A grating interferometry apparatus

Abstract

The application provides a grating interferometry device, comprising a light source unit for outputting first polarized laser and second polarized laser; a reading head unit comprising a first optical conversion unit and a first photoelectric detector, the second polarized laser as reference light passes through the first optical conversion unit and is incident into the first photoelectric detector; the first polarized laser as measurement light returns to the first optical conversion unit and is incident into the first photoelectric detector; an angle self-compensation unit comprising a first optical assembly and a grating, the first optical assembly receives the first polarized laser emitted from the first optical conversion unit and makes it incident into the grating at a first angle, the first-order diffracted light diffracted by the grating returns along the original light path after multiple reciprocating actions between the first optical assembly and the grating, and is incident into the first photoelectric detector as measurement light. The application aims to construct a grating interferometry system suitable for high line density grating, which can effectively suppress the coherent light separation phenomenon in the presence of large angle deviation.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of grating measurement, and in particular, to a grating interferometry device. BACKGROUND

[0002] In the field of precision displacement measurement, optical measurement methods have become a research hotspot in the field of ultra-precision measurement due to their comprehensive advantages of large range, high precision, and high measurement speed. Among them, the grating interferometry scheme takes the grating pitch as the measurement reference. If a low-expansion or zero-expansion material is selected as the grating substrate, the influence of external environmental factors (such as temperature, air pressure, humidity, etc.) on the grating pitch can be effectively suppressed. Compared with the interferometer taking the laser wavelength as the reference, the dependence on environmental control is significantly reduced, and strict constant temperature, constant pressure, and constant humidity conditions are not required, thereby greatly reducing the environmental requirements of the system. The grating interferometry system has the characteristics of compact structure, strong multi-freedom expansion capability, and excellent environmental disturbance resistance, and is widely used in the fields of microelectronic manufacturing, nanometer measurement, and semiconductor processing. Benefiting from its comprehensive performance in high precision and large range, the grating interferometry displacement measurement equipment has an urgent application demand in high-end manufacturing fields such as high-end numerical control machine tools and aerospace.

[0003] To overcome the angle error problem faced by the grating interferometer in practical application, relevant technical personnel have proposed various technical paths. Among them, the common optical path and heterodyne interference type scheme improves the angle tolerance capability of the system to a certain extent through the coordinated innovation of optical path structure and detection technology. For example, a high-tolerance common optical path grating interferometer divides the system into a light source module, a common optical path module, and a post-processing module through modular design, and uses an optical fiber for signal transmission, effectively suppressing the influence of environmental disturbances. The scheme introduces a backward mirror structure in the optical path, further improving the alignment tolerance between the read head and the grating. In addition, the symmetric Littrow structure double-grating common mode error suppression technology adopts a "sandwich" structure, encapsulating the core optical path between two reference gratings with consistent optical parameters, and constructing two equal optical path complementary measurement arms. Its core advantage lies in the common mode suppression mechanism: when an angle change occurs, the errors suffered by the two measurement arms are in a conjugate relationship, making the interference beams remain stable and combined, not only avoiding the introduction of additional optical path differences, but also maintaining a high signal-to-noise ratio. However, this structure still cannot completely immune to three-dimensional large-angle deflection, limiting its further popularization and application.

[0004] Therefore, the existing grating interferometer still has technical problems such as insufficient angle tolerance, which need to be solved. SUMMARY

[0005] The purpose of the present disclosure is to provide a grating interferometry device that can solve at least one of the above technical problems. The specific scheme is as follows:

[0006] The application provides a grating interferometry device, comprising:

[0007] a light source unit configured to output at least one beam of orthogonally polarized difference frequency laser, the difference frequency laser comprising first polarized laser and second polarized laser, the first polarized laser having a first frequency, the second polarized laser having a second frequency, the first frequency being different from the second frequency, the first polarized laser being horizontally polarized, and the second polarized laser being vertically polarized;

[0008] a read head unit comprising a first optical conversion unit and a first photodetector, the second polarized laser being incident into the first photodetector after passing through the first optical conversion unit as reference light; the first polarized laser being incident into the first photodetector after passing through the first optical conversion unit and the first optical component as measurement light, and interfering with the reference light to measure the displacement of the target object.

[0009] an angle self-compensation unit comprising a first optical component and a grating, the first optical component receiving the first polarized laser from the first optical conversion unit and making the first polarized laser incident into the grating at a first angle, the first-order diffracted light diffracted by the grating returning along the original light path after multiple reciprocating actions between the first optical component and the grating, and being incident into the first photodetector as the measurement light.

[0010] In some embodiments, the first optical conversion unit comprises a first plane mirror, a first quarter-wave plate, a first polarization beam splitter prism and a second quarter-wave plate; wherein the second polarized laser is reflected by the first polarization beam splitter prism, passes through the first quarter-wave plate and the first plane mirror, and then passes through the first quarter-wave plate again, and the polarization state is parallel polarization, and the second polarized laser enters the first photodetector through the first polarization beam splitter prism; the first polarized laser passes through the first polarization beam splitter prism and the second quarter-wave plate, and then passes through the second quarter-wave plate again after being reflected by the first plane mirror, and the polarization state is vertical polarization, and the first polarized laser enters the first photodetector after being reflected by the first polarization beam splitter prism.

[0011] In some embodiments, the first optical assembly comprises a third plane mirror, a first corner cube prism, and a fourth plane mirror, wherein the first polarized laser light emitted from the first optical conversion unit enters the grating at a first angle via the third plane mirror to generate first 1st-order diffracted light, the first 1st-order diffracted light passes through the first corner cube prism and then interacts with the grating again to generate second 1st-order diffracted light, the second 1st-order diffracted light passes through the fourth plane mirror and returns to the grating to generate third 1st-order diffracted light and fourth 1st-order diffracted light, and the fourth 1st-order diffracted light returns to the grating via the third plane mirror to form the measurement light.

[0012] In some embodiments, the read head unit further comprises:

[0013] The read head unit further comprises a second optical conversion unit and a second photodetector, wherein the second polarized laser light passes through the second optical conversion unit and then enters the second photodetector as reference light, and the first polarized laser light is used to measure the target object after being emitted from the second optical conversion unit, returns to the second optical conversion unit as measurement light, and then enters the second photodetector to interfere with the reference light to measure the displacement of the target object.

[0014] The angle self-compensation unit further comprises a second optical assembly, which receives the first polarized laser light emitted from the second optical conversion unit and enters the grating at a first angle, and the 1st-order diffracted light diffracted by the grating returns along the original light path after multiple reciprocating actions between the second optical assembly and the grating, and then enters the second photodetector as the measurement light.

[0015] In some embodiments, the second optical conversion unit comprises a fifth plane mirror, a third quarter-wave plate, a second polarizing beam splitter, and a fourth quarter-wave plate, wherein the second polarized laser light is reflected by the second polarizing beam splitter, passes through the third quarter-wave plate, and then passes through the fifth plane mirror and the third quarter-wave plate again, and then enters the second photodetector as reference light with a parallel polarization state; and the first polarized laser light passes through the second polarizing beam splitter and the fourth quarter-wave plate, and then passes through the second optical assembly and the fourth quarter-wave plate again, and then enters the second photodetector as measurement light with a perpendicular polarization state after being reflected by the second polarizing beam splitter.

[0016] In some embodiments, the second optical assembly comprises a sixth plane mirror, a second corner cube prism, and a seventh plane mirror, wherein the first polarized laser emitted from the second optical conversion unit enters the grating through the sixth plane mirror at a first angle to generate a fifth first-order diffracted light, the fifth first-order diffracted light passes through the second corner cube prism and then interacts with the grating again to generate a sixth first-order diffracted light, the sixth first-order diffracted light passes through the seventh plane mirror and returns to the grating to generate a seventh first-order diffracted light and an eighth first-order diffracted light, and the eighth first-order diffracted light returns to the grating through the sixth plane mirror to form the measurement light.

[0017] In some embodiments, the light source unit comprises a heterodyne light source, a beam splitter prism, and an eighth plane mirror, wherein the difference frequency laser emitted by the heterodyne light source is split into two beams of difference frequency laser by the beam splitter prism, one beam of difference frequency laser is reflected by the beam splitter prism and enters the first optical conversion unit, and the other beam of difference frequency laser is reflected by the eighth plane mirror after passing through the beam splitter prism and enters the second optical conversion unit.

[0018] In some embodiments, the light source unit comprises a first heterodyne light source and a second heterodyne light source, wherein the first heterodyne light source outputs first polarized laser and second polarized laser which enter the first read head unit, and the second heterodyne light source outputs first polarized laser and second polarized laser which enter the second read head unit.

[0019] In some embodiments, the light source unit comprises:

[0020] a first polarized light source and a second polarized light source for emitting the first polarized laser and the third polarized laser, respectively, wherein the first polarized laser and the third polarized laser are both horizontally polarized, and the first polarized laser and the third polarized laser have different frequencies; and the first polarized laser and the third polarized laser output by the first polarized light source and the second polarized light source enter the first read head unit.

[0021] a third polarized light source and a fourth polarized light source for emitting the first polarized laser and the third polarized laser, respectively, wherein the first polarized laser and the third polarized laser are both horizontally polarized, and the first polarized laser and the third polarized laser have different frequencies; and the first polarized laser and the third polarized laser output by the third polarized light source and the fourth polarized light source enter the second read head unit.

[0022] In some embodiments, the grating is a 1200gr / mm high-line diffraction grating, the first angle is 11.4°, and the diffraction angle of the first-order diffracted light is 35.2°.

[0023] Compared with the prior art, the above scheme of the embodiments of the present disclosure has at least the following beneficial effects:

[0024] The present application aims to construct a grating interferometry device suitable for high line density gratings, which can effectively suppress the coherent light separation phenomenon in the presence of large angle deviation, expand the measurement dimension of the system, and significantly improve the angle tolerance capability. The system introduces an angle self-compensation unit in the optical path, which fundamentally eliminates the influence of grating three-dimensional angle error on the measurement result, thereby realizing high-precision, large-angle tolerance, and multi-degree-of-freedom displacement measurement. It provides a reliable measurement solution for harsh industrial scenes such as semiconductor manufacturing and precision machining. BRIEF DESCRIPTION OF DRAWINGS

[0025] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the present disclosure and, together with the specification, serve to explain the principles of the present disclosure. It is clear that the drawings in the following description are only some embodiments of the present disclosure, and other drawings can be obtained from these drawings without creative labor for those skilled in the art. In the drawings:

[0026] Figure 1 is a structural schematic diagram of a single-arm grating interferometry device shown in some embodiments.

[0027] Figure 2 is a structural schematic diagram of a double-arm grating interferometry device shown in some embodiments.

[0028] Figure 3 is a structural schematic diagram of a double-arm grating interferometry device shown in some other embodiments.

[0029] Figure 4 is a structural schematic diagram of a light source unit of a double-arm grating interferometry device shown in some other embodiments.

[0030] Fig. 5(a), Fig. 5(b), and Fig. 5(c) are simulation schematic diagrams of a double-arm grating interferometry device shown in some other embodiments.

[0031] Explanation of reference signs:

[0032] Light source unit 100, heterodyne light source 1, beam splitter prism 2, eighth plane mirror 3, first heterodyne light source 110, second heterodyne light source 120, first polarized light source 130, second polarized light source 140, third polarized light source 150, fourth polarized light source 160;

[0033] The read head unit 200, the first optical conversion unit 210, the first plane mirror 4, the first quarter-wave plate 5, the first polarization beam splitter prism 6, the second quarter-wave plate 8, the first photodetector 7, the second optical conversion unit 220, the fifth plane mirror 12, the third quarter-wave plate 13, the second polarization beam splitter prism 14, the fourth quarter-wave plate 16, and the second photodetector 15;

[0034] The angle self-compensation unit 300, the first optical assembly 310, the third plane mirror 9, the first corner cube prism 11, the fourth plane mirror 10, the second optical assembly 320, the sixth plane mirror 17, the second corner cube prism 19, the seventh plane mirror 18, and the grating 330. DETAILED DESCRIPTION

[0035] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0036] In the related art, although the grating interferometer has significant advantages, it still has the technical problem of insufficient angle tolerance in actual industrial applications. Since the reference grating and the object to be measured are usually rigidly connected, random angle errors caused by factors such as mechanical guide rail straightness error, assembly deviation or external vibration of the moving part during operation will cause the grating three-dimensional angle to deviate from the ideal measurement position, thereby introducing an error that cannot be ignored. Such angle disturbance is difficult to completely avoid in actual industrial environment, which seriously restricts the measurement accuracy and reliability of the grating interferometer under complex working conditions.

[0037] Based on this, the present application aims to construct a grating interferometric measurement device with three-dimensional large angle tolerance, which is suitable for grating interferometric measurement of high line density gratings, can effectively suppress the coherent light separation phenomenon in the presence of large angle deviation, expand the measurement dimension of the system, and significantly improve the angle tolerance capability. The system fundamentally eliminates the influence of grating three-dimensional angle error on the measurement result by introducing an angle self-compensation unit in the optical path, thereby realizing high-precision, large-angle tolerance, and multi-degree-of-freedom displacement measurement, and providing a reliable measurement solution for harsh industrial scenes such as semiconductor manufacturing and precision machining.

[0038] The optional embodiments of the present disclosure will be described in detail below with reference to the drawings.

[0039] As Figure 1As shown, the present application provides a grating interferometric measuring device, comprising: a light source unit 100 for outputting at least one beam of vertically orthogonal polarized difference frequency laser, the laser comprising first polarized laser and second polarized laser, the first polarized laser having a first frequency, the second polarized laser having a second frequency, the first frequency being different from the second frequency, the first polarized laser being horizontally polarized, and the second polarized laser being vertically polarized; a reading head unit 200 comprising a first optical conversion unit 210 and a first photodetector 7, the second polarized laser being used as reference light and being incident into the first photodetector 7 after passing through the first optical conversion unit 210; the first polarized laser being used for measuring a target object and being returned to the first optical conversion unit 210 as measuring light after being emitted from the first optical conversion unit 210, and being incident into the first photodetector 7 to interfere with the reference light for measuring the displacement of the target object; an angle self-compensation unit 300 comprising a first optical assembly 310 and a grating 330, the first polarized laser being received from the first optical conversion unit 210 and being incident into the grating 330 at a first angle, the first-order diffracted light diffracted by the grating 330 returning along the original light path after multiple reciprocating actions between the first optical assembly 310 and the grating 330, and being incident into the first photodetector 7 as measuring light.

[0040] The measuring device of the present application uses a heterodyne light source as an incident light beam, effectively enhances the environmental interference resistance of the measuring device, and provides high-quality optical signals for interferometric measurement. The extended offset Littrow optical path structure adopted by the present application constructs the propagation and interference path of the light beam by introducing a specific offset angle and a self-compensation optical path.

[0041] In some embodiments, as shown, Figure 1 The first optical conversion unit 210 comprises a first plane mirror 4, a first quarter-wave plate 5, a first polarization beam splitter prism 6, and a second quarter-wave plate 8. The second polarized laser is reflected by the first polarization beam splitter prism 6, passes through the first quarter-wave plate 5 and the first plane mirror 4, and then passes through the first quarter-wave plate 5 again, so that the polarization state is parallel polarization, and then the second polarized laser enters the first photodetector 7 through the first polarization beam splitter prism 6. The first polarized laser passes through the first polarization beam splitter prism 6 and the second quarter-wave plate 8, and then returns after being affected by the first optical assembly 310, and then passes through the second quarter-wave plate 8 again, so that the polarization state is vertical polarization, and then the first polarized laser enters the first photodetector 7 after being reflected by the first polarization beam splitter prism 6.

[0042] In some embodiments, as shown, Figure 1As shown, the first optical component 310 includes a third plane mirror 9, a first cornerstone prism 11, and a fourth plane mirror 10. The first polarized laser emitted from the first optical transformation unit 210 enters the grating 330 at a first angle through the third plane mirror 9, generating a first first-order diffracted light. The first first-order diffracted light is then acted upon by the first cornerstone prism 11 and interacts with the grating 330 again to generate a second first-order diffracted light. The second first-order diffracted light is then acted upon by the fourth plane mirror 10 and returns along the same path, interacting with the grating 330 to generate a third first-order diffracted light and a fourth first-order diffracted light. The fourth first-order diffracted light returns along the same path through the third plane mirror 9 to form the measurement light.

[0043] The angle self-compensation unit of this application can dynamically guide the beam path, effectively compensating for beam direction changes caused by grating deflection before interference occurs. This avoids coherent beam separation caused by angle deflection, ensuring that the phase center of the interference signal remains stable even under large angular disturbances, thereby maintaining a high-contrast interference signal.

[0044] In some embodiments, such as Figure 2 As shown, this embodiment employs a dual-arm measurement structure. Based on the aforementioned embodiment, the reading head unit 200 of this embodiment further includes a second optical conversion unit 220 and a second photodetector 15. The second polarized laser, serving as a reference light, passes through the second optical conversion unit 220 and then enters the second photodetector 15. The first polarized laser, after exiting the second optical conversion unit 220, measures the target object and returns as measurement light to the second optical conversion unit 220, then enters the second photodetector 15, interfering with the reference light to measure the offset of the target object. The angle self-compensation unit 300 further includes a second optical component 320. The second optical component 320 receives the first polarized laser emitted from the second optical conversion unit 220 and enters the grating 330 at a first angle. The first-order diffracted light, after multiple reciprocating actions between the second optical component 320 and the grating 330, returns along the original optical path and enters the second photodetector 15 as measurement light.

[0045] In some embodiments, such as Figure 2As shown, the second optical conversion unit 220 includes a fifth plane mirror 12, a third quarter wave plate 13, a second polarization beam splitter prism 14, and a fourth quarter wave plate 16; wherein the second polarization laser is reflected by the second polarization beam splitter prism 14, and then passes through the third quarter wave plate 13 and the fifth plane mirror 12, and then passes through the third quarter wave plate 13 again, and the polarization state is parallel polarization, and then enters the second photodetector 15 by passing through the second polarization beam splitter prism 14; the first polarization laser passes through the second polarization beam splitter prism 14 and the fourth quarter wave plate 16, and then returns by passing through the second optical assembly 320, and then passes through the fourth quarter wave plate 16 again, and the polarization state is vertical polarization, and then enters the second photodetector 15 by being reflected by the second polarization beam splitter prism 14.

[0046] In some embodiments, as shown in FIG. 2, the first optical conversion unit 210 includes a first plane mirror 11, a first quarter wave plate 12, a first polarization beam splitter prism 13, and a second quarter wave plate 14; wherein the first polarization laser f1 passes through the first plane mirror 11, and then passes through the first quarter wave plate 12, and then passes through the first polarization beam splitter prism 13, and then passes through the second quarter wave plate 14, and then enters the first photodetector 7; the second polarization laser f2 passes through the first polarization beam splitter prism 13 and the second quarter wave plate 14, and then returns by passing through the second optical assembly 320, and then passes through the second quarter wave plate 14 again, and then enters the first photodetector 7 by being reflected by the first polarization beam splitter prism 13. Figure 2 As shown, the second optical assembly 320 includes a sixth plane mirror 17, a second corner cube prism 19, and a seventh plane mirror 18; wherein the first polarization laser emitted from the second optical conversion unit 220 enters the grating 330 by the sixth plane mirror 17 at a first angle, and generates a fifth 1st order diffracted light, and then the fifth 1st order diffracted light is acted on by the second corner cube prism 19, and then acts on the grating 330 again to generate a sixth 1st order diffracted light, and then the sixth 1st order diffracted light is acted on by the seventh plane mirror 18 to return to the original path, and then acts on the grating 330 to generate a seventh 1st order diffracted light and an eighth 1st order diffracted light, and then the eighth 1st order diffracted light returns to the original path by the sixth plane mirror 17 to form the measurement light.

[0047] The measurement principle of the present embodiment is theoretically described as follows.

[0048] The complex amplitude of the orthogonal linearly polarized light with a certain frequency difference output by the difference frequency laser can be expressed as:

[0049]

[0050] In the formula, E and E respectively represent the initial phases of the first polarization laser f1 and the second polarization laser f2, and E0 represents the amplitude.

[0051] According to the optical path characteristics, for the interference light accepted by the first photodetector 7 and the second photodetector 15, the second polarization laser f2 with vertical polarization is the reference light, and the first polarization laser f1 with horizontal polarization is the measurement light, and therefore the complex amplitude of the interference light is expressed as follows:

[0052]

[0053] In the formula, E c1 represents the measurement light accepted by the first photodetector 7, E m1 represents the reference light accepted by the first photodetector 7.c2 E2 represents the measured light received by the second photodetector 15 m1 E2 represents the measured light received by the second photodetector 15 E1 and E2 represent the phase changes introduced by the movement of the grating respectively E1 and E2 represent the phase changes introduced by the movement of the grating respectively

[0054] It can be seen that the interference signals received by the first photodetector 7 and the second photodetector 15 are:

[0055]

[0056] When the grating pitch is d, and Δf = |f1-f2|, the phase change introduced by the movement of the grating in the X direction is: When the grating moves along the grating vector at a speed v in the X direction, the m-order diffracted light will produce a Doppler frequency shift effect, and its general expression is:

[0057]

[0058] Since there are 4 diffractions in the optical path, the Doppler frequency shift is 4 times that of single diffraction, so the phase change introduced by the movement of the grating in the X direction is:

[0059]

[0060] In the formula, Sx represents the displacement of the grating moving in the X direction. When the grating moves in the Z direction (i.e. along the grating normal direction), the displacement is Sz, and the phase change can be obtained by combining the geometric calculation of the optical path:

[0061]

[0062] In the formula, θ1 represents the incident angle and θ2 represents the diffraction angle. The displacement of the grating movement can be obtained as:

[0063] In the formula, θ1 represents the incident angle and θ2 represents the diffraction angle. The displacement of the grating movement can be obtained as:

[0064]

[0065] The following takes the optical path in the measurement beam as an example: third plane mirror 9-grating 330-first corner cube prism 11-grating 330-fourth plane mirror 10-grating 330-first corner cube prism 11-grating 330-third plane mirror 9. By modeling and analyzing this closed optical path, it is shown that regardless of the change in the grating attitude, the final outgoing beam propagation direction always remains parallel to the initial incident beam.

[0066] In the spherical coordinate system, the incident angle of the incident beam from the third plane mirror 9 to the measurement grating 330 is (θ1, φ1), and the direction vector corresponding to the incident beam is: ​

[0067] a = (sinφ1cosθ1, sinφ1sinθ1, cosφ1) (11)

[0068] The exit angle of the diffracted beam is (θ2, φ2), and the corresponding direction vector of the diffracted beam is:

[0069] β = (sinφ2cosθ2, sinφ2sinθ2, cosφ2) (12)

[0070] Then we have:

[0071] β = A (θ,φ,ω) a (13)

[0072]

[0073] In the formula, A(θ, ф, ω) represents the transmission matrix of the measurement grating, θ and φ represent the included angle between the incident light and the normal line of the measurement grating, and ω represents the roll angle of the measurement grating. When the direction of the incident beam is certain, the direction of the corresponding diffracted beam is related to the included angle between the normal line of the measurement grating and the incident beam and the roll angle of the measurement grating, that is, related to the attitude of the measurement grating. The roles of the first corner cube prism 11 and the fourth plane mirror 10 in the process are to make the incident beam parallel to the exit, so their corresponding transmission matrix is -E, where E is a third-order unit matrix. Assuming that the attitude information of the measurement grating is represented as (θ3, φ3, ω), the direction vector of the final exit beam is γ = (x, y, z).

[0074] Then, the third plane mirror 9-grating 330-first corner cube prism 11-grating 330-fourth plane mirror 10-grating 330-first corner cube prism 11-grating 330-third plane mirror 9, this process can be expressed as:

[0075]

[0076] According to the optical path reversibility principle, we can get:

[0077]

[0078] Combined with formulas (15) and (16), we can calculate γ = -a, that is, the propagation direction of the final exit beam is parallel to the incident beam, and the propagation direction of the exit beam is independent of the attitude of the measurement grating.

[0079] Therefore, the three-dimensional large-angle tolerance grating measurement device based on the extended offset Littrow structure can realize two-dimensional position measurement and three-dimensional large-angle tolerance, and high resolution can be obtained by using a high-line diffraction grating.

[0080] This application constructs a measurement optical path with automatic correction capability by extending the bias Littrow structure and angle self-compensation unit. When the grating deflects, the resulting change in beam pointing is corrected within the optical path. This fundamentally eliminates the coherent light separation phenomenon caused by three-dimensional angle errors, eliminating the need for complex error models and real-time calculations. The system response is faster, the reliability is higher, and the purity and stability of the signal are guaranteed from the source.

[0081] In some embodiments, such as Figure 2 As shown, the light source unit 100 includes a heterodyne light source 1, a beam splitter 2, and an eighth plane mirror 3. The difference frequency laser emitted by the heterodyne light source 1 is split into two difference frequency lasers by the beam splitter 2. One difference frequency laser is reflected by the beam splitter 2 and enters the first optical conversion unit 210. The other difference frequency laser passes through the beam splitter 2 and is reflected by the eighth plane mirror 3 and enters the second optical conversion unit 220.

[0082] In some embodiments, such as Figure 3 As shown, the light source unit 100 includes a first heterodyne light source 110 and a second heterodyne light source 120. The first heterodyne light source 110 outputs a first polarized laser and a second polarized laser and then enters the first optical conversion unit 210. The second heterodyne light source 120 outputs a first polarized laser and a second polarized laser and then enters the second optical conversion unit 220.

[0083] In some embodiments, such as Figure 4 As shown, the light source unit includes:

[0084] A first polarization source 130 and a second polarization source 140 are used to emit a first polarized laser and a third polarized laser, respectively. Both the first and third polarized lasers are horizontally polarized, and their frequencies are different. The first and third polarized lasers output from the first and second polarization sources are incident on the first optical conversion unit. A third polarization source 150 and a fourth polarization source 160 are used to emit the first and third polarized lasers, respectively. Both the first and third polarized lasers are horizontally polarized, and their frequencies are different. The first and third polarized lasers output from the third and fourth polarization sources are incident on the second optical conversion unit. Using spatially separated heterodyne sources avoids the influence of frequency aliasing on the measurement system, reduces the attenuation of the measured light intensity due to multiple diffractions, and further improves the quality of the interference signal.

[0085] In some embodiments, the grating 330 is a 1200 gr / mm high-resolution diffraction grating with a first angle of 11.4° and a first-order diffraction angle of 35.2°.

[0086] According to the grating interferometer device described in the embodiment of the present application, the corresponding optical elements are assembled to the non-sequence mode of ZEMAX for simulation. The light source adopts Gaussian light source with wavelength of 633 nm, for example, heterodyne light source with wavelength of 633.00682 nm and 633.00684 nm, and the beam diameter is 0.5 mm. The polarization beam splitter prism for light splitting is 14 mm, the aperture mirror of the plane mirror is 16.67 mm, the aperture of the corner cube prism is 15 mm, and the length is 11.3 mm. The receiving area of the photodetector is 3 mm*3 mm, the photodetector pixel size is 3 μm, and the quarter-wave plate is 4. The grating line density is set to 1200 gr / mm. In the initial optical path configuration, the light beam is incident at 11.4°, and the corresponding diffraction angle is 35.2°. The working surface of the corner cube prism is perpendicular to the incident light beam, the distance from the intersection point of the working surface and the first-order diffracted light beam to the center of the working surface of the corner cube prism is 3.5 mm, and the plane mirror is perpendicular to the incident light beam and the light beam passes through the center of the mirror. The distance between the first two light beams and the grating action point is 18 mm.

[0087] Fig. 5(a) shows the measurement light and reference light spots received by the first photodetector 7 and the second photodetector 15 when Rx=0.1°; Fig. 5(b) shows the measurement light and reference light spots received by the first photodetector 7 and the second photodetector 15 when Ry=0.1°; and Fig. 5(c) shows the measurement light and reference light spots received by the first photodetector 7 and the second photodetector 15 when Rz=0.1°. Simulation verification shows that the light spot does not separate when the grating attitude changes, and the optical path structure and principle analysis of the measurement device of the present application are consistent.

[0088] The present application provides a grating interferometer device with three-dimensional large-angle tolerance. The measurement device realizes the internal immunity of three-dimensional angle error, and significantly improves the measurement stability and precision of the interferometer under complex working conditions.

[0089] The angle self-compensation unit can dynamically guide the light beam path, so that the change of the light beam direction caused by the three-dimensional deflection of the grating is effectively compensated before the interference is formed. The coherent light separation phenomenon caused by angle deflection is avoided, and the phase center of the interference signal remains stable even under large angle disturbance, so that the high-contrast interference signal is maintained.

[0090] The present application also includes a signal processing unit, which converts the electrical signal into an electrical signal through a photodetector and transmits it to the signal processing unit for signal conditioning and phase calculation, and finally outputs accurate displacement information. The grating interferometer device realizes multi-dimensional and high-precision measurement while having excellent angle tolerance performance, providing a reliable technical solution for the harsh measurement requirements of semiconductor manufacturing and precision machining fields.

[0091] It should be noted that the various embodiments described in the specification are intended to be illustrative only and are not in any way limiting. Although the present application has been described in considerable detail, various modifications and changes can be made to the present application by one skilled in the art and it is intended that the application not be limited to any one embodiment, but encompass numerous alternatives, modifications and equivalents. Therefore, the scope of the application should be determined by the broadest permissible interpretation of the claims so as to encompass all such alternatives, modifications and equivalents.

[0092] The above embodiments are only used to illustrate the technical solutions of the present application, but not limit the present application; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalent replacements; and the modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A grating interferometric measurement device, characterized in that, include: A light source unit is used to output at least one beam of vertically orthogonally polarized difference-frequency laser. The difference-frequency laser includes a first polarized laser and a second polarized laser. The first polarized laser has a first frequency, and the second polarized laser has a second frequency. The first frequency and the second frequency are different. The first polarized laser is horizontally polarized, and the second polarized laser is vertically polarized. The reading head unit includes a first optical conversion unit and a first photodetector. The second polarized laser, as a reference light, passes through the first optical conversion unit and then enters the first photodetector. After the first polarized laser is emitted from the first optical conversion unit, it measures the target object, returns as the measurement light to the first optical conversion unit, and enters the first photodetector, interfering with the reference light to measure the offset of the target object. An angle self-compensation unit includes a first optical component and a grating. The first optical component receives the first polarized laser emitted from the first optical transformation unit and enters the grating at a first angle. The first-order diffracted light diffracted by the grating returns along the original optical path after multiple reciprocating actions between the first optical component and the grating, and is then used as the measurement light to enter the first photodetector. The first optical component includes: a third plane mirror, a first cornerstone prism, and a fourth plane mirror; wherein, the first polarized laser emitted from the first optical transformation unit enters the grating at a first angle through the third plane mirror, generating a first first-order diffracted light; the first first-order diffracted light, after being acted upon by the first cornerstone prism, interacts again with the grating to generate a second first-order diffracted light; the second first-order diffracted light, after being acted upon by the fourth plane mirror, returns along the same path and interacts with the grating to generate a third first-order diffracted light and a fourth first-order diffracted light; the fourth first-order diffracted light returns along the same path through the third plane mirror to form the measurement light; The reading head unit further includes a second optical conversion unit and a second photodetector. The second polarized laser, as a reference light, passes through the second optical conversion unit and then enters the second photodetector. The first polarized laser, after being emitted from the second optical conversion unit, measures the target object, returns as measurement light to the second optical conversion unit, and enters the second photodetector, interfering with the reference light to measure the offset of the target object. The angle self-compensation unit further includes a second optical component. The second optical component receives the first polarized laser emitted from the second optical transformation unit and enters the grating at a first angle. The first-order diffracted light diffracted by the grating returns along the original optical path after multiple reciprocating actions between the second optical component and the grating, and is then used as the measurement light to enter the second photodetector.

2. The grating interferometric measuring device according to claim 1, characterized in that, The first optical transformation unit includes a first plane mirror, a first quarter-wave plate, a first polarizing beam splitter, and a second quarter-wave plate; The second polarized laser, after being reflected by the first polarizing beam splitter, passes through the first quarter-wave plate and interacts with the first plane mirror, then passes through the first quarter-wave plate again, with a parallel polarization state, and enters the first photodetector after passing through the first polarizing beam splitter. The first polarized laser, after passing through the first polarizing beam splitter and the second quarter-wave plate, and returning after being acted upon by the first optical component, passes through the second quarter-wave plate again, with a vertical polarization state, and enters the first photodetector after being reflected by the first polarizing beam splitter.

3. The grating interferometric measuring device according to claim 1, characterized in that, The second optical transformation unit includes a fifth plane mirror, a third quarter-wave plate, a second polarizing beam splitter, and a fourth quarter-wave plate; The second polarized laser, after being reflected by the second polarization beam splitter, passes through the third quarter-wave plate and interacts with the fifth plane mirror, then passes through the third quarter-wave plate again, exhibiting parallel polarization, and enters the second photodetector after passing through the second polarization beam splitter. The first polarized laser, after passing through the second polarization beam splitter and the fourth quarter-wave plate, and returning after being acted upon by the second optical component, passes through the fourth quarter-wave plate again, exhibiting vertical polarization, and enters the second photodetector after being reflected by the second polarization beam splitter.

4. The grating interferometric measuring device according to claim 1, characterized in that, The second optical component includes: a sixth plane mirror, a second corner bevel prism, and a seventh plane mirror; The first polarized laser emitted from the second optical transformation unit enters the grating at a first angle through the sixth plane mirror, generating a fifth first-order diffracted light. The fifth first-order diffracted light is then acted upon by the second corner prism and interacts with the grating again to generate a sixth first-order diffracted light. The sixth first-order diffracted light is then acted upon by the seventh plane mirror and returns along the same path, interacting with the grating to generate a seventh first-order diffracted light and an eighth first-order diffracted light. The eighth first-order diffracted light returns along the same path through the sixth plane mirror to form the measurement light.

5. The grating interferometric measuring device according to claim 1, characterized in that, The light source unit includes: a heterodyne light source, a beam splitter, and an eighth plane mirror; The difference-frequency laser emitted by the heterodyne light source is split into two beams by the beam splitter. One beam is reflected by the beam splitter and enters the first optical conversion unit, while the other beam is reflected by the eighth plane mirror through the beam splitter and enters the second optical conversion unit.

6. The grating interferometric measuring device according to claim 1, characterized in that, The light source unit includes: a first heterodyne light source and a second heterodyne light source. The first heterodyne light source outputs a first polarized laser and a second polarized laser and then enters the first optical conversion unit. The second heterodyne light source outputs a first polarized laser and a second polarized laser and then enters the second optical conversion unit.

7. The grating interferometric measuring device according to claim 1, characterized in that, The light source unit includes: A first polarization source and a second polarization source are used to emit a first polarized laser and a third polarized laser, respectively. The first polarized laser and the third polarized laser are both horizontally polarized, and the first polarized laser and the third polarized laser have different frequencies. The first polarized laser and the third polarized laser output by the first polarization source and the second polarization source are injected into the first optical conversion unit. The third polarization source and the fourth polarization source are used to emit the first polarization laser and the third polarization laser, respectively. The first polarization laser and the third polarization laser are both horizontally polarized, and the first polarization laser and the third polarization laser have different frequencies. The first polarization laser and the third polarization laser output by the third polarization source and the fourth polarization source are injected into the second optical conversion unit.

8. The grating interferometric measuring device according to claim 1, characterized in that, The grating is a 1200gr / mm high-resolution diffraction grating, the first angle is 11.4°, and the diffraction angle of the first-order diffracted light is 35.2°.

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