CN113376716B - Method for coating antireflection film on surface of diffraction optical device - Google Patents

Abstract

The invention discloses a method for coating an anti-reflection film on the surface of a diffractive optical device. By optimizing the coating parameters of atomic layer deposition, a film coating process for conformal growth of the microstructure surface of the diffractive optical device is obtained; with the optimized coating parameters, optical polishing A high-refractive-index film layer and a low-refractive-index film layer were plated on the test substrate respectively, and the optical constant and thickness of the film layer were determined by ellipsometry, and the relationship between the film thickness and the atomic layer deposition coating period was determined; according to the film layer Design the anti-reflection coating with optical constants, calculate the number of atomic layer deposition coating cycles of each film layer in the anti-reflection coating; optimize the microstructure of the diffractive optical device according to the structure of the anti-reflection coating, and prepare the substrate of the diffractive optical device; according to the structure of the anti-reflection coating The order of the film layers from the substrate to the air, each film layer is plated on the surface of the diffractive optical device in turn to prepare the anti-reflection film. The coating method proposed by the invention can effectively improve the optical transmittance of the diffractive optical device.

Description

Coating method for antireflection film on surface of diffractive optical device

technical field

The invention relates to the processing field of micro-nano optical elements, in particular to a method for coating an anti-reflection film on the surface of a diffractive optical device for improving the light transmittance of the diffractive optical device.

Background technique

Diffractive optics is a device that achieves extremely high diffraction efficiency and novel optical functions by etching a multi-step or even continuous relief structure on the surface of the substrate, film, and traditional optical devices to control the optical phase through microfabrication. Diffractive optical devices are necessary devices for the realization of computer holographic imaging methods to detect aspheric surface shape, super-resolution imaging and other novel imaging optical functions, and are also an important way to realize the miniaturization and integration of optical systems. In recent years, the development of microstructure processing capabilities It has promoted the rapid development of the processing level of micro-nano optical devices and the large-scale application of micro-nano optical devices in optical systems. Similar to traditional optical devices, the residual reflection on the surface of diffractive optical devices will lead to low transmittance of the system. It is necessary to coat the surface with an anti-reflection coating to effectively improve the light utilization efficiency of the device. Traditional optical thin film coating methods are mainly physical vapor deposition methods such as ion beam sputtering, thermal evaporation, and ion beam assisted deposition. The incident angle and other parameters are closely related to each other. When there is occlusion on the molecular transmission path, the growth of the film after the occlusion area can be restricted. Due to the shielding effect of the microstructure, when using physical vapor deposition to coat the microstructure, the deposited film on the microstructure facing the direction of the molecular beam flow is larger, and the film cannot be deposited on the direction away from the molecular beam flow, so the thickness cannot be plated. Uniform optical film with controllable properties, the prepared film has many defects. More seriously, the inhomogeneity of the film will destroy the microstructural features of the diffractive optical device.

Contents of the invention

In order to solve the technical problem of anti-reflection film coating on the surface of diffractive optical devices, the present invention proposes the use of atomic layer deposition coating method to simultaneously prepare multilayer dielectric films with the same film stacking sequence and deposition thickness on different surfaces of diffractive optical devices to improve the diffraction efficiency. Transmittance of optics. Specifically, the invention discloses a method for coating an anti-reflection film on the surface of a diffractive optical device, comprising the following steps:

Step 1, select the high-refractive-index film layer material and low-refractive-index film layer material that make up the anti-reflection film, and determine the chemical reaction source material for the atomic layer deposition growth of the high-refractive index film layer material and the low-refractive index film layer material ;

Step 2, using the atomic layer deposition method to plate a high-refractive index film layer and a low-refractive-index film layer respectively on the test substrate, respectively determining the relationship between the coating thickness and the coating period of the high-refractive index film layer and the low-refractive index film layer, and Refractive index dispersion of each film layer;

Step 3, according to the refractive index dispersion of the high refractive index film layer and the low refractive index film layer, design the film system structure of the anti-reflection film, so that the diffractive optical device has a target transmittance at the working wavelength; the film system structure includes The total number of layers, the material of each layer from the substrate to the air, and the thickness of each layer;

Step 4, according to the thickness of each film layer in the film system structure, and the relationship between the thickness of the coating film and the coating film cycle, calculate the coating cycle of each film layer in the film system structure;

Step 5, optimizing and adjusting the microstructural parameters of the diffractive optical device according to the film structure, and preparing the microstructure of the diffractive optical device on the substrate of the diffractive optical device;

Step 6, using the chemical reaction source material to simultaneously plate thin films on multiple surfaces of the diffractive optical device substrate, the preparation sequence of the film layers is consistent with the sequence of film layers from the substrate to the air determined in step 3, The coating cycle of the film layer is determined by step 4.

Optionally, step 2 includes the following steps:

Step 21, optimizing the parameters of the atomic layer deposition coating process, so that the thin film coated by atomic layer deposition uniformly covers and grows on the surface of the microstructure;

Step 22, selecting a substrate with a difference between the optical constant and the optical constant of the thin film greater than the set threshold as the test substrate, and the test substrate is single-sided polished;

Step 23, using the optimized coating process parameters to prepare thin film layers with different atomic layer deposition coating cycles on the polished surface of the test substrate;

Step 24, using a spectroscopic ellipsometer to measure the ellipsometric spectra of the films prepared in different atomic layer deposition cycles;

Step 25, establish the physical model of the film layer, inversely calculate the ellipsometric spectrum, calculate the thickness of the film layer and the refractive index dispersion relationship, and establish the coating thickness and coating cycle of the film layer according to the thickness of the film layer prepared by different atomic layer deposition cycles Relationship.

Optionally, the step 21 includes the detection and judgment of the coating effect of atomic layer deposition, and is realized through the following steps: performing atomic layer deposition coating on the deeply etched microstructure, and measuring the coating with a scanning electron microscope or a transmission electron microscope Afterwards, deeply etch the thin film structure grown on the surface of the microstructure, and judge whether the coating process parameters used can realize the conformal growth of the film on the surface of the microstructure; if yes, it means that the coating process parameters meet the requirements; if not, continue to optimize the coating process parameter.

Optionally, in step 25, according to the thicknesses of the films prepared in different atomic layer deposition periods, the relationship between the coating thickness of the film layer and the coating period is established by linearly fitting the relationship between the film thickness and the atomic layer deposition period.

Optionally, the microstructural parameters include lateral dimensions of concave-convex positions in the microstructure.

Optionally, the coating thin film described in step 6 uses two kinds of reactive gas molecules that alternately enter the coating vacuum chamber to saturate chemical adsorption on different regions of the surface of the diffractive optical device substrate, and a chemical reaction occurs to generate a corresponding film layer.

Compared with prior art, the beneficial effect of the present invention:

(1) The present invention can realize the high-uniformity preparation of the multilayer film on the surface of the microstructure through the atomic layer deposition method, and improve the transmittance of the microstructure device;

(2) The anti-reflection film plated by the coating method proposed by the present invention has an accurate and controllable film structure, so that it can be used as a part of the microstructure device and optimized in the microstructure design process to further improve the performance of the diffractive optical device;

(3) The coating method of the anti-reflection film on the surface of the diffractive optical device of the present invention can realize the preparation of a multilayer film with a protective effect and an anti-reflection effect on the surface of the organic device, isolate the influence of water vapor, atomic oxygen, etc., and improve the use of organic materials as Substrates for use in diffractive optics.

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and thus It should be regarded as a limitation on the scope, and those skilled in the art can also obtain other related drawings based on these drawings without creative work.

Figure 1 is a schematic diagram of the structure of a diffractive optical device coated with an anti-reflection coating.

Fig. 2 is a schematic diagram of the atomic layer deposition coating process on the surface of the diffractive optical element.

Fig. 3 is a schematic diagram of a single-layer film structure of an Al ₂ O ₃ film plated with optimized parameters on the surface of a deeply etched silicon microstructure.

Fig. 4 is a schematic diagram of the relationship between the single-layer film thickness of atomic layer deposition Al ₂ O ₃ and TiO ₂ and the coating cycle.

Among them: 101-diffractive optical device substrate, 102-anti-reflection coating on microstructure surface, 103-anti-reflection coating on plane surface, 104-high refractive index film layer, 105-low refractive index film layer, 106-anti-reflection film Total thickness, 201-trimethylaluminum molecule, 202-Al ₂ O ₃ thin film grown before this atomic layer deposition coating cycle, 203-chemisorbed trimethylaluminum molecule monolayer, 204-water molecule, 205-a Al ₂ O ₃ monolayer conformally grown periodically by atomic layer deposition coating; 301-monocrystalline silicon substrate, 302-channel microstructure etched on silicon substrate, 303-Al ₂ O ₃ monolayer grown on top of microstructure steps Film, 304-Al ₂ O ₃ monolayer film grown on the side of microstructure steps, 305-Al ₂ O ₃ monolayer film grown on the bottom of microstructure steps, 401-Measurement of Al ₂ O ₃ thin films deposited at different atomic layer deposition cycles Thickness, 402-measured thickness of TiO ₂ films plated with different atomic layer deposition cycles, 403-fitting linear relationship between deposition thickness of Al ₂ O ₃ monolayer film and deposition cycle, 404-fitting deposition of TiO ₂ monolayer film Linear relationship between thickness and deposition period.

detailed description

The present invention takes the diffractive microstructure on a planar substrate as an example to clearly and completely describe the technical solutions in the embodiments of the present invention. The embodiments of the invention generally described and illustrated in the figures herein may be implemented in different sequences. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents an implementation process. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts belong to the protection scope of the present invention.

The structure of the diffractive optical device of the embodiment of the present invention is shown in Figure 1, 101 is the substrate of the diffractive optical device, a diffractive microstructure is etched on one surface of the substrate, and the other surface is a plane; The multi-layer anti-reflection film grown in the shape is called the anti-reflection film 102 on the microstructure surface, and the multi-layer anti-reflection film with the same structure as the microstructure surface film system on the plane surface is called the anti-reflection film 103 on the plane surface .

The antireflection coating 102 on the surface of the microstructure is composed of a high refractive index film layer 104 and a low refractive index film layer 105, and the antireflection coating 103 on the plane surface is also composed of a high refractive index film layer 104 and a low refractive index film layer 105, and in the anti-reflection film 102 on the microstructure surface and the anti-reflection film 103 on the planar surface, the material and film thickness of each layer of film starting from the substrate surface are the same.

The purpose of this embodiment is to achieve high transmittance of the diffractive optical device on the quartz substrate within the wavelength range of 500nm-700nm.

The high-refractive-index film layer and the low-refractive-index film layer are thin film materials with high transmittance at the working wavelength of the diffractive optical device. Within the wavelength range of the embodiment, any one or more of Nb ₂ O ₅ , TiO ₂ , Ta ₂ O ₅ and HfO ₂ materials can be selected as the high refractive index film material, and Al ₂ O ₃ and SiO ₂ materials can be used Any one or more of them are used as the material of the low refractive index film.

It should be clarified that, depending on the working wavelength of the microstructure device, the coating material may be nitride, oxide, sulfide, fluoride, etc. Coating films of different materials on devices with different working wavelengths can be realized by the method described above. This embodiment only shows the coating process of the oxide thin film on the surface of the microstructure, rather than limiting the coating material.

The anti-reflection coating on the surface of the diffractive optical lens is realized by atomic layer deposition coating technology. Atomic layer deposition is an improved chemical vapor deposition method. Its essence is to use two kinds of gas molecules alternately entering the vacuum chamber to adsorb saturated chemical adsorption on the surface of a solid substrate and undergo a chemical reaction to form a coating of the desired film. method. Figure 2 shows the process of growing Al ₂ O ₃ thin film with Al(CH ₃ ) ₃ and H ₂ O to show the principle of ALD thin film on microstructured surface. A coating cycle of atomic layer deposition includes four steps, including:

(1) Injection of reaction gas Al(CH ₃ ) ₃ . 201 shows Al(CH ₃ ) ₃ molecules injected into the vacuum chamber, and 202 shows the coated microstructure substrate or the Al ₂ O ₃ thin film grown on the surface of the microstructure substrate before the atomic layer deposition coating cycle. Al(CH ₃ ) ₃ molecules move randomly in the vacuum chamber to reach various positions of the microstructure substrate and react chemically with H ₂ O chemisorbed on the surface to form Al-O chemical bonds, and the reaction product is CH ₄ ;

(2) Purging of inert gas such as N ₂ and Ar gas. During the purging process, the physically adsorbed gas molecules, the residual gas molecules in the vacuum chamber, and the reaction product _CH4 molecules are discharged from the vacuum chamber through the vacuum pump, thereby forming a uniform chemically adsorbed trimethylaluminum molecular monolayer 203 on the surface;

(3) The injection of reaction gas H ₂ O; 204 is the H _{2 O molecule injected into the vacuum chamber, and the H 2 O} molecule will also move randomly in the vacuum chamber to reach various positions of the microstructure substrate and react with the active methyl groups on the surface The reaction generates CH ₄ , so that Al and O form a chemical bond;

(4) Purging of inert gas such as N ₂ and Ar gas for the second time. During the purging process, the physically adsorbed H ₂ O molecules, the residual H ₂ O molecules in the vacuum chamber, and the reaction product CH ₄ are discharged from the vacuum chamber through the vacuum pump, thereby forming a uniform chemically adsorbed monomolecular layer on the surface.

The atomic layer deposition coating process consists of multiple cycles as shown in FIG. 2 , and in each cycle, an Al ₂ O ₃ layer conformal to the microstructure substrate is grown.

In the coating method of the diffractive optical device, the atomic layer deposition coating method is used to simultaneously deposit high-refractive-index film layers and low-refractive-index film layers of a specific thickness in a specified order on the microstructure surface and other conventional optical surfaces, Specifically include the following steps:

Step 1, selecting the high-refractive-index film layer and the low-refractive-index film layer that make up the anti-reflection film, and determining the chemical reaction source material for the growth of the high-refractive index film layer material and the low-refractive index film layer material by atomic layer deposition;

In this embodiment, TiO ₂ is selected as the high-refractive index film layer, and Al ₂ O ₃ is selected as the low-refractive index film layer. The Al ₂ O ₃ thin film is grown by reaction with trimethylaluminum Al(CH ₃ ) ₃ and H ₂ O as source materials. The chemical reaction principle is as follows:

Al(CH ₃ ) ₃ +H ₂ O→Al ₂ O ₃ +CH ₄ .

The TiO ₂ thin film is grown by reacting with TiCl ₄ and H ₂ O as source materials. The chemical reaction principle is:

TiCl ₄ +H ₂ O→TiO ₂ +HCl.

Step 2, use the atomic layer deposition method to coat the high-refractive index film layer and the low-refractive index film layer respectively, and determine the relationship between the coating thickness of the high-refractive index film layer and the low-refractive index film layer and the atomic layer deposition period , and the refractive index dispersion of the film;

The preparation of the high-refractive-index film material and the low-refractive-index film material is achieved through the following sub-steps:

Step 21, optimizing the parameters of the ALD coating process, so that the ALD-coated thin film covers and grows uniformly on the surface of the microstructure; that is, the thin film material must uniformly cover different areas of the diffractive optical device, including the top, bottom and side walls of the microstructure .

Further, this step also includes the detection and judgment of the coating effect of atomic layer deposition;

Specifically: carry out the process of atomic layer deposition coating on the deep-etched silicon microstructure respectively, and use scanning electron microscope or transmission electron microscope to measure the film structure on the surface of the deep-etched microstructure after coating, and judge whether the coating parameters can realize the thin film in the silicon microstructure. Conformal growth of the microstructure surface; if it can, it means that the ALD coating process parameters meet the requirements, if not, continue to optimize the ALD coating process parameters. The coating process parameters include the temperature of the coating substrate, the time the substrate is exposed to the source material, the injection amount of the source material into the vacuum chamber each time, and the like.

Figure 3 shows the coating results obtained by using optimized process parameters on the deep-etched silicon microstructure surface during the growth of Al ₂ O ₃ films by the reaction of trimethylaluminum Al(CH ₃ ) ₃ and H ₂ O, in which 301 In order to prepare a single crystal silicon substrate with a microstructure, 302 is a channel etched on the silicon substrate, 301 and 302 form a micro-step structure for experiments on the surface of the silicon substrate, and 303, 304 and 305 respectively show the microstructure top , Al ₂ O ₃ film grown on the side wall and bottom, the optimized ALD coating parameters realize the Al ₂ O ₃ monolayer film 303 grown on the top of the step, the Al ₂ O ₃ monolayer film 304 grown on the side of the step and the bottom of the step The grown Al ₂ O ₃ monolayer film 305 has high thickness uniformity.

Preferably, the substrate and film materials used to detect the microstructures have different electronic properties so that they can be clearly resolved in electron microscope images.

Step 22, selecting a substrate suitable for the detection of optical properties of the thin film. Preferably, the optical constants of the selected test substrate and the optical constant of the film are significantly different, for example, the difference is greater than a set threshold, and the test substrate is single-sided polished.

In this embodiment, a silicon substrate polished on one side is selected as the growth substrate of the Al ₂ O ₃ film, and is used to detect the film thickness and optical constant of the Al ₂ O ₃ film.

Step 23, using the optimized coating process parameters to prepare thin film layers with different atomic layer deposition coating cycles on the polished surface of the test substrate;

In the examples shown, Al ₂ O ₃ thin films of 100 cycles, 200 cycles, 300 cycles, 400 cycles, and ALD were prepared respectively.

Step 24, using a spectroscopic ellipsometer to measure the ellipsometric spectra of the films prepared in different atomic layer deposition cycles;

It can be understood that the wavelength range measured by the spectroscopic ellipsometer includes the working wavelength range of the diffractive optical device.

Step 25, establish the calculation model of the film layer, invert and calculate the ellipsometric spectrum, calculate the thickness of the film layer and the refractive index dispersion relationship, and establish the coating thickness and atomic layer of the film layer according to the thickness of the film layer prepared in different atomic layer deposition cycles The relationship between the deposition period.

In this embodiment, the same coating process is performed on the high-refractive-index TiO ₂ thin film, and a TiO ₂ atomic layer deposition coating process suitable for coating diffractive optical devices can be obtained.

It can be understood that, within the wavelength range in this embodiment, the dispersion relationship of the refractive index _of the high refractive index _TiO2 film layer and the low refractive index _Al2O3 film layer can be described by the Cauchy model, and using The constants in the Cauchy model and the thickness of the film are multi-parameter fitted to the ellipsometry, and the thickness and refractive index of the high refractive index TiO ₂ film layer and the low refractive index Al ₂ O ₃ film layer with different thicknesses are calculated.

Figure 4 shows the thickness of Al ₂ O ₃ and TiO ₂ plated with different ALD cycles. The point 401 represents the actual thickness of the Al ₂ O ₃ film measured by the spectroscopic ellipsometry method, and the point 402 represents the actual thickness of the TiO ₂ film measured by the spectroscopic ellipsometry method.

Using the thickness of films with different periods, the relationship between the coating thickness and the atomic layer deposition period is linearly fitted. Solid line 403 in Fig. 4 has shown Al ₂ O ₃ The linear relationship between the atomic layer deposition period and the plated film thickness of thin film is

d=0.170818×n-2.8483 (1)

Dotted line 404 shows the linear relationship between the atomic layer deposition period and the thickness of the plated film of _TiO2 film as:

d=0.06694×n-2.08 (2)

Step 3, using the dispersion relationship of the optical constants of the high-refractive-index film layer and the low-refractive-index film layer determined in step 2, to design the film system structure of the anti-reflection film, so that the diffractive optical device has a target transmittance at the working wavelength, said The film structure includes the total number of film layers, the material type of each film layer from the substrate to the air, and the thickness of each film layer.

In the described embodiment, the specific method of designing the anti-reflection coating in the 500nm-700nm wavelength range on the surface of the quartz substrate is: taking the transmittance of the working wavelength of 100% as the target value, and continuously optimizing the high refractive index and low refractive coating. thickness, to achieve high transmittance on the surface of the quartz substrate.

Preferably, the process of optimizing the thickness of the multilayer film can be realized by commercial film system design software. In the design, the quartz material with infinite thickness is used as the substrate, and the thickness of the high-refractive index film layer and the low-refractive index film layer are optimized to achieve high transmittance on the substrate surface.

An optimized film design result is sub/17.65nmH/38.17nmL/68.30nmH/91.48nm/air, where H stands for TiO ₂ , L stands for Al ₂ O ₃ , air stands for air medium, and sub stands for fused silica substrate.

Step 4, according to the thickness of each film layer in the multilayer film system designed in step 3, and the relationship between the coating thickness and the number of coating cycles determined in step 2, calculate the atomic layer of each film layer in the multilayer film system Deposition coating cycle.

As shown in Figure 4, there is a linear relationship between the thickness of the film and the coating period. For each film in the film system design, the high refractive index film layer and the low The number of ALD cycles for the refractive index layer. The atomic layer deposition film layer sequence and coating cycle number of the film system design are 250 cycles of TiO ₂ , 240 cycles of Al ₂ O ₃ , 1051 cycles of TiO ₂ , and 552 cycles of Al ₂ O ₃ .

Step 5, according to the designed film structure of the anti-reflection film, optimize and adjust the microstructure parameters of the diffractive optical device, and prepare the optimized microstructure on the substrate.

One of the most basic processes for optimizing and adjusting microstructure parameters is as follows: Referring to Figure 1, it can be seen that due to the influence of the film layer of atomic layer deposition, the lateral size of the microstructure (concave-convex position in the figure) will change; such as antireflection coating The total thickness 106 of is d, then the width of the step is increased by 2d. In order to make the imaging effect of the microstructure device containing the multilayer film consistent with the imaging effect of the initial microstructure device not containing the multilayer film, the initial step width of the processed microstructure is smaller than that of the microstructure device not containing the multilayer film. The width needs to be reduced by 2d. Furthermore, the thin film structure can be used as a part of the microstructure device, and the microstructure parameters of the substrate can be optimized during the microstructure design process to further improve the performance of the diffractive optical device;

Step 6, with the chemical reaction source material of each film layer determined in step 1, a thin film is simultaneously plated on the surface of the substrate prepared in step 5, the preparation sequence of the film layer and the from substrate to air film determined in step 3 The layers are arranged in the same order, and the coating cycle of each film layer atomic layer deposition is determined by step 4.

Preferably, in the process of atomic layer deposition coating, each surface of the diffractive optical device is exposed to a chemical reaction gas at the same time, and each surface is purged with an inert gas, so that the gas molecules are simultaneously chemically reacted on different surfaces such as the microstructure surface. Adsorption of monomolecular layers enables simultaneous preparation of anti-reflective coatings on different surfaces of substrates.

Further preferably, the atomic layer deposition coating chamber can be connected in vacuum through a vacuum connection mechanism such as a gate valve and the microstructure etching equipment. After the etching is completed, the gate valve is opened, and the diffractive optical device is transferred from the etching vacuum chamber by a vacuum drive device. To the atomic layer deposition coating chamber, realize vacuum in-situ coating of etched devices, avoid pollution caused by particles in the air, and oxidation of the substrate by air.

It can be understood that, using the above-mentioned atomic layer deposition coating method, the thin film material can uniformly cover different areas of the diffractive optical device, including the top, bottom and sidewall of the microstructure, so that the organic diffractive optical device can be protected at low altitudes on the earth. The orbital work is free from environmental influences such as direct erosion of atomic oxygen, which effectively expands the working environment of the organic diffractive optical device and improves the life of the organic diffractive optical device.

The above descriptions are only preferred embodiments of the present invention, and do not limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention. It should be noted that like numerals and letters denote similar items in the following figures, therefore, once an item is defined in one figure, it does not require further definition and explanation in subsequent figures.

The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Anyone skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present invention. Should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (6)

1. A coating method for an anti-reflection film on the surface of a diffractive optical device, characterized in that, the atomic layer deposition coating method is used to prepare a multilayer film with the same film stacking sequence and film deposition thickness on different surfaces of the diffractive optical device, specifically comprising the following step: Step 1, select the high-refractive-index film layer material and low-refractive-index film layer material that make up the anti-reflection film, and determine the chemical reaction source material for the atomic layer deposition growth of the high-refractive index film layer material and the low-refractive index film layer material ; Step 2, using the atomic layer deposition method to plate a high-refractive index film layer and a low-refractive-index film layer respectively on the test substrate, respectively determining the relationship between the coating thickness and the coating period of the high-refractive index film layer and the low-refractive index film layer, and Refractive index dispersion of each film layer; Step 3, according to the refractive index dispersion of the high refractive index film layer and the low refractive index film layer, design the film system structure of the anti-reflection film, so that the diffractive optical device has a target transmittance at the working wavelength; the film system structure includes The total number of layers, the material of each layer from the substrate to the air, and the thickness of each layer; Step 4, according to the thickness of each film layer in the film system structure, and the relationship between the thickness of the coating film and the coating film cycle, calculate the coating cycle of each film layer in the film system structure; Step 5, optimize and adjust the microstructural parameters of the diffractive optical device according to the film structure, and prepare the microstructure of the diffractive optical device on the substrate of the diffractive optical device; the optimization and adjustment of the microstructural parameters of the diffractive optical device is specifically: if the If the total thickness of the film system structure is d, the initial step width of the prepared microstructure increases by 2d, and the initial step width of the prepared microstructure decreases compared with the step width of the microstructure that does not contain the film system structure 2d; step 6, using the chemical reaction source material to simultaneously plate thin films on multiple surfaces of the diffractive optical device substrate, the preparation sequence of the film layers is consistent with the sequence of film layers determined in step 3 from the substrate to the air, The coating cycle of each film layer is determined by step 4. 2. the coating method of anti-reflection film on the surface of a kind of diffractive optical device according to claim 1, is characterized in that, described step 2 comprises the following steps: Step 21, optimizing the parameters of the atomic layer deposition coating process, so that the thin film coated by atomic layer deposition uniformly covers and grows on the surface of the microstructure; Step 22, selecting a substrate with a difference between the optical constant and the optical constant of the thin film greater than the set threshold as the test substrate, and the test substrate is single-sided polished; Step 23, using the optimized coating process parameters to prepare thin film layers with different atomic layer deposition coating cycles on the polished surface of the test substrate; Step 24, using a spectroscopic ellipsometer to measure the ellipsometric spectra of the films prepared in different atomic layer deposition cycles; Step 25, establish the physical model of the film layer, inversely calculate the ellipsometric spectrum, calculate the thickness of the film layer and the refractive index dispersion relationship, and establish the coating thickness and coating cycle of the film layer according to the thickness of the film layer prepared by different atomic layer deposition cycles Relationship. 3. the coating method of a kind of diffractive optical device surface anti-reflection coating according to claim 2, it is characterized in that, described step 21 comprises the detection and judgment to atomic layer deposition coating effect, and realizes by following steps: Atomic layer deposition coating film on the etched microstructure, use scanning electron microscope or transmission electron microscope to measure the film structure grown on the surface of the etched microstructure after coating, and judge whether the coating process parameters used can realize the conformal growth of the film on the surface of the microstructure ; If yes, it means that the coating process parameters meet the requirements; if not, continue to optimize the coating process parameters. 4. the coating method of anti-reflection film on the surface of a kind of diffractive optical device according to claim 2, is characterized in that, In step 25, according to the thickness of the film layers prepared in different atomic layer deposition cycles, the relationship between the coating film thickness of the film layer and the coating film cycle is established by linear fitting. 5 . The method for coating an anti-reflection film on the surface of a diffractive optical device according to claim 1 , wherein the optimization and adjustment of the microstructure parameters of the diffractive optical device includes adjusting the lateral size of the concave-convex position in the microstructure. 6 . 6. the coating method of a kind of diffractive optical device surface antireflection film according to claim 1, is characterized in that, the coating thin film described in the described step 6 is to utilize two kinds of reactive gas molecules that alternately enter coating vacuum chamber The chemical adsorption is saturated on different regions of the substrate surface of the diffractive optical device, and a chemical reaction occurs to form the corresponding film layer.

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