JPH0476348B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for vapor phase synthesis of diamond.
More specifically, the present invention relates to a method and apparatus for synthesizing diamond or a diamond-like hard film at low cost using graphite as a raw material and a mixed gas of hydrogen and oxygen or an oxygen compound as a medium.

(Conventional technology) In recent years, diamond vapor phase synthesis technology has progressed.
Various diamond synthesis methods have been proposed.
For example, in addition to conventional high-pressure synthesis, it has become possible to artificially synthesize diamond or diamond-like hard carbon films from the gas phase with hardness and crystallinity comparable to natural diamond. The range of applications for the synthesis of diamond from the gas phase is expanding, and cutting tools that take advantage of diamond's excellent properties such as hardness, thermal conductivity, elastic modulus, semiconductivity, optical properties, and corrosion resistance are being developed. Applications are being considered for wear-resistant parts, heat sinks, semiconductors, audio equipment parts, optical products, and corrosion-resistant parts.

Conventionally, the following methods have been used for vapor phase synthesis of diamond.

For example, Journal of Crystal Growth, 52
(1981) 219, a hydrocarbon gas or a mixture of hydrocarbons and hydrogen is thermally decomposed to create a carbon supersaturated atmosphere, and diamond is chemically deposited on a heated substrate placed in this atmosphere. Methods of transport and deposition.

For example, Journal of Applied Physics.
Vol. 42. No. 7 (1971) 2953, a method of accelerating carbon ions to synthesize a diamond-like carbon film on a substrate at room temperature.

For example, JP-A-58-91100 or Japanese
Journal of Applied Physics.Vol.25.No.6
(1986) as shown in L519, a mixed gas of hydrocarbons, alcohols, or ketones and hydrogen is pyrolyzed using a high-temperature thermofilament.
A method of chemically creating active atoms or molecules and synthesizing diamonds on a heated substrate.

Using a mixed gas of hydrocarbons or alcohols and hydrogen as a raw material, in an atmosphere of these gases, for example, by direct current discharge as shown in JP-A-60-221395, or by high-frequency discharge as shown in JP-A-58-135117, Or JP-A-58-
110494, a method of generating plasma using microwave discharge to create active chemical species and synthesizing diamond on a heated substrate.

For example, the magazine "New Diamond",
As shown in Vol. 4, No. 2 (1988) 30, a powerful thermal plasma stream is created in a jet-like manner by direct current discharge into a mixed gas of hydrocarbons, hydrogen, and argon or helium. How to synthesize diamonds.

For example, the magazine "New Diamond",
Vol. 4, No. 3 (1988) 34, a method of synthesizing diamonds in a combustion flame of a mixed gas of hydrocarbon or alcohol and hydrogen or oxygen.

Among these methods, method 1 synthesizes diamond by thermally decomposing hydrocarbon gas or a mixed gas of hydrocarbon and hydrogen and using a chemical transfer method, but detailed test methods are not provided and reproducibility is difficult. Therefore, it is not generally practiced at present. Furthermore, the diamond-like carbon film synthesized by the method described above generally has low hardness, and it is difficult to synthesize the film over a wide area at high speed, which is industrially disadvantageous.

Therefore, at present, among the above methods, ~ is used as a method to form a good diamond. That is, in the vapor phase synthesis of diamond shown in ~ above, carbon, which is the raw material for diamond, is a compound gas composed of carbon and hydrogen like hydrocarbons, or a compound gas composed of carbon, hydrogen, and oxygen like alcohols, ketones, etc. In the presence of a thermal filament or plasma in a mixed gas atmosphere of these gases and hydrogen gas,
Diamond synthesis has been performed on substrates heated to 600°C to 1200°C. At this time, a large amount of hydrogen gas is added to the reaction gas together with the carbon source because hydrogen activated by the thermal filament or plasma has the effect of selectively removing graphite, which is precipitated in large quantities with diamond during diamond synthesis. Because there is. It is also known that diamond can be synthesized at high speed when alcohols or ketones are used as the carbon source; It is thought that this is because the effect is superimposed on the effect of the activated hydrogen, making it possible to supply more carbon sources. In addition, a rare gas such as argon is sometimes added to the mixed gas in order to lower the discharge voltage and perform stable discharge when creating discharge plasma.

(Problem to be solved by the invention) However, in the method ~ mentioned above, carbon, which is a raw material for diamond, is obtained from carbon compound gas, so even though the amount of carbon deposited on the substrate as diamond is small, However, there is a drawback that gases mixed at a predetermined ratio must be kept flowing during diamond synthesis.

(Means for Solving the Problems) The present invention first involves mixing hydrogen gas with oxygen gas, oxygen compound gas, or oxygen gas and oxygen compound gas in a vacuum chamber containing graphite heated to a temperature above 600°C and below 2000°C. Add one of the gases and fill with a mixed gas in which the ratio of the number of hydrogen atoms to the number of oxygen atoms is adjusted to 1:0.001 to 0.3, and fill with a plasma generated in the atmosphere or a heated mixed gas death,
Placed in the plasma generated in this atmosphere or near the heated filament at a temperature of 600℃ or higher
It relates to a diamond vapor phase synthesis method in which diamond is synthesized on a substrate heated to 1200°C or less.

In other words, graphite generates carbon monoxide or carbon dioxide in the presence of oxygen at temperatures above 600°C.
It is also well known that it reacts with the water produced as a result of the reaction between oxygen and hydrogen, producing carbon monoxide and hydrogen.

The carbon compounds released into the atmosphere by these reactions are decomposed and activated near the thermal filament or in the plasma, and deposit diamond on the substrate. Although carbon is removed from the atmosphere by diamond precipitation, oxygen and hydrogen still remain in the atmosphere, so they circulate as water and react with graphite again, creating a carbon compound gas mainly consisting of hydrogen monoxide in the atmosphere. This will contribute to the reaction to which it is supplied.
The temperature of graphite can be raised to near its melting point as long as it is above 600℃, but in practical terms
The following are preferred.

If the temperature of the substrate is below 600℃, it is not preferable because a large amount of graphite component will precipitate together with diamond, and if it exceeds 1200℃, the precipitated diamond will change to graphite, so it is not preferable to set the temperature of the substrate above 600℃ or 1200℃. Limited to below ℃.

The present invention further provides a vacuum chamber that is connected to a gas inlet pipe and a vacuum exhaust pipe and that includes a substrate, a substrate support, and a filament inside, and supplies carbon atoms as a carbon compound gas to a mixed gas filled in the vacuum chamber. A diamond vapor phase synthesis device characterized by incorporating heated graphite in a vacuum chamber for the purpose of
and a diamond vapor phase synthesis apparatus, which has a substrate and a substrate support inside a vacuum chamber connected to a gas inlet pipe and a vacuum exhaust pipe, and is equipped with means for generating plasma around the substrate. This is related to a diamond vapor phase synthesis apparatus characterized by having a heated black gas built into a vacuum chamber in order to supply carbon atoms as a carbon compound gas to a mixed gas filled in the chamber, and a vacuum serving as a reaction chamber. By making slight improvements to the conventional gas-phase synthesis equipment, in which heated graphite is installed in a tank, the method of the present invention reduces the amount of reaction gas consumed and synthesizes diamond at low cost. .

(Example) The method and apparatus of the present invention will be described below with examples.

Example 1 Diamond was synthesized in a vapor phase using an apparatus as shown in FIG. That is, a molybdenum heater 3 supported by a heater current introduction terminal 12 for heating graphite is provided in the vacuum chamber 1, and graphite powder 2 is placed on the molybdenum heater. Further, above the molybdenum heater, a substrate support 5 having a built-in heater 13 connected to the substrate support and heater current introduction terminal 11 is formed, and a substrate made of a tungsten plate is mounted on the substrate support. 6 is placed. Furthermore, a filament 4 is supported by a current introduction terminal 10 for filament with a gap of 3 to 5 mm above the base. Note that 7 is a vacuum exhaust pipe, 8 is an exhaust valve disposed on the vacuum exhaust pipe, and 9 is a gas introduction pipe.

The method of implementation is to first evacuate the inside of the vacuum chamber to 10 ^-4 Torr through the vacuum exhaust pipe 7, and then heat the graphite powder placed on a molybdenum heater to 800 to 1000°C by energizing it.
After the vacuum reaches 10 ^-5 Torr, the exhaust valve connected to the vacuum exhaust pipe is closed, and a hydrogen:steam mixture gas with a molar ratio of 100:2 is passed through the gas introduction pipe to reduce the pressure inside the vacuum chamber. was introduced until it reached 100 Torr, and then the filament was energized to about 100 Torr.
Diamond synthesis was carried out on a substrate placed below the filament by heating to 2000°C. During diamond synthesis, electricity was applied to the heater attached to the substrate support to raise the temperature of the substrate support to 800°C, and the substrate placed on it was heated. As a result, after 2 hours of synthesis processing, many diamonds with euhedral surfaces were synthesized on the substrate directly below the filament, and the thickest part was 12 μm thick.
The thickness was warm.

The pressure in the vacuum chamber during diamond synthesis increased due to the temperature of the mixed gas in the vacuum chamber rising when electricity started flowing to the filament, but remained almost constant thereafter.

Example 2 Diamond was synthesized in a vapor phase using an apparatus as shown in FIG. That is, a graphite plate 2' supported by a heater current introduction terminal 12 for heating graphite is provided inside the vacuum chamber 1, and a WC-Co is placed on an anode 14 which stands up from the bottom of the vacuum chamber and is provided with a cooling port 18. A base cemented carbide base body 6 is placed. Approximately 40 mm above the base, a cathode 4 made of a thoria-filled tungsten filament is connected to a current introduction terminal 1 for the filament.
It is located connected to 0. The vacuum exhaust pipe 7, exhaust valve 8 and gas introduction pipe 9 are arranged in the same manner as in FIG.

The method is to first evacuate the inside of the vacuum chamber to 10 ^-4 Torr, then continue to evacuate the graphite plate while heating it to approximately 1000℃ by energizing it, and when the degree of vacuum reaches 10 ^-5 Torr, close the exhaust valve and evacuate. A mixture of hydrogen gas and oxygen gas with a volume ratio of 100:6 was introduced into the vacuum chamber through the gas introduction tube until the pressure reached 30 Torr, and then the supply was stopped, and then the tungsten filament containing thoria was energized. Plasma is generated between the filament and the anode by heating it to approximately 2000℃ and passing a 4A current between the filament and the anode.
Diamond synthesis was performed on a substrate placed on an anode.

During diamond synthesis, the temperature of the substrate increases due to the influence of plasma, so the anode is cooled by passing water through the cooling port provided inside the anode, and the temperature of the substrate placed on it is kept within a range of 700 to 1000℃. I kept it.

After 3 hours of processing, WC
A diamond film consisting of polycrystalline polycrystals with approximately 10 μm thick euhedral surfaces was synthesized on -Co-based cemented carbide.

Example 3 As shown in Fig. 3, a graphite plate 2' that can be heated by electricity is provided in a vacuum chamber 1 having a structure that allows internal gas to circulate through convection, and plasma is generated in the gas within the vacuum chamber. Microwave oscillator 1 for
5, a waveguide 16 for introducing microwaves into the vacuum chamber, a plunger 17 for adjusting the state of plasma, and other accessories; and a substrate for placing the substrate 6 in the plasma. Diamond was synthesized by the following method using an apparatus having a support 5.

A tungsten plate was used as a base, and this was placed on a base support, and vacuum evacuation and graphite heating were performed in the same manner as in Example 2. A mixed gas of hydrogen gas and nitrogen monoxide gas with a molar ratio of 100:4 was used. into a vacuum chamber
The plasma was filled to 30 Torr, a 350 W microwave was generated, and diamond was synthesized on a substrate placed in this plasma. The temperature of the base at this time is 800
Estimated to be ~900℃.

After 3 hours of treatment using this method, a film consisting of polycrystalline diamond with euhedral planes and a thickness of approximately 5 μm was synthesized on a tungsten substrate.

In Examples 2 and 3 above, water and nitrogen monoxide were used as the oxygen compound gas, but in addition to these, gases made of carbon, hydrogen, and oxygen such as nitrogen dioxide, carbon monoxide, carbon dioxide, or alcohol A similar effect can be obtained even when a compound gas is used. Further, in Examples 2 and 3, discharge plasma was generated by direct current discharge and microwaves, but similar effects can be obtained when high frequency waves are used as a means for generating plasma.

Example 4 Diamond was synthesized in a vapor phase using an apparatus as shown in FIG. That is, a molybdenum heater 3 supported by a heater current introduction terminal 12 for heating graphite is provided in the vacuum chamber 1, and graphite powder 2 is placed on the molybdenum heater. Further, above the molybdenum heater, a base support 5 having a built-in heater 13 connected to the base support and heater current introduction terminal 11 is formed, and a 10 mm x 10 mm x 3 mm base support is formed on the base support. A base body 6 made of a tungsten plate is mounted. Furthermore, a filament 4 is supported by a current introduction terminal 10 for filament with a gap of 3 to 5 mm above the base. Further, the mixed gas in the vacuum chamber is sucked from the lower side of the vacuum chamber, pressurized by the gas circulation pump 20, and then passed through the gas flow meter 19 and injected into the vacuum chamber from the upper part of the vacuum chamber. Note that 7 is a vacuum exhaust pipe, 8 is an exhaust valve disposed on the vacuum exhaust pipe, and 9 is a gas introduction pipe.

The method of implementation is to first evacuate the inside of the vacuum chamber to 10 ^-4 Torr through the vacuum exhaust pipe 7, and then heat the graphite powder placed on a molybdenum heater to 800 to 1000°C by energizing it.
After the vacuum level reaches 10 ^-5 Torr, the exhaust valve connected to the vacuum exhaust pipe is closed, and a mixture of hydrogen and oxygen with a molar ratio of 95:5 is passed through the gas introduction pipe to reduce the pressure inside the vacuum chamber. The gas in the vacuum chamber is introduced until it reaches 50Torr, and then the circulation pump is used to pump the gas in the vacuum chamber.
Diamond was synthesized on a substrate placed below the filament by circulating at a flow rate of 500 CCM and then heating the filament to about 2000°C by passing an electric current through it. During diamond synthesis, electricity was applied to the heater attached to the substrate support to raise the temperature of the substrate support to 800°C, and the substrate placed on it was heated.
As a result, after 2 hours of synthesis processing,
Diamond is synthesized on the top surface of the tungsten substrate, and the film thickness is approximately 16θμm in the thick part and approximately 16θμm in the thin part.
It was 8 μm.

As a comparative example, diamond was synthesized under the same conditions as above except that the circulation pump was not operated, and the diamond film thickness was approximately 10 μm in the thick part.
The thickness of the thin part was about 2 μm, and the growth rate of the film was slower and the variation in film thickness was larger than when gas was not circulated.

Example 5 Diamond was synthesized in a vapor phase using an apparatus as shown in FIG. That is, a graphite plate 2' supported by a heater current introduction terminal 12 for heating graphite is provided inside the vacuum chamber 1, and a JIS symbol is placed on an anode 14 that stands up from the bottom of the vacuum chamber and is provided with a cooling water hole 18.
A WC-Co-based cemented carbide substrate 6 of the SNGN120408 type is placed. Approximately 40 mm above the base is a cathode 4 made of a thoria-filled tungsten filament.
is located connected to the filament current introduction terminal 10. The gas circulation pump 20, gas flow meter 19, vacuum exhaust pipe 7, exhaust valve 8, and gas introduction pipe 9 are arranged in the same manner as in FIG. 4.

The method is to first evacuate the inside of the vacuum chamber to 10 ^-4 Torr, then continue to evacuate the graphite plate while heating it to approximately 1000℃ by energizing it, and when the degree of vacuum reaches 10 ^-5 Torr, close the exhaust valve and evacuate. A mixture of hydrogen gas and carbon monoxide gas with a volume ratio of 90:10 was introduced into the vacuum chamber through the gas introduction pipe until the pressure reached 30 Torr, then the supply was stopped, and the gas circulation pump was started to fill the vacuum chamber. The gas inside is circulated at a flow rate of 500SCCM, then the thoria-filled tungsten filament is heated to approximately 2000℃ by electricity, and plasma is generated between the two electrodes by passing a discharge current of 4A between the filament and the anode. Then, diamond was synthesized on the substrate placed on the anode. During diamond synthesis, the temperature of the substrate increases due to the influence of plasma, so the anode is cooled by passing water through the cooling water hole provided inside the anode, and the temperature of the substrate placed on it is increased to 700 to 1000℃. I kept it within range. After 3 hours of treatment, a diamond film consisting of polycrystals with euhedral surfaces was synthesized on the WC-Co-based cemented carbide substrate, and the film thickness was approximately 25 μm at the periphery of the upper surface. It was approximately 12 μm in the center.

As a comparative example, when diamond was synthesized under the same conditions as above except that the gas circulation pump was not operated, a thickness of about 15 μm was formed around the top surface of the WC-Co-based cemented carbide substrate, and a thickness of about 3 μm was formed at the center of the top surface. A diamond film was synthesized. In the case of the comparative example, the film growth rate was slower and the film thickness was more nonuniform than when gas was circulated.

Embodiment 6 As shown in FIG. 6, a graphite plate 2 which can be heated by electricity is placed in a vacuum chamber 1 which has a structure in which the gas inside can be circulated using a gas circulation pump 20 while measuring the flow rate with a gas flow type 19. ' has a microwave oscillator 15 for generating plasma in the gas in the vacuum chamber, a waveguide 16 for introducing microwaves into the vacuum chamber, a plunger 17 for adjusting the state of the plasma, and other components. A microwave plasma generator consisting of accessories and a substrate 6 in the plasma
Diamond was synthesized by the following method using an apparatus having a gas support stand 5 for placing the diamond.

A WC-Co based cemented carbide of JIS symbol SNGN120408 type was used as a base, placed on a base support, and vacuum evacuated and graphite heated in the same manner as in Example 5, with a hydrogen gas:water vapor molar ratio of 95. : Fill the vacuum chamber with the mixed gas prepared in 5 to 30 Torr, circulate the gas in the vacuum chamber at a flow rate of 200 SCCM using a gas circulation pump, and then introduce 350 W microwaves to control the mixed gas in the vacuum chamber. A discharge plasma was formed inside the chamber, and diamond was synthesized on a substrate placed in this plasma. At this time, the temperature of the substrate is 800~
The temperature was estimated to be 900℃.

After 3 hours of treatment using this method,
Approximately 7μm on the periphery of the top surface of the base, and approximately 4μm on the center of the top surface
A film consisting of euhedral polycrystalline diamond with a thickness of .

As a comparative example, the type of filling gas, pressure, graphite temperature, type of substrate, substrate temperature,
When diamond was synthesized using the same microwave output and processing time as above, the thickness of the diamond film was approximately 5 μm at the periphery of the upper surface of the substrate and approximately 2 μm at the center of the upper surface of the substrate, indicating that the film growth rate was slow. At the same time, the non-uniformity of the film thickness also increased.

As shown in Examples 4 to 6 above, a gas circulation pump is provided to circulate the gas in the vacuum chamber, and the amount of carbon compound gas supplied to the diamond synthesis area, which is the raw material for diamond vapor phase synthesis, is provided. By increasing the diamond synthesis rate, we were able to improve the uniformity of the thickness of the synthesized diamond film.

(Effects) According to the method of the present invention, instead of continuously supplying carbon, which is a raw material for diamond, from a gas such as hydrocarbon gas or hydrogen carbonate compound gas in the conventional method, carbon is supplied into a vacuum chamber, which is a reaction vessel. By using a device equipped with graphite that can be heated and using a mixed gas containing at least hydrogen and oxygen as a reaction gas, it is possible to continuously supply a carbon source from graphite, and the consumption of reaction gas is also significantly reduced. Therefore, it is very advantageous industrially because diamond can be synthesized at low cost.
Furthermore, the method of the present invention can be carried out by making slight improvements to a conventional gas phase synthesis apparatus, making it extremely easy and economical.

Furthermore, by providing a means for forcibly circulating the gas in the vacuum chamber, it becomes possible to synthesize diamond uniformly at high speed, which is very advantageous industrially. Moreover, it can be implemented with only slight improvements to the conventional method.

[Brief explanation of the drawing]

1 to 6 are schematic diagrams of a diamond vapor phase synthesis apparatus according to the present invention. 1 is a vacuum chamber, 2 is graphite powder, 2' is a graphite plate, 3
is a heater for graphite heating, 4 is a filament, 5 is a gas support base, 6 is a base body, 7 is a vacuum exhaust pipe, 8 is an exhaust valve, 9 is a gas introduction pipe, 10 is a current introduction terminal for the filament, 11 is a base support base 12 is a heater current introduction terminal for heating the graphite; 13 is a heater for heating the substrate support; 14 is an anode; 15 is a microwave oscillator; 16 is a waveguide;
7 is a plunger, 18 is a cooling water hole, 19 is a gas flow meter, and 20 is a gas circulation pump.

Claims (1)

[Claims] 1 Hydrogen gas and oxygen gas in a vacuum chamber containing graphite heated to 600°C or more and 2000°C or less;
Add either oxygen compound gas; or a mixed gas of oxygen gas and oxygen compound gas; fill the mixed gas with the ratio of the number of hydrogen atoms to the number of oxygen atoms adjusted to 1:0.001 to 0.3, and fill the atmosphere with 1. A method for vapor phase synthesis of diamond, characterized in that diamond is synthesized on a substrate heated to 600°C or more and 1200°C or less, which is placed in a discharge plasma generated by or near a heated filament. 2. The diamond vapor phase synthesis method according to claim 1, wherein the mixed gas in the vacuum chamber is forcibly circulated. 3 A vacuum chamber connected to a gas inlet pipe and a vacuum exhaust pipe and equipped with a substrate, a substrate support, and a filament inside, for supplying carbon atoms as a carbon compound to the mixed gas filled in the vacuum chamber. A diamond vapor phase synthesis device characterized by a vacuum chamber containing graphite that can be heated by electricity. 4. A vacuum chamber connected to a gas inlet pipe and a vacuum exhaust pipe and having a substrate and a substrate support therein, provided with means for generating plasma around the substrate, and filled with the vacuum chamber. A diamond vapor phase synthesis apparatus characterized in that a vacuum chamber contains graphite that can be heated by electricity or plasma in order to supply carbon atoms as a carbon compound gas to a mixed gas. 5. The diamond vapor phase synthesis apparatus according to claim 3 or 4, further comprising means for circulating the mixed gas filled in the vacuum chamber.