JPH04124089A - Production of compound semiconductor single crystal - Google Patents

Abstract

PURPOSE:To prevent the generation of crack and dislocation in a single crystal in the production of a compound semiconductor single crystal by a liquid-encapsulating Kyropoulos process, etc., by cooling the crystal under the encapsulant using a specific method without pulling up the crystal after the growth of the single crystal. CONSTITUTION:A molten raw material 5 in a crucible 3 placed in a pressure vessel 1 is covered with a liquid encapsulant layer 6, the pressure vessel 1 is filled with high-pressure inert gas atmosphere and the molten raw material 5 is slowly cooled to effect the growth of a compound semiconductor single crystal 9. The grown single crystal 9 is cooled under the encapsulant layer 6 without being pulled out of the crucible and, when the temperature of the encapsulant layer 6 reaches 500-650 deg.C in the cooling process, the inert gas pressure in the pressure vessel 1 is decreased to expand the inert gas, gas of group V element, group VI element, etc., dissolved in the liquid encapsulant layer 6 to foam the encapsulant layer. The contacting area between the encapsulant 6 and the grown crystal 9 is decreased by this process and the crack caused by the difference of thermal expansion coefficients is generated mainly in the encapsulant layer to prevent the generation of cracks in the grown crystal 9.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a compound semiconductor single crystal by a liquid-enclosed chiroporous method (hereinafter referred to as LEK method) or a vertical slow cooling method.

[Prior art] In general, ■- of GaP, GaAs, TnP, CdTe, etc.
Because group III and I[-VT compound semiconductors have high vapor pressures near their melting points, single crystals can be grown using a liquid sealing method in which the raw material melt is covered with a liquid sealant layer made of BtO, etc. It is being done. Currently, liquid sealing methods such as the liquid sealing Czochralski method (LEC method) and the LEK method are known.

The LEC method is a method in which a seed crystal is pulled up as the crystal grows, and it has been industrialized because the crystal orientation can be controlled by seeding and it is easy to obtain high-purity crystals, but it is difficult to control the diameter and it is difficult to obtain uniform crystals. It is difficult to obtain a straight body, and the temperature gradient in the melt during crystal growth is large, resulting in large thermal stress and many dislocation defects.

On the other hand, in the LEK method, the crystal is grown in a refractory crucible without pulling the crystal, so the diameter of the grown crystal depends on the inner diameter of the crucible. Therefore, it is easy to control the diameter, and the humidity gradient in the melt during crystal growth is reduced to several degrees Celsius/cm.
This is one order of magnitude smaller than that of the LEC method, so it has the advantage of low thermal stress and fewer dislocation defects.

[Problems to be Solved by the Invention] However, in the conventional general LEK method, first, a seed crystal is immersed in a raw material melt covered with a sealant using a crystal pulling shaft, and then the crucible and the pulling shaft are connected. A single crystal was grown while rotating without being pulled up, and after the crystal growth was completed, the crystal was pulled into a high-pressure inert gas above the liquid sealant and cooled in order to separate it from the raw material melt.

In this way, in the conventional general LEK method mentioned above, the crystal is cooled in a high-pressure container filled with high-pressure inert gas. Since the crystal is cooled, thermal stress in the crystal becomes large and dislocations are likely to occur.

On the other hand, in order to compensate for the above drawbacks, after the crystal growth by the LEK method is completed, the grown crystal is cooled under the sealant in the crucible without being lifted above the sealant, and in addition, there is a difference in the thermal expansion coefficient between the sealant and the crystal. In order to suppress cracks that occur due to thermal stress, a method of slow cooling at a cooling rate of 5° C./min or less has been proposed (Japanese Patent Application No. 1-199200).

However, since the properties of a compound semiconductor single crystal vary greatly depending on the method of cooling the crystal, it is preferable that there be no limit to the cooling rate.

The present invention was made to solve the above-mentioned drawbacks, and its purpose is to prevent the occurrence of cracks in the grown crystal without limiting the cooling rate, and to grow a crystal with few dislocations. Our goal is to provide a possible crystal manufacturing technology.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention covers a raw material melt in a crucible placed in a high-pressure container with a liquid sealant layer, and a high-pressure inert layer inside the high-pressure container. In a compound semiconductor single crystal production method in which a single crystal is grown by gradually cooling the raw material melt in a gas atmosphere, the crystal is cooled under a sealant without being pulled up after the single crystal growth, and the crystal is cooled under a sealant during the cooling process. When the temperature of the sealant reached 500 to 650°C, the inert gas pressure in the high-pressure container was reduced to foam the liquid sealant.

[Effect] The reason why cracks appear in the grown crystal is because the crystal and the encapsulant have good wettability and the difference in coefficient of thermal expansion is large, so the encapsulant applies a large stress to the crystal during cooling. be. This can be prevented by preventing the sealant from coming into close contact with the crystal. However, it is not possible to change the wettability of the encapsulant and the crystal. However, according to the above-mentioned means, in order to lower the pressure of the inert gas in the high-pressure container during the cooling process after the completion of crystal growth, the inert gas, group Ⅰ, and group Ⅰ gases dissolved in the sealant are removed. The sealant expands and becomes foamed. As a result, the contact area between the encapsulant and the grown crystal decreases, and the strength of the encapsulant decreases, so cracks caused by differences in thermal expansion coefficients tend to occur on the encapsulant side. , it is possible to prevent the occurrence of cracks in the grown crystal. However, since cooling is performed under a sealant, rapid cooling due to convection can be avoided and the occurrence of dislocations can be reduced compared to the case where cooling is carried out by dipping into an inert gas.

The timing of pressure reduction during cooling was set when the temperature of the encapsulant reached 500 to 650°C, because the viscosity of the encapsulant would not become sufficiently large unless the temperature reached 650°C or lower. This is because gas escapes from the agent, making it impossible to maintain the foamed state, and at lower temperatures than 500° C., the viscosity of the sealant becomes too high, causing the sealant to solidify without allowing the gas contained therein to expand.

In addition, the reason why the pressure of the inert gas in the high-pressure container immediately after depressurization was set to 2 to 20 kg/cfl in gauge pressure is because unless the pressure is reduced to 20 kg/7 or less, the gas will not expand sufficiently and the sealant will not foam sufficiently. This is because if the pressure is reduced to less than 2 kg/cnf, the inside of the high-pressure container becomes negative pressure when it is subsequently cooled to room temperature, and there is a risk that outside air will enter and the crystals will be oxidized.

[Example 1] An example in which the present invention is applied to crystal growth by the LEK method will be described below.

FIG. 1 schematically shows a crystal growth apparatus using the LEK method. That is, in this crystal growth apparatus, a cylindrical heater 2 is arranged in a closed high-pressure container 1, and a refractory roof 3 is arranged in the center of the heater 2. Moreover, this Ruppo 3 is rotatably supported by a support shaft 4 fixed to its lower end. And this crucible 3
A raw material melt 5 such as 1, n P is placed inside, and the upper surface of the raw material melt 5 is covered with a liquid sealant layer 6 made of B505 or the like.

On the other hand, a crystal pulling shaft 7 is suspended from above the crucible 3 into the high pressure vessel 1 so as to be able to move up and down and freely rotate. can be brought into contact with the surface of Furthermore, a gas introduction pipe 8 for introducing high-pressure inert gas is connected to the upper side wall of the high-pressure container 1.
The pressure inside the high-pressure container 1 can be set to a predetermined pressure.

In this embodiment, in a crystal growth apparatus as shown in FIG. 1, a predetermined amount of raw materials and a sealant are placed in a crucible 3, placed in a high-pressure container 1, and the container is filled with high-pressure inert gas. After that, the raw material is heated and melted by the heater 2, and then the seed crystal is immersed into the surface of the raw material melt 5 by the crystal pulling shaft 7.
A single crystal is grown while rotating the crucible 3 and the bow shaft 7.

Then, the crystal is not pulled up during crystal growth, and after the growth is completed, cooling is started in that state, and when the temperature has dropped to 500 to 650°C, the high pressure inert gas in the high pressure container 1 is pumped at a gauge pressure of 2 to 20 kg/g. The pressure is reduced to - and then cooled to room temperature.

- As an example, an InP single crystal was grown using the crystal growth apparatus shown in FIG. 1 using a pBN crucible with an inner diameter of 60 II 1 m.

First, as raw materials: 1. InP polycrystal of Okg and B, O, as sealants are placed in the crucible 3, heated by the heater 2 to raise the temperature in the furnace to 1100℃ or more, and B, Os and I are placed in the crucible 3.
The nP was melted. At this time, the amount of the sealant was determined so that the thickness of the liquid sealant layer (B, ○,) 6 sealing the surface of the raw material melt 5 was 30 mm. In addition, in order to prevent phosphorus from scattering, argon gas is introduced from the gas introduction pipe 8.
The interior of the high-pressure container 1 was made into an argon gas atmosphere of 50 kg/d (gauge pressure).

Next, the power of the heater 2 is adjusted so that the temperature of the surface of the InP melt reaches the melting point of InP, and the seed crystal is applied to the raw material melt 5 using the crystal pulling shaft 7 and is thoroughly blended. Crystal growth was performed over 30 hours while cooling at a rate of 1° C./hr. At this time, the crystal pulling shaft 7 is rotated at 5 rpm, and the crucible 3 is rotated at 1.5 rpm in the opposite direction. Orp
Rotated at m.

After 30 hours, when the crystal had grown almost to the bottom of the crucible, the growth was terminated, the rotation of the crystal and crucible was stopped, and the crystal was cooled at 50° C./min. When the temperature of BjO during cooling reached 550° C., the pressure inside the furnace was reduced to 6 kg/cot (gauge pressure), and the crystal was cooled to room temperature at the same cooling rate. In addition, when the pressure inside the furnace was measured just before the pressure reduction, it was 28 kg/cffl (gauge pressure). This is because the argon gas contracted as it cooled.

When the thus obtained crystal was taken out and observed, it was found that no cracks had occurred in the crystal as shown in FIG. 2(A).

Further, when a crystal was grown under the same conditions and cooled without reducing the pressure midway through, many cracks were generated in the upper part of the crystal as shown in FIG. 2(B).

[Effects of the Invention] As described above, the method for producing a compound semiconductor single crystal of the present invention covers a raw material melt in a crucible placed in a high-pressure container with a liquid sealant layer, and also provides a high-pressure sealant inside the high-pressure container. In a compound semiconductor single crystal manufacturing method in which a raw material melt is gradually cooled in an active gas atmosphere to grow a single crystal, the crystal is cooled under a sealant without being pulled up after the single crystal growth, and during the cooling process When the temperature of the sealant reaches 500 to 650°C, the inert gas pressure inside the high-pressure container is reduced, so that the inert gas dissolved in the sealant and the The gas expands and the sealant becomes foamed, resulting in a decrease in the contact area between the sealant and the grown crystal and a decrease in the strength of the sealant, which is caused by a difference in thermal expansion coefficient. Cracks are more likely to occur on the side of the sealant, making it possible to prevent cracks from forming in the grown crystal. Moreover,
Since cooling is performed under a sealant, rapid cooling due to convection is avoided compared to the case where the material is cooled by being pulled up into an inert gas, which has the effect of reducing the occurrence of dislocations.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view showing an example of a crystal growth apparatus used in carrying out the present invention, and Figs. 2 (A) and (B) show cracks in crystals grown by the present invention and conventional crystal manufacturing methods. FIG. 1... High pressure container, 3... Crucible, 5... Raw material melt, 6... Liquid sealant layer, 7... Crystal pulling axis, Fig. 2 ( A) (B)

Claims (2)

[Claims] (1) Cover the raw material melt in a crucible placed in a high-pressure container with a liquid sealant layer, create a high-pressure inert gas atmosphere inside the high-pressure container, and gradually cool the raw material melt to grow a single crystal. In the method for manufacturing a compound semiconductor single crystal, the crystal is cooled under a sealant without being pulled up after growing the single crystal, and the temperature of the liquid sealant is 500 to 650°C during the cooling process.
A method for manufacturing a compound semiconductor single crystal, characterized in that the inert gas pressure in the high-pressure container is reduced to foam the liquid sealant at the time when the liquid sealant reaches the temperature. (2) The pressure in the high-pressure container after pressure reduction in the above cooling process is 2 kg/cm^2 or more 20 kg/c in gauge pressure.
2. The method for manufacturing a compound semiconductor single crystal according to claim 1, wherein the manufacturing method is carried out so that m^2 or less.