JPH0348160B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high quality gallium arsenide single crystals.

Recently, high-quality single crystals of - group compound semiconductors have become available, and they have come to be widely used in high-speed integrated circuits, opto-electronic integrated circuits, materials for electronic devices, and the like. Among - group compound semiconductors, gallium arsenide (GaAs) has a much faster electron mobility than silicon and a specific resistance of 10 ⁷ Ω. It is attracting attention because it is easy to manufacture large wafers with high resistance of cm or more. GaAs like this
Currently, single crystals are mainly manufactured by the liquid-sealed pulling method, but in this method, the interface between the crystal raw material melt and the sealant in the crucible, the interface between the crystal raw material melt and the crystal being pulled, and the inside of the crystal are produced. Because of the large temperature gradient, thermal stress occurs within the formed crystal, which causes the generation of dislocations, which are a type of crystal defect, and the dislocation density is usually significantly larger in the tail region than in the body region of the crystal. There is. The reason for this is that in the process of separating the grown crystal from the crystal raw material melt, the pulling speed of the crystal was set at 10 to 100 times the speed of forming the body of the crystal.
This resulted in a large temperature change in the lower half of the crystal, generating excessive thermal stress and increasing the dislocation density in the tail portion of the crystal. Therefore, when such a crystal is made into a wafer, the yield as a product decreases, and in particular, the lower half of the crystal up to the tail cannot be made into a product, resulting in waste.

The purpose of this invention is to suppress the increase in dislocation density from the lower half of the crystal to the tail, and to create a crystal in which the dislocation density distribution is substantially uniform from the head of the crystal to the tail. An object of the present invention is to provide a method for producing a single crystal.

The method for producing GaAs single crystals using the liquid seal pulling method is to use a crucible whose upper surface is coated with a liquid sealant and whose interface with the sealant is heated to 1238°C under an inert gas atmosphere of 10 to 70 atmospheres. A seed crystal is brought into contact with the crystal raw material melt in the crucible, and while the crucible and the seed crystal are rotated, the seed crystal is pulled up at a speed of about 8 to 12 mm for 1 hour when the crystal diameter is 50 mm to grow the crystal. When the grown crystal reaches the desired length, the pulling speed of the seed crystal is rapidly increased to 100-1000.
mm/hour, separating the crystal from the GaAs melt. As a result, the tail of the crystal becomes flat or hemispherical, but from the bottom half of the crystal, the tail rapidly passes through a liquid sealant with a large temperature difference and is placed in an inert gas. Therefore, this large temperature change generates thermal stress, resulting in an increase in dislocation density from the lower half of the crystal to the tail.

Therefore, in this invention, when the grown GaAs crystal reaches the desired length and the process of separating the crystal from the melt begins, the pulling speed of the crystal is gradually increased, and the surface of the crystal raw material melt in the crucible is The temperature also gradually rises.

The rate of increase in the crystal pulling speed mentioned above should be 3 times or less than the pulling speed at which the body of the crystal was created. Specifically, when pulling a crystal with a diameter of 50 mm, 1
Increase the speed to about 20 to 30 mm per hour. In other words, if the crystal pulling speed is 10 mm/hour, the limit is about 30 mm/hour, and if the pulling speed is suddenly reduced, the temperature change will increase and dislocations will tend to increase in the crystal, so the specified speed will not be reached. Gradually increase the speed over a period of about 40 minutes to 1 hour.

On the other hand, the temperature increase range of the surface of the crystal raw material melt that is in contact with the crystal is set to 15℃ above the temperature at the completion of growth of the body of the crystal, taking into account the state of the crystal that is pulled at an increased speed. Adjust the rate of increase. That is, if the outer diameter of the tail portion of the crystal does not begin to decrease even if the surface temperature of the melt is gradually increased at a predetermined rate of increase, the temperature increase allowance is further increased. As a result, the diameter of the crystal gradually becomes smaller at the tail portion of the crystal, forming a downwardly convex conical shape, and finally separates from the crystal raw material melt in the crucible in a thin thread-like state. At this time, the lower half of the crystal passes through the liquid sealant at a speed 2 to 3 times faster than the pulling speed of the body of the crystal. It does not cause sudden temperature changes and therefore does not create excessive temperature gradients within the crystal.
The increase in dislocations is suppressed. Furthermore, if the range of increase in the surface temperature of the above-mentioned crystal raw material melt exceeds 15° C. or if the temperature is rapidly raised to a predetermined temperature, the portions that have already solidified into crystals may melt, which is not preferable.

As is clear from the above description, the growth of the body of the crystal is completed by the method of the present invention, and in the process of separating the crystal from the melt, the pulling speed of the crystal and the temperature of the surface of the melt are gradually adjusted as described above. speed increase,
By increasing the temperature, it became possible to suppress the increase in dislocations in the lower half of the crystal to be formed, and to obtain a crystal with a nearly uniform dislocation density distribution throughout the crystal, which made it possible to commercialize GaAs crystals. Yield is significantly improved and high quality wafers can be provided at low cost.

Next, this invention will be explained using examples.

Put 500 g of Ga, 540 g of As, and 300 g of boron oxide (B ₂ O ₃ ) as a liquid sealant into a pyrolithic boron nitride crucible with an inner diameter of 95 mm and a depth of 100 mm.The crucible was placed in a high-pressure container and heated with argon gas for 50 g.
Pressurize to atmospheric pressure and heat the crucible to 1300℃ to produce GaAs.
A melt was synthesized.

Next, the temperature at the interface between GaAs melt and B ₂ O ₃ is 1238℃.
After adjusting the seed crystal so that , the seed crystal was pulled at a speed of 10 mm for 1 hour. As a result of the 7-hour lifting operation,
A cylindrical crystal with a diameter of about 50 mm and a length of about 80 mm was formed, so the crystal pulling speed was multiplied by 1 hour to 20
The speed is increased to mm/hour, and the surface temperature of the crystal melt is 1240.
The temperature was raised to ℃. As a result of increasing the speed to 20 mm/hour and pulling the crystal for another 1 hour and 30 minutes, the tail of the crystal was separated from the crystal raw material melt.

A conical tail with a height of approximately 50 mm was formed in the GaAs crystal obtained. This crystal was cut along the crystal length and the dislocation density distribution was measured.
The dislocation density distribution of crystals up to 80 mm is 1×10 ⁴ to 5×
It was 10 ⁴ cm ^-2 .

For comparison, a crystal was grown under the same conditions, and when a cylindrical crystal with a diameter of about 50 mm and a length of about 80 mm was formed, the crystal pulling speed was increased to 500 mm/hour to remove the crystal tail and crystal raw material melt. The liquid was separated.

The shape of the tail part of the obtained crystal was semicircular. When this crystal was cut along the crystal length and the dislocation density distribution was measured, the dislocation density distribution of the crystal up to 50 mm from the head was 1× The dislocation density distribution of the crystal at ^a position ⁸⁰ mm from the head was 5× ^{10 6 .}
It was warm at cm ^-2 .

Claims (1)

[Claims] 1. In a method for manufacturing a gallium arsenide single crystal using a liquid-sealed pulling method in which a seed crystal is brought into contact with a gallium arsenide melt whose surface temperature has been adjusted to the optimum temperature for crystal pulling, the growth of the body of the crystal is completed. However, when separating this crystal from the melt,
The pulling speed of the crystal is increased to 2 times or more and 3 times or less the pulling speed when the body was formed, and the temperature of the surface of the melt is increased from the temperature at the time when the growth of the body is completed. A method for producing gallium arsenide single crystal, which is characterized by gradually increasing the temperature within a range of up to 15°C.