JPS6236009A - Thermal decomposition type boron nitride - Google Patents

Abstract

PURPOSE:To decrease the laminar surface exfoliation which is observed with the conventional thermal decomposition type boron nitride crucible and to extend the life of the crucible by forming the thermal decomposition type boron nitride in such a manner that the X-ray diffraction intensity of the hexagonal boron nitride is made smaller than the X-ray diffraction intensity of the boron nitride having the irregular laminar structure in the crystal structure of the thermal decomposition type boron nitride. CONSTITUTION:This thermal decomposition type boron nitride has the crystal structure consisting of the hexagonal boron nitride and the boron nitride of the irregular laminar structure having the larger inter-plane spacing of the C plane than the hexagonal boron nitride and has the diffraction strength of the hexagonal boron nitride smaller than the diffraction intensity of the boron nitride of the irregular laminar structure in the X-ray diffraction. The laminar surface exfoliation is prevented simply by controlling the lamination state of the C plane in the stage of forming the film of the boron nitride by a thermal decomposition method, for example, CVD method. The lamination state of the C plane is controllable by, for example, CVD conditions and the examination of the lamination state is possible by X-ray diffraction.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to pyrolytic boron nitride, and
Crucible or vacuum evaporation or molecular beam epitaxy (MBE) used to grow group compound semiconductor single crystals
), etc. This relates to pyrolytic boron nitride suitable for applications such as AI melting crucibles.

[Conventional technology]

■-When pulling group V compound semiconductor single crystals, such as GaAs single crystals and InP single crystals, it is necessary to prevent the volatilization of component elements.
EC law) has been adopted.

The crucible used in the LEC method is Juweishi'A (S
io t) Crucibles etc. were not used. However, when GaAs is pulled using a quartz crucible, for example, there is a problem in that Si is mixed into the crystal as an impurity.

For this reason, it is known that the material is usually pulled up by doping it with Cr, but a new problem arises in that doping with Cr lowers the insulation properties and makes it unsuitable as an IC substrate.

Therefore, recently, in order to obtain a non-doped semi-insulating substrate,
Crucibles made of pyrolytic boron nitride (p-BN) have come to be used as crucibles.

Boron nitride (BN) is a ■-■ group compound, and does not form an impurity level even when mixed into a single crystal, and p-BN crucibles manufactured by pyrolysis can have extremely high purity. This is the reason why it has come to be used as a crucible.

[Problem that the invention seeks to solve]

However, conventionally known p-B N crucibles are prone to layered surface delamination and have a lifespan of 4 to 5 pulls.This short lifespan makes it difficult to industrially mass-produce GaAs single crystals. This is a major obstacle.

The object of the invention is to create a "p-B N crucible" that significantly reduces the occurrence of layered surface peeling as seen in the conventional p-B N crucible.
The objective is to realize BN and thereby provide a long-life crucible.

[Means for solving problems]

The present invention is a BN produced by a pyrolysis method, which has a crystal structure consisting of hexagonal boron nitride and turbostratic boron nitride with a larger spacing between the 0 planes than the hexagonal boron nitride, and has a hexagonal crystal structure determined by X-ray diffraction. It is characterized in that the diffraction intensity of boron nitride is lower than the diffraction intensity of turbostratic boron nitride.

The inventors of the present application presumed that the cause of layered surface peeling in conventional p-BN crucibles was due to the crystal structure of BN, and conducted detailed research on the relationship between the crystal structure and strength.

As a result, since the crystal structure of BN is hexagonal, when it is synthesized by a thermal decomposition method, such as a CVD method (chemical vapor deposition method), the 0-plane, which is the most densely packed surface, tends to be formed parallel to the substrate. It was discovered that the lattice constant of 6.66A for the 0-plane of BN is larger than the lattice constant of 2°504A for the a-plane, and therefore the mutual bonding force between the C-planes is weak. For this reason, it was assumed that BN synthesized by the CVD method or the like is likely to cause layered surface peeling.

Therefore, in order to prevent layered surface peeling, we thought that it would be sufficient to remove the layered state on the zero surface when forming BN into a film using a thermal decomposition method, such as a CVD method, and this led us to complete the present invention. be.

In the present invention, the stacking state on the zero surface can be controlled, for example, by CVD conditions, and the stacking state can be inspected by XM diffraction.

Figure 1 shows the (002) plane of the BN film made by the CVD method.
The line diffraction pattern is shown.

Note that samples A to D were prepared using external heating type reduced pressure CVI:lfi under the conditions shown in Table 1, and Co was used as the tarded material when measuring the X#i diffraction pattern.

tJS1 Table The X#1 diffraction pattern of the single-crystal structure usually has a Gaussian distribution with a single peak. However, the diffraction patterns in FIG. 1 all have two peaks, and it is considered that the 2#i type crystal structures are mixed, rather than a single crystal structure. The lattice spacing of the peak on the high-angle side is approximately 3.35A, which is similar to the lattice spacing of so-called hexagonal BN (h-BN).
Match.

The lattice spacing of the peak on the low angle side is as large as approximately 3.45A, which is the so-called disordered Nl1II structure (BND-BN).
It is considered to be equivalent to

In addition, in XM diffraction, if the crystal grain sizes are similar,
The better the orientation of the 0 plane, the sharper the diffraction pattern, and the more disordered the orientation, the broader the diffraction pattern6. For example, the diffraction pattern of h-BN is sharp, as seen in samples C and D, but the t The diffraction pattern of -BN is broad, h-BN has better orientation in the 0 plane, and t-
It is thought that the orientation of the 0-plane is more disordered in B and I'J.

As a result of evaluating the peeling strength between the eyebrows, t-BN diffraction intensity 1
(t-BN) is the diffraction intensity of h-BN (h-BN)
The stronger sample A was found to be the best.

In addition, the hardness of these samples was measured.

The hardness of sample A is high with I (t-BN) > I (h-BN), and the hardness is high with I (t-BN) < I (h-
BN) was found to be low.

That is, it was found that hardness depends on the content of two types of crystal structures, t-BN and h-BN, and is closely correlated with peel strength.

〔Example〕

Hereinafter, a detailed explanation will be given based on examples.

Example 1 In an external heating type reduced pressure CVD apparatus, BCl3 and N were used as reactants.
BN was synthesized using H, and H2.

BCIs was used alone, H2 was used as a carrier gas, the reaction temperature was fixed at 1,800° C., and the reaction flow rate and reaction pressure were varied to synthesize BN under various conditions shown in Table 2.

Table 2 The crystal structure was evaluated by performing X#1 diffraction and using a diffraction intensity ratio of 1
(t-BN)/I (h-BN) was measured. The interlayer peeling strength was evaluated by measuring the length of cracks generated when a Vickers indenter was pressed into the polished cross section of the BN film. The shorter the crack length, the better the peeling strength between the layers.

Furthermore, in order to evaluate the lifespan of the crucible, a 4-inch crucible was prepared, and GaAs single crystals were repeatedly pulled in an LEC furnace to evaluate the lifespan.

The results of each evaluation are shown in Table 3.

Table 3: Number of times a GaAs single crystal can be pulled As shown in Table 3, the diffraction intensity ratio 1 (-BN)/I (h-
When BN) is 1 or more, the cracking time is short, and in the single crystal pulling life test, the number of times the GaAs single crystal can be pulled is more than twice that of conventional materials, indicating that both peel strength and life are excellent.

Example 2 A 20φ×401 crucible was prepared under the same conditions as in Table 1 to be used as a crucible for AI vacuum deposition. AI was repeatedly vacuum-deposited as a crucible in an induction-heating vacuum evaporation device, and its lifespan was evaluated.

The evaluation results are shown in Table 4.

As shown in Table 4 of the tlSA table, the diffraction intensity ratio [(1-BN)/
In the Af vacuum evaporation life test when I (h-BN) is 1 or more, the life is almost twice as long as that of conventional products.

Example 3゜The same CVD* equipment as in Example 1 was used, and the reaction temperature was 1.4
00℃ to 1.900℃, reaction pressure from 5Torr to 1
5 Torr* and various B under the conditions shown in Table 5.
A N film was prepared and the diffraction intensity ratio and hardness were evaluated.

As shown in Table 5, the diffraction intensity ratio 1(t-BN)/
When I (h-BN) is 1 or more, the hardness is H
v80 or higher.

From the results of Examples 1 and 2, ID-BN)
It is known that when /I (h-BN) is 1 or more, the peel strength is excellent, and therefore the hardness Hv
If the value is 80 or more, it can be judged that the interlayer peel strength is excellent.

According to this embodiment, the peel strength can be easily determined by simply measuring the strength of the BN film without necessarily measuring the diffraction intensity ratio.

〔Effect of the invention〕

As mentioned above, the p-BN according to the present invention has excellent peel strength, so the crucible using this p-BN has significantly reduced surface peeling, has a lifespan more than twice as long as conventional crucibles, and has
This will greatly contribute to the mass production of aAs single crystals.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the X#1 diffraction pattern of the (OO2) plane of BNll.

Claims (4)

[Claims] (1) The crystal structure consists of hexagonal boron nitride and turbostratic boron nitride, which has a larger C-plane spacing than hexagonal boron nitride, and in X-ray diffraction, the diffraction intensity of hexagonal boron nitride is higher than that of turbostratic boron nitride. Pyrolytic boron nitride characterized by a diffraction intensity of less than or equal to . (2) The pyrolytic boron nitride according to claim 1, which is used as a crucible for pulling a GaAs single crystal. (3) The pyrolytic boron nitride according to claim 1, which is used as a crucible for Al vacuum deposition. (4) The pyrolytic boron nitride according to claim 1, which has a hardness of Hv80 or more.