阅读说明：本技术 一种套刻误差测量装置及测量方法 (Overlay error measuring device and method ) 是由 许翱鹏 周钰颖 于 2019-11-28 设计创作，主要内容包括：本发明实施例公开了一种套刻误差测量装置及测量方法。装置包括光源、光束传输模块、镜头及测量模块；测量模块包括第一成像单元、第二成像单元及处理单元；光源提供照明光束；光束传输模块将照明光束传输至镜头；接收待测物体衍射并经镜头透射后的信号光束并分束成第一信号光束和第二信号光束；第一信号光束包括待测物体的负级次衍射光,第二信号光束包括正级次衍射光,第一信号光束传输至第一成像单元,第二信号光束传输至第二成像单元；处理单元根据第一成像单元和第二成像单元获取的信号计算待测物体的套刻误差。本发明实施例的技术方案,可同时测量套刻标记的正/负级次衍射光,无需进行光阑切换,提高套刻误差测量效率,提高产率。(The embodiment of the invention discloses an overlay error measuring device and a measuring method. The device comprises a light source, a light beam transmission module, a lens and a measurement module; the measuring module comprises a first imaging unit, a second imaging unit and a processing unit; a light source providing an illumination beam; the light beam transmission module transmits the illumination light beam to the lens; receiving a signal beam diffracted by an object to be detected and transmitted by a lens and splitting the signal beam into a first signal beam and a second signal beam; the first signal light beam comprises negative-order diffraction light of an object to be detected, the second signal light beam comprises positive-order diffraction light, the first signal light beam is transmitted to the first imaging unit, and the second signal light beam is transmitted to the second imaging unit; the processing unit calculates the alignment error of the object to be measured according to the signals acquired by the first imaging unit and the second imaging unit. According to the technical scheme of the embodiment of the invention, the positive/negative order diffracted light of the overlay mark can be measured simultaneously, diaphragm switching is not needed, the overlay error measurement efficiency is improved, and the yield is improved.)

1. An overlay error measuring device is characterized by comprising a light source, a light beam transmission module, a lens and a measuring module;

the measurement module comprises a first imaging unit, a second imaging unit and a processing unit, and the first imaging unit and the second imaging unit are connected with the processing unit;

the light source is used for providing an illumination light beam;

the light beam transmission module is used for transmitting the illumination light beam to the lens, and the illumination light beam forms preset illumination distribution on a pupil surface of the lens;

the beam transmission module is also used for receiving the signal beam diffracted by the object to be detected and transmitted by the lens and splitting the beam to form a first signal beam and a second signal beam;

the signal light beam comprises positive-order diffraction light, negative-order diffraction light and 0-order diffraction light, wherein the illumination light beam is diffracted by the object to be detected, the first signal light beam is obtained by filtering out the 0-order diffraction light and the positive-order diffraction light from part of the signal light beam, the second signal light beam is obtained by filtering out the 0-order diffraction light and the negative-order diffraction light from part of the signal light beam, the first signal light beam is transmitted to the first imaging unit, and the second signal light beam is transmitted to the second imaging unit;

the processing unit is used for calculating the alignment error of the object to be measured according to the signals acquired by the first imaging unit and the second imaging unit.

2. The overlay error measuring apparatus of claim 1 wherein the beam transmission module comprises a beam splitting unit and a diffractive light splitting unit;

the beam splitting unit is used for receiving the illumination light beam emitted by the light source, transmitting the illumination light beam to the lens, receiving the signal light beam transmitted by the lens and transmitting part of the signal light beam to the diffraction light separation unit;

the diffraction light separation unit comprises a first output end and a second output end, the first output end is used for filtering out 0-order diffraction light and positive-order diffraction light in the signal light beams to form the first signal light beams, and the second output end is used for filtering out 0-order diffraction light and negative-order diffraction light in the signal light beams to form the second signal light beams.

3. The overlay error measuring apparatus according to claim 2, wherein the diffracted light separating unit includes a light splitting member, a first light shielding member, and a second light shielding member;

the beam splitting component is used for splitting the signal light beam into two beams of light transmitted along a first direction and a second direction, the first shading component is used for shading 0-order diffraction light and positive-order diffraction light in the first direction, the second shading component is used for shading 0-order diffraction light and negative-order diffraction light in the second direction, and the first direction is intersected with the second direction.

4. The overlay error measuring apparatus of claim 2 wherein the beam splitting assembly comprises a beam splitting prism or a half mirror.

5. The overlay error measuring apparatus according to claim 2, wherein the diffracted light separating unit includes a reflecting member and a third light shielding member;

the reflecting component is used for reflecting part of light rays in the signal light beam so as to separate negative-order diffraction light from positive-order diffraction light in the signal light beam;

the third shading component is used for shading 0-order diffraction light in the signal light beam.

6. The overlay error measuring apparatus of claim 5 wherein said reflective assembly comprises a flat mirror.

7. The overlay error measurement apparatus of claim 2 wherein the measurement module further comprises a third imaging unit, the third imaging unit being connected to the processing unit;

the beam splitting unit is further used for splitting the signal light beam into a first light beam and a second light beam, the first light beam is transmitted to the third imaging unit, and the second light beam is transmitted to the diffraction light separation unit;

the processing unit is further configured to normalize the light intensities obtained by the first imaging unit and the second imaging unit according to the light intensity obtained by the third imaging unit.

8. The overlay error measurement apparatus of claim 7 wherein the beam delivery module further comprises a first power zoom group disposed between the light source and the beam splitting unit, and/or

A second magnification zoom lens group disposed between the beam splitting unit and the diffractive light separating unit, and/or

A third power zoom lens group disposed between the beam splitting unit and the third imaging unit;

the first magnification zoom lens group, the second magnification zoom lens group and the third magnification zoom lens group are used for enlarging or reducing light spots of light beams.

9. The overlay error measuring apparatus of claim 2 wherein the beam delivery module further comprises a first lens group and a second lens group;

the first lens group comprises at least one convergent lens, is positioned between the first output end of the diffraction light separation unit and the first imaging unit, and is used for converging the first signal light beam to a photosensitive surface of the first imaging unit;

the second lens group comprises at least one converging lens and is positioned between the second output end of the diffraction light separation unit and the second imaging unit, and the second lens group is used for converging the second signal light beam to a photosensitive surface of the second imaging unit.

10. The overlay error measuring apparatus of claim 1 further comprising an illumination diaphragm positioned between the light source and the beam delivery module, the illumination diaphragm having a light aperture disposed at a center thereof.

11. The overlay error measuring apparatus of claim 1 wherein the lens is a microscope objective.

12. The overlay error measuring apparatus of claim 1 wherein the light source further comprises a polarizing device for adjusting the polarization state of the illumination beam.

13. An overlay error measurement method, performed by the overlay error measurement apparatus according to any one of claims 1 to 12, the overlay error measurement method comprising:

the light source generates an illumination beam;

the light beam transmission module transmits the illumination light beam to the lens, receives a signal light beam which is diffracted by an object to be detected and transmitted by the lens and splits the signal light beam into a first signal light beam and a second signal light beam;

the illumination light beam forms preset illumination distribution on a pupil surface of the lens, the signal light beam comprises positive-order diffracted light, negative-order diffracted light and 0-order diffracted light which are diffracted by the illumination light beam through the object to be detected, the first signal light beam is obtained by filtering out the 0-order diffracted light and the positive-order diffracted light from part of the signal light beam, the second signal light beam is obtained by filtering out the 0-order diffracted light and the negative-order diffracted light from part of the signal light beam, the first signal light beam is transmitted to the first imaging unit, and the second signal light beam is transmitted to the second imaging unit;

and the processing unit calculates the overlay error of the object to be measured according to the signals acquired by the first imaging unit and the second imaging unit.

14. The overlay error measurement method of claim 13, wherein the calculating of the overlay error of the object to be measured by the processing unit based on the signals obtained by the first imaging unit and the second imaging unit comprises:

the first imaging unit acquires-1-order diffraction light intensity I of an object to be detected₁ ^-；

The second imaging unit acquires the +1 st order diffraction light intensity I of the object to be measured₁ ⁺；

The asymmetry of the +1 st order diffracted intensity and-1 st order diffracted intensity is calculated according to:

wherein k represents a scale factor, Δ represents a preset offset of the overlay mark, and ε represents an overlay error;

calculating the overlay error of the object to be measured according to the following formula:

Technical Field

The embodiment of the invention relates to the semiconductor technology, in particular to an overlay error measuring device and an overlay error measuring method.

Background

According to a photolithography measurement Technology Roadmap given by an International Technology Roadmap for Semiconductors (ITRS), as Critical Dimensions (CD) of a photolithography pattern enter 22nm and below process nodes, especially as Double exposure (Double Patterning) Technology is widely applied, a measurement accuracy requirement for photolithography process overlay (overlay) has entered the sub-nanometer field. Due to the limitation of Imaging resolution limit, the traditional Imaging-Based overlay measurement (IBO) technology Based on Imaging and image recognition has gradually failed to meet the requirements of new process nodes on overlay measurement. The overlay measurement technology (DBO) Based on Diffraction light detection is becoming the main means of overlay measurement.

The basic principle of the overlay measurement technology based on diffraction light is as follows: an overlay measuring mark comprising an upper layer of grating and a lower layer of grating is formed on an object to be measured, when measuring light is normally incident on the overlay measuring mark, the overlay error of the object to be measured is calculated by utilizing the asymmetry of a mark structure caused by the overlay error and the asymmetry of the light intensity of positive/negative order diffracted light. The existing overlay error measuring device needs to set a diaphragm to shield 0-order and negative-order diffracted light when measuring positive-order diffracted light, and needs to set the diaphragm to shield 0-order and positive-order diffracted light when measuring negative-order diffracted light, namely, the diaphragm must be switched at least once for one measurement, so that the measurement speed is low, and the yield is greatly influenced.

Disclosure of Invention

The embodiment of the invention provides an overlay mark measuring device and a measuring method, the device can simultaneously measure the positive/negative order diffraction light of an overlay mark, diaphragm switching is not needed, overlay error measuring efficiency can be improved, and yield is improved.

In a first aspect, an embodiment of the present invention provides an overlay error measurement apparatus, including a light source, a light beam transmission module, a lens, and a measurement module;

the measurement module comprises a first imaging unit, a second imaging unit and a processing unit, and the first imaging unit and the second imaging unit are connected with the processing unit;

the light source is used for providing an illumination light beam;

the light beam transmission module is used for transmitting the illumination light beam to the lens, and the illumination light beam forms preset illumination distribution on a pupil surface of the lens;

the beam transmission module is also used for receiving the signal beam diffracted by the object to be detected and transmitted by the lens and splitting the beam to form a first signal beam and a second signal beam;

the signal light beam comprises positive-order diffraction light, negative-order diffraction light and 0-order diffraction light, wherein the illumination light beam is diffracted by the object to be detected, the first signal light beam is obtained by filtering out the 0-order diffraction light and the positive-order diffraction light from part of the signal light beam, the second signal light beam is obtained by filtering out the 0-order diffraction light and the negative-order diffraction light from part of the signal light beam, the first signal light beam is transmitted to the first imaging unit, and the second signal light beam is transmitted to the second imaging unit;

the processing unit is used for calculating the alignment error of the object to be measured according to the signals acquired by the first imaging unit and the second imaging unit.

In a second aspect, an embodiment of the present invention further provides an overlay error measuring method, which is performed by using the overlay error measuring apparatus, where the overlay error measuring method includes:

the light source generates an illumination beam;

the light beam transmission module transmits the illumination light beam to the lens, receives a signal light beam which is diffracted by an object to be detected and transmitted by the lens and splits the signal light beam into a first signal light beam and a second signal light beam;

the illumination light beam forms preset illumination distribution on a pupil surface of the lens, the signal light beam comprises positive-order diffracted light, negative-order diffracted light and 0-order diffracted light which are diffracted by the illumination light beam through the object to be detected, the first signal light beam is obtained by filtering out the 0-order diffracted light and the positive-order diffracted light from part of the signal light beam, the second signal light beam is obtained by filtering out the 0-order diffracted light and the negative-order diffracted light from part of the signal light beam, the first signal light beam is transmitted to the first imaging unit, and the second signal light beam is transmitted to the second imaging unit;

and the processing unit calculates the overlay error of the object to be measured according to the signals acquired by the first imaging unit and the second imaging unit.

The overlay error measuring device provided by the embodiment of the invention comprises a light source, a light beam transmission module, a lens and a measuring module; the measuring module comprises a first imaging unit, a second imaging unit and a processing unit, and the first imaging unit and the second imaging unit are connected with the processing unit; providing an illumination beam by a light source; the illumination light beams are transmitted to the lens through the light beam transmission module, and preset illumination distribution is formed on the pupil surface of the lens by the illumination light beams; then, a signal beam which is diffracted by the object to be detected and transmitted by the lens is received by the beam transmission module and split into a first signal beam and a second signal beam; the signal light beam comprises positive-order diffraction light, negative-order diffraction light and 0-order diffraction light, wherein the illumination light beam is diffracted by an object to be detected, the first signal light beam is obtained by filtering out the 0-order diffraction light and the positive-order diffraction light in a part of signal light beams, the second signal light beam is obtained by filtering out the 0-order diffraction light and the negative-order diffraction light in a part of signal light beams, the first signal light beam is transmitted to the first imaging unit, and the second signal light beam is transmitted to the second imaging unit; and calculating the alignment error of the object to be measured by the processing unit according to the signals acquired by the first imaging unit and the second imaging unit. The overlay error measuring device provided by the embodiment splits a signal light beam into a first signal light beam comprising negative-order diffracted light and a second signal light beam comprising positive-order diffracted light through a light beam transmission module, and respectively receives the first signal light beam and the second signal light beam through a first imaging unit and a second imaging unit, so that the positive/negative-order diffracted light of an overlay mark is measured simultaneously, the overlay error is calculated through a processing unit, diaphragm switching is not required, the overlay error measuring efficiency can be improved, and the yield is improved.

Drawings

Fig. 1 is a schematic structural diagram of an overlay error measurement apparatus according to an embodiment of the present invention;

FIG. 2 is a schematic structural diagram of an object under test according to an embodiment of the present invention;

FIG. 3 is a schematic top view of the overlay mark of the object to be measured in FIG. 2;

FIG. 4 is a schematic structural diagram of another overlay error measurement apparatus provided in an embodiment of the present invention;

FIG. 5 is a schematic diagram of an optical path of an illumination beam when the illumination beam diffracts on a surface of an object to be measured according to an embodiment of the present invention;

FIG. 6 is a schematic structural diagram of another overlay error measurement apparatus according to an embodiment of the present invention;

FIG. 7 is a schematic structural diagram of another overlay error measurement apparatus according to an embodiment of the present invention;

FIG. 8 is a schematic structural diagram of another overlay error measurement apparatus according to an embodiment of the present invention;

FIG. 9 is a schematic structural diagram of another overlay error measurement apparatus according to an embodiment of the present invention;

FIG. 10 is a schematic structural diagram of another overlay error measurement apparatus according to an embodiment of the present invention;

FIG. 11 is a schematic structural diagram of another overlay error measurement apparatus according to an embodiment of the present invention;

FIG. 12 is a schematic flow chart illustrating a method for measuring overlay error according to an embodiment of the present invention;

FIG. 13 is a schematic structural diagram of a micro tag provided in an embodiment of the present invention;

FIG. 14 is a schematic illustration of the principle of measuring overlay error using the micro-marks shown in FIG. 13;

FIG. 15 is a schematic view of an image acquired by the third imaging unit;

FIG. 16 is a schematic diagram of a simulation input condition provided by an embodiment of the present invention;

FIG. 17 is a schematic diagram of a simulated angular spectrum image of a third imaging unit;

FIG. 18 is a schematic view of an angular spectrum image of a first imaging unit and a second imaging unit;

fig. 19 is a schematic view of images acquired by the first imaging unit and the second imaging unit.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.

The terminology used in the embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. It should be noted that the terms "upper", "lower", "left", "right", and the like used in the description of the embodiments of the present invention are used in the angle shown in the drawings, and should not be construed as limiting the embodiments of the present invention. In addition, in this context, it is also to be understood that when an element is referred to as being "on" or "under" another element, it can be directly formed on "or" under "the other element or be indirectly formed on" or "under" the other element through an intermediate element. The terms "first," "second," and the like, are used for descriptive purposes only and not for purposes of limitation, and do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

Fig. 1 is a schematic structural diagram of an overlay error measurement apparatus according to an embodiment of the present invention. Referring to fig. 1, the overlay error measuring apparatus includes a light source 10, a light beam transmission module 20, a lens 30, and a measuring module 40; the measurement module 40 includes a first imaging unit 41, a second imaging unit 42 and a processing unit 43, and the first imaging unit 41 and the second imaging unit 42 are both connected with the processing unit 43; the light source 10 is used for providing an illumination light beam a; the light beam transmission module 20 is configured to transmit the illumination light beam a to the lens 30, and the illumination light beam a forms a preset illumination distribution on a pupil surface of the lens 30; the beam transmission module 20 is further configured to receive the signal beam b diffracted by the object to be measured 100 and transmitted through the lens 30, and split the signal beam b into a first signal beam b1 and a second signal beam b 2; the signal light beam b comprises positive-order diffraction light, negative-order diffraction light and 0-order diffraction light, wherein the illumination light beam is diffracted by an object to be detected, the first signal light beam b1 is obtained by filtering out the 0-order diffraction light and the positive-order diffraction light from part of the signal light beam b, the second signal light beam b2 is obtained by filtering out the 0-order diffraction light and the negative-order diffraction light from part of the signal light beam b, the first signal light beam b1 is transmitted to the first imaging unit 41, and the second signal light beam b2 is transmitted to the second imaging unit 42; the processing unit 43 is used for calculating an alignment error of the object 100 to be measured according to the signals acquired by the first imaging unit 41 and the second imaging unit 42.

The alignment error measuring device provided by the embodiment is used for measuring the alignment error of an object to be measured, wherein the object to be measured can be an integrated circuit chip. Fig. 2 is a schematic structural diagram of an object to be measured in an embodiment of the invention, and fig. 3 is a schematic top view of an overlay mark of the object to be measured in fig. 2. Referring to fig. 2, the object to be measured includes a substrate 1, a first grating structure 2 formed on the substrate 1, a second grating structure 4, and an intermediate layer 3 located between the first grating structure 2 and the second grating structure 4, where the first grating structure 2 is made of a previous exposure pattern by semiconductor processes such as development, etching, and deposition, and the second grating structure 4 is usually a photoresist pattern after this exposure and development. The material and distribution of the intermediate layer 3 are common knowledge and will not be described herein. In the standard preset case, there is a preset offset 5, denoted Δ, between the first grating structure 2 and the second grating structure 4. However, due to various factors, the actual situation is as shown in fig. 3, and the offset 6 between the first grating structure 2 and the second grating structure 4 is Δ + epsilon, where epsilon is the overlay error, i.e. the amount to be obtained in this embodiment. When the preset offset is 5, the preset offset is-delta. The offset 6 of the second measurand is-delta + epsilon with overlay error.

Where the light source 10 is used to provide the illumination beam a, optionally, the light source 10 may comprise a composite light source producing at least two discrete wavelengths or a light source producing a continuous wavelength. Because the wavelengths of the measuring lights required by different processes are different, the light source in this embodiment may adopt a plurality of monochromatic light combined light sources, and the light is combined by devices such as a dichroic mirror, a grating, a beam combining optical fiber, and the like, or may adopt a broadband light source that generates continuous wavelengths, and a filter, a monochromator, and the like are configured as required to realize output of a specified wavelength or a specified wavelength band, and the specific light source module is set according to the lighting conditions required by the actual processes, which is not limited in the embodiments of the present invention. In other embodiments, it may be desirable to control the polarization state of the illumination beam, and optionally, the light source 10 may further include a polarizing device for adjusting the polarization state of the illumination beam a. The polarizing device may be arranged to be adjustable or switchable to achieve different polarized light illumination. The light beam transmission module 20 is configured to receive and transmit the illumination light beam a, and further configured to receive a signal light beam b diffracted by the object 100 to be measured, where the signal light beam b includes diffracted light passing through the object 100 to be measured, where the diffracted light includes 0 th-order diffracted light, positive-order (e.g., +1, +2, … …) diffracted light, and negative-order (e.g., -1, -2, … …) diffracted light, and realizes separation of the positive-order and negative-order diffracted light, and transmits the separated light to the first imaging unit 41 and the second imaging unit 42, respectively, and the first imaging unit 41 and the second imaging unit 42 may be electrically connected to the processing unit 43. The lens 30 is used for converging the illumination light beam a to the object 100 to be measured and for collecting the signal light beam b diffracted by the object 100 to be measured, and optionally, the lens 30 may be a microscope objective. In specific implementation, the lens 30 is a large NA objective lens with NA >0.8, so as to meet the requirement of measurement accuracy. Each of the first and second imaging units 41 and 42 may be a two-dimensional area-array camera, for example, a photo-coupled device (CCD) camera. It should be noted that the positional relationship of the modules shown in fig. 1 is only schematic, and in practical implementation, the relative positional relationship of the modules may be adjusted according to an actual optical path, the light rays shown in the drawing are only for illustrating the direction and the path of the light rays, and for convenience of description, the light rays are separately shown, and in the actual optical path, the paths of partial light beams overlap.

According to the technical scheme, the signal light beam is split into the first signal light beam comprising the negative-order diffraction light and the second signal light beam comprising the positive-order diffraction light by the light beam transmission module, the first signal light beam and the second signal light beam are respectively received by the first imaging unit and the second imaging unit, so that the positive/negative-order diffraction light of the overlay mark is measured simultaneously, the overlay error is calculated by the processing unit, diaphragm switching is not needed, the overlay error measuring efficiency can be improved, the yield is improved, and the method has the advantages of being simple in structure, low in cost and the like.

On the basis of the above technical solution, fig. 4 is a schematic structural diagram of another overlay error measurement apparatus provided in an embodiment of the present invention. Referring to fig. 4, alternatively, the light beam transmission module 20 includes a beam splitting unit 21 and a diffracted light separating unit 22; the beam splitting unit 21 is used for receiving the illumination light beam a emitted by the light source 10, transmitting the illumination light beam a to the lens 30, and is also used for receiving the signal light beam b transmitted by the lens 30, and transmitting part of the signal light beam b to the diffraction light separation unit 22; the diffractive light separation unit 22 includes a first output end 22a and a second output end 22b, the first output end 22a is used for filtering out the 0 th order diffractive light and the positive order diffractive light in the signal light beam b to form a first signal light beam b1, and the second output end 22b is used for filtering out the 0 th order diffractive light and the negative order diffractive light in the signal light beam b to form a second signal light beam b 2.

Fig. 5 is a schematic diagram illustrating an optical path of an illumination beam when the illumination beam diffracts on the surface of the object to be measured according to an embodiment of the present invention. Referring to FIG. 5, when the illumination beam is perpendicularly incident to the surface of the object 100 to be measured, the 0 < th > order diffractive light I₀Returning in the incident direction, diffracted light I of positive order₊₁And negative order diffracted light I_-1(only +1 and-1 st order diffracted lights are shown in FIG. 5, and the +1/-1 st order diffracted lights are explained below) are emitted in different directions, and are converged by a lens to obtain positive order diffracted light I₊₁0 order diffraction light I₀And negative order diffracted light I_-1The optical fiber grating diffraction grating can be separated in space, can split signal beams through the diffraction light separation unit, then can shield at a preset position, can realize the separation of positive-order diffraction light and negative-order diffraction light, and the first imaging unit and the second imaging unit respectively receive the negative-order diffraction light and the positive-order diffraction light at the same time, so that the diaphragm switching can be avoided, and the measurement efficiency can be improved.

Fig. 6 is a schematic structural diagram of another overlay error measurement apparatus according to an embodiment of the present invention. Referring to fig. 6, alternatively, the diffracted light separation unit 22 includes a light splitting member 221, a first light shielding member 222, and a second light shielding member 223; the beam splitting assembly 221 is configured to split the signal beam b into two beams transmitted along a first direction x and a second direction y, and the first light shielding assembly 222 is configured to shield the first direction xUpper 0 th order diffracted light I₀And positive order diffracted light I₊₁The second light shielding component 223 is used for shielding the 0 th order diffraction light I in the second direction y₀And negative order diffracted light I_-1The first direction x intersects the second direction y.

Optionally, the light splitting assembly 221 includes a light splitting prism or a half mirror.

For example, the light splitting assembly shown in fig. 6 is a light splitting prism, and the first light shielding assembly 222 and the second light shielding assembly 223 are light blocking plates disposed on the light exit side of the light splitting prism, it is understood that the light shielding assembly may also be a light absorbing layer plated on the light exit side of the light splitting prism, in other embodiments, the light splitting assembly 221 may also be a half mirror, which is not limited in this embodiment of the present invention.

Fig. 7 is a schematic structural diagram of another overlay error measurement apparatus according to an embodiment of the present invention. Referring to fig. 7, alternatively, the diffractive light separation unit 22 includes a reflective member 224 and a third light shielding member 225; the reflective component 224 is used for reflecting a part of the light in the signal beam b to make the negative-order diffracted light I in the signal beam b_-1And positive order diffracted light I₊₁Separating; the third light shielding component 225 is used for shielding the 0 < th > order diffractive light I in the signal beam b₀. Optionally, the reflective assembly 224 comprises a flat mirror.

It is understood that the embodiment in fig. 6 employs a light splitting assembly, which splits a light beam into two beams, so that the light intensity received by the first imaging unit 41 and the second imaging unit 42 is weak, which may affect the signal-to-noise ratio of the imaging. In the embodiment shown in FIG. 7, the diffracted light I of the positive order is separated by reflection rather than by beam splitting₊₁And negative order diffracted light I_-1It is advantageous to improve the signal-to-noise ratio of the first imaging unit 41 and the second imaging unit 42.

In the embodiment of FIG. 7, reflective element 224 reflects the negative diffracted light I_-1And 0 th order diffracted light I₀In other embodiments, the reflective component 224 can be configured to reflect the diffracted light I of the positive order₊₁And 0 th order diffracted light I₀And the specific implementation can be flexibly selected according to the actual situation. In addition, Ginseng radix can be addedReferring to fig. 7, a fourth light shielding component 226 may be further disposed in the optical path for shielding the stray background light to improve the signal-to-noise ratio of the imaging unit.

Fig. 8 is a schematic structural diagram of another overlay error measurement apparatus according to an embodiment of the present invention. Referring to FIG. 8, unlike in FIG. 7, the reflective member 224 reflects only the negative order diffracted light I_-1The third light shielding component 225 directly shields the 0 th order diffraction light I in the signal beam b₀When the method is implemented, only the negative order diffraction light I is ensured_-1And positive order diffracted light I₊₁May be received by the first and second imaging units 41 and 42, respectively.

Fig. 9 is a schematic structural diagram of another overlay error measurement apparatus according to an embodiment of the present invention. Referring to fig. 9, optionally, the measurement module 40 further includes a third imaging unit 44, and the third imaging unit 44 is connected to the processing unit 43; the beam splitting unit 21 is further configured to split the signal beam b into a first beam b 'and a second beam b ", the first beam b' being transmitted to the third imaging unit 44, the second beam b" being transmitted to the diffractive light separation unit 22; the processing unit 43 is further configured to normalize the light intensities acquired by the first imaging unit 41 and the second imaging unit 42 according to the light intensity acquired by the third imaging unit 44.

It can be understood that due to the different magnitude of the overlay error, the positive order diffracted light I₊₁And negative order diffracted light I_-1May have a large difference that cannot be corrected, the third imaging unit 44 is provided as an additional module for normalizing the light signal to improve the overlay error measurement accuracy. Illustratively, the third imaging unit 44 and the processing unit 43 may be electrically connected.

Optionally, the light beam transmission module further includes a first power zoom lens set disposed between the light source and the beam splitting unit, and/or a second power zoom lens set disposed between the beam splitting unit and the diffractive light separation unit, and/or a third power zoom lens set disposed between the beam splitting unit and the third imaging unit; the first magnification zoom lens, the second magnification zoom lens and the third magnification zoom lens are used for magnifying or reducing the light spots of the light beams.

Fig. 10 is a schematic structural diagram of another overlay error measurement apparatus according to an embodiment of the present invention. Referring to fig. 10, the light beam transmission module further includes a first magnification zoom group 23 disposed between the light source 10 and the beam splitting unit 21, a second magnification zoom group 24 disposed between the beam splitting unit 21 and the diffractive light separation unit 22, and a third magnification zoom group 25 disposed between the beam splitting unit 21 and the third imaging unit 44; the first power zoom lens group 23, the second power zoom lens group 24 and the third power zoom lens group 25 may adopt lens groups with the same structure for adjusting the size of the light spot, and may be designed according to actual requirements in specific implementation.

It should be noted that, in other embodiments, the first magnification zoom lens group 23, the second magnification zoom lens group 24, and the third magnification zoom lens group 25 are arranged according to actual requirements of the optical path, and all three positions may be provided with the magnification zoom lens group, none of the three positions may be provided, or one or two positions may be provided, which is not limited in this embodiment of the present invention.

Fig. 11 is a schematic structural diagram of another overlay error measurement apparatus according to an embodiment of the present invention. Referring to fig. 11, optionally, the beam delivery module further includes a first lens group 26 and a second lens group 27; the first lens group 26 includes at least one converging lens, which is located between the first output end of the diffractive light separation unit 22 and the first imaging unit 41, and the first lens group 26 is configured to converge the first signal light beam b1 to the photosensitive surface of the first imaging unit 41; the second lens group 27 includes at least one converging lens, and is located between the second output end of the diffractive light separation unit 22 and the second imaging unit 42, and the second lens group 27 is configured to converge the second signal light beam b2 to the photosensitive surface of the second imaging unit 42.

It is understood that the first lens group 26 and the second lens group 27 shown in fig. 11 each include a single convergent lens is only illustrative, and in other embodiments, the number and type of lenses of the first lens group 26 and the second lens group 27 are selected according to actual light transmission conditions, and embodiments of the present invention do not limit this.

With reference to fig. 11, optionally, the overlay error measuring apparatus according to the embodiment of the present invention further includes an illumination diaphragm 50, which is located between the light source 10 and the light beam transmission module 20, and a light through hole is disposed in the center of the illumination diaphragm 50.

Fig. 11 also schematically shows the structure of the illumination diaphragm 50, and in this embodiment, the hollowed-out portion of the opening at the center of the illumination diaphragm 50 is smaller than one third of the numerical aperture of the diaphragm (< NA/3) to meet the illumination requirement. It should be noted that, in the drawings of the above embodiments, some of the drawings may be used to refine or simplify some of the modules, while simplifying the structures of other modules, and the structures in the drawings may be combined with each other to obtain more embodiments without conflict, and all of the embodiments are within the scope of the present invention.

Fig. 12 is a schematic flow chart of an overlay error measurement method according to an embodiment of the present invention, where the method may be executed by any one of the overlay error measurement apparatuses according to the embodiments, and the method includes:

step S110, the light source generates an illumination beam.

Alternatively, the light source module may comprise a composite light source generating at least two discrete wavelengths or a light source generating a continuous wavelength. Because the wavelengths of the measuring lights required by different processes are different, the light source in this embodiment may adopt a plurality of monochromatic light combined light sources, and the light is combined by devices such as a dichroic mirror, a grating, a beam combining optical fiber, and the like, or may adopt a broadband light source that generates continuous wavelengths, and a filter, a monochromator, and the like are configured as required, so as to realize the output of a specified wavelength or a specified waveband.

And step S120, the light beam transmission module transmits the illumination light beam to the lens, receives the signal light beam diffracted by the object to be detected and transmitted by the lens and splits the signal light beam into a first signal light beam and a second signal light beam.

The illumination light beam forms preset illumination distribution on a pupil surface of the lens, the signal light beam comprises positive-order diffraction light, negative-order diffraction light and 0-order diffraction light which are diffracted by the illumination light beam through an object to be measured, the first signal light beam is obtained by filtering out the 0-order diffraction light and the positive-order diffraction light from part of signal light beams, the second signal light beam is obtained by filtering out the 0-order diffraction light and the negative-order diffraction light from part of signal light beams, the first signal light beam is transmitted to the first imaging unit, and the second signal light beam is transmitted to the second imaging unit;

step S130, the processing unit calculates the overlay error of the object to be measured according to the signals acquired by the first imaging unit and the second imaging unit.

According to the technical scheme, the signal light beam is split into the first signal light beam comprising the negative-order diffraction light and the second signal light beam comprising the positive-order diffraction light by the light beam transmission module, the first signal light beam and the second signal light beam are respectively received by the first imaging unit and the second imaging unit, so that the positive/negative-order diffraction light of the overlay mark is measured simultaneously, the overlay error is calculated by the processing unit, diaphragm switching is not needed, the overlay error measuring efficiency can be improved, the yield is improved, and the method has the advantages of being simple in structure, low in cost and the like.

On the basis of the above technical solution, optionally, the calculating, by the processing unit, the overlay error of the object to be measured according to the signals acquired by the first imaging unit and the second imaging unit includes:

the first imaging unit obtains the-1 st order diffraction light intensity I of the object to be measured₁ ^-；

The second imaging unit obtains the +1 st order diffraction light intensity I of the object to be measured₁ ⁺；

The asymmetry of the +1 st order diffracted intensity and-1 st order diffracted intensity is calculated according to:

wherein k represents a scale factor, Δ represents a preset offset of the overlay mark, and ε represents an overlay error;

calculating the overlay error of the object to be measured according to the following formula:

the overlay error measurement method provided in this embodiment may utilize overlay error measurement of micro marks (μ DBO), where the size of the micro mark is about 1/50-1/40 of the conventional overlay mark compared to the conventional overlay mark, as shown in fig. 13, a structural diagram of the micro mark provided in the embodiment of the present invention is shown, referring to fig. 13, the mark is divided into 4 pads, the pad in the 1 st and 3 rd quadrants measures the overlay error in the Y direction, and the two pads in the 2 nd and 4 th quadrants measure the overlay error in the X direction. The preset offsets of the two marks in the same line direction are opposite.

Fig. 14 is a schematic diagram showing a principle of measuring overlay error using the micro-mark shown in fig. 13, in which fig. 14(a) shows a signal of a first imaging unit and fig. 14(b) shows a signal of a second imaging unit. Within the circle of the dotted line is the illumination field of view area. The signal of the micro-mark is divided into four areas, for example, the first imaging unit, which measures the image formed by-1 st order diffracted light, XP in the upper left corner_1-Is the image of the marked region with positive preset offset delta in the X direction, and the average light intensity in the region is I_1x ^-(ii) a YP of upper right corner_1-Is an image of a mark region in which a preset offset amount Delta in the Y direction is positive, and the average light intensity in the region is I_1y ^-(ii) a YP of lower left corner_2-Is the image of the marked area with negative preset offset delta in the Y direction, and the average light intensity in the area is I_2y ^-(ii) a XP of lower right corner_2-Is the image of the marked area with negative preset offset delta in the X direction, and the average light intensity in the area is I_2x ^-. Similarly, I can be acquired in the first imaging unit_1x ⁺，I_1y ⁺，I_2x ⁺，I_2y ⁺。

Fig. 15 is a schematic diagram of an image acquired by the third imaging unit. The positive center area is 0 order reflected light, the-1X and-1Y areas are-1 order diffracted light marked in the X direction and the Y direction, and the total light intensity in the two areas is proportional to I_1x ^-+I_2x ^-+I_1y ^-+I_2y ^-I.e. the total signal strength of the first imaging unit. Similarly, the total light intensity of the +1X and +1Y regions is proportional to the total signal intensity of the second imaging unit. The total light intensity of-1X and-1Y and the total light intensity of +1X and +1Y on the third imaging unitThe ratio of (a) to (b) can be used to normalize the ratio of light intensities in the optical path after the splitting assembly. Normalizing the I_1x ^-，I_1y ^-，I_2x ^-，I_2y ^-，I_1x ⁺，I_1y ⁺，I_2x ⁺，I_2y ⁺The overlay error in the X direction and the Y direction can be obtained by substituting the above equations (1) and (2).

While the conventional overlay error measuring device requiring diaphragm switching needs about 130ms for one measurement, the overlay error measuring device provided in this embodiment needs about 60ms for one measurement, which can effectively improve the measurement speed.

In order to verify the overlay error measurement method provided by the embodiment, the imaging conditions of the first imaging unit and the second imaging unit can be obtained through simulation. Fig. 16 is a schematic diagram of simulation input conditions according to an embodiment of the present invention, and referring to fig. 16, simulation is performed by considering only the mark in the X direction, the grating period of the simulated mark is 800nm, the preset offset is 10nm (fig. 16, left), and the illumination mode is a through hole with σ being 0.2 (fig. 16, right). Fig. 17 is a schematic diagram of an angular spectrum image of a third imaging unit obtained by simulation, and fig. 18 is a schematic diagram of an angular spectrum image of a first imaging unit and an angular spectrum image of a second imaging unit, wherein a left diagram corresponds to the first imaging unit, and a right diagram corresponds to the second imaging unit. Fig. 19 is a schematic diagram of images acquired by the first imaging unit and the second imaging unit, in which the left image corresponds to the first imaging unit and the right image corresponds to the second imaging unit, four light intensity signal regions with overlay error information are displayed in fig. 19, the calculated simulated overlay error is consistent with the set overlay error, and the deviation is less than 0.1nm, so that the feasibility of the method can be verified.

It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.