JPH09255473A - Crucible for pulling single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crucible capable of carrying out pulling a single crystal by preventing increase of the consumed electric powder without requiring long time in order to melt a raw material. SOLUTION: A circular heat-insulating part 5 having a prescribed width is inserted in the boundary part between a cylindrical part and bowl-like lower part of outer vessel 3 of the crucible 1. The heat-insulating part 5 is made of graphite and the heat conductivity is lower by 2-3 girder than that of outer vessel 3. As a result, since it is prevented that heat conducting the interior of wall of the outer container 3 is transmitted to the lower part of the crucible 3 without preventing heat release due to radiation from the peripheral face of the lower part of the outer container 3, increase of temperature of melted liquid L on the bottom of the crucible 1 is prevented.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a crucible used for pulling a single crystal by the Czochralski method (CZ method).

[0002]

2. Description of the Related Art FIG. 5 is a schematic side sectional view showing an essential part of an apparatus used for pulling a single crystal by the CZ method and a conventional crucible. In the crucible 21, an outer container 23 made of graphite, which is similar in shape to the inner container 22, is externally fitted to an inner container 22 made of quartz, which has a bowl-shaped lower portion at the lower end of a cylindrical body. The crucible 21 is placed on a pan 11 in which a recess is formed in the center of the upper surface of a graphite disk, and the pan 11 and the crucible 21 are attached by a graphite rotating shaft 12 attached to the bottom center of the pan 11. It is designed to be rotated and raised and lowered.

On the outside of the crucible 21, a resistance-heating type cylindrical heater 13 is arranged concentrically with the crucible 21. Also, crucible 21
A rod-shaped or wire-shaped pull-up shaft 14 is arranged on the central axis of, and a seed crystal 15 is attached to the lower end of the pull-up shaft 14.

In order to pull a single crystal by the CZ method with such an apparatus, the raw material charged into the crucible 21 by the heater 13 is melted to form a melt L, and the seed crystal attached to the lower end of the pulling shaft 14 is used. 15 is brought into contact with the surface of the molten liquid L, and the pulling shaft 14 and the rotating shaft 12 are rotationally driven in opposite directions, and the pulling shaft 14 is pulled up at a predetermined speed, so that a single crystal is formed below the seed crystal 15. Grow 16 Then, as the melt L is reduced by pulling up the single crystal 16, the crucible 21 is raised by the rotating shaft 12 to keep the height of the surface of the melt L substantially constant.

In such a crucible 21, the surface of the melt L is lowered to a temperature close to the melting point as the single crystal 16 is pulled up, while the melt L near the bottom of the crucible 21 is heated by the heater.
It is kept above the melting point by heat input from 13. Therefore, there is a problem that convection occurs in the melt L and the concentration of impurities such as oxygen or dopant eluted from the inner surface of the inner container 22 becomes nonuniform and the quality of the single crystal 16 deteriorates.

To solve this problem, Japanese Patent Publication No. 57-55680
In the publication, there is proposed a crucible made of graphite, in which an outer container is composed of an upper member and a lower member that are vertically separable, and the lower member has a lower thermal conductivity than the upper member. As a result, heat conduction to the melt near the bottom of the crucible is suppressed, the temperature of the melt in the vertical direction is made uniform, and convection is prevented.

On the other hand, the applicant of the present invention discloses in Japanese Examined Patent Publication No. 4-75880 that the outer container is composed of an upper member and a lower member which can be divided into upper and lower parts, and the upper member has a lower thermal conductivity than that of the lower member. There is disclosed a crucible in which a ring-shaped spacer is provided at the joint portion between the upper member and the lower member. As a result, the upper side of the crucible protrudes from the upper end of the heater as the crucible rises, and supercooling of the molten liquid due to radiation from the protruding portion is prevented.

[0008]

[Problems to be solved by the invention]
In the crucible described in Japanese Patent No. 57-55680, since the lower member of the outer container is formed of a material having a low thermal conductivity, it takes a large amount of power and a long time to melt the charged raw material. was there. Further, when the volume of the melt decreases due to the pulling of the single crystal and the position of the interface becomes lower than the upper end of the lower member, heat conduction from the upper member with high thermal conductivity disappears, so the temperature of the melt is maintained. Therefore, the power of the heater must be greatly increased, and the power consumption is large. Furthermore, graphite, which has low thermal conductivity, has low mechanical strength,
There was also a problem that the crucible had a short life. On the other hand, special fairness 4
Even the crucible disclosed in the −75880 publication cannot solve these problems.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a heat insulating portion at a predetermined distance from the bottom of the outer container so as to prevent heat radiation from the bottom of the outer container. Providing a crucible capable of pulling a single crystal while preventing the increase in power consumption without interrupting the heat conduction in the outer container wall reaching the bottom of the outer container and requiring a long time for melting the raw material. To do.

[0010]

In a crucible for pulling a single crystal according to a first aspect of the present invention, an outer container provided with a heat insulating portion in a circumferential direction is fitted in an inner container for storing a molten liquid of a raw material, In a crucible used for pulling a single crystal from a molten liquid, the heat insulating portion is provided below a position half the height of the inner container.

A crucible for pulling a single crystal according to the second invention is
In the first invention, the outer container is provided with a bowl-shaped lower portion at a lower end of a cylindrical straight body portion, and the heat insulating portion is provided at a boundary portion between the straight body portion and the lower portion.

A crucible for pulling a single crystal according to the third invention is
1st or 2nd invention WHEREIN: The said heat insulation part is cyclic | annular, It is characterized by the above-mentioned.

A crucible for pulling a single crystal according to a fourth invention is
In the first or second aspect of the invention, a plurality of the heat insulating parts are provided at appropriate intervals in the circumferential direction of the outer container.

FIG. 4 is an explanatory diagram for explaining heat conduction in the crucible during pulling of a single crystal. Most of the heat Q _h given to the crucible 21 from the heater 13 is the outer container 23 and the inner container 22.
Is given to the melt L by conducting the
It becomes the heat Q _w conducted in the wall of 23. On the other hand, in the bowl-shaped lower portion of the crucible 21, heat Q _e is radiated downward from the lower end of the heater 13 from the peripheral surface of the outer container 23. Then, from this heat Q _e , the heat Q _w conducted to the lower part of the crucible 21 and the heater 13
When the sum of the heat and the heat Q _h given to the lower part of the crucible 21 is larger, the difference heat Q _cond is the melt L at the bottom of the crucible 21.
The temperature of the melt L in the lower part of the crucible 21 becomes higher than that of the melt L in the vicinity of the surface, and the convection in the vertical direction is generated in the melt L.

Therefore, by providing a heat insulating portion in the outer container 23 so as to reduce the heat Q _w conducted to the bottom of the outer container 23 without hindering the release of the heat Q _e by radiation as much as possible, the heat Q _e is reduced. It is possible to efficiently reduce the _{co nd} . In particular,
The outer container is provided with a heat insulating part as follows.

The outer container 23 is provided with an annular heat insulating portion. The position where this heat insulating portion is provided may be below the half height position of the inner container 22 and at a position separated from the bottom of the outer container 23 by a predetermined distance, but the optimum position is the outer container 23. It is the boundary between the cylindrical straight body part and the lower part of the bowl. As a result, the heat Q _w can be prevented from being conducted to the bottom of the crucible 21 without blocking the release of the heat Q _e by radiation from the bowl-shaped lower portion of the outer container 23. On the other hand, the heat insulating part does not prevent heat input from the heater 13 to the lower part of the crucible 21, so that the heat efficiency as a whole is high and the power consumption is low.

A plurality of heat insulating parts may be provided at a predetermined distance in the circumferential direction of the outer container 23 depending on the conditions such as the size of the crucible and the size of the heater. In this case, the amount of heat Q _w conducted to the lower part of the crucible 21 is adjusted by adjusting the area of each heat insulating portion. Further, by providing the heat insulating portion in this way, a connecting portion between the straight body portion and the lower portion of the outer container 23 is formed, and a decrease in mechanical strength of the outer container is prevented.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a schematic side sectional view showing a main part of an apparatus used for pulling a single crystal by the CZ method and a crucible according to the present invention, and FIG. 2 is a side view of the crucible shown in FIG. The crucible 1 includes an inner container 2 made of quartz, which is formed by providing a bowl-shaped lower portion at a lower end of a cylindrical straight body portion, and an inner container 2
An outer container 3 made of graphite, which is similar in shape to, is fitted on the outside. The crucible 1 is a pan 11 in which a recess is formed in the center of the upper surface of a graphite disk.
The tray 11 and the crucible 1 are placed on the top of the tray 11. The tray 11 and the crucible 1 are rotated by a rotating shaft 12 made of graphite attached to the center of the lower surface of the tray 11 and moved up and down.

On the outside of the crucible 1, a resistance-heating type cylindrical heater 13 is arranged concentrically with the crucible 1. Also, crucible 1
A rod-shaped or wire-shaped pull-up shaft 14 is arranged on the central axis of, and a seed crystal 15 is attached to the lower end of the pull-up shaft 14.

In order to pull a single crystal by the CZ method with such an apparatus, the raw material charged into the crucible 1 is melted by the heater 13 to form a molten liquid L, and the seed crystal attached to the lower end of the pulling shaft 14 is used. By bringing 15 into contact with the surface of the melt L and rotating the pulling shaft 14 and the rotating shaft 12 in opposite directions while pulling up the pulling shaft 34 at a predetermined speed, a single crystal is formed below the seed crystal 15. Grow 16 Then, as the melt L is reduced by pulling up the single crystal 16, the crucible 1 is raised by the rotary shaft 12 to keep the surface height of the melt L substantially constant.

An annular heat insulating portion 5 having a predetermined width is provided at a boundary portion between the straight body portion and the bowl-shaped lower portion of the outer container 3 described above. The heat insulating part 5 is made of graphite and has a thermal conductivity lower than that of the outer container 3 by 2 to 3 digits. This prevents the heat conducted in the wall of the outer container 3 from being transferred to the lower part of the crucible 1 without hindering the heat radiation by the radiation from the lower peripheral surface of the outer container 3, so that the melt at the bottom of the crucible 1 is prevented. The temperature rise of L is prevented. On the other hand, the heat insulating unit 5 does not hinder the heat input from the heater 13 to the lower portion of the outer container 3, and thus has high thermal efficiency as a whole and therefore consumes less power. The position where the heat insulating portion 5 is provided is optimal at the boundary portion described above. It is because the straight body part of the outer container 3 faces the heater 13, and when the heat insulating part 5 is provided above the boundary portion, it enters the straight body part below the heat insulating material 5 by the radiation from the heater 13. This is because heat is conducted to the molten liquid L on the bottom of the crucible 1. However, the above-mentioned effect is obtained by the heat insulating
Since the position where the heat insulating material 5 is provided is below half of the height of the inner container 2 and a position separated from the bottom of the outer container 3 by a predetermined distance, the position where the heat insulating material 5 is provided is within such a range. It is determined according to the size of the crucible 1 and the degree of the desired effect.

Although the heat insulating portion 5 shown in FIG. 1 has the same thickness as that of the outer container 3, the present invention is not limited to this and may be thinner than the outer container 3. In this case, an annular groove is provided on the outer peripheral surface of the outer container 3, and a heat insulating member having the same thickness as the depth of the groove is fitted into the groove to form the heat insulating portion 5. This improves the mechanical strength of the outer container 3.

Further, as described above, when the annular heat insulating portion 5 is interposed in the outer container 3, the heat insulating portion 5 is formed by sintering fibrous graphite in an annular shape. In such a heat insulating portion 5, since it has a large amount of voids inside, the heat conductivity is small. Furthermore, since it is sintered, it has a large mechanical strength and can be used as a part of the outer container 3 without any problem. On the other hand, when fitting the heat insulating part 5 to the groove provided on the outer peripheral surface of the outer container 3, the mechanical strength does not need to be considered so much, so sintering is omitted and fibrous graphite is used.

FIG. 3 is a side view showing another embodiment according to the present invention. A plurality of block-shaped heat insulating parts 6, 6, ... Are provided at predetermined intervals in the circumferential direction at the boundary between the straight body part of the outer container 3 and the bowl-shaped lower part. 、…
This reduces the amount of heat conducted downward in the wall of the outer container 3. On the other hand, the straight body part and the bowl-shaped lower part of the outer container 3 are
The mechanical strength of the outer container 3 is higher than that of the outer container 3 shown in FIGS. 1 and 2 because the heat insulating parts 6 and the heat insulating part 6 are connected by a gap. The reduction of the amount of heat conducted to the lower part of the crucible 1 can be adjusted by the area and shape of the heat insulating parts 6, 6, ....

[0025]

EXAMPLES Next, the results of a pulling test of a single crystal using a crucible provided with a heat insulating portion as shown in FIGS. 2 and 3 will be described. A single crystal was pulled under the conditions of Table 2 using a crucible having a diameter of 16 inches and a height of 14 inches and provided with a heat insulating portion as shown in Table 1 below.

[0026]

[Table 1]

[0027]

[Table 2]

As a result of examining the heat removal effect from the bottom of the crucible, the temperature rise of the melt in the bottom of the crucible was suppressed in all cases, and the effect was improved in the order of C <A <D <B.

[0029]

As described in detail above, in the crucible for pulling a single crystal according to the first aspect of the present invention, the wall of the outer container is placed inside the wall of the outer container without hindering heat radiation from the lower peripheral surface of the outer container. The amount of heat conducted to the lower part of the crucible is reduced, and the temperature rise of the melt at the bottom of the crucible is efficiently suppressed. On the other hand, the heat insulating portion does not hinder the heat input from the heater to the lower portion of the outer container, and thus has high thermal efficiency as a whole and low power consumption. Further, since the area occupied by the heat insulating portion is not wide, the mechanical strength of the outer container is prevented from being lowered, and the life of the crucible is long.

In the crucible for pulling a single crystal according to the second aspect of the present invention, since the heat insulating portion is provided at the boundary between the straight body portion of the outer container and the bowl-shaped lower portion, the temperature rise of the melt at the bottom of the crucible is increased. Has the highest suppression effect.

In the crucible for pulling a single crystal according to the third aspect of the invention, since the heat insulating portion is provided in an annular shape, the effect of reducing the amount of heat conducted through the wall of the outer container to the lower part of the outer container is great.

In the crucible for pulling a single crystal according to the fourth aspect of the invention, since a plurality of heat insulating portions are provided at a predetermined distance in the circumferential direction of the outer container, the deterioration of the mechanical strength of the outer container is further suppressed. Etc., the present invention has excellent effects.

[Brief description of drawings]

FIG. 1 is a schematic side sectional view showing a main part of an apparatus used for pulling a single crystal by a CZ method and a crucible according to the present invention.

FIG. 2 is a side view of the crucible shown in FIG.

FIG. 3 is a side view showing another embodiment according to the present invention.

FIG. 4 is an explanatory diagram illustrating heat conduction in a crucible during pulling of a single crystal.

FIG. 5 is a schematic side sectional view showing an essential part of an apparatus used for pulling a single crystal by the CZ method and a conventional crucible.

[Explanation of symbols]

 1 Crucible 2 Inner Vessel 3 Outer Vessel 5 Heat Insulation Part 6 Heat Insulation Part 13 Heater 16 Single Crystal L Molten Liquid

Claims (4)

[Claims] 1. A crucible used for pulling a single crystal from the melt, wherein an outer container provided with a heat insulating portion in the circumferential direction is fitted to an inner container for storing the melt of the raw material. Is a crucible for pulling a single crystal, wherein the crucible is provided below a position half the height of the inner container. 2. The outer container is provided with a bowl-shaped lower portion at the lower end of a cylindrical straight body portion, and the heat insulating portion is provided at a boundary portion between the straight body portion and the lower portion. Crucible for pulling crystals. 3. The heat insulating portion has a ring shape.
The single crystal pulling crucible described. 4. The crucible for pulling a single crystal according to claim 1, wherein a plurality of the heat insulating parts are provided at appropriate intervals in the circumferential direction of the outer container.