JPH0822799B2 - Method for producing oxide single crystal - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an oxide single crystal such as LiNbO ₃ or LiTaO ₃ , and more particularly to a method for producing such an oxide single crystal by a pulling method. It is a thing.

(Background Art) Conventionally, as a method for producing this type of oxide single crystal,
Various methods are known, but the pulling method (Czochralski method), which is one of them, is a method of pulling a target oxide single crystal from a melt in a crucible while growing it. It has been put to practical use as a method for producing a high-quality oxide single crystal with a caliber.

By the way, in order to grow a high quality single crystal by such a pulling method, it is important to control the solid-liquid interface of the single crystal. For this reason, conventionally, in order to heat the crucible containing the melt. The single crystal is grown by moving the work coil of (1), slowing the relative number of rotations of the crucible and the single crystal, or reducing the pulling speed. It is said that it is desirable that the solid-liquid interface shape is flat in order to grow a good quality single crystal. If the solid-liquid interface shape is not flat, macroscopic defects such as cracks and bubbles will appear in the single crystal grown by pulling.

However, there is a problem in that it is difficult to control the solid-liquid interface of the single crystal in the pulling method in a good condition only by changing the conditions proposed in the related art, and thus a good single crystal cannot be obtained.

(Problem to be Solved) Here, the present invention has been made in view of such circumstances, and the problem is that the shape of the melt-solid interface at the time of pulling the oxide single crystal in the pulling method It is to provide a method capable of effectively controlling

(Solution) The present invention, in order to solve such a problem, when growing an oxide single crystal from a melt in a crucible by a pulling method, the ratio of the crystal diameter of the pulled single crystal to the crucible inner diameter is 0.65. The gist of the invention is a method for producing an oxide single crystal, which is characterized in that the growth is performed at 0.75 or less.

(Concrete Structure / Function) In summary, it has been conventionally known that the solid-liquid interface shape depends on the rotation speed of the crystal when pulling the oxide single crystal in the pulling method, but the present inventors have made various studies. As a result, it was found that the solid-liquid interface shape depends on the ratio (crystal diameter / crucible diameter) between the pulled crystal and the inner diameter (diameter) of the melting crucible used for pulling, and the present invention is , Was completed based on such knowledge.

That is, an example of the pulling method is schematically shown in FIG. 1. In such pulling method, the crystal diameter (L) is
As the ratio of the / crucible diameter (φ) increases, the solid-liquid interface shape of the crystal becomes a convex shape downward, and in the present invention, the crystal has such a L / φ ratio of 0.65 to 0.75. It is intended to grow a single crystal obtained by making the solid-liquid interface shape flat or slightly convex to improve the crystallinity, thereby suppressing the generation of crystal defects. Has improved the quality of.

The present invention can be applied to any of various methods known as a pulling method, thereby advantageously providing an oxide single crystal such as LiNbO ₃ and LiTaO ₃ produced by such a pulling method. It is a thing.

For example, in the pulling method schematically shown in FIG. 1, a high-frequency induction heating furnace is used, and the work coil (induction coil) 2 thereof heats the crucible 4. Then, in the crucible 4, a melt 6 of an oxide that gives a target single crystal is housed, and the melt 6 is seeded with a seed crystal in a known manner. While growing the crystal, the grown single crystal 8 is gradually pulled out from the melt 6. In addition,
In growing such a crystal 8, the single crystal 8 is rotated around its axis or the crucible 4 is rotated as in the conventional case, so that the single crystal 8 and the crucible 4 are relatively rotated. Is performed. Also, the crystal diameter (L) of the single crystal 8
The control of (1) will be performed using a known crystal size automatic control device (ADC) or the like. This automatic crystal size controller (AD
C) is the crystal diameter (L) from the weight measurement of the grown single crystal 8.
Is measured and the heating amount by the work coil 2 or the like is controlled so that the grown single crystal 8 has a target crystal diameter (L).

In the pulling method as described above, the present invention grows the single crystal 8 so that the ratio of the crystal diameter (L) / the crucible diameter (φ) is 0.65 to 0.75, whereby the single crystal 8 is shown in FIG. As described above, the single crystal 8 having the outer shape in which the tail portion is flat or slightly convex is obtained.
When L / φ is less than 0.65, the shape ratio (a / L) of the solid-liquid interface becomes a value smaller than −0.05, and the interface shape becomes concave (upward convex) and the crystallinity deteriorates. On the other hand, when L / φ exceeds 0.75, although the interface shape is downwardly convex, the crystallinity deteriorates and it becomes difficult to improve the quality of the obtained single crystal 8. .

(Examples) Hereinafter, representative examples of the present invention will be shown to clarify the present invention in more detail. However, the present invention does not impose any restrictions due to the description of such examples. Needless to say, it is not something to receive.

First, put the LiNbO ₃ sintered body in a platinum crucible of 120 mmφ,
By high frequency induction heating, heat to 1300 ℃ and melt
Then, after seeding, the crystal shoulder is grown and the pulling speed: 3
mm / hr, crystal rotation speed: 8 rpm, crucible rotation speed: 0 rpm, the crystal diameter was set as shown in Table 1 below, and LiNbO _{3 was} controlled by the crystal diameter automatic control device (ADC). Single crystals were grown. Then, after pulling, the obtained single crystal was cut and the interface shape (a / L) thereof was observed, and the results are shown in Table 1 below. Further, the results of growing a LiNbO ₃ single crystal in the same manner as above using a 150 mmφ crucible are also shown in Table 1 below. Further, the results shown in Table 1 are shown in FIG.

From the results shown in Table 1 and FIG. 3, it was found that the solid-liquid interface was flattened or convexed downward by setting L / φ to 0.65 or more.

Further, when various crystal defects were measured for each of the various LiNbO ₃ single crystals thus obtained, when the crystal diameter / crucible diameter (L / φ) was 0.65 to 0.75, the solid-liquid interface shape (a / L ) Was -0.05 to 0.10. It was found that good crystals with few crystal defects were obtained.

In addition, the quality of crystal defects is 0.5 m from each single crystal.
A wafer having a thickness of m was cut out and judged from a photograph measured by an X-ray topography. That is, the inside of the wafer is divided into 7 mm square cells, the presence or absence of defects in the cells is measured, and the ratio of the cells having defects to all the measured cells is calculated to be 0 to 10
%: Good: ○, 10 to 20%: Medium: △, and a defect rate of 20% or more is bad: ×
And The results are also shown in Table 1 below.

(Effects of the Invention) As is clear from the above description, according to the present invention, it is possible to arbitrarily control the solid-liquid interface shape in the production of the oxide single crystal by the pulling method, which is effective. By growing at the solid-liquid interface shape, a high quality single crystal can be advantageously obtained.

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing an example of a single crystal pulling apparatus, FIG. 2 is an outline drawing showing an example of a single crystal produced by such a pulling apparatus, and FIG. ,
Various crystal diameters / crucible diameters (L / φ) obtained in the examples
3 is a graph showing the results of solid-liquid interface shape (a / L) with respect to FIG. 2: Work coil, 4: Crucible 6: Melt, 8: Single crystal

Claims (2)

[Claims] 1. When growing an oxide single crystal from a melt in a crucible by a pulling method, the growth is performed with a ratio of the crystal diameter of the pulled single crystal to the inner diameter of the crucible being 0.65 or more and 0.75 or less. A method for producing an oxide single crystal. 2. The method according to claim 1, wherein the oxide single crystal is LiNbO ₃ .