An interferometer measurement system and method

Abstract

The application provides an interferometer measuring system and a measuring method, which realizes secondary diffraction by setting a light refraction assembly and a back reflection assembly, and eliminates the included angle interference caused by the rotation of a target to be measured by using the parallel light emitting effect of the back reflection assembly. By using the back reflection assembly, the included angle interference can be eliminated, and the whole interferometer is more integrated and compact, so that the temperature gradient of the interferometer in the measuring environment can be better controlled in the measurement, thereby reducing the influence of environmental factors on the precision of the interferometer.

Description

Technical Field

[0001] This application relates to the field of precision measurement technology, and in particular to an interferometer measurement system and measurement method. Background Technology

[0002] Precision machining is inseparable from precision measurement. As production equipment demands ever-increasing processing accuracy, even higher requirements are being placed on measurement precision. Measurement requirements for precision equipment such as immersion lithography machines have even reached the sub-nanometer level. Grating interferometers use the grating pitch as the measurement reference, and the grating lines are insensitive to changes in environmental factors. Therefore, compared to laser interferometers, they reduce the requirements for the light source. The reading head of a grating interferometer has a more compact structure and a symmetrical optical path. Thus, with the improvement of grating manufacturing capabilities, its superior stability and lower measurement cost have led to a wider range of applications.

[0003] Grating interferometry, with its short optical path length, ensures higher environmental robustness, making its advantages even more significant in sub-nanometer measurements. Existing commercial interferometers can generally meet nanometer-level displacement measurement requirements. However, in actual displacement measurements, factors such as object motion can cause offsets or rotations in the grating or mirrors. Directly receiving the interference light information using a photodetector results in a low AC / DC ratio in the interference signal due to interference fringes appearing within the interference spot area. Furthermore, temperature fluctuations in precision measurements also affect the accuracy of the measuring instrument, necessitating temperature control of the operating environment. Therefore, eliminating angular interference from the receiver to remove interference fringes, and designing a highly integrated, high-resolution interferometer to control the temperature gradient, are problems that urgently need to be addressed in practical measurements. Summary of the Invention

[0004] To address the problems in the aforementioned related technologies, this application provides an interferometer measurement system and method. Secondary diffraction is achieved by setting up a refractive component and a retroreflection component. Furthermore, the parallel light emission effect of the retroreflection component eliminates angular interference caused by the rotation of the target object. Using a retroreflector not only eliminates angular interference but also makes the interferometer more integrated and compact. This allows for better control of the temperature gradient of the interferometer in the measurement environment, reducing the impact of environmental factors on the interferometer's accuracy.

[0005] In a first aspect, the present invention provides an interferometer measurement system comprising:

[0006] A laser emitting component for generating at least two parallel incident laser beams;

[0007] A polarizing beam splitter is configured to correspond to the emitting end of the laser emitting component. The polarizing beam splitter is used to split the incident laser beam into measurement laser beams with different propagation directions.

[0008] A refractive component, disposed in the emission direction of the polarizing beam splitter, is used to refract the measuring laser beam sequentially toward the reflecting grating, so that the measuring laser beam undergoes at least two diffractions on the reflecting grating sequentially.

[0009] An interference component for receiving the diffracted measurement laser beam emitted by the refractive component, so as to cause pairwise interference of the multiple measurement laser beams; and

[0010] A photoelectric detection component is used to receive the measurement laser beam after interference emitted by the interference component and convert it into an electrical signal, and to measure the displacement of a moving target based on the electrical signal.

[0011] In one embodiment, the reflective grating is mounted on the moving target to be measured, and the reflective grating is capable of moving with the moving target within the target plane.

[0012] In one embodiment, each incident laser beam forms two measurement laser beams that propagate along a first direction and a second direction respectively at the polarization beam splitter. The refractive component includes a retroreflection component, a first refractive component, and a second refractive component, with the first refractive component and the second refractive component respectively corresponding to the measurement laser beams propagating along the first direction and the second direction.

[0013] The measurement laser beam, after passing through the refractive assembly, is refracted towards the reflective grating and diffracted on the reflective grating before returning along the same path. The measurement laser beam returning to the refractive assembly is refracted towards the retroreflection assembly, then refracted again by the retroreflection assembly and towards the reflective grating. After being diffracted again on the reflective grating, the measurement laser beam returns to the refractive assembly along the same path and is emitted by the refractive assembly to the interference component.

[0014] In one embodiment, the refractive assembly includes a quarter-wave plate, a first refractive unit, and a second refractive unit. The quarter-wave plate is disposed in the emission direction of the measurement laser beam formed at the polarizing beam splitter, and the first refractive unit and the second refractive unit are disposed side by side behind the quarter-wave plate.

[0015] The measuring laser beam passes sequentially through the quarter-wave plate and the first refractive unit, then is refracted towards the reflective grating and returns along the same path. The measuring laser beam that returns to the quarter-wave plate then passes through the polarizing beam splitter and enters the retroreflection assembly. The measuring laser beam that is emitted in reverse through the retroreflection assembly passes sequentially through the quarter-wave plate and the second refractive unit, then is refracted towards the reflective grating again and returns along the same path. The measuring laser beam that returns to the quarter-wave plate again passes through the polarizing beam splitter and enters the interference component.

[0016] In one embodiment, the refractive unit includes at least two refractive elements, each of which corresponds to a measurement laser beam that is refracted by the refractive element toward the reflective grating.

[0017] In one embodiment, of the at least two measurement laser beams propagating in the same direction, one measurement laser beam, after passing through the refractive element, is incident on the reflective grating at a first-order Literow diffraction angle, and the other measurement laser beam, after passing through the refractive element, is incident on the reflective grating at a second-order Literow diffraction angle.

[0018] In one embodiment, at least two parallel incident laser beams are generated in the same propagation direction by the polarizing beam splitter to produce at least two corresponding parallel measurement laser beams. After the at least two measurement laser beams are emitted in the opposite direction by the retroreflection assembly, their relative positions are swapped.

[0019] In one embodiment, the first refractive component and the second refractive component have the same structure, and the components in the first refractive component and the second refractive component are symmetrically distributed about the plane where the polarizing beam splitter is located.

[0020] In one embodiment, the laser emitting component includes a laser source, a non-polarizing beam splitter prism, and a reflector. The non-polarizing beam splitter prism is used to partially transmit and partially reflect the laser emitted by the laser source towards the reflector. The laser reflected towards the reflector is reflected again by the reflector and then emitted parallel to the laser transmitted through the non-polarizing beam splitter prism, thereby forming two parallel incident laser beams; or

[0021] The laser emitting component includes at least two laser sources, which are capable of emitting two parallel incident laser beams.

[0022] In one embodiment, a beam splitter is further included, which is disposed between the interferometer and the photoelectric detection component, and is used to split the interferometric measurement laser beam into multiple outgoing laser beams that enter the photoelectric detection component.

[0023] In one embodiment, the incident laser beam generated by the laser emitting component is 45-degree polarized light, and the two measurement laser beams with different propagation directions generated after the 45-degree polarized light passes through the polarizing beam splitter are P-polarized light and S-polarized light, respectively.

[0024] Secondly, the present invention provides an interferometer measurement method, comprising:

[0025] Obtain at least two parallel incident laser beams;

[0026] The incident laser beam is divided into measurement laser beams with different propagation directions;

[0027] The measuring laser beam is diffracted at least twice sequentially on the reflecting grating.

[0028] The diffracted measurement laser beams are subjected to pairwise interference; and

[0029] The interferometric laser beam is converted into an electrical signal, and the displacement of the moving target is measured based on the electrical signal.

[0030] The above-mentioned technical features can be combined in various suitable ways or replaced by equivalent technical features, as long as the purpose of the present invention can be achieved.

[0031] The interferometer measurement system and method provided by this invention have at least the following advantages compared with the prior art:

[0032] By utilizing the parallel light emission effect of the retroreflector component, the measurement effect of interference fringes caused by the angular interference of the laser used for measurement due to the rotation of the object under test is eliminated;

[0033] By using multiple sets of refractive components and changing the laser angle, the laser used for measurement produces secondary diffraction at the Littoral first-order diffraction angle and the Littoral second-order diffraction angle respectively in the reflection diffraction component (measuring reflection grating), resulting in a higher optical subdivision number.

[0034] By utilizing retroreflection components (reflectors) and multiple sets of refractive components, the interferometer is made more integrated and compact, thereby allowing for better control of the temperature gradient in the measurement environment and reducing the impact of environmental factors on the accuracy of the interferometer.

[0035] A refractive component and a quarter-wave plate can be symmetrically arranged on both sides of the adhesive layer of the polarizing beam splitter, so that the secondary diffracted light with different positive and negative poles can be used as the measurement signal, achieving the purpose of high subdivision of the signal to the quasi-twelfth order.

[0036] With no interference fringes and advantages such as high measurement accuracy, high integration, large measurement stroke, and small environmental disturbance error, it can be used as a position measurement system for the ultra-precision workpiece stage of immersion lithography machine, improving the overall performance of the aforementioned workpiece stage. Attached Figure Description

[0037] The invention will now be described in more detail with reference to embodiments and the accompanying drawings.

[0038] Figure 1 A schematic diagram of the zero-difference interferometer measurement system of the present invention is shown;

[0039] Figure 2 A schematic diagram of the optical path transmitted at the polarization beam splitter in the zero-difference interferometer measurement system of the present invention is shown;

[0040] Figure 3 A schematic diagram of the optical path reflected at the polarization beam splitter in the zero-difference interferometer measurement system of the present invention is shown;

[0041] Figure 4 The diagram shows a schematic of the heterodyne interferometer measurement system formed by removing the non-polarizing beam splitter and the reflector and adding a laser source, according to the present invention.

[0042] In the accompanying drawings, the same parts use the same reference numerals. The drawings are not to scale.

[0043] Figure label:

[0044] 1-First laser source, 2-Unpolarized beam splitter, 3-Photodetector group, 4-First quarter-wave plate, 5-First upper refracting grating, 6-Second lower refracting grating, 7-First lower refracting grating, 8-Second upper refracting grating, 9-Reflection grating, 10-Fourth upper refracting grating, 11-Third lower refracting grating, 12-Fourth lower refracting grating, 13-Third upper refracting grating, 14-Second quarter-wave plate, 15-Polarizing beam splitter, 16-Reflection assembly, 17-Interference component, 18-Beam splitter, 19-Reflector, 20-Second laser source, 21-Photodetector. Detailed Implementation

[0045] The invention will now be further described with reference to the accompanying drawings. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. The described embodiments should not be regarded as limitations on this application. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0048] In the following description, references are made to “some embodiments,” which describe a subset of all possible embodiments. However, it is understood that “some embodiments” may be the same subset or different subsets of all possible embodiments and may be combined with each other without conflict.

[0049] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing this invention and simplifying the description, and do not 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. If similar descriptions such as "first," "second," and "third" appear in the application documents, the following explanation is added: In the following description, the terms "first," "second," and "third" are merely used to distinguish similar objects and do not represent a specific order of objects. It is understood that "first," "second," and "third" can be interchanged in a specific order or sequence where permitted, so that the embodiments of this application described herein can be implemented in an order other than that illustrated or described herein.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit this application.

[0051] Example 1

[0052] This application provides a zero-difference interferometer measurement system based on second-order diffraction, including:

[0053] The laser emitting component is used to generate two parallel incident laser beams, which are 45-degree polarized light. The laser emitting component includes a laser source, a non-polarized beam splitter 2, and a reflector 19. The non-polarized beam splitter 2 is used to transmit part of the laser emitted by the laser source and reflect part of it to the reflector 19. The laser reflected to the reflector 19 is reflected again by the reflector 19 and emitted parallel to the laser transmitted at the non-polarized beam splitter 2, so as to form two parallel incident laser beams.

[0054] The reflective grating 9 is installed on the moving target to be measured, and the reflective grating 9 can move with the moving target in the target plane;

[0055] The polarizing beam splitter 15 is configured to correspond to the emitting end of the laser emitting component. The polarizing beam splitter 15 is used to split each incident laser beam into two measurement laser beams with different propagation directions.

[0056] A refractive component, disposed between the reflecting grating 9 and the polarizing beam splitter 15, is used to refract the measurement laser beam twice toward the reflecting grating 9, so that the measurement laser beam undergoes two diffractions on the reflecting grating 9. The refractive component includes a retroreflection assembly 16 (retroreflector), a first refractive assembly, and a second refractive assembly, which correspond to the measurement laser beams propagating along the first and second directions, respectively. The refractive assembly includes a quarter-wave plate, a first refractive unit, and a second refractive unit. The quarter-wave plate is disposed in the emission direction of the measurement laser beam formed at the polarizing beam splitter 15, and the first and second refractive units are arranged side by side behind the quarter-wave plate. The first and second refractive assemblies have the same structure, and the components in the first and second refractive assemblies are symmetrically distributed about the plane of the polarizing beam splitter 15.

[0057] Interference component 17 is used to receive multiple measurement laser beams after diffraction by the refractive component, so that the multiple measurement laser beams interfere in pairs. Interference component 17 uses a 45-degree polarizer.

[0058] A photoelectric detection component, used to receive the interferometric measurement laser beam emitted by the interferometer 17 and convert it into an electrical signal to measure the displacement of a moving target; and

[0059] Beam splitter 18 is disposed between interferometer 17 and photoelectric detector 17. It is used to split the interferometric measurement laser beam into multiple outgoing laser beams that enter the photoelectric detector 17. Beam splitter 18 uses a beam splitter grating.

[0060] The above describes the basic structure of the measurement system in this embodiment. The specific structure and operating principle of the measurement system in this embodiment are further explained below:

[0061] For ease of description, this embodiment uses some directional terms, which will be explained first. In this embodiment, directional terms such as "up" or "on the road" refer to... Figure 1 The positive y-axis direction in the orientation indicator is shown in the figure. The orientation indicator shows the x and z directions. The positive y-axis direction is the direction from the origin of the x and z axes towards the reader. In this embodiment, "down" or "down road" refers to the negative y-axis direction. In this embodiment, "right" refers to the positive x-axis direction, and "left" refers to the negative x-axis direction.

[0062] Refer to the attached diagram. Figures 1 to 3The planar structural diagram of the measurement system shown in this embodiment includes a laser emitting component comprising a first laser source 1, a non-polarizing beam splitter 2, and a reflector 19; and a refractive component comprising a retroreflection assembly 16 and two refractive assemblies with identical structures. The first refractive assembly comprises a first quarter-wave plate 4, a first refractive unit composed of a first upper refractive grating 5 (refractive element) and a first lower refractive grating 7, and a second refractive unit composed of a second upper refractive grating 8 and a second lower refractive grating 6. The second refractive assembly comprises a second quarter-wave plate 14, a third refractive unit composed of a third upper refractive grating 13 and a third lower refractive grating 11 (equivalent to the first refractive unit), and a fourth refractive unit composed of a fourth upper refractive grating 10 and a fourth lower refractive grating 12 (equivalent to the second refractive unit).

[0063] Refer to the attached diagram. Figure 1 With the plane of the polarizing beam splitter 15 as the reference, the plane of the reflecting grating 9 is perpendicular to the plane of the polarizing beam splitter 15. In addition, the grating surface of the reflecting grating 9 needs to maintain a specific installation angle to ensure that the beam can be diffracted twice on the measuring reflecting grating 9. The planes of the first quarter wave plate 4, the second quarter wave plate 14, the unpolarizing beam splitter 2, the reflecting mirror 19, the beam splitter 18 (beam splitter grating), and the interference component (45-degree polarizer) 17 are all at a 45-degree angle to the plane of the polarizing beam splitter 15.

[0064] The third upper refracting grating 13, the third lower refracting grating 11, the fourth lower refracting grating 12, the fourth upper refracting grating 10, the second quarter wave plate 14, the first laser source 1, the non-polarizing beam splitter 2, the reflector 19, the polarizer 17, the beam splitter grating 18, and the photodetector group 3 are located on the left side of the plane where the polarizing beam splitter 15 is located. The first upper refracting grating 5, the first lower refracting grating 7, the second lower refracting grating 6, the second upper refracting grating 8, the first quarter wave plate 4, and the retroreflection assembly 16 are located on the right side of the plane where the polarizing beam splitter 15 is located. The second quarter-wave plate 14 and the first quarter-wave plate 4, the third upper refracting grating 13 and the first upper refracting grating 5, the fourth lower refracting grating 12 and the second lower refracting grating 6, the third lower refracting grating 11 and the first lower refracting grating 7, and the fourth upper refracting grating 10 and the second upper refracting grating 8 are symmetrically distributed about the plane of the polarizing beam splitter 15.

[0065] Figure 2 and Figure 3 The diagram shown is an optical path schematic of the measurement system in this embodiment, wherein... Figure 2 The diagram shows the optical path of the measurement laser beam transmitted through the polarizing beam splitter 15. Figure 3 The diagram shows the optical path of the measurement laser beam reflected at polarizing beam splitter 15. Figure 2 and Figure 3The optical path is actually generated simultaneously after beam splitting at point 15 of the polarizing beam splitter. The reason for this is that the beams are generated separately at point 15. Figure 2 and Figure 3 The purpose of this representation is to more clearly express the optical path structure. Furthermore, Figure 2 and Figure 3 In order to represent two parallel beams of light on a plane, two parallel lines are used to represent them. Therefore, the point of the beams falling on the reflection grating 9 shown in the figure is offset. However, when viewed from the perspective shown in the attached figure, the point of the parallel beams of light is actually unique.

[0066] Figure 2 In the diagram, solid lines represent the upper optical path (referred to as "upper path"), and dotted lines represent the lower optical path (referred to as "lower path"). Figure 3 In the diagram, the short horizontal dashed line represents the upper optical path (referred to as "upper path"), and the dotted dashed line represents the lower optical path (referred to as "lower path").

[0067] The first laser source 1 emits a beam of 45-degree polarized light as the incident laser beam. The incident laser beam undergoes partial (50% in this embodiment) transmission and partial (50% in this embodiment) reflection after passing through the non-polarizing beam splitter 2. The transmitted portion forms the first incident laser beam, and the reflected portion is reflected by the reflector 19 to form an incident laser beam L2 that is parallel to and has the same propagation direction as the incident laser beam L1. The incident laser beams L1 and L2 propagate to the polarizing beam splitter 15, where partial transmission and reflection occur again, separating the 45-degree polarized light into s-polarized light and p-polarized light. The incident laser beams L1 and L2 are transmitted through the polarizing beam splitter 15 to form two p-polarized beams, which serve as two measurement laser beams P1 and P2. These beams enter the first refractive assembly on the right side of the polarizing beam splitter 15, and are reflected to form two s-polarized beams, which then enter the second refractive assembly on the left side of the polarizing beam splitter 15.

[0068] The following sections will describe the subsequent optical paths and operating principles of the measuring laser beams P1 and P2, and the measuring laser beams S1 and S2.

[0069] First, for the two p-polarized beams formed by the transmission of incident laser beams L1 and L2 at the polarization beam splitter 15, the formation and operating principle of the subsequent optical paths of the two measurement laser beams P1 and P2 are as follows:

[0070] like Figure 2As shown, the two measurement laser beams P1 and P2 are parallel vertically. Initially, P1 is in the upper path and P2 is in the lower path. P1 and P2 first pass together through the first quarter-wave plate 4 of the first refractive assembly, and then propagate to the first upper refractive grating 5 and the first lower refractive grating 7, which are set at specific angles, respectively. P1 passes through the first upper refractive grating 5 and is incident at the reflection grating 9 at an incident angle of first-order Littorau diffraction angle θ1 before returning along the same path. P2 passes through the first lower refractive grating 7 and is incident at the reflection grating 9 at an incident angle of second-order Littorau diffraction angle θ2 before returning along the same path. The returned P1 and P2 beams pass together in the opposite direction through the first quarter-wave plate 4. At this time, the p-polarized light P1 and P2 become s-polarized light s. 01 With s 02 After being reflected at the polarizing beam splitter 15, it enters the retroreflection assembly 16.

[0071] p-polarized light P1 and P2 are converted into s-polarized light s by the first quarter-wave plate 4. 01 With s 02 After passing through the retro-emission component 16, it is emitted in the opposite direction, but at this time s 01 With s 02 The relative positions of s have been reversed. 01 Move to the lower level, s 02 Move to the upper level. 01 With s 02 After being reflected by the polarizing beam splitter 15, they pass together through the first quarter-wave plate 4 and propagate to the second upper refractive grating 8 and the second lower refractive grating 6, which are set at specific angles, respectively. 02 After passing through the second upper refractive grating 8 and incident at an incident angle of second-order Littoral diffraction angle θ2, the light returns along the same path. 01 After passing through the second lower refractive grating 6 and incident at an incident angle of first-order Littoral diffraction angle θ1, the light returns along the same path. 01 With s 02 The light rays pass through the first quarter-wave plate 4 in opposite directions, at which point the s-polarized light s 01 With s 02 Become p-polarized light p 01 With p 02 After being transmitted through the polarizing beam splitter 15, the beam enters the interference component 17 and interferes. Then, after being split by the beam splitter 18, it is received by the photoelectric detection component (photoelectric detector group 3).

[0072] It should be noted that the retroreflection assembly 16 used in this invention not only needs to achieve a 180° reverse emission of the beam, but also needs to swap the positions of the two vertically parallel beams. Therefore, there are certain requirements for the structure of the retroreflection assembly 16. (See attached figures) Figure 2The structure of the retroreflection component 16 shown is merely illustrative; in reality, a three-dimensional retroreflection component 16 with a multiple reflection structure is required. This type of retroreflection component 16 is also relatively existing, and here we will only describe the required structural type without further elaboration on its specific structure.

[0073] Secondly, for the two s-polarized beams formed by the reflection of the incident laser beams L1 and L2 at the polarization beam splitter 15, the formation and operating principle of the subsequent optical paths of the two measurement laser beams S1 and S2 are as follows:

[0074] like Figure 3 As shown, the two second measurement laser beams S1 and S2 are parallel vertically. Initially, S1 is in the upper path and S2 is in the lower path. S1 and S2 first pass together through the second quarter-wave plate 14 of the second refractive assembly, and then propagate to the third upper refractive grating 13 and the third lower refractive grating 11, which are set at specific angles, respectively. S1 passes through the third upper refractive grating 13 and is incident at the reflection grating 9 at an incident angle of the first-order Littorau diffraction angle θ1 before returning along the same path. S2 passes through the third lower refractive grating 11 and is incident at the reflection grating 9 at an incident angle of the second-order Littorau diffraction angle θ2 before returning along the same path. After returning, S1 and S2 pass together in the opposite direction through the second quarter-wave plate 14. At this time, the s-polarized light S1 and S2 become p-polarized light p 01 'and p 02 After being transmitted through the polarizing beam splitter 15, it enters the retroreflection assembly 16.

[0075] s-polarized light S1 and S2 are converted into p-polarized light p by the first quarter-wave plate 4. 01 'and p 02 After passing through the retroreflector assembly 16, it is emitted in the opposite direction, but at this time p 01 'and p 02 The relative positions of ' have been reversed, p 01 'Switch to the lower level, p' 02 Move to the upper level. 01 'and p 02 After transmission through the polarizing beam splitter 15, they all pass through the second quarter-wave plate 14 and propagate to the fourth upper refractive grating 10 and the fourth lower refractive grating 12, which are set at specific angles, respectively. 02 After passing through the fourth upper refractive grating 10 at an incident angle of second-order Littoral diffraction angle θ2, the light returns along the same path. 01 After passing through the fourth lower refractive grating 12 and incident at an incident angle of first-order Littoral diffraction angle θ1, the light returns along the same path. 01 'and p 02 'The two beams pass in opposite directions through the second quarter-wave plate 14, at which point the p-polarized light p 01 'and p 02'Transformed into s-polarized light s 01 'and s 02 After being reflected at the polarization beam splitter 15, the beam enters the interference component 17 and interferes. Then, after being split by the beam splitter 18, it is received by the photoelectric detection component (photoelectric detector group 3).

[0076] For the interfering component 17, it simultaneously receives the emitted p 01 With p 02 s 01 'and s 02 The four beams interfere in pairs at the interferometer 17, and then are split into multiple beams (usually four beams) by the beam splitter 18 before reaching the photoelectric detection unit (photoelectric detector group 3, which has multiple detectors). The beams are then converted into measurement signals through photoelectric conversion. The four beams always converge to the detector and remain parallel without any angles during propagation. Therefore, interference fringes caused by angular interference are basically not observed.

[0077] In this embodiment, the reflective grating 9 in the measurement system moves two-dimensionally within the target plane along with the target object. This measurement system is used to measure the displacement of the object. The four beams reaching the interference component 17 undergo pairwise interference, where p... 01 With p 02 Interference occurs, s 01 'and s 02 Interference occurs, forming two interference signals. The photodetector 21 component converts the signal into an electrical signal through photoelectric conversion, thus forming two measurement signals.

[0078] The phase detection result of the first measurement signal is:

[0079] The phase detection result of the second measurement signal is:

[0080] Where -2, +1, +2, and -1 all represent the diffraction orders of the measured reflection grating 9, and thus, the final calculated displacement is:

[0081]

[0082]

[0083]

[0084] As shown in the attached diagram, the z-direction is parallel to the normal direction of the reflecting grating 9. Δx and Δz are the displacements calculated in the x and z directions, respectively. λ is the wavelength of the laser in air. φ1 and φ2 represent the phase changes in the laser signal caused by the Doppler frequency shift resulting from the movement of the reflecting grating 9, and are the phase changes obtained in the measured interference signal. θ1 and θ2 are the first-order and second-order Littoral diffraction angles, respectively. p is the period of the reflecting grating 9. The second diffraction by the grating improves the resolution of the displacement measurement.

[0085] The periodic nonlinear error of the grating interferometer of the present invention mainly originates from light leakage caused by imperfections in the polarization device in the optical path and reflected light generated by ghosting of the optical device entering the photodetector 3. These factors cause deviations when the laser polarization state changes according to the design state, resulting in alternative propagation paths. The leakage and reflected light that do not propagate along the designed path entering the photodetector 3 will cause periodic nonlinear errors in the measurement. The embodiment of this application uses an optical path propagation structure composed of a retroreflection component 16 and two symmetrically placed quarter-wave plates along the polarization beam splitter 15. This structure ensures that the portion of the leakage light that does not propagate along the aforementioned path returns to the direction of the first laser source 1 along the original path, and that the portion of the leakage light that initially propagates along the aforementioned path exits in a different manner, not entering the photodetector 3. Furthermore, the ghosting reflected light also returns to the direction of the first laser source 1 along the original path and does not enter the photodetector 3. This can reduce the periodic nonlinear error caused by light leakage in the interferometer of the embodiment of this application.

[0086] The zero-difference interferometer measurement system based on secondary diffraction in this application embodiment is a two-degree-of-freedom zero-difference grating dry displacement measurement system based on secondary diffraction light. It utilizes the retroreflection component 16 to eliminate the influence of interference fringes caused by the rotation of the object under test on the measurement. It utilizes the parallel light output effect of the retroreflection component 16 to ensure that, for example, there is no beam angle between each pair of the four measurement beams generated by the non-polarizing beam splitter prism 2. After eliminating the interference fringes, the size of the light spot can be reduced, thereby providing a wider angle measurement range and displacement measurement stroke in the measurement and giving the system a larger angle tolerance.

[0087] This application embodiment can simultaneously measure large-stroke linear displacements in both the z and x directions, using multi-channel lasers rich in displacement information. The high integration of the system is achieved through the use of a refracting grating and a retroreflection component, and the highly integrated interferometer is less susceptible to environmental influences. Furthermore, secondary diffraction occurs on both sides of the adhesive layer of the polarizing beam splitter 15, achieving quasi-twelfth-order subdivision of the measurement signal (where the optical subdivision of the secondary diffraction is four subdivisions, with +1 and -2 order diffracted light producing a 3-fold subdivision). This achieves higher optical subdivision compared to single-order diffraction measurement systems and ordinary secondary diffraction measurement systems with reference light. Secondary diffraction improves the resolution of displacement measurement; in this application embodiment, the signal period is 200 nm, and subdivision achieves sub-nanometer resolution.

[0088] The measurement system of this application has the advantages of high measurement accuracy, high integration, large angle measurement range, air disturbance error, small size, light weight, and easy layout. It can be used as an ultra-precision workpiece stage position measurement system for immersion lithography machines to improve the overall performance of the workpiece stage.

[0089] This embodiment uses a single-frequency laser transmission light source, eliminating the periodic nonlinear error caused by frequency aliasing from coaxial dual-frequency light sources. Current interferometers address interference fringes by increasing the measurement spot size to ensure a sufficiently large interference range between the two spots, but this leads to low laser utilization and introduces significant air disturbance. This embodiment utilizes the parallel light output effect of the retroreflection component 16 to eliminate the angle caused by the rotation of the object under test in the interference measurement light. Since this embodiment solves the problems of interference fringes and fringe contrast attenuation introduced by the rotation of the object under test, interference fringes are also eliminated. Therefore, the measurement spot size can be smaller, resulting in less error introduced by air disturbance.

[0090] Example 2

[0091] Unlike Embodiment 1, the laser emitting component in this embodiment includes two laser sources, eliminating the non-polarizing beam splitter prism 2, reflector 19, and beam splitter 18. The two laser sources emit lasers at different frequencies, specifically a first laser source 1 and a second laser source 20, as shown in the attached figures. Figure 4 As shown by the solid and dashed lines, the photoelectric detection component in this embodiment is a photoelectric detector 21 (one detector). This embodiment is a heterodyne interferometer measurement system based on secondary diffraction. The zero-difference system in Embodiment 1 can be changed to a heterodyne system to adapt to different needs. Its planar structure schematic diagram is shown below. Figure 4 As shown.

[0092] The system operation process of this embodiment is similar to that of Embodiment 1, and will not be described again here.

[0093] Example 3

[0094] This application provides an interferometer measurement method, including:

[0095] Step S100: Obtain at least two parallel incident laser beams through the laser emitting component;

[0096] Step S200: Use a polarizing beam splitter to split the incident laser beam into multiple measurement laser beams with different propagation directions;

[0097] Step S300: Using a refractive component, the measurement laser beam is diffracted at least twice on the reflection grating corresponding to the moving target;

[0098] Step S400: Receive the diffracted measurement laser beams and perform pairwise interference on the multiple diffracted measurement laser beams; and

[0099] Step S500: The interferometric measurement laser beam is converted into an electrical signal by the photoelectric detection component, and the displacement of the moving target is measured based on the electrical signal.

[0100] It should be understood that the phrase "one embodiment" or "an embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of this application. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. It should be understood that in the various embodiments of this application, the sequence numbers of the above-described processes do not imply a sequential order of execution; the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application. The sequence numbers of the above-described embodiments are merely descriptive and do not represent the superiority or inferiority of the embodiments.

[0101] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0102] In the several embodiments provided in this application, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are merely illustrative. For example, the division of the group and functional components is only one functional division, and in actual implementation, there may be other division methods, such as: multiple units or components can be combined, or integrated into another system, or some features can be ignored or not executed. In addition, the coupling, direct coupling, or communication connection between the various components shown or discussed can be through some interfaces, and the indirect coupling or communication connection between devices or units can be electrical, mechanical, or other forms.

[0103] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units. They may be located in one place or distributed across multiple network units. Some or all of the units may be selected to achieve the purpose of this embodiment according to actual needs.

[0104] The above description is merely an embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An interferometer measurement system, characterized by, The application relates to a laser displacement measuring device, comprising: a laser emitting component for generating at least two mutually parallel incident laser beams; a polarization beam splitter prism arranged corresponding to the emitting end of the laser emitting component, the polarization beam splitter prism being used for splitting the incident laser beams into measurement laser beams with different propagation directions; a light folding component arranged in the outgoing direction of the polarization beam splitter prism, used for sequentially folding the measurement laser beams to a reflection grating so that the measurement laser beams are diffracted on the reflection grating at least twice; an interference component for receiving the diffracted measurement laser beams emitted by the light folding component so that the measurement laser beams interfere with each other; and a photoelectric detection component for receiving the interfered measurement laser beams emitted by the interference component and converting them into electrical signals, and measuring the displacement of a moving target according to the electrical signals; each of the incident laser beams forms two measurement laser beams propagating along a first direction and a second direction at the polarization beam splitter prism, and the light folding component comprises a back reflection assembly, a first light folding assembly and a second light folding assembly, the first light folding assembly and the second light folding assembly correspond to the measurement laser beams propagating along the first direction and the second direction respectively; wherein the measurement laser beams are folded to the reflection grating after passing through the light folding assembly, and return to the light folding assembly after being diffracted on the reflection grating, the measurement laser beams folded to the reflection grating by the light folding assembly are folded to the back reflection assembly, the measurement laser beams passing through the back reflection assembly are folded to the light folding assembly again and are folded to the reflection grating again, the measurement laser beams diffracted on the reflection grating again return to the light folding assembly again and are emitted to the interference component by the light folding assembly.

2. The system of claim 1, wherein, The reflection grating is installed on the moving target to be measured, and the reflection grating can move with the moving target in a target plane.

3. The system of claim 1, wherein, The light folding assembly comprises a 1 / 4 wave plate, a first light folding unit and a second light folding unit, the 1 / 4 wave plate is arranged in the outgoing direction of the measurement laser beams formed at the polarization beam splitter prism, and the first light folding unit and the second light folding unit are arranged side by side; the measurement laser beams are folded to the reflection grating after passing through the 1 / 4 wave plate and the first light folding unit and return to the back reflection assembly after passing through the polarization beam splitter prism again, the measurement laser beams emitted by the back reflection assembly in the reverse direction pass through the 1 / 4 wave plate and the second light folding unit again and are folded to the reflection grating again and return to the polarization beam splitter prism again, and the measurement laser beams passing through the polarization beam splitter prism again enter the interference component.

4. The system of claim 3, wherein, The light folding unit comprises at least two light folding elements, each of the light folding elements corresponds to one of the measurement laser beams, and the measurement laser beams folded to the reflection grating by the light folding elements.

5. The system of claim 3, wherein, Among the at least two beams of the measurement laser beams propagating in the same direction, one of the measurement laser beams is incident on the reflection grating at a first-order Littrow diffraction angle after passing through the light folding unit, and another of the measurement laser beams is incident on the reflection grating at a second-order Littrow diffraction angle after passing through the light folding unit.

6. The system of claim 1, wherein, The at least two beams of the incident laser beams are parallel to each other, and the at least two beams of the measurement laser beams are generated in the same direction after passing through the polarization beam splitter prism.

7. The system according to any one of claims 3 to 6, characterized in that, The first light folding unit and the second light folding unit are structurally identical, and each component in the first light folding unit and the second light folding unit is symmetrically distributed with the plane in which the polarization beam splitter prism is located as a symmetric plane.

8. The system according to any one of claims 1 to 6, characterized in that, The laser emitting component includes a laser light source, a non-polarization beam splitter prism, and a mirror. The non-polarization beam splitter prism is used to partially transmit and partially reflect the laser light emitted by the laser light source to the mirror. The laser light reflected to the mirror is reflected again by the mirror and exits in parallel with the laser light transmitted at the non-polarization beam splitter prism to form two beams of the incident laser beams which are parallel to each other; or The laser emitting component includes at least two laser light sources, and the two laser light sources can emit two beams of the incident laser beams which are parallel to each other.

9. The system according to any one of claims 1 to 6, characterized in that, A beam splitting device is further included and is arranged between the interference component and the photoelectric detection component. The beam splitting device is used to split the measurement laser beams after interference into multiple beams of the exit laser beams entering the photoelectric detection component.

10. The system of any one of claims 1 to 6, wherein, The incident laser beams generated by the laser emitting component are 45-degree polarized light. Two beams of the measurement laser beams generated after the 45-degree polarized light passes through the polarization beam splitter prism are P-polarized light and S-polarized light, respectively.

11. An interferometer measurement method, characterized by, The application is applied to the interferometer measurement system of any one of claims 1-10, comprising: obtaining at least two beams of the incident laser beams which are parallel to each other; dividing the incident laser beams into measurement laser beams which propagate in different directions; making the measurement laser beams diffract on the reflection grating for at least two times in sequence; interfering the measurement laser beams after diffraction two by two; and converting the measurement laser beams after interference into an electric signal, and measuring the displacement of the moving target according to the electric signal.

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