JP2012101963A - Electromagnetic casting apparatus and method for silicon ingot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide electromagnetic casting apparatus and method for a silicon ingot in which a crack or a burr generated during cutting of an ingot can be prevented when producing an ingot having a rectangular sectional shape by using an electromagnetic casting apparatus provided with after-heaters each having a square sectional shape.SOLUTION: (1) The electromagnetic casting apparatus includes a bottomless cooling mold 2, an induction coil 1, and after-heaters 4 for slow-cooling an ingot 5, wherein the apparatus is configured to allow the power control of the after-heaters to be individually performed for two or more pairs of heaters, wherein a pair of opposed heaters (for example, heaters 14-1 and 14-3) are defined as one pair. (2) The electromagnetic casting method includes individually controlling the output of after-heaters for two or more pairs of heaters using the electromagnetic casting apparatus. When the output of the after-heaters is controlled so that the variation in temperature in the surface of the ingot will be 10°C or less, a crack or a burr will be extremely effectively prevented.

Description

  The present invention relates to an electromagnetic casting apparatus and electromagnetic casting method for a silicon ingot for producing polycrystalline silicon by applying a continuous casting technique using electromagnetic induction, and more particularly, to an after heater having a cross-sectional shape different from the cross-sectional shape of the ingot. An ingot manufactured by an ingot manufacturing apparatus can prevent cracks and cracks (roughness of the cut surface) that occur during cutting, and can efficiently produce polycrystalline silicon with a high yield. And an electromagnetic casting method.

  According to the continuous casting method using electromagnetic induction (hereinafter referred to as “electromagnetic casting method”), the molten material (here, molten silicon) and the mold are hardly in contact with each other. Can be manufactured. Since there is no contamination from the mold, there is an advantage that it is not necessary to use a high-purity material as the material of the mold, and since it can be continuously cast, the manufacturing cost can be greatly reduced. Therefore, the electromagnetic casting method has been conventionally applied to the production of polycrystalline silicon used as a substrate material for solar cells.

  In this electromagnetic casting method, a material (usually copper) having good electrical and thermal conductivity, which is electrically insulated from each other in the circumferential direction and water-cooled inside, is formed into a strip shape inside the high frequency induction coil. Use a lined bottomless cooling mold (or crucible). The shape of the coil and the shape of the portion surrounded by the strip-shaped object functioning as a bottomless mold may be either cylindrical or rectangular. Further, a support base that can move downward is provided at the bottom of the bottomless mold.

  When a silicon raw material is charged into a copper mold configured as a melting container and an alternating current is passed through a high-frequency induction coil, the strip-shaped pieces constituting the mold are electrically separated from each other. The current forms a loop in the piece, and the current on the inner wall side of the mold forms a magnetic field in the mold, so that the silicon in the mold can be heated and melted. The molten silicon in the mold is melted in a non-contact state with the mold by receiving a force in the inner normal direction of the surface of the molten silicon due to the interaction between the magnetic field generated by the current on the inner wall of the mold and the current of the molten silicon skin.

  When the support that holds the molten silicon is moved downward while melting the silicon in the mold in this manner, the induced magnetic field decreases as the distance from the lower end of the high-frequency induction coil decreases. The calorific value decreases, and unidirectional solidification proceeds upward at the bottom of the molten silicon. Under the heating induction coil, an after-heater is installed for heating the solidified ingot (silicon ingot) to prevent rapid cooling (that is, slow cooling).

  The polycrystalline silicon ingot can be continuously cast while solidifying in one direction by continuously charging the raw material from above the mold in accordance with the downward movement of the support base and continuing melting and solidification. it can.

  As the after-heater, a multi-stage arrangement of devices to which heating means (electric heating heater) arranged in a state where the entire ingot is wrapped is generally used. Since an ingot originally needs to be processed in a square cross-sectional shape, the cross-sectional shape is usually a square. For this reason, the cross-sectional shape of the after heater is also often square, and the output of the after heater is usually controlled so that the four heaters have the same output. However, in practice, an ingot having a rectangular cross section may be used from the viewpoint of improving the yield.

  When an ingot having a square cross section is produced by an apparatus having an after heater having a square cross section, there is no problem even if the outputs of the four heaters are the same. However, when an ingot having a rectangular cross section is manufactured with this apparatus, if the outputs of the four heaters are the same, a temperature difference occurs between the long side and the short side of the ingot, and cooling (slow cooling) is performed in that state. As it progresses, stress is generated inside the ingot. Due to this stress, cracks and burr are generated when the ingot is cut in the subsequent process, and the yield of the ingot is reduced. Cracks are mainly cracks that occur in the vertical direction, and the crust is rough with a depth of 2 mm or less appearing on the cut surface, and in many cases, the stress remaining in the ingot is released at the time of cutting.

  In this case, it is only necessary to change the structure of the after-heater so that the cross-sectional shape is changed from a rectangle to a square, but the after-heater has a height of 4 m or more and the number of stages is more than ten, so it is not easy to change the setup. , Takes a long time. In addition, it is desirable that the after-heater be a device that can change the output for each side of the heater, but additional heaters, heater power supplies, control thermocouples, etc. are required, which increases costs and causes problems in installation space. It is extremely difficult.

  There is no published document regarding the structure of the after heater in the case of manufacturing an ingot having a rectangular cross section with an apparatus having an after heater having a square cross section. For example, Patent Document 1 discloses a casting method in which a cross-sectional shape of an ingot is changed from a conventional square to a rectangle, and an ingot having an increased cross-sectional area can be manufactured while maintaining a casting speed equivalent to that of the conventional one. The production efficiency can be greatly improved. However, nothing is described about changes in the structure and usage of the after-heater associated with making the cross-sectional shape of the ingot rectangular.

JP 2008-156166 A

  In the present invention, when an ingot having a rectangular cross-sectional shape is manufactured by an electromagnetic casting apparatus having an after-heater having a square cross-sectional shape, a crack (crack) or crease (roughness of the cut surface) generated when the ingot is cut in a subsequent process It is an object of the present invention to provide a silicon ingot electromagnetic casting apparatus and an electromagnetic casting method that can efficiently manufacture a silicon ingot with a high yield.

  In order to solve the above-mentioned problems, the present inventor has investigated the extent to which the temperature variation in the ingot plane (that is, each part in the cross section of the ingot) causes cracks and sacrificials. Specifically, when two silicon blocks obtained by cutting an ingot obtained with an actual machine perpendicularly to the casting direction are used as a pair, a thermocouple is attached to each part between these blocks, and heated with a soaking heater The relationship between the temperature variation in the thermocouple mounting surface and the occurrence rate of cracks and chaff was investigated. In addition, since these two silicon blocks simulate the ingot being cast, in the following, it will be referred to as “ingot” and the temperature variation within the thermocouple mounting surface (that is, within the ingot surface) will be expressed as “ This is called “in-plane temperature variation of the ingot”.

  2A and 2B are explanatory diagrams of a method for investigating temperature variations in the ingot surface. FIG. 2A is a diagram showing a thermocouple installation position on the ingot, and FIG. 2B is a soaking heater with the ingot attached with the thermocouple. It is the figure arrange | positioned in the inside and is a cross-sectional view in the surface containing a thermocouple installation position. As shown in FIG. 2A, two silicon ingots 5-1 and 5-2 are stacked so that their casting directions are perpendicular to each other, and reference signs A to F of the boundary surfaces of the ingots 5-1 and 5-2. The thermocouple was attached so that the tip of the thermocouple was located at the part marked with. Thereafter, the ingots 5-1 and 5-2 were arranged at the center of the soaking heater 16 (corresponding to an actual afterheater) as shown in FIG. Heaters 14-1, 14-2, 14-3 and 14-4 and thermocouples 15-1, 15-2, 15-3 and 15-4 are attached to the inner side surface of the soaking heater 16.

  The thermocouple 15-1 reaches the reference temperature while controlling the thermocouple 15-1 as a control thermocouple so that the outputs of the heaters 14-1, 14-2, 14-3 and 14-4 are the same. The temperature was raised to. Subsequently, the temperature difference in the ingot plane at that time (here, the difference between the maximum temperature and the minimum temperature in the portions denoted by reference signs A to F), that is, the variation in the ingot plane temperature is 50 ° C. or more, 30 ° C. or more or In each case that was within 10 ° C., the ingot 5 was cooled to a predetermined temperature at a cooling rate of 30 ° C./h from the reference temperature, or 20 ° C./h or 15 ° C./h lower than that. The cooling rate of 30 ° C./h is a reference cooling rate that simulates a normal cooling rate in an actual aftercooler.

  Thereafter, the ingot 5 was taken out from the soaking heater 16 and cut into a large number of small blocks, and the crack generation rate and the saliva generation rate were investigated. The “crack generation rate” and the “saglet generation rate” are the ratio (percentage) of the number of crack generation blocks or the number of block generations to the total number of blocks after cutting.

  The survey results are summarized in Table 1.

  As apparent from Table 1, the smaller the temperature difference in the ingot plane at the reference temperature (that is, the smaller the variation in in-plane temperature of the ingot), the lower the incidence of cracks and burr. Furthermore, even when the temperature difference in the ingot surface is the same, the lower the cooling rate, the smaller the occurrence rate of cracks and salmon.

  For example, when the temperature difference in the ingot plane at the reference temperature was 50 ° C. or more, the crack generation rate was 46% and the saliva generation rate was 100% at the reference cooling rate of 30 ° C./h. In order to suppress the generation of cracks and make the generation of crusted light (that is, in order not to leave stress in the ingot), the cooling rate needs to be low, for example, 15 ° C./h. . On the other hand, when the temperature difference in the ingot surface was within 10 ° C., cracks did not occur even at the reference cooling rate of 30 ° C./h, and the occurrence of crust was slight.

  That is, it has been found that if the temperature difference in the ingot surface at the reference temperature can be within 10 ° C., it is possible to prevent cracks and sacrificials that occur when cutting the ingot while maintaining the normal reference cooling rate.

  Therefore, the present inventor has repeatedly studied a method of setting the temperature difference in the ingot surface to 10 ° C. or less when manufacturing an ingot having a rectangular cross section with an apparatus having an after-heater having a square cross section. As a result, it was confirmed that this can be achieved by controlling the output of the four surfaces of the after heater for every two surfaces facing each other and providing a temperature difference between the two surfaces.

  The present invention has been made on the basis of such examination results, and the gist thereof is the following (1) silicon electromagnetic casting apparatus and (2) silicon ingot electromagnetic casting method.

(1) A conductive bottomless cooling mold in which a part in the axial direction is divided into a plurality in the circumferential direction, an induction coil surrounding the mold, and a solidified silicon ingot placed under the mold and gradually cooled. A silicon ingot electromagnetic casting apparatus for lowering and solidifying molten silicon by electromagnetic induction heating by the induction coil, wherein the cross-sectional shape of the after-heater is square and the cross-sectional shape is rectangular When the ingot is slowly cooled, the output control of the after heaters arranged opposite to the four surfaces of the ingot can be performed individually for two or more pairs of heaters with two heaters facing each other. An electromagnetic casting apparatus for a silicon ingot, characterized in that
Here, “the after heater disposed opposite to the four surfaces of the ingot” means that the four surfaces of the after heater are opposed to the four surfaces of the ingot, respectively, and the corresponding surfaces of the ingot according to the long side and the short side of the ingot, respectively. Means that they are arranged equidistant from each other. In addition, “two heaters facing each other” is a heater attached to each of the two opposing faces.

(2) Using the silicon ingot electromagnetic casting apparatus as described in (1) above, a silicon ingot is solidified by charging a silicon raw material into a mold, melting it by electromagnetic induction heating, and lowering the molten silicon downward Is an electromagnetic casting method of a silicon ingot that is gradually cooled by an after heater, and when an ingot having a rectangular cross-sectional shape is gradually cooled, the output of the after heater disposed to face four surfaces of the ingot is A method for electromagnetic casting of a silicon ingot, wherein two or more heaters are individually controlled with a pair of heaters so as to provide a temperature difference between the two or more heaters to reduce in-plane temperature variation of the ingot.
Here, “the in-plane temperature variation of the ingot” means the temperature variation in each part in the cross section perpendicular to the casting direction of the ingot as described above.

  In the electromagnetic casting method for a silicon ingot according to the present invention, if the output of the after heater is controlled so that the in-plane temperature variation of the ingot is 10 ° C. or less, cracks and saglet that are generated when the ingot is cut are removed. It can be surely prevented or significantly reduced.

  The silicon ingot electromagnetic casting apparatus of the present invention comprises an after-heater having a square cross-sectional shape, and is configured so that the output control of the after-heater arranged opposite to the four surfaces of the ingot can be individually performed for two or more pairs of heaters. Device. According to the electromagnetic casting method of the present invention using this electromagnetic casting apparatus, when an ingot having a rectangular cross-sectional shape is gradually cooled, cracks and scrapes generated when the ingot is cut are prevented, and a silicon ingot is efficiently produced with a high yield. Can be manufactured.

It is a figure which shows typically the example of schematic structure of the electromagnetic casting apparatus of the silicon ingot of this invention, (a) is a longitudinal cross-sectional view of the whole principal part, (b) is an AA arrow enlarged view of (a), It is a figure which shows the cross-sectional shape of an after heater. It is explanatory drawing of the investigation method of the dispersion | variation in the temperature in an ingot surface, (a) is a figure which shows the thermocouple installation position to an ingot, (b) has arrange | positioned the ingot which attached the thermocouple in the soaking | uniform-heating heater. It is a figure and is a cross-sectional view in the surface containing a thermocouple installation position. It is explanatory drawing of the apparatus used in the Example, and is a figure which shows typically the state which has arrange | positioned the ingot which attached the thermocouple in the soaking | uniform-heating heater.

  An electromagnetic casting apparatus for a silicon ingot according to the present invention is a conductive bottomless cooling mold in which a part in the axial direction is divided into a plurality of parts in the circumferential direction, an induction coil surrounding the mold, and a lower part of the mold. It is premised on an electromagnetic casting apparatus having an after heater for gradually cooling the solidified silicon ingot.

  The premise of such an electromagnetic casting apparatus is that, when producing polycrystalline silicon used as a substrate material for a solar cell, casting is performed in a mold with almost no contact between the molten silicon and the mold. This is because there is no metal contamination, and polycrystalline silicon suitable as a substrate material for solar cells can be produced.

  The above-mentioned after-heater gradually cools the ingot in order to prevent the silicon ingot moving downward from the induction coil from being rapidly cooled and causing excessive thermal stress due to the difference in shrinkage due to the temperature difference to cause cracking in the ingot. It has a function of cooling (that is, heating moderately to prevent rapid cooling).

  The electromagnetic casting apparatus of the present invention may further include a plasma torch as a heating source. The combined use of electromagnetic induction heating and plasma arc heating is desirable because it reduces the burden of electromagnetic induction heating and increases the efficiency of raw material melting.

  In the electromagnetic casting apparatus of the present invention, when the ingot having a square cross-sectional shape and a rectangular cross-sectional shape is slowly cooled, the output control of the after-heater arranged facing the four surfaces of the ingot is confronted. It is characterized by being configured so that two pairs of heaters can be individually implemented for two or more pairs of heaters.

  FIG. 1 is a diagram schematically showing a schematic configuration example of an electromagnetic casting apparatus for a silicon ingot according to the present invention, in which (a) is a longitudinal sectional view of the entire main part, and (b) is an AA view of (a). It is an enlarged view and is a figure which shows the cross-sectional shape of an after heater. As shown in FIG. 1 (a), a longitudinally long copper plate that can be cooled with water inside the induction coil 1 for heating is parallel to the winding axis direction of the induction coil 1 and inside the induction coil 1. Then, they are arranged in a state of being insulated from each other, and the space surrounded by the plate-like pieces constitutes a mold (that is, a bottomless cooling mold whose side walls are water-cooled) 2. For the cooling mold 2, a water-cooled copper mold having a plate-like piece as a copper piece is usually used.

  At the lower end position of the heating induction coil 1 (that is, the position corresponding to the bottom of the cooling mold 2), a support base 3 that can move downward is installed. An after heater 4 is installed below the heating induction coil 1. The silicon ingot 5 is drawn downward by a drawing device (not shown).

  Above the cooling mold 2, a raw material charging machine 7 capable of charging the silicon raw material 6 into the mold 2 during melting is installed. Further, in this example, a plasma torch 8 for heating the silicon raw material 6 is attached above the mold 2.

  These devices are installed in an airtight container (chamber 10) so that the molten silicon 9 and the high-temperature silicon ingot 5 do not come into direct contact with the atmosphere. A gas inlet 11 is attached to the upper part of the chamber 10 and an exhaust outlet 12 is provided to the lower part. Usually, the inside of the chamber 10 is replaced with an inert gas so that continuous casting can be performed in a slightly pressurized state. It is configured.

  Moreover, as shown in FIG.1 (b), the cross-sectional shape of the after heater 4 is square, and heating means (electric heating type heaters 14-1 and 14-2) are provided on the inner four surfaces of the frame formed of the heat insulating material 13. 14-3 and 14-4), and thermocouples 15-1, 15-2, 15-3, and 15-4 for control or temperature measurement are attached. The individual devices configured in this way are arranged in multiple stages, and the after heater 4 shown in FIG. 1A is configured. The after heater 4 is disposed to face four surfaces of the silicon ingot 5 having a rectangular cross-sectional shape.

  The two heaters facing each other are the heater 14-1 and the heater 14-3, and the heater 14-2 and the heater 14-4 in the case of the after heater illustrated in FIG. In this example, two pairs of heaters are attached with two heaters facing each other as a pair.

  In the electromagnetic casting apparatus for a silicon ingot according to the present invention, when the cross-sectional shape of the after heater is square and the ingot having a rectangular cross-sectional shape is gradually cooled, the output control of the after heater arranged to face the four surfaces of the ingot It is assumed that the two heaters facing each other can be individually implemented for two or more pairs of heaters when cutting a cast ingot, as will be described later in detail. This is in order to prevent cracks and sacrificial.

  Here, the reason why the number of heaters capable of individually controlling the output is two or more is that three or more pairs of heaters may be installed in accordance with the four surfaces of the after heater. That is, the electromagnetic casting apparatus shown in FIG. 1 is an example in which one heater is arranged on each surface of the after heater and two pairs of heaters are installed as shown in FIG. For example, it is conceivable that the heater is divided into two or three on each of the opposing faces of the after heater, in which case the facing heaters are three or four. In such a case, in the silicon ingot electromagnetic casting apparatus of the present invention, the output control of the after heater is not limited to two pairs of heaters, but can be performed individually for three or more pairs of heaters.

  The method of electromagnetic casting of a silicon ingot according to the present invention uses the electromagnetic casting apparatus according to the present invention (that is, an apparatus having an after-heater having a square cross-sectional shape) to insert a silicon raw material into a mold and perform electromagnetic induction heating. It is assumed that the silicon ingot is an electromagnetic casting method in which a silicon ingot that has been melted and solidified by pulling the molten silicon downward is gradually cooled by an after heater. The reason for this assumption is as described above.

  Based on this premise, the electromagnetic casting method of the present invention, when gradually cooling an ingot having a rectangular cross-sectional shape, outputs the output of an after heater disposed opposite to the four surfaces of the ingot to two heaters facing each other. In this method, two or more pairs of heaters are individually controlled as a pair, and a temperature difference is provided between the two or more pairs of heaters to reduce in-plane temperature variation of the ingot.

  The after-heater shown in FIG. 1B will be described as an example. This after-heater is composed of two heaters facing each other, two pairs of heaters (a heater 14-1 and a heater 14-3, and a heater). 14-2 and heater 14-4). In this case, these two pairs of heater outputs are individually controlled.

  The control of the output of the after heater is performed separately for the two pairs of heaters, for example, compared to the case where the outputs of the four surfaces of the after heater considered as a general control means are individually controlled. This is because the control method can be simplified and the variation in in-plane temperature of the ingot can be sufficiently reduced. That is, in the electromagnetic casting method of the present invention, since the two heaters facing each other are controlled as a pair, it is not necessary to provide a control thermocouple, a heater, and a power supply for each heater. Further, it is possible to employ a simple control method in which the output of the after heater is individually controlled as described above and a temperature difference is provided between the two pairs of heaters.

  The reason for setting the temperature difference between the two heaters by individually controlling the output of the after heater is that, as shown in the examples described later, by providing the temperature difference, it is possible to reduce the in-plane temperature variation of the ingot. is there.

  The details are as shown in the examples described later. A heater 14-1 and a heater 14-2 are each attached with a control thermocouple and heated until the heater 14-1 reaches the reference temperature. The two pairs of heater outputs are individually controlled so that the temperature difference between the heater 14-2 and the heater 14-2 becomes + 15 ° C. As a result, the in-plane temperature variation of the ingot can be reduced to 10 ° C. or less.

  The temperature difference provided in the two pairs of heaters is not particularly limited. Since the temperature difference between the heater 14-1 and the heater 14-2 varies depending on the distance between the two heaters facing each other and the size of the ingot, the heater necessary to make the in-plane temperature variation of 10 ° C. or less. The temperature difference between 14-1 and the heater 14-2 is obtained in advance. By conducting such a preliminary investigation and accumulating as operation data, even when the distance between the heaters or the size of the ingot is changed, the temperature difference between the heaters 14-1 and 14-2 is set to a predetermined temperature. By a simple means of setting, it becomes possible to prevent cracks and burr that occur when cutting an ingot.

  In the electromagnetic casting method of the present invention, as described above, the output of the after heater is controlled individually for the two pairs of heaters, and a temperature difference is provided between the two pairs of heaters to reduce variations in the in-plane temperature of the ingot.

  There is no particular limitation on the degree of reduction in in-plane temperature variation of the ingot. As apparent from Table 1 above, the smaller the in-plane temperature difference of the ingot, the lower the occurrence rate of cracks and salmons. Therefore, if the in-plane temperature variation of the ingot can be reduced even slightly, the corresponding effect (crack and A decrease in the incidence of sacres is expected.

  The case where two pairs of heaters are installed on the four sides of the after heater has been described above. However, when three or more pairs of heaters are installed on the four sides of the after heater, the number of target heaters to be controlled is complicated. However, the same idea of managing the temperature difference of the heater with the control thermocouple can be applied, and the equipment and control method can be simplified sufficiently compared to the case of controlling the heater output individually. It is.

  The uniformity of the temperature in any plane in the longitudinal (height) direction of the after heater can be maintained by increasing the heat retention in the after heater, but it can be controlled for each stage of the heater. desirable.

  In the silicon ingot electromagnetic casting method of the present invention, it is desirable to employ an embodiment in which the output of the after heater is controlled so that the in-plane temperature variation of the ingot is 10 ° C. or less.

  As shown in Table 1 above, when the in-plane temperature variation of the ingot exceeds 10 ° C., cracks and sacraments can be prevented unless the cooling rate (that is, the gradual rate of the after heater) is reduced. Therefore, the casting speed must be reduced. However, when the in-plane temperature variation of the ingot is 10 ° C. or less, even if the after-heating is performed at a normal cooling rate, cracks and sacrificials that occur when the ingot is cut are reliably prevented or significantly reduced. Therefore, casting can be performed efficiently.

  As described above, if the silicon ingot electromagnetic casting apparatus of the present invention is used and the electromagnetic casting method of the present invention is applied, the electromagnetic casting apparatus having an after-heater having a square sectional shape is an ingot having a rectangular sectional shape. In the case of manufacturing a silicon ingot, it is possible to efficiently prevent a crack or a crease that occurs when the ingot is cut in a subsequent process, and to efficiently manufacture a silicon ingot with a high yield.

  A silicon ingot cast with an actual machine is cut perpendicularly to the casting direction, and the obtained two block-shaped ingots are used to attach a thermocouple in the ingot surface as shown in FIG. The ingot was placed in a soaking heater.

  FIG. 3 is a diagram schematically showing a state where an ingot with a thermocouple attached is arranged in a soaking heater. In FIG. 3, thermocouples 15-1 and 15-2 are control thermocouples, and thermocouples 15-3 and 15-4 are thermocouples for measurement only. The soaking heater 16 controls the outputs of the heater 14-1 and the heater 14-3 at the temperature measured by the thermocouple 15-1, and outputs the heater 14-2 and the heater 14-4 at the temperature measured by the thermocouple 15-2. It can be controlled.

  When raising the temperature of the soaking heater 16, the heater 14-1 and the heater 14-3 are measured at the temperature measured by the control thermocouple 15-1 so that the in-plane temperature variation of the ingot is reduced based on the results of previous studies. When the temperature of the thermocouple 15-1 is raised to the reference temperature while controlling the output of the heater 14-2 and the heater 14-4 at the measured temperature by the control thermocouple 15-2, The temperatures indicated by the other thermocouples 15-2, 15-3 and 15-4 and the temperatures indicated by the thermocouples A to F attached in the ingot surface were measured. That is, the outputs of the two pairs of heaters 14-1 and 14-3, and heaters 14-2 and 14-4 were individually controlled.

  On the other hand, as a comparative example, while controlling the outputs of the heaters 14-1, 14-2, 14-3, and 14-4 to be the same at the temperature measured by the control thermocouple 15-1, the thermocouple 15-1 When the temperature was increased until the temperature reached the reference temperature, the temperature indicated by thermocouples 15-2, 15-3 and 15-4 and the temperature indicated by thermocouples A to F were measured in the same manner.

  Table 2 shows the measurement results. The measurement result was displayed as a difference with respect to the temperature measured by the control thermocouple 15-1 as a reference (0 ° C.). In Table 2, when the sign “−” is attached to the display value, it indicates that it is lower than the reference, and when it is not indicated, it is higher than the reference. The “temperature difference between thermocouples A to F” is the difference between the highest value and the lowest value.

  In Table 2, in the present invention example, the difference between the thermocouples A to F is 6 ° C., and referring to the results shown in Table 1, the ingot in-plane temperature difference corresponds to “within 10 ° C.”. On the other hand, the difference in the measured temperature of the thermocouple 15-2 with respect to the measured temperature of the thermocouple 15-1 was + 15 ° C.

  That is, in the ingot and the after heater of the cross-sectional shape and size used in this example, the difference in the measured temperature of the thermocouple 15-2 with respect to the measured temperature of the thermocouple 15-1 used as the control thermocouple is + 15 ° C. It was found that by controlling the outputs of the heaters 14-1 and 14-3 and the heaters 14-2 and 14-4 so that the in-plane temperature variation of the ingot can be suppressed to 10 ° C. or less. As a result, no stress remains in the ingot, and it is possible to prevent cracks and sacrificials that occur when the ingot is cut.

  According to the electromagnetic casting apparatus and electromagnetic casting method of a silicon ingot of the present invention, when an ingot having a rectangular cross section is produced by an apparatus having an after-heater having a square cross section, cracks and sagles that are generated when the ingot is cut are removed. Therefore, a silicon ingot can be efficiently manufactured with a high yield. Therefore, the present invention can be effectively used in the field of manufacturing solar cells.

1: induction coil, 2: mold, 3: support base,
4: After heater, 5, 5-1 and 5-2: Silicon ingot,
6: Silicon raw material, 7: Raw material charging machine,
8: Plasma torch, 9: Molten silicon, 10: Chamber
11: Gas introduction port, 12: Exhaust port, 13: Heat insulating material,
14-1, 14-2, 14-3, 14-4: heater,
15-1, 15-2, 15-3, 15-4: Thermocouple
16: Soaking heater

Claims (3)

Conductive bottomless cooling mold having a part in the axial direction divided into a plurality of parts in the circumferential direction, an induction coil surrounding the mold, and an after-heater which is disposed below the mold and gradually cools the solidified silicon ingot A silicon ingot electromagnetic casting apparatus for pulling down and solidifying molten silicon by electromagnetic induction heating by the induction coil,
The after-heater has a square cross-sectional shape,
When slowly cooling an ingot having a rectangular cross-sectional shape, the output control of the after heater arranged opposite to the four surfaces of the ingot is performed individually for two or more heaters with the two heaters facing each other as one pair. An electromagnetic casting apparatus for a silicon ingot, characterized in that it is configured to be able to do so. Using the silicon ingot electromagnetic casting device according to claim 1, a silicon raw material is charged into a mold, melted by electromagnetic induction heating, and the silicon ingot solidified by pulling down the melted silicon is lowered by an after heater. An electromagnetic casting method of a silicon ingot that is gradually cooled,
When slowly cooling an ingot having a rectangular cross-sectional shape,
The temperature of the two or more heaters is controlled by individually controlling the output of the after heaters arranged opposite to the four surfaces of the ingot, with the two heaters facing each other as a pair, and providing a temperature difference between the two or more heaters. A method for electromagnetically casting a silicon ingot, characterized in that variations in in-plane temperature of the silicon ingot are reduced.   The method of electromagnetic casting of a silicon ingot according to claim 2, wherein the output of the after heater is controlled so that the in-plane temperature variation of the ingot becomes 10 ° C or less.

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