JP2691183B2 - Method for synthesizing cubic boron nitride crystals - Google Patents

Description

The present invention relates to a method for synthesizing cubic boron nitride (hereinafter referred to as cBN) crystals.

Since cBN has hardness second only to diamond and is superior to diamond in chemical stability, especially to iron-based work materials, the amount of cBN used as grinding abrasive grains is increasing. In addition, with the advancement of ultra-precision finishing technology in recent years
Development of cBN single crystal is desired.

Further, when attention is paid to the performance as a semiconductor, only p-type semiconductors can be produced from diamond, but cBN crystal can produce both p-type and n-type semiconductors. Utilizing such semiconductor characteristics, it is necessary to manufacture millimeter-sized cBN crystals in order to manufacture a device composed of a pn element. Therefore, from the viewpoint of application of cBN crystals to semiconductors, development of high-quality and large-sized cBN single crystals is desired.

(Prior Art) For the synthesis of cBN, a boron nitride source and a cBN seed crystal were
A method (hereinafter referred to as a seed crystal method) in which the cubic boron nitride is stable and the cubic boron nitride is stable under the temperature and pressure conditions and at a temperature higher than the melting point of the cBN synthesis catalyst is known. is there.

As a method for synthesizing large crystals of cBN, a method utilizing the fact that the solubility of cBN in a catalyst melt under high temperature and high pressure changes with temperature (generally called the temperature difference method) is disclosed in JP-A-57-15.
It is being developed in 6399. As a method combining the seed crystal method and the temperature difference method, in JP-A-57-156399, a mixture of hexagonal boron nitride (hBN) and fine crystals of cBN is arranged in the high temperature part of a high temperature and high pressure device. Then, a seed crystal of cBN is placed in the low temperature part, and these are separated by a solvent part and subjected to high temperature and high pressure treatment for about 24 hours to grow a cBN crystal of about 2.2 mm on the seed crystal. Here, strontium boron nitride or barium boron nitride used as a solvent is cB up to a certain particle size.
It is explained that there is a feature that the growth rate of N is fast.

(Problems to be Solved by the Invention) However, a large-sized cB of high quality is produced by the conventional temperature difference method.
In order to synthesize N crystal, it is necessary to slowly grow the crystal over time.

The present inventors have conducted various studies on synthetic tests of large cBN single crystals produced by a conventional method, and have obtained the following findings. That is, a good-quality cBN single crystal has eight {111} planes as the outer constitutional basic planes. To examine the relationship between this fact and crystal growth,
In the growth of cBN crystals, it is almost certain that it is necessary to perform so-called creeping growth in which {111} planes are stacked one on top of another at the molecular and atomic levels. Here, the growth rate of crystal grains is understood as a combination of the growth rates in the directions parallel to and perpendicular to the {111} plane. The former is related to the rate of growing a crystal with a wide {111} plane, and if both the former and the latter grow at a higher rate, it becomes possible to efficiently synthesize desired mm-sized crystal grains. The larger the crystal, the larger the area of each of the {111} planes, so in order to maintain proper creeping growth, the growth rate in the {111} plane parallel direction should be {1}.
It is necessary to make the growth rate relatively higher than the growth rate in the 11} plane vertical direction. In order to perform creeping growth in a general crystal growth method including a temperature difference method, it is necessary to suppress the supersaturation degree of the solution around the crystal to be low to reduce the precipitation rate of irregular crystals. Therefore, in order to synthesize a large sound crystal, the crystal synthesis time must be lengthened.

When the temperature difference is increased in order to increase the growth rate in order to obtain a large crystal by the temperature difference method, the precipitation rate increases accordingly and the growth rate in the direction parallel to the {111} plane becomes insufficient, resulting in {111}. Surfaces other than the surface, such as {100}, are generated incidentally, making it difficult to obtain a sound crystal.

Therefore, it is an object of the present invention to provide a cBN synthesis method which does not have the above-mentioned drawbacks and can grow a large-sized cBN crystal of good quality in a short period of time.

(Means for Solving the Problem) The inventors of the present invention have proposed a Japanese Patent Application No. 63-18166 concerning cBN grinding abrasive grains.
In No. 9 and No. 63-185464, we proposed a method to obtain a good quality cBN crystal by increasing the growth rate of {111} plane in the horizontal direction relative to the growth rate in the vertical direction.
This method obtains a desired effect by performing a high temperature and high pressure treatment in a system in which a C source, a Si source and an alkali hydride or an alkaline hydride are interposed. By applying the effects of the C source, the Si source, and the alkali hydride or alkaline earth hydride in this method to the cBN crystal synthesis by the temperature difference method, it was found that a large-sized and good-quality cBN single crystal can be synthesized. .

The present invention, the boron nitride source on the high temperature side and the cBN seed crystal on the low temperature side are arranged by being separated by a cBN synthesis catalyst, and under the temperature and pressure conditions where cBN is stable and at the melting point or higher of the cBN synthesis catalyst. In the method for synthesizing a cBN crystal, a system in which a C source, a Si source and an alkali hydride or an alkaline earth hydride are combined is arranged so as to come into contact with at least one of a boron nitride source and a cBN synthesis catalyst. This is a method for synthesizing a cubic boron nitride crystal characterized by performing the above synthesis.

 Hereinafter, the configuration of the present invention will be described.

The source of boron nitride is selected from the group consisting of hexagonal boron nitride (hBN) having a graphite-like structure, hexagonal boron nitride (wBN) having a wurtzite structure, and cubic boron nitride (cBN). It is preferable to use at least one kind, but the material is not limited to these, and any substance that can supply B and N can be used.

If the temperature difference between the high temperature side and the low temperature side is too large, irregular growth tends to occur, while if it is too small, the growth time becomes long. This temperature range partially overlaps with the conventional temperature difference method, but is on the low temperature side, and specifically, the temperature difference is 50 to 200 ° C.

The cBN seed crystal may be commercially available and is not particularly limited. It is preferable that the outer configuration surface is composed of a {111} plane, but there may be a configuration surface other than the {111} plane. The particle size is preferably # 60 to 20, but particles outside this range can also be used.

At least one of the boron nitride source and the cBN synthesis catalyst is treated during high-temperature high-pressure treatment by a system that combines a C source, a Si source, and an alkali hydride or an alkaline earth hydride (hereinafter referred to as a creeping growth promoting system). Both the creeping growth promoting system and the boron nitride source are preferably arranged so as to be in contact with each other over as large an area as possible so as to receive the action described later.
The simplest way of this arrangement is to mix the creeping growth promoting system with the cBN synthesis catalyst. In addition to this, it is possible to arrange it by forming a thin sheet and laminating these.

As the C source, fatty acids such as stearic acid and palmitic acid, hydrocarbons such as docosane (CH ₃ (CH) ₂₀ CH ₃ ), terphenyl and the like, carbon such as melamine and the like, carbon as an inorganic compound, carbon black, B ₄ C Etc. can be used. Of these carbon sources, it is a constituent of the compound when added as described above, rather than a stable crystallized one like graphite, but it must be in an active state that decomposes from the compound during cBN growth. Is desirable.

The amount of the carbon source used is preferably determined so as to be 0.1 to 100 moles of C based on 1 mole of B ₂ O _{3 that} accompanies the BN source and the cBN synthesis catalyst as a foreign substance. For normal-purity HBN, the amount of C source used is 0.001 to 15% based on the total amount of raw materials.

As the Si source, compounds such as Si powder, B ₄ Si and Si ₃ N ₄ can be used. A raw material mixture may be mixed as the Si source, but it is preferable that the Si source is contained in the cBN synthesis catalyst in advance in order to increase the Si content in cBN. As a method of containing this, a method of heating and melting the Si source and the cBN synthesis catalyst is adopted. The amount of the Si source used is preferably 10 ⁻⁵ to 10 ⁻² mol of Si based on 1 mol of the BN source and the cBN synthesis catalyst. If the amount used is less than 10 ^-5 , cB of Si
If the solid solution in N becomes insufficient, on the other hand, if it exceeds 10 ^-2 mol, Si
Has a macroscopic defect in cBN, so the amount of the Si source used is preferably within the above range.

As the alkali hydride and alkaline earth hydride,
LiH, NaH, CaH ₂ , SrH _{2 and the} like can be used. When used in combination with other cBN synthesis catalysts, the amount of these hydrogen sources used is preferably 0.1 to 50% with respect to the cBN synthesis catalyst.

As the cBN synthesis catalyst, (a) alkali such as Li, Na, K,
These nitrides (Li ₃ N, Na ₃ N, etc., double nitrides (Li ₃ BN
₂ ), (b) alkaline earths such as Ca, Sr, Mg, Ba, etc., and their nitrides (Ca ₃ N ₂ , Sr ₃ N ₂ , Mg ₃ N ₂ , Ba ₃ N ₂ etc.), double nitrides (Ca ₃
(BN ₂ etc.) and (c) alkali and alkaline earth composite nitrides (LiCaBN ₂ , LiBaBN ₂ etc.) can be used.
Since the amount of B ₂ O ₃ in the raw material is large, when the amount of the C source added is large, boron is produced according to the following reaction formula.

B ₂ O ₃ + 3C → B + 3CO Since this B is not desirable in the synthesis of cBN single crystal grains having a desired tip, it is preferable to add an N source and fix B as BN to render it harmless. Melamine is the source of N
Urea or the like can be used. Although the amount used depends on the amount of B generated, it is usually preferably 10 ⁻⁴ to 10 ⁻¹ mol per 1 mol of the BN source and the cBN synthesis catalyst.

(Function) The creeping growth promoting system increases the growth rate in the direction parallel to the {111} plane. Therefore, favorable conditions for creeping growth are set.
Also, as a result of increasing the growth rate in the {111} plane parallel direction,
Irregular growth does not occur even if the growth rate in the {111} plane vertical direction is increased. That is, a healthy crystal that increases the crystal growth rate can be grown quickly and efficiently.

 Hereinafter, the present invention will be described in more detail with reference to examples.

(Example) FIG. 1 schematically shows the high temperature and high pressure processing apparatus and the material to be processed used in the example.

In the figure, 1 is a Mo container, 2 is a Mo lid, 3 is a Mo container body, 4 is a
cBN seed crystal, 5 solvent part, 6 boron nitride source green compact,
Reference numeral 7 is a pressure medium using hBN powder, 8 is a graphite heater, 9 is a pressure medium made of pyrophyllite, and 10 is a Mo foil used as a seed mask.

Example 1 The solvent portion 5 is LiCaB in which 87 wt% contains 0.5 wt% Si.
N (cBN synthesis catalyst), 10wt% is LiH, 2wt% is hBN, and the rest is 1wt
% Of melamine. The above 3 types are mixed well in powder form, then diameter 8mm, thickness 6
What was shape | molded to mm was used.

49.5 wt% of the boron nitride source green compact 6 is cBN
(Showa Denko SBN-T, G-45 average particle size about 40 μm), 49.5 wt
% HBN (Showa Denko UHP-1 average particle size about 15 μm), the rest
A mixture containing 1 wt% melamine in advance with a diameter of 8 mm and a thickness of 2 mm
What was shape | molded was used.

The above-mentioned boron nitride source green compact 6 and the solvent portion 5 were vertically packed in the Mo container body 1, and the synthetic space capsule covered with the Mo lid 3 was produced. The seed crystal 4 has a particle size of # 30/40 (about 500 μm)
Three cBN abrasive grains were placed on the bottom of the Mo container 2.

The synthetic reaction system constructed as above was run at 55 kb and 1600 ° C for 10
After maintaining at high temperature and high pressure for an hour, cBN was recovered. About 1.5-2.
Three transparent brown cBN crystals were obtained which grew to a diameter of 0 mm and had large {111} faces.

Example 2 The same synthesis as in Example 1 was carried out except that 99 wt% cBN and the remaining melamine were used as the boron nitride source.
And similar results were obtained.

Example 3 Docosane was used in place of the melamine of the solvent portion 5 used in Example 1, and synthesis was carried out in the same manner as in Example 1 under other conditions, and the obtained cBN particles had a diameter of 1.5 to
2.0 mm. The color of the grain was blackish.

Comparative Example 1 LiH and melamine of the solvent portion 5 used in Example 1 were removed, and the solvent portion was prepared by increasing the amount of cBN synthesis catalyst by the corresponding amount. Other conditions were the same as in Example 1, and synthesis was carried out. The diameter of the obtained cBN particles was 1.5-2.0 mm. However, the crystals obtained here do not have a clear crystal habit due to the complicated combination of the planes considered to be {111}, {100} and {311}. In addition, a number of streaks (surface defects that seem to be lined up in a certain direction) that are considered to occur as crystals in which creeping growth is inhibited were recognized.

Therefore, this crystal is not suitable for monolithic tools and diodes.

(Effects of the Invention) As described above, according to the present invention, a healthy large cBN is used.
Crystals are efficiently obtained.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a high temperature and high pressure processing apparatus and a material to be processed. 1 ... Mo container, 2 ... Mo lid, 3 ... Mo container body, 4 ...
cBN seed crystal, 5 ... Solvent part, 6 ... Boron nitride source powder, 7 ... hBN pressure medium, 8 ... Graphite heater, 9 ... Pyrophyllite pressure medium, 10 ... Mo foil

Claims (4)

(57) [Claims] 1. A high temperature side boron nitride source and a low temperature side cubic boron nitride seed crystal are separated by a cubic boron nitride synthesis catalyst, and the cubic boron nitride is stable under temperature and pressure conditions. And a method for synthesizing a cubic boron nitride crystal at a temperature above the melting point of the cubic boron nitride synthesizing catalyst, C
A source, a Si source, and a system in which an alkali hydride or an alkaline earth hydride is combined are arranged so as to be in contact with at least one of the boron nitride source and the cubic boron nitride synthesis catalyst to perform synthesis. A method for synthesizing a characteristic cubic boron nitride crystal. 2. The source of boron nitride is at least one selected from the group consisting of hexagonal boron nitride having a graphite-like structure, hexagonal boron nitride having a wurtzite structure, and cubic boron nitride. The method for synthesizing a cubic boron nitride crystal according to claim 1, wherein the above is used. 3. The method for synthesizing a cubic boron nitride crystal according to claim 1, wherein an N source is further combined with the system. 4. The cubic boron nitride synthesizing catalyst also serves as a Si source and at least one of an alkali hydride and an alkaline earth hydride. A method for synthesizing the described cubic boron nitride crystal.