JP3573257B2 - Single crystal manufacturing equipment - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a single crystal manufacturing apparatus using a pulling method. More specifically, for example, in the production of an optical single crystal such as an oxide single crystal (more specifically, for example, strontium barium niobate (SBN)), a change in the composition of the single crystal due to a temperature change in the melt The present invention relates to a single crystal manufacturing apparatus capable of solving the problem of deterioration of crystal characteristics resulting from the above, for example, deterioration of optical characteristics such as a change in m refractive index.
[0002]
[Prior art]
Conventionally, a pulling method has been used for growing, for example, an optical single crystal that requires high quality. It is known that when the temperature of the melt fluctuates during crystal pulling in the pulling method, the crystal composition is slightly changed due to the segregation phenomenon, and as a result, the optical refractive index is also changed. An SBN crystal, which is an oxide single crystal, is also an example.
[0003]
In order to use an SBN crystal for an optical element, it is desirable to suppress the change in the refractive index to 10 ⁻⁵ or less. For this purpose, it is necessary to minimize the change in the temperature of the melt. There are two main factors that cause temperature fluctuations. One is due to the temperature fluctuation of the atmosphere gas surrounding the melt and the crucible, and the other is due to convection in the melt.
[0004]
The former can be prevented by suppressing the temperature fluctuation of the heating source, keeping the inside of the heating furnace close to hermeticity, blocking the influence of outside air, and suppressing the turbulence of the atmosphere gas. This precaution is already commonly used in crystal pullers.
[0005]
On the other hand, the temperature fluctuation of the melt due to the latter can be prevented by stopping the convection in the melt. In the case of SBN crystal, a method of reducing the depth of the melt or putting a circular metal plate in the melt to effectively reduce the influence of convection has been attempted. However, the distance between the growth interface and the crucible bottom or metal plate must be made sufficiently small (usually several mm), making crystal growth difficult and impractical.
[0006]
Further, in a semiconductor crystal such as Si, convection is stopped by placing the melt in a magnetic field to suppress temperature fluctuation. However, this method requires that the melt be a good electrical conductor, and the optical crystal is generally a high-resistance material, so the convection prevention effect is weak, and a large-scale device that generates a strong magnetic field is required, and this method is practical. Was not.
[0007]
Therefore, sufficient measures have not been taken against temperature fluctuation due to convection.
[0008]
For this reason, an SBN crystal having no change in optical refractive index cannot be obtained, the characteristics of the optical device vary, and no practical application has been realized at present.
[0009]
[Problems to be solved by the invention]
When an optical crystal is grown by the conventional technique, a change in the crystal characteristics corresponding to the temperature change in the crystal (if the crystal is an optical crystal, the optical refractive index cannot be suppressed because the temperature fluctuation in the melt cannot be suppressed to a small value). Change).
[0010]
For this reason, for example, in the case of an optical crystal, there is a problem that sufficient reliability cannot be obtained by using it for an optical device.
[0011]
The present invention suppresses the convection in the melt by adjusting the temperature distribution in the axial direction and suppresses the temperature fluctuation in the melt, so that there is no change in crystal characteristics in the crystal (for example, a change in the optical refractive index). The present invention aims to provide a single crystal manufacturing apparatus capable of manufacturing a crystal having no).
[0013]
The apparatus for producing a single crystal according to the present invention comprises: a crucible;
A crucible support made of a heat-resistant cylindrical multi-tube,
In a single crystal manufacturing apparatus by a pulling method having
A gas supply pipe opening toward the center of the bottom outer surface of the crucible is provided in the innermost pipe of the cylindrical multiple pipe,
Further, a cylinder having an outer diameter smaller than the inner diameter of the innermost pipe and having an inner diameter larger than the outer diameter of the gas supply pipe is provided integrally with the crucible at the bottom of the crucible, and the depth of the melt is set to 20. and ~ 30 mm, the ratio of the melt depth to diameter of the crucible as a 2 / 10-1 3/10, suppress the temperature fluctuation of the melt just below the crystal growth part stopping the flow of the melt central axis of the melt It is characterized by doing so.
[0014]
The apparatus for producing a single crystal according to the present invention comprises: a crucible;
A crucible support made of a heat-resistant cylindrical multi-tube,
In a single crystal manufacturing apparatus by a pulling method having
The lower part of the innermost tube of the cylindrical multiple tube is opened, and a cylinder that can move up and down is provided in the innermost tube, the depth of the melt is set to 20 to 30 mm, and the melt depth with respect to the diameter of the crucible is set. as the ratio of 2 / 10-1 3/10, characterized in that it has to suppress the temperature fluctuation of the melt just below the crystal growth part stopping the flow of the melt central axis of the melt.
[0015]
The crystal manufacturing apparatus of the present invention comprises: a crucible;
A crucible support made of a heat-resistant cylindrical multi-tube,
In a single crystal manufacturing apparatus by a pulling method having
The inside of the innermost tube of the cylindrical multiple tube is communicated with the outside, a heater is provided inside the innermost tube, the depth of the melt is 20 to 30 mm, and the ratio of the melt depth to the crucible diameter is 2. / of 10 to 3/10, characterized in that it has to suppress the temperature fluctuation of the melt just below the crystal growth part stopping the flow of the melt central axis of the melt.
[0016]
[Action]
The present invention uses the following method as a specific means for solving the above-mentioned problems. First, the normal temperature distribution in the melt is such that the temperature is lower toward the center than the crucible wall in the radial direction, and lower toward the melt surface from the lower part of the crucible in the axial direction. ing. Therefore, the convection generated in the melt rises near the crucible wall and falls at the center of the crucible.
[0017]
Thus, in the present invention, by providing a means for locally cooling only the center of the crucible bottom, the temperature gradient in the axial direction of the center of the crucible is adjusted so that the temperature of the central portion of the melt is nearly uniform. State. As a result, the range in which convection occurs is limited only near the crucible wall, and does not exist in the central portion of the melt. Thus, the temperature fluctuation in the central part of the melt is suppressed.
[0018]
In the case of a material having a low thermal conductivity such as an SBN crystal, the latent heat is released not to the crystal but to the liquid. Cooling the crucible bottom has an effect of absorbing the released latent heat and is more effective because it serves as a driving force for continuing the crystal growth.
[0019]
By the above means and operation, it is possible to manufacture a crystal without a change in crystal characteristics (for example, a change in crystal refractive index) while suppressing a temperature change of the melt.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
As a means for locally cooling only the center of the crucible bottom, for example, the following technique can be cited.
[0021]
(1) First, a gas supply pipe that opens toward the center of the bottom outer surface of the crucible is provided in the innermost pipe of the cylindrical multiple pipe, and further has an outer diameter smaller than the inner diameter of the innermost pipe. This is a technique in which a cylinder having an inner diameter larger than the outer diameter of the supply pipe is provided integrally with the crucible at the bottom of the crucible.
[0022]
In the present technology, the cooling gas is blown from the gas supply pipe toward the center of the bottom outer surface of the crucible. If the cylinder is not provided integrally with the crucible, the cooling gas will flow through the gap between the upper end of the innermost cylinder and the outer surface of the crucible bottom, and not only the center but also the entire crucible will be cooled. It is cooled by gas.
[0023]
However, when the cylinder is provided integrally with the crucible at the bottom of the crucible, the cooling gas blown out from the opening of the gas supply pipe hits the bottom of the crucible, flows right and left along the outer surface of the crucible bottom, but hits the inner wall of the cylinder in the direction of And flows downward between the inner wall of the cylinder and the outer wall of the innermost tube, and is discharged to the outside. Thereby, only the portion corresponding to the inner diameter of the cylinder at the bottom of the crucible can be locally cooled.
[0024]
By such a technique, a temperature gradient can be formed such that the central portion is low and uniform in the radial direction in the melt, and the temperature gradient rapidly increases in the peripheral portion.
[0025]
The inner diameter of the innermost tube is preferably half of the crucible, more preferably 10 to 20 mm.
[0026]
The inner diameter of the gas supply pipe is preferably half of the crucible, and more preferably 3 to 10 mm. By adopting such a diameter range, the temperature gradient can be formed so that the central portion is lower and uniform in the radial direction in the melt more effectively, and the temperature gradient is sharply increased in the peripheral portion. Single crystals can be produced.
[0027]
As a gas supplied from the gas supply pipe, for example, a gas such as air, argon, or helium gas may be used. The cooling gas may be supplied at room temperature for convenience in use, but the gas temperature may be appropriately controlled.
[0028]
In order to discharge the cooling gas to the outside, a hole A may be provided on the side of the cylindrical multi-tube, but the upper and lower ends of the innermost tube are opened, and the cooling gas is discharged to the outside from the opening. It is good also as a structure which does.
[0029]
{Circle around (2)} Another technique is to provide a vertically movable cylinder in the innermost tube of a cylindrical multiple tube.
[0030]
First, when the cylinder is positioned above the innermost pipe, the flow of heat from the upper part to the lower part is interrupted in the innermost pipe. On the other hand, when the cylinder is moved downward, the flow of heat is not interrupted and the lower part of the temperature distribution in the central axis in the innermost tube is cooled, and the temperature decreases from the lower part of the crucible toward the open end. Thereby, only the center of the crucible bottom is locally cooled.
[0031]
Since the convection of the melt occurs during the change of the diameter of the crystal during the crystal pulling, the downward movement of the cylinder may be performed during the change of the crystal.
[0032]
{Circle around (3)} As another technique, the inside of the innermost tube of the cylindrical multiple tube is communicated with the outside, and a heater is provided inside the innermost tube.
[0033]
Since the innermost tube of the cylindrical multiple tube communicates with the outside, the portion corresponding to the innermost tube on the outer surface of the crucible bottom is locally cooled as compared with other portions. However, simply connecting the innermost tube to the outside is affected by the temperature fluctuation due to the outside air, so that the heater is turned on as necessary to supplement the heat and suppress the temperature fluctuation.
[0034]
【Example】
(Example 1)
FIG. 1 shows a single crystal manufacturing apparatus according to the first embodiment.
[0035]
The crystal manufacturing apparatus of the present embodiment includes a crucible 3 and a crucible support 7 composed of heat-resistant cylindrical multi-tubes 7a and 7b, and a gas supply pipe 8 opening toward the center of the bottom outer surface of the crucible 3 is provided. A cylinder 9 having an outer diameter smaller than the inner diameter of the innermost pipe 7b and an inner diameter larger than the outer diameter of the gas supply pipe 8 is provided in the crucible 3 at the bottom of the crucible 3. 3 and provided integrally.
[0036]
Hereinafter, the present embodiment will be described in more detail.
In this example, an example in which the present invention is applied to pulling a Ce-doped SBN single crystal is shown.
[0037]
In FIG. 1, reference numerals 1 and 2 denote resistance heating heaters of a vertical heating furnace having upper and lower two zones, and adjust the temperature of the upper and lower heaters to set a temperature gradient in a vertical direction.
[0038]
The temperature gradient in the vertical direction was set at 10 to 30 ° C / cm. At that time, the temperature gradient in the radial direction was 0.5 to 1 times the gradient of 20 ° C./cm or less.
[0039]
Reference numeral 3 denotes a platinum crucible having a diameter of 10 cm, reference numeral 4 denotes a melt having a harmonic melting composition of SBN single crystal, which has a temperature of 1450 to 1600 ° C. and a depth of 20 to 30 mm. Reference numeral 5 denotes a growing SBN single crystal. is there. Reference numeral 6 denotes a single crystal pulling rod, which is first brought into contact with the melt 4 and brought into contact with the melt 4 and rotated and pulled in the directions of arrows R and X while adjusting the melt temperature to pull up the single crystal.
[0040]
The rotation speed was 3 to 30 rpm according to the crystal diameter, and the pulling speed was 0.1 to 10 mm / hour. Reference numeral 7 denotes a heat resistant cylindrical double tube made of ceramics, which constitutes a crucible support for supporting the crucible 3. This example shows an example of the double cylindrical tubes 7a and 7b. Of course, a triple or quadruple cylindrical tube may be used. In this example, the inner diameter of the innermost tube 7b of the double cylindrical tube is set to 20 mm.
[0041]
Reference numeral 8 denotes a cooling gas supply pipe, which opens toward the center of the bottom outer surface of the crucible 3. The diameter of the opening of the gas supply pipe was 3 to 4 mm.
[0042]
Reference numeral 9 denotes a platinum cylinder integrated with the crucible 3. In this embodiment, the outer diameter is slightly smaller than the inner diameter (20 mm) of the innermost tube 7b. Therefore, when placing the crucible 3 on the crucible support 7, if the cylinder 9 is fitted into the innermost tube 7 b, the innermost tube 7 b serves as a guide for the cylinder 9 and supports the crucible 3 without causing displacement. It can be easily placed on the table 7. Accordingly, it is possible to prevent uneven heating of the melt caused by the displacement of the crucible 3 in the furnace in the left-right direction.
[0043]
In this example, holes A are provided on the sides of the cylindrical multiple tubes 7a and 7b in order to discharge the gas to the outside.
[0044]
When the cooling gas is blown from the opening of the gas supply pipe 8 to the center of the bottom outer surface of the crucible 3, the direction of the blown gas is changed by the cylinder 9 and flows downward along the side wall of the cylinder 9. Was discharged into.
[0045]
Reference numeral 10 denotes a heat-resistant fiber for heat insulation.
Crystal growth of Ce-doped SBN was performed using the apparatus shown in FIG.
[0046]
First, a cooling gas was flowed at a flow rate of 0, 10, and 15 L / min (liter / minute) from the gas supply pipe 8, and the results of the temperature fluctuation suppression near the melt surface at each flow rate were measured. The result is shown in FIG.
[0047]
As shown in FIG. 2, the temperature fluctuation was ± 1.5 ° C. without gas cooling. However, the surface temperature decreased with an increase in the flow rate, but the temperature fluctuation was small. That is, the temperature fluctuation in the central part of the melt could be suppressed from ± 1.5 ° C. to ± 0.3 ° C. or less by gas cooling. As a result, a CBN single crystal with no change in optical refractive index could be produced with good reproducibility.
[0048]
The apparatus of this example was used for pulling a Ce-doped SBN crystal in the C-axis direction. The obtained crystal was sliced in a thickness of 2 mm in parallel with the C axis, processed into a plate shape of 40 mm × 40 mm size, and polished on both sides to be used as a recording medium of a digital hologram memory. Since this crystal has a small change in the refractive index of 10 ⁻⁵ or less and is manufactured under a low temperature gradient and has good crystallinity and photorefractive characteristics, a high-density recording device with few reading and writing errors can be realized.
[0049]
(Example 2)
FIG. 3 shows a single crystal manufacturing apparatus according to the second embodiment.
The apparatus for producing a single crystal according to the present embodiment has a crucible 3 and a crucible support 7 composed of a heat-resistant cylindrical multi-tube, and a vertically movable cylinder 11 is provided in the innermost tube 11 of the cylindrical multi-tubes 7a and 7b. Is provided.
[0050]
Hereinafter, this will be described in more detail.
In FIG. 3, reference numeral 11 denotes a heat-resistant vertically movable cylinder, and reference numeral 7b denotes an innermost tube of a cylindrical multi-tube constituting the heat-resistant crucible support 7. In this embodiment, the lower atmosphere is cooled by opening the lower part of the innermost tube 7b constituting the cylindrical crucible support 7 and the position of the heat-resistant movable cylinder 11 inserted inside is changed up and down. The temperature at the bottom was adjusted.
[0051]
To explain the principle in Figure 3. First, the temperature distribution on the central axis in the innermost tube 7b when the cylinder 11 is not provided is such that the temperature is lower toward the open end from the lower part of the crucible because the lower part is cooled.
[0052]
Here, when the cylinder 11 is inserted, the flow of heat from the upper part to the lower part is shut off. Therefore, when the position is A1 shown in FIG. 3, the temperature distribution is 3 on the right, and when the position is A2, the temperature distribution is 4; A temperature drop of several tens of degrees Celsius occurs.
[0053]
By adjusting the positions of A1 and A2, the temperature of the crucible bottom could be adjusted in the same manner as in Example 1. Therefore, since the melt is locally cooled centering directly above the crucible, a temperature gradient could be formed such that the central portion was low and uniform in the radial direction in the melt and rapidly increased in the peripheral portion.
[0054]
In this way, temperature fluctuations in the central part of the melt could be suppressed. As a result, a CBN single crystal with no change in optical refractive index could be produced with good reproducibility.
[0055]
(Example 3)
FIG. 4 shows a single crystal crystal manufacturing apparatus according to the third embodiment.
The apparatus for producing a single crystal according to the present embodiment has a crucible 3 and a crucible support 7 composed of heat-resistant cylindrical multi-tubes 7a and 7b, and allows the inside of the innermost tube 7b of the cylindrical multi-tube to communicate with the outside. The heater 13 was provided inside the innermost tube 7b.
[0056]
In FIG. 4, a small heater 13 is inserted into the innermost tube 7b. By changing the temperature of the heater, the same effect as that of the movable cylinder of Example 2 was realized. Therefore, since the melt is locally cooled centering directly above the crucible, a temperature gradient could be formed such that the central portion was low and uniform in the radial direction in the melt, and rapidly increased at the peripheral portion. In this way, temperature fluctuations in the central part of the melt could be suppressed.
[0057]
As a result, a CBN single crystal with no change in optical refractive index could be produced with good reproducibility.
[0058]
【The invention's effect】
As described above, the present invention provides a simple method of locally cooling the crucible lower part, by adjusting the temperature gradient in the center of the crucible in the axial direction to be gentle to make the temperature of the central part of the melt nearly uniform. Since the range of convection occurs only near the crucible wall and does not exist in the central part of the melt, the temperature fluctuation in the central part of the melt can be suppressed to ± 0.3 ° C or less, and the change in crystal characteristics is extremely small. Single crystals can be produced.
[Brief description of the drawings]
FIG. 1 is a sectional view of a single crystal manufacturing apparatus according to a first embodiment.
FIG. 2 is a graph showing a temperature fluctuation suppressing effect in Example 1.
FIG. 3 is a graph showing a cross section of the edge makeup manufacturing apparatus according to the second embodiment and a temperature change depending on a cylinder position.
FIG. 4 is a sectional view of a single crystal manufacturing apparatus according to a third embodiment.
[Explanation of symbols]
1,2 vertical resistance heating heaters in two vertical zones,
3 platinum crucible,
4 SBN melt,
5 growing SBN single crystal,
6 Single crystal pulling rod,
7 Crucible support,
7a, 7b cylindrical multi-tube 7b innermost tube,
8 gas supply pipes,
9 cylinders,
10 heat-resistant fibers for heat insulation,
11 heat-resistant vertically movable cylinder,
12 Heat-resistant cylindrical crucible support,
13 Small heater.

Claims (3)

Crucible and
A crucible support made of a heat-resistant cylindrical multi-tube,
In a single crystal manufacturing apparatus by a pulling method having
A gas supply pipe opening toward the center of the bottom outer surface of the crucible is provided in the innermost pipe of the cylindrical multiple pipe,
Further, a cylinder having an outer diameter smaller than the inner diameter of the innermost pipe and having an inner diameter larger than the outer diameter of the gas supply pipe is provided integrally with the crucible at the bottom of the crucible, and the depth of the melt is set to 20. and ~ 30 mm, the ratio of the melt depth to diameter of the crucible as a 2 / 10-1 3/10, suppress the temperature fluctuation of the melt just below the crystal growth part stopping the flow of the melt central axis of the melt An apparatus for producing a single crystal, characterized in that: Crucible and
A crucible support made of a heat-resistant cylindrical multi-tube,
In a single crystal manufacturing apparatus by a pulling method having
The lower part of the innermost tube of the cylindrical multiple tube is opened, and a cylinder that can move up and down is provided in the innermost tube, the depth of the melt is set to 20 to 30 mm, and the melt depth with respect to the diameter of the crucible is set. as 2 / 10-1 3/10 ratio, crystal manufacturing apparatus is characterized in that so as to suppress the temperature fluctuation of the melt just below the crystal growth part stopping the flow of the melt central axis of the melt. Crucible and
A crucible support made of a heat-resistant cylindrical multi-tube,
In a single crystal manufacturing apparatus by a pulling method having
The inside of the innermost tube of the cylindrical multiple tube is communicated with the outside, a heater is provided inside the innermost tube, the depth of the melt is 20 to 30 mm, and the ratio of the melt depth to the crucible diameter is 2. / 10 as 1-3 / 10, crystal manufacturing apparatus is characterized in that so as to suppress the temperature fluctuation of the melt just below the crystal growth part stopping the flow of the melt central axis of the melt.

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