JPH0474795A - Method for vapor phase synthesis of diamond - Google Patents

Abstract

PURPOSE:To improve growth rate and quality by applying an electric field across a nozzle for producing a combustion flame and a substrate and carrying out vapor phase synthesis of diamond in the aforementioned state. CONSTITUTION:A combustible gas (A), a combustion improving gas (B) and an oxygen atom-containing gas (C) are fed to a nozzle for producing a combustion flame arranged in an evacuative reaction vessel so as to provide molar ratios of 0.5<(A/B)<20 and 0.00001<(C/A)<0.1. The gases are then burned under 10-760 Torr pressure in a reducing atmosphere to form a flame composed of an inner flame and a flame cone. A DC or AC electric field is then applied across the nozzle and the substrate heated at 600-1200 deg.C to perform vapor phase synthesis of diamond on the substrate while producing a plasma.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for vapor phase synthesis of diamond using a combustion flame, specifically, a method for producing diamond with high purity, high crystallinity, high thermal conductivity, low dielectricity, and high translucency. The present invention relates to a new gas phase synthesis method that allows diamond to be synthesized inexpensively, rapidly, and stably for a long period of time for use in applications requiring high specific elasticity, wear resistance, etc.

[Conventional technology]

Conventionally, synthetic diamonds have been synthesized under thermodynamic stabilization at high temperatures and high pressures, but recently it has become possible to synthesize diamonds from the gas phase. This gas-phase synthesis method uses hydrocarbon scum diluted with hydrogen gas (usually 10 times or more) as a raw material, and excites this raw material scum with plasma or hot filament to form a diamond layer on the base material in a reaction chamber. ing. However, the growth rate is 0.1 μm/h to 2.0 μm/h.
It was slow at 0 μm/h, which was still a problem for industrial use.

Diamond synthesis using combustion flame has also been proposed as a new process for gas phase synthesis (Hirose et al., No. 35
Collected lecture abstracts of the Japan Association of Physical Sciences Association Lectures, 434
p. 29a-T-1, April 1986).

Furthermore, diamond synthesis using a combustion flame under reduced pressure has also been proposed (Yanagisawa et al., 37th Japan Society of Applied Physics, Proceedings, p. 358, April 1990).

However, there were still many problems in using these methods to stably synthesize diamond with good crystallinity over a long period of time with good reproducibility, and to apply them industrially.

In order to achieve high-speed vapor phase synthesis and high purity of diamond, the present inventors have already published a document in Japanese Patent Application No. 1-15456 entitled "Reducing atmosphere of a combustion flame in which a combustible gas is burned with a combustion-supporting gas". A method of synthesizing diamond on a substrate using a method, characterized in that the humidity of the synthesis atmosphere is set to 35% or more and 80% or less, stabilizes the synthesis of diamond, improves the growth rate, and reduces the precipitation area. We have found that it is possible to enlarge diamonds and improve the quality of diamonds, and have proposed the above method.

[Problem to be solved by the invention]

Part 2 Conventional techniques, especially diamond synthesis methods using combustion flames, have a short history (currently, the appropriate synthesis conditions are not fully understood). In contrast, due to the high degree of supersaturation of carbon, the surface of the precipitated diamond tends to become graphitized or amorphous, and a diamond film with good crystallinity can be deposited stably over a long period of time, such as several hours or more. Furthermore, since diamond synthesis using a combustion flame is usually carried out in a system open to the atmosphere, there is also the problem that nitrogen is incorporated into the precipitated diamond due to nitrogen diffusion from the atmosphere. If nitrogen is introduced randomly, problems such as the film quality becoming blackish or an increase in non-diamond components in addition to diamond components may occur.

The purpose of the present invention is to further improve the growth rate, prevent nitrogen contamination, etc., and stably grow high-quality diamond films and diamond particles over a long period of time in a diamond vapor phase synthesis method using combustion flame. The objective is to provide a synthetic method that allows

[Means to solve the problem]

In order to solve these problems, the present inventors have conducted extensive research into a method of synthesizing diamond using the reducing atmosphere of combustion flames. Were we able to synthesize a film that does not contain nitrogen atoms? In this state, the diamond precipitation rate,
Although the surface area and quality are still insufficient, it is possible to stably coat diamond by applying a direct current or alternating current electric field between the combustion flame generating crater and the base material to generate plasma. Preferably, by adding an oxygen atom-containing gas to the synthesis atmosphere in addition to the combustion-supporting gas for combustion flame generation, it is possible to improve the diamond precipitation rate, expand the area, and stabilize the quality. This discovery led to the present invention.

That is, the present invention is a method for synthesizing diamond on a base material using the reducing atmosphere of a combustion flame obtained by burning a combustible gas with a combustion-supporting gas. This method is characterized by synthesizing diamond while an electric field is applied and plasma is generated.

In a particularly preferred embodiment of the present invention, the above-mentioned synthesis reaction is carried out in a reaction vessel which can be evacuated, and an oxygen atom-containing gas, especially preferably may include the above-mentioned method characterized in that water vapor is added.

At this time, the combustible scum (A), the combustion-supporting gas (B), and the oxygen atom-containing gas added to the reaction atmosphere separately from the combustion-supporting gas are present in the atmosphere in the reaction vessel that can be evacuated. It is particularly preferable that the molar ratio of the scum (C) [hereinafter also referred to as added oxygen atom-containing gas] satisfies the following conditions: 0.5<A/B<20 and 0.00001<C/A<0.1 .

Further, in the present invention, the atmosphere inside the reaction vessel which can be evacuated may contain an inert gas, in which case the combustible gas (A), the combustion supporting gas (B), and the above-mentioned oxygen atom-containing gas. It is particularly preferable that the molar ratio of (C) and inert gas (D) satisfies the following condition: D<A+B0C.

It is particularly preferable that the reaction pressure of the present invention is 10 Torr or more and 760 Torr or less.

[Effect]

In the present invention, in a method for synthesizing diamond using the reducing atmosphere of a combustion flame obtained by burning a combustible gas with a combustion-supporting gas, a direct current or alternating current electric field is applied between a combustion flame generating crater and a base material, The first feature is that plasma is generated, and the second feature is that the synthesis reaction is performed in a reaction container that can be evacuated, such as a vacuum chamber, and the vacuum chamber atmosphere contains an oxygen atom-containing gas. .

Thirdly, the method is characterized in that an inert gas is added to the atmosphere.

FIG. 1 is a schematic explanatory diagram of a specific example of the present invention, showing a state in which plasma is generated by applying an electric field between a combustion flame generating crater and a base material. The presence of this plasma results in stable increases in scum temperature, improvement in diamond growth rate, higher quality of diamond film, and densification of diamond film and crystal grains (this is especially advantageous when used in tools, etc.). Effects and effects can be obtained. Furthermore, since plasma is used, an inert gas can be introduced into the atmosphere, which can widen the area of diamond precipitation.

In order to prevent the diffusion and contamination of nitrogen from the atmosphere, the diamond synthesis reaction of the present invention is carried out in a reaction vessel that can be evacuated, such as a Hera cell or a vacuum chamber that can be evacuated, or by using a shield gas etc. It is preferable that the process be carried out in a state where the diffusion of

If nitrogen gas is present in the reaction atmosphere, nitrogen atoms will be incorporated into the precipitated Diacene 1 film, which is undesirable. In particular, in the case of the present invention that uses plasma, it is easy to incorporate nitrogen atoms, so there is a risk that the quality of the diamond film will deteriorate (increase in non-diamond components) and defects such as dislocations will increase in the diamond crystal. It is empty.

Addition of an inert gas to the atmosphere has the effect of increasing the gas temperature of the combustion flame and stabilizing the plasma, and is therefore also effective in expanding the deposition area.

In addition, in conventional diamond synthesis using a combustion flame that does not use plasma generation, adding an inert gas to the atmosphere lowers the gas temperature of the combustion flame and has the opposite effect.

FIG. 7 is a schematic diagram showing the structure of a general combustion flame generating crater and a normal combustion flame. Usually, a needle valve is placed inside the crater as shown in the figure, and all flammable gas is squeezed out and drawn into the surrounding combustion-supporting gas to flow. In normal atmosphere, the flame structure can be roughly divided into three parts: the flame core (core), the inner flame (acetylene feather in the case of an acetylene-oxygen flame), and the outer flame (3). is the inner flame part 2 with high reducing property. When the combustible gas and the combustion-supporting gas are completely combusted, the inner flame 2 does not exist, and the structure consists of only the flame core 1 and the outer flame 3. However, in this case, the flame becomes an oxidizing flame, so diamonds cannot be synthesized from this state. Therefore, by increasing the flow rate of the flammable gas from this state to create a state in which the inner flame 2 exists, and bringing this inner flame 2 into contact with the base material as shown in Figure 8, diamond synthesis is possible. Become. FIG. 8 is a schematic diagram showing a conventional diamond synthesis method using a combustion flame in the atmosphere. In Figure 7.8, d indicates the length of the flame core and d indicates the length of the inner flame.

On the other hand, in the present invention, since the combustion is performed while isolated from the outside air using a vacuum chamber or the like, the outer flame part 3 disappears and the inner flame part 2 increases as shown in FIG.

At this time, the length dz (m) of the inner flame 2 and the length d of the flame core, (
mm) or 1 < d 2 / d l ≦ 40 The distance between the tip of the flame core and the base material is 1 (mω) or 0 (IlII
o) < l ≦ 100100 (it is preferable to satisfy each of the following conditions).

In addition, since the present invention is carried out in a state where the atmosphere is shut off and the internal flame is increased, the optimum mixing ratio of combustible gas and combustion supporting gas is slightly oxygen Soften to a state where there is a large amount of

In the present invention, the combustible gases for generating combustion flames used as raw materials for diamond synthesis include acetylene, propane,
Ethylene, propylene, butane, butylene, Hensen,
Flammable IJ gases such as methane, ethane, carbon oxide, JI
Liquefied petroleum gas specified in S standard 22401980 (
LPG), city gas defined in JIS Standard 52121-1979, natural gas whose main component is methane and some other soft hydrocarbons, and petroleum-based fuels such as thermal cracking, catalytic cracking, hydrocracking, or partial combustion. Coke oven scum (C0G), which is obtained by reducing the molecular weight by the operation of
BFG), converter gas (L
DG) Gaseous substances such as coal gasification gas whose main components are Co and Hf, and liquid organic compounds containing a small amount of oxygen in the molecule such as alcohols, ketones, aldehydes, etc. The gas may be one type or a mixed gas of two or more types of compounds containing.

The combustion-supporting gas for generating a combustion flame in the present invention may be oxygen or a gas containing oxygen as a main component, such as a gas containing oxygen as a main component and impurities such as CO, Cot, CHt, etc.

In addition, in the present invention, it is preferable that an oxygen atom-containing gas is added to the reaction atmosphere in addition to the above-mentioned combustion-supporting gas for combustion flame generation, and the presence of this added oxygen atom-containing gas significantly reduces the diamond quality. The growth rate and film quality are improved, and the precipitation area is increased. The reason for this is that when an oxygen atom-containing gas is added to the reaction atmosphere, the reduction flame of the combustion flame (
This is thought to be due to an increase in highly active molecular species during internal inflammation.

The gas containing the added oxygen atoms is, for example, oxygen (Ox).
, Co, CO2, H2O, HtO2,
Examples include CzHsOHCH308, and water vapor is particularly preferred. This is a dissociation reaction of water vapor or an endothermic reaction, and a reaction during diamond formation or an exothermic reaction, so from the viewpoint of free energy change,
It is also thought that it acts as a kind of catalytic reaction that promotes the diamond-forming reaction.

However, these interpretations are only speculations because the process by which diamond is synthesized from the gas phase has not been elucidated.

The number of moles of each of the above gases is combustible gas (A),
When the combustion-supporting gas (B) and the gas containing added oxygen atoms (C), the molar ratio is 0.5<A/B<20 and 0.000
It is preferable to satisfy the following condition: 01<C/A<0.1.

When A/B≦0.5, the carbon concentration is low and no diamond is precipitated, and when 20≦Δ/B, the carbon concentration is high and non-diamond components other than Diacene 1- are significantly precipitated.

Similarly, gas containing added oxygen atoms (C) and flammable gas (A
) means that the molar ratio of each is 0.00001<C/Δ< 01,
When the molar ratio is C/A<0.00001, there is no effect of adding oxygen atom-containing scum, and when 0.1<C/A, on the other hand, conditions are such that diamond does not precipitate.

The addition of an inert gas to the reaction atmosphere is particularly effective in improving the stability of plasma discharge, as described above, but it is especially effective for improving the stability of plasma discharge. It is preferable that the molar ratio of (C) and inert gas (D) satisfies the following condition: D<A+B+C. This is because if an inert gas is mixed under the condition of D≧A+B+C, the temperature of the gas will drop significantly, and more non-diamond components will be precipitated.

Here, the inert gas of the present invention includes argon gas, helium gas, Kryton gas, xenon gas, and radon gas, and may be one type or a mixture of two or more of these gases.

The reaction pressure is preferably 10 Torr or more and 760 Torr or less. If it is less than 10 Torr, the diamond growth rate will be extremely reduced, and if it exceeds 760 Torr, it will be in a pressurized state in the atmosphere and the equipment will be large-scale, which is disadvantageous.

Is it preferable for the substrate temperature to be between 600°C and 1200°C, or is it possible to precipitate diamond even if the temperature is lower than 600°C due to the problem of lowering the growth rate or the melting point of the coating substrate? be.

On the other hand, it is not preferable for the surface temperature of the base material to exceed 1100° C., since the base material tends to contain graphite components and amorphous components in addition to the diamond film quality.

The base material used in the present invention may be any base material commonly used in this type of diamond vapor phase synthesis method, such as Si, SiC, SuN, BBCBN, etc.
, BCN, W, WC, Mo, Mo, CNb, Ta,
Af', A1'N, C, Ti, Tic, Ti
N.Cu.

Examples include SiOx and Al20s.

According to the method of the present invention, it is possible to synthesize high-quality diamonds uniformly using plasma application (compared to the conventional method, which does not contain oxygen atoms in the combustion atmosphere), at a growth rate several times higher than that of the conventional method, which does not contain oxygen atoms in the combustion atmosphere, and which does not contain non-diamond components. In addition, it was found that it could be produced stably for a long period of time (several hours).

〔Example〕

The present invention will be explained below with specific examples, but the present invention is not limited thereto.

Examples 1 to 11 and Comparative Examples 12 to 15 FIGS. 1 to 4 are schematic diagrams showing examples of the vacuum chamber type combustion flame generator used in the present examples, and show the flame generation section of the device. As shown in FIG. 5, this is an internal mixing type of combustible scum and combustion-supporting gas, and has an injector structure with a needle valve so that the gas ejection speed can be adjusted.

In addition, the base material is placed on a support stand equipped with a cooling device using cooling water, etc., and a stabilized power source capable of applying a direct current or alternating current electric field is installed between the base material and the crater for generating combustion flames above the base material. The crater and cooling support are fixed to the vacuum chamber via insulators.

Figure 1 shows an example in which the reaction atmosphere gas consists of only combustion-supporting gas and combustible gas, where the combustible gases are CzHsOH,
It is bubbled through a constant temperature bath containing (CH3)2C0, etc., and then introduced into the combustion crater.

FIG. 2 is a diagram showing an example in which a gas containing added oxygen atoms is introduced into the reaction vessel.

FIG. 3 is a diagram showing an example in which water vapor is introduced into the reaction vessel as the added oxygen atomic gas, and the water vapor generated in the thermostatic chamber is introduced through a needle valve.

Figure 4 shows an inert gas or a gas containing added oxygen atoms introduced from a nozzle concentrically surrounding the outside of the generated combustion flame, and an inner flame and an outer flame (reducing flame). This is a diagram illustrating an example of controlling and stabilizing incomplete combustion (which may result in an external flame that normally disappears in a vacuum).

In this example and comparative example, the base material was 3 mm thick with a thickness of 2.5 mm.
#5000 (1/2-3
The surface was polished using diamond powder of IA).

The diamond film synthesis time was 5 hours for each.

The created film was examined using an optical microscope and a scanning electron microscope (SEM).
), surface observation and cross-sectional surface observation were performed, and crystal structure was evaluated using X-ray diffraction, Raman spectroscopy, and transmission electron microscopy.

Raman spectroscopic analysis was performed using an Ar laser with a wavelength of 514 nm and a backscattering method. As shown in the Raman spectrum diagram in Figure 6, the index of diamond crystallinity determined by this Raman spectroscopic analysis is 1332,5±5 c+
The ratio (F/E) between the diamond component peak (E) appearing at n-' and the non-diamond component peak (F) mainly appearing at 1100 to 1700 cF-' was determined and used as an index of diamond crystallinity. . The peak indicating the presence of non-diamond components has a size of 1400 to 1600.
In most cases, those appearing in the cm-' range usually have the highest intensity. The smaller this value (F/E) is, the less non-diamond components are mixed in, indicating that the diamond is of high quality.

In addition, the state of nitrogen atoms mixed in diamond is ESR (
It was measured by the electron spin resonance) method.

Table 1 below shows the experimental conditions, and Table 2 shows the experimental results.

Table 2 Nα1 to Nα11 which are examples of the present invention and Nα14 which is a comparative example. As can be seen by comparing Nα15, by generating plasma and synthesizing diamond in a reaction vessel that excludes nitrogen gas, it contains almost no non-diamond components and no nitrogen atoms are mixed into the film. This indicates that it will be possible to synthesize diamond films with fewer defects.

Next, in order to evaluate the tool performance, diamond with a thickness of 100ρ was coated on the Si base material under the same conditions as Nα1 in the example and Nn14 in the comparative example, only the coating time was changed, and cutting was performed using laser processing. After dissolving with fluoronitric acid, the cemented carbide pedestal was treated with blades.

An A390 alloy (Ai'-17%Sl) round bar with four grooves extending in the axial direction on its outer peripheral surface was used as the work material, cutting speed was 400 m/min, depth of cut was 0.2 mm, and feed rate was O.
, 1 mm/rev, and the tool performance was evaluated.

The sample made under the conditions of Nα1 in the example had a V b cutting edge wear amount or 24 capes in 60 minutes of cutting, or the Nα in the comparative example.
The sample prepared under the conditions of No. 14 had a VB cutting edge wear amount of 55 in one minute of cutting.

Nα1 to Nα11 of the examples of the present invention in which water vapor and oxygen atom-containing gas were added to the atmosphere are the k of the comparative examples without addition.
It can be seen that it is possible to synthesize a higher quality diamond than that of 12 to Nα15.

Addition of an inert gas was found to be effective in expanding the precipitation area, as can be seen by comparing Nαl of the example and Nα9 of the example. However, evaluation of diamond film quality by Raman spectroscopy revealed that the film quality was slightly inferior due to the addition.

From the above results, particularly preferred embodiments of the present invention are: (1) using acetylene gas as the flammable gas and oxygen scum as the combustion-supporting gas; (2) introducing water vapor gas into the reaction atmosphere; (1) l O
It was found that the reaction was conducted in the range of Torr to 760 Torr.

〔Effect of the invention〕

Normally, the method of synthesizing diamond using the one-dimensional atmosphere of a combustion flame is carried out in the atmosphere, or in this case, nitrogen in the atmosphere is incorporated into the precipitated diamond, resulting in the precipitation of many non-diamond components or defects. There were many drawbacks. In the present invention, an electric field is applied between the combustion flame generation crater and the base material to generate plasma, prevent nitrogen from entering the reaction vessel that can be evacuated, and introduce oxygen atom-containing gas such as water vapor into the atmosphere. By adding it, it became possible to synthesize high-quality diamond over a large area at high speed. In addition, stable synthesis over a long period of time becomes possible, and reproducibility is improved.

Diamond according to the present invention has high thermal conductivity, low dielectric property,
Fields that require high light transmittance, high specific elasticity, high strength, wear resistance, etc., such as cutting tools, bodding tools, IC substrates, diaphragms, various window materials such as X-ray/CO7 window materials, and environmental resistance. It is expected that it will be provided as a device.

[Brief explanation of the drawing]

Figures 1 to 4 are schematic explanatory diagrams showing various embodiments of diamond synthesis in a vessel that can be evacuated according to the present invention, and Figure 5 shows the state of the combustion flame when the atmosphere is shut off according to the present invention. FIG. 6 is a Raman spectrum diagram illustrating a method for determining the F/E value of diamonds obtained in Examples and Comparative Examples of the present invention. FIG. 7 is a schematic diagram showing an example of a typical combustion flame generating crater, and FIG. 8 is a schematic illustration of diamond synthesis using a typical combustion flame in the atmosphere.

Claims (1)

[Scope of Claims] (1) In a method for synthesizing diamond on a base material using a reducing atmosphere of a combustion flame obtained by burning a combustible gas with a combustion-supporting gas, A diamond vapor phase synthesis method characterized by a synthesis reaction in which plasma is generated by applying a direct current or alternating current electric field to the diamond. (2) The above synthesis reaction is carried out in a reaction vessel that can be evacuated, and an oxygen atom-containing gas is added to the atmosphere inside the reaction vessel in addition to the combustion supporting gas for generating combustion flames. The method for vapor phase synthesis of diamond according to claim (1). (3) The flammable gas (A), the combustion-supporting gas (B), and the oxygen atom-containing gas (C) added separately from the combustion-supporting gas in the atmosphere in the evacuated reaction vessel. 2. The method for vapor phase synthesis of diamond according to claim 2, wherein the molar ratio of 0.5<A/B<20 and 0.00001<C/A<0.1 is satisfied. (4) Claim (2) characterized in that the oxygen atom-containing gas added to the atmosphere in the reaction vessel separately from the combustion-supporting gas is water vapor.
) or the diamond vapor phase synthesis method described in (3). (5) Claim (2) or (3) characterized in that the atmosphere within the reaction vessel that can be evacuated contains an inert gas.
The method of vapor phase synthesis of diamond described. (6) Flammable gas (A), combustion-supporting gas (B), oxygen atom-containing gas (C) added to the atmosphere inside the reaction vessel separately from the combustion-supporting gas, and inert gas (D) The method for vapor phase synthesis of diamond according to claim 5, wherein the molar ratio of D satisfies the following condition: D<A+B+C. (7) The diamond according to claim (5) or (6), wherein the inert gas to be added is one or a mixture of two or more of argon gas, helium gas, Kryton gas, xenon gas, and radon gas. vapor phase synthesis method. (8) The method for vapor phase synthesis of diamond according to any one of claims (1) to (7), characterized in that the reaction pressure is 10 Torr or more and 760 Torr or less.