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

Abstract

The present invention relates to the field of grating interferometry, and in particular to a multi-degree-of-freedom measurement device based on grating interference fringes, wherein a first beam splitter prism is located on the outgoing optical path of a single-frequency laser light source, and is used to split the laser beam into a reference light and a measurement light. An optical reference element is located on the optical path of the reference light, and is used to return the reference light to the first beam splitter prism. A measuring grating is located on the optical path of the measurement light, and is used to receive the measurement light, generate diffracted light, and return the diffracted light to the first beam splitter prism. A camera is located on the outgoing optical path of the first beam splitter prism, and at least two reference light beams and at least two diffracted light beams returned 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 the interference of the reference light and the diffracted light. A computer is connected to the camera, and the computer is used to determine the position change of the measuring grating based on the change of the interference fringes. While ensuring that multi-degree-of-freedom position measurement can be achieved, the design of the optical path structure is simpler.

Description

Technical Field

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

[0002] In the semiconductor manufacturing and photolithography processes, the two-dimensional horizontal motion of the plane where the stage is located is the main measurement target for precision measurement. In addition to the one-dimensional and two-dimensional displacement measurements in the horizontal plane, the accompanying vertical focusing motion and the small angular errors of rotation around three axes also need to be precisely monitored. At present, the main technologies that can meet the high-precision multi-degree-of-freedom measurement needs of photolithography include laser interferometry and grating interferometry. Laser interferometry uses the laser wavelength as the measurement reference and is usually sensitive to environmental changes. Grating interferometry uses the grating pitch as the measurement reference. The grating material is usually made of materials with ultra-low thermal expansion coefficients, and the optical path of the grating interferometry optical path exposed to the air is shorter, making it less susceptible to environmental influences. In addition, the optical path distribution of the grating interferometry principle is more symmetrical, so the requirements for the light source are also smaller.

[0003] Existing multi-degree-of-freedom measurement methods based on grating interferometry fall into two main categories. One category involves multi-degree-of-freedom measurement methods based on grating interferometry and a beam position detector, such as the invention patent application with Chinese patent publication number CN114459516A, published on July 28, 2023, entitled "An Absolute Six-Degree-of-Freedom Grating Encoder," and the invention patent application with Chinese patent publication number CN106091940A, published on November 9, 2016, entitled "A Heterodyne Four-Degree-of-Freedom Grating Motion Measurement System." Both utilize diffracted light interferometry combined with a four-step phase shift structure to measure X-direction displacement, and utilize ±1st-order diffracted light combined with a QPD (Quadrant Photoelectric Detector) to measure Z-direction displacement and three angular degrees of freedom. Another type is a multi-degree-of-freedom measurement method based on a combination of linear displacement sensing heads using multiple laser grating interference, such as the invention patent application with Chinese patent publication number CN106017308A, published on October 12, 2016, and entitled "A Six-Degree-of-Freedom Interference Measurement System and Method." A single probe can measure three axial linear displacements, and the grating angle offset can be approximately calculated using the three linear displacements and the probe spacing. However, the accuracy, resolution, and other indicators of the measurement results from grating interference and beam position detection differ by dozens of times. Together, they constitute the grating six-degree-of-freedom position and posture measurement results, which can cause serious positioning accuracy mismatch problems. With a combination of multiple probes, displacement measurement is affected by angular deflection, making it impossible to separate and decouple the degrees of freedom. Consequently, there is a problem of multiple coupling results, and the grating area cannot be effectively utilized. Furthermore, the system structure is complex, and high installation accuracy requirements are placed on the experimental device.

[0004] The Chinese patent application, CN112857208A, published on May 28, 2021, and titled "Single-beam three-degree-of-freedom laser interferometer based on high-speed camera," can simultaneously measure angles and displacements. However, its simple Michelson interferometer structure can only measure three degrees of freedom, and when the target mirror to be measured moves along the optical axis, the device's angular measurement range will be limited. The greater the displacement of the target mirror along the optical axis, the smaller the angular measurement range. At the same time, the laser interferometer is also 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, which can achieve multi-degree-of-freedom posture measurement while simplifying the design of the optical path structure.

[0006] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0007] A multi-degree-of-freedom measurement device based on grating interference fringes, comprising:

[0008] A single-frequency laser light source for emitting a laser beam;

[0009] A first beam splitter prism is located on the outgoing light path of the single-frequency laser light source and is used to split the laser beam into a reference light and a measurement light;

[0010] an optical reference element, located on an optical path of the reference light and configured to return the reference light to the first beam splitter prism;

[0011] 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;

[0012] The camera is located on the output light path of the first beam splitter prism. The at least two reference beams and the at least two diffracted beams that return 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 the interference of the reference beams and the diffracted beams.

[0013] The computer is connected to the camera and is used to determine the position change of the measuring grating according to the change of the interference fringes.

[0014] Furthermore, it also includes a beam splitting component, which is located on the optical path from the single-frequency laser light source to the first beam splitting prism and is used to split the emitted laser beam into two parallel beams;

[0015] The light splitting component includes a transmission light splitting grating and a refractive element, wherein the transmission light splitting grating is located on the optical 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

[0016] The light splitting component includes a second light splitting prism. The emission direction of the single-frequency laser light source is parallel to the bonding surface of the second light splitting prism but are not on the same plane.

[0017] Furthermore, the measuring grating is a one-dimensional measuring grating; the multi-degree-of-freedom measuring device further comprises an optical component, which is located on the optical path from the first beam splitter prism to the measuring grating;

[0018] The optical assembly includes a first reflector and a second reflector, and the first reflector and the second reflector are used to make the measuring light incident on the measuring grating at a Littrow angle; or

[0019] The optical component is a one-dimensional refractive grating.

[0020] Furthermore, 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.

[0021] Furthermore, 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;

[0022] The angular change of the measurement grating is solved based on the current spatial frequency and the initial spatial frequency.

[0023] Furthermore, the angle change includes a yaw angle change , the yaw angle change of the measuring grating is calculated by the following formula: Perform the solution:

[0024]

[0025] Angle changes also include pitch angle changes , the pitch angle change of the measuring grating is calculated by the following formula: Perform the solution:

[0026]

[0027] 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.

[0028] Furthermore, the at least two diffracted light beams include +1-order diffracted light and -1-order diffracted light; the camera is used to capture a first set of interference fringes formed by the interference of a reference light beam and the +1-order diffracted light, and a second set of interference fringes formed by the interference of another reference light beam and the -1-order diffracted light; the position change of the measurement 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: Perform the solution:

[0029]

[0030] in, is the lateral distance between the center of the first set of interference fringes and the center of the second set of interference fringes, is the longitudinal distance between the center of the first set of interference fringes and the center of the second set of interference fringes.

[0031] Furthermore, the position change of the measuring grating includes the displacement change; the computer is used to determine the light intensity distribution of the interference fringes, and perform spectral analysis on the interference fringes to extract the phase of each frame between the current moment and the initial moment, and unwrap 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; based on the phase difference, the displacement change of the measuring grating is solved.

[0032] Furthermore, the at least two diffracted light beams include +1-order diffracted light and -1-order diffracted light; the camera is used to capture a first set of interference fringes formed by interference of a reference light beam and the +1-order diffracted light, and a second set of interference fringes formed by interference of another reference light beam and the -1-order diffracted light; 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: Perform the solution:

[0033]

[0034] The displacement change of the measuring grating along the second direction is calculated by the following formula: Perform the solution:

[0035]

[0036] in, 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.

[0037] Furthermore, 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 beam into four parallel beams; the measuring grating is a two-dimensional measuring grating.

[0038] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0039] The multi-degree-of-freedom measuring device based on grating interference fringes provided by the embodiment of the present invention can realize the measurement of the three angular degrees of freedom of the measuring grating through the interference fringes in a single-frame interference image, and realize the measurement of at least two displacement degrees of freedom of the measuring grating through the interference fringes in continuous multi-frame interference images. And it is possible to solve the angle and displacement of the measuring grating from the frequency, phase and other information 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 measuring device, the optical path structure of the multi-degree-of-freedom measuring device created by the present invention is simple, and only a single camera is used to realize the measurement of the multi-degree-of-freedom posture of the measuring grating, and it has the advantages of a large angle measurement range, etc., which meets the high-precision requirements of processes such as photolithography for displacement and angle measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0041] Figure 1 A schematic structural diagram of a multi-degree-of-freedom measurement device according to an embodiment of the present invention;

[0042] Figure 2 A schematic structural diagram of another embodiment of the spectroscopic component of the multi-degree-of-freedom measurement device according to an embodiment of the present invention;

[0043] Figure 3 A schematic structural diagram of another embodiment of the optical assembly of the multi-degree-of-freedom measurement device according to an embodiment of the present invention;

[0044] Figure 4 A schematic structural diagram of another embodiment of a camera of the multi-degree-of-freedom measurement device according to an embodiment of the present invention;

[0045] Figure 5 A schematic structural diagram of another embodiment of the optical reference element of the multi-degree-of-freedom measurement device according to an embodiment of the present invention;

[0046] Figure 6 A schematic diagram illustrating the change in spatial frequency of interference fringes when the measuring grating of the multi-degree-of-freedom measurement device according to an embodiment of the present invention rotates about a third direction;

[0047] Figure 7 A schematic diagram illustrating position changes of a first set of interference fringes and a second set of interference fringes when the measuring grating of the multi-degree-of-freedom measuring device according to an embodiment of the present invention rotates about a second direction;

[0048] Figure 8A schematic diagram illustrating the phase change of interference fringes when a measuring grating of a multi-degree-of-freedom measurement device according to an embodiment of the present invention produces a displacement along a first direction;

[0049] Figure 9 A schematic diagram illustrating the phase change of interference fringes when the measuring grating of the multi-degree-of-freedom measurement device according to an embodiment of the present invention produces a displacement along the second direction;

[0050] Figure 10 This is a schematic structural diagram of another embodiment of the multi-degree-of-freedom measurement device described in the embodiment of the present invention.

[0051] Description of reference numerals:

[0052] 10. Multi-degree-of-freedom measurement device; 11. Single-frequency laser light source; 12. First beam splitter prism; 13. Optical reference element; 14. Measuring grating; 15. Camera; 16. Computer; 17. Spectral component; 18. Transmission beam splitter grating; 19. Refraction element; 20. Second beam splitter prism; 21. Optical component; 22. First reflector; 23. Second reflector; 24. One-dimensional refraction grating; 25. Reference reflector; 26. Right-angle reflector; 27. Third beam splitter prism; 28. Fourth beam splitter prism; 29. ​​First line array camera; 30. Second line array camera; 31. Third line array camera; 32. Fourth line array camera; 33. First reflection assembly; 34. Second reflection assembly; 35. Third reflector; 36. Fourth reflector; 37. Fifth reflector; 38. Sixth reflector; 39. Beam splitter prism group; 40. Fifth beam splitter prism; 41. Sixth beam splitter prism; 42. Reflector group. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction 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 use associated similar element numbers. In the following embodiments, many detailed descriptions are intended to enable the present invention to be 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, or methods. In some cases, some operations related to the present invention are not shown or described in the specification. This is to avoid the core part of the present invention being overwhelmed by too much description. For those skilled in the art, it is not necessary to describe these related operations in detail. They can fully understand the related operations based on the description in the specification and the general technical knowledge in the art.

[0054] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other to form various implementation methods. At the same time, the steps or actions in the method description can also be interchanged or adjusted in a manner that is obvious to those skilled in the art. Therefore, the various orders in the description and the drawings are only for the purpose of clearly describing a certain embodiment and are not intended to be a required order, unless otherwise specified that a certain order must be followed.

[0055] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are 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 cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0056] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art can understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0057] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0058] See also Figures 1 to 10 As shown, the present invention provides a multi-degree-of-freedom measuring device 10 based on grating interference fringes. The multi-degree-of-freedom measuring device 10 includes a single-frequency laser light source 11, a first beam splitter prism 12, an optical reference element 13, a measuring grating 14, a camera 15 and a computer 16.

[0059] The single-frequency laser light source 11 is used to emit a laser beam.

[0060] 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 split the laser beam into reference light and measurement light.

[0061] The optical reference element 13 is located on the optical 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.

[0062] The measuring grating 14 is located on the optical path of the measuring light, and is used to receive the measuring light, generate diffracted light, and return the diffracted light to the first beam splitter prism 12 .

[0063] Camera 15 is located on the optical path of the first beam splitter prism 12. The at least two reference beams and at least two diffracted beams returning to the first beam splitter prism 12 pass through the first beam splitter prism 12 and are incident on camera 15. Camera 15 is used to capture interference fringes formed by the interference of the reference and diffracted beams. Camera 15 can capture at least two sets of interference fringes. 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 a first direction X. The measurement grating 14 and camera 15 are located on opposite sides of the first beam splitter prism 12 along a second direction Z.

[0064] The computer 16 is connected to the camera 15 and can acquire and process the interference fringe image captured by the camera 15. The computer 16 is used to determine the position change of the measurement grating 14 based on the change of the interference fringe.

[0065] See also Figures 1 to 5 As shown, there are two reference beams, and at least two diffracted beams include +1-order diffracted light and -1-order diffracted light. Camera 15 can be used to capture two sets of interference fringes. Camera 15 is used to capture a first set of interference fringes formed by the interference of one reference beam and the +1-order diffracted light, and a second set of interference fringes formed by the interference of another reference beam and the -1-order diffracted light.

[0066] See also Figure 1 and Figure 2 As shown, in one embodiment, the multi-degree-of-freedom measuring device 10 further includes a beam splitter component 17, which 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 split the emitted laser beam into two parallel beams. Figure 1 In the embodiment shown, the beam splitting assembly 17 includes a second beam splitting prism 20. The emission direction of the single-frequency laser light source 11 is parallel to the bonding surface of the second beam splitting prism 20 but not on the same plane. In this way, the laser beam can be split into two parallel beams by the second beam splitting prism 20. The first beam splitting prism 12 and the second beam splitting prism 20 can both be depolarizing beam splitting prisms. Figure 2In the illustrated embodiment, the beam splitting assembly 17 includes a transmissive beam splitter grating 18 and a refractive element 19. The transmissive beam splitter grating 18 is located in the optical path from the single-frequency laser light source 11 to the refractive element 19. The refractive element 19 is used to parallelize the laser beam. The transmissive beam splitter grating 18 splits the emitted laser beam into two beams, which then pass through the refractive element 19 to become parallel.

[0067] See also Figure 1 and Figure 3 As shown, in one embodiment, the measuring grating 14 is a one-dimensional measuring grating. The multi-degree-of-freedom measuring device 10 further includes an optical component 21, which is located on the optical path from the first beam splitter prism 12 to the measuring grating 14 and is used to allow the measuring light to be incident on the measuring grating 14 and to allow the diffracted light generated by the measuring grating 14 to return to the first beam splitter prism 12 along the incident optical path of the measuring light. Figure 1 In the embodiment shown, the optical assembly 21 includes a first reflector 22 and a second reflector 23. The first reflector 22 and the second reflector 23 can allow the measuring light to be incident on the measuring grating 14 at a Littrow angle. Figure 3 In the illustrated embodiment, the optical component 21 includes a one-dimensional refractive index grating 24 .

[0068] See also Figure 1 and Figure 4 As shown, in Figure 1 In the embodiment shown, the camera 15 is an area array camera. By introducing an area array camera to collect interference fringes, multiple degrees of freedom measurements can be achieved using only a single camera, greatly simplifying the optical path structure of the multi-degree-of-freedom measurement device 10. Fewer optical components and a simpler and more compact optical path structure can be used while ensuring measurement accuracy, avoiding the accuracy mismatch problem caused by the use of position-sensitive detectors and the complex layout of the instrument with multiple probe combinations, and can be better applied in complex environments. Figure 4In the illustrated embodiment, the cameras 15 are four line scan cameras. These four line scan cameras include a first line scan camera 29, a second line scan camera 30, a third line scan camera 31, and a fourth line scan camera 32. The multi-degree-of-freedom measurement device 10 also includes a right-angle mirror 26, a third beam splitter prism 27, and a fourth beam splitter prism 28. The right-angle mirror 26 is located on the optical path from the first beam splitter prism 12 to the four line scan cameras. It is used to separate the two interference light beams emitted from the first beam splitter prism 12. The two interference light beams are formed by the interference of one reference light beam with the +1st-order diffracted light, and the other reference light beam with the -1st-order diffracted light. The interference light beam is split by the third beam splitter prism 27 into two first sub-interference light beams. The two first sub-interference light beams are incident on the first line scan camera 29 and the second line scan camera 30, respectively. 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. Thus, 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 the interference light beam, while the other can obtain the column distribution of the interference fringes of the interference light beam. The other interference light beam is split into two second sub-interference light beams by the fourth beam-splitting prism 28. The two second sub-interference light beams are incident on the third line array camera 31 and the fourth line array camera 32, respectively. The line array sensor of the third line array camera 31 extends along the first direction X, while the line array sensor of the fourth line array camera 32 extends along the third direction Y. Thus, 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 light beam, while the other can obtain the column distribution of the interference fringes of the interference light beam. In other embodiments, the camera 15 can also be a different type of industrial camera 15.

[0069] See also Figure 1 As shown, in one embodiment, the optical reference element 13 is tilted at a set angle θ. The optical reference element 13 is a reference reflector 25 , which can reflect the reference light back to the first beam splitter prism 12 .

[0070] exist Figures 1 to 4In the illustrated embodiment, the laser beam emitted by the single-frequency laser light source 11 is split into two parallel beams by the beam splitter assembly 17. The two parallel beams are then split into two parallel reference beams and two parallel measurement beams by the first beam splitter prism 12. The two parallel reference beams are transmitted through the first beam splitter prism 12, incident on the reference reflector 25, and reflected back to the first beam splitter prism 12 by the reference reflector 25. The two parallel measurement beams are then reflected by the first beam splitter prism 12 to the optical assembly 21, and then incident on the measurement grating 14. The measurement grating 14 receives the two measurement beams and generates ±1st-order diffracted beams. The ±1st-order diffracted beams return to the first beam splitter prism 12 along the incident optical path of the measurement beams. The ±1st-order diffracted beams returning to the first beam splitter prism 12, along with the two parallel reference beams, pass through the first beam splitter prism 12 before being incident on the camera 15. The ±1st-order diffracted beams are parallel to and overlap with the two parallel reference beams, and together they are incident on the camera 15. The camera 15 is used to capture a first set of interference fringes formed by the interference of a beam of reference light and the +1st order diffraction light, and a second set of interference fringes formed by the interference of another beam of reference light and the -1st order diffraction light.

[0071] See also 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 reflective assembly 33 and a second reflective assembly 34. The first reflective assembly 33 is located on the optical path from the first beam splitter prism 12 to the measurement grating 14. The first reflective assembly 33 includes a third reflector 35 and a fourth reflector 36. The measurement light split by the first beam splitter prism 12 is perpendicularly incident on the surface of the measurement grating 14, generating ±1st-order diffracted light. The +1st-order diffracted light is reflected by the third reflective mirror 35 and returns to the first beam splitter prism 12. The -1st-order diffracted light is reflected by the fourth reflective mirror 36 and returns to the first beam splitter prism 12. The second reflective assembly 34 is located on the optical path from the first beam splitter prism 12 to the optical reference element 13. The second reflective assembly 34 includes a fifth reflective mirror 37 and a sixth reflective mirror 38. The reference light separated by the first beam splitter prism 12 is incident on the surface of the optical reference element 13 and generates ±1-order reference diffraction light as the reference light. The +1-order reference diffraction light is reflected by the fifth reflecting mirror 37 and returns to the first beam splitter prism 12. The -1-order reference diffraction light is reflected by the sixth reflecting mirror 38 and returns to the first beam splitter prism 12.

[0072] exist Figure 5In the illustrated embodiment, the laser beam emitted by the single-frequency laser light source 11 is split into a reference beam and a measurement beam by a first beam splitter prism 12. The reference beam can transmit through the first beam splitter prism 12 and be incident on the surface of the optical reference element 13, thereby generating ±1st-order reference diffracted beams serving as reference beams. The ±1st-order reference diffracted beams return to the first beam splitter prism 12 via a fifth reflector 37 and a sixth reflector 38, respectively, and are then reflected by the first beam splitter prism 12 to be directed to the camera 15. The measurement beam can be reflected by the first beam splitter prism 12 and perpendicularly incident on the surface of the measurement grating 14, thereby generating ±1st-order diffracted beams. The ±1st-order diffracted beams return to the first beam splitter prism 12 via a third reflector 35 and a fourth reflector 36, respectively, and are then transmitted through the first beam splitter prism 12 to be incident on the camera 15. The camera 15 is used to capture a first set of interference fringes formed by the interference of the +1-order reference diffraction light and the +1-order diffraction light, and a second set of interference fringes formed by the interference of the -1-order reference diffraction light and the -1-order diffraction light.

[0073] See also 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 produces an inclination angle (such as a pitch angle and a yaw angle), the spatial frequency of the interference fringes will change. In one embodiment, the position change of the measurement grating 14 includes an angle change. The angle change includes a yaw angle change. , yaw angle change It refers to the angle of the measurement grating 14 rotating around the first direction X. The angle change also includes the pitch angle change , pitch angle change It refers to the angle of rotation of the measuring grating 14 around 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 row or a column in 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 14 is in the initial position. It can be seen that the spatial frequency of the interference fringes increases or , and the yaw angle is linearly related to the change of the spatial frequency, and the pitch angle is linearly related to the change of the spatial frequency. According to the current spatial frequency and the initial spatial frequency, the angle change of the measuring grating 14 is solved.

[0074] In one embodiment, the yaw angle change of the measuring grating 14 is calculated by the following formula: Perform the solution:

[0075]

[0076] The pitch angle change of the measuring grating 14 is calculated by the following formula: Perform the solution:

[0077]

[0078] 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.

[0079] See also Figure 7 As shown, when the measuring grating 14 rotates around the Z axis, the centers of the first and second groups of interference fringes captured by the camera 15 move upward and downward, respectively, from being on the same horizontal line to being offset from each other. Thus, by measuring the horizontal spacing between the centers of the first and second groups of interference fringes, as well as the vertical spacing between the centers of the first and second groups of interference fringes, the angle of rotation of the measuring grating 14 around the second direction Z, i.e., the roll angle change, can be obtained. In one embodiment, the angle change also includes a roll angle change , roll angle change It refers to the angle of the measurement grating 14 rotating around the second direction Z. The following formula is used to calculate the roll angle change of the measurement grating 14: Perform the solution:

[0080]

[0081] in, is the lateral distance between the center of the first set of interference fringes and the center of the second set of interference fringes, is the longitudinal distance between the center of the first set of interference fringes and the center of the second set of interference fringes.

[0082] See also 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 can be further reflected in the displacement of the measurement grating 14. When the measurement grating 14 produces a displacement along the first direction X or the second direction Z, the phase of the interference fringes will change. The figure only shows the phase change of one set of interference fringes in the first and second sets of interference fringes. Since the two sets of interference fringes are respectively generated by the coherent superposition of the ±1st order diffracted light and the reference light, and the optical paths are symmetrical. Therefore, the two sets of interference fringes contain and The displacement information of the two sets of interference fringes needs to be extracted frame by frame respectively, and the two displacement information needs to be extracted respectively by summing and differencing operations. In one embodiment, the position change of the measuring grating 14 includes the displacement change. The computer 16 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 unwrap 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 measuring grating 14 is solved.

[0083] In one embodiment, the displacement change includes a displacement change along the first direction X. and the displacement change along the second direction Z , the displacement change of the measuring grating 14 along the first direction X is calculated by the following formula: Perform the solution:

[0084]

[0085] The displacement change of the measuring grating 14 along the second direction Z is calculated by the following formula: Perform the solution:

[0086]

[0087] in, 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.

[0088] The multi-degree-of-freedom measuring device 10 based on grating interference fringes provided by the embodiment of the present invention can realize the measurement of the three angular degrees of freedom of the measuring grating 14 through the interference fringes in a single-frame interference image, and realize the measurement of the two displacement degrees of freedom of the measuring grating 14 through the interference fringes in continuous multi-frame interference images. And it is possible to solve the angle and displacement of the measuring grating 14 from the frequency, phase and other information 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 measuring devices, the optical path structure of the multi-degree-of-freedom measuring device 10 created by the present invention is simple, and only a single camera 15 is used to realize the measurement of the multi-degree-of-freedom posture of the measuring grating 14, and it has the advantages of a large angle measurement range, etc., which meets the high-precision requirements of processes such as photolithography for displacement and angle measurement.

[0089] See also Figure 10As shown, there are four reference beams and four diffracted beams. Camera 15 can be used to capture four sets of interference fringes. Camera 15 is used to capture a first set of interference fringes formed by the interference of the first reference beam and the +1st order diffracted light in the first direction X, a second set of interference fringes formed by the interference of the second reference beam and the -1st order diffracted light in the first direction X, a third set of interference fringes formed by the interference of the third reference beam and the +1st order diffracted light in the third direction Y, and a fourth set of interference fringes formed by the interference of the fourth reference beam and the -1st order diffracted light in the third direction Y.

[0090] In one embodiment, the multi-degree-of-freedom measurement device 10 further includes a beam splitter assembly 39. The beam splitter assembly 39 is located on the optical path from the single-frequency laser light source 11 to the first beam splitter prism 12 and is configured to split the emitted laser beam into four parallel beams. The beam splitter assembly 39 further includes a fifth beam splitter prism 40 and a sixth beam splitter prism 41. The fifth beam splitter prism 40 is configured to split the emitted laser beam into two parallel beams, and the sixth beam splitter prism 41 is configured to split the two parallel beams emitted from the fifth beam splitter prism 40 into four parallel beams.

[0091] The measuring grating 14 is a two-dimensional measuring grating. The multi-degree-of-freedom measuring device 10 further includes a reflector group 42. The reflector group 42 is located on the optical path from the first beam splitter prism 12 to the measuring grating 14 and is used to allow the measuring light to be incident on the measuring grating 14 and to allow the diffracted light generated by the measuring grating 14 to return to the first beam splitter prism 12 along the incident optical path. Figure 10 In the illustrated embodiment, the reflector assembly 42 includes four reflectors, which are used to allow the measuring light to be incident on the measuring grating 14 at a Littrow angle.

[0092] In one embodiment, the displacement change also includes a displacement change along the third direction Y. , the displacement change of the measuring grating 14 along the third direction Y is calculated by the following formula: Perform the solution:

[0093]

[0094] in, 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. This allows the multi-degree-of-freedom measurement device 10 to measure the six degrees of freedom of the measurement grating 14. The six degrees of freedom include yaw angle, pitch angle, roll angle, displacement along a first direction X, displacement along a second direction Z, and displacement along a third direction Y. In this way, the three angular degrees of freedom of the measurement grating 14 can be measured using interference fringes in a single-frame interference image, and the three displacement degrees of freedom of the measurement grating 14 can be measured using interference fringes in multiple consecutive frames of interference images. This enables measurement of six degrees of freedom in a simple and reliable manner.

[0095] It should be understood that the various forms of the processes shown above can be used to reorder, add, or delete steps. For example, the steps described in the present disclosure can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solutions disclosed in the present disclosure can be achieved. This is not limited herein.

[0096] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection 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 for emitting a laser beam; a first beam splitter prism, located on the outgoing light path of the single-frequency laser light source, for splitting the laser beam into reference light and measurement light; an optical reference element, located on the optical path of the reference light, and configured to return the reference light to the first beam splitter prism; a measuring grating located on an optical path of the measuring light, configured to receive the measuring light and generate diffracted light, returning the diffracted light to the first beam splitter prism; the diffracted light includes +1-order diffracted light and -1-order diffracted light; and a camera configured to capture a first set of interference fringes formed by interference between a beam of the reference light and the +1-order diffracted light, and a second set of interference fringes formed by interference between another beam of the reference light and the -1-order diffracted light. a camera located on an outgoing light path of the first beam splitter prism, wherein the at least two reference beams and the at least two diffracted beams returning to the first beam splitter prism pass through the first beam splitter prism and are incident on the camera; the camera is configured to capture interference fringes formed by interference between the reference beams and the diffracted beams; A computer is connected to the camera, and is used to determine the position change of the measuring grating according to the change of the interference fringes; the position change of the measuring grating includes angle change, and the angle change includes yaw angle change, pitch angle change and roll angle change, the yaw angle change refers to the angle of rotation of the measuring grating around the first direction X, the pitch angle change refers to the angle of rotation of the measuring grating around the third direction Y, and the roll angle change refers to the angle of rotation of the measuring grating around the second direction Z; 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 an initial spatial frequency at an initial moment when the measuring grating is in an initial position; calculating an angular change of the measuring grating according to the current spatial frequency and the initial spatial frequency; the position change of the measuring grating includes a displacement change, and the displacement change includes a displacement change of the measuring grating along a first direction X and a displacement change along a second direction Z; 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 a current phase of the interference fringes at the current moment and a phase difference between the initial phase of the interference fringes at the initial moment; The displacement change of the measurement grating is calculated based on the phase difference.

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 beam into two parallel beams; The spectroscopic component includes a transmission spectroscopic grating and a refractive element, wherein the transmission spectroscopic grating is located on the optical 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 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 is 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 includes 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 yaw angle change of the measuring grating is calculated by the following formula: Perform the solution: The angle change also includes a pitch angle change , the pitch angle change of the measuring grating is calculated by the following formula: Perform the solution: 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.

6. The multi-degree-of-freedom measurement device based on grating interference fringes according to claim 1, characterized in that: The roll angle change of the measuring grating is calculated by the following formula: Perform the solution: 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.

7. The multi-degree-of-freedom measurement device based on grating interference fringes according to claim 1, characterized in that: The displacement change of the measuring grating along the first direction is calculated by the following formula: Perform the solution: The displacement change of the measuring grating along the second direction is calculated by the following formula: Perform the solution: 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.

8. 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 beam into four parallel beams; the measuring grating is a two-dimensional measuring grating.

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