Layer-by-layer annealing hafnium oxide / silicon dioxide antireflection film for high repetition frequency femtosecond laser

Abstract

The invention discloses a layer-by-layer annealing hafnium oxide / silicon dioxide antireflection film for high repetition frequency femtosecond laser. The invention discloses a preparation method of the layer-by-layer annealing hafnium oxide / silicon dioxide antireflection film for high repetition frequency femtosecond laser. The preparation method comprises the following steps: 1, depositing a hafnium oxide film on a cleaned fused quartz substrate by using a radio frequency magnetron sputtering coating system, and putting the film into a muffle furnace for high-temperature annealing; and 2, depositing a silicon dioxide film on the annealed hafnium oxide film to obtain a hafnium oxide / silicon dioxide double-layer antireflection film, and then putting the film into a muffle furnace for secondary high-temperature annealing. The optical performance of the hafnium dioxide / silicon dioxide antireflection film is remarkably improved through the layer-by-layer annealing treatment process, good transmissivity and a high damage threshold value under high repetition frequency femtosecond laser irradiation are shown in an ultraviolet visible light region, and the hafnium dioxide / silicon dioxide antireflection film can be applied to the field of high repetition frequency femtosecond lasers.

Description

Technical Field

[0001] The present invention belongs to the technical field of femtosecond laser, and relates to a preparation method of a hafnium dioxide / silicon dioxide antireflection film for a high-repetition-rate femtosecond laser. Background Art

[0002] High-repetition-rate femtosecond lasers have attracted much attention due to their wide applications in the fields of ultrafast, ultra-high intensity, and ultra-precision machining. In order to ensure the reliable performance of optical thin films under intense laser irradiation, it is necessary to develop optical thin films with high damage thresholds. Hafnium dioxide / silicon dioxide thin films are the most widely used laser thin films. However, there are many oxygen vacancy defects and high thermal stress in hafnium dioxide thin films, which cause the hafnium dioxide layer to reach the critical electron density and critical stress intensity earlier than the silicon dioxide layer, thus becoming the starting point of laser irradiation damage and reducing the damage threshold of the overall thin film. Therefore, improving the quality of the hafnium dioxide layer in hafnium dioxide / silicon dioxide thin films has become an urgent task to improve the performance of the overall thin film.

[0003] Thermal annealing is one of the important post-treatment methods to improve the performance of thin films. By reasonably controlling the annealing temperature and holding time, the thermal annealing process can optimize the defect density, microstructure, surface morphology, and mechanical properties of thin films, thereby increasing the laser-induced damage threshold of optical thin films. For oxide thin films, annealing in air or oxygen atmosphere can also promote the entry of oxygen atoms into the thin film to form lattice oxygen, further reducing oxygen vacancy defects.

[0004] Current research mainly focuses on the overall annealing of hafnium dioxide / silicon dioxide thin films and improving their performance by optimizing annealing parameters. However, it is difficult to improve the performance of the hafnium dioxide layer in the middle, such as effectively optimizing the stoichiometric ratio and reducing the roughness. In view of this problem, the present invention adopts a layer-by-layer annealing post-treatment process to prepare a hafnium dioxide / silicon dioxide antireflection film with a high femtosecond laser damage threshold. Summary of the Invention

[0005] The purpose of the present invention is to prepare a hafnium dioxide / silicon dioxide antireflection film by reactive magnetron sputtering and perform layer-by-layer annealing treatment to reduce the defect size and defect density of hafnium dioxide and silicon dioxide thin films and improve the damage threshold under high-repetition-rate femtosecond laser irradiation.

[0006] To achieve this purpose, the following technical solutions are applied:

[0007] Etch the fused silica substrate with a configured hydrofluoric acid buffer solution, and then clean and dry it. Use a high-purity hafnium target in a magnetron sputtering system, introduce an oxygen / argon mixed gas to deposit a hafnium dioxide film on the fused silica substrate, and perform a high-temperature annealing treatment on the hafnium dioxide film. Deposit a silica dioxide film on the annealed hafnium dioxide film using a magnetron sputtering system, and perform a secondary high-temperature annealing treatment on the obtained hafnium dioxide / silica dioxide film. The specific process is as follows:

[0008] 1. Preparation and annealing treatment of hafnium dioxide film:

[0009] Install the fused silica substrate and the high-purity hafnium target in a magnetron sputtering system, introduce an oxygen / argon mixed gas in a certain ratio (flow ratio 1:3 - 1:1), and at the same time adjust the sputtering power (100 - 500 W) to prepare a hafnium dioxide film deposited on the fused silica substrate.

[0010] Put the hafnium dioxide film into a muffle furnace, with an annealing temperature of 300 - 600 °C, a holding time of 2 - 6 h, a heating rate of 2 - 10 °C / min, and an annealing atmosphere of air or oxygen.

[0011] 2. Preparation of silica dioxide film:

[0012] Install the hafnium dioxide film and the high-purity silicon target in a magnetron sputtering system, introduce an oxygen / argon mixed gas in a certain ratio (flow ratio 1:3 - 1:1), and at the same time adjust the sputtering power (100 - 200 W) to prepare hafnium dioxide / silica dioxide film samples under different deposition parameters.

[0013] Put the hafnium dioxide / silica dioxide antireflection film into a muffle furnace for secondary high-temperature annealing treatment, with an annealing temperature of 300 - 600 °C, a holding time of 2 - 6 h, a heating rate of 2 - 10 °C / min, and an annealing atmosphere of air or oxygen.

[0014] 3. High-repetition-rate femtosecond laser damage threshold test:

[0015] Use a high-repetition-rate femtosecond laser with a repetition rate of 500 kHz and wavelengths of 515 nm and 1030 nm to perform a femtosecond laser damage threshold test on the hafnium dioxide / silica dioxide film deposited on the fused silica substrate, and the test mode is S-on-1 [ISO Standard No.21254-2].

[0016] Furthermore, the air pressure in the vacuum chamber before coating in steps 1 and 2 is reduced to 5×10 -4 Pa, and after introducing gases with different flow ratios, the air pressure rises to 1.2 - 2 Pa.

[0017] Further, before the coating in Step 1 and Step 2, the pure hafnium and pure silicon targets are pre-sputtered for 5 - 10 min. The temperature of the substrate during coating is at room temperature without additional heating.

[0018] Further, in Step 5, the focused diameter of the femtosecond laser beam is 1 - 20 μm, and the laser irradiation time is set to 1 - 10 s.

[0019] In summary, the beneficial effects of the present invention are as follows:

[0020] The post-treatment of layer-by-layer annealing reduces the defect size and defect density of the hafnium dioxide film and the silicon dioxide film, and improves the microstructure and surface morphology of the film. Finally, a hafnium dioxide / silicon dioxide antireflection film with low absorption, low scattering, high optical transmittance and high laser damage threshold is obtained. Description of the Drawings

[0021] Figure 1 It is the energy dispersive spectroscopy image of the hafnium dioxide / silicon dioxide antireflection films of Comparative Example 1, Comparative Example 2 and Example 1. The results show that the layer-by-layer annealing process can optimize the stoichiometric ratio of the hafnium dioxide / silicon dioxide film, especially can significantly optimize the stoichiometric ratio of the hafnium dioxide film located in the middle.

[0022] Figure 2 It is the damage threshold of the hafnium dioxide / silicon dioxide antireflection films of Comparative Example 1, Comparative Example 2 and Example 1. The results show that the layer-by-layer annealing process can significantly improve the damage threshold of the hafnium dioxide / silicon dioxide antireflection film under high-repetition femtosecond laser irradiation. Embodiments

[0023] The following specific examples are used to further illustrate the present invention. It should be understood that the purpose of the examples given is to further elaborate the content of the present invention, and cannot be construed as a limitation to the protection scope of the present invention in any sense.

[0024] Comparative Example 1

[0025] The etched and cleaned fused quartz substrate is placed into a magnetron sputtering coating system, and a hafnium dioxide / silicon dioxide antireflection film is obtained by sequentially depositing a hafnium dioxide film and a silicon dioxide film using high-purity hafnium target and silicon target. When depositing hafnium dioxide, the sputtering power and the oxygen / argon gas flow ratio are set to 400 W and 1 / 3 respectively. When depositing silicon dioxide, the sputtering power and the oxygen / argon gas flow ratio are set to 200 W and 1 / 3 respectively.

[0026] Comparative Example 2

[0027] Put the etched and cleaned fused silica substrate into a magnetron sputtering coating system, and sequentially deposit hafnium dioxide film and silicon dioxide film using high-purity hafnium target and silicon target to obtain a hafnium dioxide / silicon dioxide antireflection film. When depositing hafnium dioxide, the sputtering power and the oxygen / argon gas flow ratio are set to 400 W and 1 / 3 respectively. When depositing silicon dioxide, the sputtering power and the oxygen / argon gas flow ratio are set to 200 W and 1 / 3 respectively. Put the hafnium dioxide / silicon dioxide antireflection film into a muffle furnace for high-temperature annealing treatment, with the annealing temperature of 400 °C, the heating rate of 2 °C / min, and the holding time of 4 h.

[0028] Example 1

[0029] Step 1: Install the fused silica substrate and the high-purity hafnium target in the magnetron sputtering machine, turn on the molecular pump, and obtain a vacuum degree of 5×10 -4 Pa. First, perform pre-sputtering in a pure argon atmosphere with a sputtering power of 200 W for 10 min. Then, perform sputtering coating for 2 h with the parameters of a sputtering power of 400 W and an oxygen-argon flow ratio of 1 / 3. Obtain a hafnium dioxide film deposited on the fused silica substrate. Put the hafnium dioxide film into a muffle furnace for high-temperature annealing treatment, with the annealing temperature of 400 °C, the heating rate of 2 °C / min, and the holding time of 4 h.

[0030] Step 2: Install the hafnium dioxide film annealed in Step 1 and the high-purity silicon target in the magnetron sputtering machine, turn on the molecular pump, and obtain a vacuum degree of 5×10 -4 Pa. Perform pre-sputtering in a pure argon atmosphere with a sputtering power of 200 W for 10 min. Then, perform sputtering coating for 2 h with the parameters of a sputtering power of 200 W and an oxygen-argon flow ratio of 1 / 3 to obtain a hafnium dioxide / silicon dioxide antireflection film. Put the hafnium dioxide / silicon dioxide antireflection film into a muffle furnace for secondary high-temperature annealing treatment, with the annealing temperature of 400 °C, the heating rate of 2 °C / min, and the holding time of 4 h.

[0031] Example 2

[0032] Step 1: Install the fused silica substrate and the high-purity hafnium target in the magnetron sputtering machine, turn on the molecular pump, and obtain a vacuum degree of 5×10 -4 Pa. First, perform pre-sputtering in a pure argon atmosphere with a sputtering power of 200 W for 10 min. Then, perform sputtering coating for 2 h with the parameters of a sputtering power of 400 W and an oxygen-argon flow ratio of 1 / 3. Obtain a hafnium dioxide film deposited on the fused silica substrate. Put the hafnium dioxide film into a muffle furnace for high-temperature annealing treatment, with the annealing temperature of 600 °C, the heating rate of 2 °C / min, and the holding time of 4 h.

[0033] Step 2: Install the annealed hafnium dioxide film and high-purity silicon target in step 1 in a magnetron sputtering machine. Turn on the molecular pump to obtain a vacuum of 5×10 -4 Pa. Perform pre-sputtering for 10 min in a pure argon atmosphere with a sputtering power of 200 W. Then, perform sputtering coating for 2 h with a sputtering power of 200 W and an oxygen-argon flow ratio of 1 / 3 to obtain a hafnium dioxide / silicon dioxide antireflection film. Put the hafnium dioxide / silicon dioxide antireflection film into a muffle furnace for secondary high-temperature annealing treatment. The annealing temperature is 600 °C, the heating rate is 2 °C / min, and the holding time is 4 h.

[0034] Example 3

[0035] Step 1: Install the fused silica substrate and high-purity hafnium target in a magnetron sputtering machine. Turn on the molecular pump to obtain a vacuum of 5×10 -4 Pa. First, perform pre-sputtering for 10 min in a pure argon atmosphere with a sputtering power of 200 W. Then, perform sputtering coating for 2 h with a sputtering power of 400 W and an oxygen-argon flow ratio of 1 / 3 to obtain a hafnium dioxide film deposited on the fused silica substrate. Put the hafnium dioxide film into a muffle furnace for high-temperature annealing treatment. The annealing temperature is 400 °C, the heating rate is 2 °C / min, and the holding time is 8 h.

[0036] Step 2: Install the annealed hafnium dioxide film and high-purity silicon target in step 1 in a magnetron sputtering machine. Turn on the molecular pump to obtain a vacuum of 5×10 -4 Pa. Perform pre-sputtering for 10 min in a pure argon atmosphere with a sputtering power of 200 W. Then, perform sputtering coating for 2 h with a sputtering power of 200 W and an oxygen-argon flow ratio of 1 / 3 to obtain a hafnium dioxide / silicon dioxide antireflection film. Put the hafnium dioxide / silicon dioxide antireflection film into a muffle furnace for post-annealing treatment. The annealing temperature is 400 °C, the heating rate is 2 °C / min, and the holding time is 8 h.

[0037] The above-described embodiments are only used to explain and illustrate the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the protection scope of this application. It should be noted that for those of ordinary skill in the art, any modifications and changes made to the present invention without departing from the concept of the technical solution of this application fall within the protection scope of this application.

Claims

1. A layer-by-layer annealed hafnium dioxide / silicon dioxide antireflection film for high-repetition-rate femtosecond lasers, characterized in that, it has the following preparation steps: (1) Using a radio frequency magnetron sputtering coating system, deposit a hafnium dioxide film on the cleaned fused silica substrate, and put the hafnium dioxide film into a muffle furnace for high-temperature annealing treatment; (2) Using a radio frequency magnetron sputtering coating system, deposit a silicon dioxide film on the annealed hafnium dioxide film to obtain a hafnium dioxide / silicon dioxide antireflection film, and then put the hafnium dioxide / silicon dioxide antireflection film into a muffle furnace for secondary high-temperature annealing treatment.

2. The preparation method of a layer-by-layer annealed hafnium dioxide / silicon dioxide antireflection film for high-repetition-rate femtosecond lasers according to claim 1, characterized in that: The annealing temperature in steps (1) and (2) is 300 - 600 °C, the holding time is 2 - 6 h, the heating rate is 2 - 10 °C / min, and the annealing atmosphere is air or oxygen.

3. The preparation method of a layer-by-layer annealed hafnium dioxide / silicon dioxide antireflection film for high-repetition-rate femtosecond lasers according to claim 1, characterized in that: In steps (1) and (2), high-purity hafnium and silicon are used as sputtering targets respectively, and an oxygen / argon mixed gas is introduced for reactive magnetron sputtering.

4. A layer-by-layer annealed hafnium dioxide / silicon dioxide antireflection film for high-repetition-rate femtosecond lasers prepared as claimed in claim 1 exhibits high transmittance and excellent anti-damage performance under high-repetition-rate femtosecond laser irradiation.

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