JPS5927754B2 - Diamond synthesis method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for synthesizing diamond by chemical vapor deposition.

Conventionally, the following method is known as a diamond synthesis method using a vapor phase precipitation method.

1) A chemical vapor deposition method in which hydrocarbons are introduced onto the heated substrate surface and thermally decomposed using the thermal energy to generate free carbon and precipitate diamond.

2) An ion beam method that combines arc discharge and sputtering techniques to generate a positive carbon ion beam, which is accelerated, focused, and collided with the substrate surface to deposit diamond.

3) A direct current discharge is generated between the electrodes, and the high-energy electrons in the discharge are used to release the chemical bonds of hydrocarbons and at the same time generate excited carbon atoms, creating a chemical gas that precipitates diamonds on the substrate surface. Phase precipitation method.

4) Enclose graphite, a substrate, and hydrogen gas, place the graphite in a high-temperature area and the substrate in a low-temperature area, generate atomic hydrogen from the hydrogen gas thermally or by electric discharge, and use a disproportionation reaction. , a chemical transport method that deposits diamond on the surface of a substrate, etc.

In the chemical vapor deposition method described in 1) above, hydrocarbons are thermally decomposed on the surface of a substrate heated to a temperature of 1100°C or less under reduced pressure to form a diamond layer. Precipitation is inevitable.

These inhibit diamond formation.

Therefore, it is necessary to periodically repeat the precipitation operation and the operation of introducing oxygen gas or hydrogen gas to remove graphite and non-diamond carbon deposited on the substrate surface.

Further, there are drawbacks such as slow deposition rate and the substrate being limited to diamond.

The ion beam method (2) above has the advantage that diamond can be deposited on the surface of a substrate made of various materials at room temperature.

The device for generating a positive carbon ion beam and its focusing device are expensive, and the atoms of the inert gas used to sustain the discharge are trapped in the precipitated diamond lattice.

In the method of 3) above, in which diamond is synthesized by periodically generating plasma in synchronization with the introduction of the reaction gas, it is difficult to maintain the plasma density uniformly over the entire area.

This non-uniform density has the disadvantage that non-diamond carbon is deposited in addition to diamond.

The chemical transport method (4) above is a sealed tube method, which utilizes hydrocarbons produced by a reaction between graphite and atomic hydrogen in a sealed tube, and therefore is difficult to operate continuously.

It also has the disadvantage that synthesis conditions such as the concentration of reaction gas, its ratio, and heating temperature cannot be varied independently.

The method of the present invention aims to improve the drawbacks of the conventional method described above, and it is easy to independently vary synthesis conditions such as the concentration of reaction gas, its ratio, heating temperature, and pressure of the reaction system. This method provides a method for stably synthesizing granular diamond or film-like diamond on the surface of a substrate.

The present invention uses a mixed gas in which hydrogen gas is passed through a microwave non-electrode discharge and then mixed with a hydrocarbon, or a mixed gas in which a mixed gas of hydrocarbon and hydrogen is passed through a microwave non-electrode discharge. The above object was achieved by a method in which diamond was precipitated by thermal decomposition of hydrocarbons in an excited state by introducing the diamond onto the surface of a substrate heated to 1300°C.

The principle of the method of the present invention is that in order to synthesize diamond at a temperature and pressure at which graphite is thermodynamically stable, individual carbon atoms must be generated, and these carbon atoms must be in an excited state. In addition, it is necessary to satisfy conditions such as that this excited state persists until a diamond nucleus is formed.

In addition, in order to grow diamond from free carbon produced by thermal decomposition of hydrocarbons, it is necessary to supply reaction energy sufficient to cause bonding of SF3 to the free carbon.

In the method of the present invention, hydrogen gas is passed through a microwave non-polar discharge and then mixed with a hydrocarbon, or after the hydrocarbon and hydrogen gas are mixed, the hydrogen gas is passed through a microwave non-polar discharge to form an excited state. Produces hydrocarbons, excited or atomic hydrogen.

When this excited hydrocarbon is thermally decomposed on the heated substrate surface, reaction energy sufficient to cause SP3 bonding is supplied to the free carbon atoms generated.

Also, excited or atomic hydrogen causes the growth of graphite and non-diamond carbon in SF3. It reacts with nuclei with SP bonds, converting them to SP3 bonds, or producing hydrocarbons, which acts to clean the surface on which diamond grows.

In the method of the present invention, a stable microwave non-polar discharge was used to sustain the discharge stably.

In the case of DC discharge, electrodes are used, so it is difficult to generate a discharge continuously for a long time because the electrodes will be damaged.

Furthermore, the occurrence of nonpolar discharge at frequencies below several megahertz strongly depends on the pressure of the thread.

Microwave non-polar discharge can reduce the dependence of thread pressure.

A few tens of megahertz is insufficient to provide sufficient excitation in hydrocarbons to deposit diamond.

The mixing ratio of hydrocarbon and hydrogen gas in the mixed gas used can be varied over a wide range, but from the viewpoint of preventing the precipitation of graphite and non-diamond carbon, it is desirable that the upper limit is 10 or less.

It is desirable that it be about 0.01 or less for synthesizing granular diamond, and about 0.1 or more for depositing film-like diamond.

The substrate temperature needs to be at a temperature necessary to prevent the reverse transition of precipitated diamond to graphite and to cause thermal decomposition of excited hydrocarbons on the substrate surface.
The temperature is preferably 00 to 1300°C.

Particularly preferred is 500 to 1000°C.

The pressure within the tube that generates the non-polar discharge is preferably in the range of 0.05 to 400 Torr in order to maintain stable discharge.

Since the method of the present invention is an open tube method, by adjusting the mixing ratio of hydrocarbon and hydrogen gas, the gas flow rate, the substrate temperature, and the output of the microwave oscillator, it is possible to Since the amount of hydrogen produced in each state can be independently controlled, it is easy to control the nucleation rate.

By controlling this nucleation rate, granular diamond or film-like diamond can be easily synthesized.

Next, the embodiment of the apparatus for carrying out the method of the present invention is shown in FIGS. 1 and 2.

Figure 1 shows a method in which hydrogen gas is passed through a microwave non-polar discharge and then mixed with hydrocarbon gas, and Figure 2 shows a method in which a mixed gas of hydrocarbon and hydrogen gas is passed through a microwave non-polar discharge. This is a method of forcing people to do something.

In FIG. 1 and FIG. 2, 1 is a hydrocarbon gas supply device;
2 is a hydrogen gas supply device, 3 is a microwave oscillator, 4 is a waveguide, 5 is a reaction chamber, and 6 is an exhaust device.

A support stand 8 for supporting the substrate 7 is installed in the precipitation chamber 5.
In FIG. 1, the substrate is heated in a resistance heating furnace 9.

In FIG. 2, heating is performed in an infrared concentrated irradiation furnace 10 that condenses light emitted from a halogen lamp.

12, 13, and 14 are cocks that adjust the flow rates of hydrogen gas and hydrocarbon gas as well as the pressure inside the device.

15 is an exhaust port. After placing the substrate 7 on a support inside the reaction chamber 5, the exhaust device 6 is activated to reduce the pressure inside the device, and the cocks 12, 13, and 14 are adjusted to adjust the flow rate of hydrogen gas. and maintain the pressure within the device at a predetermined value.

Next, the substrate is maintained at a predetermined temperature using the resistance heating furnace 9.

In the case of an infrared concentrated irradiation furnace, the substrate temperature is controlled by adjusting the current flowing through the halogen lamp 11.

Next, the microwave oscillator is activated to generate a microwave non-polar discharge, and a hydrocarbon gas whose flow rate has been adjusted in advance is introduced.

Example 1 Molybdenum is used as a substrate, and methane gas and hydrogen gas are used as reaction gases.

Activate the exhaust system to reduce the pressure in the reaction system.

Next, hydrogen gas is supplied at a flow rate of 1 oocc per minute, and the cocks 12 and 13 are adjusted to reduce the pressure in the reaction system to Q, 5.
Adjust to Torr.

A microwave oscillator generates a non-polar electrical discharge.

Next, the base temperature is raised to 900° C., and methane gas is supplied at a flow rate of 20 cc per minute, mixed with the hydrogen gas that has passed through the non-polar electrode discharge, and introduced onto the heated substrate.

Precipitation was carried out for 3 hours, and a diamond precipitated layer of about 1 μm was obtained on the substrate surface.

Example 2 A silicon wafer is used as a substrate, and methane gas and hydrogen gas are used as reaction gases.

Activate the exhaust system to reduce the pressure in the reaction system.

Next, hydrogen gas and hydrocarbon gas are each added to occ per minute.
y i occ and adjust the cock 12.13 to bring the pressure inside the reaction system to 0. Adjust to ITorr.

Next, the substrate temperature is raised to 700° C., and a non-polar electric discharge is generated by a microwave oscillator.

Precipitation was carried out for 3 hours, and diamond particles of about 2 μm were deposited on the substrate surface.

[Brief explanation of the drawing]

FIGS. 1 and 2 show embodiments of a synthesis apparatus for carrying out the method of the present invention. 1... Hydrocarbon gas supply device, 2...
Hydrogen gas supply device, 3...Microwave oscillator
4 sa+llll+' wave guide, 5...
Reaction chamber, 6...exhaust device, 7...substrate, 8...support stand, 9...-heating furnace, 1o
...Infrared concentrated irradiation furnace, 11... History rogen lamp, 12.13,14 ... Cook, 15
・Exhaust port.

Claims (1)

[Claims] 1 Hydrogen gas is passed through a microwave non-electrodischarge and then a mixed gas mixed with a hydrocarbon or a mixed gas of hydrocarbon and hydrogen gas is passed through a microwave non-electrodischarge. A diamond synthesis method characterized by introducing a mixed gas onto the surface of a substrate heated to 300 to 1300°C and depositing diamond by thermal decomposition of hydrocarbons. 2 The mixing ratio of hydrocarbon and hydrogen gas is 100 to 0.0
01. A method for synthesizing diamond according to claim 1.