JPH0218391A - Method for synthesizing thin diamond film in vapor phase - Google Patents

Abstract

PURPOSE:To stably obtain a good-quality thin diamond film by keeping the activated state of the raw gas activated by a thermoelectron radiating material with the high-temp. plasma flame obtained by the arc discharge in an inert gas and introducing the concd. activated species to a substrate. CONSTITUTION:A substrate 6 and the thermoelectron radiating material 12 are arranged in a reaction vessel 1, an inert gas 9 and gaseous hydrogen 11 are supplied into the vessel 1, an electric discharge is generated from a non- transferable DC arc discharge torch 4 in the gases to produce a high-temp. plasma flame. A raw gas 14 contg. an org. gas is introduced into the vessel 1, pyrolyzed by the thermoelectron radiating material 12, and activated. The activated state is kept by the plasma flame. The concd. active specifies are introduced to the substrate 6 to stably obtain a good-quality thin diamond film.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is directed to thermionic emission of a raw material gas (hereinafter simply referred to as a raw material gas containing an organic compound) consisting of an organic compound alone or a mixed gas with hydrogen gas in advance. The raw material gas containing the organic compound is activated by thermal decomposition, and the active state of the raw material gas containing the organic compound is maintained by a high-temperature plasma flame generated by non-transitional DC arc discharge in a mixed gas consisting of an inert gas and hydrogen gas. The present invention relates to a vapor phase synthesis method for rapidly and stably forming a diamond thin film of good quality by introducing active species to a substrate at a high concentration.

[Conventional technology]

Conventionally, the following methods are known as methods for synthesizing diamond from a gas phase at low pressure.

1) Discharge sensation: Ion beam method or ion brating method in which carbon ions or hydrocarbon ions are created, accelerated by a potential gradient, and collided with substrate surface groups to precipitate diamond.

2) A vapor phase synthesis method in which raw material gas consisting of hydrocarbon gas and hydrogen gas is activated by generating low-temperature plasma by electric discharge at low pressure, and diamond is deposited on the substrate surface in the plasma.

3) A vapor phase synthesis method in which a raw material gas consisting of hydrocarbon gas and hydrogen gas is activated with a heated thermionic emitter to precipitate diamond on the substrate surface (for example, Japanese Patent Application Laid-Open No. 58-9110
0).

4) activating hydrocarbons in the high-temperature plasma by generating high-temperature plasma by electric discharge in a single gas or a mixed gas selected from hydrocarbon gas, hydrogen gas, and inert gas;
A vapor phase synthesis method in which diamond is deposited on the surface of a substrate (for example, JP-A-62-158195 and Proceedings of the 35th Applied Physics Association Conference, 29a-T-7).

However, each of these methods has the following advantages and problems that need to be solved in the future.

Method 1) has the advantage of being able to deposit a diamond-like carbon film on the surface of a substrate made of various materials at room temperature, but because accelerated ions are used, the deposited diamond has many defects and is not a diamond with good crystallinity. Since it is difficult to obtain and the ion beam density cannot be increased, there is a problem that the deposition rate is slow.

Method 2) can obtain diamond microcrystals on the surface of a substrate made of various materials, but because it uses low-temperature plasma caused by glow discharge, plasma will not be generated unless the gas pressure is low, usually 0.3 atmospheres or less. Furthermore, since the concentration of active species such as ions and radicals is low at a maximum of about 1096, there is a problem that the growth rate of diamond is slow (maximum several μm/h). The gas (ion, atomic, molecule) temperature in this low-temperature plasma is approximately 1.400° C. or lower.

Method 3) can obtain C2 diamond microcrystals on the substrate surface of various materials;
- The gas temperature tends to drop during the process, and when the gas temperature drops, the concentration of active species drops, so it is necessary to make the distance between the thermionic emitting material and the substrate extremely narrow, 1 to 5 aa. Therefore, the area over which a high-quality diamond thin film can be obtained is limited to an extremely narrow range, and the film-forming rate is as slow as several μm/h.

In addition, a method has been proposed that is an improved version of this method, that is, a method in which a DC voltage is applied to the thermionic emitting material with the substrate as positive, and the substrate is irradiated with thermionic electrons emitted from the thermal electron emitting material. However, similar problems still remain with this method.

Since method 4) uses high-temperature plasma, it has a higher concentration of active species than the method using low-temperature plasma, and can synthesize a diamond thin film at a higher speed, increasing the discharge power and the amount of organic compound supply. However, when limiting the method to non-transfer type DC arc discharge, supplying an organic compound together with a plasma generating gas can reduce fluctuations in the gas mixture state and Carbonization of the electrode during the decomposition of the compound causes fluctuations in the discharge state, making it difficult to form a diamond thin film stably, and increasing the film formation rate at a constant discharge power. In order to achieve this, it is necessary to increase the amount of organic compounds supplied, but at this time, the organic compounds are decomposed in high-temperature plasma, so the decomposition efficiency does not increase.
There are problems such as an increase in the graphitic carbon content in the resulting diamond and a deterioration in the quality of the diamond film.

[Problem to be solved by the invention]

The present invention has been made to improve the problems in method C of 3) and 4) above, and its purpose is to achieve a clear diamond crystal shape with a low graphitic carbon content when compared at the same discharge power. This invention was made in order to provide a method for rapidly and stably depositing a high-quality diamond thin film having a visible surface.

[Means to solve the problem]

The present invention began research with the aim of industrially applying a method that utilizes high-temperature plasma by non-transfer type DC arc discharge, but it was difficult to obtain a stable high-temperature plasma flame.In order to solve this problem, As a result of extensive research in order to solve the new problems that arose at that time, the present invention was completed. First, the shape of the cathode and the shape of the anode nozzle hole are selected, and after the plasma generation gas is discharged as a mixed gas of argon gas and hydrogen gas to generate a high-temperature plasma flame, a raw material containing an organic compound is selected. Supplying gas to the high temperature plasma flame S: Therefore, the plasma flame could finally be stabilized. However, at this stage, the graphitic carbon content in the resulting diamond was high, and only a thin film with rounded diamond crystal shapes could be obtained. Therefore, the raw material gas containing organic compounds is thermally decomposed and activated using a thermionic emitter, and then supplied to a high-temperature plasma flame. Only then can a diamond thin film in which the diamond crystal form can be clearly seen be stabilized. Now you can get it. The present invention was made based on the above findings, and the raw material gas containing organic compounds, which is a carbon supply source, is activated by a thermionic emission material, and the raw material gas containing organic compounds is activated by a high-temperature plasma flame. This method is characterized by maintaining the activated state of the raw material gas and guiding active species to the substrate at a high concentration.

In the method of the present invention, first, a supply nozzle for a raw material gas containing an organic compound and a thermionic emitting material are installed in a reaction vessel, the raw material gas is thermally decomposed and activated by the thermionic emitting material, and then the raw material gas is activated in the reaction vessel. A non-transfer type DC arc discharge plasma generation torch is installed inside the chamber, and a mixed gas consisting of an inert gas and hydrogen gas is discharged to generate a high temperature plasma flame, and the organic compound is distributed along the outer periphery of the high temperature plasma flame. This is an improved method that maintains the active state of the raw material gas contained and guides active species to the substrate at a high concentration.

In the present invention, tungsten, tantalum, or the like is used as the thermionic emitting material.

The temperature of the thermionic emission material is preferably in the range of 1.000°C or higher, preferably 1.500°C or higher and 4800°C.

In the present invention, a mixed gas consisting of an inert gas such as argon or helium and hydrogen gas is used as the plasma generating gas. The amount of hydrogen gas supplied is related to the amount of organic compounds supplied and is not uniquely determined by the mixing ratio with the inert gas, but in order to contract the plasma and increase the plasma temperature, Oli VOI is It is preferable to set it as 4 or more.

Examples of organic compounds include hydrocarbons such as methane, ethane, propane, butane, ethylene, and benzene; organic compounds containing oxygen, nitrogen, or sulfur in the molecule such as methyl alcohol, ether alcohol, acetone, pyridine, and methyl mercaptan; Examples include halogenated carbons such as carbon chloride.

The internal pressure of the reaction vessel can range from 10 to 5×10 atm. In order to maintain a low flow rate, large-scale exhaust gas equipment is required, and high pressure requires a pressure vessel, which is not economical. For this reason, 10-2~l
A range of Qatm is preferred.

The plasma temperature generated by the non-transfer type DC arc discharge is 1.5% for the purpose of guiding the raw material gas containing the organic compound thermally decomposed and activated by the thermionic emitting material to the substrate while maintaining it in an active state. , 500℃ or higher is sufficient, but
1.700 to supply active species to the substrate at a higher concentration.
It is preferable that the temperature is ℃ or higher.

The substrate temperature is preferably maintained at 400 to 1.700°C. At temperatures below 400°C, the content of graphitic carbon in diamond increases, and at temperatures above 1.700°C, no diamond precipitation is observed.

[Effect]

The present invention generates a large amount of active species by thermally decomposing a raw material gas containing organic compounds using a thermionic emitter, and utilizes the temperature of a high-temperature plasma flame generated by non-transfer type DC arc discharge. According to Kanji, by maintaining the active state of the raw material gas containing the organic compound and guiding the active species to the substrate at a high concentration, at this time, the raw material gas containing the organic compound is activated in advance with a thermionic emitter. Since this invention improves the high-temperature plasma flame to avoid cooling, it is faster and produces a diamond film with better quality than the conventional method using a thermionic emitter or the method of decomposing organic compounds in a high-temperature plasma flame. This has the effect of stably depositing a thin film.

〔Example〕

Examples of the present invention will be described below.

Example 1 FIG. 1 is a schematic diagram of a reaction apparatus used in an example of the present invention. In FIG. 1, the internal sea of the reaction vessel 1,
A commercially available constant current non-transfer type direct current arc discharge torch (manufactured by Osaka Electric Co., Ltd.) 4 which has a thorium-containing tungsten electrode 2 with an outer diameter of 4 mm as a cathode and a water-cooled copper torch nozzle 3 with a nozzle hole with an outer diameter of 5 mm as an anode. A silicon wafer (manufactured by Shin-Etsu Chemical Co., Ltd.) 6 having a (100) surface and previously scratched with 1 μm diamond paste was placed on a water-cooled copper substrate holder 5 facing it. Then, a thermocouple 7 was installed so that its contacts were in contact with the back surface of the substrate 6.

After evacuating the reaction vessel 1 to 0.1 ■Hg from the gas outlet 8, argon gas is passed through the gas mixing tank 10 from the argon gas inlet 9 to 151! /min, and a constant current DC arc discharge of 6OA was started between the thorium-containing tungsten electrode 2 and the water-cooled copper torch nozzle 3 to generate a high-temperature plasma flame. The shape of the high temperature plasma flame at this time was 101 cm in diameter and 50 cm in length.

Next, hydrogen gas is passed through the gas mixing tank 10 from the hydrogen gas population 11 to 1.5 l! /min. The shape of the high-temperature plasma flame at this time is 5 circles in diameter.
It had shrunk to a length of 30 mm.

And the outer diameter is 31, which was made by processing a tungsten wire with an outer diameter of 0.5 mm and a length of 120 m+, installed at a position 50 from the outlet of the water-cooled copper torch nozzle 3! ll11 coil 1
2, an AC voltage of 6 cm was applied to the temperature of 2,100°C. And methane gas methane gas population 13 to 667 /
Then, hydrogen gas was supplied at a rate of 5 Q d /min from the hydrogen gas population 15, and was thermally decomposed and activated in the coil 12. The activated gas was then guided to the substrate 6 along the outer periphery of the high temperature plasma flame. At this time, the high-temperature plasma flame had expanded to a diameter of 10 mm and a length of 60 mm.

Subsequently, the substrate 6 fixed to the water-cooled copper substrate holder 5 was pushed into a plasma flame at a temperature of 1.800°C, and cooled so that the temperature of the back surface of the substrate became 430°C.

Chemical vapor deposition was performed for 20 minutes while adjusting the exhaust volume so that the internal pressure of the reaction vessel 1 was 250 tm Hg. During this chemical vapor deposition, the shape of the plasma flame did not vary and was very stable, and the temperature on the back surface of the substrate remained constant within a range of ±1°C.

As a result, when the chemical vapor deposited substrate was observed with a scanning electron microscope, it was found that a high-quality thin film with a thickness of 9.0 μm was formed, with a surface showing a clear diamond crystal shape. A surface photograph at this time is shown in Figure 2, and a cross-sectional photograph is shown in Figure 3.

Furthermore, it was confirmed by X-ray ω analysis that this thin film was composed of cubic diamond microcrystals.

Comparative Example 1 This comparative example is based on the method of the present invention and
For the purpose of comparison with the method of Example 1, chemical vapor deposition was performed under the same conditions as in Example 1, except that no thermionic emitting material was used.

In this comparative example, the apparatus used in Example 1 was used as is.

In Example 1, chemical vapor deposition was performed in exactly the same manner as in Example 1, except that methane gas was supplied from the methane gas port 14 as a mixture with the plasma generation gas without applying a voltage to the tungsten coil 12. The state of the plasma flame at this time was the same as in Example 1 regarding the diameter, but the length fluctuated non-periodically during chemical vapor deposition, and the temperature on the back surface of the substrate fluctuated within a maximum range of ±20°C. Ta.

As a result, only a small portion of the surface of the substrate was melted.

When the chemical vapor deposited substrate was observed with a scanning electron microscope, it was found that a thin film with a thickness of 3.0 μm had been formed on the surface where a diamond crystal form was observed. A surface photograph at this time is shown in FIG. 4, and a cross-sectional photograph is shown in FIG.

That is, it can be seen that if the chemical vapor deposition conditions except for the thermionic emitting material are the same, the method of the present invention can stably obtain a diamond thin film of better quality at three times the deposition rate than the method of this comparative example. .

Comparative Example 2 This comparative example uses a thermionic emissive material for the purpose of comparing the method of the present invention and the method of the 35th Association of Applied Physics Conference Proceedings, 29a-T-7. Chemical vapor deposition was performed under the same conditions as in Example 1 except for this.

In this comparative example, the apparatus used in Example 1 was used as is.

In Example 1, chemical vapor deposition was performed in exactly the same manner as in Example 1, except that no voltage was applied to the tungsten coil 12. The state of the high-temperature plasma flame at this time is
This was the same as in Example 1, and the temperature on the back surface of the substrate was also constant within a range of ±1°C.

As a result, when the chemical vapor deposited substrate was observed using a scanning electron microscope, it was found that a thin film with a thickness of 2.7 μm was formed, with a rounded surface with no diamond crystal shape. . A surface photograph at this time is shown in FIG. 6, and a cross-sectional photograph is shown in FIG.

That is, if the chemical vapor deposition conditions except for the thermionic emitting material are the same, the method of the present invention can produce a diamond thin film with better quality than the method of this comparative example at three times the deposition rate. I understand.

Comparative Example 3 This comparative example was conducted under the same conditions as in Example 1, except that argon gas was used alone as the plasma generating gas, in order to examine the effect of hydrogen gas in the plasma generating gas on the state of diamond precipitation. Chemical vapor deposition was performed.

In this comparative example, the reaction apparatus used in Example 1 was used as is. In Example 1, the plasma generation gas is argon gas alone and is supplied from the argon gas inlet 9, and the methane gas is supplied from the methane gas population 13 to 60 m//
m” supply rate, hydrogen gas population 15 to 3
Chemical vapor deposition was carried out in the same manner as in Example 1 except that the supply rate was 0.001 nl/min. At this time, the high temperature plasma flame was in a stable state with a diameter of 8 mm and a length of 40 m.

However, when argon gas was used alone as the plasma generating gas, the plasma flame temperature did not rise at a constant current value of 60 A, and the chemical vapor deposition was eventually completed at a substrate backside temperature of 340° C.

As a result, when the chemical vapor deposited substrate was observed with a scanning electron microscope, it was found that a thin film with a thickness of 25 μm and a rounded surface with no diamond crystal shape was formed. A surface photograph at this time is shown in FIG. 8, and a cross-sectional photograph is shown in FIG. 9.

That is, when argon gas was used alone as the plasma generating gas and hydrogen gas was not used in combination, a diamond thin film of good quality that would increase the temperature of the plasma flame could not be obtained.

〔Effect of the invention〕

As explained above, the state of the plasma flame varies greatly depending on the composition and mixing state of the plasma generating gas, the shape of the reactor, the discharge power, etc., and the state of diamond precipitation is also greatly affected. Therefore, it is difficult to make a comparison with the prior art method under exactly the same chemical vapor deposition conditions, but when compared with the gas composition and discharge conditions shown in the examples of this application, according to the present invention, the prior art method A method of thermally decomposing a raw material gas containing organic compounds using a thermionic emitting material, and a method of decomposing organic compounds in a high-temperature plasma flame. Thin films can be formed faster and more stably.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram of the reaction apparatus for synthesizing diamond used in Example 1 of the present invention, and Figure 2 is a scanning electron beam image of the surface of the sample obtained in Example 1 with a magnification of 4,000 times. The micrograph, Figure 3, shows the cross section of the sample obtained in Example 1 at a magnification of 4.
．． 000x scanning electron micrograph, Figure 4 is Comparative Example 1
Figure 5 shows a scanning electron micrograph of the sample surface obtained in Comparative Example 1 at a magnification of 4.000x.
Fig. 6 is a scanning electron micrograph of the surface of the sample obtained in Comparative Example 2 at a magnification of 4.000x, and Fig. 7 is a scanning electron micrograph of the cross section of the sample obtained in Comparative Example 2 at a magnification of 4,0
00x scanning electron micrograph, Figure 8 is a scanning electron micrograph of the sample surface obtained in Comparative Example 3 at a magnification of 4.000x, and Figure 9 is a scanning electron micrograph of the sample surface obtained in Comparative Example 3 at a magnification of 4.000x. 4.00
This is a scanning electron micrograph at 0x magnification. DESCRIPTION OF SYMBOLS 1... Reaction vessel, 2... Thorium-containing tungsten electrode, 3... Water-cooled copper torch nozzle, 4... Constant current non-transfer type DC arc discharge torch, 5... Water-cooled copper substrate holder 6... Silicon wafer 7...Thermocouple, 8
...Gas exhaust port, 9...Argon gas inlet, 10.
...Gas mixing tank, 11...Hydrogen gas inlet,
12... Tungsten coil, 13... Methane gas inlet, 14... Methane gas inlet, 15... Hydrogen gas inlet, 16... Cooling water inlet, 17... Cooling water outlet. Illustration %fL $/Illustration, glaze πnzansho (method) October 12, 1986

Claims (1)

[Claims] A substrate and a thermionic emitting material are placed in a reaction vessel, a raw material gas containing an organic compound is introduced into the reaction vessel, and this raw material gas is thermally decomposed by the thermionic emitter to generate active species such as radicals or ions. In the diamond vapor phase synthesis method, which generates active species and guides the active species to the substrate to deposit diamond on the substrate surface, the high temperature generated by non-transitional DC arc discharge in a mixed gas consisting of an inert gas and hydrogen gas is used. A method for vapor phase synthesis of a diamond thin film, characterized in that a plasma flame is used to maintain the activated state of the raw material gas containing the organic compound and to guide active species at a high concentration to the substrate.