JPH06247795A - Formation of diamond single crystal film - Google Patents

Abstract

PURPOSE:To easily form a diamond single crystal film as a thin continuous film having a smooth surface. CONSTITUTION:A nickel single crystal film or a nickel-contg. alloy single crystal film is epitaxial-grown on an oxide single crystal a substrate having a perovskite type structure and then a diamond single crystal film is formed on the grown film by a chemical vapor growth method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a diamond single crystal film, and more particularly to a method for simply forming a diamond single crystal film useful as various highly functional materials.

[0002]

2. Description of the Related Art In recent years,
A method of synthesizing diamond by a chemical vapor method has been developed in various fields, and it has become possible to produce a diamond film useful for electronic materials, optical materials and the like, but the obtained one is usually a polycrystalline film.

It is known that diamond is made into a semiconductor by adding a specific impurity, but even if an attempt is made to make the above-mentioned polycrystalline film into a semiconductor, since the crystal grains are randomly arranged, the impurities due to the orientation It is difficult to obtain a high-performance semiconductor device because of non-uniform concentration. Furthermore,
It is known that grain boundaries in a polycrystalline film deteriorate electrical and optical properties, and that various high-density defects exist inside each crystal grain. Therefore, as is apparent from the example of the silicon semiconductor, it is essential to use a single crystal material for a high-performance material that is required to have excellent original crystal properties.

Against this background, various attempts have been made to establish a method for forming a diamond single crystal film. For example, a method of growing a homoepitaxial film on a diamond substrate is known, but the substrate is obtained naturally or by high-pressure synthesis, and is a practical method because of its size and cost. Is hard to say.
There is also known a method of so-called heteroepitaxial growth of a diamond single crystal film on a cubic boron nitride (cBN) substrate, but the formation of the cBN substrate requires ultrahigh pressure and is difficult to form. Therefore, the above method also does not have great industrial value.

Recently, a method has been reported in which nickel having a lattice constant close to that of diamond is used as a substrate and a diamond film is epitaxially grown thereon [Abstracts of the 4th Diamond Symposium pp. 1
3-14 (1991)]. Nickel can easily form a large single crystal as compared with the diamond or cBN, and is expected to be put to practical use as a substrate material for forming a diamond single crystal film.

However, since nickel has a property of dissolving carbon in solid solution, some problems resulting from this have occurred. One is that since the nucleus generation density of diamond is low, the smoothness of the film surface deteriorates, and in extreme cases, a continuous film cannot be formed. Another is that the diamond is eroded by nickel because a reaction occurs at the interface between the deposited diamond and nickel.

In order to solve the problem caused by the solid solution of nickel with carbon, a nickel single crystal film is epitaxially grown on a magnesium oxide (MgO) single crystal,
As a result, an attempt to reduce the volume of nickel has been proposed [Proceedings of the 39th Joint Lecture on Applied Physics, p. 423 (1992)].

However, since the above method uses the MgO single crystal as the underlayer, the Mg
Since the O single crystal is reduced and carbonized, a part of the nickel film is peeled off or an incomplete diamond film containing magnesium carbide crystals is formed, and it is difficult to efficiently form a good diamond single crystal film. Is.

Therefore, it has been desired to develop a method for solving the above problems and simply forming a diamond single crystal film having a smooth surface and a thin film thickness.

[0010]

Means for Solving the Problems The inventors of the present invention have made earnest studies in view of such circumstances, and as a result, provided a nickel single crystal film on an oxide single crystal having a perovskite structure, and then performing chemical vapor deposition on the nickel single crystal film. It was found that a diamond single crystal film having a very smooth surface and a thin film thickness can be easily obtained by forming a diamond film by the method, and completed the present invention.

That is, according to the present invention, after a nickel single crystal film or a nickel-containing alloy single crystal film is epitaxially grown on an oxide single crystal substrate having a perovskite structure, diamond single crystal film is grown on the film by chemical vapor deposition. The present invention provides a method for forming a diamond single crystal film, which is characterized by forming a crystal film.

The oxide single crystal having a perovskite structure used in the present invention may be a single crystal ingot cut out or a single crystal film obtained by epitaxial growth on a single crystal material such as silicon. As an oxide single crystal material having a perovskite structure,
Any material that can form a single crystal film of nickel and a nickel-containing alloy on it may be used, such as strontium titanate (SrTiO ₃ ), lead titanate (PbTiO ₃ ), calcium titanate (CaTiO ₃ ), barium titanate. (BaTi
O ₃ ), lead zirconate (PbZrO ₃ ), barium zirconate (BaZrO ₃ ), and solid solutions of these. Of these, strontium titanate, barium titanate, and the like, which have a lattice constant close to that of both nickel and diamond and can maintain a stable crystal structure even when heated at high temperature for forming a diamond single crystal film, are preferable.

In the present invention, a single crystal film of nickel or a nickel-containing alloy is epitaxially grown on the oxide single crystal substrate having the perovskite structure.
Epitaxial growth can be performed under ordinary conditions by a known means such as a sputtering method or a vacuum vapor deposition method.

The film thickness is not particularly limited, but for example, in the case of a single crystal film of nickel only, 10 nm to 10 μm is preferable. If it exceeds 10 μm, it becomes difficult to generate nuclei, and the formed diamond is easily corroded by nickel, which is not preferable. On the other hand, when the thickness is less than 10 nm, the vapor pressure of nickel is relatively high at a high temperature, so that nickel is evaporated during the diamond film formation, and particularly when the plasma method is used, nickel is sputtered by plasma and the film is formed. It may disappear, which is not preferable.

As described above, by adjusting the film thickness of the nickel single crystal film or the nickel-containing alloy single crystal film, it is possible to reduce the nucleus generation density of diamond and suppress corrosion by nickel.

Examples of the metal other than nickel forming the nickel-containing alloy used in the present invention include palladium, copper, cobalt, iron, platinum, chromium, gold, titanium, manganese and the like. Among them, nickel and Palladium, copper, which has a close crystal structure and lattice constant and is easy to form a solid solution,
Cobalt and iron are preferred. These metals other than nickel may be used alone or in combination of two or more.

The content of metals other than nickel in the nickel-containing alloy is 50 atm% or less for palladium, copper, cobalt and iron, and 10 atm for other metals.
% Or less is preferable. In this way, by controlling the composition of the nickel-containing alloy, its lattice constant can be approximated to that of diamond, and the solubility of carbon in the alloy can be reduced, while the content of metals other than nickel can be reduced. If the amount is too large, the epitaxial growth of the diamond single crystal film is often hindered.

In the present invention, a diamond single crystal film is epitaxially grown by a chemical vapor deposition method on the nickel single crystal film or the nickel-containing alloy single crystal film formed on the oxide single crystal.

The chemical vapor deposition method (hereinafter sometimes referred to as "CVD method") used in the present invention has been conventionally
Various CVD methods using a carbon-containing gas as a raw material, which have been used for forming a diamond film, can be used. Specific examples include a hot filament CVD method that utilizes the thermal decomposition of gas by a filament that has been heated red, and a microwave plasma CVD that converts gas into plasma by electric discharge.
Method, high frequency plasma CVD method, direct current plasma CVD method,
Various plasma CVD such as DC arc plasma CVD method
Method, a combustion flame CVD method using a combustion flame of acetylene-oxygen mixed gas, and the like.

Examples of the gas used in the above CVD method include hydrocarbons such as methane, ethane, acetylene and benzene, alcohols such as ethanol, carbon-containing gas such as carbon monoxide diluted with hydrogen gas, and carbon. You may use what added oxygen containing gas, such as oxygen, steam, and carbon dioxide, to the containing gas. Furthermore, if necessary, argon,
You may mix inert gas, such as helium, and nitrogen.

In the present invention, any one of the above CVDs
The diamond single crystal film can be epitaxially grown by applying the method under normal conditions by appropriately using the above gases.

[0022]

According to the method of the present invention, a diamond single crystal film can be easily obtained. Moreover, according to the method of the present invention, since the nucleus generation density is high at the initial stage of diamond single crystal film formation, it is possible to easily form a thin continuous film having a very smooth surface. Further, it is possible to obtain a high-purity diamond single crystal film in which contamination of contaminants from the substrate material is extremely reduced.

[0023]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto.

Example 1 First, the size is 15 mm × 15 mm × 1 mmt, and the azimuth (001)
A 500 nm-thick nickel thin film was formed on the strontium titanate single crystal substrate on the surface using a sputtering apparatus. As the conditions for forming the nickel thin film, argon was used as the atmosphere gas, the pressure was 1.5 Pa, the substrate temperature was 400 ° C., and the plasma density was 6.8 W / cm ² . As a result of measuring the orientation of this nickel thin film by RHEED (reflection high-energy electron diffraction), it was a (001) single crystal thin film, which had a parallel epitaxy relationship with the underlying strontium titanate. The substrate prepared by the above method was placed on a substrate holder in a quartz glass reaction tube having an inner diameter of 40 mm, and the reaction tube was evacuated by a rotary pump and an oil diffusion pump. After exhausting to 10 ⁻⁴ Torr, hydrogen gas was caused to flow at a flow rate of 99.2 ml / min to adjust the pressure inside the reaction tube to 6.7 kPa. Next, a microwave having a frequency of 2.45 GHz was applied from the outside of the reaction tube to the place where the substrate was placed in a direction perpendicular to the reaction tube to generate plasma. After the plasma was turned on, the microwave input power was adjusted to set the substrate temperature to 890 ° C. The microwave input power at this time was 500W. The substrate temperature was measured with a radiation thermometer through a quartz window above the reaction tube. When the substrate temperature became constant at 890 ° C, methane gas was added at a flow rate of 0.8 ml / min, and the pressure in the reaction tube was adjusted to 6.
Readjusted to be 7 kPa. When a film was formed under the above conditions for 30 minutes, a substance having a uniform crystallographic orientation was granularly deposited on nickel. Raman spectroscopy confirmed that these granular materials were diamonds. The density of this granular diamond is 10 ⁷ to 10 ⁸ pieces / cm ²
It was about. Further, it was found by RHEED that these granular diamonds were epitaxially grown in parallel on the substrate. When film formation was performed for another 5 hours under the same conditions, a diamond (001) single crystal film having a film thickness of about 5 μm and a smooth surface was obtained.

Example 2 A 1 μm thick nickel thin film was formed on a strontium titanate single crystal substrate having a size of 15 mm × 15 mm × 1 mmt and an orientation (001) plane under the same conditions as in Example 1 using a sputtering apparatus. Formed. As a result of measuring the orientation of this nickel thin film by RHEED, it was found to be a (001) single crystal thin film, which had a relationship of parallel epitaxy with the underlying strontium titanate. A film was formed on the substrate prepared by the above method by the microwave plasma CVD method shown in Example 1 under the same conditions as in Example 1 for 30 minutes. Deposited on. Raman spectroscopy confirmed that these granular materials were diamonds. The density of this granular diamond was slightly lower than that of Example 1 and was about 10 ⁶ to 10 ⁷ pieces / cm ² . Moreover, it was found by RHEED that these granular diamonds were epitaxially grown in parallel on the substrate. When film formation was performed for 5 hours under the same conditions, a diamond (001) single crystal film having a film thickness of about 5 μm and a relatively smooth surface was obtained.

Example 3 A nickel thin film having a thickness of 500 nm was formed under the same conditions as in Example 1 on a strontium titanate single crystal substrate having a size of 15 mm × 15 mm × 1 mmt and an orientation (111) plane under the same conditions as in Example 1. Formed. As a result of measuring the orientation of this nickel thin film by RHEED, it was found to be a (111) single crystal thin film and had a relationship of parallel epitaxy with the underlying strontium titanate. A film was formed on the substrate prepared by the above method by the microwave plasma CVD method shown in Example 1 under the same conditions as in Example 1 for 30 minutes. It was precipitated in a granular form. Raman spectroscopy confirmed that these granular materials were diamonds. The density of this granular diamond was about 10 ⁷ to 10 ⁸ pieces / cm ² . Also RH
It was found by EED that these granular diamonds were epitaxially grown in parallel on the substrate. When the film is formed for another 5 hours under the same conditions, the film thickness is about 5μ.
A diamond (111) single crystal film having a smooth m surface was obtained.

Example 4 A nickel thin film having a thickness of 500 nm was formed on a barium titanate single crystal substrate having a size of 7 mm × 7 mm × 1 mmt and an orientation (001) plane using a sputtering apparatus under the same conditions as in Example 1. Formed. As a result of measuring the orientation of this nickel thin film by RHEED, it was found to be a (001) single crystal thin film, which had a relationship of parallel epitaxy with the underlying barium titanate. A film was formed on the substrate produced by the above method by the microwave plasma CVD method shown in Example 1 under the same conditions as in Example 1 for 5 hours. As a result, the surface epitaxially grown in parallel on the substrate had a film thickness of 5 μm. A smooth diamond (001) single crystal film was obtained.

Example 5 A nickel thin film having a thickness of 500 nm was formed under the same conditions as in Example 1 on a strontium titanate single crystal substrate having a size of 15 mm × 15 mm × 1 mmt and an orientation (001) plane by using a sputtering apparatus. Formed. As a result of measuring the orientation of this nickel thin film by RHEED, it was found to be a (001) single crystal thin film, which had a relationship of parallel epitaxy with the underlying strontium titanate. The substrate created by the above method has an inner diameter of 4
It was installed on a substrate holder in a 0 mmφ quartz glass reaction tube, and the reaction tube was evacuated by a rotary pump and an oil diffusion pump. After exhausting to 10 ⁻⁴ Torr, hydrogen gas was caused to flow from above the reaction tube at a flow rate of 99.2 ml / min to adjust the pressure in the reaction tube to 6.7 kPa. Next, the substrate is heated by an electric furnace outside the reaction tube, and further above the substrate 10
energize the tungsten filament installed in mm, 210
It was red-hot at 0 ° C. When the substrate temperature reached 890 ° C., methane gas was added at a flow rate of 0.8 ml / min, and the pressure inside the reaction tube was readjusted to 6.7 kPa. When the film formation was performed for 5 hours under the above conditions, a diamond (001) single crystal film having a smooth surface and a film thickness of about 5 μm was obtained on the substrate.

Example 6 The same conditions as in Example 1 except that a nickel-palladium alloy was used as a target on a strontium titanate single crystal substrate having a size of 15 mm × 15 mm × 1 mmt and an orientation (001) plane by using a sputtering apparatus. Thus, a nickel-palladium alloy thin film having a thickness of 500 nm was formed. As a result of quantitative analysis by EPMA, the composition of this alloy thin film was nickel 84-palladium 16 atm%. As a result of measuring the orientation of this alloy thin film by RHEED, it was found to be a (001) single crystal thin film, which had a relation of parallel epitaxy with the underlying strontium titanate. A film was formed on the substrate prepared by the above method by the microwave plasma CVD method shown in Example 1 under the same conditions as in Example 1 for 30 minutes. It was precipitated in a granular form. Raman spectroscopy confirmed that these granular materials were diamonds. The density of this granular diamond was about 10 ⁷ to 10 ⁸ pieces / cm ² . Further, it was found by RHEED that these granular diamonds were epitaxially grown in parallel on the substrate. When film formation was performed for another 5 hours under the same conditions, a diamond (001) single crystal film having a film thickness of about 5 μm and a smooth surface was obtained.

Example 7 A sputtering apparatus was used on a strontium titanate single crystal substrate having a size of 15 mm × 15 mm × 1 mmt and an orientation (001) plane, and a nickel-copper alloy was used as a target.
Under the same conditions as above, a 500 nm thick nickel-alloy thin film was formed. As a result of quantitative analysis by EPMA, the composition of this alloy thin film was nickel 70-copper 30 atm%. As a result of measuring the orientation of this alloy thin film by RHEED, it was found to be a (001) single crystal thin film, which had a relation of parallel epitaxy with the underlying strontium titanate. A film was formed on the substrate prepared by the above method by the microwave plasma CVD method shown in Example 1 under the same conditions as in Example 1 for 5 hours. Diamond (001) single crystal epitaxially grown in parallel on the substrate A film was obtained. A film was formed on the substrate prepared by the above method by the microwave plasma CVD method shown in Example 1 under the same conditions as in Example 1 for 30 minutes. It was precipitated in a granular form. Raman spectroscopy confirmed that these granular materials were diamonds. The density of this granular diamond is 10 ⁷ to 1
0 was ⁸ pieces / cm ² or so. Moreover, it was found by RHEED that these granular diamonds were epitaxially grown in parallel on the substrate. When film formation was performed for another 5 hours under the same conditions, a diamond (001) single crystal film having a film thickness of about 5 μm and a smooth surface was obtained.

Comparative Example 1 Size 12 mmφ × 1 mm cut out from a single crystal ingot
Synthesis was performed for 30 minutes under the same conditions as in Example 1 on the nickel single crystal substrate having the t and orientation (001) plane by the microwave plasma CVD method shown in Example 1, and the crystallographic orientation on nickel was obtained. A uniform substance was deposited in a granular form. Raman spectroscopy confirmed that these granular materials were diamonds. The density of this granular diamond was about 10 ⁴ to 10 ⁵ pieces / cm ² . Also RHEED
As a result, it was found that these granular diamonds were epitaxially grown in parallel on the substrate. Even if film formation was performed for 5 hours under the same conditions, diamond remained granular and a diamond single crystal continuous thin film could not be obtained.

Comparative Example 2 A sputtering apparatus was used on a magnesium oxide single crystal substrate having a size of 15 mm × 15 mm × 1 mmt and an orientation (001) plane.
Under the same conditions as in Example 1, a nickel thin film having a thickness of 500 nm was formed. As a result of measuring the orientation of this nickel thin film by RHEED, it is a (001) single crystal thin film,
There was a relationship between the underlying magnesium oxide and parallel epitaxy. A film was formed on the substrate formed by the above method by the microwave plasma CVD method shown in Example 1 under the same conditions as in Example 1. As a result, a part of the nickel film was peeled off and magnesium ions were included in the plasma. A green light emission, which is considered to be derived from, was observed. After 30 minutes of synthesis,
On the substrate, both crystallographically oriented substances and non-oriented substances were deposited in a granular form. Raman spectroscopy and X
It was confirmed by line diffraction method that these granular substances were diamond and magnesium carbide. When a film was formed for another 5 hours under the same conditions, although the granular diamonds were locally bonded to each other, the film was an incomplete film containing regular hexahedral magnesium carbide crystals. Further, no diamond was observed in the portion where the nickel thin film was peeled off, and only magnesium carbide was observed.

Claims (4)

[Claims] 1. A nickel single crystal film or a nickel-containing alloy single crystal film is epitaxially grown on an oxide single crystal substrate having a perovskite structure, and then a diamond single crystal film is formed on the film by chemical vapor deposition. A method for forming a diamond single crystal film, which comprises: 2. The method for forming a diamond single crystal film according to claim 1, wherein the oxide having a perovskite structure is strontium titanate or barium titanate. 3. The method for forming a diamond single crystal film according to claim 1, wherein the nickel-containing alloy contains a metal other than nickel in an amount of 50 atm% or less. 4. A metal other than nickel is palladium,
The method for forming a diamond single crystal film according to claim 3, which is one kind or two or more kinds selected from copper, cobalt and iron.