JPH0524982A - Vapor phase synthesis method for diamond - Google Patents

Abstract

PURPOSE:To stably synthesize diamond of quality mixed with no electrode material, at the time of precipitating diamond by a vapor phase shythesis method by d.c. arc discharge, by using an inert gas contg. no hydrogen as a discharge gas. CONSTITUTION:The inside of a vacuum tank 13 is deposited with a water cooling type substrate holder 12 fitted with a substrate 11 together with a plasma torch 1 having an anode 2 and a cathode 3. A discharge gas feed port 4 of the plasma torch 1 is fed with an inert gas 6 such as Ar contg. no hydrogen as a discharge gas, and voltage is impressed on the space between the anode 2 and the cathode 3 by a d.c. power source 8 to generate a plasma jet 9 in a stable condition. At the same time, the plasma jet 9 is fed with a mixed gas 7 of a carbon-contg. gas such as methane and a hydrogen gas from a gas feed port 5 on the anode nozzle part. By using the inert gas such as Ar contg. no hydrogen as a discharge gas, discharge power is stabilized, and diamond 10 of quality can be formed on the surface of the substrate 11 without the fusion of electrode material such as copper in the plasma torch 1 at a high speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for vapor phase synthesis of diamond, and more particularly to a method for vapor phase synthesis of diamond capable of depositing high quality diamond at high speed.

[0002]

2. Description of the Related Art There are various vapor phase synthesis methods of diamond, but a thermal plasma CVD method aiming at a high deposition rate is described in JP-A-62-158195. Further, among the above thermal plasma CVD methods, a direct current thermal plasma CVD method is described in Japanese Patent Application Laid-Open No. 64-33096 as a specific method limited to the use of direct current.

An apparatus used for the DC thermal plasma CVD method is usually "Seiichiro Matsumoto: Diamond Synthesis by Thermal Plasma CVD Method, New Diamond Magazine, No. 8, VO".
l. 4, No. 1, p26 (1988) (published by New Diamond Forum) ”is used. This device basically has a plasma torch having a nozzle-shaped anode and a water-cooled substrate holder. Then, argon gas and hydrogen gas are supplied between both electrodes of the plasma torch to cause discharge, and a hydrocarbon gas such as methane gas is supplied from the middle of the nozzle of the plasma torch to obtain a plasma jet, which is water-cooled as described above. By applying the plasma jet to the substrate placed in close contact with the substrate holder, diamond is deposited on the substrate and synthesized.

Under the synthesis conditions of the DC thermal plasma CVD method, important parameters are gas composition, discharge power,
There are the chamber internal pressure, the distance between the plasma torch and the substrate, the substrate temperature, etc., and it is necessary to optimize the above parameters in order to synthesize high quality diamond at high speed. The parameters are not independent of each other but affect each other. For example, when the discharge power or the chamber internal pressure is changed in a certain gas composition, the length of the plasma jet is changed, so that the specific cooling condition and the substrate temperature at a specific position are changed. Therefore, it is important to stabilize the above parameters during diamond synthesis.

[0005]

However, the diamond synthesis by the above-mentioned DC thermal plasma CVD method has a problem that the discharge power is likely to be unstable. If the fluctuation range of the discharge power is large, it exceeds the control range of the power supply, and the discharge is stopped or the power rises, resulting in a runaway state. However, usually
Even in the event of a runaway condition, the safety device can prevent the plasma torch from being destroyed. If the fluctuation range of the discharge power is large, the plasma jet becomes unstable and the quality of the obtained diamond deteriorates. This problem is more likely to occur when the power is increased for the purpose of increasing the deposition area of diamond than when the power is low, because the substrate temperature is more likely to change, and the quality of the precipitate is more likely to deteriorate.

If the discharge power is unstable, the electrode material of the plasma torch such as copper is likely to melt or evaporate and mix into the synthesized diamond. Therefore, a method of stabilizing the discharge voltage by setting the chamber internal pressure to 30 torr or less is proposed in Japanese Patent Application Laid-Open No. 2-55296.

Further, as a method of stabilizing the discharge voltage without lowering the pressure in the chamber, it is usually composed of hydrogen and argon which are supplied between the electrodes of the plasma torch.
A method of completely mixing discharge gases of at least one kind in advance has been proposed by the applicant in Japanese Patent Application No. 2-3060.

However, in any of the above methods, since hydrogen, which is more difficult to discharge than an inert gas such as argon, is discharged, the discharge power tends to be more unstable than when an inert gas such as argon is discharged. There was a problem.

The present invention has been made in view of the conventional problems as described above, and an object thereof is to make it possible to manufacture a high-quality diamond in which discharge power is stable and electrode materials are not mixed. It is intended to provide a vapor phase synthesis method of diamond.

[0010]

According to the present invention, a plasma torch has an anode and a cathode, and a gas supplied between the electrodes is turned into plasma by a discharge between the electrodes to obtain a plasma jet containing a carbon source material. In a vapor phase synthesis method by direct current arc discharge in which a plasma jet is applied to a substrate to synthesize diamond, a gas containing no hydrogen and containing an inert gas is used as a discharge gas supplied between electrodes, and It is characterized in that hydrogen gas is excited and decomposed separately from the discharge gas.

Further, as one means for exciting and decomposing the hydrogen gas separately from the discharge gas, the hydrogen gas is provided in at least one of the anode nozzle part inside the plasma torch or the plasma jet part generated from the plasma torch. To supply.

Argon or helium is preferably used alone as the inert gas used as the discharge gas. In addition, the carbon source gas can be supplied to at least one of the space between the electrodes, the anode nozzle portion, or the atmosphere of the plasma jet. As the carbon source gas, at least one of a hydrocarbon gas such as methane and ethane, carbon monoxide, carbon dioxide, and an organic compound containing an oxygen atom such as acetone and ethanol can be used.

The substrate on which the plasma jet is applied to synthesize diamond is placed in close contact with a water-cooled substrate holder.

In the present invention, the synthesis conditions such as gas composition, discharge power, chamber pressure, substrate temperature and the like can be the same as in the normal DC thermal plasma CVD method, but hydrogen is efficiently excited and decomposed. For this purpose, the discharge power is preferably 5 KW or higher, more preferably 10 KW or higher, though it depends on the device.

[0015]

In the conventional direct-current thermal plasma CVD method, hydrogen, which is more difficult to discharge than argon, is discharged, so that the discharge power is more likely to be unstable than when argon is discharged. On the other hand, in the present invention, the discharge power becomes stable because hydrogen or the like is discharged and argon or the like is discharged. On the other hand, hydrogen is thermally excited and decomposed by being added to plasma of high temperature argon or the like at the anode nozzle portion or plasma jet portion in the plasma torch, and is rapidly mixed with the plasma. Therefore, the resulting plasma jet is in the same state as the plasma jet when hydrogen and argon are discharged and before reaching the substrate, and diamond can be similarly synthesized. A method for synthesizing diamond by thermally exciting and decomposing hydrogen and carbon sources is disclosed in Japanese Examined Patent Publication 63
The hot filament method described in JP-A-53159 is well known.

[0016]

EXAMPLES The present invention will now be described in detail based on examples, but the present invention is not limited thereto. EXAMPLE FIG. 1 is a schematic diagram for explaining a vapor phase synthesis apparatus for diamond by DC arc discharge used in the present invention. In the figure, 13 is a vacuum chamber, and inside the vacuum chamber 13,
A water-cooled substrate holder 12 to which a substrate 11 is attached is provided together with a plasma torch 1 having an anode 2 and a cathode 3, and cooling water 14 is injected into the substrate holder 12.

Further, 4 is a discharge gas supply port to which the discharge gas 6 is supplied, 5 is an anode nozzle part gas supply port to which the anode nozzle part supply gas 7 is supplied, 8 is a DC power supply, 9 is a plasma jet, and 11 is Diamond, 15 is exhaust gas.

This apparatus is basically the same as a generally known apparatus, but is manufactured so that argon can be supplied as a discharge gas 6 and hydrogen and methane can be supplied as an anode nozzle portion supply gas 7 by a gas supply device (not shown). did.

With this apparatus, synthesis was performed under the following conditions. (Synthesis conditions) Discharge gas: Argon gas 451 / min Anode nozzle supply gas: Hydrogen gas 201 / min, Methane gas 1.01 / min Gas flow control: Mass flow controller manufactured by STEC Co., Ltd. Discharge power: 15 kW Discharge voltage: 30 V Chamber Internal pressure: 150 torr Distance between plasma torch and substrate: 66 mm Substrate: 25 mm x 25 mm x 3 mm molybden metal plate,
Niraco Co., Ltd. Synthesis time: 20 minutes As a result of synthesis under the above conditions, the fluctuation range of discharge power is ± 0.
It was 3 kW. The appearance of the compound obtained on the substrate was a gray color close to white and reflected light well, and had an area of about 15 mm in diameter. X-ray diffraction, laser Raman spectroscopy, and S
When evaluated using EM, the film thickness is 50 over the entire area.
It was confirmed that the film was a polycrystalline film of cubic diamond with a thickness of μm, and there were almost no peaks other than diamond in laser Raman spectroscopy, and it was found that the obtained diamond was of good quality. Further, when the surface of this film was observed using an optical microscope, no metal or the like was found to be mixed. Furthermore, when a portion of 10 ml of an ammonium persulfate aqueous solution in which this substrate was immersed was taken and examined by an atomic absorption method, copper was not detected at a detection sensitivity of 0.01 ppm or less. Comparative Example Basically the same as the device used in the example, but the gas supply device was changed and argon gas 451 / was used as the discharge gas.
Min, hydrogen gas 201 / min, methane gas 1.01 / min as the supply gas for the anode nozzle, and discharge voltage 73 V, except that the synthesis was performed under the same conditions as in the example. As a result, the fluctuation range of the discharge power was ± 1.9 KW. Further, the appearance and the area of deposition of the obtained compound on the substrate were the same as those in the examples. When this composite was evaluated using X-ray diffraction, laser Raman spectroscopy, and SEM, it was found to be a high-quality diamond as in the example except that the film thickness at the outer periphery of a few mm was reduced to 30 μm. . Further, as a result of observing the surface of this film with an optical microscope, a dozen or more contaminants considered to be metals were found. Furthermore, when an aqueous solution obtained in the same manner as in the example was examined by an atomic absorption method, 0.7 ppm of copper was detected. It is considered that the copper, which is the anode material, was melted and mixed into the film.

[0020]

According to the method for synthesizing diamond in the vapor phase of the present invention, the discharge power becomes stable and it is possible to synthesize high-quality diamond without the inclusion of electrode materials and the like.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a diamond synthesizing apparatus by DC arc discharge according to an embodiment of the present invention.

[Explanation of symbols]

1 plasma torch 2 anode 3 cathode 4 Discharge gas supply port 5 Anode nozzle gas supply port 6 discharge gas 7 Anode nozzle supply gas 8 DC power supply 9 Plasma jet 10 diamonds 11 board 12 Water-cooled substrate holder 13 vacuum chamber 14 cooling water 15 exhaust gas

Claims (2)

[Claims] 1. A plasma torch has an anode and a cathode, a gas containing no hydrogen and containing an inert gas is used as a discharge gas supplied between the electrodes, and the hydrogen gas is the discharge gas. A method for vapor phase synthesis of diamond by direct current arc discharge characterized by being separately excited and decomposed. 2. A means for exciting and decomposing hydrogen gas supplies the hydrogen gas to at least one of an anode nozzle part inside a plasma torch or a plasma jet part generated from the plasma torch. The method for vapor phase synthesis of diamond according to claim 1.