JPH0542398B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] 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.

A known method for synthesizing diamond is the high-pressure method in which graphite is used as a carbon raw material and Ni, Cr, Mn, etc. are used as catalysts at high temperatures and pressures of 40,000 to 70,000 atm and 1,000 to 2,000°C. A gas phase synthesis method using hydrocarbons as a carbon feedstock under low pressure conditions has also been developed. 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, predetermined amounts of H ₂ gas and CH ₄ gas are discharged from the H ₂ supply device 5 and CH ₄ supply device 6, respectively, and mixed at a predetermined ratio (for example, CH ₄ 1%-
H ₂ (99%) is supplied into the reaction chamber 3 via the supply pipe 7. 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, and a diamond deposition substrate 15 such as a Si wafer is placed on this support stand 11.

When oscillating radio waves such as microwaves are introduced into the reaction chamber 3 to which the mixed gas is supplied in this way, the mixed gas component molecules are decomposed into atoms, ions, and radicals by high-energy electrons. A steady plasma is generated within 3. The substrate 15 is arranged in a plasma generation region, and the substrate 1
Diamond crystals are deposited on 5 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 diamonds, diamond-like crystals, and diamond-like crystals can be obtained by changing the mixing ratio of the mixed gas. Crystalline carbon having a different crystal structure such as aite 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.

Other examples of diamond vapor phase synthesis equipment include:
Techniques using high frequencies as shown in FIG. 2 have also been developed. In this technique, a high frequency power source 2 is used instead of the microwave irradiation device 1 shown in FIG.
0 is used to conduct high frequency waves from a high frequency power source 20 to an operating coil 21 to generate high frequency plasma in the reaction chamber 3. 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 (CH ₄ ), as the carbonaceous raw material in the gas phase synthesis apparatus shown in FIGS.
Hydrocarbons such as acetylene, ethylene, ethane, benzene, etc. were commonly used. this is,
When the above hydrocarbons are used, the by-products from 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 cannot be treated as waste gas. This is for the negative reason that it is easy. Furthermore, the substances that are incorporated into the lattice defects, surfaces, grain boundaries, etc. of crystalline carbon that grows on the substrate are limited to hydrogen atoms and those that are about the size of hydrogen molecules, and have a large effect on the crystal structure of crystalline carbon. This is because it is expected that there will be no.

However, when the above-mentioned hydrocarbons were used as carbon raw materials, there was a problem that the crystal growth rate of crystalline carbon was 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 refers to _the general formula C _l H _n X _o (l, m, n are l≧2, m≧3, n≧1
This is a general term for fluorinated organic substances represented by (an integer).

The polar organic material selected in the present invention has a large dipole moment. For example, the dipole moment of CH ₃ F is 1.85×10 ⁻¹⁸ esu·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 large, which has the advantage that molecular dissociation is promoted accordingly.

On the other hand, the dissociated F atoms undergo side reactions.
Exhausted as HF, _F2 molecules or other organic molecules. 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. The device shown may be used. That is, instead of the CH ₄ supply device 6, a polar organic substance such as CH ₃ F may be supplied into the reaction chamber 3 alone or together with H ₂ gas at a predetermined mixing ratio. When the method of the present invention is carried out, the dissociation of polar organic substances proceeds with a small amount of microwave or high-frequency power even with conventionally used general equipment, so crystalline carbon is dissolved in the gas phase. Cost reduction in synthesis can be achieved.

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

CH ₄ gas and CH ₃ F gas were used as carbonaceous raw materials, and the respective cases were compared. The above carbonaceous raw material gas was diluted to 1% with H ₂ and used as a mixed gas for gas phase synthesis.

The mixed gas flow rate is 100SCCM (Standard Cubic
Centimeter), the internal pressure of the reaction chamber 3 was maintained at 40 Torr, and the microwave power was 300 W. As the substrate 15, a surface-treated Si wafer was used, and the substrate temperature during operation of the apparatus was 850°C.

After forming a diamond thin film on the substrate 15 for 6 hours in this manner, SEM (Scanning
The cross section of the thin film was observed using an electron microscope.
When the film thickness was measured at five locations, the average film thickness when CH ₄ gas was used as the carbonaceous raw material was 2.1 μm, whereas the average film thickness when CH ₃ F gas was used was 2.4 μm. It was hot.

It is clear from this result that when CH ₃ F gas is used as a carbonaceous raw material, compared to the case where conventionally used hydrocarbons (CH ₄ etc.) are used,
It is seen that the crystal growth rate increases by about 19%.

[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]

FIG. 1 and FIG. 2 are schematic explanatory diagrams showing an example of a vapor phase synthesis apparatus. 1... Microwave irradiation device, 2... Waveguide, 3
...Reaction chamber, 15...Substrate, 20...High frequency power supply.

Claims (1)

[Claims] 1. A method for vapor phase synthesis of crystalline carbon, which is characterized in that a polar organic substance containing element F in its molecule is used as a carbonaceous raw material.