JPH03122091A - Method for synthesizing diamond at high speed - Google Patents

Abstract

PURPOSE:To improve deposition rate and area, etc., by carrying out DC discharge of a specific gas, generating a thermal plasma, applying a positive bias voltage to a substrate or a substrate holder, supplying a carbon source, decomposing the carbon source and depositing diamond on the substrate. CONSTITUTION:In a method for generating a thermal plasma (e.g. a DC plasma torch 1) at >=1700K gas temperature in hydrogen or a mixed gas thereof and an inert gas by DC discharge (e.g. a DC power source 2) to decompose or evaporate an organic compound or carbonaceous material in the plasma and depositing diamond from the resultant gas on a substrate 3, a positive bias voltage (e.g. a bias power source 11) is applied to the substrate 3 or a substrate holder 3'. The bias voltage can be applied to an electrode in the form of a ring (e.g. a ring electrode 12) or mesh placed near the substrate 3. Even a bias electrode at a negative bias voltage can be used. Low-frequency AC, high-frequency or microwave devices can be also used as the discharge power source in place of the DC power source.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in a method for high-speed synthesis of diamond by thermal plasma CVD.

(Prior art and problems to be solved) As a high-speed diamond synthesis method, a method of producing diamonds using a gas temperature of 1,700 or more generated by direct current, low-frequency alternating current, high frequency, or microwave discharge, or by a combined discharge of these, is used. A method using thermal plasma is known (Japanese Unexamined Patent Publication No. 158195/1983).

According to this method, the diamond growth rate increases about 100 times compared to the conventional low-temperature plasma CVD method, but the gas temperature is high and the spatial distribution of chemical species in the gas phase is Because it tends to change rapidly, it is difficult to control the substrate temperature and deposition rate, and the deposition area on the substrate is narrow, making the film thickness distribution likely to be uneven. Furthermore, crystal grains tend to become large, and surface smoothness is poor. There was a drawback.

The purpose of the present invention is to solve the above-mentioned problems of the prior art, and to provide a high-speed synthesis method for diamond that allows easy control of substrate temperature and precipitation rate, has a large precipitation area, and has good surface smoothness. It is.

(Means for Solving the Problems) In view of the above problems, the present inventors have developed a thermal plasma CVD method.
As a result of trying to apply a bias voltage to the substrate inside,
We discovered that it is possible to take into account the elongation effect of plasma or the effect of interaction of electrons and ions with the substrate,
This is what led to the completion of the present invention.

That is, the high-speed diamond synthesis method according to the present invention is as follows:
In short, a thermal plasma with a temperature of 1700°C or more is generated in hydrogen or a mixed gas of hydrogen and an inert gas by direct current discharge, low frequency alternating current discharge, high frequency discharge, microwave discharge, or a combination of these discharges, and in the plasma In a method of depositing diamond on a substrate from a gas obtained by decomposing or evaporating an organic compound or carbon material, a positive or negative bias is applied to the substrate or substrate holder, or to a ring-shaped or mesh-shaped electrode placed near the substrate. It is characterized by applying a voltage.

The present invention will be explained in more detail below.

(Function) As a method for generating thermal plasma, a method using electrical discharge is simple, and discharge using direct current, low frequency alternating current, high frequency or microwave, or a combination thereof is used.

As the plasma generating gas used in the present invention, hydrogen gas alone or a mixed gas of hydrogen gas, argon, helium, etc. is used.

Any carbon source may be used as long as it decomposes in a thermal plasma of 1700° C. or more and generates ion species and radical species. For example, saturated or unsaturated aliphatic or aromatic hydrocarbons such as methane, ethane, propane, ethylene, benzene, and cyclohexane; organic compounds containing oxygen such as alcohols, acetone, and aldehydes; organic compounds containing nitrogen such as amines and amides; , organic compounds containing halogens such as methyl chloride and chloroform, organic compounds containing sulfur such as thiophene,
Organic compounds containing phosphorus such as phosphine, polymeric compounds such as polyethylene, -carbon oxide, carbon dioxide, etc. are used. Furthermore, solid graphite material can also be used by being introduced into the plasma.

The plasma gas pressure can range from 10@-4 to 5.times.10' atmospheres. If the pressure is too low, the diamond precipitation rate will be slow, and if the pressure is too high, it will take time to handle the container and the equipment will be expensive.
~10 atm is desirable.

As the substrate, any metal, semiconductor, or ceramic can be used.

The bias voltage applied to the substrate, substrate holder, or ring-shaped or mesh-shaped electrode varies from -5 kV to -5 kV depending on the gas pressure and the position of the substrate relative to the plasma flame.
Used in the +5kV range.

This bias voltage causes the plasma to extend onto the substrate. Furthermore, if the substrate or substrate holder is a bias electrode, some increase in the substrate temperature is observed, but this substrate temperature and the extension of plasma onto the substrate can be controlled by changing the bias voltage and current. This is much easier to control than controlling the position of the substrate without bias or cooling the substrate holder with a coolant.

Furthermore, in the case of applying a positive bias, the diamond precipitation rate increases and the precipitation area also increases.

On the other hand, in the case of a negative bias, the diamond crystal grains become finer and the surface smoothness improves.

In the present invention, the reasons why the application of a positive bias voltage improves the deposition rate of diamond and increases the deposition area are as follows: (1) The high-density plasma extends closer to the substrate, allowing active species to reach the substrate. an increase in the amount of

(2) It is thought that the impact effect of electrons on the substrate increased, leading to an increase in chemical reactions on the substrate.

On the other hand, the reason why the surface smoothness increases with negative bias is as follows.
It is thought that the number of nucleation sites on the growth surface increases due to an increase in the IQ effect of ions on the substrate.

Next, an example of an apparatus used to carry out the present invention will be described with reference to the drawings.

Figure 1 shows the reaction apparatus for DC discharge, where 1 is a DC plasma torch, 2 is a DC power source, 3 is a substrate, 3' is a substrate holder, 4 is a deposition chamber, 5 is an exhaust device, and 6 is a gas In the supply device, 7.7' is a gas flow rate adjustment valve, 11 is a bias power supply, and 12 is a ring electrode.

In this case, the operating procedure is as follows: First, the deposition chamber 4 is evacuated by the exhaust device 5, and then plasma generating gas is supplied through the gas flow rate adjustment valve 7.

After setting the pressure to a predetermined value, power is supplied between the poles of the plasma torch 1 from the DC type rX2 to generate plasma. Diamond is deposited on the substrate by applying a bias voltage to the substrate, the substrate holder, or the ring electrode, and supplying a carbon source into the plasma from the valve 7'.

Figure 2 shows the reactor for high-frequency discharge.
1 is a high-frequency plasma torch, 9 is a high-frequency oscillator, 10 is a work coil, 13 is a counter electrode for bias, and the other parts are the same as in FIG.

In this operating procedure, first, the deposition chamber 4 is evacuated using the exhaust device 5, and then the carrier gas is flowed through the gas flow rate adjustment valve 7, the plasma gas is flowed through the valve 7', and the sheath gas is flowed through the valve 7', and the work coil 10 is powered. Power is supplied from 9 to generate plasma. Base body 3 and counter electrode 13
Apply a bias voltage between the gas flow rate adjustment valve 7''
A carbon source is supplied to deposit diamond on the substrate. As described above, if there is nothing in the torch that can be used as an electrode opposite to the bias electrode, it is often effective to place a new counter electrode.

Note that as a device for low-frequency alternating current discharge and microwave discharge, one appropriately configured in accordance with each of the above-mentioned device examples may be used.

(Example) Next, examples of the present invention will be shown.

Using the apparatus shown in FIG. 1 and using a molybdenum substrate with a diameter of 20++ on, the deposition chamber was evacuated to below 0.1 Torr, and then argon was pumped through valve 7 at 30 Q/mi.
n, hydrogen was flowed at 10 Q/min, methane was flowed at 0.75 fl/min from valve 7' as a carbon source, and 140
Discharge was performed for 10 minutes at a power output of 10 kW under Torr. At this time, a bias current of +200V and 3A was applied to the substrate, and the substrate temperature was 950°C. As a result, the obtained film was identified as diamond based on the results of X-ray diffraction and Raman spectroscopy. The film thickness was 150 μm at the highest point. The diameter of crystalline diamond precipitation is approximately 16 m.
It was m.

On the other hand, in a precipitation experiment under the same conditions without bias, the substrate temperature was 850° C., the maximum film thickness was 60 μm, and the crystalline diamond precipitation diameter was 12 mm.

In addition, when a bias of 280 mm and 3 A was applied to the ring electrode instead of the substrate, the substrate temperature was 870 DEG C., the maximum film thickness was 9 S .mu.m, and the crystalline diamond precipitation diameter was 16 mm.

Using the apparatus shown in Figure 2, using a molybdenum substrate with a diameter of 20 mm, the precipitation chamber was evacuated to approximately 0.1 Torr, and then methane IQ/n+in was pumped through valve 7''.
Argon 2Q/n+in from valve 7', argon IQ/min from valve 7', argon 2QQ/min from valve 7'
A mixed gas of 8 Q/min of hydrogen and 8 Q/min of hydrogen was flowed, and 60 kW of human power was applied to the work coil under a pressure of 1 atm to generate plasma, which was then discharged for 10 minutes.

A diamond film with an average thickness of 22 μm was obtained at a substrate bias of -600 V, a bias current of 240 mA, and a substrate temperature of about 930'C. The average particle size was approximately 1 μm.

On the other hand, in the case of no bias, the substrate temperature was about 900° C., and the average film thickness and average grain size of the obtained diamonds were 20 μm and 5 μm, respectively.

(Effects of the Invention) As detailed above, according to the present invention, a bias voltage is applied to the substrate or the electrode near the substrate.

The controllability of the substrate temperature and deposition rate is improved, and by elongating the plasma and increasing the interaction between electrons or ions and the substrate, excellent effects such as improving the deposition rate, deposition area, and surface smoothness can be obtained. It will be done.

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams showing an example of a reaction apparatus used in carrying out the present invention, with FIG. 1 showing a case of direct current discharge and FIG. 2 showing a case of high frequency discharge. 1... DC plasma torch, 2... DC power supply, 3...
...Substrate, 3'...Substrate holder, 4...Precipitation chamber,
5... Exhaust device, 6... Gas supply device, 7.7',
7'7''... Gas flow rate adjustment valve, 8... High frequency plasma torch, 9... High frequency oscillator, 10... Work coil, 11... Bias power supply, 12... Ring electrode, 13 ...Counter electrode.

Claims (4)

[Claims] (1) A thermal plasma with a gas temperature of 1700K or more is generated in hydrogen or a mixed gas of hydrogen and an inert gas by direct current discharge, and an organic compound or carbon material is decomposed or evaporated in the plasma. 1. A method for rapidly synthesizing diamond, which comprises applying a positive bias voltage to the substrate or a substrate holder. (2) The method according to claim 1, wherein the bias voltage is applied to a ring-shaped or mesh-shaped electrode placed near the substrate. (3) The method according to claim 1 or 2, wherein the bias voltage is a negative bias voltage. (4) The method according to claim 1, 2 or 3, wherein low frequency alternating current, high frequency or microwave is used as the discharge power source instead of the direct current.