A method for controlling the surface shape of an optical element based on target-base eccentric deposition

Abstract

A method for surface shape control of optical elements based on target-substrate eccentric deposition includes the following steps: First, select the coating material for the surface shape control layer, calculate the non-uniformity of the film thickness distribution of the coating material under different target-substrate eccentric angles, and determine the actual target-substrate eccentric angle for preparing the surface shape control layer; next, fit the calculated film thickness distribution of the surface shape control layer under the target-substrate eccentric angle to obtain the compensated surface shape power value achieved by the surface shape control layer within a certain deposition time; then, determine the actual deposition time for preparing the surface shape control layer based on the power value to be compensated for the optical element; finally, prepare the surface shape control layer using magnetron sputtering technology. This invention achieves surface shape control by adjusting the relative eccentricity angle between the target and the substrate during magnetron sputtering deposition, adapting to any surface shape optical element without modifying hardware and without affecting the element's optical performance; the thickness of the surface shape control layer is significantly reduced compared to traditional methods, which helps to improve the damage threshold of laser thin film elements.

Description

Technical Field

[0001] This invention belongs to the field of optical thin film preparation technology, specifically relating to a method for active control of the surface shape of optical elements based on target-substrate eccentric deposition. It is applicable to low-frequency surface shape error compensation of optical substrates and coated elements, and can be used in fields with high requirements for the surface shape accuracy of optical elements, such as high-power laser systems and precision imaging systems. Background Technology

[0002] The surface accuracy of optical components has a crucial impact on the beam quality of the entire optical system. For example, low-frequency surface errors (such as large-scale deformations like defocus) can directly cause the wavefront phase distribution to deviate from the ideal state, leading to systematic aberrations, reducing the resolution and contrast of the optical system, and even causing image field distortion or uneven energy distribution in precision imaging systems. For instance, in laser systems, low-frequency surface deviations not only degrade laser beam quality, affecting focusing and transmission characteristics, but also reduce beam coherence due to wavefront distortion, thereby weakening the accuracy of laser processing or detection. In imaging systems, low-frequency errors directly limit the high-frequency response of the modulation transfer function, leading to the loss of detail information. Especially in high-resolution scenarios such as lithography objectives and astronomical telescopes, even small low-frequency surface deviations can cause unacceptable image quality degradation.

[0003] Currently, commonly used methods for controlling the surface shape of optical components include the following: ① Substrate pre-shaping (e.g., CN201910246126.X and CN202111237698.5): The substrate surface is processed into a surface shape with the same magnitude but opposite direction as the thin film surface shape change, so that the substrate surface shape and the thin film surface shape compensate for each other, thereby obtaining optical components with high surface shape accuracy. However, this method significantly increases the time cycle and cost of substrate processing; ② Backside coating compensation (e.g., CN202210237570.7 and CN202110959643.9): A film layer with the same structure or stress as the coating surface is deposited on the non-coated surface of the substrate. However, this method increases the coating cost and is not suitable for components where both sides of the substrate need to be coated; ③ Film stress control: Different deposition techniques are used to prepare high and low refractive index films with opposite stresses. This method requires changing the coating equipment every time a film is prepared, and the actual preparation process is extremely difficult. For example, Stress compensated anti-reflection coating for high power laser deposited with IBS SiO2 and ALD Al2O3, Applied Surface Science, 2019, 476: 521-527 or CN202010190180.X, depositing an ion beam-assisted mixture monolayer film on the non-coated surface of the substrate or on the relatively concave surface to be coated after coating, forming an optical dummy layer with the same refractive index as the substrate to tune the surface shape of the coated component. This method requires a thick compensation layer. ④ Pattern-based stress compensation methods (e.g., Thermal oxide patterning method for compensating coating stress in silicon substrates, Optics Express, 2019, 27(2): 1010-1024): These methods require not only back-side deposition but also photoresist application, complex patterning, etching, and precision cleaning. ⑤ Shape control based on correction baffles (e.g., Stress compensation by deposition of a nonuniform corrective coating, Applied Optics, 2020, 59(5): A54-A57): This method uses a thickness correction baffle to control the thickness distribution of the shape control layer. Then, the correction baffle of the shape control layer is updated to a correction baffle of the functional layer before the functional layer is deposited.However, this method has the following difficulties: First, it requires the design and processing of correction baffles for different surface compensation amounts, which is complex, costly and lacks versatility; Second, it requires the addition of complex correction baffles in the vacuum chamber to replace the mechanical structure, or the opening of the vacuum chamber door to replace the correction baffles and continue coating, which requires additional hardware or additional processes, which also leads to an increase in cost or cycle.

[0004] Furthermore, traditional methods such as back-side coating compensation often rely on thicker compensation layers. However, thicker layers increase the likelihood of introducing defects, lowering the component's damage threshold and limiting its application in high-power lasers and other fields with stringent performance requirements. Therefore, efficiently and accurately controlling low-frequency surface errors while avoiding the negative impact of the compensation layer on other performance aspects has become a key issue in improving the performance of optical components. Summary of the Invention

[0005] This invention aims to overcome the shortcomings of existing methods for controlling the low-frequency surface shape of optical components, such as complex hardware modifications, long process cycles, high costs, and a decrease in the laser damage threshold due to excessively thick compensation layers. It provides a method for controlling the surface shape of optical components based on target-substrate eccentric deposition. This method requires no hardware modifications and can be adapted to optical components of any surface shape (including optical substrates and thin-film components). Surface shape control is achieved by adjusting the relative eccentricity angle between the target and the substrate during magnetron sputtering deposition, without affecting the optical performance of the component. Furthermore, this method comprehensively utilizes differences in film thickness distribution and film surface shape distribution to control the low-frequency surface shape of the optical component, significantly reducing the thickness of the surface shape control layer and helping to improve the damage threshold of laser thin-film components.

[0006] The technical solution of the present invention is as follows:

[0007] A method for controlling the surface shape of optical elements based on target-base eccentric deposition, characterized by the following steps:

[0008] S1. Material selection: Select a coating material for the surface shape control layer, wherein the difference Δn between the refractive index of the surface shape control layer and the refractive index of the substrate is ≤0.1;

[0009] S2. Calculation of film thickness distribution under different target-base eccentricity angles:

[0010] Input the optical component parameters, target sputtering yield distribution parameters, and coating machine geometric layout parameters to calculate the deposition time t. Unit The non-uniformity U of the film thickness distribution of the surface shape control layer under different target-substrate eccentricity angles θ is given by the following formula:

[0011] U=(D Center –D Edge ) / D Center (1)

[0012] Among them, D Center D is the thickness of the surface shape control layer at the center of the optical element. Edge The thickness of the surface shape control layer at the edge of the optical element;

[0013] S3. Selection of eccentric angle:

[0014] The target-base eccentricity angle corresponding to the maximum positive value of the film thickness distribution non-uniformity is taken as the convex eccentricity angle θ. Convex It is used for surface shape compensation of concave optical elements;

[0015] The target-base eccentricity angle corresponding to the minimum negative value of the film thickness distribution non-uniformity is taken as the concave eccentricity angle θ. Concave It is used for surface shape compensation of convex optical elements;

[0016] S4. Fitting the film thickness distribution and calculating the compensation capability per unit time under the selected eccentricity angle:

[0017] If the surface of the optical element is concave, then the eccentricity angle θ for the convex surface is... Convex The film thickness distribution under the given conditions was fitted with a quadratic curve.

[0018] If the surface of the optical element is convex, then the eccentricity angle θ for the concave surface is... Concave The film thickness distribution under the given conditions was fitted with a quadratic curve.

[0019] The formula for calculating the difference in fitted film thickness Δd between the center and edge positions of the optical element is as follows:

[0020] Δd=D Center-fit –D Edge-fit (2)

[0021] Among them, D Center-fit To determine the thickness of the surface shape control layer at the center position of the fitted optical element, D Edge-fit The thickness of the surface shape control layer at the edge position of the optical element after fitting;

[0022] Calculate the deposition time t Unit The compensation surface power value P achieved by the inner surface shape control layer Unit ;

[0023] P Unit =-Δd / λ (3)

[0024] Where λ is the surface shape test wavelength;

[0025] S5. Calculate the theoretical deposition time t of the surface shape control layer. T The formula is as follows:

[0026] t T =t Unit×P Target / P Unit (4)

[0027] Among them, P Target The surface shape of the optical element needs to be compensated;

[0028] S6. Preliminary Experiment and Deposition Time Correction: The deposition time of the surface-controlled layer was corrected through preliminary experiments to obtain the corrected deposition time t. C ;

[0029] S7. Deposition of the surface shape control layer: Magnetron sputtering technology is used to deposit the layer at a selected convex surface with an eccentric angle θ. Convex Or concave eccentricity θ Concave Below, a surface shape control layer is deposited on the surface of the optical element to be controlled, and the deposition time is t. C .

[0030] Furthermore, the calculation of the film thickness distribution under different target-base eccentricity angles specifically includes the following steps:

[0031] S2.1 Establish a three-dimensional rectangular coordinate system based on a magnetron sputtering deposition equipment;

[0032] S2.2 A mathematical model for the film thickness distribution under a target-base eccentricity angle θ is established based on the following formula, and the film thickness distribution at each sampling point under different target-base eccentricity angles θ at deposition time t is obtained. Unit The thickness of the deposited film inside :

[0033]

[0034] in, d is the distance from the center of the target surface to the origin of the coordinate system, i.e., the revolution radius; d is the length of the target material. The width of the target material; The horizontal distance from the sampling point on the coated element to the rotation axis; Let be the sputtering yield distribution function of the target material; m is the contribution of a point on the target surface to the film thickness at the sampling point, calculated as follows:

[0035]

[0036] Where U is the coating calibration coefficient, which is a constant; The distance between a point on the target surface and a sampling point; For the splash angle, The deposition angle; Let be the sputtered particle angular distribution function. The sputtering factor of the target material;

[0037] S2.3 Calculate the film thickness distribution non-uniformity U under each target-base eccentricity angle θ according to formula (1).

[0038] Furthermore, the aforementioned preliminary experiment and deposition time correction specifically include the following steps:

[0039] S6.1 Pre-coating surface shape test: Perform surface shape test on the pre-experimental substrate to obtain the substrate surface shape Power value P. E-Substrate ;

[0040] S6.2 Substrate clamping: Place the pre-experimental substrate in the center of the workpiece tray, with the surface to be coated facing opposite to the upper surface of the target material of the coating equipment, and clamp the workpiece tray into the coating machine;

[0041] S6.3 Target-Base Eccentricity Adjustment: Adjust the position of the workpiece disk so that the eccentricity angle between the center of the pre-experiment substrate and the center of the target material is the convex eccentricity angle θ selected in step S3. Convex Or concave eccentricity θ Concave Positioning error ≤ 0.1°;

[0042] S6.4 Vacuum Acquisition: Close the vacuum chamber door and evacuate to a background vacuum better than 9 × 10⁻⁶. -5 Pa;

[0043] S6.5 Thin Film Deposition: The vacuum chamber is filled with process gas, and the working pressure is adjusted to 0.5 Pa~5 Pa. The workpiece disk is turned on, and the cathode of the coating material is activated. A surface shape control layer is deposited on the surface of the pre-experimental substrate. The deposition time is the theoretical deposition time t. T ;

[0044] S6.6 Close the cathode, rotation, and process gas flow control valves to complete the coating process;

[0045] S6.7 Post-coating surface shape test: The surface shape of the pre-experimental substrate after the deposition of the surface shape control layer is tested to obtain its surface shape power value P. Layer ;

[0046] S6.8 Deposition time correction: Calculate the corrected deposition time t C ;

[0047] t C =t T ×P Target / (P Layer –P E-Substrate (5).

[0048] Furthermore, the deposition of the surface shape control layer specifically includes the following steps:

[0049] S7.1 Substrate clamping: Place the optical element to be controlled in the center of the workpiece tray, with the surface of the surface shape control layer to be deposited facing opposite to the upper surface of the target material of the coating equipment, and clamp the workpiece tray into the coating machine;

[0050] S7.2 Target-base eccentricity adjustment: Adjust the position of the workpiece disk so that the eccentricity angle between the center of the optical element to be controlled and the center of the target material is the convex eccentricity angle θ selected in step S3. Concave Or concave eccentricity θ Convex Positioning error ≤ 0.1°;

[0051] S7.3 Vacuum Acquisition: Close the vacuum chamber door and evacuate to a background vacuum better than 9 × 10⁻⁶. -5 Pa;

[0052] S7.4 Thin Film Deposition: The vacuum chamber is filled with process gas, and the working pressure is adjusted to 0.5 Pa to 5 Pa. The workpiece disk is turned on, and the cathode of the coating material is turned on. A surface shape control layer is deposited on the surface of the optical element. The deposition time is the corrected deposition time t obtained in step S6. C ;

[0053] S7.5 Close the cathode, rotation, and process gas flow control valves to complete the coating process.

[0054] Furthermore, the magnetron sputtering technology is DC magnetron sputtering, radio frequency magnetron sputtering, or reactive magnetron sputtering.

[0055] Furthermore, the optical element is an optical substrate or a thin-film element on which a functional thin film is deposited.

[0056] Furthermore, in step S2, the range of the target-base eccentricity angle θ is determined according to the actual geometric layout of the coating equipment as -40°≤θ≤40°, and within this range, multiple discrete angles are selected in a step size of no more than 4° to calculate the film thickness distribution.

[0057] Compared with the prior art, the technical effects of the present invention are as follows:

[0058] This invention is ideal for the fabrication of thin-film elements that require compensation for changes in wavefront quality caused by film stress; it is also applicable to the compensation of substrate surface shape during the surface polishing process of optical elements, so as to improve the efficiency and quality of the substrate polishing process.

[0059] 1. Wide adaptability: This invention requires no hardware modifications and achieves low-frequency surface shape control by adjusting the target-substrate eccentricity angle. It can be adapted to optical elements with any surface shape and is suitable for optical substrates and optical coating elements.

[0060] 2. Simplified preparation process: Compared with traditional methods, the present invention avoids complex steps such as designing and processing correction baffles, replacing mechanical structures, or opening the vacuum chamber door to replace correction baffles, thus simplifying the preparation process and reducing coating costs and preparation cycle.

[0061] 3. Thin control layer thickness: By comprehensively utilizing differences in film thickness distribution and surface shape distribution, the thickness of the surface shape control layer is significantly reduced compared to traditional methods. This helps reduce the probability of introducing defects, improves the surface quality of optical components, and lowers the laser damage threshold, making it particularly suitable for fields with high component performance requirements. Attached Figure Description

[0062] Figure 1 This is a schematic diagram of the optical element surface shape control based on target-base eccentric deposition in Embodiment 1 of the present invention.

[0063] Figure labeling: 1-Optical substrate; 2-Surface shape control layer; 3-Functional thin film.

[0064] Figure 2 is a schematic diagram of target-base eccentric deposition in an embodiment of the present invention. (a) Top view; (b) Side view. Detailed Implementation

[0065] The present invention will now be described in detail with reference to the embodiments and accompanying drawings, but the listed embodiments should not limit the scope of protection of the present invention.

[0066] Example 1

[0067] This embodiment uses an optical element on a silicon (Si) substrate with multiple thin films to be deposited as an example to illustrate the target-substrate eccentric deposition method for optical element shape control described in this invention. The optical element without shape control has a concave shape of 0.5λ (λ = 632.8 nm), meaning the edge of the element is 0.5 wavelengths higher than the center. Therefore, a shape control layer with a convex shape distribution needs to be deposited, with a compensation amount P. Target =-0.5λ. For example... Figure 1 As shown, the optical element with surface shape control includes an optical substrate 1, a surface shape control layer 2, and a functional thin film 3. The surface shape control method includes the following steps:

[0068] S1. Material selection: Select Si, the same material as the optical substrate 1, as the coating material for the surface shape control layer 2.

[0069] S2. Establish a coordinate system and a mathematical model for film thickness distribution:

[0070] A three-dimensional Cartesian coordinate system is established based on a magnetron sputtering deposition device, such as Figure 2 As shown. The key geometric parameters of the equipment are as follows:

[0071] A mathematical model for the film thickness distribution under a target-base eccentricity angle θ is established based on the following formula, and the film thickness distribution at each sampling point under different target-base eccentricity angles θ at deposition time t is obtained. Unit The thickness of the deposited film inside, in this embodiment the target-base eccentricity angle θ ranges from -40°≤θ≤40°;

[0072]

[0073] in, d is the distance from the center of the target surface to the origin of the coordinate system, i.e., the revolution radius; d is the length of the target material. The width of the target material; The horizontal distance from the sampling point on the coated element to the rotation axis; Let be the sputtering yield distribution function of the target material; m is the contribution of a point on the target surface to the film thickness at the sampling point, and the calculation formula is as follows.

[0074]

[0075] Where U is the coating calibration coefficient, which is a constant; The distance between a point on the target surface and a sampling point; For the splash angle, The deposition angle; Let be the sputtered particle angular distribution function. denoted as the sputtering factor of the target material.

[0076] S3. Calculation of film thickness distribution of the surface shape control layer under different target-base eccentricity angles:

[0077] Input optical element shape parameters: planar element with a diameter of 100 mm;

[0078] Input the sputtering yield distribution parameters of the Si target: the radius of the semi-circular bend of the target runway is 21.5 mm, the length of the straight section of the target runway is 110 mm, the standard deviation parameter of the Gaussian function of the target runway cross section is 5.7, the Gaussian function parameters of the target bend depth variation are -4.9 and 63.4, and the material sputtering factor of the target is 0.215;

[0079] Input the geometric layout parameters of the coating machine: the distance between the target surface and the substrate surface is 50 mm, the revolution speed of the workpiece disk is 0, the rotation speed of the workpiece disk is 150 rpm, the target length is 200 mm, and the target width is 85 nm.

[0080] The deposition time t was calculated. Unit =60 s, film thickness distribution curves of the surface shape control layer under different target-substrate eccentricity angles θ;

[0081] The non-uniformity of film thickness distribution under different target-base eccentricity angles θ is calculated according to formula (1), and the specific values ​​are shown in Table 1;

[0082] U =(D Center –D Edge ) / D Center (1)

[0083] Among them, D Center The thickness of the surface shape control layer at the center of the component, D Edge The thickness of the surface shape control layer at the edge of the component refers to the thickness of the film.

[0084] Table 1. Non-uniformity of film thickness distribution under different target-base eccentricity angles θ

[0085]

[0086] S4. Selection of eccentric angle for concave and convex surfaces:

[0087] Since this embodiment requires a convex control layer to compensate for the concave element, the eccentricity angle corresponding to the maximum positive value of the film thickness non-uniformity is selected as the convex eccentricity angle θ. Convex As shown in the table above, U = 72.4% is the maximum positive value when θ = 0°, therefore we take θ as the maximum positive value. Convex =0°.

[0088] S5. Fitting the film thickness distribution at the selected eccentric angle:

[0089] The surface of the multilayer optical element is concave: the target-base eccentricity angle θ Convex When the surface shape control layer thickness distribution is 0°, a quadratic curve is fitted, and the thickness difference between the center position and the edge position of the optical element is obtained according to formula (2) Δd = 68.24 nm.

[0090] Δd=D Center-fit –D Edge-fit (2)

[0091] The compensating surface shape Power value P of the surface shape control layer deposited within the deposition time (60 s) is calculated according to formula (3). Unit =-0.108λ;

[0092] P Unit =-Δd / λ (3)

[0093] Wherein, λ = 632.8 nm.

[0094] S6. Calculate the theoretical deposition time t T The theoretical deposition time t of the shape-controlled layer is calculated according to formula (4). T ;

[0095] t T = t Unit ×P Target / P Unit =60×(-0.5λ) / (-0.108λ)=277 s (4)

[0096] Among them, PTarget The surface shape of the optical element needs to be compensated.

[0097] S7. Preliminary experiments on surface shape control layer and correction of deposition time, specifically including the following steps:

[0098] Pre-coating surface shape test: The surface shape of the substrate used for preliminary experiments is tested to obtain the substrate surface shape Power value P. E-Substrate =0.1λ;

[0099] Substrate clamping: Clean and dry the substrate; place the clean pre-experimental substrate in the center of the workpiece tray, with the surface to be coated facing opposite to the upper surface of the target material of the coating equipment; clamp the workpiece tray into the coating machine;

[0100] Target-base eccentricity adjustment: Adjust the position of the workpiece disk so that the eccentricity angle between the center of the pre-experiment substrate and the center of the target material is θ. Convex =0° (positioning error: ≤0.1°);

[0101] Vacuum acquisition: Close the vacuum chamber door and evacuate to a background vacuum better than 9 × 10⁻⁶. -5 Pa;

[0102] Thin film deposition: Close the high-pressure valve, open the flow control valves for argon and other process gases according to process requirements, and fill the vacuum chamber with argon and other process gases. Adjust the working pressure to P (0.5 Pa ≤ P ≤ 5 Pa), start the rotation of the workpiece disk, turn on the cathode of the coating material, and deposit a surface shape control layer on the surface of the pre-experimental substrate. The deposition time is t. T =277 s;

[0103] Turn off the cathode, stop the rotation, and close the process gas flow control valve. The coating process is now complete.

[0104] Post-coating surface shape testing: The surface shape of the substrate after deposition of the surface shape control layer is tested to obtain its surface shape Power value P. Layer =-0.38λ;

[0105] Correction of deposition time for shape-controlled layer: The deposition time is corrected using formula (5) to obtain the corrected deposition time t of the shape-controlled layer. C .

[0106] (5)

[0107] S8. Deposition surface shape control layer, specifically including the following steps:

[0108] Substrate clamping: Clean the substrate and let it dry; place the clean optical element to be controlled in the center of the workpiece tray, with the surface to be coated with the shape control layer facing opposite to the upper surface of the target material of the coating equipment; clamp the workpiece tray into the coating machine;

[0109] Target-base eccentricity adjustment: Adjust the position of the workpiece disk so that the eccentricity angle between the center of the optical element to be controlled and the center of the target material is θ. Convex =0° (positioning error: ≤0.1°);

[0110] Vacuum acquisition: Close the vacuum chamber door and evacuate to a background vacuum better than 9 × 10⁻⁶. -5 Pa;

[0111] Thin film deposition: Close the high pressure valve, open the argon flow control valve, fill the vacuum chamber with argon gas, adjust the working pressure to P (0.5 Pa ≤ P ≤ 5 Pa), start the workpiece disk rotation, turn on the cathode of the coating material, and deposit the surface shape control layer on the surface of the optical element. The deposition time is t. C =289 s;

[0112] Turn off the cathode, turn off the rotation, turn off the argon gas, and the coating process is complete.

[0113] Example 2

[0114] Taking a fused silica substrate as an example, this invention illustrates the method for controlling the surface shape of optical elements based on target-substrate eccentric deposition. The fused silica substrate is convex with a diameter of -0.2λ, where λ = 632.8 nm; therefore, a concave shape control layer is required for adjustment, with a concave shape compensation amount P. Target =0.2λ. This surface shape control method includes the following steps:

[0115] S1. Material selection: Select the same material as the substrate, namely the SiO2 layer as the surface shape control layer. The SiO2 layer is formed by sputtering and depositing Si target material as the initial coating material in an oxygen environment.

[0116] S2. Same as Example 1.

[0117] S3. Calculation of film thickness distribution under different target-base eccentricity angles:

[0118] Input optical element shape parameters: fused silica substrate with a diameter of 100 mm;

[0119] Input the sputtering yield distribution parameters of the Si target: the radius of the semi-circular bend of the target runway is 21.5 mm, the length of the straight section of the target runway is 110 mm, the standard deviation parameter of the Gaussian function of the target runway cross section is 5.7, the Gaussian function parameters of the target bend depth variation are -4.9 and 63.4, and the material sputtering factor of the target is 0.215;

[0120] Input the geometric layout parameters of the coating machine: the distance between the target surface and the substrate surface is 45 mm, the revolution speed of the workpiece disk is 0, the rotation speed of the workpiece disk is 150 rpm, the target length is 200 mm, and the target width is 85 nm.

[0121] The deposition time t was calculated. Unit =60 s, film thickness distribution curves of the surface shape control layer under different target-substrate eccentricity angles θ;

[0122] The film thickness distribution non-uniformity under different target-base eccentricity angles θ is calculated according to formula (1), and the specific values ​​are shown in Table 2;

[0123] U =(D Center –D Edge ) / D Center (1)

[0124] Among them, D Center The film thickness at the center of the component, D Edge This refers to the film thickness at the edge of the component.

[0125] Table 2. Non-uniformity of film thickness distribution under different target-base eccentricity angles θ

[0126]

[0127] S4. Selection of eccentric angle for concave and convex surfaces:

[0128] The target-base eccentricity angle with the minimum (negative) film thickness distribution non-uniformity is taken as the concave eccentricity angle θ. Concave =24°, used for compensation of convex optical elements.

[0129] S5. Fitting the film thickness distribution at the selected eccentric angle:

[0130] The fused silica substrate has a convex shape: eccentricity angle θ between the target and substrate. Concave When the surface shape control layer thickness distribution is 24°, a quadratic curve is fitted, and the thickness difference Δd between the center and edge positions of the fitted curve is obtained according to formula (2) as Δd = -10.56 nm.

[0131] Δd=D Center-fit –D Edge-fit (2)

[0132] The compensating surface shape Power value P of the surface shape control layer deposited within the deposition time (60 s) is calculated according to formula (3). Unit =0.017λ;

[0133] P Unit =-Δd / λ (3)

[0134] Wherein, λ = 632.8 nm.

[0135] S6. Calculate the theoretical deposition time t T The theoretical deposition time t of the shape-controlled layer is calculated according to formula (4). T ;

[0136] t T = t Unit ×P Target / P Unit =60×(0.2λ) / (0.017λ)=706 s (4)

[0137] Among them, P Target The surface shape compensation amount for the fused silica substrate.

[0138] S7. Preliminary experiments on surface shape control layer and correction of deposition time, specifically including the following steps:

[0139] Pre-coating surface shape test: The surface shape of the substrate used for preliminary experiments is tested to obtain the substrate surface shape Power value P. E-Substrate =-0.2λ;

[0140] Substrate clamping: Clean and dry the substrate; place the clean pre-experimental substrate in the center of the workpiece tray, with the surface to be coated facing opposite to the upper surface of the target material of the coating equipment; clamp the workpiece tray into the coating machine;

[0141] Target-base eccentricity adjustment: Adjust the position of the workpiece disk so that the eccentricity angle between the center of the pre-experiment substrate and the center of the target material is θ. Concave =24° (positioning error: ≤0.1°);

[0142] Vacuum acquisition: Close the vacuum chamber door and evacuate to a background vacuum better than 9 × 10⁻⁶. -5 Pa;

[0143] Thin film deposition: Close the high-pressure valve, open the flow control valves for argon and other process gases according to process requirements, and fill the vacuum chamber with argon and other process gases. Adjust the working pressure to P (0.5 Pa ≤ P ≤ 5 Pa), start the rotation of the workpiece disk, turn on the cathode of the coating material, and deposit a surface shape control layer on the surface of the pre-experimental substrate. The deposition time is t. T =706 s;

[0144] Turn off the cathode, stop the rotation, and close the process gas flow control valve. The coating process is now complete.

[0145] Post-coating surface shape testing: The surface shape of the substrate after deposition of the surface shape control layer is tested to obtain its surface shape Power value P. Layer =0.02λ;

[0146] Correction of deposition time for shape-controlled layer: The deposition time is corrected using formula (5) to obtain the corrected deposition time t of the shape-controlled layer. C .

[0147] (5)

[0148] S8. Deposition surface shape control layer, specifically including the following steps:

[0149] Substrate clamping: Clean the substrate and let it dry; place the clean optical element to be controlled in the center of the workpiece tray, with the surface to be coated with the shape control layer facing opposite to the upper surface of the target material of the coating equipment; clamp the workpiece tray into the coating machine;

[0150] Target-base eccentricity adjustment: Adjust the position of the workpiece disk so that the eccentricity angle between the center of the optical element to be controlled and the center of the target material is θ. Concave =24° (positioning error: ≤0.1°);

[0151] Vacuum acquisition: Close the vacuum chamber door and evacuate to a background vacuum better than 9 × 10⁻⁶. -5 Pa;

[0152] Thin film deposition: Close the high pressure valve, open the argon flow control valve, fill the vacuum chamber with argon gas, adjust the working pressure to P (0.5 Pa ≤ P ≤ 5 Pa), start the workpiece disk rotation, turn on the cathode of the coating material, and deposit the surface shape control layer on the surface of the optical element. The deposition time is t. C =642 s;

[0153] Turn off the cathode, turn off the rotation, turn off the argon gas, and the coating process is complete.

[0154] The two embodiments described above illustrate the compensation process for concave and convex optical elements according to the present invention. Those skilled in the art should understand that, for a given coating equipment and target material, steps S2 and S3 are required to calculate the film thickness non-uniformity under different eccentric angles, identifying the angles corresponding to the maximum positive and minimum negative values, which are then used as the eccentric angles for the convex and concave shapes, respectively. Calculation results may vary depending on the equipment and target material, but the method is universally applicable. The preferred material for the control layer is a dielectric material with a refractive index similar to that of the substrate (Δn≤0.1), such as Si, SiO2, Al2O3, MgF2, etc. Alternatively, the same material as the substrate can be used to completely eliminate spectral influences. The present invention employs magnetron sputtering technology, which can use DC sputtering (e.g., Si, metal targets), radio frequency sputtering (e.g., dielectric targets), or reactive sputtering (e.g., Si target + O2 to prepare SiO2). Process parameters (working pressure, power, temperature, etc.) should be optimized to ensure a dense film layer and near-zero stress. Deposition time correction in preliminary experiments is a crucial step, effectively compensating for deviations between theoretical models and actual processes. This invention is not only applicable to surface shape compensation of single substrates or components to be coated, but can also be extended to mass production: for components with good surface shape consistency within the same batch, t can be determined through a single preliminary experiment. C Then, the shaping layer is deposited in batches. Furthermore, for large-diameter devices (e.g., 300 mm in diameter), the film thickness distribution needs to be recalculated based on the actual geometry, but the process remains identical. This method comprehensively utilizes differences in film thickness distribution and film surface shape distribution for shaping, significantly reducing the thickness of the shape-controlled layer compared to traditional methods. This significantly reduces film defects and helps improve the laser damage threshold.

[0155] The specific embodiments described herein are for illustrative purposes only and do not constitute any limitation on the scope of protection of the claims. Those skilled in the art, based on an understanding of the inventive concept, can easily make equivalent substitutions, conventional improvements, or adaptive adjustments to the technical solutions; such derivatives should still be considered within the scope of protection defined by the claims of this invention.

Claims

1. A method for controlling the surface shape of optical elements based on target-base eccentric deposition, characterized in that, Includes the following steps: S1. Material selection: Select a coating material for the surface shape control layer, wherein the difference Δn between the refractive index of the surface shape control layer and the refractive index of the substrate is ≤0.1; S2. Calculation of film thickness distribution under different target-base eccentricity angles: Input the optical component parameters, target sputtering yield distribution parameters, and coating machine geometric layout parameters to calculate the deposition time t. Unit The non-uniformity U of the film thickness distribution of the surface shape control layer under different target-substrate eccentricity angles θ is given by the following formula: U=(D Center –D Edge ) / D Center (1) Among them, D Center D is the thickness of the surface shape control layer at the center of the optical element. Edge The thickness of the surface shape control layer at the edge of the optical element; S3. Selection of eccentric angle: The target-base eccentricity angle corresponding to the maximum positive value of the film thickness distribution non-uniformity is taken as the convex eccentricity angle θ. Convex It is used for surface shape compensation of concave optical elements; The target-base eccentricity angle corresponding to the minimum negative value of the film thickness distribution non-uniformity is taken as the concave eccentricity angle θ. Concave It is used for surface shape compensation of convex optical elements; S4. Fitting the film thickness distribution and calculating the compensation capability per unit time under the selected eccentricity angle: If the surface of the optical element is concave, then the eccentricity angle θ for the convex surface is... Convex The film thickness distribution under the given conditions was fitted with a quadratic curve. If the surface of the optical element is convex, then the eccentricity angle θ for the concave surface is... Concave The film thickness distribution under the given conditions was fitted with a quadratic curve. The formula for calculating the difference in fitted film thickness Δd between the center and edge positions of the optical element is as follows: Δd=D Center-fit –D Edge-fit (2) Among them, D Center-fit To determine the thickness of the surface shape control layer at the center position of the fitted optical element, D Edge-fit The thickness of the surface shape control layer at the edge position of the optical element after fitting; Calculate the deposition time t Unit The compensation surface power value P achieved by the inner surface shape control layer Unit ; P Unit =-Δd / λ (3) Where λ is the surface shape test wavelength; S5. Calculate the theoretical deposition time t of the surface shape control layer. T The formula is as follows: t T =t Unit ×P Target / P Unit (4) Among them, P Target The surface shape of the optical element needs to be compensated; S6. Preliminary Experiment and Deposition Time Correction: The deposition time of the surface-controlled layer was corrected through preliminary experiments to obtain the corrected deposition time t. C ; S7. Deposition of the surface shape control layer: Magnetron sputtering technology is used to deposit the layer at a selected convex surface with an eccentric angle θ. Convex Or concave eccentricity θ Concave Below, a surface shape control layer is deposited on the surface of the optical element to be controlled, and the deposition time is t. C .

2. The method for controlling the surface shape of optical elements based on target-base eccentric deposition according to claim 1, characterized in that, The calculation of film thickness distribution under different target-base eccentricity angles specifically includes the following steps: S2.1 Establish a three-dimensional rectangular coordinate system based on a magnetron sputtering deposition equipment; S2.2 A mathematical model for the film thickness distribution under a target-base eccentricity angle θ is established based on the following formula, and the film thickness distribution at each sampling point under different target-base eccentricity angles θ at deposition time t is obtained. Unit The thickness of the deposited film inside : in, d is the distance from the center of the target surface to the origin of the coordinate system, i.e., the revolution radius; d is the length of the target material. The width of the target material; The horizontal distance from the sampling point on the coated element to the rotation axis; Let be the sputtering yield distribution function of the target material; m is the contribution of a point on the target surface to the film thickness at the sampling point, calculated as follows: Where U is the coating calibration coefficient, which is a constant; The distance between a point on the target surface and a sampling point; For the splash angle, The deposition angle; Let be the sputtered particle angular distribution function. The sputtering factor of the target material; S2.3 Calculate the film thickness distribution non-uniformity U under each target-base eccentricity angle θ according to formula (1).

3. The method for controlling the surface shape of optical elements based on target-base eccentric deposition according to claim 1, characterized in that, The aforementioned preliminary experiments and deposition time correction specifically include the following steps: S6.1 Pre-coating surface shape test: Perform surface shape test on the pre-experimental substrate to obtain the substrate surface shape Power value P. E-Substrate ; S6.2 Substrate clamping: Place the pre-experimental substrate in the center of the workpiece tray, with the surface to be coated facing opposite to the upper surface of the target material of the coating equipment, and clamp the workpiece tray into the coating machine; S6.3 Target-Base Eccentricity Adjustment: Adjust the position of the workpiece disk so that the eccentricity angle between the center of the pre-experiment substrate and the center of the target material is the convex eccentricity angle θ selected in step S3. Convex Or concave eccentricity θ Concave Positioning error ≤ 0.1°; S6.4 Vacuum Acquisition: Close the vacuum chamber door and evacuate to a background vacuum better than 9 × 10⁻⁶. -5 Pa; S6.5 Thin Film Deposition: The vacuum chamber is filled with process gas, and the working pressure is adjusted to 0.5 Pa~5 Pa. The workpiece disk is turned on, and the cathode of the coating material is activated. A surface shape control layer is deposited on the surface of the pre-experimental substrate. The deposition time is the theoretical deposition time t. T ; S6.6 Close the cathode, rotation, and process gas flow control valves to complete the coating process; S6.7 Post-coating surface shape test: The surface shape of the pre-experimental substrate after the deposition of the surface shape control layer is tested to obtain its surface shape power value P. Layer ; S6.8 Deposition time correction: Calculate the corrected deposition time t C ; （5）。 4. The method for controlling the surface shape of optical elements based on target-base eccentric deposition according to claim 1, characterized in that, The deposition of the surface shape control layer specifically includes the following steps: S7.1 Substrate clamping: Place the optical element to be controlled in the center of the workpiece tray, with the surface of the surface shape control layer to be deposited facing opposite to the upper surface of the target material of the coating equipment, and clamp the workpiece tray into the coating machine; S7.2 Target-base eccentricity adjustment: Adjust the position of the workpiece disk so that the eccentricity angle between the center of the optical element to be controlled and the center of the target material is the convex eccentricity angle θ selected in step S3. Concave Or concave eccentricity θ Convex Positioning error ≤ 0.1°; S7.3 Vacuum Acquisition: Close the vacuum chamber door and evacuate to a background vacuum better than 9 × 10⁻⁶. -5 Pa; S7.4 Thin Film Deposition: The vacuum chamber is filled with process gas, and the working pressure is adjusted to 0.5 Pa to 5 Pa. The workpiece disk is turned on, and the cathode of the coating material is turned on. A surface shape control layer is deposited on the surface of the optical element. The deposition time is the corrected deposition time t obtained in step S6. C ; S7.5 Close the cathode, rotation, and process gas flow control valves to complete the coating process.

5. The method for controlling the surface shape of optical elements based on target-base eccentric deposition according to claim 1, characterized in that, The magnetron sputtering technology is DC magnetron sputtering, radio frequency magnetron sputtering, or reactive magnetron sputtering.

6. The method for controlling the surface shape of optical elements based on target-base eccentric deposition according to claim 1, characterized in that, The optical element is an optical substrate or a thin film element on which a functional thin film is deposited.

7. The method for controlling the surface shape of optical elements based on target-base eccentric deposition according to claim 1, characterized in that, In step S2, the range of the target-base eccentricity angle θ is determined according to the actual geometric layout of the coating equipment as -40°≤θ≤40°, and within this range, multiple discrete angles are selected in a step size of no more than 4° to calculate the film thickness distribution.

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