JP3461559B2 - Cerium-activated gadolinium silicate single crystal growth method - Google Patents

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 used in electronic equipment and the like.

[0002]

2. Description of the Related Art In a method in which a seed crystal is brought into contact with a raw material melt and a single crystal is grown while gradually pulling up the seed crystal, the conventional rotation speed of the shoulder is such that the melt is separated from the melt (the seed crystal is cut from the melt). Therefore, the growth is carried out at a rotation speed lower than or the same as the rotation speed at the time of growing the straight body portion which is the parallel portion thereafter. (Reference Kazumasa Takagi, Mitsuru Ishii: Laboratory of Experimental Physics 13, Sample Preparation and Processing: Kyoritsu Shuppan (1981) P.381)

[0003]

However, according to this method, the shape of the solid-liquid interface, which changes depending on the size of the diameter (peripheral velocity), changes greatly from the shoulder to the boundary between the parallel portions, so that strain at the upper portion of the crystal becomes large. Take in. This is a residual strain, and a brittle crystal having characteristics such as anisotropy in thermal expansion and cleavage is problematic in that cracks occur near the crystal shoulder during or after the cooling of the growth. The present invention provides a method for growing a single crystal in which cracking does not occur.

[0004]

In order to achieve the above object, the inventors of the present invention heated a raw material in a crucible to form a melt, and brought the lower end of the seed crystal into contact with the melt to form the seed crystal. Cerium activated gadolinium silicate that grows single crystals while pulling
The growth conditions for shoulder formation, which is the process of expanding the crystal size from the seed crystal to the target size in the growth of the um single crystal, were examined. As a result, the rotation speed at the time of shoulder formation is made larger than that at the time of growing the straight body part which is the parallel part thereafter, and the peripheral speed is changed by the crystal diameter so as to be almost constant, or at the time of shoulder formation. by the rotation speed constant speed greater Ri by the parallel portion, by finding that the object can be achieved, the present invention has been made.

[0005]

[Function] The raw material in the crucible is heated to form a melt, and the lower end of the seed crystal is brought into contact with the melt to grow the single crystal while pulling up the seed crystal. The reason why cracking can be prevented by making the diameter larger than the parallel portion (straight body portion) is considered as follows. In a crystal in which the solid-liquid interface shape when pulling a single crystal is convex downward, the solid-liquid interface shape changes depending on the rotation speed and the crystal diameter, that is, the peripheral speed. The melt in the crucible has convection that flows from the outside to the vicinity of the center due to the heating of the crucible, but by increasing the rotation speed, the forced convection from the center to the outside increases. When the circumferential velocity (rotational velocity) is increased, the solid-liquid interface shape approaches a flat shape due to the effect of this forced convection. When the crystal is pulled up with the rotation speed kept constant or the shoulder rotation speed smaller than that of the parallel portion, the diameter of the shoulder portion from the seeding to the front of the parallel portion is smaller than that of the parallel portion. The velocity is small and the solid-liquid interface shape becomes more convex. Then, when the parallel portion is pulled up, the shape of the solid-liquid interface approaches a flat shape and becomes constant. Therefore, a region where the solid-liquid interface shape changes abruptly occurs from the shoulder to the initial stage of parallel growth.
Once near the center of the crystallized part at the solid-liquid interface at that time,
When the interface shape changes, melting again occurs, and the interface shape after the change causes solidification again (meltback). (Reference: Ibid.) It is considered that this causes strain due to lattice defects and causes cracks in the vicinity of shoulders in weak crystals. Therefore, according to the method of the present invention, the rotational speed at the time of forming the shoulder portion is made larger than that at the parallel portion and is changed by the crystal diameter so that the peripheral speed becomes almost constant, or the rotational speed at the time of forming the shoulder portion is changed. By making the solid-liquid interface shape at the time of shoulder formation close to the shape in the parallel section by making the constant speed larger than the parallel section, the effect of meltback is reduced and the solid-liquid interface shape is made uniform. ,
It is possible to prevent cracking.

[0006]

【Example】

Example 1 Cerium-activated gadolinium silicate single crystal (Ce: Gd ₂ S)
An example will be described in which the shoulder peripheral velocity is set to be substantially constant in the case of iO ₅ ). As a raw material, about 3260 g of Gd ₂ O ₃ ,
Approximately 540 g of SiO _{2 and} approximately 10 g of CeO ₂ with a diameter of 100 mm
Was placed in an Ir crucible of and a crystal of φ50 × 180 mm was grown by the Czochralski method. The crucible was heated by high frequency induction heating to use the raw material as a melt, and the lower end of the seed crystal was brought into contact with the crucible, and the seed crystal was grown while being pulled up at 1 to 5 mm / hour. The seed crystal was rotated at 100 rpm before seeding. By adjusting the temperature of the melt, the crystal diameter is expanded to φ50 mm while being pulled up by 30 to 50 mm, and accordingly the rotation speed is from 100 to 30 rpm and the peripheral speed is 1.25 c.
Gradually reduce it so that it is almost constant at m / sec.
Formed shoulders. Then, the automatic diameter control was started, the rotation speed was kept at 30 rpm, the parallel part was pulled up for about 180 mm, the crystal was separated, and the cooling was performed for about 50 hours.

Example 2 Cerium activated gadolinium silicate single crystal (Ce: Gd ₂ S)
An example in which the shoulder rotation speed is constant in the case of i0 ₅ ) will be described. As a raw material, about 3260 g of Gd ₂ O ₃ , about 540 g of SiO _{2 and} about 10 g of CeO ₂ were put into an Ir crucible of φ100 mm, and a crystal of φ50 × 180 mm was grown by the Czochralski method. The crucible is heated by high frequency induction heating to make the raw material a melt, and the lower end of the seed crystal is brought into contact with the melt,
It was grown while being pulled up at m / hour. The seed crystal is rotated at 40 rpm from before seeding and the temperature of the melt is adjusted so that the crystal diameter is φ while being pulled by 30 to 50 mm.
Expanded to 50 mm to form shoulders. After that, the automatic diameter control is started, the rotation speed is reduced to 30 rpm, and about 180
After pulling up the mm parallel part, the crystal was separated and cooled for about 50 hours. Comparative Example The rate of occurrence of cracks caused by growing in Example 1 and Example 2, the rotational speed of the conventional method, shoulder 25rp
In the case of the same growth at m and 30 rpm of the parallel part, the rotation speed was compared with the case of similar growth at the shoulder part of 30 rpm and the parallel part of 30 rpm. The results are shown in Table 1.

[0008]

[Table 1] GSO cracking rate ────────────────────────────────── Comparative Example Example 1 Implementation Example 2 ────────────────────────────────── Shoulder rotation speed (rpm) 25 30 100 to 30 40 ─ ───────────────────────────────── Parallel section rotation speed (rpm) 30 30 30 30 30 ─────── ────────────────────────────
Cracking Yes Yes Yes No None ──────────────────────────────────

As can be seen from this table, even in the conventional method, there was a tendency to reduce cracks by changing the rotational speed of the shoulder portion from a speed smaller than that of the parallel portion (straight body portion) to the same speed. Then, in this method, the rotation speed at the time of shoulder growth is made higher than that of the parallel portion, and the rotation speed of the shoulder portion is made smaller than that of the parallel portion by decreasing the circumferential speed to be almost constant as the diameter increases. It was also possible to prevent cracks by setting a large constant speed.

[0010]

EFFECTS OF THE INVENTION According to the growing method of the present invention, in particular, a fragile crystal having characteristics such as anisotropy in thermal expansion and cleavage, the shoulder during cooling due to residual strain and after cooling It is possible to prevent the occurrence of cracks near the portion. Further, even in a crystal in which cracking is unlikely to occur, the fact that the internal residual strain can be reduced by the present invention is effective in improving the quality of the crystal.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-7-144998 (JP, A) JP-A-54-152683 (JP, A) JP-A-59-13692 (JP, A) JP-A-60- 77197 (JP, A) JP-A-2-239183 (JP, A) JP-B-54-31470 (JP, B2) (58) Fields investigated (Int.Cl. ⁷ , DB name) C30B 1/00-35 / 00

Claims (3)

(57) [Claims] 1. A method for growing a cerium-activated gadolinium silicate single crystal in which a raw material in a crucible is heated to form a melt, the lower end of the seed crystal is brought into contact with the melt, and the single crystal is grown while pulling up the seed crystal. The rotation speed of the seed crystal during shoulder growing, which is the process of expanding the crystal diameter from the seed crystal to the target diameter, is made higher than the rotation speed during straight body growing, which is the parallel portion thereafter. Cerium-activated gadolinium silicate
Method for growing a chloride single crystal. 2. The rotational speed of the seed crystal during shoulder growth, which is the process of expanding the crystal diameter from the seed crystal to the target diameter, is the peripheral speed at the time of growing the straight body part whose peripheral speed is the parallel portion thereafter. The method for growing a cerium-activated gadolinium silicate single crystal according to claim 1, characterized in that the crystal diameter is changed so as to be substantially the same as the above. 3. The rotation speed of the seed crystal during shoulder growth, which is the process of expanding the crystal diameter from the seed crystal to the target diameter, is higher than the rotation speed during subsequent straight body growth, which is a parallel portion. Cerium according to claim 1, characterized in that the speed is set.
Method for growing activated gadolinium silicate single crystal.