JPH0371396B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for manufacturing a compound semiconductor single crystal using a liquid-sealed pulling method.

Recently, it has become possible to obtain high-quality single crystals of compound semiconductors from the group compound semiconductors, and they have come to be widely used as materials for high-speed integrated circuits, opto-electronic integrated circuits, and electronic devices. Among − group compound semiconductors, gallium arsenide (GaAs) has much faster electron mobility than silicon and has a lower resistivity.
It is attracting attention because high-quality large wafers of 10 ⁷ Ωcm or more can be easily obtained. Currently, such GaAs single crystals are mainly produced using the liquid confinement pulling method (LEC method), which directly synthesizes a crystal raw material melt.
Manufactured by. One embodiment of this single crystal manufacturing apparatus will be described with reference to the schematic diagram in FIG. 1. Reference numeral 1 is a high-pressure container, and the outer periphery of the high-pressure container 1 is housed and held in a crucible support jig 4 made of carbon material or the like. A crucible 3 is provided, and this crucible 3 is supported by a rotation support shaft 9 so as to be rotatable and movable up and down,
A heating furnace 2 is provided around the crucible 3 to heat and maintain the crucible at a predetermined temperature. A pulling shaft 8 with a seed crystal 7 attached to the lower end is provided in the upper part of the crucible 3, and this pulling shaft is configured to rotate and move up and down. A heat insulating material 11 made of a carbon material is provided around the outer periphery of the heating furnace 2 .

In the single crystal manufacturing apparatus configured as described above, a predetermined amount of crystal raw material and liquid sealant raw material are put into the crucible 3, an inert gas such as argon or nitrogen is pressurized into the high pressure container 1, and the heating furnace is heated. 2, the crystal raw material and liquid sealant in the crucible are heated at a temperature higher than the melting temperature of the crystal raw material and melted.

When the raw material in the crucible 3 is completely melted and a liquid sealant layer 6 is formed on the upper part and a crystal raw material melt layer 5 is formed on the lower part, the pulling shaft 8 is lowered and the seed crystal 7 is transferred to the crystal raw material melt layer 5. The crystal 10 is grown by bringing the seed crystal 7 into contact with the seed crystal 7 and pulling it up while rotating it at a predetermined speed.

By the way, since the upper part of the high-pressure container has a large space and is forcibly cooled from the outside, the heat convection caused by the high-pressure gas is intense, rapidly cooling the surface of the grown crystal 10, and causing the crystal 10 and crystal raw material to melt. A large temperature difference is likely to form at the interface of the liquid 5 in the radial direction and above the interface, and as a result, thermal stress is generated within the grown and formed crystal, which causes the generation of dislocations, which are a type of crystal defect. The dislocation density distribution becomes W-shaped, with high distribution at the center and periphery of the crystal.

The purpose of this invention is to suppress the occurrence of the above-mentioned dislocations,
It is an object of the present invention to provide a compound semiconductor single crystal manufacturing apparatus capable of manufacturing high quality compound semiconductor single crystals with good reproducibility by preventing dropout of high vapor material.

The purpose of reducing the temperature gradient near the interface between the crystal and the crystal raw material melt and at the top of the crucible in the conventional crystal pulling method (CZ method) that does not use a liquid sealant for single semiconductor single crystals such as silicon, oxide crystals, etc. It was known that installing a cylinder made of alumina, carbon, etc. in the upper space of the crucible had a remarkable effect on suppressing the occurrence of crystal dislocations. In the production of compound semiconductor single crystals using a liquid encapsulant (LEC method), as shown in Figure 1, a cylinder 12 of alumina, carbon, etc. is provided in the upper space of the crucible, and crystal growth is performed within the cylinder. The occurrence of dislocations was about half that of the case without a cylinder, and although some effect was recognized, the effect was much smaller than that of the pulling method (CZ method) that does not use a liquid sealant.

In this way, the effect of cylinder installation in the LEC method is
As a result of considering the reason why it is smaller than the CZ method, we found that
The dislocation density generated within a crystal increases when the pulled crystal reaches a certain temperature (for example, in GaAs, about
It was found that this was determined by the magnitude of the maximum temperature gradient experienced until cooling to 800°C. That is, C.Z.
The temperature gradient inside the crucible during crystal pulling by the method is the maximum temperature gradient near the solid-liquid interface between the crystal and the crystal raw material melt, as shown in Figure 2a.
The temperature gradient at other locations is approximately constant. this
In crystal growth by the CZ method, when a cylinder is installed in the space above the crucible as described above, the temperature gradient inside the crucible is as shown in Figure 2b, and the maximum temperature gradient exists near the solid-liquid interface, but its size is is significantly reduced, and as a result, the number of dislocations in the formed crystal is also drastically reduced. On the other hand, in the LEC method, when no cylinder is provided, the temperature gradient gradually increases upward from the solid-liquid interface, reaching its maximum near the boundary between the liquid sealant and the space, as shown in Figure 3a. The temperature gradient in the space above the liquid sealant is approximately constant. However, when a cylinder is provided, as shown in Figure 3b, the temperature gradient near the solid-liquid interface decreases slightly, but the temperature gradient near the boundary between the liquid sealant and the space exhibiting the maximum temperature gradient, that is, the maximum temperature gradient. remains almost unchanged,
Therefore, it is considered that the effect of suppressing the generation of dislocations in the grown crystal was not so great. The reason why such a large temperature gradient occurs near the boundary between the liquid sealant and the space is because the thermal conductivity of the liquid sealant is much lower than that of the crystal raw material melt, and is also much higher than the thermal conductivity of the atmospheric gas in the space. This is due to the high
In the crystal pulling method using a liquid sealant, it is inevitable that it is difficult to reduce the occurrence of dislocations in the crystal below a certain level.

Therefore, as a result of further studies to reduce the temperature gradient near the boundary between the liquid sealant in the crucible and the space, we decided to use a cylindrical heat-insulating cylinder made of carbon material with its lower end immersed in the liquid sealant. It was discovered that by installing the liquid sealant in this manner and performing crystal growth inside the heat-insulating cylinder, the temperature gradient near the top surface of the liquid sealant was significantly reduced.

This invention was completed based on the above knowledge, and its gist is to form a liquid sealant layer on the upper part and a crystal raw material melt layer on the lower part, and to form a crystal raw material melt layer on the lower part. In a compound semiconductor single crystal manufacturing device that pulls and grows a crystal by bringing a seed crystal into contact with it, a cylindrical heat-insulating cylinder having an inner diameter larger than the diameter of the crystal to be pulled is made of carbon material, and the cylindrical heat-insulating cylinder is attached to a crucible. The reason is that it is provided concentrically with the center and its lower end is brought into contact only with the liquid sealant layer in the crucible, and this state is maintained during crystal growth.

FIG. 4 shows an embodiment of a compound semiconductor single crystal device according to the present invention, in which the crystal raw material and liquid sealant raw material in the crucible 3 are completely melted, a liquid sealant 6 is formed in the upper part, and a liquid sealant 6 is formed in the lower part. Once the crystal raw material melt 5 is formed, a cylindrical heat-insulating cylinder 13 having an inner diameter larger than the diameter of the crystal to be grown is inserted into the liquid sealant 6 at its lower end.
Place it concentrically with the center of crucible 3 so that it is immersed only in the water. To give a specific example, a flange 13' is protruded at an appropriate position on the outer peripheral surface of the cylindrical heat insulating tube 13, and an annular carbon base 14 having an appropriate height is placed on the heater heat insulating material 11. Set up. In this state, after putting a predetermined amount of crystal raw material and liquid sealant into the crucible, the position of the crucible is lowered, and then the heat insulating cylinder 13 is hooked with its collar 13' on the annular stand 14 so that its lower end is It is inserted into the crucible and placed so that its center coincides with the center of the crucible. At this time, the position of the crucible is lowered, and the raw material in the crucible does not come into contact with the lower end of the heat-insulating cylinder. The crucible is heated in this state, and when the raw material is completely melted, the crucible is raised to a position where the liquid sealant contacts the lower end of the heat insulating cylinder. Of course, the heat insulating cylinder may be placed in a predetermined position relative to the crucible in advance, and then the raw material may be put into the crucible and heated and melted.

The inner diameter of this heat-insulating cylinder 13 corresponds to the diameter of the crystal to be pulled.
A range of 1.3 to 1.6 times is appropriate; if the diameter is too small, when the crystal diameter becomes even slightly larger than the specified value, the crystal may come into contact with the heat-insulating cylinder and fall.
Vibration prevents low dislocation, resulting in polycrystalline,
This leads to the occurrence of twin crystals. On the other hand, if the diameter of the heat-insulating tube is too large than the above range, rotation and vertical movement of the crucible will be hindered, and the space will be too large, making it impossible to obtain sufficient effects.

The length of the heat-insulating cylinder is sufficient to accommodate the crystals that have completed their growth. Further, the wall thickness of the heat-insulating cylinder is determined mainly by the thermal conductivity of the material, but if it is too thin, the temperature of the gas phase inside the heat-insulating cylinder will change quickly due to the influence of thermal convection caused by the high-pressure gas in the upper part of the high-pressure container, which is undesirable.

The material constituting the heat retaining cylinder must be heat resistant, have high thermal conductivity, and be a substance that is difficult to dissolve into B ₂ O ₃ . For example, carbon and pyrolytic boron nitride (PBN) can be considered as substances that meet these requirements, but PBN is
When brought into contact with B ₂ O ₃ and cooled to room temperature, the surface of PBN itself may peel off, making it unusable after several uses. On the other hand, unlike PBN, carbon can be used many times without peeling off even when cooled to room temperature. However, if carbon is inserted into the crystal raw material melt, it will elute, making it impossible to obtain a desired thermal conductivity result.

Therefore, in this invention, the cylindrical heat insulating cylinder is made of carbon material, and the lower end of the cylindrical heat insulating cylinder is brought into contact only with the liquid sealant layer in the crucible to allow crystal growth. be. Therefore, in the present invention, a high quality single crystal having a uniform dislocation density distribution and a predetermined thermal conductivity can be obtained.

As mentioned above, the lower end of the heat insulating cylinder 13 is connected to the crucible 3.
The pulling shaft 8 with the seed crystal 7 attached to the lower end is placed so that it contacts only the liquid sealant 6 inside the cylinder and its center coincides with the pulling shaft 8. The crystal descends until it comes into contact with the crystal raw material melt 5. When the seed crystal comes into contact with the crystal raw material melt, the pulling shaft is pulled up while rotating at a predetermined speed. Further, the crucible is rotated in the opposite direction to the pulling axis as necessary to start crystal growth.
When the sealant liquid level in the crucible drops as the crystal grows, the crucible is raised by that amount, so that the lower end of the heat-insulating tube is always inserted only into the liquid sealant during crystal growth. shall be.

When crystal growth is performed in a state surrounded by a heat-insulating cylinder in this way, the temperature gradient from the solid-liquid interface between the crystal raw material melt and the crystal to the vicinity of the boundary between the liquid sealant and the space becomes significant as shown in Figure 5. Although the maximum temperature gradient is still located near the top of the liquid encapsulant, its size has decreased significantly, and as a result, the occurrence of dislocations in the formed crystal has been drastically reduced to more than 1/10 of the conventional level, and the crystal wafer The dislocation density distribution within the crystal becomes U-shaped with relatively high density only at the periphery, and furthermore, the escape of high vapor pressure materials such as As and P from the crystal surface is suppressed.

High-quality single crystals are formed in this way by improving (reducing) the temperature gradient in the liquid encapsulant and near the boundary between the liquid encapsulant and the space, and by improving (reducing) the temperature gradient around the crystal during cooling. It is thought that because the volume of the space is partitioned by the heat-insulating tube, the space volume in which high-vapor materials such as As and P can diffuse in the vapor phase is reduced, and their escape from the crystal is suppressed. Furthermore, even when the crystal is separated from the crystal raw material melt and cooled, the crystal remains in the heat insulating cylinder until it reaches a certain temperature, so rapid cooling is avoided, and the introduction of defects such as cracks into the crystal during cooling is also prevented.

As is clear from the above explanation, this invention uses a heat insulating tube to reduce the temperature gradient near the top surface of the liquid sealant, where the temperature gradient is the largest, and pulls the crystal. By applying this method not only to the production of semiconductor single crystals but also to the production of all single crystals using liquid encapsulants, the generation of dislocations can be suppressed and high quality single crystals with uniform dislocation density distribution can be obtained. , high-speed integrated circuits,
This will greatly contribute to the production of opto-electronic integrated circuits.

Next, embodiments of this invention will be described.

After putting 500 g of Ga, 500 g of As, and 300 g of disk-shaped boron oxide (B ₂ O ₃ ) as a liquid sealant into a pyrolithic boron nitride crucible with an inner diameter of 100 mm and a depth of 100 mm, lower the position of the crucible. A carbon heat-insulating tube with an inner diameter of 75 mm, a length of 120 mm, and a wall thickness of 5 mm was placed in a predetermined position using an annular stand placed on top of the heater heat-insulating material.Then, the crucible was pressurized to 20 atm with argon gas and heated to 1300℃. When the crystal raw material and liquid sealant are completely melted, the lower end of the heat insulating cylinder
The crucible was raised to a position where it was immersed in the liquid sealant by about 10 mm. The heating temperature was lowered to 1240°C, the seed crystal was lowered to contact the crystal raw material melt, and the crucible was rotated 20 times per minute and the seed crystal was rotated 6 times in the opposite direction at a rate of 10 mm per hour. GaAs of approximately 50 mm in diameter and approximately 90 mm in length by pulling up a time seed crystal.
A single crystal was obtained. During the crystal pulling operation, the crucible was raised at a speed of 1.6 mm for 1 hour, and the lower end of the heat-insulating cylinder was adjusted to remain in contact with the liquid sealant at all times.

The dislocation density distribution of the (100) circular wafer made of the obtained GaAs single crystal was measured, and the result was as shown by curve a in FIG. In other words, the dislocation density was approximately 5 × 10 ⁴ cm ^-2 at the periphery, but it decreased to approximately 6 × 10 ³ cm ^-2 at a radius of about 20 mm or more, less than 1/10 of the conventional value, showing a U-shape. Ta.

For comparison, a GaAs single crystal was manufactured under the same conditions as above except for the installation of a heat insulating cylinder, and the dislocation density distribution was measured on a wafer.As shown in curve b in Figure 6, the center of the wafer The area and the periphery were approximately 10 ⁵ cm ^-2 and exhibited a W-shape.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a compound semiconductor single crystal manufacturing apparatus using a conventional liquid encapsulant;
Fig. 2 is a graph showing the temperature gradient above the solid-liquid interface by the CZ method, Fig. 3 is a graph showing the temperature gradient near the top of the liquid sealant from the solid-liquid interface by the LEC method, and Fig. 4 is a graph showing the invention. 5th sectional view of essential parts showing an embodiment of a single crystal manufacturing apparatus according to
The figure is a graph showing the temperature gradient in the vicinity of the upper surface of the liquid sealant from the solid-liquid interface according to the present invention, and FIG. 6 is a graph showing the dislocation density distribution of a GaAs single crystal produced by the apparatus of the present invention. 1... High pressure container, 2... Heating furnace, 3... Crucible, 5... Crystal raw material melt, 6... Liquid sealant, 7
... Seed crystal, 8 ... Pulling shaft, 10 ... Growing crystal, 13 ... Heat insulation tube, 14 ... Annular stand.

Claims (1)

[Claims] 1. A liquid sealant layer is formed in the upper part of a crucible in a high-pressure container, and a crystal raw material melt layer is formed in the lower part thereof, and a seed crystal is brought into contact with the crystal raw material melt layer, and the seed crystal is pulled up. In a compound semiconductor single crystal production device for growing crystals, a cylindrical heat-insulating cylinder having an inner diameter larger than the diameter of the crystal to be pulled is constructed of carbon material, and the cylindrical heat-insulating cylinder is arranged concentrically with the center of the crucible and at its lower end. 1. An apparatus for manufacturing a compound semiconductor single crystal, characterized in that a part is provided in contact only with a liquid sealant layer in a crucible, and this state is maintained during crystal growth.