JPH0274591A - Deposition of diamond film - Google Patents

Abstract

PURPOSE:To efficiently provide a high quality diamond film having excellent adhesivity to a substrate without relating to the surface condition of the substrate and not causing any crack and peeling by limiting the C/H ratio of reactive gases is the vicinity of the substrate in a process for depositing the diamond film on the substrate with a high temperature plasma. CONSTITUTION:When thermal plasma is generated in mixed gases comprising a hydrocarbon gas, hydrogen gas and a rare gas with high frequency to deposit a diamond film on a substrate, the C/H ratio of the reactive gases at in the vicinity of the substrate is set to >=0.07. The setting of the above-mentioned condition increases the concentration of active seeds per unit volume in the plasma and cools the plasma in the vicinity of the substrate to produce a non- equilibrium state, consequently raising the supersaturation degree of the active seed concentration to bring a remarkable increase in the generation rate of nuclei.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for depositing a diamond film using high temperature plasma.

[Conventional technology]

The synthetic diamond film formed on the substrate surface has excellent hardness, wear resistance, and high elastic modulus, so it is already useful in cutting tools, wear-resistant tools, bearings, sliding parts, etc. However, in recent years, it has been expected to be used as a functional material that takes advantage of its thermal, optical, and electrical properties.

Conventional diamond vapor phase deposition methods include thermal CVD, which decomposes raw material gas and hydrogen using heat, plasma CVD, which decomposes raw material gas and hydrogen in plasma using direct current, high frequency, or microwave excitation, and hydrocarbon deposition. An ion beam M deposition method is known in which plasma decomposition of ions is carried out using an ion gun or the like, and ions are drawn out and deposited using an electric field.

From an industrial standpoint, all of these methods are carried out under conditions of low pressure, and therefore, the number of diamond crystal nuclei that precipitate on the substrate surface in the early stage of the reaction is small, making it difficult to form a diamond film of a predetermined thickness. It takes a very long time. In order to eliminate this drawback, methods include roughening the surface of the substrate (Japanese Unexamined Patent Publication No. 60-200897) and polishing with polishing powder of less than 1% (Japanese Unexamined Patent Publication No. 62-108798).
is being attempted.

On the other hand, contrary to the low-pressure conditions mentioned above, there is a method of growing high-grade synthetic diamond at high speed by increasing the concentration of active species using high-temperature plasma at relatively high pressure (
JP-A-62-158195) has been proposed.

[Means to be Solved by the Invention] However, film-like diamond synthesized using conventional thermal plasma, as typified by the invention of JP-A No. 62-158195, has a difficulty in adhesion to the substrate, and Alternatively, there is a problem in that the diamond film easily peels off from the substrate surface due to cracks that occur in the diamond film after synthesis.

As a result of intensive research aimed at resolving the above-mentioned problems when using high-temperature plasma, the inventors found that if the composition ratio of carbon and hydrogen in the reactive gas near the substrate is set and maintained above a certain value, the substrate The present invention was developed based on the finding that the adhesion to the precipitated diamond film is significantly improved regardless of the surface condition.

[Means to solve the problem]

That is, the method for depositing a diamond film according to the present invention is as follows:
In a method of depositing a diamond film on a substrate surface by generating thermal plasma using high frequency in a mixed gas consisting of hydrocarbon gas, hydrogen gas, and rare gas, the C/H ratio of the reaction gas in the vicinity of the substrate is set to 0.07 or more. The configuration feature is to set.

Hydrocarbon gases such as methane, ethane, propane, butane, ethylene, and benzene, hydrogen gas, and rare gases such as argon and helium are used as reactive gas sources for plasma generation. Furthermore, metals such as molybdenum, silicon, and stainless steel, and ceramic materials such as alumina and silicon carbide are used as the substrate for forming the diamond film.

The precipitation reaction of the diamond film is carried out at a temperature of the substrate of 500 to 1
The temperature is raised to 500° C., and the C/H ratio of the reaction gas in the vicinity of the substrate is set to 0.07 or more while the pressure in the system is maintained at 10 −4 to 1 atm. When the C/H ratio falls below 0.07, the precipitated diamond film begins to exhibit a dendritic cross section, and its adhesion to the substrate is significantly reduced.

-II, C which is a hydrocarbon gas or its decomposition product
Since the diffusion rate of ions and radicals such as H, C, and C2 into the rare gas is significantly lower than that of t+z and H, it is difficult to obtain a uniform diffusion state within the plasma generation chamber.

Therefore, it is effective to adjust the C/H ratio by introducing a hydrocarbon gas, a rare gas, and a hydrogen gas into the plasma generation chamber through separate routes while mutually controlling the AM. It has been confirmed by emission spectroscopy that the introduced hydrocarbons and their decomposition products do not diffuse uniformly within the plasma generation chamber and reach the substrate surface with a diameter smaller than the inside diameter of the plasma generation chamber.

For example, as shown in FIG. 1, a work coil 2 connected to a high-frequency electric current tAl is connected to the peripheral part, and a central nozzle 8 connected to the reactant gas supply device 3 and pulp 4,5,6,7 is connected to the upper part.
A high-frequency plasma torch is configured with a triple-structured feeding cylinder 9 equipped with a plasma generating chamber 13 equipped with a support 11 on which a substrate IO is placed at the bottom, and an exhaust device 12. By increasing the jetting velocity of the hydrocarbon gas and rare gas to be supplied from the outermost cylinder than the flow velocity of the hydrogen gas introduced from the outermost cylinder, the concentration of ions and radicals (concentration of active species) such as CH, C, and cz in the vicinity of the substrate can be relatively high. It is possible to adjust to.

[For production]

If the C/H ratio of the reactive gas in the vicinity of the substrate is set to 0.07 or more during the formation of a diamond film by thermal plasma, the concentration of active species per unit volume in the plasma increases and the plasma is cooled in the vicinity of the substrate. This results in a non-equilibrium state, resulting in an increase in the degree of supersaturation of the active species concentration, leading to a significant increase in the nucleation rate.

Furthermore, the cross section of the diamond film deposited when the C/H ratio is less than 0.07 has a dendritic shape;
．． 07 or higher, it transforms into a highly adhesive continuous film consisting of macroscopically massive diamond grains.

As a result of these various effects, a high-quality diamond film with excellent adhesion and no cracking or peeling is efficiently deposited regardless of whether the surface is mirror-like or rough.

〔Example〕

The present invention will be described below based on Examples and Comparative Examples.

Example 1 Using the high frequency plasma torch shown in FIG.
0.44 via! Methane gas was flowed at a flow rate of 1/min, and argon gas was simultaneously sent through the valve 5 at a flow rate of 101/min.
) erupted from Argon gas from valve 6 at a flow rate of 421/min and 7.0 ffi through valve 7.
Hydrogen gas was introduced into the outermost cylinder in 7 minutes. In this case, the C/H ratio of the reaction gas near the substrate was about 0.4.

The substrate 10 was made of molybdenum whose surface was not polished, and the substrate temperature was maintained at 890°C. Others, plasma generation chamber 1
3 (diameter 55m5. length 190ai) pressure crab 1 atm,
A thermal plasma was generated under the conditions of a power supply frequency of 4 MHz and a vacuum tube power of 65 KVA, and a diamond film was deposited on the substrate surface for 10 minutes.

The obtained diamond film was a homogeneous film with a thickness of 16 to 18 nm with good adhesion, and exhibited a continuous layered structure of massive diamond grains, as shown in the 32M photograph (1440x magnification) in Figure 2. No cracks or interfacial peeling 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-adjacent, and a mirror-finished silicon wafer was used as the substrate 10. In this case, the C/H ratio of the reaction gas near the substrate was about 0.1. As in Example 1, the obtained diamond film was a homogeneous film with excellent adhesion and no cracks or peeling.

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 set to 10 mm and the jetting speed of methane gas was lowered. At this time, the C/H ratio of the reaction gas near the substrate was 0.026.

The diamond film precipitated in this way is
The crystal structure shown in the 32M photograph (magnification: 1680x) exhibits crystallinity with a dendritic cross section, and cracks that easily caused interfacial peeling were observed.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to efficiently deposit and form a diamond film with extremely good adhesive properties without cracking, peeling, etc. using thermal plasma regardless of the surface condition of the substrate.

Therefore, an industrial effect is brought about in which functional materials that are expected to have new uses, including mechanical parts such as cutting tools, can be manufactured at low cost.

3... Reaction gas supply device, 4.5.6.7... Valve, 8... Central nozzle) L
/, 9... feeding tube, IO... base, 11.
...Support, 12...Exhaust device, 13...
Plasma generation room.

Patent applicant: Tokai Carbon Co., Ltd.

Claims (1)

[Claims] 1. In a method of depositing a diamond film on a substrate surface by generating thermal plasma using high frequency in a mixed gas consisting of hydrocarbon gas, hydrogen gas, and rare gas, the C/H ratio of the reaction gas in the vicinity of the substrate is set to 0.07 or more. A method for depositing a diamond film, characterized in that: