Multi-degree-of-freedom measuring device based on grating interference fringes

Abstract

The invention relates to the field of grating interference measurement, in particular to a multi-degree-of-freedom measuring device based on grating interference fringes, which is characterized in that a first beam splitter prism is positioned on an emergent light path of a single-frequency laser light source and is used for splitting a laser beam into reference light and measuring light; the optical reference element is located on the light path of the reference light and used for returning the reference light to the first beam splitter prism. The measuring grating is located on a light path of the measuring light and used for receiving the measuring light, generating diffraction light and enabling the diffraction light to return to the first beam splitter prism. The camera is located on an emergent light path of the first beam splitter prism, and the at least two beams of reference light and the at least two beams of diffraction light returning to the first beam splitter prism pass through the first beam splitter prism and are incident to the camera. The camera is used for capturing interference fringes formed by interference of the reference light and the diffracted light. And the computer is connected to the camera and is used for determining the pose change of the measuring grating according to the change of the interference fringes. The design of the light path structure is simpler while it is ensured that multi-degree-of-freedom pose measurement can be achieved.

Description

Technical Field

[0001] The present invention belongs to the field of grating interference measurement, and particularly relates to a multi-degree-of-freedom measurement device based on grating interference fringes. Background Art

[0002] In the processes of semiconductor manufacturing and lithography processing, the two-dimensional horizontal movement of the plane where the stage is located is the main measurement target of precision measurement. In addition to the one-dimensional and two-dimensional displacement measurements in the horizontal plane, the accompanying vertical focusing movement and the minute angular errors of rotation around the three axes also need to be precisely monitored. Currently, the main technologies that can meet the high-precision multi-degree-of-freedom measurement requirements of lithography processing include laser interference measurement and grating interference measurement. Laser interference measurement uses the laser wavelength as the measurement reference and is usually sensitive to environmental changes. Grating interference measurement uses the grating pitch as the measurement reference. The grating material is usually made of a material with an ultra-low coefficient of thermal expansion. Moreover, the optical path of grating interference measurement exposed to the air has a shorter optical path length and is less susceptible to the environment. In addition, the principle optical path distribution of grating interference measurement is relatively symmetric, so the requirements for the light source are also smaller.

[0003] The existing multi-degree-of-freedom measurement methods based on grating interference are mainly divided into two categories. One is the multi-degree-of-freedom measurement method based on grating interference and beam position detectors, such as the invention patent application with the Chinese patent publication number CN114459516A, publication date July 28, 2023, and patent name "An absolute six-degree-of-freedom grating encoder". And the invention patent application with the Chinese patent publication number CN106091940A, publication date November 9, 2016, and patent name "An heterodyne four-degree-of-freedom grating motion measurement system". Both use the interference of diffracted light combined with a four-step phase shift structure to measure the displacement in the X direction, and use the ±1st order diffracted light combined with a QPD (Quadrant Photoelectric Detector) to achieve the measurement of the displacement in the Z direction and three angular degrees of freedom. The other is the multi-degree-of-freedom measurement method based on a combination of linear displacement sensing probes with multiple laser grating interferences, such as the invention patent application with the Chinese patent publication number CN106017308A, publication date October 12, 2016, and patent name "A six-degree-of-freedom interference measurement system and method". It can measure the linear displacements of three axes with a single probe, and the grating angle offset can be approximately calculated through the three linear displacements and the probe spacing. However, the accuracy, resolution and other indicators of the measurement results of grating interference and beam position detection differ by dozens of times. They jointly constitute the measurement results of the six-degree-of-freedom position and attitude of the grating, which will cause serious problems of positioning accuracy mismatch. For the method of combining multiple probes, its displacement measurement is affected by angular deflection, and the various degrees of freedom cannot be separated and decoupled, so there are problems of coupling of multiple results. At the same time, the area of the grating cannot be effectively utilized, and the system structure is complex, and the installation accuracy requirements for the experimental device are relatively high.

[0004] The invention patent application with the Chinese patent publication number CN112857208A, publication date May 28, 2021, and patent name "A single-beam three-degree-of-freedom laser interferometer based on a high-speed camera" can simultaneously measure angles and displacements. However, its simple Michelson interference structure can only achieve the measurement of three degrees of freedom. And when the target mirror to be measured moves along the optical axis direction, the angular measurement range of this device will be limited. The greater the displacement generated by the target mirror along the optical axis direction, the smaller the angular measurement range. At the same time, the laser interferometer is more sensitive to environmental changes. Summary of the Invention

[0005] In view of this, the present invention aims to provide a multi-degree-of-freedom measurement device based on grating interference fringes, while ensuring the realization of multi-degree-of-freedom position and attitude measurement, the design of the optical path structure is simpler.

[0006] To achieve the above object, the technical solution of the present invention is realized as follows: A multi-degree-of-freedom measurement device based on grating interference fringes, which includes: A single-frequency laser light source for emitting a laser beam; A first beam-splitting prism located on the light path of the emitted light from the single-frequency laser light source for splitting the laser beam into a reference light and a measurement light; An optical reference element located on the light path of the reference light for returning the reference light to the first beam-splitting prism; A measurement grating located on the light path of the measurement light for receiving the measurement light and generating diffracted light to return the diffracted light to the first beam-splitting prism; A camera located on the light path of the emitted light from the first beam-splitting prism. At least two reference lights and at least two diffracted lights that return to the first beam-splitting prism pass through the first beam-splitting prism and are incident on the camera. The camera is used to capture the interference fringes formed by the interference of the reference light and the diffracted light; A computer connected to the camera. The computer is used to determine the pose change of the measurement grating according to the change of the interference fringes.

[0007] Further, it also includes a beam-splitting component located on the light path from the single-frequency laser light source to the first beam-splitting prism for splitting the emitted laser beam into two parallel lights; The beam-splitting component includes a transmission beam-splitting grating and a refractive element. The transmission beam-splitting grating is located on the light path from the single-frequency laser light source to the refractive element. The refractive element is used to make the laser beam emit in parallel; or The beam-splitting component includes a second beam-splitting prism. The emission direction of the single-frequency laser light source is parallel to the bonding surface of the second beam-splitting prism but not in the same plane.

[0008] Further, the measurement grating is a one-dimensional measurement grating. The multi-degree-of-freedom measurement device also includes an optical component located on the light path from the first beam-splitting prism to the measurement grating; The optical component includes a first reflector and a second reflector. The first reflector and the second reflector are used to make the measurement light incident on the measurement grating at the Littrow angle; or The optical component is a one-dimensional refractive grating.

[0009] Further, both the measurement grating and the optical reference element are one-dimensional measurement gratings. The multi-degree-of-freedom measurement device also includes a first reflection component and a second reflection component. The first reflection component is located on the light path from the first beam-splitting prism to the measurement grating. The second reflection component is located on the light path from the first beam-splitting prism to the optical reference element.

[0010] Further, the pose change of the measurement grating includes an angular change. The computer is used to determine the light intensity distribution of the interference fringes and perform spectral analysis on the interference fringes to determine the current spatial frequency of the interference fringes at the current moment and the initial spatial frequency at the initial moment when the measurement grating is in the initial position; Calculate the angular change of the measurement grating based on the current spatial frequency and the initial spatial frequency.

[0011] Further, the angular change includes yaw angle change , and calculate the yaw angle change of the measurement grating through the following formula:

[0012] The angular change also includes pitch angle change , and calculate the pitch angle change of the measurement grating through the following formula:

[0013] where is the frequency difference between the current spatial frequency of the interference fringes in the horizontal direction and the initial spatial frequency in the horizontal direction, is the frequency difference between the current spatial frequency of the interference fringes in the vertical direction and the initial spatial frequency in the vertical direction, is the wavelength of the laser in vacuum, is the refractive index of air.

[0014] Further, at least two diffracted light beams include +1 order diffracted light beam and -1 order diffracted light beam; the camera is used to capture the first set of interference fringes formed by the interference of a reference light beam and the +1 order diffracted light beam, and the second set of interference fringes formed by the interference of another reference light beam and the -1 order diffracted light beam; the pose change of the measurement grating includes angular change, and the angular change also includes roll angle change , and calculate the roll angle change of the measurement grating through the following formula:

[0015] where is the lateral spacing between the center of the first set of interference fringes and the center of the second set of interference fringes, is the longitudinal spacing between the center of the first set of interference fringes and the center of the second set of interference fringes.

[0016] Further, the pose change of the measurement grating includes displacement change; the computer is used to determine the light intensity distribution of the interference fringes, perform spectral analysis on the interference fringes to extract the phase of each frame between the current moment and the initial moment, and perform phase unwrapping processing on the phase of each frame to obtain the phase difference between the current phase of the interference fringes at the current moment and the initial phase of the interference fringes at the initial moment; calculate the displacement change of the measurement grating according to the phase difference.

[0017] Further, at least two diffracted lights include a +1-order diffracted light and a -1-order diffracted light; the camera is used to capture a first set of interference fringes formed by the interference of a reference light and the +1-order diffracted light, and a second set of interference fringes formed by the interference of another reference light and the -1-order diffracted light; the displacement change includes a displacement change in the first direction and a displacement change in the second direction , and the displacement change of the measurement grating in the first direction is resolved through the following formula :

[0018] The displacement change of the measurement grating in the second direction is resolved through the following formula :

[0019] wherein is the phase difference of the first set of interference fringes, is the phase difference of the second set of interference fringes, is the grating constant, is the diffraction order, is the wavelength of the laser in vacuum, is the refractive index of air

[0020] Further, a beam splitting prism group is further included. The beam splitting prism group is located on the optical path from the single-frequency laser light source to the first beam splitting prism and is used to divide the emitted laser beam into four parallel light beams; the measurement grating is a two-dimensional measurement grating

[0021] Compared with the prior art, the present invention can achieve the following beneficial effects The multi-degree-of-freedom measurement device based on grating interference fringes provided by the embodiment of the present invention can measure the three angular degrees of freedom of the measurement grating through the interference fringes in a single-frame interference image, and measure at least two displacement degrees of freedom of the measurement grating through the interference fringes in a series of consecutive interference images. And the angle and displacement of the measurement grating can be calculated from the information such as the frequency and phase of the interference fringes, thereby avoiding the problem of coupling of multi-degree-of-freedom results. At the same time, compared with the existing multi-degree-of-freedom measurement devices, the optical path structure of the multi-degree-of-freedom measurement device of the present invention is simple, and only a single camera can be used to measure the multi-degree-of-freedom pose of the measurement grating, and has advantages such as a large angle measurement range, meeting the high-precision requirements for displacement and angle measurement in processes such as lithography processing Description of the Drawings

[0022] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings Figure 1 Schematic structural diagram of the multi-degree-of-freedom measurement device according to the embodiment of the present invention; Figure 2 Schematic structural diagram of another embodiment of the beam splitting component of the multi-degree-of-freedom measurement device according to the embodiment of the present invention; Figure 3 Schematic structural diagram of another embodiment of the optical component of the multi-degree-of-freedom measurement device according to the embodiment of the present invention; Figure 4 Schematic structural diagram of another embodiment of the camera of the multi-degree-of-freedom measurement device according to the embodiment of the present invention; Figure 5 Schematic structural diagram of another embodiment of the optical reference element of the multi-degree-of-freedom measurement device according to the embodiment of the present invention; Figure 6 Schematic diagram of the change in the spatial frequency of interference fringes when the measurement grating of the multi-degree-of-freedom measurement device according to the embodiment of the present invention rotates around the third direction; Figure 7 Schematic diagram of the position change of the first group of interference fringes and the second group of interference fringes when the measurement grating of the multi-degree-of-freedom measurement device according to the embodiment of the present invention rotates around the second direction; Figure 8 Schematic diagram of the phase change of interference fringes when the measurement grating of the multi-degree-of-freedom measurement device according to the embodiment of the present invention generates a displacement along the first direction; Figure 9 Schematic diagram of the phase change of interference fringes when the measurement grating of the multi-degree-of-freedom measurement device according to the embodiment of the present invention generates a displacement along the second direction; Figure 10 Schematic structural diagram of another embodiment of the multi-degree-of-freedom measurement device according to the embodiment of the present invention.

[0023] Explanation of reference numerals: 10. Multi-degree-of-freedom measuring device; 11. Single-frequency laser light source; 12. First beam-splitting prism; 13. Optical reference element; 14. Measuring grating; 15. Camera; 16. Computer; 17. Beam-splitting component; 18. Transmission beam-splitting grating; 19. Refractive element; 20. Second beam-splitting prism; 21. Optical component; 22. First reflector; 23. Second reflector; 24. One-dimensional refractive grating; 25. Reference reflector; 26. Right-angle reflector; 27. Third beam-splitting prism; 28. Fourth beam-splitting prism; 29. First line array camera; 30. Second line array camera; 31. Third line array camera; 32. Fourth line array camera; 33. First reflection component; 34. Second reflection component; 35. Third reflector; 36. Fourth reflector; 37. Fifth reflector; 38. Sixth reflector; 39. Beam-splitting prism group; 40. Fifth beam-splitting prism; 41. Sixth beam-splitting prism; 42. Reflector group. Detailed implementation mode

[0024] In order to make the purpose, technical solution and advantages of the present invention clearer, the following further details the present invention in combination with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation to the present invention. Similar elements in different embodiments adopt related similar element numbers. In the following embodiments, many details are described to make the present invention better understood. However, those skilled in the art can easily recognize that some of the features can be omitted in different situations, or can be replaced by other elements, materials, and methods. In some cases, some operations related to the present invention are not shown or described in the specification, which is to avoid the core part of the present invention being overwhelmed by excessive description. For those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations according to the description in the specification and the general technical knowledge in the art.

[0025] It should be noted that, without conflict, the embodiments and features in the embodiments of the present invention can be combined with each other to form various implementation modes. At the same time, the steps or actions in the method description can also be reordered or adjusted in an obvious manner by those skilled in the art. Therefore, the various sequences in the specification and drawings are only for clearly describing a certain embodiment and do not mean that they are the necessary sequences, unless it is stated that a certain sequence must be followed.

[0026] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. In addition, terms such as "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0027] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "mounted", "connected", "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection, an electrical connection; it may be directly connected, or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific circumstances.

[0028] The present invention will be described in detail below with reference to the drawings and in conjunction with embodiments.

[0029] See Figures 1 to 10 As shown, the present invention provides a multi-degree-of-freedom measurement device 10 based on grating interference fringes. The multi-degree-of-freedom measurement device 10 includes a single-frequency laser light source 11, a first beam splitter prism 12, an optical reference element 13, a measurement grating 14, a camera 15, and a computer 16.

[0030] The single-frequency laser light source 11 is used to emit a laser beam.

[0031] The first beam splitter prism 12 is located on the outgoing light path of the single-frequency laser light source 11 and is used to divide the laser beam into a reference light and a measurement light.

[0032] The optical reference element 13 is located on the light path of the reference light and is used to return the reference light to the first beam splitter prism 12. The reference light can be incident on the optical reference element 13 and return to the first beam splitter prism 12 through the optical reference element 13.

[0033] The measurement grating 14 is located on the optical path of the measurement light, and is used to receive the measurement light and generate diffracted light, so that the diffracted light returns to the first beam splitter prism 12.

[0034] The camera 15 is located on the outgoing optical path of the first beam splitter prism 12. At least two reference lights and at least two diffracted lights that return to the first beam splitter prism 12 pass through the first beam splitter prism 12 and are incident on the camera 15. The camera 15 is used to capture the interference fringes formed by the interference of the reference light and the diffracted light. The camera 15 can capture at least two sets of interference fringes. Among them, the single-frequency laser light source 11 and the optical reference element 13 are located on opposite sides of the first beam splitter prism 12 along the first direction X. The measurement grating 14 and the camera 15 are located on opposite sides of the first beam splitter prism 12 along the second direction Z.

[0035] The computer 16 is connected to the camera 15. The computer 16 can acquire and process the interference fringe images captured by the camera 15. The computer 16 is used to determine the pose change of the measurement grating 14 according to the change of the interference fringes.

[0036] See Figures 1 to 5 As shown, there are two reference lights, and at least two diffracted lights include +1-order diffracted light and -1-order diffracted light. The camera 15 can be used to capture two sets of interference fringes. The camera 15 is used to capture the first set of interference fringes formed by the interference of one reference light and the +1-order diffracted light, and the second set of interference fringes formed by the interference of the other reference light and the -1-order diffracted light.

[0037] See Figure 1 and Figure 2 As shown in Figure 1 and Figure 2 In the shown embodiment, the multi-degree-of-freedom measurement device 10 further includes a beam splitting component 17. The beam splitting component 17 is located on the optical path from the single-frequency laser light source 11 to the first beam splitter prism 12, and is used to divide the outgoing laser beam into two parallel beams. In

[0038] See Figure 1 and Figure 3As shown, in one embodiment, the measurement grating 14 is a one-dimensional measurement grating. The multi-degree-of-freedom measurement device 10 further includes an optical component 21. The optical component 21 is located on the optical path from the first beam splitter prism 12 to the measurement grating 14, and is configured to make the measurement light incident on the measurement grating 14 and make the diffracted light generated by the measurement grating 14 return to the first beam splitter prism 12 along the incident optical path of the measurement light. In Figure 1 In the embodiment shown, the optical component 21 includes a first mirror 22 and a second mirror 23. The first mirror 22 and the second mirror 23 can make the measurement light incident on the measurement grating 14 at the Littrow angle. In Figure 3 In the embodiment shown, the optical component 21 includes a one-dimensional refractive grating 24.

[0039] Referring to Figure 1 and Figure 4 As shown, in Figure 1 In the embodiment shown, the camera 15 is an area array camera. Introducing an area array camera to collect interference fringes can realize the measurement of multiple degrees of freedom using only a single camera, greatly simplifying the optical path structure of the multi-degree-of-freedom measurement device 10. It is possible to use fewer optical elements and a simpler and more compact optical path structure on the premise of ensuring the measurement accuracy, avoiding the accuracy mismatch problem caused by using a position-sensitive detector, and the complex instrument layout problems of the multi-probe combination method, and can be better applied in complex environments. In Figure 4In the illustrated embodiment, the camera 15 is a line array camera, and the number of line array cameras is four. The four line array cameras include a first line array camera 29, a second line array camera 30, a third line array camera 31, and a fourth line array camera 32. The multi-degree-of-freedom measurement device 10 further includes a right-angle reflector 26, a third beam splitter prism 27, and a fourth beam splitter prism 28. Among them, the right-angle reflector 26 is located on the optical path from the first beam splitter prism 12 to the four line array cameras, and the right-angle reflector 26 is used to separate two interference beams emitted from the first beam splitter prism 12. Among them, the two interference beams are respectively formed by the interference of a reference beam and a +1-order diffracted beam, and the interference of another reference beam and a -1-order diffracted beam. One interference beam is split into two first sub-interference beams by the third beam splitter prism 27, and the two first sub-interference beams are respectively incident on the first line array camera 29 and the second line array camera 30. Among them, the line array sensor of the first line array camera 29 extends along the first direction X, and the line array sensor of the second line array camera 30 extends along the third direction Y. In this way, one of the first line array camera 29 and the second line array camera 30 can obtain the row distribution of the interference fringes of one interference beam, and the other can obtain the column distribution of the interference fringes of this interference beam. The other interference beam is split into two second sub-interference beams by the fourth beam splitter prism 28, and the two second sub-interference beams are respectively incident on the third line array camera 31 and the fourth line array camera 32. Among them, the line array sensor of the third line array camera 31 extends along the first direction X, and the line array sensor of the fourth line array camera 32 extends along the third direction Y. In this way, one of the third line array camera 31 and the fourth line array camera 32 can obtain the row distribution of the interference fringes of the other interference beam, and the other can obtain the column distribution of the interference fringes of this interference beam. In some other embodiments, the camera 15 can also be other industrial cameras 15.

[0040] See Figure 1 As shown, in one embodiment, the optical reference element 13 is set at an inclined angle θ. The optical reference element 13 is a reference mirror 25, and the optical reference element 13 can reflect the reference light back to the first beam splitter prism 12.

[0041] In Figures 1 to 4In the illustrated embodiment, the laser beam emitted by the single-frequency laser light source 11 can be split into two parallel light beams by the beam splitting component 17. The two parallel light beams are split into two parallel reference light beams and two parallel measurement light beams by the first beam splitting prism 12. Among them, the two parallel reference light beams can transmit through the first beam splitting prism 12, be incident on the reference mirror 25, and be reflected back to the first beam splitting prism 12 by the reference mirror 25. The two parallel measurement light beams can be reflected by the first beam splitting prism 12 to the optical component 21 and be incident on the measurement grating 14 through the optical component 21. The measurement grating 14 receives the two measurement light beams and generates ±1-order diffracted light. The ±1-order diffracted light returns to the first beam splitting prism 12 along the incident light path of the measurement light. After the ±1-order diffracted light returning to the first beam splitting prism 12 and the two parallel reference light beams pass through the first beam splitting prism 12, they are incident on the camera 15. The ±1-order diffracted light is parallel and coincident with the two parallel reference light beams and is jointly incident on the camera 15. The camera 15 is used to capture the first set of interference fringes formed by the interference of a reference light beam and the +1-order diffracted light, and the second set of interference fringes formed by the interference of the other reference light beam and the -1-order diffracted light.

[0042] See Figure 5 As shown, in one embodiment, both the measurement grating 14 and the optical reference element 13 are one-dimensional measurement gratings. The multi-degree-of-freedom measurement device 10 further includes a first reflection component 33 and a second reflection component 34. The first reflection component 33 is located on the optical path from the first beam splitting prism 12 to the measurement grating 14. The first reflection component 33 includes a third mirror 35 and a fourth mirror 36. The measurement light split by the first beam splitting prism 12 is vertically incident on the surface of the measurement grating 14 and generates ±1-order diffracted light. The +1-order diffracted light is reflected by the third mirror 35 and returns to the first beam splitting prism 12. The -1-order diffracted light is reflected by the fourth mirror 36 and returns to the first beam splitting prism 12. The second reflection component 34 is located on the optical path from the first beam splitting prism 12 to the optical reference element 13. The second reflection component 34 includes a fifth mirror 37 and a sixth mirror 38. The reference light split by the first beam splitting prism 12 is incident on the surface of the optical reference element 13 and generates ±1-order reference diffracted light serving as reference light. The +1-order reference diffracted light is reflected by the fifth mirror 37 and returns to the first beam splitting prism 12. The -1-order reference diffracted light is reflected by the sixth mirror 38 and returns to the first beam splitting prism 12.

[0043] In Figure 5In the illustrated embodiment, the laser beam emitted by the single-frequency laser light source 11 is split into a reference light beam and a measurement light beam by the first beam splitting prism 12. The reference light can pass through the first beam splitting prism 12 and be incident on the surface of the optical reference element 13, generating ±1-order reference diffraction light as the reference light. The ±1-order reference diffraction lights return to the first beam splitting prism 12 through the fifth mirror 37 and the sixth mirror 38 respectively, and are reflected by the first beam splitting prism 12 to the camera 15. The measurement light can be reflected by the first beam splitting prism 12 and vertically incident on the surface of the measurement grating 14, generating ±1-order diffraction lights. The ±1-order diffraction lights return to the first beam splitting prism 12 through the third mirror 35 and the fourth mirror 36 respectively. The ±1-order diffraction lights can pass through the first beam splitting prism 12 and be incident on the camera 15. The camera 15 is used to capture the first set of interference fringes formed by the interference of the +1-order reference diffraction light and the +1-order diffraction light, and the second set of interference fringes formed by the interference of the -1-order reference diffraction light and the -1-order diffraction light.

[0044] See Figure 6 As shown, the spatial frequency of the interference fringes depends on the angle between the optical reference element 13 and the measurement grating 14. Therefore, when the measurement grating 14 generates tilts (such as pitch angle and yaw angle), the spatial frequency of the interference fringes will change. In one embodiment, the pose change of the measurement grating 14 includes an angular change. The angular change includes a yaw angle change , and the yaw angle change refers to the angle by which the measurement grating 14 rotates about the first direction X. The angular change also includes a pitch angle change , and the pitch angle change refers to the angle by which the measurement grating 14 rotates about the third direction Y. The computer 16 is used to determine the light intensity distribution of the interference fringes, and can be used to determine the light intensity distribution of a certain row or column in the interference fringes, and perform spectral analysis on the interference fringes to determine the current spatial frequency of the interference fringes at the current moment and the initial spatial frequency at the initial moment when the measurement grating 14 is in the initial position. It can be known that the spatial frequency of the interference fringes has increased or , and the change of the yaw angle and the spatial frequency is a linear relationship, and the change of the pitch angle and the spatial frequency is a linear relationship. According to the current spatial frequency and the initial spatial frequency, the angular change of the measurement grating 14 is resolved.

[0045] In one embodiment, the yaw angle change of the measurement grating 14 is resolved by the following formula:

[0046] The pitch angle change of the measurement grating 14 is resolved by the following formula:

[0047] Among them, is the frequency difference between the current spatial frequency of the interference fringes in the horizontal direction and the initial spatial frequency in the horizontal direction, is the frequency difference between the current spatial frequency of the interference fringes in the vertical direction and the initial spatial frequency in the vertical direction, is the wavelength of the laser in vacuum, is the refractive index of air.

[0048] See Figure 7 As shown, when the measurement grating 14 rotates around the Z axis, the centers of the first group of interference fringes and the second group of interference fringes captured by the camera 15 will move upward and downward respectively, changing from a position on the same horizontal line to a position offset vertically. Thus, by measuring the lateral spacing between the center of the first group of interference fringes and the center of the second group of interference fringes, and the longitudinal spacing between the center of the first group of interference fringes and the center of the second group of interference fringes, the angle of rotation of the measurement grating 14 around the second direction Z, that is, the roll angle change, can be obtained. . In one embodiment, the angle change also includes the roll angle change , and the roll angle change refers to the angle of rotation of the measurement grating 14 around the second direction Z. Through the following formula, the roll angle change of the measurement grating 14 is solved:

[0049] Among them, is the lateral spacing between the center of the first group of interference fringes and the center of the second group of interference fringes, is the longitudinal spacing between the center of the first group of interference fringes and the center of the second group of interference fringes.

[0050] See Figure 8 and Figure 9 As shown, the phase of the interference fringes depends on the optical path difference between the reference light and the measurement light, and further can be reflected in the displacement of the measurement grating 14. When the measurement grating 14 generates a displacement along the first direction X or the second direction Z, the phase of the interference fringes will change. Only the phase change of one group of interference fringes among the first group of interference fringes and the second group of interference fringes is shown in the figure. Since the two groups of interference fringes are respectively generated by the coherent superposition of the ±1 order diffracted light and the reference light, and the optical paths are symmetric. Therefore, the two groups of interference fringes respectively contain and The displacement information. It is necessary to extract the phase of each frame of the two sets of interference fringes respectively, and use addition and subtraction operations to extract the two displacement information respectively. In one embodiment, the pose change of the measurement grating 14 includes a displacement change. The computer 16 is used to determine the light intensity distribution of the interference fringes, perform spectral analysis on the interference fringes to extract the phase of each frame between the current moment and the initial moment, and perform phase unwrapping on the phase of each frame to obtain the current phase of the interference fringes at the current moment and the phase difference between the initial phase of the interference fringes at the initial moment. According to the phase difference, the displacement change of the measurement grating 14 is resolved.

[0051] In one embodiment, the displacement change includes a displacement change along the first direction X and a displacement change along the second direction Z , through the following formula, the displacement change of the measurement grating 14 along the first direction X is resolved:

[0052] Through the following formula, the displacement change of the measurement grating 14 along the second direction Z is resolved:

[0053] Wherein, is the phase difference of the first set of interference fringes, is the phase difference of the second set of interference fringes, is the grating constant, is the diffraction order, λ is the wavelength of the laser in vacuum, is the refractive index of air.

[0054] The multi-degree-of-freedom measurement device 10 based on grating interference fringes provided by the embodiments of the present invention can measure three angular degrees of freedom of the measurement grating 14 through the interference fringes in a single-frame interference image, and measure two displacement degrees of freedom of the measurement grating 14 through the interference fringes in a series of consecutive interference images. And it can calculate the angle and displacement of the measurement grating 14 from information such as the frequency and phase of the interference fringes, thereby avoiding the problem of coupling of multi-degree-of-freedom results. At the same time, compared with the existing multi-degree-of-freedom measurement devices, the optical path structure of the multi-degree-of-freedom measurement device 10 of the present invention is simple, and only a single camera 15 can be used to measure the multi-degree-of-freedom pose of the measurement grating 14, and has advantages such as a large angular measurement range, meeting the high-precision requirements for displacement and angle measurement in processes such as lithography processing.

[0055] See Figure 10As shown, both the reference light and the diffracted light are four beams. The camera 15 can be used to capture four sets of interference fringes. The camera 15 is used to capture the first set of interference fringes formed by the interference of the first reference light beam and the +1-order diffracted light in the first direction X, the second set of interference fringes formed by the interference of the second reference light beam and the -1-order diffracted light in the first direction X, the third set of interference fringes formed by the interference of the third reference light beam and the +1-order diffracted light in the third direction Y, and the fourth set of interference fringes formed by the interference of the fourth reference light beam and the -1-order diffracted light in the third direction Y.

[0056] In one embodiment, the multi-degree-of-freedom measurement device 10 further includes a beam splitting prism group 39. The beam splitting prism group 39 is located on the optical path from the single-frequency laser light source 11 to the first beam splitting prism 12 and is used to divide the emitted laser beam into four parallel light beams. The beam splitting prism group 39 further includes a fifth beam splitting prism 40 and a sixth beam splitting prism 41. The fifth beam splitting prism 40 is used to divide the emitted laser beam into two parallel light beams, and the sixth beam splitting prism 41 is used to divide the two parallel light beams emitted from the fifth beam splitting prism 40 into four parallel light beams.

[0057] The measurement grating 14 is a two-dimensional measurement grating. The multi-degree-of-freedom measurement device 10 further includes a mirror group 42. The mirror group 42 is located on the optical path from the first beam splitting prism 12 to the measurement grating 14 and is used to make the measurement light incident on the measurement grating 14 and make the diffracted light generated by the measurement grating 14 return to the first beam splitting prism 12 along the incident optical path. In Figure 10 the shown embodiment, the mirror group 42 includes four mirrors, and the four mirrors are used to make the measurement light incident on the measurement grating 14 at the Littrow angle.

[0058] In one embodiment, the displacement change further includes the displacement change along the third direction Y , and through the following formula, the displacement change of the measurement grating 14 along the third direction Y is resolved:

[0059] where is the phase difference of the third set of interference fringes, is the phase difference of the fourth set of interference fringes, is the grating constant, is the diffraction order. In this way, the multi-degree-of-freedom measuring device 10 can measure the six-degree-of-freedom pose of the measurement grating 14. The six-degree-of-freedom pose includes yaw angle, pitch angle, roll angle, displacement along the first direction X, displacement along the second direction Z, and displacement along the third direction Y. In this way, the measurement of the three angular degrees of freedom of the measurement grating 14 can be realized through the interference fringes in a single-frame interference image, and the measurement of the three displacement degrees of freedom of the measurement grating 14 can be realized through the interference fringes in a series of consecutive interference images. Thus, the measurement of six degrees of freedom can be achieved, and the implementation method is simple and reliable.

[0060] It should be understood that various forms of the processes shown above can be used, steps can be reordered, added or deleted. For example, the steps described in the disclosure of the present invention can be executed in parallel, sequentially, or in a different order, as long as the desired results of the technical solutions disclosed in the present invention can be achieved, and no limitation is made herein.

[0061] The above specific embodiments do not constitute a limitation to the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A multi-degree-of-freedom measurement device based on grating interference fringes, characterized in that: include: A single-frequency laser light source, used for emitting a laser beam; A first beam splitter prism, located on the outgoing light path of the single-frequency laser light source, and used for splitting the laser beam into a reference light and a measurement light; an optical reference element, located on the optical path of the reference light, and used to return the reference light to the first beam splitter prism; a measuring grating, located on the optical path of the measuring light, for receiving the measuring light and generating diffracted light, so that the diffracted light returns to the first beam splitter prism; A camera is located on the outgoing light path of the first beam splitter prism, and at least two beams of the reference light and at least two beams of the diffracted light returning to the first beam splitter prism pass through the first beam splitter prism and are incident on the camera; the camera is used to capture interference fringes formed by interference between the reference light and the diffracted light; A computer is connected to the camera, and is used to determine the change of the position and posture of the measuring grating according to the change of the interference fringes.

2. The multi-degree-of-freedom measurement device based on grating interference fringes according to claim 1, characterized in that: It also includes a beam splitter component, which is located on the optical path from the single-frequency laser light source to the first beam splitter prism and is used to split the emitted laser light beam into two parallel light beams; The beam splitting component comprises a transmission beam splitting grating and a refracting element, wherein the transmission beam splitting grating is located on the optical path from the single-frequency laser light source to the refracting element; the refracting element is used to make the laser light beam emit in parallel; or The light splitting component includes a second light splitting prism, and the emission direction of the single-frequency laser light source is parallel to the bonding surface of the second light splitting prism but not on the same plane.

3. The multi-degree-of-freedom measurement device based on grating interference fringes according to claim 2, characterized in that: The measuring grating is a one-dimensional measuring grating; the multi-degree-of-freedom measuring device further comprises an optical component, and the optical component is located on the optical path from the first beam splitter prism to the measuring grating; The optical assembly comprises a first reflector and a second reflector, wherein the first reflector and the second reflector are used to make the measuring light incident on the measuring grating at a Littrow angle; or The optical component is a one-dimensional refractive grating.

4. The multi-degree-of-freedom measurement device based on grating interference fringes according to claim 1, characterized in that: The measuring grating and the optical reference element are both one-dimensional measuring gratings; the multi-degree-of-freedom measuring device also includes a first reflecting component and a second reflecting component; the first reflecting component is located on the optical path from the first beam splitter prism to the measuring grating; the second reflecting component is located on the optical path from the first beam splitter prism to the optical reference element.

5. The multi-degree-of-freedom measurement device based on grating interference fringes according to claim 1, characterized in that: The position change of the measuring grating includes an angle change; the computer is used to determine the light intensity distribution of the interference fringes, and perform spectrum analysis on the interference fringes to determine the current spatial frequency of the interference fringes at the current moment, and the initial spatial frequency at the initial moment when the measuring grating is in the initial position; The angle change of the measurement grating is resolved according to the current spatial frequency and the initial spatial frequency.

6. The multi-degree-of-freedom measurement device based on grating interference fringes according to claim 5, characterized in that: The angle change includes a yaw angle change , the yaw angle change of the measuring grating is calculated by the following formula: Solve: The angle change also includes a pitch angle change , the pitch angle change of the measuring grating is calculated by the following formula: Solve: in, is the frequency difference between the current spatial frequency of the interference fringes in the horizontal direction and the initial spatial frequency in the horizontal direction, is the frequency difference between the current spatial frequency of the interference fringes in the vertical direction and the initial spatial frequency in the vertical direction, is the wavelength of the laser in vacuum, is the refractive index of air.

7. The multi-degree-of-freedom measurement device based on grating interference fringes according to claim 1, characterized in that: At least two beams of diffracted light include +1-order diffracted light and -1-order diffracted light; the camera is used to capture a first group of interference fringes formed by interference of a beam of the reference light and the +1-order diffracted light, and a second group of interference fringes formed by interference of another beam of the reference light and the -1-order diffracted light; the position change of the measuring grating includes an angle change, and the angle change also includes a roll angle change , the roll angle change of the measuring grating is calculated by the following formula: Solve: in, is the lateral distance between the center of the first group of interference fringes and the center of the second group of interference fringes, is the longitudinal distance between the center of the first group of interference fringes and the center of the second group of interference fringes.

8. The multi-degree-of-freedom measurement device based on grating interference fringes according to claim 1, characterized in that: The position change of the measuring grating includes a displacement change; the computer is used to determine the light intensity distribution of the interference fringes, and perform spectrum analysis on the interference fringes to extract the phase of each frame between the current moment and the initial moment, and perform unwrapping processing on the phase of each frame to obtain the current phase of the interference fringes at the current moment and the phase difference between the initial phase of the interference fringes at the initial moment; The displacement change of the measuring grating is calculated according to the phase difference.

9. The multi-degree-of-freedom measurement device based on grating interference fringes according to claim 8, characterized in that: The at least two diffracted light beams include a +1-order diffracted light beam and a -1-order diffracted light beam; the camera is used to capture a first group of interference fringes formed by interference between a reference light beam and the +1-order diffracted light beam, and a second group of interference fringes formed by interference between another reference light beam and the -1-order diffracted light beam; the displacement change includes a displacement change along a first direction. and the displacement change along the second direction , the displacement change of the measuring grating along the first direction is calculated by the following formula: Solve: The displacement change of the measuring grating along the second direction is calculated by the following formula: Solve: in, is the phase difference of the first group of interference fringes, is the phase difference of the second group of interference fringes, is the grating constant, is the diffraction order, is the wavelength of the laser in vacuum, is the refractive index of air.

10. The multi-degree-of-freedom measurement device based on grating interference fringes according to claim 1, characterized in that: It also includes a beam splitter prism group, which is located on the optical path from the single-frequency laser light source to the first beam splitter prism and is used to split the emitted laser light beam into four parallel light beams; the measuring grating is a two-dimensional measuring grating.

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