JPH06298599A - Production of diamond and diamond-like carbon - Google Patents

Abstract

PURPOSE:To enable high-speed formation of high crystallinity diamond film of excellent uniformity even in a large area by allowing a hydrogen halide to coexist in the reaction system in the synthesis of diamond-like carbon on the base through the CVD process. CONSTITUTION:In the synthesis of diamond or diamond-like carbon on the base through the CVD process, the synthesis is performed in the coexistence of a hydrogen halide in the reaction system. Preferably, the concentrations of carbon and hydrogen halide in the atmosphere near the base are controlled and fed so that these concentrations may satisfy the equation (x is the concentration of hydrogen halide; y is the concentration of carbon-containing molecules; n is the number of carbon atoms in one carbon-containing molecule. Thus, in comparison with the case that, for example, a carbon-containing molecule such as methane and hydrogen gas are used, more carbon radicals are formed, when methane gas and hydrogen halide gas (hydrogen chloride gas) are used, to accelerate the reaction rate of the diamond synthesis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing diamond or diamond-like carbon (hereinafter sometimes simply referred to as diamond), and more particularly to a method for synthesizing diamond faster by using a CVD method. Is.

[0002]

2. Description of the Related Art Conventionally, a method of synthesizing diamond on a substrate by a CVD method has been widely used, and is particularly applied in the field of electronic technology. The following methods are known as specific CVD methods for synthesizing diamond.

Method using thermal plasma: A hydrocarbon-based source gas and hydrogen gas are excited by using a linear arc discharge or a high frequency, and high temperature thermal plasma generated here is rapidly cooled to grow diamond on a substrate. Low-temperature plasma method: A hydrocarbon-based source gas and hydrogen gas are excited by using microwave or direct-current glow discharge, and diamond is grown on a substrate by using low-temperature plasma generated here. Hot filament method: A filament material heated to a high temperature by energization thermally decomposes a hydrocarbon-based source gas and hydrogen gas, and diamond is grown on a substrate by active species generated at this time.

[0004]

In the case of the above-mentioned method using thermal plasma, the concentration of active species in the thermal plasma is high, so that there is an advantage that the film formation rate is high, but the area where the thermal plasma is generated is large. Since it is limited to a narrow range, it is difficult to coat a large area, and the temperature distribution of the generated thermal plasma is not uniform, so that the film thickness and crystallinity of the synthesized diamond are likely to be inhomogeneous. .

In the case of the above-mentioned low temperature plasma method, the non-equilibrium low temperature plasma can be spread over a wide range. Therefore, if this is used, it is possible to coat a uniform diamond film even in a large area. Since the concentration of active species in plasma is as low as 10% at maximum, there is a problem that it takes a long time to synthesize diamond.

In the case of the above pyrolysis method, it is possible to coat the entire surface of the substrate with diamond by using a plurality of filaments.
Although it has an advantage that the apparatus is simpler than the method described above, there is a problem that the film formation rate is slow because the active species concentration in the gas phase is low as in the case of the above method.

The present invention has been made to solve the above problems, and an object thereof is to provide a method capable of synthesizing diamond having a uniform crystal in a wide range at a high speed.

[0008]

The method for producing diamond or diamond-like carbon according to the present invention is carried out by including hydrogen halide in the reaction gas when synthesizing diamond on the substrate by the CVD method. It is desirable that the ratio of the hydrogen halide to the carbon-containing molecule in the atmosphere gas near the substrate satisfies the following formula (1). 0.001 ≦ n · y / x ≦ 0.1 (1) x: concentration of hydrogen halide y: concentration of carbon-containing molecule n: number of carbon atoms contained in one molecule of carbon-containing molecule

[0009]

The present invention will be described below with reference to the case where methane is used as the carbon-containing molecule for supplying the carbon source and hydrogen chloride is used as the hydrogen halide. In the process of synthesizing diamond on the substrate by the CVD method,
First, methyl radicals (CH ₃ ·) are generated from methane in the vapor phase, and the generated methyl radicals reach the substrate by diffusion and react with the diamond nuclei generated on the substrate, so that SP ³ single atoms are generated between carbon atoms. Diamonds grow by forming bonds.

The film formation rate of this diamond synthesis largely depends on how much methane is converted into methyl radicals (CH _3. ) That are active species. That is, when the concentration of converted methyl radicals is high, the film formation speed is high, and conversely, when the concentration is low, the film formation speed is low.

When methane gas and hydrogen gas are used as source gas (reaction gas), conversion of methane to methyl radical occurs only by cleavage of bond between carbon atom and hydrogen atom in methane molecule due to thermal vibration. The reaction formula (2) is shown below. CH ₃ -H → CH ₃ + H ... (2)

On the other hand, when methane gas and hydrogen chloride gas are used as the source gas, in addition to the reaction shown in the above reaction formula (2), chlorine radicals (Cl.
) Abstracts a hydrogen atom from the methane molecule, and this reaction also produces a methyl radical from methane. The reaction formula (3) is shown below. CH ₃ -H + Cl · → CH ₃ · + H-Cl (3)

Comparing the bond cleavage reaction by the thermal vibration shown in the reaction formula (2) with the hydrogen abstraction reaction by the chlorine radical shown in the reaction formula (3), the latter abstraction reaction has a higher reaction rate. Therefore, compared with the case where hydrogen gas is used as the source gas (reaction gas), a large amount of methyl radicals are generated when hydrogen chloride gas is used, and as a result, the diamond synthesis rate becomes faster.

Regarding the amount of this hydrogen chloride gas, it is not necessary to replace all of the hydrogen gas used conventionally with this hydrogen chloride gas. That is, the chlorine radicals (Cl.) Generated by the decomposition of HCl draw hydrogen from methane and
And such a reaction occurs as a chain reaction. Therefore, a great effect is expected even if a small amount of HCl molecules are present at the beginning, and the object of the present invention is achieved if the concentration of HCl with respect to H ₂ is 1% or more.

The above is a representative example of a combination of methane and hydrogen chloride. Other carbon-containing molecules such as ethane, ethylene, propane, acetylene, benzene and the like, and other hydrogen halides such as fluorinated. Similar effects can be obtained even in combination with hydrogen, hydrogen iodide, hydrogen bromide and the like.

[0016]

【Example】

Example 1 FIG. 1 shows the hot filament CV used in the present invention.
It is a schematic diagram which shows D device. In the figure, 5 is a CVD reactor, 1 is a silicon substrate for synthesizing diamond, 2 is a substrate holder for holding the substrate 1, and 3 is an upper portion of the substrate 1 10 mm.
The reaction gas in the vicinity of the substrate 1 is heated by the tungsten filament arranged at the position. Reference numeral 6 is a gas introduction pipe provided above the reaction furnace 5, 7 is an exhaust pipe provided below the reaction furnace 5, and 4 is a heater provided outside the reaction furnace 5. Next, an example in which diamond synthesis is performed by the method of the present invention will be described.

First, the inside of the reaction furnace 5 was evacuated by operating the vacuum pump. Then, the tungsten filament 3 was energized and heated to 2100 ° C., and at the same time, the temperature of the substrate 1 was set to 800 ° C. by heating the heater 4.

Next, using methane gas and hydrogen chloride gas as reaction gases, while introducing methane gas at a flow rate of 5 cc / min and hydrogen chloride gas at a flow rate of 500 cc / min into the reaction furnace 5 through the gas introduction pipe 6, the reaction furnace 5 The internal gas pressure was set to 10 Torr. Then, the temperature of the substrate 1, the gas pressure in the reaction furnace 5, and the gas flow rate were kept constant at the above values, and a CVD process was performed for 10 hours.

After that, the supply of the reaction gas was stopped, the energization of the filament 3 and the heater 4 was stopped to lower the temperature of the substrate 1, the reaction furnace 5 was opened, and the substrate 1 was taken out. For the film formed on the substrate 1, a scanning electron microscope (hereinafter referred to as SEM
(Hereinafter referred to as)) and analyzed by Raman spectroscopic analysis. As a result, the product on the substrate 1 was a film-like substance containing diamond as a main component, and the film thickness was 15 μm.

<Comparative Example 1> Methane gas and hydrogen gas were used as reaction gases, and the flow rates were 5 cc / min and 250 cc / min, respectively.
Diamond synthesis was carried out in the same manner as in Example 1 except that the above was introduced into the reaction furnace 5. Then, the film formed on the substrate 1 was observed by SEM and analyzed by Raman spectroscopic analysis as in Example 1 above.

As a result, the product on the substrate 1 was a film-like material containing diamond as a main component, and its crystallinity was not different from that in Example 1 above. The film thickness was 9 μm. From the results of Example 1 and Comparative Example 1 described above, the hydrogen gas shown in Comparative Example 1 was used as the reaction gas, and
It can be seen that the use of hydrogen chloride gas significantly increases the diamond film formation rate, as shown in FIG.

As described above, in these experiments, the hydrogen gas flow rate was 250 cc / min and the hydrogen chloride gas flow rate was 500 cc / min. However, by using twice as much hydrogen chloride gas as hydrogen gas, It can be seen that diamond having the same crystallinity can be synthesized.

Next, the reason for using twice the amount of hydrogen chloride gas will be explained. During the synthesis of diamond by the CVD method, the diamond component and the graphite component grow at the same time, but atomic hydrogen in the atmospheric gas near the substrate etches the graphite component, leaving only the diamond structure and leaving the diamond film. Is obtained. As described above, atomic hydrogen is an element necessary for improving the crystallinity, but the atomic hydrogen at this time is higher in the hydrogen chloride gas (HCl) than in the hydrogen gas (H ₂ ). The amount produced is halved. Therefore, in order to obtain diamond having the same crystallinity, it is necessary to supply twice as much hydrogen chloride gas as the reaction gas as compared with the case where hydrogen gas is used. It should be noted that in industrial practice, it is desired to adjust within the range of 1 to 3 times.

<Embodiment 2> Next, a case will be described in which diamond synthesis is performed in the same manner as in Embodiment 1 except that the concentration ratios of hydrogen chloride and methane are variously changed. FIG. 2 is a graph showing the relationship between the ratio of methane gas concentration to hydrogen chloride concentration (y / x) and the film formation rate, when the diamond synthesis is performed with various concentrations of methane gas while keeping the hydrogen chloride concentration constant. FIG. 3 is a graph showing the relationship between the Raman shift and the Raman intensity when the concentration ratio y / x is used as a parameter, which is obtained by the analysis using the Raman effect.

The product on the substrate 1 was observed when the methane concentration ratio (y / x) to the hydrogen chloride concentration was 0.001 or more, but was not observed when it was less than 0.001. Further, as can be seen from FIG. 2, the film formation rate of diamond increases as the methane concentration increases. On the other hand, when the crystallinity of the product was evaluated by Raman spectroscopy (see FIG. 3), y /
When x is 0.001, crystalline diamond containing no graphite component is generated, but when the concentration ratio of methane is increased, the graphite component is included, and y / x is 0.1.
In this case, the diamond component was still slightly contained, but when y / x was 0.11, only the graphite component was present and no diamond component was recognized.

From the above results, when synthesizing diamond by using methane gas and hydrogen chloride gas as reaction gases, the concentration of methane gas is 0.001 relative to the concentration of hydrogen chloride gas.
It turns out that the ratio should be ~ 0.1.

In Example 2, since methane having 1 carbon atom was used as the carbon-containing molecule, good diamond was synthesized within the above concentration range. However, depending on the number of carbon atoms in one molecule of the carbon-containing molecule, The concentration range will be different. In other words, when a carbon-containing molecule containing n carbon atoms in one molecule is used as a raw material, it is equivalent to using methane gas with n times the concentration as compared with the case of using methane containing one carbon atom. It will show the effect. Therefore,
When the range of the methane gas concentration with respect to the hydrogen chloride gas concentration is more generally expressed as the range of the concentration (y) of the carbon-containing molecule with respect to the hydrogen halide concentration (x), the following formula (1) is obtained.
Becomes 0.001 ≦ n · y / x ≦ 0.1 (1) n: number of carbon atoms contained in one molecule of carbon-containing molecule

In the raw material gas recommended in the present invention, the partial pressure of hydrogen halide is 1 Torr or more at the furnace pressure, and the partial pressure of carbon-containing molecules is 0.1 Torr or more at the furnace pressure. If the partial pressure is less than this value, the film formation rate will be extremely slow even if diamond can be synthesized. Therefore, considering the industrial scale, it is preferable that the partial pressure is more than that.

Although the hot filament CVD method is used as the CVD method in the first and second embodiments, the present invention is not limited to this, and other CVD methods using non-equilibrium plasma, such as microwaves, are used. It can also be applied to the plasma method, the high frequency plasma method, the direct current glow discharge plasma method, and the like.

[0030]

As described above, according to the present invention, hydrogen halide is allowed to coexist in the reaction system of the CVD method, so that diamond having a uniform and good crystallinity even in a large area can be produced at a high speed. It can be formed.

[Brief description of drawings]

FIG. 1 is a diagram showing a general hot filament CVD apparatus.

FIG. 2 is a graph showing a relationship between a methane gas concentration ratio with respect to hydrogen chloride concentration and a film formation rate.

FIG. 3 is a diagram showing a graph of the relationship between Raman intensity and Raman shift when the concentration ratio y / x is used as a parameter.

[Explanation of symbols]

 1 Silicon substrate 2 Substrate holder 3 Tungsten filament 4 Heater 5 Reactor 6 Gas introduction pipe 7 Exhaust pipe

Claims (2)

[Claims] 1. A method for synthesizing diamond or diamond-like carbon on a substrate by a CVD method, which is carried out in the presence of hydrogen halide in a reaction system. 2. The concentrations of carbon-containing molecules and hydrogen halide contained in the atmosphere gas near the substrate are expressed by the following formula (1).
The method for producing diamond or diamond-like carbon according to claim 1, wherein the diamond or diamond-like carbon is supplied so as to satisfy the above condition. 0.001 ≦ n · y / x ≦ 0.1 (1) x: concentration of hydrogen halide y: concentration of carbon-containing molecule n: number of carbon atoms contained in one molecule of carbon-containing molecule