JPS6350478A - Formation of thin film - Google Patents

Abstract

PURPOSE:To form a uniform thin film at a low cost and a high rate by converting a gaseous mixture prepd. by properly diluting a gas contg. a film forming component with a rare gas into plasma by glow discharge under a pressure close to atmospheric pressure. CONSTITUTION:A substrate 9 such as a metallic plate is placed on a support plate 7 with an insulating plate 8 in-between in a reactor 1. A gaseous mixture 3 consisting of >=about 90% rare gas such as He, a gaseous hydrocarbon contg. a film forming component such as CH4 and a dehydrogenating gas such as a halogenated hydrocarbon is introduced into the reactor 1 from the feed hole 2a of an inner tube 2 through the tube 2 so as to regulate the internal pressure of the reactor 1 to about 200Torr-2 atm, preferably about 1 atm. Glow discharge is then caused between a counter electrode 4 in the lower part of the inner tube 2 and an external electrode 10 with an RF wave generator 6 to convert the gaseous mixture 3 into plasma. The hydrocarbon in the mixture 3 is decomposed and a thin carbon film is formed on the substrate 9.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a thin film forming method for forming a thin film such as a carbon film or a fluorocarbon film on a metal or ceramic.

(Prior Art) Conventionally, techniques are known for forming a thin film on the surface of a solid material, applying a coating treatment to protect the material, and improving the adhesiveness and water repellency of the material surface.

For example, carbon materials have excellent heat resistance and wear resistance, high thermal conductivity, and self-lubricating properties, so they can be made into thin films to coat the surfaces of bearings, tools, etc., and can be used to improve heat dissipation. It is being considered to coat the surface of electronic circuit boards.

Furthermore, fluorocarbon membranes are known for their excellent water repellency and lubricity, and household goods and industrial products are made that take advantage of these properties.

By the way, a thin film forming technique using low-temperature plasma is known as one of the surface treatment methods for solid materials.

Regarding the carbon film mentioned above, for example, Japanese Patent Laid-Open No. 59-26
Recent manufacturing techniques are disclosed in No. 906 and Japanese Unexamined Patent Publication No. 60-210597. In the former, a hydrocarbon-based substance is turned into a plasma in a vacuum chamber by the action of an RF high-frequency electric field, and an amorphous carbon film is deposited and formed on a silicon substrate and a slide glass substrate, and in the latter, hydrocarbons with C≦20 are used as raw materials. The mixed gas with H2 gas is heated at low pressure (1
00 to 10-2 Torr) to generate a diamond thin film on the Si or Si compound substrate.

In either method, a highly vacuum atmosphere is required, and the equipment for that purpose is expensive, and especially when a large area is treated, the equipment becomes extremely expensive, which poses a practical problem.

On the other hand, regarding the above-mentioned fluorocarbon membrane, for example, as disclosed in Japanese Patent Publication No. 60-32120, a high voltage of DC or AC is applied in a vacuum atmosphere of 10-1 to 10-2 mbar to heat and evaporate while causing glow discharge. A method for forming a thin film of fluororesin by vapor depositing fluororesin on a metal surface is disclosed.

In this case as well, since a highly vacuum atmosphere is required, there is a problem that the equipment becomes expensive.

(Object and Structure of the Invention) The present invention has been made in view of the above points, and an object of the present invention is to make it possible to form thin films such as carbon films and fluorocarbon films under pressure close to atmospheric pressure. In order to achieve this objective, a mixed gas of about 90% or more of a rare gas and a gas containing film components is made into a plasma state by glow discharge under a pressure in the range of about 200 Torr to 2 atmospheres, and a plasma is formed on the substrate. It is formed as a thin film.

(Example) The present invention will be explained in detail below.

FIG. 1 is a schematic diagram of an apparatus for forming a carbon film according to the present invention.

Reference numeral 1 denotes a reaction vessel whose interior is maintained at atmospheric pressure, and an inner cylinder 2 extends at the center of the interior, and at the top of the inner cylinder 2 is a supply port through which a mixed gas 3 of rare gas, hydrocarbon, etc. involved in plasma polymerization is supplied. 2a is provided. Further, a counter electrode (high voltage electrode) 4 is provided near the lower end of the inner cylinder 2, and power having an RF (radio frequency) frequency is supplied to the counter electrode 4 from an RF oscillator 6 via a high voltage input section 5. A mixed gas outlet 1a is provided at the top of the 0 reaction vessel 1.

At the bottom of the reaction vessel 1, there is provided a conductive support substrate 7 made of stainless steel, for example, which acts as a sample electrode (low voltage electrode), and on top of that is an insulating plate 8 made of an insulating material such as Kapton.
is placed thereon, and a substrate 9 on which a carbon film is to be formed is placed. The support substrate 7 is normally grounded. Reference numeral 10 indicates an external electrode made of copper foil wrapped around the outside of the reaction vessel, but as long as this external electrode IO exists, the support substrate 7 does not need to be conductive.

FIG. 2 shows the state of the substrate 9 placed at the bottom of the reaction vessel l.

The internal pressure of the reaction vessel 1 can range from about 200 Torr to 2 atmospheres, which is much higher than conventional devices of this type, but atmospheric pressure is most preferred.

The mixed gas used in the reaction is a rare gas such as helium, neon, or argon, a hydrocarbon gas such as methane, ethane, propane, or butane, and a halogen to extract hydrogen that enters the carbon film at the beginning of the reaction. It consists of carbonized hydrocarbons, halogens, oxygen, hydrogen, and hydrogen extraction gases such as NF:l, SFa, and CF4, and the component ratio is about 90% or more of rare gases and about 10% or less of other gases. The rare gas can be used not only as a single type but also as a mixture with other rare gases.

The plasma used to form this type of thin film is a glow discharge,
It is formed by various discharges such as corona discharge, silent discharge, and arc discharge, but with the exception of glow discharge, spark columns called streamers tend to form, and the current flows locally, forming one electrode. The energy is concentrated at a specific location on the solid material (corresponding to the substrate 9 in the present invention), producing a large number of pinholes on the material surface and significantly deteriorating the film quality. Therefore, glow discharge without such defects is desired, but normally glow discharge does not easily occur under pressure close to atmospheric pressure.

However, rare gases are easily excited by electric discharge, have many metastable states, and can produce many active particles in excited states. The presence of highly excited active particles at a high density makes it easy to increase the degree of dissociation of hydrocarbons and halogenated hydrocarbons. There are also parts that spread the discharge because ions can easily diffuse in rare gases. The present invention focuses on such properties of rare gases and enables glow discharge under pressure close to atmospheric pressure.

The substrate 9 on which the carbon film is formed in the present invention is a metal material, an inorganic material such as ceramics or glass, or an organic material such as a polymer material. An insulating plate 8 is necessary to prevent localization of the insulating plate 8, but in the case of a non-conductive material, the insulating plate 8 is not necessary.

Next, an example in which a carbon film was formed according to the present invention will be shown.

A mixed gas consisting of He and CH mixed at a ratio of 99:1 was heated to 1 atm (760 T) at a flow rate of 4.000 cm'' per minute.
The reaction time for forming a carbon film on a glass substrate (at room temperature) was 10 minutes, and the film growth rate was 0.7 microns/10 minutes. During the reaction, glow discharge was observed over the entire surface of the specimen, and the film formed on the glass substrate was brown and uniform.

On the other hand, when the plasma situation inside the reaction vessel was observed by changing the component ratio of rare gas in the mixed gas, the following results were observed. The ratio of He:CH4 is 9'7:3.
At 95:5, a wide glow discharge occurs, or at 92
:8, the spread of claw discharge becomes narrower and becomes 90:1.
When the temperature reached 0, corona discharge was observed instead of glow discharge. Spark discharge was observed when the component ratio was 89.5:10.5.

Next, the case of forming a fluorocarbon film according to the present invention will be described.

Using the apparatus shown in FIG. 1, one of the following (a) to (d) is used as a mixed gas. However, the rare gas may be helium, neon, or argon alone or in a mixture, but helium, which has a light mass, is preferable in order to minimize sputtering on the film.

(a) Mixed gas of rare gas, hydrocarbon gas, and fluorine (NF or SF6 may be used instead of fluorine) (b) Addition of halogen or hydrogen other than fluorine to the above (a) for hydrogen extraction from the membrane Mixed gas (c) Mixed gas of rare gas, fluorinated hydrocarbon (CF), and hydrocarbon (d) Mixture of the above (c) with halogen other than fluorine or hydrogen for extracting hydrogen from the membrane Gas Next, an example in which a fluorocarbon film was formed according to the present invention will be described.

A mixed gas consisting of a mixture of CH, CF, and He in a ratio of 1:1:98 was passed through a reaction vessel at 1 atm (760 Torr) at a flow rate of 4,000 cm' per minute onto a thin stainless steel plate (at room temperature). A fluorocarbon film was formed on the surface. The reaction time was 2 minutes, and the film formed was brown in color. In this experiment, as the proportion of CF in the mixed gas component increased, the spread of glow discharge gradually became narrower, and CH4:CF4:
It was confirmed that when the ratio of He was 1:9:90, glow discharge changed to corona discharge.

Carbon membrane made according to the first example (thickness: 7437 mm)
The results of measuring the transmittance of infrared light using an infrared spectrometer for the fluorocarbon film (approximately 100 mm thick) made according to the second example are shown in Figures 3 (a) and (b). It becomes as shown in .

From this analysis result, the infrared absorption wavelength of hydrocarbons (CH) is 3001.0 cm'-'' (33,898 people), and the infrared absorption wavelength of fluorocarbon is 1199.1 cm-'' (8
(3,395 people), a drop in permeability was observed, confirming the presence of a carbon film and a fluorocarbon film.

It has been known that the fluorocarbon film, which is one of the thin films formed by the present invention, has excellent water repellency. By forming the fins, a droplet-like condensation surface with excellent water repellency can be obtained, making it difficult for water droplets to adhere to the fins, thereby preventing a decrease in the power of the heat exchanger.

Although the present invention has been exemplified above with respect to a carbon film and a carbon fluoride film, it goes without saying that the present invention can be similarly applied to the formation of other thin films such as silicon nitride films, amorphous silicon, and silicon carbide films. be.

(Effect of the invention) As explained above, in the present invention, approximately 200 T
A mixture of about 90% or more rare gas and gas containing film components is made into a plasma by glow discharge under a pressure within the range of 2 atm from orr to 2 atm, and is formed as a thin film on the substrate. This eliminates the need for vacuum equipment such as vacuum pumps, vacuum valves, and pelgers that require special welding to create a vacuum atmosphere, significantly reducing equipment costs. Furthermore, even if the area of the substrate on which the thin film is to be formed is large, it can be done with equipment under atmospheric pressure, which is advantageous in terms of cost. Furthermore, since the pressure is high, the film growth rate is also faster than in the conventional method.

According to the present invention, since the method utilizes plasma generated by glow discharge, it is possible to uniformly coat a thin film even on the surface of a substrate having a complicated shape, such as a radiation fin of a heat exchanger, at low cost.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an apparatus for carrying out the thin film forming method according to the present invention, FIG. 2 is a partially enlarged perspective view of the apparatus shown in FIG. 1,
FIG. 3 is a graph showing the results of infrared spectroscopic analysis of a thin film formed according to the present invention. l...Reaction container, 2...Inner cylinder, 2a...Mixed gas supply port, 3...Mixed gas, 4...Counter electrode, 6...-RF
Oscillator, 7...Support substrate (sample pole), 8...Insulating plate, 9...Substrate, 10...External electrode Patent applicant Tokyo Gas Co., Ltd. Agent Patent attorney Hiroshi Suzuki, : 4. , C Cao Hui @ Breaking

Claims (1)

[Claims] Under a pressure in the range of about 200 Torr to 2 atmospheres, about 9
A thin film forming method characterized by forming a mixed gas of 0% or more of a rare gas and a gas containing film components into a plasma state by glow discharge, and forming the mixture as a thin film on a substrate.