JPH01201098A - Synthesis of diamond - Google Patents

Abstract

PURPOSE:To quickly and efficiently obtain a high-quality diamond having excellent uniformity and adhesivity, by activating a raw material gas composed of CO and/or CO2 gas and H2 gas and contacting the obtained hot plasma to a substrate of a temperature lower than that of the plasma. CONSTITUTION:A plasma generation chamber 4 of a reactor acting e.g. by differential exhaust is supplied with a reaction gas composed of CO and/or CO2 and Ar through a reaction gas inlet port 1, a plasma gas consisting of Ar through a plasma gas inlet port 2 and a sheath gas consisting of H2 and Ar through a sheath gas inlet port 3. The gases are activated at a plasma output of >=1kw under a pressure of 10Torr-5atm and the mixed gas obtained by the decomposition with the resultant hot plasma of >=1,000k is blasted into a deposition chamber 6 through e.g. a water-cooled copper nozzle 5. A diamond film is formed on a substrate 7 which is placed in the deposition chamber 6, made of a high-melting metal such as Si, Tl, Pt, Ti, W, Mo, etc., its oxide, carbide or nitride and cooled at 400-1,700 deg.C which is lower than the hot plasma temperature.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a diamond synthesis method, and more specifically, to fields related to various protective films, optical materials, electronic materials, chemical industrial materials, abrasive materials, etc. Concerning a method of synthesizing diamonds useful for.

[Prior art and its problems] In recent years, diamond synthesis technology has made remarkable progress, and diamond has come to be widely used, for example, as various protective films, optical materials, electronic materials, chemical industrial materials, and the like.

In the past, the common method was to form diamonds on the surface of a base material, such as the pyrolysis-type synthesis method in which hydrocarbon gas is pyrolyzed by a filament and diamonds are deposited on the surface of a seed crystal. , a chemical transport synthesis method that uses a non-uniform chemical reaction to form a diamond film on a substrate surface, a plasma decomposition synthesis method that attempts to deposit diamond by plasma decomposing hydrocarbon gas, a hot cathode PIG gun, a cold cathode PIG gun, etc. Ionization vapor deposition methods are known, in which carbon is ejected using a gun, sputter gun, etc., the carbon is ionized in an arc discharge space, and then deposited on a substrate.

Among these, the plasma decomposition synthesis method, in which diamond is precipitated by plasma decomposition of hydrocarbon gas, does not require a diamond seed crystal and can deposit diamond on a substrate made of any material other than diamond. It has been suggested that the deposition rate of diamond can be dramatically increased, especially when using a thermal plasma.

By the way, when diamond is precipitated and synthesized on a substrate or in the gas phase using a hydrocarbon as a raw material using a thermal plasma method, if the reaction pressure is increased to increase the diamond precipitation rate, the thermal plasma temperature becomes high. To,
On the contrary, the precipitation rate of diamond becomes slower, the crystallinity of the deposit becomes lower, and only diamond-like carbon (DLC), which is different from the original diamond, is obtained.
When diamond is formed as a film, there is a problem in that the uniformity and adhesion of the film are not necessarily good.

Therefore, as a means to further increase the rate of diamond precipitation, there are several ways to: 1) directly cool the substrate, 2) circulate Ar gas within the reaction chamber to remove the heat within the reaction chamber, and 2) increase the flow rate of the raw material gas into the reaction chamber. Proposals have been made such as separating the reaction chamber into a plasma generation chamber and a precipitation chamber whose temperature is lower than that in the plasma generation chamber, and moving the plasma to the precipitation chamber to deposit diamond. Yes, but
When hydrocarbons are used as raw materials, the current situation is that both the diamond precipitation rate and the quality of the produced diamonds are still unsatisfactory.

Furthermore, as industrial synthetic diamonds have become extremely versatile in various fields, there is a demand for not only diamonds that are grown on a substrate, but also diamonds that are grown independently of the substrate, depending on how the diamond is used. However, when hydrocarbons are used as raw materials, as mentioned above, the precipitation rate of diamond is not sufficient, so it is extremely difficult to generate diamonds without depending on the substrate, or even if diamonds are formed, However, it had the disadvantage that the quality of the diamond was extremely poor.

An object of the present invention is to solve the above-mentioned problems, to be able to efficiently generate high-quality diamond at a high deposition rate whether on a substrate or in the gas phase, and to produce diamond of high quality using thermal plasma. When diamond crystals are deposited on top, a diamond film with excellent uniformity and adhesion can be obtained, and when diamond crystals are deposited in the gas phase, ultrafine crystal diamond or diamond with controlled grain size can be obtained. The purpose of this invention is to provide a method for synthesizing diamonds.

[Means for Solving the Problems] In order to solve the above problems, the inventors have made extensive studies and found that carbon monoxide gas is used instead of conventional hydrocarbon gas as a raw material gas. It has been discovered that diamond can be deposited efficiently and at a high deposition rate in a substrate or gas phase by using a thermal plasma excited with a mixed gas of carbon dioxide gas and hydrogen gas. When the atmosphere in the gas phase is cooled, diamond with higher crystallinity can be synthesized at a faster precipitation rate, and when diamond crystals are deposited on a substrate, uniformity and adhesion are improved. The inventors have arrived at this invention by discovering that an excellent diamond film can be obtained, and that when diamond crystals are precipitated in the gas phase, ultrafine crystalline diamond or diamond with controlled particle size can be obtained.

That is, the invention according to claim 1 applies a thermal plasma obtained by activating a raw material gas consisting of carbon monoxide gas and/or carbon dioxide gas and hydrogen gas to a substrate at a temperature lower than the thermal plasma. A method for synthesizing diamond, characterized in that the diamond synthesis method is characterized in that the diamond synthesis method is characterized in that the diamond synthesis method is characterized in that the diamond synthesis method is characterized in that the diamond synthesis method is characterized in that the diamond synthesis method is characterized in that the diamond synthesis method is performed by activating a raw material gas consisting of carbon monoxide gas and/or carbon dioxide gas, and hydrogen gas. A diamond synthesis method is characterized in that diamond is precipitated in a gas phase at a temperature lower than that of the plasma.

This invention will be explained in detail below.

First, in the method according to claim 1, the carbon monoxide gas and the carbon dioxide gas are used as carbon sources for obtaining diamond.

As the raw material gas, any one of (1) carbon monoxide gas and hydrogen gas, (2) carbon dioxide gas and hydrogen gas, and (2) carbon monoxide gas, carbon dioxide gas and hydrogen gas can be used.

In any of (1) to (2) above, each component of the raw material gas may be supplied to the plasma generation chamber separately, or each of the components may be mixed and then supplied to the plasma generation chamber.

Further, the carbon monoxide gas is not particularly limited, and for example, sufficiently purified generator gas or water gas obtained by a hot reaction of coal, coke, etc. with air or water vapor may be used. can.

The carbon dioxide gas is not particularly limited and can be obtained, for example, by igniting limestone or burning coal, but usually commercially available carbon dioxide gas can be suitably used.

As the hydrogen gas, those obtained by, for example, electrolysis of water, denaturation of water gas, reaction of iron and steam, gasification of petroleum, denaturation of natural gas, gasification of coal, etc., are sufficiently purified and used. be able to.

The hydrogen gas forms atomic hydrogen and the like by thermal plasma. This atomic hydrogen, etc. has the function of removing the carbon of the graphite structure that precipitates at the same time as the diamond is precipitated, and the function of maintaining the Sp3 structure of the carbon atoms in the precipitated diamond crystals even at high temperatures.

The ratio of each component in the raw material gas is, for example, 0.5 to carbon monoxide and/or carbon dioxide.
50 cycles/min, preferably 1 to 30 cycles/min, and for hydrogen gas 5 to 30 cycles/min, preferably 7 to 25 cycles/min.
It's a minute. However, the ratio of carbon monoxide gas to hydrogen gas is 0.0 in volume ratio (CO and/or Co/H2). O1
It is preferable to set it within the range of ~0.99.

Examples of means for decomposing the raw material gas to obtain thermal plasma include a reactor using differential pumping shown in FIG. 1, and a high-frequency induction system shown in FIGS. 2 and 3 (a and b in FIG. 2). , pulse discharge method (C and d in Figure 3)
, a DC arc discharge method (e in FIG. 4), a microwave discharge method (f in FIG. 4), and the like. These methods can be suitably used in this invention.

Regardless of which method is adopted, the temperature of the thermal plasma is 1
,000 K or more (Claim 3), preferably 1.500 K or more
℃ or higher.

Methods for bringing thermal plasma into contact with the substrate at a temperature lower than that of the thermal plasma include, for example, adding an inert gas such as argon gas to the source gas, or supplying hydrogen gas to the plasma generation chamber separately from the source gas. method, method to directly cool the substrate, method to increase the flow rate of raw material gas,
An example of this method is to provide a deposition chamber separate from the plasma generation chamber and having a temperature lower than that of the plasma generation chamber, and to place the substrate within this deposition chamber.

The means for bringing the thermal plasma into contact with the substrate at a temperature lower than that of the thermal plasma may be a combination of the various methods described above, or may be one of the various methods described above.
Preferred is a method in which an inert gas such as argon gas is added to the raw material gas (Claim 2).

When adopting a method of adding argon gas to the raw material gas, the supply rate of the argon gas is 0.5 to 100 JI/min, preferably 1 to 100 JI/min.
50 sentences/minute.

Furthermore, when this argon gas is used as a carrier gas for the source gas, the atmosphere of the base is cooled and the quartz tube for plasma generation is protected.

When adopting a method of supplying hydrogen gas to the plasma generation chamber separately from the raw material gas, the sum of the amount of hydrogen gas in the raw material gas and the hydrogen gas added separately from the hydrogen gas in this raw material gas is 5. It is best to adjust the rate to ~30 views/minute, preferably 7 to 25 sentences/minute.

When the substrate is directly cooled, it is preferable to place the substrate on a cooling-capable substrate support, for example. This may be achieved by utilizing the absorption of heat generated at the contact point when current is passed through the contact point with the substrate, that is, by utilizing the Peltier effect.

Among the above-mentioned cooling means, when adopting a method in which a precipitation chamber is provided at a lower temperature than the plasma generation chamber separately from the plasma generation chamber, and a substrate is installed in this precipitation chamber, for example, a reaction having a structure as shown in FIG. 1 is adopted. It is better to use equipment.

The temperature of the substrate surface and the temperature of the precipitation chamber are usually 40°C.
The temperature is 0 to 1.700°C, preferably 700 to 1,200°C. If this temperature is lower than 400° C., the diamond precipitation rate may be slow or excited state carbon may not be produced. On the other hand, if the temperature is higher than 1.700°C, the diamond deposited on the substrate will be etched away, and the deposition rate may not be improved or graphite may be mixed in.

There are no particular restrictions on the material of the substrate to be used; for example, high melting point materials such as silicon, thallium, platinum, titanium, tungsten, and molybdenum, oxides of these materials,
Nitride and carbide, their alloys, Al2h3-F
e series, Tiejc-Ni series, Tie-G.

Cermets such as Tie-TiN, 84C-Fe, and various glasses, Al2O3, WC, Mob,
5iC1Tie, TiN, MoSi2, WSi2
Any material selected from ceramics such as . . . can be used.

Further, there is no particular restriction on the shape of this base, and any shape such as a plate, a line, or a pipe can be used. Moreover, this base body may be a cutting tool or the like.

In the method according to claim 1, the reaction proceeds under the following conditions to deposit diamond on the substrate.

That is, the temperature of the substrate surface is as described above.

The reaction pressure is usually 10 torr to 5 torr.

In the method of the present invention, plasma generation and diamond precipitation may be performed in one reaction chamber, or may be separated into a plasma generation chamber and a deposition chamber whose temperature and pressure are lower than the pressure inside the plasma generation chamber. In the case of differential pumping, the pressure inside the plasma generation chamber is usually 400 torr to normal pressure, and the pressure inside the deposition chamber is usually 1 to 100 torr.

Plasma power is typically lkw or more. If the plasma output is lower than lkw, sufficient plasma may not be generated.

The plate power for setting the plasma power in this range is typically 2 kVA.

The reaction time is usually 1 to 60 minutes.

The reaction under the above conditions can be carried out using, for example, a reaction apparatus as shown in FIG.

FIG. 1 is a conceptual diagram of a reaction apparatus in which the method of the present invention is carried out by so-called differential pumping.

That is, the reactant gas (CO+Ar, CO2+Ar, or CO+CO2+Ar) is introduced into the plasma through the reactant gas inlet 1, the plasma gas (Ar) through the plasma gas inlet 2, and the sheath gas (H2+Ar) through the sheath gas inlet 3, respectively. It is introduced into the generation chamber 4. The mixed gas plasma decomposed in the plasma generation chamber 4 is injected into the precipitation chamber 6 from a nozzle 5 made of water-cooled copper, for example.
A diamond film is formed on the substrate 7 placed in the deposition chamber 6.

Next, the invention according to claim 5 will be explained.

The means for obtaining the raw material gas and thermal plasma are similar to the method described in claim 1.

In the invention according to claim 5, unlike the invention according to claim 1, diamond is deposited not on the substrate but in a cooled gas phase.

This cooling can be performed in the same manner as the method according to claim 1. For example, a method of adding an inert gas such as argon gas or hydrogen gas to the raw material gas,
A method of increasing the flow rate of the raw material gas, a method of providing a deposition chamber separate from the plasma generation chamber and having a temperature lower than that of the plasma generation chamber, etc. can be suitably employed.

Further, the flow rates of the raw material gas, the inert gas, and the hydrogen gas, the raw material gas, etc. are the same as those of the invention according to claim 1. Further, the reaction pressure, plasma output, reaction time, etc. are also the same as in the case of the invention described in claim 1.

According to the method of the present invention, diamond in the form of a film or diamond in the form of particles or fine powder can be produced on a substrate or in a gas phase. Such diamonds can be used for various types of protection, such as surface protection films for cutting tools. It can be suitably used for I films, optical materials, electronic materials, chemical industrial materials, abrasive materials, and the like.

[Example] Next, Examples and Comparative Examples of the present invention will be shown to further specifically explain the present invention.

(Example 1) A torch equipped with a double quartz concentric tube and a metal gas ejection tube was used, the base temperature was 900°C, and the plasma generation chamber (water-cooled)
Under the condition of a pressure of 1 atm, the plate output of the high frequency power source of Kawanami a4M) Iz was set to 75 kW, and the gas flow rate into the plasma generation chamber was set to 1 ton/min of carbon monoxide gas, 11/min of hydrogen gas, and argon gas. The reaction rate was set at 25 sentences/min and the reaction was carried out for 10 minutes to obtain a deposit having an average thickness of 15 gm on the substrate controlled at the above temperature. Note that molybdenum was used for the base.

When the obtained deposit was subjected to Raman spectroscopic analysis, a peak attributed to diamond was observed near 1333 cm-' in the Raman scattering spectrum, confirming that it was diamond without impurities.

(Example 2) Among the high-frequency induction methods, the H discharge method shown in FIG. At the same time, the pressure inside the plasma generation chamber 4 was set to 760 torr, the plate output of the high frequency power supply 10 with a frequency of 4 MHz was set to 75 kvA, and the gas flow rate into the plasma generation chamber 4 was set at the inlet 8. The thermal plasma generated in the plasma generation chamber 4 was heated by setting carbon monoxide gas at a rate of 3IL/min, hydrogen gas at a rate of 6/min, and argon gas at a rate of 451/min. By contacting the substrate 7 for 5 minutes, a deposit having an average thickness of 10 JLm was obtained on the substrate 7 whose temperature was controlled as above.

Note that molybdenum was used for the base 7. When the obtained deposit was subjected to Raman spectroscopic analysis, a peak attributed to diamond was observed near 1333 cm-' in the Raman scattering spectrum, and as a result of identification by X-ray diffraction and reflection electron beam diffraction, it was found to be free of impurities. It was confirmed that it was a diamond.

(Example 3) The same procedure as in Example 2 was carried out, except that instead of the molybdenum used in Example 2, a molybdenum substrate whose surface was polished with 5 to 10 gm of diamond powder for 10 minutes was used. .

As a result, a deposit with an average thickness of 10 μm was obtained on the substrate.

When the obtained deposit was subjected to Raman spectroscopy, a peak attributed to diamond was observed near 1333 cm-' in the Raman scattering spectrum, and as a result of identification by X-ray diffraction and reflection electron beam diffraction, it was found to be free of impurities. It was confirmed that it was a diamond.

(Example 4) In the H discharge method shown in FIG. 101/
A powder was obtained.

As a result of observing the powder with a transmission electron W4 microscope, it was found that 100
It was found that the following crystals were obtained, and as a result of identification by reflection electron beam diffraction, it was confirmed that they were diamonds with no impurities.

(Example 5) Using the H discharge method shown in FIG. 2b among the high-frequency induction methods, water was supplied to the substrate support 9 at 3 m/min to raise the temperature of the substrate 7 to 1100° C., and the plasma generation chamber 4 pressure to 800
Tart and a high frequency power supply with a frequency of 4 MHz! The plate output of 0 is set to 40 -, and the gas flow rate into the plasma generation chamber 4 is set to 4! l/min,
Hydrogen gas was set at 7 J/min and argon gas was set at 36 J/min, and the reaction was carried out for 20 minutes to control the temperature of the substrate 7.
A deposit with an average thickness of 40 uLm was obtained on top.

Note that molybdenum was used for the base 7. The obtained deposit was identified by reflection electron beam diffraction, and it was confirmed that it was diamond with a grain size of 3 JLm without any impurities.

(Example 6) Using the DC arc discharge method shown in Fig. 4 e among the high frequency induction methods, without using a substrate, the pressure in the plasma generation chamber 4 was set to 1 atm, the voltage was set to jOV, and the current was set to 86 A. At the same time, the gas flow rate into the plasma generation chamber was set to 0.22/min for carbon dioxide gas, 71/min for hydrogen gas, and 201/min for argon gas, and the reaction was carried out for 20 minutes. Synthesis was carried out at a controlled temperature of 200°C to obtain a powder.

As a result of identification by reflection electron beam diffraction, it was confirmed that the diamond was free from impurities and had a particle size of 5 μLm.

(Comparative Example 1) A deposit was obtained on a substrate in the same manner as in Example 1 except that methane gas was used instead of carbon monoxide gas.

The average thickness of the resulting deposit was 9 gm, and the deposition rate was slower than in Example 1.

In addition, when the Raman scattering spectrum of the obtained deposit was measured, in addition to the peak caused by diamond near 1333 cm-', a broad peak was observed near 1500 cF1, indicating that the crystallinity was slightly inferior. It was confirmed.

[Effects of the Invention] According to the present invention, (1) high-quality diamond can be efficiently produced at a high precipitation rate whether on a substrate or in a gas phase; (2) diamond can also be formed on a substrate; When crystals are precipitated, a diamond film with excellent uniformity and adhesion can be obtained; (3) When diamond crystals are precipitated in the gas phase, ultrafine crystal diamond or diamond with controlled particle size can be obtained. It is possible to provide an industrially advantageous method for synthesizing diamond, which has the following effects.

[Brief explanation of the drawing]

FIGS. 1 to 4 are schematic diagrams illustrating a reaction apparatus that can be suitably used in the method of the present invention. FIG. 1 is a conceptual diagram of the differential pumping system. Figure 2 shows a high-frequency induction type reactor; (a) in Figure 2 is an E-discharge type, and (b) is an H-discharge type in which a cooling means and a hydrogen gas inlet are provided on the base support. FIG. FIG. 3 shows a pulse discharge type reaction apparatus, and FIG. 3(C) is a conceptual diagram of the pulse Z discharge type, and FIG. 3(d) is a conceptual diagram of the pulse e discharge type. FIG. 4(e) is a conceptual diagram of the DC arc discharge method, and FIG. 4(f) is a conceptual diagram of the microwave discharge method. 1- Reaction gas inlet 2 Plasma gas inlet 3e Sheath gas inlet 4 Φ Plasma generation chamber 5 Os water-cooled copper nozzle 6 Deposition chamber
7...Base 8φΦ Inlet port for raw material gas and sheath gas 9...Substrate support stand lO, pot, high frequency power source 11
・・ΦHigh frequency generation electrode 12・High frequency generation coil 1311・・Hydrogen gas inlet 14・・Water cooling condenser pipe 15・・Electrode 16・Written・Switch 17・・・
Capacitor 18... e-coil 19, fist, DC power supply 20, war, microwave oscillator 21...◆Waveguide 2
No. 2... Plunger Figure 1 Figure 2 1゜ (a) E imitation electric method (b) H imitation electric method Figure 3 (c) 1 Rumata e discharge million people Figure 4 (e) Naoki Ryo - Fu Ryoho Sobun 2 (f) My Furomi skin it Hojo Roku:

Claims (1)

[Claims] (1) A thermal plasma obtained by activating a raw material gas consisting of carbon monoxide gas and/or carbon dioxide gas and hydrogen gas is brought into contact with a substrate at a temperature lower than the temperature of the thermal plasma. A diamond synthesis method characterized by: (2) The diamond synthesis method according to claim 1, wherein the raw material gas contains an inert gas. (3) Claim 1, wherein the temperature of the thermal plasma is 1,000K or more.
Or the manufacturing method according to claim 2. (4) The manufacturing method according to any one of claims 1 to 3, wherein the substrate is cooled to 400 to 1,700°C. (5) Diamond is precipitated in a gas phase at a temperature lower than the plasma using thermal plasma obtained by activating a raw material gas consisting of carbon monoxide gas and/or carbon dioxide gas and hydrogen gas. How to synthesize diamonds.