JPH0355435B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing diamond using high temperature plasma.

Prior Art The present applicant has previously discovered that high-temperature plasma with a gas temperature of 1700 K or higher generated using direct current, low-frequency alternating current, high frequency, or microwave is effective for high-speed synthesis of diamond. However, since high-temperature plasma has a high gas temperature, in order to synthesize a substance that is unstable at high temperatures, such as diamond, it is necessary to lower the gas temperature without lowering the concentration of active species.

The methods to lower the temperature so far have been (1) by bringing it into contact with a solid surface that has been cooled to a low temperature by cooling with water or a refrigerant; (2) Method of spraying cold gas or refrigerant.
(3) A method of cooling gas by adiabatically expanding it. (4) We discovered a method of cooling by magnetohydrodynamic action using a magnetic field. However, methods (1) and (2) have the drawback that temperature non-uniformity tends to occur on the substrate surface where diamond grows or in the growth space, making it difficult to control. It had the disadvantage of requiring large equipment such as a magnetic field generator.

Purpose of the Invention The present invention has been made to eliminate the drawbacks of conventional methods, and is a simple method that does not require large equipment, and can maintain the temperature of a diamond deposition substrate at a uniform and appropriate temperature, thereby allowing diamond to be deposited uniformly. We are here to provide you with a way to get it done.

Composition of the Invention As a result of intensive research to achieve the above object, the present inventor has found that when depositing diamond on a substrate using high-temperature plasma, the relative position between the substrate and the plasma is changed by moving the substrate or the plasma torch. It has been found that it is possible to easily control the surface temperature of the substrate uniformly and obtain a uniform layer of diamond. The present invention was completed based on this knowledge.

The gist of the present invention is to generate a high-temperature plasma with a gas temperature of 1700K or more by electric discharge in a single gas or a mixture of gases selected from hydrocarbon gas, hydrogen gas, and inert gas, and to generate organic compounds or carbon materials in the plasma. In this method, diamond is deposited from the gas obtained by decomposing or evaporating diamond into the plasma or onto a substrate placed in the plasma tail flame, while changing the relative position of the substrate and the plasma by moving the substrate or plasma torch. A method for producing diamond, characterized by depositing diamond on a substrate.

The plasma used in the present invention is preferably a high-temperature plasma with a gas temperature of 1700 K or higher obtained by discharge; if it is lower than this, the deposition rate will be slow. The power source used for discharge may be any one of direct current, low frequency alternating current, high frequency, and microwave, and may be electroded or electrodeless.

Hydrocarbon gas,
An inert gas such as argon or helium or hydrogen gas may be used alone or as a mixed gas.

When an inert gas or hydrogen gas is used as a plasma generating gas, an organic compound or carbon material is injected into the plasma as a carbon source. The organic compound may be gaseous, liquid, or solid, as long as it can be decomposed in plasma to generate carbon-containing ionic species or radical species.

For example, methane, ethane, propane, butane,
Hydrocarbons such as ethylene and benzene, polymeric substances such as polyethylene and polypropylene, or oxygen-containing, nitrogen-containing, halogen-containing, sulfur-containing, phosphorus-containing substances such as alcohol, acetone, amines, methyl chloride, thiophene, triethylphosphine, etc. Examples include organic compounds.

Further, when hydrogen gas or hydrocarbon is mixed into the plasma, carbon monoxide or carbon dioxide can be used as a carbon source, and graphite or the like can be used as a solid carbon source.

The plasma gas pressure used is in the range of 10 ^-4 to 5×10 ² atm. At low pressures, the rate of diamond precipitation is slow, and at high pressures, the disadvantage is that the container is difficult to handle.

The base can be moved by rotating the base or a holder on which the base is mounted, or by reciprocating the base. In other words, the temperature distribution of high-temperature plasma is used to move the substrate between a high-temperature part and a low-temperature part, or between a position where the plasma hits and a position where it does not hit, and the surface temperature of the base is controlled by the speed of movement, period, etc. can get. This makes it possible to uniformly deposit diamond on the surface of the substrate. Similar control can be obtained by moving the plasma torch instead of moving such a substrate.

This operation of moving the base body can be performed using external power such as a motor, but it can also be performed using a gas flow.

Furthermore, by connecting an appropriate load such as an electric resistance to the outside along with this moving operation, the energy of the flow can be taken out to the outside through a motor or the like, and the temperature of the gas hitting the base can be lowered. In this case, the amount of energy taken out can be controlled independently of the movement speed of the base by changing the gear ratio of the motor and holder and the load resistance.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An apparatus for carrying out the method of the present invention will be explained based on the drawings. FIG. 1 is a schematic diagram using high frequency discharge, and FIG. 2 is a schematic diagram using direct current discharge.

In FIG. 1, 1 is a high-frequency plasma torch;
2 is a high frequency power source, 3 is a base, and 3' is a disc-shaped base holder which can be rotated by a motor from the outside. 4 is a plasma, 5 is a deposition chamber, 6 is an exhaust device, 7 is a gas supply device, and 8 to 8'' are gas flow rate control valves.

The operating procedure is to first evacuate the deposition chamber 5 and the plasma torch section using the exhaust device 6, then open the valves 8',
8″ to supply a predetermined plasma generation gas,
After setting the precipitation chamber 5 to a predetermined pressure, the work coil 1
3 from the power source 2 to generate plasma. A raw material gas is supplied into this plasma from the valve 8 or a raw material is supplied from the solid/fluid raw material supply device 14, and diamond is deposited on the substrate 3 which has been rotated in advance. Instead of this rotation, the substrate holder may be moved reciprocatingly or in a two-dimensional manner.

In FIG. 2, 21 is a DC plasma torch;
22 is a DC power supply, 3'' is a screw-shaped base holder, 9 is a generator motor, 9' is a load resistor,
The rest is the same as in FIG.

The operating procedure is the same as that shown in FIG. 1 (although the plasma generation power source is different) to generate plasma and decompose the source gas, and deposit diamond on the substrate 3.

In this case, the substrate holder 3'' is rotated by the gas flow of the plasma torch, and electrical energy is taken out to the load resistor 9'. By matching the load resistors, it is possible to increase the effect of lowering the temperature of the substrate. Incidentally, instead of the screw-like rotor, an axial-flow type rotor may be used for the rotary base holder 3''.

As the substrate, metals such as monbuden and stainless steel, semiconductors such as silicon, ceramics such as alumina, single crystal diamond, etc. are used. The substrate temperature is preferably 400 to 1700°C. In addition to the method of the present invention described above, the temperature may be adjusted by cooling the substrate and substrate holder using a refrigerant or gas.

Effects of the Invention According to the method of the present invention, it is possible to easily control the cooling of the substrate temperature using a simple method without the need for large-scale equipment as in the conventional method, thereby depositing a diamond film with a uniform thickness on the substrate. can be obtained.

Example 1 Using the device shown in Figure 1, 1.1 from valve 8
g/min alcohol vapor and argon 4/min
mixed gas, argon 4/min from valve 8',
Argon 10/min and hydrogen 12/min from valve 8″
Flow min mixed gas into plasma torch 1,
Frequency 4MHz under atmospheric pressure, vacuum tube plate input
It was discharged for 10 minutes using a high frequency of 50kw. The plasma temperature was approximately 8000K. A 70φ water-cooled substrate holder was rotated at 1 rotation/second, and diamond was deposited on six 20φ molybdenum substrates on the substrate holder. The substrate temperature was approximately 900°C. A diamond film with a thickness of 8 μm was obtained on the substrate. The produced film thickness distribution was ±5% in the tangential direction of the rotational motion of the substrate holder and ±15% in the radial direction, and the film thickness was uniform.

Comparative Example 1 When the test was carried out under the same conditions as in Example 1 without rotating the substrate holder, the molybdenum substrate was melted and no diamond film was obtained. Therefore, when we fixed the molybdenum substrate tightly to the substrate holder with screws and did not rotate it, the substrate temperature was approximately 1000℃.
The film thickness is about 30μm at the center of the board, and about 30μm at the periphery of the board.
The diamond had an uneven thickness of 60 μm.

Example 2 Using the device shown in Figure 2, a mixed gas of 25/min of argon and 5/min of hydrogen was flowed through valve 8, and 1/min of methane was flowed through valve 8', and the power output was
A 20kw discharge was applied for 10 minutes.

A diamond film was formed on a 10 mmφ molybdenum plate fixed on a propeller-shaped rotating substrate boulder with an outer diameter of 40 mmφ. At this time, the pressure in the precipitation chamber was set to about 150 Torr during the reaction, and the output to the load resistor 9' was set to about 150 Torr.
It was set to 10W. The resulting diamond film thickness is approximately 5μ
It had a uniformity of m.

[Brief explanation of drawings]

The drawing is a schematic diagram of an apparatus for carrying out the method of the present invention.
FIG. 1 is an embodiment of an apparatus for depositing diamond on a substrate by generating plasma using high frequency discharge and FIG. 2 using direct current discharge. 1: High frequency plasma torch, 2: High frequency oscillator, 3: Substrate, 3', 3'': Substrate holder, 4: Plasma, 5: Deposition chamber, 6: Exhaust device, 7: Gas supply device, 8, 8', 8″: Valve, 9: Generator,
9': Load resistance, 13: Work coil, 14: Solid, fluid raw material introduction device, 21: DC plasma torch, 22: DC power source.

Claims (1)

[Claims] 1 Generate high-temperature plasma with a gas temperature of 1700K or higher by electric discharge in a single gas or a mixed gas selected from hydrocarbon gas, hydrogen gas, and inert gas,
In this method, diamond is deposited from the gas obtained by decomposing or evaporating an organic compound or carbon material in the plasma onto a substrate placed in the plasma or in the plasma tail flame, in which the substrate or the plasma torch is moved to separate the substrate and the plasma. A diamond manufacturing method characterized by depositing diamond on a substrate while changing its relative position with the substrate.