JPS59232991A - Production of thin diamond film - Google Patents

Abstract

PURPOSE:To synthesize efficiently a thin diamond film in which free carbon does not exist mixedly on a base material by installing the base material heated to a specific temp. in a vacuum vessel and passing and introducing the gaseous raw material to be introduced through a tungsten filament zone and a high frequency electric field zone. CONSTITUTION:A base material heated to 150-500 deg.C is installed in a vacuum vessel maintained under 10<-5>-1Torr in production a thin diamond film by a vapor phase synthesis method. The gaseous raw material (>=1 kind among methane and ethane) to be introduced is then passed through an activation zone using a high temp. tungsten filament of >=1,500 deg.C installed in the vessel and further through an ionization zone by the high frequency applied from the outside of the vessel or the DC electrolysis, thereby forming the thin diamond film on the base material.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field The present invention relates to a method for producing a diamond thin film by vapor phase synthesis.

(b) Background of the technology The vapor phase synthesis of diamond or pseudo-diamond has been researched in many countries for several decades. The synthesis methods are mainly divided into two as follows.

■CVD method: Hydrocarbons such as methane are introduced into a furnace heated to 600°C or higher using hydrogen as a carrier, and are deposited on diamond seed crystals, Si single crystals, silica, polycrystalline Mo, etc. that have been placed in the furnace in advance. A method in which a film of several microns consisting of microcrystalline particles of diamond or pseudodiamond or an aggregation thereof is formed by thermal decomposition of hydrocarbons.

■ PVD method: Using the so-called ion beam evaporation method, carbon is sputtered with Ar ions, etc., and the sputtered carbon ions are accelerated to hundreds to thousands of volts and are bombarded against the substrate for vapor deposition. , At the same time, Ar ions are accelerated in the same way and hit the base material, causing a 5P2-5P3 electron orbit change, thereby forming a thin film of diamond or pseudodiamond with a thickness of several microns or less. Each of these methods has its own advantages and disadvantages. For example, the CVD method has the advantage that the equipment is simple and inexpensive, but because it lacks a raw material gas activation mechanism, it has the disadvantage that free carbon is likely to be mixed in the diamond or pseudo-diamond, and that the 600°
It also has the drawback that it cannot be synthesized at low temperatures below C, and therefore the base material is limited. On the other hand, the latter PVD method has a unique activation mechanism and has the advantage of not having to worry about the heat resistance of the base material because it can be deposited at low temperatures, but the equipment is an ion sputter gun in a high vacuum chamber. It is expensive to install, and also has the disadvantage that the deposition is selectively carried out only on specific surfaces of the substrate, resulting in poor coverage.

9 Disclosure of the Invention The present invention takes advantage of the advantages of both of the above methods.
This method provides a method that improves the shortcomings.

The present invention relates to a method for producing a diamond thin film by vapor phase synthesis, in which a base material heated to 150 to 500°C is installed in a vacuum container, and raw material gas introduced into the heated tung-free filament zone. High frequency electric field or
It is located where it passes through a zone where a DC electric field is applied. Further, the temperature of the tungsten filament is 1500° C. or higher, the raw material gas is one or more of methane and ethane, and the pressure inside the vacuum container is 10 −5 to 1 torr. Note that the term "substrate" as used herein means a substance on which a diamond thin film is formed. In the present invention, 15006
This problem was solved by activating the raw material gas by thermionic radiation from a tungsten filament heated above C and ionization of the gas by applying a high frequency or DC electric field. By doing so, it is possible to avoid using expensive parts and power supplies such as sputter guns and acceleration grids that are used in the ion beam method.

The present invention is a diamond vapor phase synthesis method in which vapor deposition is performed on the surface of a base material. and the total pressure of other gases is 10-
The raw material is introduced at a pressure in the range of 5 to 1 torr, but the raw material passes through an activation zone created by a high-temperature tungsten filament of 1500°C or higher installed inside the container, and then passes through an ionization zone created by a high frequency or DC electric field applied from outside the container. , and then reaches the substrate. ”
1. The order of passage through the activation zone and ionization zone is not limited, but it is better to pass the activation zone first. By passing the reaction gas continuously through these two activation zones, diamond CH4or can be efficiently deposited on the substrate without the presence of free carbon.
Activating C2H6 hydrocarbon gas with a tungsten filament and high frequency or DC electric field improves the reactivity of the raw material gas, suppresses the generation of soot-like free carbon, and promotes reactions such as CH4-C+2H2). Even if it grows once and generates it (.2H6-+2c+3H5
- This is an essential condition for the ionized H2 gas formed to selectively etch away free carbon and efficiently promote the synthesis of the diamond film. Other gases are used as carriers for CH4 and C2H6 and reaction promoting gases. This kind of gas is preferably an inert gas or a reducing gas. In addition, at this time, thermionic radiation from the heated tungsten filament is important for activating the raw material gas.
aCtor, but when the temperature is below 1500°C, the amount of thermionic electrons emitted is small, and the synthesized diamond film also contains some free carbon. Next, the reason why methane and ethane are included in the raw material gas is that when other hydrocarbon gases such as ethylene or acetylene are used, the weight ratio of carbon in an equimole is large. This is because a large amount of carbon is mixed in, and even with the same methane-based gas, when the gas has a higher molecular weight than propane, even under the same activation conditions, the activation level of carbon atoms is low and free carbon is more likely to be generated. In addition, the total gas pressure in the vacuum container is 1o-5 to 1 torr, and the substrate temperature is 150' to 500°C.
One of the reasons for limiting this is the synthesis efficiency. That is, 10-”t
At low pressures below orr and at low temperatures below 150°C, the growth rate of the diamond film is extremely slow at 0.01 μm//11r or less, resulting in extremely poor yields. On the other hand, at a high pressure of 1 torr or higher or a high temperature of 500° C. or higher, the interlayer growth rate is excellent, but the reaction gas is not activated sufficiently and the rate of free carbon generation increases.

Details will be explained below in Examples.

C) T4 gas was heated to 350°C using infrared heating.
Supply at 0CC/f11in, total gas pressure is 2.5X
The pressure was adjusted to 10-3 torr. The tungsten filament is powered at 180
Heat it to 0°C and wrap a 5-turn coil underneath it.
Plasma was generated by a high frequency of 13.56 MT (z). After 5 hours of vapor deposition under these conditions, the spectrum of the same sample was measured by infrared spectroscopy. SEM observation of the fractured surface of the same sample revealed that a 6.5 μm thick Diarnnd film had been synthesized.

Example 2 A polished Mo plate was placed in the same vacuum container as in Example 1, and a reaction was carried out for 3 hours. At this time, the DC electrode (2[]O
Plasma was generated at V 10A). The board temperature is 45
The temperature of the 0°C1W filament was 2600°C, but the film formed was LEELS (Low Electron E
energy loss spectrometry) revealed that it was a diamond.

Example 6 The electron diffraction results of the film prepared are summarized in (Table 1). From this, the diamond synthesis conditions are that the substrate temperature is 150~
500°CW filament heating temperature 1500°C or more,
It has been found that a degree of vacuum of 10-5 to 1 ton is optimal.

Table 1 Correlation between vapor deposition conditions and film quality 9-

Claims (1)

[Scope of Claims] (1) In a method for producing a diamond thin film by vapor phase synthesis, a base material heated to 150 to 500°C is placed in a vacuum container, and a tungsten filament zone where the raw material gas introduced is heated. A method for producing a diamond thin film, characterized by passing through a zone to which a high frequency electric field or a direct current electric field is applied. (2) Temperature of heated tungsten filament (6
) The source gas is comprised of one or more of methane (CH4) and ethane (C2H6).
1) A method for producing a diamond thin film as described in section 1). (4) The method for producing a diamond thin film according to claim (1), wherein the pressure within the vacuum container is 10 -5 to jtorr.