JP2001106597A - Method and device for producing single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for producing a single crystal, which is capable of improving the growing velocity and with which the single crystal stable in characteristics can be produced. SOLUTION: A plate-like seed 19 and a raw material 20 for growing are filled in a crucible 15. When a single crystal is produced, the crucible 15 is gradually raised into a vertical Bridgman furnace 11 by a driving mechanism 16, and a temperature gradient is set by heating with a heater 12 and by cooling with a cooler 14 in order to melt the raw material 20 for growing. When the position P of the solid-liquid interface of lithium tetraborate reaches a position corresponding to the melting point temperature of lithium borate single crystal in the vertical Bridgman furnace 11, raising of the crucible 15 is stopped and the crucible is kept at the position. Thereafter, the crucible is lowered to grow the crystal and, when the crucible 15 is lowered by a prescribed distance, the crucible is stopped, thereby growing of the crystal is completed.

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 a single crystal used for producing a single crystal for producing a high-quality ingot and an apparatus for producing the same.

[0002]

2. Description of the Related Art In general, lithium tetraborate single crystals (Li
₂ B ₄ O ₇ ) has a zero temperature coefficient and a relatively large electromechanical coupling coefficient, and is a material widely used for surface acoustic wave (SAW) devices. Known methods for growing this lithium tetraborate single crystal include the CZ method and the vertical Bridgman method.

[0003] Among them, the CZ method is also called a pulling method,
In this method, a raw material previously filled in a crucible serving as a container is melted by heating, a seed crystal called a seed is brought into contact with the melt, and then gradually pulled up while rotating.

The CZ method is a major method for growing a single crystal ingot from a melt, and has an advantage that the growth rate can be set relatively high. However, it is difficult to control the shape, and the temperature gradient is steep, so that distortion occurs and cracks easily occur.

[0005] On the other hand, in the vertical Bridgman method or the vertical temperature gradient solidification method, a seed is placed in a lower portion of a crucible as a container, and a raw material for growing is filled on the seed, and then a grown crystal is grown by a heater of a furnace. The growth zone is heated and melted. As the furnace, a furnace whose temperature gradient is set so that the upper side is higher than the melting point temperature and the lower side is lower than the melting point temperature based on the melting point temperature of the grown crystal is used. It is heated and melted by ascending it from below and inserting it.

In this case, the crystal is grown by adjusting the crucible position or temperature so that the solid-liquid interface between the melt and the solid is at an arbitrary position in the vertical direction of the seed, and then gradually lowering the crucible. Let me.

In the vertical Bridgman method, since the crystal shape depends on the shape of the crucible, it is easy to control the shape, the distortion is relatively small, and the crystal is hardly broken.

[0008]

However, in the conventional vertical Bridgman method, since the temperature gradient in the growing zone uses the temperature difference due to the heater, the temperature gradient is almost always the upper temperature of the growing zone having the highest temperature. It depends on. Since the temperature of the heater above the growth zone must be a temperature that does not cause the composition change of the melt, the upper limit of the temperature is necessarily limited, and as a result, the temperature gradient of the growth zone is also reduced. It is almost determined in a narrow range.

For this reason, in the Bridgman method, the temperature gradient is considerably reduced as compared with the CZ method or the like, and this is one of the causes of lowering the growth rate.

On the other hand, in the process of growing a single crystal, as the melt crystallizes, that is, solidifies at the solid-liquid interface in the growth zone, and the area of the single crystal increases, the ratio of the amount of the single crystal to the amount of the melt increases. Due to the fluctuation, the temperature gradient at the solid-liquid interface actually changes, or the position of the surrounding liquid interface itself fluctuates, causing the problem that the talking characteristics of the single crystal differ in the straight body length direction. I have.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a method for producing a single crystal capable of improving the growth rate and producing a single crystal ingot having stable characteristics, and a production apparatus therefor.

[0012]

According to the present invention, a seed crystal is accommodated in a lower portion of a container, a raw material for growth is filled on the seed crystal, and the melting point of the crystal to be grown is determined based on the melting point of the crystal to be grown. It is heated and melted by a furnace with a temperature gradient cooled to a temperature higher than the temperature and lower to a temperature lower than the melting point temperature, and after this melting, the crystal grows. This increases the temperature gradient between the upper part and the lower part, thereby increasing the growing speed.

Further, the temperature gradient is variable, and even if the temperature gradient gradually shifts from the initial growth of the crystal, the temperature gradient can be substantially changed by arbitrarily changing the cooling amount. It can be kept constant, and the crystal becomes uniform even in the straight body length direction.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, reference numeral 11 denotes a vertical Bridgman furnace as a single crystal manufacturing apparatus. The vertical Bridgman furnace 11 has a cylindrical heater 12 arranged in a vertical direction. Numeral 12 designates an arbitrary temperature setting in the vertical direction, and a furnace tube 13 made of alumina or the like is integrally attached to an inner portion of the heater 12. Below the heater 12, an industrial cooler 14 as a cylindrical cooling device is provided similarly to the heater 12.

Further, reference numeral 15 denotes a crucible as a container, and the crucible 15 is integrally mounted on a base 17 which can be moved up and down by a drive mechanism 16, and a lithium tetraborate is provided below the crucible 15 inside. A so-called seed 19, which is a disc-shaped seed crystal having a thickness of about 10 mm, is placed, and the seed 19 is filled with a growing material 20.

The heating amount of the heater 12 is adjusted so that the upper portion thereof is about 1000 ° C. with reference to a temperature position at which the melting point of lithium tetraborate single crystal 917 ° C. occurs, and the lower portion is cooled by the cooler 14. The temperature gradient is set variably in the range of about 10 ° C./cm to 40 ° C./cm.

The crucible 15 is filled with a plate-like seed 19 and a growing material 20 located on the seed 19. When a single crystal is produced, the crucible 15 is driven by a driving mechanism 16.
As a result, the temperature is gradually raised into the vertical Bridgman furnace 11, a temperature gradient is set in accordance with the heating of the heater 12 and the cooling of the cooler 14, and the internal growth material 20 is melted.

Here, when the solid-liquid interface position P of lithium tetraborate reaches the melting point temperature of the lithium tetraborate single crystal in the vertical Bridgman furnace 11, the rise of the crucible 15 is stopped and held at that position. . Thereafter, the crucible 15 is lowered to grow crystals, and when the crucible 15 is lowered a predetermined distance, the crucible 15 is stopped to complete the growth.

Comparing the above-described embodiment using the cooler 14 with the comparative example having no cooler, the temperature gradient of the growing zone without the cooler is 10 ° C./cm to 20 ° C./cm. Can be set only in the range of 10 ° C./cm to 40 ° C./c with the cooler 14.
m can be set arbitrarily, and a homogeneous single crystal ingot equal to or greater than that produced in the comparative example is 0.3 mm / h of the comparative example.
It was able to grow at a speed of 0.5 mm / h.

Further, not only the growth rate of the single crystal can be increased as a whole, but also a single crystal ingot can be grown uniformly in the straight body length direction.

[0022]

According to the present invention, since the upper part has an upper temperature limit, by cooling the lower part, the temperature gradient between the upper part and the lower part can be increased, and the growth rate of the single crystal can be increased.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an apparatus used in an embodiment of the method for producing a single crystal of the present invention.

[Explanation of symbols]

 11 Vertical Bridgman furnace as single crystal production equipment 12 Heater 14 Cooler as cooling device 15 Crucible as container 19 Seed as seed crystal 20 Raw material for growing

Claims (4)

[Claims] 1. A seed crystal is accommodated in a lower portion of a container, and a seeding material is filled on the seed crystal. An upper portion is higher than the melting point temperature and a lower portion is lower than a melting point temperature of the crystal to be grown. A method for producing a single crystal, comprising heating and melting in a furnace having a temperature gradient cooled to a temperature lower than the melting point, and growing the crystal after the melting. 2. The method according to claim 1, wherein the temperature gradient is variable. 3. A container in which a seed crystal is accommodated in a lower part and a seeding material is filled on the seed crystal, an upper part having a temperature higher than the melting point and a lower part having a melting point based on the melting point position of the crystal to be grown. An apparatus for producing a single crystal, comprising: a heater for heating the inside of a container with a temperature gradient set to a temperature lower than the temperature; and a cooling device for cooling the inside of the container below a crystal to be grown. 4. A temperature gradient set by a heater and a cooling device is variable.
An apparatus for producing a single crystal according to the above.