KR20120015981A - Electromagnetic casting apparatus for silicon ingot - Google Patents

Abstract

PURPOSE: An electronics molding device of a silicon ingot is provided to accurately monitor the temperature variation of a casting surface of the silicon ingot based on temperature data which is consecutively outputted from a radiation thermometer. CONSTITUTION: A monitor window(15) is installed in the sidewall of a chamber(1). A radiation thermometer(16) is installed on the outer side of the monitor window. A heat resisting plate(18) absorbs radiant heat from the casting surface of an adjacent ingot(3). A controller monitors the temperature variation of a casting surface of the ingot based on temperature data outputted from the radiation thermometer. The controller adjusts a set value of a current which is applied in an induction coil(8).

Description

Electronic casting device of silicon ingot {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 unidirectional solidification as a material, and is produced 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 at 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 "electronic casting method") has been put into practical use.

4 is a diagram schematically showing a configuration of a conventional representative electronic casting device used in the electronic casting method. As shown in this figure, the electronic casting apparatus 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 upper wall of the chamber 1 is connected with the raw material supply apparatus which is not shown in figure through the raw material supply shutter 2 which can be opened and closed. 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 longitudinal direction, leaving the upper and lower portions, and are divided into a plurality of small rectangular pieces in the circumferential direction by the slits. Forced cooling by the cooling water flowing through.

The induction coil 8 is provided concentrically with the cooling crucible 7 so as to surround the cooling crucible 7, and is connected to the power supply device which is not shown in figure. The after-heater 9 is provided at the bottom of the cooling crucible 7 in contiguous condensation with the cooling crucible 7 to heat the silicon ingot 3 drawn out from the cooling crucible 7 and is suitable in the axial direction thereof. Give a temperature gradient.

In addition, in the chamber 1, a raw material introduction pipe 10 is provided below the raw material supply shutter 2. In accordance with the opening and closing of the raw material supply shutter 2, the silicon raw material 11 in a particulate state or agglomerate state is supplied from the raw material supply device to the raw material introduction pipe 10, and the cooling crucible 7 through the raw material introduction pipe 10. It is put in.

In the bottom wall of the chamber 1, an outlet 4 for pulling out the ingot 3 is provided just below the after heater 9, and the outlet 4 is sealed with gas. The ingot 3 is pulled down while being supported by the support 14 which descends 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 a plasma power supply device (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 the electroforming method using such an electronic casting apparatus, 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 the small pieces of rectangular shape constituting the cooling crucible 7 are electrically divided from each other, an eddy current is generated in each piece according to the electromagnetic induction by the induction coil 8, and thus the cooling crucible ( An eddy current on the inner wall side of 7) generates a magnetic field in the cooling crucible 7. As a result, the silicon raw material 11 in the cooling crucible 7 is induction-heated and melted to form molten silicon 12.

In addition, a plasma arc is generated between the plasma torch 13, the silicon raw material 11, and the molten silicon 12. The silicon raw material 11 is also heated and dissolved by the joule heat, and the burden of electromagnetic induction heating is caused. And the molten silicon 12 is formed efficiently.

The molten silicon 12 has an inner normal to the surface of the molten silicon 12 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. Since a force (pinch force) is applied in the direction, it is maintained in a non-contact state with the cooling crucible 7. When the support 14 supporting the molten silicon 12 is gradually lowered while dissolving 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 peripheral part by cooling from the cooling crucible 7. Then, as the support 14 is lowered, the silicon raw material 11 is sequentially introduced into the cooling crucible 7 and the melting and solidification are continued to solidify the molten silicon 12 in one direction, thereby continuing the ingot 3. I can cast it.

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 converted into a chamber ( It is sequentially discharged from the exhaust port 6 of the lower side wall of 1). At this time, Si (silicon) violently evaporates from the molten silicon 12 by the plasma arc from the plasma torch 13, and this Si vapor agglomerates in the chamber 1 to become a Si fume and inert gas. Together with the discharge from the exhaust port 6.

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

Patent Document 1: International Publication WO02 / 053496 Pamphlet

Usually, in the electroforming method, the temperature of the casting surface of the ingot 3 is monitored directly under the cooling crucible 7 and the set value of the current applied to the induction coil 8 is adjusted in accordance with the variation of the casting surface temperature. Operation is performed. For this reason, in the conventional electronic casting apparatus mentioned above, as shown in the said FIG. 4, the monitoring window 15 in which the transparent glass plate was inserted is provided in the side wall of the chamber 1, and the The radiation thermometer 16 is provided outside. The radiation thermometer 16 directly measures the temperature of the casting surface of the ingot 3 directly under the cooling crucible 7, thereby monitoring the temperature variation of the casting surface of the ingot 3.

However, in the conventional electronic casting apparatus, during the casting, Si fume is remarkably generated in the chamber 1 as the raw material is dissolved by energizing the plasma torch 13 and using plasma arc heating together, as shown in FIG. 4. Similarly, the Si fume F is in an irregular floating state between the monitoring window 15 and the ingot 3 immediately below the cooling crucible 7. For this reason, even if the actual temperature of the casting surface of the ingot 3 is constant, the radiant heat energy reaching the radiation thermometer 16 from the casting surface of the ingot 3 changes according to the amount of floating Si fume F. A situation arises in which the temperature measured by the radiation thermometer 16 changes. That is, the difference between the actual temperature of the casting surface of the ingot 3 and the measured temperature by the radiation thermometer 16 (hereinafter referred to as "measurement error") is not constant. As a result, the temperature fluctuations of the casting surface of the ingot 3 cannot be accurately monitored.

This invention is made | formed in view of the said problem, Even when a Si fume generate | occur | produces in a chamber according to raw material melt | dissolution which combined plasma arc heating with a plasma torch at the time of continuous casting of a silicon ingot, a measurement error is made constant. Therefore, an object of the present invention is to provide an electronic casting device of a silicon ingot capable of accurately monitoring the temperature variation of the casting surface of the ingot directly under the cooling crucible.

MEANS TO SOLVE THE PROBLEM The present inventors obtained the following knowledge as a result of earnestly examining in order to achieve the said objective. Even if Si fume is irregularly floating between the monitoring window and the ingot just below the cooling crucible, in order to keep the measurement error constant, a heat-resistant tube is provided between the monitoring window and the casting surface of the ingot, It is effective to close the end surface of the ingot side with a heat resistant plate and measure the temperature of the heat resistant plate through the inside of the heat resistant tube with a radiation thermometer. Since the heat-resistant plate absorbs radiant heat from the casting surface of the ingot one by one, and heats up in accordance with the radiant heat, the temperature of the heat-resistant plate is one that reflects the casting surface temperature of the ingot one by one. This is because the inside of the heat resistant tube is prevented from entering Si fume which is a obstacle of temperature measurement.

This invention is completed based on said knowledge, The summary is the electroforming apparatus of the silicon ingot shown below. That is, a silicon raw material is put into a non-floating cooling crucible disposed in the chamber, and the silicon raw material is dissolved by electromagnetic induction heating from an induction coil surrounding the non-floating cooling crucible. In an electronic casting device that continuously casts silicon ingots by solidifying while pulling them out of a cooling crucible that is not present, a watch window is installed on the sidewall of the chamber and near the casting surface of the silicon ingot just below the watch window and the bottomless cooling crucible. A heat-resistant tube is installed between the heat-resistant tubes, the end face of the silicon ingot side of the heat-resistant tube is blocked by a heat-resistant plate, and the temperature of the heat-resistant plate is measured through the inside of the heat-resistant tube by a radiation thermometer disposed outside the monitoring window. The temperature of the casting surface temperature of the silicon ingot is monitored based on the measured temperature of the heat-resistant plate. It is an electronic casting device of a silicon ingot.

In the above electronic casting device, it is preferable that the heat-resistant plate is made of quartz. In this case, it is preferable that the heat-resistant plate is opaque.

According to the electronic casting apparatus of the silicon ingot of the present invention, even when Si fume is irregularly suspended between the monitoring window and the ingot immediately below the cooling crucible when the silicon ingot is continuously cast, the heat-resistant tube occluded by the heat-resistant plate. The inside of the Si fume is prevented from entering and the Si fume does not exist, and since the heat-resistant plate is glowing by the radiant heat from the casting surface of the ingot, the radiation thermometer becomes a temperature reflecting the casting surface temperature of the ingot sequentially. By measuring the temperature of the heat-resistant plate through the inside of the heat-resistant tube, the measurement error can be made constant, and based on the temperature data sequentially output from the radiation thermometer, it is possible to accurately monitor the temperature variation of the casting surface of the ingot. Become.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically the structure of the electronic casting apparatus of this invention.
FIG. 2 is a diagram showing the relationship between the measured temperature by the radiation thermometer and the applied power to the induction coil with respect to the casting length of the ingot as a test result of Example 1. FIG.
FIG. 3 is a diagram showing the relationship between the measured temperature by the radiation thermometer and the applied power to the induction coil with respect to the casting length of the ingot as a test result of Example 2. FIG.
4 is a diagram schematically showing a configuration of a conventional representative electronic casting device used in the electronic casting method.

EMBODIMENT OF THE INVENTION Below, the embodiment is described in detail about the electroforming 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, and the overlapping description is abbreviate | omitted suitably.

As shown in FIG. 1, the electronic casting apparatus of this invention is provided between the monitoring window 15 provided in the side wall of the chamber 1, and the casting surface vicinity of the ingot 3 just under the cooling crucible 7 The heat-resistant pipe 17 is provided. In this heat-resistant tube 17, the end surface of the ingot 3 side is closed by the heat-resistant plate 18, and the end surface of the monitoring window 15 on the opposite side is opened.

Moreover, the radiation thermometer 16 is provided in the outside of the monitoring window 15 on the extension line of the heat resistant tube 17. As shown in FIG. The radiation thermometer 16 is connected to the control part which is not shown in figure which controls the operating conditions of an electronic casting apparatus. This control part monitors the temperature variation of the casting surface of the ingot 3 based on the temperature data sequentially output from the radiation thermometer 16, and adjusts the set value of the electric current applied to the induction coil 8. As shown in FIG.

In addition to the heat resistance, the heat resistant plate 18 sequentially absorbs radiant heat from the casting surface of the adjacent ingot 3 and needs to be glowing according to the radiant heat. Thus, the transparent quartz, opaque quartz, carbon, and PNB (pyrolytic nitriding) are required. Ceramics such as boron) and alumina can be employed. Among them, the heat-resistant plate 18 employing transparent quartz or opaque quartz is suitable because of its high emissivity and no fear of impurity contamination to the ingot 3. In particular, opaque quartz is most suitable as heat-resistant plate 18 in view of higher emissivity and excellent heat resistance as compared with transparent quartz.

The heat-resistant tube 17 is not limited to an ideal material having heat resistance, but it is preferable to adopt the same material as the heat-resistant plate 18 described above. In addition, the heat-resistant tube 17 and the heat-resistant plate 18 may be integrally molded, or may be separately molded and combined.

As for the clearance gap of the end surface of the heat-resistant tube 17 on the side of the ingot 3, ie, the heat-resistant plate 18 and the casting surface of the ingot 3, about 10-30 mm is preferable. If the gap is too small, the heat resistant plate 18 may come into contact with the ingot 3, and if too large, the absorption time delay of radiant heat from the casting surface of the ingot 3 to the heat resistant plate 18 is remarkable. For it is done.

As for the cross section of the monitoring window 15 side of the heat resistant tube 17, and the clearance gap of the monitoring window 15, about 20-50 mm is preferable. This gap may be eliminated by contact between the two, but if it is too large, Si fume F, which is an obstacle to temperature measurement, enters the gap.

According to the electronic casting apparatus of such a structure, when continuously casting a silicon ingot, since the heat-resistant plate absorbs radiant heat from the casting surface of the ingot sequentially, and heats up according to the radiant heat, the temperature of the heat-resistant plate is the casting surface temperature of the ingot. Will be reflected sequentially. At this time, even if Si fume is generated in the chamber and the Si fume is irregularly floated between the monitoring window and the ingot immediately below the cooling crucible, in accordance with dissolution of the raw material by using plasma arc heating with a plasma torch. Since the entry of Si-fume is prevented and Si-fume does not exist in the heat-resistant tube occluded by, the measurement error can be made constant by measuring the temperature of a heat-resistant plate through a heat-resistant tube with a radiation thermometer. As a result, it is possible to accurately monitor the temperature variation of the casting surface of the ingot based on the temperature data sequentially output from the radiation thermometer.

[Example]

In order to confirm the effect by the electronic casting apparatus of this invention, the test which continuously casted the silicon ingot of 345 mm square cross section and 4000 mm in total length was done. In this test, the monitoring windows are provided on both side walls of the chamber in which the ingot is sandwiched, and an electronic casting device in which a radiation thermometer is arranged outside of each monitoring window is used. As shown in FIG. 1, the heat-resistant tube 17 was provided, and nothing was provided inside the other monitoring window as shown in FIG.

(Example 1)

In the test of Example 1, an opaque quartz plate was affixed as a heat-resistant plate on the end surface of the heat-resistant tube at the ingot side, and the ingot was continuously cast. In that case, the measurement temperature by the radiation thermometer of the side which arrange | positioned the heat-resistant tube as the example of this invention according to the casting length of an ingot, and the measurement temperature by the radiation thermometer of the side which does not arrange the heat-resistant tube as a comparative example, and an induction coil The power applied to the furnace was investigated.

FIG. 2 is a diagram showing the relationship between the measured temperature by the radiation thermometer and the applied power to the induction coil with respect to the casting length of the ingot as a test result of Example 1. FIG. In this figure, it is the situation of the end of casting which stopped supply of the silicon raw material to a cooling crucible, switching the electricity supply to a plasma torch to non-energization, and the state before and after stopping raw material melt | dissolution by plasma arc heating is shown. In addition, the unit [a.u.] of a vertical axis | shaft and a horizontal axis | shaft in this figure means arbitrary unit.

As shown in this figure, although the power applied to the induction coil is substantially constant, in the comparative example, the measured temperature fluctuates greatly, and in particular, generation of Si fume occurs when the raw material dissolution by the plasma arc heating is stopped. As it calmed down, the measurement temperature rose rapidly above 100 ° C. On the other hand, in the example of this invention, it is the same tendency as the applied electric power to an induction coil, and the measurement temperature became substantially constant.

(Example 2)

In the test of Example 2, a transparent quartz plate was attached as a heat-resistant plate to the end surface of the heat-resistant tube at the ingot side, and the ingot was continuously cast. In that case, like the test of the said Example 1, according to the casting length of an ingot, the measurement temperature by the radiation thermometer of the side which arrange | positioned the heat-resistant tube as the example of this invention, and the side which does not arrange | position the heat-resistant tube as a comparative example The measured temperature by the radiation thermometer and the applied power to the induction coil were examined.

FIG. 3 is a diagram showing the relationship between the measured temperature by the radiation thermometer and the applied power to the induction coil with respect to the casting length of the ingot as a test result of Example 2. FIG. In this figure, it is the situation of the middle of casting which sequentially injects a silicon raw material into a cooling crucible, The state which energized a plasma torch and continued melting of raw material by plasma arc heating is shown. In addition, the unit [a.u.] of a vertical axis | shaft and a horizontal axis | shaft in this figure means arbitrary unit.

As shown in this figure, although the applied power to the induction coil was constant, in the comparative example, the measured temperature varied greatly. On the other hand, in the example of this invention, it is the same tendency as the applied electric power to an induction coil, the measurement temperature became substantially constant, and the fluctuation was also very small.

According to the electronic casting apparatus of the silicon ingot of the present invention, the entry of Si fume is prevented from entering into the heat-resistant tube occluded by the heat-resistant plate, and the Si-fume does not exist, and the heat-resistant plate is radiant heat from the casting surface of the ingot. It is accumulated by and becomes the temperature reflecting the casting surface temperature of the ingot one by one. Therefore, if the temperature of the heat-resistant plate is measured through the inside of the heat-resistant tube with a radiation thermometer, measurement error can be made constant and the temperature of the casting surface of the ingot It is possible to accurately monitor the change. Therefore, the electronic casting apparatus of this invention is very useful at the point which can adjust the setting value of the electric current applied to an induction coil precisely according to the fluctuation of the casting surface temperature of an ingot.

1: Chamber 2: Raw material supply shutter
3: silicon ingot 4: outlet
5: inert gas inlet 6: exhaust vent,
7: Cooling crucible without bottom 8: Induction coil
9: After heater 10: Raw material introduction pipe
11: silicon raw material 12: molten silicon,
13: Plasma torch 14: Support stand
15: Watch window 16: Radiation thermometer
17: Heat-resistant pipe 18: Heat-resistant board
F ： Si fume

Claims (3)

The silicon raw material is placed in a conductive bottomless cooling crucible disposed in the chamber, and the silicon raw material is dissolved by electromagnetic induction heating from an induction coil surrounding the bottomless cooling crucible, and the molten silicon is cooled without bottoms. In the electronic casting device which solidifies while pulling down from the crucible, the continuous casting of the silicon ingot,
A monitoring window is installed on the side wall of the chamber, and a heat-resistant tube is installed between the monitoring window and the vicinity of the casting surface of the silicon ingot just below the bottomless cooling crucible. Occluded by hotplate,
The temperature of the heat-resistant plate is measured through the inside of the heat-resistant tube by a radiation thermometer disposed outside the monitoring window, and the variation of the surface temperature of the casting surface of the silicon ingot is monitored based on the measured temperature of the heat-resistant plate. Electronic casting device. The method according to claim 1,
Electro-casting device of a silicon ingot, characterized in that the heat-resistant plate is made of quartz. The method according to claim 2,
Electro-casting device of a silicon ingot, characterized in that the heat-resistant plate is opaque.

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