JPH0341436B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for synthesizing diamonds in the form of films, particles, etc. from organic carbon compounds by a gas phase method.

Conventional technology The gas phase method for synthesizing diamond involves mixing hydrogen gas with an organic carbon compound, which is excited or decomposed using heat, electron beams, ion beams, microwaves, radio frequency waves, etc., to produce atomic hydrogen, Hydrocarbon radicals and the like are generated and guided to a heated substrate, where the decomposed carbon atoms are precipitated into a diamond structure. Most conventional raw material gases are hydrocarbons, but
A mixture of CO gas has also been proposed (Japanese Unexamined Patent Publication No. 60-191097) Problems to be Solved by the Invention In vapor phase diamond synthesis, the carbon produced by the decomposition of organic carbon compounds is diamond and non-diamond carbon. (hereinafter referred to as non-diamond carbon). Non-diamond carbon is then removed by atomic hydrogen. Diamond hardly reacts with atomic hydrogen, so it remains as is. This action of precipitation of diamond and non-diamond carbon and removal of diamond carbon is repeated to grow diamond. Therefore, unless the removal action of non-diamond carbon is sufficient, the rate of diamond formation cannot be accelerated. Conventional products using hydrocarbons as raw materials often yield products containing a mixture of diamond and diamond carbon because the removal action of this non-diamond carbon is not sufficient. Also, a mixture of hydrocarbons and CO gas does not have a sufficient effect of removing non-diamond carbon.

Diamond crystals synthesized by the vapor phase method are generally a mixture of (111) and (100) crystals. The properties of diamond differ depending on the orientation of the crystal.
For example, materials grown on the (111) plane have densely packed atoms, high Vickers hardness, and are less likely to cause chemical reactions. In the conventional method using hydrocarbon and hydrogen as raw material gases, it was difficult to control the crystal growth direction of the produced diamond.

An object of the present invention is to provide a diamond synthesis method that makes it possible to accelerate the precipitation rate of diamond, increase the diamond purity of the precipitate, and furthermore, make it possible to control the orientation of diamond crystals.

Means and Effects for Solving the Problems The present invention achieves the above object by mixing water with an organic carbon compound, hydrogen, or a mixed gas thereof as raw materials in vapor phase diamond synthesis.

Organic carbon compounds used as raw materials include methane, ethane,
Hydrocarbons such as propane, butane, pentane, ethylene, acetylene, microhexane, alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, dimethyl alcohol, allyl alcohol, acetone, ethyl methyl ketone,
Ketones such as diethyl ketone and acetophenone,
Esters such as methyl acetate and ethyl acetate, aldehydes such as formaldehyde and acetaldehyde, and other nitrogen-containing compounds such as methylamine, ethylamine, trimethylamine, and halogen-containing compounds can also be used. In the vapor phase diamond synthesis method, it is thought that carbon from the generated methyl groups tends to form a diamond structure, and in this sense, it is preferable that the raw material gas be decomposed to generate methyl groups.

Conventionally, most of the raw material gases used were hydrocarbons, but according to research by the present inventors, diamonds can be produced from oxygen-containing organic compounds, nitrogen-containing organic compounds, etc. mentioned above at a faster rate than before. I understand, so I applied for a patent (patent application 1986-264519).

As a result of further research, the present invention was made based on the fact that mixing water with the above-mentioned hydrocarbons, oxygen-containing organic compounds, etc. is more effective for diamond synthesis.

By adding moisture to the raw material gas, diamond can be deposited at a faster rate. This is because moisture increases the removal effect of the diamond carbon precipitated, so that even if the supply amount and energy of the raw material gas are increased and the total amount of precipitation is increased, only the diamonds can remain. This also means that diamonds of high purity can be produced. The mechanism of the carbon removal effect of water is not clear, but it is due to the hydrogas reaction between water vapor and carbon (C + H ₂ O
→CO+H ₂ ) can be considered as one mechanism. As mentioned above, a method of mixing CO gas with the raw material gas is known, but since the hydrogas reaction does not occur with CO gas, it is thought that H ₂ O and CO gas have completely different effects on carbon.

It is appropriate to determine the amount of water added based on the hydrogen in the carrier gas. According to experiments, the ratio of hydrogen to water is the gas volume ratio: H ₂ O/H ₂ =
0.0001 to 0.1 is suitable.

Therefore, water is added to the raw material gas so that it falls within this range. If the water content is less than the above range, there will be little effect, while if it is too much, not only will the speed of diamond precipitation slow down, but the precipitated diamond will become immersed.

The ratio of water to hydrogen is as described above, but the ratio of organic carbon compound to hydrogen gas is suitably 0.0001 to 1 (organic carbon compound/hydrogen) in terms of gas volume ratio.

In the present invention, conventionally known methods can be used as they are for steps other than the use of water.
To explain the outline, first, the gas is heated to 1500 to 2500℃.
By passing through a thermal filament that has been heated to a certain degree, or by turning it into plasma using microwaves, high frequency waves, etc., and further by irradiating electron beams, ultraviolet rays, etc., atomic hydrogen, methyl radicals, and their ions can be brought into a so-called excited state. is necessary. As mentioned earlier, the role of hydrogen gas in this case is to remove the precipitated non-diamond carbon, and for that purpose, it is necessary to convert hydrogen into atomic hydrogen and bring it into contact with the precipitated non-diamond carbon. is necessary. Therefore, it is essential to bring the hydrogen gas into an excited state such as atomic hydrogen. On the other hand, it is believed that organic carbon compounds decompose and the non-diamond carbon is precipitated as diamond through methyl groups in the middle. Therefore, when depositing diamond on a substrate, the organic carbon compound must be mixed with hydrogen gas. It is also possible to decompose the organic carbon compound into diamond near the base material or on the base material surface without excitation. This means that if the organic carbon compound can be decomposed on the surface of the substrate depending on the temperature of the substrate, it is not necessarily necessary to decompose the organic carbon compound using the above-mentioned thermal filament or plasma.

In the present invention, generally, an organic carbon compound and water are mixed in the form of a gas, and then hydrogen gas is mixed with the gas to lead to the above-described excitation zone.

However, as described above, only hydrogen gas may be excited, and other gases may be supplied into the diamond precipitation apparatus without passing through the excitation zone, and guided onto the base material.

Diamond deposition takes place on the substrate. The base material is a substrate of Si, W, Mo, etc., or SiC,
Particulate materials such as Si are used. In the case of a Si substrate, a mirror-polished one or one whose surface has been scratched with diamond fine powder is suitable. Base material is 300~
Heated to 1000℃. When a gas is excited with a thermal filament, the radiant heat often brings the temperature of the base material into the above-mentioned temperature range. A heating mechanism can also be separately attached to the base material.

When depositing diamond, the position of the substrate must be such that the excited hydrogen comes into contact with the non-diamond carbon before it loses its excited state, and for this the distance between the substrate and, for example, in the case of a thermal filament, must be It is better to be as small as possible, and although it depends on the temperature of the thermal filament, 5 mm or less is generally suitable. The substrate may be rotated slowly to uniformly deposit the diamond on its surface.

In the present invention, the gas pressure when depositing diamond can be varied over a wide range, which is also one of the features of the present invention. According to experiment 30Torr
The diamond growth rate hardly changes from 1000 Torr to 1000 Torr. Therefore, it is a great advantage of the present invention that it can be carried out at normal pressure (760 Torr).
The amount of gas supplied is organic carbon compound gas, water vapor,
Diamond precipitation surface 1cm ³ with hydrogen gas mixture
0.1 to 100c.c./min is appropriate.

The shape of the diamond obtained by the present invention varies depending on the type of substrate, etc. If a mirror-polished silicon (Si) substrate is used, granular diamonds will precipitate, and this mirror-polished surface can be coated with diamond paste or the like. If the surface is polished and scratched, it becomes a membrane diamond. Furthermore, when a granular base material such as SiC is used, diamond particles are deposited on the surface of the granule at intervals or in contact with each other. The diamond deposition rate is higher than that of conventional methods because the method of the present invention has a greater ability to remove non-diamond carbon, and in the case of film-like diamond, a rate of 10 to 15 μm/hr is possible in terms of the film.

Next, regarding the crystal form of the precipitated diamond, vapor-grown diamond generally has a mixture of (111) and (100) crystal forms. It is difficult to arbitrarily control these crystal forms. However, according to the present invention, many of the (111) planes in which carbon atoms are densely packed can be obtained. If the water concentration is increased as much as possible, it is possible to form an aggregate of particles with almost all (111) planes grown. The reason for this is not clear, but water (H ₂ O) has a higher reactivity with carbon than hydrogen, and because it is not tightly packed in diamond, it has a relatively high reactivity (100).
It is thought that this is because surface-grown diamond reacts with moisture and is removed.

Additionally, the diamond according to the invention has high purity. Usually, the precipitation surface of the base material is mostly (111) in the center.
Diamonds have grown faces or (100) faces, and as they move toward the periphery, they become spherical diamonds, and on the outside, non-diamond carbon, such as amorphous carbon, and graphite. In the method of the present invention, the removal effect of diamond carbon by moisture is strong, so that only diamond grown with (111) planes or diamond mainly composed of (111) planes are grown in the center of the substrate.

Effects of the Invention According to the present invention, diamond can be precipitated at a faster rate than conventional methods, and it is also possible to precipitate diamond at near normal pressure, which is extremely advantageous from an industrial perspective. Another feature of the present invention is that it is possible to obtain diamonds with high purity, and furthermore, it is also possible to control the crystal form of diamonds. The present invention brings about the above-mentioned effects through a simple operation of mixing water into raw material gas, and has great industrial utility value.

Example 1 (Hydrocarbon system) An experiment was conducted using the apparatus schematically shown in FIG. In the figure, reference numeral 1 denotes a reaction vessel, which has a raw material gas inlet 2 at its upper part, an exhaust port 7 at its lower part, and a pressure gauge 4 at its side. Further, the gas from the inlet is discharged directly above the tungsten filament 3 through the gas introduction pipe 2'. Both ends of the filament 3 are connected to a power source, and the temperature is controlled by adjusting the voltage. (The length of the filament coil part is 0.5 cm). A silicon substrate (the surface was scratched with diamond paste after mirror polishing, size of the substrate: 1 cm x 1 cm) was placed on the substrate support 6. . The distance between the surface of the substrate and the bottom of the filament (bottom surface of the coil) is approximately 3
mm.

Using this device, CH ₄ 1% by volume was used as the raw material gas,
Using a mixed gas of 1% by volume of H ₂ O and 98% by volume of H ₂ , this was supplied from gas inlet 2 at a rate of 50 c.c./min, and the filament temperature was approximately 2000°C (measured with a pyrometer) and the pressure was 50 Torr. , diamond was grown for 1 hour at a substrate temperature (measured by thermocouple) of 650°C. As a result, a 4 μm thick diamond film was formed on the silicon substrate. The diamond crystal was a film covered with (111) planes.

Example 2 (Oxygen-containing organic compound system) CH ₃ COCH ₃ (acetone) gas was used instead of CH ₄ . The composition was 2% by volume of CH ₃ COCH ₃ , 0.5% by volume of H ₂ O, and 97.5% by volume of H ₂ , and the mixed gas pressure was 100 Torr. Other conditions were the same as in Example 1.

As a result, a 35 μm diamond film was formed in 3 hours. The diamond crystal was the same as in Example 1.

Example 3 Methyl alcohol (CH ₃ OH) was used as the raw material gas, and the composition was CH ₃ OH 1.5% by volume, H ₂ O 1% by volume,
The residual H ₂ was 97.5% by volume, and the mixed gas pressure was 760 Torr.
The rest is the same as in Example 1.

As a result, an 8 μm diamond film was synthesized in 4 hours. The crystal form was the same as in Example 1.

Example 4 The same procedure as in Example 2 was carried out except that a glass substrate on which SiC particles of 9 μm were dispersed was used as the base material, and the mixed gas was set to 760 Torr.

The results showed that diamond particles of 5μ to 7μ were produced in 1 hour.
Several were attached around the SiC particles.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing one example of an apparatus used for carrying out the present invention. DESCRIPTION OF SYMBOLS 1... Reaction container, 2... Gas inlet, 3... Tungsten filament, 5... Substrate, 7... Exhaust port.

Claims (1)

[Scope of Claims] 1. A method for synthesizing diamond by a vapor phase method, characterized in that in a method of precipitating diamond from an organic carbon compound and hydrogen gas by a vapor phase method, water is mixed with the gas. 2. The method for synthesizing diamond by a gas phase method according to claim 1, wherein the gas mixing ratio of hydrogen gas and water is 0.0001 to 0.1 expressed as a volume ratio of H ₂ O/H ₂ .