JPH06183872A - Device for growth of compound semiconductor crystal - Google Patents

Abstract

PURPOSE:To provide a device for the growth of a compound semiconductor crystal by a vertical Bridgman method or a vertical gradient freezing method, capable of symmetrically securing temperature distributions on horizontal surfaces including the tip surface of a seed crystal and of readily growing the compound semiconductor crystal excellent in the crystallizing property from the tip of the seed crystal. CONSTITUTION:The compound semiconductor crystal growth device having a receiving section for setting a seed crystal at the lower part of a growth container for receiving a melted raw material and further having a means for gradually setting crystallization temperatures from the seed crystal-receiving section toward the upper part of the growth container is characterized by disposing a space facilitating the flow charging of the melted raw material between the seed crystal and the inner wall of the seed crystal container.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for growing a compound semiconductor crystal such as GaAs by a vertical Bridgman method or a vertical gradient freeze method.

[0002]

2. Description of the Related Art FIG. 5 is an explanatory diagram showing a state of a conventional vertical Bridgman method or a vertical gradient freeze method immediately before the start of growth. A seed crystal is loaded into the seed crystal storage section at the bottom of the growth vessel, the raw material is put into the growth vessel, and then the
After melting the raw material by providing a temperature gradient like the above, and holding the upper end of the seed crystal to the melting point of the crystal, in the vertical Bridgman method, the growth container is moved toward the low temperature side (downward). Alternatively, the compound semiconductor crystal is grown from the upper end of the seed crystal by moving the heating means upward. In the vertical gradient freeze method,
The compound semiconductor crystal is grown from the upper end of the seed crystal by controlling the heating means and lowering the temperature while maintaining the temperature gradient. In addition, B ₂ O ₃
There is also a method of performing crystal growth by coating with a liquid sealing agent such as.

[0003]

In the apparatus shown in FIG. 5, the seed crystal was loaded in the seed crystal storage portion at the lower end of the growth container without any gap. If there is a gap around a part of the seed crystal, the molten raw material will flow into that part, which will induce asymmetry in the temperature distribution on the horizontal plane, and cause a polycrystal to be generated from the part that has flowed in. Specifically, using a growth container made of PBN, Ga
When growing As crystals, 100 μm on the surface of the container
It is difficult to avoid unevenness and deformation exceeding the range, and the molten raw material often intrudes into the gap of 100 μm due to this unevenness and deformation.

Therefore, in the present invention, the above-mentioned problems are solved, symmetry is ensured in the temperature distribution on the horizontal plane including the tip of the seed crystal, and a compound semiconductor crystal having excellent crystallinity is easily grown from the tip of the seed crystal. It is intended to provide an enabling device.

[0005]

According to the present invention, an accommodating portion for accommodating a seed crystal is provided at a lower end of a growth container for accommodating a molten raw material, and the crystallization temperature is gradually increased from the seed crystal accommodating portion toward the upper part of the growth container. In the apparatus for growing a compound semiconductor crystal provided with a means for shifting to, a gap for allowing a molten raw material to easily flow in is provided between the seed crystal and the inner wall of the seed crystal accommodating portion. As a means for supporting the seed crystal, a seed crystal container provided with a recess having a shape corresponding to the lower part of the seed crystal is used, and the seed crystal container is installed at the bottom of the seed crystal container of the growth container or the lower end of the seed crystal container is used. The growth container with the opening is supported by a growth container base having an opening in the center, and a seed crystal container provided with a through-hole having a shape corresponding to the lower part of the seed crystal is slidably contacted with the lower part of the seed crystal container to grow the container. Seal the lower end of
It is preferable to adjust the protruding length of the seed crystal from the seed crystal container by supporting the lower part of the seed crystal penetrating the seed crystal container with the seed crystal holder.

[0006]

According to the present invention, in an apparatus for growing a compound semiconductor crystal by the vertical Bridgman method or the vertical gradient freeze method, a molten raw material flows between the inner wall of the seed crystal accommodating portion below the growth container and the seed crystal. By actively providing a gap, it is intended to ensure thermal symmetry in the horizontal plane including the tip of the seed crystal, which enables the growth of a compound semiconductor crystal with excellent crystallinity from the tip of the seed crystal. is there.

In the present invention, it is necessary to create a coexisting state of the seed crystal and the molten raw material before the start of growth, but this can be realized by loosening the temperature gradient in the vertical direction. Further, by providing a temperature gradient such that the temperature gradually rises from the center of the seed crystal toward the outer periphery in the cross section of the seed crystal accommodating portion of the growth container, and by further efficiently radiating heat from the lower portion of the seed crystal, the coexistence of the above The state can be easily realized.

The gap around the seed crystal into which the molten raw material flows is
Although it is necessary to allow the molten raw material to flow in easily, if it is too wide, convection may occur in the molten raw material, and the seed crystal may be partially dissolved before entering the growth step. From the experience, this gap is optimally in the range of 0.5 to 3 mm. Also,
In order to maintain the symmetry of the thermal environment, it is preferable to make the cross-sectional shape of the seed crystal of the portion projecting into the seed crystal accommodating portion circular. When the length of the part where the seed crystal protrudes into the container and comes into contact with the molten raw material exceeds the diameter of the seed crystal, melting at the upper end becomes noticeable, and the symmetry of the thermal environment collapses, making it difficult to grow a single crystal. Therefore, the protrusion length of the seed crystal in the vertical direction is preferably shorter than the diameter of the seed crystal.

If the upper end of the seed crystal is located in the tapered portion of the growth vessel where the molten raw material is largely convected, the temperature fluctuation of the seed crystal itself increases, and an unstable state tends to occur at the start of growth. The upper end of the crystal is preferably held in the seed crystal accommodating portion which is a small diameter portion at the lower end of the growth container.

FIG. 1 is a conceptual diagram of an apparatus for growing a compound semiconductor crystal, which is one embodiment of the present invention. This device
A recess for mounting a seed crystal is provided at the bottom of the seed crystal storage portion in the lower part of the growth container, and a gap is provided around the seed crystal for allowing the molten raw material to flow. In the apparatus of FIG. 1, since the process of forming the concave portion in the bottom of the seed crystal housing is complicated, the lower part of the seed crystal can be attached to the housing by grinding the upper part of the seed crystal as shown in FIG. Alternatively, the molten raw material may be caused to flow around the upper portion of the seed crystal.

In the apparatus shown in FIG. 3, the seed crystal is processed into a simple shape such as a cylinder or a prism, and the seed crystal is mounted in a seed crystal container having a recess corresponding to the lower portion of the seed crystal. The seed crystal can be attached to the bottom of the seed crystal housing. The seed crystal container is preferably made of high-purity PBN or quartz in order to prevent impurities from being mixed into the grown crystal.

In the apparatus of FIG. 4, the seed crystal is processed into a simple shape such as a cylinder or a prism, and in order to make it possible to adjust the protruding length of the seed crystal into the seed crystal accommodating portion, the seed of the growth container is adjusted. A growth container in which the lower end of the crystal container is opened and supported by a growth container table having an opening in the center, and a seed crystal container having a through hole having a shape corresponding to the lower part of the seed crystal is slidably contacted with the lower part of the seed crystal container. The lower end of the seed crystal is sealed, and the lower part of the seed crystal penetrating the seed crystal container is supported by the seed crystal holder. The condition of the tip of the seed crystal can be constantly grasped by fluoroscopy or the like. In addition, by making the seed crystal holder with a material with high thermal conductivity such as carbon, the amount of heat dissipation through the seed crystal is increased and the coexistence of the seed crystal and the molten raw material before growth is maintained in a stable state. Is preferred.

In the apparatus shown in FIGS. 3 and 4, the gap between the seed crystal container and the seed crystal, and the gap between the seed crystal container and the inner wall of the seed crystal container of the growth container are set to 20 μm or less. It is possible to substantially prevent the inflow of the molten raw material into the above-mentioned gaps by eliminating the surface irregularities of both of them and performing precision processing into a predetermined shape, thus further facilitating single crystal growth and further improving the crystal quality. be able to.

Among the factors that inhibit single crystallization, twins have the highest probability of occurrence. Twins are particularly likely to occur in the initial stage of growth and are often introduced from the crystal surface in contact with the growth container. Therefore, it is effective to apply B ₂ O ₃ to the inner wall of the container in advance in order to reduce the generation of nuclei on the inner wall of the container in order to significantly reduce twinning. In the present invention, it is preferable to apply a B ₂ O ₃ thin film on the inner wall of the seed crystal containing portion of the growth container.

[0015]

Example A growth vessel is a PBN vessel having an inner diameter of the raw material storage portion of 50 mm and an open upper end, and a lower end portion of the seed crystal storage portion closed by a thin tube portion of 8 mm. Grinding was performed to reduce surface irregularities. A seed crystal having a diameter of 4 mm and having a circular shape is shown in FIG.
It was inserted into a BN seed crystal container and held in a state of protruding by 3 mm. The seed crystal used had an orientation of <100>. After charging 2 kg of GaAs polycrystal as a raw material, a PBN lid was placed on the upper end of the growth vessel and placed in a heating furnace.

First, the growth vessel was placed below the heater, the heater was heated to reach a steady state, and then the growth vessel was slowly raised and stopped at a predetermined position. In this state, the seed crystal portion was at the melting point and the melting point was above the melting point, so the raw material polycrystal was melted and the temperature gradient in the vertical direction of the seed crystal portion was 0.4 ° C./cm. To improve the symmetry of the thermal environment of the growth system, the growth container is set to 5 rp.
It was rotated at m. After the steady state is reached, the growth container is set to 0.
It was moved at 9 mm / hr for crystal growth. The resulting GaAs crystal, with 50mm in diameter, 550 cm ^-2 dislocation density at the tip of the crystal, and 920 cm ^-2, 800 cm ^-2 at the rear portion at an intermediate portion, was indicative of excellent crystallinity .

[0017]

According to the present invention, by adopting the above-mentioned constitution, the molten raw material is positively introduced between the inner wall of the seed crystal container and the seed crystal so that the symmetry of the thermal environment around the seed crystal can be improved. Since it can be held, it becomes possible to grow a high quality compound semiconductor crystal having excellent crystallinity with good reproducibility.
Further, if precision processing is performed to reduce the gap between the seed crystal and the seed crystal container, it is possible to prevent the molten raw material from flowing into that portion itself, so that it is possible to grow crystals of higher quality.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a compound semiconductor crystal growth apparatus that is one specific example of the present invention.

FIG. 2 is an enlarged view of a seed crystal accommodating portion of a compound semiconductor crystal growth apparatus that is another specific example of the present invention.

FIG. 3 is an enlarged view of a seed crystal accommodating portion of a compound semiconductor crystal growth apparatus that is still another specific example of the present invention.

FIG. 4 is an enlarged view of a seed crystal accommodating portion of a compound semiconductor crystal growth apparatus that is another specific example of the present invention.

FIG. 5 is an explanatory diagram showing a relationship between a conventional compound semiconductor crystal growth apparatus and a temperature gradient.

Claims (3)

[Claims] 1. A compound provided with a container for installing a seed crystal at a lower end of a growth container for containing a molten raw material, and means for gradually shifting the crystallization temperature from the seed crystal container to an upper part of the growth container. A growth apparatus for a compound semiconductor, comprising: a growth apparatus for a semiconductor crystal, wherein a gap into which a molten raw material easily flows is provided between the seed crystal and an inner wall of the seed crystal housing. 2. The compound semiconductor growth apparatus according to claim 1, wherein a seed crystal container provided with a recess having a shape corresponding to the lower part of the seed crystal is installed at the bottom of the seed crystal container of the growth container. 3. A seed crystal container having a through hole having a shape corresponding to the lower part of the seed crystal is supported by supporting a growth container having an opening at the lower end of the seed crystal container with a growth container table having an opening at the center. Seed crystal holding that makes the lower end of the growth container sealed by slidingly contacting the lower part of the part, supports the lower part of the seed crystal that penetrates the seed crystal container, and makes it possible to adjust the protruding length of the seed crystal from the seed crystal container. The compound semiconductor growth apparatus according to claim 1, further comprising a tool.