JPS63182289A - Method for growing single crystal - Google Patents

Abstract

PURPOSE:To prevent the generation of the segregation of impurities and strains and to grow a uniform high-quality single crystal by arranging a specified barrel supported by an auxiliary shaft in a raw material melt, and moving the barrel as the single crystal grows at the time of growing a single crystal by a pulling up method. CONSTITUTION:The auxiliary shaft 6 is provided in a high-frequency heating crystal pulling up device, the barrel 8 made of platinum, etc., having 10-50mm length and the outer diameter within + or -10mm of the difference between the outer diameter and the diameter of the single crystal to be grown is arranged in the raw material melt 2 in the platinum crucible 1 so that the upper end of the barrel is always positioned at the distance 2-15mm below the surface of the melt, and the position of the barrel is made adjustable through a support 7. A seed crystal 4 fixed to the tip of a lifting shaft 3 is dipped in th3 melt 2, a single crystal 5 is pulled up while being rotated, the barrel 8 is lowered in accordance with the lowering of the surface of the melt 2, the natural convection of the melt 2 is controlled by the barrel 8 to keep the solid-liq. interface flat, and the high-quality single crystal 5 is grown.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for growing single crystals by the Czochralski method.

[Conventional technology]

The pulling method is one of the most common methods for growing single crystals, and its heating methods include resistance heating using a carbon heater, etc., and direct heating of a metal crucible using high frequency heating. . In the case of high-frequency heating, high-melting point noble metals such as platinum, platinum-rhodium, and iridium are generally used as the material for the crucible. Furthermore, for the purpose of improving the shape controllability of the single crystal to be grown, a method called a coracle in which a ring is floated on the raw material melt surface is also known. Furthermore, a method is known in which the crucible has a double structure for the purpose of uniformizing the composition of the raw material melt for growing a single crystal.

One of the problems with growing single crystals by the pulling method is the difficulty in controlling the shape of the solid-liquid interface. In order to grow a strain-free single crystal, it is desirable that the solid-liquid interface be flat, but it is difficult to flatten the solid-liquid interface due to effects such as natural convection caused by heating the crucible or forced convection caused by the rotation of the pulled crystal. difficult to maintain.

[Problem that the invention seeks to solve]

The present invention aims to eliminate the drawbacks of conventional single crystal growth methods and provide a single crystal growth method that makes it possible to pull a single crystal while maintaining a flat solid-liquid interface by completely suppressing natural convection. That is.

[Means for solving problems]

The present invention has the following features: (1) A raw material placed in a crucible is melted in a bath by high-frequency heating, a seed crystal is immersed, and the cylinder is pulled while rotating.In the total single crystal growth method, a cylinder supported by a secondary axis is placed in the raw material melt. A method for growing a single crystal characterized by arranging and moving the single crystal as it grows. (2) The method for growing a single crystal according to item (1) above, characterized in that the upper end of the cylinder is adjusted to be located 2 m to 15 cm below the surface of the raw material melt. (3) The method for growing a single crystal according to item (1) or item (2) above, wherein the length of the cylinder is 10 m to 50 m. (4) The outer diameter of the above cylinder is
The single crystal growing method described in item (3) above is characterized in that the diameter of the single crystal to be grown is within a range of ±10 m.

FIG. 1 shows an apparatus for carrying out the present invention, in which a sub-shaft 6 is provided in a normal high-frequency heating single crystal pulling apparatus, and a support 7 is provided.
The cylinder 8 fixed by is submerged in the raw material melt 2. The cylinder 8 is moved up and down by the subshaft 6, so that the upper end of the cylinder is always located at a constant distance from the surface of the raw material melt. A nine-seed crystal 4t is attached to the tip of a pulling shaft 3 into the raw material melt 2 in the crucible 1, and the single crystal 5 is pulled up while rotating it. As the liquid level of the raw material melt 2 falls as it is pulled up, the cylinder 8 is lowered to match it. Note that 9 is a heater, 10 is a heat insulating material, and 11 is a thermocouple for measuring the melt temperature.

[Effect]

FIG. 2 shows the relationship between the rotational speed W of the pulled crystal and convection in the melt. The number of rotations W of the pulled crystal increases in the order of (a), (1)), (C), and (d). When the crystal rotation speed w1 is small (a), natural convection from the side of the crucible toward the center is dominant, and the solid-liquid interface becomes convex downward. At such times, impurity segregation, the appearance of facets (preferential growth surfaces), and the generation of strain may occur, causing cracks. In other words, when the solid-liquid interface becomes convex downward, nine crystal planes with various angles appear, so strain is induced at the interface between the fast-growing preferential growth plane and other planes, and impurities are removed. I get pushed into it. Furthermore, as the crystal rotation speed W2 increases, the forced convection from the center to the outside increases, and the solid-liquid interface finally becomes convex upward (Ill). There is a crystal rotation speed W3 in the middle where the solid-liquid interface becomes flat (C), but the appearance of these convections varies depending on the depth of the raw material melt and the weight of the grown crystal, so it is always optimal. It is difficult to maintain the rotation speed. In the present invention, by submerging the circle WU8 into the raw material melt 2, natural convection from the side of the crucible toward the center is suppressed. As a result, convection is weak near the solid-liquid interface,
It becomes relatively easy to flatten the solid-liquid interface and maintain that state. By flattening the solid-liquid interface, segregation of impurities and generation of strain are suppressed, and a homogeneous and high-quality single crystal can be obtained.

Note that the outer diameter of the cylinder is preferably within a range of ±10 m with respect to the diameter of the single crystal. Rotating the growing crystal is essential to increase the axial symmetry of the crystal's temperature environment, but the forced convection that accompanies rotation tends to convex the solid-liquid interface upward, and this effect can be minimized. In order to do this, the diameter of the cylinder can be made smaller to introduce more flow toward the center of the crucible. FIG. 3 is a diagram for explaining the relationship between the cylinder diameter, single crystal diameter, and crystal rotation speed. Figure 3 (II
L) has a relatively low crystal rotation speed Wa, so there is a weak tendency to make the solid-liquid interface convex upward, and the cylinder diameter can be relatively large, but
When the crystal rotation speed wb is relatively high as shown in Figure 3(b), there is a strong tendency for the crystal to convex above the solid-liquid interface, so the cylinder diameter is made relatively small to reduce the flow toward the center of the crucible. It is better to introduce many different types. In this way, it is preferable to select the diameter of the cylinder depending on the convection situation of the melt.

〔Example〕

Using the pulling device shown in FIG. 1, bismuth silicon oxide 81. ．． A single crystal was grown at 10 w per day (hereinafter abbreviated as B2O). Bismuth oxide (Bi203) and silicon oxide (Sin, ) were mixed at a molar ratio of 6:1 in a cylindrical platinum crucible with an inner diameter of 100+omφ and a depth of 150 m, and the next raw material was charged at 78,009 m.

After the raw material was melted in a t-bath by high-frequency heating, a platinum cylinder attached to a subshaft was submerged in the melt. The shape of the cylinder has an inner diameter of 52
It has a diameter of 1aIIIφ, a length of 20mm, and a wall thickness of α5m. A seed crystal T attached to a pulling shaft was immersed in the raw material melt and pulled up while rotating to fully grow a single crystal. The pulling speed is t
Owai, / k, rotation speed from 20 rpm to 8 r, p
It was changed continuously to m. The platinum cylinder was moved by the counter shaft as the liquid level decreased until the upper end was located 5 mm below the surface of the raw material melt.

The obtained BSO single crystal had a diameter of 50 m+φ, a straight body length of 60 wm, a crystal weight of 1400 f, and was of good quality without any zigzag, core, or distortion.

This B2O had high homogeneity so that it could be used as an optical element for original image processing elements, hologram elements, optical electrolytic sensors, and the like.

〔Effect of the invention〕

By adopting the above configuration, the present invention facilitates flattening of the solid-liquid interface, and as a result, there is no segregation of impurities or generation of distortion in the grown crystal, and it is possible to obtain a uniform, high-quality single crystal. did it.

[Brief explanation of the drawing]

Figure 1 is a front cross-sectional view of a crystal pulling apparatus for carrying out the present invention, and Figures 2 (a) to (d) are for explaining the relationship between the rotational speed W of the pulled crystal and convection in the melt. Schematic diagram, Figure 3 (
a) and <b) are diagrams for explaining the relationship between the cylinder diameter, the single crystal diameter, and the crystal rotation speed. Figure 3 (hi (b,)

Claims (4)

[Claims] (1) The raw material placed in a crucible is melted by high-frequency heating, a seed crystal is immersed, and the single crystal is pulled up while rotating. In this method, a cylinder supported by a secondary shaft is placed in the raw material melt and a single crystal is grown. A method for growing a single crystal, characterized by moving the single crystal as it grows. (2) The upper end of the above cylinder is 2 mm to 1 mm from the raw material melt surface.
2. The method for growing a single crystal according to claim 1, wherein the single crystal is adjusted to be located 5 mm below. (3) The method for growing a single crystal according to claim 1 or 2, wherein the length of the cylinder is 10 mm to 50 mm. (4) The method for growing a single crystal according to claim 3, wherein the outer diameter of the cylinder is within ±10 mm of the diameter of the single crystal to be grown.