures can be taken to compensate, counteract, or mitigate the effect of the state of charge on the clamping force (i.e., residual or permanent clamping force).

Alternatively or additionally to controlling the power supply of the electrostatic clamp during unloading, the power supply of the electrostatic clamp may also be controlled during clamping of the object based on the determined electrical characteristic. In particular, in one embodiment of the invention, the charge state of the electrostatic clamp or the effect of the charge state on the clamping force may be taken into account during clamping of the object: by appropriately powering the electrostatic clamp, the effect of the measured or determined state of charge of the electrostatic clamp can be taken into account, thereby ensuring that the required clamping force is obtained. For example, when the charge on the surface of the clamp near the negative pole of the clamp is negative, a smaller clamping voltage is required to produce the same net clamping force. Similarly, a negative charge near the positive clamping electrode will require a larger positive voltage on the positive clamping electrode to achieve the same clamping force, since the surface charge cancels the clamping force there.

According to the second aspect of the present invention, based on the determined electrical characteristic, the power supply to or the power supplied to the electrostatic chuck may be controlled as follows: this way the adhesion force can be at least partly compensated, counteracted or moderated. Furthermore, by doing so, electrical discharges between the object and the stage (e.g., a high voltage electrode on the stage) may also be avoided.

Fig. 15 schematically shows an embodiment of the object table 1500 according to the second aspect of the invention. In fig. 15, an object table 1500 according to an embodiment of the invention is schematically shown, the object table 1500 comprising a support member 610, similar to the object table 600 of fig. 6, the support member 610 having a support surface 610.1 for supporting an object 620 (e.g. a semiconductor substrate). In the embodiment shown, the electrostatic clamp 630 is arranged below the support surface 610.1, for example embedded in the support member 610. In the illustrated embodiment, the stage further includes an electrode 640 and a loading/unloading mechanism 650 as optional features. Further details, such as the electrode arrangement of the electrostatic clamp 630 or the voltage source of the electrode 640, are omitted for clarity. According to a second aspect of the invention, the stage 1500 further comprises a measurement unit 1510, the measurement unit 1510 being configured to determine an electrical characteristic of the electrostatic clamp, represented by dashed line 1510.1, the electrical characteristic being indicative of a charge state of the electrostatic clamp 630. According to a second aspect of the invention, the object table 1500 further comprises a control unit 1520 configured to control a power supply 1530 of the electrostatic clamp 630 based on the determined electrical characteristic during unloading of the object 620. Line 1530.1 represents the electrostatic clamp 630 being powered by a power supply 1530.

The power supply 1530 may power the electrostatic clamp 630, for example, by providing a suitable voltage to one or more electrodes of the electrostatic clamp 630. The power source 1530 may be controlled, for example, by the control unit 1520 of the stage 1500. According to a second aspect of the invention, the control unit 1520 is configured to control the power supply 1530 of the electrostatic chuck 630 during unloading of the object 620 based on the determined electrical characteristic, indicated by arrow 1520.1, which may be provided to the control unit 1520, for example, by means of the input signal 1520.2.

According to a second aspect of the invention, the measurement unit 1510 of the stage 1500 is configured to determine an electrical characteristic indicative of a state of charge of the electrostatic clamp. The charge state of the electrostatic clamp may, for example, indicate a surface charge that has accumulated on the surface of the electrostatic clamp.

In accordance with the present invention, various methods are devised to determine electrical characteristics and control the power supply of the electrostatic chuck based on the determined electrical characteristics.

A first method of determining the electrical characteristics of the electrostatic chuck is to perform measurements during an initial portion of an unloading sequence of the object (e.g., a portion of the unloading sequence that begins while the object is still on the support surface).

In one embodiment, the measurement unit 1510 is configured to determine an electrical characteristic of the electrostatic clamp indicative of the charge state of the clamp by performing a measurement during the initial portion. The measurement may be, for example, a measurement of a characteristic of the electrostatic chuck or a measurement of a characteristic of the object being unloaded.

In the former case, i.e. where a measurement of a characteristic of the electrostatic clamp is performed, the measurement unit 1510 may for example be configured to measure a current from or to one or more electrodes of the clamp as the electrical characteristic. In this case, the power supply 1530 may, for example, be configured to maintain the electrode at a predetermined potential, such as zero volts, during an initial portion of the unloading sequence, i.e., where the power supply provides a voltage of 0V to the electrode.

However, to maintain the voltage at 0V during unloading, current will flow into or out of the electrodes due to the presence of charge on the electrostatic clamp. This can be understood as: when the object is unloaded, i.e. the distance between the object and the holder increases, a voltage is induced in the object (as described above) due to a change in the capacitance formed by the object and the holder and the surface charge on the electrostatic holder. This change in capacitance also affects the electrodes of the electrostatic chuck because, due to the presence of surface charges, the voltage on the electrodes also changes in case it is not applied by the power supply. Thus, to remain at 0V, during the unload sequence, there will be current flow from or to the electrodes when the power supply 1530 of the electrostatic clamp 630 holds the clamp at 0V. Since the current is due to the presence of a surface charge on the chuck, the current can be considered to be indicative of the charge state of the electrostatic chuck or the surface charge on the chuck. After measuring the current as an electrical characteristic representative of the state of charge, the control unit 1520 may then control the power supply 1530 of the electrostatic chuck 630 based on the electrical characteristic. In particular, the control unit 1520 may control the power supply in a manner that is capable of providing a voltage to one or more electrodes that counteracts or mitigates the effects of the state of charge of the electrostatic chuck.

The voltage required to mitigate the effects of the charge state of the electrostatic chuck may be determined, for example, from empirical data (e.g., experimental data), e.g., in combination with simulations.

In another embodiment, the measurement unit may be configured to measure the voltage of one or more electrodes of the chuck as an electrical characteristic of the electrostatic chuck indicative of the charge state of the chuck, e.g., during an unloading sequence or a portion thereof. In such embodiments, the power supply 1530 may be configured to disconnect one or more electrodes of the electrostatic clamp from the power supply, for example, during the unloading sequence or a portion thereof. By doing so, the potential or voltage at one or more electrodes becomes floating or indeterminate. As a result, the potential or voltage of the electrode may change during the unloading sequence or a portion thereof. When there is a surface charge on the electrostatic chuck, the voltage on one or more electrodes does change when the object is unloaded due to the change in capacitance. Thus, in this embodiment, the measurement unit 1510 can be configured to measure a voltage at one or more electrodes of the electrostatic chuck during an unloading sequence of the object as an electrical characteristic representative of a charge state of the electrostatic chuck. Based on the electrical characteristic, the control unit 1520 controlling the power supply 1530 may then control the power supply of the electrostatic chuck 630. In particular, the control unit 1520 may control the power supply 1530 in a manner that is capable of providing a voltage to one or more electrodes that counteracts or mitigates the effects of the state of charge of the electrostatic chuck.

In yet another embodiment, as described above, the measurement unit 1510 is configured to determine an electrical characteristic representative of a state of charge of the electrostatic chuck by performing a measurement on an object other than the electrostatic chuck. As explained above in relation to the first aspect of the invention, when an object is unloaded from an electrostatic chuck having a surface charge, a voltage will be induced in the above voltage (assuming the object is not grounded) due to the surface charge and due to the change in capacitance when the object is removed from the chuck. Thus, in an embodiment, the measurement unit applied in the object table according to the invention may be configured to measure the voltage induced in the object during an initial part of the unloading sequence. Since the induced voltage is directly related to the surface charge or state of charge of the electrostatic chuck 630, it can be used to determine an electrical characteristic of the electrostatic chuck that is indicative of the state of charge of the chuck. Once the electrical characteristic is determined, it may be applied in a manner similar to that described above to control the power supply 1530 that powers the electrostatic clamp 630. In order to measure the voltage induced in the object during the initial part of the unloading sequence, an electrical connector or conductor as described above may for example be applied. In particular, the manner of use can be realized, for example, by measuring the induced voltage in the object by means of a conductive pin-shaped member of the loading/unloading mechanism as a probe. As such, based on the measured voltage induced in the object during the initial portion of the unloading sequence, the control unit may control the power supply that powers the electrostatic clamp in the following manner: this approach enables a voltage to be provided to one or more electrodes that counteracts or mitigates the effects of the state of charge of the electrostatic chuck.

In yet another embodiment, the measurement unit 1510 is configured to determine an electrical characteristic representative of a charge state of the electrostatic clamp by performing a current measurement on the object. If the object is connected to a predetermined potential, such as ground potential, during the unloading sequence, current will flow into or out of the object when the object is unloaded in a manner similar to the manner in which current will flow into or out of the electrodes of the electrostatic chuck when the electrodes are connected to a zero voltage source during unloading. Since this current is directly related to the surface charge or state of charge of the electrostatic chuck 630, it can be used to determine an electrical characteristic of the electrostatic chuck that is indicative of the state of charge of the chuck. Once the electrical characteristics are determined, they may be applied in a manner similar to that described above to control the power supply 1530 that powers the electrostatic clamp 630. In order to measure the current flowing into or out of the object during the initial part of the unloading sequence, an electrical connector or conductor as described above may for example be applied. As mentioned above, such electrical connectors or conductors are configured to remain in contact with the object during at least a portion of the unloading sequence, thereby enabling monitoring/measuring of the voltage of the object. As such, based on the measured voltage induced in the object during the initial portion of the unloading sequence, the control unit may control the power supply that powers the electrostatic clamp in the following manner: this approach enables a voltage to be provided to one or more electrodes that counteracts or mitigates the effects of the state of charge of the electrostatic chuck.

In the embodiments of the object table according to the second aspect of the invention described so far, the object table, in particular the measurement unit and the control unit of the object table, are configured to: when a specific object is to be unloaded,

-determining an electrical characteristic of the electrostatic clamp by performing a measurement during an initial part of the unloading sequence, and

-controlling a power supply to power the electrostatic clamp before and/or during at least a portion of the unloading sequence based on the electrical characteristic.

In the described embodiments, during the unloading sequence, or a portion thereof, the electrical characteristics of the electrostatic clamp are determined based on current or voltage measurements of the electrostatic clamp or object.

Such a determination may be performed, for example, during a portion or portion of an unloading sequence (e.g., an initial portion of an unloading sequence of an object). When the electrical characteristics of the fixture are determined during the initial portion of the unloading, this information can be immediately applied to control the power source that powers the fixture during the next portion of the unloading sequence. In such an embodiment, the control of the power supply during unloading of the object is therefore based on measurements performed during an initial part of the unloading sequence of the object as described above. Such an arrangement may require relatively fast measurement processing and/or relatively fast power control. Another method is described below.

It is important to note that the electrical characteristics of the electrostatic clamp indicative of the state of charge of the electrostatic clamp may be determined in other ways as well. In this regard, it is worth mentioning that the surface charge of the electrostatic chuck does not change rapidly but gradually during the process of processing a plurality of objects. When this is taken into account, it can be appreciated that the electrical characteristics of the electrostatic clamp can be determined at other times than during the initial portion of the unloading sequence of the object. In particular, the electrical characteristic representative of the charge state of the electrostatic clamp may also be determined earlier than during the initial portion of the unloading sequence of the object.

In particular, an electrical characteristic indicative of a charge state of the electrostatic clamp may also be determined during loading of the object. During loading of the object, the object may, for example, be lowered onto an electrostatic chuck, for example by a loading/unloading mechanism as described above, during which a voltage may be induced in the object, or a current may flow from or to the object, depending on whether the object is insulated or grounded. Such induced voltage or generated current may also be used to determine an electrical characteristic of the electrostatic clamp, as it is directly related to or caused by the charge state of the electrostatic clamp. Thus, in one embodiment of the invention, the object table may be configured to:

-determining an electrical characteristic of the electrostatic clamp by performing a measurement during a loading sequence of an object on the electrostatic clamp, an

-controlling a power supply powering the electrostatic clamp before and/or during at least a part of an unloading sequence of the object based on the electrical characteristic.

Alternatively, an electrical characteristic indicative of a charge state of the electrostatic clamp may be determined during loading or unloading of a previous object. In such embodiments, the charge state determined during loading or unloading of the first object is used to control the powering of the electrostatic clamp during at least a portion of an unloading sequence of a second subsequent object. Such an embodiment provides the advantage that more time is available for determining the state of charge and determining the power control required for the electrostatic chuck.

Since it has been observed that the charge state of the electrostatic clamp only changes gradually over time, it is not even necessary to determine the electrical characteristics of the electrostatic clamp for each object to be unloaded. In other words, it is sufficient to determine the electrical characteristic representative of the charge state of the electrostatic clamp once per n (e.g., equal to 5 or 10) objects processed. In one embodiment, the number n may be determined, for example, based on a history of identified charge states or identified charging phases of the electrostatic chuck. For example, a smaller number n may be selected when the identified charge state is larger or the change in charge state in successive measurements is larger. However, N may be as small as 1.

In such embodiments, the electrical characteristics of the electrostatic clamp may thus be determined during loading and/or unloading of a first object, while the determined electrical characteristics are used to control the power supply during unloading of a second object different from the first object. Thus, in one embodiment, the object table according to the second aspect of the invention may be configured to:

-determining an electrical characteristic of the electrostatic clamp while on or respectively under the electrostatic clamp by performing a measurement during a loading and/or unloading sequence of the first object, and

-controlling a power supply powering the electrostatic clamp before and/or during at least a part of an unloading sequence of a second object different from the first object based on the electrical characteristic.

The charge state distribution of the electrostatic chuck may be non-uniform across all or a portion of the chuck surface. That is, the charge state may be unevenly distributed over an area of the clamping surface corresponding to the clamping electrode of the electrostatic clamp. For example, a combination of negative and positive charges, or multiple charges of the same sign but different magnitudes, may be present across the region.

A clamping voltage may be applied to the clamping electrodes to generate a repelling force or neutralize the charge on the clamping surface. For each electrode, the applied voltage may be determined from the net charge of the surface of the fixture. However, in the case of charge distribution, such a single voltage of the clamping electrodes may not be suitable or sufficient. The residual force distribution is not uniform over the entire or parts of the chuck surface, since a single determined voltage may be too low or too high, and for certain parts of the chuck surface a combination of negative and positive surface charges or a plurality of surface charges of equal sign but different magnitude may be present around the chucking electrodes over the entire chuck surface.

In yet another embodiment, the above-mentioned problems can be avoided by arranging the charge distribution to be evenly distributed over the whole or part of the clamp surface. For example, a semiconductive coating may be applied to an area of the fixture surface. The semiconductive coating should be arranged such that it does not electrically connect regions of the clamping surface corresponding to different clamping electrodes, such that some of these clamping electrodes are not electrically connected and form an electrical short.

In yet another embodiment, the above problem is solved by providing two or more electrodes and controlling the voltage applied to each electrode separately. For example, instead of having a single positive electrode and a single negative electrode, the present embodiment includes having two or more positive electrodes and/or two or more negative electrodes. A separate voltage may be suitably applied to each electrode to overcome the uneven charge distribution in the surface area of the fixture surrounding the electrode. According to a second aspect of the invention, each voltage applied to an individual electrode may be determined according to at least some of the techniques for determining the voltage to be applied at the electrode. Each electrode may also be a clamping electrode for applying a holding force to the object or releasing the object. Alternatively, one or more electrodes may be used only to apply a force to counteract a residual force caused by the local charge distribution at the one or more electrodes, while the one or more electrodes are not used to apply a holding force to the object.

Specific orientations have been given when describing the relative arrangement of components. It should be understood that these orientations are given by way of example only and are not intended to be limiting. For example, the xy-stage of the positioning apparatus 180 has been described as being operable to position an object in a substantially horizontal plane. The xy stage of the positioning apparatus 180 may alternatively be operable to position the object in a vertical plane or an inclined plane. The orientation of the components may be different from the orientations described herein while maintaining the intended functional effect of the components described above.

Fig. 16 schematically depicts an embodiment of an object table 1600 according to the third aspect of the invention. The object table 1600 may have substantially the same structure as the object table described above, except for the following aspects. The object table 1600 is used to hold an object 620. The stage 1600 comprises an electrostatic clamp 630, an ionizer device 1610, a control unit 1520 and a measurement unit comprising, for example, a force sensor 1620 and/or a gap sensor 1630 and/or a height sensor 1640. The electrostatic clamp 630 is used to clamp the object 620 to the stage 610. The measurement unit is configured to provide a force signal 1520.3 representative of the residual force exerted by the electrostatic clamp 630 on the object 620 when the object 620 is unloaded from the electrostatic clamp 630. The ionizer device 1610 is configured to provide an ionized stream 1610.1 of gas to the electrostatic chuck 630 to act as a neutralizer to neutralize residual charge on the electrostatic chuck 630. The control unit 1520 is arranged to control the ionizer device 1610 based on the force signal 1520.3.

In an alternative embodiment, the stage 1600 may include an electrostatic clamp 630, an ionizer device 1610, and a control unit 1520. An electrostatic clamp is used to clamp the object 620 to the stage 610. The ionizer device 1610 is for providing an ionized flow of gas. The control unit 1520 is arranged to control the ionizer device 1610 to provide an ionized flow of gas to the electrostatic clamp.

The control unit 1520 may be arranged to receive an information signal representing the residual force or the residual charge. During unloading of the object 620 from the electrostatic clamp 630, a residual force is exerted on the object 620 by the electrostatic clamp 630. The residual charge is the electrostatic charge that exists on the electrostatic clamp 630 when no charging voltage is applied to the electrostatic clamp 630. The control unit 1520 may be arranged to control the ionizer device 1610 based on the information signal. Ideally, there is no residual force and no residual charge during the unloading of the object 620 from the electrostatic chuck 630. However, due to the charge accumulation on the electrostatic clamp 630, residual force and/or residual charge may still be present even when no charging voltage is applied to the electrostatic clamp 630.

The information signal may comprise measurement information. As shown below, the measurement unit may provide measurement information in the form of a measurement signal. Further examples of measurement information are given below and may include information about the amount of force required to lift the object 620 from the stage 610, or information about the gap or capacitance between the object 620 and the stage 610. Other measurement information may indicate the shape of the object 620 and/or the amount of power required to release and unload the object 620 from the stage 610. The information signal may be an internal signal of the electrostatic clamp 630 and/or the loading/unloading mechanism that represents a residual force and/or a residual charge, such as a signal representing a detection that the loading/unloading mechanism is unable to lift the object 620 from the electrostatic clamp 630.

The information signal may comprise estimation information. The measurement information is based on measurements representing residual forces or residual charges, while the estimation information is based on other parameters, such as empirical data and simulations. The estimated information may include that after a certain length of time or after unloading a certain amount of the object 620, the control unit 1520 needs to control the ionizer device 1610 and/or the discharge voltage to counter the accumulated residual charge or residual force. The simulation may predict the edges where the residual charge and residual force are at acceptable levels after how much time or times the object 620 is unloaded. The estimated information may include information obtained from outside the object table 1600, for example via an external measurement device that measures the residual charge of the object 620 outside the object table 1600, for example in other processing steps of the object 620. The estimation information may comprise the estimated residual charge according to embodiments of the present invention, in particular embodiments of the second and fifth and sixth aspects of the present invention. The control unit 1520 may utilize the measurement information or the estimation information or a combination of the measurement information and the estimation information.

The object table 1600 may further include a measurement unit. The measurement unit is configured to provide a measurement signal representing the residual force or the residual charge. The information signal comprises a measurement signal. The control unit 1520 is arranged to control the ionizer device 1610 based on the measurement signal.

In one embodiment, an object table 1600 is provided that includes an electrostatic clamp 630 and a control unit 1520. The electrostatic clamp 630 is used to clamp the object 620 to the stage 610. The control unit 1520 is to provide the electrostatic chuck 630 with a charging voltage for clamping the object 620 on the electrostatic chuck 630 and a discharging voltage for releasing the object 620 from the electrostatic chuck 630. The discharge voltage may loosen the object 620 by reducing the clamping force to, for example, substantially zero or by providing a repulsive force to push the object 620 away from the electrostatic clamp 630. The control unit 1520 is arranged to receive an information signal representing the residual force or the residual charge. The control unit 1520 is arranged to provide a discharge voltage by the power supply to act as a neutralizer for neutralizing residual charge on the electrostatic chuck 630 based on the information signal.

The discharge voltage may have a polarity opposite to the charge voltage. In one embodiment, the stage 1600 can further include an ionizer device, such as ionizer device 1610, for providing an ionized stream 1610.1 of the gas to the electrostatic chuck 630. The control unit 1520 is arranged to control the ionizer device 1610 based on the information signal.

After the object 620 is clamped using the electrostatic clamp 630, residual charge may remain on the electrostatic clamp 630 even if the charging voltage is no longer applied. Ideally, when the charging voltage is no longer applied, there will be no residual charge, and thus the electrostatic clamp 630 will not exert a force on the object 620. The residual force is generated by residual charge and gravity. Gravity increases the residual force by the weight of the object 620 supported by the electrostatic clamp 630. The residual charge may have a much greater effect on the residual force than on gravity, for example 10 times or 100 times or more. The residual force keeps the object 620 clamped on the electrostatic clamp 630. To unload the object 620 from the electrostatic chuck 630, an unloading force exceeding the residual force needs to be applied to the object 620. However, the higher the unloading force, the more particles are generated during unloading of the object 620. The particles may contaminate the object 620 or the environment in which the object 620 is processed. After repeated loading and unloading of the object 620 on and from the electrostatic chuck 630, the residual force may become so great that at some point it is no longer possible to unload the object 620 from the electrostatic chuck 630 without taking extreme measures. An extreme measure may be to manually unload the object 620 from the electrostatic chuck 630.

The stage 1600, as schematically shown in fig. 16, can remove, mitigate or alleviate the necessity of such measures by using an ionizer device 1610, by applying a discharge voltage, or a combination thereof. When the measurement unit 1620 provides a measurement signal, the control unit 1520 is arranged to evaluate whether the measurement signal 1520.3 is within an acceptable range. When the measurement signal is within an acceptable range, the object 620 can be properly removed from the electrostatic chuck 630. However, when the measurement signal is not within the acceptable range, the control unit 1520 may take action.

The control unit 1520 may be arranged to send a control signal 1520.1 to the power supply 1530. The power supply 1530 is arranged to provide power 1530.2 to the ionizer device 1610. By providing power, the control unit 1520 may turn on the ionizer device 1610 and may control the amount of ionized flow 1610.1 of the gas. The control unit 1520 may control movement of the ionizer device 1610 to move across the entire surface of the electrostatic chuck 630 to provide an ionized stream 1610 of gas to the entire surface of the electrostatic chuck 630. Alternatively, the ionizer device 1610 may be stationary and arranged to fill the space around the electrostatic chuck 630 with an ionized gas. In another embodiment, the ionizer apparatus 1610 is stationary and the stage 620 is moved by the control unit 1520 to provide an ionized stream 1610.1 of gas to the entire surface of the electrostatic chuck 630. The ionized gas neutralizes the residual charge on the electrostatic chuck 630.

Note that the ionized flow of gas 1610.1 should be able to contact the electrostatic clamp 630. Thus, preferably, no object 620 should be present on the electrostatic clamp 630 when the ionizer device 1610 is operated. Thus, when the control unit 1520 determines that the information signal is not within an acceptable range when unloading the object 620, the object 620 is first unloaded before activating the ionizer device 1610. The residual charge of the next object 620 will be lower due to the neutralization of the residual charge by the ionizer device 1610. The acceptable range may be set such that the object 620 may still be unloaded from the electrostatic chuck 630 without generating too many particles when the information signal is just outside the acceptable range.

Alternatively, the control unit 1520 may send the control signal 1520.1 to the power supply 1530, the power supply 1530 providing power 1530.1 to the electrostatic chuck 630. During clamping of the object 620, the control unit 1520 provides a charging voltage to the electrostatic clamp 630 through the power supply 1530 to clamp the object 620. Upon unloading, the control unit 1520 stops supplying the charging voltage. When the control unit 1520 evaluates that the information signal is not within the acceptable range during unloading, the control unit 1520 provides a discharge voltage to the electrostatic chuck 630. The discharge voltage may at least partially neutralize the residual charge. By neutralizing the residual charge, the object 620 can be unloaded with an acceptable unload force. Applying the discharge voltage is particularly beneficial when the unloading force is insufficient to remove the object 620 from the electrostatic chuck 630.

In one embodiment, the control unit 1520 may control both the ionizer apparatus 1610 and the electrostatic chuck 630. In such embodiments, the stage 1600 may be operated until the information signal exceeds an acceptable range. The control unit 1520 controls the discharge voltage to temporarily reduce the residual charge so that the object 620 can be normally removed from the electrostatic chuck 620. After the object 620 is removed from the electrostatic clamp 620, the control unit 1520 stops providing the discharge voltage, which increases the residual charge on the electrostatic clamp 620. The residual charge from the electrostatic clamp 620 is then neutralized using the ionizer device 1610. This embodiment may have the advantage of using as little of the ionizer device 1610 as possible, and thus may interfere as little as possible with the operational use of the stage 1600.

The control unit 1520 may be arranged to receive an updated information signal representing an updated residual force or an updated residual charge. The updated residual force or updated residual charge is based on the residual force or residual charge and the discharge voltage provided to the electrostatic clamp 630. When the control unit 1520 provides the discharge voltage to the electrostatic chuck 630, the measurement unit may detect a change in the measurement signal. The change in the measurement signal causes the measurement signal to form an updated information signal. The control unit 1520 may use the updated information signal to adjust the discharge voltage. The updated information signal may be lower than the information signal. In this case, the polarity of the discharge voltage is correct. However, when the updated information signal is higher than the information signal, the polarity of the discharge voltage may not be correct. As a result, the control unit 1520 may apply a discharge voltage having an opposite polarity or may apply a smaller discharge voltage.

The stage 1600 can include an unloading mechanism for unloading the object 620 from the electrostatic clamp 630. The unloading mechanism may include lift pins, such as pin-shaped members 650, or may include any other type of mechanism, such as a robotic arm, a hand grip that engages the bottom surface 620.1 of object 620, or a vacuum hand grip that engages the top surface of object 620. The measurement unit may be arranged to monitor the lifting force exerted by the unloading mechanism on the object 620 to lift the object 620 from the electrostatic clamp 630 during unloading. The lifting force is based on the residual force and/or the residual charge. To lift the object 620 from the electrostatic clamp 630, the unloading mechanism needs to provide a lifting force to overcome the residual force due to the weight of the object 620 and the gravitational force. In general, the applied measuring unit may comprise any type of sensor suitable for monitoring the lifting force. For example, the measurement unit may include a strain gauge attached to the unloading mechanism, a power meter that monitors the amount of power required by the unloading mechanism to lift the object 620 from the electrostatic clamp 630, and/or a force sensor that monitors the lifting force applied by the unloading mechanism.

In the embodiment of fig. 16, the unloading mechanism includes a pin-shaped member 650. The pin-shaped member is provided with a force sensor 1620, the force sensor 1620 forming part of the measuring unit. The force sensor 1620 is arranged to monitor the lifting force. A lifting force is generated when the pin-shaped member 650 pushes up against the object 620 to unload the object 620 from the electrostatic chuck 630. The lifting force propagates from the object 620 through the pin-shaped member 650 and the force sensor 1620. Force sensor 1620 sends a force signal 1520.3 to control unit 1520.

The measurement unit may comprise a gap sensor 1630, the gap sensor 1630 being arranged to provide a measurement signal based on the object 620 in the first state and the object 620 in the second state. In the first state, the object 620 is held by the electrostatic chuck 630. In the second state, the object is away from the electrostatic chuck 630. For example, in the second state, the object 610 is held by the unloading mechanism. When the object 620 is in the first state, the gap sensor 1630 may measure a distance or gap between the gap sensor 1630 and the object 620 (e.g., the bottom surface 620.1). In the second state, the gap sensor 1630 may measure a greater distance or a greater gap between the gap sensor 1630 and the object 620 because the object 620 is farther away from the electrostatic clamp 630. In the second state, a portion (e.g., a central portion) of the object 620 may be farther away from the electrostatic chuck 630 while another portion (e.g., an edge portion) of the object 620 remains clamped to the electrostatic chuck 630.

The object 620 may perform a movement from a first state to a second state. The object 620 may jump from the first state to the second state. The change in jump may represent a change in residual force or residual charge. The measurement signal may represent movement, such as distance or speed of movement. The object 620 may remain in the first state when the unloading mechanism begins to provide a lifting force to the object 620. When the unloading mechanism increases the lifting force, the object 620 may suddenly disengage from the electrostatic clamp 620 when the lifting force exceeds the residual force. A sudden disengagement may cause the object 620 to move a distance or at a speed. The greater the residual force, the greater the specific distance or specific speed may be. The gap sensor 1630 may monitor distance and/or velocity as a measure of residual force. Other known parameters that may affect distance or velocity may be the stiffness, mass or damping of the unloading mechanism, and the stiffness, mass or damping of the object 620. The gap sensor 1630 may include or may be a capacitive sensor. The gap sensor 1630 may be disposed in or at the electrostatic chuck 630.

Alternatively or in addition to the gap sensor 1630, a height sensor 1640 may be used. The height sensor 1640 is arranged to determine the height of the object 620, e.g. relative to the object table 1600 or any other reference. The height sensor 1640 may be arranged to determine the flatness of the object 620. The height sensor 1640 may be arranged as part of the stage 1600 or may be arranged separately, e.g. attached to a metrology system. The height sensor 1640 may be an optical distance measuring sensor, such as an interferometer.

The control unit 1520 is arranged to compare the information signal with a threshold value. When the force signal does not exceed the threshold, the control unit 1520 does not need to take any action. As mentioned above, the control unit 1520 is arranged to take action when the information signal exceeds the threshold value.

Stage 1600 may be used in any suitable device, such as a particle beam device, electron beam device, scanning electron microscope, electron beam writer, electron beam projection lithography device, electron beam inspection device, electron beam defect verification device, electron beam metrology device, lithography device, and metrology device.

The object 620 may be unloaded from the electrostatic chuck 630 by performing the following method: unloading the object 620 from the electrostatic chuck 630; and provides an ionized flow of gas to the electrostatic chuck 630. Providing the ionized flow of gas may occur after the object 620 has been unloaded from the electrostatic chuck 630.

The method may further comprise the step of providing an information signal representing the residual force or charge. A residual force is exerted on the object 620 by the electrostatic clamp 630 during unloading of the object 620 from the electrostatic clamp 630. When no charging voltage is applied to the electrostatic chuck 630, residual charges exist on the electrostatic chuck 630. The method further includes the step of providing a discharge voltage based on the information signal to release the object 620 from the electrostatic chuck 630. The method can also include providing an ionized flow 1610.1 of the gas to the electrostatic clamp 630 based on the information signal.

Note that the power supply 1530 may be split into separate power supplies for each of the ionizer device 1610 and the electrostatic clamp 630. The power supply 1530 may be integrated with the ionizer device 1610 and/or the electrostatic clamp 630.

When clamping the object 620 to the electrostatic clamp 630, the charging voltage (also referred to as the clamping voltage) needs to be sufficient to properly clamp the object 620. Proper clamping means that the object 620 is pressed flat enough against the electrostatic clamp 630. The object 620 may not be flat, but may be, for example, bowl-shaped, saddle-shaped, or umbrella-shaped, before the object 620 is gripped. In order to place the object 620 flat on the electrostatic chuck 630, a high chucking voltage is required. However, if the clamping voltage becomes higher, more particles are generated. It is therefore desirable to apply as low a clamping voltage as possible while properly clamping the object 620 to the electrostatic clamp 630.

According to a fourth aspect of the invention, this may be achieved by clamping the object 620 on the electrostatic clamp 630 using: i) providing an object 620 on an electrostatic chuck 630; ii) increasing the clamping voltage of the electrostatic clamp 630 until a clamped state is detected in which the object 620 is clamped on the electrostatic clamp 630; iii) determining the first clamping voltage as the clamping voltage in the clamped state; iv) providing a second clamping voltage, less than the first clamping voltage, to the electrostatic clamp 630. When the clamp parameter is within the threshold, the clamp state may be detected. The chucking parameter may include one of a flatness of the object, a change in a shape of the object caused by a change in a chucking voltage, and a contact of a central portion of the object with the electrostatic chuck.

By this approach, the first clamping voltage is a clamping voltage sufficient to properly clamp the object 620 to the electrostatic clamp 620. By doing so, an excessively high voltage, i.e., an unnecessarily high clamping voltage, can be avoided. Further, the inventors have found that a first clamping voltage needs to be applied to level the object 620, but a lower clamping voltage is sufficient to keep the object 620 level on the electrostatic clamp 620. Therefore, after the first clamping voltage is applied, the second clamping voltage may be set to a value lower than the first clamping voltage. As a result, the second clamping voltage provides fewer particles than if the first clamping voltage was maintained.

Figure 17 schematically presents the clamping voltage V provided to the electrostatic clamp 630 as a function of time t, in accordance with an embodiment of the present invention. When t is equal to 0, the clamping voltage is increased until t is equal to t₁When the first clamping voltage V is reached_max. In a time period 0-t₁During this time, the deformation of the object 620 is monitored, for example, by the gap sensor 1630 or the height sensor 1640, or any other suitable deformation sensor. Thus, during the time period 0-t₁During which the deformation of the object 620 is determined as a function of the increase in the clamping voltage. For the bowed object 620, as the clamping voltage begins to increase, deformation may occurWith a large variation. However, when the arcuate object 620 is laid flat against the electrostatic clamp 630, the deformation will not change or will change almost negligibly in response to another increase in clamping voltage. Thus, it can be found that the deformation due to the increase of the clamping voltage is below a threshold, e.g. a predetermined threshold. When another increase in the clamping voltage does not lead to any significant difference in deformation, it can be concluded that: the object 620 is placed flat on an electrostatic chuck 630. Referring to fig. 17, this occurs when t ═ t₁Then (c) is performed. At t ═ t₁The voltage applied can thus be regarded as the first clamping voltage V_max。

While supplying the first clamping voltage V to the electrostatic clamp 630_maxThereafter, the chucking voltage is reduced by providing a chucking voltage reduction to the electrostatic chuck 630, and deformation of the object 620 caused by the chucking voltage reduction is determined. This process is repeated until the deformation is above another threshold. The clamping voltage is reduced until the clamped state is no longer detected. Then, when the deformation is higher than another threshold, a third clamping voltage V is determined_min. Third clamping voltage V_minThe clamping voltage when the clamped state is no longer detected, for example, the first value of the clamping voltage when the clamped state is no longer detected. Second clamping voltage V_finalIs applied to an electrostatic chuck 630. Final clamping voltage V_finalHigher than the third clamping voltage V_min。

As shown in fig. 17, when t equals t_lTo t ═ t₂From a first clamping voltage V_maxDown to a third voltage V_min. At V_minThe clamping force applied by the electrostatic clamp 630 has been reduced to the point where the object 620 becomes again uneven. The determined deformation of the object 620 indicates that the object 620 has become uneven. Note that when t is equal to t₂The object 620 may still be much flatter than when t is 0.

In fig. 17, t is t₂To t ═ t₃In between, the clamping voltage is increased to a first clamping voltage V_max. This can be done by simply applying the time t₁The same clamping voltage is applied or by determining the deformation of the object 620 until the deformation is again below the threshold.At time t₃The object 620 is planarized by an electrostatic chuck 630. At t₃Thereafter, the clamping voltage is reduced to be higher than the third clamping voltage V_minAnd is lower than the first clamping voltage V_maxSecond clamping voltage V_final. In this way, the object 620 maintains proper flatness at low clamping voltages.

In the above-described embodiment, instead of determining the first clamping voltage V based on the deformation of the object 620_maxA second clamping voltage V_finalAnd a third clamping voltage V_minOne or more of these clamping voltages may be based on whether the central portion of the object 620 is in contact with the electrostatic clamp 630, or on any other suitable clamping parameter.

Second clamping voltage V_finalMay be less than the third clamping voltage (V)_min) E.g. less than 140% or less than 130% or less than 120% or less than 110% or less than 105%

Figure 18 schematically presents a clamping voltage provided to an electrostatic clamp 630 in accordance with another embodiment of the invention. Similar to the embodiment of fig. 17, the clamping voltage is t ═ t₁Is set to a first clamping voltage V_maxAnd when t is equal to t₂Is set to a third clamping voltage V_min. However, in the present embodiment, the third clamping voltage V_minThe lower flatness is sufficient to process the object 620. Thus, when t equals t₂To t ═ t₃From a third clamping voltage V_minIncreased to a second clamping voltage V_final. Due to the third clamping voltage V_minThe flatness of the lower edge is sufficiently flat so that it is not necessary to increase the clamping voltage back to the first clamping voltage V_maxTo re-planarize the object 620. Clamping voltage from third clamping voltage V_minIncreased to a second clamping voltage V_finalTo ensure that the object 620 remains clamped to the electrostatic clamp 630 during processing of the object 620.

Figure 19 schematically presents a clamping voltage provided to an electrostatic clamp 630 in accordance with yet another embodiment of the invention. When at time t₁Applying a first clamping voltage V_maxBetween the object 620 and the electrostatic chuck 630 is determinedThe clamping force of (3). Providing a second clamping voltage V based on the clamping force_final. For example, at a first clamping voltage V_maxA high clamping force at this point may indicate a good clamping of the object 620, and thus the second clamping voltage V may be applied_finalIs set relatively low. On the other hand, at the first clamping voltage V_maxA lower clamping force may indicate a poor clamping of the object 620 and thus the second clamping voltage V may be applied_finalIs set relatively high.

Stage 1600 may be arranged to set the clamping voltage as shown in fig. 17-19. The stage 1600 may include an electrostatic clamp 630 for clamping the object 620 and may include a control unit 1520 for providing a clamping voltage to the electrostatic clamp 630. The object table 1600 may comprise a measurement unit for providing a measurement signal representing the deformation of the object 620 to the control unit 1520. For example, the measurement unit includes a gap sensor 1630. The gap sensor 1630 may be arranged to determine a gap between the object and the electrostatic clamp 630. Alternatively, the measurement unit is arranged separate from the object table 1600, such as a height sensor 1640, which may be arranged on the metrology system. The height sensor 1640 may be arranged to determine the height of the object 620. The measurement unit may be arranged to determine whether the object 620 is flat or arcuate. Based on whether the object 620 is flat or arcuate, the control unit 1520 may use the method of fig. 17, 18, or 19, or any other suitable method.

Fig. 20 shows another embodiment of the present invention. Stage 2000 may be identical to stage 1600, except as follows. Stage 2000 includes a force sensor 2010. Force sensor 2010 may be identical to force sensor 1620. The force sensor 2010 may extend beyond the surface of the electrostatic clamp 630 such that at time t₁During the period when the maximum clamping voltage V is applied_maxAt this point, the object 620 is partially clamped onto the force sensor 2010. In this way, the force sensor 2010 is arranged to detect a clamping force by which the object 620 is clamped on the electrostatic clamp 630 while the first clamping voltage V is applied_maxIs applied to an electrostatic chuck 630. At time t₁May be moved to the direction indicated by the dashed line after the clamping force of (c) is determinedA lower position 2011. In the downward position 2011, the force sensor 2010 is retracted below the surface of the electrostatic clamp 630, and thus the force sensor 2010 is not in contact with the object 620. When the force sensor 2010 is in the down position, the object 620 can be properly planarized on the electrostatic clamp 630. Although fig. 20 shows a single force sensor 2010, multiple force sensors 2010 may be applied distributed along the electrostatic chuck 630.

The control unit 1520 may comprise a machine learning unit arranged to predict the third clamping voltage V based on the clamping voltage and the clamping parameter_min. For example, the machine learning unit may account for changes in clamping voltage over time, deformation over time, and/or clamping force determined by the force sensor 2010. The machine learning unit may be provided with information of the object 620 acquired outside the object table 1600, such as the material of the object 620, the dimensions of the object 620, and other measurement information about the object 620.

According to a fifth aspect of the invention, there is provided a method of determining a residual charge of a clamping mechanism of a stage. As described above, residual charges may accumulate on an insulating surface over time, such as a surface of a chucking mechanism applied to a lithographic apparatus or an inspection apparatus (such as a particle beam inspection tool or an electron beam inspection tool). Such residual charge may build up, for example, over multiple object processing cycles and may affect the grip of the object to the gripping mechanism. Within the meaning of the present invention, the residual charge of the clamping means may also refer to the charge on one or more surfaces close to or covering the clamping surface of the clamping means. Within the meaning of the present invention, such a surface surrounding or enclosing or covering the actual surface generating the clamping force may be considered to be part of the clamping mechanism.

In an embodiment according to the fifth aspect of the invention, it is proposed to determine or estimate the residual charge present on the clamping mechanism by probing the clamping mechanism with a particle beam (e.g. a particle beam available in the examination apparatus). In particular, in one embodiment, the present invention provides the following method: a method of determining a residual charge of a fixture by impacting or detecting a surface of the fixture with a particle beam, determining or detecting a response of the fixture to the impact or detecting the surface, and determining the residual charge of the fixture based on the detected response. Fig. 21 schematically shows a flow chart 2100 of a method of determining a residual charge of a clamping mechanism according to the present invention. In a first step 2110, the method includes striking a surface of a clamping mechanism of a stage with a particle beam. Particle beams such as ion beams or electron beams are well known and are applied to inspection apparatuses to inspect the surface or structure of an object such as a semiconductor substrate. In such devices, the object to be inspected is typically held (e.g., clamped) to a clamping mechanism of the stage. During inspection, a particle beam (such as an electron beam) is used to probe or impact an object. Such detection or impingement may result in the generation of radiation and particles emitted by the object. For example, probing an object with an electron beam may cause the object to emit secondary electrons or generate scattered electrons. In the method according to the invention, a particle beam (e.g. an electron beam) is used to impinge on the surface of the holding means of the stage, instead of the object that is normally held on the stage. Given the typical layout of the stage used in an inspection apparatus, applying a particle beam to the surface of the clamping mechanism would require the stage not to hold the object. Without such an object, the particle beam may be made to interact with the clamping mechanism, rather than with the object.

In a second step 2120, the method according to the invention comprises detecting a response of the clamping mechanism to the particle beam striking the surface. When the particle beam strikes the surface of a clamping mechanism (e.g., an electrostatic clamp), this may result in the generation of radiation and/or surface-emitted particles. For example, an electron beam striking a surface of the clamping mechanism may cause secondary or scattered electrons to be generated. In an embodiment of the invention, the electrons may be detected by a detector. Such a detector may for example be configured to determine the number of secondary electrons and/or the energy or energy spectrum of the secondary electrons.

In a third step 2130, the method according to the invention comprises determining a residual charge of the clamping mechanism based on the response. With regard to this third step, it may be noted that the response to the particle beam detected by the detector will be different when there is a residual charge on the clamping mechanism. This can be understood as follows: particle beams, such as electron beams, are known for inspecting objects, such as semiconductor substrates. During such an examination a voltage difference is applied between the object and the particle beam source, which voltage difference causes the particles to strike the object with a certain amount of energy. The response of the object to the impacting particle (i.e., the impact of the impacting particle) will depend on the magnitude of this energy. The energy of a particle when it strikes an object may also be referred to as the Landing Energy (LE). The response will vary depending on the amount of energy the particle has when it strikes the object; the amount of radiation and/or emitted particles (such as secondary electrons) generated will depend on the landing energy. This will affect the landing energy of particles striking the object if there is a positive or negative charge on the object under examination. Thus, the charge on the object will result in a different response of the object to the impinging particle beam. If the clamping mechanism (e.g., comprising an electrostatic clamp) is subjected to the particle beam, the presence of an electrical charge on the clamping mechanism can be determined based on the response of the clamping mechanism due to the impinging particle beam. In one embodiment, the presence of charge on the fixture may be determined using, for example, an experimental data set and/or a model representing the relationship between the impinging particle beam and the response of the fixture.

As an alternative to using the particle beam for determining the residual charge, mention may also be made of using an electrostatic voltmeter or voltmeter. In such embodiments, care should be taken to position the voltmeter close enough to the substrate or stage, but far enough away from the high voltage region.

Those skilled in the art will appreciate that the presence of an electrical charge on the clamping mechanism may result in a repulsive or attractive force on the applied particle beam. In case the particle beam comprises an electron beam, the positive charge on the clamping mechanism will create an attraction force on the electrons of the electron beam, resulting in an increased landing energy. If there is a negative charge on the clamping mechanism, the electrons of the electron beam will be repelled, resulting in a reduced landing energy.

In one embodiment of the invention, the clamping mechanism applied comprises an electrostatic clamp. Such an electrostatic chuck may include one or more electrodes, for example embedded in a surface of the electrostatic chuck.

In one embodiment, the step 2110 of striking a surface of the clamping mechanism includes striking the surface at a plurality of different locations on the surface. By doing so, the presence of charge on the fixture can be determined for different positions. In such an embodiment, the method according to the invention may comprise determining a residual charge distribution over the entire surface of the fixture. In such embodiments, the method may, for example, comprise positioning the clamping mechanism relative to the particle beam, for example using a stage device, such that the particle beam impinges on different locations on the surface. Alternatively or additionally, the position of the particle beam, and thus the position at which the particle beam impinges on the clamping mechanism, may also be controlled.

An embodiment according to a sixth aspect of the invention provides a particle beam device configured to perform the method 2100 according to the invention. Fig. 22 schematically shows an embodiment of such a device.

Fig. 22 schematically shows a particle beam device 2200 according to an embodiment of the present invention. In the illustrated embodiment, the particle beam device comprises a particle beam generator 2210 configured to generate a particle beam 2220, e.g., one ion beam or electron beam or a plurality of electron beams. In the illustrated embodiment, apparatus 2200 also includes a stage 2230 for holding object 2240, stage 2230 including a clamping mechanism 2250 for clamping object 2240 to stage 2230. In one embodiment, the clamping mechanism 2250 may comprise, for example, an electrostatic clamp. Such an electrostatic chuck may include one or more electrodes that may be connected to a power source. In the illustrated embodiment, the device 2200 also includes a detector 2260. Such a detector 2260 may be configured to detect a response of object 2240 when object 2240 is exposed to particle beam 2220. In particular, detector 2260 may be configured to detect radiation and/or particles generated in response to the impact of particle beam 2220 on object 2240. In response to impact of particle beam 2220 on the object, the object may, for example, emit secondary or scattered electrons, which may be detected by detector 2260. According to the present invention, detector 2260 is configured to detect response 2220.1 of clamping mechanism 2250 when the clamping mechanism is struck by particle beam 2220. In the illustrated embodiment, the apparatus 2200 also includes a control unit 2270. According to the invention, the control unit is configured to:

controlling the particle beam generator 2210 to cause the particle beam 2220 to strike the surface 2250.1 of the clamping mechanism 2250;

receive detector signal 2260.1 from detector 2260, detector signal 2260.1 representing the response of clamping mechanism 2250 to impinging particle beam 2220, and

determine the residual charge on the clamping mechanism 2250 based on the detector signal 2260.1.

The device 2200 according to the invention is therefore able to determine the residual charge present on the gripping means. Knowing such residual charges may help to unload objects, such as object 2240, when the object has been processed by the device.

In one embodiment, the apparatus 2200 in accordance with the present invention is configured to strike a surface of the clamping mechanism at a plurality of different locations on the surface. By doing so, the presence of charge on the clamping mechanism 2250 may be determined for different locations. To do so, apparatus 2200 also includes a platform or platform arrangement 2280 configured to position stage 2230 relative to particle beam 2220. In particular, platform arrangement 2280 may be configured to scan clamping mechanism 2250 below particle beam 2220. Such platform means 2280 may, for example, comprise one or more motors or actuators for positioning stage 2230. In such embodiments, control unit 2270 may also be configured to control the positioning of stage 2230, e.g., by generating suitable control signals for motors or actuators of stage or platform arrangement 2280. In one embodiment, the apparatus 2200 may further comprise a position measurement system, e.g. an interferometer-based or encoder-based measurement system, configured to measure the position of the platform apparatus 2280 relative to the particle beam generator 2210 or relative to a reference or frame of reference. When the residual charge of the clamping mechanism 2250 is determined at different locations, the control unit 2270 may be configured to determine the residual charge distribution over the entire surface of the clamping mechanism 2250.

The determined residual charge may advantageously be used to control or regulate the unloading process of object 2240 that has been processed on stage 2230. As an example, the clamping mechanism applied may be or comprise an electrostatic clamp with one or more electrodes, for example. The voltage applied to the electrodes during the unloading sequence of object 2240 may be controlled in view of the determined residual charge or residual charge distribution. In one embodiment, a repulsive force may be generated between object 2240 and clamping mechanism 2250. This may be done, for example, by applying the same voltage to object 2240 and grip mechanism 2250. In this embodiment, gripping mechanism 2250 may have one or more electrodes to apply a voltage to object 2240. This creates a repulsive force between object 2240 and clamping mechanism 2250 that is constant over a distance. In one embodiment, the force applied by a loading/unloading mechanism, such as loading/unloading mechanisms 550, 650 described above, may be removed first, and a repelling force may then be applied between object 2240 and gripping mechanism 2250. The repulsive force may be smaller than the gravitational force. The object 2240 may then be lifted using the load/unload mechanism. If object 2240 remains adhered to grip mechanism 2250, a higher repelling force may be used. Object 2240 may stop as soon as it moves with a higher repulsive force. Thus, the loading/unloading mechanism may be arranged to contact the object 2240 and exert a smaller force. The position of the loading/unloading mechanism can be measured. Once motion is detected (e.g., 50 μm displacement), the repulsive force must be removed.

According to a seventh aspect of the present invention, there is provided a method of reducing surface charge of a clamping mechanism. Such a method is schematically depicted in the flow chart of fig. 23. According to the present invention, a method of reducing the surface charge of the clamping mechanism 2300 utilizes a particle beam to reduce the surface charge on the clamping mechanism (e.g., a clamping mechanism applied to a stage of a particle beam device). In particular, the method according to the invention comprises a first step 2310 of generating a particle beam configured to have a Secondary Emission Yield (SEY) substantially equal to 1 in a surface of the clamping mechanism. Those skilled in the art will appreciate that when a particle beam is applied to the surface of an object, for example, an electron beam is applied to a semiconductor substrate for inspection, an interaction between the electron beam and the object can occur. Such interaction may, for example, cause the generation of secondary electrons. The number of secondary electrons generated generally depends on the voltage difference applied between the object and the particle beam source. Therefore, by controlling the applied voltage difference, the amount of secondary electrons generated can be controlled. According to a first step 2310 of the method 2300 according to the invention, a particle beam is generated having a Secondary Emission Yield (SEY) substantially equal to 1. Within the meaning of the present invention, the expression of an electron beam with a SEY substantially equal to 1 is applied, the number of electrons causing an interaction with the object on average corresponding to the number of electrons emitted by the object, called secondary electrons. In order to achieve such a condition that one secondary electron is emitted for each electron that reaches the object on average, the arriving or landing electrons need to have a specific energy or energy level. The energy of an electron when it lands on an object or object surface is generally referred to as landing energy. Those skilled in the art will appreciate that the Landing Energy (LE) of an electron depends on the voltage difference applied between the object and the particle beam source. Thus, the electron landing energy of the electron beam can be controlled by controlling the voltage difference between the object and the particle beam source. Thus, the applied voltage difference may be controlled such that the Landing Energy (LE) of the electrons enables to acquire an SEY substantially equal to 1. In this regard, it may be noted that in an inspection apparatus using a particle beam to inspect an object, the stage holding the object may be provided with one or more additional electrodes, for example electrodes other than, for example, electrodes of the clamping mechanism. Such an electrode may be for example simply a high pressure plate. Such one or more electrodes may for example be arranged along the circumference of the object or stage and may be connected during use to a voltage source such as a high voltage source. When applying such electrodes, it will be clear to the skilled person that these electrodes may also have an effect on the Landing Energy (LE) of the electrons. Therefore, such electrodes should also be considered when determining the voltage difference required to reach the proper Landing Energy (LE) resulting in SEY substantially equal to 1. As will be explained in more detail below, the Landing Energy (LE) may also depend on the charge state of the object. Thus, when referring to a voltage difference or landing energy LE resulting in an SEY of about 1, it is assumed that the object is in a neutral state, i.e. no surface charge. In one embodiment of the invention, the first step 2310 of the method 2300 may precede or include the steps of:

-determining the voltage difference between the particle beam source and the clamping mechanism required to obtain a SEY substantially equal to 1, and

-generating a particle beam by applying the determined voltage difference.

In a second step 2320 of the method 2300 according to the invention, the generated particle beam is used to impinge on a surface of the clamping mechanism. By subjecting the surface of the fixture to a particle beam adjusted to have a SEY substantially equal to 1, it can be shown that the residual charge on the fixture can be reduced.

As the skilled person will appreciate, LE resulting in SEY substantially equal to 1 will generally depend on the material subjected to the particle beam. Thus, to ensure that the generated particle beam produces a SEY substantially equal to 1, the material of the clamping mechanism and the relationship between its SEY and LE characteristics should be known, at least the LE value required to achieve a SEY substantially equal to 1 should be known, in order to determine which voltage difference is to be applied between the particle beam source and the object. It may be noted that such material properties may be determined empirically, such as the LE value corresponding to a SEY substantially equal to 1, the relationship between SEY and LE properties.

Fig. 24 schematically shows a typical relationship between SEY and LE characteristics 2400, i.e. the characteristics of Secondary Electron Yield (SEY) as a function of the Landing Energy (LE) of the electrons of the particle beam. It can be seen that the graph or characteristic 2400 has two energy levels E1 and E2 resulting in SEY substantially equal to 1. In case the characteristic has more than one energy level resulting in a SEY substantially equal to 1, it is important to select an energy level around which the graph or characteristic 2400 has a negative slope as the required landing energy LE. As shown in fig. 24, graph 2400 has a positive slope 2410 near energy level E1 and a negative slope 2420 near energy level E2. Or, in other words, the derivative of SEY with respect to landing energy is positive near energy level E1 and negative near energy level E2. When the landing energy E2 is applied, i.e., the energy value near which map 2400 has a negative slope or negative derivative, this may result in a reduction or neutralization of any residual charge on the surface. This can be explained as follows: if no surface charge is present on the clamping mechanism, applying a voltage difference between the particle beam source and the clamping mechanism resulting in a landing energy E2 will on average cause one secondary electron to be emitted per impinging electron. If this voltage difference is applied to a surface having a positive charge, the electrons will be attracted by the positive charge, resulting in an increase in the landing energy LE, in particular a landing energy greater than E2, for example E3. As can be seen from graph 2400, such landing energy E3 will have a corresponding SEY of less than 1. When SEY is less than 1, the number of electrons provided to the surface is greater than the number of electrons emitted by the surface, resulting in a reduction or neutralization of the surface's positive charge. In case a voltage difference is applied to a surface having a negative charge, the electrons will be more repelled or less attracted by the above negative charge, resulting in a reduced landing energy LE, in particular a landing energy less than E2, e.g. landing energy E4. As can be seen from graph 2400, such landing energy E4 will have a corresponding SEY greater than 1. When SEY is greater than 1, the number of electrons provided to the surface is less than the number of electrons emitted by the surface, resulting in a reduction or neutralization of the negative surface charge.

According to an eighth aspect of the invention, the method 2300 of reducing a surface charge of a clamping mechanism according to the invention may advantageously be performed by a particle beam device according to the invention.

Such an apparatus configured to perform the method 2300 as schematically shown in fig. 23 is shown in fig. 25.

The schematically illustrated apparatus 2500 may have a similar structure to the apparatus 2200 shown in fig. 22. In the illustrated embodiment, the particle beam device 2500 includes two particle beam generators 2510, 2520. In the illustrated embodiment, the apparatus 2500 includes a first particle beam generator 2510, which first particle beam generator 2510 may be used, for example, to generate a particle beam 2510.1, such as an electron beam for inspecting an object. The apparatus as shown further comprises a second particle generator 2520 for generating a second particle beam 2520.1, which second particle beam 2520.1 may for example be used for neutralizing the charge of the object before or after the object is examined. Such a particle beam generator 2520 may also be referred to as a flood gun. Note that, in general, both particle beam generators 2510, 2520 may be oriented to generate a particle beam in a direction substantially perpendicular to the object 2540.

It is proposed that any one of the particle beam generators may be used in order to perform a method of reducing the surface charge of the clamping mechanism.

In the illustrated embodiment, apparatus 2500 further includes a stage 2530 for holding object 2540, and stage 2530 includes a gripping mechanism 2550 for gripping object 2540 to stage 2530. In the illustrated embodiment, the apparatus 2500 further comprises a control unit 2570, the control unit 2570 being configured as any one of the particle beam generators 2510, 2520 to generate the particle beams 2510.1, 2520.1, the particle beams 2510.1, 2520.1 being configured to have a Secondary Emission Yield (SEY) substantially equal to 1 in the surface of the holding mechanism 2550. In one embodiment, the particle beam generated by any one of the particle beam generators comprises one or more electron beams. Referring to the method 2300 described above, this means that the control unit 2570 is configured to control the particle beam generator 2510 or 2520 such that the landing energy of the particles of the particle beam results in SEY being substantially equal to 1. As mentioned above, such controlling may comprise controlling the voltage difference between the particle beam source and the clamping mechanism at a suitable value to obtain the required landing energy. In the illustrated embodiment, reference numeral 2570.1 indicates, for example, a control signal generated by the control unit 2570 for controlling the particle beam generator 2520 to generate the desired particle beam. According to the invention, the control unit 2570 is further configured to control the generated particle beam for impinging on the surface of the clamping mechanism 2550. By doing so, as explained above with reference to fig. 24, any residual charge on the gripping mechanism 2550 may be at least reduced.

Due to this reduction of residual charges that may have accumulated, the unloading or loosening of the object inspected by the device may be facilitated. In the illustrated embodiment, the apparatus 2500 further includes a stage apparatus 2580 configured to move the stage 2530 relative to the particle beam generator. By doing so, the entire surface of the gripping mechanism 2550, or a specific portion thereof, may be exposed to the particle beam to reduce residual charge on the gripping mechanism.

It may be provided that the application of the method 2300 according to the invention may be applied periodically to reduce the residual charge on the clamping mechanism. The method may be applied, for example, at predetermined intervals, such as each treatment (e.g.,examine) a particular number of objects. Alternatively or additionally, indications or observations obtained during processing of the object may be used. In particular, the above-described method capable of determining residual charge or an indication thereof (such as an increased unload force) may be applied to trigger application of the method 2300 to reduce residual charge on a clamping mechanism, such as the clamping mechanism 2550. It may also be provided that the particle beam generator 2510 and/or 2520 may be provided with focusing means for controlling the cross-section of the particle beam impinging on the surface of the clamping mechanism 2550. The cross section of the applied particle beam determines the density of the particles applied to the clamping mechanism. The higher the cross-section of the particle beam, the lower the density of the particles. Depending on the actual amount of residual charge present at a particular location on the fixture, that location will require a certain amount of particles to neutralize the surface at that location. During the scanning of the particle beam through the clamping mechanism, the density of the applied particle beam should therefore be taken into account when determining the scanning speed in order to ensure a sufficient reduction of the residual charge. The inventors have concluded that when a typical particle beam is applied to a known clamping mechanism, for example, the cross-section is 5-6mm²And a particle beam of SiO₂The resulting clamping mechanism, the time to remove approximately 95% of the residual charge, can be achieved to within 0.5 milliseconds. Based on these parameters, a typical fixture can be substantially neutralized in less than 20 seconds.

It will be clear to a person skilled in the art that the method of reducing the surface charge of a clamping mechanism according to the eighth aspect of the invention may be initiated based on a predicted, estimated or measured residual force or residual charge according to other aspects of the invention described in this document.

According to the ninth aspect of the present invention, when the object 2601 is held by the electrostatic chuck, the object 2601 may be charged to a high voltage by one or more electrodes of the electrostatic chuck that extend out of the stage 2602 and contact the lower surface of the object 2601. This may be the reason for charge accumulation that holds the object 2601 to the stage 2602. In one embodiment, one or more additional electrodes extending beyond the stage 2602 and contacting the lower surface of the object 2601 are used to discharge any accumulated charge. The number of further electrodes may be, for example, three. This embodiment is shown in fig. 26. In fig. 26, the left electrode has been used to charge the object 2601 to a high voltage. The right electrode has been in contact with the object 2601 to discharge the accumulated charge. The right-hand electrode may be connected at the other end to the end that brings the object 2601 into contact with ground potential.

In an embodiment of the ninth aspect of the invention, the same electrode or electrodes used to charge the object 2601 also discharge the object 2601. It is therefore possible to improve discharge by increasing the number of electrodes for charging the object 2601. In addition to discharging the object 2601 using one or more additional electrodes, the number of electrodes used to charge the object 2601 may also be increased.

According to the tenth aspect of the present invention, the stage is cleaned to reduce residual force that may continue to hold the object 2601 to the stage 2602 due to the charge of the electrostatic chuck after the electrostatic chuck is controlled to stop holding the object 2601. For example, a cleaning stone may be provided within the system to clean particles and/or contaminants on the stage 2602, particularly the surface of the electrostatic chuck, that may cause or enhance the charge build up on the surface of the electrostatic chuck. The cleaning stone may rotate and/or translate on the stage 2602, particularly on the surface of the electrostatic chuck. Alternatively, the cleaning stone may be stationary and the stage 2602 moved to rotate and/or translate it relative to the cleaning stone. The stage 2602 and the cleaning stone may also be moved during a cleaning operation to clean the surface of the stage 2602, particularly an electrostatic clamp. By providing a cleaning stone within the system, the cleaning operation by the stone can be performed without interruption by opening the system.

According to an eleventh aspect of the invention, unloading object 2601 from object table 2602 may be performed while the residual force, or at least a portion thereof, continues to hold object 2601 to object table 2602.

In one embodiment, the lift pin positioning apparatus 2605 is more powerful than known implementations of lift pin positioning apparatuses. The lift pin positioning device 2605 moves the lift pin 2604 with a greater force, thereby lifting the object 2601 with a greater force. This is expected to have the effect that the force exerted by the lift pins 2604 is sufficient to overcome the residual force that resists the lifting of the object 2601 from the stage 2602.

In another embodiment, the lift pin positioning device 2605 vibrates the lift pin 2604 in the z-direction such that an end of the lift pin 2604 strikes the object 2601. The vibrating motion of the lift pins 2604 contacting the object 2601 is expected to more easily achieve the effect of lifting the object 2601 above the stage 2602 by the lift pins 2604.

In yet another embodiment, the primary pointing device 506 vibrates in the xy-plane and/or directions in the xy-plane. The vibratory motion of the primary positioning device 506 applies a horizontal vibratory force to the object 2601 through the lift pins 2604. This is expected to make it easier to achieve the effect of lifting the object 2601 over the stage 2602 by the lift pins 2604.

In yet another embodiment, the platform positioning device 2603 vibrates the stage 2602 in one or more of the directions in the xy plane, and the z direction. Additionally or alternatively, the vibratory motion may also rotate with motion about one or more of the x-axis, y-axis, and z-axis. The oscillating motion of the object table 2602 is expected to more easily achieve the effect of lifting the object 2601 above the object table 2602 by the lifting pins 2604.

In the above embodiments, the applied vibrational motion may be along one or more of the directions in the xy-plane, the xy-plane and the z-direction. The applied vibratory motion may additionally or alternatively rotate with motion about any of the x-axis, y-axis, and z-axis. The platform positioning device 2603, the lift pin positioning device 2605, and the positioning device 2606 may make any possible motion to apply the vibration. For example, if the positioning device 2606 is capable of moving in the z-direction, the positioning device 2606 may impart a vibratory motion in the z-direction.

The vibratory motion may be dependent on any of a number of different types of control signals. For example, the signal may be a sawtooth wave, a sine wave, a noise signal, and/or a pseudo noise signal.

Yet another embodiment is shown in fig. 28. In yet another embodiment, the platform positioning device 2603 moves the carriage table 2602 in the z-direction in a direction toward the lift pin positioning device 2605, as indicated by arrow 28 in fig. 28. The position of the lift pin 2604 in the z direction may be mechanically locked, thereby preventing movement of the lift pin 2604 in the z direction. The effect of this is that the object 2601 is pressed against the end of the lift pin 2604, and it is expected that this will effect the removal or easier removal of the object 2601 from the stage 2602.

In this embodiment, the actuators of the platform positioning device 2603 may be more powerful than the actuators of the lift pin positioning device 2605. The actuators of the platform positioning device 2603 may also have a larger servo bandwidth than the actuators of the lift pin positioning device 2605, and this will allow the force applied by the platform positioning device 2603 to be controlled faster than the force applied by the lift pin positioning device 2605. In an alternative implementation of this embodiment, the platform positioning device 2603 may move the stage 2602 in the z-direction in a direction toward the lift pin positioning device 2605, and the lift pin positioning device 2605 may also control the lift pins 2604 to move in the z-direction toward the object 2601.

This embodiment may also allow the platform positioning device 2603 to be designed with a stronger actuator than known platform positioning devices and the lift pin positioning device 2605 to be designed with a weaker actuator than known lift pin positioning devices. This will simplify the design and implementation of the lift pin positioning apparatus 2605. In addition to being able to apply greater force than the lift pin positioning device 2605, the platform positioning device 2603 may also include more actuators than the lift pin positioning device 2605. The platform positioning device 2603 typically includes 3 or 4 actuators for imparting motion in the z-direction.

In yet another embodiment, the object 2601 may be effectively peeled from the stage 2602.

This embodiment is shown in fig. 29. In this embodiment, platform positioning device 2603 rotates stage 2602 about the x-axis and/or the y-axis. The range of rotation angles shown in fig. 29 is large, and therefore the rotation can be clearly explained. The actual angle of rotation may be much smaller than that shown in figure 7. The position of the one or more lift pins 2604 in the z-direction may be mechanically locked, so that movement of the lift pin(s) 2604 in the z-direction is prevented. Alternatively, the position of the one or more lift pins 2604 in the z-direction is not mechanically locked. One or more lift pins 2604 may be moved in the z-direction to increase the force applied to the object 2601. The effect of this is that the object 2601 is pressed against the ends of one or more lift pins 2604. This is an effect intended to achieve removal or make easier removal of the object 2601 from the stage 2602, because the object 2601 can be efficiently peeled off from the stage 2602.

In yet another embodiment, one or more, but not all, of the lift pins 2604 are controlled to apply a force to lift the object 2601. Alternatively, all of the lift pins 2604 may be controlled to apply a force for lifting the object 2601, but some lift pins 2604 are controlled to apply a greater force than others. The effect of this is that the lift pins 2604 may exert a greater force on one side of the object 2601 than the other side of the object 2601. This is expected to achieve the effect of removing or making easier the removal of the object 2601 from the stage 2602, because the object 2601 can be efficiently peeled off from the stage 2602.

In the above-described embodiments of aspects of the present invention, further comprising increasing the force that may be applied by each lift pin 2604 beyond that applied according to known techniques. There may be any number of lift pins 2604. For example, the number of lift pins 2604 may be 3, 6, 12, or more. Embodiments include having the ends of the lift pins 2604 that contact the object 2601 have an increased diameter over known lift pins 2604. Both of these and increasing the number of lift pins 2604 improves the force exerted by the lift pins 2604 on the surface of the object 2601, thereby reducing the risk of damage to the object 2601 by the exerted force.

In embodiments of aspects of the invention, the vibrations preferably have a small amplitude, so that they cause only small movements. Any of the techniques of the embodiments of the aspects of the invention may be combined with each other. For example, when the stage positioning device 2603 rotates the stage 2602 with respect to the z-direction, the lift pins 2604 may vibrate in the z-direction. In this implementation according to embodiments, the vibrating poppet pin 2604 is not mechanically locked in place.

Further examples may be described in the following clauses:

1. an object stage comprises

-a gripping mechanism for gripping an object;

-a loading/unloading mechanism configured to contact the object to load or unload the object;

-an electrical conductor configured to electrically connect the object to a voltage source or to electrical ground to apply a predetermined voltage to the object during at least a part of an unloading sequence of the object.

2. The object table of clause 1, wherein the electrical conductor is configured to form a low mechanical stiffness connection when the object is held on the object table.

3. The object table of clause 1 or clause 2, wherein the electrical conductor has a cross-section and wherein the electrical conductor has a mechanical stiffness that is lower than a mechanical stiffness of a wire having the same cross-section.

4. The stage of clause 2, wherein the mechanical stiffness is substantially zero for at least a portion of the time span when the object is held on the stage.

5. The object table of any of the preceding clauses wherein the electrical conductor is configured to disconnect the object from the voltage source or electrical ground when the object is held on the object table.

6. The object table of any of the preceding clauses, wherein the electrical conductor comprises a wire having a coiled portion.

7. The object table of clause 6, wherein the coiled portion comprises one or more windings or turns.

8. The object table according to clause 6 or 7, wherein the coiled portion is arranged in a spiral manner around a pin-shaped member of the loading/unloading mechanism.

9. The object table of clause 8, wherein an end of the coiled portion is connected to the pin-shaped member.

10. The object table of any of the preceding clauses, further comprising an electrode.

11. The object table of clause 10, wherein the electrode is mounted at or near a top surface of the object table.

12. The object table of clause 10 or 11, wherein the electrode substantially surrounds the clamping mechanism.

13. The object table of any of clauses 10-12, wherein the electrical conductor is configured to electrically connect the object to the electrode or the electrical ground.

14. The object table of any of clauses 10-13, wherein the elevated voltage is configured to be applied to the electrode during the at least a portion of an unloading sequence.

15. The object table of any of clauses 10-14, wherein the electrode is electrically insulated from the object during the at least a portion of an unloading sequence.

16. The object table of any of clauses 10-15, wherein

17. The electrode is configured to move away from the object prior to the at least a portion of the unloading sequence.

18. The object table of any of clauses 10-16, wherein the clamping mechanism is configured to move away from the electrode prior to the at least a portion of an unloading sequence.

19. The object table of any of clauses 10-17, wherein the loading/unloading mechanism comprises one or more pin-shaped members for contacting the object to unload the object.

20. The object table of clause 18, wherein the electrical conductor electrically connects at least one of the one or more pin members with the electrode or the electrical connection.

21. The object table of clause 19, wherein at least a portion of the electrical conductor is electrically shielded.

22. The object table of clause 20, wherein the object table comprises an electrical shield configured to shield at least a portion from the electrical conductor, the electrical shield being electrically connected to the electrode.

23. The object table of any of clauses 1-8, wherein the electrical conductor comprises a pin-shaped member for contacting the object during the at least a portion of the unloading sequence of the object.

24. The object table of clause 22, further comprising an electrode, wherein the electrical conductor is retractable when the electrode is charged to avoid a discharge from the electrode to the electrical conductor.

25. The object table of clause 23, wherein the electrical conductor is retractable to a position in which the electrical conductor is not surrounded by the clamping mechanism.

26. The object table of any of the preceding clauses, wherein the loading/unloading mechanism comprises one or more pin-shaped members for contacting the object to unload the object, at least one of the one or more pin-shaped members forming at least a portion of the electrical conductor.

27. The object table of any of clauses 22-25, wherein the pin-shaped member comprises an ionizable gas.

28. The object table of clause 26, wherein the pin member is configured to receive an ionizable gas.

29. The object table of clause 26 or 27, wherein the ionizable gas comprises Ar or Ne.

30. The object table of any of the preceding clauses, wherein the electrical connector comprises a first connector member and a second connector member, wherein the first connector member and the second connector member are configured to form an electrical connection during the at least part of the unloading sequence of the object.

31. The object table of clause 29, wherein the first connector member or the second connector member comprises a cantilever arm.

32. The object table of clause 30, wherein the cantilever comprises a bendable electrical conductor.

33. The object table of clause 29, wherein the first connector member comprises an aperture and the second connector member is configured to protrude through the aperture.

34. The object table of clause 32, wherein the first connector member or the second connector member comprises a plurality of brush wires to form the electrical connection when the second connector member protrudes out of the aperture.

35. The object table of any of the preceding clauses, wherein the electrical connector comprises an end actuator grip.

36. An object stage comprises

-a support structure;

-a gripping mechanism for holding an object, the gripping mechanism being arranged on the support structure;

-a loading/unloading mechanism configured to contact the object to load or unload the object;

-an electrode mounted to the support structure;

-an electrical conductor configured to electrically connect the object to the electrode during at least a part of an unloading sequence of the object.

37. The object table of clause 35, wherein the electrode substantially surrounds the clamping mechanism.

38. The object table of clause 35, wherein the electrical conductor includes a flexible portion configured to deform during the at least a portion of the unloading sequence of the object to maintain contact with the object.

39. An object table comprising:

an electrostatic chuck configured to hold an object;

a measurement unit configured to determine one or more electrical characteristics of the electrostatic chuck, the one or more electrical characteristics being indicative of one or more charge states of the electrostatic chuck;

a control unit configured to control one or more power supplies of the electrostatic chuck based on the determined one or more electrical characteristics before and/or during unloading of the object.

40. The stage of clause 38, wherein the electrostatic chuck comprises one or more electrodes for generating one or more electric fields between the object and the electrostatic chuck.

41. The stage of clause 38 or 39, wherein the measurement unit is configured to measure one or more voltages of the electrostatic clamp as the one or more electrical characteristics.

42. The stage of clause 40 when dependent upon clause 39, wherein the one or more voltages of the electrostatic clamp comprise one or more voltages of the one or more electrodes.

43. The object table of any of clauses 38-41, wherein the measurement unit is configured to measure one or more currents provided to the electrostatic clamp as the one or more electrical characteristics.

44. The stage of clause 42 when dependent upon clause 39, wherein the one or more currents provided to the electrostatic clamp comprise one or more currents provided to the one or more electrodes.

45. The object table of any of clauses 38-43, wherein the measurement unit is configured to measure one or more voltages of the object and/or one or more currents provided from/to the object.

46. The object table of clause 44, wherein the object table includes a connection pin configured to electrically connect to the object when the object is positioned on the object table, and wherein the measurement unit is configured to measure at least one of the one or more voltages of the object via the connection pin.

47. The object table of any of clauses 38-45, wherein the object table comprises a loading/unloading mechanism for loading and unloading the object.

48. The stage of clause 46, wherein the loading/unloading mechanism comprises a lift mechanism configured to lift the object from the electrostatic clamp.

49. The object table of any of clauses 38-47, wherein the measurement unit is configured to measure the one or more electrical characteristics of the electrostatic clamp during loading or unloading of the object.

50. The stage of any of clauses 38-48, wherein the stage further comprises an electrode surrounding the electrostatic clamp.

51. The stage of any of clauses 38-49, wherein the one or more charge states comprise a surface charge on a surface of the electrostatic chuck or a distribution of surface charges on a surface of the electrostatic chuck.

52. The stage of clause 50, wherein the control unit is configured to control one or more power supplies of the electrostatic chuck to generate one or more electric fields configured to at least partially compensate for an electric field generated by the surface charge to at least partially compensate for adhesion of the object caused by the surface charge of the electrostatic chuck.

53. The object table of any of clauses 1-37, wherein the at least a portion of the electrical conductor is electrically shielded.

54. An object table for holding an object, comprising:

an electrostatic clamp for clamping the object on the stage;

an ionizer device for providing an ionized flow of gas;

a control unit arranged to control the ioniser device to provide an ionised flow of the gas to the electrostatic clamp.

55. The stage of clause 53, wherein the control unit is arranged to receive an information signal representing a residual force or a residual charge, wherein the residual force is exerted on the object by the electrostatic clamp during unloading of the object from the electrostatic clamp, and wherein the residual charge is an electrostatic charge present on the electrostatic clamp when no charging voltage is applied to the electrostatic clamp, and wherein the control unit is arranged to control the ionizer device based on the information signal.

56. The object table according to clause 54, comprising a measurement unit for providing a measurement signal representing the residual force or the residual charge, wherein the information signal comprises the measurement signal, and wherein the control unit is arranged to control the ionizer device based on the measurement signal.

57. An object table for holding an object, comprising:

an electrostatic clamp for clamping the object on the stage;

a control unit arranged to provide the electrostatic clamp with a charging voltage for clamping the object on the electrostatic clamp and a discharging voltage for unclamping the object from the electrostatic clamp,

wherein the control unit is arranged to receive an information signal representing a residual force or a residual charge,

wherein the control unit is arranged to provide the discharge voltage based on the information signal.

58. The stage of clause 56, wherein the discharge voltage has an opposite polarity to the charge voltage.

59. The object table of clause 56 or 57, comprising an ionizer device for providing an ionized flow of a gas to the electrostatic clamp, wherein the control unit is arranged to control the ionizer device based on the information signal.

60. The object table of clauses 53-58, wherein the information signal comprises at least one of measurement information and/or estimation information.

61. The object table of any of clauses 56-59, wherein during unloading the control unit is arranged to receive an updated information signal representing an updated residual force or an updated residual charge, wherein the control unit is arranged to adjust the discharge voltage based on the updated information signal or the control unit is arranged to adjust the control of the ionizer device based on the updated information signal.

62. The object table of any of clauses 53-60, comprising an unloading mechanism, wherein the measurement unit is arranged to monitor a lifting force exerted by the unloading mechanism on the object to lift the object from the electrostatic clamp during unloading, wherein the measurement signal comprises a measurement of the lifting force.

63. The object table of clause 61, wherein the measurement unit comprises a force sensor for providing the measurement of the lifting force.

64. The stage of clause 62, wherein the unload mechanism comprises at least one lift pin arranged to push the object away from the electrostatic clamp during unloading, wherein the lift pin comprises the force sensor.

65. The object table of any of clauses 53-63, wherein the measurement unit comprises a gap sensor arranged to provide the measurement signal based on the object being in a first state and the object being in a second state, wherein in the first state the object is on the electrostatic clamp, and wherein in the second state the object is remote from the electrostatic clamp.

66. The object table of clause 64, wherein the object performs a motion from the first state to the second state, wherein the measurement signal is representative of the motion.

67. The object table of clause 64 or 65, wherein the gap sensor comprises a capacitive sensor.

68. The object table of any of clauses 53-66, wherein the control unit is arranged to compare the information signal to a threshold value.

69. An apparatus comprising the stage of any of clauses 53-67, wherein the apparatus is one of a particle beam apparatus, an electron beam apparatus, a scanning electron microscope, an electron beam writer, an electron beam projection lithography apparatus, an electron beam inspection apparatus, an electron beam defect verification apparatus, an electron beam metrology apparatus, a lithography apparatus, and a metrology apparatus.

70. A method for unloading an object from an electrostatic chuck, the method comprising:

unloading the object from the electrostatic chuck;

providing an ionized flow of a gas to the electrostatic chuck.

71. A method for unloading an object from an electrostatic chuck, the method comprising:

providing an information signal representative of a residual force or a residual charge, wherein the residual force is exerted on the object by the electrostatic clamp during unloading of the object from the electrostatic clamp, and wherein the residual charge is present on the electrostatic clamp when no charging voltage is applied to the electrostatic clamp;

providing a discharge voltage based on the information signal to release the object from the electrostatic chuck.

72. The method of clause 70, including the step of providing an ionized flow of gas to the electrostatic clamp based on the information signal.

73. A method for clamping an object to an electrostatic clamp, the method comprising:

i) providing the object on the electrostatic chuck;

ii) increasing the clamping voltage until a clamped state is detected in which the object is clamped on the electrostatic clamp;

iii) applying a first clamping voltage (V)_max) Determining the clamping voltage in the clamped state;

iv) providing less than the first clamping voltage (V) to the electrostatic clamp_max) Second clamping voltage (V)_final)。

74. The method of clause 72, wherein the gripping status is detected when a gripping parameter is within a threshold.

75. The method of clause 73, wherein the clamping parameter comprises one of a flatness of the object, a change in shape of the object caused by a change in the clamping voltage, and a central portion of the object in contact with the electrostatic clamp.

76. The method according to clause 74, comprising between steps iii) to iv):

v) reducing the clamping voltage until the clamped state is no longer detected;

vi) applying the third clamping voltage (V)_min) Determining the clamping voltage at which the clamping state is no longer detected；

vii) providing a voltage (V) to the electrostatic clamp higher than the third clamping voltage_min) Said second clamping voltage (V)_final)。

77. The method according to clause 75, comprising between steps vi) to vii):

viii) increasing the clamping voltage to the first clamping voltage (V)_max)。

78. The method of clauses 75 or 76, wherein the second clamping voltage (V)_final) Less than the third clamping voltage (V)_min) E.g. less than 140% or less than 130% or less than 120% or less than 110% or less than 105%.

79. The method of clause 72, including:

ix) during step iii), determining a clamping force between the object and the electrostatic clamp, an

x) providing the second clamping voltage (V) based on the clamping force_final)。

80. An object table for holding an object, wherein the object table is arranged to perform the method according to the preceding clauses 72 to 78.

81. The object table of clause 79, wherein the object table comprises:

the electrostatic clamp is used for clamping the object; and

a control unit to provide the clamping voltage to the electrostatic clamp.

82. The object table of clause 80, comprising a measurement unit for providing a measurement signal representative of the clamping parameter to the control unit.

83. The object table of clause 81, wherein the measurement unit is arranged to determine whether the object is flat or arcuate.

84. The stage of clause 81 or 82, wherein the measurement unit is arranged to determine a gap or capacitance between the object and the electrostatic clamp.

85. The object table of any of clauses 81-83, wherein the measurement unit is arranged to determine a height of the object.

86. The object table of any of clauses 79-84, comprising a force sensor, wherein during step iii) the force sensor is arranged to detect a clamping force when the first clamping voltage (V) is applied_max) When applied to the electrostatic clamp, the object is clamped on the electrostatic clamp by the clamping force.

87. The object table of clause 85, wherein the force sensor is movable to contact the object during step iii) and not contact the object during step iv).

88. The object table of clauses 79-86, wherein the control unit comprises a machine learning unit arranged to predict the third clamping voltage (V) based on the clamping voltage and the clamping parameter_min)。

89. An apparatus comprising the stage of any of clauses 79 to 87, wherein the apparatus is one of a particle beam apparatus, an electron beam apparatus, a scanning electron microscope, an electron beam writer, an electron beam projection lithography apparatus, an electron beam inspection apparatus, an electron beam defect verification apparatus, an electron beam metrology apparatus, a lithography apparatus, and a metrology apparatus.

90. The apparatus of clause 88, including lift pins for moving the object from and onto the electrostatic clamp, wherein the control unit is arranged to determine the clamping parameters based on the positions of the lift pins.

91. The apparatus of clause 88 or 89, comprising a height sensor for determining a height of the object, wherein the control unit is arranged to determine the clamping parameter based on a height signal from the height sensor.

92. A method of determining a residual charge of a clamping mechanism of a stage, the method comprising:

-impacting a surface of the clamping mechanism with a particle beam;

-detecting a response of the clamping mechanism caused by the impact of the surface, and

-determining the residual charge of the gripping mechanism based on the response.

93. The method of clause 91, wherein the particle beam comprises one or more electron beams.

94. The method of clauses 91 or 92, wherein the step of detecting the response comprises detecting secondary or scattered electrons emitted by the clamping mechanism.

95. The method of clause 93, wherein the step of detecting secondary electrons comprises measuring an energy spectrum of the secondary electrons.

96. The method of any of clauses 91-94, wherein the step of impacting the surface of the clamping mechanism is preceded by the step of positioning the clamping mechanism within an operating range of the particle beam.

97. The method of any of clauses 91-95, wherein the clamping mechanism comprises an electrostatic clamp.

98. The method of clause 96, wherein the electrostatic clamp comprises one or more electrodes.

99. The method of clause 97, wherein the one or more electrodes are embedded in the surface of the electrostatic chuck.

100. The method of any of clauses 91-98, wherein the step of impacting the surface comprises impacting the surface at a plurality of locations on the surface, and wherein the step of determining the residual charge comprises determining a residual charge distribution across the surface of the clamping mechanism.

101. The method of any of clauses 91-99, further comprising the step of applying one or more voltages to the gripper mechanism based on the response to at least partially dissipate the residual charge of the gripper mechanism.

102. A particle beam device configured to perform the method according to any of clauses 91-100.

103. A particle beam device, comprising:

-a particle beam generator;

-an object table for holding an object, the object table comprising a clamping mechanism for clamping the object to the object table;

-a detector;

-a control unit configured to:

o controlling the particle beam generator to cause a particle beam to impinge on a surface of the clamping mechanism;

-the detector configured to detect a response of the clamping mechanism caused by the clamping mechanism being impacted by the particle beam;

-the control unit, further configured to:

o receiving a detector signal from the detector, the detector signal being representative of the response of the gripper mechanism;

determining a residual charge on the clamping mechanism based on the detector signal.

104. The particle beam device of clause 102, wherein the particle beam comprises one or more electron beams.

105. The particle beam device of clause 102 or 103, wherein the device further comprises a positioning apparatus for positioning the stage relative to the particle beam generator.

106. The particle beam device of any of clauses 102-104, wherein the response comprises secondary or scattered electrons emitted by the clamping mechanism.

107. The particle beam device of clause 105, wherein the detector is configured to measure an energy spectrum of the secondary electrons.

108. The particle beam apparatus according to any of clauses 102-106, wherein the positioning device is configured to position the clamping mechanism within an operating range of the particle beam before the particle beam impacts the surface.

109. The particle beam device of any of clauses 102-107, wherein the clamping mechanism comprises an electrostatic clamp.

110. The method of clause 108, wherein the electrostatic clamp comprises one or more electrodes.

111. The method of clause 109, wherein one or more electrodes are embedded in the surface of the electrostatic chuck.

112. The method according to any of clauses 102 to 110, wherein the control unit is configured to control the particle beam to impinge on the surface at a plurality of locations on the surface, and wherein the control unit is configured to determine a residual charge distribution across the surface of the clamping mechanism.

113. The method according to any of clauses 102 to 111, wherein the control unit is further configured to further comprise the steps of: applying one or more voltages to the clamping mechanism based on the response to at least partially eliminate the residual charge of the clamping mechanism.

114. A method of reducing a surface charge of a clamping mechanism, the method comprising:

-generating a particle beam configured to have a Secondary Emission Yield (SEY) substantially equal to 1 in a surface of the clamping mechanism;

-impacting the surface of the clamping mechanism with the particle beam.

115. The method of clause 113, wherein the SEY is deemed substantially equal to 1 when the surface of the gripping mechanism is in a neutral state.

116. The method of clause 113 or 114, wherein the step of generating the particle beam comprises:

-determining a voltage difference between a source of the particle beam and the clamping mechanism required to obtain the SEY substantially equal to 1, and

-generating the particle beam by applying the determined voltage difference.

117. The method of clause 115, wherein the voltage difference is based on a material characteristic of the clamping mechanism.

118. The method of clause 115 or 116, wherein the voltage difference is selected such that when the surface of the clamping mechanism is in a neutral state, particles of the particle beam have a Landing Energy (LE) corresponding to the SEY substantially equal to 1.

119. The method of clause 100, wherein the voltage difference is selected based on a derivative of the SEY with respect to the LE of the clamping mechanism, wherein the derivative of the SEY is negative near the Landing Energy (LE).

120. The method of any of clauses 113-118, further comprising scanning the particle beam across the surface of the clamping mechanism.

121. The method of clause 119, wherein the particle beam comprises one or more electron beams.

122. The method of any of clauses 113-120, wherein the material of the clamping mechanism comprises SiO₂。

123. A particle beam device, comprising:

-a particle beam generator;

-an object table for holding an object, the object table comprising a clamping mechanism for clamping the object to the object table;

-a control unit configured to:

o controlling the particle beam generator to generate a particle beam configured to have a Secondary Emission Yield (SEY) substantially equal to 1 in a surface of the clamping mechanism;

o controlling the particle beam to impinge on the surface of the clamping mechanism.

124. The particle beam device of clause 122, wherein the control unit is further configured to:

o determining a voltage difference between a source of the particle beam and the clamping mechanism, the voltage difference being selected to cause the SEY to be substantially equal to 1, an

Controlling the particle beam generator to generate the particle beam by applying the determined voltage difference.

125. The particle beam device of clauses 122 or 123, wherein the particle beam generator comprises an electron beam generator.

126. The particle beam device of any of clauses 122-124, wherein the particle beam generator comprises a flood gun.

127. The particle beam device of any of clauses 122-125, further comprising a platform device configured to position the stage relative to the particle beam.

128. The particle beam device of any of clauses 122-126, wherein the SEY is considered substantially equal to 1 when the surface of the clamping mechanism is in a neutral state.

129. The particle beam device according to clauses 123-127 of reference clause 123, wherein the voltage difference is based on a material characteristic of the clamping mechanism.

130. The particle beam device of clause 127 or 128, wherein the voltage difference is selected such that when the surface of the clamping mechanism is in a neutral state, particles of the particle beam have a Landing Energy (LE) corresponding to the SEY substantially equal to 1.

131. The particle beam device of clause 129, wherein the voltage difference is selected based on a derivative of the SEY with respect to the LE of the clamping mechanism, wherein the derivative of the SEY is negative near the Landing Energy (LE).

132. The particle beam device of any of clauses 122-130, wherein the control unit is configured to control the particle beam generator to scan the particle beam across the surface of the clamping mechanism.

133. The particle beam device of clause 131, wherein the particle beam comprises one or more electron beams.

134. The particle beam device of any of clauses 122-132, wherein the material of the clamping mechanism comprises SiO₂。

135. An electron beam device comprising a particle beam device according to any of clauses 122 to 132.

136. An electron beam apparatus comprising a particle beam apparatus according to any of clauses 122 to 132, said particle beam apparatus comprising a first electron beam generator for processing said object and a second electron beam generator for at least partially counteracting or neutralizing the charge of said surface of said clamping mechanism.

137. An object table for holding an object, comprising:

an electrostatic clamp arranged to clamp the object on the stage;

one or more lift pins arranged to lift the object from the stage; and

a controller configured to send an actuation signal to one or more lift pin positioning devices to vibrate at least a portion of the one or more lift pins and/or the stage.

138. The stage of clause 136, wherein vibrating the one or more lift pins and/or the at least a portion of the stage comprises:

moving the one or more lift pins and/or the at least a portion of the stage in a direction substantially orthogonal to a surface of the electrostatic chuck; and/or

Moving the one or more lift pins and/or the at least a portion of the stage in a direction substantially parallel to the surface of the electrostatic chuck.

139. The object table of clauses 136 or 137, further comprising a positioning system comprising the one or more actuators.

140. The object table of clause 138, wherein the positioning system comprises:

a lift pin positioning apparatus comprising at least one actuator arranged to move each of the one or more lift pins;

a stage positioning apparatus comprising at least one actuator arranged to move the electrostatic clamp; and/or

A primary positioning device comprising at least one actuator arranged to move the platform positioning device.

141. An object table comprising:

an electrostatic clamp arranged to clamp the object on the stage;

one or more lift pins arranged to lift the object from the stage; and

a controller configured to send an actuation signal to one or more actuators to move at least a portion of the stage such that when the object is on the electrostatic clamp, the object is pressed against the one or more lift pins to move the object away from the electrostatic clamp.

142. The object table of clause 140, further comprising a locking system arranged to prevent the one or more lift pins from moving when the object is pressed against the one or more lift pins.

143. The object table of clause 141, wherein the locking system comprises one or more mechanical locks.

144. The object table of any of clauses 140-142, wherein one or more lift pins and/or at least a portion of the object table are arranged to vibrate in response to an actuation signal from the controller.

145. An object table comprising:

an electrostatic clamp arranged to clamp the object on the stage;

a plurality of lift pins arranged to lift the object from the stage; and

a controller configured to send actuation signals to one or more actuators to control movement of at least a portion of the stage and/or at least one of the plurality of lift pins such that when the object is on the surface of the support structure, at least one of the lift pins contacts the object and not all of the plurality of lift pins apply the same force to the object at the same time.

146. The stage of clause 144, wherein when the object is on the electrostatic clamp, the stage and/or the plurality of lift pins are arranged to tilt the object relative to the electrostatic clamp when the object is removed from the electrostatic clamp in response to the actuation signal sent by the controller.

147. The object table of clause 145, further comprising a locking system arranged to prevent movement of the one or more lift pins when the object is rotated.

148. The object table of clause 146, wherein the locking system comprises one or more mechanical locks.

149. The object table of any of clauses 144-147, wherein the controller is configured to send an actuation signal to one or more actuators to control the movement of the object table and/or the plurality of pins such that the object is rotationally vibrated when the object is on the electrostatic clamp.

150. The object table of any of clauses 144-148, wherein one or more lift pins and/or at least a portion of the object table are arranged to vibrate in response to the actuation signal and/or a further actuation signal from the controller.

151. An object table comprising:

an electrostatic clamp arranged to clamp the object on the stage; and

one or more electrodes arranged to charge the object;

wherein a first set of electrodes of the one or more electrodes is arranged to apply an electrical charge to the object; and

a second set of electrodes of the one or more electrodes is arranged to discharge the object.

152. The stage of clause 150, wherein the second set of electrodes of the one or more electrodes is used to discharge the object but not to apply an electrical charge to the object.

153. The stage of clauses 150 or 151, further comprising one or more lift pins configured to lift the object off the electrostatic clamp.

154. An object table comprising:

an electrostatic clamp arranged to clamp the object on the stage; and

cleaning equipment;

wherein the cleaning apparatus is arranged to clean the electrostatic clamp.

155. The object table of clause 153, wherein, when used with an object, the cleaning device is arranged to clean a surface of the object.

156. The stage of clauses 153 or 154, further comprising one or more lift pins configured to lift the object off the electrostatic clamp.

157. An object table for holding an object, comprising:

an electrostatic clamp arranged to clamp the object on the stage;

a neutralizer arranged to neutralize residual charge of the electrostatic chuck;

a control unit arranged to control the neutralizer.

158. The stage of clause 156, wherein the control unit is arranged to receive an information signal indicative of a residual force or the residual charge, wherein the residual force is exerted on the object by the electrostatic clamp during unloading of the object from the electrostatic clamp, wherein the residual charge is an electrostatic charge present on the electrostatic clamp when no voltage is applied to the electrostatic clamp, and wherein the control unit is arranged to control the neutralizer based on the information signal.

159. The object table of clause 157, wherein the information signal comprises at least one of measurement information, estimation information, and internal signal information.

160. The object table of clauses 157 or 158, further comprising a measurement unit, wherein the measurement unit comprises a force sensor configured to provide a measurement of the residual force and/or a gap sensor configured to provide a measurement of a gap between the object and the electrostatic clamp.

161. The stage of clause 157 or 158, further comprising a further measurement unit, wherein the further measurement unit is configured to determine the information signal indicative of the residual charge of the electrostatic chuck, the one or more electrical characteristics being indicative of the residual charge of the electrostatic chuck, and wherein the further measurement unit is configured to measure one or more voltages of the electrostatic chuck as the one or more electrical characteristics or the further measurement unit is configured to measure one or more currents provided to the electrostatic chuck as the one or more electrical characteristics.

162. The object table of clause 157 or 158, further comprising

A particle beam generator configured to generate a particle beam;

a detector configured to detect the particle beam;

wherein the control unit is configured to control the particle beam generator to impinge the particle beam on a surface of the electrostatic clamp,

wherein the detector is configured to detect a response of the electrostatic clamp, the response being caused by the electrostatic clamp being impacted by the particle beam, and

wherein the control unit is further configured to:

receiving a detector signal from the detector, the detector signal being indicative of the response of the electrostatic clamp, an

Determining the information signal representative of the residual charge on the electrostatic chuck based on the detector signal.

163. The stage of clause 156, wherein the neutralizer comprises a power source configured to apply a discharge voltage to the electrostatic clamp, and wherein the control unit is arranged to control the discharge voltage to the power source.

164. The object table of any of clauses 157-161, wherein the neutralizer comprises a power supply configured to apply a discharge voltage to the electrostatic chuck, and wherein the control unit is arranged to control the discharge voltage to the power supply based on the information signal representing the residual charge.

165. The object table of any of clauses 157-161, wherein the neutralizer is an ionizer device arranged to provide an ionized stream of a gas, and wherein the control unit is arranged to control the ionizer device to provide the ionized stream of the gas to the electrostatic clamp.

166. An apparatus comprising the stage of any of clauses 156-164, wherein the apparatus is one of a particle beam apparatus, an electron beam apparatus, a scanning electron microscope, an electron beam writer, an electron beam projection lithography apparatus, an electron beam inspection apparatus, an electron beam defect verification apparatus, an electron beam metrology apparatus, a lithography apparatus, and a metrology apparatus.

167. A method for unloading an object from an electrostatic chuck, the method comprising:

unloading the object from the electrostatic chuck;

neutralizing a residual charge of the electrostatic chuck before, during, and/or after the unloading step.

168. The method of clause 166, which comprises:

providing an information signal representative of a residual force or the residual charge, wherein the residual force is exerted on the object by the electrostatic clamp during unloading of the object from the electrostatic clamp, wherein the residual charge is present on the electrostatic clamp when no charging voltage is applied to the electrostatic clamp, and wherein the step of neutralizing the residual charge is based on the information signal.

169. The method of clause 167, wherein the information signal includes at least one of measurement information, estimation information, and internal signal information.

170. The method of any of clauses 166-168, comprising the step of providing an ionized flow of gas to the electrostatic chuck based on the information signal and/or the step of providing a discharge voltage to the electrostatic chuck based on the information signal.

Although specific reference is made in this document to electrostatic chucks, the invention of this document may be applied to any electrical chuck that utilizes similar electrical phenomena.

Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications. Other possible applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, Liquid Crystal Displays (LCDs), thin film magnetic heads, etc.

Although specific reference may be made in this text to embodiments of the invention in the context of lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection device, a metrology device, or any device that measures or processes an object such as a wafer (or other substrate) or a mask (or other patterning device). These devices may be generally referred to as lithographic tools. Such a lithography tool may use vacuum conditions or ambient (non-vacuum) conditions.

Although specific reference may be made herein to embodiments of the invention in the context of an inspection apparatus, the stage may be adapted to: an electron beam device, a scanning electron microscope, an electron beam writer, an electron beam projection lithography device, an electron beam inspection device, an electron beam defect verification device, or an electron beam measurement device.

While the invention has been explained in relation to its preferred embodiments, it is to be understood that other modifications and variations may be made without departing from the spirit and scope of the invention as hereinafter claimed.