JPH0196093A - Method for pulling single crystal - Google Patents

Abstract

PURPOSE:To increase the weight of single crystal by making the shape of cru cible bottom in a partial spherical shape convex to the outside, and specifying the ratio of the radius of curvature of partial spherical part to the diameter of the crucible trunk part and the temp. gradient near the solid-liquid boundary surface of single crystal and melting liquid. CONSTITUTION:In the method for pulling single crystal by the capsule Czochralski method, the shape of bottom of a crucible 7 is made in a partial spherical shape convex to the outside. And, the ratio of the radius R of curva ture of the partial spherical part to the diameter 2r of the crucible trunk part is regulated to 0.75<=2r/R<=2. Moreover, the temp. gradient near the solid-liquid boundary surface of a single crystal 10 and the melting liquid is made to be >=5 deg.C/cm and to be <=40 deg.C/cm. By this method, the crystal boundary surface grows in convex shape, which prevents the single crystal from being brought into contact with the crucible bottom, and the single crystal of large weight with low dislocation density is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is based on the liquid capsule Czochralski method (hereinafter referred to as LE
The present invention relates to a method of pulling a single crystal using a method (referred to as C method), and particularly to a method of pulling a single crystal with a low dislocation density.

[Conventional technology]

Group ■-■ compound semiconductors of the periodic table, such as GaAs,
High-pressure LEC as a method for growing single crystals such as InP
There is a law.

■-V group compound semiconductors have high dissociation pressure near their melting point,
The dissociation pressure of As at the melting point of GaAs is about 1 atm, and the dissociation pressure of P in InP is about 27 atm. Therefore, in the high-pressure LEC method, as shown in FIG. 1, B20. into the high-pressure inert gas atmosphere (2) in the pressure vessel (1).
), the raw material is heated and melted to form a raw material melt (8), and its surface is 8□0. Cover the raw material melt with melt (9), immerse the seed crystal θ0 on the surface of the raw material melt, let it blend, and then pull up the seed crystal while rotating to pull up the single crystal 0ω.

This method has the advantage that single crystallization in the <100> growth direction is easy and that a large, circular substrate can be obtained.

[Problem that the invention seeks to solve]

In order to improve the quality and yield of single crystals, it is necessary to solve problems regarding the shape of the melt-solid interface.In order to reduce the dislocation density, the temperature gradient at the solid-liquid interface must be increased to 30"C. /c11~40℃/cm, and at that time, the temperature gradient in the melt is 30℃ (:7cm
The following is true. In addition, it is desirable that the interface shape be flat or slightly convex with respect to the melt. When crystal growth progresses under such a temperature gradient, the solid-liquid interface becomes greatly convex with respect to the melt at the tail of the crystal. As the melt decreases,
The crystal and the bottom of the crucible come into contact and the crystal falls out. As mentioned above, in the conventional technology, the temperature gradient in the melt is
``C/cn or less, there was a problem that it became difficult to pull the crystal.The present invention was made in view of the above points, and its purpose is to reduce the temperature gradient in the melt. A method of growing a ■-V group compound semiconductor single crystal with a low dislocation density by controlling the interface shape at the crystal tail part to be flat or slightly convex with respect to the melt at a temperature of 30°C/cm or less. Our goal is to provide the following.

[Means for solving problems]

In order to achieve the above object, the present invention provides a method for pulling a single crystal using the liquid force Buseltygochralski method, in which the shape of the bottom of the crucible is made into a partially spherical shape convex to the outside. The ratio of the radius of curvature R to the crucible body diameter 2r is 0.75≦2 r/R≦2, and the temperature gradient in the melt near the solid-liquid interface between the single crystal and the melt is 5"C7.
A method for pulling a single crystal is provided, characterized in that the pulling temperature is 40° C./cm or more and 40° C./cm or less.

[Effect]

The shape of the solid-liquid interface in the crucible is determined by the central axis of the crucible near the interface (
It is determined by the temperature gradient distribution in the vertical direction.

That is, the shape of the interface is determined by the magnitude of the heat flow within the interface.

The thermal conductivity of the liquid phase is Kt, and the thermal conductivity of the solid phase is , ? e
The axial temperature gradient of the phase is GL, and the axial temperature gradient of the solid phase is G.
3. Letting L be the generated latent heat, ρ be the density, and V be the crystal growth rate, the following equation holds true.

K, G, = KLGL + L・ρV Therefore, v-(KSGS KLGL)/L-ρ, and since K5, KL, L2 ρ are constant, V is G8, G
Determined by L.

Assuming that G is approximately constant, the crystal growth rate changes according to the temperature gradient distribution of the melt, and crystal growth is promoted where the temperature gradient is small. As shown in Figure 2 (a), when the interface temperature gradient at the center axis of the crucible is small, crystal growth near the center axis is fast, the crystals grow in a convex shape in the melt, and the bottom of the crucible is flat. If so, the tail of the crystal will come into contact with the bottom of the crucible and the crystal will fall off the pulling shaft. Next, when the bottom of the crucible is made spherical, the temperature gradient around the interface becomes almost uniform compared to when the bottom of the crucible is flat, as shown in Figure 2 [0]). The shape of the crucible is flat or slightly convex with respect to the melt, thereby avoiding the problems that would occur if the bottom of the crucible was flat. Assuming that the diameter of the body of the crucible is 2r and the radius of curvature of the bottom of the crucible is R, from the results of experiments, it is most desirable that 2r/R21, but it is desirable that at least 2r/R≧0.75.

Furthermore, in order to lower the dislocation density, it is necessary to reduce the interface temperature gradient, which imposes restrictions on the interface temperature gradient.

If the dislocation density (EPD) is to be less than 5 xlo'Clm-'', the interfacial temperature gradient must be less than 40° (: / Cm), and in order to sustain the growth of the single crystal, the interface temperature gradient must be less than 5°. Must be C/ or higher.

(Example) The present invention will be explained below based on Examples.

An undoped semi-insulating GaAs single crystal with a diameter of approximately 4 inches is grown by the high-pressure LEC method. In the method of the present invention, the radius of curvature of the spherical surface of the crucible is set to 156 eaves, and the temperature gradient in the melt near the interface is set to 20°C/ cva, in the conventional method, the bottom of the crucible is made flat and the temperature gradient in the melt near the interface is set at 50° (/cm
And so.

The single crystal growth conditions are as follows.

Ga (purity 99.99995%) 2500gAs
(Purity 99.99999%) 2718gBzOi
700g crucible
PBN (pyrolytic boron nitride) A “Gas pressure 10kg/cJ Pulling speed
5~10+a/llr upper shaft rotation
6rρm lower shaft rotation
The weight of the single crystal formed at 2Orpm was about 5100 g in the method of the present invention and about 4000 g in the conventional method. Table 1 shows the results of measuring the average dislocation density (EPD) of the front and tail portions of the single crystal.

From the results shown in Table 1, the present invention can reduce the dislocation density and increase the weight of the single crystal formed compared to the conventional method.

〔Effect of the invention〕

As explained above, according to the present invention, the shape of the crucible bottom is made partially spherical, and the temperature gradient in the melt near the solid-liquid interface is reduced by 5.
Since the temperature is controlled between °C/cta and 40"C7cm, it is possible to prevent the crystal interface from growing convexly and contacting the bottom of the crucible, thereby obtaining a heavy single crystal with a low dislocation density. It has the beneficial effect of being able to.

[Brief explanation of the drawing]

Figure 1 is a sectional view of the main parts of a single crystal pulling device using the LEC method.
FIG. 2(a), 0)) is a diagram illustrating the relationship between the magnitude of heat inflow and crystal growth. 1...Heat-resistant container, 2...Inert gas atmosphere, 3
...Upper axis, 4...Lower axis, 5...Heater,
6... Susceptor, 7... Crucible, 8... Raw material melt, 9... B20. Melt, 10... Single crystal,
11...Seed crystal, 12...High pressure seal.

Claims (1)

[Claims] In the method of pulling a single crystal by the liquid capsule Czochralski method, the shape of the crucible bottom is made into a partially spherical shape convex to the outside, and the ratio of the radius of curvature R of the partially spherical shape to the crucible body diameter 2r is 0.75. ≦2r/R≦2, and the temperature gradient in the melt near the solid-liquid interface between the single crystal and the melt is 5
A method for pulling a single crystal, characterized in that the pulling temperature is ℃/cm or more and 40℃/cm or less.