JP2585342B2 - Diamond vapor phase synthesis - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a diamond vapor phase synthesis method for uniformly coating diamond on a substrate having a complicated shape at high speed.

[Conventional technology]

In the gas phase synthesis method of diamond, a mixed gas of hydrocarbon and hydrogen is excited by heat, and the hydrocarbon is thermally decomposed on a heated base material to synthesize diamond, thereby coating the base material. Thermal CVD method (Japanese Patent Laid-Open No. 58-91100) or microwave plasma CVD in which excitation is performed by microwave discharge
A method (Japanese Patent Application Laid-Open No. 58-110494) and the like are known.

Also, a mixed gas of an organic compound containing oxygen and hydrogen is used instead of a mixed gas of hydrocarbon and hydrogen as a raw material gas (reaction gas) (Japanese Patent Application Laid-Open No. 61-183198), or a mixed gas of hydrocarbon and hydrogen is used. There is known a method of improving the rate of synthesizing diamond and forming a film by adding oxygen gas to gas and using the gas (Japanese Patent Application Laid-Open No. 61-158899).

[Problems to be solved by the invention]

In the prior art, the following three conditions were required to synthesize diamond from the gas phase. That is,
The reaction gas consisting of hydrogen and hydrocarbons (generally methane) is sufficiently excited, and the substrate temperature is 700 ° C
That is, it is heated to 1100 ° C. or less, and atomic hydrogen is sufficiently present in the reaction gas. These conditions are based on the fact that the mechanism of diamond formation is that methane is excited to form methyl radicals, and these methyl radicals are bonded to the carbon atoms that have diamond bonds on the substrate, and diamond grows. I'm wearing However, in terms of thermodynamics, graphite is considered to be dominant because graphite is more stable than diamond.However, atomic hydrogen selectively etches graphite, and as a result, diamond It is believed that it can be synthesized.

Considering the film formation rate, which is an important factor in industrially efficiently synthesizing diamond from the gas phase according to the prior art, the amount of hydrocarbons in the reaction gas should be increased as much as possible to reduce the amount of methyl radicals. The need to increase is self-evident.

However, when the amount of hydrocarbons is actually increased, high-quality diamond cannot be obtained, and a large amount of graphite or amorphous carbon is deposited. It is considered that this is because the amount of atomic hydrogen that selectively etches graphite or the like is relatively insufficient due to an increase in hydrocarbons.

Therefore, as a method of increasing the supply amounts of hydrocarbons and hydrogen, a method of increasing the pressure of a mixed gas is generally used. However, since the mean free path of the gas particles is inevitably reduced due to the increase in the pressure of the mixed gas, the flight distance of so-called excited particles such as atomic hydrogen becomes short. Inevitably, the diamonds cannot be synthesized when the distance from the excitation source is long.

Table 1 shows that in the thermal CVD method, a tungsten (W) filament was heated to 2200 ° C. as an excitation source, and a molybdenum (Mo) plate was used as a substrate to keep the surface temperature constant at 980 ° C. ₂ ) When a 97: 3 (volume ratio) mixed gas of methane and CH ₃ was flowed at 100 Torr to perform a synthesis reaction,
The relationship between the distance between the excitation source and the substrate and the diamond deposition rate is shown.

This fact is not particularly problematic when the surface of a flat substrate is coated with diamond, but is important when the surface of a substrate having a three-dimensional shape, such as a drill, is uniformly coated with diamond. In practice, uniform coating has been extremely difficult or impossible.

In order to coat a three-dimensional substrate with diamond, the mean free path of excited particles such as methyl radicals and atomic hydrogen may be increased to increase the flight distance. That is, the pressure of the mixed gas of hydrogen and hydrocarbon may be reduced, but the supply of methyl radicals is significantly insufficient, and satisfactory diamond coating is generally not obtained.

An object of the present invention is to solve the above-mentioned difficulties and to provide a method for uniformly vapor-phase synthesizing a diamond coating even on a three-dimensional substrate.

[Means for solving the problem]

The present invention provides a gas phase of diamond that synthesizes diamond by decomposing organic compounds by introducing a mixed gas of an organic compound gas, hydrogen gas and oxygen gas into a substrate heated to 700 ° C. to 1200 ° C. In the synthesis method, when the pressure of the mixed gas is PTorr and the number of carbon atoms contained in one molecule of the organic compound is N, P <10 and 10 <P ×
The relationship N <100 is satisfied, and the oxygen partial pressure in the mixed gas is 0.0001 × PTorr or more and 0.03 × PTorr or less,
A diamond vapor phase synthesis method characterized in that the hydrogen partial pressure is 0.9 × PTorr or more and 0.999 × PTorr or less.

The present invention uses conventional hydrogen gas (H ₂ ) and methane gas (CH ₄ )
Alternatively, instead of CH ₄ in a method using a mixed gas of H ₂ , CH ₄ and oxygen gas (O ₂ ) as a raw material, organic compounds such as hydrocarbons, alcohols, ketones, etc., containing more carbon atoms in one molecule than CH ₄ Compounds, for example, a hydrocarbon represented by a general formula such as CnH _{2n + 2} (2 ≦ n ≦ 10), an alcohol represented by a general formula of CnH _{2n + 1} OH, C
By using a ketone represented by a general formula such as nH _{2n + 1} COCmH _{2m + 1} , the number of active methyl radicals is increased as compared with the case of CH ₄ without lowering the relative ratio of active hydrogen atoms. In addition, as these hydrocarbons, alcohols, and ketones, those having only unsaturated bonds without unsaturated bonds are more likely to cause less deposition of carbon other than diamond in the formed diamond, preferable.

In the present invention, the oxygen partial pressure is 0.0001 × PTorr or more 0.03
× PTorr or less, which corresponds to a volume ratio in the mixed gas of 0.01% or more and 3% or less. At the same time, the hydrogen partial pressure is in the range of 0.9 × PTorr or more and 0.999 × PTorr or less, which is also equivalent to 90% or more and 99.9% or less (volume ratio) in the mixed gas.

As a method for exciting the mixed gas, a conventional technique may be used,
Heat Specifically, preheating by metal filament, plasma,
Specifically, excitation by plasma such as DC, RF, microwave,
Further, various means such as a combined use of these means, an arc, ECR plasma utilizing ECR resonance, and optical excitation using a laser can be employed.

[Action]

The present invention increases the flight distance of excited species such as methyl radicals and atomic hydrogen in the mixed gas by lowering the pressure of the mixed gas when depositing diamond from a mixed gas of an organic compound and hydrogen. This is a method by which a substrate having a three-dimensional shape can be uniformly coated with diamond.

If the pressure of the mixed gas is reduced, the conventional technology lacks methyl radicals and cannot achieve a satisfactory film formation rate. Therefore, the lower limit of the pressure is at most 5 to 10 Torr. In order to increase the amount of methyl radicals, it is only necessary to increase the ratio of hydrocarbons in the mixed gas. However, inevitably, the amount of atomic hydrogen decreases and precipitation of non-diamond carbon becomes remarkable. This has already been described.

Therefore, the present invention increases the amount N of carbon atoms contained in an organic compound in order to increase the amount of methyl radicals without reducing the amount of atomic hydrogen. Specifically, assuming that the pressure of the mixed gas is PTorr, P
It was found that the relationship of <10,10 <P × N <100 should be satisfied. When P is 10 Torr or more, there is no difference from the prior art. Further, if P × N is 100 or more, precipitation of non-diamond is not hindered regardless of other conditions, and P × N
When N is less than 10, diamond does not precipitate.

Further, the deposition of non-diamond-like carbon cannot be completely prevented only under the conditions of P <10, 10 <P × N <100, because the pressure of the mixed gas is low and the atomic hydrogen is also relatively small. . Therefore, addition of oxygen is indispensable to supplement the effect. Oxygen is also known to have the effect of selectively etching graphite like atomic hydrogen, but is generally smaller than the selective effect of atomic hydrogen. It is said that atomic hydrogen etches graphite at a rate more than 100 times faster than diamond, while oxygen is about 10 times faster. However, the graphite etching rate of oxygen is fast enough,
It is effective with a very small amount of addition. That is, the amount of oxygen added is such that the oxygen partial pressure in the mixed gas is 0.0001 × PTorr or more.
It is preferable to be 0.03 × PTorr or less. 0.0001 × PTorr
If it is less than 0.03 × PTorr, the effect is not recognized, and if it exceeds 0.03 × PTorr, the deposition rate of diamond is decreased, which is not preferable. This oxygen may be derived from an oxygen atom contained in the organic compound.

Furthermore, the hydrogen partial pressure is 0.999
× PTorr or less is preferable. Hydrogen partial pressure 0.9 × PT
Less than orr does not prevent non-diamond carbon deposition, 0.999
If it exceeds × PTorr, the amount of organic compounds relatively decreases, which is not preferable.

In addition, it is preferable that a base material temperature is 700 to 1200 degreeC. If the temperature is less than 700 ° C or exceeds 1200 ° C, diamond does not precipitate.

〔Example〕

Example 1 In a thermal CVD apparatus, tungsten filament was 225
The temperature was set to 0 ° C., a molybdenum (Mo) plate was used as the substrate, and the temperature of the substrate was kept at 980 ° C., and the distance between the filament and the substrate was variously changed, and diamond coating was attempted. The mixed gas of the conventional method is H ₂ : CH ₄ = 99: 1 (volume ratio), and the mixed gas of the present invention is H ₂ : n-C ₄ H ₁₀ : O ₂ = 98: 1.9: 0.1 (volume ratio). is there. In each case, the reaction was continued for 5 hours, and after coating, the film thickness was measured and the obtained film was identified by Raman spectroscopy. Table 2 shows the results.

Example 2 Using the same thermal CVD apparatus as in Example 1, a mixed gas of H ₂ : n-C ₄ H ₁₀ : O ₂ = 98: 1.9: 0.1 (volume ratio) was used as in the method of the present invention of Example 1. Flow at 5 Torr, and place a cemented carbide twist drill φ1.0 at a distance of 2.5 cm from the tungsten filament.
The drill was placed in parallel with the gas flow so that the tip of the drill came in mm, and the diamond was coated for 3 hours. As a result, the cutting edge of the drill was uniformly coated with diamond.

Example 3 In a microwave plasma CVD apparatus, 30 c
m away from the cemented carbide chip (ISO K-10, model number SPG
321) was arranged, and diamond coating was performed under various conditions shown in Table 3 for 5 hours. The results are shown in Table 3, which shows that the three-dimensional chip can be uniformly coated with diamond under the limited conditions of the present invention. In addition, it can be said that the larger the distance over which the diamond can be covered from the rake face, the more uniformly the diamond can be covered.

Example 4 In the same microwave plasma CVD apparatus as in Example 3, a cemented carbide chip (ISO K-10, model number SPG322) was placed 3.0 cm away from the center of the waveguide, and a microwave of 2.45 GHz was used. Power of 500 W and 5 Torr of H ₂ as reactant gas:
_{n-C 4 H 9 OH =} 98: it flowed a gaseous mixture of 2 (volume ratio). Incidentally, since P = 5 and N = 4 under this condition, P × N = 20
It is. The oxygen partial pressure is 5 × 2/100 × 1/2 = 0.05 (Tor
Since r), 0.05 / 5 = 0.01 for P and the hydrogen partial pressure is 0.98 for P, so both are within the scope of the present invention. After coating for 2 hours under the above conditions,
A diamond having a thickness of 5 μm was coated at least 1 mm from the rake face. Note that this embodiment and Examples 1 to 3
The film was identified by Raman spectroscopy.

〔The invention's effect〕

As described above, the present invention is a very practical diamond vapor-phase synthesis method capable of uniformly coating a three-dimensional substrate with diamond.

Claims (1)

(57) [Claims] An organic compound gas, a hydrogen gas and an oxygen gas are introduced into a substrate heated to 700 ° C. to 1200 ° C. in an excited state to decompose said organic compound to synthesize diamond. In the gas phase synthesis method, when the pressure of the mixed gas is PTorr and the number of carbon atoms contained in one molecule of the organic compound is N, P <10 and 10 <P ×
The relationship N <100 is satisfied, and the oxygen partial pressure in the mixed gas is 0.0001 × PTorr or more and 0.03 × PTorr or less,
A diamond gas phase synthesis method, wherein the hydrogen partial pressure is 0.9 × PTorr or more and 0.999 × PTorr or less.