A method and system for detecting the surface shape of an extreme ultraviolet lithography objective lens based on subwavelength structure computational holography

Abstract

The present invention discloses a method and system for detecting the surface shape of an EUV lithography objective lens based on subwavelength structured computational holography. This method, based on subwavelength structured computational holography, utilizes the design and application of subwavelength structured computational holographic sheets to obtain high-precision aspheric surface shape data for EUV lithography objectives, achieving an RMS detection accuracy of less than 1 nm. The computational holograms of this invention are highly uniform, greatly facilitating low-cost precision etching processes, and possess greater phase modulation capabilities than conventional step-type computational holograms.

Description

Technical Field

[0001] The present invention relates to the technical field of optical element surface shape detection technology, and in particular to an extreme ultraviolet lithography objective lens surface shape detection method and system based on subwavelength structure computational holography. Background Art

[0002] The EUV lithography objective is one of the key components of the EUV lithography machine, and high-precision detection of the surface shape of optical elements in the EUV lithography objective is a key issue.

[0003] In order to solve the problem of aspheric surface shape detection in the EUV lithography objective system, the Lawrence National Laboratory and the ZYGO team proposed a high-precision zero-position interferometry method based on computer-generated holography (Holger Glatzel, Dominic Ashworth, Dan Bajuk, et al , "Projection optics for EUVL micro-field exposure tools with 0.5 NA," Proc. SPIE 9048, Extreme Ultraviolet(EUV) Lithography V, 90481K (17 April 2014); https: / / doi.org / 10.1117 / 12.2048643). Different from the traditional spherical null-position interferometry principle, this high-precision null-position interferometry measurement method based on computational holography uses a computationally generated hologram (CGH) as a phase compensation device based on the surface gradient distribution of the aspheric surface to compensate for the phase deviation of the aspheric surface, thereby achieving high-precision aspheric surface shape detection and expanding its application to optical system adjustment (Liu Fei. Research on the Design of Coaxial Extreme Ultraviolet Projection Lithography Objectives[D]. Beijing Institute of Technology, 2014.).

[0004] However, the traditional processing technology makes the characteristic line width of the ring-shaped computer-generated hologram (CGH) remain at the micron level. At the same time, it relies on multi-step etching processing, which greatly limits the further improvement of the accuracy of the computer-generated hologram, thereby affecting the imaging resolution of the EUV lithography objective system, and further restricting the EUV lithography machine from entering the stage of higher-precision chip processing. The low surface shape detection accuracy of the EUV lithography objective optical element is one of the important factors limiting the EUV lithography machine from being put into production and use (Yu Jun, Wang Zhanshan, Huang Qiushi, et al. Ultra-precision processing and detection of ultra-smooth mirrors in the EUV and X-ray bands [J]. Optical Precision Engineering, 2022, 30(21): 2688-2697. DOI: 10.37188 / OPE.20223021.2688.). Summary of the Invention

[0005] The purpose of the present invention is to provide an extreme ultraviolet lithography objective lens surface shape detection method based on subwavelength structure computational holography, which adopts a large-area computational hologram (CGH) with subwavelength nanostructure to solve the demand for high-precision detection of aspheric surface shape in existing extreme ultraviolet lithography objective lens systems.

[0006] A method for detecting the surface shape of an extreme ultraviolet lithography objective lens based on subwavelength structure computational holography, wherein the extreme ultraviolet lithography objective lens is an aspheric reflector, comprises the following steps:

[0007] (1) According to the design surface shape data of the aspheric reflector to be measured, the placement position of the subwavelength structure computational hologram that matches it is determined, and based on the placement position and surface shape data, the continuous phase distribution function of the subwavelength structure computational hologram is calculated;

[0008] (2) Perform discrete phase numerical processing of N gray levels on the continuous phase distribution function obtained in step (1), where N=2 k , k is a positive integer;

[0009] (3) Design a mapping data table between the structural parameters of the subwavelength structural unit in the subwavelength structure computational hologram and the discretized phase data, and use this mapping data table as the basis for the structural design of the subwavelength structure computational hologram;

[0010] (4) Based on the mapping data table in step (3), the discretized phase values ​​in step (2) are converted to obtain a subwavelength structure unit design scheme of the subwavelength structure computer-generated hologram, and pattern processing is performed on the substrate according to the subwavelength structure unit design scheme to obtain the subwavelength structure computer-generated hologram;

[0011] (5) The subwavelength structured computer-generated hologram is placed at the placement position determined in step (1), and the light for detection is emitted by the standard interferometer, which is processed into a plane wave by the standard plane mirror, and a part of the plane wave is reflected back to the standard interferometer to form a reference light path, and the other part of the plane wave is transmitted through the standard plane mirror and incident on the subwavelength structured computer-generated hologram, and the incident plane wave is converted into an aspheric wave, and the aspheric wave matches the surface shape of the aspheric reflector to be measured, and the aspheric wave is incident on the aspheric reflector to be measured, and after being reflected by the aspheric reflector to be measured, it returns to the standard interferometer along the original path to form a test light path;

[0012] (6) Adjust the spatial posture of the aspheric reflector to be measured so that the light of the test light path interferes with the light of the reference light path in the standard interferometer to form a zero-position interference measurement, and obtain the surface shape data of the aspheric reflector to be measured by solving the obtained interference pattern.

[0013] Preferably, when determining the placement position of the subwavelength structured computer-generated hologram, the subwavelength structured computer-generated hologram is placed between the standard interferometer and the aspheric reflector to be measured, and the distance between the standard interferometer and the vertex of the aspheric reflector to be measured is L. Then, the distance between the subwavelength structured computer-generated hologram and the standard interferometer is between L / 2 and 2L / 3, and the distance between the subwavelength structured computer-generated hologram and the aspheric surface of the aspheric reflector to be measured satisfies the Fraunhofer diffraction propagation distance.

[0014] Preferably, in step (1), the principle for calculating the continuous phase distribution function of the subwavelength structure computational hologram is as follows: assuming that the plane wave emitted by the standard interferometer is P(x,y;z), the function for calculating the subwavelength structure computational hologram is Phi(x,y;z), and the aspheric surface shape function of the aspheric reflector to be measured is y(x,y;z), then there exists a mathematical relationship Phi(x,y;z)=IN{P(x,y;z)}×IFS{y(x,y;z)}, where IN{P(x,y;z)} represents the inverse matrix of P(x,y;z); IFS{y(x,y;z)} represents the inverse Fresnel diffraction transformation of y(x,y;z).

[0015] In computer programming operations, if it is difficult to directly calculate Phi(x,y;z)=IN{P(x,y;z)}×IFS{y(x,y;z)}, the Newton iteration method, the steepest descent method and the damped least squares method can be used to alternately iterate and optimize the calculation to obtain the continuous phase distribution function of the subwavelength structure computational hologram.

[0016] More preferably, in step (2), when the continuous phase distribution function obtained in step (1) is subjected to discrete phase numerical processing of N gray levels, the continuous phase distribution function is divided into M phase periods, and the M phase periods are divided into N equal parts respectively, and the nth part is subjected to 2π / N×n quantization processing, and the principle of quantization processing is rounding, where n is a positive integer ≤ N; M is a positive integer, and the value is determined by the continuous phase distribution function, and the function for calculating the subwavelength structure hologram is Phi(x,y;z) divided by 2π, and the number obtained is a positive integer.

[0017] Preferably, in step (3), the subwavelength structural unit is a cylinder or a circular hole cylinder.

[0018] More preferably, the height of the cylinder or hole cylinder is: lamda / (g-1), wherein lamda is the wavelength of the light emitted by the standard interferometer for detection, and g is the refractive index of the sub-wavelength structure calculation hologram.

[0019] Further preferably, in step (3), the mapping relationship between the structural parameters of the sub-wavelength structural unit in the sub-wavelength structure computational hologram and the discretized phase data is:

[0020] When the subwavelength structural unit is a cylinder, lamda represents the wavelength of the light emitted by the standard interferometer for detection, the diameter of the cylinder is R1, the refractive index of the cylinder is g, the incident light is a plane wave, and the height H1 of the cylinder is lamda / (g-1). R1 ​​is set as a variable parameter, and lamda, g, and H1 are substituted into the Maxwell equations as constant variable parameters. The output variable is the phase. The time-domain finite difference method is used as the approximate numerical calculation principle. R1 is scanned from 60nm to 700nm at intervals of 10nm, and the output phase value is recorded to obtain the mapping relationship between the cylinder and the discretized phase data.

[0021] When the subwavelength structural unit is a circular hole column, lamda represents the wavelength of the light emitted by the standard interferometer for detection, the outer diameter of the cylindrical hole is R2, the diameter of the central hole of the circular hole column is r2, the refractive index of the cylinder is g, the incident light is a plane wave, and the height H2 of the circular hole column is lamda / (g-1). R2 and r2 are set as variable parameters, lamda, g, and H2 are used as constant variable parameters and substituted into the Maxwell equations. The output variable is the phase. The time-domain finite difference method is used as the approximate numerical calculation principle. R2 and r2 are both scanned from 60nm to 700nm at intervals of 10nm. The output phase value is recorded to obtain the mapping relationship between the circular hole column and the discretized phase data.

[0022] Preferably, the substrate is made of quartz.

[0023] The present invention also provides a system dedicated to the method for detecting the surface shape of an extreme ultraviolet lithography objective lens based on subwavelength structure computational holography, comprising:

[0024] A standard interferometer, used to emit light for detection and detect the reflected light,

[0025] a standard plane mirror, provided at the optical path exit of the standard interferometer, for processing the light emitted by the standard interferometer into a plane wave, wherein a portion of the plane wave is reflected back to the standard interferometer to form a reference optical path, and another portion of the plane wave is transmitted through the standard plane mirror;

[0026] A subwavelength structured computer-generated hologram, wherein a plane wave transmitted through the standard plane mirror is incident on the subwavelength structured computer-generated hologram, the incident plane wave is converted into an aspheric wave, and the aspheric wave matches the surface shape of the aspheric reflector to be measured. The aspheric wave is incident on the aspheric reflector to be measured, and after being reflected by the aspheric reflector to be measured, it returns to the standard interferometer along the original path to form a test light path. The light of the test light path interferes with the light of the reference light path in the standard interferometer to form an interference pattern.

[0027] The six-dimensional adjustment frame is used to clamp and adjust the position and angle of the aspheric mirror under test during the test process.

[0028] This method for detecting the surface shape of an EUV lithography objective lens based on subwavelength structured computer-generated holography (CGH) utilizes the design and application of a subwavelength structured CGH to obtain high-precision aspheric surface shape data for EUV lithography objectives, achieving an RMS (root mean square) accuracy of less than 1 nm. The CGH produced by this method is highly uniform, facilitating cost-effective precision etching and fabrication, while also offering greater phase modulation capabilities than conventional step-type CGHs. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the optical path structure of the EUV lithography objective lens surface shape detection method based on subwavelength structure computer-generated holography of the present invention.

[0030] Figure 2 Schematic diagram of dividing the continuous phase distribution function into M phase periods according to the present invention.

[0031] Figure 3 This is a surface diagram of the designed extreme ultraviolet concave aspheric surface according to an embodiment of the present invention.

[0032] Figure 4 This is a diagram illustrating the principle of quantization and grading of cylinder diameters for sub-wavelength structured computer-generated holography (CGH) according to an embodiment of the present invention.

[0033] Figure 5 Schematic diagrams of the cylindrical (left) and hole-cylinder (right) structures of the subwavelength structured computer-generated holography (CGH) of the present invention.

[0034] Figure 6 The interferogram (left) and measurement result diagram (right) of the extreme ultraviolet concave aspheric surface shape measurement based on subwavelength structured computer-generated holography (CGH) according to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] like Figure 1 As shown, a system dedicated to the surface shape detection method of extreme ultraviolet lithography objective lens based on subwavelength structure computer-generated holography includes a standard interferometer 1, a standard plane mirror 2, a subwavelength structure computer-generated hologram 3, and a six-dimensional adjustment frame 5.

[0036] The six-dimensional adjustment frame 5 is used to clamp and adjust the position and angle of the aspheric reflector 4 under test during the test process. The six-dimensional adjustment frame 5 uses a high-precision six-dimensional adjustment structure, which can achieve six-directional movement and adjustment: movement in the three directions of X, Y, and Z, and adjustment of the angles in the three directions of θX, θY, and θZ.

[0037] The standard interferometer 1 is used to emit light for detection and detect the reflected light.

[0038] The standard plane mirror 2 is provided at the optical path exit of the standard interferometer 1 and is used to process the light emitted by the standard interferometer 1 into a plane wave. Part of the plane wave is reflected back to the standard interferometer 1 to form a reference optical path, while the other part of the plane wave is transmitted through the standard plane mirror 2. The plane wave transmitted through the standard plane mirror 2 is incident on the subwavelength structured computer-generated hologram 3, which converts the incident plane wave into an aspheric wave. The aspheric wave matches the surface shape of the aspheric reflector 4 to be measured. The aspheric wave is incident on the aspheric reflector 4 to be measured, and after being reflected by the aspheric reflector 4 to be measured, it returns to the standard interferometer 1 along the original path to form a test optical path. The light of the test optical path interferes with the light of the reference optical path in the standard interferometer 1 to form an interference pattern.

[0039] A method for detecting the surface shape of an extreme ultraviolet lithography objective lens based on subwavelength structure computational holography, wherein the extreme ultraviolet lithography objective lens is an aspheric reflector, comprises the following steps:

[0040] (1) According to the design surface shape data of the aspheric reflector to be measured, the placement position of the subwavelength structured computational hologram (CGH) that matches it is determined, and based on the placement position and surface shape data, the continuous phase distribution function of the subwavelength structured computational hologram is calculated.

[0041] Specifically, when determining the placement position of the subwavelength structured computer-generated hologram, the subwavelength structured computer-generated hologram is placed between the standard interferometer and the aspheric reflector to be measured. The distance between the standard interferometer and the vertex of the aspheric reflector to be measured is L. Then, the distance between the subwavelength structured computer-generated hologram and the standard interferometer is between L / 2 and 2L / 3, and the distance between the subwavelength structured computer-generated hologram and the aspheric surface of the aspheric reflector to be measured satisfies the Fraunhofer diffraction propagation distance.

[0042] The principle of calculating the continuous phase distribution function of the subwavelength structure computational hologram: suppose the plane wave emitted by the standard interferometer is P(x,y;z), the function of calculating the subwavelength structure computational hologram is Phi(x,y;z), and the aspheric surface shape function of the aspheric reflector to be measured is y(x,y;z), then there is a mathematical relationship Phi(x,y;z)=IN{P(x,y;z)}×IFS{y(x,y;z)}, where IN{P(x,y;z)} represents the inverse matrix of P(x,y;z); IFS{y(x,y;z)} represents the inverse Fresnel diffraction transformation of y(x,y;z).

[0043] In computer programming operations, if it is difficult to directly calculate Phi(x,y;z)=IN{P(x,y;z)}×IFS{y(x,y;z)}, the Newton iteration method, the steepest descent method and the damped least squares method can be used to alternately iterate and optimize the calculation to obtain the continuous phase distribution function of the subwavelength structure computational hologram.

[0044] (2) If Figure 2 As shown, the continuous phase distribution function obtained in step (1) is subjected to a discrete phase numerical process of N gray levels, where N=2 k , k is a positive integer.

[0045] When the continuous phase distribution function obtained in step (1) is subjected to the discrete phase numerical processing of N gray levels, the continuous phase distribution function is divided into M phase periods, and the M phase periods are divided into N equal parts respectively, and the nth part is subjected to 2π / N×n quantization processing. The principle of quantization processing is rounding, where n is a positive integer ≤ N; M is a positive integer, and the value is determined by the continuous phase distribution function. The function for calculating the hologram of the subwavelength structure is Phi(x, y; z) divided by 2π, and the positive integer part of the obtained number is taken.

[0046] (3) Design a mapping data table between the structural parameters of the subwavelength structural unit in the subwavelength structure computational hologram and the discrete phase data, and use this mapping data table as the basis for the structural design of the subwavelength structure computational hologram.

[0047] The subwavelength structural unit is a cylinder or a circular hole cylinder. The height of the cylinder or circular hole cylinder is: lamda / (g-1), where lamda is the wavelength of the light emitted by the standard interferometer for detection, and g is the refractive index of the subwavelength structure calculation hologram.

[0048] Specifically, the mapping relationship between the structural parameters of the sub-wavelength structural unit in the sub-wavelength structured computer-generated hologram and the discretized phase data is:

[0049] When the subwavelength structural unit is a cylinder, lamda represents the wavelength of the light emitted by the standard interferometer for detection, the diameter of the cylinder is R1, the refractive index of the cylinder is g, the incident light is a plane wave, and the height H1 of the cylinder is lamda / (g-1). R1 ​​is set as a variable parameter, and lamda, g, and H1 are substituted into the Maxwell equations as constant variable parameters. The output variable is the phase. The time-domain finite difference method is used as the approximate numerical calculation principle. R1 is scanned from 60nm to 700nm at intervals of 10nm, and the output phase value is recorded to obtain the mapping relationship between the cylinder and the discretized phase data.

[0050] When the subwavelength structural unit is a circular hole column, lamda represents the wavelength of the light emitted by the standard interferometer for detection, the outer diameter of the cylindrical hole is R2, the diameter of the central hole of the circular hole column is r2, the refractive index of the cylinder is g, the incident light is a plane wave, and the height H2 of the circular hole column is lamda / (g-1). R2 and r2 are set as variable parameters, lamda, g, and H2 are used as constant variable parameters and substituted into the Maxwell equations. The output variable is the phase. The time-domain finite difference method is used as the approximate numerical calculation principle. R2 and r2 are both scanned from 60nm to 700nm at intervals of 10nm. The output phase value is recorded to obtain the mapping relationship between the circular hole column and the discretized phase data.

[0051] (4) Based on the mapping data table in step (3), the discretized phase values ​​in step (2) are converted to obtain a subwavelength structure unit design scheme of the subwavelength structure computer-generated hologram, and pattern processing is performed on a substrate according to the subwavelength structure unit design scheme to obtain the subwavelength structure computer-generated hologram. The material of the substrate is preferably quartz.

[0052] (5) The subwavelength structured computer-generated hologram is placed at the placement position determined in step (1), and the light for detection is emitted by the standard interferometer, which is processed into a plane wave by the standard plane mirror, and a part of the plane wave is reflected back to the standard interferometer to form a reference light path, and the other part of the plane wave is transmitted through the standard plane mirror and incident on the subwavelength structured computer-generated hologram, converting the incident plane wave into an aspheric wave, and the aspheric wave matches the surface shape of the aspheric reflector to be measured, and the aspheric wave is incident on the aspheric reflector to be measured, and after being reflected by the aspheric reflector to be measured, returns to the standard interferometer along the original path to form a test light path.

[0053] (6) Adjust the spatial posture of the aspheric reflector to be measured so that the light of the test light path interferes with the light of the reference light path in the standard interferometer to form a zero-position interference measurement, and obtain the surface shape data of the aspheric reflector to be measured by solving the obtained interference pattern.

[0054] Example 1: Take the detection of an extreme ultraviolet concave aspheric surface as an example.

[0055] The surface features of the tested extreme ultraviolet concave aspheric surface are: aperture 40mm, curvature radius -120mm, quadratic surface coefficient -0.8, and the ideal surface shape is as follows: Figure 3 As shown, the above-mentioned extreme ultraviolet concave aspheric surface is obtained by processing.

[0056] The surface shape information of the processed extreme ultraviolet concave aspheric surface is detected using the surface shape detection method of the extreme ultraviolet lithography objective lens based on subwavelength structure computer-generated holography of the present invention. The method steps are as follows:

[0057] Step 1: Combine Figure 3According to the surface shape data of the aspheric reflector under test, the placement position of the matching subwavelength structured computational generated hologram (CGH) is determined, and the continuous phase distribution function of the CGH is calculated based on the placement position and surface shape data.

[0058] Step 2: Combine Figure 4 , the continuous phase distribution function obtained in the first step is subjected to 8 grayscale discretization numerical processing, specifically: the continuous phase distribution function is divided into 262 phase periods, and the 262 phase periods are divided into 8 equal parts, and the nth part is quantized by 2π / N×n. The principle of quantization processing is rounding, where n=1, 2, 3, ..., 8.

[0059] Step 3: Combine Figure 5 , design a mapping data table between the structural parameters of the sub-wavelength cylinder in the computational hologram and the discretized phase data. This data table will serve as the basis for the structural design of the computational hologram.

[0060] Step 4: Based on the mapping data table, the discretized phase data obtained in step 2 is converted to complete the subwavelength structure design of the subwavelength structure computer-generated hologram (CGH), and nano-patterning is performed on the quartz substrate.

[0061] Step 5: Combine Figure 1 The processed computer-generated hologram is placed at the designed position in the optical path of the standard interferometer. The light emitted by the standard interferometer is converted into a plane wave through a standard plane mirror, and then passes through the computer-generated hologram to become an aspheric wave that matches the aspheric reflector to be measured.

[0062] Step 6: Combine Figure 6 , a high-precision six-dimensional adjustment structure is used to clamp the aspheric mirror under test, and the spatial posture of the aspheric mirror under test is precisely adjusted, so that the aspheric wave incident on the aspheric mirror under test returns along the original path until it enters the standard interferometer, forming a zero-position interference measurement. By solving the obtained interference pattern, the high-precision surface shape data of the aspheric mirror under test can be obtained with an RMS of 0.2nm.

Claims

1. A method for detecting the surface shape of an extreme ultraviolet lithography objective lens based on subwavelength structure computational holography, wherein the extreme ultraviolet lithography objective lens is an aspheric reflector, characterized in that: The following steps are involved: Step 1: Determine the placement position of a subwavelength structured computational hologram that matches the aspheric reflector under test based on its design surface shape data, and calculate the continuous phase distribution function of the subwavelength structured computational hologram based on the placement position and the surface shape data; Step 2: Perform discrete phase numerical processing of N gray levels on the continuous phase distribution function obtained in step 1, where N=2 k , k is a positive integer; Step 3: Design a mapping data table between the structural parameters of the sub-wavelength structural units in the sub-wavelength structure computational hologram and the discretized phase data, and use this mapping data table as a basis for the structural design of the sub-wavelength structure computational hologram; Step 4: Based on the mapping data table in step 3, the discretized phase values ​​in step 2 are converted to obtain a subwavelength structure unit design scheme of the subwavelength structure computer-generated hologram, and pattern processing is performed on the substrate according to the subwavelength structure unit design scheme to obtain the subwavelength structure computer-generated hologram; Step 5: placing the subwavelength structured computer-generated hologram at the placement position determined in step 1; emitting detection light from a standard interferometer, which is processed into a plane wave by a standard plane mirror; and reflecting a portion of the plane wave back to the standard interferometer to form a reference light path; while another portion of the plane wave is transmitted through the standard plane mirror and incident on the subwavelength structured computer-generated hologram; converting the incident plane wave into an aspheric wave, and matching the surface shape of the aspheric reflector to be measured; and then incident on the aspheric reflector to be measured, and after being reflected by the aspheric reflector to be measured, returning to the standard interferometer along the original path to form a test light path; Step 6: Adjust the spatial posture of the aspheric reflector to be measured so that the light of the test light path interferes with the light of the reference light path in the standard interferometer to form a zero-position interferometry measurement, and obtain the surface shape data of the aspheric reflector to be measured by solving the obtained interference pattern. In step 3, the subwavelength structural unit is a cylinder or a circular hole cylinder; The height of the cylinder or hole cylinder is: lamda / (g-1), where lamda is the wavelength of the light emitted by the standard interferometer for detection, and g is the refractive index of the sub-wavelength structure calculation hologram; In step 3, the mapping relationship between the structural parameters of the sub-wavelength structural unit in the sub-wavelength structure calculation hologram and the discretized phase data is: When the subwavelength structural unit is a cylinder, lamda represents the wavelength of the light emitted by the standard interferometer for detection, the diameter of the cylinder is R1, the refractive index of the cylinder is g, the incident light is a plane wave, and the height H1 of the cylinder is lamda / (g-1). R1 ​​is set as a variable parameter, and lamda, g, and H1 are substituted into the Maxwell equations as constant variable parameters. The output variable is the phase. The time-domain finite difference method is used as the approximate numerical calculation principle. R1 is scanned from 60nm to 700nm at intervals of 10nm, and the output phase value is recorded to obtain the mapping relationship between the cylinder and the discretized phase data. When the subwavelength structural unit is a circular hole column, lamda represents the wavelength of the light emitted by the standard interferometer for detection, the outer diameter of the cylindrical hole is R2, the diameter of the central hole of the circular hole column is r2, the refractive index of the cylinder is g, the incident light is a plane wave, and the height H2 of the circular hole column is lamda / (g-1). R2 and r2 are set as variable parameters, lamda, g, and H2 are used as constant variable parameters and substituted into the Maxwell equations. The output variable is the phase. The time-domain finite difference method is used as the approximate numerical calculation principle. R2 and r2 are both scanned from 60nm to 700nm at intervals of 10nm. The output phase value is recorded to obtain the mapping relationship between the circular hole column and the discretized phase data.

2. The method for detecting the surface shape of an EUV lithography objective lens based on subwavelength structure computational holography according to claim 1, wherein: When determining the placement position of the subwavelength structured computer-generated hologram, the subwavelength structured computer-generated hologram is placed between the standard interferometer and the aspheric reflector to be measured. The distance between the standard interferometer and the vertex of the aspheric reflector to be measured is L. The distance between the subwavelength structured computer-generated hologram and the standard interferometer is between L / 2 and 2L / 3, and the distance between the subwavelength structured computer-generated hologram and the aspheric surface of the aspheric reflector to be measured satisfies the Fraunhofer diffraction propagation distance.

3. The method for detecting the surface shape of an EUV lithography objective lens based on subwavelength structure computational holography according to claim 1, wherein: In step 1, the principle of calculating the continuous phase distribution function of the subwavelength structure computational hologram is: suppose the plane wave emitted by the standard interferometer is P(x,y;z), the function of calculating the subwavelength structure computational hologram is Phi(x,y;z), and the aspheric surface shape function of the aspheric reflector to be measured is y(x,y;z), then there is a mathematical relationship Phi(x,y;z)=IN{P(x,y;z)}×IFS{y(x,y;z)}, where IN{P(x,y;z)} represents the inverse matrix of P(x,y;z); IFS{y(x,y;z)} represents the inverse Fresnel diffraction transformation of y(x,y;z).

4. The method for detecting the surface shape of an EUV lithography objective lens based on subwavelength structure computational holography according to claim 3, wherein: In step 2, when performing discretized phase numerical processing of N gray levels on the continuous phase distribution function obtained in step 1, the continuous phase distribution function is divided into M phase periods, and each of the M phase periods is divided into N equal parts, and a quantization process of 2π / N×n is performed on the nth part. The principle of quantization processing is rounding, where n is a positive integer ≤ N; M is a positive integer, and its value is determined by the continuous phase distribution function. The function for calculating the hologram of the subwavelength structure is Phi(x, y; z) divided by 2π, and the resulting number is a positive integer.

5. The method for detecting the surface shape of an EUV lithography objective lens based on subwavelength structure computational holography according to claim 1, wherein: The substrate is made of quartz.

6. The system for detecting the surface shape of an EUV lithography objective lens based on subwavelength structure computer-generated holography according to any one of claims 1 to 5, comprising: A standard interferometer, used to emit light for detection and detect the reflected light, a standard plane mirror, provided at the optical path exit of the standard interferometer, for processing the light emitted by the standard interferometer into a plane wave, wherein a portion of the plane wave is reflected back to the standard interferometer to form a reference optical path, and another portion of the plane wave is transmitted through the standard plane mirror; A subwavelength structured computer-generated hologram, wherein a plane wave transmitted through the standard plane mirror is incident on the subwavelength structured computer-generated hologram, the incident plane wave is converted into an aspheric wave, and the aspheric wave matches the surface shape of the aspheric reflector to be measured. The aspheric wave is incident on the aspheric reflector to be measured, and after being reflected by the aspheric reflector to be measured, it returns to the standard interferometer along the original path to form a test light path. The light of the test light path interferes with the light of the reference light path in the standard interferometer to form an interference pattern. The six-dimensional adjustment frame is used to clamp and adjust the position and angle of the aspheric mirror under test during the test process.

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