JP2005279663A - Apparatus for casting silicon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for casting silicon in which a problem that the yield of the silicon is caused to reduce by peeling off and damaging releasing material coated on the inner surface of a mold and mixing into the molten silicon, is solved, when the molten silicon is tapped off into the mold. <P>SOLUTION: This casting apparatus is provided with heating means 6, 7, a melting crucible 1 for forming the molten silicon by heating and melting silicon raw material 3 held in the inner part with the heating means 6, 7, a molten silicon tapping hole 4 arranged at the bottom part of the melting crucible 1 and tapping off the molten silicon, the mold 8 arranged at the lower part of the melting crucible 1 and having the opening part at the upper part and also, for holding and solidifying the molten silicon 10 tapped off from the molten silicon tapping hole 4 in the inner part, the releasing material 9 arranged in the inner part of the mold 8 and for example, a mold driving device 11, as the molten silicon dispersing means further increasing the size of molten silicon colliding range collided against the releasing material 9, arranged in the inner part of the mold 8 by dropping down the molten silicon 10 tapped off from the molten silicon tapping hole 4. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a silicon casting apparatus for producing a polycrystalline silicon ingot used for producing a semiconductor substrate for a solar cell, for example.

  Solar cells are expected to be put to practical use in a wide range of fields, from small households to large-scale power generation systems, as a clean petroleum alternative energy source. These are classified into crystalline, amorphous, and compound types depending on the type of raw materials used, and most of them currently on the market are crystalline silicon solar cells. This crystalline silicon solar cell is further classified into a single crystal type and a polycrystalline type. Single crystal silicon solar cells have the advantage that the conversion efficiency is easy to increase because the quality of the substrate is good, but the disadvantage is that the manufacturing cost of the substrate is high.

  On the other hand, polycrystalline silicon solar cells have been distributed in the market for a long time, but in recent years, the demand is increasing as interest in environmental issues is increasing, and higher conversion efficiency is required at lower cost. . In order to cope with such a demand, it is necessary to reduce the cost and quality of the polycrystalline silicon substrate, and it is required to produce a high-purity silicon ingot with a high yield.

  A polycrystalline silicon substrate used for a polycrystalline silicon solar cell is generally manufactured by a method called a casting method. In this casting method, a silicon melt melted by heating at high temperature is poured into a mold made of graphite or the like coated with a release material and solidified in one direction from the bottom of the mold, or a silicon raw material is placed in the mold and dissolved once. Thereafter, the silicon ingot is formed by unidirectionally solidifying again from the bottom. The ends of the silicon ingot are removed, cut into a desired size, and the cut silicon ingot is sliced to a desired thickness to obtain a polycrystalline silicon substrate for forming a solar cell.

  FIG. 8 shows a general silicon casting apparatus for producing such a polycrystalline silicon ingot.

  A melting crucible 1 for melting the silicon raw material 3 is disposed in the upper part and is held by a holding crucible 2, and a nozzle having a hot water outlet 4 for discharging a silicon melt at the bottom of the melting crucible 1 and the holding crucible 2. 5 is provided. Further, an upper heating means 6 and a side heating means 7 are arranged on the upper and side portions of the melting crucible 1 and the holding crucible 2, respectively, and a mold in which the silicon melt 10 is poured into the lower portions of the melting crucible 1 and the holding crucible 2. 8 is arranged.

  As such a mold 8, one in which a mold release material is coated on the inner surface of a mold made of graphite, or one in which a mold release material is coated on an inner surface of a mold made of silica, which is an integral structure, is used. It is done. In general, as the release material 9, powders such as silicon nitride (Si 3 N 4), which is silicon nitride, silicon carbide (SiC), which is silicon carbide, silicon dioxide (SiO 2), which is an oxide of silicon, are used. Is mixed in a solution composed of a suitable binder and solvent and stirred to form a slurry, and the inner wall of the mold is coated by a means such as coating or spraying (for example, a known technique) Non-patent document 1).

For example, the silicon raw material 3 placed in the melting crucible 1 made of high-purity quartz or the like is composed of a resistance heating type heater, an induction heating type coil or the like, and upper and side upper heating means 6 and side heating means 7. Is heated and melted to form a silicon melt, discharged from the nozzle 5 having the bottom outlet 4 into the lower mold 8 and cooled and solidified to obtain a polycrystalline silicon ingot. (For example, refer to Patent Document 1). These are all arranged in a vacuum vessel (not shown).
JP 11-43318 A 15th Photovoltaic Specialists Conf. (1981), P576-P580, 'A NEW DIRECTIONAL SOLIDIFICATION TECHNIQUE FOR POLYCRYSTALLINE SOLAR GRADE SILICON'

  However, in the initial stage of pouring, the silicon melt passing through the nozzle 5 having the pouring spout 4 is pushed out by the pressure depending on the water level and concentrated in the mold immediately below the nozzle. Due to the impact, the mold release material 9 at the center of the mold directly under the nozzle is deformed into a crater shape. In some cases, the mold release material 9 is peeled and damaged, and mixed into the silicon melt 10, thereby causing a defect in the silicon ingot. There was a problem of increasing or degrading characteristics. In addition, if a part of the release material is peeled and damaged, the heat removal capability of the part is increased, and the quality of the solar cell ingot may be deteriorated. In extreme cases, cracks due to thermal stress and damage to the release material may cause fusion between the mold base and the silicon ingot. In addition, since the silicon melt immediately after pouring is concentrated in one place in the center of the mold, the melt is not sufficiently stirred, resulting in a non-uniform distribution of the melt in the mold and uniform solidification. A layer cannot be formed.

  The present invention has been made in view of such problems of the prior art. When the molten silicon melt is poured into the mold, the mold release material covering the inner surface of the mold is peeled and damaged. An object of the present invention is to provide a silicon casting apparatus that solves the problems of mixing in the liquid and reducing the yield, and the problem that a uniform solidified layer is not formed.

  In order to achieve the above object, a silicon casting apparatus according to claim 1 of the present invention includes a heating means, and a melting crucible for heating and melting a silicon raw material housed therein to form a silicon melt. A melt outlet provided at the bottom of the melting crucible, and a hot water outlet for pouring out the silicon melt, provided below the melting crucible and having an opening at the top, and the silicon melt discharged from the hot water outlet is A mold for holding and solidifying inside, a mold release material provided in the mold, and the mold melt provided in the mold by dropping the silicon melt discharged from the tap Melt dispersion means for further increasing the size of the colliding melt collision region.

  The silicon casting apparatus according to a second aspect of the present invention is the silicon casting apparatus according to the first aspect, wherein the melt dispersing means is configured such that the silicon melt discharged from the pouring spout is the opening of the mold. This is a horizontal movement mechanism that changes the relative positional relationship in the horizontal direction between the tap and the casting mold within a range that can be captured by the mold.

  The silicon casting apparatus according to a third aspect of the present invention is the silicon casting apparatus according to the second aspect, wherein the horizontal movement mechanism is a mold driving mechanism provided on the mold side.

  A silicon casting apparatus according to a fourth aspect of the present invention is the silicon casting apparatus according to the third aspect, wherein the mold driving mechanism includes a rotation mechanism that rotates the mold, and the opening of the mold is The mold central axis, which is the substantially central axis in the vertical direction, and the melt central axis, which is the substantially central axis in the vertical direction when the silicon melt discharged from the pouring spout falls, do not overlap each other. It is configured.

  A silicon casting apparatus according to a fifth aspect of the present invention is the silicon casting apparatus according to the fourth aspect, wherein the shortest distance between the mold central axis and the melt central axis is 2 cm or more.

  A silicon casting apparatus according to a sixth aspect of the present invention is the silicon casting apparatus according to the third aspect, wherein the mold driving mechanism includes a rotation mechanism that rotates the mold, and the opening of the mold. Thus, the mold center axis, which is a substantially central axis in the vertical direction, and the rotation center axis, which is the vertical center axis of the rotation mechanism, are configured so as not to overlap each other.

  A silicon casting apparatus according to a seventh aspect of the present invention is the silicon casting apparatus according to the first aspect, wherein the melt dispersing means divides the pouring gate into a plurality of sizes to thereby determine the size of the melt collision area. Try to increase.

  The silicon casting apparatus according to an eighth aspect of the present invention is the silicon casting apparatus according to the first aspect, wherein the melt dispersing means is configured such that an inner diameter of a front end portion of the pouring gate is 5 mm or more and 20 mm or less. The size of the melt collision area is increased.

  As described above, in the present invention, the heating means, the melting crucible for forming the silicon melt by heating and melting the silicon raw material contained therein by the heating means, and the bottom of the melting crucible are provided. A hot water outlet for pouring the melt, a mold provided below the melting crucible, having an opening at the top, and a mold for holding and solidifying the silicon melt discharged from the hot water outlet, The mold release material provided inside the mold and the size of the melt collision area where the silicon melt discharged from the tap port falls and collides with the mold release material provided inside the mold And a melt dispersion means for increasing the temperature, so that the silicon melt discharged into the mold is not concentrated in the center of the mold directly under the outlet as in the prior art, and the melt is dispersed. By means In order to further increase the size of the melt collision area that collides with the mold release material, the mold release material is deformed in a crater shape or is peeled and damaged, and silicon is mixed into the silicon melt in the mold. It is possible to suppress an increase in ingot defects and deterioration of characteristics. In addition, by preventing damage to the mold release material at the center of the mold, it is possible to suppress deterioration in the quality of the silicon ingot without changing the heat removal capability of the center of the mold. Further, there is no possibility that the mold base material and the silicon ingot are fused due to cracks due to thermal stress or damage to the release material.

  In addition, the melt dispersion means is configured so that the silicon melt discharged from the pouring gate can be captured by the opening of the mold in a horizontal relative direction between the pouring gate and the mold. Since the horizontal movement mechanism is configured to change the positional relationship, for example, the mold drive mechanism provided on the mold side, when the silicon melt is poured from the melting crucible into the mold, the horizontal movement mechanism causes the pouring gate. If the relative positional relationship in the horizontal direction with the mold is changed, the hot water can be dispersed in the mold and discharged without being concentrated in the mold central portion immediately below the pouring gate. Therefore, it is possible to prevent the release material from being peeled and damaged, and to suppress an increase in defects of the silicon ingot and a deterioration in characteristics due to the release material being mixed into the silicon melt in the mold.

  The mold driving mechanism includes a rotation mechanism that rotates the mold, and a mold center axis that is a substantially central axis in a vertical direction with respect to the opening of the mold, and the hot water discharged from the pouring gate. The melt central axis that is the substantially central axis in the vertical direction when the silicon melt falls is configured not to overlap each other. Therefore, when the mold is rotated by such a mold driving mechanism, the mold itself moves spirally with respect to the melt central axis, and the silicon melt in the mold has a stirring action. The silicon melt immediately after pouring does not concentrate at one place in the center of the mold, but is dispersed in the mold and discharged to have a uniform distribution, so that a uniform solidified layer can be formed.

  Further, the mold driving mechanism includes a rotation mechanism for rotating the mold, a mold center axis that is a substantially central axis in a vertical direction with respect to the opening of the mold, and a vertical direction of the rotation mechanism. The rotation center axis that is the center axis is configured not to overlap each other. Therefore, when the mold is rotated by such a mold driving mechanism, the mold itself revolves around the rotation central axis, and the silicon melt in the mold has a stirring action and the tapping water is discharged. Immediately after the silicon melt is not concentrated in one place at the center of the mold, the molten silicon is dispersed in the mold and discharged to have a uniform distribution, so that a uniform solidified layer can be formed.

  Further, the melt dispersing means may increase the size of the melt collision area by dividing the pouring gate into a plurality of parts, and in this way, the melt is dispersed around the center of the mold. This prevents the release material from being peeled and damaged, and prevents an increase in defects in the silicon ingot and deterioration of properties due to the release material being mixed into the silicon melt in the mold. it can.

  In addition, the rotation mechanism according to the present invention has the above-described configuration of the melt central axis, the mold central axis, and the rotation central axis, so that the relative positional relationship in the horizontal direction between the tap and the mold is maintained. In the present specification, the rotation mechanism according to such a configuration is also treated as belonging to the horizontal movement mechanism because it has a function of changing.

  Hereinafter, the invention according to each claim will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic cross-sectional view of a first embodiment of the silicon casting apparatus of the present invention, wherein 1 is a melting crucible, 2 is a holding crucible, 3 is a silicon raw material, 4 is a tap, 5 is a nozzle, Are upper heating means and side heating means, which are heating means, 8 is a mold, 9 is a release material, 10 is a silicon melt, 11 is a mold drive mechanism (an example of a horizontal movement mechanism which is an example of a melt dispersion means) ).

  As shown in FIG. 1, the melting crucible 1 heats and melts the silicon raw material 3 housed therein to form a silicon melt, and the bottom of the melting crucible 1 discharges the formed silicon melt. A pouring gate 4 is provided, and the silicon melt is discharged into a mold 8 provided below, cooled and solidified to obtain a polycrystalline silicon ingot. In addition, the silicon ingot melted in the melting crucible 1, poured out into the mold 8, cooled and solidified is used, for example, as a polycrystalline silicon substrate material for solar cells.

  The melting crucible 1 is used to melt the silicon raw material 3 that has been charged, and high-purity quartz or the like is usually used in consideration of the fire resistance and the fact that impurities do not diffuse into the semiconductor material. There is no particular limitation as long as the purity is such that melting, evaporation, softening, deformation, decomposition, and the like do not easily occur at a temperature higher than the temperature and do not deteriorate the solar cell characteristics. The size of the melting crucible 1 needs to be a size that can enclose the silicon raw material 3 according to the amount of melting that is melted at a time. The dissolution amount of the silicon raw material 3 is, for example, in the range of 1 kg to 150 kg. Further, since the melting crucible 1 is softened at a high temperature and cannot keep its shape, it is held by a holding crucible 2 made of graphite or the like.

  An upper heating means 6 and a side heating means 7, which are heating means according to the present invention, are arranged on the upper and side portions of the melting crucible 1 and the holding crucible 2, for example, a resistance heating type heater or an induction heating type heater. A coil or the like can be used. By these heating means, the silicon raw material 3 stored in the melting crucible 1 can be heated and melted to form a silicon melt.

  At the bottom of the melting crucible 1 and the holding crucible 2, a hot water outlet 4 is provided so that the molten silicon raw material 3 can be discharged into the mold 8 installed below. Then, a nozzle 5 may be provided at the outlet 4 as shown in FIG. The nozzle 5 is made of, for example, quartz or the like, and is formed integrally with the melting crucible 1 in a cylindrical shape as a whole. This nozzle 5 is for suppressing splashing of the melted silicon melt, and it is desirable that the nozzle 5 has a shape that does not hinder the falling direction of the silicon melt discharged from the hot water outlet 4. In addition, in this specification, when the nozzle 5 is provided, the exit of the nozzle 5 shall be regarded as a hot water outlet.

  In the initial stage of pouring, the melt passing through the tap 4 is pushed out by the pressure depending on the water level. However, since the pressure due to the water level almost disappears in the latter half of the pouring, the melt flows out of the tap 4 due to its own weight. Become. Therefore, in order to discharge hot water without waste, the bottom of the melting crucible 1 needs to have a certain inclination or more. Moreover, the shape of the main body of the melting crucible 1 is not particularly limited.

  The casting mold 8 provided below the melting crucible 1 has an opening at the top, and can hold and solidify the silicon melt 10 inside thereof. The mold 8 is made of graphite, a silica member, a carbon fiber reinforced graphite material (C / C material), etc., and one bottom member 8a constituting the bottom of the mold and four side members 8b constituting the side of the mold. It is composed of divided molds that can be assembled and divided molds that can be assembled.

  The bottom member 8a and the side member 8b are assembled in a separable manner by fixing with bolts (not shown), or fixed with a frame member (not shown) in which the bottom member 8a and the side member 8b just fit. And assembled in a splittable manner.

A mold release material 9 is provided on the inner surface of the mold 8. By such a release material 9, the inner wall of the mold 8 and the silicon ingot are not fused after the silicon melt 10 inside the mold 8 is solidified, and the bottom member 8a and the side member 8b are repeated many times. Can be used. As such a release material 9, for example, silicon nitride (Si ₃ N ₄ ) powder is mixed with a polyvinyl alcohol aqueous solution and coated on the inner surface of the mold 8 by drying. By mixing silicon nitride with an aqueous polyvinyl alcohol solution or the like, powdered silicon nitride becomes a slurry and can be easily applied to the graphite mold 8.

  As the silicon nitride powder, one having an average particle diameter of about 0.4 to 0.6 μm is used, and mixed with such silicon nitride and a polyvinyl alcohol aqueous solution having a concentration of about 5 to 15% by weight. The inner surface of the mold 8 is covered with a spatula or a brush. Usually, when coating the release agent 9 made into a slurry by mixing powder and an organic binder aqueous solution such as polyvinyl alcohol, the heat decomposable product of the organic binder is mixed into the silicon melt by subsequent heating. In order to prevent this, a degreasing process is performed, and after natural drying or drying on a hot plate, the silicon melt 10 is poured into the mold 8.

  The release material 9 can be applied to the inner surface of the mold 8 by applying a mixture of silicon nitride and silicon dioxide powder. In addition to applying slurry, the release material 9 may be provided directly using a plasma spraying machine.

  In addition, as a coating method, a brush, a spatula, or the like can be used, or a spray method or the like can be used. From the viewpoint of productivity, a brush that can secure a coating thickness by a single coating is used. desirable. Further, as a drying method, a conventionally known method such as a hot plate or an oven can be used.

  Further, the silicon casting apparatus of the present invention further increases the size of the melt collision area where the silicon melt discharged from the tap 4 falls and collides with the release material 9 provided in the mold 8. A liquid dispersion means is provided. Hereinafter, the melt dispersion means will be described.

  The first embodiment of the silicon casting apparatus of the present invention shown in FIG. 1 has a horizontal movement mechanism that can move the mold 8 in the horizontal direction as the melt dispersion means. Specifically, the mold drive mechanism 11 corresponds. The mold driving mechanism 11 is configured to be able to move the horizontal position of the mold 8 within a range in which the silicon melt discharged from the tap 4 can be captured by the opening of the mold 8. . Moving the horizontal position beyond this range is not preferable because the silicon melt leaks outside the mold 8.

  With such a structure, when the silicon melt is discharged from the melting crucible 1 to the mold 8, the mold drive mechanism 11 is driven to move the mold 8 in the horizontal direction so that it is concentrated at the center of the mold. Without being poured out, it can be dispersed in the mold and poured out. As a result, the size of the melt collision area where the silicon melt discharged from the tap 4 falls and collides with the release material 9 provided inside the mold 8 can be further increased. Since the impact is reduced, it is possible to prevent the release material 9 from being peeled and damaged, and to suppress an increase in defects of the silicon ingot and deterioration of characteristics due to the release material being mixed into the silicon melt 10 in the mold. it can. Then, the mold drive mechanism 11 may be stopped in a state in which the silicon melt is filled, for example, about one third of the mold height from the start of the hot water, or the hot water is completely discharged from the melting crucible 1 to the mold 8. The mold drive mechanism 11 may be stopped later.

  The method for moving the mold 8 in the horizontal direction by the mold drive mechanism 11 is not particularly limited. However, if the mold 8 described below is configured to rotate, the present invention has a simple structure. The effect can be obtained satisfactorily.

  FIG. 2 shows an example of a configuration for rotating the mold 8. 2A is a schematic cross-sectional view, and FIG. 2B is a view of the mold 8 as viewed from above. In the example shown in this figure, the mold drive mechanism 11 includes a rotation mechanism configured by combining, for example, a motor and a gear in order to rotate the mold 8, and is perpendicular to the opening of the mold. The mold central axis p, which is a substantially central axis, and the melt central axis o, which is a substantially central axis in the vertical direction when the silicon melt discharged from the tap 4 is dropped, are configured not to overlap each other. Yes. With such a configuration, when the silicon melt 10 is poured out while the mold drive mechanism 11 rotates the mold 8, the locus of the melt collision region where the silicon melt is poured out and collides with the inside of the mold 8 is shown in FIG. As shown in FIG. 2B, a circle is drawn inside the mold 8. Therefore, the hot water is dispersed and discharged in the mold 8 and does not concentrate at the center of the mold as in the prior art, so damage to the release material 9 inside the mold 8 can be reduced. Further, when the temperature of the mold 8 at the time of tapping is lower than the melting point 1412 ° C. of the silicon melt, the silicon melt 10 poured into the mold 8 is deprived of heat by the mold 8 and solidifies. Distribution tends to be non-uniform. At this time, the silicon melt in the mold 8 is agitated by rotating the mold 8, so that the distribution of the silicon melt immediately after tapping becomes uniform, and a uniform solidified layer can be formed.

  Further, as shown in FIG. 2B, it is desirable that the shortest distance d between the mold center axis p and the melt center axis o is 2 cm or more. The direction of the silicon melt flowing out from the tap 4 may be shifted due to the deformation of the melting crucible 1 and the deformation of the nozzle 5 repeatedly used. At this time, if the shortest distance is less than 2 cm, the molten silicon melt Are discharged at the same position, and the release material 9 is peeled and damaged, and mixed in the silicon melt 10 in the mold, there is a possibility that the defect of the silicon ingot increases or the characteristics deteriorate. The maximum value of the distance between the mold center axis p and the melt center axis o may be within a range in which the silicon melt discharged from the tap 4 can be captured by the opening of the mold 8.

  The distance d between the position of the tip of the nozzle and the center of the mold is such that the tap 4 having the nozzle 5 hanging down directly is provided at the approximate center of the melting crucible 1 as shown in FIG. The center axis p and the melt center axis o may be shifted, or the outlet 4 having the nozzle 5 hanging down just below is provided at a position shifted from the center of the melting crucible 1 as shown in FIG. Thus, the mold center axis p and the melt center axis o may be shifted. Moreover, as shown in FIG.3 (b), the nozzle 5 inclined diagonally with respect to the tap 4 may be provided, and the mold center axis | shaft p and the melt center axis | shaft o may be shifted.

  Next, another example of the configuration for rotating the mold 8 is shown in FIG. In the example shown in FIG. 4, the mold drive mechanism 11 includes a rotation mechanism that rotates the mold 8, and rotates with a mold center axis p that is a substantially central axis in the vertical direction with respect to the opening of the mold 8. The rotation center axis q which is the center axis in the vertical direction of the mechanism is configured not to overlap each other. With such a configuration, if the silicon melt 10 is discharged while the mold 8 is rotated by the mold driving mechanism 11, the locus of the melt collision region where the silicon melt is discharged and collides with the inside of the mold 8 is shown in FIG. A circle can be drawn inside the mold 8 in the same manner as shown in 2 (b), and the same effect can be obtained.

  As described above, when the mold 8 is rotated, the mold 8 may be rotated in one direction. However, if the mold 8 is rotated in both forward and reverse directions, the mold 8 may be rotated. It is preferable because the effect of stirring the silicon melt 10 inside is increased. When the mold 8 is rotated in one direction, the rotation speed is preferably in the range of 2 to 10 rpm. When the mold 8 is rotated in both forward and reverse directions, for example, the maximum rotation speed is 15 sec. If the speed is set to 5 rpm, the effect of the present invention is excellent.

  The above explanation is an example of a horizontal movement mechanism in which the relative positional relationship in the horizontal direction between the tap 4 and the mold 8 is changed as the melt dispersion means. An example of melt dispersion means will be shown.

In the silicon casting apparatus of the present invention shown in FIG. 5, as the melt dispersion means, the nozzle 5 is divided into a plurality of parts, so that the tap 4 is divided into a plurality of parts and the size of the melt collision area is increased. It is an example. Except this part, it is completely the same as the above-mentioned silicon casting apparatus. FIG. 5B shows the detailed structure of the nozzle portion. Since the tip portion of the nozzle 5 is divided into a plurality of divided nozzles 5 a, the size of the melt collision area where the silicon melt falls from the tap 4 and collides with the release material 9 provided inside the mold 8. It is possible to increase the length by the number obtained by dividing the tip portion of the nozzle. As a result, since the pressure depending on the water level of the silicon melt in the melting crucible at the nozzle tip is also dispersed, it is possible to disperse the impact of the silicon melt to be poured out. It is possible to prevent an increase in defects of the silicon ingot and a deterioration in characteristics due to mixing of the release material into the silicon melt 10 inside the mold 8.

  FIG. 6 shows a cross-sectional structure of a melting crucible according to the silicon casting apparatus of the present invention. In this example, as the melt dispersion means, the size of the melt collision area is increased by setting the inner diameter r of the tip of the tap 4 of the melting crucible 1 to 5 mm to 20 mm. Since the silicon melt discharged from the tip of the nozzle 5 which is the outlet of the melting crucible 1 is focused by the nozzle 5, it does not scatter around the mold 8, and the discharged silicon melt does not flow out of the mold 8. Guided to the center. At this time, by setting the inner diameter of the tip of the hot water outlet 4 (that is, the nozzle 5) within the above range, the hot water is not concentrated in one place in the central portion of the mold as in the prior art, but around the central portion of the mold. Dispersed water can be discharged. Therefore, it is possible to prevent the release material 9 provided in the mold 8 from being peeled and damaged, and to increase the defect of the silicon ingot due to mixing of the release material into the silicon melt 10 in the mold 8 and to deteriorate the characteristics. Can be suppressed.

  Here, if it is smaller than the above range, the silicon melt is guided to a narrower region at the center of the mold, which may damage the mold release material 9, and the silicon melt 10 inside the mold may be separated. The mold material is mixed to increase the defect of the silicon ingot and deteriorate the characteristics. On the other hand, if it is larger than this range, it is impossible to suppress the scattering of the silicon melt, and the silicon melt may be scattered around the mold 8 to reduce the productivity.

  Hereinafter, the function and effect of the present invention when the silicon casting apparatus of the present invention is used will be described with reference to FIG.

  After supplying the silicon raw material 3 into the melting crucible 1, it is heated to a predetermined temperature by the upper heating means 6 and the side heating means 7 which are heating means provided on the upper and side portions of the melting crucible, and gradually from above. Dissolve. Initially, it is desirable to close the pouring gate 4 with a part of the silicon raw material in the melting crucible, and when the silicon raw material 3 which has been melted from above and plugs the pouring gate 4 is completely melted, The silicon melt 10 flows out from the gate 4. The method is not limited to this method, and for example, the hot water outlet 4 may be closed by mechanical means (such as a lid) so that the silicon melt flows at a predetermined timing. The flowing silicon melt is discharged into the mold 8 located below the melting crucible 1.

  Since the silicon melt discharged to the mold 8 is dispersed and discharged from the mold 8 by the above-described melt dispersing means, the size of the melt collision area that collides with the release material is further increased. As a result, the impact impacting the release material 9 can be mitigated, so that the release material 9 is deformed into a crater shape or peeled off and mixed into the silicon melt 10 in the mold 8. It is possible to suppress an increase in defects of silicon ingots and deterioration of characteristics. In addition, by preventing damage to the mold release material at the center of the mold, it is possible to suppress deterioration in the quality of the silicon ingot without changing the heat removal capability of the center of the mold. Further, there is no possibility that the mold base material and the silicon ingot are fused due to cracks due to thermal stress or damage to the release material.

  It should be noted that the embodiment of the present invention is not limited to the above-described example, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

  For example, the above-described silicon casting apparatus of the present invention has been described with the mold drive mechanism 11 that can move the mold 8 in the horizontal direction as the horizontal movement mechanism that is the melt dispersion means, but is not limited to this. A crucible drive mechanism (not shown) that is a horizontal movement mechanism may be provided on the side of the melting crucible 1 as the liquid dispersion means. Thus, the relative positional relationship in the horizontal direction between the tap 4 and the mold 8 is changed within a range in which the silicon melt discharged from the tap 4 can be captured by the opening of the mold 8. If configured, the effects of the present invention are excellent. Further, just as in the case of the mold drive mechanism 11 described above, this crucible drive mechanism is configured to be rotatable, and the relationship between the mold center axis, the melt center axis, and the rotation center axis is respectively determined by the mold drive mechanism. The same effect can be obtained by configuring as a similar relationship to that when 11 is used.

  In addition, as the mold drive mechanism 11 having the rotation mechanism described in FIGS. 2 to 4, the melt center axis o, the mold center axis p, and the rotation center axis q are each three so that they do not all overlap. You may comprise so that it may exist on a different straight line of a book. Further, the rotation operation and the linear operation may be combined. However, the movable region of the mold drive mechanism 11 is preferably within a range in which the silicon melt discharged from the tap 4 can be captured by the opening of the mold 8, and if this range is exceeded, For example, a lid is provided on the pouring gate 4 so that the silicon melt does not pour out from the pouring gate 4, and the pouring gate 4 is covered in synchronization with the movement of the mold 8. It is necessary to prevent leakage.

  Further, the mold driving mechanism 11 may be in a standby state and driven in synchronism with the start timing of the hot water from the melting crucible 1. As a method for detecting the start timing of the hot water, for example, a method in which the operator monitors the silicon casting apparatus from near the hot water time and visually confirms the start of the hot water, as shown in FIG. 7, the thermocouple 12 applied to the mold 8 is used. Thus, it is possible to use a method for measuring a temperature change during solidification of the melt, a method for monitoring with a radiation thermometer 13 arranged so as to monitor a portion immediately below the nozzle, and the like. It is desirable that the temperature measured by the control device 14 connected to the radiation thermometer 13 is detected to detect the timing of the hot water of the silicon melt 10 because the control operation can be performed more reliably.

  In addition, in order to solidify the silicon melt 10 in one direction, a mold heat insulating material may be provided on the side of the mold 8 so as to surround the outer periphery thereof. The purpose of providing this mold heat insulating material is to suppress heat removal from the side of the mold 8 when the silicon melt 10 is held in the mold 8, and to facilitate unidirectional solidification. As the mold heat insulating material, a material having carbon as a main component, such as graphite felt, is desirable, and particularly when the surface is coated with carbon powder, it deteriorates when the silicon melt adheres. This is desirable because it can reduce the problem.

  Further, a mold heating means may be provided between the melting crucible 1 and the mold 8 to heat the silicon melt 10 held inside the mold 8. By supplying heat by this mold heating means, it is easier to control the solidification of the silicon melt inside the mold 8 and to perform the unidirectional solidification. As the mold heating means, for example, a resistance heating type heater or an induction heating type coil can be used.

  Then, a cooling means may be provided below the mold 8 so that the silicon melt 10 held inside the mold 8 can be removed from below. It is further prepared to perform unidirectional solidification from the lower part to the upper part of the silicon melt 10 by simultaneously removing heat from the lower part of the silicon melt 10 by the cooling means and simultaneously heating by the mold heating means described above. can do. As the cooling means, for example, a metal plate such as stainless steel (SUS) can be used, and heat can be effectively removed from the silicon melt 10 inside the mold 8 by circulating a coolant such as water inside. Configure. In the present invention, it is desirable to incorporate in the mold drive mechanism 11.

It is a cross-sectional schematic diagram which shows one Embodiment of the silicon casting apparatus of this invention. It is a figure for demonstrating the example of the casting_mold | template drive mechanism concerning the silicon | silicone casting apparatus of this invention, (a) is a cross-sectional schematic diagram, (b) is a schematic diagram explaining an operation | movement from a top figure. . (A), (b) is a cross-sectional schematic diagram which shows the example of the pouring gate concerning the silicon | silicone casting apparatus of this invention. It is a cross-sectional schematic diagram which shows another example of the casting_mold | template drive mechanism concerning the silicon | silicone casting apparatus of this invention. (A) is a cross-sectional schematic diagram which shows other embodiment of the silicon | silicone casting apparatus of this invention, (b) is an expansion perspective view of the nozzle which is a melt dispersion means. It is a cross-sectional schematic diagram of the crucible part concerning other embodiment of the silicon casting apparatus of this invention. It is a cross-sectional schematic diagram which shows the method of detecting the tapping timing in the silicon casting apparatus of this invention. It is a cross-sectional schematic diagram which shows the conventional silicon | silicone casting apparatus.

Explanation of symbols

1: Melting crucible 2: Holding crucible 3: Silicon raw material 4: Outlet 5: Nozzle 5a: Split nozzle as an example of melt dispersion means 6: Upper heating means as heating means 7: Side heating means as heating means 8: Mold 8a: Bottom member 8b: Side member 9: Release material 10: Silicon melt 11: Mold drive mechanism 12 which is a horizontal movement mechanism which is an example of melt dispersion means 12: Thermocouple 13: Radiation thermometer 14: Control Apparatus o: Melt center axis p: Mold center axis q: Rotation center axis d: Shortest distance between melt center axis and mold center axis r: Inner diameter of nozzle (nozzle)

Claims (8)

Heating means;
A melting crucible for forming a silicon melt by heating and melting the silicon raw material housed inside by the heating means,
Provided at the bottom of the melting crucible, and a hot water outlet for pouring the silicon melt;
A mold provided below the melting crucible, having an opening at the top, and a mold for holding and solidifying the silicon melt discharged from the hot water outlet,
A mold release material provided inside the mold,
Silicon having a melt dispersion means for further increasing the size of a melt collision area in which the silicon melt discharged from the hot water outlet falls and collides with the mold release material provided in the mold. Casting equipment. The melt dispersion means has a horizontal relative positional relationship between the hot water outlet and the mold within a range in which the silicon melt discharged from the hot water outlet can be captured by the opening of the mold. The silicon casting apparatus according to claim 1, wherein the silicon casting apparatus is a horizontal movement mechanism configured to change the angle. The silicon casting apparatus according to claim 2, wherein the horizontal movement mechanism is a mold driving mechanism provided on the mold side. The mold drive mechanism includes a rotation mechanism for rotating the mold,
A mold central axis that is a substantially central axis in the vertical direction with respect to the opening of the mold, and a melt central axis that is a substantially central axis in the vertical direction when the silicon melt discharged from the tap is dropped. The silicon casting apparatus according to claim 3, which is configured not to overlap each other. The silicon casting apparatus according to claim 4, wherein a shortest distance between the mold central axis and the melt central axis is 2 cm or more. The mold drive mechanism includes a rotation mechanism for rotating the mold,
The mold center axis that is a substantially central axis in the vertical direction with respect to the opening of the mold and the rotation center axis that is the center axis in the vertical direction of the rotation mechanism are configured so as not to overlap each other. 3. The silicon casting apparatus according to 3. 2. The silicon casting apparatus according to claim 1, wherein the melt dispersing means increases the size of the melt collision area by dividing the pouring gate into a plurality of portions. 3. 2. The silicon casting apparatus according to claim 1, wherein the melt dispersion means increases the size of the melt collision region by setting an inner diameter of a tip portion of the tap outlet to 5 mm or more and 20 mm or less.

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