JP2005213088A - Casting mold and casting device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a casting mold and a casting device, by which the strain of a polycrystalline silicon ingot formed by unidirectional solidification is reduced, and an ingot hardly generating cracks in a cutting process is obtained. <P>SOLUTION: The casting mold 1 has a bottom plate 1a having a quadrangular shape, four side plates 1b each having such a trapezoidal shape that the lower base is longer than the upper base, an inner surface part comprising the bottom plate 1a and the four side plates 1b, which is formed by surrounding the outer periphery of the side faces of the bottom plate 1a with trapezoid upper bases, each having length corresponding to that of each side of the bottom plate 1a, forming an opening part by trapezoid lower bases, and fitting sides of the adjacent side plates to each other, eight ridge line parts where the bottom plate 1a contacts with four side plates 1b, and the four side plates 1b mutually contacts, and a releasing material layer provided on the inner surface part. In the casting mold 1, the taper angle of a reversed taper shape formed by each inner face of the side plates 1b is set to be ≥1° and ≤5°. The casting device is equipped with the casting mold 1 and a plurality of heat insulating members for the casting mold 1, which are arranged so as to surround the outer periphery of the casting mold 1 and to be separable in the vertical direction of the casting mold 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a mold suitable for casting a polycrystalline silicon ingot for a solar cell and a casting apparatus using the mold.

  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 conversion efficiency can be easily increased 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 manufacture 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. This casting method includes a mold made of graphite, silica, or the like coated with a release material which is a slurry obtained by mixing powder such as silicon nitride or silicon oxide in a solution composed of an appropriate binder and a solvent, and stirring. Formed by pouring molten silicon melt into the mold with the inner surface of the mold coated with a thermal spray coating such as silicon nitride or silicon oxide, heating from the upper part of the mold, cooling from the lower part, and solidifying in one direction. Is melted once in a mold and then solidified in one direction from the bottom again to form a silicon ingot. 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.

  A general silicon casting apparatus for producing such a polycrystalline silicon ingot is shown in FIG.

  A melting crucible 108 for melting the raw material silicon 110 is disposed on the upper part while being held by a holding crucible 109, and a hot water outlet 111 for discharging a silicon melt is provided at the bottom of the melting crucible 108 and the holding crucible 109. . Further, an upper heating means 112 and a side heating means 113 are disposed on the upper and side portions of the melting crucible 108 and holding crucible 109, respectively, and a mold into which the silicon melt 104 is poured below the melting crucible 108 and holding crucible 109. 101 is disposed and a mold heat insulating material 103 is provided on the outside thereof. Further, a cooling means 107 is provided below the mold 101, and a mold heating means 106 for controlling the solidification of the silicon melt 104 is disposed above the mold 101.

  For example, a silicon raw material put in a melting crucible 108 made of high-purity quartz or the like is heated and melted by an upper heating means 112 and a side heating means 113 made of a resistance heating type heater, an induction heating type coil, etc. As a melt, it is poured from the bottom hot water outlet 111 into the lower mold 101.

The mold 101 is made of, for example, graphite, and is composed of, for example, a divided mold in which one bottom member 101a and four side members 101b are combined and assembled. The release material layer 102 is made of powder such as silicon nitride (Si ₃ N ₄ ) that is silicon nitride, silicon carbide (SiC) that is silicon carbide, or silicon oxide (SiO ₂ ) that is an oxide of silicon. It is known as a known technique that these powders are mixed in a solution composed of an appropriate binder and a solvent, stirred to form a slurry, and coated on the inner wall of the mold by means such as coating or spraying ( For example, refer nonpatent literature 1). The mold heat insulating material 103 suppresses heat removal and is made of a material containing carbon as a main component in consideration of heat resistance, heat insulating properties and the like. As the mold heating means 106, a resistance heating type heater, an induction heating type coil or the like is used. The side wall of the mold 101 is covered with a mold heat insulating material 103 made of a graphite molded body, etc., and the silicon melt 104 poured into the mold 101 by the cooling means 107 is cooled from below, so that the silicon from above the mold 101 By simply heating the melt, the silicon melt can be solidified in one direction from the lower part to the upper part to obtain a polycrystalline silicon ingot (see, for example, Patent Document 1). These are all arranged in a vacuum vessel (not shown).
Japanese Patent Laid-Open No. 9-263489 15th Photovoltaic Specialists Conf. (1981), P576-P580, "A NEW DIRECTIONAL SOLIDIFICATION TECHNIQUE FOR POLYCRYSTALLINE SOLAR GRADE SILICON"

  When the silicon melt 104 is solidified in one direction by the above-described method, the shape of the solid-liquid interface is flattened so that the stress due to solidification expansion is released upward. However, in practice, it is difficult to completely insulate the side wall of the mold, so that lateral expansion occurs, a large stress is applied to the side of the mold, and it becomes impossible to pull out the ingot from the mold. In particular, there is a problem that cracks caused by thermal stress occur at the corner of the mold bottom where the crystal grown from the mold side and the crystal grown from the mold bottom collide, and the manufacturing yield is lowered.

  In order to solve such a problem, it is necessary to cool and solidify the crystal at a uniform solidification rate and solidification direction to obtain a healthy ingot having a uniform thermal stress distribution. Usually, when discussing the unidirectional solidification phenomenon, it is important to control the characteristic values of the solidification rate X (m / s), the cooling rate α (K / s), and the temperature gradient G (K / s). Although it is necessary to increase the G / X ratio in the mold, it is not possible to achieve the required G / X ratio by simply solidifying it in the mold. In order to increase G and decrease X, various unidirectional solidification furnaces such as a mold drawing type unidirectional solidification furnace and a power-down type unidirectional solidification furnace are often used.

  If such a unidirectional solidification furnace is used, a healthy ingot having an ideal unidirectional solidification structure can be obtained, but the initial investment for introducing the apparatus is expensive, and it can be flexibly adapted to various ingot sizes. There is a problem that cannot be done.

  In view of such circumstances, an object of the present invention is to provide a mold and a casting apparatus for reducing the distortion of a polycrystalline silicon ingot formed by unidirectional solidification and obtaining an ingot in which cracks are hardly generated in the cutting process of the silicon ingot. It is said.

  The inventor tried to achieve the above-mentioned object only by improving the mold shape and structure, and realized the result as the present invention.

  That is, the mold according to claim 1 of the present invention is a mold having a mold opening extending upward, and has a bottom plate having a square shape and a trapezoidal shape in which the lower base is longer than the upper base. Four side plates having a trapezoidal upper base having a length corresponding to each side of the bottom plate, surrounding the outer periphery of the side surface of the bottom plate, forming the mold opening by the trapezoid lower bottom, and adjacent sides A side plate fitted side by side, and a release material layer provided on the inner surface of the mold composed of the bottom plate and the four side plates, and each inner surface of the side plate is perpendicular to the vertical direction. It has a taper angle of 1 ° or more and 5 ° or less.

  And the casting_mold | template concerning Claim 2 of this invention is a casting_mold | template of Claim 1, The said mold release material layer is the said ridgeline part in which the said bottom plate, the said side plate, and the said four side plates mutually contact, It was made thicker than other parts of the inner surface of the mold.

  According to a third aspect of the present invention, there is provided a casting apparatus according to the first or second aspect, and a plurality of molds that surround the outer periphery of the mold and are separable in the longitudinal direction of the mold. And a mold heat insulating material.

  A casting apparatus according to a fourth aspect of the present invention is the casting apparatus according to the third aspect, wherein the plurality of mold heat insulating materials are further arranged so as to be divided in a lateral direction of the mold.

  Furthermore, a casting apparatus according to a fifth aspect of the present invention is the casting apparatus according to the third or fourth aspect, wherein at least a part of the inner peripheral surface of the plurality of mold heat insulating materials is an outer peripheral surface of the mold. It arrange | positions so that it may contact | abut at least one part.

  A casting apparatus according to claim 6 of the present invention is the casting apparatus according to any one of claims 3 to 5, wherein an inner peripheral surface of the plurality of mold heat insulating materials, an outer peripheral surface of the mold, And a plurality of abutting members arranged in correspondence with at least each side plate of the mold.

  A casting apparatus according to a seventh aspect of the present invention is the casting apparatus according to any one of the third to sixth aspects, wherein the casting apparatus is disposed on an outer peripheral portion of the plurality of mold heat insulating materials, A restraining member for restraining the material from being displaced is further provided.

  Furthermore, in the casting apparatus according to an eighth aspect of the present invention, the plurality of mold heat insulating materials in the casting apparatus according to the seventh aspect is configured to have a substantially cylindrical shape when arranged so as to surround an outer periphery of the mold. I made it.

  Moreover, the casting apparatus concerning Claim 9 of this invention is a casting apparatus as described in any one of Claim 3-8. WHEREIN: The holder main part which mounts the said mold, and the said mold heat insulating material are mounted. A mold holder comprising a holder outer peripheral part, wherein the holder main part further comprises a mold holder having a higher thermal conductivity than the holder outer peripheral part, and a chill plate for mounting and cooling the mold holder I did it.

  That is, the mold according to the present invention is a mold having a mold opening extending upward, and includes a single bottom plate having a quadrilateral shape and four pieces having a trapezoidal shape in which the lower base is longer than the upper base. A side plate that surrounds the outer periphery of the side surface of the bottom plate by a trapezoidal upper base having a length corresponding to each side of the bottom plate, forms the mold opening by the trapezoidal lower bottom, and fits adjacent side sides And a release material layer provided on the inner surface of the mold composed of the bottom plate and the four side plates, and each inner surface of the side plate has a vertical direction of 1 ° or more 5 Has a taper angle of less than °. In this way, the side plates constituting the mold are placed on the bottom plate and the side plates are assembled together so that they can be freely assembled / disassembled. Therefore, the mold can be easily disassembled after the silicon melt is solidified, and the silicon ingot can be easily taken out. And since it spreads in a reverse taper shape at an appropriate angle upward, horizontal stress concentration due to solidification expansion of silicon can be avoided, and accumulation of strain in the silicon ingot can be reduced. Can do.

  Further, the eight ridge lines where the bottom plate, the side plate and the four side plates contact each other are securely sealed because the thickness of the release material layer is larger than the other portions of the inner surface portion of the mold, and the melt is discharged to the outside. There is no leakage.

  Further, a casting apparatus comprising the mold according to the present invention and a plurality of mold heat insulating materials that surround the outer periphery of the mold and that can be divided in the vertical direction of the mold is a mold divided in the vertical direction. The heat insulating material can be easily removed, and the mold can be easily disassembled to release the silicon ingot.

  The plurality of mold heat insulating materials are further arranged so as to be separable in the lateral direction of the mold, thereby making it easier to remove the mold heat insulating materials.

  Furthermore, since the plurality of mold heat insulating materials are arranged such that at least a part of the inner peripheral surface thereof is in contact with at least a part of the outer peripheral surface of these molds, the external force applied to the side plates of the mold accompanying the solidification and expansion of the silicon ingot It is possible to release the stress inside the ingot upward from the side surface of the mold having a reverse taper shape.

  Further, by arranging a plurality of abutting members corresponding to at least each side plate of the mold in the gap between the inner peripheral surface of the plurality of mold heat insulating materials and the outer peripheral surface of the mold, and contacting each surface In addition to being able to suppress the external force to the side plate of the mold accompanying the solidification and expansion of the silicon ingot by these mold heat insulating materials, it is possible to more strongly press the side plate of the mold so as not to move by these contact members, The stress inside the ingot can be surely released upward from the side surface of the mold having a reverse tapered shape.

  Moreover, since the restraint member which is arrange | positioned on the outer peripheral part of a some mold heat insulating material and restrains so that these mold heat insulating materials may not displace is further provided, said effect can be made still more reliable. And since these multiple mold heat insulating materials have a substantially cylindrical shape when they are placed so as to surround the outer periphery of the mold, they can be uniformly pressed from the outside by the restraining member, and the stress distribution is more uniform. It becomes.

  Further, a mold holder comprising a holder main part for placing the mold and a holder outer peripheral part for placing the mold heat insulating material is configured such that the holder main part has higher thermal conductivity than the holder outer peripheral part. Since the holder was placed on the chill plate and cooled, when the heat was removed from the chill plate, the flow was evenly rectified from the area at the bottom of the mold without removing heat from the area other than the bottom plate of the mold. Since heat is taken away, it is easy to obtain a uniform heat flow, and the control of the solidification rate is easier than before. Further, the crystal does not grow from the bottom of the side surface of the mold, and the unidirectional solidification is greatly improved.

  In this way, by using the mold and casting apparatus of the present invention, the stress on the mold side wall caused by the solidification expansion in the horizontal direction caused when the molten silicon in the mold is solidified in one direction by heat removal from the bottom of the mold is reduced. Since it is avoided and the unidirectional solidification property is improved, an ingot can be obtained in which cracks such as vertical cracks and horizontal cracks generated on the cut surface hardly occur in the cutting process of the silicon ingot.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic view of a casting apparatus of the present invention, where (a) is a top view and (b) is a side view. FIG. 2A is a cross-sectional view in the AA direction of FIG. In the figure, 1 is a mold, 1a is a bottom plate, 1b is a side plate, 2 (2a to 2d) is a mold heat insulating material, 3 (3a to 3d) is a wedge (wedge) that is a contact member, and 4 is a ring that is a restraining member. The shaped member, 5 is a mold holder, and 6 is a chill plate.

  In the example shown in the figure, the mold heat insulating material 2 (2a to 2d) is divided into three in the lateral direction of the mold, and the wedge 3 and the ring-shaped member 4 are also configured as three kinds of members correspondingly. Has been. In the drawings, U, M, and L are shown after the symbols of the three types of upper, middle, and lower members, but they are omitted in the description of the present specification unless otherwise required. Moreover, hatching is added to a portion corresponding to the middle (M) of the mold heat insulating material 2 divided into three in the lateral direction of the mold in FIG.

  The mold according to the present invention is an upper open mold, and includes a single bottom plate 1a having a quadrangular shape and a side plate 1b having a trapezoidal shape having a lower bottom longer than the upper bottom. As such a mold member, graphite, silica plate or the like can be used, but it is desirable to use a carbon fiber reinforced carbon material (C / C material) which is light and has high strength.

  In order to assemble these mold members, as shown in FIG. 3, the side surface outer periphery of the bottom plate 1a is surrounded by a trapezoidal upper base having a length corresponding to each side of the bottom plate 1a, and the two side portions of the side plate 1b adjacent to each other are surrounded. By forming and processing the recessed ridges and the cutouts of the ridges in combination with each other, a mold opening is formed by the trapezoidal lower bottom, and an inverted taper shape in which each inner surface of the side plate 1b spreads toward the opening. Assembled to form.

  As shown in FIG. 2B, the lengths of the upper and lower bases of the trapezoidal shape of the side plate 1b are such that when the side plates 1b are combined with each other, the inner surfaces of the side plates 1b are tapered relative to the vertical direction. The dimension is set so that the angle θ is 1 ° to 5 °, and the stress concentration in the horizontal direction due to the solidification expansion of silicon is avoided.

  In addition, when a notch-shaped fitting portion as shown in FIG. 3 is provided on the side portion of the side plate 1b, it is not strictly a trapezoid, but if these are fitted and combined, The side plate 1b can be regarded as a trapezoidal shape.

  The mold 1 assembled in this manner has a mold release material on the inner surface of the mold composed of the bottom plate 1a and the side plate 1b, and the eight ridge lines where the bottom plate 1a, the side plate 1b and the four side plates 1b contact each other. Layer 7 is provided. 4A and 4B are diagrams showing the configuration of the release material layer. FIG. 4A is an enlarged structural view of a portion B of FIG. 1A, that is, a ridge line portion between adjacent side plates 1b, and FIG. It is an expanded structure figure of C part of (a), ie, the ridgeline part of bottom board 1a and side board 1b. As shown in the figure, a release material layer 7 is provided on the inner surface of the mold 1 constituted by each member and the ridge line portion between the members.

The release material layer 7 can be formed by, for example, mixing silicon nitride (Si ₃ N ₄ ) powder with a PVA (polyvinyl alcohol) aqueous solution and applying it to the inner surface of the mold 1. By mixing with a PVA aqueous solution or the like, powdered silicon nitride becomes a slurry and can be easily applied to the mold 1.

  As the silicon nitride powder, one having an average particle size 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. It is applied to the inner surface of the mold 1 with a spatula, a brush, a dispenser or the like. The release material layer 7 can be applied to the inner surface of the mold 1 by applying a mixture of silicon nitride and silicon dioxide powder.

  By providing such a release material layer 7, the inner wall of the mold 1 and the silicon ingot are less likely to be fused after the mold 1 and the silicon melt are solidified, and these members are repeated many times. Can be used.

  In addition, a release material layer 7 is provided so as to be thicker than other portions of the inner surface of the mold at the connection portion between the bottom plate 1a and the side plate 1b and the connection portion between the side plates 1b, that is, the eight ridge lines. Is desirable. In this way, since these ridge portions are reliably sealed by the release material layer 7, leakage of the silicon melt is reduced.

  A specific method for forming the release material layer 7 is desirably performed through the following three steps. As a first step, the release material slurry in the form of a slurry as described above is applied to the surfaces of the bottom plate 1a and the four side plates 1b and dried. Next, as a second step, four side plates 1b are erected with the bottom plate 1a as the bottom surface, and assembled into a box shape so that the surface to which the release material is applied is on the inside. Then, as a third step, a release material is added to, for example, a dispenser on the eight ridge lines where the bottom plate 1a, the side plate 1b, and the four side plates 1b are in contact with each other, and are applied and dried.

  If these three steps are performed, before assembling the mold 1, a mold release material is applied to each mold member, assembled into the shape of the mold 1, and then the mold release material is applied only to the joint portion of each mold member. Since only additional coating is required, the operation is dramatically simplified and the work efficiency is greatly improved. Further, the release material layer 7 in the ridge line portion can be thickened.

  As shown in FIGS. 1 and 2, the outer periphery of the mold 1 configured in this way is surrounded by a plurality of mold heat insulating materials 2 (2a to 2d) divided into four in the vertical direction, and is also a restraining member. A certain ring-shaped member 4 is arranged and securely fixed to a gap portion between the side plate 1b of the mold 1 and the mold heat insulating material 2 by a wedge 3 which is an abutting member abutting on each of the gaps. Thus, the casting apparatus of the present invention is obtained. If a plurality of wedges 3 are arranged corresponding to at least each side plate 1b of the mold 1, the side plate 1b can be fixed securely. Further, according to the example shown in FIGS. 1 and 2, the plurality of mold heat insulating materials 2 (2 a to 2 d) are further divided into three parts in the lateral direction of the mold 1.

  As the mold heat insulating material 2, a material having carbon as a main component, such as graphite felt, is desirable. In particular, if a material whose surface is coated with carbon powder is used, the silicon melt adheres and deteriorates. This is desirable because it can reduce problems.

  Further, it is desirable to use graphite (graphite) or the like as the wedge 3 and a carbon fiber reinforced carbon material (C / C material) that is light and high in strength as the ring-shaped member 4.

  A method for producing an ingot using the casting apparatus according to the present invention shown in FIGS. 1 to 4 will be described with reference to FIG.

  First, the mold 1 is placed on a mold holder 5 on a chill plate 6 (not shown in the drawing) (see FIG. 5A).

  Next, the lowermost mold heat insulating material 2 is disposed so as to surround the periphery of the mold 1 on the mold holder 5. Then, the wedge 3 is pushed between the mold 1 and the outer periphery of the mold heat insulating material 2 is securely fixed by the ring-shaped member 4 (see FIG. 5B). In the drawing, the illustration of the mold heat insulating material on the front side is omitted for easy viewing.

  Then, the middle mold heat insulating material 2 and the uppermost mold heat insulating material 2 are respectively disposed, and the wedge 3 and the ring-shaped member 4 are respectively provided (see FIG. 5C).

  Thereafter, for example, by a conventionally known method shown in FIG. 7, a molten silicon melt is poured into the mold 1, heated from the upper part of the mold, cooled from the lower part, and solidified in one direction. Is melted once in a mold and then solidified in one direction from the bottom again to form a silicon ingot.

  In order to extract the manufactured ingot, the mold heat insulating material 2 divided in the lateral direction of the mold 1 is pulled out in the lateral direction, then the wedge 3 is removed from the upper part of the mold 1, and then the ring-shaped member 4 is shifted downward (FIG. 5). (See (d)).

  And after releasing the fitting state between the side plates of the mold 1 and releasing the mold from the ingot, the ingot may be pulled upward (see FIG. 5E).

  Thus, since the mold heat insulating material 2 divided in the vertical direction and the horizontal direction can be removed very easily, the mold 1 can be easily disassembled to facilitate the release of the silicon ingot.

  Moreover, the external force to the side plate 1b of the mold 1 accompanying the solidification expansion of the silicon ingot can be suppressed by these mold heat insulating materials 2, and the stress inside the ingot can be released upward from the side surface of the mold having a reverse tapered shape. Further, by providing the wedge 3 in the gap between the mold 1 and the mold heat insulating material 2, the side plate 1b of the mold 1 can be more strongly pressed so as not to move, so that the stress in the ingot has a reverse taper shape. It is possible to escape from the side upward.

  Moreover, since it arrange | positions at the outer peripheral part of the some mold heat insulating material 2, and is restrained by the ring-shaped member 4 so that these mold heat insulating materials 2 may not displace, said effect can be made still more reliable. . Since the plurality of mold heat insulating materials 2 are arranged so as to have a substantially cylindrical shape so as to surround the outer periphery of the mold 1, they can be uniformly pressed from the outside by the ring-shaped member 4, and the stress can be reduced. Distribution is more uniform.

  It should be noted that the taper angle θ that has a reverse taper shape upward from the inner surface of the side wall of the mold 1 is limited to the range of 1 ° to 5 °. This is because the effect cannot be obtained, and if it exceeds 5 °, the end region to be cut off after casting increases, and the cost of the silicon raw material increases.

  The casting apparatus according to the present invention is devised to reduce the solidification expansion in the horizontal direction by improving the unidirectionality in the mold height direction.

  A mold holder used for a conventional mold is formed of the same material (for example, graphite) having good thermal conductivity, or a through hole is provided in the center of the mold holder to remove heat from the mold bottom by radiation conduction. In the former case, the heat removal from the chill plate is uniformly removed to the area other than the mold bottom plate, so that, for example, the bottom of the mold side surface is also cooled, and the crystal grows from the location, so that one direction of the crystal The coagulation property was poor. In the latter case, radiation control is more difficult to control the solidification rate because it is more susceptible to the influence of the surrounding temperature environment and it is difficult to obtain a uniform heat flow than the heat conduction effect in the solid substance.

  On the other hand, as shown in FIG. 6, the mold holder according to the casting apparatus of the present invention is made of a holder outer peripheral portion 5b made of a material having poor thermal conductivity and a material having good thermal conductivity arranged at the center thereof. 1 bottom plate 1a and a holder main portion 5a having substantially the same size.

  Such a material is desirably selected on the basis of the thermal conductivity at high temperature. As the holder main part 5a of the mold holder 5, for example, graphite (thermal conductivity: about 50 W / mk) or SiC (thermal conductivity: A material such as graphite felt (thermal conductivity: about 0.6 W / mk) or CCM (registered trademark of Nippon Carbon Co., Ltd.) can be used as the outer peripheral portion 5b of the mold holder 5. A carbon fiber reinforced carbon material (C / C material) (thermal conductivity: about 1 W / mk) can be used.

  Thus, in order to interpose the holder main part 5a having good thermal conductivity only between the bottom plate 1a of the mold 1 and the chill plate 6, the area other than the bottom plate 1a of the mold 1 is removed when heat is removed from the chill plate 6. Since heat is evenly rectified from the region of the bottom plate 1a of the mold without being removed from the heat, unidirectional solidification is greatly improved as compared with the conventional case. And since the solidification expansion to a mold side wall can be suppressed rather than the solidification expansion to the height direction of the casting_mold | template 1, the stress concentration to a mold side wall can be avoided.

  According to such a mold and casting apparatus of the present invention, distortion of a polycrystalline silicon ingot formed by unidirectional solidification can be reduced, so that it is possible to obtain an ingot in which cracks are unlikely to occur in the silicon ingot cutting process. it can.

  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, in the above description, the mold heat insulating materials 2 are arranged, and then fixed by the wedge 3 as a contact member or the ring-shaped member 4 as a restraining member. However, the fixing method is not limited at all. However, various modifications are possible as long as the method can constrain the external force applied to the side wall accompanying the solidification and expansion of the ingot. For example, the side plates 1b can be fixed with bolts. Further, a fitting portion may be provided between the mold heat insulating materials 2 so as to be fitted and fixed to each other.

  Further, in the figure, the description has been given with the bottom plate 1a having the square shape constituting the mold 1, and the side plate 1b having the isosceles trapezoidal shape and the same shape with all the four plates, but is not limited thereto. The bottom plate 1a may have a rectangular shape (rectangular shape), and the side plate 1b is a combination of trapezoidal shapes having an upper base corresponding to each side of the bottom plate 1a having the rectangular shape. What is necessary is just to make it become the same length when the sides of the trapezoid to be combined.

  Further, the mold heat insulating material 2 is disposed so as to surround the outer periphery of the mold 1, but this does not mean that the mold heat insulating material 2 is completely disposed without any gap. Need only be provided.

  The mold heat insulating material 2 and the wedge 3 that is a contact member do not need to be in contact with the side plate 1b of the mold 1 over the entire surface. The effects of the present invention can be effectively achieved.

It is the schematic of the casting apparatus concerning this invention, (a) is a top view, (b) is a side view. (A) is sectional drawing of the AA direction of FIG. 1, (b) is sectional drawing which showed only the casting_mold | template. It is a figure explaining the method of combining the baseplate and side plate of a casting_mold | template concerning this invention. It is a figure which shows the structure of a mold release material layer, (a) is an enlarged structure figure of the B section of Fig.1 (a), (b) is an enlarged structure figure of the C section of Fig.2 (a). (A)-(e) is a figure for demonstrating the ingot manufacturing method by the casting apparatus concerning this invention. It is a figure which shows the structure of the casting_mold | template holder concerning this invention, and is a top view and sectional drawing. This is a general silicon casting apparatus for producing a polycrystalline silicon ingot.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1: Mold 1a: Bottom plate 1b: Side plate 2: Mold heat insulating material 3: Wedge 4: Ring-shaped member 5: Mold holder 5a: Holder main part 5b: Holder outer peripheral part 6: Chill plate 7: Release material layer 101: Mold 101a: Bottom member 101b: Side member 102: Release material layer 103: Mold heat insulating material 104: Silicon melt 106: Mold heating means 107: Cooling means 108: Melting crucible 109: Holding crucible 110: Raw material silicon 111: Outlet 112: Top heating Means 113: Side heating means θ: Taper angle

Claims (9)

A mold having a mold opening extending upward;
One bottom plate having a rectangular shape;
Four side plates having a trapezoidal shape in which the lower base is longer than the upper base, surrounding the outer periphery of the side surface of the bottom plate by a trapezoid upper base having a length corresponding to each side of the bottom plate, and the mold by the trapezoid lower base While forming an opening, a side plate that fits adjacent sides,
A release material layer provided on the inner surface of the mold composed of the bottom plate and the four side plates,
Each inner surface of the side plate is a mold having a taper angle of 1 ° to 5 ° with respect to the vertical direction. 2. The mold according to claim 1, wherein the release material layer is thicker than other portions of the inner surface of the mold at eight ridge lines where the bottom plate, the side plate, and the four side plates contact each other. . A mold according to claim 1 or claim 2;
A casting apparatus comprising: a plurality of mold heat insulating materials which surround the outer periphery of the mold and are arranged so as to be separable in the vertical direction of the mold. The casting apparatus according to claim 3, wherein the plurality of mold heat insulating materials are arranged so as to be further divided in a lateral direction of the mold. The casting apparatus according to claim 3 or 4, wherein the plurality of mold heat insulating materials are arranged such that at least a part of an inner peripheral surface thereof abuts at least a part of the outer peripheral surface of the mold. A plurality of abutting members arranged to abut each surface in the gap between the inner peripheral surface of the plurality of mold heat insulating materials and the outer peripheral surface of the mold, and corresponding to at least each side plate of the mold The casting apparatus according to any one of claims 3 to 5, further comprising: The casting apparatus according to any one of claims 3 to 6, further comprising a restraining member that is disposed on an outer peripheral portion of the plurality of mold heat insulating materials and restrains the mold heat insulating materials from being displaced. The casting apparatus according to claim 7, wherein the plurality of mold heat insulating materials have a substantially cylindrical shape when arranged so as to surround an outer periphery of the mold. A mold holder comprising a holder main part for placing the mold and a holder outer peripheral part for placing the mold heat insulating material, wherein the holder main part has a higher thermal conductivity than the holder outer part,
The casting apparatus according to any one of claims 3 to 8, further comprising a chill plate that mounts and cools the mold holder.

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