JPH11199367A - Refrigerator-cooling type superconductive magnet device for pulling-up device of single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a refrigerator cooling type superconductive magnet device suitable for a device for pulling up a single crystal by a MCZ (Magnetic field- impressed type Czochralski) method. SOLUTION: This refrigerator-cooling type superconductive magnet device has a vacuum vessel 10 storing a superconductive coil 11a and 11b for providing a magnetic field to molten silicon, and arranged around a single crystal growing device, and a refrigerator 12a arranged at the upper part of the vacuum vessel 10 and used for cooling the superconductive coil. The superconductive coil is supported by a heat-conductive body 13 for cooling the coil as a coiling frame in the vacuum vessel, and the refrigerating stage 12-1 and 12-2 of the refrigerator is in the vacuum vessel and extended to the neighbor of a connecting part 13-1 installed in the heat-conductive body 13 for cooling the coil. The cold head 12-21 at the tip of a second stage refrigerating stage is connected to a connecting part by a flexible heat-conductive member 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refrigerator-cooled superconducting magnet device, and more particularly to a refrigerator-cooled superconducting magnet suitable for applying a magnetic field to molten silicon in a single crystal growing apparatus for producing a single crystal semiconductor from molten silicon. It relates to a magnet device.

[0002]

2. Description of the Related Art In the production of silicon single crystals, there is known a Czochralski method (CZ method) in which polycrystalline silicon is melted and grown into a single crystal seed crystal. In this method, since the molten silicon is melted in the crucible, thermal convection is generated and the quality of the generated single crystal may be deteriorated.
Therefore, a method of applying a magnetic field to molten silicon and suppressing convection by electromagnetic braking has been known for the purpose of improving the quality of the generated single crystal. This method is called a magnetic field application type Czochralski method (MCZ method).

[0003] As a method of applying a magnetic field, three types of a vertical magnetic field method, a horizontal magnetic field method, and a cusp magnetic field are known, and one example thereof is disclosed in JP-A-8-188493. As a means for applying a magnetic field, a normal conducting magnet and a superconducting magnet are used. However, the normal conducting magnet is heavy in weight because the use of an iron core is indispensable, and requires enormous power and cooling water. On the other hand, a superconducting magnet usually requires liquid helium cooling, so that the device becomes complicated and large. In addition, the handling of liquid helium is complicated and requires the skill of an operator. In addition, liquid helium must be replenished, and liquid helium costs are high.

[0004]

By the way, a superconducting magnet (helium-free superconducting magnet) device using an oxide superconducting current lead and conducting and cooling a superconducting coil only with a small refrigerator is provided. This type of superconducting magnet device is called a refrigerator-cooled superconducting magnet device, is easy to operate, and is considered suitable for a silicon single crystal pulling device. However, the above-mentioned single crystal pulling apparatus by the MCZ method is required to have performances such as stable generation of a magnetic field, simple operation, high reliability, and a small leakage magnetic field.

Accordingly, an object of the present invention is to provide a refrigerator-cooled superconducting magnet apparatus for a single crystal pulling apparatus capable of satisfying the above-mentioned performance.

[0006]

According to the present invention, there is provided a refrigerator cooled superconducting magnet apparatus for applying a magnetic field to molten silicon in a single crystal growth apparatus for producing a single crystal semiconductor from molten silicon. A vacuum vessel arranged around the device and containing a superconducting coil for generating the magnetic field, and a refrigerator disposed on the upper part of the vacuum vessel for cooling the superconducting coil, wherein the superconducting coil is , Is supported by a coil cooling heat conductor as a winding frame in the vacuum vessel, and a refrigeration stage of the refrigerator is provided in the vacuum vessel and has a connection portion provided on the coil cooling heat conductor. It extends to the vicinity and is connected between the cold head at the tip of the refrigeration stage and the connection portion by a flexible heat transfer member.

It is preferable that the vacuum vessel has a double cylindrical structure capable of surrounding the single crystal growing apparatus, and the heat conductor for cooling the coil has a cylindrical shape. The superconducting coil includes two split coils for applying a caps-like magnetic field to the molten silicon, and each split coil is concentric with the center of the vacuum vessel above and below the coil cooling heat conductor. It is wound so that it becomes.

[0008] Further, the two split coils and the heat conductor for cooling the coil may be a double cylindrical heat shield disposed in the vacuum vessel together with the cold head and the heat transfer member at the tip of the refrigeration stage. Housed in a container.

In order to separate the electric motor constituting a part of the refrigerator from the superconducting coil, a mounting portion of the motor in the vacuum vessel is extended upward in a cylindrical shape, and a refrigeration stage of the refrigerator is provided. Preferably, the extension of the refrigeration stage is accommodated by extending a portion corresponding to the heat shield container upward in a cylindrical shape.

In this case, it is preferable that a plurality of slits are formed at intervals in the circumferential direction in a region below the cylindrical extension in the heat shield container.

The number of the refrigerators may be one. However, when at least two refrigerators are arranged, they are preferably arranged adjacent to each other or at a position facing each other in the diametrical direction of the vacuum vessel.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. A refrigerator-cooled superconducting magnet device according to the first embodiment is disposed around a single crystal growth device (not shown), and includes a vacuum vessel 10 containing superconducting coils 11a and 11b for generating a magnetic field.
The superconducting coil 11a, which is arranged on the upper part of the vacuum vessel 10,
It is provided with two refrigerators 12a and 12b for cooling 11b. A compressor for compressing and supplying and circulating helium gas as a refrigerant is connected to the refrigerators 12a and 12b. Briefly, the refrigerators 12a and 12b shown include an electric motor that switches a rotary valve for switching the introduction and discharge of helium gas, and a reciprocating motion that is connected to a displacer and converts the reciprocating motion into a rotary motion. And a motion conversion mechanism for setting the upper and lower limits. The details are disclosed in JP-B-63-53469, so that illustration and description are omitted here.
The superconducting coils 11a and 11b are supported in the vacuum vessel 10 by a coil cooling heat conductor 13 as a winding frame.
Since the refrigerators 12a and 12b have exactly the same structure,
Hereinafter, only the refrigerator 12a will be described.

The refrigerator 12a has a first stage refrigeration stage 12-1 having a 50K first stage cold head 12-11.
And a second-stage refrigeration stage 12-2 having a 4K second-stage cold head 12-21.
The refrigeration stages 12-1 and 12-2 are located in the vacuum vessel 10, and particularly, the refrigeration stage 12-2 extends to near the connection portion 13-1 provided on the coil-cooling heat conductor 13. The second stage cold head 12-21 at the tip of the refrigeration stage 12-2 and the connection portion 13-1 are connected by a heat transfer member 14 having flexibility.

The vacuum vessel 10 has a double cylindrical structure capable of surrounding the periphery of a single crystal growth apparatus, and the heat conductor 13 for cooling the coil is also formed in a cylindrical shape. That is, the single crystal growth apparatus is arranged in a space formed inside vacuum chamber 10. Since this single crystal growth apparatus may be the same as the conventional one, illustration and description are omitted. The superconducting coils 11a and 11b are two split type coils for applying a caps-like magnetic field to the molten silicon in the crucible of the single crystal growing apparatus. The superconducting coils 11a and 11b formed by these two split type coils are wound so as to be concentric with the center of the vacuum vessel 10 above and below the coil cooling heat conductor 13.

Further, two superconducting coils 11a, 11b
The heat conductor 13 for cooling the coil is connected to the refrigeration stage 12-
2 and the heat transfer member 14 are housed in a double cylindrical heat shield container 15 arranged in the vacuum container 10.
The heat shield container 15 is for preventing radiant heat from entering. Two superconducting coils 11a, 11b,
Coil cooling heat conductor 13 and heat shield container 15
Is supported by a plurality of load supports 16a and 16b provided at intervals in the circumferential direction at the top and bottom in the vacuum vessel 10. Needless to say, the vacuum container 10 has a sealed structure, but the heat shield container 15 is also preferably formed to have a sealed structure from the viewpoint of preventing intrusion of radiant heat. In addition, although one refrigerator may be used, when two refrigerators are arranged as in this example, they are arranged adjacent to each other as shown in the figure, or are arranged at positions facing each other in the diameter direction of the vacuum vessel 10. Is preferred.

Next, each of the above components will be described.

The vacuum container 10 is a container for maintaining adiabatic vacuum, and serves as a fulcrum for supporting loads of the superconducting coils 11a and 11b, the heat shield container 15, the refrigerator, and the like. The vacuum vessel 10 can be formed by a welding structure or a flange structure. In the case of a flange structure as in this embodiment,
It can be easily disassembled. In the case of a welding structure, it is preferable to provide a partially removable box so that maintenance can be performed only on the portion where the current lead and the refrigerator are installed.

The superconducting coils 11a and 11b are formed of a metal or oxide superconducting wire. The superconducting coils 11a and 11b are of a split type in which two coils wound in a cylindrical shape are installed at intervals in the vertical direction.
Currents in opposite directions are applied to each coil to form a cusp-shaped magnetic field. With respect to the winding diameter D of the superconducting coils 11a and 11b, the coil interval G is set to 0.1D <G <0.5D
And

Although not shown, a current lead is used as a means for supplying a current from outside the vacuum vessel 10 to the internal superconducting coils 11a and 11b. As the current lead, a current lead made of an oxide superconductor is used to supply current to the superconducting coils 11a and 11b while reducing the heat entering the heat shield container 15. As a material, a bismuth-based or yttrium-based material is used. In addition, a bulk body or a wire can be used as the oxide superconductor. In this case, since the material has a small mechanical strength, the junction with the superconducting coil that needs to reduce heat generation is fixed, and the other end is anchored to the temperature of the first stage refrigeration stage of the refrigerator. Free end for stress relaxation due to thermal shrinkage. That is, they are joined by a flexible member to which a laminated board, a flat wire, or the like is applied. Both ends of the oxide superconductor are coated with silver by thermal spraying, and electrodes are joined thereon by soldering. As a result, a current lead having a small contact resistance and a small Joule heat can be obtained.

As the refrigerators 12a and 12b, use small reliable refrigerators such as GM refrigerators. When a two-stage refrigerator is applied as in the present embodiment, the first-stage cold head 12-11 is attached to the heat-shield container 15, and the first-stage refrigeration stage 12-1 is used to remove the heat-shield container 15. After cooling, the second stage cold head 12-21 is connected to the connection portion 13-
1, the superconducting coils 11a and 11b can be cooled by the second freezing stage 12-2. Note that another refrigerator may be added exclusively to the heat shield container 15. The cold head of each refrigeration stage and the superconducting coils 11a, 11b or the heat shield container 15 may be directly joined. However, in order to prevent the occurrence of stress due to heat shrinkage, the stress is reduced as in the present embodiment. It is effective to interpose a heat transfer member 14 having a function of performing the heat transfer.

The coil cooling heat conductor 13 is formed of a material having a high heat conductivity such as copper or aluminum. In the case of using a material having poor thermal conductivity, for example, stainless steel or FRP, a foil-like high heat conductive material such as copper or aluminum is attached to the surface thereof.

The heat transfer member 14 is, for example, a laminate of a copper plate and a high-purity aluminum plate. As an example, it is assumed that a laminate of two copper plates each having a thickness of 1 mm and a high-purity aluminum plate is bent into a substantially U shape as illustrated. One end of the heat transfer member 14 is bolted to the second cold head 12-21 of the second refrigeration stage 12-2, and the other end is bolted to a connection portion of the heat conductor 13 for cooling the coil.
When the heat transfer member 14 having such a laminated structure is used, the time required for cooling is the same as that using a copper-only plate, and the cooling characteristic is better than that using a copper-only plate at a low temperature (about 4K). The number of layers of the copper plate and the high-purity aluminum plate is not limited to two, but it is preferable that the total thickness be small.

The heat shield container 15 includes the superconducting coil 11
In order to reduce the heat intrusion into the superconducting coils 11a and 11b, heat radiation is reduced by surrounding the superconducting coils 11a and 11b. This heat shield container 15 is joined to the first stage call head 12-11 of the first stage cooling stage 12-1 of the refrigerator. Also in this case, it is preferable to realize a thermally favorable joint by a flexible member so that excessive thermal stress is not generated in the cylinder of the refrigerator due to heat shrinkage. In order to enhance the effect of reducing heat radiation, a multilayer heat insulating material (super insulation) can be used in combination. The heat shield container 15 is made of a material having excellent heat transfer characteristics, such as copper and aluminum. If you need mechanical strength,
It is also possible to use stainless steel as the strength member and to use copper and aluminum together as the heat member. Further, in order to prevent quench of the superconducting coils 11a and 11b and eddy current due to rapid magnetic field fluctuation, a slit may be partially formed in the length direction as described later. In this case, the width of the slit is set to several mm in consideration of the influence of heat radiation.

The load supports 16a, 16 are members for supporting the superconducting coils 11a, 11b, the coil cooling heat conductor 13, and the heat shield container 15, and have excellent heat insulation performance while maintaining mechanical strength. There is a need. As the material, for example, GFRP, CFRP, stainless steel, etc. can be applied. As an example of the support structure, a superconducting coil
A configuration in which a plurality of pipe-shaped GFRP materials are supported from a vacuum container is known. This pipe-shaped GFRP material has a heat shield container and an anchor at an intermediate portion to reduce invasion heat due to conduction. In the present embodiment, a plurality of pipe-shaped load supports 16a and 16b are provided at intervals above and below the vacuum vessel 10 and in the circumferential direction, respectively, and support the superconducting coils 11a and 11b insulated.
With such a simple support structure, it is possible to provide not only a load in the vertical direction but also a load support function in the lateral direction. In some cases, wires or pipes that protrude from the lateral direction are used to support the lateral load.However, a structure that supports the superconducting coil with only vertical members is simple, easy to manufacture, and reliable. It is highly likely.

In addition to the above components, if necessary,
By providing a magnetic shield made of a ferromagnetic material on the outside (upper and lower surfaces, outer peripheral surface, or both) of the vacuum vessel 10, it is possible to reduce the leakage magnetic field to the peripheral part of the vacuum vessel 10.

With the above configuration, a refrigerator-cooled superconducting magnet device suitable for the magnetic field application type Czochralski method which is simple in structure, resistant to thermal stress, lightweight and compact, easy to operate, and highly reliable can be provided. .

Next, a second embodiment of the present invention will be described with reference to FIGS. The feature of the second embodiment is that the installation locations of the electric motors 12a-1 and 12b-1 constituting the above-described refrigerators 12a and 12b are separated from the superconducting coil as compared with the first embodiment. It is in.
This is because a refrigerator, particularly an electric motor, may malfunction due to leakage magnetic flux from the superconducting coil. Therefore, the configuration is the same as that of the first embodiment except that the installation positions of the motors 12a-1 and 12b-1 are separated from the superconducting coil, and the same parts as those in FIGS. Description is omitted. Again, the refrigerator 12a
Will be described.

In order to separate the electric motor 12a-1 of the refrigerator 12a from the superconducting coil 11a, a mounting portion of the electric motor 12a-1 in the vacuum vessel 10 is formed to extend upward in a cylindrical shape. That is, the cylindrical vacuum vessel extension 1 is attached to the upper end of the vacuum vessel 10 corresponding to the mounting portion of the electric motor 12a-1.
0-1 is provided. In accordance with this, a heat shield extension 15-1 is also provided at the upper end of the heat shield container 15. Further, the second refrigeration stage 12- of the refrigerator 12a
The second cold head 12-21 is provided with a cold head extension 12-22.
−22 is connected to the connecting portion 13 of the coil cooling heat conductor 13.
It is located near -1. This is because the length of the heat transfer body 14 is preferably as short as possible. Conversely, if the length of the heat transfer body 14 is increased, it is necessary to increase the plate thickness in order to improve heat conduction. When the plate thickness is increased, the rigidity is increased, and it becomes impossible to cope with heat shrinkage. The heat shrinkage is caused by the shrinkage of the superconducting coil when it is cooled. Since the temperature difference is large, the distortion due to heat increases.

The heat shield extension 15-1 is made of a material having good heat conductivity, such as copper or aluminum. Here, the heat shield extension 15-1 has a cylindrical shape with a thickness of 20 mm, and eight slits are formed in the lower region at intervals in the circumferential direction. Then, the heat shield container 1 is provided at the lower end of the heat shield extension 15-1 divided into eight equal parts.
5 is bolted to the upper end. The reason why the slits are provided as described above is that a large distortion due to heat shrinkage occurs in the heat shield container 15 made of a thin plate, and this distortion acts on the heat shield extension 15-1, and absorbs this distortion. That's why. In other words, the shield extension 15-
If 1 is a cylindrical rigid body, the difference in heat shrinkage between the cylindrical rigid body and the heat shield container 15 is large, so that the cylindrical rigid body is distorted. To absorb such distortion,
A slit is provided in the shield extension 15-1.

The cold head extensions 12-22 are also made of copper,
It uses a material with good thermal conductivity, such as aluminum, but is made in a block shape instead of hollow.

The refrigerator-cooled superconducting magnet apparatus according to the present invention described above is suitable for generating a cusp-type magnetic field as a magnetic field source in a silicon single crystal pulling apparatus using a magnetic field applying Czochralski method.

[0032]

The refrigerator-cooled superconducting magnet apparatus according to the present invention does not require any operation related to cooling once the refrigerator is started, and does not require any skill for cooling. Then, after several hours to several tens of hours, the superconducting coil reaches the superconducting temperature. When required, the excitation power supply can be operated to generate a predetermined magnetic field.

Further, the heat convection of the molten silicon is suppressed by the generated cusp magnetic field, and a silicon single crystal of stable quality can be obtained.

Further, since only the power of the compressor for the refrigerator, the water and the power of the power supply for exciting the superconducting coil are required, the running cost can be greatly reduced.

Since the magnet device is lightweight and compact, it can be operated with low power when changing the height of the magnet in the lifting process.

[Brief description of the drawings]

FIG. 1 is a plan view of a refrigerator-cooled superconducting magnet device according to a first embodiment of the present invention.

FIG. 2 is a longitudinal sectional view taken along line AA of FIG.

FIG. 3 is a diagram showing a structure around a refrigerator in FIG. 2;

FIG. 4 is a plan view of a refrigerator-cooled superconducting magnet device according to a second embodiment of the present invention.

FIG. 5 is a longitudinal sectional view taken along line BB in FIG. 4;

FIG. 6 is a diagram showing a structure around a refrigerator in FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Vacuum container 10-1 Vacuum container extension part 11a, 11b Superconducting coil 12a, 12b Refrigerator 12a-1, 12b-1 Electric motor 12-1 First refrigeration stage 12-2 Second refrigeration stage 12-11 Single-stage cold head 12-21 Second-stage cold head 12-22 Cold head extension 13 Heat conductor for coil cooling 13-1 Connection 14 Heat transfer member 15 Heat shield container 15-1 Heat shield extension 16a, 16b Load Support

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 21/208 H01F 7/22 G

Claims (7)

[Claims] 1. A refrigerator cooled superconducting magnet apparatus for applying a magnetic field to said molten silicon in a single crystal growth apparatus for producing a single crystal semiconductor from molten silicon, wherein said magnetic field is disposed around said single crystal growth apparatus. A vacuum vessel containing a superconducting coil for generating a vacuum vessel, and a refrigerator disposed on the upper portion of the vacuum vessel for cooling the superconducting coil, wherein the superconducting coil is used as a bobbin in the vacuum vessel. And a refrigeration stage of the refrigerator is provided in the vacuum vessel and extends close to a connection portion provided on the coil cooling heat conductor, and the refrigeration stage A refrigerator-cooled superconducting magnet device for a single crystal pulling device, wherein a cold head at the tip and the connecting portion are connected by a heat transfer member having flexibility. 2. The refrigerator according to claim 1, wherein the vacuum vessel has a double cylindrical structure capable of surrounding the periphery of the single crystal growth apparatus, and the heat conduction for cooling the coil. A refrigerator-cooled superconducting magnet device for a single crystal pulling device, wherein the body has a cylindrical shape. 3. The refrigerator-cooled superconducting magnet device according to claim 2, wherein the superconducting coil comprises two split coils for applying a caps-like magnetic field to the molten silicon. A refrigerator-cooled superconducting magnet device for a single crystal pulling device, which is wound above and below the coil cooling heat conductor so as to be concentric with the center of the vacuum vessel. 4. The refrigerator-cooled superconducting magnet device according to claim 3, wherein the two split coils and the heat conductor for cooling the coil are provided together with a cold head and a heat transfer member at the tip of the refrigeration stage. A refrigerator-cooled superconducting magnet device for a single crystal pulling device, which is housed in a double cylindrical heat shield container disposed in a vacuum container. 5. The refrigerator-cooled superconducting magnet device according to claim 4, wherein a mounting portion of the vacuum vessel for mounting the motor is separated from the superconducting coil in order to separate a motor constituting a part of the refrigerator from the superconducting coil. Along with being configured to extend upward in a cylindrical shape, the refrigeration stage of the refrigerator is also extended, and a portion corresponding to the heat shield container is extended upward to accommodate a portion corresponding to the heat shield container. A refrigerator-cooled superconducting magnet device for a single crystal pulling device, characterized in that: 6. The refrigerator-cooled superconducting magnet device according to claim 5, wherein a plurality of slits are formed at intervals in a circumferential direction in a region below the cylindrical extension in the heat shield container. A refrigerator cooled superconducting magnet device for a single crystal pulling device. 7. The refrigerator-cooled superconducting magnet device according to claim 4, wherein the refrigerator is at least two times.
A refrigerator-cooled superconducting magnet device for a single crystal pulling device, which is arranged adjacent to each other or at a position facing the diameter direction of the vacuum vessel.