JP3115145B2 - Single crystal manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a single crystal, and more particularly to a method for producing lithium niobate as an optical single crystal and bismuth germanate as a scintillator crystal by the Bridgman method.

[0002]

2. Description of the Related Art Conventionally, lithium niobate (hereinafter abbreviated as LN) as an optical single crystal and bismuth germanate (hereinafter abbreviated as BGO) as a scintillator crystal have been produced by the Czochralski method. Recently, however, a method of growing by the Bridgman method has been proposed, which is performed by using a seed crystal stored in a seed tube (Japanese Patent Laid-Open No. 2-271989, Kaihei 3-
No. 290390).

However, since the crystal growth rate of the Bridgman method is lower than that of the Czochralski method, the use of a seed tube increases the time from the small diameter of the seed tube to the diameter of the body of the crystal. However, there is a disadvantage that productivity is deteriorated. Therefore, the present inventors have proposed an example of eliminating this disadvantage as a method for producing a lithium tetraborate single crystal, including an example of growing a crystal using a seed crystal having a diameter equal to the body diameter of the crystal, An embodiment in which the inner diameter of the seed tube is increased is disclosed (see Japanese Patent Application No. 4-80430).

[0004]

However, LN and B
When the GO crystal was grown from a seed tube having a large inner diameter, there was no particular problem up to a seed tube diameter of about 5 mm, but when the seed tube diameter was increased to 50 mm or more, Although the time from the seed portion to the body portion could be remarkably reduced, in this case, there was a problem that the obtained single crystal was cracked, and it was found that this measure was required.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method for producing a single crystal which solves such disadvantages and problems, and which grows a single crystal from a melt using a seed crystal by the Bridgman method. In the method, the inner diameter of the seed tube is set to D (m
m), and when the thickness of the seed crystal to be used is T (mm), this D and T satisfy the relation of T <(3.75 × 10 ³ / D) −15. It is assumed that.

That is, the present inventors have made various studies on the method of growing a single crystal by the Bridgman method, and found that a single crystal was manufactured by preparing a crucible in which the inner diameter of a seed tube was variously changed. However, the inner diameter of the seed tube is D (m
m), when the thickness of the seed crystal used is T (mm), the relationship between D and T is such that T <(3.75 × 10 ³ / D) −15 is satisfied, thereby preventing cracks in the crystal. The inventors have found out what can be done and completed the present invention. This is described in more detail below.

[0007]

The present invention relates to a method for producing a single crystal, which is a method for growing a single crystal from a melt by a Bridgman method using a seed crystal, wherein the inner diameter of the seed tube is D (mm).
And when the thickness of the seed crystal to be used is T (mm),
It is characterized in that D and T satisfy the relationship of T <(3.75 × 10 ³ / D) −15. According to this, the occurrence of cracks in the crystal is prevented. Therefore, there is an advantage that a target single crystal can be obtained with high yield.

The production of a single crystal according to the present invention is performed by the Bridgman method as described above. This Bridgman method is known, and is carried out, for example, with the apparatus shown in FIG. FIG. 1 is a longitudinal sectional view of a single crystal growing apparatus using the Bridgman method, in which a platinum crucible 2 is installed in an electric furnace 1 and a polycrystal charged in the platinum crucible. The body is heated by a heater (not shown) and held as a melt 3 in the crucible 2.
A seed tube 4 is provided below the platinum crucible 2, and a seed crystal 5 is inserted at the tip thereof.

In the growth of a single crystal by this apparatus, the temperature of the seed crystal portion is maintained slightly higher than the melting point of the crystal, and a part of the seed crystal is melted to bring the melt 4 completely into contact with the seed crystal. The speed of this is adjusted according to the crystal grown below the furnace 1 maintained at a lower temperature, for example, 0.3 to 10 mm for an LN crystal.
/ H, about 15 mm at a descent speed of 0.1 to 5 mm / h for BGO crystal.
When the melt 3 is lowered by 0 mm, the melt 3 grows into a single crystal in the crucible 2, so that the platinum crucible may be taken out after the furnace temperature is lowered to room temperature after descending, and the platinum may be broken and taken out.

However, in this case, if the inner diameter of the seed tube 4 is increased in order to improve the productivity of the single crystal, it has been confirmed that cracks occur in the grown single crystal. A crucible in which the inner diameter of the seed tube 4 is D (mm), the thickness of the seed crystal 5 is T (mm), and the inner diameter D of the seed tube 4 and the thickness T of the seed crystal are variously changed is prepared. When a single crystal was grown by changing the temperature at the start of crystal growth and the crucible position, the thermal stress at the time of seeding was not eliminated under the condition of T ≧ (3.75 × 10 ³ / D) −15 for D and T. Although cracks occur in the grown single crystal,
When D and T satisfy the relationship of T <(3.75 × 10 ³ / D) −15, it was found that no crack was generated in the grown single crystal.

Therefore, in growing a single crystal by the Bridgman method, the inner diameter D of the seed tube and the thickness T of the seed crystal are set so as to satisfy the relationship of T <(3.75 × 10 ³ / D) −15, If the seed crystal is melted to a desired thickness in accordance with the inner diameter D of the seed tube so that the seed crystal is deformed in the seed tube, the thermal stress can be eliminated, and thus cracks in the grown single crystal can be eliminated. The advantage is given that the occurrence is prevented.

Although the inner diameter of the seed tube may be different from the inner diameter of the body of the platinum crucible, the workability of the crucible is improved, the necessity of forming a cone is eliminated, and the productivity is improved. It is preferable that the inner diameter of the seed tube is equal to the inner diameter of the body of the crucible.

[0013]

Next, examples of the present invention and comparative examples will be described. Example 1, Comparative Example 1 After mixing lithium carbonate having a purity of 4N and niobium pentoxide at a ratio of 1: 1 (molar ratio), the mixture was calcined at 1,200 ° C., and two pieces having an inner diameter of 80 mm and a length of 180 mm were obtained. Each of the platinum crucibles
2,300g was charged at a time.

Then, a disc-shaped seed crystal having a diameter of 77 mm and a thickness of 50 mm housed in a seed tube having an inner diameter of 77 mm is inserted into these crucibles, and the peak temperature of the furnace is set at 1,300 ° C. so that the seed crystal is not completely melted. The temperature near the seed crystal is slightly higher than the melting point of the LN crystal, the growth position is changed by 20 mm for the two crucibles, the seed crystal is partially melted, and the crystal is grown at a descent rate of 0.5 mm / hour. After growing the platinum crucible and examining the thickness of the seed crystal and the presence or absence of cracks in the grown crystal, the higher the growing position, the seed crystal thickness was 25 mm and no cracks were observed, but the lower growing position On the other hand, the seed crystal had a thickness of 42 mm and cracks were observed in the grown crystal.

Example 2, Comparative Example 2 Bismuth oxide having a purity of 4N and germanium dioxide were mixed with
After mixing at a ratio of 3 (molar ratio), calcine at 900 ° C,
A seed tube with a diameter slightly smaller than this inner diameter and finished to a length of 65 mm was inserted into a seed tube with an inner diameter of 50 mm to 150 mm.
12,000 g of the calcined raw material was charged into a 50 mm, 200 mm long platinum crucible for the Bridgman method.

Next, in order not to completely melt these seed crystals, the peak temperature of the furnace was set to 1,200 ° C., the temperature in the vicinity of the seed crystals was slightly higher than the melting point of the BGO crystal, and the seeding crystal was grown by changing the growth starting position. The crystals were partially melted and grown at a descent rate of 0.5 mm / hr. After growth, the platinum crucible was broken to take out a single crystal, and the thickness of the seed crystal and the presence or absence of cracks in the grown crystal were examined. Based on this figure, the seed tube inner diameter on the horizontal axis of this graph was defined as the reciprocal of the seed tube inner diameter (1 / seed tube inner diameter), and the relationship between this and the seed crystal thickness was examined. However, the result as shown in FIG. 3 was obtained.

[0017]

The present invention relates to a method for producing a single crystal, which is a method for growing a single crystal from a melt by a Bridgman method using a seed crystal as described above. (Mm) and the thickness of the seed crystal used is T
(Mm), D and T satisfy the relation of T <(3.65 × 10 ³ / D) −15. Since the occurrence of cracks in the single crystal obtained by increasing the diameter of the crucible and having the same diameter as the body of the crucible is prevented, the advantage that the desired single crystal can be obtained with good yield is provided. Can be

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a single crystal manufacturing apparatus according to the Bridgman method used in the present invention.

FIG. 2 is a graph showing the relationship between the inner diameter of a seed tube and the thickness of a seed crystal during the production of a single crystal according to an embodiment of the present invention.

FIG. 3 is a graph showing the relationship between the reciprocal of the inner diameter of a seed tube and the thickness of a seed crystal during the production of a single crystal according to an embodiment of the present invention.

[Explanation of symbols]

 1: electric furnace, 2: platinum crucible, 3: melt, 4: seed tube, 5: seed crystal.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Toshihiko Nagao 2-13-1 Isobe, Annaka-shi, Gunma Prefecture Shin-Etsu Chemical Co., Ltd. Precision Functional Materials Research Laboratories (56) References JP-A-3-40987 ( JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C30B 11/00-11/14 C30B 28/00-35/00

Claims (3)

(57) [Claims] In a method for growing a single crystal from a melt by a Bridgman method using a seed crystal, the inner diameter of the seed tube is set to D.
(Mm), and when the thickness of the seed crystal to be used is T (mm), it is assumed that D and T satisfy the relation of T <(3.75 × 10 ³ / D) −15. Characteristic single crystal production method. 2. The method according to claim 1, wherein the single crystal is lithium niobate. 3. The method for producing a single crystal according to claim 1, wherein the single crystal is bismuth germanate.