JPH09249408A - Production of diamond - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing diamond, capable of producing the diamond free from strain in an improved production speed by imparting high density energy to an organic compound in an inactive atmosphere under a specific pressure outside a thermodynamically state region to thermally decompose the organic compound. SOLUTION: This is a method for producing diamond outside a thermodynamically sable region, wherein high density energy is imparted to an organic compound in an inactive atmosphere under a pressure of 300-2,000 bar to thermally decompose the organic compound. The content of oxygen in the inactive atmosphere is preferably 0.0005-0.1%. The organic compound includes 1-4C alkyls, alkanes, alkenes, alcohols and polysaccharides. The temperature of the above atmosphere is 500-2,000 deg.C. The high density energy is preferably imparted with plasma or filaments.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diamond production method capable of producing a diamond having a high production rate and a small strain outside the thermodynamically stable region of diamond.

[0002]

2. Description of the Related Art Conventionally, as a method for producing diamond, for example, a chemical vapor deposition method in which a thin film of diamond is grown on a high temperature substrate having a diamond structure after thermally decomposing an organic gas such as methane at atmospheric pressure or lower. Phase pyrolysis method (CV
D method) is known.

[0003]

However, when it is attempted to produce diamond with good purity and characteristics by the chemical vapor phase pyrolysis method, the production rate is several μm /
It is hr, and at least 100 hr or more is required to obtain a necessary thickness in consideration of practical use. Further, if the production rate is increased, the purity of diamond will be deteriorated and the characteristics will be deteriorated. Therefore, it is desired to obtain diamond having good purity and characteristics and to dramatically increase the production rate of the obtained diamond.
Further, there is a problem in that the diamond produced at high temperature is taken out of the container and the diamond is destroyed by strain or the like.

Therefore, as a result of intensive research, the inventor found that
It was found that the cause of the decrease in the purity of diamond and the deterioration of its properties is that the conversion rate of diamond is decreased, and this does not mean that the method of thermal decomposition of diamond is a problem. It turns out that there is a problem with the environment.

The present invention, outside the thermodynamic stability region,
It is an object of the present invention to provide a method for producing a diamond which has a high rate of diamond generation while suppressing the decomposition reaction of diamond into carbon and which has less distortion.

[0006]

In order to achieve the above-mentioned object, the present invention is a method for producing diamond outside the thermodynamically stable region, the method comprising the steps of forming an organic compound in an inert atmosphere under a pressure of 300 to 2000 bar. It is characterized in that high density energy is applied to the compound and the organic compound is thermally decomposed to generate diamond.

According to the present invention, C (diamond) → C (ca
By suppressing the decomposition reaction of rbon) and controlling the reaction system so as to promote the conversion reaction of carbon to diamond, the production rate of diamond can be improved.

According to the present invention, the diamond is prevented from being broken by the strain generated by the difference in thermal expansion from the substrate when the diamond is pressed at a predetermined pressure.
Although the stability of the produced atomic carbon after thermal decomposition is improved and the mean free path is reduced as a result, the production rate thereof can be remarkably increased.

The pressure in the inert atmosphere is 300 to 200.
0 bar is preferred. By applying pressure, thermal expansion of the substrate can be suppressed, distortion can be reduced, and a film formation area can be increased. In this case, the reaction equation of carbon-diamond is considered to be a pressure-dependent equation, and therefore ultrahigh pressure is preferable, but it is difficult to generate plasma under ultrahigh pressure, and there is no such method at present. Therefore, it is possible to generate plasma, and 300 to 2000 bar is preferable as the pressure for enhancing the stability of diamond.

If the pressure is less than 300 bar, the efficiency of the conversion reaction from carbon to diamond is low, which is unsuitable. If it exceeds 2000 bar, the efficiency of the conversion reaction is improved, but the entire apparatus becomes large and complicated. Therefore, there is a problem that it becomes expensive.

The high density energy is preferably applied by, for example, an arc plasma, a gas plasma or a hot filament. In this case, arc discharge may be generated by sequentially discharging capacitors arranged in parallel. Further, the arc discharge may be generated in a state where the diamond raw material is sandwiched between the electrodes or in a state where the raw material is laminated on the substrate. In the hot filament, it is desirable to provide a plurality of gas supply ports in parallel in order to improve the generation rate in relation to the conversion rate to diamond.

The ambient temperature is preferably 500 to 2000 ° C. If the temperature is lower than 500 ° C, the undecomposed raw material in the reaction system has a large influence, and it is difficult to increase the production rate while maintaining the quality and characteristics of the produced diamond. Further, when the temperature exceeds 2000 ° C, the production rate does not increase, and carbon-
This is inconvenient because it promotes the decomposition of diamond into carbon in the reaction of diamond.

The optimum ambient temperature is 800-18.
00 ° C. This is because the production rate of diamond is dramatically increased as compared with the conventional one, and the effect is very large.

The oxygen content in the inert atmosphere is 0.0
005-0.1% is suitable. This is because oxygen reacts with carbon generated when the organic compound is thermally decomposed to generate diamond, and acts to remove the carbon out of the system.
If the oxygen content is less than 0.0005%, there is no effect of oxygen and the content of carbon in the produced diamond is high, which is not suitable in that the characteristics are deteriorated. Further, when the atmospheric temperature is high, if the oxygen content exceeds 0.1%, not only the undecomposed raw material gas is removed, but also the generated diamond is oxidized and decomposed to deteriorate the characteristics.

[0015]

EXAMPLE 1 FIG. 1 is a schematic configuration diagram of a diamond manufacturing apparatus for carrying out the diamond manufacturing method according to the present invention.

This diamond manufacturing apparatus 10 is provided in a first high-pressure container 12, a heater 16 for heating arranged in a first chamber 14 closed by the first high-pressure container 12, and in the first chamber 14. The second high pressure container 18 and the second
A first electrode 22 and a second electrode 24 arranged in a second chamber 20 closed by a high-pressure container 18, and the second chamber 2
And a pipe 28 for communicating high pressure gas to the second chamber 20 or for discharging the high pressure gas introduced into the second chamber 20 to the outside under the opening and closing action of the high pressure control valves 26a to 26c. . A sampling port 29 for extracting oxygen generated in the second chamber 20 under the opening operation of the high pressure control valve 26d is formed in the pipe 28.

The first electrode 22 is fixed to the sample table 30, and the second electrode 24 is provided via a position control motor 32 so as to be displaceable in the arrow direction. The position control motor 32
A control unit 34 is connected to the control unit 3 and
Under the control of the position control motor 32 by the first electrode 2
The distance between the second electrode 24 and the second electrode 24 is freely adjusted. The first electrode 22 and the second electrode 24 are connected to the DC power source E, respectively. Further, the control unit 34 is
The ambient temperature in the first chamber 14 is detected through the passage 36, and the temperature in the first chamber 14 is adjusted while the heater 16 is biased or deenergized.

The first electrode 22 and the second electrode 24 are each made of a graphite material and are used as a substrate (raw material).
The first electrode 22 on the side is formed by solidifying sucrose, and the second electrode 24 is formed by heating graphite impregnated with water in a closed system. Arc plasma is continuously generated between the first electrode 22 and the second electrode 24 under the control action of the control unit 34.

The raw material for the first electrode 22 is 30% sucrose.
After being solidified at a pressure of 0 MPa, carbonization and sintering are performed to remove the pores in the pellets of the raw material, and consideration is given to prevent melting and deformation with temperature rise as much as possible, as shown in FIG. After being incorporated in the diamond manufacturing apparatus 10, the temperature rising rate and the pattern are taken into consideration.

In this case, the reason why sucrose or graphite is used as the raw material of the electrode is to qualify the heating action by the arc plasma. The diamond conversion rate (%) shown below is a value calculated by the ratio of the area converted to diamond to the area irradiated with plasma. In the part converted to diamond, the diamond component is almost 1
Since it was 00% and it was transparent, the area ratio was measured after confirming that the portion was diamond by X-ray diffraction or the like.

Nitrogen (N) and argon (Ar) were used as the pressurizing medium. From the viewpoint of characteristics, it was assumed that argon is preferable because a small amount of water is added to the raw material (second electrode 24) and oxygen, hydrogen and nitrogen in the water react at high temperature. In the measurement of the thermal conductivity in the characteristic measurement of the obtained diamond, 1.5 to 1.7 kW
/ MK and no clear difference was observed.

FIG. 2 shows the relationship between the pressure and the conversion rate of diamond when the atmospheric temperature in the second chamber 20 is kept constant at 1000.degree. As can be easily understood from FIG. 2, 30
At pressures above 0 bar, the conversion rate of diamond is 90
% Or more.

Next, the pressure applied by the high pressure gas is set to 800 b.
FIG. 3 shows the relationship between the atmospheric temperature and the conversion rate of diamond when ar is kept constant. In this case, 800 ℃ ~ 14
In the temperature range of 00 ° C, 9
It is understood from FIG. 3 that 0% or more of the diamond was converted into diamond.

Next, FIG. 4 shows the relationship between the oxygen concentration and the conversion rate of diamond when the atmospheric temperature is kept constant at 1000.degree. Pressure is 300 bar (solid line) and 1000
The experiment was carried out by setting to (bar) (broken line). During the test, oxygen was sampled by opening and closing the high pressure control valve 26d and heating the first electrode 22 to extract oxygen from the sampling port 29. The oxygen concentration in the gas in the second chamber 20 is C
Although observed in O, CO ₂ , NO _x, etc., they were counted as atoms and calculated as O ₂ . As is clear from FIG. 4, the oxygen concentration is 0.001 to 0.1% {log (-
In the range of 3) to log (-1)%}, the conversion of diamond was almost 100% in both cases of 300 bar and 1000 bar.

At 300 bar and 1000 bar, the conversion rate of diamond is shifted with respect to the oxygen concentration. This occurs because the samples are the same and the plasma generation conditions are the same, and the total number of oxygen atoms is different with respect to the change in pressure.

As described above, conventionally, it was thought that diamond could be produced within the stable region (ultra high pressure region) of diamond or only by the CVD method.
It was possible to easily manufacture diamond at a pressure of about 300 to 2000 bar.

In this example, the plasma irradiation area was 300 cm ² .

The diamond obtained in this experiment has a thickness of 0.8 mm, which sufficiently satisfies the required thickness of 0.635 mm when the diamond is used as a heat sink. 300 cm with the 0.8 mm film thickness
^The time required to convert the area of ² to diamond is
It was several minutes to several tens of minutes, and diamond could be formed in an extremely short time.

Although this is not as high as the conventional ultrahigh pressure, it is convenient for synthesizing under high pressure, and when plasma is used to synthesize diamond, that portion becomes conductive. To high insulation, and the interface easily grows and forms continuously. However, there is a correlation between this performance and the film formation rate, and if the limit value is exceeded, the characteristics deteriorate.

The thermal conductivity characteristics of the diamond obtained in this experiment were about 1.5 to 1.7 kW / mK, as described above. Therefore, the heat sink performance is 8 to 10 times as high as that of the commercially available aluminum nitride and is very excellent, and also the insulating property is excellent.

The obtained surface is 1.6 to 3.2 s on the synthesis side,
It is slightly worse on the board side.

Therefore, although it is necessary to process the surface, QF
It is suitable to be used as a heat sink for P, power transistors, thyristors, and multi-chip module substrates, and can also be used as elements such as thermistors and diodes. Example 2 FIG. 5 shows a schematic configuration of another diamond manufacturing apparatus for carrying out the diamond manufacturing method according to the present invention.

The diamond manufacturing apparatus 40 communicates with a high pressure container 42, heaters 44a and 44b for heating contained in the high pressure container 42, and a chamber 46 closed by the high pressure container 42, and a first high pressure control valve. A gas supply pipe 50a for supplying a source gas and a high-pressure gas to the chamber 46 under the opening and closing action of the valve 48a, and a second high-pressure control valve 48b.
And a gas discharge pipe 50b for discharging the gas supplied to the chamber 46 to the outside under the opening and closing action. A gas supply port 52 facing the chamber 46 is formed at one end of the gas supply pipe 50a.

A sample table 54 is fixed in the chamber 46, and a growth substrate 56 is placed on the sample table 54. Between the gas supply port 52 and the growth substrate 56,
A hot filament 58 is provided. A cooling unit 60 for cooling the growth substrate 56 is formed on the sample table 54, and cooling water is circulated through a passage 62 communicating with the cooling unit 60.

The growth substrate 56 is composed of a first growth substrate made of a silicon wafer material and having a size of 5 inches, and a second growth substrate made of graphite material and having a size of 4 inches. The above two types were used to grow diamond to a film thickness of 0.8 mm.

In order to quantitatively supply the raw material gas loaded on the carrier into the chamber 46 through the gas supply pipe 50a, the high-pressure pipe must be laid around, and the compressor, the pipe, etc. Consideration is important. The pressure in the high-pressure container 42 is about 500 bar at maximum.

As the carrier, hydrogen gas diluted with argon and an inert gas similar thereto is used, and gasified raw material gas such as alkyl having 1 to 4 carbon atoms, alkane, alkene or alcohol is used. High-pressure gas containing 5 to 8% was introduced into the chamber 46.

The atmospheric temperature in the chamber 46 heated by the heaters 44a and 44b is set to 800 ° C., and the pressure is set to several tens of ba.
Experiments were performed varying from r to 500 bar. Here, the relationship between the film formation rate and the diamond conversion rate is shown in FIG. In FIG. 6, ● indicates a first growth substrate formed of a silicon wafer, Δ indicates a second growth substrate formed of graphite, and the film formation rate is a unit area of the growth substrate 56. It is the rate at which the thickness of the diamond film formed around increases.

A first growth substrate formed of a silicon wafer having a crystal structure similar to that of diamond, and a second growth substrate formed of graphite having a completely different crystal structure from the diamond.
Experiments were performed using the growth substrate and, as can be understood from FIG. 6, the results indicate that the crystal structure of the growth substrate 56 does not influence the growth of diamond.

Further, the kind of the raw material gas was tested with the structure of the raw material material, that is, the material having the same carbon number but different bonding structure, but in this experiment, a clear difference was observed at almost 100% conversion. It was not observed.

In this experiment, as shown in FIG. 6, when the first growth substrate formed of a silicon wafer was used,
With a conversion rate of almost 100%, a diamond film formation rate of 20
It could be improved to 0 μm / hr.

[0042]

According to the present invention, the following effects can be obtained.

That is, it is possible to increase the production rate of diamond while suppressing the decomposition reaction from diamond to carbon, to obtain a diamond with less distortion and excellent quality and characteristics.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a diamond manufacturing apparatus for carrying out a diamond manufacturing method according to the present invention.

FIG. 2 is a graph showing the relationship between pressure and diamond conversion.

FIG. 3 is a graph showing the relationship between the temperature in the atmosphere and the conversion rate of diamond.

FIG. 4 is a graph showing a relationship between oxygen concentration and conversion rate of diamond.

FIG. 5 is a schematic configuration diagram of another diamond manufacturing apparatus for carrying out the diamond manufacturing method according to the present invention.

FIG. 6 is a graph showing the relationship between the film formation rate and the conversion rate of diamond.

[Explanation of symbols]

10, 40 ... Diamond manufacturing equipment 12, 18, 4
2 ... High-pressure container 14, 20, 46 ... Chamber 16, 44a,
44b ... Heating heater 22, 24 ... Electrodes 26a to 26d, 48a, 48b ... High pressure control valve 28, 50a, 50b ... Pipe 29 ... Sampling port 32 ... Position control motor 34 ... Control unit 52 ... Gas supply port 56 ... Growth Substrate 58 ... Thermal filament

Claims (5)

[Claims] 1. A method for producing diamond outside a thermodynamically stable region, which comprises applying high-density energy to an organic compound in an inert atmosphere under a pressure of 300 to 2000 bar to thermally decompose the organic compound. A method for producing a diamond, which comprises producing a diamond by the method. 2. The method for producing diamond according to claim 1, wherein the oxygen content in the inert atmosphere is 0.0005 to 0.1%. 3. The method for producing a diamond according to claim 1, wherein the organic compound is one of alkyls, alkanes, alkenes, alcohols or polysaccharides having a carbon number of C1 to C4. Method. 4. The method for producing diamond according to claim 1, wherein the ambient temperature is 500 to 2000 ° C. 5. The method for producing diamond according to claim 1, wherein the high density energy is applied by plasma or filament.