JPS60180993A - Pulling method of gaas single crystal - Google Patents

Abstract

PURPOSE:To dispense with formation of a flanging part of complicated shape, and to grow easily the titled single crystal by specifying the size of the seed crystal to be used in the method for pulling a GaAs single crystal with the liquid-capsule Czochralski method. CONSTITUTION:The material melt 1 is charged into a crucible which is heated with a heater, and the surface is covered with a B2O3 melt 2. A seed crystal 9 fixed at the lower end of a pulling shaft 7 is immersed into the surface of the melt 1. And a single crystal is pulled up while rotating the seed crystal 9. The size of the cross section of the seed crystal 9 is regulated so that the diameter of the seed crystal may be equal to the outer diameter of the single crystal or close to the outer diameter (>50% of the outer diameter). The shape of the cross section of the seed crystal 9 is not limited to circular form, and other shapes such as a square of a polygon can also be used. Namely, any shape having cross- sectional area close to that of the single crystal can be used.

Description

Detailed Description of the Invention (Technical Field) The present invention is based on the liquid capsule Czochralski method (hereinafter referred to as L
The present invention relates to a method for pulling GaAs single crystals using the EC method (referred to as the EC method).

(Background Art) In the LIC method, as shown in an example in FIG. In this method, the seed crystal 3 attached to the lower end of the pulling shaft 7 is immersed in the water, and the single crystal 4 is pulled up by pulling up the seed crystal 3 while rotating it.

Conventionally, in this method, a seed crystal 3 having a diameter much smaller than the outer diameter of the desired single crystal was used to gradually grow a single crystal having the shape shown in the figure. However, it is difficult to control the shape of the crystal until it reaches a predetermined maximum diameter, there is no reproducibility in the shape of the shouldered portion 8, and the quality of the straight body portion also varies widely.

(Disclosure of the Invention) The present invention has been made to solve the above-mentioned problems, and by using a seed crystal close to the outer diameter of the single crystal to be pulled, a protruding part with a complicated shape can be formed. It is an object of the present invention to provide a method for pulling a GaAs single crystal, which does not require the following steps, allows easy growth of the single crystal, and allows easy control of the temperature gradient in the single crystal.

The present invention is a method for pulling a GaAs single crystal, which is characterized in that the GaAs single crystal is pulled by the liquid capsule Czochralski method using a seed crystal with a cross-sectional dimension close to the outer diameter of the single crystal to be pulled. be.

Hereinafter, the present invention will be explained by examples using the drawings, and the numbers indicate the same parts. In the figure, 9 is a seed crystal,
The cross-sectional dimension is equal to or close to the outer diameter of the single crystal (50% or more of the outer diameter).

However, the cross-sectional shape of the seed crystal 9 is not limited to a circle, and may be other shapes such as a square or a polygon, as long as its cross-sectional area is close to that of a single crystal.

This GaAs seed crystal is produced by processing a low-dislocation GaAs' single crystal produced by, for example, the horizontal Bridgman method (hereinafter referred to as HB method) into a cylindrical shape having a predetermined diameter.

The upper part of this seed crystal 9 is covered with a suitable covering, such as a heat insulating material 10.
It is covered with a metal fitting 11 and attached to the lower end of the pulling shaft 7. Further, the sides of the seed crystal may be covered with a suitable covering (eg, a heat insulating material).

When a cover is provided on the top or side of the seed crystal 9 in this way,
As shown in FIG. 4, since the heat transferred from the seed crystal 9 to the pulling shaft 7 is suppressed, the temperature gradient within the single crystal 12 can be lowered, and dislocations can be reduced.

On the other hand, in the conventional method, as shown in FIG. 3, heat radiation from the head of the single crystal 4 is large, resulting in a steep temperature gradient, resulting in an increase in dislocations.

FIG. 5 is a longitudinal sectional view showing an example of a seed crystal section used in another embodiment of the present invention. In the figure, the same reference numerals as in FIG. 2 indicate the same parts. In the figure, I8 is a thick seed crystal with a cross section similar to that described above, and a Boron nitland (BN) lit heater block +4 is fixed on top of the seed crystal with screws 16. is attached to the bottom end of the An auxiliary heater 15 is attached to the heater block 14 and heats the first seed crystal 13 from above. Note that this auxiliary heater may be provided on the side of the seed crystal. 17 is a seed crystal part thermocouple.

By providing an auxiliary heater on the top or side of the seed crystal in this way, by heating the seed crystal, the heat transferred to the pulling axis through the seed crystal is suppressed, and the temperature gradient within the single crystal can be lowered. This makes it possible to reduce dislocation.

(Example) Using a seed crystal and an apparatus as shown in FIG.
The single crystal was pulled by the LEC method.

A seed crystal 13 having a diameter of 50+u+ and a length of 80 rsm was cut out in the 100> direction from a GaAs single crystal produced by the HB method, and was fixed to the heater block 14.

High purity Ga0.5#, high purity As0.6#, B in a pyrolytic, poron, nitride (PBN) crucible
2080.2 was charged, heated under an As pressure of 60 atmospheres, reacted to synthesize GaAa polycrystals, and further heated to melt this.

By lowering the temperature of the melt, generating small crystals on the melt, and melting it slowly enough again, the surface of the melt can be changed to GaA.
The seed crystal 13 is slowly heated to around the melting point of CB2.
After soaking in the 0B melt, the temperature was lowered at 20 am (1 o'clock). During this time, the weight of the seed crystal was monitored, the B2O3 buoyancy (which could be easily calculated due to the cylindrical shape) was excluded from the calculation, and the temperature was adjusted so that the seed crystal did not melt. During this time, the pulling shaft rotation speed was O1 and the crucible shaft rotation speed was 1Or, p, m, and closed.

Further, the auxiliary heater +5 was adjusted so that the thermocouple of the seed crystal part was about 1200°C. When the seed crystal arrived at the GaAs melt, it was confirmed that no solid material would grow from the seed crystal, and after the seed crystal was fully absorbed, the temperature of the furnace heating (main) heater was gradually lowered. When the temperature is lowered to a certain extent, a single crystal tends to grow, and as shown in FIG. 6, the meniscus 18 is lowered, giving a signal that the weight of GaAs, where the crystal density is lower than that of the melt, is decreasing.

In FIG. 6, the left diagram shows when the seed crystal has arrived at the GaAs melt, and the right diagram shows when it has been cooled.

After confirming that the weight had decreased by about 3 years, the seed crystal was pulled up at a speed of about 6 mm/hour, and the temperature of the seed crystal thermocouple I7 was gradually lowered while normal pulling was carried out.

A 9 cm long section from the top of the seed crystal of the obtained GaAs single crystal was formed into a wafer and its characteristics were evaluated. The original seed crystal was undoped, and the resistance and dislocation density of this seed crystal to 46In and 6 cm from the top of the seed crystal were as shown in Table 1.

Table 1 From Table 1, it can be seen that according to the present invention, the resistance is increased due to the high purity that is a feature of the LEC method, and the dislocation density is decreased due to the low temperature gradient within the crystal.

(Effects of the Invention) The GaAs single crystal pulling method of the present invention configured as described above has the following effects.

((a) Since a seed crystal with a cross-sectional size close to the outer diameter of the single crystal to be pulled is used, there is no need to form an exposed shoulder as in the conventional method, and the operation is easy and the single crystal of a predetermined diameter can be easily pulled. Can be manufactured.

That is, a furnace with a low temperature gradient (e.g., As
In pressurized phosphor furnaces, etc., if the seed crystals are thin and have a small heat capacity, as in conventional methods, even small temperature fluctuations can cause the melt to drop. Furthermore, since the temperature fluctuations in the center are large and tendritic growth is likely to occur, it is disadvantageous to start growth from the center as in the conventional method. In contrast, in the present invention, such a phenomenon does not occur during seeding.

(b) It is possible to provide a cover or an auxiliary heater on the top or side of the seed crystal, and by these,
As described above, the upward temperature gradient within the single crystal can be easily lowered, and the dislocation density can be lowered.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view for explaining an example of a conventional pulling method. FIG. 2 is a longitudinal sectional view for explaining an embodiment of the method of the present invention. FIG. 8 and FIG. 4 are longitudinal cross-sectional views showing temperature gradients within a single crystal in the conventional method and the method of the present invention, respectively. FIG. 5 is a longitudinal sectional view showing an example of a seed and a crystal portion used in another embodiment of the method of the present invention. FIG. 6 is a longitudinal sectional view showing the state of the meniscus in an embodiment of the method of the present invention. ... Pulling shaft, 8. Chest part, 10... Insulation material, I
I...Mounting fee JL,! 4... Heater block, 15
...Auxiliary heater, 16...Screw, 17...Seed crystal part thermocouple. Kanl Leap University 2 figure 7Y3M ``A'4 figure

Claims (3)

[Claims] (1) A method for pulling a GaAs single crystal, characterized in that the GaAs single crystal is pulled by the liquid force Pselchoklarnuki method using a seed crystal with a cross-sectional dimension close to the outer diameter of the single crystal to be pulled. (2) The method for pulling a GaAs single crystal according to claim 1, wherein the seed crystal is provided with a cover on its top or side surface, thereby lowering the temperature gradient in the single crystal. (3) The seed crystal is provided with an auxiliary heater on the top or side, thereby lowering the temperature gradient in the single crystal. How to pull up.