阅读说明：本技术 用于测量对准标记的位置的设备和方法 (Apparatus and method for measuring position of alignment mark ) 是由 O·V·沃兹纳 于 2019-06-27 设计创作，主要内容包括：一种用于测量衬底上的多个对准标记中的每一个对准标记的位置的设备,包括：照射系统,配置成将来自辐射源的辐射束引导到所述衬底上的多个对准标记上；投影系统,配置成投影来自所述衬底的多个对准标记的图像,所述多个对准标记的图像是由所述辐射束从所述多个对准标记的衍射产生的；光学块,配置成调制来自所述衬底的被投影的多个对准标记的图像,并且其中所述光学块配置成将多个对准标记的被调制的图像投影到感测元件上以产生信号,多个对准标记中的每一个对准标记的位置根据所述信号被并行地确定。(An apparatus for measuring a position of each of a plurality of alignment marks on a substrate, comprising: an illumination system configured to direct a beam of radiation from a radiation source onto a plurality of alignment marks on the substrate; a projection system configured to project images of a plurality of alignment marks from the substrate, the images of the plurality of alignment marks resulting from diffraction of the radiation beam from the plurality of alignment marks; an optical block configured to modulate the projected images of the plurality of alignment marks from the substrate, and wherein the optical block is configured to project the modulated images of the plurality of alignment marks onto a sensing element to generate a signal from which a position of each of the plurality of alignment marks is determined in parallel.)

1. An apparatus for measuring a position of each of a plurality of alignment marks on a substrate, comprising:

an illumination system configured to direct a beam of radiation onto the plurality of alignment marks on the substrate,

a projection system configured to project images of the plurality of alignment marks from the substrate, the images of the plurality of alignment marks resulting from diffraction of the radiation beam from the plurality of alignment marks;

an optical block configured to modulate the projected images of the plurality of alignment marks from the substrate, and

wherein the optical block is configured to project the modulated images of the plurality of alignment marks onto a sensing element configured to generate a signal from which a position of each of the plurality of alignment marks is determined in parallel.

2. The apparatus of claim 1, wherein the projection system is configured such that images of the plurality of alignment marks are projected simultaneously into the optics block, and the optics block is configured to project modulated images of the plurality of alignment marks simultaneously onto different portions of the sensing element.

3. The apparatus of claim 1, wherein the apparatus is configured such that the modulated images of the plurality of alignment marks are projected sequentially onto the sensing element.

4. The apparatus of claim 3, wherein the projection system comprises an optical element, wherein the optical element is configured to sequentially direct images of the plurality of alignment marks into the optics block.

5. The apparatus of claim 4, wherein the optical element is a rotatable mirror, wherein the rotatable mirror is configured to rotate within a range of angles such that images of the plurality of alignment marks are sequentially reflected by the rotatable mirror into the optical block.

6. The apparatus of any preceding claim, wherein the sensing element comprises a plurality of pixels, wherein each of the plurality of pixels of the sensing element is configured to convert a periodic intensity variation caused by each of the plurality of alignment marks scanned by the radiation beam into the signal, wherein the signal is a separate signal for each of the plurality of alignment marks.

7. The device of claim 6, wherein the optical module is configured to project each of the modulated images of the plurality of alignment marks onto more than one of the plurality of pixels of the sensing element, and the sensing element is configured to combine signals from each of the plurality of pixels onto which the modulated images of the alignment marks are projected.

8. The apparatus of claim 6 or 7 when dependent on claims 3-5, wherein the sensing element is configured to generate the signal such that the signal can be sampled to construct the separate signal for each of the plurality of alignment marks.

9. The device of claims 3-5, wherein the sensing element comprises a single pixel, wherein the single pixel is configured to convert periodic intensity variations caused by the plurality of alignment marks being scanned into the signal such that the signal can be sampled to construct a separate signal for each of the plurality of alignment marks.

10. The apparatus of any of claims 3-5 and 9, wherein the projection system further comprises a transport system configured to transport the radiation beam from a first pupil plane to a second pupil plane of the projection system, wherein the optical element is located in the second pupil plane.

11. A metrology apparatus comprising an apparatus according to any one of the preceding claims.

12. A lithographic apparatus arranged to project a pattern from a patterning device onto a substrate, the lithographic apparatus comprising an apparatus according to any of claims 1-10.

13. A method of measuring a position of each of a plurality of alignment marks on a substrate, the method comprising:

directing a beam of radiation from a radiation source onto the plurality of alignment marks on the substrate using an illumination system;

projecting images of the plurality of alignment marks from the substrate using a projection system, the images of the plurality of alignment marks resulting from diffraction of the radiation beam from the plurality of alignment marks;

modulating the projected images of the plurality of alignment marks from the substrate in an optical block, an

Projecting the modulated images of the plurality of alignment marks onto a sensing element to generate a signal from which a position of each of the plurality of alignment marks is determined in parallel.

14. The method of claim 13, further comprising: simultaneously projecting images of the plurality of alignment marks into the optical block, and simultaneously projecting modulated images of the plurality of alignment marks onto different portions of the sensing element.

15. The method of claim 13, further comprising sequentially directing the modulated images of the plurality of alignment marks onto the sensing element.

Technical Field

The present invention relates to an apparatus and method for measuring the position of an alignment mark.

Background

A lithographic apparatus is a machine that is configured to apply a desired pattern onto a substrate. Lithographic apparatus can be used, for example, in the manufacture of Integrated Circuits (ICs). A lithographic apparatus may, for example, project a pattern (also often referred to as a "design layout" or "design") of a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate (e.g., a wafer).

As semiconductor manufacturing processes continue to advance, the size of circuit elements has been steadily decreasing while the amount of functional elements (such as transistors) per device has been steadily increasing for decades, following a trend commonly referred to as "Moore's law". To keep pace with Moire's Law, the semiconductor industry is pursuing technologies that enable the creation of smaller and smaller features. To project a pattern onto a substrate, a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features patterned on the substrate. Typical wavelengths currently used are 365nm (i-line), 248nm, 193nm and 13.5 nm. Lithographic apparatus using Extreme Ultraviolet (EUV) radiation having a wavelength in the range 4nm to 20nm, for example 6.7nm or 13.5nm, may be used to form smaller features on a substrate than lithographic apparatus using radiation having a wavelength of, for example, 193 nm.

In the manufacture of complex devices, a number of lithographic patterning steps are typically performed, whereby functional features are formed in successive layers on a substrate. A key aspect of the performance of a lithographic apparatus is therefore the ability to correctly and accurately place the applied pattern relative to features placed by a previous layer (either by the same apparatus or a different lithographic apparatus). To this end, the substrate is provided with one or more sets of marks. Each marker is a structure whose position can be later measured using a position sensor, typically an optical position sensor. The position sensor may be referred to as an "alignment sensor" and the mark may be referred to as an "alignment mark".

The lithographic apparatus may comprise one or more (e.g. multiple) alignment sensors by which the position of an alignment mark provided on the substrate can be accurately measured. The alignment (or position) sensor may use optical phenomena such as diffraction and interference to obtain position information from an alignment mark formed on the substrate. An example of an alignment sensor used in current lithographic apparatus is based on a self-referencing interferometer as described in US 69661116. Various enhancements and modifications of the position sensor have been developed, for example as disclosed in US2015261097a 1. Image sensor based alignment sensors are also known and can be applied to the present invention. The contents of all of these publications are incorporated herein by reference.

The mark or alignment mark may comprise a series of bars formed on or in a layer provided on the substrate or (directly) in the substrate. The bars may be regularly spaced and act as grating lines, so that the mark can be considered as a diffraction grating with a well-known spatial period (pitch). Depending on the orientation of these raster lines, the markers can be designed to allow measurement of position along the X-axis or along the Y-axis (which is oriented approximately perpendicular to the X-axis). The indicia comprising the bars arranged at +45 degrees and/or-45 degrees relative to both the X-axis and the Y-axis allow for combined X and Y measurements using the techniques described in US2009/195768A, which is incorporated herein by reference.

The alignment sensor optically scans each mark with a spot of radiation to obtain a periodically varying signal, such as a sine wave. The phase of the signal is analysed to determine the position of the mark relative to the alignment sensor and hence the position of the substrate relative to the alignment sensor, which in turn is fixed relative to a reference frame of the lithographic apparatus. So-called coarse and fine marks may be provided, associated with different (coarse and fine) mark sizes, so that the alignment sensor is able to distinguish between different cycle periods of the periodic signal and the exact position (phase) within a cycle period. Marks of different pitches may also be used for this purpose.

Measuring the position of the marks may also provide information about the deformation of the substrate on which the marks are arranged, e.g. in the form of a grid of wafers. Deformation of the substrate may occur, for example, due to electrostatic clamping of the substrate to the substrate table and/or heating of the substrate when the substrate is exposed to radiation.

It would be desirable to provide apparatus and methods for measuring the position of alignment marks that overcome or alleviate one or more problems associated with the prior art.

Disclosure of Invention

According to a first aspect of the present invention, there is provided an apparatus for measuring the position of each of a plurality of alignment marks on a substrate, comprising: an illumination system configured to direct a beam of radiation onto a plurality of alignment marks on a substrate; a projection system configured to project images of a plurality of alignment marks from the substrate, the images of the plurality of alignment marks resulting from diffraction of the radiation beam from the plurality of alignment marks; an optical block configured to modulate the projected images of the plurality of alignment marks from the substrate, and wherein the optical block is configured to project the modulated images of the plurality of alignment marks onto a sensing element configured to generate a signal from which the position of each of the plurality of alignment marks is determined in parallel (i.e., substantially simultaneously or in synchronism).

This has the following advantages: the positions of the plurality of alignment marks can be measured in parallel (substantially simultaneously or substantially simultaneously), and the plurality of alignment marks can be aligned in parallel. This may lead to an improvement of the overlay without having an impact on the productivity of the lithographic apparatus. Furthermore, the alignment sensor may measure any alignment mark on the substrate W without any limitation on the distance between the alignment marks. Furthermore, no detection grating is required.

The projection system may be configured such that images of the plurality of alignment marks are projected synchronously (temporally in parallel or substantially simultaneously) into the optical block, which may be configured to project modulated images of the plurality of alignment marks synchronously onto different portions of the sensing element.

The apparatus may be configured such that the modulated images of the plurality of alignment marks are projected sequentially onto the sensing element.

The projection system may include an optical element, wherein the optical element is configured to sequentially direct images of the plurality of alignment marks into the optics block.

The optical element may be a rotatable mirror, wherein the rotatable mirror may be configured to rotate within a range of angles such that images of the plurality of alignment marks are sequentially reflected by the rotatable mirror into the optical block.

The rotatable mirror may be configured such that the angular range causes all images of the illuminated plurality of aligned marks of the alignment mark to be reflected from the rotatable mirror into the optical block.

The sensing element comprises a plurality of pixels, wherein each of the plurality of pixels of the sensing element may be configured to convert a periodic intensity variation caused by each of a plurality of alignment marks scanned by the radiation beam into the signal, wherein the signal is a separate signal for each of the plurality of alignment marks. An advantage of using a sensing element with a plurality of pixels is that by selecting the appropriate pixels, the modulated image of the alignment mark can be separated from the other images surrounding the alignment mark.

The optical module may be configured to project each of the modulated images of the plurality of alignment marks onto more than one of the plurality of pixels of the sensing element, and the sensing element may be configured to combine signals from each of the plurality of pixels of the modulated images of the projected alignment marks.

The sensing element may comprise a CCD sensor or a CMOS sensor.

The size of the sensing element may be substantially equal to the size of an exposure slit of the lithographic apparatus.

The sensing elements may be configured to generate signals such that they may be sampled to construct a separate signal for each of the plurality of alignment marks.

The sensing element may include a single pixel, wherein the single pixel may be configured to convert periodic intensity variations caused by the plurality of alignment marks being scanned into the signal such that the signal may be sampled to construct a separate signal for each of the plurality of alignment marks. The advantage of using a single detector (with a single pixel) is that it is not affected by pixel signal drift that may occur, for example, with a CCD detector.

The projection system may further comprise a transport system configured to transport the radiation beam from a first pupil plane of the projection system to a second pupil plane, wherein the optical element is located in the second pupil plane.

The apparatus may comprise a radiation source configured to generate a beam of radiation.

The apparatus may include a lens to direct the beam of radiation to the plurality of alignment marks.

The apparatus may include a lens to project images from a plurality of alignment marks of the substrate.

The lens may be common to both the projection system and the illumination system.

The optics block may be a self-aligning interferometer.

According to a second aspect of the present invention, there is provided a metrology apparatus comprising the apparatus described above.

According to a third aspect of the invention, there is provided a lithographic apparatus arranged to project a pattern from a patterning device onto a substrate, the lithographic apparatus comprising an apparatus as described above.

According to a fourth aspect of the present invention, there is provided an apparatus for measuring the position of each of a plurality of alignment marks on a substrate, comprising: directing a beam of radiation from a radiation source onto a plurality of alignment marks on the substrate using an illumination system; projecting images of the plurality of alignment marks from the substrate using a projection system, the images of the plurality of alignment marks resulting from diffraction of the radiation beam from the plurality of alignment marks; modulating the projected images of the plurality of alignment marks from the substrate in an optical block, and projecting the modulated images of the plurality of alignment marks onto a sensing element to generate a signal from which the position of each of the plurality of alignment marks is determined in parallel.

The method may further comprise: synchronously projecting images of the plurality of alignment marks into the optical block and synchronously projecting modulated images of the plurality of alignment marks onto different portions of the sensing element.

The method further comprises the following steps: the modulated images of the plurality of alignment marks are sequentially directed onto the sensing element.

Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which:

FIG. 1 depicts a schematic view of a lithographic apparatus according to an embodiment of the invention;

fig. 2 depicts a schematic block diagram of a known alignment sensor AS;

FIG. 3 depicts a schematic view of an alignment sensor according to an embodiment of the invention;

FIG. 4 depicts a schematic view of the sensing elements of the alignment sensor according to an embodiment of the invention;

FIG. 5 depicts a diagram of sensed electrical signals from an alignment sensor according to an embodiment of the invention;

FIG. 6 depicts a schematic view of an alignment sensor according to an embodiment of the invention;

FIG. 7 depicts a schematic view of an alignment sensor according to an embodiment of the invention;

fig. 8 depicts a flow chart of a method for determining the position of an alignment mark according to an embodiment of the invention.

Detailed Description

In the present context, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g. having a wavelength of 365nm, 248nm, 193nm, 157nm or 126 nm) and extreme ultraviolet radiation (EUV, e.g. having a wavelength in the range of about 5-100 nm).

The terms "reticle", "mask" or "patterning device" as used herein may be broadly interpreted as referring to a generic patterning device that can be used to impart a patterned cross-section to an incident radiation beam, the patterned cross-section corresponding to a pattern to be created in a target portion of the substrate. The term "light valve" can also be used in this context. Examples of other such patterning devices, in addition to classical masks (transmissive or reflective, binary, phase-shift, hybrid, etc.), include programmable mirror arrays and programmable LCD arrays.

FIG. 1 schematically depicts a lithographic apparatus LA. The lithographic apparatus LA comprises: an illumination system (also referred to as an illuminator) IL configured to condition a radiation beam B (e.g. UV radiation, DUV radiation or EUV radiation); a mask support (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA in accordance with certain parameters; a substrate support (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate support in accordance with certain parameters; and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.

In operation, the illumination system IL receives a radiation beam from a radiation source SO, e.g., via a beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, and/or controlling radiation. The illuminator IL may be used to condition the radiation beam B to have a desired spatial and angular intensity distribution in its cross-section at the plane of the patterning device MA.

The term "projection system" PS as used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and/or electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, and/or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term "projection lens" herein may be considered as synonymous with the more general term "projection system" PS.

The lithographic apparatus LA may be of the type: wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the projection system PS and the substrate W, also referred to as immersion lithography. More information on immersion technology is given in US6952253, which is incorporated herein by reference.

The lithographic apparatus LA may also be of a type having two or more substrate supports WT (also referred to as "dual stage"). In such "multiple stage" machines the substrate supports WT may be used in parallel, and/or steps in preparation for subsequent exposure of a substrate W may be carried out on a substrate W positioned on one substrate support WT while another substrate W on another substrate support WT is used to expose a pattern on another substrate W.

In addition to the substrate support WT, the lithographic apparatus LA may include a metrology stage. The measuring platform is arranged to hold the sensor and/or the cleaning device. The sensor may be arranged to measure a property of the projection system PS or a property of the radiation beam B. The measurement platform may hold a plurality of sensors. The cleaning device may be arranged to clean a part of the lithographic apparatus, for example a part of the projection system PS, or a part of the system in which the immersion liquid is provided. The measurement platform may be moved under the projection system PS while the substrate support WT is away from the projection system PS.

In operation, the radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the mask support MT, and is patterned by the pattern (design layout) presented on the patterning device MA. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position measurement system PMS, the substrate support WT can be moved accurately, e.g. so as to position different target portions C in the path of the radiation beam B at positions which are focussed and aligned. Similarly, the first positioner PM and possibly another position sensor (which is not explicitly depicted in fig. 1) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B. Patterning device MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although substrate alignment marks P1, P2 are shown to occupy dedicated target portions, they may be located in spaces between multiple target portions. Substrate alignment marks P1, P2 are referred to as scribe-lane alignment marks when they are located between target portions C.

For the purpose of illustrating the invention, a cartesian coordinate system is used. The cartesian coordinate system has three axes, namely, an x-axis, a y-axis, and a z-axis. Each of the three axes is orthogonal to the other two axes. Rotation about the x-axis is referred to as Rx rotation. Rotation about the y-axis is referred to as Ry rotation. Rotation about the z-axis is referred to as Rz rotation. The x-axis and y-axis define a horizontal plane, while the z-axis is along the vertical direction. The cartesian coordinate system is not limiting to the invention and is used for illustrative purposes only. Instead, another coordinate system (such as a cylindrical coordinate system) may be used to illustrate the invention. The cartesian coordinate system may differ in orientation, for example such that the z-axis has a component along the horizontal plane.

Fig. 2 is a schematic block diagram of an embodiment of a known alignment sensor AS, such AS for example described in US 69661116, which is incorporated herein by reference. The invention is not limited to this embodiment of the alignment sensor but may also be applied to other types of alignment sensors. The radiation source RSO provides a radiation beam RB of one or more wavelengths which is diverted as an illumination spot SP by the diverting optics onto a mark, such as a mark AM located on the substrate W. In this example, the steering optics comprise a spot mirror SM and an objective lens OL. The diameter of the illumination spot SP used for illuminating the mark AM may be slightly smaller than the width of the mark itself.

The radiation diffracted by the marks AM is collimated (in this example via the objective lens OL) into an information-carrying beam IB. The term "diffraction" is intended to include zeroth order diffraction (which may be referred to as reflection) from the mark. The self-referencing interferometer SRI (e.g. of the type disclosed in US 69661116 mentioned above) utilizes a self-interfering beam IB which is then received by the photodetector PD. Additional optics (not shown) may be included to provide separate beams in the event that the radiation source RSO produces more than one wavelength. The photodetector may be a single element or may comprise a plurality of pixels (if desired). The photodetector may include a sensor array.

The steering optics, which in this example comprises the spot mirror SM, can also be used to block the zero order radiation reflected from the marks, so that the information-carrying beam IB comprises only the higher order diffracted radiation from the marks AM (which is not essential for the measurement, but improves the signal-to-noise ratio).

The intensity signal SI is supplied to the processing unit PU. The values for the X-position and the Y-position on the substrate with respect to the reference frame RF are output by a combination of the optical processing in the block SRI and the calculation processing in the unit PU.

A single measurement of the type shown fixes the position of the marks only within a certain range corresponding to one pitch of the marks. A coarser measurement technique is used in conjunction with the single measurement to identify which period of the sine wave is the period containing the marked location. To increase accuracy and/or to robustly measure the marks, regardless of the material from which the marks are made and over or under which materials the marks are located, the same process at a coarser and/or finer level may be repeated at different wavelengths. The wavelengths may be multiplexed and demultiplexed optically to process the wavelengths synchronously and/or the wavelengths may be multiplexed using time or frequency division.

In this example, the alignment sensor and spot SP remain stationary while the substrate W moves. Thus, the alignment sensor can be rigidly and accurately mounted to the reference frame while effectively scanning the mark AM in a direction opposite to the direction of movement of the substrate W. In this movement, the substrate W is controlled by mounting it on a substrate support and a substrate positioning system that controls the movement of the substrate support. A substrate support position sensor (e.g., an interferometer) measures the position of a substrate support (not shown). In an embodiment, one or more (alignment) marks are provided on the substrate support. Measuring the position of a mark provided on the substrate support allows the position of the substrate support determined by the position sensor to be calibrated (e.g. relative to a frame to which the alignment system is connected). Measuring the position of the alignment marks provided on the substrate allows determining the position of the substrate relative to the substrate support.

Fig. 3 is a schematic diagram of an apparatus 10 for measuring the position of a plurality of alignment marks 12 on a substrate W. The alignment marks 12 may be periodic gratings. The device 10, which may be referred to AS an alignment sensor, is in this embodiment similar to the known alignment sensor AS shown in fig. 2, but with some differences which will become apparent.

The device 10 is a measuring device. The apparatus 10 may be or form part of a metrology apparatus. Metrology apparatus is used to determine properties of the substrate W, in particular how properties of different substrates W vary, or how properties associated with different layers of the same substrate W vary between layers. The apparatus 10 may for example be integrated into the lithographic apparatus LA or may be a stand-alone device. It will be appreciated that the apparatus may be located elsewhere in the lithographic apparatus LA and/or may be used to measure different alignment marks located on different substrates.

The alignment sensor 10 comprises a radiation source 14 for generating a radiation beam 16, the radiation beam 16 being used to illuminate an alignment mark 12 on the substrate W. The arrows show the path of the radiation beam 16 through the alignment sensor 10. In other embodiments, the radiation source 14 may not be part of the alignment sensor 14, but a separate component.

The radiation beam 16 passes through an illumination system 18, the illumination system 18 being configured to direct the radiation beam 16 to an alignment mark 12 on the substrate W. The illumination system 18 includes a first illumination lens 20 and a second illumination lens 22, the first illumination lens 20 collimating the radiation beam 16, the second illumination lens 22 focusing the radiation beam 16 onto a spot mirror 24. An image of the radiation source 14 is projected in a pupil plane in which the spot mirror 24 is located. The spot mirror 24 reflects the radiation beam 16 onto a lens 26, the lens 26 being configured to direct (and focus) the radiation beam 16 onto the three alignment marks 12. Thus, each of the three alignment marks 12 is illuminated by the radiation beam 16 in parallel or in parallel (substantially simultaneously). In this embodiment, alignment marks 12 are each illuminated by a beam of radiation 16 from the same radiation source 14. However, the alignment marks can be illuminated by different radiation sources at the same time. However, to determine where the alignment marks are aligned, the same radiation source or combination of sources should be used for all alignment marks. The alignment marks 12 being imaged may be located anywhere on the substrate W as long as they are capable of being irradiated by the incident radiation beam 16, i.e. there is no need for the alignment marks 12 to be at a particular maximum or minimum distance in order to be imaged. It should be appreciated that in other embodiments, lens 26 may direct beam of radiation 16 onto a different number of alignment marks 12, assuming that alignment mark 12 is more than one alignment mark 12, i.e., more generally, lens 26 directs beam of radiation 16 onto multiple alignment marks 12.

Lens 26 focuses radiation beam 16 into an illumination spot that is incident on alignment mark 12. The alignment mark 12 is located in the focal (object) plane of the lens 26. The diameter of the illumination spot may be smaller than the width of the grating (alignment mark 12) in the X-direction. The radiation beam 16 is scanned across the substrate W (i.e. the substrate W is moved in the X direction relative to the alignment sensor 10) so that the illumination spot moves across the grating 12. The radiation beam 16 is diffracted by the gratings 12 and the diffracted radiation may be considered as an image of the plurality of gratings 12.

The image of the grating 12 (alignment mark) is projected by the same lens 26 that directs the beam of radiation 16 onto the alignment mark 12. Lens 26 may be more generally referred to as a projection system (or a portion of a projection system), which may include other optical components in other embodiments. In this embodiment, the lens 26 is common to both the projection system and the illumination system. It will be appreciated that in other embodiments, the projection system and illumination system may not have one or more lenses in common, and may be formed from additional or different optical components to direct and project the radiation beam, such as mirrors and beam splitters.

Lens 26 is configured to project an image of alignment mark 12 into optics block 28, as indicated by the arrow in FIG. 3. Optical block 28 is a self-referencing interferometer and may be considered to function in the same or similar manner as self-referencing interferometer SRI in fig. 2. For example, optics block 28 may split the radiation beam into two beams at the pupil plane and apply a 180 degree rotation between the split beams before combining the split beams again. This may be considered as modulation of the radiation beam. In other words, optical block 28 is configured to modulate the image of the plurality of alignment marks 12 to produce a modulated image of the plurality of alignment marks 12. These modulated images allow the position of the alignment marks 12 to be determined as will be described. It will be appreciated that in other embodiments, the modulation of the image of the alignment mark may be performed in a different manner.

The use of optics block 28 means that a detector plate (grating) need not be used to determine the position of alignment mark 12. The inspection board is typically a transparent plate with an inspection pattern that is the same as the image of the alignment marks. The detector plate is used to modulate the alignment mark light beam during movement along the image of the detector plate due to the alignment mark scanning. The detector will collect the image beam modulated by the detector plate and convert it into an electrical signal, which can then be used to determine the position of the alignment mark.

In this embodiment of the apparatus (alignment sensor) 10, each of the images of the plurality of alignment marks 12 is projected into the optics block 28 in parallel, i.e. substantially simultaneously. Optics block 28 then modulates the image of alignment marks 12 and generates a modulated image of alignment marks 12. The modulated images of alignment marks 12 are then projected from optics block 28 onto sensing elements 30 in parallel (i.e., simultaneously), as indicated by the arrows in fig. 3.

The sensing element 30 may be an intensity sensor. Each of the modulated images of the alignment marks 12 is projected onto a different portion of the sensing element 30. The sensing element 30 has a plurality of pixels 32. Thus, the modulated images of the alignment marks 12 are projected onto different pixels 32 of the sensing element 30. The size of the sensing element 30 may be substantially equal to the size of the exposure slit of the lithographic apparatus LA. In this embodiment, the sensing element 30 is a CCD sensor, but it should be appreciated that in other embodiments, the sensing element 30 may be a different type of sensor, such as a CMOS sensor.

Fig. 4 shows a schematic diagram of a sensing element 30, wherein a modulated image of the alignment mark 12 is shown on a plurality of pixels 32. Optical block 28 is configured to project the modulated image of alignment mark 12 onto more than one of the plurality of pixels 32 of sensing element 30. The modulated image of the alignment marks is displayed at the image sensor plane of the sensing element 30 as a periodic raster image 34. The raster image 34 is shown on different parts of the sensing element 30 and thus covers different pixels 32. That is, each raster image 34 covers a plurality of pixels 32, and does not cover the same pixels 32 as any other raster image 34. Thus, each raster image 34 may be analyzed separately and independently of each of the other raster images 34. Each of the raster images 34 should be projected onto a different pixel 32 for two reasons. First, if they are on the same pixel 32, it will be difficult to separate the signals of the overlapping alignment marks 12 to determine the aligned position of the alignment marks 12. Second, the optical design assumes that the grating image 34 is located at the same position (i.e., the optical axis of the lens 26 of the alignment sensor 10) relative to the center of the sensing element 30 as compared to the position at which the actual alignment mark 12 is located relative to the optical axis of the alignment sensor 10. In other embodiments, the raster image 34 may be located on one pixel, as long as the raster image 34 is a different pixel.

As previously described, radiation beam 16 is diffracted from alignment mark 12 to produce an image of alignment mark 12. During scanning of the alignment mark 12, an illumination spot moves over the alignment mark 12, which produces a periodic intensity variation in the modulated image of the alignment mark 12 when viewed by the sensing element 30. Scanning of alignment mark 12 relative to alignment sensor 10 results in a periodic intensity variation from zero to maximum intensity (after image modulation of alignment mark 12). This process is described in more detail above with reference to fig. 2.

Each of the plurality of pixels 32 of sensing element 30 is configured to convert periodic intensity variations caused by each of the plurality of alignment marks 12 scanned by radiation beam 16 into an electrical signal (hereinafter referred to as a signal). Since the modulated images of the alignment marks 12 are located on separate portions of the sensing element 30, i.e. covering different pixels 32, each of the modulated images of the alignment marks can be analyzed separately and independently. That is, the signal may be considered an independent signal for each of the plurality of alignment marks 12. By using these signals, the position of each of the alignment marks 12 is determined in parallel (i.e., simultaneously or simultaneously).

As described above, each of the modulated images of the alignment marks 12 is incident on (i.e., projected onto) more than one pixel 32 on the sensing element 30. The sensing element 30 (or another separate component) is configured to combine the signals from each of a plurality of pixels 32 onto which the modulated image of the alignment mark 12 is projected. Thus, the signals from all pixels 32 covered by the modulated image of the alignment mark 12 can be combined into one electrical signal.

Fig. 5 shows an example of a periodic electrical signal generated from a modulated image of one of the alignment marks 12 on the sensing element 30. During the scanning of the alignment mark 12, the amplitude of the electrical signal of the modulated image changes from a maximum value to a minimum value. In this case the whole pupil will be used, so the signal shape is triangular. A separate, similar periodic electrical signal will be present for each of the plurality of alignment marks 12. Thus, each of the alignment marks 12 may be processed independently. Therefore, the aligned position of each of the plurality of alignment marks 12 is independently determined. This determination of the positions of the alignment marks 12 occurs in parallel or in parallel, as multiple alignment marks 12 are imaged in parallel (i.e., simultaneously). In other embodiments, the shape of the electrical signal may be different (although still varying from a maximum and minimum value during scanning of the alignment mark). For example, in the case of a single use of an image of the alignment mark (e.g., first or third order, etc.), the signal may be a sine wave.

The signal, which is an intensity signal, is supplied to a processing unit (not shown). The processing unit performs calculation processing on the signal and outputs the position of the alignment mark 12. The processing unit may output values for the X and Y positions on the substrate W relative to the reference frame. The position of the alignment mark 12 may be set with respect to the substrate W.

Once the positions of the alignment marks 12 have been determined (i.e. measured by the alignment sensor 10), the aligned positions of the alignment marks 12 may be used, for example, to position patterns (layers) on the substrate W relative to each other. A processing unit may be used to align the alignment marks 12. More than one alignment mark is required in order to align the pattern on the substrate W. Since the positions of the alignment marks 12 have been determined in parallel, the alignment of the alignment marks 12 may also be performed in parallel or in parallel. That is, alignment may be performed on a plurality of alignment marks 12 in parallel or simultaneously.

Other measurement devices may include a single channel alignment sensor with a single detector (with or without a detection plate) and may not be able to align multiple alignment marks in parallel. Alternatively, other measurement devices may include multiple channel alignment sensors with several alignment sensor channels and several detectors. These multi-channel alignment sensors can align multiple alignment marks in parallel, but cannot align the alignment marks at arbitrary positions on the substrate W. This is because the distance between the alignment marks must be at least shorter than the distance between the alignment sensor channels. The alignment marks must be located in the center of the channel and the required size of the components of the channel determines the distance the alignment marks must be spaced apart. The minimum distance depends on the optical design of the alignment sensor. It must be large enough to prevent optical cross-talk between adjacent marks. Typically, the minimum distance is much smaller in this sense than the distance between sensor channels, which depends on the hardware design (lens, mirror size, etc.). The minimum distance is also dependent on the position to be aligned using the alignment marks with sufficient accuracy to perform the distance required for wafer alignment. For example, if only two alignment marks are used to align the wafer, the distance between the marks must typically be in the range of tens of millimeters in order to be able to accurately calculate, for example, the rotation and expansion of the wafer.

The alignment sensor 10 is advantageous in that it can measure the positions of a plurality of alignment marks 12 in parallel (i.e., simultaneously), and align the plurality of alignment marks 12 in parallel. In addition, the alignment sensor 10 does not need to detect a grating (plate). Furthermore, the alignment sensor 10 may measure any alignment mark 12 on the substrate W without any limitation on the distance between the alignment marks 12. Furthermore, the alignment sensor 10 is less complex than a multi-channel alignment sensor, at least because fewer components are required (e.g., no duplicate components of multiple channels are required). For example, the alignment sensor 10 may have only one optical block and one detector, while the multi-channel alignment sensor may have several optical blocks and several detectors (i.e., one optical block and one detector is imaged in parallel for each alignment mark).

The alignment sensor 10 may have the advantage that parallel alignment may be performed during substrate map measurements. Therefore, the number of alignment marks to be aligned can be increased without lowering productivity. In addition, for a lot including a plurality of substrates or wafers having a measurement-side limited sequence, productivity improvement can be achieved. The lithographic apparatus may have a measurement side and an exposure side. The substrate processing sequence on the measurement side of the lithographic apparatus may be: a wafer is loaded onto a wafer stage of a wafer stage chuck, a wafer z (height) map is then measured, and wafer alignment is then performed on a plurality of wafer alignment marks. Simultaneously, another platen chuck loaded with a wafer performs an exposure-side wafer processing sequence: lot correction (on the first wafer of the lot) followed by reticle alignment and then wafer exposure. If the duration of the measurement-side sequence is longer than the exposure-side sequence, the processing sequence of this batch is said to be measurement-side limited (from a productivity perspective). Using the alignment sensor 10 means that the measurement of the z (height) map of the wafer can be performed simultaneously with the wafer alignment. Therefore, since the alignment of the alignment marks is performed in parallel, the number of wafer alignment marks does not affect the productivity. The use of the alignment sensor 10 may result in improved overlay. An advantage of the alignment sensor 10 is that the throughput of the lithographic apparatus is independent of the number of alignment marks. The overlay performance of the lithographic apparatus depends on the number of alignment marks. That is, the more alignment marks that are measured, the more accurate the wafer alignment, thus improving overlay performance. Thus, the alignment sensor 10 provides the advantage of improving overlay performance without affecting the productivity of the lithographic apparatus.

Fig. 6 shows a further embodiment of the measuring device, which is an alignment sensor 40. Alignment sensor 40 is similar to alignment sensor 10 shown in fig. 3, and the same reference numerals have been used for the same components.

The alignment sensor 40 includes the same radiation source 14 and illumination system 18 as in fig. 3. The alignment sensor 40 has a projection system 42, which projection system 42 includes the lens 26, but also includes additional components to be described. Projection system 42 includes a transport system 44 (optical system), which transport system 44 is configured to transport the radiation beam (i.e., the image of alignment mark 12) from a first pupil plane PP1 to a second pupil plane PP2 of projection system 42. The second pupil plane PP2 is the pupil of the projection system or the pupil plane of the alignment sensor 10. This is the pupil plane in which the diffraction order of alignment mark 12 lies. The pupil plane PP2 is in principle identical to the pupil plane PP 1. Located in the second pupil plane PP2 is an optical element, which in this embodiment is a rotatable mirror 46. In order to sequentially image alignment marks 12 onto optics block 28 and sensing element 50, rotatable mirror 46 must be located at the pupil plane. Since the first pupil plane PP1 is already occupied by spot mirror 24, the transport system is used to create a second pupil plane PP2, in which the rotatable mirror 46 is located in the second pupil plane PP 2. The exact optical layout is not important, i.e. many different optical layouts may provide the desired result.

The rotatable mirror 46 performs rotational scanning during scanning of the plurality of alignment marks 12. Rotatable mirror 46 may be rotated through a range of angles in the direction indicated by double-headed arrow 48. This means that rotatable mirror 46 can be rotated within this angular range so that images of multiple alignment marks 12 are sequentially reflected by rotatable mirror 46 into optics block 28 (i.e., only one image of one of the alignment marks is allowed to enter the optics block at a time). Thus, rotatable mirror 46 (optical element) is configured to sequentially direct images of the plurality of alignment marks 12 into optical block 28. Rotatable mirror 46 reflects only a single image of alignment mark 12 (light beam) at a time and blocks the other images of alignment mark 12 (light beam).

The range of motion of rotatable mirror 46 may be selected so that it covers all images of alignment mark 12 illuminated along the X-axis on substrate W. In other words, the rotatable mirror 46 has an angular extent such that all images of the plurality of illuminated alignment marks 12 in the alignment mark 12 may be reflected (reflected) from the rotatable mirror 46 into the optics block 28. In other embodiments, in the described settings, the optical element may not be a rotatable mirror, and there may be other optical components configured to block all but one of the images of the alignment marks. As an example, to block all but one of the images of the alignment marks, the optical block and the sensing element may be rotated as a single body around the center of pupil PP 2. More generally, the alignment sensor 10 may be configured such that the modulated images of the alignment marks are sequentially projected onto the sensing elements.

Since only one image of the plurality of alignment marks 12 is directed into the optics block 28, only a single image of the alignment marks 12 is modulated at any one time in the optics block 28. That is, the images of the plurality of alignment marks 12 are sequentially modulated in optics block 28. Thus, only a single modulated image of the alignment mark 12 is incident on the sensing element 50 of the alignment sensor 40 at any one time, i.e. the modulated images of the alignment mark 12 are projected onto the sensing element 50 sequentially. As previously mentioned, the exact configuration of the optical arrangement (e.g., the transmission system 44 and the rotatable mirror 46) is not important. However, in this embodiment, it is important that the images of alignment marks 12 are placed sequentially in optics block 28 and on sensing element 50, since a single detector is used as sensing element 50.

In this embodiment, the sensing element 50 is a single detector, i.e. has a single pixel 52. The sensing element 50 may be an intensity sensor. The individual pixels 52 are configured to convert the periodic intensity variations caused by the scanning of the plurality of alignment marks 12 into electrical signals (similar to the electrical signals shown in fig. 5). Since only a single modulated image of alignment mark 12 is incident on sensing element 50 during a particular time period, the signal generated during that time period will be due only to the periodic intensity variations from that particular alignment mark 12. When the rotatable mirror 46 is rotated, then contributions from other alignment marks 12 will be included in the signal. The signal may then be sampled to isolate one or more samples of each alignment mark 12, which may be used to construct the signal for each alignment mark 12. That is, the signal may be sampled to construct a separate signal for each of the plurality of alignment marks 12. The sampling may be done in the processing unit or another component.

Once the signal for each alignment mark 12 is obtained, the position of each alignment mark 12 may be determined in a similar manner as the alignment sensor 10. That is, a signal (which is an intensity signal) is supplied to the processing unit to perform calculation processing on the signal and output the position of the alignment mark 12. The processing unit may output values for the X and Y positions on the substrate W relative to the reference frame. The position of the alignment mark 12 may be set with respect to the substrate W.

Thus, the position of each of the plurality of alignment marks 12 is independently determined. This determination of the position of the alignment marks 12 occurs in parallel or in parallel, as more than one alignment mark 12 will be imaged sequentially for each sample position scanned across the substrate W. Because all signal samples are collected during a single scan of the substrate W relative to the alignment sensor 40, the positions of the plurality of alignment marks 12 are derived in parallel (i.e., substantially simultaneously). The alignment of the alignment marks 12 may also be performed in parallel by using the positions of the alignment marks 12 determined in parallel.

The alignment sensor 40 allows parallel or simultaneous alignment on multiple alignment marks 12 using the sensing element 50 as a single detector. The advantage of using a single detector is that it is not affected by pixel signal drift that can occur with CCD detectors. Furthermore, the advantage of using a single detector is that an inexpensive detector can be used.

Fig. 7 shows a further embodiment of the measuring device, which is an alignment sensor 60. Alignment sensor 60 is the same as alignment sensor 40 in fig. 6 except that it has a different sensing element. The same reference numerals are used for the same components as in fig. 6, and will not be described again for the sake of brevity.

The alignment sensor 60 includes a sensing element 62, the sensing element 62 having a plurality of pixels 64 in this embodiment. The sensing element 62 may be the same as the sensing element 30 in fig. 3 or may, for example, be different, e.g., have a different number of pixels, etc. The sensing element 62 may be a CCD sensor or a CMOS sensor.

Alignment sensor 60 functions in the same manner as alignment sensor 40, i.e., the modulated images of the plurality of alignment marks 12 are sequentially projected from optics block 28 onto sensing element 62. In this case, however, the modulated image of the alignment mark 12 may cover more than one pixel 64 on the sensing element 62. In this embodiment, it is also important that the images of alignment marks 12 be placed sequentially into optics block 28 and projected onto sensing element 60, since the same pixel 64 is used for each alignment mark 12.

Each of the plurality of pixels 64 of sensing element 62 is configured to convert periodic intensity variations caused by each of the plurality of alignment marks 12 scanned by radiation beam 16 into an electrical signal. The sensing elements 62 are configured to generate signals such that they may be sampled to construct a separate signal for each of the plurality of alignment marks 12. Thus, the signal is a separate signal for each of the plurality of alignment marks 12 in the same manner as described with respect to sensing element 50 of FIG. 6.

However, optics block 28 is configured to project each modulated image of the plurality of alignment marks (albeit sequentially) onto more than one pixel 64 of sensing element 62. Sensing element 62 is configured to combine the signals from each pixel onto which the modulated image of alignment mark 12 is projected into a combined electrical signal in a similar manner as described with respect to sensing element 30 in fig. 3.

One or more signals (intensity signals) are supplied to a processing unit (not shown) to perform computational processing on the signals and output the position of the alignment mark 12. The positions of the alignment marks 12 may then be used to align the alignment marks 12 in parallel.

An advantage of using sensing element 62 (multiple pixels) instead of sensing element 50 (with a single detector) is that the modulated image of alignment mark 12 can be separated from other images surrounding alignment mark 12 by selecting the appropriate pixels. In this way, any influence of neighboring structures around the alignment mark 12 on the signal can be eliminated or at least reduced.

FIG. 8 is a flow chart representing a method according to an embodiment of the present invention. The method is described with respect to the alignment sensor 10 in fig. 3, but it will be appreciated that the method is applicable to other embodiments with the necessary modifications.

The first step of the method is to generate a radiation beam 16 in a radiation source 14 (step 100 of fig. 8). A radiation beam 16 is directed from a radiation source onto a plurality of alignment marks 12 on substrate W using illumination system 18 (step 102 in fig. 8). Radiation beam 16 is diffracted by alignment mark 12 (the grating), which produces an image of alignment mark 12. The method further comprises the following steps: an image of alignment mark 12 (i.e., a beam of radiation) is projected from substrate W (step 104 in fig. 8) in parallel (i.e., simultaneously) into optics block 28 using a projection system (lens 26).

Once the radiation beam, which retains information about the image of alignment mark 12, enters optics block 28, optics block 28 modulates the image of the alignment mark (step 106 in FIG. 8). The optics block 28 may be, for example, a self-referencing interferometer. In this case the modulation is performed by separating and self-aligning the radiation beams of the image of the alignment marks 12.

The next step is to project the modulated images of the plurality of alignment marks 12 onto the sensing element 30 in parallel (i.e., substantially simultaneously or simultaneously) (step 108 in fig. 8). Pixels 32 of sensing element 30 convert the periodic intensity variations caused by each alignment mark 12 scanned by beam of radiation 16 into electrical signals (step 110 in FIG. 8). This signal is a separate signal for each alignment mark 12.

The next step is to determine the position of each of the plurality of alignment marks 12 in parallel (step 112 in fig. 8). This can be done by computing the processing signal in a processing unit. Finally, the final step is to align a plurality of alignment marks 12 in parallel on the substrate W. This may be done by any method that uses the position of the alignment marks to align the alignment marks, e.g. to align a pattern on the substrate W.

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. Possible other applications include integrated optical systems, guidance and detection patterns for magnetic domain memories, the manufacture of flat panel displays, Liquid Crystal Displays (LCDs), thin film magnetic heads, etc.

Although specific reference may be made in this text to the use of 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 apparatus, a metrology apparatus, or any apparatus 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 have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention is not limited to optical lithography, and may be used in other applications, for example imprint lithography, where the context allows.

Where the context allows, embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include Read Only Memory (ROM); random Access Memory (RAM); a magnetic storage medium; an optical storage medium; a flash memory device; electrical, optical, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc., or other apparatus that, when executed, may cause an actuator or other device to interact with the physical world.

While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The above description is intended to be illustrative and not restrictive. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.