JPH0419198B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for depositing particulate or film diamond by thermally decomposing hydrocarbons in a hydrogen gas atmosphere.

Several methods have been known to synthesize diamond by thermal decomposition of hydrocarbon or carbon compound gases. For example, JP-A-47-
42286 discloses that diamond seed crystal powder can be placed in a catalytic heater with hydrogen gas as a carrier gas and the diamond seed crystal particle size can be increased using the following reaction.

(1) CH ₄ → C (diamond) + 2H ₂ (2) 2CO → C (diamond) + CO ₂ (3) CnH _2o+2 → C (diamond) + H ₂ (however, n≦5) However, in general, the gas phase of diamond In synthesis,
The precipitation of amorphous carbon other than diamond and graphite prevents the subsequent formation of diamond. Therefore, it is necessary to prevent the formation of non-diamond substances such as amorphous carbon and graphite other than diamond.

As a means of this, Pt, Ir, Os, Re, Au, Pd,
Synthesis is carried out in the presence of a catalytic heater such as Ru, Re, Au, Pd. Ru, Rh, Ag, Ni, etc., under reduced pressure or a pressure of 1 to 10 atm, and at a temperature range of 900°C to 1200°C. has been revealed. It is known that the generated amorphous carbon or graphite can be removed on diamond by the reaction of C (amorphous or graphite) + 2H ₂ →CH ₄ by the action of the catalyst heater described above.

However, in the disclosed conventional method,
Both methods require diamond seed crystals, and it is impossible to completely remove amorphous carbon or graphite. It is true that the conventional method was effective only while the diamond seed crystal was small, that is, during the seed crystal diameter of about 0.1 μm or less at the beginning of the synthesis reaction, but as the seed crystal became larger, the effect of the catalytic heater gradually increased. The diamond becomes thinner and a large amount of non-diamond substances such as amorphous carbon or graphite precipitates, resulting in the problem of inhibiting the growth of seed crystals, making it difficult to obtain diamonds with large grain sizes. Ta. Furthermore, it has been impossible to deposit diamond on materials other than diamond seed crystals, or to obtain a film of diamond on a flat surface.

Another method, such as the Japanese Journal of Applied Phgsics published in 1982.
The paper on page L183 of Volume 21 states that methane (CH ₄ ) gas is catalytically heated and thermally decomposed using a dungsten heater heated to approximately 2000°C and hydrogen gas as a carrier. describes a method for depositing diamond. This method is excellent in that it allows diamond to be precipitated on materials other than diamond, but since the tungsten heater is heated to a high temperature of approximately 2000°C, the vapor pressure of tungsten itself is high. There is also the problem that it wears out in a short period of time, and that evaporated tungsten adheres to the diamond surface. In addition, once heated, the tungsten heater becomes extremely brittle and easily cut due to the growth of tungsten microcrystal particles and the absorption of gas molecules, so the tungsten heater must be replaced frequently and the equipment must be operated for long periods of time. difficult to do,
Further, there were other problems, such as changes in the tungsten heater wire over time, which caused changes in the thermal decomposition conditions of the reactant gas, making it difficult to uniformly deposit a film of diamond over a wide area.

Still another method is to use the reaction gas under reduced pressure,
There is a method in which diamond is precipitated by causing the reaction of formula (1) above on a substrate placed in plasma gas generated by microwave discharge or high-frequency discharge, and a method in which diamond is precipitated by colliding ionized carbon with the substrate. Attempts have also been made to synthesize film-like diamond, but each method has the problem of precipitation of non-diamond substances such as amorphous carbon or graphite.

Furthermore, it has been impossible to deposit a single crystal film on a single crystal substrate other than a diamond seed crystal, such as Si, gallium arsenide (GaAs), or saphire, using conventional methods.

The purpose of this is to improve the various drawbacks mentioned above, promote the decomposition of hydrocarbons, and prevent the formation of non-diamonds such as amorphous free carbon or graphite. An object of the present invention is to provide a vapor phase synthesis method and apparatus capable of precipitating only the above substances.

That is, the present invention is a method for depositing particulate or film-like diamond by a gas phase reaction of hydrocarbons in the presence of hydrogen gas. A vapor phase synthesis method characterized by including a step of irradiating onto a substrate, a reaction chamber in which a heater is installed, a reaction gas supply device for supplying a reaction gas to the reaction chamber, and a hydrogen plasma light source. This diamond vapor phase synthesis apparatus is characterized by comprising a hydrogen plasma light generation chamber installed adjacent to the reaction chamber through a transparent wall. In order to excite the reactant gas, in addition to the heating effect of the gas by the light, direct excitation due to the light energy is possible using light of a certain wavelength. The shorter the wavelength of the light, the greater the energy of the light, which makes it possible to excite the reactant gas molecules to a high-energy unstable state, so it is expected that the chemical reaction will proceed more quickly. In order to produce diamonds from methane through a photochemical reaction, the absorption of methane must be extremely large.
It is effective to use light of 200 mm or less.

But halogen lamp xenon lamp high pressure,
All low-pressure mercury lamps have extremely weak light intensity in the short wavelength range due to the wavelength distribution of light intensity, and moreover, the light intensity is 184.7 mm.
Wavelengths below this cannot be used.

Furthermore, a reduction in the rate of light reaching the substrate due to adhesion of reaction products to the walls of the reaction tube is also an extremely serious problem.

The wavelength distribution of the light intensity of hydrogen plasma light is extremely strong even on the short wavelength side of around 150 mm, which is extremely advantageous for utilizing photochemical reactions.

Embodiments of the vapor phase synthesis method and apparatus thereof according to the present invention will be described below with reference to the drawings.

The figure is an example of a gas phase reactor according to the invention. The apparatus consists of a quartz reaction chamber 1 with a diameter of 90 mm and a hydrogen plasma light generation chamber 2 made of a quartz pipe with a diameter of 50 mm. To generate hydrogen plasma,
High-frequency power is supplied to the coil 3 from the high-frequency power supply 12 to generate plasma gas in a hydrogen plasma light generation chamber equipped with a water-cooled wall 4, and the ultraviolet light induced at that time is passed through the hydrogen plasma light transmission wall 5 and heated to an appropriate temperature in advance. It is arranged so that it can be irradiated onto a heated 2-inch silicon substrate 6. 7 is a heater for heating the substrate.

Hydrogen gas is introduced from outside the hydrogen plasma light generation chamber through an introduction pipe 8'. Further, the reaction gas is introduced into the reaction chamber 1 from the gas supply device 11 via the supply pipe 8 . The reaction chamber 1 is made of a reaction tube 9 made of quartz, and is evacuated by a vacuum evacuation device 10 so as to work under a total pressure of 760 Torr to 0.1 Torr.

Normally, the wavelength distribution of the emission intensity generated by hydrogen plasma is extremely dependent on gas pressure, and the pressure inside the hydrogen plasma light generation chamber 2 is adjusted by an exhaust device 13 installed separately. The pressure of the gas used for hydrogen plasma light generation is usually 10 Torr ~
It is 760 Torr. For this reason, a pressure difference between 0.1 Torr and the reaction chamber 1 of several tens of Torr occurs. The partition wall 5 was manufactured by bundling glass capillary tubes in order to reduce the intrusion of gas from the hydrogen plasma light generation chamber into the reaction chamber and to transmit only light such as ultraviolet or visible light. It is desirable that the diameter of the capillary tube be as small as possible so as to provide high resistance to the gas flow.
In this example, pieces having a length of 20 mm, an outer diameter of 0.5 mm, and an inner diameter of 0.3 mm were bundled and fixed by adhesive. In order to control the degree of intrusion of excess ions generated in the hydrogen plasma into the reaction chamber, it was also effective to deposit a metal on the partition wall of the capillary tube and use it as an electrode to apply a sink voltage. Furthermore, a material such as MgF ₂ that easily transmits short wavelength light can also be used as the hydrogen plasma transmission wall. A synthetic reaction was carried out using the apparatus described above under the following conditions. To generate hydrogen plasma light,
Hydrogen gas is injected into the generation chamber from gas inlet 4 at a flow rate of 5 per minute, and high-frequency power of approximately 4 MHz is applied.
10KW was applied to the work coil 3 from the high frequency power supply 12.

It was also effective to create a spiral gas flow along the tube wall of the generation chamber to stabilize the plasma flow. The pressure during plasma generation was set to about 20 Torr by adjusting the exhaust device 13.

As the reaction gas, a mixed gas of methane gas and hydrogen gas containing 0.5 vol% of methane gas (CH ₄ ) was flowed twice per minute, and the substrate temperature was about 1000°C. The pressure in the reaction chamber was approximately 100 Torr.

Depending on the above conditions, the substrate temperature may range from 700℃ to 1000℃.
We were able to grow a thin film of diamond on a silicon substrate. The thin film was 0.1-0.5μ and the growth rate was 0.5μ per hour. However, it is possible to grow diamond by combining appropriate conditions with respect to the flow rate of the reaction gas, the pressure in the reaction chamber, the pressure in the hydrogen plasma light generation chamber, the mixing ratio of methane and hydrogen in the reaction gas, etc., in a range other than the above conditions.

It was confirmed from the transmission electron diffraction pattern that it was diamond.

When hydrogen plasma light was not irradiated, no diamond precipitation occurred and only graphite-like carbon films or particles were observed.

As described above, the vapor phase synthesis method and apparatus according to the present invention can easily deposit a diamond film by vapor phase reaction of hydrocarbons in the presence of hydrogen gas.

By mixing 1 to 10 volume% of a rare gas such as argon or xenon into the hydrogen gas that serves as the hydrogen plasma light source, it is easy to obtain a wavelength distribution of light intensity that cannot be obtained with hydrogen plasma alone. Because it can be done, the practical value is extremely large.

[Brief explanation of drawings]

The figure is a schematic diagram of a vapor phase synthesis apparatus showing an embodiment of the present invention. In the figure, 1 is a reaction chamber, 2 is a hydrogen plasma light generation chamber, 3 is a coil, 4 is a water cooling wall, 5 is a hydrogen plasma light transmission wall, 6 is a substrate, 7 is a heater, 8 is a reaction gas supply pipe, 8' 1 is a hydrogen introduction pipe, 9 is a reaction tube, 10 and 13 are evacuation devices, 11 is a reaction gas supply device, and 12 is a high frequency power source.

Claims (1)

[Claims] 1. A method for depositing particulate or film diamond by a gas phase reaction of hydrocarbons in the presence of hydrogen gas, in which synchrotron radiation such as ultraviolet rays and visible light generated by hydrogen plasma is used. A vapor phase synthesis method comprising the step of irradiating a substrate on which diamond is to be deposited. 2 A reaction chamber in which a heater is installed,
A diamond-based diamond apparatus comprising: a reaction gas supply device for supplying a reaction gas to the reaction chamber; and a hydrogen plasma light generation chamber installed adjacent to the reaction chamber through a hydrogen plasma light transmission wall. Gas phase synthesis equipment.