CN111378934A - Coating method for improving spectrum and stress aging stability of electron beam evaporation film element - Google Patents

Abstract

Using a combination of conventional electron beam evaporation and plasma-assisted deposition, a coating technology to improve the spectral and stress aging stability of electron beam evaporation thin film elements is proposed. The functional film is prepared by conventional electron beam evaporation technology to obtain a high resistance to laser damage threshold; the dense outer layer is prepared by plasma-assisted deposition technology, and the entire conventional electron beam evaporated film is wrapped in it to prevent water Molecules move in and out of the membrane. The invention can reduce the stress level of the entire film system and improve the spectral and stress aging stability of the electron beam evaporation film element while maintaining the high damage threshold of the electron beam film without increasing the difficulty of film system design.

Description

Coatings to Improve Spectral and Stress-Aging Stability of Electron Beam Evaporated Thin Film Components method

technical field

The invention relates to the field of optical thin films, and relates to a coating method for improving the spectrum and stress aging stability of electron beam evaporation thin film elements.

Background technique

Since the invention of the laser, the damage threshold of optical components has not changed much compared to the yearly increase in laser energy. In high-energy laser systems, the size of optical components is also increasing in order to reduce laser damage. Electron beam evaporation thin film elements are widely used in various large-scale high-power laser systems due to their excellent optical properties, high damage threshold, and good uniformity of large apertures. However, with the change of the use environment, or with the increase of aging time in the same environment, the properties of the film will deviate from the preset indicators, such as atmospheric-vacuum effect leading to spectral drift, changing the electric field distribution of the film system and then It reduces the anti-laser damage performance of the thin film element; another example is the aging effect that causes the mechanical properties of the thin film to be unstable, causing surface deformation, affecting the transmission and focusing of the beam; excessive compressive stress may lead to thin film wrinkles, delamination / delamination, and Excessive tensile stress can cause film cracking in severe cases. The porous structure of e-beam-evaporated films easily interacts with polar molecules such as water vapor in the environment, which is the main reason for the changes in various properties of the film, and brings great challenges to the long-term reliable and stable operation of the laser system. Therefore, reducing the porosity of the thin-film element helps to improve its stability. Commonly used dense film deposition technologies include ion-assisted deposition technology, ion beam sputtering deposition technology, magnetron sputtering deposition technology, etc. Although the stability of the prepared thin-film components has been improved, the stress is large, mechanical failure is prone to occur, and the Laser damage performance is generally inferior to electron beam evaporation thin film components. In addition, atomic layer deposition technology, which is widely used in the preparation of thin films with high barrier properties, can prepare ultra-high stability thin films, but its deposition rate is low and it is not easy to be extended to prepare large-sized thin-film elements.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to overcome the above-mentioned deficiencies of the prior art, and to provide a coating method for improving the spectral and stress aging stability of electron beam evaporation thin film elements. While the damage threshold of the beam thin film is higher, the stress level of the entire film system is reduced and the spectral and stress aging stability of the electron beam evaporated thin film element is improved.

Technical solution of the present invention

A coating technology for improving the spectral and stress aging stability of electron beam evaporation thin film elements, characterized in that the essence of the method is to prepare functional multilayer films by electron beam evaporation technology to obtain a higher anti-laser damage threshold On the basis of , the outer wrapping layer of the film system is prepared by ion-assisted deposition technology to obtain a dense moisture barrier layer, which wraps the film surface and sides of the entire conventional electron beam evaporation film to prevent the ingress and egress of water vapor.

The method includes the following steps:

1) Fixture plate design:

Two clamping discs A and B of equal diameter are designed with different blank holder sizes. The pressing edge of the clamp plate A is larger than that of the clamp plate B. The difference between A and B clamp plate blank holder is greater than or equal to 2mm;

2) Membrane system design:

Design the film system according to the required optical performance requirements: S|MN ₁ N ₂ |A, where S represents the substrate, M represents the conventional electron beam multilayer film, and N ₁ represents the sub-external dense film, which is used to prevent the change of the chuck plate. A large number of water molecules enter the film system, N ₂ represents the outermost dense wrapping layer, preventing water vapor from entering and leaving the upper surface and side of the film system, the thickness d _N of the N1 and N2 layers is calculated as follows:

(对于高反膜，Z为正整数)

(For highly reflective films, Z is a positive integer)

Among them, λ is the design wavelength of the multilayer film system; n is the refractive index of the medium, here is the refractive index of the dense protective layer prepared by ion beam assisted deposition technology; θ is the incident angle of light;

3) Substrate cleaning: the substrate is cleaned and dried;

4) Film preparation:

(1) First, use the clamp plate A with a larger blank holder:

①According to the designed film system, the multi-layer film M is deposited by electron beam evaporation technology:

Heat the substrate to 120℃～250℃; when the vacuum degree is better than 9.0×10 ^-4 Pa, turn on the electron gun, and use electron beam evaporation technology to prepare high and low refractive index films according to the designed film sequence;

②Ion beam assisted deposition technology is used to coat the secondary outer dense protective layer N ₁ to prevent a large amount of water molecules from being adsorbed in the film system when the fixture plate is changed later:

After the multilayer film M is deposited, the plasma source is turned on, the plasma bias is set to 100V _- 200V, and the N1 layer is started to be plated, and the plasma source and the electron gun are turned off after the film is plated;

(2) Replace the clamp plate B with the smaller blank holder to coat the outermost dense wrapping layer N ₂ :

After the substrate is cooled, the cavity is opened quickly, and the thin film element in step ② is replaced with the clamp plate B with a smaller blank holder. This process should be carried out in a temperature and humidity controlled environment for a limited time (<1h) to minimize the exposure of the thin film element to the atmosphere. time. The substrate is heated to 120℃～250℃; when the vacuum degree is better than 9.0×10 ^-4 Pa, the plasma source is turned on, the plasma bias voltage is set to 100V～200V, and the outermost wrapping layer N ₂ is plated. At this time, due to the replacement of the clamp plate, a film-free area equal to the size difference between the clamp plate A and B will be vacated between the outer periphery of the film system and the blank holder of the clamp plate B, and the _N2 layer will run along this area and The film surface grows, covering the entire film system;

(3) The coating is finished.

The substrate is optical glass or crystal.

Technical effect of the present invention:

1. The present invention comprehensively adopts electron beam evaporation technology and ion-assisted deposition technology: uses electron beam evaporation technology to deposit functional thin films to obtain higher resistance to laser damage; uses plasma-assisted deposition technology to prepare dense outer layer wrapping layer, which wraps the entire conventional electron beam evaporation film to prevent water molecules from entering and leaving the film.

2. The present invention can reduce the stress level of the entire film system and improve the spectral and stress aging stability of the electron beam evaporation film element while maintaining the high damage threshold of the electron beam film without increasing the difficulty of film system design.

3. The method is simple and easy to implement, and has the characteristics of strong pertinence and high efficiency. It is suitable for the preparation of high-stability thin-film components for large-scale high-power laser systems.

Description of drawings

Figure 1 shows the prepared multilayer highly reflective film, wherein (a) is prepared by conventional electron beam evaporation technology, (b) only the top layer is prepared by ion-assisted technology, (c) is prepared by the method of the present invention

Figure 2 is the spectral aging and stress aging of the prepared multilayer highly reflective film, wherein (a) conventional electron beam evaporation, only the top layer adopts ion-assisted technology, (b) adopts the method of the present invention.

Detailed ways

The present invention will be further described below with reference to the embodiments and accompanying drawings.

Please refer to FIG. 1 first. FIG. 1 is a schematic diagram of the film system of the multilayer high-reflection film prepared by conventional electron beam evaporation technology, only the top layer is prepared by ion-assisted preparation, and prepared by the method of the present invention. HfO ₂ , the low refractive index material is SiO ₂ , and the film system designs are: S|MB|A, S|MN|A and S|MN ₁ N ₂ |A multilayer film as an example to illustrate that the present invention is used for improving The coating technology of electron beam evaporation thin film element's spectrum and stress aging stability, wherein M=4L(HL) ¹² H, B=N=N ₁ =N ₂ =4L, the technology includes the following steps:

1) Fixture plate design:

Two sets of clamping discs A and B with equal diameters are designed, and the difference between the two blank holders is greater than or equal to 2mm. In this embodiment, the edge blank of the clamp plate A is 3 mm, and the edge blank of the clamp plate B is 1 mm.

2) Membrane system design:

According to the requirements of spectral performance: 0°incidence, R≥99.5%@1064nm, the designed film system is: S|4L(HL) ¹² H 4L|A, where L represents the low-refractive index material SiO ₂ , and H represents the high-refractive index material HfO ₂ , the 4L layer is the protective layer;

3) Substrate cleaning: the substrate is cleaned and dried;

4) Film preparation:

(1) Conventional electron beam evaporation technology:

①According to the designed film system, use electron beam evaporation technology to deposit functional layer M=4L(HL) ¹² H:

The substrate was heated to 200°C; when the vacuum degree was better than 9.0×10 ^-4 Pa, the electron gun was turned on, and the high and low refractive index films M were prepared by electron beam evaporation technology according to the designed film sequence. If the layer is a HfO ₂ layer, the oxygen partial pressure is ^{2×10 -2 Pa} and the deposition rate is 0.2nm/s; if the layer is a SiO ₂ layer, the oxygen partial pressure is 5.0×10 ^-3 Pa and the deposition rate is 0.4 nm/s.

②Use electron beam evaporation technology to deposit protective layers other than functional layer M:

After the multi-layer film M=4L (HL) ¹² H is deposited, the protective layer B=4L is continuously deposited by the electron beam evaporation technique. In this case, the layer is a SiO ₂ layer, the oxygen partial pressure is 1.5×10 ^-2 Pa, and the deposition rate is 0.4 nm/s. Turn off the electron gun after plating the film.

③ Finished coating.

(2) Only the top layer is prepared by ion-assisted preparation to obtain a dense film:

①According to the designed film system, use electron beam evaporation technology to deposit functional layer M=4L(HL) ¹² H:

The substrate was heated to 200°C; when the vacuum degree was better than 9.0×10 ^-4 Pa, the electron gun was turned on, and the high and low refractive index films M were prepared by electron beam evaporation technology according to the designed film sequence. If the layer is a HfO ₂ layer, the oxygen partial pressure is ^{2×10 -2 Pa} and the deposition rate is 0.2nm/s; if the layer is a SiO ₂ layer, the oxygen partial pressure is 5.0×10 ^-3 Pa and the deposition rate is 0.4 nm/s.

②The top layer N is deposited by the ion beam assisted deposition process:

After the multilayer film M=4L (HL) ¹² H is deposited, the plasma source is turned on, the plasma bias is set to 170V, the APS is fixed with oxygen for 5 sccm, and the top protective layer N=4L is deposited. In this case the layer is a SiO ₂ layer with a deposition rate of 0.4nm/s. After plating the film, the plasma source and electron gun were turned off.

③ Finished coating.

(3) the inventive method: the wrapping layer and the secondary outer layer are prepared by ion beam assisted deposition technology to obtain the dense film layer; the remaining layers adopt the electron beam deposition technology to obtain high laser damage threshold:

①First, use the clamp plate A with a larger blank holder:

i According to the designed film system, use the electron beam evaporation technology to deposit the functional layer M=4L(HL) ¹² H:

The substrate was heated to 200°C; when the vacuum degree was better than 9.0×10 ^-4 Pa, the electron gun was turned on, and the high and low refractive index films M were prepared by electron beam evaporation technology according to the designed film sequence. If the layer is a HfO ₂ layer, the oxygen partial pressure is ^{2×10 -2 Pa} and the deposition rate is 0.2nm/s; if the layer is a SiO ₂ layer, the oxygen partial pressure is 5.0×10 ^-3 Pa and the deposition rate is 0.4 nm/s.

ii Deposition of the outermost protective layer using an ion beam assisted deposition process:

After the multilayer film M=4L (HL) ¹² H is deposited, the plasma source is turned on, the plasma bias is set to 170V, the APS is fixed with oxygen for 5 sccm, and the dense protective layer N ₁ =4L is deposited. In this case the layer is a SiO ₂ layer with a deposition rate of 0.4nm/s. After plating the film, the plasma source and electron gun were turned off.

② Replace the clamp plate B with the smaller blank holder to coat the outermost dense wrapping layer N ₂ :

After the substrate is cooled, the cavity is quickly opened, and the thin film element in step ii is replaced with a clamp plate B with a smaller edge holder, and the coating time from the opening of the cavity to the closing of the cavity again is controlled within 1 hour to reduce the time that the thin film element is exposed to the atmosphere. The substrate was heated to 200°C; when the vacuum degree was better than 9.0×10 ^-4 Pa, the plasma source was turned on, the plasma bias was set to 170V, the APS was fixed with oxygen for 5 sccm, and the dense wrapping layer N ₂ =4L was deposited. In this case the layer is a SiO ₂ layer with a deposition rate of 0.4nm/s. At this time, due to the replacement of the clamp plate, there will be a 2mm non-film area between the outer periphery of the film system and the pressing edge of the clamp plate B, and the _N2 layer grows along this area and the film surface, covering the entire film system in the Inside, the plasma source and electron gun are turned off after plating the film.

③ Finished coating.

5) adopt the spectrometer and the interferometer to measure the spectrum and stress of the high reflection film prepared by conventional electron beam evaporation technology, only the top layer is prepared by ion-assisted technology and prepared by the method of the present invention respectively with aging time:

All the prepared high-reflection films were stored in an environment with constant temperature and humidity,

①Measure the transmittance of the spectrum at regular intervals and extract the change of the center wavelength of the reflection band with the aging time. Test angle: 0°, test range 300nm-1400nm.

②Measure the surface shape at regular intervals and calculate the change of stress with aging time.

Several experiments show that the method of the present invention adopts the ion beam assisted deposition technology to prepare the secondary outer layer and the wrapping layer, so as to obtain a dense film layer and prevent water molecules from entering and leaving the upper surface and side surface of the multi-layer laser thin film element; the remaining functional layers are deposited by electron beams. technology to achieve high laser damage thresholds. On the premise of not increasing the difficulty of film system design and coating process, it can effectively block the moisture absorption and desorption of porous films prepared by electron beam evaporation technology, thereby improving the spectral and stress aging stability of multi-layer thin film elements, and reducing the entire film. the stress level of the system.

Claims (2)

1. a kind of coating method that promotes the spectrum of electron beam evaporation film element and stress aging stability, it is characterized in that, this method adopts electron beam evaporation technology to prepare functional multilayer film to obtain higher anti-laser damage threshold value On the basis, the outer wrapping layer of the film system is prepared by ion-assisted deposition technology to obtain a dense moisture barrier layer, which wraps the film surface and sides of the entire conventional electron beam evaporation film to prevent the ingress and egress of water vapor. Include the following steps: 1) Fixture plate design: Two kinds of clamp plates A and B with different blank holder sizes and equal diameters are designed, wherein the blank holder of the holder plate A is larger than that of the holder plate B, and the difference between the holder plate A and the holder plate B is greater than or equal to 2mm; 2) Membrane system design: Design the film system according to the required optical performance requirements: S|MN ₁ N ₂ |A, where S represents the substrate, M represents the conventional electron beam multilayer film, and N ₁ represents the sub-external dense film, which is used to prevent the change of the chuck plate. A large number of water molecules enter the film system, and N ₂ represents the outermost dense wrapping layer, preventing water vapor from entering and leaving the upper surface and sides of the film system; the thickness d _N of the N ₁ and N ₂ layers is calculated as follows:

(For highly reflective films, Z is a positive integer) Among them, λ is the design wavelength of the multilayer film system; n is the refractive index of the medium, here is the refractive index of the dense protective layer prepared by ion beam assisted deposition technology; θ is the incident angle of light; 3) Substrate cleaning: the substrate is cleaned and dried; 4) Film preparation: (1) First, use the clamp plate A with a large blank holder: ①According to the designed film system, use the electron beam evaporation technique to deposit the multilayer film M: heat the substrate to 120℃～250℃; when the vacuum degree is better than 9.0×10 ^-4 Pa, open the electron gun, according to the designed The film series adopts electron beam evaporation technology to prepare high and low refractive index film layers; ②Ion beam assisted deposition technology is used to coat the secondary outer dense protective layer N ₁ to prevent a large amount of water molecules from being adsorbed in the film system when the fixture plate is changed later: After the multilayer film M is deposited, the plasma source is turned on, the plasma bias is set to 100V _- 200V, and the N1 layer is started to be plated, and the plasma source and the electron gun are turned off after the film is plated; (2) Replace the clamp plate B with the smaller blank holder to coat the outermost dense wrapping layer N ₂ : After the substrate is cooled, the cavity is opened quickly, and the thin film element in step ② is replaced with the clamp plate B with a smaller blank holder. This process should be carried out in a temperature and humidity controlled environment for a limited time (<1h) to minimize the exposure of the thin film element to the atmosphere. heating the substrate to 120℃～250℃; when the vacuum degree is better than 9.0×10 ^-4 Pa, turn on the plasma source, set the plasma bias voltage to 100V～200V, and coat the outermost wrapping layer N ₂ ; (3) The coating is finished. 2 . The coating method according to claim 1 , wherein the substrate is optical glass or crystal. 3 .

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