JPH06171910A - Formation of boron nitride in vapor phase - Google Patents

Abstract

PURPOSE:To industrially and advantageously form boron nitride having a high content of c-BN by supplying a gas contg. N and B into the combustion zone of the combustion gas contg. H atom and blowing the combustion flame directly against a substrate. CONSTITUTION:Gas contg. nitrogen and boron is supplied into the combustion zone of the combustion gas contg. hydrogen atom, the combustion flame is blown directly against the substrate, and the desired boron nitride is formed. The gaseous mixture of at least one kind selected from acetylene, ethylene and propane and oxygen is preferably used as the gas contg. hydrogen atom. The combustion temp. is preferably controlled to >=1900 deg.C at which hydrogen becomes free radical. The excitating source is controlled to about 3000 deg.C while considering that the substrate temp. is easily controlled. Gaseous nitrogen and diborane are preferably used as the gases contg. nitrogen and boron.

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 boron nitride mainly composed of cubic boron nitride (hereinafter abbreviated as c-BN) by a vapor phase method.

[0002]

2. Description of the Related Art Boron nitride includes hexagonal boron nitride (hereinafter abbreviated as h-BN) and c-BN. h-BN
Is soft and has excellent lubricity, and c-BN is hard and has excellent thermal conductivity and electrical insulation properties, and is therefore widely used in fields that make use of their respective properties.

There are a chemical vapor deposition method (hereinafter abbreviated as CVD) and a physical vapor deposition method (hereinafter abbreviated as PVD) as a method for synthesizing boron nitride by a vapor phase method. CVD is a method in which a gas containing boron and nitrogen is decomposed in a reaction container by means such as thermal excitation, activated, and deposited on a substrate. As a concrete example of the exciting means, plasma (Japanese Patent Laid-Open No.
196710) and plasma + hot filament (JP-A-2-250969) are known. PVD
Is a method of evaporating boron in a nitrogen gas plasma and depositing it on a substrate. An electron beam (Japanese Patent Laid-Open No. 52-42480), a laser (Japanese Patent Laid-Open No. 63-35767) and the like have been devised as specific examples of the means of evaporation.

[0004]

In conventional CVD or PVD, most of the boron nitride formed on the substrate is h-.
BN contains almost no c-BN. Therefore, the conventional vapor phase method is not suitable for forming a high-hardness boron nitride film. It is an object of the present invention to provide a method for forming boron nitride by a vapor phase method, which is capable of industrially forming boron nitride containing a high proportion of c-BN.

[0005]

Means for Solving the Problem (1) The above object is to blow a combustion flame directly onto a substrate while supplying a gas containing nitrogen and boron into a combustion region of a combustion gas containing hydrogen atoms. Is achieved by a method of forming boron nitride.

[0006]

The present inventors have found that the conventional method does not form boron nitride containing a large amount of c-BN based on the following two reasons. (1) Excited boron and nitrogen radicals are not efficiently transported to the substrate. (2) c-
The h-BN deposited at the same time as BN was not removed.

According to the method of the present invention, the above (1) and (2)
It is thought that the reason for is removed. That is, like the method of the present invention, while supplying a gas containing nitrogen and boron into the combustion region of a combustion gas containing hydrogen atoms, the boron and nitrogen radicals decomposed and excited in the combustion flame are excited on the substrate. When it is directly sprayed onto the substrate, the temperature gradient becomes large, the excited boron and nitrogen radicals are efficiently transported onto the substrate to form c-BN at high speed, and at the same time, in the combustion flame containing hydrogen atoms, h- Since a large amount of hydrogen radicals that can remove BN by gasification exist, it is considered that the precipitated h-BN is efficiently removed by the hydrogen radicals, and boron nitride containing a high proportion of c-BN is precipitated.

[0008]

Means for Solving the Problems (2) The method of the present invention utilizes a combustion flame of a combustion gas containing hydrogen atoms.
Specific examples of the combustion gas include acetylene, ethylene, methylacetylene, methane, propane, butane, hydrogen, and the like, and a mixed gas containing any one or more of these and oxygen as a combustion supporting gas is used. . Particularly preferred is a mixed gas of at least one selected from acetylene, ethylene and propane and oxygen.

The combustion flame is classified into a reducing flame, a neutral flame and an oxidizing flame depending on the mixing ratio of the hydrogen atom-containing combustion gas component in the combustion gas and oxygen. For forming boron nitride, a mixture having a mixing ratio near neutral flame is preferable. In an oxidizing flame, the boron nitride deposited on the substrate is easily decomposed, so the growth rate decreases,
In a reducing flame, carbon tends to be mixed in boron nitride and the quality tends to deteriorate. Specifically, as a volume ratio of combustion gas to oxygen, acetylene and methane are 0.9 to 1.2, ethylene is 0.7 to 1.0, and methylacetylene is 0.5 to 0.
8, propane is 0.3 to 0.6, hydrogen is 1.4 to 1.
7, carbon monoxide is preferably 1.5 to 1.8.

The combustion temperature is 1900 at which hydrogen radicalizes.
C. or higher is preferable. In particular, it is desirable that the temperature of the excitation source is around 3000 ° from the viewpoint of easy control of the substrate temperature. By mixing water vapor into the combustion gas, hB
It is possible to promote radicalization of boron, nitrogen, and hydrogen by enhancing the etching effect of N and mixing an inert gas. As the inert gas, it is preferable to use at least one selected from argon and helium. The mixing ratio of steam and inert gas does not lower the temperature of the flame, so the volume ratio to the combustion gas containing hydrogen atoms is 3% or less for steam and 10% for inert gas.
The following are preferred.

Specific examples of the gas containing nitrogen and boron to be supplied to the combustion region of the combustion gas include nitrogen gas and ammonia gas, nitrogen-containing compound gas such as nitric oxide as the nitrogen source, and boron source. Examples include diborane, boric acid, borate esters and the like. Among these, nitrogen gas and diborane are preferable. The introduction amount of these gases is preferably 0.1 to 10% as a volume ratio with respect to the combustion gas containing hydrogen atoms. Further, the introduction volume ratio of the nitrogen gas or the nitrogen-containing compound gas and the boron-containing compound gas is preferably in the range of the former / latter = 0.1 to 10.

An example of an apparatus used to carry out the method of the present invention is shown in FIG. Acetylene and other combustible gas containing hydrogen atoms (cylinder 6) and oxygen (cylinder 7) are supplied to the torch 1 to form a combustion flame 2. In this combustion flame 2, diborane or other boron-containing compound (cylinder 8), nitrogen-containing component such as nitrogen gas or ammonia (cylinder 9), and if desired, argon or other inert gas (cylinder 10) and steam ( The steam generator 11) is mixed in the gas mixer 5 and supplied to the torch 1. The combustion flame is blown directly onto the deposition substrate 3. The deposition substrate 3 is placed on a water-cooled substrate table 4 cooled by the circulating water 12 and is maintained at a predetermined temperature, and c-BN is contained as a main component from a combustion flame sprayed on the deposition substrate 3. Boron nitride is deposited on the substrate to form a film.

[0013]

EXAMPLES The present invention will be specifically described below with reference to examples. Example 1 The method of the present invention was carried out using the apparatus shown in FIG. 2 l / min of acetylene, 2 l / min of oxygen gas,
Each was fed to form a combustion flame. Nitrogen gas (N ₂ ) of 50 cc / min and diborane (B ₂ H ₆ ) of 10 cc / min were used as raw material gases mixed into the combustion flame. Inside the flame formed under the above conditions, a 12.7 × 12.7 × 4 mm-sized cemented carbide substrate (WC, Co8%) cooled with water and maintained at 1000 ° C. was placed at a distance of 20 mm from the crater. And was synthesized for 1 hour.

After the synthesis, the substrate was observed to have a thickness of 1.
A film-like precipitate having a size of 5 μm and a deposition area of about 8 mmφ was formed. The analysis result using the FT-IR method is shown in FIG.
As can be seen in the figure, c-BN near 1100 cm ^-1.
Has a large absorption peak derived from
There is a small absorption peak derived from h-BN near cm ^-1 . From this result, it was found that the precipitate was a boron nitride film containing a large amount of c-BN.

Example 2 Boron nitride was synthesized under the same conditions as in Example 1. However, 100 cc / min of argon was further mixed in the combustion gas. When the shape of the flame during synthesis was observed, it was observed that the flame slightly spread as compared with Example 1. Observation on the substrate after synthesis showed a thickness of 1.8 μm and a deposition area of about 9.5 m.
A film-shaped precipitate of mφ was formed. The analysis results using the FT-IR method are shown in FIG. Although no change in film quality was observed in Example 1, the deposition area and deposition amount were improved.

Example 3 Boron nitride was synthesized under the same conditions as in Example 1. However, steam was further mixed into the combustion gas at 3 cc / min using a steam generator. When the substrate was observed after the synthesis, a film-like precipitate having a thickness of 1.1 μm and a deposition region of about 8 mmφ was formed. The analysis result using the FT-IR method is shown in FIG. Compared to Example 1, c-BN around 1100 cm ^-1
The absorption peak due to
It can be seen that the absorption peak derived from h-BN near 0 cm ⁻¹ is lowered and the film quality is improved. The amount of precipitation is Example 1
It was slightly lower than.

[Brief description of drawings]

FIG. 1 is an example of an apparatus used for an embodiment of the method of the present invention.

2 is an FT-I of the boron nitride film synthesized in Example 1. FIG.
The R spectrum is shown.

FIG. 3 FT-I of the boron nitride film synthesized in Example 2
The R spectrum is shown.

FIG. 4 FT-I of the boron nitride film synthesized in Example 3
The R spectrum is shown.

[Explanation of symbols]

 1 Torch 2 Flame 3 Precipitation Substrate 4 Water-cooled Substrate 5 Gas Mixer 6 Acetylene Cylinder 7 Oxygen Cylinder 8 Diborane Cylinder 9 Nitrogen Cylinder 10 Argon Cylinder 11 Steam Generator 12 Cooling Water

Claims (5)

[Claims] 1. A method for forming boron nitride, which comprises spraying a combustion flame directly onto a substrate while supplying a gas containing nitrogen and boron into a combustion region of a combustion gas containing hydrogen atoms. 2. The method for forming boron nitride according to claim 1, wherein a mixed gas containing at least one selected from acetylene, ethylene and propane and oxygen is used as the gas containing hydrogen atoms. 3. The method for forming boron nitride according to claim 1, wherein nitrogen gas and diborane are used as the gas containing nitrogen and boron. 4. The method for forming boron nitride according to claim 1, wherein the combustion gas is further mixed with at least one gas selected from an inert gas and steam. 5. The method for forming boron nitride according to claim 4, wherein at least one selected from argon and helium is used as the inert gas.