JP2002241190A - Single crystal growth device and single crystal growth method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a single crystal growth device capable of stably producing a single crystal having excellent quality by, in the process of single crystal growth, allowing the central-symmetric natural convection of a melt and thereby inhibiting variation in temperature of the melt at the growth interface, and also to provide a single crystal growth method using the device. SOLUTION: The single crystal growth device 1 using a Czochralski method is provided with a plurality of cooling tubes 6a-6d for cooling a lower part of the peripheral side face of a crucible 4 and a means for controlling the flow rate and/or temperature of a coolant flowing through the inside of each of the cooling tubes 6a-6d.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an apparatus for growing a single crystal by the Czochralski method and a method for growing a single crystal using the same.

[0002]

2. Description of the Related Art Conventionally, the Czochralski method has been used as one of the methods for growing single crystals. In this method, in a single crystal growing apparatus, a single crystal raw material is put into a noble metal crucible made of platinum or the like provided in an area surrounded by a heat insulating material (hereinafter, referred to as a hot zone), and a high-frequency induction heating placed around the crucible is used. Melting the single crystal raw material by heating means such as
This is performed by bringing a seed crystal into contact with the melt and pulling the melt in the vertical direction.

In order to stably grow a high-quality single crystal, it is necessary to minimize the temperature fluctuation of the melt at the crystal growth interface. For this purpose, it is conceivable to control convection in the melt, which is one of the causes of the temperature fluctuation of the melt.

[0004] Melt convection includes natural convection generated by heating from around the crucible and forced convection generated by rotation of the single crystal during growth. Of these, natural convection is generated by a temperature gradient in the central axis direction (hereinafter, referred to as an axial direction) of the crucible and a temperature gradient in a crucible radial direction (hereinafter, referred to as a radial direction) on the surface of the melt.

[0005] The temperature gradient in the axial direction around the crucible is set such that the latent heat of the grown crystal is released upward and the crystal growth from the bottom of the crucible depends on the position of the heating device and the configuration of the hot zone in order to suppress the crystal growth from the bottom of the crucible. The temperature decreases toward the surface. The temperature gradient in the radial direction of the melt surface is lower toward the center than the crucible wall because the melt is heated from the surroundings. Therefore, the natural convection generated in the melt rises near the crucible wall, moves from the crucible wall toward the center on the melt surface, and falls at the crucible center.

This natural convection is affected by the temperature distribution around the crucible, causes a temperature change of the melt at the crystal growth interface, and affects the shape and quality of the single crystal to be grown. Therefore, in growing a single crystal, natural convection needs to flow in an optimal manner.

The optimal flow of natural convection is that the central symmetry is always obtained, that is, the natural convection always flows symmetrically with respect to the central axis of the crucible. It is important for suppressing fluctuation and stably growing a single crystal.

However, if the positions of the hot zone and the heating means for the crucible are shifted, the symmetry of the thermal environment related to the crystal growth is not established, and as a result, the natural convection cannot obtain the central symmetry. Disappears, causing various obstacles to the growth of single crystals.

For example, when forming a single crystal straight body, in order to flatten the shape of the solid-liquid interface, the number of crystal rotations is controlled to balance forced convection and natural convection of the melt. . At this time, if natural convection does not have central symmetry, it is difficult to obtain a flat solid-liquid interface even if the number of crystal rotations is controlled. Also, when the shoulder portion is formed by enlarging the diameter of the single crystal, if the natural convection does not have the central symmetry, the central symmetry of the crystal is broken and the hetero-oriented growth is likely to occur.

Heretofore, some countermeasures have been taken to control natural convection, but they have been insufficient as means for realizing the central symmetry of natural convection. For example, JP 2000
JP-A-72586 introduces a method in which one gas supply pipe opening toward the center of the outer bottom of the crucible is arranged below the hot zone, and a cooling gas is blown to the center of the bottom of the crucible. ing.

[0011]

However, this method is based on the premise that natural convection flows while maintaining the central symmetry, and locally cools the center of the bottom of the crucible to thereby reduce the center of the crucible. Slow the temperature gradient of the melt in the axial direction,
The purpose is to suppress natural convection in this part. Therefore, when natural convection does not flow while maintaining the central symmetry, even if this method is used, natural convection cannot flow with the central symmetry.

Accordingly, an object of the present invention is to provide an excellent method by controlling the temperature fluctuation of the melt at the crystal growth interface by allowing the natural convection of the melt to have central symmetry during single crystal growth. It is an object of the present invention to provide a single crystal growing apparatus capable of stably growing a single crystal of high quality and a growing method using the same.

[0013]

According to a first aspect of the present invention, there is provided a single crystal growing apparatus according to the first aspect of the present invention, wherein the plurality of cooling pipes for cooling a lower side surface around a crucible are provided. Means for controlling the amount or temperature of the coolant flowing through the cooling pipe.

Further, in claim 2, the cooling pipe is
The crucible is provided symmetrically with respect to the central axis.

Further, in claim 3, the cooling pipe is
The crucible is provided so as to directly or indirectly cool the side surface thereof.

According to a fourth aspect of the present invention, in the method for growing a single crystal, the convection or the temperature distribution of the raw material melt is checked while the convection or the temperature distribution of the raw material melt is checked using the single crystal growing apparatus. So that it is symmetrical about the central axis of
Controlling the amount or temperature of the coolant flowing through the plurality of cooling pipes,
It is characterized by growing a single crystal.

Thus, during the growth of the single crystal, the lower part of the side surface around the crucible is locally cooled to reduce the temperature gradient of the melt on the side surface of the crucible, and the side surface of the crucible is naturally convected upward. The strength can be controlled so that natural convection can achieve central symmetry.

Further, by disposing the cooling pipe symmetrically with respect to the central axis of the crucible, the cooling pipe required for controlling the central symmetry of natural convection can be effectively used.

Further, by disposing the cooling pipe so as to directly or indirectly cool the side surface of the crucible, the crucible can be effectively cooled according to the type of the coolant.

By growing a single crystal using the above-described single crystal growing apparatus, it becomes easy to maintain the natural convection of the melt and the central symmetry of the temperature distribution. A single crystal of excellent quality can be stably produced by suppressing temperature fluctuation.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Natural convection of a melt is generated by a temperature gradient of the melt. Therefore, the temperature distribution of the crucible itself that holds the melt affects the temperature gradient in the melt, and further affects the strength distribution of natural convection. Therefore, natural convection can be controlled by controlling the temperature distribution of the crucible.

Accordingly, the inventor of the present invention cools the lower portion of the side surface around the crucible while adjusting the amount and temperature of the coolant with a plurality of cooling pipes during the growth of the single crystal. It was thought that the strength of natural convection flowing upward in the axial direction of the crucible could be changed by controlling the temperature gradient of the crucible.

FIG. 1 is a sectional view showing an example of a single crystal growing apparatus according to the present invention, and FIG. 2 is a partial perspective view showing the crucible of FIG. It is.

As shown in FIG. 1, a single crystal growing apparatus 1 comprises:
Mainly, a high-frequency induction coil 2 for heating and melting a single crystal raw material, a heat insulating material 3 of alumina and a hot zone 3a surrounded by it, a crucible 4 for holding a raw material melt, and a single crystal for holding a seed crystal at the tip. And a lifting rotary shaft 5 provided with a vertical movement and rotation mechanism.

Inside the hot zone 3a, there are provided four cooling pipes 6a to 6d for supplying an atmospheric gas from the outside (in the figure, the cooling pipe 6a is located on the opposite side of the crucible 4,
Further, the position of the cooling pipe 6 c is disposed on the front side of the crucible 4. ). In addition, the cooling pipes 6a to 6d
Outside of a, valves 8a to 8d for adjusting the amount of supplied atmospheric gas are provided.

As shown in FIG. 2, the cooling pipes 6a to 6d
The crucible 4 is disposed near the side of the crucible that is symmetrical with respect to the central axis of the crucible 4. Openings 7 a to 7 d are provided at the tip and bent in the direction of the central axis of the crucible 4. 1 and 2, arrows in the cooling pipe indicate the direction in which the gas flows.

The atmosphere gas flowing through the cooling pipes 6a to 6d is blown from the openings 7a to 7d to the crucible 4 and supplied into the hot zone, and the cooling is performed by adjusting the valve to increase the gas supply amount. More atmospheric gas is blown from the tube to directly cool the lower side of the crucible 4. In this case, it is preferable to use an inert gas having a low oxygen content as the atmosphere gas. The reason is that when a gas body having a high oxygen content is used, the crucible made of a noble metal is oxidized and the life of the crucible is shortened.

Next, FIG. 3 is a sectional view showing another example of the single crystal growing apparatus according to the present invention, and FIG. 4 is a crucible of FIG. FIG. The same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

The basic structure of the single crystal growing apparatus 11 is the same as that shown in FIG.
There is a difference in the piping structure of the cooling pipe for a. That is,
In the single crystal growing apparatus 1 of FIG. 1, the cooling pipes 6 a to 6 d serve to supply the atmospheric gas into the hot zone 3 a and increase the amount of the gas blown to the crucible as needed, and
It also serves to cool a specific portion of the side surface of the device. On the other hand, in the single crystal growing apparatus 11 of FIG. 3, the gas pipe 12 for supplying the atmosphere gas to the hot zone 3a and the four cooling pipes 13a to 13d for supplying the gas for cooling the crucible 4 are separately provided. The cooling pipes 13a to 13d are arranged so as to go out from the lower part of the hot zone 3a to the outside again. The cooling pipes 13a to 13d are provided outside the hot zone 3a with valves 14a to 1d for adjusting the amount of cooling gas supplied to the hot zone 3a.
4d.

As shown in FIG. 4, the cooling pipes 13a to 13d for cooling the crucible 4 are disposed so as to be folded back at the lower side of the crucible 4. 3 and 4, the arrows in the gas pipe and the cooling pipe indicate the direction in which the gas flows.

The cooling gas flowing through the cooling pipes 13 a to 13 d indirectly cools the lower side portion of the crucible 4 when passing by the crucible 4. Note that these cooling tubes may be provided in contact with the side surface of the crucible 4 or may be provided slightly away from the crucible. As the cooling gas, the gas collected outside the hot zone may be cooled again and used repeatedly, or the gas once used for cooling may be exhausted each time and a new cooling gas may be supplied. When the cooling gas is used repeatedly, it is necessary to provide fins or the like for radiating heat taken after cooling the crucible on the surface of the cooling pipe.

Hereinafter, embodiments of the present invention will be described based on examples.

(Example 1) The single crystal to be grown was a lanthanum gallium silicon oxide (L) having a langasite structure having a Ca ₃ Ga ₂ Ge ₄ O ₁₄ crystal structure as an oxide single crystal.
a ₃ Ga ₅ SiO ₁₄₎ to select, as the single crystal growth for raw material therefor, a _{La 2 O 3 1537.1g, Ga 2} O 3 and 14
73.9 g and 189.0 g of SiO ₂ were weighed and prepared. And dry-mix these ingredients,
After press-molding the obtained mixed raw material, the outer diameter is 100 m.
m, a thickness of 2 mm, and a height of 100 mm into a platinum rhodium crucible.

Next, N ₂ gas is supplied from the cooling pipes 6a to 6d of the single crystal growing apparatus 1 shown in FIG.
A mixed gas mixed with vol% O ₂ gas was flowed into the hot zone 3a at 0.5 liter / min.

The crucible 4 was heated by high-frequency induction heating using the high-frequency induction coil 2 to melt the raw materials. As the seed crystal 21, a rod-shaped La perpendicular to the <001> plane orientation is used.
₃ Ga ₅ SiO ₁₄ single crystal (dimensions: 5 mm square, length 50 m)
m) was attached to the tip of the rotary shaft 5, which was lowered to contact the melt 22 a in the crucible 4. Then, the surface of the melt 22a in the crucible 4 was observed with a melt surface monitor (not shown) provided in the single crystal growing apparatus.

FIG. 5 is a plan view showing a spoke pattern of natural convection appearing on the melt surface at this time. In the figure, cooling pipes 6a and 6c and 6b and 6
The intersection of two dashed lines connecting d and d indicates the position of the central axis of the crucible 4, and a plurality of lines extending radially from the upper right portion of the central axis to the periphery indicate a spoke pattern.

The spoke pattern revealed that the center 23a of natural convection was displaced from the central axis of the crucible. By observing the melt surface monitor, the valves 8c and 8d shown in FIG. 1 were adjusted. Cooling pipes 6c and 6d shown in FIG.
From the initial 0.5 l / min to 0.1 g / min.
At a rate of 8 liters / min, the portion at the lower side of the crucible 4 was cooled.

In this way, by taking the temperature from the lower part of the side of the crucible, the temperature gradient of the melt in the axial direction of the crucible is reduced, and the strength of natural convection flowing upward in the axial direction of the crucible is controlled. The center of natural convection was aligned with the central axis of the crucible.

Thereafter, the single crystal was pulled up at a crystal rotation speed of 19 rpm and a pulling speed of 1.5 mm / hour, and the diameter of the single crystal was increased to 50 mm by gradually lowering the temperature of the melt in forming the shoulder. . Subsequently, while maintaining the crystal diameter, the straight body was pulled up over 30 hours, and finally the single crystal was separated from the melt and gradually cooled.

The obtained grown single crystal was cut in parallel with the pulling direction and polished on both sides to confirm that the solid-liquid interface had a flat shape, and that the crystal had a central symmetry. Was kept.

Example 2 Example 1 was applied to a single crystal to be grown.
The same raw material as in Example 1 was selected, and the same raw materials as in Example 1 were dry-blended in the same manner. The mixed raw material was press-molded, and then filled in a platinum rhodium crucible having the same dimensions as in Example 1.

Next, the same atmospheric gas as in the first embodiment was supplied from the gas pipe 12 of the single crystal growing apparatus 11 shown in FIG.
It flowed into the hot zone 3a at liter / minute. Cooling pipe 1
Raw materials were melted in the same manner as in Example 1 except that no cooling gas was flowed through 3a to 13d. Subsequently, a seed crystal 21 of the same type and the same size as in Example 1 was brought into contact with the melt 22b in the same manner as in Example 1. Then, the surface of the melt 22b in the crucible 4 was observed in the same manner as in Example 1.

FIG. 6 is a plan view showing a spoke pattern of natural convection appearing on the melt surface at this time. In the figure, cooling pipes 13a and 13c and 13 provided around the crucible 4 are shown.
The intersection of two broken lines connecting b and 13d indicates the position of the central axis of the crucible 4, and a plurality of lines extending radially from the lower left portion of the central axis to the periphery indicate a spoke pattern.

Since it was found from the spoke pattern that the center 23b of natural convection was displaced from the central axis of the crucible 4, the valves 14a and 14b shown in FIG. flowing each 0.7 l / min 0.5 l / min of N ₂ gas to the cooling pipe 13a and 13b shown in and cooling the portion of the lower side of the crucible 4.

In this way, by taking the temperature from the lower side of the crucible, the temperature gradient of the melt in the axial direction of the crucible is reduced, and the strength of natural convection flowing upward in the axial direction of the crucible is controlled. The center of natural convection was aligned with the central axis of the crucible.

Thereafter, the single crystal was pulled in the same manner as in Example 1, the shoulder was formed, and the straight body was pulled. Finally, the single crystal was separated from the melt and gradually cooled.

The obtained grown single crystal was cut and polished on both sides in the same manner as in Example 1. As a result, a flat solid-liquid interface was obtained, and the central symmetry of the crystal was also confirmed. Was kept.

In the above embodiment, the gas is used as the coolant flowing through the cooling pipe. However, the present invention is not limited to this, and the liquid may be cooled instead of the gas by the structure of the cooling pipe and the piping method. It can also be used as a material.

In addition to the mechanism for controlling the amount of coolant flowing through the cooling pipe, a mechanism for controlling the temperature of the coolant may be provided. If both mechanisms are provided and used together, the crucible can be cooled more efficiently. It can be controlled precisely.

Further, during the growth of the single crystal, for example, the fluctuation of the temperature distribution of the melt is detected by using a thermocouple, and the bias of the temperature distribution of the melt is corrected using the crucible cooling method of the present invention. Alternatively, the temperature distribution of the melt may have a central symmetry.

[0051]

According to the present invention, in growing a single crystal by the Czochralski method, the natural convection is controlled by controlling the strength of the natural convection of the melt flowing upward in the axial direction on the side of the crucible to obtain the central symmetry. It will be possible to be. Therefore, temperature fluctuation of the melt at the crystal growth interface caused by natural convection in which the central symmetry is broken can be suppressed, and a single crystal having excellent quality can be stably manufactured.

Also, since the cooling capacity of each cooling pipe disposed around the crucible can be adjusted, not only the strength of natural convection flowing upward in the axial direction on the side of the crucible, but also the inner circumference of the crucible along the crucible. By controlling the strength of convection, it is possible to suppress the fluctuation of the temperature distribution in this direction.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a single crystal growing apparatus according to the present invention.

FIG. 2 is a partial perspective view showing the crucible of FIG. 1 and a cooling pipe disposed at a lower portion of a side surface around the crucible.

FIG. 3 is a sectional view showing another example of the single crystal growing apparatus according to the present invention.

FIG. 4 is a partial perspective view showing the crucible of FIG. 3 and a cooling pipe disposed at a lower portion of a side surface around the crucible.

FIG. 5 is a plan view showing a spoke pattern of the melt of Example 1.

FIG. 6 is a plan view showing a spoke pattern of a melt of Example 2.

[Explanation of symbols]

 1,11 Single crystal growing apparatus 4 Crucible 6a-6d, 13a-13d Cooling pipe 22a-22c Melt

Claims (4)

[Claims] 1. An apparatus for growing a single crystal by the Czochralski method, comprising: a plurality of cooling pipes for cooling a lower side portion around a crucible; and means for controlling an amount or a temperature of a coolant flowing through the cooling pipe. An apparatus for growing a single crystal, comprising: 2. The single crystal growing apparatus according to claim 1, wherein the cooling pipe is disposed symmetrically with respect to a central axis of the crucible. 3. The single crystal growing apparatus according to claim 1, wherein the cooling pipe is disposed so as to directly or indirectly cool the side surface of the crucible. 4. The method according to claim 1, wherein the convection or temperature distribution of the raw material melt is adjusted to the center of the crucible while confirming the convection or temperature distribution of the raw material melt. A method for growing a single crystal, comprising growing a single crystal by controlling the amount or temperature of a coolant flowing through a plurality of cooling pipes so as to be symmetric with respect to an axis.