Nanometer grating pose calibration system based on laser interferometer

Abstract

The utility model relates to a nanometer grating pose calibration system based on a laser interferometer, which comprises a light path system and a displacement table driving system, the displacement table driving system comprises a four-axis displacement table, a nanometer grating support used for installing a nanometer grating and the laser interferometer are arranged on an installation table top of the four-axis displacement table, and the laser interferometer is arranged on the installation table top of the four-axis displacement table. The three-axis direction angles of the nano grating are sequentially corrected through the four-axis displacement table, wherein the three-axis direction angles comprise free rotation in three degrees of freedom of pitching, rolling and deflection and linear displacement in the axis direction of the grating. According to the utility model, the measurement value of the laser interferometer is used as the correction feedback of the grating attitude, the measurement value of the grating displacement measurement system is compared with the measurement value, the adjustment direction of each axis of the four-axis displacement table is judged, and finally, the four-axis displacement table is driven for many times to adjust the nano grating bracket to an ideal position, so that the problem of the pose error of the nano grating is solved.

Description

Technical Field

[0001] The utility model relates to an optical device for a grating displacement measurement system, in particular to a nano-grating position calibration system based on a laser interferometer, belonging to the technical field of optical devices. Background Art

[0002] Nanogratings are key components for precision displacement measurement in today's integrated circuit industry, ultra-precision machining, and precision scientific instrumentation. With their widespread application in various instruments, the requirements for grating-based instruments are gradually increasing. Grating displacement measurement systems are subject to five unavoidable errors: environmental error, model error, installation error, switching error, and instrument error. Installation error of nanogratings is a significant factor among these. Minimizing nanograting position errors to ensure a reliable optical path in the grating measurement system is key to ensuring the accuracy of precision measurement results.

[0003] The determination of the grating period is usually done by optical diffraction or metrological atomic force microscopy. Optical diffraction is the most commonly used grating period measurement method in the laboratory. Its measurement principle is based on the grating equation. When the laser is incident at the Littrow angle, ,in is the Littrow angle, λ is the wavelength of the laser, n is the refractive index of air, d is the period of the grating, and k is the diffraction order. The incident light is a 405nm semiconductor laser. The wavelength of the incident light is known, and the incident angle is measured. and the refractive index of air can be used to obtain the period of the grating.

[0004] Coupling errors between the grating and the workpiece stage are the primary contributors to installation errors. Nonlinearities and straightness errors in the workpiece stage on which the grating is mounted can cause the two diffracted beams returning along the original path in the Littrow structure to deviate from their ideal positions, significantly reducing the signal-to-noise ratio of the interference signal and even introducing additional phase differences, leading to measurement errors. The most significant factor contributing to these errors is the nanograting's mounting position—that is, the positional relationship between the grating and the translation stage regarding the three degrees of freedom (Pitch, Roll, and Yaw).

[0005] Therefore, solving the problem that causes the nano-grating posture error can effectively improve the overall accuracy of the grating displacement measurement system.

[0006] Traditional nano-grating calibration methods typically use a multi-degree-of-freedom clamping bracket and verify the perfection of the grating posture adjustment through feedback from the output waveform of the entire optical system, which has a high degree of uncertainty. Furthermore, because most brackets are mechanical structures, they are usually adjusted manually, and arc-second-level micro-movements cannot be achieved. Therefore, adjustment is difficult, and the adjustment time and effect largely depend on the user's experience. Therefore, adjusting the optical path results in a significant waste of manpower and time. Adjustment accuracy cannot be guaranteed, and the relationship between the nano-grating posture and the output signal of the optical system cannot be further quantified, which makes it inconvenient to calibrate the nano-grating posture. Summary of the Invention

[0007] The purpose of the utility model is to solve the defects of the existing technology and design a nano-grating posture calibration system based on laser interferometer. The stability and high sensitivity of the laser interferometer are used as correction feedback for the grating posture. The feedback information of the photodetector is collected by the signal processing system and processed by the algorithm to obtain the correction value. The nano-grating bracket is then adjusted to the ideal position by driving the four-axis translation stage, so as to minimize the posture error caused by the nano-grating during installation, solve the problem of nano-grating posture error, and improve the measurement accuracy of the overall grating displacement measurement system.

[0008] The utility model is implemented as follows: a nano-grating posture calibration system based on a laser interferometer, characterized in that it includes an optical path system and a displacement stage drive system, the displacement stage drive system includes a four-axis displacement stage, a nano-grating bracket and a laser interferometer are provided on the mounting table of the four-axis displacement stage, a nano-grating is installed on the nano-grating bracket, the optical path system includes a laser, a wave plate I, a wave plate II, a wave plate III, a polarization beam splitter prism, a polarizer, an interferometer measurement light reflector, a plane reflector I and a plane reflector II, the wave plate I and the polarization beam splitter prism are sequentially arranged on the optical path of the laser emission light, the wave plate III and the plane reflector II are sequentially arranged on the optical path of the horizontally polarized light of the polarization beam splitter prism, the wave plate II and the plane reflector I are sequentially arranged on the optical path of the vertically polarized light of the polarization beam splitter prism, the nano-grating is arranged on the reflected light path of the plane reflector II and the plane reflector I, and the nano-grating is respectively The reflected light forms a corresponding diffracted light path, and is combined after passing through a polarization beam splitter prism to form a diffracted light path. Polarizers and photodetectors are sequentially arranged on the diffracted light path. The interferometer measuring light reflector is arranged on a laser interferometer. The four-axis translation stage performs a four-axis displacement motion consisting of rotational motion in the x, y, and z directions and linear motion in the x-axis direction.

[0009] In the optical path system, the laser's emitted light passes through wave plate I and is incident on a polarization beam splitter prism, where it is divided into a vertically polarized light path and a horizontally polarized light path in equal proportion. The vertically polarized light path and the horizontally polarized light path, incident on the nanograting surface at the Littrow angle, form two diffracted light paths that return along their original paths to the polarization beam splitter prism before being combined to form combined diffracted light. The combined diffracted light is then filtered by a polarizer and received by a photodetector, forming an optical path for collecting the interference signal of the photodetector.

[0010] The nanograting is fixed to a four-axis translation stage via a nanograting bracket. The stage drives the grating to rotate freely in pitch, roll, and yaw, as well as to move linearly along the grating axis, correcting the grating's position. The linear motion along the x-axis is kept as parallel as possible to the nanograting's axis. The stage is controlled by a host computer and driven by a drive module.

[0011] The interferometer measurement light reflector required by the laser interferometer is installed on the side of the nano grating bracket, and the normal line of the interferometer measurement light reflector is orthogonal to the normal line of the nano grating bracket.

[0012] The wave plate I is a half wave plate, and the wave plates II and III are respectively a quarter wave plate.

[0013] After the nano-grating bracket and the four-axis translation stage are installed, the center position of the translation stage is calibrated by a three-coordinate machine or by adding a vertical auxiliary bracket. The four-axis translation stage is calibrated for orthogonality by installing an orthogonal bracket between the interferometer measurement light reflector and the nano-grating bracket.

[0014] The correction of the nano-grating posture is to correct the angles of the three-axis directions of the nano-grating in turn. The movement direction of the nano-grating, the laser incident direction of the laser interferometer and the movement direction of the four-axis translation stage are all consistent. The display value of the laser interferometer is a reference for the actual displacement of the nano-grating after being driven by the four-axis translation stage. The interference signal collected by the photoelectric detector is converted into a current signal and transmitted to the signal processing system. Through the signal processing system, the displacement of the grating displacement measurement system is obtained based on the light intensity and grating displacement formula, and compared with the laser interferometer display value. When the single-axis rotation angle is corrected until the actual displacement displayed by the photoelectric detector is closest to the reference displacement, it is used as a sign that the correction of the axis is completed.

[0015] The processing path of the photoelectric signal in the signal processing system of the nano-grating posture calibration system is as follows: the laser light source emitted by the laser is converted into an electrical signal by the photodetector after the system optical path adjustment, and then transmitted to the acquisition card through the signal amplifier. At the same time, the electrical signal of the laser interferometer is also transmitted to the acquisition card. The two electrical signals received by the acquisition card are then transmitted together to the host computer for data processing. The driving module in the translation stage driving system drives the four-axis translation stage to perform correction work according to the displacement obtained after processing by the host computer.

[0016] The beneficial effects of the present invention are as follows: the present invention uses the data collected by the laser interferometer as a reference, combines the angle adjustment of the four-axis translation stage to realize the numerical control calibration of the nano-grating, utilizes the good stability and high sensitivity of the laser interferometer as the correction feedback of the grating posture, and adopts the host computer to collect the feedback information of the photoelectric detector, and obtains the correction value after algorithm processing, and finally adjusts the nano-grating bracket to the ideal position by driving the four-axis translation stage, thereby minimizing the posture error caused by the nano-grating during installation and improving the measurement accuracy of the overall grating displacement measurement system.

[0017] In terms of industrial production, the application of this utility model can enable production enterprises to achieve more accurate dimensional measurement and quality control during the production process, thereby reducing product defect rates, improving production efficiency, and reducing the cost of unqualified products, thereby achieving cost control effects.

[0018] At the same time, because this utility model introduces a laser interferometer, it can trace the nanograting position calibration back to the laser interferometer's laser wavelength, greatly improving its traceability and enhancing the accuracy and reliability of the measurement results. Therefore, in scientific research and experiments, the application of this utility model can reduce the measurement error of the grating displacement measurement system, making experimental results more reliable and repeatable, helping to verify research hypotheses, ensuring the accuracy of experimental data, and supporting the verification of scientific theories.

[0019] The system of this utility model can be widely used in various high-tech industries such as medical care, aerospace, semiconductors, and environmental testing, and contributes to the comprehensive promotion of industrial intelligent development. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the overall composition of the system and the optical path system of the utility model.

[0021] Figure 2 This is a schematic diagram of the pitch angle adjustment of the nano-grating bracket in the system of the utility model.

[0022] Figure 3 This is a schematic diagram of the roll angle adjustment of the nano-grating bracket in the system of the utility model.

[0023] Figure 4 This is a schematic diagram of the deflection angle adjustment of the nano-grating bracket in the system of the utility model.

[0024] Figure 5 This is a schematic diagram of the workflow of the utility model system for performing single-axis direction angle correction on nano gratings.

[0025] Figure 6 It is a schematic diagram of the installation position structure of the four-axis translation platform and the components on the installation table in the system of the utility model.

[0026] Figure 7 It is a schematic block diagram of the photoelectric signal processing flow of the signal processing system in the system of the utility model.

[0027] In the figure: 1. Laser;

[0028] 21. Wave plate I; 22. Wave plate II; 23. Wave plate III; 24. Polarization beam splitter; 25. Polarizer;

[0029] 3. Translation stage drive system; 31. Interferometer measurement light reflector; 32. Nano grating bracket; 33. Four-axis translation stage;

[0030] 41. Plane reflector I; 42. Plane reflector II;

[0031] 5. Laser interferometer; 6. Photodetector. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0033] According to the attached Figure 1-Figure 4 and Figure 6The utility model is a nano-grating posture calibration system based on a laser interferometer, comprising an optical path system and a translation stage drive system 3, wherein the translation stage drive system 3 comprises a four-axis translation stage 33, a nano-grating bracket 32 ​​and a laser interferometer 5 are provided on the mounting surface of the four-axis translation stage 33, a nano-grating bracket 32 ​​is provided with a nano-grating, and the optical path system comprises a laser 1, a wave plate I 21, a wave plate II 22, a wave plate III 23, a polarization beam splitter prism 24, a polarizer 25, an interferometer measurement light reflector 31, a plane reflector I 41 and a plane reflector II 42, wherein the wave plate I 21 and the polarization beam splitter prism 24 are sequentially arranged on the optical path of the light emitted by the laser 1, the wave plate III 23 and the plane reflector II 42 are sequentially arranged on the optical path of the horizontally polarized light of the polarization beam splitter prism 24, the wave plate II 22 and the plane reflector I 41 are sequentially arranged on the optical path of the vertically polarized light of the polarization beam splitter prism 24, and the nano-grating is arranged on the plane reflector II 42 and the reflected light path of the plane reflector I 41, the nano grating forms a corresponding diffraction light path for the reflected light from the plane reflector II 42 and the plane reflector I 41, and forms a diffraction light path after the reflected light is combined after passing through the polarization splitter prism 24. A polarizer 25 and a photodetector 6 are sequentially arranged on the diffraction light path, and the interferometer measurement light reflector 31 is arranged on the laser interferometer 5, wherein the wave plate I 21 adopts a half wave plate, and the wave plate II 22 and the wave plate III 23 adopt a quarter wave plate respectively.

[0034] In the optical path system, the emitted light of the laser 1 is incident on the polarization splitter prism 24 through the wave plate I 21, and is divided into a vertical polarization light path and a horizontal polarization light path in equal proportion after passing through the polarization splitter prism 24. The two diffracted light paths formed by the vertical polarization light path and the horizontal polarization light path after being incident on the nano-grating surface at the Littow angle return to the polarization splitter prism 24 along the original light paths respectively and are then combined. The combined diffracted light is filtered by the polarizer 25 and then received by the photodetector 6.

[0035] The nano-grating is fixed on the four-axis translation stage 33 through the nano-grating bracket 32 ​​, and the linear motion of the four-axis translation stage 33 in the x-axis direction should be as parallel as possible to the axis of the nano-grating.

[0036] The four-axis translation stage 33 is a high-precision four-axis translation stage controlled by a host computer and driven by a drive module to perform displacement motion. It can achieve rotational motion in the x, y, and z axes and linear motion in the x-axis direction, that is, free rotation in the pitch, roll, and yaw degrees of freedom, as well as linear displacement in the grating axis direction, to achieve correction of the grating position. The displacement range of its x-axis displacement is ±6.5mm, and the resolution reaches 5μm. Its three-degree-of-freedom parameters are: pitch range: ±2.5°, pitch resolution: 29.3 inches; roll range: ±4°, roll resolution: 33 inches; yaw range: ±2.5°, yaw resolution: 27.8 inches.

[0037] The display value of the laser interferometer 5 is a reference for the actual displacement of the nano-grating after being driven by the four-axis translation stage 33. If a traceable single-wavelength laser interferometer is used, the system can make the overall nano-grating posture correction system traceable and realize the calibration of the system.

[0038] like Figure 6 As shown, the interferometer measurement light reflector 31 required by the laser interferometer 5 is installed on the side of the nano grating bracket 32, and the normal line of the interferometer measurement light reflector is orthogonal to the normal line of the nano grating bracket 32.

[0039] According to the attached Figure 5 During correction, the three-axis direction angles of the nano-grating are corrected in turn until the posture correction of the three axes is completed.

[0040] Single-axis correction process: First, reset the adjustment axis, displacement direction, and total rotation value of the four-axis translation stage to zero. Determine the rotation step size. Set a larger rotation step size first, and drive the four-axis translation stage to rotate the specified distance in a single direction. Observe whether the rotation step size data closely matches the actual displacement data indicated by the laser interferometer 5. If the trend is opposite to the desired direction, determine that the rotation direction is reverse, and drive the stage in the reverse direction again by the current step size. After each drive is completed, add or subtract the current rotation step size to the total rotation value based on the positive or reverse direction of the current rotation step size, and simultaneously reset the four-axis translation stage to zero along the displacement direction. If the rotation step size data closely matches the actual displacement data indicated by the laser interferometer 5, observe whether it is the minimum step size. If so, the axis correction is considered complete, and the total rotation value is read as the correction value for the four-axis translation stage. Otherwise, reduce the rotation step size, and repeat until the rotation angle step size is equal to the minimum step size of the four-axis translation stage.

[0041] Correction for the remaining two axes is the same as above. Due to the presence of nano-grating pose errors, the actual displacement will be slightly smaller than the reference displacement. Correction for a single axis is completed when the photodetector 6 shows the actual displacement closest to the reference displacement.

[0042] In order to minimize the three-axis coupling effect generated during correction, the nano-grating bracket 32 ​​and the four-axis translation stage 33 should be calibrated after installation. Before the correction begins, the three-coordinate machine calibration should be performed at the center of the four-axis translation stage or a vertical auxiliary bracket should be installed to minimize the correction error caused by the coupling between the two and reduce the installation error generated during the installation of the nano-grating bracket.

[0043] During correction, the entire system of the present invention should be placed on a horizontal table. A tilted table or ground will affect the incident angle of the laser 1, causing the incident light on the nanograting surface to be inconsistent with the theory. This situation should be avoided as much as possible.

[0044] First, the orthogonality calibration of the four-axis translation stage 33 should be completed. The calibration can be achieved by using a collimator to calibrate the angles of the interferometer measurement light reflector 31 and the nano-grating support 32. Figure 1 As shown, the optical path system of the system optical platform is completed.

[0045] During correction, the moving direction of the nano-grating, the incident direction of the laser interferometer 5 and the moving direction of the four-axis translation stage 33 should be kept consistent.

[0046] The interference signal collected by the photodetector 6 is converted into a current signal and transmitted to the signal processing system, which processes the interference signal and calculates the current signal based on the light intensity and grating displacement formula. Convert and obtain the displacement, where I is the interference signal intensity, I0 is the laser output intensity, is the displacement of the stage, and d is the grating period of the grating used.

[0047] Then, the displacement obtained after conversion is compared with the actual displacement data shown by the laser interferometer 6 to see if the data are consistent. If not, the Figure 5 The single-axis correction process shown here corrects the three-axis angles (pitch, roll, and yaw) of the nanograting.

[0048] According to the attached Figure 7 The signal processing system in the nano-grating posture calibration system processes the photoelectric signal as follows: the laser light source emitted by the laser 1 is adjusted by the system optical path and then received by the photodetector 6 for conversion from the optical signal to the electrical signal. The optical signal is then passed through the signal amplifier and the corresponding electrical signal is received by the acquisition card. The electrical signal is transmitted to the host computer together with the electrical signal of the laser interferometer 5 collected by the acquisition card for data processing. The driving module in the translation stage driving system 3 drives the four-axis translation stage 33 for correction according to the displacement obtained after processing by the host computer.

[0049] The above describes in detail the preferred specific embodiments of the present invention. It should be understood that the optical path system described in the present invention is not unique. Any system that can use nano-gratings to achieve the purpose of displacement measurement can apply the posture calibration system described in the present invention. Ordinary technicians in this field can make many equivalent or equivalent changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained through logical analysis, reasoning, or a limited number of experiments based on the concept of the present invention on the basis of the existing technology in the field should be included in the scope of protection determined by the claims of the present invention.

Claims

1. A nano-grating position calibration system based on laser interferometer, characterized by: The optical path system comprises an optical path system and a translation stage drive system, wherein the translation stage drive system comprises a four-axis translation stage, a nano-grating bracket and a laser interferometer are provided on the mounting surface of the four-axis translation stage, a nano-grating bracket is provided with a nano-grating, and the optical path system comprises a laser, a wave plate I, a wave plate II, a wave plate III, a polarization beam splitter prism, a polarizer, an interferometer measurement light reflector, a plane reflector I and a plane reflector II, wherein the wave plate I and the polarization beam splitter prism are sequentially arranged on the optical path of the laser emission light, the wave plate III and the plane reflector II are sequentially arranged on the optical path of the horizontally polarized light of the polarization beam splitter prism, the wave plate II and the plane reflector I are sequentially arranged on the optical path of the vertically polarized light of the polarization beam splitter prism, the nano-grating is arranged on the reflected optical paths of the plane reflector II and the plane reflector I, and the nano-grating respectively reflects the light from the plane reflector II. The reflected light from the plane reflector I forms a corresponding diffracted light path, and is combined after passing through a polarization beam splitter to form a diffracted light path. Polarizers and photodetectors are sequentially arranged on the diffracted light path. The interferometer measuring light reflector is arranged on a laser interferometer. The four-axis translation stage performs a four-axis displacement motion consisting of rotational motion in the x, y, and z directions and linear motion in the x-axis direction.

2. The laser interferometer-based nanograting position calibration system according to claim 1, characterized in that: In the optical path system, the laser's emitted light passes through wave plate I and is incident on a polarization beam splitter prism, where it is divided into a vertically polarized light path and a horizontally polarized light path in equal proportion. The vertically polarized light path and the horizontally polarized light path, incident on the nanograting surface at the Littrow angle, form two diffracted light paths that return along their original paths to the polarization beam splitter prism before being combined to form combined diffracted light. The combined diffracted light is then filtered by a polarizer and received by a photodetector, forming an optical path for collecting the interference signal of the photodetector.

3. The laser interferometer-based nanograting position calibration system according to claim 1, characterized in that: The nanograting is fixed on a four-axis translation stage through a nanograting bracket. The four-axis translation stage drives the free rotation in the three degrees of freedom of pitch, roll and yaw, as well as the linear displacement in the direction of the grating axis, to achieve the correction of the grating posture. The linear motion in the x-axis direction performed by the four-axis translation stage is as parallel as possible to the axis of the nanograting.

4. The laser interferometer-based nanograting position calibration system according to claim 1, characterized in that: The interferometer measurement light reflector required by the laser interferometer is installed on the side of the nano grating bracket, and the normal line of the interferometer measurement light reflector is orthogonal to the normal line of the nano grating bracket.

5. The laser interferometer-based nanograting position calibration system according to claim 1 or 2, characterized in that: The wave plate I is a half wave plate, and the wave plates II and III are respectively a quarter wave plate.

6. The laser interferometer-based nanograting position calibration system according to claim 1, characterized in that: After the nano-grating bracket and the four-axis translation stage are installed, the center position of the four-axis translation stage is calibrated by a three-coordinate machine or by adding a vertical auxiliary bracket. The four-axis translation stage realizes orthogonality calibration by calibrating between the interferometer measurement light reflector and the nano-grating bracket using a collimator.

7. The nano-grating position calibration system based on laser interferometer according to any one of claims 1 to 3, characterized in that: The correction of the nanograting posture is to correct the angles of the three axes of the nanograting in turn, so that the movement direction of the nanograting, the laser incident direction of the laser interferometer and the movement direction of the four-axis translation stage are kept consistent.

8. The nano-grating position calibration system based on laser interferometer according to any one of claims 1 to 3, characterized in that The signal processing flow of the signal processing system in the nanograting posture calibration system: The processing path of the photoelectric signal in the signal processing system in the nanograting posture calibration system: the laser light source emitted by the laser is converted into an electrical signal by the photodetector after the system optical path adjustment, and then transmitted to the acquisition card through the signal amplifier. At the same time, the electrical signal of the laser interferometer is also transmitted to the acquisition card. The two electrical signals received by the acquisition card are then transmitted together to the host computer for data processing. The driving module in the translation stage driving system drives the four-axis translation stage to perform correction work according to the displacement obtained after processing by the host computer.

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