A method for surface shape correction of a thin film element based on a high steepness filter

Abstract

The present invention relates to a method for surface shape correction of a thin film element based on a high steepness filter, which solves the problem of how to accurately control the thickness of the SiO₂ film during double-sided coating to achieve the control of the surface shape of the thin film element by using the stress of the SiO₂ film. The present invention establishes a mathematical model for surface shape correction of the thin film element, obtains the mathematical model between the thickness of the SiO₂ film and the deformation of the thin film element after two surface shape corrections of the same thin film element. Subsequently, a high steepness filter is prepared by using two materials with high and low refractive indexes and coated on the front surface of the substrate. The thickness of the SiO₂ film for the first surface shape correction is calculated according to the thickness of the high steepness filter on the front surface of the substrate for the first surface shape correction. Subsequently, the thickness of the SiO₂ film for the second surface shape correction is calculated according to the mathematical model for surface shape correction of the thin film element for the second surface shape correction. According to the relationship between the thickness of the SiO₂ film and the deformation of the thin film element after two surface shape corrections of the same thin film element, two surface shape corrections can achieve an ideal surface shape.

Description

Technical Field

[0001] The present invention relates to a surface shape correction method, and particularly to a surface shape correction method for thin film elements based on high steepness filters. Background Art

[0002] As an important indicator for measuring the surface quality of optical elements, surface shape accuracy has penetrated into all aspects of optical element processing. With the rapid development of China's aerospace industry, higher requirements are put forward for the functions of optical systems applied thereto. And as an indispensable key element in optical systems, the surface shape accuracy of optical thin film elements is becoming increasingly important.

[0003] When measuring the surface shape accuracy of thin film elements, generally the sag value, peak-to-valley value and root mean square are measured. Among them, the sag value is the distance from the center point of the element surface to the corresponding point of the best fitting sphere, which is a characterization of the macroscopic deformation of the element. The peak-to-valley value represents the numerical difference between the highest point and the lowest point of the element surface shape, which reflects the overall processing situation of the element. And the root mean square is the root mean value of the sum of the squares of the optical path differences between the entire measured wavefront (or optical surface) and the best-matched reference wavefront, which is a characterization of the average error over the entire surface. The smaller its value, the better the surface shape of the entire surface.

[0004] For thin film elements with wide spectral requirements, not only do they need to have good spectral quality, but also high surface shape accuracy. However, such thin film elements will be coated during manufacturing, and the increase in the number and thickness of the film layers will inevitably cause the thin film elements to bend, resulting in a decrease in surface shape accuracy, thereby reducing the imaging quality and reliability of the optical system. Usually, this phenomenon of decreased surface shape accuracy is attributed to the residual stress of the film layer, and the residual stress mainly comes from the thin film preparation process. First, there is the substrate stress. Since it is inevitable to introduce residual thermal stress during the melting process of the substrate material, and there will be processing stress after the substrate is polished, the two stresses temporarily form a balanced state. With the heating during film coating, this balanced state is broken, and the residual stress of the substrate is redistributed irregularly and uncertainly, thus making the surface shape of the thin film element out of controllability. Secondly, during the film formation process, the thermal stress caused by the temperature difference, the intrinsic stress formed by the mutual extrusion or stretching between molecules, especially the stress development of multi-layer films involves the combined influence of the thermal physical parameters of multiple thin film materials and the mechanical matching problems of multiple interfaces, which increases the difficulty of controlling the surface shape accuracy of thin film elements during film coating. Although research shows that under the conditions where the substrate, film material and deposition method are determined, the thin film stress can be regulated by changing the deposition process parameters, but the regulation degree of this method is limited, and it is only applicable to single-layer films or multi-layer films with the same film layer thickness in each period.

[0005] However, for thin film components with different film layer thicknesses, it is impossible to achieve the surface shape control of the thin film component during the film coating process. In addition, external stresses will inevitably be introduced during the clamping test, transportation, and other processes of the thin film component. The combined action of these stresses makes it difficult to control the surface shape accuracy of the thin film component after the film coating process.

[0006] Given that it is difficult to perform surface shape control during the film coating process, a large number of current studies focus on the surface shape correction of thin film components after film coating. Research shows that the double-sided film coating technology can achieve the surface shape control of thin film components, that is, a complex film system with a thicker film layer is deposited on the front surface, and a stress-matching film is deposited on the back surface. Most complex thin films deposited by ion beam-assisted electron beam evaporation show a compressive stress state. SiO2 is the most important low refractive index material, and at the same time, the SiO2 film has similar optical properties to most glass substrates and can be used as a stress-matching film for surface shape correction. Research shows that the thin film stress is sensitive to the selection of process parameters. By controlling the deposition process parameters, the SiO2 film can always show a compressive stress state, and the change in the surface shape curvature of the thin film component caused by the stress is related to the film thickness. Therefore, by controlling the thickness of the SiO2 film, the stresses on the front and back surfaces of the substrate can be restricted from each other, achieving the purpose of controlling the surface shape of the thin film component using the stress of the SiO2 film. However, if the thickness of the SiO2 film cannot be accurately grasped, repeated polishing of the substrate or multiple film coatings will occur when using this method, which will increase the risk of substrate damage and the coating cost. Summary of the Invention

[0007] The object of the present invention is to solve the technical problem of how to accurately grasp the thickness of the SiO2 film during double-sided film coating to achieve the control of the surface shape of the thin film component using the stress of the SiO2 film, and to provide a surface shape correction method for thin film components based on high-steepness filters.

[0008] In order to achieve the above object of the invention, the present invention provides the following technical solutions:

[0009] A surface shape correction method for thin film components based on high-steepness filters, which is characterized in that it includes the following steps:

[0010] S1. Establish a mathematical model for surface shape correction of the thin film component;

[0011] S2. Use a high refractive index material as the high refractive index layer and a low refractive index material as the low refractive index layer to prepare a high-steepness filter, and deposit the high-steepness filter on the front surface of the substrate;

[0012] S3. Calculate the thickness of the SiO2 film for the first surface shape correction according to the thickness of the high-steepness filter on the front surface of the substrate, and deposit the SiO2 film on the back surface of the substrate according to the calculated thickness for the first surface shape correction;

[0013] According to the mathematical model for surface shape correction of the thin film element, calculate the thickness of the SiO2 film for the second surface shape correction, and deposit the SiO2 film according to the calculated thickness for the second surface shape correction;

[0014] S4. Deposit an anti-reflection film on the SiO2 film after correction to complete the surface shape correction of the thin film element based on the high-steepness filter.

[0015] Further, step S1 is specifically as follows:

[0016] S1.1. Obtain the relationship between the thickness of the SiO2 film and the sag of the thin film element through the study of the stress characteristics of the SiO2 film

[0017]

[0018] Where: is the sag of the thin film element, is the thickness of the SiO2 film, , are linear factors;

[0019] S1.2. Obtain the residual stress of the thin film element based on the Stoney formula corrected by beam theory

[0020]

[0021] Where: is the residual stress of the thin film element, is the Young's modulus of the substrate, is the Poisson's ratio of the substrate, is the thickness of the substrate, is the diameter of the substrate, is the thickness of the SiO2 film, is the change in the sag of the thin film element;

[0022] S1.3. Establish a mathematical model between the thickness of the SiO2 film after two surface shape corrections of the same thin film element and the deformation of the thin film element

[0023]

[0024] Where: is the thickness of the SiO2 film for the first surface shape correction, is the thickness of the SiO2 film for the second surface shape correction, is the change in the sag of the substrate caused by the thickness of the SiO2 film for the first surface shape correction, is the change in the sag of the substrate caused by the thickness of the SiO2 film for the second surface shape correction.

[0025] Further, step S2 is specifically as follows:

[0026] S2.1. Measure the peak-to-valley value PV, root mean square RMS, and sagittal height Power0 of the substrate, and observe the deviation of the peak-to-valley value PV and root mean square RMS from the ideal plane through Power0;

[0027] S2.2. Use Ta2O5 with a high refractive index as the high refractive index layer and SiO2 with a low refractive index as the low refractive index layer, and prepare a high-steepness filter by means of ion beam-assisted electron beam thermal evaporation, and coat the high-steepness filter on the front surface of the substrate;

[0028] S2.3. Measure the surface shape of the thin film element after coating the high-steepness filter to obtain the sagittal height Power1 of the thin film element after coating the high-steepness filter.

[0029] Furthermore, step S3 is specifically as follows:

[0030] S3.1. Calculate the SiO2 film thickness for the first surface shape correction according to the thickness of the high-steepness filter on the front surface of the substrate

[0031]

[0032] Where: is the actual total thickness of the high refractive index layer in the high-steepness filter, is the actual total thickness of the low refractive index layer in the high-steepness filter, is a constant;

[0033] S3.2. Coat a SiO2 film on the back surface of the substrate according to the calculated SiO2 film thickness for the first surface shape correction for the first surface shape correction;

[0034] S3.3. After coating, measure the sagittal height Power2 of the thin film element after the first surface shape correction;

[0035] S3.4. Calculate the change in the sagittal height of the substrate caused by the SiO2 film thickness after the first surface shape correction

[0036] ;

[0037] S3.5. Calculate the SiO2 film thickness for the second surface shape correction according to the mathematical model between the SiO2 film thickness and the deformation of the thin film element after two surface shape corrections of the same thin film element

[0038]

[0039] Where: is the change in the sagittal height of the thin film element when the antireflection film acts on the surface of the thin film element;

[0040] S3.6. According to the calculated thickness of the SiO2 film for the second surface shape correction Deposit the SiO2 film to perform the second surface shape correction.

[0041] Further, step S3.2 is specifically as follows: Pump the base vacuum to 8.5×10 -4 Pa, set the baking temperature to 160 °C, set the ion beam anode voltage to 130 V and the current to 50 A, set the gas filling amount to 50 sccm, and according to the calculated thickness of the SiO2 film for the first surface shape correction Deposit the SiO2 film on the back surface of the substrate to perform the first surface shape correction;

[0042] Step S3.6 is specifically as follows: Pump the base vacuum to 8.5×10 -4 Pa, set the baking temperature to 160 °C, set the ion beam anode voltage to 130 V and the current to 50 A, set the gas filling amount to 50 sccm, and according to the calculated thickness of the SiO2 film for the second surface shape correction Deposit the SiO2 film to perform the second surface shape correction.

[0043] Further, in step S2.1, the material of the substrate is K9 glass.

[0044] Further, in step S2.1, an interferometer is used to measure the peak-to-valley value PV, root mean square RMS, and sag Power0 of the substrate;

[0045] In step S2.3, the surface shape of the thin film element after depositing the high-steepness filter film is measured by an interferometer.

[0046] Further, in step S3.1, the value is 0.3.

[0047] Further, in step S3.2, before depositing the SiO2 film on the back surface of the substrate, the substrate is pre-cleaned by an ion beam.

[0048] Compared with the prior art, the beneficial effects of the present invention are:

[0049] A method for surface shape correction of a thin film element based on a high steepness filter provided by the present invention first establishes a mathematical model for surface shape correction of the thin film element, obtains a mathematical model between the thickness of the SiO2 film and the deformation of the thin film element after two surface shape corrections of the same thin film element. Subsequently, a high steepness filter is prepared using two materials with high and low refractive indices and is coated on the front surface of the substrate of the thin film element. The thickness of the SiO2 film for the first surface shape correction is calculated based on the thickness of the high steepness filter on the front surface of the substrate, and the first surface shape correction is performed. Subsequently, the thickness of the SiO2 film for the second surface shape correction is calculated based on the mathematical model for surface shape correction of the thin film element, and the second surface shape correction is performed. According to the mathematical model between the thickness of the SiO2 film and the deformation of the thin film element after two surface shape corrections of the same thin film element, for the same thin film element, two surface shape corrections can achieve an ideal surface shape. An anti-reflection film is coated on the SiO2 film after the correction is completed, and the surface shape correction of the thin film element based on the high steepness filter is completed, achieving the control of the surface shape of the thin film element using the stress of the SiO2 film. The present invention can accurately calculate the thickness of the SiO2 film required for surface shape correction, can accurately correct the surface shape of the thin film element, and avoids the damage to the thin film element caused by excessive correction. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a demonstration diagram of the surface shape correction of a thin film element in an embodiment of a method for surface shape correction of a thin film element based on a high steepness filter according to the present invention;

[0051] Figure 2 It is a flowchart of a method for surface shape correction of a thin film element based on a high steepness filter according to the present invention;

[0052] Figure 3 It is a transmittance spectrum curve diagram of a thin film element after double-sided coating in an embodiment of a method for surface shape correction of a thin film element based on a high steepness filter according to the present invention;

[0053] Figure 4 It is a relationship diagram between the surface shape change of the SiO2 film and the sag of the thin film element in an embodiment of a method for surface shape correction of a thin film element based on a high steepness filter according to the present invention;

[0054] Figure 5 It is a schematic diagram of the deformation of the thin film - substrate in an embodiment of a method for surface shape correction of a thin film element based on a high steepness filter according to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0055] The present invention will be further described below with reference to the drawings and exemplary embodiments.

[0056] Refer to Figures 1-5 , a method for surface shape correction of a thin film element based on a high steepness filter according to the present invention includes the following steps:

[0057] S1. Establish a mathematical model for surface shape correction of thin film components.

[0058] S1.1. Obtain the relationship between the thickness of the SiO2 film and the sag of the thin film component through the study of the stress characteristics of the SiO2 film

[0059]

[0060] Where: is the sag of the thin film component, is the thickness of the SiO2 film, , are linear factors;

[0061] , The values of are related to the characteristics of the substrate and the coating process. When the substrate material and the coating process are determined, the two linear factors , are constant values.

[0062] The derivation process of the above formula is as follows:

[0063] In the study, it was found that coating the SiO2 film on the substrate of the thin film component would cause a change in the sag of the thin film component. For the same substrate, under the condition of the same coating process, coating the SiO2 film twice would cause an approximate change in the sag of the thin film component as

[0064]

[0065] Where: represents the sag of the thin film component after the second coating of the SiO2 thin film, is the sag of the thin film component after the first coating of the SiO2 thin film;

[0066] After a large number of experiments, the relationship diagram as shown in Figure 4 was obtained. Figure 4 In, lines 1# and 2# respectively represent the change in the sag of the thin film component caused by coating different thicknesses of the SiO2 thin film on the same thin film component under the same process. It can be seen that the relationship between the sag of the thin film component and the thickness of the SiO2 thin film is a linear function, that is ;

[0067] S1.2. Obtain the residual stress of the thin film component based on the Stoney formula modified by beam theory

[0068]

[0069] Where: is the residual stress of the thin film component, is the Young's modulus of the substrate, is the Poisson's ratio of the substrate, is the thickness of the substrate, is the base diameter, is the change in the sag of the thin film element;

[0070] The derivation process of the above formula is as follows:

[0071] First, establish the relationship between the thin film stress and the base bending through the Stoney formula, and its expression is

[0072]

[0073] Among them: is the radius of curvature of the thin film element after coating.

[0074] The beam theory uses the biaxial elastic modulus to replace the Young's modulus of the base, and on this basis, it is proposed that when evaluating the residual stress, the curvature should be expressed as the reciprocal of the radius of curvature of the thin film element minus the reciprocal of the initial radius of curvature of the base , so the Stoney formula is modified to

[0075]

[0076] From Figure 5 the geometric relationship and approximation relationship in it, it can be known that

[0077]

[0078]

[0079] Among them: is the diameter of the thin film element, is half of the central angle corresponding to the arc length of the thin film element after bending.

[0080] From this, the relational expression is obtained;

[0081]

[0082] Then the change in the sag of the thin film element can be expressed as

[0083]

[0084] Combined with the Stoney formula, the residual stress of the thin film element is

[0085]

[0086] S1.3. Establish a mathematical model between the SiO2 film thickness and the deformation of the thin film element after two surface shape corrections of the same thin film element

[0087]

[0088] Among them: The thickness of the SiO2 film for the first surface shape correction The thickness of the SiO2 film for the second surface shape correction The amount of change in the substrate sag caused by the thickness of the SiO2 film for the first surface shape correction The amount of change in the substrate sag caused by the thickness of the SiO2 film for the second surface shape correction

[0089] Substitute into the residual stress formula of the thin film element, then the stress of the SiO2 film can be expressed as

[0090]

[0091] It can be seen from the above formula that for the same substrate, the linear factor a is a constant value, then the stress of the SiO2 film is a constant value, that is

[0092]

[0093]

[0094] It can be known from the above formula that when using the SiO2 film for surface shape correction, in order to achieve an ideal sag change, that is , it is necessary to combine the amount of change in the substrate sag caused by the thickness of the SiO2 film for the first surface shape correction and the thickness of the SiO2 film for the first surface shape correction . Thus, in this method, for the same thin film element, performing two surface shape corrections can achieve an ideal surface shape accuracy

[0095] S2. Use a material with a high refractive index as the high refractive index layer and a material with a low refractive index as the low refractive index layer to prepare a high-steepness filter, and coat the high-steepness filter on the front surface of the substrate

[0096] S2.1. Use an interferometer to measure the peak-to-valley value PV, root mean square RMS, and sag Power0 of the substrate, and observe the deviation of the peak-to-valley value PV and root mean square RMS from the ideal plane through Power0

[0097] The substrate is made of K9 glass material, which has good thermal stability, and good hardness, wear resistance, and impact resistance

[0098] S2.2. Use Ta2O5 with a high refractive index as the high refractive index layer and SiO2 with a low refractive index as the low refractive index layer, and prepare a high-steepness filter by the ion beam-assisted electron beam thermal evaporation method, and coat the high-steepness filter on the front surface of the substrate

[0099] The film system structure of the high-steepness filter is (HL) 25, where H is a high refractive index material, L is a low refractive index material, the refractive index of Ta2O5 is 2.3, and the refractive index of SiO2 is 1.46.

[0100] S2.3. Measure the surface shape of the thin film element after coating the high-steepness filter using an interferometer to obtain the sagitta Power1 of the thin film element after coating the high-steepness filter.

[0101] The surface shapes of the thin film elements before and after coating the high-steepness filter are shown in the following table:

[0102]

[0103] Note: In the above table, λ represents the laser wavelength of the interferometer, and its value is 632.8 nm.

[0104] S3. Calculate the SiO2 film thickness for the first surface shape correction based on the thickness of the high-steepness filter on the front surface of the substrate, and deposit a SiO2 film on the back surface of the substrate according to the calculated thickness for the first surface shape correction;

[0105] According to the surface shape correction mathematical model of the thin film element, calculate the SiO2 film thickness for the second surface shape correction, and deposit a SiO2 film according to the calculated thickness for the second surface shape correction.

[0106] S3.1. Calculate the SiO2 film thickness for the first surface shape correction based on the thickness of the high-steepness filter on the front surface of the substrate

[0107]

[0108] Where: is the actual total thickness of the high refractive index layer in the high-steepness filter, is the actual total thickness of the low refractive index layer in the high-steepness filter, is a constant;

[0109] S3.2. Pump the background vacuum to 8.5×10 -4 Pa, set the baking temperature to 160 °C, set the ion beam anode voltage to 130 V and the current to 50 A, set the gas filling amount to 50 sccm, first clean the substrate by ion beam before coating, and then deposit a SiO2 film on the back surface of the substrate according to the calculated SiO2 film thickness for the first surface shape correction for the first surface shape correction;

[0110] After coating, measure the sagitta Power2 of the thin film element after the first surface shape correction;

[0111] S3.4. Calculate the change in the sagitta of the substrate caused by the SiO2 film thickness after the first surface shape correction

[0112] ;

[0113] S3.5. Calculate the SiO₂ film thickness for the second surface shape correction according to the mathematical model between the SiO₂ film thickness and the deformation of the thin film element after two surface shape corrections of the same thin film element.

[0114]

[0115] Where: is the change in sagitta of the thin film element when the antireflection film acts on the surface of the thin film element;

[0116] S3.6. Pump the background vacuum to 8.5×10 -4 Pa, set the baking temperature to 160 °C, set the ion beam anode voltage to 130 V, the current to 50 A, and the gas filling amount to 50 sccm. Deposit the SiO₂ film according to the calculated SiO₂ film thickness for the second surface shape correction and perform the second surface shape correction.

[0117] In this embodiment, is 3078.69 nm, is 4390.21 nm, is a constant related to the film deposition process. In this embodiment, its value is 0.3. Through calculation, is 3719.67 nm. Then, perform the first surface shape correction according to this thickness, and then measure the sagitta of the thin film element after the first surface shape correction with an interferometer Power2 = 1.222λ. Then, according to = Power2 - Power1, calculate to be 1.245λ.

[0118] When calculating the SiO₂ film thickness , the change in sagitta of the thin film element when the antireflection film acts on the surface of the thin film element is a known quantity. In this embodiment, it is 0.228λ. And the ideal surface shape, that is, , is the final surface shape minus the surface shape value when the antireflection film acts on the surface of the thin film element. It can be obtained that . Through calculation, is 0.966λ. According to , calculate = 2886.11 nm.

[0119] The surface shapes of the thin film element before and after the surface shape correction are as follows in the table

[0120]

[0121] Note: In the above table, λ represents the laser wavelength of the interferometer, and its value is 632.8 nm.

[0122] S4. Coat an antireflection film on the SiO2 film after the correction is completed to finish the surface shape correction of the thin film element based on the high-steepness filter.

[0123] As Figure 3 shown, for the thin film element corrected by the method provided by the present invention, its spectral characteristics ensure high quality. It can be seen that for the thin film element with the requirement of double-sided coating, the present invention can accurately correct its surface shape and avoid the damage to the element caused by excessive correction or multiple corrections.

[0124] The embodiments described above are only for describing the specific implementation manners of the present invention, rather than limiting the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for surface shape correction of a thin film element based on a high-steepness filter, characterized in that: The following steps are involved: S1. Establishing a mathematical model for surface shape correction of thin film elements; S2. Using a high refractive index material as the high refractive index layer and a low refractive index material as the low refractive index layer to prepare a high-steepness filter, and coating the high-steepness filter on the front surface of the substrate; S3, calculating the thickness of the SiO2 film for the first surface shape correction according to the thickness of the high-steepness filter on the front surface of the substrate, and coating the SiO2 film on the rear surface of the substrate according to the calculated thickness to perform the first surface shape correction; According to the mathematical model of the surface correction of the thin film element, the thickness of the SiO2 film for the second surface correction is calculated, and the SiO2 film is plated according to the calculated thickness for the second surface correction; Step S3 is specifically as follows: S3.

1. Calculate the SiO2 film thickness t for the first surface correction based on the thickness of the high-gradient filter on the front surface of the substrate. f1 : t f1 =0.7(Kt H +t L ); Where: t H is the actual total thickness of the high refractive index layer in the high steepness filter, t L is the actual total thickness of the low refractive index layer in the high steepness filter, K is a constant; S3.2, according to the calculated SiO2 film thickness t of the first surface correction f1 A SiO2 film is deposited on the rear surface of the substrate to perform the first surface correction; S3.

3. After the coating is completed, measure the sag Power2 of the thin film element after the first surface correction; S3.

4. Calculate the substrate height change Δ caused by the SiO2 film thickness after the first surface correction power1 : Δ power1 =Power2-Power1; S3.

5. Based on the mathematical model between the SiO2 film thickness and the deformation of the thin film element after two surface corrections of the same thin film element, calculate the SiO2 film thickness t of the second surface correction f2 : Where: Δ power0 It is the change in the sag produced by the thin film element when the antireflection film acts on the surface of the thin film element; S3.6, according to the calculated second surface correction SiO2 film thickness t f2 Coating SiO2 film, and performing second surface correction; S4. An anti-reflection film is deposited on the corrected SiO2 film to complete the surface shape correction of the thin film element based on the high-steepness filter.

2. The method for surface shape correction of a thin film element based on a high-steepness filter according to claim 1, characterized in that: Step S1 is specifically as follows: S1.

1. The relationship between SiO2 film thickness and the sag height of thin film components is obtained through the study of SiO2 film stress characteristics: power=at f +b; Where: power is the sag of the thin film element, t f is the SiO2 film thickness, a and b are linear factors; S1.

2. The residual stress of the thin film element is obtained based on the Stoney formula modified by beam theory: Where: σ is the residual stress of the thin film element, E s is the Young's modulus of the substrate, v s is the Poisson's ratio of the base, t s is the substrate thickness, D s is the substrate diameter, Δpower is the change in the sag of the thin film element; S1.

3. Establish a mathematical model between the SiO2 film thickness and the deformation of the thin film element after two surface corrections of the same thin film element: Where: t f1 is the thickness of the SiO2 film for the first surface correction, t f2 is the thickness of the SiO2 film after the second surface correction, Δ power1 is the change in substrate height caused by the thickness of the SiO2 film during the first surface correction, Δ power2 is the change in substrate vector height caused by the thickness of the SiO2 film during the second surface correction.

3. The method for surface shape correction of a thin film element based on a high-steepness filter according to claim 2, characterized in that: Step S2 is specifically as follows: S2.

1. Measure the peak-to-valley value (PV), root mean square (RMS), and sag height (Power0) of the substrate. Use Power0 to observe the deviation of the peak-to-valley value (PV) and root mean square (RMS) from the ideal plane. S2.2, using high-refractive-index Ta2O5 as the high-refractive-index layer and low-refractive-index SiO2 as the low-refractive-index layer, and preparing a high-steepness filter by ion-beam-assisted electron-beam thermal evaporation, and coating the high-steepness filter on the front surface of the substrate; S2.

3. Measure the surface shape of the thin-film element after being coated with the high-steepness filter, and obtain the vector height Power1 of the thin-film element after being coated with the high-steepness filter.

4. The method for surface shape correction of a thin film element based on a high-steepness filter according to claim 3, characterized in that: Step S3.2 is as follows: the background vacuum is reduced to 8.5×10 -4 Pa, set the baking temperature to 160℃, the ion beam anode voltage to 130V, the current to 50A, the gas volume to 50sccm, and the SiO2 film thickness t calculated for the first surface correction. f1 A SiO2 film is deposited on the rear surface of the substrate to perform the first surface correction; Step S3.6 is as follows: the background vacuum is reduced to 8.5×10 -4 Pa, set the baking temperature to 160℃, the ion beam anode voltage to 130V, the current to 50A, the gas volume to 50sccm, and the SiO2 film thickness t calculated for the second surface correction. f2 Coat SiO2 film and perform second surface correction.

5. The method for surface shape correction of a thin-film component based on a high-steepness filter according to claim 3, characterized in that: In step S2.1, the substrate is made of K9 glass.

6. The method for surface shape correction of a thin-film component based on a high-steepness filter according to claim 3, characterized in that: In step S2.1, an interferometer is used to measure the peak-to-valley value PV, root mean square RMS, and vector height Power0 of the substrate; In step S2.3, the surface shape of the thin film element after being coated with the high-steepness filter film is measured by an interferometer.

7. The method for surface shape correction of a thin-film component based on a high-steepness filter according to claim 4, characterized in that: In step S3.1, the value of K is 0.

3.

8. The method for surface shape correction of a thin-film component based on a high-steepness filter according to claim 4, characterized in that: In step S3.2, before the SiO2 film is deposited on the rear surface of the substrate, the substrate is first cleaned by an ion beam.

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