JPS63117994A - Device for synthesizing diamond in vapor phase - Google Patents

Abstract

PURPOSE:To reduce the cost required for the synthesis of diamond by synthesizing diamond in a vapor phase while introducing a gaseous mixture of a carbon dioxide and hydrogen into the title vapor-phase synthesis device. CONSTITUTION:The microwave transmitted from a magnetron oscillator 1 is passed through an isolator 2, power monitor 3, tuner 4, and waveguide 5 in the order described, and then projected on a substrate 7 set in a reaction tube 6 made of quartz and pierced through the waveguide 5. A metallic material such as Ta, Co, W, Mo, etc., can be used for the substrate 7, however an Si wafer is generally used as the substrate. The substrate 7 is arranged at a specified position by a holder 9 made of quartz. The gaseous mixture of the carbon dioxide and hydrogen is introduced into the reaction tube 6 from the reaction tube inlet 11 side. A specified amt. of the introduced gaseous mixture is sucked and exhausted from an exhaust port 13 side, and the inside of the reaction tube 6 is kept at a preset pressure. The substrate 7 is arranged in a plasma producing region 14, and the diamond crystal is deposited on the substrate 7 with the carbon in the gaseous mixture as the raw material.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for vapor phase synthesis of diamond.

[Prior Art] Diamond has long been widely used mainly in cutting tools because of its high hardness. On the other hand, in recent years, attention has been paid to its high thermal conductivity and its potential to be used as a semiconductor by doping with impurities. The application of diamond has been studied, and the latter property has also been applied to the field of electronic technology such as semiconductor devices, and techniques for forming diamond are being rapidly developed.

The synthesis method for diamond uses graphite as a carbon raw material,
40,000 to 70,000 atmospheres using Ni, Cr, Mn, etc. as a catalyst, 10
A high-pressure method is known in which synthesis is carried out at high temperatures and pressures of 00 to 2000°C, but gas phase synthesis methods have also been developed in which gaseous hydrocarbons are used as carbon raw materials and carried out under low-pressure conditions. It has been pointed out that the disadvantage of diamond synthesis using the vapor phase synthesis method is that the diamond crystals are smaller compared to the high-pressure method. The advantage that it is easy to form has attracted attention, and it is positioned as a useful technology.

FIG. 1 is a schematic diagram showing an example of a diamond vapor phase synthesis apparatus. The device is a technology that applies microwaves, and its outline is as follows.

In FIG. 1, a microwave (2.45 GHz) emitted from a magnetron oscillation 811 is guided through an isolator 2, a power monitor 3, a tuner 4, and a waveguide 5 in the order shown. A substrate 7 placed in a quartz reaction tube 6 which is provided through it is irradiated. Although a metal material such as Ta, Co, W, or Mo may be used as the substrate 7, generally a Si wafer is used, and the substrate 7 is placed at a predetermined position by a support base 9 made of quartz. ing. Inside the reaction tube 6 is a reaction tube inlet 11.
From the side, a mixed gas of H2 gas and CH4 gas mixed at a predetermined ratio (for example, CH41%-H299%) is about 100%
CCM (Standard CubicCenti
meters per minute).

A predetermined amount of the introduced mixed gas is suctioned and exhausted from the exhaust port 13 side, and the inside of the reaction tube 6 is maintained at a predetermined pressure (for example, 40 to 50
Torr).

When oscillating radio waves (approximately 300 W) such as microwaves are introduced into the reaction tube 6 into which the mixed gas is supplied in this way, the mixed gas component molecules are converted into atoms, ions, and radicals by high-energy electrons. It is decomposed and a steady plasma is generated in the reaction tube 6. The substrate 7 is placed in the plasma generation region 14, and diamond crystals are deposited on the substrate 7 using carbon in the mixed gas as a raw material. and board 7
Depending on the type of diamond and processing conditions, diamonds can be obtained in different forms, such as microcrystals or thin films.

In the diamond vapor phase synthesis apparatus shown in FIG. 1, if a Si wafer is used as the substrate 7, the substrate temperature will be approximately 850°C under the above-mentioned processing conditions, and a Crystalline diamond precipitates at a growth rate. Reference numeral 15 in FIG. 1 is a plunger, which is used to adjust the reflection of microwaves so that the substrate 7 is accurately located at the center of the plasma generation region 14.

A member designated by reference numeral 20 is an applicator, which functions to prevent the reaction tube 6 from being excessively heated by supplying cooling water from the supply pipe 21 and discharging it from the discharge pipe 22.

[Problems to be Solved by the Invention] In addition to the above-mentioned methane (C) (4), carbonized materials such as acetylene, ethylene, ethane, benzene, etc. Hydrogen was commonly used. This is because when the above-mentioned hydrocarbons are used, the byproducts of the plasma reaction that progresses in the reaction chamber are hydrogen and carbon.

This is because they are limited to hydrocarbons and the like, and these are not highly toxic or corrosive, and are easy to treat as waste gas.

However, although the above-mentioned hydrocarbons cannot be said to be expensive, they cannot be said to be cheap enough to be consumed in large quantities. Therefore, when these hydrocarbons are used in large quantities as carbon raw materials, the cost of raw materials becomes non-negligible.

An object of the present invention is to provide a vapor phase synthesis method that can reduce the cost required for diamond synthesis as much as possible.

[Means for Solving the Problems] The present invention, which has achieved the above object, uses carbon dioxide as a carbon raw material and feeds the mixed gas of carbon dioxide and hydrogen into a vapor phase synthesis apparatus in the vapor phase synthesis of diamond. This diamond vapor phase synthesis method has the key point of performing vapor phase synthesis while introducing diamond.

[Operations] Although the present invention is constructed as described above, the main feature is that carbon dioxide (CO2) is used as the carbon raw material. That is, as a result of various studies to find a carbon raw material that can be substituted for hydrocarbons and is cheaper than hydrocarbons, the present inventors found that C, which is cheaper than hydrocarbons, was found as a carbon raw material.
The present invention was completed by discovering that diamonds can be obtained using O2 gas in the same way as when using hydrocarbons.

On the other hand, when CH4 gas is used as a carbon raw material as described in the conventional technology, CH4 gas is diluted with H2 gas, but this H2 gas contains non-diamond materials such as graphite that are generated at the same time as diamond. It was used for its removal effect. That is, H
Atomic hydrogen produced by the decomposition of the two gases in plasma is more likely to bond with graphite than with diamond, and the graphite produced simultaneously with diamond during vapor phase synthesis is etched away by the atomic hydrogen. - In the power tree invention, H2 gas is required as is, and Co2 gas as a carbon raw material is diluted with H2 gas and introduced into the vapor phase synthesis apparatus. The mixing ratio of C02 gas and H2 gas is not limited in any way, but if the amount of H2 gas is too small (relatively too much C), non-diamond substances such as graphite will be likely to be generated. Considering this point, it is preferable that CO2/H2 is about 0.001 to 0.5.

As mentioned above, the present invention uses Co2 gas as a carbon raw material. When this CO2 gas is introduced into the hydrogen plasma atmosphere of a vapor phase synthesis apparatus, C is produced by the decomposition of 002 molecules, and this C is used to form diamonds. This will contribute to the growth of More preferably, C as the carbon raw material
When using 02 gas, the oxygen atoms and ion species generated by the decomposition of CO2 are highly reactive with non-diamond substances, and non-diamond substances can be removed more efficiently than in the conventional case. It also has the effect of

In carrying out the method of the present invention, there is no need to separately provide any special equipment, and basically the equipment shown in FIG. 1 may be used. That is, in the apparatus shown in FIG. 1, instead of the mixed gas of cH4 + H2, a mixed gas of CO2 + H2 mixed at a predetermined ratio is used, and while the mixed gas is introduced into the reaction tube 6, gas phase synthesis is performed. do it.

[Example] The method of the present invention was carried out using the apparatus shown in FIG.

A mixed gas prepared by diluting Co2 gas with H2 gas to 10% by volume was supplied to the reaction tube 6 shown in FIG. 1 for gas phase synthesis. The flow rate of the mixed gas was 11,005 cc, the internal pressure of the reaction tube 6 was maintained at 4° Torr, and the output of the microwave was 350 W. As the substrate 7, a 0.5 mm thick S i (111) wafer polished for 1 hour with diamond paste of 10 μm (20×10 mm) was used.
), the plunger 15 was adjusted so that the substrate 7 was located approximately at the center of the plasma generation region 14. The substrate temperature during operation of the apparatus was 830°C.

After performing the synthesis reaction in this manner for 7 hours, the surface of the Si substrate was examined using a scanning electron microscope (SEM).

Scanning Electron Micro
When observed with a scope), it was confirmed that a diamond thin film with a thickness of about 2 μm had grown on the substrate 7.

[Effects of the invention] As described above, according to the present invention, CO2 is used as a carbon raw material.
By using gas, it became possible to obtain diamonds at a lower cost.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram showing an example of a diamond vapor phase synthesis apparatus. 1... Magnetron oscillator 5... Waveguide 6... Reaction tube 7... Substrate 14... Plasma generation region 15... Plunger Fig. 1

Claims (1)

[Claims] A method for vapor phase synthesis of diamond, characterized in that carbon dioxide is used as a carbon raw material, and gas phase synthesis is carried out while introducing a mixed gas of carbon dioxide and hydrogen into a vapor phase synthesis apparatus.