JPH05170594A - Production of single crystal - Google Patents

Abstract

PURPOSE:To obtain single crystal in higher yield by pulling a high-purity compound semiconductor single crystal from a pBN crucible set in a vessel. CONSTITUTION:A susceptor 16 is installed in an outer vessel 11, and a pBN crucible 17 on the susceptor 16. The upper end of the crucible 17 is fitted with a heat shielding plate 26. At the center of the plate, a hole is provided with its diameter smaller than the inner diameter of the crucible 17 but larger than the outer diameter of a GaAs single crystal 20 to be pulled. In this state, the pBN crucible 17 is charged with a GaAs melt 7 and heated through a heater 18 in an inert gas 21; concurrently, the GaAs single crystal 20 is gradually pulled from the melt 7 using the upper revolving shaft 19, thus obtaining the objective single crystal 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a single crystal for pulling a high-purity compound semiconductor single crystal by using a pyrolytic boron night raid crucible (hereinafter referred to as "pBN crucible"), and more particularly to a single crystal. The present invention relates to a method for producing a single crystal that can improve the conversion rate.

[0002]

2. Description of the Related Art Generally, GaAs, InP, GaP, I
As a method for producing a compound semiconductor single crystal of nAs, CdTe or the like, a liquid capsule pulling method (hereinafter referred to as “LEC method”) and a vapor pressure pulling method (hereinafter referred to as “PCZ method”) are industrially carried out. In these pulling methods, a quartz crucible or a pyrolysis boron night raid crucible (hereinafter referred to as “pBN crucible”) is used as a crucible for containing a raw material, but pB is generally used for pulling a high-purity crystal.
N crucibles are used.

An outline of the method for producing the compound semiconductor single crystal will be described with reference to FIG. 6 for the LEC method and FIG. 7 for the PCZ method, taking the case of producing a high-purity GaAs single crystal as an example.

FIG. 6 shows a manufacturing state of a GaAs single crystal by the LEC method. A susceptor 2 is rotatably installed around the axis of the sealed outer container 1, and a pBN crucible 3 is installed on the susceptor 2. Further, the periphery of the pBN crucible 3 is surrounded by the heater 4, and the periphery thereof is further covered with the heat insulating cylinder 5. Furthermore, p
An upper rotary shaft 6 is installed above the BN crucible 3 so as to be coaxial with the susceptor 2 and vertically movable.

In FIG. 6, Ga is placed in the pBN crucible 3.
As melt 7 and B ₂ which is a capsule covering the surface thereof
O ₃ 8 was introduced, and the GaAs single crystal 10 was gradually pulled up by using the upper rotary shaft 6 while heating the pBN crucible 3 by the heater 4 in the inert gas 9 filled in the outer container 1, so that the GaAs single crystal 10 was pulled up. The single crystal 10 is manufactured.

FIG. 7 shows a GaAs single crystal 2 produced by the PCZ method.
0 shows the production status of 0. Sealed outer container 11
Inside, an upper container 13 that can be divided into upper and lower parts by a seal part 12
Also, a lower container 14 is provided therein, and a lower rotary shaft 15 is rotatably installed in the lower container 14 about the axis thereof. Further, on the lower rotary shaft 15, a pB via a susceptor 16 is provided.
N crucible 17 is installed. On the other hand, a heater 18 is installed outside the upper container 13 and the lower container 14,
Above the BN crucible 17, an upper rotary shaft 19 is installed coaxially with the susceptor 16 and vertically movable.

In FIG. 7, only the GaAs melt 7 is put into the pBN crucible 17. Heating is performed by the heater 18, and the GaAs single crystal 20 is heated by the upper rotary shaft 19.
It is obtained by gradually pulling up. In this case, the pulling atmosphere gas 21 is a gas mainly composed of As vapor, and its pressure is maintained by the control of the heater 22.
The upper rotary shaft 19, the upper container 13, the lower rotary shaft 15
And the lower container and the seal part 12 are made of B ₂ O ₃ 24 respectively.
It is sealed by.

[0008]

However, when a compound semiconductor single crystal is manufactured by using these conventional apparatuses, the GaAs melt 7 in the pBN crucibles 3 and 17 is laterally aligned in order to reduce crystal defects in the pulled crystal. When the temperature gradient in the direction is made small, unnecessary nuclei or suspended matter in which unnecessary nuclei are often generated from the inner wall of the pBN crucibles 3, 17 are generated.
In some cases, these adhered to the pulled crystal to become a polycrystal, making it difficult to obtain a complete single crystal.

This phenomenon is considered to be due to the thermal conductivity of the pBN crucibles 3 and 17 used for obtaining high-purity crystals exhibiting anisotropy in the vertical and horizontal directions. That is, the thermal conductivity of the pBN crucibles 3, 17 in the vertical direction is about 20 times larger than that in the horizontal direction (width direction), and about 10 to 20 times larger than that of the GaAs crystal. The heat dissipation in the vertical direction of the crucibles 3, 17 becomes large, and the inner wall of the pBN crucibles 3, 17 and the GaAs
It is presumed that the temperature of the contact point of the melt is lowered and, as a result, nuclei of GaAs are generated and further grow into a suspended substance.

Therefore, for the purpose of preventing these nucleation and suspended matter, a method using a heat shield plate described in JP-A-54-150378 was examined. However, p
In pulling up GaAs using a BN crucible
When the heat shield plate described in JP-A-4-150378 was used, the single crystallization rate was extremely reduced as compared with the method in which the heat shield plate was not used. As a result of various studies on the cause, it was found that the effect of the heat shield plate was completely different between the silicon pulling method and the GaAs pulling method.

The effect of the heat shield plate in pulling up silicon is that the silicon monoxide condensate formed during the pulling operation does not reach the solidification surface, as described in detail in JP-A-54-150378. This is to form a flow path of an inert gas that forms a pulling atmosphere in and to prevent the pulling crystal from being irradiated with heat from the crucible wall and the surface of the melt during the pulling operation. That is, by lowering the temperature of the crystal during the pulling operation, the pulling temperature is increased, and as a result, stacking faults (OSF) due to oxygen uptake are reduced.

On the other hand, in pulling a single crystal, lowering the crystal temperature means that the shape of the solid-liquid interface becomes convex or M-shaped with respect to the crystal side. Crystals can be pulled up. On the other hand, in the case of GaAs pulling, the crystallization rate is low when the solid-liquid interface is convex or M-shaped with respect to the crystal side. It is impossible.

The reason is that since silicon has a large critical shear stress, dislocation, which is one of crystal defects, does not occur.
In GaAs, it is difficult to completely prevent the transition because the critical shear stress is small, and if the surface temperature of the pulled crystal is lowered to make the shape of the solid-liquid interface convex toward the crystal side or M-shaped, the local concentration of the transition occurs. This is because the so-called lineage develops into a polycrystal, making it impossible to pull a single crystal.

Therefore, when pulling up GaAs,
It is necessary to raise the surface temperature of the pulled crystal, especially the surface temperature of the crystal near the solid-liquid interface, and make the shape of the solid-liquid interface convex or flat on the melt side. It has been found that the heat shield plate as described above cannot be used for pulling up GaAs, which has an ideologically different action.

The object of the present invention is to suppress the generation of nuclei or floating substances formed by the growth of nuclei at the contact points between the pBN crucible 3,17 wall and the GaAs melt in the production of a compound semiconductor single crystal by pulling, and at the same time, pulling up. The purpose is to raise the surface temperature of the crystal, especially the surface temperature of the crystal in the vicinity of the solid-liquid interface, and make the shape of the solid-liquid interface convex or flat with respect to the melt side to improve the single crystallization rate.

[0016]

In order to obtain a high-purity compound semiconductor, the present invention is a method for producing a single crystal by pulling using a pBN crucible, in which heat dissipation from the upper end of the pBN crucible is suppressed and the pulled crystal is used. For the purpose of increasing the surface temperature of the crystal, especially the surface temperature of the crystal near the solid-liquid interface, and making the shape of the solid-liquid interface convex or flat with respect to the melt side, a heat shield plate is attached to the upper end of the pBN crucible to provide a compound semiconductor. It was decided to pull up a single crystal.

[0017]

As described above, by attaching the heat shield plate to the upper end of the pBN crucible used when pulling up the compound semiconductor single crystal, heat dissipation from above the pBN crucible is suppressed by the heat shield plate, As a result, it is possible to prevent the temperature of the crucible wall surrounding the pulled crystal from decreasing, and
It is possible to prevent a temperature drop on the single surface of the crystal near the contact point between the pBN crucible wall and the compound semiconductor melt and near the solid-liquid interface. Therefore, generation of unnecessary nuclei or suspended matter in which they grow can be eliminated, and the shape of the solid-liquid interface can be made convex or flat on the melt side, and the single crystallization rate is improved.

[0018]

Embodiments of the present invention will now be described in more detail with reference to the drawings. FIG. 1 shows a GaAs single crystal pulling apparatus as an example of the LEC method of the present invention. The same parts as those of the conventional example shown in FIG.

In the device shown in FIG. 1, pBN crucible 3
A heat shield plate 25 is attached to the upper end of the. The heat shield plate 25 is a disc-shaped plate made of opaque quartz, and a hole having a diameter smaller than the inner diameter of the pBN crucible 3 and larger than the outer diameter of the pulled GaAs single crystal 10 is formed in the center thereof.

A GaAs melt 7 and B ₂ O ₃ 8 covering the surface of the GaAs melt 7 are charged into the pBN crucible 3 and the p is added in an inert gas 9.
While heating the BN crucible 3 with the heater 4, the GaAs single crystal 10 was gradually pulled up from the GaAs melt 7 using the upper rotary shaft 6, and the GaAs single crystal 10 was obtained at a crystallization rate of about 90%. It was Since the single crystallization rate in the ordinary LEC method without using the heat shield plate 25 is about 50%, it can be said that the use of the heat shield plate 25 significantly improved the single crystallinity ratio.

FIG. 2 shows G as an example of the PCZ method of the present invention.
7 shows an aAs single crystal pulling apparatus, and the same parts as those of the conventional example shown in FIG.

In the apparatus shown in FIG. 2, pBN crucible 1
A heat shield plate 26 is attached to the upper end of 7. The heat shield plate 26 is a disk-shaped one made of pyrolytic boron nitride, and a hole having a diameter smaller than the inner diameter of the pBN crucible 17 and larger than the outer diameter of the pulled GaAs single crystal 20 is formed in the center thereof. ing.

When the GaAs melt 7 was put into the pBN crucible 17 and the pBN crucible 17 was heated by the heater 18 in the pulling atmosphere gas 21, the GaAs single crystal 20 was gradually pulled up by using the upper rotary shaft 19. A GaAs single crystal 20 was obtained with a single crystallization rate of about 90%. Since the single crystallization rate in the normal PCZ method without using the heat shield plate 26 is about 40%, it can be said that the present invention significantly improves the single crystallization rate.

Further, in order to more efficiently suppress the dissipation of heat from the pBN crucible 17, the inner circumference is bent downward as shown in FIG. 3, and the bending length L is 6 mm and the bending angle θ is 90 degrees. Using the heat shield plate 27, similarly
When the s single crystal 20 was pulled up, the single crystallization rate was 9
The GaAs single crystal 20 was obtained at a ratio of 0 to 100%, and the effect of the heat shield plate 27 was improved. Furthermore, the bending angle θ is 12
When the GaAs crystal was pulled up using the 0 degree heat shield plate 27, the single crystallization rate was deteriorated to 40 to 50%. That is, it was determined that the bending angle θ has a certain limit.

Further, the distance Ymm between the horizontal portion of the heat shield plate 27 and the upper end of the pBN crucible 17 or the distance Xmm between the bottom end of the bent portion of the heat shield plate and the inner wall of the pBN crucible 17 or the length Lmm of the bent portion is changed. After raising the price, it became clear that there were some restrictions between them. FIG. 4 shows a series of experimental results in which the length L of the bent portion is fixed at 6 mm and the bending angle θ is taken as the horizontal axis and the single crystallization rate is taken as the vertical axis.

As a result, as is clear from FIG. 4, pB
To prevent heat dissipation from the upper end of the N crucible 17,
Either the distance Xmm between the lowermost end of the bent portion and the inner wall of the pBN crucible 17 or the distance Ymm between the horizontal portion of the heat shield plate 27 and the upper end of the pBN crucible 17 is 5 mm or less, and the bending angle θ is smaller than 110 degrees. It is desirable that the angle be 90 degrees or less. This is because if either the distance Xmm or the distance Ymm is 5 mm or less, the heat shield plate 2
This is because heat flow between 7 and the pBN crucible 17 is sufficiently prevented. Therefore, if the distance Xmm and the distance Ymm are both increased by 5 mm, the heat flow becomes easy and the heat dissipation from the upper end of the pBN crucible 17 increases.

When the bending angle θ is larger than 110 degrees, the heat flow along the same bending portion becomes strong,
It helps dissipate heat from the upper end of the pBN crucible 17. Further, when an experiment was performed while changing the length Lmm of the bent portion, it was found that the single crystallization rate was not significantly affected by the length Lmm of the bent portion and was largely dependent on the position of the tip of the bent portion during pulling. It became

This phenomenon will be described with reference to FIG. If the tip of the bent portion is above a virtual line AB connecting the tip A of the pBN crucible 17 and the outermost portion B of the solid-liquid interface of the pulled crystal, the crystal surface of the pulled crystal is the wall of the pBN crucible 17 and the melt. It is possible to maintain a sufficiently high temperature by radiating heat from the surface, but when the tip of the bent portion is below the imaginary line AB, the bent portion hinders heat radiation from the wall of the pBN crucible 17 and the melt surface, The surface temperature of the pulled crystal is lowered, and as a result, the outermost portion of the crystal is solidified quickly, and the solid-liquid interface shape becomes M-shaped as shown in FIG.

Unlike a silicon crystal, a GaAs crystal has a small critical shear stress and is likely to have dislocations. This dislocation grows perpendicularly to the solid-liquid interface and concentrates at the C portion of the crystal. For this reason, dislocations concentrate in the C portion of the crystal, resulting in the development of lineage, and finally polycrystallization progresses from the lineage, making it impossible to obtain a single crystal.

In FIG. 4, the bending angle θ is 11
The single crystallization rate is better when the bending angle θ is 0 ° than when it is 0 °, because when the bending angle θ is 110 °, heat is dissipated from the upper end of the pBN crucible 17 at the bending angle θ. Although the effect is almost the same as when the bending angle θ is 0 degree, when the bending angle θ becomes 110 degrees, the effect of cooling the tip of the crystal pulled by the bent portion is added, so that the bending angle θ is more than that when the bending angle θ is 0 degree. This is because the crystallization rate decreases.

[0031]

As described above, in the method for producing a single crystal of the present invention, the heat shield plate is attached to the upper end of the pBN crucible used for pulling up the compound semiconductor single crystal, so that the pBN crucible can be removed from above. Of the heat is suppressed by the heat shield plate, and the temperature drop at the contact point between the pBN crucible wall and the compound semiconductor melt is prevented. Therefore, the generation of nuclei and floating substances are eliminated, and the surface temperature of the pulled crystal, especially the surface temperature of the crystal near the solid-liquid interface is increased, and the shape of the solid-liquid interface becomes convex or flat on the melt side. Therefore, the single crystallization rate is improved.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of a method for producing a single crystal using the LEC method in the present invention.

FIG. 2 is an explanatory diagram showing an example of a single crystal production method using the PCZ method in the present invention.

FIG. 3 is an explanatory diagram showing a relationship between a heat shield plate and a pulled crystal according to the present invention.

FIG. 4 is a diagram showing the relationship between the bending angle of the heat shield plate and the single crystallization rate when the length of the bent portion of the heat shield plate is constant.

FIG. 5 is an explanatory diagram showing the relationship between the heat shield plate according to the present invention and the solid-liquid interface of the crystal being pulled.

FIG. 6 is an explanatory diagram showing an example of a conventional single crystal manufacturing method using the LEC method.

FIG. 7 is an explanatory view showing an example of a conventional single crystal manufacturing method using the PCZ method.

[Explanation of symbols]

1,11 Outer container 2,16 Susceptor 3,17 pBN crucible 4,18,22 Heater 5 Insulating cylinder 6,19 Upper rotating shaft 7 GaAs melt 8,24 B ₂ O ₃ 9 Inert gas 10,20 GaAs single crystal 12 Seal part 13 Upper container 14 Lower container 15 Lower rotating shaft 21 Atmosphere gas 25, 26, 27 Heat shield plate A ... pBN crucible tip B ... Outermost part of solid-liquid interface of pulled crystal C ... Part where crystal dislocation concentrates X … The distance between the lowermost end of the bent part of the heat shield plate and the inner wall of the pBN crucible Y… The distance between the horizontal part of the heat shield plate and the upper end of the pBN crucible L… The bent length of the heat shield plate θ… The horizontal part of the heat shield plate Angle with the folded part

Claims (4)

[Claims] 1. A pyrolytic boron night raidle crucible (pB).
N crucible) for pulling a compound semiconductor single crystal, wherein the crucible has a hole at the upper end thereof having a diameter smaller than the inner diameter of the crucible and larger than the outer diameter of the pulled crystal. Is attached and the compound semiconductor single crystal is pulled up through this hole. 2. The inner periphery of the hole formed in the heat shield plate is bent downward, and the angle between the horizontal portion and the bent portion of the heat shield plate is greater than 0 degrees and less than 110 degrees. The method for producing a single crystal according to claim 1, wherein 3. The distance between any one of the bent portions of the heat shield plate bent downward and the inner wall of the pBN crucible is within 5 mm or the horizontal portion of the heat shield plate and pBN.
The method for producing a single crystal according to claim 1 or 2, wherein the distance from the upper end of the crucible is within 5 mm. 4. The lower end of the bent portion of the heat shield plate bent downward is not lower than the line connecting the outermost part of the solid-liquid interface of the crystal being pulled and the uppermost end of the crucible. The method for producing a single crystal according to claim 1, wherein