JPH06199595A - Method for synthesizing diamond - Google Patents

Abstract

PURPOSE:To provide a method for synthesizing diamond by which a high purity and high quality thin film of single crystalline diamond almost free from crystal defects in the thin film can efficiently be formed using a light excitation process. CONSTITUTION:Reactive gas prepd. by mixing hydrogen with methane is introduced into a vacuum chamber 4 with a disposed substrate 5 and it is irradiated with vacuum UV having <=750Angstrom wavelength. By this irradiation, the reactive gas is photodecompased and CH3 and H radicals are selectively generated. During film formation, the amts. of hydrogen and methane to be mixed and the mixing ratio are properly regulated through a gas valve 2. The generated CH3 and H radicals are efficiently fed to the surface of the substrate 5 and a thin diamond film is precisely formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for synthesizing diamond, and more particularly to a method for synthesizing diamond by vapor phase synthesis using a photoexcitation process.

[0002]

2. Description of the Related Art Diamond has excellent properties such as having the highest hardness among the substances known so far, being an electrically excellent insulator, and having high thermal conductivity. It is a functional material.

Further, diamond is excellent in light transmissivity over a wide wavelength range except a part of infrared region, and further has a characteristic that it becomes a semiconductor by adding impurities. Utilizing these excellent properties, the coating of diamond on various tool surfaces and the application to electronic parts, particularly heat sinks for semiconductor lasers, ICs, etc. have been promoted.

In order to apply diamond to the electronics field, it is essential to establish a technique for forming a single crystal thin film.

Recently, as a method for forming a diamond thin film by vapor phase synthesis, (1) a method of activating a source gas by causing a discharge by a direct current or an alternating electric field, (2)
A method of heating the thermionic emission material and activating the source gas,
(3) a method of bombarding the surface on which diamond is grown with ions, (4) a method of burning a raw material gas, (5) a method of exciting the raw material gas with light such as laser or high-power ultraviolet light,
Various methods have been tried.

[0006]

In the photochemical synthesis method of diamond using the conventional photoexcitation process, when the diamond thin film is formed on the substrate, the reaction gas in which hydrogen and methane are mixed is photolyzed. For this purpose, a laser beam having a relatively long wavelength is often used.

Therefore, it is difficult to specify the radical species generated from the reaction gas by photolysis, and it is almost impossible to selectively generate only the desired radical species.

Further, in the past, since a reaction system in which a predetermined amount of a reaction gas in which hydrogen and methane were constantly mixed was constantly introduced into a reaction vessel in which a substrate was usually installed, a photoexcitation was adopted. In the process, the film growth sometimes proceeds without the ideal supply amount of radicals generated from the reaction gas and supplied onto the substrate or the ratio of the supplied radical species to be set.

For the above reasons, when diamond is synthesized according to the conventional photochemical synthesis method of diamond, there is a problem that a defective diamond thin film in which crystal defects or impurities having different crystallinities are mixed is easily formed in the film. there were.

The present invention has been made to solve the conventional problems, and is a method for synthesizing diamond capable of efficiently forming a high quality single crystal diamond thin film having few crystal defects and high purity in the film. The purpose is to provide a method.

[0011]

[Means for Solving the Problems] Conventionally, in the photochemical synthesis method of diamond, methane was used as a carbon raw material,
When photolysis is performed with a laser beam having a relatively long wavelength, a reaction represented by the following formula (Formula 1) generally proceeds, and CH ₃ radicals, CH ₂ radicals, CH radicals, and the like are generated.

[0012]

[Chemical 1] Above all, when the decomposition of methane into CH ₂ radicals or CH radicals is increased, impurities having different crystallinity are mixed or crystal defects are likely to be generated at the time of forming a diamond thin film.

Therefore, the present inventor has conducted various studies on film forming conditions in order to suppress the mixing of impurities and the generation of crystal defects as much as possible when forming a diamond thin film. To 750Å
By using vacuum ultraviolet light having the following wavelengths in a limited manner, methane as a carbon raw material is converted into CH _{2 in} photolysis.
The present invention has been completed by finding that the decomposition into radicals or CH radicals is almost completely suppressed, and that only CH ₃ radicals and H radicals are selectively produced.

The method for synthesizing diamond according to the present invention is a method for forming a diamond thin film by depositing at least a reaction gas in which hydrogen and methane are mixed with carbon atoms released by photolysis on a substrate. Upon photolysis,
The reaction gas is irradiated with vacuum ultraviolet light having a wavelength of 750 Å or less to selectively generate hydrogen radicals and methyl radicals.

In the present invention, as the vacuum ultraviolet light source, synchrotron radiation, undulator, or ultrahigh temperature plasma such as laser plasma can be preferably used.

Further, in the present invention, the film thickness and the state of the film surface can be detected at the time of forming the diamond thin film, for example, by Fourier transform infrared spectroscopy using infrared rays. Depending on the film thickness or the state of the film surface thus detected, the mixing amount and mixing ratio of hydrogen and methane in the reaction gas can be adjusted manually or automatically.

The mixing amount and mixing ratio of hydrogen and methane of the reaction gas can be adjusted relatively easily by adjusting the supply amount of methane using a gas valve capable of pulse operation, for example.

[0018]

In the photochemical method for synthesizing diamond using the photoexcitation process according to the present invention, 750Å is used instead of the conventional laser light having a relatively long wavelength during photolysis.
By irradiating the reaction gas in which hydrogen and methane are mixed with vacuum ultraviolet light having the following wavelengths, hydrogen and methane in the reaction gas are efficiently decomposed to selectively select only desired hydrogen radicals and methyl radicals. Will be able to generate.

Therefore, hydrogen radicals and methyl radicals can be efficiently supplied onto the substrate, and a diamond single crystal with high purity and few crystal defects can be accurately synthesized.

Further, in the method for synthesizing diamond according to the present invention, when the diamond thin film is formed, the mixing amount and mixing ratio of hydrogen and methane of the reaction gas can be adjusted while detecting the film thickness or the state of the film surface. it can.

For example, when the growth rate of the film thickness is extremely slow, the supply amount of methane is increased and the mixing amount and the mixing ratio of methane in the reaction gas are increased, whereby methyl produced by photolysis is produced. Radicals can be increased to accelerate the rate of diamond synthesis.

On the other hand, when many irregularities are formed on the film surface and the film state is poor, the supply amount of methane is reduced and the mixing amount and the mixing ratio of hydrogen in the reaction gas are increased.
It is possible to effectively suppress the occurrence of crystal defects in the film and the mixing of impurities having different crystallinities, and synthesize a diamond thin film having a smooth surface and good quality.

As described above, if the mixing amount and mixing ratio of hydrogen and methane of the reaction gas are appropriately controlled according to the film thickness or the state of the film surface during the diamond film formation, more ideal film forming conditions can be obtained. Diamond can be synthesized. Therefore, a good quality diamond thin film having few crystal defects and good crystallinity can be accurately formed on the substrate.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing an example of a diamond synthesizing apparatus used in an embodiment of the present invention.

As shown in FIG. 1, in the diamond synthesizing apparatus 100, Si for forming a diamond thin film is used.
The substrate 5 made of is placed in the vacuum chamber 4. Board 5
Is adjusted to room temperature to several hundreds of degrees Celsius by the heater 6.

Further, a monitor light source 11 is arranged, and infrared rays emitted from this light source 11 are introduced through an optical window in the vacuum chamber 4 and irradiated onto the substrate 5. By detecting the infrared rays radiated on the substrate 5 by the Fourier transform infrared spectroscopy using the detector 12, the growth state of the diamond thin film on the substrate 5 can be detected.

An exhaust port 10 is provided in the vacuum chamber 4, and the inside of the vacuum chamber 4 is exhausted by the vacuum exhaust system 7 through the exhaust port 10 to maintain a predetermined reaction pressure.

After evacuation, methane gas (CH ₄ ) and hydrogen gas (H ₂ ) as reaction gases above the substrate 5 in the vacuum chamber 4 are adjusted in weight from gas cylinders 9 and 9'by mass flowmeters 8 and 8 ', respectively. One of them is intermittently supplied through the gas valve 2 capable of pulse operation.

In this apparatus 100, the supply amount of radicals supplied above the substrate and the supply ratio of radicals are freely changed by adjusting the inflow amount of methane gas (CH ₄ ) according to the formation state of the diamond thin film. can do.

Therefore, in the present embodiment, by appropriately adjusting the supply amount of the methane gas (CH ₄ ) by the pulse valve 2 based on the information obtained from the detector 12, it is possible to facilitate more suitable film forming conditions. Can be realized.

Next, synchrotron radiation (SR) light is generated from the light source system 1 using an electron storage ring or the like. The generated SR light is introduced into the vacuum chamber 4 through the optical window 3 and irradiated on the reaction gas above the substrate 5.

Here, by changing the electron energy in the light source system 1 using an electron storage ring, S
The spectrum of R light can be freely changed.

By changing the spectrum of SR light, as shown in FIG. 2, the production rate of hydrogen radicals produced from the reaction gas by photolysis greatly changes.

From the results shown in FIG. 2, it can be seen that H radicals are efficiently generated only in SR light in the wavelength region of 700 to 1000 Å.

Further, by similarly changing the spectrum of SR light, as shown in FIG. 3, CH _n radical species (n = 1, 2, 3) generated from the reaction gas by photolysis.
And its production rate also changes.

As is clear from the result of FIG. 3, 750Å
In the shorter wavelength region, only CH ₃ radicals are produced from the reaction gas at a high rate, in the wavelength region of 750 to 1050Å, CH radicals are produced from the reaction gas at a high rate, and in the wavelength region longer than 1050Å, the reaction gas is produced. To CH
It can be seen that only _two radicals are produced at a high rate.

Therefore, from the results of FIG. 2 and FIG.
By limiting the use of SR light having a wavelength of 750 Å or less, it is possible to almost completely suppress the production of CH radicals and CH ₂ radicals from the reaction gas, and at the same time, selectively generate only H radicals and CH ₃ radicals. I understand.

Therefore, in this embodiment, upon photolysis,
750 for reaction gas consisting of hydrogen gas and methane gas
By irradiating SR light having a wavelength of Å or less, only H radicals and CH ₃ radicals are selectively generated, and these radicals are efficiently supplied above the substrate 5 made of Si to be liberated from methane. Carbon atoms are deposited on the substrate 5 to form a diamond thin film.

In this embodiment, the desired radical species and the amount of radicals supplied during thin film formation are set to be almost ideal, so that impurities with few crystal defects and different crystallinity are mixed in the film. It is possible to form a small number of high quality diamond single crystal thin films.

[0041]

According to the method of synthesizing diamond according to the present invention, a high quality diamond single crystal thin film can be accurately formed. Therefore, the present invention can be applied to the production of diamond thin films for semiconductor materials such as elements for environment resistance, and its effect is great.

Further, by using the method for synthesizing diamond according to the present invention, the time required for forming a diamond single crystal thin film can be shortened, and a steady gas supply method is not used, so that the raw material The gas can be used at a high yield, which can contribute to cost saving.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a diamond synthesizing apparatus used in an embodiment of the present invention.

FIG. 2 is a graph showing the wavelength dependence of the production rate of hydrogen radicals by photolysis.

FIG. 3 shows CH _n radicals (n = 1, 2,
It is a graph which shows the wavelength dependence of the production rate of 3).

[Explanation of symbols]

 1 Light Source System 2 Gas Valve 3 Optical Window 4 Vacuum Chamber 5 Substrate 6 Heater 7 Vacuum Exhaust System 8,8 'Weight Flowmeter 9,9' Gas Cylinder 10 Exhaust Port 11 Monitor Light Source 12 Detector 100 Diamond Synthesizer Among them, the same reference numerals indicate the same or corresponding parts.

Claims (2)

[Claims] 1. A method for synthesizing diamond, which comprises forming a diamond thin film by depositing carbon atoms liberated by photolysis of a reaction gas containing at least hydrogen and methane, the method comprising the steps of: A method for synthesizing diamond, which comprises selectively generating hydrogen radicals and methyl radicals by irradiating the reaction gas with vacuum ultraviolet light having a wavelength of 750 Å or less. 2. The method for synthesizing diamond according to claim 1, wherein the mixing amount and the mixing ratio of hydrogen and methane in the reaction gas are adjusted while detecting the film thickness or the state of the film surface.