JPS62278193A - Vapor-phase synthesis of crystalline carbon - Google Patents

Abstract

PURPOSE:To increase the rate of crystal growth of a crystalline carbon in a vapor-phase synthesis of crystalline carbon, by using a carbonaceous raw material consisting of a polar organic substance containing F element in the molecule. CONSTITUTION:A polar organic substance containing F element in the molecule is used as a carbonaceous raw material in the vapor-phase synthesis of crystal line carbon. The polar organic substance is a fluorinated organic substance expressed by general formula ClHmFn (l, m and n are integers of >=1, >=3 and >=1, respectively) e.g. CH3F. The cost of vapor-phase synthesis of a crystalline carbon can be reduced by the above process since the decomposition of the polar organic substance proceeds with a slight microwave or high-frequency power even by using a conventional universal apparatus.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for vapor phase synthesis of crystalline carbon such as 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 focused on the high thermal conductivity and the possibility of using it as a semiconductor by doping with impurities. The latter characteristic has also been applied to electronic technology fields such as semiconductor devices, and techniques for forming diamond films 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, microwaves emitted from a microwave irradiation device 1 are guided into a reaction chamber 3 through a waveguide 2. In FIG. On the other hand, H2 supply device 5
A predetermined amount of H, gas, and CH4 gas are respectively discharged from the CH4 supply device 6 and mixed at a predetermined ratio (for example, CH41%).
-H299%) is supplied to the reaction chamber 3 via the supply pipe 7.
supplied within. On the other hand, the inside of the reaction chamber 3 is brought to a predetermined pressure (for example, 40 to 50 Torr) by suctioning and exhausting a predetermined amount of the mixed gas (8 indicates an exhaust device). A support stand 11 fixed at a predetermined position by a support rod 10 is provided in the reaction chamber 3.
A substrate 15 for diamond deposition on Si is placed above.

A microwave-like vibration is generated in the reaction chamber 3 to which the mixed gas is supplied in this way! ! ] When radio waves are introduced, the mixed gas component molecules are decomposed into atoms, ions, and radicals by high-energy electrons, and a steady plasma is generated in the reaction chamber 3. The substrate 15 is placed in a plasma generation region, and diamond crystals are deposited on the substrate 15 using carbon in the mixed gas as a raw material. Depending on the type of substrate 15 and processing conditions, different forms such as microcrystals or thin films can be obtained, while crystalline diamond can be obtained by changing the mixing ratio of the mixed gas.

Crystalline carbon with different crystal structures such as diamond-like crystals and graphite can be obtained. In the figure, reference numeral 13 denotes a reflecting plate, which serves to reflect the microwaves diffused within the reaction chamber 3.

As another example of a diamond gas phase synthesis apparatus, a technique using high frequency as shown in FIG. 2 has also been developed.

In this technique, a high frequency power source 20 is used in place of the microwave irradiation device 1 shown in FIG. It is. Other basic principles are the same as the technique shown in FIG. 4, and corresponding parts are given the same reference numerals to avoid redundant explanation.

[Problems to be Solved by the Invention] In addition to the above-mentioned methane (CH4), acetylene,
Hydrocarbons such as ethylene, ethane, benzene, etc. were commonly used. This is because when the above hydrocarbons are used, the byproducts of the plasma reaction that progresses in the reaction chamber are limited to hydrogen, carbon, hydrocarbons, etc., and these are not highly toxic or corrosive and can be disposed of. This is because of the negative reason that gas treatment is easy. In addition, the lattice defects of crystalline carbon growing on the substrate are limited to hydrogen atoms and those that are about the size of hydrogen molecules, and they have a large effect on the crystal structure of the crystalline carbon. This is because it is expected that there will be no.

However, when the above-mentioned hydrocarbons are used as carbon raw materials, there is a problem that the crystal growth rate of crystalline carbon is slow. That is, in the above gas phase synthesis method, the interaction between hydrocarbon molecules and high-energy electrons, especially the collision between electrons and molecules due to short-range interaction, contributes to plasma generation. In this case, the reactive collision cross section will be small and the generation efficiency of atoms, ions, and plasma species necessary for crystalline carbon will be low.

The present invention was made to solve the problems of the prior art, and its purpose is to provide a vapor phase synthesis method that increases the crystal growth rate of crystalline carbon. be.

[Means for Solving the Problems] The structure of the present invention that can solve the above problems is that in vapor phase synthesis of crystalline carbon, a polar organic substance containing F element in the molecule is used as a carbonaceous raw material. The gist lies in the way it is used.

[Function] The present invention is configured as described above, but the point is that the crystal growth rate of crystalline carbon is increased by vapor phase synthesis using a polar organic substance containing F element in the molecule as a carbonaceous raw material. That's what I got. Here, the above-mentioned polar organic substance is a general term for fluorinated organic substances represented by the general formula C2HmFn (u, m, and n are integers such as 1≧2, m≧3, and n≧1), such as CH3F. It is something to do.

The polar organic material selected in the present invention has a large dipole moment. For example, the dipole moment of CH3F is
It is 1.85xlO-1aesu-cm. The interaction energy between an electron and a dipole moment is proportional to γ-2, where γ is the electron-dipole moment distance.

The above-mentioned polar organic substance has a relatively large interaction, so its dissociation rate is higher than that of general hydrocarbons. Furthermore, since the polar organic substance contains F atoms with a large atomic radius in the molecule, the electron collision cross section is also large, which has the advantage that molecular elucidation is promoted accordingly.

On the other hand, the dissociated F atoms are exhausted as HF, F2 molecules or other organic molecules through a side reaction. Under normal processing conditions, only a very small amount of the polar organic substance is consumed, so the F atoms exhausted as described above can be easily and sufficiently removed by normal adsorption processing, chiller processing, etc. Furthermore, since the atomic radius of F atoms is large, the amount of F atoms incorporated into crystalline carbon is extremely small.

Although the present invention uses the polar organic substance described above as a carbon raw material, there is no need for special equipment to carry out the method of the present invention, and basically the method shown in FIGS. 1 and 2 is used. The device shown may be used.

That is, instead of the CHa supply device 6, a polar organic substance such as CH3F may be supplied into the reaction chamber 3 alone or together with H2 gas at a predetermined mixing ratio. When the method of the present invention is carried out, dissociation of polar organic substances proceeds with a small amount of microwave or high-frequency power even with conventionally used general equipment. Cost reduction can be achieved.

[Example 1] A diamond thin film crystal growth experiment was conducted using a microwave CVD apparatus.

Using CH4 gas and CH3F gas as carbonaceous raw materials,
Each case was compared. Note that the carbonaceous raw material gas is H2
The mixture was diluted to 1% and used as a mixed gas for gas phase synthesis.

The mixed gas flow rate is 100 S CCM (Standard
dCubic Centimeter) and reaction chamber 3.
The internal pressure was kept at 40 Torr, and the microwave power was 3
It was set to 00w. As the substrate 15, surface-treated S
An i-wafer was used, and the substrate temperature during device operation was 850°C.

After forming a diamond thin film on the substrate 15 for 6 hours in this manner, SEM (ScanningE
The cross section of the thin film was observed using an electron microscope.

When the film thickness was measured at five locations, CH
The average film thickness when using 4 gases was 2.1 μm, while the average film thickness when using CH3CfL was 2.1 μm.
It was 4 μm.

It is clear from this result that CH3 is used as a carbonaceous raw material.
It is understood that when F gas is used, the crystal growth rate increases by about 19% compared to when conventionally used hydrocarbons (CH4, etc.) are used.

[Effects of the Invention] As described above, according to the present invention, by employing the above-described configuration, a vapor phase synthesis method in which the crystal growth rate of crystalline carbon is increased can be realized.

[Brief explanation of drawings]

7jS1 and FIG. 2 are schematic explanatory diagrams showing examples of vapor phase synthesis and storage. 1...Microwave irradiation device 2...Waveguide 3...Reaction chamber 15...Substrate 2o...High frequency power supply personnel Kobe Steel, Ltd.

Claims (1)

[Claims] A method for vapor phase synthesis of crystalline carbon, characterized in that a polar organic substance containing element F in its molecule is used as a carbonaceous raw material.