JPH0791150B2 - Diamond synthesis method using coke oven gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention makes it possible to inexpensively supply a raw material gas suitable for synthesis to a diamond vapor phase synthesis apparatus when a diamond particle thin film is formed on a substrate by a vapor phase synthesis method. A method of adjusting and supplying.

(Prior Art) There are many methods for physicochemical synthesis of carbonaceous diamond. For the purpose of forming a diamond thin film on the above-mentioned substrate, a mixed gas of hydrocarbon gas such as methane and hydrogen gas is used. A gas phase synthesis method using as a raw material is suitable, and also as an implementation method, (i) thermal filament method, (ii) high frequency plasma CVD (Chemical Vapor Deposition) method, (iii) microwave plasma CVD method, (iv) electron Ray assisted CVD method, (v)
DC plasma CVD method, (vi) thermal plasma CVD method, (vii)
The arc discharge method, (viii) plasma jet method, (ix) combustion method, etc. have been proposed.

FIG. 3 shows a system diagram of a prior art diamond thin film vapor phase synthesis method in which hydrogen gas and hydrocarbon gas from gas cylinders (a) and (b) are reduced in pressure (c) and flow control valve (d), respectively. And adjust the ratio to introduce into the film forming chamber (e) of various methods to form a diamond thin film on the substrate,
The gas that has not participated in the formation is sent to the waste gas treatment chamber (g) through the vacuum pump (f) to maintain the degree of vacuum in the chamber. In this way, regardless of which method is used, a high-purity gas that is filled in a gas cylinder and is commercially available is used as a raw material gas. This is to directly adjust the blending ratio of raw material gas components for diamond synthesis. This is to maintain the accuracy as a target and to prevent unnecessary impurities in the raw material gas from being unnecessarily taken into the synthesized diamond.

(Problems to be solved by the invention) The prices of these commercially available high-purity gases are considerably high. For example, in the case of methane gas having a purity of 99.9%, the purity is about 30,000 yen per Nm ³ ,
With 99.99% hydrogen gas, it is about 3,000 yen per 1 Nm ³ . In the gas phase synthesis reaction of diamond, methane gas is usually diluted with hydrogen gas to about 1% to be used as a raw material gas, and it is very technically difficult to increase the carbon utilization efficiency of the diamond synthesis reaction. If this is taken into consideration, the burden of the raw material gas unit for industrial implementation becomes large. For example, in synthesizing a diamond thin film having a diameter of 3 inches and a thickness of 10 μm, the raw material gas cost alone is about 10,000 yen.

(Means for Solving Problems) The present invention has been made in order to solve the above problems in the prior art, and a raw material gas for vapor phase synthesis of diamond can be obtained stably and inexpensively, and further, can be synthesized. Use a gas source that does not adversely affect the results, and adjust the components to obtain the target component ratio.

That is, the diamond synthesizing method of the present invention has a hydrocarbon gas / hydrogen gas ratio of C / H = 0.0 by adding hydrogen gas to a coke oven gas or a mixed gas thereof as a whole.
After being adjusted to 01 to 0.1, the adjusted gas is subjected to diamond vapor phase synthesis.

Coke oven gas is a large amount of by-produced when the ironmaking raw material coke to be charged into the blast furnace at a steel mill is produced by carbonization of caking coal.
Gas) is also called. It was once manufactured as city gas, but its use has disappeared due to the natural gasification of city gas, and its reuse is an important issue at steelworks, so large quantities can be obtained at low cost. Is.

And the composition of the coke oven gas is about 25% CH ₄ , about 50 H _2.
%, Other C ₂ H ₂ , CO ₂ , CO, O ₂ , N ₂ etc. are about 25%. Mainly CH ₄ of this coke oven gas is used as a hydrocarbon gas source, and by mixing with an appropriate amount of the shortage H ₂ gas to adjust the components, the raw material gas for diamond vapor phase synthesis can be used. For that purpose, hydrogen gas is added and adjusted so that the ratio of the hydrocarbon gas to the hydrogen gas in the adjusted mixed gas is 0.001 to 0.1 in C / H, and this adjusted gas is directly used as a raw material gas for diamond vapor phase synthesis. To serve. As a result, the cost of raw material gas can be reduced.

The thin film diamond thus synthesized does not have a disadvantageous effect because it does not show qualitative qualitatively and quantitatively extra inclusion of the impurity element as confirmed by the operation described later.

Also, from the coke oven gas, purified H _{2 with a} purity of about 99.99%
It is possible to produce a large amount of gas. Therefore, this purified H ₂ gas is applied to the hydrogen gas source of the diamond vapor phase synthesis raw material gas, and the coke oven gas is applied to the carbon hydrogen gas source as described above to adjust the raw material gas components. . According to this embodiment of the present invention, it is possible to further reduce the cost of the raw material gas.

(Operation) According to the diamond synthesis method of the present invention, a diamond thin film having quality comparable to that of the conventional technique is formed.

FIG. 1 is a spectrum diagram showing the results of Raman measurement of a diamond thin film according to the method of the present invention, with the horizontal axis representing the wave number and the vertical axis representing the Raman intensity. Even if coal carbonization gas is used according to the present invention, if the C / H is the same as the prior art, it is 1333 cm ^-1.
The diamond spectrum and intensity are almost the same.
The spectrum at 1550 cm ^-1 shows graphite and amorphous carbon. Therefore, according to the present invention, a diamond thin film having the same quality as the prior art can be formed. If C / H is 0.001 to 0.1, good quality thin film diamond can be synthesized. If it is less than 0.001, almost no film is formed, and if it is more than 0.1, the diamond quality becomes poor.

(Example) For specific explanation of the method of the present invention, a gas supply system for carrying out the vapor phase synthesis method of the diamond thin film of the present invention is shown by the systematic diagram of FIG.

A part of the coal carbonization gas generated from the coke oven gas generator (1) is supplied to the diamond vapor phase synthesizer (3) by any of various vapor phase synthesis methods via the line (2). On the other hand, hydrogen gas is supplied via line (4). This hydrogen gas is filled with commercially available high-purity hydrogen gas such as a gas cylinder, or high-purity hydrogen gas obtained by purifying another part of the coke oven gas by a hydrogen gas purifier (5) as shown in the figure.

Both gases were adjusted to C / H 0.001-0.1 by the gas flow rate regulators (6) and (7) of the lines (2) and (4), respectively, according to the calculation results considering the components, and the diamond vapor phase synthesizer was used. It is supplied to (3), where a diamond thin film is formed.

The residual gas is recirculated to the coke oven gas generator through the gas recirculation line (9) by the vacuum pump (8).

[Example I]

Coal carbonization gas as a raw material gas: Commercial hydrogen gas is adjusted to a concentration of 8:92, and this raw material gas is used to form a diamond thin film on a silicon wafer by using a diamond gas phase synthesis system (3) of microwave plasma CVD method. Synthesized.
The reaction pressure was 200 Torr, the microwave power was 3 KW, and the substrate temperature was 820 ° C., and the synthesis reaction was carried out for 6 hours.

As a result, a 6 μm thick hard film was formed on a circular area having a diameter of 7 cm on a silicon wafer substrate.

When structural analysis was carried out by X-ray, the lattice constant of the hard film agreed with the value of crystalline diamond. In addition, in the Raman scattering spectrum, a spectrum having a sharp peak at 1333 cm ^-1 was obtained. From the above, it was concluded that this hard film is polycrystalline diamond with good crystallinity.

When the composition of this thin film was analyzed, 99.5% or more was carbon and impurities were 0.5% or less. This impurity was mainly Si used in the microwave introduction hole of the reaction chamber, and impurities such as S in coal carbonization gas were not detected.

Example II

A coke oven gas and purified hydrogen gas from the hydrogen gas purifier (5) were used as raw material gases, the concentrations of both gases were adjusted to 8:92, and the method of the present invention was performed under the same conditions as in Example I. Carried out.

The same results as in Example I were obtained.

(Effect of the invention) Since the price of the coke oven gas and the purified H ₂ gas from the coke oven gas are both about 20 yen or less per 1 Nm ³ , the raw gas The price is shown in the following table in comparison with the conventional technology. The table also shows the impure concentration of synthetic diamond.

By circulating the gas not used for diamond synthesis, the cost of the raw material gas can be further reduced.

As described above, according to the present invention, the economical formation of the diamond thin film is possible without adversely affecting the quality.

[Brief description of drawings]

FIG. 1 is a Raman scattering spectrum diagram of a thin film synthesized by the method of the present invention, FIG. 2 is a system diagram of a gas supply system for carrying out the vapor phase synthesis method of the diamond thin film of the present invention, and FIG. FIG. 3 is a system diagram of the diamond thin film vapor phase synthesis method of FIG. (1) …… Coke oven gas generator, (2) …… Line, (3) …… Diamond vapor phase synthesizer, (4) ……
Line, (5) ... Hydrogen gas refining equipment, (6) (7) ...
… Gas flow controller, (8)… Vacuum pump, (9)…
… Gas recirculation line, (a) (b) …… Gas cylinder,
(C) …… Reducing valve, (d) …… Flow control valve, (e) ……
Deposition chamber, (f) ... vacuum pump, (g) ... waste gas treatment chamber.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takeo Yoshigae 2-3-1 shinonohara, Noboru Shinohara, Nada-ku, Kobe-shi, Hyogo (72) Inventor Hideo Tachimichi 2-chome Maikodai, Tarumi-ku, Kobe-shi, Hyogo 30-822 (72) Inventor Fumio Tomimatsu 1958-80 Shinya, Hiraoka-cho, Kakogawa-shi, Hyogo (56) References Nao Inuzuka, Atsuhito Sawabe "Diamond thin film" (Sho 62-9-21) Sangyo Tosho Co., Ltd. 93-101

Claims (2)

[Claims] 1. A hydrogen gas is added to a coke oven gas to adjust the ratio of hydrocarbon gas and hydrogen gas to 0.001 to 0.1 in C / H, and the adjusted gas is used as a raw material gas for diamond vapor phase synthesis. A method for synthesizing diamond using a coke oven gas, which is characterized in that 2. The diamond synthesis method according to claim 1, wherein H gas obtained by purifying a coke oven gas is used as the hydrogen gas source.