JP2645867B2 - Method of depositing diamond film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for depositing a diamond film using high-temperature plasma.

[Conventional technology]

Synthetic diamond films formed on the substrate surface have excellent hardness, wear resistance, high elastic modulus, etc., and are already useful for cutting tools, wear-resistant tools, bearings, sliding members, etc. However, recently, it is expected to be used as a functional material utilizing its thermal, optical, and electrical properties.

Conventionally, as a vapor phase deposition method of diamond, there are a thermal CVD method in which a raw material gas and hydrogen are decomposed by heat, a plasma CVD method in which a raw material gas and hydrogen are decomposed in a plasma excited by direct current, high frequency and microwave, and a hydrocarbon. There is known an ion beam vapor deposition method in which plasma decomposition is performed by an ion gun or the like, and ions are extracted and vapor deposited by an electric field.

All of these methods are performed under low pressure conditions from an industrial point of view. Therefore, in the initial stage of the reaction, the number of diamond crystal nuclei precipitated on the substrate surface is small, so that a diamond film having a predetermined thickness can be formed. It takes an extremely long time. In order to solve this drawback, a method has been attempted in which the surface of the substrate is roughened (JP-A-60-200897) or polished with an abrasive powder of less than 1 μm (JP-A-62-108798). .

On the other hand, contrary to the above low pressure conditions, a method of growing high-quality synthetic diamond at high speed by increasing the concentration of active species by using high-temperature plasma at a relatively high pressure (Japanese Patent Laid-Open No. 62-158195) ) Has been proposed.

[Means to be Solved by the Invention]

However, conventional film-form diamond synthesized by thermal plasma typified by the invention of JP-A-62-158195 has a problem in adhesion to a substrate, and cracks generated in the diamond film during or after synthesis. Accordingly, there is a problem that a phenomenon of easily peeling off from the substrate surface is caused.

The inventors have conducted intensive studies with the aim of solving the above-mentioned problems when using high-temperature plasma, and as a result, when the composition ratio of carbon and hydrogen of the reaction gas in the vicinity of the substrate is set and maintained at a certain value or more, the substrate The inventors have found that the adhesion to the deposited diamond film is significantly improved regardless of the surface state, and have led to the development of the present invention.

[Means for solving the problem]

In other words, the method of depositing a diamond film according to the present invention is a method of depositing a diamond film on a substrate surface by generating a high-frequency thermal plasma in a mixed gas comprising a hydrocarbon gas, a hydrogen gas, and a rare gas, thereby forming a reaction in the vicinity of the substrate. It is characterized in that the C / H ratio of the gas is set to 0.07 or more.

As a reaction gas source for generating plasma, hydrocarbon gases such as methane, ethane, propane, butane, ethylene, and benzene, and hydrogen gases and rare gases such as argon and helium are used. Further, as a substrate for forming a diamond film, a metal such as molybdenum, silicon, and stainless steel, or a ceramic material such as alumina and silicon carbide is applied.

The deposition reaction of the diamond film raises the temperature of the substrate to 500 to 150
The C / H ratio of the reaction gas in the vicinity of the substrate is set to 0.07 or more while the temperature is raised to 0 ° C. and the pressure in the system is maintained at 10 ⁻⁴ to 1 atm. When the C / H ratio is less than 0.07, the deposited diamond film has a dendritic cross section, and the adhesion to the substrate is significantly reduced.

Generally, hydrocarbon gas or its decomposition product, C
Since ions and radicals such as H, C, and C ₂ have a significantly lower diffusion rate into the rare gas than H ₂ and H, it is difficult to obtain a uniform diffusion state in the plasma generation chamber. Therefore, for the adjustment of the C / H ratio, it is effective to introduce a hydrocarbon gas, a rare gas, and a hydrogen gas into the plasma generation chamber while controlling the flow rates of the gases through different routes. It has been confirmed by emission spectroscopy that the introduced hydrocarbon and its decomposition products do not diffuse uniformly in the plasma generation chamber and reach the substrate surface with a diameter smaller than the diameter of the plasma generation chamber.

For example, as shown in FIG. 1, a work coil 2 connected to a high-frequency power supply 1 is provided at a peripheral portion, and a central nozzle 8 connected to a reactive gas supply device 3 via valves 4, 5, 6, and 7 at an upper portion.
A plasma generating chamber including a triple-structured feed tube 9 having a support, a support 11 having a base 10 mounted on a lower portion thereof, and an exhaust device 12.
By using a high-frequency plasma torch constituted by 13 and increasing the ejection speed of the hydrocarbon gas and the rare gas sent from the central nozzle 8 from the flow rate of the hydrogen gas sent from the outermost cylinder, CH, C, C ions and radicals concentrations such ₂ (active species concentration) can be adjusted relatively high.

[Action]

If the C / H ratio of the reaction gas in the vicinity of the substrate is set to 0.07 or more during the formation of the diamond film by thermal plasma, the concentration of active species per unit volume of the plasma increases, and the plasma is cooled near the substrate and becomes non-conductive. An equilibrium is created, resulting in increased supersaturation of the active species concentration, resulting in a marked increase in nucleation rate.

The cross section of the diamond film deposited when the C / H ratio is less than 0.07 is dendritic. Invert.

Due to such various actions, a high-quality diamond film which is always excellent in adhesion and has no cracks or peeling is efficiently deposited irrespective of a mirror surface or a rough surface.

〔Example〕

Hereinafter, the present invention will be described based on examples and comparative examples.

Example 1 Using the high-frequency plasma torch shown in FIG. 1, methane gas was flowed at a flow rate of 0.4 l / min through a valve 4 and, simultaneously, argon gas was fed at a flow rate of 10 l / min through a valve 5 to mix the two. Gas was ejected from the central nozzle 8 (diameter 2 mm) as gas. Argon gas at a flow rate of 42 l / min from valve 6
Then, hydrogen gas was fed into the outermost cylinder via the valve 7 at 7.0 l / min. In this case, the C / H of the reaction gas near the substrate
The ratio was about 0.4.

The substrate 10 was made of molybdenum whose surface was not polished, and the temperature of the substrate was kept at 890 ° C. In addition, plasma generation chamber 13
(55mm diameter, 190mm length) Pressure: 1 atm, Power frequency: 4M
Thermal plasma was generated under the conditions of Hz, vacuum tube input: 65 KVA, and a diamond film was deposited on the substrate surface for 10 minutes.

The resulting diamond film is a homogeneous film having a good adhesiveness with a thickness of 16 to 18 μm, and has a layered structure in which massive diamond grains are continuous like the crystal structure shown in the SEM photograph (magnification: 1440 ×) of FIG. No cracks and interfacial delamination were observed.

Example 2 A diamond film was deposited under the same conditions as in Example 1 except that the diameter of the central nozzle 8 was 4 mm and a mirror-finished silicon wafer was used for the substrate 10. In this case, the C / H ratio of the reaction gas near the substrate was about 0.1. The obtained diamond film was a homogeneous film having excellent adhesion without cracking and peeling, as in Example 1.

Comparative Example A diamond film was deposited under the same conditions as in Example 1 except that the diameter of the central nozzle 8 was 10 mm and the jetting speed of methane gas was reduced. At this time, the C / H ratio of the reaction gas in the vicinity of the substrate was 0.026.

The diamond film thus deposited has a crystalline structure having a dendritic cross section as shown in the crystal structure shown in the SEM photograph (1680 times magnification) of FIG. Admitted.

〔The invention's effect〕

As described above, according to the present invention, it is possible to efficiently deposit and form a diamond film having very good adhesion without cracking or peeling by thermal plasma regardless of the surface properties of the substrate.

Therefore, there is provided an industrial effect that it is possible to inexpensively manufacture functional materials, which are expected to have new uses, including mechanical members such as cutting tools.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a high frequency plasma torch used to carry out the method of the present invention. FIG. 2 is an SEM photograph in which the crystal structure of the diamond film deposited and formed in the example of the present invention is enlarged (magnification: 1440 times). FIG. 3 is an enlarged crystal structure of the diamond film deposited and formed in the comparative example (magnification: magnification).
(1680x) DESCRIPTION OF SYMBOLS 1 ... High frequency power supply, 2 ... Work coil, 3 ... Reaction gas supply device, 4, 5, 6, 7 ... Valve, 8 ... Central nozzle, 9 ... Sending cylinder, 10 ... Base, 11 ...... Supports, 12 ...
... Exhaust device, 13 ... Plasma generation chamber.

Claims (1)

(57) [Claims] 1. A method of generating a thermal plasma by high frequency in a mixed gas comprising a hydrocarbon gas, a hydrogen gas and a rare gas to deposit a diamond film on a substrate surface, wherein a C / H ratio of a reaction gas in the vicinity of the substrate is determined. A diamond film deposition method characterized by being set to 0.07 or more.