JPH0351675B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method and apparatus for photochemical deposition synthesis of diamond.

[Prior art]

Artificial diamonds, which are used in cutting tools, are synthesized and manufactured by subjecting graphite to ultra-high pressure and high temperatures.

Recently, ion beam deposition synthesis methods (plasma
CVD method), and thermochemical deposition synthesis method (thermal CDV
Experiments on diamond crystal synthesis have been conducted, for example, in Japanese Patent Application Laid-open No. 58-91100. The latter thermochemical deposition synthesis method uses a high-temperature tungsten filament or a high-temperature substrate on which long-wavelength laser light is focused as a high-heat source.

As mentioned above, methods for synthesizing diamond can be roughly divided into synthesis methods under ultra-high pressure and high temperature;
There are synthesis methods using ion beam deposition and thermochemical deposition. However, the ultra-high-pressure, high-temperature synthesis method requires an ultra-high pressure generator, which has the disadvantage of increasing the size of the apparatus. Compared to this ultra-high pressure and high temperature synthesis method, the ion beam deposition synthesis method and thermochemical deposition synthesis method have the advantage that diamond crystals can be synthesized under low pressure conditions. However, in the ion beam deposition synthesis method, not only carbon ions but also ions of other atoms are generated due to the discharge, so impurities may be formed, and in the thermochemical deposition synthesis method, hydrocarbon molecules are decomposed thermochemically. Therefore, there is a drawback that the production efficiency of carbon atoms is poor, and since it is difficult to locally concentrate carbon ions or carbon atoms in both methods, there is a drawback that the growth rate of diamond crystals is slow.

[Purpose of the invention]

This invention was made to eliminate the above-mentioned drawbacks, and uses a photochemical deposition synthesis method (photoCVD method).
The main purpose of this invention is to provide a method and apparatus that can synthesize diamond crystals and thin films under low pressure and low temperature conditions and at a high growth rate.

[Embodiments of the invention]

First, an outline of the principle of this invention will be explained.

In this invention, the dissociation of hydrocarbon molecules is induced by irradiation with ultraviolet light and vacuum ultraviolet light, and the carbon atoms liberated at this time are deposited on a substrate to synthesize diamond crystals. The principle is as follows.

A hydrocarbon molecule is composed of a carbon atom C and a hydrogen molecule H, and has C-H bond branches, C-C bond branches,
It consists of a C=C bond branch and a C≡C bond branch. The chemical bond energies of these bonding branches are 98 Kcal/mol for the C-H branch, 80 Kcal/mol for the C-C branch, and C=
145Kcal/mol in C branch, 198Kcal/mol in C≡C branch
It is. Irradiation with high-energy particles that have energy greater than the chemical bond energy of these bonding branches can sever the bonding branches and separate the carbon atoms from the hydrocarbon molecules.
Such high-energy particles include photons,
Examples include fast ions and fast electrons.

Here we will describe the energy possessed by light quanta.
If the frequency of light is ν, the wavelength is λ, and the speed of light is c, then
The quantum energy of one photon of this light is hν=ch/
It is expressed as λ. Here, h is Planck's constant. For example, the photon energy of a wavelength of 300 nm
95Kcal/mol, the photon energy at a wavelength of 200nm is 143Kcal/mol, and the photon energy at a wavelength of 100nm is 286Kacl/mol. Therefore, since the hydrocarbon molecule methane CH ₄ is composed of C-H branches, the chemical bond energy of the C-H branches is 98 Kcal/mol.
When you irradiate light with larger photon energy, that is, light with a wavelength shorter than about 300 nm,
This means that methane can be decomposed by cutting the C-H branch, but the optical absorption band of methane is 160n.
Therefore, methane can be decomposed most efficiently by irradiating light with a wavelength shorter than 160 nm, and carbon atoms can be liberated. That is, carbon atoms can be liberated by the following process.

CH ₄ +hν (λ<160nm) → CH ₃ +H, CH ₂ H ₂ , CH+H ₂ +H, C+2H _2In this way, the wavelength for photolysis of methane is 160nm.
It would be better to irradiate the diamond with shorter light, but when trying to synthesize diamond crystals by depositing carbon atoms released through photolysis, it is necessary to use a high-power light source and a lens to increase the crystal growth rate. It is desirable to focus the light onto the substrate. As a high-power vacuum ultraviolet light source with a wavelength of 160 nm or less,
Examples include fluorine _F2 laser (wavelength 157nm) and argon _Ar2 excimer laser (wavelength 126nm). Lasers with a wavelength of 160 nm or less are used for photodecomposition of methane through a one-photon absorption process.
Considering the case of photolysis due to a two-photon absorption process,
Photolysis of methane is also possible by irradiating light with a wavelength shorter than 320 nm. wavelength is
As a high-power vacuum ultraviolet light source shorter than 320nm,
Xenon chlorine XeCl excimer laser (wavelength 308n)
m), krypton fluorine KrF excimer laser (wavelength 249 nm), argon fluorine ArF excimer laser (wavelength 193 nm), and many others.

As mentioned above, in order to synthesize diamond crystals, a thermochemical method has traditionally been used to decompose hydrocarbons and generate free carbon atoms, but in this invention, It focuses on the fact that by irradiating light with a photon energy greater than the chemical bond energy of the bonding branches in the hydrocarbon, it is possible to dissociate the bonding branches of hydrocarbons and liberate carbon atoms.
Compared to conventional thermochemical deposition synthesis methods, the photochemical deposition synthesis method of the present invention is a direct process that acts on the molecules themselves, and is also a low-pressure, low-temperature process, so it is energy-saving.

The same principle of the diamond synthesis method using photochemical deposition synthesis can be applied not only to methane but also to other paraffinic hydrocarbons CnH _2o+2 . In addition, the optical absorption band of ethylene H ₂ C=CH ₂ , which is one of the hydrocarbons with a double bond C=C branch, is
The wavelength is 210 nm or less, and the C=C branch is dissociated by light irradiation with a wavelength of 197 nm or less. Therefore, when an argon-fluorine ArF excimer laser (wavelength: 193 nm) is used as a light source, ethylene can be photolyzed in a one-photon absorption process.

Next, a photochemical deposition synthesis apparatus based on the above principle will be explained with reference to the drawings.

The drawing shows one embodiment of the present invention, in which high-output light in the ultraviolet and vacuum ultraviolet range emitted from a known high-output ultraviolet light generator 1, particularly laser light or coherent light, is emitted by a reflecting mirror 2 and a condenser lens. 3 and is focused through a window 10 onto a substrate 5 placed in a reactor 4. Hydrocarbon or a mixed gas of hydrocarbon and hydrogen is supplied to the reactor 4 from the reaction gas supply device 8 . The hydrocarbons are photolyzed by ultraviolet light and vacuum ultraviolet light, and the carbon atoms liberated at this time are deposited on the substrate 5, and diamond crystals grow on the substrate 5. Since the quality and growth rate of the diamond crystal grown on the substrate 5 depend on the substrate temperature, a heater 6 for heating is installed under the substrate 5 in order to optimize the substrate temperature. The temperature of the heater 6 is controlled by a temperature controller 7. The used reaction gas is exhausted by a gas exhaust device 9.

For example, a KrF excimer laser (wavelength: 248 nm, laser pulse energy: 100 mJ) is used as the high-power ultraviolet light emitting device 1, and the laser beam is passed through a lens into a substrate 5 (material: silicon, Si, The light is focused on the surface of the substrate (substrate temperature: 500℃). Using the reaction gas supply device 8, the reaction gas (mixed gas of acetylene C ₂ H ₂ and hydrogen H ₂ , acetylene concentration: 10%, gas pressure: 10 Torr, gas flow rate 50
ml/min) into reactor 4. Under these conditions, the laser pulse repetition rate is 50 hertz (Hz), the total number of laser pulses is 120,000 pulses (total irradiation energy: 1
In the results of an experiment in which the surface of the substrate 5 was irradiated with 2,000 J), formation of a thin film was observed. Furthermore, when the scattering spectrum was measured using a laser Raman spectrometer, the Raman shift peaked at 1330 cm ^-1 , which proved that diamond was formed.

The acetylene used here has a triple bond (C≡
C) is a hydrocarbon. Therefore, under these experimental conditions, methane and ethylene bonds can be sufficiently photodissociated to form a diamond film.

〔Effect of the invention〕

As explained above, the present invention decomposes a hydrocarbon reaction gas by irradiating the substrate with high-power ultraviolet light, and at the same time decomposes the carbon atoms liberated by the decomposition of the reaction gas onto the heated substrate. Since diamond crystals are grown by deposition, compared to conventional thermochemical deposition synthesis, it is a low-pressure, low-temperature process, and the growth rate is fast, resulting in less energy consumption and lower manufacturing costs. have In addition, since the device according to the present invention is configured to intensively irradiate high-power ultraviolet light onto the substrate through a condensing lens, it has the advantage of being able to synthesize crystals on the substrate with high efficiency, and has a high output as a light source. By using an excimer laser, it is also possible to grow large crystals. Furthermore, this device has a simple structure and is easy to manufacture, so it is very inexpensive.

[Brief explanation of drawings]

The drawing is a schematic diagram showing an embodiment of the present invention. In the figure, 1 is a high-power ultraviolet light generator, 2 is a reflecting mirror, 3 is a condensing lens, 4 is a reactor, 5 is a substrate, and 6
7 is a heater, 7 is a temperature controller, 8 is a reaction gas supply device, 9 is a gas exhaust device, and 10 is a window.

Claims (1)

[Claims] 1. Irradiating a hydrocarbon-based reactive gas with high-power ultraviolet light to decompose the reactive gas and deposit carbon atoms liberated by the decomposition of the reactive gas on a heated substrate. 1. A photochemical deposition synthesis method for diamond, characterized by growing diamond crystals and thin films. 2. A high-power ultraviolet light generator, a reactor that introduces the high-power ultraviolet light from the high-power ultraviolet light generator through a condensing lens and irradiates the substrate therein, a heater that heats the substrate, and 1. An apparatus for photochemical deposition and synthesis of diamond, comprising a reaction gas supply device for supplying a reaction gas to a reactor, and a gas exhaust device for exhausting the reaction gas in the reactor.