JP2005306629A - Method for manufacturing compound semiconductor single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently manufacture a high-quality compound semiconductor single crystal. <P>SOLUTION: The method for manufacturing a compound semiconductor single crystal includes steps of: forming a boron oxide film (2) by allowing the inner surface of a boron nitride crucible (1) having a housing part (1a) for a seed crystal (3) in the bottom; charging the housing part in the bottom of the crucible with a seed crystal and disposing a boron oxide underlay (4A) to cover the bottom of the crucible; disposing a compound semiconductor raw material block (5) on the boron oxide underlay while leaving a predetermined small gap (6) between the boron oxide film and the polycrystalline block to prevent contact with each other; filling the gap with a melt by melting the boron oxide underlay; melting the compound semiconductor source block and part of the upper part of the seed crystal; and then growing the compound semiconductor single crystal by one direction solidification from the seed crystal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a compound semiconductor single crystal, and more particularly to an improvement in a method for producing a compound semiconductor single crystal by unidirectional solidification from a seed crystal in a crucible.

  Since compound semiconductors composed of III-V group compounds (GaAs, GaP, InP, etc.) and II-VI group compounds (CdTe, ZnSe, etc.) have various different characteristics compared to silicon, in recent years, they have been used in various electronic devices. The demand for the use of is increasing. However, with compound semiconductors, it is difficult to produce a single crystal by the rotational pulling method as in the case of silicon. Therefore, a compound semiconductor single crystal is generally grown by unidirectional solidification from a seed crystal in a crucible.

  However, when a compound semiconductor single crystal is grown in a crucible by unidirectional solidification from a seed crystal, undesired crystal nuclei are generated due to inhomogeneities in the inner wall of the crucible in contact with the compound semiconductor melt. It is known that it may crystallize. In the prior art, a method of growing a compound semiconductor single crystal while avoiding direct contact between the compound semiconductor melt and the inner wall of the crucible has been attempted.

  FIG. 5 schematically illustrates a method for producing a compound semiconductor single crystal disclosed in Japanese Patent Application Laid-Open No. 2000-154089 of Patent Document 1. When a compound semiconductor single crystal is grown by this method, a compound semiconductor seed crystal 23 is first loaded into a recess provided in the bottom of the crucible 21. A tapered portion 21 a is provided between the concave portion and the main body portion of the crucible 21. A substantially hollow conical boron oxide underlay 25 is disposed so as to cover the tapered portion 21a. The crucible 21 in which the boron oxide underlay 25 is disposed is filled with a plurality of compound semiconductor polycrystalline pieces 24.

  If the crucible 21 is heated in this state, the boron oxide underlay 25 having a melting temperature lower than that of the compound semiconductor raw material 24 is first softened and melted. In general, boron oxide is a glassy substance and melts at about 450 ° C. or higher. On the other hand, compound semiconductors generally have a higher melting point than boron oxide. For example, the melting point of GaAs is about 1238 ° C.

  Therefore, if the temperature of the crucible is further raised to dissolve the compound semiconductor raw material 24, the boron oxide melt is pushed up along the inner wall of the crucible 21 by the weight of the compound semiconductor melt. Then, it is considered that a boron oxide melt layer is formed between the inner wall of the crucible 21 and the compound semiconductor melt. As a result, it is expected that direct contact between the compound semiconductor melt and the inner wall of the crucible 21 is avoided, and polycrystallization during single crystal growth by unidirectional solidification from the seed crystal 23 can be prevented.

  FIG. 6 schematically illustrates a method for producing a compound semiconductor single crystal disclosed in Japanese Patent Application Laid-Open No. 2003-146791 of Patent Document 2. When growing a compound semiconductor single crystal by this method, the boron oxide thin film 32 is first formed by oxidizing the inner wall of the boron nitride crucible 31. This boron oxide thin film is formed by heating a boron nitride crucible to high temperature in air.

  A compound semiconductor seed crystal 33 is loaded into a recess provided at the bottom of the crucible 31. And the boron oxide piece 34 is arrange | positioned as a sealing agent on the taper part provided between the recessed part in which the seed crystal 33 was loaded, and the crucible main-body part. Further, a compound semiconductor polycrystalline block 35 is installed on the tapered portion. At this time, the periphery of the lower surface of the polycrystalline block 35 is supported by the taper portion of the crucible, but the side surface of the block 35 is arranged so as not to contact the boron oxide thin film 32 formed on the inner wall of the crucible.

When the crucible 31 is heated in this state, boron oxide and the compound semiconductor are sequentially melted. At this time, the melt in which the boron oxide pieces 34 are dissolved is pushed up by the weight of the compound semiconductor melt and rises along the inner wall of the crucible already covered with the melt of the boron oxide film 32. Then, it is considered that the compound semiconductor melt and the inner wall of the crucible can be prevented from contacting each other by the boron oxide melt layer having a thickness larger than the thickness of the boron oxide film 32. As a result, it is expected that polycrystallization during single crystal growth by unidirectional solidification from the seed crystal 33 can be prevented.
JP 2000-154089 A JP 2003-146791 A

  When the inventor attempted a method for producing a compound semiconductor single crystal according to FIG. 5, it was not possible to completely prevent polycrystallization during the growth of the single crystal.

  Further, when the present inventor tried a method for producing a compound semiconductor single crystal according to FIG. 6, it was not possible to completely prevent polycrystallization during the growth of the single crystal.

  In view of such a situation in the prior art, the object of the present invention is to sufficiently prevent polycrystallization of a compound semiconductor single crystal in the case of growing a compound semiconductor single crystal by unidirectional solidification in a crucible, and to provide a high-quality compound semiconductor single crystal. It is possible to make it possible to manufacture efficiently.

  In the method for producing a compound semiconductor single crystal according to the present invention, a boron oxide film is formed on at least the inner surface of the boron nitride crucible having a seed crystal storage portion at the bottom and in contact with the raw material melt, and the seed crystal storage portion at the bottom of the crucible A seed crystal is loaded and a boron oxide underlay is placed at the bottom of the crucible, and a compound semiconductor raw material block is placed on the boron oxide underlay, preventing contact between the boron oxide film and the raw material block. A predetermined small gap is provided, and the predetermined small gap is filled with a melt obtained by melting the boron oxide underlay, and in this state, a part of the upper part of the compound semiconductor raw material block and the seed crystal is melted, and then the seed crystal It is characterized by growing a compound semiconductor single crystal by unidirectional solidification.

The boron oxide film is preferably formed by reacting one or more oxidizing substances selected from air, water vapor, CO ₂ , and oxygen on the inner surface of the heated boron nitride crucible. Further, an additional boron oxide piece is further arranged on the raw material block arranged on the boron oxide underlay, and a small gap between the boron oxide film and the side surface of the raw material block is formed by the melt of the additional boron oxide piece. And the upper surface of the raw material block is preferably covered. Furthermore, the small gap between the boron oxide film and the raw material block is preferably in the range of 1 mm to 20 mm. Furthermore, it is preferable that the crucible body and the seed crystal storage at the bottom thereof are connected by a conical taper, and the raw material block and the boron oxide underlay have a conical shape that fits the taper. It is preferable.

  According to the present invention, the compound semiconductor raw material block and the melt thereof are sufficiently prevented from coming into direct contact with the inner wall of the boron nitride crucible, and the polycrystal when growing the compound semiconductor single crystal by unidirectional solidification from the seed crystal Can be sufficiently prevented.

  In making the present invention, the present inventor examined the reason why it was not possible to completely prevent the occurrence of polycrystallization during the growth of the single crystal depending on the method for producing the compound semiconductor single crystal according to FIG. The cause was considered to be that the polycrystalline semiconductor piece 24 was already in direct contact with the inner wall of the crucible 21 when the crucible 21 was filled with the compound semiconductor polycrystalline piece 24 in the crucible 21.

  That is, when there is a portion where the compound semiconductor polycrystalline piece 24 is in direct contact with the inner wall of the crucible 21 from the beginning, the boron oxide melt enters the interface between the polycrystalline piece 24 and the inner wall of the crucible 21. It is difficult to form the melt layer. Even after the compound semiconductor polycrystalline piece 24 is melted to form a melt, it is difficult to push the compound semiconductor melt in direct contact with the inner wall of the crucible 21 to form the boron oxide melt interface layer. Let's go. Therefore, it was considered that crystal nuclei were generated from the locations where the crucible 21 and the compound semiconductor melt were in direct contact, and this resulted in polycrystallization.

  The present inventor also examined the reason why it was not possible to completely prevent polycrystallization during the growth of the single crystal even by the method for producing a compound semiconductor single crystal according to FIG. In FIG. 6, the periphery of the lower surface of the compound semiconductor polycrystalline block 35 is supported by the taper portion of the crucible 31. A boron oxide thin film 32 is formed on the inner wall of the crucible 31, and the boron oxide thin film is very thin and has a glassy and brittle nature. Therefore, it is considered that the boron oxide thin film 32 may cause a defect in a region in contact with the lower surface periphery of the polycrystalline block 35. In such a defect, the compound semiconductor block 35 and the boron nitride crucible 31 are in direct contact. In general, polycrystallization is likely to occur from the vicinity of the corner portion, which is the connection region between the crucible body portion and the taper portion, and it is considered that it is not easy to avoid the nonuniformity of the inner wall of the crucible, particularly near the corner portion. It is done.

  In order to improve the problems discussed with respect to the prior art as described above, a method for manufacturing a compound semiconductor single crystal according to the present invention is described below with reference to the examples illustrated in FIG. 1 to FIG. Can be done as follows.

First, referring to the schematic cross-sectional view of FIG. 1, a boron nitride crucible 1 is prepared. The crucible 1 has a concave portion 1a for loading the compound semiconductor single crystal 3 at the bottom, and a tapered portion 1b for connecting the concave portion 1a and the crucible main body. The taper portion 1b preferably has a conical shape. The inner wall of the boron nitride crucible 1 is oxidized to form a boron oxide film 2. As for the method of forming the boron oxide film 2 on the inner surface of the crucible, it is sufficient to cause a solid, liquid, gas, or the like having oxidizing power to react with the inner surface of the crucible. It is preferably formed by reacting at least one of water vapor, air, CO ₂ , oxygen and the like. Moreover, it is preferable that the thickness of this boron oxide film exists in the range of 1-50 micrometers.

  Thus, the compound semiconductor seed single crystal 3 is loaded into the recess 1a at the bottom of the boron nitride crucible 1 having the boron oxide film 2 on the inner surface. And in the crucible 1, the boron oxide underlay 4A is arrange | positioned so that the taper part 1b may be covered. More preferably, the bottom of the boron oxide underlay 4A has a conical shape so as to fit the conical tapered portion 1b of the crucible 1. Further, a compound semiconductor raw material block 5 is installed on the boron oxide underlay 4A. At this time, the raw material block 5 is inserted into the crucible 1 without being brought into contact with the boron oxide film 2, and a predetermined gap 6 is provided between the raw material block 5 and the boron oxide film 2. Further, the entire lower surface of the raw material block 5 is supported by the boron oxide underlay 4A and does not come into contact with the boron oxide film 2 on the tapered portion 1b. Furthermore, it is preferable that an additional boron oxide piece 4 </ b> B is disposed on the raw material block 5. However, such an additional boron oxide piece 4B can be omitted if desired. Further, like the bottom of the boron oxide underlay, it is more preferable that the bottom of the raw material block has a conical shape so as to match the conical tapered portion 1b of the crucible.

  FIG. 2 illustrates a situation where the crucible in the state of FIG. 1 is heated to melt the boron oxide material. That is, if the temperature of the crucible is increased, boron oxide having a lower melting temperature than the compound semiconductor starts to melt first. Then, the melt 4a in which the boron oxide underlay 4A is melted is pushed up by the weight of the raw material block 5 and rises while filling the gap 6 between the block 5 and the boron oxide film 2. After the compound semiconductor raw material 5 is finally melted, the boron oxide melt layer 4a interposed between the raw material melt and the crucible inner surface can have a thickness in the range of 50 to 2000 μm.

  On the other hand, the additional boron oxide piece 4B is also melted to become a melt 4b, and the melt 4b flows into the gap 5 between the block 5 and the boron oxide film 2 by its own weight. The boron oxide melt 4b remaining on the upper surface of the compound semiconductor block 5 can act to protect the upper surface of the compound semiconductor.

  As will be understood from FIG. 2, the gap 6 between the raw material block 5 and the boron oxide film 2 is preferably not narrow and not too wide. For example, the gap 6 is preferably in the range of about 1 mm to 20 mm. This is because if the gap 6 is too narrow, the block 5 may come into contact with the boron oxide film 2 and be damaged when the polycrystalline block 5 is inserted into the crucible 1. On the other hand, if the gap 6 is too wide, a large amount of boron oxide underlay 4A and additional boron oxide pieces 4B are required to fill the gap with the boron oxide melt. In addition, when there is an excessive amount of boron oxide melt between the raw material block 5 and the crucible 1, the compound semiconductor block and the melt become unstable. That is, the raw material block is preferably set as densely as possible in the crucible, and is ideal if it is the same cylindrical shape as the crucible shape. In particular, it is effective if 70% or more of the cross-sectional area of the crucible is occupied by the raw material block.

  Referring to FIG. 3, the entire surface of compound semiconductor polycrystalline block 5 is covered with melt 4 in which melt 4 a of boron oxide underlay and melt 4 b of additional boron oxide pieces are combined. At this time, of course, the boron oxide film on the inner wall of the crucible is also the liquid layer 2a. Thereafter, the compound semiconductor block is melted to form the compound semiconductor melt 5a, and the upper part of the compound semiconductor seed crystal 3 is also partially dissolved. After the compound semiconductor melt 5a and the seed crystal 3 are thus connected, the melt 5a is slowly solidified in one direction from the seed crystal 3 side upward.

  FIG. 4 schematically illustrates the unidirectional solidification process of the compound semiconductor melt 5a. Such unidirectional solidification can be performed in various ways, as is well known to those skilled in the art. That is, for example, the crucible 1 may be slowly lowered with respect to the heating furnace (not shown), and conversely, the heating furnace may be raised with respect to the crucible 1. Further, the temperature may be controlled so that the temperature of the heating furnace having a lower temperature distribution in the lower part than in the upper part is slowly lowered. Thus, the compound semiconductor single crystal 3 having the same crystal orientation as that of the seed crystal 3 can be grown by slowly generating unidirectional solidification upward from the seed crystal 3.

  During this unidirectional solidification, the compound semiconductor melt 5a is prevented from being brought into direct contact with the boron nitride crucible 1 by the liquid layer of the boron oxide melt 4 and the boron oxide film 2 without generating new crystal nuclei. The compound semiconductor single crystal 3 can be grown.

  In the above embodiment, the example in which the integral compound semiconductor raw material block 5 is loaded into the crucible 1 has been described. However, the raw material block may be a dense assembly of a plurality of blocks if desired. Needless to say, it is good. In this case, however, it should be noted that any compound semiconductor block should be loaded so as not to directly contact the inner wall of the boron nitride crucible 1. In addition, it is not necessary that all of the plurality of compound semiconductor blocks be polycrystalline blocks, and it is needless to say that a single crystal block may be arranged in a part or all of them if preferred.

  Further, although a plurality of boron oxide pieces 4B are arranged on the compound semiconductor block 5 in FIG. 1, the plurality of boron oxide pieces may be arranged as an integral boron oxide piece, or the boron oxide underlay 4A is provided. If the amount is sufficient, there is no need to arrange it.

  As described above, according to the present invention, when a compound semiconductor single crystal is grown by unidirectional solidification in a crucible, the polycrystallization is sufficiently prevented and a high-quality compound semiconductor single crystal is efficiently manufactured. It becomes possible.

It is typical sectional drawing which shows the initial state in the crucible in the manufacturing method of the compound semiconductor single crystal by this invention. It is a typical sectional view showing the state where the crucible of Drawing 1 is heated and the boron oxide in the crucible is melted. It is typical sectional drawing which shows the state which heated the crucible of FIG. 2 further and melted the compound semiconductor block in the crucible. FIG. 4 is a schematic cross-sectional view showing a state in which a single crystal is grown by unidirectionally solidifying a compound semiconductor melt in the crucible of FIG. 3 from a seed crystal. It is typical sectional drawing illustrating an example of the manufacturing method of the compound semiconductor single crystal by a prior art. It is typical sectional drawing illustrating the other example of the manufacturing method of the compound semiconductor single crystal by a prior art.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Boron nitride crucible, 1a Crucible seed crystal storage part, 1b Crucible taper part, 2 Boron oxide film, 2a Boron oxide melt layer, 3 Compound semiconductor seed crystal, 4, 4a, 4b Boron oxide melt layer, 4A Oxidation Boron underlay, 4B boron oxide piece, 5 compound semiconductor raw material block, 5a compound semiconductor melt, 6 gap.

Claims (1)

A method for producing a compound semiconductor single crystal comprising:
A boron oxide film is formed on at least the inner surface of the boron nitride crucible having a seed crystal storage portion at the bottom, which is in contact with the raw material melt,
The seed crystal is loaded into the storage part at the bottom of the crucible, and a boron oxide underlay is placed at the bottom of the crucible,
A compound semiconductor raw material block is disposed on the boron oxide underlay, and at this time, a predetermined small gap is provided between the boron oxide film and the raw material block to prevent mutual contact,
Melting the boron oxide underlay, filling the predetermined small gap with the boron oxide melt,
In this state, the compound semiconductor raw material block and a part of the upper part of the seed crystal are melted,
Then, a compound semiconductor single crystal is grown by unidirectional solidification from the seed crystal.

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