Workpiece table displacement measurement system

Abstract

The application discloses a workpiece table displacement measurement system, which comprises a total light path and two light paths of X-axis and Y-axis with the same structure; the total light path comprises a laser, a right-angle reflector, a middle gray mirror and a 50% beam splitter arranged in sequence, and the laser is divided into two beams with equal energy and propagates along the X-axis and Y-axis respectively; the light path comprises a 25% beam splitter, a comprehensive adjuster, a three-axis interference mirror and a fiber coupler; the three-axis interference mirror divides the laser into three beams which are perpendicularly incident on the workpiece table reflector, and the displacement is calculated after reflection and coupling. The application realizes high-precision decoupling measurement of the displacement and attitude of the workpiece table in a complex vacuum environment through symmetrical light path and three-beam measurement.

Description

Technical Field

[0001] This invention relates to the field of precision measurement technology, and more specifically to a workpiece stage displacement measurement system. Background Technology

[0002] In high-end equipment fields such as semiconductor manufacturing, vacuum coating, and high-energy physics experiments, workpiece stages typically require precise movements at the nanometer or even sub-nanometer level in ultra-high vacuum environments. To ensure process stability, real-time, high-precision measurement of the workpiece stage displacement is essential. Currently, laser interferometry is the mainstream high-precision displacement measurement method. However, in complex vacuum environments, existing measurement solutions still face numerous challenges. On the one hand, the laser and most optical components are usually placed outside the vacuum cavity, and the laser beam must pass through a viewing window to enter the vacuum cavity. The optical path is long and spans both the atmosphere and the vacuum. Environmental temperature gradients, airflow disturbances, and vacuum fluctuations can all cause changes in the air refractive index, leading to wavelength drift and introducing significant measurement errors. On the other hand, the workpiece stage inevitably experiences pitch and yaw changes during high-speed movement. Traditional single-point or dual-point measurement methods cannot effectively decouple the attitude angle from the linear displacement, making it difficult to eliminate Abbe errors. Furthermore, if there is energy inconsistency or structural asymmetry in the X-axis and Y-axis optical paths, it will further reduce the synchronization accuracy and reliability of multi-axis measurements. Therefore, there is an urgent need for a workpiece stage displacement measurement system that can achieve high precision, high stability, and attitude decoupling capability in complex vacuum environments. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a workpiece stage displacement measurement system that is compact, easy to operate and highly stable, in order to solve the problem of high-precision measurement of workpiece stage posture in complex vacuum environment.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A workpiece stage displacement measurement system includes a main optical path and two split optical paths with identical structures, X-axis and Y-axis. The main optical path provides a light source for measurement, and the X-axis and Y-axis split optical paths are used to measure the displacement of the workpiece stage in the X-plane and Y-plane in the vacuum chamber, respectively. The overall optical path includes a laser, a right-angle mirror, a neutral density mirror, and a 50% beam splitter arranged in sequence. The laser emitted by the laser is reflected by the right-angle mirror and then passes through the neutral density mirror. The neutral density mirror reduces the energy of the laser to 90% of its original energy. The 50% beam splitter splits the reduced-energy laser into two beams of equal energy, which propagate along the X-axis and Y-axis of the workpiece stage, respectively. The beam splitting path includes a 25% beam splitter, a comprehensive regulator, a three-axis interferometer, and a fiber coupler arranged sequentially. The laser beam exiting the 50% beam splitter passes through the 25% beam splitter, which splits the laser beam into two beams with an intensity ratio of 1:3. The 75% intensity laser beam passes through the comprehensive regulator and enters the three-axis interferometer, which splits the 75% intensity laser beam into three equal beams. These beams are then perpendicularly incident on a reflector on the side of the workpiece stage through a viewing window on the side of the vacuum cavity. After reflection, the laser beam enters the fiber coupler and is coupled to the control cabinet to calculate the displacement of the workpiece stage.

[0005] As a further improvement of the present invention, the beam splitting path also includes a single-axis interferometer and a reference mirror located in the vacuum cavity; the single-axis interferometer is close to the 25% beam splitter, and reference mirrors are provided along the X-axis and Y-axis of the workpiece stage side, with the single-axis interferometer and the reference mirror corresponding one-to-one; the 25% intensity laser light split by the 25% beam splitter is directed to the surface of the reference mirror after passing through the single-axis interferometer, in order to measure the error of the laser light due to environmental influences during the distance from the laser to the reference mirror.

[0006] As a further improvement of the present invention, the reference reflector is disposed at the middle position on the side of the workpiece stage.

[0007] As a further improvement of the present invention, the three laser beams with 75% intensity separated by the 25% beam splitter are incident perpendicularly on the reflector on the side of the workpiece stage in a triangular pattern.

[0008] As a further improvement of the present invention, the three laser beams are incident on the reflector to form light spots A, B, and C, respectively; wherein, the designed distance from the center of light spot A to the horizontal center of light spots B and C is d1, the designed horizontal distance between the center of light spot B and the center of light spot C is d2, and the actual offset distance between the center of light spot B and the center of light spot C is d23. Then, the deflection angle α1 of light spot C is the deflection angle of the reflector. .

[0009] As a further improvement of the present invention, the light spot A is located exactly in the middle of the light spot B and the light spot C, then the pitch angle α2 of the light spot A is the pitch angle of the reflecting mirror: .

[0010] As a further improvement of the present invention, the reflector is a triangular prism.

[0011] As a further improvement of the present invention, the right-angle reflector includes a first right-angle reflector and a second right-angle reflector arranged in sequence, the first right-angle reflector being close to the laser and the second right-angle reflector being close to the neutral density filter.

[0012] As a further improvement of the present invention, a vacuum wavelength compensator is provided inside the vacuum cavity; an atmospheric wavelength compensator is provided outside the vacuum cavity.

[0013] As a further improvement of the present invention, the laser is a dual-frequency laser interferometer.

[0014] Compared with the prior art, the workpiece stage displacement measurement system provided by the present invention has the following advantages: (1) By constructing two beam splitting paths with the same structure, X-axis and Y-axis, the optical path of the dual-axis measurement is kept strictly consistent in terms of optical element configuration, optical path length and energy distribution. This eliminates the systematic measurement error caused by the asymmetry of the dual-axis optical path from a physical level and improves the accuracy and reliability of multi-axis synchronous measurement.

[0015] (2) By setting a neutral density mirror in the total optical path to pre-attenuate the laser energy, and then splitting the beam into two equal beams by a 50% beam splitter, the laser energy entering each beam splitter is in the optimal linear response range of the subsequent detection device. This avoids nonlinear distortion caused by signal saturation and ensures a sufficient signal-to-noise ratio, providing stable light source conditions for high-precision interferometric measurements.

[0016] (3) The measurement beam is divided into three beams by a triaxial interferometer and incident perpendicularly onto the reflector on the side of the workpiece stage. Based on the geometric principle that three points determine a plane, redundant and geometrically constrained optical measurement data are provided for the calculation of the displacement of the workpiece stage. Compared with the traditional single-point or double-point measurement method, it can effectively improve the accuracy and robustness of displacement measurement.

[0017] (4) The reflected interference signal is coupled and transmitted to the control box for calculation through the fiber optic coupler, which realizes the reliable transmission of the measurement signal in the vacuum cavity to the external processing system, avoids the transmission loss and electromagnetic interference of electrical signals in the vacuum environment, and ensures the integrity of the signal and the stability of the system in long-term operation. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structural principle of the workpiece stage displacement measurement system in a specific embodiment of the present invention; Figure 2 This is a schematic diagram of the deflection measurement of the reflector in a specific embodiment of the present invention; Figure 3 This is a schematic diagram of the elevation measurement of the reflector in a specific embodiment of the present invention.

[0019] Legend: 1. Laser; 2. First right-angle mirror; 3. Second right-angle mirror; 4. Neutral density mirror; 5. 50% beam splitter; 6. 25% beam splitter; 7. Single-axis interferometer; 8. Integrated regulator; 9. Three-axis interferometer; 10. Fiber optic coupler; 11. Reference mirror; 12. Control cabinet; 13. Vacuum wavelength compensator; 14. Workpiece stage; 15. Vacuum cavity; 16. Atmospheric wavelength compensator; 17. Mirror. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0021] In the description of this invention, it should be understood that the terms "side", "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0022] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more unless otherwise explicitly specified.

[0023] Example like Figure 1 As shown, the workpiece stage displacement measurement system of the present invention includes a main optical path and two split optical paths with identical structures for the X and Y axes. The main optical path provides the light source for measurement, while the X and Y axis split optical paths are used to measure the displacement of the workpiece stage 14 within the vacuum cavity 15 in the X and Y planes, respectively. Specifically, through the dual-axis symmetrical optical path architecture design, the consistency of the X-axis and Y-axis measurement references is ensured at the physical level, effectively avoiding systematic errors introduced by differences in optical path structure, and laying a solid foundation for subsequent high-precision planar displacement calculation. It should be understood that although the X-axis and Y-axis split optical paths are orthogonally arranged in this embodiment, in other embodiments, depending on the motion degree of freedom requirements of the workpiece stage 14, the two split optical paths can also be arranged at a non-orthogonal angle, as long as independent measurement of the multidimensional displacement of the workpiece stage 14 can be achieved.

[0024] like Figure 1 As shown, the overall optical path includes a laser 1, a right-angle mirror, a neutral density mirror 4, and a 50% beam splitter 5 arranged sequentially. In this embodiment, the laser 1 is preferably a frequency-stabilized dual-frequency laser, whose emitted laser light first undergoes optical path deflection and collimation via the right-angle mirror. Specifically, the right-angle mirror includes a first right-angle mirror 2 and a second right-angle mirror 3, which guides the beam to a predetermined height and into subsequent optical components through two-stage reflection. The folded optical path design not only saves internal space but also reduces assembly difficulty by utilizing the self-collimation characteristics of the right-angle mirror. After being reflected by the right-angle mirror, the laser light passes through the neutral density mirror 4, which reduces the laser energy to 90% of its original energy.

[0025] It is important to note that the neutral density mirror 4 serves not only to reduce light intensity, but more importantly, to match the optimal linear response range of the downstream photodetector. In practical engineering applications, the output power of laser 1 may fluctuate slightly. Directly feeding this power into a high-sensitivity detector could easily lead to signal saturation or nonlinear distortion. By pre-attenuating the energy to 90%, sufficient signal-to-noise ratio margin is maintained, while a safe buffer is provided for light source fluctuations, ensuring that the entire measurement chain always operates within the dynamic range of optimal linearity. Of course, 90% is only a preferred attenuation ratio. Depending on the actual power of laser 1 and the sensitivity of the detector, this ratio can be adjusted between 80% and 95%, as long as detector saturation is avoided and a sufficient signal-to-noise ratio is maintained.

[0026] In this embodiment, the 50% beam splitter 5 splits the de-energized laser into two beams of equal energy, which propagate along the X-axis and Y-axis of the workpiece stage 14, respectively. Only when the X-axis and Y-axis obtain completely identical initial light intensities can the gain errors generated by the two signals during subsequent transmission, interference, and photoelectric conversion remain highly correlated, thus being effectively canceled out in the differential operation.

[0027] like Figure 1 As shown, the beam splitting path includes a 25% beam splitter 6, a general adjustment mechanism 8, a three-axis interferometer 9, and a fiber coupler 10 arranged sequentially. The laser beam exiting the 50% beam splitter 5 passes through the 25% beam splitter 6, which splits the laser beam into two beams with an intensity ratio of 1:3. The 75% intensity laser beam serves as the main measurement beam, passing through the general adjustment mechanism 8 and entering the three-axis interferometer 9; the remaining 25% intensity laser beam is distributed to the auxiliary optical path.

[0028] In this embodiment, the 1:3 beam splitting ratio is the optimal solution verified through extensive experiments: on the one hand, the 75% energy allocation ensures that the main measurement optical path still has sufficient signal strength when it reaches the detector after long-distance transmission, multiple beam splitting, and transmission loss through the vacuum window, guaranteeing the signal-to-noise ratio of nanometer-level displacement measurement; on the other hand, the 25% energy is sufficient to support the normal operation of the auxiliary optical path, while avoiding energy waste or crosstalk to the main optical path caused by an excessively strong reference optical path. It should be understood that 1:3 is only an exemplary ratio. Without departing from the concept of this invention, this ratio can also be adjusted to 1:2 or 1:4, etc., depending on the actual optical path loss and detector performance, as long as the minimum signal-to-noise ratio requirements of the main and auxiliary optical paths are met.

[0029] In this embodiment, the triaxial interferometer 9 divides the 75% intensity laser light into three beams, which are perpendicularly incident on the reflector 17 on the side of the workpiece stage 14 through the viewing window on the side of the vacuum cavity 15. The three laser beams are arranged in a specific geometric distribution in space (e.g., a triangular shape), forming a stable planar measurement reference. Compared with traditional single-beam or dual-beam measurements, the three beams can not only measure linear displacement, but also provide the necessary geometric constraints for subsequent calculation of the pitch and yaw attitude angles of the workpiece stage 14, fundamentally solving the Abbe error problem. The integrated regulator 8 is located before the triaxial interferometer 9 and is used to finely adjust the polarization state, spot size, and divergence angle of the beam to ensure that the beam quality entering the triaxial interferometer 9 meets the stringent requirements of interferometric measurement.

[0030] After being reflected by mirror 17, the laser beam enters fiber optic coupler 10 and is then coupled to control chassis 12 to calculate the displacement of workpiece stage 14. The function of fiber optic coupler 10 is to efficiently and stably couple the interference signal in free space into the optical fiber for transmission to control chassis 12. Using fiber optic transmission not only achieves electrical isolation between the measuring head and the control system, effectively shielding against strong electromagnetic interference sources such as motor drivers near the vacuum chamber 15, but also makes the signal transmission path more flexible, facilitating internal layout optimization. The high-performance processor built into control chassis 12 performs real-time calculations on the received interference signal, and, combined with preset optical models and environmental compensation parameters, finally outputs accurate displacement data of workpiece stage 14 in the X and Y planes. Through the collaborative design of energy management and optical path topology, this embodiment constructs a highly stable, high-precision displacement measurement infrastructure with good environmental adaptability, providing a reliable physical carrier for subsequent implementation of environmental compensation and attitude decoupling functions.

[0031] like Figure 1As shown, the beam splitting path also includes a single-axis interferometer 7 and a reference mirror 11 located within the vacuum cavity 15. The single-axis interferometer 7 is positioned close to the 25% beam splitter 6, and reference mirrors 11 are positioned along both the X and Y axes of the workpiece stage 14, with each single-axis interferometer 7 corresponding to a specific reference mirror 11. The 25% intensity laser beam split by the 25% beam splitter 6 passes through the single-axis interferometer 7 and is then directed onto the surface of the reference mirror 11 to measure the error caused by environmental influences on the laser beam as it travels from the laser 1 to the reference mirror 11.

[0032] Since the 25% beam shares the complete transmission path from laser 1 to the 25% beam splitter 6 with the main measurement beam, common interference factors such as the frequency drift of laser 1, temperature and pressure fluctuations in the atmospheric optical path, and thermal deformation of optical components are synchronously applied to this reference beam. When the reference beam enters the vacuum cavity 15 and is reflected back by the fixed reference mirror 11, the phase change it carries accurately characterizes the systematic error introduced by the aforementioned common path. By acquiring this reference signal in real time and differentially subtracting it from the main measurement signal, the control chassis 12 can effectively eliminate common-mode noise caused by cross-medium transmission and light source instability, significantly improving absolute measurement accuracy.

[0033] Furthermore, the reference mirror 11 is positioned at the middle of the side of the workpiece stage 14. In this embodiment, the "middle position" refers not only to the geometric center of the mechanical stroke of the workpiece stage 14, but more preferably to the thermodynamic equivalent center of the thermal field distribution within the vacuum cavity 15. In ultra-high vacuum environments, heat transfer primarily relies on radiation, often resulting in a nonlinear temperature gradient distribution within the cavity. If the reference mirror 11 is positioned at the end of the stroke, the local ambient temperature it senses may significantly deviate from the average temperature of the actual working area of ​​the workpiece stage 14, leading to overcompensation or undercompensation in the compensation model at different points in the stroke. By placing the reference mirror 11 at the middle position, the spatial averaging effect ensures that the environmental error parameters measured at that point have the best statistical representativeness for the entire stroke, thereby minimizing the residual error caused by the nonlinearity of the temperature gradient.

[0034] In this embodiment, three laser beams with 75% intensity, split by the 25% beam splitter 6, are incident perpendicularly in a triangular pattern on the reflector 17 on the side of the workpiece stage 14. For example... Figure 2 and Figure 3As shown, the "pin" - shaped layout forms a stable isosceles - triangle measurement reference in space. Compared with the traditional single - point or double - point measurement, the three - point layout strictly follows the geometric principle that "three points determine a plane". It can not only measure the linear displacement of the workpiece stage 14, but also provides the necessary geometric constraints for synchronously calculating the pitch and yaw attitude angles of the mirror 17 relative to the ideal plane. It should be understood that although the three laser beams are symmetrically distributed in a standard "pin" - shaped pattern in this embodiment, in other embodiments, as long as the projection points of the three laser beams on the mirror 17 are not collinear and the relative position relationship is known, a non - isosceles triangle or other irregular - triangle layout can also be adopted. Only the solution matrix needs to be adjusted accordingly in the control chassis 12 to achieve a complete observation of the displacement and attitude.

[0035] To achieve an accurate calculation of the deflection angle, three laser beams are incident on the mirror 17, forming light spots A, B, and C respectively. In this embodiment, since there are pitch and yaw angles for all three measurement light spots, there are displacement errors in the measurement directions of the measurement values of the three light spots. Therefore, the three light spots actually form a three - dimensional surface rather than a plane perpendicular to the measurement beam. To obtain the angle error, theoretically, light spot B and light spot C are on the same horizontal line, and light spot A is on the perpendicular bisector of the line connecting light spot B and light spot C, and the three form an isosceles triangle. As shown in Figure 2, define the designed distance from the center of light spot A to the center of the horizontal line where light spot B and light spot C are located as d1, and the designed distance between the center of light spot B and the center of light spot C in the horizontal direction as d2. These two parameters d1 and d2 are fixed baseline values determined by the internal optical structure and installation position of the three - axis interferometer 9, and are known constants after the system alignment is completed. At the same time, the system monitors in real - time the actual offset distance between the center of light spot B and the center of light spot C as d23. It should be noted that d23 is a pure differential signal, which represents the relative displacement change amount of points B and C in the horizontal direction. Since the linear displacement of the workpiece stage 14 will simultaneously cause points B and C to move in the same direction and with the same amplitude, when calculating d23, the linear - displacement component is naturally canceled, and only the relative misalignment caused by the rotation around the vertical axis is retained. Based on this, the deflection angle α1 of light spot C is the deflection angle of the mirror 17, and its calculation formula is: .

[0036] This formula directly reflects the trigonometric - function relationship between the deflection angle, the horizontal baseline d2, and the differential displacement d23. Since d23 has eliminated the common - mode interference, the calculation result of α1 is completely insensitive to the X - direction linear motion of the workpiece stage 14, thus achieving the orthogonal decoupling of the deflection angle and the linear displacement at the physical level, and greatly improving the dynamic accuracy of the attitude measurement.

[0037] As Figure 3As shown in the figure, further, for the calculation of the pitch angle, the light spot A is located exactly in the middle of the light spots B and C. Then, the pitch angle α2 of the light spot A is the pitch angle of the mirror 17, and its calculation formula is: .

[0038] In this formula, the numerator d23 also uses the aforementioned differential mechanism to characterize the relative tilt amount in the vertical direction. It should be noted that: here, d23 refers to the differential displacement of point A relative to the midpoint of the BC connection line in the vertical direction in the context of pitch calculation. For the convenience of symbol unification, d23 is used to represent the differential variable corresponding to the axial direction and can be obtained by an independent channel in actual applications. The "2×d1" in the denominator of the formula has a clear physical meaning: since the light spot A is located on the perpendicular bisector of the BC connection line, the vertical distance from point A to the midpoint of the BC connection line is d1. In the effective lever arm equivalent model under small-angle approximation, considering the relationship between the optical path difference of interference measurement and geometric projection, the effective lever arm length is reflected as 2 times of d1. This design makes the calculation of the pitch angle α2 only depend on the geometric constraints in the vertical direction and is decoupled from the deflection movement in the horizontal direction. Through the combination of the above "pin" - shaped layout and the supporting calculation formula, the present invention successfully realizes the independent and synchronous measurement of the four key parameters of X / Y displacement, deflection, and pitch in six - degree - of - freedom motion, avoiding both the calculation singularity caused by over - constraint that may be introduced by the four - point layout and the under - constraint defect that the two - point layout cannot solve the biaxial attitude simultaneously, and providing reliable multi - dimensional feedback information for the high - precision closed - loop control of the workpiece stage 14 in the vacuum environment.

[0039] In this embodiment, the mirror 17 is a triangular prism. Selecting a triangular prism (i.e., a corner - cube prism) as the target mirror takes advantage of its unique retro - reflective optical characteristics. Different from the traditional plane mirror, the triangular prism can make the incident light beam return strictly parallel to the incident direction after three internal reflections within a certain range of incident angles. This characteristic is crucial for high - speed and precision measurement in a vacuum environment. When the workpiece stage 14 performs nano - level stepping or high - speed scanning motion, it will inevitably produce small deflection and pitch attitude changes. If a plane mirror is used, even a micro - radian - level attitude jitter will cause the reflected light beam to deviate from the original optical path, resulting in a sharp decrease in the light intensity entering the fiber coupler 10 or even complete loss of the signal, causing the measurement to interrupt. However, the self - collimation tolerance of the triangular prism can effectively absorb this attitude perturbation and ensure the continuity and stability of the return light signal during the dynamic movement of the workpiece stage 14.

[0040] As Figure 1As shown, to address the refractive index fluctuation problem caused by laser transmission across media, a vacuum wavelength compensator 13 is installed inside the vacuum cavity 15; an atmospheric wavelength compensator 16 is installed outside the vacuum cavity 15. In laser interferometry, displacement calculation directly depends on the laser wavelength, which is modulated by the refractive index of the propagation medium. Since the measurement optical path of this system spans two completely different media environments—atmosphere and vacuum—the interference factors it experiences are also different: the atmospheric segment is mainly affected by macroscopic fluctuations in ambient temperature, air pressure, and humidity; while the vacuum segment, although the air pressure is extremely low, still has residual gas composition changes and local temperature gradients caused by motor heating and thermal radiation. These factors also lead to microscopic drift in the refractive index. If only a single atmospheric wavelength compensator is installed outside the cavity, the subtle changes in the vacuum environment inside the cavity cannot be detected, resulting in a blind zone in the compensation model; conversely, if only cavity compensation is relied upon, the significant error introduced by long-distance atmospheric transmission is ignored. This embodiment constructs a refined refractive index correction model covering the entire optical path by deploying dedicated wavelength compensators inside and outside the cavity. The atmospheric wavelength compensator 16 collects external environmental parameters in real time to correct errors in the common optical path, while the vacuum wavelength compensator 13 focuses on the precise elimination of residual effects inside the cavity. The two work together to fundamentally eliminate scale factor errors caused by differences in the medium and environmental gradients, ensuring the long-term stability of nanometer-level measurement accuracy.

[0041] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A workpiece stage displacement measurement system, characterized in that, It includes a main optical path and two split optical paths with the same structure, X-axis and Y-axis. The main optical path provides a light source for measurement, and the two split optical paths of X-axis and Y-axis are used to measure the displacement of the workpiece stage (14) in the vacuum cavity (15) in the X plane and Y plane, respectively. The total optical path includes a laser (1), a right-angle mirror, a neutral density mirror (4), and a 50% beam splitter (5) arranged in sequence. The laser emitted by the laser (1) is reflected by the right-angle mirror and then passes through the neutral density mirror (4). The neutral density mirror (4) reduces the energy of the laser to 90% of its original energy. The 50% beam splitter (5) splits the reduced-energy laser into two laser beams with equal energy, which propagate along the X-axis and Y-axis of the workpiece stage (14), respectively. The beam splitting path includes a 25% beam splitter (6), a comprehensive regulator (8), a three-axis interferometer (9), and a fiber coupler (10) arranged in sequence. The laser beam exiting the 50% beam splitter (5) passes through the 25% beam splitter (6), which splits the laser beam into two beams with an intensity ratio of 1:

3. The 75% intensity laser beam enters the three-axis interferometer (9) through the comprehensive regulator (8), which splits the 75% intensity laser beam into three beams. The beams are perpendicularly incident on the reflector (17) on the side of the workpiece stage (14) through the viewing window on the side of the vacuum cavity (15). After reflection, the laser beam enters the fiber coupler (10) and is coupled to the control box (12) to calculate the displacement of the workpiece stage (14).

2. The workpiece stage displacement measurement system according to claim 1, characterized in that, The beam splitting path also includes a single-axis interferometer (7) and a reference mirror (11) located in the vacuum cavity (15); the single-axis interferometer (7) is close to the 25% beam splitter (6), and reference mirrors (11) are provided along the X-axis and Y-axis of the side of the workpiece stage (14), and the single-axis interferometer (7) and the reference mirror (11) correspond one-to-one; the 25% intensity laser beam split by the 25% beam splitter (6) passes through the single-axis interferometer (7) and is directed to the surface of the reference mirror (11) to measure the error of the laser beam due to environmental influences during the distance from the laser (1) to the reference mirror (11).

3. The workpiece stage displacement measurement system according to claim 2, characterized in that, The reference mirror (11) is located at the middle position on the side of the workpiece stage (14).

4. The workpiece stage displacement measurement system according to any one of claims 1 to 3, characterized in that, The three laser beams with 75% intensity separated by the 25% beam splitter (6) are incident vertically in a triangular pattern on the reflector (17) on the side of the workpiece stage (14).

5. The workpiece stage displacement measurement system according to claim 4, characterized in that, The three laser beams are incident on the reflector (17) and form light spots A, B and C respectively; wherein, the designed distance from the center of light spot A to the center of the horizontal line where light spots B and C are located is d1, the designed horizontal distance between the center of light spot B and the center of light spot C is d2, and the actual offset distance between the center of light spot B and the center of light spot C is d23. Then, the deflection angle α1 of light spot C is the deflection angle of the reflector (17): 。 6. The workpiece stage displacement measurement system according to claim 5, characterized in that, Since the light spot A is located in the middle of the light spots B and C, the pitch angle α2 of the light spot A is the pitch angle of the reflecting mirror (17): 。 7. The workpiece stage displacement measurement system according to any one of claims 1 to 3, characterized in that, The reflector (17) is a triangular prism.

8. The workpiece stage displacement measurement system according to any one of claims 1 to 3, characterized in that, The right-angle reflector includes a first right-angle reflector (2) and a second right-angle reflector (3) arranged in sequence. The first right-angle reflector (2) is close to the laser (1), and the second right-angle reflector (3) is close to the neutral density mirror (4).

9. The workpiece stage displacement measurement system according to any one of claims 1 to 3, characterized in that, The vacuum cavity (15) is also provided with a vacuum wavelength compensator (13); the vacuum cavity (15) is provided with an atmospheric wavelength compensator (16).

10. The workpiece stage displacement measurement system according to any one of claims 1 to 3, characterized in that, The laser (1) is a dual-frequency laser interferometer.

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