JP2690419B2 - Single crystal growing method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to semiconductors such as Si and Ge, and Ga.
Method and apparatus for growing single crystals of III-V group compound semiconductors such as As, InP, II-VI group compound semiconductors such as CdTe, oxides such as BSO, LBO by the vertical Bridgman method or gradient freezing method .

[0002]

2. Description of the Related Art The above single crystal has been conventionally grown by a vertical Bridgman method, a horizontal Bridgman method, a gradient freezing method, a pulling method or the like. The vertical Bridgman method is a method in which a vertical container containing a raw material melt is placed in a temperature gradient furnace, and the raw material melt is cooled and solidified from below by moving the container downward to grow a single crystal. is there. The gradient freezing method is a method of arranging a vertical container containing a raw material melt in a temperature gradient furnace and changing the temperature distribution in the furnace to cool and solidify the raw material melt from below. According to these methods, a columnar single crystal along the side wall of the vertical container can be easily grown.

By the way, the bottom of a vertical container is generally of an inverted conical shape for the purpose of accommodating a seed crystal or growing a single crystal by limiting the number of crystal nuclei generated, or a thin tube at its tip. The attached shape is used. As a method of supporting these vertical containers, a susceptor for accommodating the entire bottom of the container is generally used for stable support of the container. This type of susceptor is suitable for growing good-quality crystals because it promotes the heat flow from the bottom of the container and promotes the formation of a vertical heat flow in the container. Therefore, the material of the susceptor having good thermal conductivity is used.

[0004]

However, the above-mentioned susceptor has a structure as shown by an arrow in FIG. 3 when the melt of the inverted conical portion of the vertical container is solidified, that is, in the step of increasing the diameter of the grown crystal. Since the heat flow flows through the susceptor, the solid-liquid interface becomes concave as shown by the dotted line. That is, the soaking effect is produced by the susceptor, and a concave solid-liquid interface is formed.
When the solid-liquid interface becomes concave during crystal growth, the crystal grain boundaries generated near the container wall are taken into the growing crystal, which becomes a cause of inhibiting single crystallization. In addition, many small-angle grain boundaries are generated in this portion. On the other hand, supporting the vertical container above,
When the susceptor is not used or when the susceptor is made of a material with low thermal conductivity, the heat flow in the vertical direction is small, and the solidification-liquid heat generated at the solid-liquid interface also causes the solid-liquid interface to be concave. easy. In the above method, in order to avoid the concave state of the solid-liquid interface, the growth rate is reduced to suppress the generation of heat of solidification, or the furnace internal structure such as the heater and the heat insulating material and the optimum temperature profile are optimized. It is possible, but generally difficult. Therefore, the present invention eliminates the above-mentioned problems, and includes the process of increasing the diameter of the grown crystal and the process of forming the straight body part, and by constantly maintaining the solid-liquid interface in a convex state, the crystal defects are mixed. Therefore, the present invention aims to provide a growth method and an apparatus therefor capable of preventing the above phenomenon and enabling the growth of a high quality single crystal.

[0005]

According to the present invention, a raw material is contained in a vertical container having a small cylindrical protrusion at the tip of an inverted conical bottom, and the solid is cooled and solidified from below in a temperature gradient furnace to form a single crystal. In the vertical Bridgman method or the gradient freezing method of growing the, until the solid-liquid interface reaches the straight body part of the vertical container, the cylindrical protrusion is fixed to a support rod to support the vertical container, and an inverted cone. Characterized in that the shaped bottom is kept substantially exposed, and then, in the straight body forming step, the upper surface of the support receives the inverted conical bottom to dissipate heat from the bottom through the support. And a method for growing a single crystal, and
In a vertical Bridgman device or a gradient freezing device in which a small cylindrical protrusion is provided at the tip of the inverted conical bottom of the vertical container, and the vertical container is arranged to be able to descend in a temperature gradient furnace, the cylindrical protrusion is A support bar having a support rod having a recess at the upper end for fitting and supporting the vertical container, and a receiving surface having a through hole for the support rod and capable of contacting the outer surface of the inverted conical bottom portion. And a support unit and a support table provided with independent lifting means.

[0006]

When the present inventors support the entire inverted cone-shaped bottom of a vertical container with a susceptor having good thermal conductivity as shown in FIG. 3, a heat flow flows as shown by the solid line in the figure, and solid-liquid It was confirmed that the interface showed a concave state of a dotted line, and then, as shown in FIG. 4, only the thin tube protruding to the bottom of the inverted conical shape was supported by a supporting rod having good thermal conductivity and the solid-liquid interface was examined. , It was found that the heat flow flows through the support rod as shown by the solid line, and the solid-liquid interface shows a convex state as shown by the dotted line. By keeping the solid-liquid interface in a convex state in this way, it is possible to prevent crystal defects generated near the container wall from entering the growing crystal. However, since the heat flow that flows downward through the supporting rod that supports the thin tube is small, the heat of solidification cannot be effectively escaped downward in the process of forming the straight body portion of the grown crystal, and the solid-liquid interface becomes concave. It is difficult to reliably prevent the entry of crystal defects. At that time, if the rate of descending the container, that is, the growth rate of crystals is reduced to suppress the heat of solidification, the prevention of polycrystallization can be prevented to some extent, but it is not always sufficient and the productivity is remarkably increased. Spoil.

Therefore, the present inventors have invented the Bridgman device of FIG. 1 by taking advantage of the advantages of FIGS. 3 and 4. FIG. 1 is a cross-sectional view of a Bridgman device which is one example of the present invention. The vertical container 1 has a small cylindrical protrusion 3 at the tip of the inverted conical bottom 2, and a support rod 4 supporting the vertical container 1 has a recess 5 at the upper end for fitting with the cylindrical protrusion 3. In order to support the outer surface of the inverted conical bottom part 2 in contact with it, the support base 6 is provided with a receiving surface 7, and the support base 6 is provided with a through hole 8 for allowing the support rod 4 to pass therethrough. A means (not shown) for independently raising and lowering the rod 4 and the support base 6 is attached. The heaters 11 to 14 are arranged around these to form a temperature gradient furnace, and the chamber 1 lined with a heat insulating material 16 is provided.
5 housed.

Next, a method for growing a single crystal by using the Bridgman apparatus shown in FIG. 1 will be described. The raw material melt 9 is housed in the vertical container 1 and a liquid sealant is housed if necessary, or the upper end of the container is closed, and a predetermined temperature gradient is formed in the axial direction by the heaters 11 to 14 around the container. Then, the support base 6 is shown in FIG.
As shown in FIG.
By gradually moving downward while rotating, the raw material melt 10 is cooled and solidified from the lower part, and the solid-liquid interface reaches from the cylindrical protrusion 3 to the inverted conical bottom 2 and, as shown in FIG. Increase the diameter. During this time, the heat flow including the solidification heat generated at the solid-liquid interface mainly flows through the cylindrical protrusion 3 to the support rod 4, so that the solid-liquid interface shows a convex state as shown in the figure.
Before and after the solid-liquid interface reaches the straight body part of the vertical container 1, the support table 6 is raised upward to bring the outer surface of the inverted conical bottom part 2 of the vertical container 1 into contact with the state of FIG. The table 6 and the support rod 4 are integrally rotated, and gradually moved downward to form a straight body portion of the crystal.

In this way, when the diameter of the solid-liquid interface of the grown crystal is relatively small and the heat flow is small, the support base 6 is kept in a state of being separated downward from the vertical container 1, and then the straight body of the grown crystal is kept. When forming the portion, the supporting table 6 is brought into contact with the inverted conical bottom part 2 of the vertical container 1 to thereby form the supporting table 6
Also, a large amount of heat flow can be escaped downward via the support rod 4, and the solid-liquid interface can always be maintained in a convex state. as a result,
The inclusion of crystal defects is prevented and the growth rate is not reduced,
It has become possible to easily grow a high quality single crystal. Although the device of FIG. 1 has been described as a Bridgman device,
In order to carry out the gradient freezing method, FIG.
In the device, the vertical container 1 is fixed and the heaters 11 to 1
By varying the temperature gradient formed by 4,
By cooling and solidifying the raw material melt from below to grow a single crystal, it is possible to produce a single crystal as in the Bridgman method.

[0010]

EXAMPLE A CdTe single crystal was grown using the apparatus shown in FIG. 400 g of CdT in a 36 mm diameter quartz crucible
e After adding polycrystal and evacuating the crucible to 1 × 10 ⁻⁶ Torr, the crucible was covered with a quartz cap. The crucible was placed in the center of the chamber with the lower protrusion of the crucible fitted into the recess of the tip of the molybdenum support rod and separated from the carbon support. Then, a temperature gradient in the vertical direction was formed in the furnace by the four heaters, and first, the crucible was placed in a high temperature portion in the furnace to melt the raw material. Then, the crucible was moved downward at a descending rate of 3 mm / hr in a temperature gradient of ° C / mm to perform crystal growth, and when the solid-liquid interface of the crystal proceeded to the straight body part of the crucible, the support base was moved. The crucible was moved upward and brought into contact with the bottom of the crucible. While maintaining this state, the crucible was moved downward at a descending speed of 3 mm / hr to form a straight body portion of the crystal. In the obtained CdTe crystal, no small-angle grain boundary, which was often seen in the increased diameter region in the past, could be confirmed at all, and a high-quality CdTe single crystal having excellent crystallinity could be obtained. It was also confirmed from the growth stripes that the shape of the solid-liquid interface was always convex.

[0011]

According to the present invention, by adopting the above-mentioned constitution, the shape of the solid-liquid interface can always be kept in a convex state, and as a result, the intrusion of crystal defects can be prevented and the crystallinity can be improved. It has become possible to grow excellent single crystals with good yield.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a Bridgman device which is one example of the present invention.

2 is a view of forming a straight body part of a crystal with the apparatus of FIG.
It is a figure showing the physical relationship between a support and a vertical container.

FIG. 3 is an explanatory diagram showing the relationship between the flow of heat flow and the solid-liquid interface when the entire bottom of the vertical container is supported by the susceptor.

FIG. 4 is an explanatory view showing the relationship between the flow of heat flow and the solid-liquid interface when only the protruding portion at the tip of the bottom of the vertical container is supported by the support rod.

Claims (2)

(57) [Claims] 1. A vertical Bridgman method in which a raw material is contained in a vertical container provided with a small cylindrical protrusion at the tip of an inverted conical bottom, and a single crystal is grown by cooling and solidifying from below in a temperature gradient furnace, or In the gradient freezing method, until the solid-liquid interface reaches the straight body part of the vertical container, the cylindrical protrusion is fixed to a support rod to support the vertical container, and the inverted conical bottom is substantially exposed. A method for growing a single crystal, which is characterized in that the single crystal is held in a state, and then, in the straight body forming step, the inverted conical bottom is received on the upper surface of the support and the heat is dissipated from the bottom through the support. 2. A vertical Bridgman apparatus or a gradient freezing apparatus in which a small cylindrical protrusion is provided at the tip of an inverted conical bottom of a vertical container, and the vertical container is arranged so as to be lowered in a temperature gradient furnace. A support rod having a recess at the upper end for supporting a vertical container by fitting a cylindrical protrusion, and a through hole for the support rod, which is capable of contacting the outer surface of the inverted conical bottom. A single crystal growth apparatus comprising: a supporting base having a surface, and the supporting rod and the supporting base provided with independent lifting means.