JPH05319975A - Production of oxide single crystal - Google Patents

Abstract

PURPOSE:To provide an oxide single crystal production method so designed that during annealing after oxide single crystal growth by pull method, a raised part developed at the melt-solidified interface is suppressed to a minimum to avoid crystal defects due to contact of this raised part with a grown single crystal. CONSTITUTION:A seed crystal 3 is immersed in a melt 2 obtained by heating to elevated temperatures a crucible 1 having an oxide single crystal material and gradually pulled up under rotation or while revolving the crucible 1 at a constant rate to grow a single crystal 4 having the same azimuth as that of the seed crystal, and the resulting single crystal 4 is separated from the melt 2 left in the crucible and annealed, thus obtaining the objective oxide single crystal. In this case, the value A/T is set at <=0.60 (where, A is the height of the melt left in the crucible after solidification; T is the diameter of the crucible), and the rate of cooling the remaining melt during annealing is set at 50-80 deg.C/hr.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an oxide single crystal by a pulling method.

[0002]

2. Description of the Related Art The pulling method, which is one of the methods for growing a single crystal, is also known as the Czochralski method or the rotary pulling method, and is generally used in a crucible 1 heated to a high temperature as shown in FIG. A polycrystal melt 2 is put in the flask, a seed crystal 3 is put in from above, and the seed crystal 3 or the crucible 1 is gradually pulled up while rotating at a constant speed. Is a method of raising. Reference numeral 5 is a quartz tube, 6 is a work coil of a high frequency induction heater, and 7 is an after-heater. The upper and lower ends of the quartz tube 5 are sealed, and a predetermined inert gas is introduced from a gas inlet port (not shown). ing. The after-heater 7 is arranged at a position covering the periphery of the grown single crystal 4.

When the single crystal 4 having a constant size grows, the single crystal 4 and the remaining melt 2 are separated and gradually cooled so that the single crystal 4 is not cracked. As the slow cooling method, a method of gradually decreasing the output of the work coil 6 of the high frequency induction heater is usually used. By this slow cooling method, the temperature of the after heater 7 made of Pt, which was heated to a high temperature, is slowly decreased, and the radiant heat to the grown single crystal 4 is gradually reduced, and the cracks or cracks, and further bubbles or transitions. Is prevented from occurring.

Further, by gradually decreasing the output of the work coil 6, the temperature of the crucible 1 also gradually decreases, the temperature of the melt 2 remaining in the crucible 1 gradually decreases, and finally solidifies.

[0005]

As described above, in the method of growing a single crystal by the pulling method, the grown single crystal 4 is separated from the melt 2 and then the output of the work coil 6 is gradually reduced to cause cracking. Although attention is paid so that cracks do not occur, oxide B is an oxide single crystal among several types of optical crystals.
i ₁₂ GeO ₂₀ (hereinafter abbreviated as BGO) and Bi ₁₂ SiO
It has been recognized that there are the following problems when training ₂₀ (hereinafter abbreviated as BSO).

That is, many substances serving as crystallization nuclei are present in the remaining melt 2, and the BGO and BSO have α phase (monoclinic), β phase (tetragonal) and γ (cu).
bic), the melt 2 is crystallized in a pumice-like complex manner during slow cooling, and a ridge 2a of height t is formed at the solidification interface of the melt 2 as shown in FIG. The rising portion 2a may come into contact with the tail portion of the grown crystal separated.

According to the experiment, after growing the single crystal 4, 50c
If 40 cc of residual melt 2 is present in the crucible 1 of c (φ45 × t50), the height t is 8 at the center of the solidification interface.
It was observed that the raised portion 2a of about mm was formed.

After being normally grown, the single crystal 4 is kept at a position where the distance from the melt 2 is not more than 5 mm at the maximum so that defects due to temperature shock do not occur in the cooling process after being separated from the melt 2. Has been done. Therefore, when the solidified interface of the melt 2 rises to 5 mm or more due to the slow cooling, the raised portion 2a comes into contact with the single crystal 4 after the growth, and the single crystal 4 is partially deformed. Defects are likely to occur. There is a problem that the oxide single crystal 4 having such defects cannot be used as an optical crystal.

Therefore, the present invention solves the problems that occur during the growth of such conventional oxide single crystals, and minimizes the bulge portion formed at the solidification interface of the melt during slow cooling after the growth of the single crystal. It is an object of the present invention to obtain a method for producing an oxide single crystal, which can suppress the crystal defects caused by the contact of the raised portion with the grown single crystal.

[0010]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention immerses a seed crucible in a melt obtained by heating a crucible containing a raw material of an oxide single crystal to a high temperature. Or gradually pulling up the seed crystal while rotating the crucible at a constant speed to grow a single crystal in the same orientation as the seed crystal, and to oxidize the obtained single crystal so that it is slowly cooled by separating it from the remaining melt. In the method for producing a material single crystal, the residual melt amount A / T expressed by using the height A of the residual melt in the crucible after solidification and the diameter T of the crucible is set to 0.60 or less, and at the time of slow cooling. The cooling rate of the residual melt is set to 50 to 80 ° C./Hr.

[0011]

According to such a method for producing an oxide single crystal, it is possible to minimize the rising portion of the solidification interface of the melt during the slow cooling after growing the single crystal by the pulling method, and at least the rising portion. It is possible to prevent the parts from coming into contact with the separated single crystal, and to eliminate the crystal defects such as cracks and cracks of the single crystal due to such contact.

[0012]

EXAMPLES Specific examples of the method for producing an oxide single crystal according to the present invention will be described below. Using the apparatus for producing an oxide single crystal by the pulling method shown in FIG. 1, the following experiment was conducted.

First, the basic operation will be described. The quartz tube 5
A raw material of BGO is put into a 50 cc (φ45 × t50) crucible 1 made of Pt arranged inside, the crucible 1 is heated to a high temperature to form a melt 2, and a seed crystal 3 is poured from above,
The seed crystal 3 is gradually pulled up while rotating at a constant speed. Then, the single crystal 4 having the same orientation as the seed crystal 3 grows.

When a single crystal 4 having a constant size grows,
The single crystal 4 and the remaining melt 2 are separated and gradually cooled.
As this gradual cooling method, a usual method, that is, a method of gradually decreasing the output of the work coil 6 of the high frequency induction heater is used.
By this gradual cooling method, the temperature of the after-heater 7 which was heated to a high temperature is slowly decreased, the radiant heat to the grown single crystal 4 is gradually decreased, and the temperature of the crucible 1 is gradually decreased and remains. The temperature of the melt 2 is gradually decreased and finally solidified.

Then, single crystals 4 having a diameter of 23 mm were individually grown under the conditions shown in Table 1, and after the single crystals 4 after growth were separated from the remaining melt 2, the solidified interfaces of the melt 2 were gradually cooled during slow cooling. The height t (mm) of the formed raised portion 2a is measured, and the influence of the residual melt amount (A / T) and the cooling rate (° C / Hr) on the height t of the raised portion 2a is investigated. It was

[0016]

[Table 1]

The residual melt amount (A / T) in Table 1 is the height A of the residual melt 2 in the crucible 1 after solidification as shown in FIG.
And the diameter T of the crucible 1 (inner diameter). The cooling rate (° C / Hr) was expressed by using the temperature drop per unit time.

First, in order to see the influence of the above-mentioned residual melt amount,
The cooling rate of the single crystal 4 during slow cooling is 80 (° C / Hr)
The experiment was conducted by changing the residual melt amount (A / T).
As a result, the residual melt amount of the samples NO1 and NO2 was 0.90.
And 0.75, the interfacial heights t after solidification were 8.5 mm and 7.0 mm, respectively, and it was found that the heights t greatly exceeded the height limit of 5 mm. When the residual melt amounts of the samples NO3 and NO4 are 0.60 and 0.45, the interface heights t after solidification are 4.0 mm and 1.0 mm, respectively, which is the height limit of 5 mm or less. Was confirmed. Furthermore, the residual melt amount of sample NO5 is 0.3
In the case of 0, swelling of the interface after solidification was not observed.

Next, in order to examine the effect of the cooling rate (° C / Hr), the residual melt amount (A / T) was set to 0.50 and the cooling rate (° C / Hr) was changed to 120, 50, 30. I conducted an experiment. As a result, when the cooling rate is 120 (° C./Hr), the interface between the vicinity of the crucible 1 and the melt 2 solidifies while the temperature drops more rapidly than the inside of the melt, and is not partially solidified. A phenomenon was observed in which the melt 2 inside was violently blown from the center of the interface and solidified while rising on the surface, and the interface height t after solidification reached 8.0 mm.

The cooling rate is 50 (° C / Hr), 30
In the case of (° C./Hr), the interface height t after solidification was 2.0 mm and 0 mm, respectively, and it was confirmed that the height limit was 5 mm or less. The cooling rate is 50 (° C /
Even if it is set to Hr) or less, good results are obtained, but under such conditions, it takes a long time for cooling, which causes a difficulty in productivity and profitability. Therefore, the lower limit of the cooling rate is set. It was set to 50 (° C / Hr).

From the above results, it is appropriate that the residual melt amount (A / T) is 0.60 or less, and the cooling rate during slow cooling (° C / H)
It was found that r) of 50 to 80 is suitable. In the above example, the oxide single crystal was Bi ₁₂ GeO ₂₀ (B
GO) was used, but Bi ₁₂ Si which is another oxide single crystal
It was found that almost the same result was obtained even when O ₂₀ (BSO) was used.

[0022]

As described above in detail, according to the method for producing an oxide single crystal according to the present invention, the rising portion of the solidification interface of the melt is formed during the slow cooling after growing the single crystal by the pulling method. It is possible to minimize and at least prevent the raised portion from coming into contact with the separated single crystal, thereby eliminating crystal defects in the single crystal due to the contact.

Therefore, an oxide single crystal, for example, B, in which a large amount of a substance serving as a crystallization nucleus exists in the remaining melt.
Even when an oxide single crystal such as i ₁₂ GeO ₂₀ or Bi ₁₂ SiO ₂₀ is produced, the swelling portion at the solidification interface hardly occurs due to the presence of the residual melt after the growth of the single crystal. The resulting single crystal can be given a high quality suitable for use as an optical crystal.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an apparatus for producing a single crystal by a pulling method used in the present invention.

FIG. 2 is an enlarged sectional view of an essential part showing a state during cooling in the single crystal manufacturing apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Crucible 2 ... Melt 2a ... Rising part 3 ... Seed crystal 4 ... Single crystal 5 ... Quartz tube 6 ... Work coil 7 ... After heater

Claims (2)

[Claims] 1. A raw material for an oxide single crystal is placed in a crucible,
A seed crystal is placed in a melt obtained by heating the crucible to a high temperature, and the seed crystal is gradually pulled up while rotating the seed crystal or the crucible at a constant speed to grow a single crystal having the same orientation as the seed crystal. In the method for producing an oxide single crystal in which the obtained single crystal is separated from the residual melt and gradually cooled, the height A of the residual melt in the crucible after solidification and the diameter T of the crucible
The residual melt amount A / T expressed by using
The cooling rate of the residual melt during slow cooling is 50 to 80 ° C / Hr.
The method for producing an oxide single crystal is characterized in that 2. The method for producing an oxide single crystal according to claim 1, wherein the oxide single crystal is Bi ₁₂ GeO ₂₀ or Bi ₁₂ SiO ₂₀ .