JPH02279591A - Method for synthesizing diamond - Google Patents

Abstract

PURPOSE:To well hold crystallinity and to improve a film forming speed by maintaining the concn. of the carbon-contg. compd. in a gaseous mixture lower than the optimum concn. of the carbon-contg. compd. in the case of no voltage impression to a base body. CONSTITUTION:Gaseous raw materials 1 are mixed with gaseous hydrogen 2 and additive gases are mixed therewith in some cases. The gaseous raw materials are then introduced through a raw material supply nozzle 7 into a reaction vessel 6 at the flow rate controlled by a mass flow controller 5. The gaseous raw materials are thermally cracked by a thermion radiating material 10 heated by a power source 11 for heating the thermion radiating material and diamond is synthesized on the base body 8 heated on a base body holder 9. The concn. of the carbon-contg. compd. in the gaseous raw materials is decreased to the value lower than the optimum concn. of the carbon-contg. compd. at which the good crystal can be synthesized without impressed voltage according to the voltage to be impressed, by which the diamond having the good crystallinity is synthesized.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method of synthesizing diamond, and more particularly to a method of synthesizing diamond using thermal decomposition using a thermionic emitter.

<Prior Art> Diamond has various excellent physical properties such as high hardness, high thermal conductivity, excellent insulation, good translucency, and chemical stability. For this reason, Dai\Mondo is used in a wide range of fields, including applications such as coating cutting tools, coating optical materials, semiconductor heat sinks, and high-temperature operating semiconductors.

By the way, conventional diamond synthesis involves N2 at high temperature and high pressure.
This method has been carried out using a catalyst such as i, but this method has a problem of high cost. Therefore, in recent years, research on vapor phase synthesis methods at low temperatures and low pressures has been actively conducted.

There are two main methods for synthesizing diamonds at low temperatures and pressures:

1. A method using thermal decomposition using a thermionic emitting material (for example, Japanese Patent Publication No. 59-27753, etc.).

2. A method in which plasma is generated by microwave discharge, direct current discharge, high frequency discharge, etc., and reactions in the plasma are used (for example, Japanese Patent Publication No. 59-27754, etc.).

However, all of these methods have problems in that the film formation rate is slow and the film formation area is small, which hinders their practical application.

Among the above methods, the method using a thermionic emitter is considered to be relatively easy to increase the area, but in order to improve the film formation rate in this method, the electron shower from the thermionic emitter is used. For example, Japanese Patent Laid-Open No. 60-221395 discloses a technique using an electronic shower.

However, in this method, when the film formation rate is increased, a film with poor crystallinity containing graphite is synthesized, and a film with good crystallinity cannot be synthesized.

<Problems to be Solved by the Invention> The purpose of the present invention is to solve the above-mentioned problems and to propose a method for rapidly synthesizing a film with good crystallinity using thermal decomposition using a thermionic emitting material.

<t! P. Means for Solving the Problem> The present invention thermally decomposes a mixed gas of a carbon-containing compound and hydrogen using a heated thermionic emitting material, and a positive voltage is applied to the thermionic emitting material. In the method of synthesizing diamond on a substrate, the concentration of carbon-containing compounds in the mixed gas! f This is a diamond synthesis method characterized by maintaining the carbon-containing compound concentration lower than the optimum concentration when no voltage is applied to the substrate.

Effects> The structure and effects of the present invention will be explained in more detail.

During diamond synthesis using a heated thermionic emitter, the present inventors encountered a phenomenon in which the film formation rate improved but the film quality deteriorated when a positive voltage was applied to the substrate relative to the thermionic emitter. . As a result of repeated research on this phenomenon, we found that electron irradiation from the thermionic material causes the thermionic material to emit light.
It was found that the decomposition of carbon-containing compounds in the space between the substrates progressed, and the molecules involved in diamond synthesis in this space became supersaturated, which is the same as when the raw material gas concentration is high. Therefore, by reducing the raw material gas concentration from the optimum concentration when no voltage is applied, they discovered that diamond with good crystallinity was synthesized while the film formation rate remained high.

The present invention was established based on this discovery.

The present invention will be explained in more detail below with reference to FIG.

FIG. 1 is an explanatory diagram of an example of a diamond synthesis apparatus used in carrying out the present invention. Here, 1 is the raw material gas,
2 is hydrogen gas, 3 is additive gas, 4 is stop valve, 5
is a mass flow controller, 6 is a reaction vessel, 7 is a raw material supply nozzle, 8 is a substrate, 9 is a substrate holder with a built-in heater, 10 is a thermionic emissive material, 11 is a power source for heating the thermionic emissive material, I2 is a constant voltage power source It is.

In FIG. 1, a raw material gas 1 is mixed with hydrogen gas 2 and optionally an additive gas 3, and the flow rate is controlled by a mass flow controller 5 and introduced into a reaction vessel 6 through a raw material supply nozzle 7. The raw material gas is thermally decomposed by the thermionic radiation material 10 heated by the thermionic radiation material heating power source 11, and diamond is synthesized on the substrate 8 heated on the substrate holder 9. At this time, when a positive voltage is applied to the thermionic emitting material and the substrate by the constant voltage power supply 12 between the thermionic emitting material and the substrate, the decomposition of the raw material gas is promoted and the generation of nuclei is increased, thereby forming a diamond film. Speed can be improved. At this time, it is possible to synthesize diamond with good crystallinity by reducing the concentration of carbon-containing compounds in the raw material gas to a level lower than the optimal carbon compound concentration at which good crystals can be synthesized without applying voltage, depending on the applied voltage. .

The voltage applied to the substrate may be positive, but is more preferably 100V to 400V. If it is less than 1 oov, the effect will be small, and if it exceeds 400 μv, the reaction in the gas phase will proceed too much and the synthesis rate will decrease. At this time, the concentration of carbon-containing compounds in the raw material gas needs to be reduced in accordance with the applied voltage. At this time, the concentration of the carbon-containing compound is shown as follows.

(Concentration of carbon-containing compound in mixed gas) - (Optimum concentration of carbon-containing compound that allows synthesis of good crystals without applying voltage) x {
1-A×(applied voltage)) Here, A is a constant and cannot be specified because it changes depending on the type of carbon-containing compound and the synthesis conditions, but it is generally between 0.0001 and
Takes a value of 0.003. By adjusting the concentration of the raw material gas in accordance with the voltage in this way, diamond with good crystallinity can be synthesized at high speed.

Next, the diamond synthesis conditions will be described. The carbon-containing compound is not particularly limited as long as it contains carbon, and includes, for example, hydrocarbons such as methane, ethane, propane, ethylene, and acetylene, oxygen-containing carbon compounds such as methanol, ethanol, acetone, and carbon oxide, and tetrachloride. These include carbon, chlorine-containing carbon compounds such as metal chloride, etc. Among these, methane, acetylene, methanol, ethanol and the like are preferred because of their ease of handling and ease of thermal decomposition.

The base material is 600' which is the synthesis temperature of diamond.
It is preferable to use materials that do not cause damage at temperatures above C.0 For example, metals such as molybdenum and tungsten, semiconductors such as silicon, quartz,
Ceramics such as alumina.

The substrate temperature is preferably 600 to 1200°C. 600°
If the temperature is lower than C or higher than 1200℃, no diamond will be formed.

The pressure can be used in the range of 0.1 to 760 Torr, but considering the film formation rate and film quality, the pressure is 10 to 100 Torr.
r is preferred.

The flow rate cannot be limited because the optimum value changes depending on the size of the device, etc.

The material for the thermionic emitting material may be one with a melting point of 2,000"C or higher. For example, metals such as tungsten and kuntal, or alloys 1-carbide are used. The shape of the thermionic emitting material may be wire, coil, etc. depending on the case. It can be rolled into a shape or shaped like a mesh.

The temperature of the thermionic radiation material may be 1500°C or higher.

Diamond is not synthesized at temperatures below 1500°C, but in consideration of the film formation rate, temperatures of 1800°C or higher are preferred.

It is difficult to determine the optimal distance between the thermionic emitting material and the substrate because it varies depending on pressure, etc., but if the distance is too close, the modification will deteriorate due to the influence of radiant heat, and if the distance is too far, the diamond will deteriorate. is not generated.

<Example> Diamond was synthesized using the apparatus shown in FIG.

Methane was used as the raw material gas. In order to obtain the value at this time, we determined the relationship between the voltage applied between the thermionic emission material and the substrate and the methane concentration. The results are shown in Figure 2. From this figure, A
The value of is approximately 0.001.

Here, the voltage applied between the base and thermionic emission material is 50V,
100V and 200V, and the carbon-containing compound concentration (volume) in the supplied gas was changed to 0.95% and 0.9% accordingly.
, 0.8%. Other conditions included a pressure of 30 Torr and a total flow rate of 100 SCCt. Tungsten was used as the thermionic emission material and heated to 2000°C. A diamond-polished Noricon wafer was used as the substrate and heated to 900'C using a substrate holder. Table 1 shows the deposition rate and film quality of the diamond film synthesized in this manner.

Further, as a comparative example, the methane concentration in the raw material gas was fixed at 1%, a voltage was applied between the thermionic emitting material and the substrate, and the other conditions remained the same, and the film formation rate and film quality synthesized are similarly shown in Table 1.

From Table 1, it is clearly seen that the present invention improves the film formation rate while maintaining good modification.

<Effects of the Invention> According to the present invention, the film formation rate of the conventional diamond synthesis method using thermal decomposition using a thermionic emitter can be improved while maintaining good crystallinity.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an apparatus used in carrying out the present invention, and FIG. 2 is a graph showing the relationship between applied voltage and methane concentration. I... Raw material gas, 2... Hydrogen gas, 3...
Additive gas, 4...stop valve, 5...
Mass flow meter, 6... Reaction container, 7... Raw material supply nozzle, 8
...Base body, 9...Base body holder 10.
...Thermionic radiation material, 11...Thermionic radiation material for heating? ilt source, 12...
Constant voltage 'r4 source, 13...exhaust port. Patent applicant: Kawasaki Steel Corporation

Claims (1)

[Scope of Claims] 1. A mixed gas of a carbon-containing compound and hydrogen is thermally decomposed by a heated thermionic emitting material, and is guided onto a substrate to which a positive voltage is applied to the thermionic emitting material, and then diamond A method for synthesizing diamond, characterized in that the concentration of carbon-containing compounds in the mixed gas is kept lower than the optimum concentration of carbon-containing compounds when no voltage is applied to the substrate. 2. The concentration of carbon-containing compound in the mixed gas according to claim 1,
A diamond synthesis method characterized by maintaining the concentration determined by the following formula. (Concentration of carbon-containing compound in mixed gas) = (Optimum concentration of carbon-containing compound that allows synthesis of good crystals without applying voltage) x {1-
A×(applied voltage)} However, A is a constant determined by the type of carbon-containing compound and the synthesis conditions.