JPS6379792A - Device for growing single crystal - Google Patents

Abstract

PURPOSE:To prevent the generation of crystal nuclei from the wall surface of a crucible by forming ruggedness on the inner wall of the crucible to cover the greater part of a melt with a liq. sealant at the time of growing a single crystal by a liq. sealing and vertical temp. gradient solidification method. CONSTITUTION:A crucible 11 is arranged in a high-pressure vessel 1, a heating element 8 is arranged around the crucible 11, the raw material 6 is melted in the crucible 11 while the surface is sealed by the liq. sealant 7, and the obtained melt is solidified to grow a single crystal in the form corresponding to the form of the crucible 11. In this case, ruggedness consisting of grooves 12 and protrusions 13 is previously formed on the inner wall of the crucible 11. As a result, the liq. sealant 7 can be easily infiltrated along the grooves 12 on the inner wall of the crucible 11 by capillarity, the greater part of the melt is covered with the sealant, hence the generation of crystal nuclei from the wall surface of the crucible 11 is prevented, the formation of a polycrystal is also prevented, and the yield of a single crystal can be improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to the improvement of a single crystal growth system δ, and in particular to the improvement of a single crystal growth system δ, particularly for producing high-quality compound semiconductor single crystals, which are indispensable as substrates for ultra-high-speed integrated circuits, optoelectronic integrated circuits, etc., at a high yield. It is used to obtain.

[Prior Art] Conventionally, bulk single crystals of ■-v group compound semiconductors have been mainly produced by the pulling method and the boat method.

Among these methods, the pulling method is suitable for increasing the diameter of the crystal, and has the advantage that circular (100) wafers can be obtained. On the other hand, since crystal growth is performed under a large temperature gradient, there is a problem in that dislocations exist at a high density in single crystals produced by the pulling method.

On the other hand, in the boat method, crystal growth is performed under a small temperature gradient, so dislocations in the single crystal are reduced compared to the pulling method. However, the shape of the single crystal is determined by the boat shape, and it is difficult to grow <100>.
00) There is a problem that wafers cannot be obtained.

In contrast to these techniques, liquid sealing has long been used as a crystal growth method that has the potential to reduce crystal defects because it allows circular (100) wafers to be obtained and crystal growth is easy at low temperature gradients. A vertical temperature gradient solidification method has been proposed (
S, E, Slum etal, , E, C, S, , V
ol, 120. Na3. p. 588). However, this crystal growth method has not yet reached a practical stage. The main reason for this is the poor yield of single crystals.

Hereinafter, the case of growing a GaAS single crystal by the liquid confinement/vertical temperature gradient solidification method will be described with reference to FIGS. 4 to 6.

In FIG. 4, a pedestal 2 is installed at the center of the bottom of a high-pressure vessel 1, a susceptor 3 is placed on top of the pedestal 2, and a crucible 4 made of boron nitride, for example, is housed inside the susceptor 3. This crucible 4 consists of a small diameter part at the bottom for accommodating the seed crystal, a conical part at the top, and a straight body part at the top. Inside this crucible 4, from the bottom, a seed crystal 5, a GaAS polycrystal 6, and a liquid sealant B
2037 is filled. Further, a heating element 8 is arranged around the susceptor 3, and a heat insulating f is arranged around the heating element 8.
f, 9 are arranged.

Using this apparatus, crystal growth of a GaAS single crystal is performed in the following manner. First, after evacuating the inside of the furnace,
Pressurize and seal inert gas at a pressure of several to several tens of atmospheres. Thereafter, the crucible 4 is heated by the heating element 8 to sequentially melt the 82037 and the GaAS polycrystal 6. At this time, GaAS
The temperature distribution in the furnace is such that the upper part of the melt 4 is higher than the lower part so that the polycrystal 6 is melted from the upper part to the lower part.

After the GaAs melt and the seed crystal 5 are thoroughly blended, the temperature inside the furnace is gradually lowered from curve (a) to curve (b), as shown in FIG.

Note that TI in FIG. 5 is the melting point of GaAs. By this operation, assimilation starts from the interface position [Lo] of the GaAs melt 6' with the upper end of the seed crystal 5, as shown in FIG. 6(a) corresponding to the curve (a) in FIG. - Assimilation gradually progresses from the bottom to the top, and the song 1m in Figure 5
In FIG. 6(b), which corresponds to FIG. 6(b), it is solidified to the position Ll. In this way, a crystal having a shape corresponding to the shape of the crucible is finally obtained. At this time, as shown in FIGS. 6(a> and (b)), the B2O3 melt 7', which is the liquid sealant, is made of GaA
It has the effect of coating the surface of the s@ liquid 6' and preventing AS having a high vapor pressure from dissipating.

[Problems to be Solved by the Invention] The present inventors have discovered that the conventional liquid seal/vertical temperature gradient solidification method has had a poor yield of single crystals due to the following reasons. That is, conventionally, as shown in FIGS. 6(a) and 6(b), the surface of the GaAs melt 6' and its vicinity are usually only covered with the 8203 melt 7'.

For this reason, when the melt solidifies, especially immediately after the start of growth, crystal nuclei having a crystal orientation different from that of the seed crystal 5 are often generated from the wall surface of the crucible 4. The crystal nuclei thus generated from the wall surface of the crucible 4 grow larger as the melt solidifies, forming subgrains in the growing crystal, leading to polycrystalization. As a result, single crystallization was hindered and the yield of single crystals was poor. This is a particularly serious problem in the current situation where high-quality, large-diameter, and long single crystals are strongly desired for application to substrates for ultra-high-speed integrated circuits, optoelectronic circuits, and the like.

The present invention has been made in order to solve the above-mentioned problems, and most of the melt is covered with a liquid sealant at the start of crystal growth by the liquid seal/vertical temperature gradient solidification method, so that the liquid sealant is removed from the crucible wall surface. An object of the present invention is to provide a single crystal growth apparatus that can prevent the generation of crystal nuclei and improve the yield of single crystals.

[Means for Solving the Problems] The single crystal growth apparatus of the present invention includes a high-pressure container, a crucible placed in the high-pressure container, and a heating element placed around the crucible, In an apparatus for growing a single crystal in a shape corresponding to the shape of the crucible by melting a raw material in a crucible with its surface sealed with a liquid sealant and solidifying the melt, the inner wall of the crucible has irregularities. It is characterized by the formation of

In the present invention, it is desirable to form irregularities by forming grooves along the crystal growth direction on the inner wall of the crucible.

[Operation] In the conventional single crystal growth apparatus, only the surface of the melt and its vicinity were covered with the liquid sealant because the inner wall of the crucible was a simple curved surface. On the other hand, according to the above-described single crystal growth apparatus of the present invention, since the inner wall of the crucible has irregularities, the liquid sealant easily infiltrates along the recesses of the inner wall of the crucible due to capillary action. Most of the melt is covered with liquid sealant. Therefore, generation of crystal nuclei from the crucible wall surface can be prevented, polycrystallization can be prevented, and the yield of single crystals can be improved. Note that in order to cover most of the melt with the liquid sealant using capillarity, it is effective to form grooves along the crystal growth direction on the inner wall of the crucible.

[Example] Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 3.

FIG. 1 is a perspective view of a crucible used in a single crystal growth apparatus according to the present invention. In FIG. 1, a crucible 11 is made of boron nitride, and its appearance is similar to a crucible used in a conventional single crystal growth apparatus, with a small diameter part at the bottom for accommodating the seed crystal, and a conical part at the top. It consists of a section (30 degree inclination) and a straight body section above it. A rectangular groove 12 is formed on the inner wall of the crucible 11 along the growth direction (vertical direction) of the single crystal, and a rectangular convex portion 13 is formed corresponding thereto. In this example, the inner diameter (circle connecting the surfaces of the convex parts 13) is 30M1 and the groove pitch is 4m in the straight body part.
The groove depth was 3 am and the groove width was 2 m. This crucible 11
The cross-sectional view of the straight body (section along the line ■a-[a- in Fig. 1) is as shown in Fig. 2(a), whereas
The cross-sectional view of the conical part (cross section along the line mb-mb' in Figure 1) is as shown in Figure 2 (b), and as the inner diameter becomes smaller, the values of the groove pitch etc. also decrease. It's getting smaller.

The single crystal growth apparatus according to the present invention has the same configuration as the conventional single crystal growth apparatus shown in FIG. 4, except for using this crucible 11. For example, when growing a GaAS single crystal, the seed crystal, GaAs polycrystal, and B2O3 as a liquid sealant are filled, the furnace is evacuated, and the furnace is sealed under pressure with an inert gas, and then heated. 8 becomes a liquid sealant
By sequentially melting 203 and GaAs polycrystals and gradually lowering the temperature in the furnace, the melt solidifies from the bottom (seed crystal side) to the top, and finally melts into crucible 1.
GaA with a shape corresponding to the shape of 1! 9. Grow a single crystal.

Among the above steps, 8203 and G, which are liquid sealants,
When aAs polycrystals are sequentially melted, 8203 with a low melting point is melted first before the GaAs polycrystals are melted, and a part of it is efficiently transferred to the crucible through the groove 12 formed on the inner wall of the crucible 11 by the capillary ms. 11 and reach the bottom of groove 12.
Fill it all up. Next, the B2O3 melt filling the groove 12 is
The inner wall surface of the crucible 11 is expanded in the circumferential direction. Here, as long as the adjacent grooves 12 do not overlap extremely, if the groove pitch is as described above, the surfaces of the convex parts 13 other than the grooves 12 will be completely covered with the 8203 melt in a very short time. be able to. Next, the high-melting-point GaAs polycrystal has a diameter of 8203! on the entire inner wall of the crucible 11! After being covered with liquid, it is melted to form a melt. Here, the melt of a compound semiconductor such as GaAs generally has a large surface tension and has the property of trying to keep its surface area as small as possible, so it may displace the 8203 R liquid inside the groove 12 and invade the inside of the groove 12. The B2O3 melt is not pushed away even on the surface of the convex portion 13, and the GaAS melt does not come into direct contact with the inner wall of the melt 11. Figures 3(a) and (b) show the state after the GaAs polycrystal has melted through the above process (however, Figure 3(b) shows the state of B-8 in Figure 3(a)).
- is a cross-sectional view along the line), G inside the crucible 11
The periphery of the aAS melt 6', except for the interface with the seed crystal 5, is completely covered with the B2O3 melt 7-, which is a liquid sealant. Therefore, unlike in the case of conventional single crystal growth equipment, it is possible to prevent crystal nuclei from being generated from the wall surface of the Luppo 11 during crystal growth, preventing polycrystalization and improving the yield of single crystals. be able to.

In fact, using the conventional single crystal growth apparatus and the single crystal growth apparatus of the above embodiment (the material of the crucible is boron nitride), Ga of 30JIII in diameter was
When AS crystals were grown and wafers cut perpendicularly to the crystal growth axis from these crystals were wrapped and the crystal state was observed, it was found that the single crystal growth apparatus of the above example produced a good single crystal of 1fI. did. That is, when a conventional single crystal growth apparatus was used, subgrains were formed from the crystal periphery due to sticking in the cone portion of the GaAS ingot, and polycrystalization progressed considerably in the straight body portion. On the other hand, when the single crystal growth apparatus of the example was used, no subgrains were observed in either the cone part or the body part of the GaAS ingot, and the crystal orientation was the same as that of the seed crystal. have <
001> single crystal was obtained.

In the above example, a rectangular groove was formed on the inner wall of the crucible along the crystal growth direction, but the shape of the groove is not limited to a rectangular shape, but the same effect as in the above example can be obtained by using a semicircular or triangular shape. Of course, it can be done. Furthermore, the grooves formed in the inner wall of the crucible are not limited to those along the crystal growth direction, but may be formed in a spiral shape, for example. however,
Forming grooves along the crystal growth direction on the inner wall of the crucible is most suitable for the purpose of the present invention in order to efficiently introduce the liquid sealant to the bottom of the crucible in a short time. Moreover, in recent years, pyrolytic boron nitride crucibles, which are suitable for high purification, have been generally used for crystal growth of ■-V group compound semiconductors, and this pyrolytic boron nitride crucible is easy to manufacture. , a crucible having grooves along the crystal growth direction is desirable.

Furthermore, in the above embodiment, the single crystal growth apparatus of the present invention was
Although the case where it is applied to the growth of an S single crystal has been described, if the crystal growth method is to solidify a melt in a crucible, the single crystal growth apparatus of the present invention may contain such volatile elements.
It goes without saying that the method can be effectively applied not only to the growth of group compound semiconductors but also to the growth of It-Vl group compound semiconductors or semiconductor single crystals that do not contain volatile elements.

[Effects of the Invention] As detailed above, according to the single crystal growth apparatus of the present invention,
Circular (100) wafers can be obtained, and single crystals can be obtained with a high yield using the liquid confinement/vertical temperature gradient solidification method, which facilitates crystal growth at low temperature gradients. Its industrial value is extremely large, as it facilitates the production of high-quality, large-diameter, and long single crystals that can be used as substrates.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a crucible used in a single crystal growth apparatus in an embodiment of the present invention, FIG. 2 is a cross-sectional view of the same crucible, and FIG. Figure 3 (b) is a cross-sectional view taken along the nb-mb = line in Figure 1, and Figure 3 is a cross-sectional view showing the state in which the liquid sealant and GaAs polycrystal are melted in the same crucible. The figure (a> is a longitudinal cross-sectional view, the figure (b) is a cross-sectional view taken along the line B-B' in figure (a), and FIG. , Fig. 5 is an explanatory diagram showing the temperature change in the furnace in the liquid confinement/vertical temperature gradient solidification method, and Fig. 6 shows the assimilation state of the melt in the crucible when using a conventional single crystal growth apparatus. It is an explanatory diagram, and the figure (a) shows the state at the start of growth, and the figure (b)
5 shows the state when the furnace temperature corresponds to FIG. 5(b). DESCRIPTION OF SYMBOLS 1... High pressure container, 2... Bedistal, 3... Susceptor, 5... Seed crystal, 6... GaAs polycrystal,
6'...GaAS melt, 7...B2O3, 7--B2
O3 melt, 8... Heating element, 9... Heat retention cylinder, 11...
- Crucible, 12...groove, 13...convex part. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 (a) (b) Figure 6

Claims (2)

[Claims] (1) It has a high-pressure container, a crucible placed in the high-pressure container, and a heating element placed around the crucible, and the raw material is stored in the crucible with its surface sealed with a liquid sealant. A single crystal growth apparatus for growing a single crystal having a shape corresponding to the shape of the crucible by melting the melt and solidifying the melt, characterized in that the inner wall of the crucible has irregularities formed therein. (2) The single crystal growth apparatus according to claim 1, wherein the unevenness is formed by forming grooves along the crystal growth direction on the inner wall of the crucible.