Method for preparing boron carbide thin film by evaporation

Abstract

The present invention belongs to the field of vacuum coating, and discloses a method for preparing boron carbide film by evaporation. The method comprises the following steps: placing boron powder in a crucible of an evaporation coating machine, placing a cleaned and dried substrate above the crucible in the evaporation coating machine; evacuating the evaporation coating machine, turning on the electron gun to melt and evaporate the boron powder with a high-energy electron beam, and turning on the ion source at the same time. The ion source uses a mixed gas of heavy inert gas and carbon source gas, and the gas generates heavy inert gas ions and carbon ions through glow discharge. After ionization, the high-energy carbon ions react with the evaporated boron to generate a boron carbide film. The method of the present invention can prepare a boron carbide film at a low temperature, avoiding the limitation of chemical vapor deposition method requiring high-temperature plating. At the same time, it can be applied to the evaporation coating machine to realize the continuous completion of infrared anti-reflection film and boron carbide protective film.

Description

Technical Field

[0001] The invention belongs to the field of vacuum coating, and in particular relates to a method for preparing a boron carbide film by evaporation. Background Art

[0002] Boron carbide (B4C) is one of the hardest superhard materials in nature, second only to diamond in hardness. Boron carbide has a wide range of application prospects in the fields of machinery, electronics, coating, etc. due to its excellent physical properties. Boron carbide film has high transmittance in the infrared spectrum region; and has the advantages of high melting point, low density, high damage threshold, etc., which is an ideal protective material for infrared optical lenses.

[0003] Boron carbide film preparation methods mainly include chemical vapor deposition (CVD) and physical vapor deposition (PVD). Chemical vapor deposition requires very high temperatures (about 1000°C) for deposition, and many substrates cannot be deposited at such high temperatures, thus limiting the selection of substrate materials. Physical vapor deposition (PVD) includes magnetron sputtering, reactive sputtering and other methods. Although the above methods can be deposited at a lower substrate temperature, most of the deposited boron carbide films are amorphous, making it difficult to achieve a crystalline structure, and the hardness is not high enough.

[0004] A Chinese patent with publication number CN101314842A discloses a method for preparing a boron carbide film using electron beam evaporation technology. This method can prepare both amorphous boron carbide films and polycrystalline boron carbide films, as well as boron carbide films with various B and C component ratios. The prepared boron carbide films have smooth surfaces, dense films, and good uniformity. However, this method requires obtaining boron carbide materials in advance, and undergoes high-temperature sintering at 1400~1600°C during the preparation of the boron carbide materials. This mixed sintering of carbon and boron may result in poor mixing uniformity, resulting in the appearance of elemental carbon or boron during evaporation coating, rather than a compound of the two, thereby affecting the performance of the final boron carbide film. Summary of the invention

[0005] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for preparing a boron carbide film by evaporation, which can prepare a boron carbide film at a low temperature, avoiding the limitation of chemical vapor deposition (CVD) which requires high temperature plating. At the same time, it can be applied in an evaporation machine to realize the continuous completion of an infrared antireflection film and a boron carbide protective film.

[0006] To achieve the purpose of the present invention, the specific technical scheme is as follows:

[0007] A method for preparing a boron carbide film by evaporation comprises the following steps:

[0008] Put the boron powder in the crucible of the evaporation coating machine, and put the cleaned and dried substrate on the top of the crucible in the evaporation coating machine; evacuate the evaporation coating machine, turn on the electron gun to melt and evaporate the boron powder with a high-energy electron beam, and turn on the ion source at the same time. The ion source uses a mixed gas of heavy inert gas and carbon source gas. The gas generates heavy inert gas ions and carbon ions through glow discharge. After ionization, the high-energy carbon ions react with the evaporated boron to form a boron carbide film.

[0009] Preferably, the purity of the boron powder is not less than 99.9%.

[0010] Preferably, the heavy inert gas is at least one of helium, neon, argon, krypton and xenon; the carbon source gas is at least one of methane, butane and acetylene; and the substrate is a silicon substrate, a germanium substrate, a zinc sulfide substrate or a zinc selenide substrate.

[0011] Preferably, the heavy inert gas is helium; and the carbon source gas is methane.

[0012] Preferably, the ion source used is a Hall source.

[0013] Preferably, in the mixed gas used in the ion source, the heavy inert gas accounts for 1% to 20% by volume, and the carbon source gas accounts for 80% to 99% by volume.

[0014] Preferably, the evaporation coating machine is evacuated to a vacuum degree of 2.0*10 -3 Below Pa.

[0015] Preferably, during coating, the substrate temperature is controlled at 130-200°C.

[0016] Preferably, the evaporation rate of the boron powder after melting is set to 2-10 angstroms per second.

[0017] Preferably, the ion source parameters are: neutralization current 0.3~0.6A, neutralization gas flow rate 5~8sccm, anode voltage 110~200V, anode current 1.5~3A.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] According to the process scheme of the present invention, a boron carbide film can be prepared at low temperature, avoiding the limitation of high-temperature plating required by chemical vapor deposition (CVD). At the same time, it can be applied in an evaporation machine to realize the continuous completion of infrared anti-reflection film and boron carbide protective film.

[0020] The present invention does not require prefabrication of boron carbide film materials in advance, and the coating process is completed by full chemical reaction without the presence of single-substance materials. DETAILED DESCRIPTION

[0021] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and carefully in combination with preferred embodiments below, but the protection scope of the present invention is not limited to the following specific embodiments.

[0022] Unless otherwise defined, all the professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0023] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0024] Example 1

[0025] This embodiment provides a method for preparing a boron carbide film by evaporation, comprising the following steps:

[0026] (1) A 2 mm thick and 25 mm diameter germanium sheet is ultrasonically cleaned and then dried to prevent the lens surface from being dirty and causing film peeling;

[0027] (2) Place boron powder with a purity of not less than 99.9% in the crucible of the evaporation coating machine, place the cleaned germanium sheet in the fixture of the evaporation coating machine, adjust the position to be just above the opening of the crucible, and evacuate the chamber to 2.0*10 -3 Below Pa pressure, the coating heating temperature is set at 150°C;

[0028] (3) After the vacuum and temperature are reached, turn on the electron gun to melt the boron powder. Slowly increase the electron gun beam current from 0 watts to 300 watts to avoid the temperature rising too fast and causing the film material to splash. After the boron powder is melted, set the evaporation rate to 2 angstroms per second;

[0029] (4) Turn on the ion source (Hall source) while the boron powder is evaporating, set the parameters of neutralization current 0.3A, neutralization gas flow 5sccm, anode voltage 180V, anode current 2A, and set the ion source gas introduction ratio of methane to 90% by volume and argon to 10% by volume;

[0030] (5) Determine the thickness of the boron carbide film by multiplying the coating rate by the time. In this embodiment, the following settings are used: a coating rate of 2 angstroms for 1 kilosecond to obtain a boron carbide film with a thickness of 200 nanometers.

[0031] (6) After coating, let it stand for 20 minutes to cool down and release stress. Then take out the germanium sheet to obtain a boron carbide film of corresponding thickness.

[0032] Example 2

[0033] This embodiment provides a method for preparing a boron carbide film by evaporation, comprising the following steps:

[0034] (1) Clean a 2 mm thick 25 mm diameter silicon wafer with polishing liquid, acetone, and alcohol to prevent dirt on the lens surface from causing film peeling;

[0035] (2) Place boron powder with a purity of not less than 99.9% in the crucible of the evaporation coating machine, place the cleaned silicon wafer in the fixture of the evaporation coating machine, adjust the position to be just above the opening of the crucible, and evacuate the chamber to 1.5*10 -3 Below PaPa pressure, the coating heating temperature is set at 160 degrees;

[0036] (3) After the vacuum and temperature are reached, turn on the electron gun to melt the boron powder. Slowly increase the electron gun beam current from 0 watts to 300 watts to avoid the film material splashing due to the instantaneous increase in temperature caused by the power increase too quickly. After the boron powder is melted, set the evaporation rate to 3 angstroms per second;

[0037] (4) While the boron powder is evaporating, the ion source is turned on and the parameters are set to neutralization current 0.5A, neutralization gas flow rate 8sccm, anode voltage 200V, anode current 2.4A, and the ion source gas flow ratio is set to 95% methane and 5% argon;

[0038] (5) Determine the thickness of the boron carbide film by multiplying the coating rate by the time. In this embodiment, the following settings are used: 3 angstroms for 1 kilosecond to obtain a 300 nanometer thick boron carbide film.

[0039] (6) After coating, let it stand for 30 minutes to cool down and release stress. Then take out the silicon wafer to obtain a boron carbide film of corresponding thickness.

[0040] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of the present invention.

Claims

1. A method for preparing a boron carbide film by evaporation, characterized in that: The following steps are involved: Put the boron powder in the crucible of the evaporation coating machine, put the cleaned and dried substrate on the top of the crucible in the evaporation coating machine; evacuate the evaporation coating machine to a vacuum degree of 2.0*10 -3 Pa or less, turn on the electron gun to melt and evaporate the boron powder with a high-energy electron beam, and at the same time turn on the ion source, which uses a mixed gas of heavy inert gas and carbon source gas. The gas generates heavy inert gas ions and carbon ions through glow discharge. After ionization, the high-energy carbon ions react with the evaporated boron to form a boron carbide film; in: The evaporation rate of the boron powder after melting is set to 2 to 10 angstroms per second; The heavy inert gas is selected from at least one of helium, neon, argon, krypton and xenon; The carbon source gas is selected from at least one of methane, butane and acetylene; The substrate is one of a silicon substrate, a germanium substrate, a zinc sulfide substrate or a zinc selenide substrate; In the mixed gas used in the ion source, the heavy inert gas accounts for 1% to 20% by volume, and the carbon source gas accounts for 80% to 99% by volume; The ion source parameters are: neutralization current 0.3~0.6A, neutralization gas flow 5~8sccm, anode voltage 110~200V, anode current 1.5~3A; During coating, the substrate temperature is controlled at 130~200℃.

2. The method according to claim 1, characterized in that The purity of the boron powder is not less than 99.9%.

3. The method according to claim 1, characterized in that The heavy inert gas is helium; the carbon source gas is methane.

4. The method according to claim 1, characterized in that The ion source used was a Hall source.