阅读说明：本技术 一种低吸收低热畸变薄膜的实现方法 (Method for realizing low-absorption low-heat distortion film ) 是由 王胭脂 王志皓 邵建达 张宇晖 陈昌 朱晔新 晋云霞 邵宇川 易葵 贺洪波 于 2021-08-11 设计创作，主要内容包括：一种低吸收低热畸变薄膜及其制备方法,包括基础膜系选择、膜系优化、基板的超声清洗、基板的真空离子束清洗、离子束溅射制备薄膜、退火后处理；将膜系分为低吸收控制层和低热畸变控制层两部分分别优化的膜系优化方法,并通过镀膜前的基板处理及镀膜后的退火后处理降低薄膜内部的吸收性缺陷,使用双离子束溅射的沉积方式并通过沉积过程中的参数调控进一步改善薄膜的热畸变。本发明可以在整个工艺流程上获得和保障反射率大于99.995％的高反射膜,同时与普通工艺制备出的薄膜相比吸收降低99％。采用本发明制备出的薄膜在长时间工作下损耗低,具有工艺重复性好、可控性强、可靠性高等优点,适用于引力波探测、激光陀螺等高精度测量和高稳定性光学系统的使用。(A low-absorption low-heat distortion film and a preparation method thereof comprise the steps of selecting a basic film system, optimizing the film system, ultrasonically cleaning a substrate, cleaning a vacuum ion beam of the substrate, preparing a film by ion beam sputtering, and annealing post-treatment; the method is a film system optimization method which divides a film system into a low absorption control layer and a low heat distortion control layer to be optimized respectively, reduces the absorption defects in the film through substrate treatment before film coating and annealing post-treatment after film coating, and further improves the heat distortion of the film by using a deposition mode of dual ion beam sputtering and parameter regulation and control in the deposition process. The invention can obtain and guarantee the high-reflection film with the reflectivity of more than 99.995 percent on the whole process flow, and simultaneously, the absorption is reduced by 99 percent compared with the film prepared by the common process. The film prepared by the invention has low loss under long-time work, has the advantages of good process repeatability, strong controllability, high reliability and the like, and is suitable for high-precision measurement such as gravitational wave detection, laser gyro and the like and the use of high-stability optical systems.)

1. A low-absorption low-heat distortion film is characterized in that the film system is Sub/(aHbL)^{^n}H(cLdM)^{^m}/Air，H＝Ta₂O₅，L＝SiO₂，M＝Al₂O₃A, b, c, d are coefficients of quarter-wavelength optical thickness;

(aHbL)^{^n}h is a low absorption control layer, so that low absorption loss is realized; (cLdM)^{^m}A low thermal distortion control layer is used for realizing low thermal distortion; n is the number of cycles of aHbL in the low absorption control layer, and m is the number of cycles of the low heat distortion control layerThe number of cycles of cLdM, n is 15-30, and m is 1-5.

2. The low absorption and low heat distortion film of claim 1 wherein the coefficients of the quarter-wave optical thickness, a and b, are adjusted according to the absorption coefficients of H, L for the two materials, respectively, and the relationship between a and b as a function of the number of layers, x, is: a is 1.3-0.12(x-1), b is 1.3+0.12(x-1), until a is 1, b is 1, the values of a and b in the following period are kept as 1 and are not changed; c. d is adjusted according to the thermal expansion coefficients of M, L two materials, and the change relationship of c and d along with the number y of layers is as follows: c is 1+2^-y,d＝1-2^-y。

3. The method for preparing the low-absorption low-heat distortion film according to claim 1 or 2, comprising the steps of:

(1) ultrasonic cleaning of the substrate: putting the substrate into an ultrasonic cleaning tank, cleaning organic matters on the surface by using a detergent, then ultrasonically cleaning by using pure water, and drying by using a baking lamp after ultrasonically cleaning;

(2) vacuum ion beam cleaning of the substrate: clamping the substrate cleaned in the step (1), installing the substrate into a coating machine, and controlling the vacuum degree to be 1 x 10^-4torr～4×10^-4torr, cleaning the surface of the substrate by using argon and oxygen mixed gas, wherein the flow rates are respectively 5sccm and 5sccm, the ion beam cleaning time is 5-15 minutes, the ion beam voltage is 600-750V, and the ion beam current is 150-300 mA;

(3) coating a film on the substrate: firstly, a high-purity tantalum target and a high-purity silicon target are used for sputtering the substrate obtained in the step (2) according to the formula (aHbL)^{^n}Film system structure of alternately depositing Ta₂O₅And SiO₂Obtaining a low absorption control layer; depositing a layer of tantalum oxide on the low absorption control layer by using a high-purity tantalum target and a double-ion beam sputtering method; finally, using a high-purity aluminum target and a high-purity silicon target, a dual ion beam sputtering method is used to form a low absorption control layer (cLdM)^{^m}The film system structure alternately deposits Al₂O₃And SiO₂Obtaining a low thermal distortion control layer; namely, the low absorption and the low heat distortion are completedDeposition of a variable film;

(4) annealing treatment of the film: and (4) annealing the low-absorption low-heat distortion film obtained in the step (3) for 3 times, and sequentially increasing the temperature for 3 times.

4. The method of claim 3, wherein the low absorption and low heat distortion film is prepared by: the substrate material in the step (1) is one of sapphire and microcrystal, the coating area of the substrate material is ultra-smooth, and the atomic force measurement surface roughness of the coating area is less than 0.1 nm.

5. The method of claim 3, wherein the low absorption and low heat distortion film is prepared by: controlling the frequency of ultrasonic waves in the step (3) to be 40-100 KHZ and the power of the ultrasonic waves to be 1-2 KW; the cleaning agent is mirco-90, the solubility is 1-2%, and the ultrasonic time is 8-15 minutes; ultrasonically cleaning the substrate by using the cleaning agent, and ultrasonically cleaning the substrate by using deionized water, wherein the ultrasonic cleaning time of the pure water is 8-15 minutes, and the water temperature is 30-40 ℃; and drying the mixture by using a baking lamp at the temperature of 80-100 ℃ after the cleaning is finished.

6. The method of claim 3, wherein the low absorption and low heat distortion film is prepared by: in the step (4), argon and oxygen plasma are used as the ion beam, and the purity of the argon is more than 99.999 percent; the ion beam cleaning time is 5-10 minutes, the ion beam voltage is 600-750V, and the ion beam current is 150-300 mA.

7. The method of claim 3, wherein the low absorption and low heat distortion film is prepared by: the coating material in the step (5) adopts metal tantalum target (H: Ta), metal aluminum target (M: Al) and metal silicon target (L: Si), the target purity is 99.99%, and the target purity is respectively reacted with high-purity oxygen to generate Ta₂O₅、Al₂O₃And SiO₂The concentration of pure oxygen is 99.999%. The temperature of the substrate during film deposition is 100-150 ℃, the oxygen charging amount is 30-60sccm, and the deposition rate is 0.18-0.21 nm/s.

8. The method of claim 3, wherein the low absorption and low heat distortion film is prepared by: and (6) annealing the film for 3 times, wherein the temperature is 200-300 ℃, 300-350 ℃, 350-400 ℃ in sequence, and the annealing time is 5-10 h each time.

Technical Field

The invention relates to a low-absorption low-heat distortion film suitable for space gravitational wave detection and a laser gyroscope and an implementation method thereof, belonging to the technical field of film optics.

Background

Development of space gravitational wave detection and laser gyro has strategic significance on national military and national defense safety and technological development. In these optical systems, which require high-precision measurement and have high stability, the thermal distortion and the thermal absorption of the thin-film element are one of the key factors limiting the development thereof.

For meeting the requirement of space gravitational wave detection, the optical telescope system needs to reduce aberration caused by material heat distortion during use. The laser system also needs high stable laser output, and the increase of film loss under long-time operation can cause the reflectivity of the reflecting mirror to be reduced, thereby causing unstable laser performance. Therefore, the development of a high-reflective film for use therein is aimed at reflecting energy as high as possible and having good thermal stability under long-term operation, high reliability and long life.

In the process of preparing the low-heat distortion and high-reflection film, the whole process is controlled from the selection of a basic film system, the optimization of the film system to the ultrasonic cleaning of a substrate, the vacuum ion beam cleaning of the substrate, the preparation of the film by ion beam sputtering and the annealing post-treatment, the control of a single process is limited for finally obtaining the ultra-low loss and high-reflection mirror, and the whole process flow is required to be connected in series to form the complete low-absorption and low-heat distortion film.

Disclosure of Invention

The invention aims to solve the technical problem of realizing the preparation of a low-absorption low-heat distortion film, and provides a design and a process flow of a high-reflectivity low-absorption low-heat distortion film, which are selected from a basic film system, optimized from the film system, ultrasonically cleaned from a substrate, cleaned from a vacuum ion beam, sputtered from an ion beam to prepare the film, and annealed and post-treated, wherein the specific flow is as follows:

the film system of the low-absorption low-heat distortion film is Sub/(aHbL) ^ n H (cLdM) ^ m/Air, H ═ Ta₂O₅， L＝SiO₂，M＝Al₂O₃And a, b, c and d are coefficients of quarter-wavelength optical thickness. (aHbL)^{^n}H is a low absorption control layer which is used for regulating and controlling the film to realize low absorption loss; (cLdM)^{^m}Is a low thermal distortion control layer and is used for regulating and controlling the film to realize low thermal distortion. n is the number of cycles of aHbL in the low absorption control layer, m is the number of cycles of cLdM in the low thermal distortion control layer, n is 15 to 30, and m is 1 to 5.

In the invention, the coefficients a and b of the quarter-wavelength optical thickness are respectively adjusted according to the absorption coefficients of H, L two materials, and the change relationship of a and b along with the number x of layers is as follows: a is 1.3-0.12(x-1), b is 1.3+0.12(x-1), until a is 1, b is 1, the values of a and b in the following period are kept as 1 and are not changed; c. d is adjusted according to the thermal expansion coefficients of M, L two materials, and the change relationship of c and d along with the number y of layers is as follows: c is 1+2^-y,d＝1-2^-y。

The method for realizing the low-absorption low-heat distortion film comprises the following steps:

(1) ultrasonic cleaning of the substrate: putting the substrate into an ultrasonic cleaning tank, cleaning organic matters on the surface by using a detergent, then ultrasonically cleaning by using pure water, and drying by using a baking lamp after ultrasonically cleaning;

(2) vacuum ion beam cleaning of the substrate: clamping the substrate cleaned in the step (1), installing the substrate into a coating machine, and controlling the vacuum degree to be 1 x 10^-4torr～4×10^-4torr, cleaning the surface of the substrate by using argon and oxygen mixed gas, wherein the flow is 5sccm and 5sccm respectively, the cleaning time of an ion beam is 5-15 minutes, the voltage of the ion beam is 550-700V, and the current of the ion beam is 150-300 mA;

(3) coating a film on the substrate: firstly, a high-purity tantalum target and a high-purity silicon target are used for sputtering the substrate obtained in the step (2) according to the formula (aHbL)^{^n}Film system structure of alternately depositing Ta₂O₅And SiO₂Obtaining a low absorption control layer; depositing a layer of tantalum oxide on the low absorption control layer by using a high-purity tantalum target and a double-ion beam sputtering method; finally, using a high-purity aluminum target and a high-purity silicon target, a dual ion beam sputtering method is used to form a low absorption control layer (cLdM)^{^m}The film system structure alternately deposits Al₂O₃And SiO₂Obtaining a low thermal distortion control layer; namely, the deposition of the low-absorption low-heat distortion film is completed;

(4) annealing treatment of the film: and (4) annealing the low-absorption low-heat distortion film obtained in the step (3) for 3 times, and sequentially increasing the temperature for 3 times.

In the invention, the substrate material in the step (1) is one of sapphire and microcrystal, the coating area of the substrate material is ultra-smooth, and the atomic force measurement surface roughness of the coating area is less than 0.1 nm.

In the invention, in the step (3), the frequency of the ultrasonic wave is controlled to be 40-100 KHZ, and the power of the ultrasonic wave is controlled to be 1-2 KW; the cleaning agent is mirco-90, the solubility is 1-2%, and the ultrasonic time is 8-15 minutes; ultrasonically cleaning the substrate by using the cleaning agent, and ultrasonically cleaning the substrate by using deionized water, wherein the ultrasonic cleaning time of the pure water is 8-15 minutes, and the water temperature is 30-40 ℃; and drying the mixture by using a baking lamp at the temperature of 80-100 ℃ after the cleaning is finished.

In the invention, argon and oxygen plasmas are used for the ion beam in the step (4), and the purity of argon is more than 99.999 percent; the ion beam cleaning time is 5-10 minutes, the ion beam voltage is 600-750V, and the ion beam current is 150-300 mA.

In the invention, the coating material in the step (5) adopts a metal tantalum target (H: Ta), a metal aluminum target (M: Al) and a metal silicon target (L: Si), the target purity is 99.99%, and the target purities are respectively reacted with high-purity oxygen to generate Ta₂O₅、Al₂O₃And SiO₂The concentration of pure oxygen is 99.999%. The temperature of the substrate during film deposition is 100-150 ℃, the oxygen charging amount is 30-60sccm, and the deposition rate is 0.18-0.21 nm/s.

In the invention, the film is annealed in the step (6) for 3 times, the temperature is 200-300 ℃, 300-350 ℃, 350-400 ℃ in sequence, and the annealing time is 5-10 h each time.

In the invention, the key point that the reflectivity of the film is higher than 99.995% under a longer working time for incident light with the wavelength of 1064nm is to provide a film system optimization method of the low-absorption low-thermal-distortion film, the film systems of the low-absorption control layer and the low-thermal-distortion control layer are re-optimized and adjusted, and the design and the preparation method are combined to obtain the whole set of process flow control. In order to meet the development requirement of a low-absorption low-heat distortion film, the substrate is made of sapphire, microcrystal and other materials with low thermal expansion coefficient, and the coating material is made of Ta with low ultraviolet band absorption loss and low tensile stress₂O₅、Al₂O₃、SiO₂And the like. In the aspect of the film preparation method, a double-ion-beam sputtering deposition method is adopted, and through substrate ultrasonic cleaning, full-flow process control and annealing treatment after film coating, the surface roughness of a film layer is reduced, defect formation is reduced, the bonding force between the film and the substrate is improved, the reflectivity of the film is further improved, and the optical loss of the film is reduced.

The invention has the following advantages:

1. the low absorption and low heat distortion are controlled in a layered mode by optimizing and adjusting the basic high-reflection film system, and the absorption and heat distortion of the film are effectively reduced by adopting an annealing treatment mode of gradually increasing the temperature;

2. the coefficient of the quarter-wavelength optical thickness of each layer of the low absorption control layer is adjusted according to the absorption coefficients of the two materials in the low absorption control layer. For incident light with the wavelength of 1064nm, the absorption of the film is lower than 0.5ppm, and the absorption is reduced by 99% compared with the film prepared by the common method;

3. the coefficient of the quarter-wavelength optical thickness of each layer of the low absorption control layer is adjusted according to the coefficients of thermal expansion of the two materials in the low thermal distortion control layer. The film has small thermal distortion in a long-time working environment, and the deformation of the film is lower than 0.01% in 24h working time;

4. the method for sputtering and coating by using double ion beams effectively reduces the extinction coefficient of a deposited film layer and ensures the reflectivity of a high-reflection film: the reflectivity is higher than 99.995% for incident light with a wavelength of 1064 nm;

5. the preparation production efficiency of the low-absorption low-heat distortion film is greatly improved by controlling the whole process flow.

Drawings

FIG. 1 is a film layer structure diagram of a low absorption low heat distortion film.

FIG. 2 is a flow chart of the implementation of the low absorption and low heat distortion film, wherein the process flow represented by the letters in sequence is as follows: a: selecting a basic membrane system; b: optimizing a membrane system; c: ultrasonic cleaning of the substrate; d: cleaning the substrate by vacuum ion beams; e: preparing a film by ion beam sputtering; f: and (5) annealing and post-treatment.

FIG. 3 is the film reflectance of example 1.

FIG. 4 is the film reflectance of example 2.

FIG. 5 is the film reflectance of example 3.

Detailed Description

The present invention will be further described with reference to examples.

Example 1: preparing a low-absorption low-heat distortion film on a sapphire substrate: the membrane system is Sub/(aHbL)^{^15} H(cLdM)^{^4}/Air，H＝Ta₂O₅，L＝SiO₂，M＝Al₂O₃. Changing a period aHbL in the low absorption control layer according to a change of a and b with the number of layers x to make a equal to 1.3-0.12(x-1), b equal to 1.3+0.12(x-1), and changing a period cLdM in the low heat distortion control layer according to c and d with the number of layers y to make c equal to 1+2^-y,d＝1-2^-yAnd carrying out re-optimization adjustment. Placing the sapphire substrate with the surface roughness less than 0.1nm into an ultrasonic cleaning tank, and controlling the frequency of ultrasonic waves to be 80KHZ and the power of the ultrasonic waves to be 1.5 KW; the cleaning agent is mirco-90, the solubility is 2%, and the ultrasonic time is 8 minutes; ultrasonically cleaning the substrate by using deionized water after the substrate is ultrasonically cleaned, wherein the ultrasonic cleaning time of the pure water is 8 minutes, and the water temperature is 35 ℃; drying the mixture by using a baking lamp at the temperature of 100 ℃ after the cleaning is finished; the cleaned substrate is clamped and installed in a coating machine, the equipment is a Spector 1.0 coating machine of Veeco company, the coating machine is provided with 16cm and 12cm ion sources, the 12cm ion source cleans the surface of the substrate by using argon and oxygen mixed gas, the flow rate is 5sccm and 5sccm respectively, the ion beam cleaning time is 5 minutes, the ion beam voltage is 650V, and the ion beam current is 300 mA. Using a high-purity tantalum target and a high-purity silicon target, sputtering the target on a substrate by a dual ion beam sputtering method according to (aHbL)^{^15}Film system structure of alternately depositing Ta₂O₅And SiO₂Obtaining a low absorption control layer, preparing Ta₂O₅The temperature of the substrate is 120 ℃ during the film preparation, the oxygen charging amount is 60sccm, the deposition rate is 0.2nm/s, and the SiO is prepared₂Controlling the temperature of the substrate to be 120 ℃ during film forming, the oxygen charging amount to be 30sccm and the deposition rate to be 0.19 nm/s; depositing a layer of tantalum oxide on the low absorption control layer by using a high-purity tantalum target and a double-ion beam sputtering method; then, using a high purity aluminum target and a high purity silicon target, a dual ion beam sputtering method is used to form a low absorption control layer (cLdM)^{^4}The film system structure alternately deposits Al₂O₃And SiO₂Obtaining a low thermal distortion control layer, preparing Al₂O₃The substrate temperature was 120 ℃ during the film deposition, the oxygen charging amount was 50sccm, and the deposition rate was 0.18 nm/s. Annealing the film for 3 times at 200 deg.C, 300 deg.C, 400 deg.C, and annealing each timeThe length is 8 h. And (3) measuring the reflectivity of the film of the sample after the whole process is finished, wherein the reflectivity reaches 99.998%. The film is subjected to a 1064nm weak absorption test, the test result is 0.42ppm, the 1064nm weak absorption of the film prepared by the common process is 150ppm, and the absorption of the film prepared by the method is reduced by 99.72%. Performing stability test on the film, wherein the deformation amount of the film is lower than 0.01% under the working time of 24 h;

example 2: preparing a low-absorption low-heat distortion film on a sapphire substrate: the membrane system is Sub/(aHbL)^{^30} H(cLdM)^{^2}/Air，H＝Ta₂O₅，L＝SiO₂，M＝Al₂O₃. Changing a period aHbL in the low absorption control layer according to a change of a and b with the number of layers x to make a equal to 1.3-0.12(x-1), b equal to 1.3+0.12(x-1), and changing a period cLdM in the low heat distortion control layer according to c and d with the number of layers y to make c equal to 1+2^-y,d＝1-2^-yAnd carrying out re-optimization adjustment. Placing the sapphire substrate with the surface roughness less than 0.1nm into an ultrasonic cleaning tank, and controlling the frequency of ultrasonic waves to be 60KHZ and the power of the ultrasonic waves to be 1.5 KW; the cleaning agent is mirco-90, the solubility is 2%, and the ultrasonic time is 12 minutes; ultrasonically cleaning the substrate by using deionized water after the substrate is ultrasonically cleaned, wherein the ultrasonic cleaning time of the pure water is 8 minutes, and the water temperature is 35 ℃; drying the mixture by using a baking lamp at the temperature of 100 ℃ after the cleaning is finished; the cleaned substrate is clamped and installed in a coating machine, the equipment is a Spector 1.0 coating machine of Veeco company, the coating machine is provided with 16cm and 12cm ion sources, the 12cm ion source cleans the surface of the substrate by using argon and oxygen mixed gas, the flow rate is 5sccm and 5sccm respectively, the ion beam cleaning time is 15 minutes, the ion beam voltage is 600V, and the ion beam current is 150 mA. Using a high-purity tantalum target and a high-purity silicon target, sputtering the target on a substrate by a dual ion beam sputtering method according to (aHbL)^{^30}Film system structure of alternately depositing Ta₂O₅And SiO₂Obtaining a low absorption control layer, preparing Ta₂O₅The temperature of the substrate is 120 ℃ during the film preparation, the oxygen charging amount is 60sccm, the deposition rate is 0.2nm/s, and the SiO is prepared₂Controlling the temperature of the substrate to be 120 ℃ during film formation, the oxygen charging amount to be 30sccm and the deposition rate to be 0.19 nm/s; high purity of reuseA tantalum target, wherein a layer of tantalum oxide is deposited on the low absorption control layer by using a double ion beam sputtering method; then, using a high purity aluminum target and a high purity silicon target, a dual ion beam sputtering method is used to form a low absorption control layer (cLdM)^{^2}The film system structure alternately deposits Al₂O₃And SiO₂Obtaining a low thermal distortion control layer, preparing Al₂O₃The substrate temperature was 120 ℃ during the film deposition, the oxygen charging amount was 50sccm, and the deposition rate was 0.18 nm/s. And annealing the film for 3 times, wherein the temperature is 200 ℃, 350 ℃, 500 ℃ in sequence, and the annealing time is 8 hours each time. And (3) measuring the reflectivity of the film of the sample after the whole process is finished, wherein the reflectivity reaches 99.999%. The film is subjected to a 1064nm weak absorption test, the test result is 0.48ppm, the 1064nm weak absorption of the film prepared by the common process is 150ppm, and the absorption of the film prepared by the method is reduced by 99.68%. Performing stability test on the film, wherein the deformation amount of the film is lower than 0.01% under the working time of 24 h;

example 3: preparing a low-absorption low-heat distortion film on a microcrystalline substrate: the membrane system is Sub/(aHbL)^{^22} H(cLdM)^{^3}/Air，H＝Ta₂O₅，L＝SiO₂，M＝Al₂O₃. Changing a period aHbL in the low absorption control layer according to a change of a and b with the number of layers x to make a equal to 1.3-0.12(x-1), b equal to 1.3+0.12(x-1), and changing a period cLdM in the low heat distortion control layer according to c and d with the number of layers y to make c equal to 1+2^-y,d＝1-2^-yAnd carrying out re-optimization adjustment. Putting the glass-ceramic substrate with the surface roughness less than 0.1nm into an ultrasonic cleaning tank, and controlling the frequency of ultrasonic waves to be 50KHZ and the power of the ultrasonic waves to be 1.5 KW; the cleaning agent is mirco-90, the solubility is 2%, and the ultrasonic time is 15 minutes; ultrasonically cleaning the substrate by using deionized water after the substrate is ultrasonically cleaned, wherein the ultrasonic cleaning time of the pure water is 8 minutes, and the water temperature is 35 ℃; drying the mixture by using a baking lamp at the temperature of 100 ℃ after the cleaning is finished; clamping the cleaned substrate, and mounting the substrate into a coating machine, wherein the coating machine is a Spector 1.0 coating machine of Veeco, the coating machine is provided with 16cm and 12cm ion sources, the 12cm ion source cleans the surface of the substrate by using argon and oxygen mixed gas, and the flow rates are respectively5sccm and 5sccm, an ion beam cleaning time of 8 minutes, an ion beam voltage of 750V, and an ion beam current of 200 mA. Using a high-purity tantalum target and a high-purity silicon target, sputtering the target on a substrate by a dual ion beam sputtering method according to (aHbL)^{^22}Film system structure of alternately depositing Ta₂O₅And SiO₂Obtaining a low absorption control layer, preparing Ta₂O₅The temperature of the substrate is 120 ℃ during the film preparation, the oxygen charging amount is 60sccm, the deposition rate is 0.2nm/s, and the SiO is prepared₂Controlling the temperature of the substrate to be 120 ℃ during film forming, the oxygen charging amount to be 30sccm and the deposition rate to be 0.19 nm/s; depositing a layer of tantalum oxide on the low absorption control layer by using a high-purity tantalum target and a double-ion beam sputtering method; then, using a high purity aluminum target and a high purity silicon target, a dual ion beam sputtering method is used to form a low absorption control layer (cLdM)^{^3}The film system structure alternately deposits Al₂O₃And SiO₂Obtaining a low thermal distortion control layer, preparing Al₂O₃The substrate temperature was 120 ℃ during the film deposition, the oxygen charging amount was 50sccm, and the deposition rate was 0.18 nm/s. And annealing the film for 3 times, wherein the temperature is 300 ℃, 350 ℃, 400 ℃ in sequence, and the annealing time is 8 hours each time. And (3) measuring the reflectivity of the film of the sample after the whole process is finished, wherein the reflectivity reaches 99.998%. The film is subjected to a 1064nm weak absorption test, the test result is 0.45ppm, the 1064nm weak absorption of the film prepared by the common process is 150ppm, and the absorption of the film prepared by the method is reduced by 99.7%. And (3) performing a stability test on the film, wherein the deformation amount of the film is less than 0.01% under the working time of 24 h.