JPH09110575A - Crucible for producing single crystal and production of single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a single crystal few in crystal defects by specifying the shape of the increased diameter portion of a crucible for single crystal growth by longitudinal boat method to effect single crystal growth in high yield of a compound semiconductar crystal subject to developing twin crystal. SOLUTION: This crucible to be used for single crystal growth by longitudinal boat method is such that the horizontal sectional contours (A-A' section as shown in the figure) of a majority of the increased diameter portion represents three to tow times point symmetry including straight line portion and that of the cylindrical portion is circular. By using this crucible, the formation of supercooled zone in the increased diameter portion can be prevented, enabling stable facet growth of single crystal to be conducted; therefore, twin crystal development is suppressed, thus enabling single crystal growth of crystal seed having been impossible to accomplish so far.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a III-V group compound semiconductor single crystal such as GaAs or InP, and more particularly to a vertical Bridgman method or a vertical temperature gradient solidification method which is generally called a vertical boat method. The present invention relates to a crucible used for growing a single crystal by the method and a method for a single crystal using the crucible.

[0002]

2. Description of the Related Art As one of the methods for growing a compound semiconductor single crystal such as InP or GaAs, there is a vertical boat method in which a seed crystal is placed on the bottom of a crucible and a melt is solidified from the bottom to the top. In this vertical boat method, a vertical Bridgman method in which crystal growth is performed by moving from a high temperature portion to a low temperature portion in a hot zone where the crucible is adjusted to have a predetermined temperature distribution,
There is a vertical temperature gradient solidification method in which crystals are grown by gradually lowering the temperature while keeping the temperature gradient substantially constant. II
When a group IV compound semiconductor single crystal is grown by the vertical boat method, a seed crystal having a specific orientation is placed in the well portion at the bottom of the crucible, and the polycrystal raw material that has been synthesized in advance is put into Apply or liquid encapsulant (B ₂ O ₃ )
The polycrystalline raw material is melted by covering the upper part with an inert gas in the furnace, and further the upper part of the seed crystal is melted for seeding to grow crystals.

The crucible used in this vertical boat method is
Conventionally, as shown in FIG. 3, a cylindrical body, a diameter-increasing portion having a truncated cone shape (the horizontal cross-sectional shape is circular) and a well portion for accommodating a seed crystal are used. GaAs
Although it is relatively easy to obtain single crystal growth in InP, InP
However, twin crystals are unavoidable in the increased diameter region, and it is difficult to obtain single crystal growth. A crucible for producing a single crystal used in the vertical boat method is proposed in JP-A-3-54184. The crucible for crystal production is characterized in that a part or all of the crucible has an inner wall horizontal sectional shape of a polygon. This crucible is intended to reduce crystal processing loss and processing time during wafer formation processing, but even in the straight body part, some or all of the horizontal cross-sectional shape of the crucible has a polygonal horizontal cross-section. Therefore, it is difficult to manufacture the crucible, and even if the crucible can be manufactured, in the case of the PBN crucible, stress is concentrated on the corners of the crucible, and there are drawbacks such as short life and easy breakage. Further, stress concentrates even in the crystal portion grown at the corners of the crucible, crystal defects are likely to occur, and it is difficult to take out the crystal.

In Japanese Unexamined Patent Publication (Kokai) No. 6-166588, for the purpose of manufacturing a single crystal with few crystal defects, the position of the seed crystal accommodating portion is higher than the boundary position between the bottom and the side wall. Although a crucible for use has been proposed, it has a defect that the crucible has a complicated shape and is difficult to manufacture, and the joint between the upper end and the bottom of the seed crystal storage portion is easily damaged due to the shape.

[0005]

As described above, in the conventional vertical boat method, when producing a single crystal of a compound semiconductor, such as InP, in which twinning is likely to occur, avoiding twinning in the increased diameter portion. This is not easy, and the crucible proposed in the above publication is difficult to manufacture, or even if it is manufactured, it is easily damaged. The present invention was made in view of the above-mentioned problems, in which a compound semiconductor crystal in which twinning is likely to occur is grown by a vertical boat method with a high yield, and a compound semiconductor single crystal with few crystal defects is produced. It is an object to provide a crucible and a method for producing a single crystal using the crucible.

[0006]

In order to achieve this object, the inventors of the present invention have considered that the cause of twinning in the increased diameter portion of the crucible is that unstable facets in the increased diameter portion due to the formation of the supercooled region ( Focusing on the growth of edge facets), we tried to suppress the unstable growth of edge facets due to supercooling that causes twinning. Facet growth is a growth in which a part of the solid-liquid interface becomes a flat surface with a specific low-index plane orientation. For example, in InP [100] crystals by the liquid sealed Czochralski method, (111) is generally used.
Facet growth occurs in the direction parallel to the B-plane, and twins occur in the direction parallel to the facet growth. It is said that there is a correlation between the generation of twins and facet growth, and it is said that twins are likely to occur when the length of facets (edge facets) appearing on the crystal shoulders is disturbed. In actual crystal growth, the facet growth plane appears three times in the point symmetry direction in the crystal growth of the (111) plane, and appears four or two times in the point symmetry direction in the crystal growth of the (100) plane.

In the conventional vertical boat method, in the crucible having a frustoconical shape in the diameter-increased portion, a supercooled region is formed because the surface where crystals should be facet-grown in the diameter-increased portion is circular, Therefore, it was thought that irregular disorder of the edge facets would occur and twin crystals would frequently occur. Therefore, in order to prevent the formation of the supercooled region in the increased diameter portion, the inventors have conceived a crucible having an increased diameter portion having a horizontal cross-sectional shape in which a straight portion is arranged in a direction parallel to the facet growth surface. Came to. Therefore, the method of the present invention is performed 3 to 2 times with the well portion containing the seed crystal and most of the horizontal cross-sectional shape including the straight portion.
By using the point-symmetrical crucible diameter increasing portion and the crucible for crystal production, wherein the straight body portion is a cylinder,
It is characterized by performing single crystal growth.

The three-fold point symmetry and the two-fold point symmetry referred to here are 120 degrees with respect to the center point of the horizontal cross section as the origin.
It shows that it overlaps with the original shape when rotated 180 degrees. Therefore, for example, 6-fold point symmetry (see FIG. 6), 9-fold point symmetry, etc. are included in the 3-fold point symmetry, and similarly, 2-fold point symmetry is 4 times, 8 times (see FIG. 5) point symmetry, etc. Is included.
The horizontal cross-sectional shape in which the straight line portion is arranged means that the horizontal cross-sectional shape is not composed only of a circular shape or a curved surface, and that a part of the horizontal cross-sectional shape necessarily includes a straight line portion. In order to carry out the method of the present invention, for example, a seed crystal, a polycrystalline raw material, and a liquid sealing agent are placed in a crucible having a point-symmetrical horizontal cross-sectional shape of a diameter-increased portion as shown in FIGS. (B ₂ O ₃ ) is charged. This is set in a vertical boat furnace, filled with an inert gas and then heated to dissolve some of the polycrystal and the seed crystal. After that, single crystal growth is performed by vertical Bridgman or vertical temperature gradient solidification method under an appropriate temperature gradient.

[0009]

According to the method of the present invention, since the crucible in which the straight portion is arranged so as to be parallel to the facet growth surface in the horizontal section of the crystal diameter increase portion forming the facet growth surface is used, By preventing the formation of the cooling region, it becomes possible to carry out stable facet growth, so that twin crystal formation can be suppressed and single crystal growth can be carried out. Further, according to the method of the present invention, the propagation of crystal defects (dislocations) from the seed crystal to the grown crystal is reduced because of the single crystal growth by enlargement of the diameter of the seed crystal from the seed crystal, which has been impossible in the past. Since the straight body portion is a cylinder and no stress concentration portion is formed, a high quality single crystal substrate can be obtained.

[0010]

【Example】

(Example 1) When manufacturing a (100) plane InP crystal by the vertical boat method, most of the crucible diameter increasing portion shown in FIG. Yes, in the PBN crucible with a straight body, the I in the [100] direction
nP seed crystal, InP polycrystal 1000 g, B ₂ O ₃ 200
It was charged in the order of g and set in a vertical Bridgman furnace. The seed crystal used was one obtained by cutting out and etching a [100] single crystal grown by the LEC (Liquid Sealed Czochralski) method. These are heated to a predetermined temperature and B ₂ O is added.
_3. After melting the InP polycrystal, part of the upper portion of the seed crystal was melted and seeded, and the crucible was moved under a predetermined temperature distribution to grow the crystal.

(Example 2) When an InP crystal having a (111) plane is manufactured by a vertical boat method, most of the crucible diameter increasing portion shown in FIG. The PBN crucible, which has a symmetrical shape and a straight body, is cylindrical.
1] orientation InP seed crystal, InP polycrystal 1000 g, B
200 g of ₂ O ₃ was charged in this order and set in a vertical Bridgman furnace. The seed crystal used was cut out from a [111] single crystal grown by the LEC (Liquid Sealed Czochralski) method,
It was etched. After heating these to a predetermined temperature to dissolve the B ₂ O ₃ and InP polycrystals, a part of the upper part of the seed crystal is melted and seeded, and the crucible is moved under a predetermined temperature distribution to grow crystals. went.

Comparative Example 1 Using the conventional frustoconical crucible shown in FIG. 3, under the same conditions as in Example 1 (10)
InP crystal growth of the (0) plane was performed. (Comparative Example 2) Using the conventional frustoconical crucible shown in FIG. 3, the (111) plane InP was formed under the same conditions as in Example 2 above.
Crystal growth was performed.

Table 1 shows the results of crystal growth in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 described above.
Shown in Further, in the same table, the result of measuring the average dislocation density by sampling the sample wafer from the seed portion and the tail portion of the single crystal growing ingot was added.

[0014]

[Table 1]

As can be seen from Table 1, (10
In the case of InP crystal growth on the (0) plane, no single crystal was obtained in Comparative Example 1 and twinning was observed in all the grown crystals, and no single crystal was obtained.
Eight single crystals were obtained out of zero. The average dislocation density of the single crystal obtained in Example 1 is 1/10 or less of the dislocation density of the single crystal obtained by the LEC method. In Comparative Example 1, a single crystal was not obtained, so that the dislocation densities could not be compared. On the other hand, in the case of InP crystal growth of the (111) plane of Example 2, 9 out of 10 single crystals were obtained in Example 2, and 7 out of 10 single crystals were obtained in Comparative Example 2. . The average dislocation density was almost the same. According to the method of the present invention, the single crystallization rate is significantly improved as compared with the case of manufacturing using a conventional frustoconical crucible.

In the above-mentioned embodiment, the case of manufacturing by the vertical Bridgman method is shown, but the case of crystal manufacturing by another vertical boat method or another crystal seed such as GaAs crystal, ZnSe crystal by the vertical boat method. The effect obtained also in the case of manufacturing is similar to that of the above-mentioned embodiment, and description thereof is not required.
Further, regarding the crucible shape, the 3-fold point symmetry includes a point-symmetrical form of integral multiples such as 6-fold point symmetry and 9-point point symmetry. Shall be included. Further, as the material of the crucible, quartz or the like may be used instead of PBN.

[0017]

EFFECTS OF THE INVENTION According to the present invention, since the facet growth can be performed stably by preventing the formation of the supercooled region in the increased diameter portion and the generation of twins can be suppressed, the vertical boat method can be used. It is possible to grow a single crystal of a crystal seed having a high occurrence probability of twin crystals such as InP with a high yield, which is impossible in the past, and to reduce the propagation of crystal defects (dislocations) from the seed crystal to the grown crystal. A high-quality single crystal substrate can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a crucible used in Example 1 of the present invention.

FIG. 2 is a schematic sectional view of a crucible used in Example 2 of the present invention.

FIG. 3 is a conventional conical crucible.

FIG. 4 is a view showing an example of a horizontal cross-sectional shape of a diameter-increasing portion that is symmetric with respect to two points.

FIG. 5 is a view showing an example of a horizontal cross-sectional shape of a diameter-increasing portion having 2-fold point symmetry including 8-fold point symmetry.

FIG. 6 is a diagram showing an example of a horizontal cross-sectional shape of a diameter-increasing portion having 3-fold point symmetry including 6-point point symmetry.

Claims (4)

[Claims] 1. A crucible for growing a single crystal by means of a vertical boat method, wherein the horizontal cross-sectional shape of most of the increased diameter portion of the crucible is a point-symmetrical shape having three or two times including a straight line portion, A crucible for producing a single crystal, wherein the horizontal cross-sectional shape of the part is circular. 2. A method for producing a compound semiconductor single crystal, which comprises using the crucible according to claim 1. 3. A compound semiconductor crystal having a [111] crystal growth direction is grown using a crucible having a horizontal cross-sectional shape of most of the increased diameter portion of the crucible that is point-symmetrical three times including a linear portion. A method for producing a single crystal, comprising: 4. A compound semiconductor crystal having a crystal growth orientation of [100] using a crucible in which the horizontal cross-section of the increased diameter portion of the crucible is a point symmetry shape of two or four times including a straight line portion. A method for producing a single crystal, which comprises growing a.