JPH0518794B2 - - Google Patents

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, in the method described in JP-A-47-42286, diamond seed crystal powder is placed in a catalyst heater using hydrogen gas as a carrier gas, and the particle size of the diamond seed crystal is increased using the following reaction. It's clear what's possible.
In general, in the gas phase synthesis of diamond, C _o H _2o+2 → C (diamond) + H ₂ (however, n≦5)
The precipitation of amorphous carbon other than diamond and graphite prevents the subsequent precipitation of diamond, but due to the action of a catalytic heater such as platinum and palladium, the following reaction occurs on diamond. It states that it can be removed.

C (amorphous carbon or graphite) +2H ₂ −
CH ₄ However, it has the disadvantage of requiring a diamond seed crystal in order to grow diamonds. That is, there is a drawback that diamond cannot be deposited on a substrate made of other materials. Another disadvantage is that the diamond seed crystal must be kept at a high temperature. Another disadvantage is that in addition to the process of synthesizing diamond, a process of removing eutectoid non-diamond carbon must be performed.

There are also other methods, such as the Japanese Journal of Applied Physics published in 1982.
Physics) 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 approximately 2000°C using hydrogen as a carrier gas, causing thermal decomposition and depositing diamond on a silicon, molybdenum, or quartz glass substrate. This method is excellent in that it allows diamond to be deposited on materials other than diamond, but because the tungsten heater is heated to a high temperature of approximately 2100°C, the vapor pressure of tungsten itself is also high. There is also the problem that it wears out in a short period of time, and that evaporated tungsten adheres to the diamond surface. In addition, once heated, the tungsten heater becomes extremely brittle and easily cut due to reactions between tungsten and carbon and absorption of gas molecules, so the tungsten heater must be replaced frequently and the equipment must be operated for long periods of time. difficult to do. 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.

Furthermore, as another method, the Journal of Non-Crystalline Solids, No. 35 &
The paper described in Volume 36, Page 435 states that glass or molybdenum vapor-deposited on glass was used as the substrate, the pressure was 0.9 Torr, the gas flow rate was 0.5 to 1.0 cc per minute,
It is stated that an amorphous carbon film was obtained by decomposing acetylene by direct current glow discharge under the conditions of a substrate temperature of 25 to 375°C, a discharge current of 0.8 to 2 mA, and a discharge voltage of 300 to 400 V. The electrical resistivity of the amorphous carbon film is a maximum of 10 ¹⁶ Ωcm,
Although it is superior in that it provides an insulating carbon film, it has the disadvantage that the carbon film will peel off from the substrate if the film thickness exceeds 1 μm or if it is heat treated.
Further, when the substrate temperature is high, the carbon film becomes black and graphite-like. Furthermore, it has the disadvantage that a crystalline diamond film cannot be synthesized.

Still another method is to generate plasma by microwave discharge or high frequency discharge from a reaction gas under reduced pressure, place a substrate directly in the plasma or during the afterglow of the plasma, and deposit diamond on the substrate. There is also a method of synthesizing film-like diamond by bombarding a substrate with ionized carbon, but both methods have the disadvantage that the substrate must be heated in order to deposit the diamond. .

(Object of the present invention) The object of the present invention is to eliminate such conventional drawbacks, and to produce a transparent diamond thin film at room temperature that has a flat surface and strong adhesion to a substrate. The objective is to provide a synthetic method.

(Structure of the Invention) According to the present invention, in a method for depositing diamond on a substrate by decomposing and exciting a carbon compound gas or vapor in a DC glow discharge,
The gas or vapor of the carbon compound is turned into plasma by high-frequency glow discharge, and the afterglow of this plasma is introduced into the DC glow discharge,
A method for synthesizing diamond from a gas phase, which is characterized by synthesizing diamond, is obtained.

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

Generally, to synthesize diamond from a gas phase, a gas or vapor of a carbon compound is used as a carbon source. However, 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. In addition, even in methods using plasma, the process of synthesizing diamond using only a single excitation process lacks energy and requires high temperatures for stable diamond precipitation. This also results in by-products. Therefore, in the process of synthesizing diamond from the gas phase, if there is a process of decomposing and exciting the reaction gas and a process of adding energy to the decomposition and excitation, diamond can be effectively synthesized at low temperatures.

In the method of the present invention, a gas or vapor of a carbon compound is introduced into a high-frequency glow discharge region using hydrogen as a carrier gas, and is turned into plasma, thereby generating radicals and ions of the carbon compound, radicals of decomposition products of the carbon compound, and the like. ions are pre-generated and further decomposed and excited by introducing them into a DC glow discharge region;
At the same time, diamond can be synthesized at room temperature by causing ions to collide with the substrate using a DC bias electric field of the substrate. Furthermore, since the electric field applied to the substrate is uniform, a flat diamond thin film can be transparently deposited over a wide area without eutectoiding of non-diamond carbon. In addition, the adhesion of the diamond thin film to the substrate is improved due to the collision effect of the ions. The role of hydrogen in the process of growing diamond is complex, but it mainly turns into atomic hydrogen in the plasma, converts SP ² deposited on the substrate, and carbon with SP bonds, that is, non-diamond carbon, into hydrocarbons and removes it. ing.

Any high frequency that is capable of high frequency glow discharge can be used.

A high frequency output is preferable because the higher the output, the higher the concentration of active species becomes. Desirably, an output of 50W or more is appropriate.

Any carbon-containing compound can be used as the carbon compound, but methane having an SP ³ bond is preferable.

The diamond of the present invention can be synthesized in all pressure ranges where glow discharge is possible. The mixing ratio of carbon compounds to hydrogen is 0.001 to 0.001, judging from the ability of hydrogen to remove non-diamond carbon.
0.1 is preferable.

There are three regions of DC glow discharge: early, normal, and abnormal glow, but normal or abnormal glow discharge is desirable from the viewpoint of glow discharge stability.

Although the substrate may be made of any material and have any shape, it is desirable to have a flat surface from the viewpoint of stability of glow discharge. The material can be any of insulators, semiconductors, and metals.

Although the substrate temperature may be high, a diamond thin film can be synthesized even at room temperature.

Possible methods for heating the substrate include resistance heating, lamp heating, etc., and any of these methods is possible.

The DC bias may be applied either as a cathode or an anode on the substrate side, but a cathode is preferable since positive ions are thought to mainly affect the diamond growth process.

In order to expand the discharge pressure range, a rare gas may be introduced into the gas or vapor of the carbon compound and hydrogen as a carrier gas. Argon is preferable as the rare gas because it easily causes discharge.

The high frequency can be introduced by either inductive coupling or capacitive coupling, but an inductive coupling method that does not require the introduction of electrodes into the reaction system is preferable.

Hereinafter, aspects of the apparatus used in the present invention and the manufacturing process will be explained in detail using the drawings. The surface of the substrate used in the present invention was cleaned using an etching agent suitable for the substrate as a pretreatment. In the figure, the substrate 1 after cleaning was placed on the cathode 2. Next, the inside of the quartz reaction tube 4 is preliminarily evacuated to 10 ^-4 Torr using the evacuation system 3 . Exhaust gas is exhausted from the exhaust port 5. After pre-vacuum,
Open the pot 6, introduce rare gas into the reaction system from the rare gas cylinder 7, and adjust the pressure to several torr. A DC bias of several hundred volts is applied to the anode 8 and cathode 2 to sputter and clean the substrate surface. After completing the sputtering, close the tank 6 and evacuate the system to 10 ^-4 Torr again. When using a cylinder gas as a carbon source, open the gas tank 9 and simultaneously supply the carbon compound gas from the carbon compound gas cylinder 10 to the gas tank 1.
1 to introduce hydrogen gas from the hydrogen gas cylinder 12 and also rare gas, open the pot 6 and introduce the rare gas from the rare gas cylinder 7 into the reaction system. When using liquid vapor of a carbon compound as a carbon source, the liquid raw material of the carbon compound is installed in the carbon compound evaporator 13, and the vapor of the liquid raw material is introduced into the reaction system using hydrogen gas or hydrogen + noble gas as a carrier gas. . The amount of vapor of the liquid raw material is controlled by adjusting the temperature of the evaporator 13.

The growth is caused by a sputtering effect caused by a rare gas. After cleaning the substrate, it is evacuated and the cathode 2 is cooled with cooling water if the substrate temperature is to be at room temperature. After adjusting the temperature to a predetermined temperature, the reaction gas is introduced into the system, and a DC bias electric field is applied between the cathode 2 and the anode 8. After DC glow discharge, a high frequency is generated by the high frequency generator 16, and a high frequency glow is generated. This is done by causing an electric discharge.

Example 1 Using silicon as the substrate, methane gas as the carbon source, and hydrogen as the carrier gas, the substrate temperature was room temperature and the pressure was
A transparent film was obtained on the substrate by reacting for 30 minutes at 0.5 Torr, a DC discharge current density of 0.1 mA/cm ² , a high frequency frequency of 13.56 MHz, and a high frequency output of 100 W. When the film thickness and refractive index were evaluated using an ellipsometer, they were ~5200 Å and 2.40 (wavelength 6328 Å), respectively.

Further analysis using a transmission electron microscope revealed that this film was diamond. When the surface was observed with a scanning electron microscope, no irregularities were visible and it was completely flat. Furthermore, when the adhesion force was measured by the attraction method, it was found to be as large as ~500 g, indicating that the adhesiveness of the film was high.

Example 2 Using quartz glass as the substrate, acetone as the carbon source, hydrogen and argon as the carrier gas, the substrate temperature was room temperature, the pressure was 1 Torr, and the DC discharge current density was
When the reaction was carried out for 30 minutes at a high frequency of 0.2 mA/ ^cm2 at a high frequency of 13.56 MHz and a high frequency output of 200 W, a film with interference colors was obtained on the substrate. The interference color was the same across the substrate and the film was flat. When measured with an ellipsometer, the film thickness is ~6500Å, and the refractive index is 2.42 (wavelength
6328Å). Transmission electron microscopy and Raman spectroscopy revealed that the film was a single diamond phase. When surface roughness was measured using a crease step, a value comparable to that of a silicon polished surface was obtained, confirming flatness. When the adhesion force was measured by the attraction method, it was ~450g,
It had great adhesion.

Example 3 Using molybdenum for the substrate, propane for the carbon source, hydrogen and helium for the carrier gas, and controlling the substrate temperature.
100℃, pressure 2 Torr, DC discharge current density
When the reaction was carried out for 30 minutes at 0.1 mA/cm ² , a high frequency frequency of 400 KHz, and a high frequency output of 600 W, a transparent film exhibiting an interference color was obtained on the substrate. Film thickness ~2000Å, refractive index 2.39 when measured with an ellipsometer
(wavelength: 6328 Å). Evaluation by Raman spectroscopy revealed that this film was diamond. Surface observation using a scanning electron microscope revealed that the film was almost flat, with only slight irregularities observed in some areas. The adhesive force measured by the pulling method was ~600 g, and the adhesion was good.

(Comparative Example) There has been no quantitative measurement of the adhesion force of a film, and it is not possible to compare it with the adhesion force of the film synthesized according to the present invention. Therefore, the adhesion force of a diamond-like thin film synthesized using only DC glow discharge or high-frequency glow discharge was set to the value obtained by the conventional method. As a result of actual measurements, it was found that the adhesion force of diamond-like thin films cannot be measured using only the DC glow discharge method.
Approximately 100 to 200g High frequency glow discharge method alone, approximately 50g
It was ~100g.

(Effects of the Present Invention) The diamond film synthesized according to the present invention has a strong adhesive force, and if it is formed as a surface protective film on a tool etc., the wear resistance can be greatly improved. Furthermore, since it is transparent in the visible and infrared rays, it has a wide range of optical applications, but the surface of diamond films synthesized using conventional techniques is rough and has severe irregularities, which has limited its optical applications. The diamond film synthesized according to the present invention is flat, which eliminates this limitation and has rich applicability. Furthermore, with the prior art, diamond could not be synthesized without heating the substrate to a high temperature, but with the present invention, the substrate temperature could be lowered to room temperature. As a result, it is possible to greatly improve the mass productivity of diamond films, and furthermore, by lowering the substrate temperature, the application to the semiconductor field can be expanded, and its industrial value is extremely large.

Furthermore, the method of the present invention was able to increase the adhesion force of the diamond-like thin film by several to ten times compared to the conventional method.

[Brief explanation of the drawing]

The figure is a schematic diagram of an apparatus for carrying out the method of the invention. 1...Substrate, 2...Cathode, 3...Evacuation system,
4...Quartz reaction tube, 5...Exhaust port, 6...Kotuku, 7...Rare gas cylinder, 8...Anode, 9...Kottoku, 10...Carbon compound gas cylinder, 11...
Kotuku, 12...Hydrogen gas cylinder, 13...Carbon compound evaporator, 14...Reactor, 15...Resistance heater wire, 16...High frequency generator.

Claims (1)

[Claims] 1 In a method of depositing diamond on a substrate by decomposing and exciting a carbon compound gas or vapor in a direct current glow discharge, the carbon compound gas or vapor is first turned into plasma by a high frequency glow discharge, and the afterglow of this plasma is A method for synthesizing diamonds from the gas phase, which is characterized by introducing into a direct current glow discharge.