A method for suppressing periodic errors in large-aperture grating scanning etching based on frequency domain analysis

Abstract

The present invention discloses a method for suppressing periodic errors of large-aperture grating scanning etching based on frequency domain analysis. The method comprises S1, forming a path function; S2, calculating the removal amount distribution; S3, performing power spectrum density analysis to obtain the spectrum amplitude; S4, extracting the frequency; S5, calculating the scanning line spacing under the frequency; S6, forming a new scanning path; S7, processing the large-aperture grating sample; S8, judging whether the large-aperture grating sample meets the requirements, if it meets the requirements, ending and exiting, otherwise extracting the spectrum amplitude of the frequency distribution of the error in the spectrum higher than the drawing error, and jumping to execute S4. The present invention aims to solve the problems of low efficiency and easy sputtering pollution in the existing large-aperture scanning etching process, and improve the processing efficiency and processing quality of large-aperture optical elements.

Description

Technical Field

[0001] The invention belongs to the technical field of reactive ion etching processing of optical elements and micro-nano structures, and specifically relates to a method for suppressing periodic errors of large-aperture grating scanning etching based on frequency domain analysis. Background Art

[0002] In recent years, due to the rapid development of ultra-smooth optical surfaces, large-scale integrated circuits, chip wafers, large-aperture diffraction gratings and MEMS devices, the reactive ion beam etching (RIBE) technology of large-aperture optical components (≥200 mm) has been widely used. Traditional large-aperture optical component etching is carried out using reactive ion etching (RIE) technology, which requires expanding the size of the discharge chamber according to the size of the sample, increasing the volume of the discharge area and the distribution area of ​​the coil. However, the uniformity of large-aperture discharge plasma is difficult to guarantee. At the same time, it is difficult to obtain nano-precision structures, low surface damage and high verticality side walls during the RIE etching process. Therefore, the reactive ion beam etching (RIBE) technology developed based on reactive ion beam etching has been widely used in large-aperture etching. However, since the beam diameter of the reactive etching ion source is relatively small (generally ≤150 mm), when etching large-aperture samples, it is usually necessary to use a scanning method to perform full-aperture uniform processing. At present, China mostly uses adjustable apertures to block the beam to form a rectified distribution modulation, but this method reduces the etching efficiency. At the same time, long-term use will cause sputtering contamination of the adjustable aperture material on the grating surface. Summary of the invention

[0003] Technical problem to be solved by the present invention: In view of the above-mentioned problems in the prior art, a method for suppressing periodic errors in large-aperture grating scanning etching based on frequency domain analysis is provided. The present invention aims to solve the problems of low efficiency and easy sputtering pollution in existing large-aperture scanning etching processes, and to improve the processing efficiency and processing quality of large-aperture optical components.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0005] A method for suppressing periodic errors of large-aperture grating scanning etching based on frequency domain analysis, comprising:

[0006] Step S1, preliminarily determine the initial line spacing And form the path function ;

[0007] Step S2, according to the path function And the removal function calculates the removal amount distribution ;

[0008] Step S3, the removal amount distribution Perform power spectral density analysis to obtain the initial spectrum amplitude;

[0009] Step S4: extract the frequency at which the current spectrum amplitude is minimum ;

[0010] Step S5, according to Calculate frequency The corresponding scanning line spacing ;

[0011] Step S6, using frequency The corresponding scanning line spacing Forming a new scan path ;

[0012] Step S7, using the new scanning path Scanning and etching of large-aperture grating samples;

[0013] Step S8, determine whether the surface groove depth distribution of the large-aperture grating sample meets the requirements. If it does, end and exit. Otherwise, extract the spectrum amplitude of the frequency distribution in which the error in the spectrum is higher than the drawing error as the new current spectrum amplitude, and jump to step S4 to continue iteration.

[0014] Optionally, in step S1, a path function is formed The function expression is:

[0015] ,

[0016] In the above formula, is the path function The coordinates of the point on is the number of line breaks, For line spacing, is the scanning time, , , represents an integer, represents a real number, and , is the diameter of the large aperture grating sample, Express Round up; in step S6, a new scanning path is formed The function expression is:

[0017] ,

[0018] In the above formula, is the new number of line breaks, and , is the aperture of the large-aperture grating sample in the y-axis direction, Express Round up, For frequency The corresponding scanning line spacing is shown below.

[0019] Optionally, in step S2, according to the path function And the removal function calculates the removal amount distribution Refers to the calculation of the removal amount distribution based on the Gaussian removal function , and the removal amount distribution is calculated based on the Gaussian removal function The function expression is:

[0020] ,

[0021] In the above formula, represents the convolution operation, is the path function, is the Gaussian removal function, are the coordinates of points on the scanning path.

[0022] Optionally, the function expression of the Gaussian removal function is:

[0023] ,

[0024] In the above formula, is the amplitude of the Gaussian removal function, is the coordinate of the point on the scanning path, is the Gaussian distribution parameter.

[0025] Optionally, when judging whether the surface groove depth distribution of the large-aperture grating sample meets the requirements in step S8, it includes detecting the depth of the test points of the surface grooves of the large-aperture grating sample, and calculating the depth uniformity index according to the depth of the test points of the surface grooves of the large-aperture grating sample. If the depth uniformity index is greater than a preset threshold, it is determined that the surface groove depth distribution of the large-aperture grating sample meets the requirements; otherwise, it is determined that the surface groove depth distribution of the large-aperture grating sample does not meet the requirements.

[0026] Optionally, the calculation function expression of the depth uniformity index is:

[0027] ,

[0028] In the above formula, is the depth uniformity index, ~ are the depths of the test points of the 1st to nth surface grooves, is the depth of the test point of the i-th surface groove, and n is the number of test points of the surface groove.

[0029] Optionally, the feature is that the acquisition of the Gaussian removal function includes:

[0030] S101, select the same diameter as the large aperture grating sample The plane sample with the same material as the substrate of the large-aperture grating sample is used to obtain the initial surface error data of the plane sample using a laser interferometer. ;

[0031] S102, clamping the plane sample on a fixture of a vacuum etching device;

[0032] S103, according to the process requirements, introduce reactive process gas into the ion source of the vacuum etching system according to the ratio, and set the plasma discharge power With total accelerating voltage ;

[0033] S104, moving the ion source to the center of the planar sample to achieve fixed-point residence removal, and recording the residence time ;

[0034] S105, using laser interferometer to detect surface error data of the plane sample after fixed-point residence is removed , and the initial surface error data of the plane specimen Calculate the removal amount under current process conditions ;

[0035] S106, according to Calculate the removal function per unit time ;

[0036] S107, using the least squares method to remove the function within a unit time Gaussian fitting is performed to obtain a Gaussian removal function.

[0037] Optionally, in step S101, a grating having the same diameter as the large aperture grating sample is selected. When the plane sample is made of the same material as the substrate of the large-aperture grating sample, the surface accuracy PV value of the selected plane sample is better than , is the wavelength of the laser interferometer used.

[0038] Optionally, in step S101, a laser interferometer is used to obtain initial surface error data of the plane sample. And in step S105, the surface error data after the fixed point residence of the plane sample is detected by using a laser interferometer When the surface error data is obtained by multiple detections with a laser interferometer, the average value is calculated as the final surface error data. Or surface error data , and the temperature of the measurement environment for multiple tests is 20℃±0.5℃, the interference fringes have no jitter during the test, and the maximum error value of the measurement result is less than , is the wavelength of the laser interferometer used.

[0039] Optionally, the vacuum etching device used in step S102 includes a three-dimensional motion platform, a control device and a gas distribution unit, a wide beam ion source is provided on the three-dimensional motion platform, a water cooling module is provided on the wide beam ion source, a water cooling fixture for clamping and fixing the large-aperture grating sample to be processed is arranged in the ion source emission direction of the wide beam ion source, the water cooling fixture is connected to a water cooler, the gas distribution unit includes a gas mixing tank and multiple groups of gas cylinders, and each gas cylinder is connected to the gas mixing tank through a corresponding gas flow control valve, the output end of the gas mixing tank is connected to the wide beam ion source, and the water cooler, wide beam ion source, three-dimensional motion platform and gas flow control valve are all connected to the control device.

[0040] Compared with the prior art, the present invention has the following advantages: 1. The present invention iteratively extracts the frequency spectrum amplitude of the frequency distribution whose error in the spectrum is higher than the drawing error as the new current spectrum amplitude, and extracts the frequency when the current spectrum amplitude is the smallest. ; Calculate frequency The corresponding scanning line spacing ; Frequency of use The corresponding scanning line spacing Forming a new scan path ; Using the new scan path Scanning and etching large-aperture grating samples can solve the problems of low uniformity of grating groove depth distribution, low process efficiency, and easy sputtering pollution in the existing large-aperture grating scanning etching process, and improve the processing efficiency and processing quality of large-aperture grating elements. 2. The scheme of the present invention does not require any improvement or redesign of the ion source equipment, and only needs to calculate the optimal line spacing at the algorithm level, which is low in cost. At the same time, there is no need to block and modulate the ion source beam, avoiding the low etching efficiency and possible sputtering pollution caused by adding an aperture to block the beam. 3. The scheme of the present invention only needs to obtain the removal function of the ion source, which is independent of the ion source discharge mode. It can be oriented to various types of ion sources commonly used in the industry (such as DC cathode ion source, radio frequency ion source, microwave ion source, etc.), and can be oriented to various types of process parameters and process gases to meet the substrate processing of different materials. 4. The scheme of the present invention has nothing to do with the caliber of the sample to be etched. Compared with the existing RIE etching technology, the scheme of the present invention does not need to redesign the discharge chamber for large-aperture samples and calculate the plasma distribution characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the process of the embodiment of the present invention.

[0042] Figure 2 Schematic diagram of the scanning trajectory in an embodiment of the present invention.

[0043] Figure 3 Schematic diagram of the preprocessing process of the method according to the embodiment of the present invention.

[0044] Figure 4 Schematic diagram of the structure of the vacuum etching system in an embodiment of the present invention.

[0045] Figure 5 It is the removal amount collected in the embodiment of the present invention.

[0046] Figure 6 It is the normalized Gaussian distribution after fitting the removal function in the embodiment of the present invention.

[0047] Figure 7 Path function distribution when the line spacing is 10 mm in an embodiment of the present invention.

[0048] Figure 8 It is the error of periodic distribution on the surface with a line spacing of 10 mm in the embodiment of the present invention.

[0049] Fig. 9 In the embodiment of the present invention Figure 7 Spectral plot of the PSD analysis of the distribution error.

[0050] Fig.10 Schematic diagram of the grating arrangement and detection result distribution in an embodiment of the present invention.

[0051] Fig.11 It is an atomic force image of the three-dimensional distribution of microstructure grooves on the grating surface in an embodiment of the present invention. DETAILED DESCRIPTION

[0052] In order to make the technical solution of the present invention better understood by the persons skilled in the art, the technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings in the embodiments of the present invention. In this embodiment, the sample to be etched is a fused quartz substrate with a total diameter of 230 mm and an effective diameter of 220 mm. The surface of the grating sample is patterned with a HSQ photoresist mask, and the uniformity requirement is 6%. The vacuum etching system used in this embodiment is as follows: Figure 4 As shown, the vacuum etching system includes a three-dimensional motion platform 5, a control device 7 and a gas distribution unit 8. The three-dimensional motion platform 5 is provided with an ion source 3, and the ion source 3 is provided with a water cooling module 4. A water cooling fixture 1 that can be tilted and rotated is arranged in the ion source emission direction of the ion source 3. The water cooling fixture 1 is connected to a water cooler 6 and can rotate 180 degrees in the YZ plane and 360 degrees in the XY plane. The gas distribution unit 8 includes a gas mixing tank 9 and multiple groups of gas cylinders 11, and each gas cylinder 11 is connected to the gas mixing tank 9 through a corresponding gas flow control valve 10. The output end of the gas mixing tank 9 is connected to the reactive etching ion source 3, and the water cooler 6, the ion source 3, the three-dimensional motion platform 5 and the gas flow control valve 10 are all connected to the control device 7. During operation, the sample to be etched is mounted on a tiltable and rotatable water-cooling fixture 1, and vacuum thermal conductive silicone grease is applied to the back of the sample to be etched to ensure good contact with the water-cooling fixture 1. The water cooler 6 is turned on to ensure that the water cooling cycle is normal and the water cooling module 4 operates normally, so that the surface temperature of the sample to be etched does not exceed 30°C. The ion source 3 is a coaxial ECR (Electron cyclotron resonance) ion source with a beam aperture of 80mm. The ion extraction system of the ion source 3 is a double-grid structure consisting of a screen grid and an acceleration grid.

[0053] like Figure 1 As shown, the large-aperture grating scanning etching period error suppression method based on frequency domain analysis in this embodiment includes:

[0054] Step S1, preliminarily determine the initial line spacing And form the path function ;

[0055] Step S2, according to the path function And the removal function calculates the removal amount distribution ,like Figure 5 As shown;

[0056] Step S3, the removal amount distribution Perform power spectral density (PSD) analysis to obtain the initial spectrum amplitude;

[0057] Step S4: extract the frequency at which the current spectrum amplitude is minimum ;

[0058] Step S5, according to Calculate frequency The corresponding scanning line spacing ;

[0059] Step S6, using frequency The corresponding scanning line spacing Forming a new scan path ;

[0060] Step S7, using the new scanning path Scanning and etching of large-aperture grating samples;

[0061] Step S8, determine whether the surface groove depth distribution of the large-aperture grating sample meets the requirements. If it does, end and exit. Otherwise, extract the spectrum amplitude of the frequency distribution in which the error in the spectrum is higher than the drawing error as the new current spectrum amplitude, and jump to step S4 to continue iteration.

[0062] In step S1 of this embodiment, a path function is formed The function expression is:

[0063] ,

[0064] In the above formula, is the path function The coordinates of the point on is the number of line breaks, For line spacing, is the scanning time, , , represents an integer, represents a real number, and , is the diameter of the large aperture grating sample, Express In this embodiment, the path function The function expression represents the path of the raster scan with 0 and 1, that is, the position where the ion source passes. 0 means that it does not pass through the coordinate, and 1 means that it passes through the coordinate.

[0065] In step S2 of this embodiment, according to the path function And the removal function calculates the removal amount distribution Refers to the calculation of the removal amount distribution based on the Gaussian removal function , and the removal amount distribution is calculated based on the Gaussian removal function The function expression is:

[0066] ,

[0067] In the above formula, represents the convolution operation, is the path function, is the Gaussian removal function, are the coordinates of points on the scanning path.

[0068] The function expression of the Gaussian removal function in this embodiment is:

[0069] ,

[0070] In the above formula, is the amplitude of the Gaussian removal function, is the coordinate of the point on the scanning path, is the Gaussian distribution parameter.

[0071] In step S6 of this embodiment, a new scanning path is formed The function expression is:

[0072] ,

[0073] In the above formula, is the new number of line breaks, and , is the aperture of the large-aperture grating sample in the y-axis direction, Express Round up, For frequency The corresponding scanning line spacing is shown below.

[0074] like Figure 2 As shown, for x axis, is a line-feed scan, only at frequency There is a path on the integer multiple of the corresponding scanning line pitch; that is, when changing a line, the jump size is the frequency The corresponding scanning line spacing is shown below. For the y-axis, it is a continuous scan, and time t is the single-line scanning time. In other places, the ion source does not pass through, that is, there is no scanning path, so the path function .

[0075] In step S8 of this embodiment, when judging whether the surface groove depth distribution of the large-aperture grating sample meets the requirements, it includes detecting the depth of the test point of the surface groove of the large-aperture grating sample, and calculating the depth uniformity index according to the depth of the test point of the surface groove of the large-aperture grating sample. If the depth uniformity index is greater than a preset threshold, it is determined that the surface groove depth distribution of the large-aperture grating sample meets the requirements, otherwise it is determined that the surface groove depth distribution of the large-aperture grating sample does not meet the requirements. Among them, the grating groove depth detection can be completed by using atomic force microscope, laser confocal microscope, white light interferometer and other equipment according to the grating groove period and depth size, and the detection accuracy should be better than 0.5 nm.

[0076] The calculation function expression of the depth uniformity index in this embodiment is:

[0077] ,

[0078] In the above formula, is the depth uniformity index, ~ are the depths of the test points of the 1st to nth surface grooves, is the depth of the test point of the i-th surface groove, and n is the number of test points of the surface groove.

[0079] like Figure 3 As shown, the acquisition of the Gaussian removal function in this embodiment includes:

[0080] S101, select the same diameter as the large aperture grating sample The plane sample with the same material as the substrate of the large-aperture grating sample is used to obtain the initial surface error data of the plane sample using a laser interferometer. ;

[0081] S102, clamping the plane sample on a fixture of a vacuum etching device;

[0082] S103, according to the process requirements, introduce reactive process gas into the ion source of the vacuum etching system according to the ratio, and set the plasma discharge power With total accelerating voltage In this embodiment, the reactive process gas ratio is (CHF3:9sccm:O2:1sccm), and the plasma discharge power is set ( With total accelerating voltage (Screen grid voltage V s =400V, acceleration gate voltage V a =100V);

[0083] S104, moving the ion source to the center of the planar sample to achieve fixed-point residence removal, and recording the residence time , the residence time in this embodiment ;

[0084] S105, using laser interferometer to detect surface error data of the plane sample after fixed-point residence is removed , and the initial surface error data of the plane specimen Calculate the removal amount under current process conditions ;

[0085] S106, according to Calculate the removal function per unit time ;

[0086] S107, using the least squares method to remove the function within a unit time Gaussian fitting is performed to obtain the Gaussian removal function, namely:

[0087] ,

[0088] In the above formula, is the amplitude of the Gaussian removal function, is the coordinate of the point on the scanning path, is the Gaussian distribution parameter. In this embodiment, the least square method is used to perform Gaussian fitting on the removal function to obtain the parameters of the Gaussian removal function. In this embodiment, the normalized Gaussian distribution after fitting the removal function is as follows: Figure 6 shown.

[0089] In step S101 of this embodiment, a grating having the same diameter as the large aperture sample is selected. When the plane sample is made of the same material as the substrate of the large-aperture grating sample, the surface accuracy PV value of the selected plane sample is better than , is the laser wavelength of the laser interferometer used. , large aperture grating sample diameter Larger than the ion source aperture 1.2 times of the diameter, the specific diameter is The surface roughness of the fused silica optical grade flat sample is 0.5nm.

[0090] In order to ensure the repeatability and effectiveness of the measurement, in step S101 of this embodiment, a laser interferometer is used to obtain the initial surface error data of the plane sample. And in step S105, the surface error data after the fixed point residence of the plane sample is detected by using a laser interferometer When the surface error data is obtained by multiple detections with a laser interferometer, the average value is calculated as the final surface error data. Or surface error data , and the temperature of the measurement environment for multiple tests is 20℃±0.5℃, the interference fringes have no jitter during the test, and the maximum error value of the measurement result is less than , is the laser wavelength of the laser interferometer used, which is specifically 632.8 nm in this embodiment.

[0091] like Figure 4 As shown, the vacuum etching device used in step S102 of this embodiment includes a three-dimensional motion platform 5, a control device 7 and a gas distribution unit 8, a wide beam ion source 3 is provided on the three-dimensional motion platform 5, a water cooling module 4 is provided on the wide beam ion source 3, a water cooling fixture 1 for clamping and fixing the large-aperture grating sample 2 to be processed is arranged in the ion source emission direction of the wide beam ion source 3, and the water cooling fixture 1 is connected to the water cooling machine 6, and the gas distribution unit 8 includes a gas mixing tank 9 and multiple groups of gas cylinders 11, and each gas cylinder 11 is connected to the gas mixing tank 9 through a corresponding gas flow control valve 10, and the output end of the gas mixing tank 9 is connected to the wide beam ion source 3, and the water cooling machine 6, the wide beam ion source 3, the three-dimensional motion platform 5 and the gas flow control valve 10 are all connected to the control device 7. When the process gas is introduced in step S103, its gas flow is precisely controlled based on the gas mass flow meter controlled by the control device 7 (computer device). The flow control accuracy is (0.5% FS); the plasma discharge power is provided by the ion source discharge power supply (according to the ion source discharge principle, it can be divided into radio frequency power supply, microwave power supply, DC power supply, etc., with a power range of 0-500W), and the grid voltage is provided by a DC voltage-stabilized grid control power supply (voltage control accuracy ±0.3V, voltage range of 300V-1200V). In step S103, the ion source movement is controlled by the motion of the three-dimensional motion platform 5 through the numerical control program in the control device 7. The positioning accuracy of the three-dimensional motion platform 5 is better than 8 μm, and the motion range is greater than 1.2 times the caliber of the sample to be etched. The residence time is also realized by the numerical control program in the control device 7.

[0092] In step S1 of this embodiment, the initial line spacing is preliminarily determined. , forming a path function like Figure 7 As shown, the error of the surface periodic distribution is Figure 8 In step S3, the removal amount distribution Perform power spectral density (PSD) analysis to obtain the initial spectrum amplitude. The spectrum diagram is as follows: Fig. 9 As shown, Fig. 9 middle For line spacing The error frequency generated during scanning, At the same time, it can be observed in the figure that the frequency when the power spectrum density amplitude is the smallest In this embodiment, in a certain round of iteration, step S4 extracts the frequency at which the current spectrum amplitude is the minimum. ; Step S5 according to Calculate frequency The corresponding scanning line spacing ; Step S6, using frequency The corresponding scanning line spacing Forming a new scan path ; Step S7, using the new scanning path The large-aperture grating sample was scanned and etched; considering that large-size gratings are difficult to test in atomic force equipment, 16 rectangular samples with a side length of 40 mm were evenly arranged around it with a spacing of 10 mm (such as Fig.10 ) as the test sample, Fig.11 The depth uniformity index is calculated in step S8. .

[0093] In summary, this embodiment iteratively extracts the frequency spectrum amplitude of the frequency distribution whose error in the spectrum is higher than the drawing error as the new current spectrum amplitude, and extracts the frequency when the current spectrum amplitude is the smallest. ; Calculate frequency The corresponding scanning line spacing ; Frequency of use The corresponding scanning line spacing Forming a new scan path ; Using the new scan path Scanning and etching large-aperture grating samples can solve the problems of low uniformity of grating groove depth distribution, low process efficiency, and easy sputtering pollution in the existing large-aperture grating scanning etching process, and improve the processing efficiency and processing quality of large-aperture grating elements. This embodiment does not require any improvement or redesign of the ion source equipment, and only needs to calculate the optimal line spacing at the algorithm level, which is low in cost. At the same time, there is no need to block and modulate the ion source beam, avoiding the low etching efficiency and possible sputtering pollution caused by adding an aperture to block the beam. This embodiment only needs to obtain the removal function of the ion source, which is independent of the ion source discharge mode. It can be oriented to various types of ion sources commonly used in the industry (such as DC cathode ion source, radio frequency ion source, microwave ion source, etc.), and can be oriented to various types of process parameters and process gases to meet the substrate processing of different materials. This embodiment is independent of the caliber of the sample to be etched. Compared with the existing RIE etching technology, there is no need to redesign the discharge chamber for large-aperture samples and calculate the plasma distribution characteristics.

[0094] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for suppressing periodic errors in large-aperture grating scanning etching based on frequency domain analysis, characterized in that: include: Step S1, preliminarily determine the initial line spacing And form the path function ; Step S2, according to the path function And the removal function calculates the removal amount distribution ; Step S3, the removal amount distribution Perform power spectral density analysis to obtain the initial spectrum amplitude; Step S4: extract the frequency at which the current spectrum amplitude is minimum ; Step S5, according to Calculate frequency The corresponding scanning line spacing ; Step S6, using frequency The corresponding scanning line spacing Forming a new scan path ; Step S7, using the new scanning path Scanning and etching of large-aperture grating samples; Step S8, determine whether the surface groove depth distribution of the large-aperture grating sample meets the requirements. If it does, end and exit. Otherwise, extract the spectrum amplitude of the frequency distribution in which the error in the spectrum is higher than the drawing error as the new current spectrum amplitude, and jump to step S4 to continue iteration.

2. The method for suppressing periodic errors of large-aperture grating scanning etching based on frequency domain analysis according to claim 1 is characterized in that: In step S1, a path function is formed The function expression is: ， In the above formula, is the path function The coordinates of the point on is the number of line breaks, For line spacing, is the scanning time, , , represents an integer, represents a real number, and , is the diameter of the large aperture grating sample, Express Round up; in step S6, a new scanning path is formed The function expression is: ， In the above formula, is the new number of line breaks, and , is the aperture of the large-aperture grating sample in the y-axis direction, Express Round up, For frequency The corresponding scanning line spacing is shown below.

3. The method for suppressing periodic errors of large-aperture grating scanning etching based on frequency domain analysis according to claim 1 is characterized in that: In step S2, according to the path function And the removal function calculates the removal amount distribution Refers to the calculation of the removal amount distribution based on the Gaussian removal function , and the removal amount distribution is calculated based on the Gaussian removal function The function expression is: ， In the above formula, represents the convolution operation, is the path function, is the Gaussian removal function, are the coordinates of points on the scanning path.

4. The method for suppressing periodic errors of large-aperture grating scanning etching based on frequency domain analysis according to claim 3 is characterized in that: The function expression of the Gaussian removal function is: ， In the above formula, is the amplitude of the Gaussian removal function, is the coordinate of the point on the scanning path, is the Gaussian distribution parameter.

5. The method for suppressing periodic errors of large-aperture grating scanning etching based on frequency domain analysis according to claim 1, characterized in that: When judging whether the surface groove depth distribution of the large-aperture grating sample meets the requirements in step S8, it includes detecting the depth of the test point of the surface groove of the large-aperture grating sample, and calculating the depth uniformity index according to the depth of the test point of the surface groove of the large-aperture grating sample. If the depth uniformity index is greater than a preset threshold, it is determined that the surface groove depth distribution of the large-aperture grating sample meets the requirements, otherwise it is determined that the surface groove depth distribution of the large-aperture grating sample does not meet the requirements.

6. The method for suppressing periodic errors of large-aperture grating scanning etching based on frequency domain analysis according to claim 5 is characterized in that: The calculation function expression of the depth uniformity index is: ， In the above formula, is the depth uniformity index, ~ are the depths of the test points of the 1st to nth surface grooves, is the depth of the test point of the i-th surface groove, and n is the number of test points of the surface groove.

7. The method for suppressing periodic errors of large-aperture grating scanning etching based on frequency domain analysis according to claim 4 is characterized in that: The acquisition of the Gaussian removal function includes: S101, select the same diameter as the large aperture grating sample The plane sample with the same material as the substrate of the large-aperture grating sample is used to obtain the initial surface error data of the plane sample using a laser interferometer. ; S102, clamping the plane sample on a fixture of a vacuum etching device; S103, according to the process requirements, introduce reactive process gas into the ion source of the vacuum etching system according to the ratio, and set the plasma discharge power With total accelerating voltage ; S104, moving the ion source to the center of the planar sample to achieve fixed-point residence removal, and recording the residence time ; S105, using laser interferometer to detect surface error data of the plane sample after fixed-point residence is removed , and the initial surface error data of the plane specimen Calculate the removal amount under current process conditions ; S106, according to Calculate the removal function per unit time ; S107, using the least squares method to remove the function within a unit time Gaussian fitting is performed to obtain a Gaussian removal function.

8. The method for suppressing periodic errors of large-aperture grating scanning etching based on frequency domain analysis according to claim 7, characterized in that: In step S101, a grating having the same diameter as the large aperture grating sample is selected. When the plane sample is made of the same material as the substrate of the large-aperture grating sample, the surface accuracy PV value of the selected plane sample is better than , is the wavelength of the laser interferometer used.

9. The method for suppressing periodic errors of large-aperture grating scanning etching based on frequency domain analysis according to claim 8, characterized in that: In step S101, the laser interferometer is used to obtain the initial surface error data of the plane sample. And in step S105, the surface error data after the fixed point residence of the plane sample is detected by using a laser interferometer When the surface error data is obtained by multiple detections with a laser interferometer, the average value is calculated as the final surface error data. Or surface error data , and the temperature of the measurement environment for multiple tests is 20℃±0.5℃, the interference fringes have no jitter during the test, and the maximum error value of the measurement result is less than , is the wavelength of the laser interferometer used.

10. The method for suppressing periodic errors of large-aperture grating scanning etching based on frequency domain analysis according to claim 7, characterized in that: The vacuum etching device used in step S102 comprises a three-dimensional motion platform (5), a control device (7) and a gas distribution unit (8), wherein a wide beam ion source (3) is provided on the three-dimensional motion platform (5), and a water cooling module (4) is provided on the wide beam ion source (3). A water cooling fixture (1) for clamping and fixing a large-aperture grating sample (2) to be processed is arranged in the ion source emission direction of the wide beam ion source (3), and the water cooling fixture (1) is connected to a water cooling machine (6). The gas distribution unit (8) comprises a gas mixing tank (9) and a plurality of gas cylinders (11), and each gas cylinder (11) is connected to the gas mixing tank (9) via a corresponding gas flow control valve (10), and the output end of the gas mixing tank (9) is connected to the wide beam ion source (3), and the water cooling machine (6), the wide beam ion source (3), the three-dimensional motion platform (5) and the gas flow control valve (10) are all connected to the control device (7).

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