A high-precision error calibration device for a Fizeau interferometer

Abstract

The application discloses a high-precision error calibration device for a Fizeau interferometer, comprising a light source, a point diffraction interferometer and a Fizeau interferometer to be calibrated, wherein the light source is used for generating short-coherence light and performing heterodyne phase shifting; the point diffraction interferometer is used for measuring the reference surface figure of the Fizeau interferometer to be calibrated and emitting a point diffraction spherical wave; the point diffraction interferometer comprises a fiber coupler, a first converging lens, a second converging lens, a point diffraction plate, a first reflecting mirror, a first imaging lens and a first detector; the Fizeau interferometer to be calibrated comprises a standard spherical mirror, a polarization beam splitter prism, a collimating lens, a second reflecting mirror, a second imaging lens and a second detector. The device calibrates the reference surface figure error and system error of the Fizeau interferometer by using the point diffraction interferometer, and then obtains high-precision absolute surface figure data of a measured element, so that the limitation of the standard spherical mirror surface figure machining precision on the system measurement precision is broken.

Description

Technical Field

[0001] This invention relates to the field of optical measurement technology, and in particular to a high-precision error calibration device for a Fizeau interferometer. Background Technology

[0002] High-end optical equipment, exemplified by deep ultraviolet lithography projection exposure systems, poses significant challenges to the fabrication of optical components and the integration of optical systems. As an indispensable core testing device for high-precision optical component fabrication and optical system integration, the interferometer's accuracy requirements are constantly increasing. High-precision surface shape inspection interferometers mainly include Thyman-Green interferometers and Fizeau interferometers. Compared to Thyman-Green interferometers, the Fizeau interferometer's shared optical path for both reference and measurement beams gives it advantages such as simpler structure and stronger anti-interference capabilities, making it more widely used in practical applications.

[0003] To improve the measurement accuracy of Fizeau interferometers, existing methods mainly utilize spherical absolute detection techniques to calibrate the surface shape error of the reference surface or to separate the absolute surface shape information of the measured surface by processing multiple measurement results. Spherical absolute detection techniques mainly include the double-spherical method, the random sphere method, and the rotation-translation method. The double-spherical method requires three measurements of the mirror under test: at the cat's eye position (the focal position of the standard spherical mirror), the normal position (the confocal position of the standard spherical mirror and the mirror under test), and a 180-degree rotation position. The absolute surface shape data of the mirror under test is obtained through data processing. However, because it requires rotating the mirror under test, this method demands high precision in optical axis alignment and is difficult to accurately locate the cat's eye position, which will affect the absolute detection accuracy. The random sphere method involves incident the converging beam of the standard spherical mirror onto a sphere. After one measurement, the sphere is randomly rotated around its center, and the average result is obtained through multiple measurements. If the measurement results only include the surface shape error of the reference surface, it can be subtracted from the subsequent measurement results. This method has high requirements for the surface shape accuracy of the random sphere and requires a large number of tests, which also places certain demands on environmental stability. The rotation and translation method obtains the rotational asymmetric component of the surface shape error by rotating the mirror under test multiple times at equal angles, and then obtains the rotational symmetric component of the surface shape error by translation, thereby obtaining the surface shape information of the measured surface. However, this method requires a high-precision six-dimensional adjustment platform to rotate and translate the mirror under test, and the data processing algorithm is relatively complex. Summary of the Invention

[0004] The purpose of this invention is to provide a high-precision error calibration device for Fizeau interferometers. This device uses a point diffraction interferometer to calibrate the surface shape error and system error of the reference surface of the Fizeau interferometer, thereby obtaining high-precision absolute surface shape data of the measured component, so as to break the limitation of the standard spherical mirror surface shape processing accuracy on the system measurement accuracy.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A high-precision error calibration device for a Fizeau interferometer, the device comprising a light source, a point diffraction interferometer, and a Fizeau interferometer to be calibrated, wherein:

[0007] The light source is used to generate short coherent light and perform heterodyne phase shifting;

[0008] The point diffraction interferometer is used to measure the surface shape of the reference surface of the Fizeau interferometer to be calibrated, and to emit point diffraction spherical waves;

[0009] The point diffraction interferometer includes an optical fiber coupler, a first converging mirror, a second converging mirror, a point diffraction plate, a first reflecting mirror, a first imaging mirror, and a first detector, wherein:

[0010] When calibrating the surface shape error of the reference surface of the Fiso interferometer to be calibrated, the short coherent light generated by the light source is coupled to the fiber coupler inside the point diffraction interferometer through an optical fiber, and then the laser is incident on the first converging mirror and the second converging mirror respectively.

[0011] Then, a convergence point is formed at the pinhole of the point diffraction plate, and reference light and measurement light are generated by diffraction respectively. The measurement light is incident on the reference surface of the standard spherical mirror of the Fizeau interferometer to be calibrated. The point diffraction plate is located at the focal point of the standard spherical mirror. Therefore, the reflected light from the reference surface of the standard spherical mirror converges on the metal reflective film layer near the pinhole of the point diffraction plate, and enters the first imaging mirror together with the reference light through the first reflecting mirror. Finally, low-frequency heterodyne interference is generated on the first detector. The surface shape error of the reference surface of the Fizeau interferometer to be calibrated can be calculated from the interferogram acquired from the first detector.

[0012] The Fizeau interferometer to be calibrated includes a standard spherical mirror, a polarizing beam splitter, a collimating mirror, a second reflecting mirror, a second imaging mirror, and a second detector, wherein:

[0013] When calibrating the systematic error of the Fizeau interferometer to be calibrated, the relative positions of the point diffraction interferometer and the Fizeau interferometer to be calibrated are kept constant. Short coherent light generated by the light source is connected to the Fizeau interferometer to be calibrated using an optical fiber. Then, the beam passes through the polarization beam splitter and collimating lens in sequence to form collimated light, which is then incident on the standard spherical mirror. The last surface of the standard spherical mirror is a flush surface, which returns part of the beam along the original path to form reference light. The transmitted beam converges on the metal reflective film layer of the point diffraction plate of the point diffraction interferometer. Since the point diffraction plate is tilted relative to the optical axis, this part of the transmitted beam does not return to the Fizeau interferometer to be calibrated.

[0014] The short coherent light generated by the light source enters the second converging mirror through the optical fiber and the optical fiber coupler. The converging light is diffracted at the pinhole of the point diffraction plate, generating a high-quality spherical wave, which enters the Fizeau interferometer to be calibrated through the standard spherical mirror to form the measurement light.

[0015] The reference light and the measurement light pass sequentially through the collimating mirror, polarizing beam splitter, second reflecting mirror, and second imaging mirror inside the Fizeau interferometer to be calibrated before reaching the second detector; heterodyne phase shifting is performed in the second detector and multiple frames of interferograms are acquired to calibrate the system error of the Fizeau interferometer to be calibrated.

[0016] As can be seen from the technical solution provided by the present invention, the above-mentioned device uses a point diffraction interferometer to calibrate the reference surface shape error and system error of the Fizeau interferometer, thereby obtaining high-precision absolute surface shape data of the measured component, so as to break the limitation of the standard spherical mirror surface shape processing accuracy on the system measurement accuracy. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. 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.

[0018] Figure 1 This is a schematic diagram of the high-precision error calibration device for a Fizeau interferometer provided in an embodiment of the present invention;

[0019] Figure 2 This is a schematic diagram of the optical path for system error calibration of the device described in an embodiment of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments, and do not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0021] like Figure 1 The diagram shown is a schematic representation of a high-precision error calibration device for a Fizeau interferometer provided in an embodiment of the present invention. The device includes a light source 1, a point diffraction interferometer 2, and a Fizeau interferometer to be calibrated 3, wherein:

[0022] The light source 1 is used to generate short coherent light and perform heterodyne phase shifting;

[0023] The point diffraction interferometer 2 is used to measure the surface shape of the reference surface of the Fizeau interferometer 3 to be calibrated, and to emit point diffraction spherical waves;

[0024] The point diffraction interferometer 2 includes an optical fiber coupler 5, a first converging mirror 6, a second converging mirror 7, a point diffraction plate 8, a first reflecting mirror 9, a first imaging mirror 10, and a first detector 11, wherein:

[0025] like Figure 1 As shown, when calibrating the surface shape error of the reference surface of the Fiso interferometer 3 to be calibrated, the short coherent light generated by the light source 1 is coupled to the fiber coupler 5 inside the point diffraction interferometer 2 through the fiber optic 4, and then the laser is incident on the first converging mirror 6 and the second converging mirror 7 respectively.

[0026] Then, a convergence point is formed at the pinhole of the point diffraction plate 8, and reference light and measurement light are generated by diffraction respectively. The measurement light is incident on the reference surface of the standard spherical mirror 12 of the Fizeau interferometer 3 to be calibrated. The point diffraction plate 8 is located at the focal point of the standard spherical mirror 12. Therefore, the reflected light from the reference surface of the standard spherical mirror 12 converges on the metal reflective film layer near the pinhole of the point diffraction plate 8, and enters the first imaging mirror 10 together with the reference light through the first reflecting mirror 9. Finally, low-frequency heterodyne interference is generated on the first detector 11. The surface shape error of the reference surface of the Fizeau interferometer 3 to be calibrated can be calculated from the interferogram collected from the first detector 11.

[0027] like Figure 2 The diagram shown illustrates the optical path for system error calibration using the device described in this embodiment of the invention. The Fizeau interferometer 3 to be calibrated includes a standard spherical mirror 12, a polarizing beam splitter 14, a collimating mirror 15, a second reflecting mirror 16, a second imaging mirror 17, and a second detector 18, wherein:

[0028] When calibrating the system error of the Fizeau interferometer 3 to be calibrated, the relative positions of the point diffraction interferometer 2 and the Fizeau interferometer 3 to be calibrated are kept unchanged. The short coherent light generated by the light source 1 is connected to the Fizeau interferometer 3 to be calibrated using an optical fiber 13. Then, the beam passes through the polarization beam splitter 14 and the collimating lens 15 in sequence to form collimated light that is incident on the standard spherical mirror 12. The last surface of the standard spherical mirror 12 is a flush surface, which returns part of the beam along the original path to form the reference light. The transmitted beam converges on the metal reflective film layer of the point diffraction plate 8 of the point diffraction interferometer 2. Since the point diffraction plate 8 is tilted relative to the optical axis, this part of the transmitted beam does not return to the Fizeau interferometer 3 to be calibrated.

[0029] The short coherent light generated by the light source 1 enters the second converging mirror 7 through the optical fiber 4 and the optical fiber coupler 5. The converged light is diffracted at the pinhole of the point diffraction plate 8 to generate a high-quality spherical wave, which enters the Fizeau interferometer 3 to be calibrated through the standard spherical mirror 12 to form the measurement light.

[0030] The reference light and the measurement light pass sequentially through the collimating mirror 15, the polarizing beam splitter 14, the second reflecting mirror 16, and the second imaging mirror 17 inside the Fizeau interferometer 3 to be calibrated before reaching the second detector 18. Heterodyne phase shifting is performed in the second detector 18 and multiple frames of interferograms are acquired to calibrate the system error of the Fizeau interferometer 3 to be calibrated.

[0031] In specific implementation, during the calibration process using the aforementioned device:

[0032] Wavefront W of the reference optical path R (r,θ) is represented as:

[0033] W R (r,θ)=S(r,θ)+2L(r,θ)+2nA(r,θ)+I(r,θ)

[0034] Where r and θ are the polar coordinate components of the spatial point, respectively; S(r,θ) is the wavefront aberration of the illumination optical path; L(r,θ) is the wavefront aberration of the standard spherical mirror 12 in the Fizeau interferometer 3 to be calibrated; n is the refractive index of the lens corresponding to the reference surface of the standard spherical mirror; A(r,θ) is the surface shape error of the reference surface; and I(r,θ) is the wavefront aberration of the imaging optical path.

[0035] Measuring the wavefront W of the optical path T (r,θ) is represented as:

[0036] W T (r,θ)=L(r,θ)+(n-1)A(r,θ)+I(r,θ)

[0037] Subtracting the wavefront of the reference optical path from the wavefront of the measurement optical path yields the interferometric measurement result M(r,θ), expressed as:

[0038] M(r,θ)=W R (r,θ)-W T (r,θ)=S(r,θ)+L(r,θ)+(n+1)A(r,θ)

[0039] The surface shape error A(r,θ) of the reference surface of the Fizeau interferometer 3 to be calibrated is obtained by calculation, and the systematic error W is separated based on the known refractive index n of the lens. sys (r,θ) is represented as:

[0040] W sys(r,θ)=S(r,θ)+L(r,θ);

[0041] This system error is the wavefront error that is irradiated onto the surface of the component under test, and it can be corrected in subsequent measurement results.

[0042] It is worth noting that the contents not described in detail in the embodiments of the present invention belong to the prior art known to those skilled in the art.

[0043] In summary, the device described in the embodiments of the present invention has the following advantages:

[0044] 1. This device can not only calibrate the surface shape error of the reference surface, but also calibrate the systematic error of the Fizeau interferometer;

[0045] 2. This device does not require in-situ testing of the component under test. Once the interferometer under test is calibrated, it can perform batch testing of the component under test and obtain high-precision measurement results through the calibration file.

[0046] 3. The calibration process of this device only requires two measurements, and there are no moving mechanical parts, which reduces the requirements for environmental stability.

[0047] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention 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 the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims. The information disclosed in the background section is intended only to enhance the understanding of the overall background technology of the present invention and should not be construed as an admission or implication in any way that such information constitutes prior art known to those skilled in the art.

Claims

1. A high-precision error calibration device for a Fizeau interferometer, characterized in that, The device includes a light source, a point diffraction interferometer, and a Fizeau interferometer to be calibrated, wherein: The light source is used to generate short coherent light and perform heterodyne phase shifting; The point diffraction interferometer is used to measure the surface shape of the reference surface of the Fizeau interferometer to be calibrated, and to emit point diffraction spherical waves; The point diffraction interferometer includes an optical fiber coupler, a first converging mirror, a second converging mirror, a point diffraction plate, a first reflecting mirror, a first imaging mirror, and a first detector, wherein: When calibrating the surface shape error of the reference surface of the Fiso interferometer to be calibrated, the short coherent light generated by the light source is coupled to the fiber coupler inside the point diffraction interferometer through an optical fiber, and then the laser is incident on the first converging mirror and the second converging mirror respectively. Then, a convergence point is formed at the pinhole of the point diffraction plate, and reference light and measurement light are generated by diffraction respectively. The measurement light is incident on the reference surface of the standard spherical mirror of the Fizeau interferometer to be calibrated. The point diffraction plate is located at the focal point of the standard spherical mirror. Therefore, the reflected light from the reference surface of the standard spherical mirror converges on the metal reflective film layer near the pinhole of the point diffraction plate, and enters the first imaging mirror together with the reference light through the first reflecting mirror. Finally, low-frequency heterodyne interference is generated on the first detector. The surface shape error of the reference surface of the Fizeau interferometer to be calibrated can be calculated from the interferogram acquired from the first detector. The Fizeau interferometer to be calibrated includes a standard spherical mirror, a polarizing beam splitter, a collimating mirror, a second reflecting mirror, a second imaging mirror, and a second detector, wherein: When calibrating the systematic error of the Fizeau interferometer to be calibrated, the relative positions of the point diffraction interferometer and the Fizeau interferometer to be calibrated are kept constant. Short coherent light generated by the light source is connected to the Fizeau interferometer to be calibrated using an optical fiber. Then, the beam passes through the polarization beam splitter and collimating lens in sequence to form collimated light, which is then incident on the standard spherical mirror. The last surface of the standard spherical mirror is a flush surface, which returns part of the beam along the original path to form reference light. The transmitted beam converges on the metal reflective film layer of the point diffraction plate of the point diffraction interferometer. Since the point diffraction plate is tilted relative to the optical axis, this part of the transmitted beam does not return to the Fizeau interferometer to be calibrated. The short coherent light generated by the light source enters the second converging mirror through the optical fiber and the optical fiber coupler. The converging light is diffracted at the pinhole of the point diffraction plate, generating a high-quality spherical wave, which enters the Fizeau interferometer to be calibrated through the standard spherical mirror to form the measurement light. The reference light and the measurement light pass sequentially through the collimating mirror, polarizing beam splitter, second reflecting mirror, and second imaging mirror inside the Fizeau interferometer to be calibrated before reaching the second detector; heterodyne phase shifting is performed in the second detector and multiple frames of interferograms are acquired to calibrate the system error of the Fizeau interferometer to be calibrated.

2. The high-precision error calibration device for a Fizeau interferometer according to claim 1, characterized in that, During the calibration process using the aforementioned device: Wavefront W of the reference optical path R (r,θ) is represented as: W R (r,θ)=S(r,θ)+2L(r,θ)+2nA(r,θ)+I(r,θ) Where r and θ are the polar coordinate components of the spatial point, respectively; S(r,θ) is the wavefront aberration of the illumination optical path; L(r,θ) is the wavefront aberration of the standard spherical mirror in the Fizeau interferometer to be calibrated; n is the refractive index of the lens corresponding to the reference plane of the standard spherical mirror; A(r,θ) is the surface shape error of the reference plane; and I(r,θ) is the wavefront aberration of the imaging optical path. Measuring the wavefront W of the optical path T (r,θ) is represented as: W T (r,θ)=L(r,θ)+(n-1)A(r,θ)+I(r,θ) Subtracting the wavefront of the reference optical path from the wavefront of the measurement optical path yields the interferometric measurement result M(r,θ), expressed as: M(r,θ)=W R (r,θ)-W T (r,θ)=S(r,θ)+L(r,θ)+(n+1)A(r,θ) The surface shape error A(r,θ) of the reference surface of the Fizeau interferometer to be calibrated is obtained by calculation, and the systematic error W is separated based on the known refractive index n of the lens. sys (r,θ) is represented as: W sys (r,θ)=S(r,θ)+L(r,θ); This system error is the wavefront error that is irradiated onto the surface of the component under test, and it can be corrected in subsequent measurement results.

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