JPH01179789A - Vapor growth method for diamond and thermal plasma deposition method and plasma injection device - Google Patents

Abstract

PURPOSE:To synthesize a good-quality diamond film having excellent surface smoothness at a high film forming speed by supplying gaseous raw materials to the center of the plasma jet generating end without passing the same through an arc discharge part. CONSTITUTION:A discharge gas 3 such as gaseous hydrogen is heated to form hot plasma when an arc discharge 11 is generated by impressing a DC voltage between an internal electrode 1 and an external electrode 2 while passing the discharge gas. This hot plasma is made into the supersonic jet plasma 5 by an abrupt temp. rise and is ejected from a nozzle 4. The gaseous raw materials 7 formed by mixing a carbon source such as hydrocarbons, and in some cases, an inert gas such as A or Ne, gaseous oxygen such as oxygen and hydrides such as B2H6, NH3 and PH3 are supplied from a gaseous raw material port 6 provided in the central part of the internal electrode 1 into the plasma jet 5 without allowing the gaseous materials to contact the arc 11 and are bombarded against a substrate 5, by which the gaseous raw materials are rapidly cooled and the diamond film 9 is formed on the substrate.

Description

[Detailed Description of the Invention] [Summary] A method for epitaxially growing diamond on a diamond substrate, a method for epitaxially growing diamond on a diamond substrate, a method for vapor phase synthesis of diamond at a high growth rate, and a method for producing diamond with excellent stability, uniformity and smoothness. The purpose of this project is to provide a plasma jet injection device that forms a crystalline film with good properties.The purpose is to turn a discharge gas and a raw material containing at least a carbon source into thermal plasma by arc discharge, eject it as a plasma → jet, and rapidly cool it to form a diamond. The vapor phase growth method for diamond crystals is configured such that at least a raw material that makes arc discharge unstable is supplied to the center of the starting end of the plasma jet without passing through the arc discharge section. In particular, it is configured to epitaxially grow a diamond film on a diamond substrate, and consists of an external electrode that forms an enclosure, and an internal electrode that is electrically insulated and penetrates the external electrode, and the external electrode is used to introduce discharge gas. A plasma injection device that opens a hole and a jet nozzle, and forms an arc discharge surface with the side surface of the end of the internal electrode in close proximity to the side surface of the jet nozzle of the external electrode, and turns source gas into plasma by arc discharge. The plasma jet injection device is configured such that the raw material gas introduction hole extending along the central axis of the internal electrode opens at the center of the end surface of the end portion of the internal electrode.

[Industrial application field]

The present invention relates to a method for vapor phase synthesis of diamond at a high growth rate and a plasma jet injection device.

[Conventional technology]

Diamond film has a thermal conductivity of 2000 W/mK, which is four times that of copper, and has excellent hardness and insulation properties.
It is an ideal material for semiconductor heat sinks and circuit board materials. It also has excellent translucency over a wide wavelength range, making it an excellent optical material.

Furthermore, as a semiconductor, diamond has a wide bandgap of 5.4 eV and carrier mobility higher than silicon, so it can be used as a high-speed device that can operate at temperatures above 500 degrees Celsius, and as an environmentally resistant element for interspace, automobiles, and noise. It is also expected to be used as a high-speed device in computers and the like. As described above, in order to use diamond as a semiconductor element, epitaxial growth of a diamond film on a diamond substrate is essential. However, in the conventional CVD method, the film formation rate is slow at about 1 um/h, and the thickness is only 10 μm/h.
When it exceeds pM, it becomes polycrystalline and a single crystal film cannot be epitaxially grown.

As a method for synthesizing diamond at a high growth rate, there is a method in which thermal plasma generated by DC arc discharge is used as a plasma jet to strike a substrate, rapidly cooling the thermal plasma, and growing diamond on the substrate. There are two methods for supplying a source, for example, a carbon compound gas: one is to supply it as a plasma gas, and the other is to spray it from the side into a plasma jet.

The equipment for carrying out these methods includes raw carbon sources,
For example, there is a device (Fig. 3) that supplies the carbon compound of gas 7 together with the discharge gas 3 between the electrodes and injects the plasma jet 5 from the nozzle 4; There is a device (FIG. 4) that blows a raw material gas 7 from the side onto a plasma jet 5 ejected from a plasma jet 4.

According to the former, the roughness of the surface of the diamond film tends to become severe due to coarsening of crystal grains, and the discharge tends to become unstable because a carbon source, such as carbon compound gas, enters the arc.On the other hand, according to the latter, Although the surface smoothness is good,
The raw material gas is not uniformly supplied into the plasma jet, resulting in uneven film thickness and the formation of graphite around it.

[Problem to be solved by the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for epitaxially growing a diamond single crystal, and a plasma jet injection device that forms a crystal film with excellent discharge stability and good uniformity and smoothness. 7 [Means for Solving the Problem] The above problem is a method of turning discharge gas and a raw material containing at least a carbon source into thermal plasma by arc discharge, ejecting it as a plasma jet, and rapidly cooling it to grow diamond, A method for vapor phase growth of diamond, characterized in that at least a raw material that makes arc discharge unstable among the raw materials is supplied to the center of the plasma jet starting end without passing through the arc discharge part. A method of turning a discharge gas and a raw material for forming a thermal plasma deposit into thermal plasma by arc discharge, ejecting it as a plasma jet, and growing a thermal plasma deposit, wherein at least one of the raw materials makes arc discharge unstable. The thermal plasma deposition method is characterized in that the plasma is supplied to the center of the starting end of the plasma jet without passing through the arc discharge part, and the external electrode forming the enclosure is electrically insulated from the external electrode. It consists of an internal electrode that penetrates the electrode, the external electrode opens the discharge gas introduction hole and the jet nozzle, and the side surface of the end of the internal electrode is close to the side surface of the jet nozzle of the external electrode so that the arc discharge surface This is a plasma injection device that forms a raw material gas into plasma by arc discharge, and the raw material gas introduction hole extending along the central axis of the internal electrode is opened at the center of the end face of the internal electrode. This problem can be solved by a plasma injection device characterized by:

[For production]

The diamond film epitaxial growth method of the present invention is a method in which a raw material containing a carbon source is turned into thermal plasma, ejected, and rapidly cooled to grow diamond.

In the diamond growth method, the discharge gas is usually hydrogen, and the raw material gas as the carbon source can be any carbon compound, but hydrocarbons or 0/N1 halogens in the molecule may be used. Organic substances containing organic substances are preferred. An inert gas such as Ar or He may be mixed with the discharge gas or source gas. In this case, the stability of the plasma is further improved, but the film forming rate is reduced. Also,
In order to increase the etching effect of non-diamond carbon such as amorphous carbon in the raw material gas, 0□, It20, )
120□.

A small amount of oxidizing gas such as CO may be mixed.

Moreover, it is of course possible to mix hydrogen gas with the raw material gas.

Furthermore, semiconductor diamond can also be obtained by mixing a trace amount of gas such as B2H, NH3, PH, etc. with the raw material gas, or by separately supplying it into a plasma jet.

The raw material gas is supplied to the center of the starting end of the plasma jet without passing through the arc discharge section.

For this purpose, it is advantageous to use the plasma jet injection device of the present invention described below. High temperature superconducting oxide (B
When using the plasma jet injection device of the present invention for plasma spraying of a-Y-Cu-0, etc., fine powder of superconducting oxide is supplied together with carrier gas from step 7, and the superconducting oxide powder is melted in the plasma. Then, a film is formed on the substrate. Of course, in this case, the plasma atmosphere is an oxidizing atmosphere, an oxygen atmosphere, an atmospheric atmosphere, or the like.

As shown in FIG. 1, in the plasma jet injection device of the present invention, the introduction hole for the raw material gas (or the gas containing raw material powder) 7 extends along the central axis of the internal electrode 1, and the raw material gas ejection port 6 is located at the center of the jet nozzle 4 of the external electrode 2, and discharges an arc 11 between the internal electrode 1 and the external electrode 2, but the raw material gas (or gas containing raw material powder) 7 is completely separate from the arc 11. No contact. Therefore arc 1
It does not interfere with the uniform production of 1. Moreover, since the raw material gas (or gas containing raw material powder) 7 is emitted to the center of the starting end of the plasma jet 5, the distribution of plasma formed in the plasma jet 5 is made uniform, and this can be achieved by vapor phase growth or heat treatment. When used for deposit formation and growth using plasma, a uniform and smooth film can be grown.

Of course, this apparatus can be used in diamond growth to synthesize polycrystalline diamond on the surface of a material other than diamond, using a material other than diamond as the substrate.

〔Example〕

Example 1 FIG. 1 is a diagram showing the principle of growing a diamond film using the apparatus of the present invention.

This device supplies the raw material gas into the plasma jet from the jet nozzle provided at the center of the cathode, thereby ensuring that the raw material gas is uniformly supplied into the plasma jet, increasing the uniformity of the film thickness, and increasing the uniformity of the film thickness. When the gas is a carbon compound, the generation of graphite can be suppressed. ■ is a cathode, 2
is an anode, 3 is a discharge gas, 4 is a nozzle, 5 is a plasma jet, 6 is a source gas outlet, 7 is a source gas, 8 is a substrate,
9 is a diamond film, 10 is an arc power source, and 11 is an arc.

Hydrogen gas as discharge gas 3 at 20 II/min,
While flowing methane gas as the raw material gas 7 at a rate of 0.21/min, a DC voltage of 90 V and IOA is applied between the anode 2 and the cathode 1 to generate an arc discharge 11, whereby the discharge gas is heated and a voltage of 5,000 V/min is generated near the nozzle 4. It becomes a thermal plasma with temperatures above ℃. At this time, the thermal plasma becomes a supersonic plasma jet 5 due to the volume expansion caused by the rapid temperature rise, and is ejected from the nozzle 4. The raw material gas is directly supplied into the plasma jet without passing through the arc discharge section, where it is decomposed and activated.

This plasma jet is 5 × 5 × 0.5 + nm
A diamond film was grown by hitting a molybdenum substrate 8 to rapidly cool it, and a polycrystalline diamond film with a thickness of 200 mm was obtained in one hour. When the surface roughness of this film was measured, it was found that R□X was 10Im, which was significantly improved compared to R□ and 50m in the method shown in FIG. 3 in which the raw material gas was supplied together with the discharge gas.

With this device, no raw material gas enters the arc, so a stable discharge can be obtained. Furthermore, since all of the raw material gas is supplied into the plasma jet, generation of graphite can be suppressed.

In the case of diamond growth, it is generally advantageous to use hydrogen, which has a high ionization potential and is difficult to discharge, as a discharge gas, so the electrode material is preferably one that has high heat resistance and can easily generate a stable discharge. Tungsten to which lanthanum oxide, yttrium oxide, cerium oxide, etc. are added is excellent as an electrode material. Furthermore, if impurity contamination from the electrode is to be avoided, a high-purity carbon electrode is preferable.

As mentioned above, the plasma jet injection device of the present invention has the following features:
Although it can be advantageously used for diamond synthesis, it can of course also be used for other methods.

Example 2 Figure 2 shows a plasma jet CV carrying out the method of the present invention.
In the schematic diagram of device D, 13 is a Pudesma torch, 14 is a discharge gas supply pipe, 15 is an arc power supply, 16 is a cooling water pipe for the torch, 17 is a substrate holder, 18 is a diamond substrate, 1
9 is a vacuum chamber, 20 is an exhaust system, 21 is a torch manifold, 22 is a flow meter, 23 is a gas cylinder, 24 is a source gas supply pipe, and 25 is a substrate manifold.

The plasma torch 13 has a structure in which both the anode and the cathode are made of tungsten water doped with 2 wt% yttrium oxide. The position and orientation of the plasma torch 13 and substrate holder 17 can be controlled by manipulators 21 and 25, respectively, and the plasma jet and the substrate can be moved relative to each other. A diamond film can be grown uniformly on the object to be treated. Further, although not shown in this schematic diagram, a heater for heating the substrate or a water cooling mechanism may be attached to control the substrate temperature.

A 2 x 2 x O, 5m LA-type artificial diamond substrate was used as the substrate, and the inside of the chamber was 2 x 10-'.
After exhausting to Torr, 1kg/c of hydrogen is used as discharge gas.
201/min at a pressure of ++t, and 0.1 j2/mi at a pressure of 1 kg/cI11 using methane as the raw material gas.
n flow, and the pressure inside the chamber was maintained at 120 Torr.

A current of 2OA is passed through the torch from a constant current arc power supply,
The voltage was held for about 5 minutes until it became constant.

The voltage at this time was 50V. The substrate was slowly brought close to the torch, the distance between the nozzle and the substrate was fixed at 15 m, and film formation was performed for 1 hour in this state.

When the resulting diamond was evaluated by Raman spectroscopy and hardness measurement, only a diamond peak was detected in Raman spectroscopy, and the Vickers hardness was approximately 100 at a load of 500 g.
00, a value equivalent to that of natural diamond. In addition, the diamond film thickness is approximately 150-1, and the film-forming speed is 15
It was 0a/h.

In addition, X-ray diffraction using the Laue method, low-speed electron diffraction (LE
! E! D) confirmed that a single crystal diamond film was epitaxially grown on the underlying diamond substrate.

Note that the variation in arc voltage is approximately 10% in this example,
The arc stability was also improved by about 20% compared to the conventional method.

Further, in this example, no graphite was observed to be generated.

Example 3 B211. 1 in the same manner as in Example 1 except that Q, l II was mixed at a flow rate of 7/min.
When the film was formed for 0 minutes, it was found that the film was a P-type semiconductor with a specific resistance of 10 −2 Ωcm.

Example 4 A S1 wafer of 5 x 5 x 0.2 mm was used as the substrate, and after exhausting the chamber to 2 x 10-3 Torr, 201 tons of hydrogen was added as a discharge gas at a pressure of 1 kg/Cl11.
/min.

1kg/cm of methane as raw material gas! 0.5 at a pressure of
1/min flow, and the pressure inside the chamber was 100 Torr.
It was held at r.

A current of 2OA is passed through the torch from a constant current arc power supply,
The voltage was held for about 5 minutes until it became constant.

The voltage at this time was 50V. The substrate was slowly brought closer to the torch, the distance between the nozzle and the substrate was fixed at 20 mm, and film formation was carried out for 1 hour in this state.

When the resulting diamond was evaluated by X-ray diffraction, Raman spectroscopy, and hardness measurement, only diamond peaks were detected in the X-ray diffraction and Raman spectroscopy, and the Vickers hardness was approximately 10,000 at a load of 500 g, which is the same value as natural diamond. Ta. Further, the diamond film thickness was approximately 200 squares, and the film forming rate was 200 μ/h.

When the surface roughness of the synthesized diamond film was measured, R
□8 was approximately 10μ, which was significantly improved compared to the value of 50- when the raw material gas was supplied by being included in the discharge gas.

The variation in arc voltage during diamond synthesis was about 10% in this example, compared to about 20% in the conventional method, and arc stability was also improved.

Furthermore, in this example, no graphite was observed at the periphery of the substrate.

The shape of the plasma injection device, whose cross-sectional view is shown in FIG.
The raw material gas ejection port and the mouth of the nozzle 4 may have a polygonal (rectangular, etc.) or elliptical shape as long as they do not cause non-uniformity in arc discharge characteristics. Furthermore, if necessary, it is also possible to provide the electrodes with a heat-resistant insulator in the form of a comb so as not to affect the discharge. It is advantageous for coating large areas. As the substrate, in addition to diamond, silica glass, tungsten, molybdenum, etc. can be used to grow a film without surface treatment.

Although it is preferable to apply the discharge atmosphere under reduced pressure in order to stabilize the discharge, it may also be applied under atmospheric pressure or increased pressure. In the above example, we used diamond film growth as an example.
It can also be applied to the synthesis of diamond powder.

Furthermore, the plasma jet spraying apparatus of the present invention can be applied to plasma spraying of high-temperature superconducting oxides such as the Ba-Y-Cu-0 system as described above.

〔Effect of the invention〕

When growing a diamond film using the improved DC plasma jet CVD apparatus of the present invention, it is possible to synthesize a high quality diamond film with excellent surface smoothness at a deposition rate of about 200 p/h, and the application range of the diamond film is can be expanded significantly.

By performing the diamond shrimp growth using the DC plasma jet CVD method, a shrimp film as thick as 150 Ja can be obtained at an extremely high film forming rate of 150 p/h.

It is possible to gradually realize diamond heat sinks and diamond circuit boards for semiconductor devices.It is also possible to synthesize semiconductor diamonds.It can also be applied to plasma spraying of inorganic compounds such as high-temperature superconducting oxides. sell.

4.l! Brief explanation of f4 plane FIG. 1 is a principle diagram of the plasma jet injection device of the present invention, FIG. 2 is a schematic diagram of a diamond film epitaxial growth device implementing the method of the present invention, and FIGS. The figure is a principle diagram of a conventional plasma jet injection device.

■...Cathode, 2...Anode, 3...
・Discharge gas, 4... Nozzle, 5... Plasma jet, 6... Raw material gas jetting port, 7... Gas containing raw material gas or raw material powder, etc.
Substrate, 9... Diamond film, 10.
...Arc power supply, 11...Arc, 13...
- Plasma torch, 14... Discharge gas supply pipe, 15... Arc power supply, 16... Cooling water piping for torch, 17... Substrate holder, 18... Diamond substrate, 19... Vacuum chamber , 20...exhaust system, 21
...torch manipulator, 22...flow meter, 23...gas cylinder,
24... Raw material gas supply pipe, 25... Substrate manipulator.

Claims (1)

[Claims] 1. A method for growing diamond by turning discharge gas and a raw material containing at least a carbon source into thermal plasma by arc discharge, ejecting it as a plasma jet, and rapidly cooling it, comprising: A diamond vapor phase growth method characterized in that a raw material that makes arc discharge unstable is supplied to the center of the plasma jet starting end without passing through the arc discharge section. 2. The method according to claim 1, wherein the discharge gas is hydrogen. 3. The method of claim 2, wherein the discharge gas comprises an inert gas. 4. The raw material contains hydrogen, inert gas or oxidizing gas,
The method according to claim 1. 5. The method according to claim 1 or 4, wherein the raw material contains a trace amount of boron, nitrogen, or phosphorus hydride, or these gases are supplied by being blown into a plasma jet. 6. The method according to any one of claims 1 to 5, wherein the diamond film is grown on the substrate by impinging a plasma jet on the substrate. 7. The method according to any one of claims 1 to 5, wherein the diamond film is epitaxially grown on the diamond substrate by impinging the plasma jet on the diamond substrate. 8. The method according to any one of claims 1 to 7, wherein arc discharge is performed under reduced pressure. 9. A method of turning a discharge gas and a raw material for forming a thermal plasma deposit into thermal plasma by arc discharge, ejecting it as a plasma jet, and growing a thermal plasma deposit, the method comprising at least one of the raw materials that makes the arc discharge unstable. A method for thermal plasma deposition, characterized in that the raw material is supplied to the center of the starting end of the plasma jet without passing through the arc discharge section. 10. The thermal plasma deposition method according to claim 9, wherein the raw material includes raw material powder. 11. The method according to claim 10, wherein the raw material powder is a high temperature superconducting oxide. 12. Consisting of an external electrode forming an enclosure and an electrically insulated internal electrode penetrating the external electrode, the external electrode opens a discharge gas introduction hole and a jet nozzle, and the end of the internal electrode A plasma injection device whose side surface is close to the side surface of the ejection nozzle of the external electrode to mutually form an arc discharge surface, and which converts raw material gas into thermal plasma by arc discharge, and extends along the central axis of the internal electrode. The raw material gas introduction hole is
A plasma injection device characterized by having an opening at the center of an end face of an internal electrode. 13. The device according to claim 12, wherein the electrode is a tungsten electrode doped with a rare earth element oxide or a carbon electrode.