JPS62120B2 - - 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 methods are known as methods for synthesizing diamond in a low pressure region below normal pressure.

1. A chemical vapor deposition method in which hydrocarbons are heated under reduced pressure to the surface of the substrate, and the thermal energy is used to thermally decompose them to generate free carbon and precipitate diamonds.

2 Combining arc discharge and sputtering,
An ion beam method that generates a positive carbon ion beam, accelerates it, focuses it, and collides with the substrate surface to deposit diamond.

3 In a mixed gas of hydrogen gas and hydrocarbon gas,
A high frequency plasma is generated by conducting a high frequency of 30MHz or less, for example 13.5MHz, and the high energy charged particles of the plasma release the chemical bonds of hydrocarbons and at the same time generate excited state carbon atoms or excited state hydrocarbons. A plasma chemical vapor deposition method that deposits diamond on the surface of a substrate.

4. Graphite, a substrate, and hydrogen are sealed in a sealed tube, with the graphite placed in a high-temperature part and the substrate placed in a low-temperature part, and the hydrogen gas is thermally or electrically discharged to generate atomic hydrogen, causing a disproportionation reaction. A chemical transport method is used to deposit diamond on the surface of a substrate.

and so on.

However, each of these methods has the following drawbacks.

The chemical vapor deposition method described in 1 above has the disadvantage that the precipitation of diamond and graphitic carbon proceeds simultaneously, and in order to synthesize diamond, it is necessary to perform the precipitation operation and introduce oxygen or hydrogen gas to deposit on the substrate surface. It is necessary to periodically repeat the operation of removing the graphitic carbon. Therefore, the deposition rate is slow and the substrate is limited to diamond.

The ion beam method described in 2 above has the advantage of being able to deposit diamond on the surface of a substrate made of various materials at room temperature, but the device for generating a positive carbon ion beam and its focusing device are expensive, and it is difficult to sustain the discharge. There are drawbacks such as atoms of the inert gas used, such as argon gas, getting mixed into the diamond lattice.

In the high-frequency plasma chemical vapor deposition method described in 3 above, in order to generate plasma, the pressure in the reaction system must be in a low and narrow range; if the pressure is high, plasma will not be generated; The disadvantage is that there is a shift in synchronization with the plasma, and it is necessary to constantly maintain synchronization.

The chemical transport method described in 4 above has the disadvantage that continuous operation cannot be performed because it is carried out in a sealed tube.

As a result of research to improve the shortcomings of these conventional methods, the present inventors first discovered that (1) a mixed gas in which hydrogen is passed through a microwave non-polar discharge and then mixed with hydrocarbons, or a mixture of hydrogen and hydrocarbons; The mixed gas with hydrogen was passed through a microwave non-polar discharge, and then the mixed gas was
We have discovered a method (Japanese Patent Application No. 1983-204321) in which diamond is deposited on a substrate heated to ~1300°C and the hydrocarbons are decomposed.

However, with this method, it was discovered that carbon having a disordered structure or carbon bonded to hydrogen was optically observed in the synthesized diamond, resulting in a quality problem.

An object of the present invention is to solve the above-mentioned problems.

As a result of further research to overcome this problem, the inventors of the present invention found that in the above method, two microwave oscillators were used, and one oscillator had a high output so as to efficiently excite and dissociate the gas. The other oscillator oscillates microwaves to generate plasma and introduces it through a waveguide, and the other oscillator maintains the plasma and maintains the substrate temperature at a temperature suitable for the diamond synthesis temperature (300 to 1300℃). By oscillating waves to generate plasma and guiding it to the substrate with a waveguide,
It has been found that high quality diamond can be deposited on the substrate. The present invention was completed based on this knowledge.

The gist of the present invention is to provide a method for depositing diamond on a substrate using microwave non-polar discharge of a mixed gas of hydrogen and hydrocarbons, in which two waveguides for introducing microwaves are used, and one waveguide is used. Plasma is generated by introducing high-power microwaves that efficiently excite and dissociate gas, and the other waveguide maintains the plasma to maintain the substrate temperature at a temperature of 300 to 1300°C, which is suitable for diamond synthesis. A diamond synthesis method is characterized in that output microwaves are oscillated and introduced through a waveguide to generate plasma and deposit diamond on a substrate.

In the method of the present invention, the higher the output power used to excite and bring the gas into a dissociated state, the better;
200W to 5kW, preferably 500W to 2kW, on gas
Plasma is generated by introducing microwaves of 300MHz to 1000GHz.

In addition, the substrate is suitable for diamond synthesis.
The output to maintain the temperature at 1300℃ is 100W ~
1.5kW, preferably 100W~1kW, 300MHz~
Introducing 1000GHz microwave.

The microwave waveguide for exciting and dissociating the gas is preferably located at the top, and the microwave waveguide for heating the substrate is preferably located at the bottom.

Due to the generation of high-power microwave plasma at the top, the excitation and dissociation of hydrogen and hydrocarbon gas increases,
It becomes a carbon atom with enough reaction energy to create the chemical bonds of diamond. The microwave plasma guided from the microwave waveguide at the bottom maintains the plasma generated at the top around the substrate and at the same time maintains the substrate temperature at a temperature suitable for diamond synthesis. is deposited as diamond on the substrate.

In addition, excited or atomic hydrogen generated in microwave plasma reacts with Sp ² and carbon atoms with Sp bonds, which are responsible for the growth of graphite and graphitic carbon, to generate hydrocarbons and at the same time These are removed from the substrate and the substrate surface is cleaned. The above two effects work together to prevent impurities and carbon having a disordered structure from being mixed into the diamond, and to precipitate high quality diamond. Note that the substrate temperature is adjusted by selecting the material of the substrate support based on the dielectric constant and dielectric loss tangent values. For example, by using hexagonal boron nitride instead of alumina, temperatures as low as 50°C to 200°C can be obtained. Alternatively, more accurate adjustment can be achieved by placing a microwave absorber, such as graphite or stainless steel, around the substrate support, or by cooling the support directly with a coolant.

The hydrocarbon used in the present invention may be any hydrocarbon that is excited and dissociated in microwave plasma. For example, saturated methane, ethane, propane, ethylene, acetylene, benzene, etc.
Mention may be made of unsaturated aliphatic hydrocarbons and aromatic hydrocarbons.

The volume ratio of hydrocarbon A and hydrogen gas B is A/B.
It can be used in a wide range of = 1000 to 0.001. However, from the viewpoint of preventing precipitation of graphitic carbon, the upper limit is preferably 10 or less.

The temperature of the substrate needs to be in the range of 300-1300°C. If it is lower than 300°C, hydrogen may be mixed into the precipitated diamond, and if it exceeds 1300°C, there is a drawback that the precipitated diamond undergoes reverse transformation into graphite. The most preferred range is 500-1200
It is ℃. The microwave is 300MHz as mentioned above.
~1000 GHz, and the microwave output range is preferably as described above.

The pressure inside the tube that generates microwave plasma is 0.05 to 0.05 to keep the plasma stable.
Preferably it is 400 Torr. Further, in order to uniformly deposit diamond over the entire surface of the substrate, it is desirable to rotate the substrate support, and the rotation speed may be one or more rotations per hour.

Next, the first aspect of the apparatus for carrying out the method of the present invention will be described.
This will be explained based on the diagram. FIG. 1 is a schematic diagram showing this aspect. In the figure, 1 is a gas supply device, 10,
Reference numerals 11 indicate valves provided on the hydrocarbon gas and hydrogen gas supply pipes, respectively, and 12 indicates a valve provided on the mixed gas supply pipe. 3 and 5 are microwave oscillators, and the microwaves are guided into the reaction chamber 7 through waveguides 4 and 6, respectively. 8 is a substrate, 9 is a support stand, 2 is an exhaust device, 13 is an exhaust valve, and 14 is a microwave absorber.

After placing the substrate 8 on the support stand 9 in the reaction chamber 7, the exhaust device 2 is activated to reduce the pressure in the reaction chamber 7, and the valves 10, 11, 12, and 13 are adjusted to remove hydrogen gas and carbonization. The hydrogen flow rate and the pressure inside the reaction chamber are maintained at predetermined values. Next, the microwave oscillators 3 and 5 are activated with predetermined outputs to generate plasma in the reaction chamber 7 through the waveguides 4 and 6, and to heat the substrate 8. The temperature of the substrate 8 can be controlled by using the microwave absorber 14 or the support 9 with a coolant such as water.

Example 1 Using the apparatus shown in FIG. 1, a silicon wafer was used as the substrate 8, and methane and hydrogen were used as the gases. Place the silicon wafer on the support stand 9,
The exhaust device 2 was operated to reduce the pressure in the reaction chamber 7. Next, hydrogen and methane were supplied from the gas supply device 1 at flow rates of 50 c.c. and 1 c.c. per minute, respectively, and the pressure in the reaction chamber 7 was adjusted to 40 Torr by adjusting the valve 13.
Next, the frequency of the microwave oscillator 5 is 2.45GHz,
A non-polar discharge is generated with an output of 800 W, and the waveguide 6 excites the gas guided into the reaction chamber.A non-polar discharge is generated with a frequency of 2.45 GHz and an output of 400 W from the microwave oscillator 3, and the wave guide 4 causes a non-polar discharge to be generated. The substrate 8 was introduced into a reaction chamber and heated to 900°C. After 3 hours of precipitation, diamond particles of about 10 μm were deposited on the substrate 8. No disordered carbon structure or carbon bonded to hydrogen was optically observed in the diamond particles.

Example 2 Using the apparatus shown in Fig. 1, a silicon wafer with diamond powder scratches was used as the substrate 8, and methane and hydrogen were used as gases. Supplied with flow rate,
The pressure inside the reaction chamber 7 was set at 30 Torr. The microwave oscillator 5 was operated at a frequency of 2.45 GHz and an output of 1 kW, and the microwave oscillator 3 was operated at a frequency of 2.45 GHz and an output of 500 W, and the temperature of the substrate was set at 930° C. by passing water into the support stand. After 50 hours of precipitation, a diamond film with a thickness of approximately 30 μm was deposited on the substrate. No disordered carbon structure or carbon bonded to hydrogen was optically observed in the diamond film.

According to the method of the present invention, two waveguides for introducing microwaves are used, one waveguide introduces microwaves suitable for excitation dissociation of gas to generate plasma, and the other waveguide generates plasma. In order to maintain the plasma and the substrate temperature at a temperature suitable for diamond synthesis, conditions suitable for diamond synthesis can be adjusted very appropriately. Therefore, it has an excellent effect of depositing high quality diamond on the substrate.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an apparatus for carrying out the method of the invention. 1: gas supply device, 2: exhaust device, 3, 5: micro oscillator, 4, 6: waveguide, 7: reaction chamber,
8: Substrate, 9: Support stand, 10, 11, 12, 1
3: Valve, 14: Microwave absorber.

Claims (1)

[Claims] 1. In a method for depositing diamond on a substrate using microwave non-polar discharge of a mixed gas of hydrogen and hydrocarbon, two waveguides for introducing microwaves are used, and one of the waveguides is A high-power microwave is introduced to efficiently excite and dissociate gas, and plasma is generated.The plasma is maintained in the other waveguide, and the substrate temperature is maintained at 300-1300℃, which is suitable for diamond synthesis.
A method of synthesizing diamond characterized by oscillating microwaves with an output that is maintained at a temperature of 100 mL and introducing it through a waveguide to generate plasma and depositing diamond on a substrate. 2. The method of synthesizing diamond according to claim 1, wherein the temperature of the substrate is controlled by disposing a cooling material or a microwave absorbing material around the substrate.