JP4719427B2 - Pyrolytic boron nitride crucible and single crystal growth method using the same - Google Patents

Description

  The present invention relates to a pyrolytic boron nitride crucible, and more particularly to an improvement of a vertical pyrolytic boron nitride crucible used for growing a compound semiconductor single crystal.

  In FIG. 2, the method for growing a compound semiconductor single crystal disclosed in Japanese Patent No. 3216298 of Patent Document 1 is illustrated in a schematic cross-sectional view. According to this figure, the inner surface of the pyrolytic boron nitride vertical crucible 1 is covered with a boron oxide film 2. Such a boron oxide film 2 can be formed by oxidizing the inner surface of the boron nitride crucible 1 at a high temperature. The vertical crucible 1 has a seed crystal accommodating portion 1a at the bottom thereof, and the seed crystal accommodating portion 1a is connected to the main body of the crucible 1 via a tapered portion 1b.

A compound semiconductor seed crystal 3 is loaded in the seed crystal accommodating portion 1 a, and a compound semiconductor raw material 4 is accommodated in the main body portion of the crucible 1. Then, the upper part of the compound semiconductor raw material 4 and the seed crystal 3 is melted, and the raw material melt is seeded on the seed crystal 3, and then the well-known unidirectional solidification from the seed crystal 3 makes the compound semiconductor from the raw material melt. A single crystal is grown.
Japanese Patent No. 3216298

  In general, when a compound semiconductor single crystal is grown using a pyrolytic boron nitride crucible, if the compound semiconductor melt is in direct contact with the inner wall of the boron nitride crucible, crystal nuclei are likely to occur due to non-uniformity of the inner wall. It is known that polycrystallization is easy from these crystal nuclei. Therefore, in Patent Document 1, in order to prevent direct contact between the compound semiconductor melt and the inner wall of the boron nitride crucible, a boron oxide film is formed on the inner wall of the crucible.

  However, when the present inventor has grown a compound semiconductor single crystal by the method disclosed in Patent Document 1, it still cannot sufficiently prevent polycrystallization during the single crystal growth, and the compound semiconductor single crystal has a high It turned out that it cannot manufacture in a yield.

  Therefore, the present invention investigates the reason why the yield of the compound semiconductor single crystal is not sufficiently high in the method disclosed in Patent Document 1, and provides a method capable of growing the compound semiconductor single crystal with a higher yield. The purpose is to develop.

According to the present invention, a vertical pyrolytic boron nitride crucible for growing a compound semiconductor single crystal has a seed crystal accommodating portion at the bottom of its main body, and a hexagonal c-plane contained in the pyrolytic boron nitride of the crucible. Between the X-ray diffraction intensity I (hBN) from the C-plane and the X-ray diffraction intensity I (tBN) from the c-plane of the disordered layer structure having a wider plane spacing than the hexagonal crystal I (hBN) / [I (hBN) + I (TBN)] is 0 or more and less than 0.1 or 0.9 or more and 1.0 or less, and at least a desired region on the inner surface of the crucible is covered with a boron oxide film. In addition, it is preferable that the entire inner surface of the pyrolytic boron nitride crucible is covered with a boron oxide film.

  In the method of growing a compound semiconductor single crystal using such a crucible, the compound semiconductor seed crystal is loaded into the seed crystal housing portion at the bottom of the crucible, and the compound semiconductor raw material and the boron oxide sealing material are housed in the crucible body. Then, the boron oxide sealing material and the compound semiconductor raw material are melted to form a raw material melt coated with the melt of the sealing material, and the compound semiconductor single crystal is formed from the raw material melt by unidirectional solidification from the seed crystal. It is characterized by nurturing. In such a compound semiconductor single crystal growth method, a GaAs or InP single crystal can be preferably grown.

  When a compound semiconductor single crystal is grown using the pyrolytic boron nitride crucible developed according to the present invention, the thickness of the boron oxide film formed by thermal oxidation on the inner wall of the boron nitride crucible is uniform. Polycrystallization during crystal growth can be avoided and the yield of the compound semiconductor single crystal can be improved.

  In making the present invention, the present inventor first examined the reason why a sufficient single crystal yield was not obtained by the compound semiconductor single crystal growth method of Patent Document 1. As a result, it has been clarified that the crystallite structure in pyrolytic boron nitride, which is a material of the crucible, has an influence as a reason why a sufficient single crystal yield cannot be obtained.

  That is, in the pyrolytic boron nitride of the crucible material, a crystallite having a hexagonal crystal structure and a crystallite having a disordered layer structure having a c-plane having a larger interplanar spacing than the c-plane of the hexagonal crystal structure, ie, {0001} plane Are mixed. When crystallites of two different crystal structures are mixed in this way, the variation in the thickness of the boron oxide film formed on the inner surface of the crucible becomes large, and it is difficult to grow a stable compound semiconductor single crystal. . When the inner wall of the pyrolytic boron nitride crucible is thermally oxidized to form a boron oxide film, in order to make the thickness uniform, the crucible is either a hexagonal crystal structure or a disordered crystal structure crystallite. It came to the conclusion that it is desirable to mainly include one of them.

  Based on such examination results, the present inventor has produced pyrolytic boron nitride crucibles containing hexagonal crystallites and disordered layer crystallites in various proportions, and compound semiconductors using these crucibles. Attempts were made to grow single crystals. In general, the pyrolytic boron nitride crucible can be manufactured as follows.

  For example, a pyrolytic boron nitride layer is chemically vapor deposited (CVD) on the surface of a substrate such as graphite using boron halide and ammonia as raw materials. And a pyrolytic boron nitride crucible is obtained by separating and removing the graphite substrate from the pyrolytic boron nitride layer. The pyrolytic boron nitride crucible thus obtained can be formed to a thickness of about 1 to 2 mm.

  At this time, the ratio of the hexagonal crystallites and the disordered crystallites contained in the pyrolytic boron nitride crucible depends on the substrate temperature, reaction gas ratio, reaction gas pressure, deposition rate, etc. during CVD. Can change. That is, by adjusting the CVD conditions, pyrolytic boron nitride crucibles containing hexagonal crystallites and disordered layer crystallites in various ratios can be produced.

  In this way, by changing the CVD conditions in various ways, the present inventors have produced pyrolytic boron nitride crucibles containing hexagonal crystallites and disordered layer crystallites in various ratios, and these crucibles. The compound semiconductor single crystal was grown using The main part of the produced pyrolytic boron nitride crucible had a diameter of about 100 mm and a height of about 400 mm. The seed crystal accommodating part was connected to the bottom part of the crucible main body part via the taper part.

  The crystal structure of the crystallites contained in these pyrolytic boron nitride crucibles was examined by X-ray diffraction. Here, the area under the X-ray diffraction peak profile from the {0002} plane of the hexagonal structure is represented by I (hBN), and the area under the diffraction peak profile from the disordered layer structure appearing in the vicinity of the peak is expressed as I (hBN). I (tBN). The ratio of the hexagonal crystallite and the disordered crystallite is expressed by a diffraction intensity ratio I (hBN) / [I (hBN) + I (tBN)]. Based on such X-ray diffraction intensity ratio, pyrolytic boron nitride crucibles were classified into groups A to F as shown in Table 1.

  The X-ray diffraction peak from the hexagonal structure and the diffraction peak from the disordered layer structure were separated by the least square method assuming a Pearson 7 function using commercially available peak separation software.

  A boron oxide film was formed on the inner surface of each of the pyrolytic boron nitride crucibles classified into groups A to F in Table 1. This boron oxide film was formed by heat treating a pyrolytic boron nitride crucible at 1000 ° C. for 5 hours while flowing oxygen gas at a flow rate of 1 liter / min in a heat treatment furnace. After the formation of the boron oxide film, the crucible was cooled to room temperature at a rate of 10 ° C./min while oxygen gas was continuously passed through the furnace.

  FIG. 1 is a schematic cross-sectional view illustrating a method for growing a compound semiconductor single crystal using the vertical crucible for single crystal growth thus produced. The main body of the pyrolytic boron nitride crucible 11 shown here had a diameter of about 100 mm and a height of about 400 mm as described above. And the seed crystal accommodating part 11a was connected to the bottom part of the crucible main body via the taper part 11b. Further, the boron oxide film 2 was formed on the inner surface of the crucible 11 by the method described above.

  A GaAs seed crystal 3 was loaded in the seed crystal accommodating portion 11 a provided at the bottom of the crucible 11. The GaAs crystal had a cubic structure, and the longitudinal axis direction of the GaAs seed crystal 3 was parallel to the crystallographic <001> direction. In the main body of the crucible 11, 10 kg of GaAs polycrystalline raw material 4 and 130 g of boron oxide sealing material 5 were accommodated.

  The crucible 11 containing the raw material was placed in a vertical single crystal growth furnace, and the boron oxide sealing material 5 and the GaAs polycrystalline raw material 4 were melted. The upper part of the GaAs seed crystal 3 was also melted, and the melt of the GaAs raw material 4 was seeded on the seed crystal 3. In the vicinity of the solid-liquid interface at this time, the single crystal growth furnace was set to have a temperature gradient of 10 ° C./cm. Thereafter, the crucible 11 was lowered at a rate of 5 mm / hour in the furnace, and a GaAs single crystal was grown from the melt of the raw material 4 by unidirectional solidification from the seed crystal 3.

  As described above, as a result of growing a GaAs single crystal using the crucibles of groups A to F in Table 1, the number of times of growth, the number of times of single crystal realization, and the single crystallization rate (%) are the same. Shown in.

  As is clear from Table 1, crucibles belonging to groups A and B in which the X-ray diffraction intensity ratio I (hBN) / [I (hBN) + I (tBN)] is in the range of 0 to less than 0.3 are used. It can be seen that a GaAs single crystal can be obtained with a high yield of 90% or more. In addition, when using crucibles belonging to groups E and F in which the X-ray diffraction intensity ratio I (hBN) / [I (hBN) + I (tBN)] is within the range of 0.7 to 1.0 It can be seen that a GaAs single crystal is obtained with a yield of 100%.

  However, the X-ray diffraction intensity ratio I (hBN) / [I (hBN) + I (tBN)] is in the range of 0.3 to less than 0.5 and in the range of 0.5 to less than 0.7. It can be seen that when the crucibles belonging to the respective groups C and D are used, GaAs single crystals are obtained only at extremely low yields of 33% and 29%, respectively.

  That is, when the inner surface of the pyrolytic boron nitride crucible is oxidized to form a boron oxide film to prevent direct contact between the compound semiconductor raw material melt and the pyrolytic boron nitride surface, thereby increasing the single crystal yield It is desirable that the pyrolytic boron nitride of the crucible mainly contains either a hexagonal crystallite or a disordered crystallite. In other words, the X-ray diffraction intensity ratio I (hBN) / [I (hBN) + I (tBN)] of the pyrolytic boron nitride crucible is in a state of less than 0.3 or 0.7 or more. Is desired.

  The reason for this is that when the pyrolytic boron nitride of the crucible mainly contains either a hexagonal crystallite or a turbulent crystallite, the inner surface of the crucible has a uniform thickness by thermal oxidation. This is probably because the GaAs raw material melt can be more reliably prevented from coming into direct contact with the pyrolytic boron nitride on the inner surface of the crucible.

  In Table 1, a GaAs single crystal was grown, but the same tendency was observed when an InP single crystal was grown.

  As described above, by manufacturing a compound semiconductor single crystal using the vertical crucible for growing a compound semiconductor single crystal according to the present invention, a high-quality compound semiconductor single crystal can be obtained at a high yield while suppressing polycrystallization. Obtainable.

The method of growing a compound semiconductor single crystal using the crucible for single crystal growth according to the present invention is illustrated by a schematic cross-sectional view. A method for growing a compound semiconductor single crystal using a conventional single crystal growth crucible is illustrated in schematic cross-sectional view.

Explanation of symbols

  1, pyrolytic boron nitride crucible, 1a seed crystal accommodating portion, 1b taper portion of crucible, 2 boron oxide film, 3 compound semiconductor seed crystal, 4 compound semiconductor raw material, 5 boron oxide sealing material, 11 pyrolytic boron nitride crucible, 11a Seed crystal accommodating portion, 11b Tapered portion of crucible.

Claims (5)

A vertical pyrolytic boron nitride crucible for compound semiconductor single crystal growth,
The crucible has a seed crystal container at the bottom of the main body,
X-ray diffraction intensity I (hBN) from the hexagonal c-plane contained in the pyrolytic boron nitride of the crucible and X-ray diffraction intensity I (tBN) from the c-plane of the layered structure having a larger plane spacing than the hexagonal crystal. ) Ratio I (hBN) / [I (hBN) + I (tBN)] is 0 or more and less than 0.1 or 0.9 or more and 1.0 or less,
A crucible characterized in that at least a desired region of the inner surface of the crucible is covered with a boron oxide film.   The crucible according to claim 1, wherein the entire inner surface of the crucible is covered with the boron oxide film. A method for growing a compound semiconductor single crystal using the crucible according to claim 1, comprising:
A compound semiconductor seed crystal is loaded into the seed crystal accommodating portion,
A compound semiconductor raw material and a boron oxide sealing material are accommodated in the main body of the crucible,
Melting the boron oxide sealing material and the compound semiconductor raw material to produce a raw material melt coated with the sealing material melt;
Thereafter, a compound semiconductor single crystal is grown from the raw material melt by unidirectional solidification from the seed crystal.   The single crystal growth method according to claim 3, wherein the compound semiconductor is GaAs or InP. A vertical pyrolytic boron nitride crucible for compound semiconductor single crystal growth,
The crucible has a seed crystal container at the bottom of the main body,
X-ray diffraction intensity I (hBN) from the hexagonal c-plane contained in the pyrolytic boron nitride of the crucible and X-ray diffraction intensity I (tBN) from the c-plane of the layered structure having a larger plane spacing than the hexagonal crystal. The ratio I (hBN) / [I (hBN) + I (tBN)] is 0 or more and less than 0.1, or 0.9 or more and 1.0 or less.

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