Heterodyne interferometer assembly, interferometer, and semiconductor device

Abstract

The application discloses a heterodyne interferometer mirror assembly, an interferometer and a semiconductor device, relates to the technical field of semiconductor technology, and aims to solve the technical problem of reducing interference signals formed by stray light in an interference optical path. The heterodyne interferometer mirror assembly comprises a first polarization splitting device and a second polarization splitting device. The first polarization splitting device comprises a first surface, a second surface, a third surface, a first splitting surface and a fourth surface. The first surface is opposite to the second surface, and the third surface is opposite to the fourth surface. The second polarization splitting device comprises a fifth surface, a sixth surface, a seventh surface, a second splitting surface and an eighth surface. The fifth surface is opposite to the sixth surface, and the seventh surface is opposite to the eighth surface. Any two of the first surface, the second surface, the third surface and the fourth surface are not parallel and not perpendicular, and / or any two of the fifth surface, the sixth surface, the seventh surface and the eighth surface are not parallel and not perpendicular.

Description

Technical Field

[0001] This application relates to the field of semiconductor technology, and mainly to a heterodyne interferometer assembly, an interferometer, and a semiconductor device. Background Technology

[0002] A heterodyne laser interferometer is a device for measuring speed and / or distance. Due to its high precision, large dynamic range, and strong anti-interference capabilities, it is widely used in semiconductor manufacturing equipment to meet the demands of precision measurement. The heterodyne laser interferometer emits two beams: one as the measurement beam and the other as the reference beam. The measurement beam illuminates the object being measured and is reflected by the object to an interferometer array. Movement of the object causes a Doppler frequency shift in the measurement beam. The interferometer array combines the reflected measurement beam with the reference beam to form a measurement beat frequency signal, which enters a detector. The detector processes the measurement beat frequency signal to calculate the displacement information of the object being measured.

[0003] With the continuous development of semiconductor manufacturing processes, the measurement accuracy requirements of interferometers in semiconductor manufacturing equipment are constantly increasing. However, the measurement accuracy of heterodyne interferometers is limited by optical periodic nonlinear error (PNL). Optical periodic nonlinear error mainly originates from interference signals formed by stray light in the interference optical path. Related technologies compensate for this error through algorithms after calibration. However, algorithm compensation increases the machine time consumption for error calibration, affecting equipment productivity. Furthermore, the effectiveness of algorithm compensation varies under different measurement conditions, affecting the robustness of measurement performance.

[0004] Therefore, how to reduce the interference signal formed by stray light in the interference optical path is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] This application discloses a heterodyne interferometer assembly, an interferometer, and a semiconductor device to solve the technical problem of how to reduce the interference signal formed by stray light in the interference optical path.

[0006] In a first aspect, this application provides a heterodyne interferometer assembly, comprising: a first polarization beam splitter and a second polarization beam splitter. The first polarization beam splitter includes a first surface, a second surface, a third surface, a first beam-splitting surface, and a fourth surface. The first surface is used to receive a first input beam, and the first beam-splitting surface is used to transmit the first input beam to form a first measurement beam and reflect the first input beam to form a first reference beam propagating towards the fourth surface. The first surface is opposite to the second surface, and the third surface is opposite to the fourth surface. The second polarization beam splitter includes a fifth surface, a sixth surface, a seventh surface, a second beam-splitting surface, and an eighth surface. The fifth surface is used to receive a second input beam, and the second beam-splitting surface is used to transmit the second input beam to form a second measurement beam and reflect the second input beam to form a second reference beam propagating towards the eighth surface. The fifth surface is opposite to the sixth surface, and the seventh and eighth surfaces are opposite to each other. The fourth and eighth surfaces are located between the third and seventh surfaces. Any two of the first, second, third, and fourth surfaces are neither parallel nor perpendicular, and / or any two of the fifth, sixth, seventh, and eighth surfaces are neither parallel nor perpendicular.

[0007] In this embodiment, the surfaces of the first polarization beam splitter and the second polarization beam splitter are neither parallel nor perpendicular. When the first measurement beam and the first reference beam are transmitted through the respective surfaces, the generated reflected stray light cannot propagate along the incident path, thereby reducing the interference of reflected stray light on the first and second input beams and improving the measurement accuracy.

[0008] In some possible embodiments, the edge of the second surface away from the sixth surface is further away from the first surface than the edge of the second surface near the sixth surface, and the edge of the sixth surface away from the second surface is further away from the fifth surface than the edge of the sixth surface near the second surface. A first preset angle α exists between the extending direction of the second surface away from the sixth surface and the extending direction of the sixth surface near the second surface, where the first preset angle α is greater than 0° and less than 90°. This ensures that the second and sixth surfaces are not in the same plane, and the direction of the reflected stray light generated when the first measurement beam is transmitted through the second surface differs from the angle of the second reference beam reflected by the second polarization beam splitter. This reduces the effective interference between the stray light reflected by the first measurement beam and the second reference beam, thus reducing the generation of interference signals.

[0009] In some possible embodiments, the first beam-splitting surface is deflected from a first reference position by a second preset angle β. The first reference position is the position of the inclined plane in the first polarizing beam splitter with an angle of -45° to the first surface when the first polarizing beam splitter is replaced with a first polarizing beam splitter with a rectangular cross-section. The second beam-splitting surface is deflected from a second reference position by a third preset angle γ. The second reference position is the position of the inclined plane in the second polarizing beam splitter with an angle of 45° to the fifth surface when the second polarizing beam splitter is replaced with a second polarizing beam splitter with a square cross-section; the counterclockwise direction is the positive direction of the angle, and the clockwise direction is the negative direction of the angle. The product of the first preset angle α and the refractive index is equal to twice the difference between the second preset angle β and the third preset angle γ; the refractive index is the difference between 1 and the reciprocal of the refractive index of the first polarizing beam splitter.

[0010] In this way, the first preset angle α between the second surface and the sixth surface, the second preset angle β from which the first beam splitter is deflected from the first reference position, and the third preset angle γ from which the second beam splitter is deflected satisfy the constraint conditions, so that the first measuring beam and the second reference beam can be combined to form the first interference beam, and the first reference beam and the second measuring beam can be combined to form the second interference beam.

[0011] In some possible embodiments, at least one optical isolator is also included, with an optical isolator disposed on the outer side of at least one of the first, third, fifth, and seventh surfaces. This optical isolator can block stray light from outside the heterodyne interferometer assembly from transmitting through at least one of the first, third, fifth, and seventh surfaces to the heterodyne interferometer assembly, thereby preventing it from affecting the detection results and improving the accuracy of the detection.

[0012] In some possible embodiments, at least one optical isolator includes a first isolator disposed on a first surface, the first isolator including a first linear polarizer and a first quarter-wave plate, the first quarter-wave plate being located on the side of the first linear polarizer away from the first surface, and / or at least one optical isolator includes a second isolator disposed on a fifth surface, the second isolator including a second linear polarizer and a second quarter-wave plate, the second quarter-wave plate being located on the side of the second linear polarizer away from the fifth surface, and / or at least one optical isolator includes a third isolator disposed on a third surface, the third isolator including a third linear polarizer and a third quarter-wave plate, the third quarter-wave plate being located on the side of the third linear polarizer away from the third surface, and / or at least one optical isolator includes a fourth isolator disposed on a seventh surface, the fourth isolator including a fourth linear polarizer and a fourth quarter-wave plate, the fourth quarter-wave plate being located on the side of the fourth linear polarizer away from the seventh surface.

[0013] This combination of a quarter-wave plate and a linear polarizer serves as an optical isolator. Using passive components as the optical isolator eliminates the need for an external magnetic field, reducing the consumption of the heterodyne interferometer assembly. Furthermore, the optical isolator has a simple structure and low manufacturing cost, which helps to reduce the manufacturing cost of the heterodyne interferometer assembly.

[0014] In some possible embodiments, each optical isolator includes a linear polarizer and a quarter-wave plate, wherein the transmission direction of the linear polarizer in each optical isolator is neither parallel nor perpendicular to the fast axis direction of the first quarter-wave plate. This allows the optical isolator to isolate more polarized light from the heterodyne interferometer assembly.

[0015] In some possible embodiments, the transmission directions of the first and third linear polarizers are neither parallel nor perpendicular to the transmission direction of the first polarizing beam splitter; and / or the transmission directions of the second and fourth linear polarizers are neither parallel nor perpendicular to the transmission direction of the second polarizing beam splitter.

[0016] In this way, after the beam is transmitted from the polarization beam splitter to the optical isolator, the polarization direction of the reflected stray light is different from that of the original beam, thereby reducing the interference of the reflected stray light on the original beam and thus improving the accuracy of detection.

[0017] In some possible embodiments, the heterodyne interferometer assembly further includes: a half-wave plate located between the first polarization beam splitter and the second polarization beam splitter, wherein the fast axis of the half-wave plate is neither parallel to nor perpendicular to the transmission direction of the first polarization beam splitter, and the fast axis of the half-wave plate is neither parallel to nor perpendicular to the transmission direction of the second polarization beam splitter; and / or the heterodyne interferometer assembly further includes: a fifth quarter-wave plate disposed on the second surface, wherein the fast axis of the fifth quarter-wave plate is neither parallel to nor perpendicular to the transmission direction of the first polarization beam splitter; and / or the heterodyne interferometer assembly further includes: a sixth quarter-wave plate disposed on the sixth surface, wherein the fast axis of the sixth quarter-wave plate is neither parallel to nor perpendicular to the transmission direction of the second polarization beam splitter.

[0018] In this way, when the beam is transmitted from the polarization beam splitter to the half-wave plate, the fifth quarter-wave plate, or the sixth quarter-wave plate, the polarization direction can be changed, thereby allowing the beam to propagate in the heterodyne interferometer assembly.

[0019] Secondly, this application provides an interferometer, including a first light source, a second light source, a measurement detector, a reference detector, and a heterodyne interferometer assembly in any of the above embodiments. The first light source is used to emit a first input beam to a first polarization beam splitter of the heterodyne interferometer assembly. The second light source is used to emit a second input beam to a second polarization beam splitter of the heterodyne interferometer assembly. The measurement detector is opposite to a third surface of the first polarization beam splitter and is used to collect a first interference beam formed by combining the first measurement beam and the second reference beam. The reference detector is opposite to a seventh surface of the second polarization beam splitter and is used to collect a second interference beam formed by combining the first reference beam and the second measurement beam.

[0020] In this way, the heterodyne interferometer assembly is less affected by stray light, the measurement detector can collect a more accurate first interference beam, the reference detector can collect a more accurate second interference beam, and thus more accurate measurement results can be obtained.

[0021] Thirdly, this application provides a semiconductor device, including a stage and an interferometer as described in any of the above embodiments, wherein the stage is used to move a wafer. The detection port of the interferometer faces the stage and is used to detect the moving distance of the stage.

[0022] This allows the interferometer to measure the movement distance of the stage more accurately, thus making the stage position more precise and improving the wafer processing accuracy. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the structure of a semiconductor device provided in one embodiment of this application; Figure 2 This is a schematic diagram of the structure of an interferometer provided in one embodiment of the related art; Figure 3 This is a schematic diagram of the structure of a heterodyne interferometer assembly provided in one embodiment of this application; Figure 4 for Figure 3 Schematic diagram of the operation of the heterodyne interferometer assembly; Figure 5 For several types of stray light in Figure 3 A schematic diagram of propagation in the heterodyne interferometer assembly; Figure 6 for Figure 3 Schematic diagram of the deflection of each plane in the heterodyne interferometer assembly; Figure 7 for Figure 3 A schematic diagram of the optical isolator in the diagram; Figure 8 for Figure 3 A schematic diagram of the propagation of the first and second input beams in the heterodyne interferometer assembly; Figure 9 The spectrum diagrams of the first and second interference signals under static and dynamic conditions are shown. Figure 10 This is a schematic diagram of the structure of an interferometer provided in one embodiment of this application.

[0025] Explanation of reference numerals in the attached figures: 1-Exposure projection system; 2-Measuring frame; 3-Base; 4-Mobile control console; 5-Vibration isolation mechanism; 6-Interferometer; 61-First light source; 62-Second light source; 63-Measuring detector; 64-Reference detector; 65-Detection window; 7-Stage; 8-Object under test; 100-Heterodyne Interferometer Assembly; 110 - First polarization beam splitter; 111 - First surface; 112 - Second surface; 113 - Third surface; 114 - Fourth surface; 115 - First beam splitting surface; 120 - Second polarization beam splitter; 121 - Fifth surface; 122 - Sixth surface; 123 - Seventh surface; 124 - Eighth surface; 125 - Second beam splitting surface; 130 - Half-wave plate; 140 - Optical isolator; 1401 - Linear polarizer; 1402 - Quarter-wave plate; 141 - First isolator ; 1411 - First linear polarizer; 1412 - First quarter-wave plate; 142 - Second isolator; 1421 - Second linear polarizer; 1422 - Second quarter-wave plate; 143 - Third isolator; 1431 - Third linear polarizer; 1432 - Third quarter-wave plate; 144 - Fourth isolator; 1441 - Fourth linear polarizer; 1442 - Fourth quarter-wave plate; 150 - Fifth quarter-wave plate; 160 - Sixth quarter-wave plate; 170 - Mirror; 01-Light source; 02-Detector; 03-Object under test; 04-Heterodyne interferometer assembly. Detailed Implementation

[0026] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] 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. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0028] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "connected" and "linked" should be interpreted broadly, for example, they can refer to a fixed connection, a detachable connection, or an integral connection. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0029] In the embodiments of this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0030] In the description of this specification, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0031] The heterodyne interference mirror assembly 100 provided in this application can be used in semiconductor devices. Figure 1 This is a schematic diagram of the structure of a semiconductor device provided in one embodiment of this application. Figure 1 As shown, the semiconductor equipment includes an exposure projection system 1, a measurement frame 2, a base 3, a moving control console 4, a stage 7, and an interferometer 6. The exposure projection system 1 is mounted on the measurement frame 2. The base 3 is located below the exposure projection system 1 and is connected to the measurement frame 2 via a vibration isolation system. The vibration isolation system reduces the transmission of vibration from the base 3 to the measurement frame 2. The moving control console 4 is mounted on the upper side, and the stage 7 is located above the moving control console 4. The stage 7 is used to hold the wafer, and the moving control console 4 controls the stage 7 to move below the exposure projection system 1, allowing the exposure projection system 1 to expose the wafer on the stage 7. The interferometer 6 is connected to the measurement frame 2 and faces the stage 7, used to measure the moving distance of the stage 7. The moving control console 4 is electrically connected to the interferometer 6 and controls the movement of the stage 7 based on the measurement results of the interferometer 6, thereby making the movement position of the stage 7 more precise. As wafer processing precision reaches the nanometer level, the measurement precision requirements for the interferometer 6 will reach the sub-nanometer level.

[0032] Optionally, a vibration isolation mechanism 5 is provided between the base 3 and the measuring frame 2. The vibration isolation mechanism 5 is used to isolate the vibration of the base 3 and reduce the propagation of the vibration to the measuring frame 2, thereby improving the accuracy of the measurement.

[0033] Figure 2 This is a schematic diagram of the structure of an interferometer in one embodiment of the related art. For example... Figure 2 As shown, the interferometer includes a light source 01, a heterodyne interferometer assembly 04, and a detector 02. The heterodyne interferometer assembly 04 is a crucial component of the interferometer, significantly impacting its measurement accuracy. Figure 2 As shown, light source 01 emits a first input beam f1 and a second input beam f2. Figure 2 In the illustrated embodiment, the first input beam f1 and the second input beam f2 are combined into a single beam for emission. Optionally, the frequency of the first input beam f1 is lower than the frequency of the second input beam f2. The heterodyne interferometer assembly 04 separates the first input beam f1 and the second input beam f2, forming separate first input beam f1 and second input beam f2. The second input beam f2 propagates towards the detector 02. The first input beam f1 propagates towards the object under test 03 and is reflected by the object under test 03. The heterodyne interferometer assembly 04 propagates the reflected first input beam f1 back towards the detector 02. The second input beam f2 and the first input beam f1 interfere with each other. The detector 02 calculates the velocity of the object under test 03 based on the interfering second input beam f2 and first input beam f1.

[0034] The first input beam f1 and the second input beam f2 will generate two types of stray light. The presence of stray light will interfere with the first input beam f1 and / or the second input beam f2, affecting the accuracy of the measurement results. One type of stray light is caused by the cross-over of the first input beam f1 and the second input beam f2. During the separation process of the heterodyne interferometer assembly 04, it is impossible to completely separate the two beams with different frequencies, thus generating stray light with cross-over of the two beams with different frequencies. The other type of stray light is generated when the first input beam f1 and the second input beam f2 are transmitted through the heterodyne interferometer assembly 04. When the beams are transmitted through the component interfaces in the heterodyne interferometer assembly 04, since full transmission is not possible, there will be a certain residual reflectivity. That is, the first input beam f1 and the second input beam f2 will generate unwanted reflected light in the heterodyne interferometer assembly 04. These reflected light rays will interfere with the first input beam f1 and the second input beam f2, affecting the accuracy of the measurement.

[0035] It should be noted that the interferometer provided in this application is not limited to use in semiconductor equipment, but may be used in medical equipment, machine tools, aerospace equipment, etc.

[0036] Figure 3 This is a schematic diagram of the structure of a heterodyne interferometer assembly 100 provided in one embodiment of this application; Figure 4 for Figure 3 Schematic diagram of the operation of the heterodyne interferometer assembly 100; Figure 5 For several types of stray light in Figure 3 A schematic diagram of propagation in the heterodyne interferometer assembly 100.

[0037] like Figure 3 and Figure 4 As shown, this application provides a heterodyne interferometer assembly 100, including: a first polarization beam splitter 110 and a second polarization beam splitter 120. The first polarization beam splitter 110 includes a first surface 111, a second surface 112, a third surface 113, a first beam splitting surface 115, and a fourth surface 114. The first surface 111 is used to incident a first input beam f1, the first beam splitting surface 115 is used to transmit the first input beam f1 to form a first measurement beam f11, and reflect the first input beam f1 to form a first reference beam f12 that propagates toward the second polarization beam splitter 120. The first surface 111 is opposite to the second surface 112, and the third surface 113 is opposite to the fourth surface 114.

[0038] The second polarization beam splitter 120 includes a fifth surface 121, a sixth surface 122, a seventh surface 123, a second beam splitting surface 125, and an eighth surface 124 for incident on the second input beam f2. The fifth surface 121 is used to incident on the second input beam f2, and the second beam splitting surface 125 is used to transmit the second input beam f2 to form a second measurement beam f21 and reflect the second input beam f2 to form a second reference beam f22 that propagates in the direction of the first polarization beam splitter 110. The fifth surface 121 is opposite to the sixth surface 122, and the seventh surface 123 and the eighth surface 124 are opposite to each other. The fourth surface 114 and the eighth surface 124 are located between the third surface 113 and the seventh surface 123.

[0039] Any two of the first surface 111, the second surface 112, the third surface 113, and the fourth surface 114 are not parallel and not perpendicular, and / or any two of the fifth surface 121, the sixth surface 122, the seventh surface 123, and the eighth surface 124 are not parallel and not perpendicular.

[0040] like Figure 3 and Figure 4As shown, the first input beam f1 and the second input beam f2 enter the first polarization beam splitter 110 and the second polarization beam splitter 120, respectively. The fourth surface 114 of the first polarization beam splitter 110 and the eighth surface 124 of the second polarization beam splitter 120 are opposite to and connected. The third surface 113 of the first polarization beam splitter 110 is opposite to the measurement detector, and the seventh surface 123 of the second polarization beam splitter 120 is opposite to the reference detector. The first surface 111 of the first polarization beam splitter 110 and the fifth surface 121 of the second polarization beam splitter 120 are located on the same side. The second surface 112 of the first polarization beam splitter 110 and the sixth surface 122 of the second polarization beam splitter 120 are located on the same side. The second surface 112 of the first polarization beam splitter 110 can be opposite to the object under test 8, and the sixth surface 122 of the second polarization beam splitter 120 can be opposite to the reflector 170.

[0041] like Figure 4 As shown, the first input beam f1 passes through the first surface 111 and enters the first polarization beam splitter 110. A portion of the first input beam f1 is transmitted through the first beam splitter 115 to form the first measurement beam f11. The first measurement beam f11 propagates in the direction of the third surface 113 and passes through the third surface 113 towards the object 8 to be measured. Figure 1 In the illustrated embodiment, the beam propagates from the support stage 7. The object under test 8 reflects the first measurement beam f11 back to the first polarization beam splitter 110, and the first beam splitter 115 reflects the reflected first measurement beam f11 towards the measurement detector. Another part of the first input beam f1 is reflected by the first beam splitter 115 to form the first reference beam f12, and the first reference beam f12 passes through the second polarization beam splitter 120 and propagates towards the reference detector.

[0042] Optional, such as Figure 3 and Figure 4 As shown, the heterodyne interferometer assembly 100 also includes a reflector 170 connected to the second polarization beam splitter 120, and the reflector 170 is opposite to the sixth surface 122.

[0043] like Figure 4As shown, the second input beam f2 passes through the fifth surface 121 and enters the second polarization beam splitter 120. A portion of the second input beam f2 passes through the second beam splitter 125 to form the second measurement beam f21. The second measurement beam f21 propagates in the direction of the sixth surface 122 and is reflected back to the second polarization beam splitter 120 by the reflector 170. The second beam splitter 125 reflects the reflected second measurement beam f21 towards the reference detector. The second measurement beam f21 interferes with the first reference beam f12 to form a second interference beam, which is received by the reference detector. Another portion of the second input beam f2 is reflected by the second beam splitter 125 to form the second reference beam f22. The second reference beam f22 passes through the first polarization beam splitter 110 and propagates towards the measurement detector. The second reference beam f22 interferes with the first measurement beam f11 to form a first interference beam, which is received by the measurement detector. During the measurement process, the movement of the object under test 8 will cause a Doppler frequency shift in the first measurement beam f11. After processing, the displacement of the support stage 7 can be obtained from the first and second interference beams.

[0044] Since the first input beam f1 and the second input beam f2 enter the first polarization beam splitter 110 and the second polarization beam splitter 120 respectively, the optical paths of the first input beam f1 and the second input beam f2 are isolated from each other. The reflected light of one of them cannot propagate along the optical path of the other, which reduces the cross-over and superposition of the first input beam f1 and the second input beam f2, thereby reducing the generation of the first type of stray light.

[0045] When the first input beam f1 and the second input beam f2 are transmitted through a certain surface, they will generate reflected light. For example, when the first measurement beam f11 passes through the second surface 112 of the first polarization beam splitter 110, since total transmission will not occur, the second surface 112 will cause the first measurement beam f11 to form reflected light that propagates into the first polarization beam splitter 110. This reflected light forms the second type of stray light mentioned above. In this embodiment, any two of the first surfaces 111 to the fourth surfaces 114 of the first polarization beam splitter 110 are neither parallel nor perpendicular, and any two of the fifth surfaces 121 to the eighth surfaces 124 of the second polarization beam splitter 120 are neither parallel nor perpendicular. "Neither parallel nor perpendicular" means that the two surfaces are not parallel, and the angle between the two surfaces is not 90°. For example, if the first input beam f1 is incident perpendicularly from the first surface 111, since the first surface 111 and the second surface 112 are not parallel, the incident angle of the first measurement beam f11 on the second surface 112 is not 90°. Therefore, the stray light generated by the reflection of the first measurement beam f11 on the second surface 112 will not return along the original path. The included angle between the first surface 111 and the eighth surface 124 can be set as needed and is not limited here.

[0046] like Figure 5As shown, (a) represents the main propagation paths of the first input beam f1 and the second input beam f2 in the heterodyne interferometer assembly 100; (b) represents the stray light generated by the virtual reflection of the first measurement beam f11 when it passes through the second surface 112 of the first polarization beam splitter 110; (c) represents the stray light generated by the virtual reflection of the first reference beam f12 when it passes through the fifth surface 121 of the second polarization beam splitter 120; and (d) represents the stray light generated by the virtual reflection of the second reference beam f22 when it passes through the third surface 113 of the first polarization beam splitter 110. Since any two of the first surfaces 111 to the fourth surface 114 and the fifth surfaces 121 to the eighth surface 124 are neither parallel nor perpendicular, the stray light will not propagate back along the original optical path, thereby reducing the interference of stray light on the original beam, reducing the interference of the second type of stray light on the measurement results, and improving the measurement accuracy.

[0047] Optionally, the first polarizing beam splitter 110 is a first polarizing beam splitter prism, and the second polarizing beam splitter 120 is a second polarizing beam splitter prism. Of course, the first polarizing beam splitter 110 and the second polarizing beam splitter 120 can also be other optical devices, which are not limited here.

[0048] In some possible embodiments, the edge of the second surface 112 away from the sixth surface 122 is further away from the first surface 111 than the edge of the second surface 112 near the sixth surface 122, and the edge of the sixth surface 122 away from the second surface 112 is further away from the fifth surface 121 than the edge of the sixth surface 122 near the second surface 122. A first preset angle α exists between the extending direction of the second surface 112 away from the sixth surface 122 and the extending direction of the sixth surface 122 near the second surface 112, where the first preset angle α is greater than 0° and less than 90°. Thus, the second surface 112 and the sixth surface 122 are not in the same plane. The direction of the reflected stray light generated when the first measurement beam f11 is transmitted from the second surface 112 is different from the angle at which the second reference beam f22 reflected back to the second polarization beam splitter 120 is changed, reducing the interference of the reflected stray light of the first measurement beam f11 on the second reference beam f22.

[0049] Figure 6 for Figure 3 A schematic diagram of the deflection of each plane of the heterodyne interferometer assembly 100. Figure 6 Each surface is in a reference position, which is the position during the first polarization beam splitter 110 and the second polarization beam splitter. Figure 6 The cross-sections shown are all rectangular (e.g., square), with the first beam-splitting surface 115 and the second beam-splitting surface 125 being the diagonals of the two rectangles, respectively. Of course, in other embodiments, the reference position can be set as needed, and is not limited here. Figure 6In the illustrated embodiment, the second surface 112 is deflected counterclockwise about its side closest to the sixth surface 122, thereby generating a first preset angle α. Inside the heterodyne interferometer assembly 100, the angle between the second surface 112 and the sixth surface 122 is greater than 180°. Figure 5 In (b), the first measurement beam f11, after being reflected by the second surface 112, typically propagates in a direction away from the second polarization beam splitter 120. The reflected stray light is reflected by the first beam splitter 115 in the direction of the third surface 113, reducing the propagation of stray light towards the second polarization beam splitter 120. Correspondingly, this also reduces the propagation of stray light generated by the second measurement beam f21 after being reflected by the sixth surface 122 towards the first polarization beam splitter 110.

[0050] Optionally, the first preset angle α is greater than or equal to 0° and less than 45°. Since the second surface 112 is opposite to the object under test 8, selecting a smaller range for the first preset angle α facilitates the arrangement of the positional relationship between the first polarizing beam splitter 110 and the object under test 8. Of course, the first preset angle α can be any angle within the range of greater than 0° and less than 90°, and is not limited here.

[0051] In this embodiment, a first preset angle α exists between the second surface 112 and the sixth surface 122. This angle causes the second surface 112 to direct stray light away from the second polarization beam splitter 120, reducing the amount of stray light entering the second polarization beam splitter 120 and thus reducing the interference of stray light on the first input beam f1 and the second input beam f2 of the second polarization beam splitter 120. Similarly, the interference of the sixth surface 122 on the first input beam f1 and the second input beam f2 of the first polarization beam splitter 110 is also reduced, improving measurement accuracy.

[0052] In some possible embodiments, the first beam-splitting surface 115 is deflected from a first reference position by a second preset angle β. The first reference position is, when the first polarizing beam splitter 110 is replaced with a first polarizing beam splitter 110 with a rectangular cross-section, the first polarizing beam splitter 110 is inclined towards the fourth surface 114 to a 45° angle with the first surface 111. The second beam-splitting surface 125 is deflected from a second reference position by a third preset angle γ. The second reference position is, when the second polarizing beam splitter 120 is replaced with a second polarizing beam splitter 120 with a square cross-section, the second polarizing beam splitter 120 is inclined towards the eighth surface 124 to a 45° angle with the fifth surface 121. The product of the first preset angle α and the refractive index is equal to twice the difference between the second preset angle β and the third preset angle γ; the refractive index is the difference between 1 and the reciprocal of the refractive index of the first polarizing beam splitter 110.

[0053] During the measurement process, the directions of the first input beam f1 and the second input beam f2 need to be adjusted so that the first measuring beam f11 is parallel to the second reference beam f22, causing them to interfere and enter the measuring detector 63. Similarly, the first reference beam f12 is made parallel to the second measuring beam f21, causing them to interfere and enter the reference detector 64. Furthermore, the first measuring beam f11 is made perpendicular to the surface of the object 8 being measured, so that the object 8 can reflect the first measuring beam f11 back to the first polarization beam splitter 110. Figure 6 In this configuration, the first surface 111 to the eighth surface 124, as well as the first beam-splitting surface 115 and the second beam-splitting surface 125, are all located at a reference position. The second surface 112 is parallel to the surface of the object under test 8. The second surface 112 is deflected by a first preset angle α, ensuring that the first measurement beam f11 between the surface of the object under test 8 and the second surface 112 is perpendicular to the surface of the object under test 8. The first measurement beam f11 between the second surface 112 and the first beam-splitting surface 115 will be deflected counterclockwise by f(n)α, where the coefficient f(n) is a function of the refractive index n of the mirror group, and the coefficient f(n) can be calculated according to the law of refraction. Specifically, the coefficient f(n) can be approximated as f(n) = (1 - 1 / n), where in this embodiment, n is the refractive index of the first polarizing beam-splitting device 110.

[0054] The first reference position is Figure 6 The first beam-splitting surface 115 is positioned such that it is inclined toward the fourth surface 114, meaning that the distance between the first beam-splitting surface 115 and the fourth beam-splitting surface gradually decreases in the direction away from the first surface 111. Figure 6 The angle between the first beam-splitting surface 115 and the first surface 111 is 45°. The second reference position is... Figure 6 The second beam-splitting surface 125 is positioned such that it is inclined toward the eighth surface 124, meaning that the distance between the second beam-splitting surface 125 and the eighth beam-splitting surface gradually decreases in the direction away from the fifth surface 121. Figure 6 The angle between the second beam-splitting surface 125 and the fifth surface 121 is 45°.

[0055] In some embodiments, to reduce interference from the second type of stray light, the first beam-splitting surface 115 is deflected counterclockwise by a second preset angle β from the first reference position. The first beam-splitting surface 115 also serves to reflect the first measurement light reflected back from the object under test 8 to the measurement detector 63. The first beam-splitting surface 115, as a reflecting surface, is deflected counterclockwise by the second preset angle β, and the first measurement beam f11 propagating towards the measurement detector 63 is deflected counterclockwise by an angle of 2β. Combined with the counterclockwise deflection f(n)α of the first reference light between the first beam-splitting surface 115 and the second surface 112, the first measurement beam f11 propagating towards the measurement detector 63 after reflection is deflected clockwise by an angle of f(n)α. The two deflection angles are accumulated to a counterclockwise deflection of 2β - f(n)α.

[0056] In some embodiments, to reduce interference from the second type of stray light, the second beam-splitting surface 125 is deflected counterclockwise by a third preset angle γ from the second reference position. The second measurement beam f21 between the second beam-splitting surface 125 and the seventh surface 123 needs to be deflected counterclockwise by f(n)α-2β+4γ. To ensure that the second measurement beam f21 between the second beam-splitting surface 125 and the seventh surface 123 is parallel to the first reference beam f12 after optical path alignment, it is required that 2β-f(n)α=f(n)α-2β+4γ be satisfied. Therefore, the relative angular orientation between the second surface 112, the sixth surface 122, the first beam-splitting surface 115, and the second beam-splitting surface 125 must satisfy the constraint condition: f(n)α-2(β-γ)=0.

[0057] In one embodiment of this application, the first preset angle is 1°, the second preset angle is 0°, and the third preset angle is -0.1568° (the second beam-splitting surface 125 is deflected 0.1568° clockwise from the second reference position). The seventh surface 123 is deflected 1° clockwise, the third surface 113 is deflected 1° clockwise, the fifth surface 121 is deflected 1.5° counterclockwise, the first surface 111 is deflected 1.5° counterclockwise, and the fourth surface 114 and the eighth surface 124 are deflected 0°. This embodiment can reduce the interference of reflected stray light generated during the transmission of the first measurement beam f11, the first reference beam f12, the second measurement beam f21, and the second reference beam f22 on the measurement results, and can enable the first measurement beam f11 and the second reference beam f22 to be combined to form a first interference beam, and the first reference beam f12 and the second measurement beam f21 to be combined to form a second interference beam. In other embodiments, the first surface 111 to the eighth surface 124 may adopt other deflection angles, which are not limited here.

[0058] In this embodiment, the first preset angle α between the second surface 112 and the sixth surface 122, the second preset angle β from which the first beam splitting surface 115 deflects from the first reference position, and the third preset angle γ from which the second beam splitting surface 125 deflects satisfy the constraint conditions, so that the first measuring beam f11 and the second reference beam f22 can be combined to form the first interference beam, and the first reference beam f12 and the second measuring beam f21 can be combined to form the second interference beam.

[0059] like Figure 3 and Figure 4As shown, the first surface 111, the third surface 113, the fifth surface 121, and the seventh surface 123 not only allow the first input beam f1 or the second input beam f2 to pass through, but also allow external light to enter the first polarization beam splitter 110 and the second polarization beam splitter 120. External light can affect the first input beam f1 and the second input beam f2, thereby affecting the accuracy of the measurement. In some possible embodiments, the heterodyne interferometer assembly 100 further includes at least one optical isolator 140, with the optical isolator 140 located on the outer side of at least one of the first surface 111, the third surface 113, the fifth surface 121, and the seventh surface 123.

[0060] exist Figure 3 In the illustrated embodiment, optical isolators 140 are provided on the first surface 111, the third surface 113, the fifth surface 121, and the seventh surface 123. Specifically, the optical isolator 140 on the first surface 111 allows the first input beam f1 to enter the first polarization beam splitter 110, but prevents stray light exiting from the first surface 111 of the first polarization beam splitter 110 from re-entering the first polarization beam splitter 110 after reflection by the external reflecting surface. The optical isolator 140 on the fifth surface 121 allows the second input beam f2 to enter the second polarization beam splitter 120, but prevents stray light exiting from the fifth surface 121 of the second polarization beam splitter 120 from re-entering the second polarization beam splitter 120 after reflection by the external reflecting surface. The optical isolator 140 on the third surface 113 blocks light emanating from the third surface 113 from re-entering the first polarization beam splitter 110 after reflection by the external reflecting surface. The optical isolator 140 on the seventh surface 123 is used to block light emitted from the seventh surface 123 from re-entering the second polarization beam splitter 120 after being reflected by the external reflecting surface. The optical isolator 140 can be connected to the surface of the polarization beam splitter by means of bonding or other methods. Of course, the optical isolator 140 can also be provided on the outside of at least one of the first surface 111, the third surface 113, the fifth surface 121, and the seventh surface 123 as needed, and this is not limited here.

[0061] In this embodiment, the heterodyne interferometer assembly 100 can block external stray light from being transmitted to the heterodyne interferometer assembly 100 from at least one of the first surface 111, the third surface 113, the fifth surface 121, and the seventh surface 123 through the optical isolator 140, thereby reducing the impact of external stray light on the detection results and improving the accuracy of the detection.

[0062] In some possible embodiments, the optical isolator 140 includes a linear polarizer 1401 and a quarter-wave plate 1402, wherein the transmission direction of the linear polarizer 1401 of each optical isolator 140 is neither parallel nor perpendicular to the fast axis direction of the quarter-wave plate 1402.

[0063] Figure 7 for Figure 3 A schematic diagram of the structure of the optical isolator 140. Figure 7 In (a), the linear polarizer 1401 and the quarter-wave plate 1402 are distributed along the thickness direction of the linear polarizer 1401. Figure 7 In (b), the transmission direction n1 of the linear polarizer 1401 and the fast axis direction n2 of the quarter-wave plate 1402 have an included angle, which is not equal to 0° and 90°. For example, Figure 7 In (b), the transmission direction n1 of the linear polarizer 1401 is 90° and the fast axis direction n2 of the quarter-wave plate 1402 is 45°. Of course, the transmission direction n1 of the linear polarizer 1401 and the fast axis direction n2 of the quarter-wave plate 1402 can also be other angles, which are not limited here. Figure 7 In (c), 45° linearly polarized light passes through linear polarizer 1401 to form S-polarized light (i.e., 90° linearly polarized light). The S-polarized light then passes through quarter-wave plate 1402 to form right-hand circularly polarized light. After reflection, the right-hand circularly polarized light forms left-hand circularly polarized light. The left-hand circularly polarized light then passes through quarter-wave plate 1402 to form P-polarized light (i.e., 0° linearly polarized light). The P-polarized light is perpendicular to the transmission direction of linear polarizer 1401 and therefore cannot pass through it, thus blocking the left-hand circularly polarized light. In other embodiments, the transmission direction of linear polarizer 1401 and the fast axis of quarter-wave plate 1402 can be at other angles to reduce external stray light interference; this is not limited here. Of course, the optical isolator 140 can also adopt other structures; this is not limited here.

[0064] In this embodiment, the quarter-wave plate 1402 and the linear polarizer 1401 are combined to form an optical isolator 140. Using passive components as optical isolators 140 eliminates the need to introduce external magnetic fields, reducing the consumption of the heterodyne interferometer assembly 100. Moreover, the optical isolator 140 has a simple structure and low manufacturing cost, which helps to reduce the manufacturing cost of the heterodyne interferometer assembly 100.

[0065] In some possible embodiments, at least one optical isolator 140 includes a first isolator 141 disposed on a first surface 111, the first isolator 141 including a first linear polarizer 1411 and a first quarter-wave plate 1412, the first quarter-wave plate 1412 being located on the side of the first linear polarizer 1411 away from the first surface 111, and / or at least one optical isolator 140 includes a second isolator 142 disposed on a fifth surface 121, the second isolator 142 including a second linear polarizer 1421 and a second quarter-wave plate 1422, the second quarter-wave plate 1422 being located on the side of the second linear polarizer 1421 away from the fifth surface 121. On one side, and / or at least one optical isolator 140 includes a third isolator 143 disposed on the third surface 113, the third isolator 143 including a third linear polarizer 1431 and a third quarter-wave plate 1432, the third quarter-wave plate 1432 being located on the side of the third linear polarizer 1431 away from the third surface 113, and / or at least one optical isolator 140 includes a fourth isolator 144 disposed on the seventh surface 123, the fourth isolator 144 including a fourth linear polarizer 1441 and a fourth quarter-wave plate 1442, the fourth quarter-wave plate 1442 being located on the side of the fourth linear polarizer 1441 away from the seventh surface 123.

[0066] Figure 8 for Figure 3 A schematic diagram showing the propagation of the first input beam f1 and the second input beam f2 in the heterodyne interferometer assembly 100. (See diagram below.) Figure 8 As shown, the first isolator 141 and the third isolator 143 are used to block light from entering the first polarization beam splitter 110 through the first surface 111 and the third surface 113, and the second isolator 142 and the fourth isolator 144 are used to block light from entering the second polarization beam splitter 120 through the fifth surface 121 and the seventh surface 123.

[0067] In this embodiment, isolators are provided on the first surface 111, the third surface 113, the fifth surface 121 and the seventh surface 123. The distribution of the linear polarizer 1401 and the quarter-wave plate 1402 in the isolators can block the light outside the heterodyne interferometer assembly 100, reducing the impact of stray light on the measurement accuracy.

[0068] In some possible embodiments, the transmission directions of the first linear polarizer 1411 and the third linear polarizer 1431 are neither parallel nor perpendicular to the transmission direction of the first polarizing beam splitter 110; and / or the transmission directions of the second linear polarizer 1421 and the fourth linear polarizer 1441 are neither parallel nor perpendicular to the transmission direction of the second polarizing beam splitter 120.

[0069] Optionally, the transmission directions of the first linear polarizer 1411 and the third linear polarizer 1431 are both at 45° to the transmission direction of the first polarizing beam splitter 110. This ensures that the light intensities of the first measurement beam f11 generated by the first input beam f1 transmitted through the first beam splitter 115 and the first reference beam f12 generated by the reflection from the first beam splitter 115 are approximately equal. This increases the interference signal intensity, thereby reducing the ratio of interference signal intensity to interference signal intensity and helping to reduce the periodic nonlinear error contributed by stray light. The setting angles of the second linear polarizer 1421, the third linear polarizer 1431, and the fourth linear polarizer 1441 also reduce the intensity of stray light, reducing its influence on the measurement results and improving measurement accuracy. Of course, the transmission directions of the first linear polarizer 1411 and the third linear polarizer 1431 can be at other angles relative to the transmission direction of the first polarizing beam splitter 110, and the transmission directions of the second linear polarizer 1421 and the fourth linear polarizer 1441 can be at other angles relative to the transmission direction of the second polarizing beam splitter 120. No limitation is made here.

[0070] In this embodiment, when the beam is transmitted from the polarization beam splitter to the optical isolator 140, the polarization direction of the reflected stray light is different from that of the original beam, thereby reducing the interference of the reflected stray light on the original beam and thus improving the accuracy of detection.

[0071] In some possible embodiments, the heterodyne interferometer assembly 100 further includes: a half-wave plate 130, located between the first polarization beam splitter 110 and the second polarization beam splitter 120, the fast axis of the half-wave plate 130 being neither parallel nor perpendicular to the transmission direction of the first polarization beam splitter 110, and the fast axis of the half-wave plate 130 being neither parallel nor perpendicular to the transmission direction of the second polarization beam splitter 120; and / or the heterodyne interferometer assembly 100 further includes: a fifth quarter-wave plate 150, disposed on the second surface 112, the fast axis of the fifth quarter-wave plate 150 being neither parallel nor perpendicular to the transmission direction of the first polarization beam splitter 110; and / or the heterodyne interferometer assembly 100 further includes: a sixth quarter-wave plate 160, disposed on the sixth surface 122, the fast axis of the sixth quarter-wave plate 160 being neither parallel nor perpendicular to the transmission direction of the second polarization beam splitter 120.

[0072] A fifth quarter-wave plate 150 is disposed on the second surface 112. When the first measurement beam f11 passes through the fifth quarter-wave plate 150, the fifth quarter-wave plate 150 can change its polarization direction. A sixth quarter-wave plate 160 is located between the reflector 170 and the sixth surface 122, and is used to change the polarization direction of the second measurement beam f21. A half-wave plate 130 is disposed between the first polarization beam splitter 110 and the second polarization beam splitter 120. The half-wave plate 130 can change the polarization direction of the first reference beam f12 and the second reference beam f22. Figure 8 In the embodiment shown, the fast axis of the fifth quarter-wave plate 150 is at 45° to the transmission direction of the first polarization beam splitter 110, the fast axis of the sixth quarter-wave plate 160 is at 45° to the transmission direction of the second polarization beam splitter 120, and the fast axis of the half-wave plate 130 is at 45° to the transmission directions of the first polarization beam splitter 110 and the second polarization beam splitter 120.

[0073] exist Figure 8 In the illustrated embodiment, both the first input beam f1 and the second input beam f2 are right-handed circularly polarized light. The first input beam f1, after passing through the first isolator 141, becomes 45° linearly polarized light. This 45° linearly polarized light, after passing through the first beam splitter 115, becomes P-polarized light. The P-polarized light, after passing through the fifth quarter-wave plate 150, becomes right-handed circularly polarized light. This right-handed circularly polarized light, after being reflected by the test object 8, becomes left-handed circularly polarized light. The left-handed circularly polarized light, after passing through the fifth quarter-wave plate 150, becomes S-polarized light. This S-polarized light, after being reflected by the first beam splitter 115 to the measurement detector 63, and after passing through the third isolator 143, becomes right-handed circularly polarized light and enters the measurement detector 63. The first input beam f1, after passing through the first isolator 141, forms 45° linearly polarized light. After being reflected by the first beam splitter 115, it forms S-polarized light and propagates to the second polarization beam splitter 120. The S-polarized light passes through the connecting waveplate to form P-polarized light. After passing through the second beam splitter 125, the P-polarized light propagates to the reference detector 64 and passes through the fourth isolator 144 to form right-hand circularly polarized light.

[0074] The second input beam f2, after passing through the second isolator 142, forms 45° linearly polarized light. This 45° linearly polarized light, after passing through the second beam-splitting surface 125, forms P-polarized light. The P-polarized light, after passing through the sixth quarter-wave plate 160 and being reflected by the mirror 170, passes through the sixth quarter-wave plate 160 again to form S-polarized light. The S-polarized light is reflected by the second beam-splitting surface 125 towards the reference detector 64 and, after passing through the fourth isolator 144, forms right-hand circularly polarized light. This right-hand circularly polarized light interferes with the right-hand circularly polarized light of the first reference beam f12 and then enters the reference detector 64. The 45° linearly polarized light formed by the second input beam f2 after passing through the second isolator 142, after being reflected by the second beam-splitting surface 125, forms S-polarized light and propagates towards the first polarization beam-splitting device 110. S-polarized light is converted into P-polarized light by a connecting waveplate. The P-polarized light is transmitted through the first beam splitter 115 and propagates to the measurement detector 63. After passing through the third isolator 143, it becomes right-hand circularly polarized light. This right-hand circularly polarized light interferes with the right-hand circularly polarized light of the first measurement beam f11 and then enters the measurement detector 63. Of course, the fast axis of the fifth quarter-wave plate 150 and the transmission direction of the first polarizing beam splitter 110, the fast axis of the sixth quarter-wave plate 160 and the transmission direction of the second polarizing beam splitter 120, and the fast axis of the half-wave plate 130 and the transmission directions of the first polarizing beam splitter 110 and the second polarizing beam splitter 120 can be at other angles, which are not limited here.

[0075] In this embodiment, when the light beam is transmitted from the polarization beam splitter to the half-wave plate 130, the fifth quarter-wave plate 150, or the sixth quarter-wave plate 160, the polarization direction can be changed, thereby causing the light beam to propagate in the heterodyne interferometer assembly in a preset manner. To test and evaluate the periodic nonlinear error (PNL) contributed by the heterodyne interferometer assembly in precision interferometry in this embodiment, two laser beams with a frequency difference Δf = f2 - f1 of 20 MHz, a beam waist diameter of approximately 1 mm, and a wavelength λ of 633 nm are used as the first input beam f1 and the second input beam f2 of the heterodyne interferometer assembly 100. After the interference optical path is assembled and adjusted, with the object under test 8 stationary relative to the heterodyne interferometer assembly 100, the first interference signal and the second interference signal detected by the reference detector 64 and the measurement detector 63 are collected respectively, and spectral analysis is performed on both to obtain the following results: Figure 9 The spectrum diagrams shown in (a) and (b) are as follows. Since no Doppler frequency shift occurs under static conditions, the spectra of both the second and first interference signals only contain the 20MHz characteristic corresponding to the frequency difference between the second input beam f2 and the first input beam f1.

[0076] Then, the object under test 8 is controlled to move relative to the heterodyne interferometer group at a speed of v = 20 mm / s. The second interference signal and the first interference signal detected by the reference detector 64 and the measurement detector 63 are collected respectively, and the spectrum analysis of the two is performed to obtain the following results: Figure 9 The spectrum diagrams shown in (c) and (d) illustrate this. It can be seen that the second interferometric signal still only has a 20MHz characteristic frequency and no other interfering signal characteristics, therefore it will not contribute to the measurement error; while the main characteristic frequency of the first interferometric signal has shifted to 20.06319MHz, which is related to the Doppler frequency shift f. D =2v / λ, specifically 63.19kHz. The main feature shift in the spectrum of the first interference signal is consistent with the Doppler frequency shift. At the same time, it can be seen from (d) that there is a zero-order interference signal at 20MHz, which will contribute to the periodic nonlinear error.

[0077] The amplitude δ of the periodic nonlinear error contribution is related to the amplitude A of the measured signal. m The relationship between the amplitude ε0 of the interference signal (the subscript of ε0 represents the order of the interference signal; in this embodiment, only the zero-order interference signal exists) and the interference signal amplitude ε0 is: δ = ε0 / A m ×λ / 4π(1). From the spectrum of the first interference signal in (d), the interference signal intensity is -11.1dB. From the spectrum of the first interference signal in (b), the first interference signal intensity is 65.6dB. (Because the actual speed of the measured object 8 cannot be ideally uniform, the intensity of the first interference signal under the motion condition will broaden due to the uneven speed, thus weakening the signal intensity. As a result, the signal intensity of 57.5dB in (d) is lower than the signal intensity of 65.6dB in (b). Therefore, the first interference signal intensity under the static condition is more accurate.) Therefore, the signal-to-interference ratio of the measured signal and the interference signal is: 20×lg A m / ε0=65.6+11.1=76.7 dB(2), according to the two equations (1) and (2), the error amplitude δ of the periodic nonlinear error can be calculated to be 7.4pm. The error amplitude δ has reached the deep sub-nanometer level. Therefore, the heterodyne interferometer assembly 100 can be applied to various optical precision measurement occasions represented by high-end semiconductor equipment.

[0078] This application provides an interferometer 6. The interferometer 6 includes a first light source 61, a second light source 62, a measurement detector 63, a reference detector 64, and a heterodyne interferometer assembly 100 in any of the above embodiments. The first light source 61 emits a first input beam f1 to the first polarization beam splitter 110 of the heterodyne interferometer assembly 100. The second light source 62 emits a second input beam f2 to the second polarization beam splitter 120 of the heterodyne interferometer assembly 100. The measurement detector 63 is opposite to the third surface 113 of the first polarization beam splitter 110 and is used to collect a first interference beam formed by combining the first measurement beam f11 and the second reference beam f22. The reference detector 64 is opposite to the seventh surface 123 of the second polarization beam splitter 120 and is used to collect a second interference beam formed by combining the first reference beam f12 and the second measurement beam f21.

[0079] Figure 10 This is a schematic diagram of the structure of an interferometer 6 provided in one embodiment of this application. Figure 10 As shown, the first light source 61 is opposite to the first surface 111 of the heterodyne interferometer assembly 100, the second light source 62 is opposite to the fifth surface 121, the measurement detector 63 is opposite to the third surface 113, and the reference detector 64 is opposite to the seventh surface 123. The interferometer 6 also has a detection window 65, which can be opposite to the object under test 8, and the second surface 112 is opposite to the detection window 65. The first measurement beam f11 can enter and exit through the detection window 65.

[0080] In this embodiment, the heterodyne interferometer assembly is less affected by stray light, the measurement detector 63 can collect a more accurate first interference beam, and the reference detector 64 can collect a more accurate second interference beam, thereby obtaining a more accurate measurement result.

[0081] The foregoing preferred embodiments have further illustrated the objectives, technical solutions, and advantages of the present invention. It should be understood that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A heterodyne interferometer assembly, characterized in that, include: The first polarization beam splitter includes a first surface, a second surface, a third surface, a first beam splitting surface, and a fourth surface. The first surface is used to receive a first input beam, the first beam splitting surface is used to transmit the first input beam to form a first measurement beam, and to reflect the first input beam to form a first reference beam that propagates toward the fourth surface. The first surface is opposite to the second surface, and the third surface is opposite to the fourth surface. The second polarization beam splitter includes a fifth surface, a sixth surface, a seventh surface, a second beam splitting surface, and an eighth surface. The fifth surface is used to receive a second input beam. The second beam splitting surface is used to transmit the second input beam to form a second measurement beam and to reflect the second input beam to form a second reference beam that propagates toward the eighth surface. The fifth surface is opposite to the sixth surface, the seventh surface is opposite to the eighth surface, and the fourth surface and the eighth surface are located between the third surface and the seventh surface. Any two of the first surface, the second surface, the third surface, and the fourth surface are not parallel and not perpendicular, and / or Any two of the fifth, sixth, seventh, and eighth surfaces are neither parallel nor perpendicular.

2. The heterodyne interferometer assembly according to claim 1, characterized in that, The edge of the second surface away from the sixth surface is further away from the first surface than the edge of the second surface near the sixth surface, and the edge of the sixth surface away from the second surface is further away from the fifth surface than the edge of the sixth surface near the second surface. There is a first preset angle α between the extension direction of the second surface away from the sixth surface and the extension direction of the sixth surface near the second surface. The first preset angle α is greater than 0° and less than 90°.

3. The heterodyne interferometer assembly according to claim 2, characterized in that, The first beam splitting surface is deflected from the first reference position by a second preset angle β. The first reference position is when the first polarization beam splitting device is replaced with a polarization beam splitting device with a rectangular cross-section, the first polarization beam splitting device is tilted towards the fourth surface to a sloping surface position with an angle of 45° between it and the first surface. The second beam splitting surface is deflected from the second reference position by a third preset angle γ. The second reference position is when the second polarization beam splitting device is replaced with a polarization beam splitting device with a rectangular cross-section, the second polarization beam splitting device is tilted towards the eighth surface to the inclined surface position with an angle of 45° between it and the fifth surface. The product of the first preset angle α and the refractive index is equal to twice the difference between the second preset angle β and the third preset angle γ; the refractive index is the difference between 1 and the reciprocal of the refractive index of the first polarization beam splitter.

4. The heterodyne interferometer assembly according to any one of claims 1 to 3, characterized in that, It also includes at least one optical isolator, with an optical isolator provided on the outer side of at least one of the first surface, the third surface, the fifth surface, and the seventh surface.

5. The heterodyne interferometer assembly according to claim 4, characterized in that, Each optical isolator includes a linear polarizer and a quarter-wave plate. The transmission direction of the linear polarizer in each optical isolator is neither parallel nor perpendicular to the fast axis direction of the quarter-wave plate.

6. The heterodyne interferometer assembly according to claim 5, characterized in that, The at least one optical isolator includes a first isolator disposed on the first surface, the first isolator including a first linear polarizer and a first quarter-wave plate, the first quarter-wave plate being located on the side of the first surface away from the first linear polarizer, and / or The at least one optical isolator includes a second isolator disposed on the fifth surface, the second isolator including a second linear polarizer and a second quarter-wave plate, the second quarter-wave plate being located on the side of the second linear polarizer away from the fifth surface, and / or The at least one optical isolator includes a third isolator disposed on the third surface, the third isolator including a third linear polarizer and a third quarter-wave plate, the third quarter-wave plate being located on the side of the third linear polarizer away from the third surface, and / or The at least one optical isolator includes a fourth isolator disposed on the seventh surface, the fourth isolator including a fourth linear polarizer and a fourth quarter-wave plate, the fourth quarter-wave plate being located on the side of the fourth linear polarizer away from the seventh surface.

7. The heterodyne interferometer assembly according to claim 6, characterized in that, The transmission directions of both the first and third linear polarizers are neither parallel nor perpendicular to the transmission direction of the first polarizing beam splitter; and / or The transmission directions of the second and fourth linear polarizers are neither parallel nor perpendicular to the transmission direction of the second polarizing beam splitter.

8. The heterodyne interferometer assembly according to any one of claims 1 to 3, characterized in that, The heterodyne interferometer assembly further includes: a half-wave plate, located between the first polarization beam splitter and the second polarization beam splitter, wherein the fast axis of the half-wave plate is neither parallel to nor perpendicular to the transmission direction of the first polarization beam splitter, and the fast axis of the half-wave plate is neither parallel to nor perpendicular to the transmission direction of the second polarization beam splitter; and / or The heterodyne interferometer assembly further includes: a fifth quarter-wave plate, wherein the fifth quarter-wave plate is disposed on the second surface, and the fast axis of the fifth quarter-wave plate is neither parallel nor perpendicular to the transmission direction of the first polarization beam splitter; and / or The heterodyne interferometer assembly further includes a sixth quarter-wave plate, which is disposed on the sixth surface, and the fast axis of the sixth quarter-wave plate is neither parallel nor perpendicular to the transmission direction of the second polarization beam splitter.

9. An interferometer, characterized in that, It includes a first light source, a second light source, a measurement detector, a reference detector, and a heterodyne interferometer assembly as described in any one of claims 1 to 8, wherein, The first light source is used to emit a first input beam to the first polarization beam splitter of the heterodyne interferometer assembly; The second light source is used to emit a second input beam into the second polarization beam splitter of the heterodyne interferometer assembly; The measurement detector is opposite to the third surface of the first polarization beam splitter and is used to collect the first interference beam formed by combining the first measurement beam and the second reference beam; The reference detector is opposite to the seventh surface of the second polarization beam splitter and is used to collect the second interference beam formed by combining the first reference beam and the second measurement beam.

10. A semiconductor device, characterized in that, Includes a support stage and the interferometer as described in claim 9, wherein, The support platform is used to move the wafer; The detection port of the interferometer faces the support stage and is used to detect the moving distance of the support stage.

Images