JPH04321590A - Growing method of single crystal - Google Patents

Abstract

PURPOSE:To improve state of meniscus formed between raw material melt and seed crystal in pulling method. CONSTITUTION:In pulling method wherein seed crystal is brought into contact with raw material melt and pulled up to grow single crystal, at least part of the seed crystal which is brought into contact with the raw material melt is approximately cylindrical. Since the state of meniscus is improved, ratio of formation of single crystal is improved in production of single crystal.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a single crystal such as a semiconductor by a pulling method (Czochralski method).

0002

2. Description of the Related Art In the pulling method, a single crystal is grown using, for example, an apparatus as shown in FIG. Referring to FIG. 4, in this apparatus, a crucible 34 for accommodating a raw material melt 37 is supported by a susceptor 35 attached to the upper end of a lower shaft 38 that can be rotated and lowered. Further, a heater 39 is provided around the susceptor 35. Above the center of the crucible 34 is provided an upper shaft 31 that can rotate and move up and down, and a seed crystal 32 is attached to the lower end of the upper shaft 31. In order to pull a single crystal from a raw material melt in such an apparatus, the raw material is placed in a crucible 34 and heated and melted by a heater 39, and then the upper shaft 31 is lowered and a seed crystal 32 is added to the melt 37. Let it become familiar enough. On the other hand, a temperature gradient as shown in FIG. 5 is set by the heater 39 so that the surface of the raw material melt 37 has the melting point of a single crystal. and,
When the upper shaft 31 is slowly rotated and raised, the single crystal 3 with the crystal orientation aligned with the seed crystal 32 as shown in FIG.
0 is raised.

Conventionally, in such a pulling method, the seed crystal has often had a prismatic shape with a square cross section as shown in FIG.

0004

[Problems to be Solved by the Invention] When growing a single crystal as described above, when a seed crystal is blended into a raw material melt, a meniscus 70 as shown in FIG. 8 is formed due to the surface tension of the melt. is formed between the melt 37 and the seed crystal 32.

[0005] The shape of the meniscus 70 is thought to affect the growth of the single crystal. For example, if the tilt angle α shown in FIG. 8 is too large (α is 60 degrees or more) or too small (α is 30 degrees or less), defects are likely to occur in the crystal. Now, since the seed crystals conventionally used are prismatic,
As shown in FIG. 9, the inclination angle differs depending on the position of the outer periphery of the seed crystal. For example, the inclination angle is large at the center of the side surface of the seed crystal, and becomes smaller as it goes from the center to the end. The difference in inclination angle between the center portion (indicated by arrow A in FIG. 9) and the end portion (indicated by arrow B in FIG. 9) is about 60 degrees. For this reason, it has been impossible to keep the inclination angle of the formed meniscus within the range of 30 degrees to 60 degrees over the entire outer periphery. Therefore, during single crystal growth, crystal defects were likely to occur directly beneath the seed crystal.

An object of the present invention is to provide a method for growing a single crystal in which crystal defects during crystal growth are reduced by making the shape of the meniscus preferable.

[0007]

[Means for Solving the Problems] A method for growing a single crystal according to the present invention is a method of bringing a seed crystal into contact with a raw material melt and then pulling the seed crystal to grow a single crystal. It is characterized in that the portion that comes into contact with is approximately cylindrical.

[0008]

[Operation] According to the present invention, if at least the part of the seed crystal that is brought into contact with the raw material melt is approximately cylindrical, its cross section is approximately circular, so that the state of contact between the melt and the seed crystal is as shown in FIG. are approximately equal over its entire circumference. Therefore, there is almost no variation in the inclination angle of the meniscus formed between the seed crystal and the melt around the outer periphery of the seed crystal. For this reason, it becomes possible to keep the inclination angle between 30 degrees and 60 degrees. By eliminating variations in the inclination angle of the meniscus in this way, it is possible to suppress the occurrence of crystal defects directly under the seed crystal when pulling a single crystal.

[0009]

[Example] Using the apparatus shown in FIG. 2, G
A single crystal of aAs was grown.

First, the apparatus shown in FIG. 2 will be explained below. This apparatus is an apparatus for producing single crystals using a high-pressure LEC method. In this apparatus, a crucible 5 rotatably supported by a lower shaft 3 is provided inside a chamber 1 . A raw material melt 7 is contained in the crucible 5, and the surface of the raw material melt 7 is covered with a liquid sealant 8. Liquid sealant 8
prevents the high dissociation pressure elements in the raw material melt 7 from volatilizing. Further, a heater 16 is provided around the crucible 5, and a heat insulating agent 17 is provided around the heater 16 to prevent heat radiation. Above the center of the crucible 5 is provided an upper shaft 2 which can be rotated up and down in order to pull up the crystal, and a seed crystal 10 is attached to the lower end of the upper shaft 2. The seed crystal 10 has a cylindrical shape as shown in FIG. In addition, the inside of chamber 1 is under high pressure (
It is filled with N2 gas 20 at a concentration of 10 to 20 atm. The basic procedure for single crystal production in this apparatus is as shown in the prior art.

Using the apparatus constructed as described above, a single crystal was produced as follows.

As input raw material, GaAs polycrystal 4.0
kg was used. The crucible 5 is made of PBN and has an inner diameter of 6
It was inches. Further, the cylindrical seed crystal 10 having a diameter of 0.5 cm was used. After heating and melting the raw material charged into the crucible using a heater, the upper shaft 2 was lowered to fully adapt the seed crystal to the melt, and the temperature of the melt was adjusted to the crystal growth temperature using the heater. After that, move the upper axis to 3
rpm, and while rotating the lower shaft at 5 rpm, the upper shaft was pulled up at a speed of 6 mm/hr to grow a single crystal.

[0013] As a result of repeating single crystal growth 10 times under the above conditions, the dimensions of all the obtained crystals were 85 m.
It was approximately mφ×170 mm. We also observed the state of the meniscus during crystal growth. the result,
For all 10 rearings, the meniscus tilt angle was in the range of 45±10 degrees. Therefore, the conventional 45
A clear improvement was seen compared to ±30 degrees. Also,
The single crystallization rate of the obtained crystal was 80% in the above example. On the other hand, in the above apparatus, when a prismatic seed crystal with a square cross section was used instead of a cylindrical seed crystal, the single crystallization rate was 40%. As described above, it has been revealed that according to the present invention, a higher single crystallization rate than before can be obtained during crystal growth.

It should be noted that the present invention is not limited to the liquid-sealed Czochralski method shown in the above embodiments, but can be applied to, for example, the vapor pressure controlled Czochralski method or any other pulling method using seed crystals. It can also be applied to

[0015]

[Effects of the Invention] As explained above, according to the present invention, the occurrence of crystal defects at the start of crystal growth can be suppressed by improving the state of the meniscus formed between the raw material melt and the seed crystal. be able to. Therefore, if the present invention is applied to a pulling method using a seed crystal, the single crystallization rate can be improved in single crystal production.

[Brief explanation of the drawing]

FIG. 1: When pulling a single crystal according to the present invention,
FIG. 2 is a perspective view schematically showing the state of a meniscus formed between a raw material melt and a seed crystal.

FIG. 2 is a sectional view showing an example of an apparatus for carrying out the invention.

FIG. 3 is a perspective view showing the shape of a seed crystal in the apparatus of FIG. 2;

FIG. 4 is a sectional view showing an example of a device used in the pulling method.

FIG. 5 is a diagram showing an example of a temperature gradient set during single crystal production in a pulling method.

FIG. 6 is a cross-sectional view showing a state in which a crystal is pulled up in a pulling method.

FIG. 7 is a diagram showing the shape of a seed crystal used in a conventional pulling method.

FIG. 8 is a cross-sectional view illustrating the state of a meniscus formed between a raw material melt and a seed crystal in a pulling method.

FIG. 9 is a perspective view illustrating the state of a meniscus formed in a conventional pulling method.

[Explanation of symbols] 2 Upper axis 7 Raw material melt 10 Seed crystal

Claims (1)

[Claims] 1. A method for growing a single crystal in which a single crystal is grown by bringing a seed crystal into contact with a raw material melt and then pulling the seed crystal, wherein at least a portion of the seed crystal that is brought into contact with the raw material melt is approximately A method for growing a single crystal characterized by its cylindrical shape.