JPH0280395A - Formation of diamond film - Google Patents

Abstract

PURPOSE:To form a high quality diamond film at a high rate by converting gas contg. a carbon compd. into plasma with a stable and very high density electric field formed around a fine leading wire of a specified thickness or below. CONSTITUTION:A meshy electrode 1 made of stretched W wires of 0.1mmphi is fitted to one side of a ring-shaped meshy electrode holder 2 made of a leading wire of <=0.5mm thickness. The electrode 1 and a substrate holder 4 made of stainless steel and provided with a built-in heater are set in a quartz tube 5 and a substrate 3 is put on the holder 4. The tube 5 is evacuated by a vacuum pump, high voltage is impressed between the electrode 1 and the holder 4 and gaseous starting material 6 is allowed to flow in the tube 5 from the top to the bottom. A product produced by decomposition with a high electric field near the electrode 1 deposits on the substrate 3.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a low-pressure vapor phase diamond deposition method for depositing high-quality diamond at high speed. The purpose of this method is to apply a voltage to the conductive wire in an airtight channel containing a conductive wire with a thickness of 0.5 tm or less and a substrate downstream of the conductive wire, thereby causing corona to the conductive wire. Diamond is deposited on the substrate by flowing a carbon compound-containing gas around the conducting wire and then reaching the substrate while generating an electric discharge.

[Industrial application field]

The present invention relates to a low pressure vapor phase diamond deposition method for depositing high quality diamond at high speed.

Diamond has the highest hardness and thermal conductivity of all materials, is an electrical insulator, optically transparent in a wide range from ultraviolet to infrared, and has a high refractive index. Therefore,
Taking advantage of these characteristics, it is expected to be used in a variety of applications, including tools and heat sinks.

[Conventional technology]

Various methods have been proposed as a low-pressure vapor phase diamond film forming method, including a microwave plasma CVD method, an RF plasma CVD method, and a method using arc discharge. However, methods using microwaves or RF (radio frequency) have extremely slow film formation speeds (~0.5 n/h), and the film quality is darkened due to graphite, etc., making it unsatisfactory for practical use. The method using arc discharge has a high deposition rate (~200 μ
m/h), but the film quality is similarly darkened and is insufficient for practical use.

[Problem to be solved by the invention]

An object of the present invention is to provide a diamond film forming method that can form a diamond film of practically sufficient film quality at a practical high speed.

[Means to solve the problem]

The above purpose is to generate a corona discharge in the conductive wire by applying a voltage to the conductive wire in an airtight flow path that accommodates a conductive wire with a thickness Q of 5 m or less and a substrate downstream from it. This is achieved by a diamond film forming method characterized in that diamond is deposited on the substrate by flowing a carbon compound-containing gas around the conductive wire and then reaching the substrate.

In the method of the present invention, a voltage in a range that generates corona discharge is applied to a thin conductive wire with a thickness of 0.5 U+ or less, thereby stably forming an extremely high-density electric field around the conductive wire. The carbon compound-containing gas is completely decomposed and turned into plasma by this high electric field around the conductor, and only carbon (C) with the sp co-orbital, which particularly contributes to the formation of the diamond film, is present in the flow of the plasma-turned gas. It reaches the substrate and is deposited as a diamond film.

As a result, a high-quality diamond film containing no graphite or amorphous carbon can be formed at high speed.

The thickness of the conductor was 0.5 nm in order to create a high-density electric field sufficient to completely decompose the carbon compound-containing gas.
+ or less, preferably 0.3 u+ or less, and most preferably 0.1 mm or less. There is no need to particularly limit the lower limit of the thickness. However, it is sufficient that the electric field is as thin as possible to form an electric field with the energy necessary to decompose the gas, and even if the electric field is made thinner than that, the effect will not increase much. From the viewpoint of manufacturing the conducting wire, the current practical lower limit is about 101M.

The voltage applied to the conducting wire may be either a direct current voltage or an alternating current voltage, and a voltage within a range that causes corona discharge is appropriate. At a voltage higher than this range, arc discharge occurs, which makes the discharge unstable and deteriorates the quality of the diamond film.

Conversely, at a voltage lower than this range, corona discharge will not occur and a high electric field that can completely decompose the carbon compound-containing gas will not be formed. The voltage for corona discharge is appropriately selected depending on the thickness of the conducting wire, the pressure of the gas, etc.

As the carbon compound-containing gas, any gas used in the diamond vapor phase growth method can be used. Compounds containing carbon having the sp3 orbital, which makes a particularly large contribution to diamond formation, are particularly advantageous. Typical examples thereof are methane, acetone, methyl alcohol, ethyl alcohol, etc.

[For production]

The method of the present invention uses a high-density electric field formed around a thin conductive wire to generate a stable corona discharge, which completely decomposes carbon compound gas into high-energy plasma, which is transported by a gas flow. Since the diamond film is deposited on the substrate, a high quality diamond film can be formed at high speed.

In the following, the invention will be explained in more detail by means of examples with reference to the accompanying drawings.

〔Example〕

FIG. 1 shows an example of a device for carrying out the method according to the invention. (A) and (B) are the arrangement seen from above and from the front, respectively, and are partially shown in cross section.

As shown in Fig. 1, a mesh-like electrode l made of 0.1fiφ W (tungsten) wire stretched at intervals of 3f1 is used as a conductor for applying high voltage on one side of a ring-shaped mesh electrode holder (made of alumina) 2. Using. The substrate holder 4 is made of stainless steel and has a heater inside, so that the temperature can be controlled to a predetermined temperature. The mesh electrode 1 and the substrate holder 4 are placed in a quartz tube 5 and can be reduced in pressure by a vacuum pump.

While a high voltage is applied between the mesh electrode 1 and the substrate holder 4, the raw material gas 6 is caused to flow from above to below the quartz tube. Then, decomposition products due to the high electric field near the mesh electrode 1 are deposited on the substrate 3 on the substrate holder 4.

In this example, the raw material gas 6 is 1% CH.

H2 (hydrogen) gas containing (methane) was used (flow rate was 2
005CCM). As the substrate 3, a (111) Si substrate was used. The gas pressure during the reaction was set at 100 Torr, and the substrate temperature was set at 850°C. Further, the distance between the mesh electrode 1 and the substrate 3 was 15 mm, and the voltage applied therebetween was 1 kV DC.

When the reaction was carried out for 5 hours under these conditions, a cloudy, translucent film was obtained on the surface of the substrate.

Since the thickness was 120 mm, the film formation rate was 24 mm per hour. When this film was examined by X&'i1 diffraction and Raman spectroscopy, it was confirmed that it was a high quality diamond film containing almost no graphite or amorphous carbon.

In this embodiment, the raw material gas was introduced after the inside of the quartz tube was evacuated, but the raw material gas may be purged without exhausting the interior of the quartz tube, and the reaction may be performed at a gas pressure close to atmospheric pressure.

There is no need to limit the gas pressure, but it is usually between 50 and 76
It is preferable to set it in the range of 0 Torr.

For convenience, the mating electrode of the mesh electrode was set as a substrate holder, but the mating electrode may be provided separately at an appropriate position within the quartz tube as long as a corona discharge of a high electric field can be generated in the mesh electrode.

In the above embodiment, H2 and CH4 were used as the raw material gases, but it goes without saying that the material gases are not limited to these. In place of CH40, almost all carbon-containing substances having sp3 orbitals, such as acetone, methyl alcohol, and ethyl alcohol, can be used. The substrate is not limited to Si, and other substrates such as Mo and PT may also be used. Moreover, the effect is almost the same even if a large number of conductive wires stretched in parallel are used instead of the mesh electrode. The material of the electrode can be replaced with another material as long as it is a conductor.

3... Board, 5...quartz tube, 4... Board holder 6... Raw material gas.

〔Effect of the invention〕

As described above, it has been found that a semitransparent and highly pure diamond film can be obtained by the method according to the present invention. Although the film-forming speed is not as fast as the method using arc discharge, it is much higher than the method using microwaves or RF.The diamond film according to the present invention has unprecedented high quality, and It can be said that the film formation rate is also high for practical purposes.

[Brief explanation of the drawing]

FIGS. 1(A) and 1(B) show an example of an apparatus for carrying out the diamond film forming method according to the present invention;
A) is a cross-sectional view, and (B) is a longitudinal cross-sectional view.

Claims (1)

[Claims] 1. In an airtight flow path containing a conductor having a thickness of 0.5 mm or less and a substrate downstream thereof, a voltage is applied to the conductor to generate corona discharge in the conductor. While
A diamond film forming method characterized in that diamond is deposited on the substrate by flowing a carbon compound-containing gas so as to pass around the conductive wire and then reach the substrate. 2. The diamond film forming method according to claim 1, wherein the conducting wire is stretched in a mesh shape.