KR20120014534A

KR20120014534A - Electromagnetic casting apparatus for silicon ingot

Info

Publication number: KR20120014534A
Application number: KR1020100134399A
Authority: KR
Inventors: 겐이치 사사타니
Original assignee: 사무코 솔라 가부시키가이샤
Priority date: 2010-08-09
Filing date: 2010-12-24
Publication date: 2012-02-17
Also published as: JP2012036045A

Abstract

The silicon raw material is introduced into the conductive bottomless cooling crucible through the raw material introduction tube, and by the electromagnetic induction heating from the induction coil surrounding the cooling crucible, and the plasma arc heating from the plasma torch inserted at the top of the cooling crucible. In an electronic casting apparatus in which a silicon raw material is melted and the molten silicon is solidified while being pulled down from a cooling crucible to continuously cast a silicon ingot, a through hole is formed in the side wall of the cooling crucible, and the raw material introduction pipe is connected to the through hole. It is. As a result, the silicon raw material can be prevented from coming into contact with the plasma torch as the silicon raw material is introduced into the cooling crucible, the metal impurity contamination of the molten silicon can be suppressed, and the melting of the silicon raw material can be stabilized.

Description

ELECTROMAGNETIC CASTING APPARATUS FOR SILICON INGOT

The present invention relates to an electronic casting device for continuously casting a silicon ingot that is a raw material of a solar cell substrate.

As a substrate of a solar cell, it is mainstream to use a polycrystalline silicon wafer. The polycrystalline silicon wafer is made of a silicon ingot of solidification in one direction and manufactured by slicing this ingot. Therefore, in order to spread the solar cell, it is necessary to secure the quality of the silicon wafer and to reduce the cost. Therefore, it is required to manufacture the silicon ingot with high quality and low cost in the previous step. As a method which can respond to this request, for example, as disclosed in Patent Literature 1, a continuous casting method using the electromagnetic induction (hereinafter also referred to as "electron casting method") has been put into practical use.

4 is a diagram schematically showing a configuration of a conventional representative electronic casting apparatus used in the electronic casting method. As shown in this figure, the electronic casting device includes a chamber 1. The chamber 1 is a double-walled water-cooled container that keeps the interior from outside air and is kept in an inert gas atmosphere suitable for casting. The raw material supply hopper 2 is connected to the upper wall of the chamber 1. In the chamber 1, an inert gas inlet 5 is provided at an upper portion, and an exhaust port 6 is provided at a lower side wall.

In the chamber 1, a bottomless cooling crucible 7, an induction coil 8, and an after heater 9 are arranged. The cooling crucible 7 functions not only as a melting vessel but also as a mold, and is suspended in the chamber 1 by a cylindrical body made of a metal (for example, copper) having excellent thermal conductivity and conductivity. The cooling crucible 7 is formed with a plurality of slits not shown in the vertical direction, leaving the upper and lower portions, and are divided into a plurality of rectangular small pieces in the circumferential direction by the slits, and flows through the inside. Forced cooling by the cooling water.

The induction coil 8 is provided concentrically with the cooling crucible 7 so as to surround the cooling crucible 7, and is connected to a power supply device (not shown). The after-heater 9 is connected concentrically with the cooling crucible 7 to the lower part of the cooling crucible 7, heats the silicon ingot 3 drawn out from the cooling crucible 7, and heats appropriately in the axial direction. Give a gradient.

Moreover, in the chamber 1, the raw material introduction pipe | tube 110 is arrange | positioned under the raw material supply hopper 2. The granular or bulk silicon raw material 11 is supplied from the raw material supply hopper 2 to the raw material introduction pipe 110 and through this raw material introduction pipe 110 into the cooling crucible 7 from above the cooling crucible 7. Is committed.

In the bottom wall of the chamber 1, the outlet 4 for extracting the ingot 3 is provided just below the after heater 9, and the outlet 4 is sealed. The ingot 3 is pulled down while being supported by the support 14 descending through the outlet 4.

Immediately above the cooling crucible 7, the plasma torch 13 is provided to be liftable. The plasma torch 13 is connected to one pole of the plasma power supply apparatus (not shown), and the other pole is connected to the ingot 3 side. The plasma torch 13 is inserted into the upper portion of the cooling crucible 7 by lowering. In addition, the plasma torch 13 can be pivoted so as to draw a square in a horizontal plane while maintaining a constant distance from the inner wall of the cooling crucible 7 while being inserted into the upper portion of the cooling crucible 7.

In the electroforming method using such an electronic casting device, the silicon raw material 11 is injected into the cooling crucible 7, an alternating current is applied to the induction coil 8, and the plasma inserted into the upper portion of the cooling crucible 7. The torch 13 is energized. At this time, since each of the rectangular pieces constituting the cooling crucible 7 is electrically divided from each other, eddy currents are generated in each of the pieces according to the electromagnetic induction by the induction coil 8, and the inner wall of the cooling crucible 7 An eddy current on the side generates a magnetic field in the cooling crucible 7. Thereby, the silicon raw material 11 in the cooling crucible 7 is electromagnetically induction-heated and fuse | melted, and the molten silicon 12 is formed.

In addition, a plasma arc is generated between the plasma torch 13 and the molten silicon 12 that are inserted and rotated above the cooling crucible 7, and the silicon raw material 11 is heated and melted by plasma heating. The molten silicon 12 is efficiently formed by reducing the burden of electromagnetic induction heating.

The molten silicon 12 is in the inner normal direction of the molten silicon 12 surface due to the interaction of the magnetic field generated by the eddy current of the inner wall of the cooling crucible 7 and the current generated on the surface of the molten silicon 12. As a result of the force (pinch force), it remains in contact with the cooling crucible 7. When the support 14 supporting the molten silicon 12 is gradually lowered while melting the silicon raw material 11 in the cooling crucible 7, the induction magnetic field decreases as it moves away from the lower end of the induction coil 8, The amount of heat generated and the pinch force decrease, and solidification proceeds from the outer circumferential portion by cooling from the cooling crucible 7. Then, as the support 14 descends, the silicon raw material 11 is sequentially introduced from the upper side of the cooling crucible 7 through the raw material introduction pipe 110 to continue melting and solidification. It solidifies in this direction and can cast the ingot 3 continuously.

During casting, in order to maintain the inside of the chamber 1 in an inert gas atmosphere, an inert gas is sequentially supplied from the inert gas inlet 5 at the top of the chamber 1, and the inert gas in the chamber 1 is chambered. It is discharged sequentially from the exhaust port 6 of the lower side wall of (1).

According to such an electronic casting apparatus, since the contact of the molten silicon 12 and the cooling crucible 7 is reduced, the impurity contamination from the cooling crucible 7 according to the contact is reduced, and the high quality ingot 3 can be obtained. have. Moreover, since it is continuous casting, it becomes possible to manufacture the ingot 3 at low cost.

Patent Document 1: International Publication WO02 / 053496 Brochure

In the above-described conventional electronic casting apparatus, when the silicon raw material 11 is continuously introduced into the cooling crucible 7 through the raw material introduction pipe 110, the plasma torch 13 is inserted into the upper portion of the cooling crucible 7. As a result, the silicon raw material 11 introduced from the raw material introduction pipe 110 inevitably comes into contact with the plasma torch 13. This causes the following problems.

As for the plasma torch 13, the torch ram which is the outer shell is comprised by stainless steel etc., and the nozzle which is the front electrode is comprised by copper etc. For this reason, Fe, Ni, Cu, Cr, etc. are mixed in contact with the plasma torch 13, and the silicon raw material 11 is contaminated with metal impurities. As a result, the molten silicon 12 is also contaminated with metallic impurities, so that the ingot 3 cast from the molten silicon 12 is deteriorated in quality.

Moreover, since the silicon raw material 11 is disperse | distributed irregularly by contacting the turning torch 13 to rotate, since the position which falls and accumulates on the molten silicon 12 surface is changed, the silicon raw material 11 ) Fusion becomes unstable. For this reason, the special operation | movement which changes a casting speed largely and melt | dissolves the silicon raw material 11 sufficiently is forced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and when continuously casting a silicon ingot, the silicon raw material is prevented from coming into contact with the plasma torch due to the introduction of the silicon raw material into the cooling crucible, thereby preventing metal impurity contamination of the molten silicon. In addition, it aims at providing the electronic casting apparatus of the silicon ingot which can stabilize and melt | dissolve the silicon raw material.

MEANS TO SOLVE THE PROBLEM This inventor repeated earnestly, paying attention to the behavior of the silicon raw material thrown into a cooling crucible, in order to achieve the said objective. As a result, in order to prevent the silicon raw material from contacting the plasma torch, the silicon raw material is not introduced from above the cooling crucible, but a through hole is formed in the sidewall of the cooling crucible, and the silicon raw material is introduced into the cooling crucible from the through crucible. It was found that it was effective to inject and completed the present invention.

The gist of the present invention resides in an electron casting device of a silicon ingot shown below. That is, the silicon raw material is introduced into the conductive bottomless cooling crucible through the raw material introduction tube, the electromagnetic induction heating from the induction coil surrounding the bottomless cooling crucible, and the plasma inserted above the bottomless cooling crucible. In an electronic casting apparatus in which a silicon raw material is melted by plasma arc heating from a torch, and molten silicon is solidified while being pulled down from a bottomless cooling crucible to continuously cast a silicon ingot, which penetrates the sidewall of the bottomless cooling crucible. A hole is formed, and the raw material introduction pipe is connected to this through-hole, It is the electroforming apparatus of a silicon ingot.

In the above-mentioned electronic casting apparatus, it is preferable that the said raw material introduction tube is arrange | positioned at the inclination angle which inject | pours the said silicon raw material to the hot water center of the said molten silicon.

Moreover, in said electron casting apparatus, it is preferable that the inner surface of the said raw material introduction tube is covered by the silicone member.

According to the electronic casting apparatus of the silicon ingot of the present invention, when the silicon ingot is continuously cast, the silicon raw material is brought into contact with the plasma torch by injecting the silicon raw material into the cooling crucible through a raw material introduction pipe connected to the sidewall of the cooling crucible. Since it is possible to prevent the metal impurity contamination from the plasma torch, it is possible to suppress the metal impurity contamination of the molten silicon, and at the same time, the deposition position of the injected silicon raw material is constant, and the melting of the silicon raw material is stabilized.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically the structure of the electronic casting apparatus of this invention.
2 is a plan view schematically showing the appearance of a cooling crucible used in the electroforming apparatus of the present invention.
FIG. 3 is a diagram showing measurement results of metal impurity concentrations in silicon ingots by the test of Examples, FIG. 3 (a) shows Fe concentration, FIG. 3 (b) shows Ni concentration, and FIG. ) Represents Cu concentration, and FIG. 3 (d) represents Cr concentration.
4 is a diagram schematically showing a configuration of a conventional representative electronic casting apparatus used in the electronic casting method.

EMBODIMENT OF THE INVENTION Below, embodiment is described in detail about the electronic casting apparatus of the silicon ingot of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically the structure of the electronic casting apparatus of this invention. The electroforming apparatus of this invention shown in this figure is based on the structure of the electroforming apparatus shown in said FIG. 4, The same code | symbol is attached | subjected to the same structure as that, and the overlapping description is abbreviate | omitted suitably.

As shown in FIG. 1, the through-hole 7c is formed in the side wall of one of the four side walls of the cooling crucible 7 of the electronic casting apparatus of this invention. As for the raw material introduction pipe 10, the upper end is arrange | positioned directly under the raw material supply hopper 2, and the lower end is inserted in the through-hole 7c from the outer side of the cooling crucible 7, and is connected, and it is perpendicular from an upper end. It is a configuration which is bent at the side of the cooling crucible 7 and is inclined downwardly.

It is necessary to form the through hole 7c at a position higher than at least the height of the top end of the induction coil 8 and the height of the hot water surface of the molten silicon 12 in the cooling crucible 7. The through hole 7c is formed at a position higher than the top height of the induction coil 8 so as not to affect the electromagnetic induction by the induction coil 8. On the other hand, forming the through-hole 7c at a position higher than the molten silicon 12 height of the raw material is connected to the through-hole 7c while avoiding penetration of the molten silicon 12 into the through-hole 7c. This is for introducing the silicon raw material 11 onto the tap surface of the molten silicon 12 through the introduction pipe 10.

In addition, the through hole 7c is a plasma torch 13 into which the silicon raw material 11 introduced from the raw material introduction pipe 10 connected to the through hole 7c is inserted in the upper portion of the cooling crucible 7. It is necessary to form at the height which does not contact with. For example, the through hole 7c is preferably formed at a height overlapping with the front end (lower end) of the plasma torch 13 inserted in the upper portion of the cooling crucible 7 or at a lower position. In FIG. 1, the through-hole 7c has shown the example formed in the height which overlaps with the front-end | tip of the plasma torch 13. As shown in FIG.

Moreover, the inclination angle (theta) is set in the raw material introduction pipe | tube 10 so that the silicon raw material 11 may be thrown in the hot water center of molten silicon 12. As shown in FIG. It is preferable to make the inclination angle (theta) of the raw material introduction pipe 10 into the range of 40 degrees +/- 10 degrees when using each 345mm mold. This is because if the inclination angle θ is too small, the silicon raw material 11 is blocked in the raw material introduction pipe 10, so that the silicon raw material 11 can not be smoothly injected. On the contrary, when the inclination angle θ is too large, the silicon raw material 11 is largely displaced from the center of the hot water surface of the molten silicon 12 and introduced into the vicinity of one side wall of the cooling crucible 7, so that the melting of the silicon raw material 11 is unstable. For it is done.

In addition, since the silicon raw material 11 contacts the inner surface of the raw material introduction pipe 10, in order to prevent impurity contamination of the silicon raw material 11 due to this contact, a silicon member tile is bonded to the inner surface. The inner surface may be covered with a silicon member. As the silicon member, a silicon plate cut out from the ingot can be used.

2 is a plan view schematically showing the appearance of a cooling crucible used in the electroforming apparatus of the present invention. As shown in this figure, the cooling crucible 7 is formed with a plurality of slits 7a in the longitudinal direction in order to be divided into a plurality of rectangular small pieces 7b in the circumferential direction. In the inside of each small piece 7b, in order to force-cool the small piece 7b and to solidify the molten silicon in the cooling crucible 7, as shown by the broken arrow in FIG. Is formed.

Here, the space | interval of the slit 7a, the cross-sectional area and length of a cooling water path, etc. are set so that the cooling ability by cooling water may become the same over the whole circumference of the cooling crucible 7. For example, as shown in FIG. 2, in the small piece 7b in which the raw material introduction pipe 10 is connected upward, the cooling water path is longer than that of the other small pieces 7b and the cooling capacity is lowered. Therefore, the cross-sectional area of the cooling water is expanded. This suppresses the decrease in cooling capacity.

According to the electronic casting apparatus of such a structure, when continuously casting a silicon ingot, a silicon raw material can be thrown on the molten silicon in a cooling crucible without contacting a plasma torch via the raw material introduction tube connected to the side wall of a cooling crucible. . For this reason, metal impurity contamination from a plasma torch can be prevented, and metal impurity contamination of molten silicon can be suppressed, and an ingot excellent in quality can be manufactured. In addition, since the deposition position of the injected silicon raw material is constant and the melting of the silicon raw material is stabilized, no special operation for greatly varying the casting speed is required.

When the silicon raw material is placed in the center of the molten silicon, the melting of the silicon raw material is further stabilized, and since the injected silicon raw material does not come into contact with the inner wall of the cooling crucible, it is possible to prevent contamination of metal impurities from the cooling crucible. Can be.

[Example]

In order to confirm the effect by the electroforming apparatus of the present invention, a silicon ingot having a total length of 7000 mm was continuously cast in a square cross section having one side of 345 mm using the electroforming apparatus shown in FIG. 1. For comparison, silicon ingots having the same dimensions were continuously cast using the conventional electronic casting apparatus shown in FIG. 4. Any continuous casting was performed by three batches, the sample was taken from each obtained ingot, and the test which measured the density | concentration of a metal impurity was done.

The sample was extract | collected from each of the center part of an ingot and the outer peripheral part in the cross section corresponded to length 3600mm from the lower end (the position of the head of continuous casting) of an ingot. The concentration of metal impurities was measured by component analysis by all dissolution methods, and the respective concentrations of Fe, Ni, Cu, and Cr were evaluated as metal impurities.

FIG. 3 is a diagram showing measurement results of metal impurity concentrations in silicon ingots by the test of Examples, FIG. 3 (a) shows Fe concentration, FIG. 3 (b) shows Ni concentration, and FIG. 3 (c). ) Represents the concentration of Cu, and FIG. 3 (d) represents the Cr concentration. The density | concentration of each metal impurity shown in this figure is the value which divided | segmented into the example of this invention, and the comparative example, and averaged the measured value of three arrangement | positioning in each of the center part and outer peripheral part of an ingot.

From the results shown in Figs. 3A to 3D, in the example of the present invention in which the silicon raw material does not come into contact with the plasma torch when the silicon raw material is introduced, Fe and Ni are compared with the comparative example in which the silicon raw material comes in contact with the plasma torch. It has become clear that any metal impurities or concentrations of Cu, Cr and Cr can be reduced to suppress metal impurity contamination of molten silicon.

[Industrial Availability]

According to the electronic casting apparatus of the silicon ingot of the present invention, the silicon raw material can be prevented from contacting the plasma torch by introducing the silicon raw material into the cooling crucible through the raw material introduction pipe connected to the sidewall of the cooling crucible. Metal impurity contamination is prevented, and metal impurity contamination of the molten silicon can be suppressed, and at the same time, the deposition position of the injected silicon raw material is constant, and the melting of the silicon raw material is stabilized. Therefore, the electronic casting apparatus of this invention is extremely useful at the point which can manufacture the silicon ingot for solar cells excellent in quality efficiently.

1: Chamber 2: Raw material feed hopper
3: silicon ingot 4: outlet
5: inert gas inlet 6: exhaust port
7: cooling crucible without bottom 7a: slit
7b: small piece 7c: through hole
8: induction coil 9: after heater
10: raw material introduction pipe 11: silicon raw material
12: molten silicon 13: plasma torch
14: support θ: inclination angle

Claims

From the raw material introduction tube into the conductive bottomless cooling crucible, the silicon raw material is introduced, from the electromagnetic induction heating from the induction coil surrounding the bottomless cooling crucible, and from the plasma torch inserted on top of the bottomless cooling crucible. In an electronic casting apparatus for melting a silicon raw material by plasma arc heating of the molten silicon, the molten silicon is solidified while being pulled down from the bottomless cooling crucible to continuously cast a silicon ingot,
A through hole is formed in the side wall of a cooling crucible without a bottom, and the raw material introduction pipe | tube is connected to this through hole, The electronic casting apparatus of the silicon ingot.

The method according to claim 1,
The raw material introduction tube is arranged at an inclination angle to inject the silicon raw material into the center of the molten silicon of the molten silicon, characterized in that the electronic casting device of the silicon ingot.

The method according to claim 1 or 2,
The inner surface of the said raw material introduction tube is covered with the silicon member, The electronic casting apparatus of the silicon ingot.