A multi-layer structure database construction method

Abstract

The present invention provides a multi-layer structure library building method. The transmission matrix of each thickness of each layer of material is first calculated and stored in a matrix library. When calculating the thickness combination of the multi-layer material, the transmission matrix of each thickness of each layer of material saved in advance can be taken out, and the transmission matrix of each thickness combination can be obtained by multiplication. Finally, the corresponding optical theoretical reflectivity is calculated according to the transmission matrix of each thickness combination. For each thickness combination, there is no need to repeatedly calculate the transmission matrix of each thickness of each layer of material. The transmission matrix can be directly taken out from the matrix library for simple multiplication operation, thereby improving the library building efficiency of the multi-layer structure.

Description

Technical Field

[0001] The present invention relates to the field of optical films, and more specifically, to a multi-layer structure library building method. Background Art

[0002] In the field of modern optics and materials science, the design and analysis of multilayer thin film systems are of great significance. They are widely used in optical coating, semiconductor manufacturing, biosensors and other high-tech fields. Traditional multilayer thin film system analysis, as an important branch of optical engineering and physics research, has long relied on two classic and powerful theoretical tools: Transfer Matrix Method (TMM) and Fresnel Equations. These two methods have played an irreplaceable role in analyzing the reflection, transmission and phase change of light in multilayer dielectric structures due to their theoretical rigor and computational accuracy. These methods play a key role in optical design, thin film deposition process optimization, optoelectronic device development and other fields. Although they perform well in calculating the reflection, transmission and phase change of light in multilayer dielectric structures, their computationally intensive characteristics significantly reduce their efficiency when dealing with complex system design or large-scale parameter optimization tasks.

[0003] When light is incident from free space such as air to the first layer of a multilayer thin film system, each step of the calculation requires the construction of a transmission matrix from scratch. This is because changes in the incident conditions (such as angles and wavelengths) directly affect the reflection and transmission characteristics of light at the interface. This means that even within a subtle parameter adjustment or scanning range, each adjustment causes a new calculation process, starting from the initial Fresnel formula, calculating the reflection and transmission coefficients of each layer, and then constructing the transmission matrix of that layer, until all the transmission matrices of the entire system are calculated in series. Although this layer-by-layer accumulation calculation logic ensures a high degree of accuracy, it also causes a huge consumption of computing resources.

[0004] Therefore, although traditional methods guarantee high accuracy of calculation results, their computational efficiency issues become increasingly prominent when faced with complex system design or large-scale parameter optimization tasks. Summary of the invention

[0005] The present invention aims at the technical problems existing in the prior art and provides a multi-layer structure library building method, which reduces repeated calculations and improves calculation efficiency, thereby more efficiently analyzing the light propagation characteristics in a multi-layer thin film system.

[0006] The present invention provides a multi-layer structure library construction method, comprising:

[0007] Step S1, calculating the transmission matrix of the current layer material at the current thickness at the current wavelength;

[0008] Step S2, if the current thickness sequence number a4 of the current layer material is less than the number of thickness grid points of the current layer material, then a4=a4+1, and step S1 is executed; if a4=the number of thickness grid points of the current layer material, then step S3 is executed;

[0009] Step S3, if the current layer number a3 < the total number of layers, then a3 = a3 + 1, and execute step S1; if the current layer number a3 = the total number of layers, then execute step S4;

[0010] Step S4, saving the transmission matrix of each layer of material at each thickness at the current wavelength in a matrix library, and executing step S5;

[0011] Step S5, obtaining the total number of thickness combinations of the multilayer materials of the multilayer film structure, that is, the total number of grid points of the thickness combinations, and executing step S6;

[0012] Step S6, when calculating the transmission matrix of the current thickness combination at the current wavelength, find the transmission matrix of each layer of material at the corresponding thickness corresponding to the current thickness combination from the matrix library, multiply the transmission matrix of each layer of material to obtain the transmission matrix of the current thickness combination, and execute step S7;

[0013] Step S7, if the current thickness combination serial number a1 < the total number of grid points of the thickness combination, then a1 = a1 + 1; if the current thickness combination serial number a1 = the total number of grid points of the thickness combination, then execute step S8;

[0014] Step S8, if the current wave number a2 < the total wave number, then a2 = a2 + 1, and execute step S1; if the current wave number a2 = the total wave number, then execute step S9;

[0015] Step S9, obtaining the transmission matrix of the multilayer thin film structure of each thickness combination at each wavelength, and executing step S10;

[0016] Step S10, calculating the corresponding theoretical reflectivity according to the transmission matrix of the multilayer thin film structure of each thickness combination at each wavelength, and executing step S11;

[0017] Step S11, establishing a corresponding relationship between each thickness combination of the multilayer thin film structure at each wavelength and the theoretical reflectivity to form a simulation spectrum library.

[0018] The present invention provides a method for building a library for a multilayer structure. The method first calculates the transmission matrix of each layer of material at each possible thickness at each wavelength and saves it. When calculating the transmission matrix of all thickness combinations of all layers of material, the pre-saved transmission matrix of each layer of material at each possible thickness can be extracted, and the transmission matrix of each thickness combination can be obtained by directly performing multiplication operations without repeatedly calculating the transmission matrix of each layer of material at each possible thickness. The workload of calculating the transmission matrix is ​​relatively large. Therefore, the method of the present invention can improve the efficiency of building a spectral library for a multilayer thin film structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the process of light incident from the air layer to the film surface at a certain incident angle;

[0020] Figure 2 A schematic diagram of a multi-layer structure library construction method provided by the present invention;

[0021] Figure 3 The overall flow chart of the multi-layer structure library building method provided by the present invention;

[0022] Figure 4 A schematic diagram of constructing a multi-layered spectral library using the method of the present invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. In addition, the technical features in the various embodiments or single embodiments provided by the present invention can be arbitrarily combined with each other to form a feasible technical solution. This combination is not subject to the constraints of the sequence of steps and / or the structural composition mode, but must be based on the ability of ordinary technicians in this field to achieve. When the combination of technical solutions is contradictory or cannot be achieved, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0024] See also Figure 1, describes the process of light incident from the air layer to the film surface at a certain incident angle. When light enters the film layer from the air, due to the change in refractive index, part of the light is reflected at the air-film interface, and the other part of the light is transmitted into the film layer. Inside the film layer, the light continues to propagate and is partially reflected and transmitted again at the film-substrate interface. Multiple reflections and transmissions in the film layer produce interference. After multiple reflections and transmissions, the light eventually returns from the film layer to the air or transmits into the substrate layer.

[0025] For multilayer film structures, building a spectral library requires calculating the theoretical optical reflectance of each possible combination of thickness of the multilayer film. Calculating the theoretical optical reflectance requires calculating the total transmission matrix of the multilayer film. Among them, the light goes from air to the complex multilayer film structure and then to air. The calculation method of the entire transmission matrix is ​​as follows:

[0026]

[0027] The above formula describes the process of light from air to multilayer film and then to air. We use T to represent the transmission matrix of this process. p represents the total transmission matrix, which is the generalized Jones matrix. This matrix describes the transmission and reflection characteristics of light in a multilayer dielectric structure, including all the effects of the incident, transmission, and emission processes. p represents the total transmission matrix, is the incident matrix, which represents the incident matrix of light from air incident on the first film. The transmission matrix of light in multilayer thin films, L t represents the output matrix.

[0028] Figure 2 The present invention provides a method for building a multi-layer structure library, which comprises the following steps:

[0029] Step S1, calculating the transmission matrix of the current layer material at the current thickness at the current wavelength.

[0030] It is understandable that in the process of building a spectral library for a multilayer thin film structure, it is necessary to calculate the theoretical reflectivity of each thickness combination of the multilayer thin film, and the theoretical reflectivity needs to be calculated based on the total transmission matrix. Therefore, it is necessary to calculate the total transmission matrix of each thickness combination of the multilayer thin film structure. Among them, the entire transmission matrix of the multilayer thin film structure is calculated by multiplying the incident matrix, the transmission matrix, and the output matrix. The incident matrix and the output matrix are independent of the wavelength and the thickness of each layer of material. Therefore, for different wavelengths and different thickness combinations of different materials, it is only necessary to calculate the corresponding transmission matrix.

[0031] Among them, the possible thickness number N of each layer of material is defined k, is recorded as the number of grid points for the thickness of the i-th layer of material; according to the possible thickness number N of each layer of material k , calculate the total number of thickness combinations of multilayer materials in a multilayer film structure N = N1×N2×N3×...N k ×....×N n , n represents the total number of layers in the multilayer film structure.

[0032] Specifically, Dk represents the set of all possible thicknesses of the k-th layer of thin film material, which is described as follows:

[0033]

[0034] in, It indicates the minimum possible thickness of the k-th layer of material, Δlk indicates the thickness density distribution, Indicates the maximum possible thickness of the k-th layer of material.

[0035] The number of thickness combinations for each layer of material is Nk, which is the number of grid points for the kth layer of material. It represents the number of all thickness possibilities for the layer and also represents the size of the library. In theory, the denser the library, the more accurate the search value, but the longer it takes to build and search the library:

[0036]

[0037] Finally, the thickness combinations of all layers are combined through the Kronecker product, which can be expressed by the Kronecker product. Assuming that Dk represents the thickness set of the k-th layer of material and layers represents the total number of layers, the total thickness combination is:

[0038]

[0039] When building a database, see Figure 3 , first determine a wavelength, and calculate the transmission matrix of each layer of material at each possible thickness at the current wavelength. Among them, the transmission matrix Tlayer,k of each layer of material at each thickness is defined as:

[0040]

[0041]

[0042] Where Tlayer,k represents the transmission matrix of the kth layer material, q k is the propagation constant of the k-th layer of material, which is used to describe the propagation characteristics of light in the medium. nk-1 is the refractive index of the k-1th layer of the previous layer of the current k-th layer. θ k-1is the incident angle of light at the k-1th layer, expressed in radians, lk is the thickness of the kth layer material, βk is the phase change of the kth layer material, λ is the wavelength, εk is the dielectric constant of the kth layer material, and i is a complex number.

[0043] Step S2, if the current thickness sequence number a4 of the current layer material is less than the number of thickness grid points of the current layer material, then a4=a4+1, and execute step S1; if a4=the number of thickness grid points of the current layer material, then execute step S3.

[0044] It is understandable that in step S1, the possible number of grid points Nk of the thickness of each layer of film is calculated, and the current thickness number of the current material (i.e., the possible number of thickness currently calculated) is recorded as a4, and it is determined whether a4 is less than the number of grid points Nk of the thickness of the current layer of material. If it is less than, then a4=a4+1, and then step S1 is executed to continue calculating the transmission matrix of the next possible thickness of the layer of material. If a4=the number of grid points Nk of the thickness of the current layer of material, it means that the transmission matrices corresponding to all possible thicknesses of the layer of material have been calculated, and then step S3 is executed.

[0045] Step S3, if the current layer number a3 is less than the total number of layers, then a3=a3+1, and step S1 is executed; if the current layer number a3 is equal to the total number of layers, then step S4 is executed.

[0046] It is understandable that after calculating the transmission matrices corresponding to all possible thicknesses of the current k-th layer of material, the transmission matrices of all possible thicknesses of the next layer of material are calculated. Therefore, the serial number of the current layer is recorded as a3, and it is determined whether a3 is less than the total number of layers. If it is less than, it means that the transmission matrix of some material has not been calculated, then a3=a3+1, and step S1 is executed to calculate the transmission matrix of all possible thicknesses of the next layer of material. If a3 is equal to the total number of layers, it means that the transmission matrices of all layers of materials have been calculated.

[0047] Step S4, saving the transmission matrix of each layer of material at each thickness at the current wavelength in a matrix library, and executing step S5.

[0048] It is understandable that according to steps S1 to S3, the transmission matrix of each layer of material at each possible thickness at the current wavelength is calculated. This step stores the calculated transmission matrix. When storing, the wavelength, layer number, thickness and transmission matrix are stored correspondingly.

[0049] Step S5, obtaining the total number of thickness combinations of the multilayer materials of the multilayer film structure, that is, the total number of grid points of the thickness combinations, and executing step S6.

[0050] It is understandable that when calculating the transmission matrix of the multilayer materials of the multilayer film structure under different thickness combinations, the total number of thickness combinations of the multilayer materials of the multilayer film structure is obtained, wherein the above step S1 defines the number of thickness combinations of each layer of material as Nk, and the total number of layers of the material is n, then the total number of thickness combinations of the multilayer materials of the multilayer film structure N = N1×N2×N3×...N k ×....×N n .

[0051] Step S6, when calculating the transmission matrix under the current thickness combination at the current wavelength, find the transmission matrix of each layer of material corresponding to the current thickness combination at the corresponding thickness from the matrix library, multiply the transmission matrix of each layer of material to obtain the transmission matrix under the current thickness combination, and execute step S7.

[0052] It is understandable that for each thickness combination of multilayer thin film materials, the thickness of each layer of material in the combination is obtained, and the transmission matrix of each layer of material at the current thickness is extracted from the transmission matrix stored in the matrix library in step S4.

[0053] It should be noted that the transmission matrix of a multilayer film describes the overall transmission behavior of light in a multilayer medium:

[0054]

[0055] Among them, Tlayer,1, Tlayer,2, Tlayer,3 、....、 Tlayer,n represents the transmission matrix of the materials from layer 1 to layer n. By calculating the transmission matrix of each layer of material and multiplying them, the transmission matrix of the entire multilayer structure can be obtained. The transmission matrix describes the transmission characteristics of light between layers, including the effects of refractive index and thickness, which enables the prediction and analysis of the optical properties of multilayer thin film systems, including reflectivity and transmittance.

[0056] Among them, the calculation of the transmission matrix Tlayer,k of each layer of material can refer to the above step S1. Since the calculation of the transmission matrix each time is relatively complex and the amount of calculation is relatively large, the pre-calculated transmission matrix of each layer of material at each possible thickness is stored in step S4. When calculating the transmission matrix under the thickness combination, there is no need to recalculate the transmission matrix of each layer of material at each thickness. The transmission matrix of each layer of material at each thickness is directly extracted from the matrix library and then combined. That is, the transmission matrix of each layer of material at the corresponding thickness is multiplied to obtain the transmission matrix under the multi-layer film thickness combination.

[0057] Step S7, if the current thickness combination serial number a1 < the total number of grid points of the thickness combination, then a1 = a1 + 1; if the current thickness combination serial number a1 = the total number of grid points of the thickness combination, then execute step S8.

[0058] It is understandable that step S5 determines the total number N of all thickness combinations of the multilayer film structure, that is, the total number of grid points of the thickness combination, and determines the size relationship between the current thickness combination sequence number a1 of the multilayer film structure and N. If a1 is less than N, it indicates that there are still transmission matrices under the thickness combination that have not been calculated, then a1=a1+1, that is, the transmission matrix of the next thickness combination is calculated. If a1=N, it indicates that the transmission matrix of all thickness combinations of the multilayer film thickness has been calculated, and then step S8 is executed.

[0059] Step S8, if the current wave number a2 is less than the total wave number, then a2=a2+1, and execute step S1; if the current wave number a2=the total wave number, then execute step S9.

[0060] It is understandable that the above steps S1 to S8 describe the calculation of the transmission matrix of the multilayer thin film structure at different thickness combinations at one wavelength. Therefore, it is necessary to calculate the transmission matrix of the multilayer thin film structure at different thickness combinations at multiple wave numbers.

[0061] Determine whether the current wave number a2 is less than the total wave number. If so, it indicates that there are still transmission matrices under some wavelengths that have not been calculated, then a2=a2+1, execute step S1, and continue to calculate the transmission matrix under the next wavelength. If a2 is equal to the total wave number, it indicates that the transmission matrices under all wave numbers have been calculated, and execute step S9.

[0062] Step S9, obtaining the transmission matrix of the multilayer thin film structure of each thickness combination at each wavelength, and executing step S10;

[0063] Step S10, calculating the corresponding theoretical reflectivity according to the transmission matrix of the multilayer thin film structure of each thickness combination at each wavelength, and executing step S11.

[0064] It can be understood that step S8 calculates the transmission matrix of the multilayer thin film structure at each wavelength and at each thickness combination. According to the transmission matrix Calculate the theoretical reflectivity of the multilayer film structure at each thickness combination at each wavelength.

[0065] It should be noted that in order to calculate the theoretical reflectivity of the multilayer thin film structure at each wavelength and each thickness combination, it is necessary to first calculate the total transmission matrix of the multilayer thin film structure at each wavelength and each thickness combination.

[0066] Among them, the expression of the total transmission matrix of the multilayer film structure is:

[0067]

[0068] Among them, in the optical system, the incident matrix can be expressed as a mathematical tool to describe the incidence, reflection and transmission of light waves, and the inverse matrix of the incident matrix is ​​used to convert the characteristics of the incident light wave to the basis vectors of the internal multilayer medium system. The calculation formula is as follows:

[0069]

[0070] in, It is the inverse matrix of the incident matrix, which describes the process of light entering the multilayer medium from the incident environment. θair represents the incident angle in radians, and nka represents the environmental complex refractive index.

[0071] The output matrix is ​​used to describe the relationship between the characteristics of the output light wave and the last layer of substrate:

[0072]

[0073] Among them, L t Represents the output matrix, which describes the process of light emitting from multi-layer media to the final environment, nk a represents the complex refractive index of the environment, nk t represents the complex refractive index of the substrate calculated by the oscillator model. Oscillator models are used in optics and materials science to describe the oscillation behavior of electrons in a medium, thereby calculating the optical constants (refractive index n and extinction coefficient k) of the material. Various oscillator models are used here, including but not limited to the following: Lorentz Oscillator Model, Drude Model, Lorentz-Drude Model, Sellmeier Equation, Cauchy Equation, Tauc-Lorentz Model, etc.

[0074] After calculating the total transmission matrix of the multilayer thin film structure at each wavelength and each thickness combination, the corresponding theoretical reflectivity is calculated. The specific process of calculating the theoretical matrix includes:

[0075] According to the total transmission matrix T p Calculate the reflection coefficient r of the multilayer film structure for p-polarized light pp and the reflection coefficient r for s-polarized light ss ,in:

[0076]

[0077] Among them, T p,11、T p,21 、T p,33 and T p,43 is the total transmission matrix T of the multilayer film structure p The elements in .

[0078] The reflectivity R of the multilayer film structure for p-polarized light pp and the reflectivity R for s-polarized light ss ,in:

[0079] Rss=rss2, Rpp=rpp2.

[0080] The total reflectivity R (ie theoretical reflectivity) is the average of Rss and Rpp:

[0081]

[0082] Step S11, establishing a corresponding relationship between each thickness combination of the multilayer thin film structure at each wavelength and the theoretical reflectivity to form a simulation spectrum library.

[0083] It can be understood that the theoretical reflectivity of the multilayer thin film structure of each thickness combination at each wavelength is calculated, and the wavelength, thickness combination and theoretical reflectivity are stored correspondingly to form a spectral library, completing the construction process of the simulation spectral library of the multilayer thin film structure.

[0084] in, Figure 3 This is a flow chart of building a library of multilayer thin film structures of the present invention. Figure 4 This is a flow chart for building a library for a traditional multilayer thin film structure, where a1 represents the number of grid points, which is the number of possible combinations of all thicknesses combined through Kronecker product based on the maximum and minimum values ​​and step size of each layer of material set by the user. The wave number a2 is the total number of wavelengths. a3 represents the total number of layers. a4 represents the number of grid points for the current layer of material, which is set by the user.

[0085] In the traditional method, the first layer of loop is the number of grid points, the second layer of loop is the number of waves, and the third layer of loop is the total number of layers. When actually building an optical model, all thickness combinations at the same wavelength are the same, no need for repeated calculations, and the transmission matrix of each layer of material at the same thickness is the same, no need for repeated calculations. Therefore, in view of these characteristics, the present invention optimizes the program calculation structure, and the first layer of the cycle is the wave number, and the transmission matrix of light entering the first layer of material from the air at each wavelength is calculated and saved to avoid repeated calculations. For example, in a double-layer material with a grid point of 100*500 and a wave number of 100, the traditional material needs to calculate the transmission matrix of light entering the first layer of material from the air 100*500*100 times, but after optimization, it only needs to be calculated 100 times; and the transmission matrix of all layers of materials traditionally needs to be calculated 100*500*100 times, while the optimized method only needs to be calculated 100*(500+100) times.

[0086] Therefore, after the improvement of the method of the present invention, it was verified on a double-layer structure SOI, and the database construction time was counted at grid points of 30000, 79900, and 150000, and the results are shown in the following Table 1. The experimental verification shows that the method can effectively and quickly improve the efficiency of database construction.

[0087] Table 1 Database construction time statistics

[0088]

[0089] It can be seen from Table 1 that the time consumption of building a library using the method of the present invention is much shorter than that of building a library using the traditional method. Therefore, building a library using the method of the present invention greatly improves the efficiency of building a library.

[0090] The present invention provides a multi-layer structure library construction method, which has the following advantages:

[0091] (1) The traditional multilayer thin film structure analysis method needs to repeatedly calculate the incident matrix, the transmission matrix of each layer, and the output matrix in each simulation. These repeated calculations take up a lot of computing resources and time, especially when dealing with complex multilayer film structures, the computing efficiency is significantly reduced. By pre-calculating and saving the inverse matrix of the incident matrix and the transmission matrix of each layer, the present invention can avoid these repeated calculations, thereby greatly improving the computing efficiency.

[0092] (2) In traditional calculation methods, since the same matrix needs to be recalculated each time for each simulation, a large amount of computing resources is wasted. This not only increases the calculation time, but also increases the consumption of hardware resources. With the improved method, the fixed calculation results can be saved as constants to avoid repeated calculations each time, thereby saving computing resources.

[0093] (3) This invention improves the multi-layer film thickness structure library construction method, greatly improving the calculation efficiency and resource utilization, and is suitable for the rapid analysis and design of complex multi-layer film systems. In the future, the calculation algorithm can be further optimized and its application can be expanded to more application scenarios.

[0094] It should be noted that in the above embodiments, the description of each embodiment has its own emphasis, and for parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0095] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0096] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for building a multi-layer structure library, characterized in that: include: Step S1, calculating the transmission matrix of the current layer material at the current thickness at the current wavelength; Step S2, if the current thickness sequence number a4 of the current layer material is less than the number of thickness grid points of the current layer material, then a4=a4+1, and step S1 is executed; if a4=the number of thickness grid points of the current layer material, then step S3 is executed; Step S3, if the current layer number a3 < the total number of layers, then a3 = a3 + 1, and execute step S1; if the current layer number a3 = the total number of layers, then execute step S4; Step S4, saving the transmission matrix of each layer of material at each thickness at the current wavelength in a matrix library, and executing step S5; Step S5, obtaining the total number of thickness combinations of the multilayer materials of the multilayer film structure, that is, the total number of grid points of the thickness combinations, and executing step S6; Step S6, when calculating the transmission matrix of the current thickness combination at the current wavelength, find the transmission matrix of each layer of material at the corresponding thickness corresponding to the current thickness combination from the matrix library, multiply the transmission matrix of each layer of material to obtain the transmission matrix of the current thickness combination, and execute step S7; Step S7, if the current thickness combination serial number a1 < the total number of grid points of the thickness combination, then a1 = a1 + 1, and execute step S6; if the current thickness combination serial number a1 = the total number of grid points of the thickness combination, then execute step S8; Step S8, if the current wave number a2 < the total wave number, then a2 = a2 + 1, and execute step S1; if the current wave number a2 = the total wave number, then execute step S9; Step S9, obtaining the transmission matrix of the multilayer thin film structure of each thickness combination at each wavelength, and executing step S10; Step S10, calculating the corresponding theoretical reflectivity according to the transmission matrix of the multilayer thin film structure of each thickness combination at each wavelength, and executing step S11; Step S11, establishing a corresponding relationship between each thickness combination and theoretical reflectivity at each wavelength of the multilayer thin film structure to form a simulation spectrum library; Before step S1, the method further includes: Define the number of possible thicknesses N for each layer of material k , denoted as the thickness grid points of the k-th layer of material; According to the possible thickness number N of each layer of material k , calculate the total number of thickness combinations of multilayer materials in a multilayer film structure N = N1×N2×N3×...N k ×....×N n , n represents the total number of layers in the multilayer film structure; The step S1, calculating the transmission matrix of the current layer material at the current thickness at the current wavelength, includes: Where Tlayer,k represents the transmission matrix of the kth layer material, q k is the propagation constant of the k-th layer of material, which is used to describe the propagation characteristics of light in the medium. nk-1 is the refractive index of the k-1th layer of the previous layer of the current k-th layer. θ k-1 is the incident angle of the light at the k-1 layer, expressed in radians, lk is the thickness of the k-th layer material, βk is the phase change of the k-th layer material, λ is the wavelength, εk is the dielectric constant of the k-th layer material, and i is a complex number; The step S10, calculating the corresponding theoretical reflectivity according to the transmission matrix of the multilayer thin film structure of each thickness combination at each wavelength, includes: Calculate the incident and exit matrices of multilayer thin film structures; Calculate the total transmission matrix of the multilayer thin film structure according to the incident matrix, transmission matrix and output matrix of the multilayer thin film structure; The theoretical reflectivity is calculated based on the total transmission matrix of the multilayer thin film structure; The expression of the incident matrix is: in, It is the inverse matrix of the incident matrix, which describes the process of light entering the multilayer medium from the incident environment. θair represents the incident angle in radians, and nka represents the complex refractive index of the environment. The expression of the output matrix is: Among them, L t Represents the output matrix, which describes the process of light emitting from multi-layer media to the final environment, nk a represents the complex refractive index of the environment, nk t represents the complex refractive index of the substrate calculated by the oscillator model; The method of calculating the total transmission matrix of the multilayer thin film structure according to the incident matrix, the transmission matrix and the exit matrix of the multilayer thin film structure comprises: Among them, T p Represents the total transmission matrix of light from air to complex multilayer film structure and then to air. represents the inverse matrix of the incident matrix, is the transmission matrix under the current thickness combination, L t is the output matrix; The method of calculating the theoretical reflectivity according to the total transmission matrix of the multilayer thin film structure includes: According to the total transmission matrix T of the multilayer film structure p , calculate the reflection coefficient r of the multilayer film structure for p-polarized light pp and the reflection coefficient r for s-polarized light ss : Among them, T p,11 , T p,21 , T p,33 and T p,43 is the total transmission matrix T of the multilayer film structure p Elements in The reflectivity R of the multilayer film structure for p-polarized light pp and the reflectivity R for s-polarized light ss ,in: ， ； The theoretical reflectivity is:

2. The multi-layer structure library building method according to claim 1, characterized in that: The number N of possible thicknesses of each layer of material is defined k ,include: Define the set of all possible thicknesses of each layer of material, where the set of all possible thicknesses Dk of the kth layer of material is expressed as: in, represents the minimum possible thickness of the k-th layer of material, Δlk represents the thickness distribution density, Indicates the maximum possible thickness of the k-th layer of material; The possible number of thicknesses of the k-th layer of material is calculated as Nk, which is the number of grid points for the thickness of the k-th layer of material, where:

3. The multi-layer structure library building method according to claim 1, characterized in that: In step S6, when calculating the transmission matrix of the current thickness combination at the current wavelength, the transmission matrix of each layer of material corresponding to the current thickness combination at the corresponding thickness is found from the matrix library, and the transmission matrix of each layer of material is multiplied to obtain the transmission matrix of the current thickness combination, and step S7 is executed, including: According to the thickness of each layer of material in the current thickness combination at the current wavelength, the transmission matrix Tlayer,k of each layer of material is found from the matrix library, where Tlayer,k represents the transmission matrix of the kth layer of material; Transmission matrix for the current thickness combination for:

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