JPS61236691A - Vapor phase synthesis of diamond - Google Patents

Abstract

PURPOSE:To deposit diamond selectively on a large area of a substrate at low temp. by irradiating gas or vapor of a carbon compd. with ultraviolet rays having specified wavelength and electron beam. CONSTITUTION:A valve 14 is closed and a rotary pump 9 is driven after evacuating previously a vacuum cell 5 to <=10<-6>Torr with a high vacuum evacuation device 10. Carbon compd. (e.g. CH4 from a CH4 cylinder 1) and gaseous H2 from a H2 cylinder 2 are introduced into the vacuum cell 5 through mass flowmeters 3, 4 to adjust the pressure to a specified value with a pressure regulating valve 15. Then, ultraviolet rays from a vacuum ultraviolet ray generator 11 is radiated, after passing through a differential evacuation system 13 and an orifice 12, on CH4 and H2 to excite and decompose the CH4 and H2. Diamond is deposited on the whole area of a substrate 7 which is fixed on a substrate supporting bed 8 and heated at a specified temp. with a heater 6 being movable with a substrate moving device 16 while continuing irradiation during deposition. The substrate 7 is irradiated simultaneously with electron beam from an electron gum 17. Thus, diamond film is synthesized.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for depositing diamond on a substrate from the gas phase.

(Prior Art and its Problems) Several methods are conventionally known for synthesizing diamond by thermal decomposition of carbon compound gas.

For example, the Japanese Journal of Applied Physics published in 1982.
eJournal of Applied Phys
ics) Volume 21, page L183 includes the following:
A method is described in which methane gas is heated in contact with a tungsten heater heated to about 2000° C. using hydrogen as a carrier gas, thermally decomposed, and diamond is deposited on a silicon, molybdenum, or quartz glass substrate. This method requires a tungsten heater of approximately 2,000
Because it is heated to a high temperature of 0.9°C, the vapor pressure of tungsten itself becomes high, causing problems such as it being consumed in a short period of time and evaporated tungsten adhering to the diamond surface. In addition, once heated, the tungsten heater becomes extremely brittle due to the reaction between tungsten and carbon and the absorption of gas molecules, making it easy to break, so the tungsten heater must be replaced frequently.
It is difficult to fully exercise the device for a long time. In addition, changes in the tungsten heater wire over time cause changes in the thermal decomposition conditions of the reaction gas, making it difficult to uniformly deposit film-like diamond over a wide area.

Furthermore, the diamond precipitation temperature is high, making synthesis near room temperature impossible.

Fourth, another method is to use the Journal of 9 Non-Crystalline Solids published in 1980.
l of Non-Crystalline 5ol
ITS ) Vol. 35 & 36, page 435, the paper uses glass or molybdenum vapor-deposited on glass as a substrate, a pressure of 0.9 torr, a gas flow rate of 0.
5~], QCC% substrate temperature 25~375℃, discharge current 0.8~additive, discharge voltage 300~400v,
It is stated that amorphous carbon M'fr: was obtained by decomposing acetylene by direct current glow discharge.

The electrical resistivity of the above-mentioned amorphous carbon film is 10" ohm (Au), which is excellent in that it provides an insulating carbon film, but if the film thickness exceeds 1 μm or if it is heat-treated, It has the disadvantage that the carbon film peels off from the substrate.Also, when the substrate temperature is high, the carbon film turns black and becomes graphite-like.Furthermore, it has the disadvantage that a crystalline diamond film cannot be synthesized. There is.

Furthermore, as another method, plasma is generated by microwave discharge or high frequency discharge in a reaction gas under reduced pressure, and a substrate is placed directly in the plasma or during the afterglow of the plasma, and diamond is completely deposited on the substrate. There is also a method of synthesizing diamond in the form of a diamond film by bombarding a substrate with ionized carbon, but the former method has the disadvantage that the substrate must be heated to a high temperature in order to obtain the diamond phase. Historically, since the substrate is placed in plasma, plasma damage to the substrate is unavoidable. The latter method is an excellent method as it allows diamond to be synthesized at around room temperature, but it has the disadvantage that the equipment is expensive. Furthermore, in order to extract ions in a beam shape,
It has the disadvantage that the beam intensity is uneven and a uniform diamond phase cannot be obtained over a wide area.

(Objective of the Invention) The object of the present invention is to eliminate such conventional drawbacks and to provide a method for synthesizing diamond in which only diamond is selectively precipitated at low temperature and deposited as a thin film on a substrate. be.

(Structure of the Invention) According to the present invention, a diamond vapor phase synthesis method is obtained in which a gas or vapor of a carbon compound is irradiated with vacuum ultraviolet rays of a predetermined wavelength and an electron beam.

(Detailed Description of Configuration) The present invention solves the problems of the prior art by adopting the above-described configuration.

The process of diamond precipitation from the gas phase requires artificial manipulation to stabilize the thermodynamically metastable phase.
It is obvious that non-diamond carbon will be deposited on the substrate if free carbon atoms are obtained only from the thermal decomposition of the reactant gas.

Furthermore, in methods that utilize plasma, the internal energy range of the plasma is wide, and it is difficult to produce only the active species that will become diamond, so it is obvious that non-diamond carbon is likely to precipitate.

Therefore, in the present invention, in order to obtain methyl radicals, methyl cations, i-atomic hydrogen, etc. that are effective for diamond production, vacuum ultraviolet rays having a predetermined wavelength are used to mainly generate methyl cations, atomic hydrogen, etc. The present invention provides a process for efficiently producing diamond on a substrate by generating methyl radicals by irradiating it with an electron beam.

In the diamond synthesis process according to the method of the present invention, since synthesis of active species by light is used, the substrate temperature does not rise. In addition, light increases the surface diffusion of active species, making it possible to grow diamonds at low temperatures.

As an example of photosynthesis of active species, we will discuss the case where methane gas is used as a reaction gas. Methane gas does not absorb ultraviolet light like commonly used mercury lamps, and therefore cannot synthesize active species. Absorption begins at a wavelength of about 1,460 angstroms or less, and the light is decomposed into various radicals or ions depending on the wavelength of the light. Further, each of the n radicals or ions has various excited states. To make a main radical,
Vacuum ultraviolet light of 1460 angstroms or less is required, and the stronger the light intensity, the better. That is, a high-output vacuum ultraviolet source such as argon excimer radiation or synchrotron radiation is desirable.

Furthermore, since methyl cations can be synthesized in a four-way manner using light of 870 A or less, the 2y of argon excimer laser
t', child absorption, or synchrotron radiation. Furthermore, by combining these methods, it is also possible to simultaneously irradiate light with two or more wavelengths to create active species with different wavelengths.

Atomic hydrogen is a by-product when methyl radicals are created from methane using vacuum ultraviolet light. It can also be produced by photodecomposition of hydrocarbon gas, but to increase the efficiency even further, diamond total synthesis can be made more efficiently by mixing hydrogen gas into the reaction gas and photodecomposing it with vacuum ultraviolet rays.

The effect of irradiating an electron beam with vacuum ultraviolet rays is that the methyl cations that are efficiently generated by vacuum ultraviolet rays are neutralized by electrons, methyl radicals are synthesized, and the intensity of the electron beam causes the methyl radicals and methyl cations to be By changing the abundance ratio, diamond can be synthesized under optimal conditions. The device for emitting the electron beam may be an electron gun, or a tungsten wire in the form of a full ring or a line may be placed above the substrate at a location not originally irradiated and heated.

Hereinafter, an example of the device used in the present invention and a manufacturing process will be described using the first page. After preliminary evacuation of the instep of the vacuum chamber 5 to below 10' Torr using the high vacuum evacuation device 10, the bubble 1 is
4 is closed, the system is switched to the rotary pump 9, and methane gas from the methane cylinder 1 and hydrogen gas from the hydrogen cylinder 2 are introduced into the vacuum chamber 5 using their respective mass flowmeters 3 and 4.

The pressure is adjusted to a predetermined pressure using the pressure adjustment bubble 15.

The substrate 7 is fixed on a substrate support I and adjusted to a predetermined temperature by a heater 6. The light irradiated from the vacuum ultraviolet source 11 is passed through the differential pumping system 13 which is maintained at (10-5) or less by the cylinder vacuum pumping device 10 and the orifice 12.
The light then passes through the orifice 12 and is irradiated onto the substrate while exciting and decomposing the reaction gases methane and hydrogen. Further, in order to deposit diamond over the entire area of the substrate, the entire substrate is moved by the substrate moving mechanism 16, and the entire area of the substrate is irradiated with the light that has passed through the orifice 12. Simultaneously with the light irradiation, the substrate is irradiated with an electron beam using the Geshi gun 17 to synthesize diamond.

(Example) The substrate was made of silicon, molybdenum, tungsten, and glass 4, and was heated from 200°C to 600'C.

The reaction time was 30 minutes, the gas was varied from 100% methane to a methane/hydrogen mixing ratio of 001, and the pressure was 05 Torr. Argon excimer-+)'-(1260 Angstroms) was used as the vacuum ultraviolet/l source. A diamond film could be obtained using vacuum ultraviolet rays alone, but only when the substrate temperature was relatively high at 400° C. or higher. When the electron gun was energized and an electron beam was irradiated, a diamond film was formed even at a substrate temperature of 200°C. The surface of this film was smooth and the production rate was up to 2 microns per hour.

It has been found that a methane/hydrogen mixing ratio of 0.5 or less is preferable because the growth rate is higher.

(Effects of the Invention) According to the present invention, diamond single-phase can be deposited on a thin FF1K substrate. Furthermore, it has a fast growth rate and can be synthesized at low temperatures.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the apparatus used directly in the method of the invention. 1...Methane cylinder, 2...Hydrogen cylinder, 3.4...Mass flow meter, 5...X
Enclosed tank, 6... Heater, 7... Substrate, 8... Substrate support stand.

Claims (2)

[Claims] (1) A diamond vapor phase synthesis method comprising a step of irradiating a gas or vapor of a carbon compound with vacuum ultraviolet rays and electron beams of a predetermined wavelength. (2) The method for vapor phase synthesis of diamond according to claim 1, wherein hydrogen gas is mixed in the gas or vapor of the carbon compound.