JPS63117995A - Device for synthesizing diamond in vapor phase - Google Patents

Abstract

PURPOSE:To efficiently obtain a diamond at a relatively low cost by synthesizing the diamond from a solid carbonaceous material and CO2 in a hydrogen plasma atmosphere in a vapor phase. CONSTITUTION:A substrate 7 is arranged on a holder 9 in a plasma producing region 14 in a reaction tube 6 made of quartz, and a solid carbon plate 25 is arranged in the vicinity of the substrate 7 as the carbon material. A gaseous mixture of H2 and CO2 is introduced from an inlet 11, a microwave is introduced from a waveguide 5, the inside of the reaction tube 6 is filled with the hydrogen plasma atmosphere, a carbon-hydrogen plasma reaction is carried out to keep the atmosphere at high temp., hence gaseous hydrocarbons, hydrocarbon ions, hydrocarbon plasma, etc., are generated, an atomic oxygen and atomic hydrogen are also generated, and the diamond is deposited on the substrate 7.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for vapor phase synthesis of diamond, and more particularly, to a vapor phase synthesis method that can synthesize diamond relatively inexpensively and efficiently. .

[Prior Art] Diamond has been widely used in the past, mainly for cutting tools, due to its high hardness. On the other hand, in recent years, attention has been paid to its high thermal conductivity and its potential to be used as a semiconductor by doping with impurities. The application of diamond has been studied, and the latter property has also been applied to the field of electronic technology such as semiconductor devices, and techniques for forming diamond 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. 2 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. 2, the microwave (2.45 GHz) oscillated from the magnetron oscillator 1 is transmitted to the isolator 2.
, power monitor 3, tuner 4, and waveguide 5 in the stated order, and irradiates a substrate 7 installed in a quartz reaction tube 6 provided through the waveguide 5. Although a metal material such as Ta, Co, W, or Mo may be used as the substrate 7, generally a Si wafer is used, and the substrate 7 is placed at a predetermined position by a support base 9 made of quartz. ing. In the reaction tube 6, from the reaction tube population 11 side, about 1003
CCM (Standard Cubic Centim)
per minute).

A predetermined amount of the introduced mixed gas is sucked and exhausted from the exhaust port 13 side, and the inside of the reaction tube 6 is maintained at a predetermined pressure (for example, 40 to 50
Torr).

When oscillating radio waves (approximately 300 W) such as microwaves are introduced into the reaction tube 6 into 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 the reaction tube 6. The substrate 7 is placed in the plasma generation region 14, and diamond crystals are deposited on the substrate 7 using carbon in the mixed gas as a raw material. and board 7
Diamonds can be obtained in different forms, such as microcrystals or thin films, depending on the type and processing conditions.

In the diamond vapor phase synthesis apparatus shown in FIG. 2, if a Si wafer is used as the substrate 7, the substrate temperature will be approximately 850°C under the above-mentioned processing conditions, and a Crystalline diamond precipitates at a growth rate. Reference numeral 15 in FIG. 2 is a plunger, which is used to adjust the reflection of the microwave so that the substrate 7 is accurately located at the center of the plasma generation region 14.

A member designated by reference numeral 20 is an applicator, which functions to prevent the reaction tube 6 from being excessively heated by supplying cooling water from the supply pipe 21 and discharging it from the discharge pipe 22.

On the other hand, as mentioned above, CH4 gas as a carbon raw material is diluted with H2 gas, and H2 gas is used to remove non-diamond substances that are generated simultaneously with diamond. That is, %H2
Atomic hydrogen, which is produced when gas decomposes in plasma, is more effective than diamond in graphite, amorphous carbon, a-C:
It is easy to combine with non-diamond materials such as H (these non-diamond materials, which are generated simultaneously with diamond during vapor phase synthesis, are etched away by the atomic hydrogen.

[Problems to be Solved by the Invention] In addition to the above-mentioned methane (CH4), gaseous hydrocarbons such as acetylene, ethylene, ethane, and benzene can be used as carbon raw materials in the gas phase synthesis apparatus shown in FIG. was 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.

However, although the gaseous hydrocarbons mentioned above are not expensive, they cannot be said to be cheap enough to be consumed frequently in large quantities. Furthermore, when these hydrocarbons are used as carbon raw materials in the gas phase synthesis of diamond, the conversion rate to diamond is as low as about 0.01%, so large quantities have to be used, resulting in lower raw material costs. becomes something that cannot be ignored.

The present invention was made under these circumstances, and
The purpose is to provide a gas phase synthesis method that can synthesize diamond relatively inexpensively and efficiently.

[Means for Solving the Problems] The present invention, which has achieved the above object, uses a solid carbon material and carbon dioxide as carbon raw materials in the vapor phase synthesis of diamond, and performs the vapor phase synthesis in a hydrogen plasma atmosphere. This is a diamond vapor phase synthesis method that has a key point in the way it is carried out.

[Operations] The present invention is constructed as described above, but its main feature is that solid carbon and carbon dioxide are used instead of CH4 gas and other gaseous hydrocarbons as carbon raw materials.

The process by which the present invention was completed will be explained step by step.

First, the present inventors investigated various carbon raw materials that can be substituted for the gaseous hydrocarbons, and noticed that solid carbon such as graphite and powdered carbon is relatively easily produced by hand and is inexpensive. Note that, as is clear from the above purpose, the term "solid carbon" in the present invention includes powdered carbon raw materials.

Next, we conducted further intensive research based on the idea that if the solid carbon described above could be used for the gas phase synthesis of diamond, it would become a useful carbon raw material. As a result, they discovered that diamond can be efficiently synthesized under certain conditions even when solid carbon is used as a carbon raw material, leading to the completion of the present invention.

When solid carbon is used as a carbon raw material for diamond vapor phase synthesis, the solid carbon needs to be transported onto the substrate after being converted into -H gas during vapor phase synthesis, which is an inefficient carbon material. There were concerns that it might be a raw material. The existence of such preconceptions can be considered to be the reason why solid carbon has not been used as a carbon raw material for diamond vapor phase synthesis.

However, the inventors have confirmed through experiments that even when solid carbon is used as the carbon source, C
By performing gas phase synthesis while introducing O2 gas, diamond could be synthesized efficiently. This is Co
2 has strong reactivity with solid carbon, and C
This can be considered to be because solid carbon is easily vaporized when o2 is present.

On the other hand, when CO2 gas is introduced into a gas phase synthesis apparatus, oxygen atoms (or ions) and carbon are generated by the decomposition of CO2 molecules, but the generated atomic oxygen is more likely to be removed from non-diamond materials than the atomic hydrogen. The effect of having a large action can also be obtained. That is, as mentioned above, atomic hydrogen has the effect of removing non-diamond substances generated during diamond vapor phase synthesis, but atomic oxygen produced by the decomposition of CO2 has the effect of removing non-diamond substances. is even stronger than the above-mentioned atomic hydrogen, and as a result, the C concentration in the plasma atmosphere can be further increased, and the efficiency of vapor phase synthesis of diamond can be increased. Further, since C produced by the decomposition of Co2 gas contributes to the growth of diamond, CO2 can be regarded as both a reactive gas and a carbon raw material. More preferably, C02, which has the above-mentioned great effects, is relatively inexpensive and can be easily produced by hand. In this way, by allowing solid carbon and Co2 to coexist in the plasma atmosphere and allowing the reaction to proceed, diamond gas phase synthesis can be achieved relatively inexpensively and efficiently.

In addition, when a carbon plate is used as the solid carbon used in the present invention, it is also a preferable means to make the carbon plate porous to increase its surface area in order to advance gas phase synthesis more favorably. can.

Furthermore, in the present invention, it is also necessary to introduce a predetermined amount of H2 gas, which has been required in the past, into the vapor phase synthesis apparatus. This is to control the removal rate of the non-diamond material according to vapor phase synthesis conditions such as substrate temperature and gas pressure. Therefore, in carrying out the present invention, a configuration may be adopted in which a predetermined amount of a mixed gas of Co2+H2 is introduced into a gas phase synthesis apparatus in which solid carbon is placed. The optimal mixing ratio (Co2+H2) of the mixed gas in this case varies depending on the vapor phase synthesis conditions and is not limited in any way, but is preferably about 0.01 to 20.

[Example] FIG. 1 is a schematic explanatory diagram showing the main parts of an example of a vapor phase synthesis apparatus configured to carry out the method of the present invention.

The configuration of the device shown in FIG. 1 is basically the same as the configuration of the device shown in FIG. 2, and corresponding parts are given the same reference numerals to avoid redundant explanation. The magnetron oscillator 1 shown in FIG. Isolator 2. Although the power monitor 3 and tuner 4 are omitted in FIG. 1 for convenience of explanation, it goes without saying that these members are necessary when carrying out the method of the present invention.

In FIG. 1, a substrate 7 is placed on a support 9 in a plasma generation region 14 in a reaction tube 6 made of quartz, and a carbon source is placed near the substrate 7 (above in FIG. 1). A carbon plate 25 is likewise arranged by the support base 9.

In the apparatus shown in FIG. 1, the reaction tube 6 is
A mixed gas of Co2+H2 is introduced into the chamber, and microwaves are also introduced from the waveguide 5. Then, the inside of the reaction tube 6 becomes a hydrogen plasma atmosphere, and a carbon-hydrogen plasma reaction progresses to maintain a high temperature. As a result, hydrocarbon gas, hydrocarbon ions, hydrocarbon radicals, etc. are generated, and atomic oxygen and atomic hydrogen are generated by decomposition of the mixed gas, and these are transferred onto the substrate 7. Diamond particles and a diamond thin film are deposited on 7.

FIG. 3 is a schematic explanatory diagram showing another example of a vapor phase synthesis apparatus configured to carry out the method of the present invention.

In this device, as shown in the figure, a reaction tube 6 is arranged horizontally, a support stand 9 is installed inside the reaction tube 6, carbon powder 26 is placed on this support stand 9, and carbon powder 26 is placed on the support stand 9. A substrate 7 is installed on the downstream side of the reaction tube 6 (on the right side in FIG. 3). Even in such an apparatus, diamond particles or a diamond thin film can be deposited on the substrate 7 using the same principle as shown in FIG. 1.

The present inventors conducted an experiment using the vapor phase synthesis apparatus shown in FIG. 3 above. That is, the output of the microwave is set to 700 W, and the substrate 7 is placed slightly offset from the center of the waveguide 6.
A mixed gas of CO2+H2 was supplied from the population 11 side of the reaction tube 6 at a flow rate of 11005 cc.

The pressure inside the reaction tube 6 is set to 70 Torr by exhausting a predetermined amount of the mixed gas of C02+H2 from the exhaust port 13 side.
Adjusted to r. When the reaction was allowed to proceed for 7 hours,
Diamond fine particles with a diameter of 2 μm were deposited on the substrate 7.

The vapor phase synthesis apparatus for carrying out the method of the present invention is not limited to the configuration shown in FIGS. 1 and 3, and various other configurations may also be adopted. For example, Figures 4 to 8 below are examples of this, and will be explained below with reference to these figures, but since the basic principle is the same as in Figures 1 to 3, the differences in configuration will only be briefly explained. stay.

First, the vapor phase synthesis apparatus shown in FIG. 4 is an example in which a substrate 7 and a carbon plate 25 are placed facing each other in a reaction chamber 27. In this device, the mixed gas of CO2+H2 is supplied to the supply pipe 28.
Hydrogen plasma is supplied into the reaction chamber 27 and exhausted from the exhaust pipe 29, while microwaves are introduced from the waveguide 5, and hydrogen plasma is generated in the reaction chamber 27 so as to surround the substrate 7 and the carbon plate 25. It is something that makes you Reference numeral 30 in FIG. 4 is a window for introducing microwaves.

Next, the vapor phase synthesis apparatus shown in FIG. 5 is almost the same as the apparatus shown in FIG. 4, and the difference is that carbon powder 26 is used instead of carbon plate 25.

Furthermore, the vapor phase synthesis apparatus shown in FIG. 6 is an example in which waveguides 5 are provided at two locations. That is, the waveguide 5a placed on the upstream side of the reaction tube 6 heats the carbon powder 26 to react with hydrogen plasma, and the waveguide 5b placed on the downstream side of the reaction tube 6 heats the carbon powder 26 to react with hydrogen plasma around the substrate 7. A plasma atmosphere is created. The generated hydrocarbons, radicals, ion species, etc. are transferred onto the substrate 7 by a mixed gas of CO2+H2, and diamond is deposited on the substrate 7.

In the vapor phase synthesis apparatus shown in FIG. 7, carbon powder 26 is placed in the plasma generation region 14, and the downstream side of the reaction tube 6 into which the mixed gas of C02+H2 is introduced is a reaction chamber 27a having a relatively large capacity. A substrate 7 with a wide area is installed in this reaction chamber 27a, and diamond is deposited on this substrate 7. At this time, the substrate 7 is heated to 800 to 1000° C. by the auxiliary heater 33.

In the gas phase synthesis apparatus shown in FIG. 8, a heat insulating material 34 is lined on the inner wall of the reaction chamber 27, and a carbon plate 25 is placed on the heat insulating material 34. By supplying a mixed gas of CO2+)(2 into the reaction chamber 27 from the supply pipe 28 and introducing microwaves from the waveguide 5,
The inside of the reaction chamber 27 is made into a high temperature hydrogen plasma atmosphere and the substrate 7 is
Deposit diamonds on top.

[Effects of the Invention] As described above, according to the method of the present invention, solid carbon and carbon dioxide are used as carbon raw materials instead of conventional gaseous hydrocarbons, so diamond can be produced relatively inexpensively and efficiently. It is now possible to synthesize.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram showing the main parts of an example of a vapor phase synthesis apparatus configured to carry out the method of the present invention, FIG. 2 is a schematic explanatory diagram showing an example of a conventional vapor phase synthesis apparatus, and FIG. 1 is a schematic explanatory diagram showing another example of a vapor phase synthesis apparatus configured to implement the method of the present invention, and FIGS. 4 to 8 show various types of vapor phase synthesis apparatus configured to implement the method of the present invention. It is a schematic explanatory diagram showing an example. 1... Magnetron oscillator 5.5a, 5b... Waveguide 6... Reaction tube 7...
・Substrate 9...Support stand 14...Plasma generation area

Claims (1)

[Claims] A method for vapor phase synthesis of diamond, characterized in that the vapor phase synthesis of diamond is performed in a hydrogen plasma atmosphere using a solid carbon material and carbon dioxide as carbon raw materials.