JP5130337B2 - Square silica container for producing polycrystalline silicon ingot, porous silica plate, and production method thereof - Google Patents

Description

  The present invention relates to a square (square tank type) silica container for solidifying a silicon melt to produce a polycrystalline silicon ingot.

  In recent years, the demand for solar cells (solar power generation devices) has increased rapidly, and there is a demand for solar cells having higher conversion efficiency at lower costs.

  One of the materials constituting the photovoltaic part of a solar cell is polycrystalline silicon. Polycrystalline silicon is often produced as polycrystalline silicon ingots by cooling and solidifying a silicon melt. As a container for solidifying a silicon melt to produce a polycrystalline silicon ingot, a silica (silicon dioxide) container or a graphite container is used.

In a container for solidifying in a container to produce a polycrystalline silicon ingot, its inner surface is used to prevent the polycrystalline silicon ingot from fusing (adhering) to the container when the silicon melt is solidified. It is known to form a release layer in advance. Various materials are used as a release agent for forming the release layer. For example, in Patent Document 1, a release agent slurry containing Si, Si ₃ N ₄ , Si ₃ N ₄ + SiO ₂ or Si + Si ₃ N ₄ + SiO ₂ is used as a release agent in an inner layer of a silicon melting container made of quartz glass. It is described that a layer is formed. Further, Patent Document 2 describes a silicon casting mold made of silicon dioxide in which a release material layer containing silicon nitride is formed on the inner surface.

  Moreover, when producing a polycrystalline silicon ingot, it is required to produce a polycrystalline silicon ingot with as much crystal orientation as possible. For example, Patent Document 3 describes a crucible for manufacturing a polycrystalline semiconductor in which a plurality of grooves or conical or pyramidal depressions for arranging seed crystals such as 3C-SiC are formed on the bottom surface in a crucible. ing. Patent Document 3 further describes that the angle formed between the side surface of the groove and a surface perpendicular to the groove, or the angle formed between the side surface of the conical or pyramidal depression and the center line is set to 50 to 70 °. .

Japanese Patent Laying-Open No. 2005-271058 JP 2005-125380 A JP 2006-219336 A

  As described above, a release layer is generally formed on the inner surface of a container for producing a polycrystalline silicon ingot by solidifying a silicon melt in the container. However, when a material that becomes an impurity in the polycrystalline silicon ingot is used as a mold release agent, the impurity in the polycrystalline silicon ingot is removed because the release layer is peeled off and taken into the silicon melt. There was a problem that mixing was inevitable.

  On the other hand, if the release agent is not used, the polycrystalline silicon ingot is fused to the container when the silicon melt is solidified, and the surface portion of the polycrystalline silicon ingot is damaged during cooling or removal. There was a problem. As a result, for example, when a solar cell is manufactured from a polycrystalline silicon ingot, the cost of the manufactured solar cell is increased due to deterioration of the quality of the manufactured solar cell and a decrease in yield.

  Further, as in Patent Document 3, when the silicon melt is solidified in a crucible having grooves and depressions formed on the bottom surface, the releasability may be poor.

  Further, in order to obtain a larger light receiving area, it is necessary to enlarge the solar cell, and in order to obtain a larger polycrystalline silicon ingot, the silica container for storing the silicon melt must also be enlarged. The manufacture of such a large silica container requires a large-sized device, resulting in a significant increase in container manufacturing cost.

  The present invention has been made in view of such problems, has the ability to sufficiently prevent impurity contamination to silicon melt and polycrystalline silicon ingot, and excellent in releasability, An object of the present invention is to provide an extremely low-cost rectangular silica container for producing a polycrystalline silicon ingot and a method for producing the same, which can produce a polycrystalline silicon ingot having the same crystal grain size and crystal axis orientation as possible.

  It is another object of the present invention to provide a porous silica plate constituting such a rectangular silica container for producing a polycrystalline silicon ingot and a method for producing the same.

  The present invention has been made in order to solve the above problems, and is a rectangular silica container for producing a polycrystalline silicon ingot by solidifying a silicon melt, and is a parallel plate-like porous material made of porous silica. The bulk density of the surface portions of both parallel planes in the porous silica plate that forms at least the side portion of the square silica container is greater than the inner surface portion of the square silica container. The inner surface portion of the porous silica plate that is higher in the outer surface portion and forms the bottom of the rectangular silica container has a plurality of grooves or holes at a predetermined interval, and at least a part of the side surface of the groove or hole. Is formed with an inclined surface having an angle of 15 to 60 ° with respect to the vertical direction, and a rectangular silica container for producing a polycrystalline silicon ingot is provided.

  In the case of such a silica container, at least the bulk density of the inner surface portion of the porous silica plate forming the side of the container is made lower than the bulk density of the outer surface section, so that the contained silicon (silicon melt and many It is possible to obtain a low-cost rectangular silica container for producing a polycrystalline silicon ingot that is excellent in releasability while maintaining the strength of the container itself while suppressing impurity contamination to the crystalline silicon ingot). In addition, due to the presence of grooves or holes in the porous silica plate forming the bottom of the container, the size of each crystal grain of the polycrystalline silicon ingot is appropriately adjusted when solidified from the silicon melt in the container. The crystal axis orientation of the crystal grains can be adjusted to a certain direction. Moreover, since such a silica container is a combination of plates, the manufacturing cost of the container can be significantly reduced compared to a single body.

In this case, the bulk density of the porous silica plate is 1.60 to 2.20 g / cm ³ , and at least the surface portions of both parallel planes in the porous silica plate forming the side of the square silica container. It is preferable that the bulk density has a difference of 0.05 g / cm ³ or more with respect to the bulk density from the inner and outer surfaces to a depth of 3 mm.

Thus, the bulk density of the porous silica plate is 1.60 to 2.20 g / cm ^3, and the bulk density of the surface portions of both parallel planes in the porous silica plate forming the side of the square silica container is at least. If the difference in bulk density from the inner and outer surfaces to a depth of 3 mm has a difference of 0.05 g / cm ³ or more, the releasability is improved without excessively reducing the strength of the inner surface portion of the container. be able to.

Moreover, it is preferable that a mold release accelerator for promoting mold release of the polycrystalline silicon ingot is contained in at least a part of the inner surface portion of the square silica container. In this case, at least one of Ca, Sr, and Ba as the mold release accelerator is 50 to 5000 wt.% As the total value of each element from the inner surface of the square silica container to a depth of 2 mm. It is preferable that it is added at a concentration of ppm. Moreover, it is also preferable that one or more of Ca, Sr, and Ba are applied as the release accelerator at a concentration of 50 to 5000 μg / cm ² as the total value of each element.

  Thus, if the release accelerator that promotes the release of the polycrystalline silicon ingot is contained in at least a part of the inner surface portion of the square silica container, the release property can be improved more effectively. In addition, impurity contamination of the contained silicon can be sufficiently prevented. Further, it is more effective if the concentration of Ca, Sr, and Ba as a mold release accelerator is as described above.

Further, the present invention is a parallel flat plate-like porous silica plate made of porous silica, having a bulk density of 1.60 to 2.20 g / cm ³ , and having at least one surface portion of both parallel planes. A part has a plurality of grooves or holes at a predetermined interval, and at least a part of a side surface of the groove or hole is formed by an inclined surface having an angle of 15 to 60 ° with respect to a direction perpendicular to the surface. A porous silica plate is provided.

  If it is such a porous silica plate body, it can be set as the plate body which makes a bottom part among the square silica containers comprised combining a plate body. The rectangular silica container constructed in such a manner appropriately adjusts the size of each crystal grain of the polycrystalline silicon ingot when solidifying from the silicon melt in the container due to the presence of the groove or hole. The crystal axis orientation of the crystal grains can be adjusted to a certain direction.

  In this case, the shape of the groove or hole is preferably V-shaped in the case of a groove and conical or pyramid-shaped in the case of a hole. Moreover, it is preferable that a vertical wall along a direction perpendicular to the partial surface exists on the side surface of the groove or hole.

  If the groove or the hole of the plate body has such a shape, it is easier to adjust the crystal grain size and crystal axis orientation of the polycrystalline silicon ingot manufactured using the square silica container constructed by incorporating the plate body. it can.

  Moreover, when the dimension of the opening part of the said groove | channel or a hole is a groove | channel, it is preferable that a width | variety is 5-20 mm and the minimum length is 5-20 mm in the case of a hole.

  If the size of the opening of such a groove or hole is used, it is easier to adjust the crystal grain size and crystal axis orientation of a polycrystalline silicon ingot produced using a rectangular silica container constructed by incorporating a plate. It becomes. Here, the minimum length of the opening of the hole is the interval between the parallel lines having the minimum width in contact with the shape of the opening.

Moreover, it is preferable that a part of the surface portion where the groove or hole is formed contains a release accelerator that promotes release of polycrystalline silicon. In this case, at least one of Ca, Sr, and Ba as the mold release accelerator is 50 to 5000 wt. It is preferable that it is added at a concentration of ppm. Moreover, it is also preferable that one or more of Ca, Sr, and Ba are applied as the release accelerator at a concentration of 50 to 5000 μg / cm ² as the total value of each element.

  As described above, if a release accelerator for promoting release of polycrystalline silicon is contained in a part of the surface portion of the plate body in which grooves or holes are formed, this plate body is incorporated into a square shape. In the case where the silica container is configured, it is possible to improve the releasability and sufficiently prevent impurity contamination of the contained silicon. Further, it is more effective if the concentration of Ca, Sr, and Ba as a mold release accelerator is as described above.

The present invention also relates to a method for producing a parallel flat plate-like porous silica plate made of porous silica, and a step of producing silica powder having a particle size of 0.03 to 3.0 mm as the first raw material powder. And a step of producing a silica powder having a particle size of 0.1 to 10 μm as the second raw material powder, and a step of producing a mixed slurry containing the first raw material powder, the second raw material powder, and water. And the mixed slurry is dehydrated and dried in a mold, and a temporary molding step of producing a temporary molded body of a porous silica plate having a plurality of grooves or holes at a predetermined interval on one surface portion of both parallel planes And heating the temporary molded body from a surface opposite to the surface on which the groove or hole is formed at a temperature of 1200 to 1500 ° C. in an atmosphere containing an inert gas as a main component and O ₂ gas. And firing step to form a porous silica plate. To provide a method of manufacturing a porous silica plate body.

The present invention also relates to a method for producing a parallel flat plate-like porous silica plate made of porous silica, and a step of producing silica powder having a particle size of 0.03 to 3.0 mm as the first raw material powder. And a step of producing a silica powder having a particle size of 0.1 to 10 μm as the second raw material powder, the first raw material powder, the second raw material powder, and an organic binder are mixed to produce a mixed powder. And introducing the mixed powder into a mold and heating to 50 to 200 ° C. to melt the organic binder, thereby having a plurality of grooves or holes in one surface portion of both parallel planes at a predetermined interval. A step of producing a temporary molded body of a porous silica plate, and the temporary molded body in the atmosphere containing an inert gas as a main component and containing O ₂ gas at a temperature of 1200 to 1500 ° C. Baking by heating from the surface opposite to the surface where the holes are formed To provide a method of manufacturing a porous silica plate member which comprises a firing step of the porous silica plate member.

  Thus, the manufactured porous silica board can be used as the board which makes a bottom part among the square silica containers constituted combining a board. The rectangular silica container constructed in such a manner appropriately adjusts the size of each crystal grain of the polycrystalline silicon ingot when solidifying from the silicon melt in the container due to the presence of the groove or hole. The crystal axis orientation of the crystal grains can be adjusted to a certain direction.

  Further, at least after the temporary forming step, a release accelerator that promotes the release of polycrystalline silicon is applied to at least a part of the surface of the temporary formed body where the groove or hole is formed. It is preferable to add the mold release accelerator by adding the mold release accelerator by drying. Further, at least after the firing step, a mold release accelerator that promotes mold release of the polycrystalline silicon is formed on at least a part of the surface of the temporary molded body where the groove or hole is formed. It is also preferable to include the release accelerator by applying an accelerator.

  By including the release accelerator in this manner, the release accelerator can be efficiently contained in the porous silica plate. Moreover, in the square silica container incorporating the porous silica plate containing the release accelerator as described above, the releasability can be enhanced.

  In these cases, it is preferable that the release accelerator is one or more of Ca, Sr, and Ba.

  As described above, when the mold release accelerator is one or more of Ca, Sr, and Ba, in the rectangular silica container incorporating the manufactured porous silica plate, the mold release property can be more effectively increased. In addition, impurity contamination to the silicon melt and the polycrystalline silicon ingot can be sufficiently prevented.

  Further, in the method for producing a porous silica plate according to the present invention, the particle diameter obtained by collecting the second raw material powder from the second raw material powder before producing the mixed slurry or the mixed powder. A 5-500-micrometer granule is produced and the said mixing slurry or the said mixed powder can be produced using the granule of this 2nd raw material powder.

  Thus, if the mixed slurry or mixed powder is prepared after making the second raw material powder into granules, handling of the second raw material powder having a small particle size can be simplified.

  The present invention also provides a method for producing a rectangular silica container, characterized in that a porous silica plate produced by any one of the above-described methods for producing a porous silica plate is incorporated into the bottom to form a square silica container. To do.

  Thus, in the case of a rectangular silica container in which a porous silica plate manufactured by any one of the above-described porous silica plate manufacturing methods is incorporated at the bottom, the presence of grooves or holes causes the silicon melt in the container. When solidifying from, the size of each crystal grain of the polycrystalline silicon ingot can be appropriately adjusted, and the crystal axis orientation of each crystal grain can be adjusted in a certain direction. Moreover, since such a silica container is a combination of plates, the manufacturing cost of the container can be remarkably reduced compared to a single body.

  The rectangular silica container for producing a polycrystalline silicon ingot according to the present invention has mold releasability while maintaining the strength of the container itself while suppressing impurity contamination to the contained silicon (silicon melt and polycrystalline silicon ingot). An excellent rectangular silica container for producing a polycrystalline silicon ingot can be obtained. In addition, since the silica container according to the present invention is a combination of plates, the container manufacturing cost can be significantly reduced as compared with a single body. Further, when solidifying from the silicon melt in the container, the size of each crystal grain of the polycrystalline silicon ingot can be appropriately adjusted, and the crystal axis orientation of each crystal grain can be adjusted in a certain direction.

Moreover, if it is the porous silica board which concerns on this invention, it can be set as the porous silica board which makes the bottom part of such a square silica container for polycrystalline silicon ingot manufacture.
Moreover, according to the method for producing a porous silica plate according to the present invention, such a silica plate material can be produced at a low cost.

  Thus, according to the present invention, a high-quality and low-cost rectangular polycrystalline ingot can be provided, which is particularly suitable for a solar cell.

It is a figure which shows an example of the square silica container which concerns on this invention, (a) is a schematic top view, (b) is a schematic sectional drawing. It is a figure which shows another example of the square silica container which concerns on this invention, (a) is a schematic top view, (b) is a schematic sectional drawing. It is a perspective view which shows an example of the shape of the porous silica board which concerns on this invention. It is a figure which shows the example of installation of the square silica container which concerns on this invention, (a) is a schematic top view, (b) is a schematic sectional drawing. It is the schematic which shows an example of the shape of the board which makes the bottom part of the square silica container which concerns on this invention, (a) is a top view, (b) is sectional drawing. It is the schematic which shows an example of the shape of the board which makes the bottom part of the square silica container which concerns on this invention, (a) is a top view, (b) is sectional drawing. It is the schematic which shows an example of the shape of the board which makes the bottom part of the square silica container which concerns on this invention, (a) is a top view, (b) is sectional drawing. It is the schematic which shows an example of the shape of the board which makes the bottom part of the square silica container which concerns on this invention, (a) is a top view, (b) is sectional drawing. It is a schematic sectional drawing which shows an example of the cross-sectional shape of the groove | channel or hole formed in the plate which makes the bottom part of the square silica container which concerns on this invention. It is a schematic sectional drawing which shows an example of the cross-sectional shape of the groove | channel or hole formed in the plate which makes the bottom part of the square silica container which concerns on this invention. It is a schematic sectional drawing which shows an example of the cross-sectional shape of the groove | channel or hole formed in the plate which makes the bottom part of the square silica container which concerns on this invention. It is a schematic sectional drawing which shows an example of the cross-sectional shape of the groove | channel or hole formed in the plate which makes the bottom part of the square silica container which concerns on this invention. It is a schematic sectional drawing which shows another example of the square silica container which concerns on this invention. It is a flowchart which shows the outline of an example of the manufacturing method of the porous silica board which concerns on this invention. It is a flowchart which shows the outline of another example of the manufacturing method of the porous silica board which concerns on this invention. It is a conceptual diagram which shows an example of the baking furnace which bakes the porous silica board which concerns on this invention. It is the schematic which shows the shape of the through-hole of the board | plate material which can be comprised in the square silica container for polycrystalline silicon ingot manufacture which concerns on this invention. It is explanatory drawing which showed typically the mode of the crystal growth from the groove | channel or hole formed in the bottom plate. It is sectional drawing which shows typically a mode that the polycrystalline silicon ingot was grown with the square silica container for polycrystalline silicon ingot manufacture which concerns on this invention.

  In the present invention, for example, a rectangular silica container for producing a polycrystalline silicon ingot, which can obtain a rectangular polycrystalline silicon ingot suitable for a solar cell, has the following problems.

  The first is to make a square silica container having excellent releasability (improvement of releasability). In other words, when a polycrystalline silicon ingot is produced by solidification of a silicon melt contained in a rectangular silica container, the fusion (adhesion) of the polycrystalline silicon ingot to the rectangular silica container is suppressed. The silicon ingot should be easily removed from the square silica container.

  Secondly, a rectangular silica container capable of preventing impurity contamination is used. This means that various impurity metal elements contained in the square silica container move and diffuse to the contained silicon (silicon melt, polycrystalline silicon ingot, etc.) even at high temperatures during the production of polycrystalline silicon. As a result, impurity contamination of the silicon melt and the polycrystalline silicon ingot is sufficiently prevented. In particular, it is necessary to prevent impurity contamination by the release agent itself.

  The third is to make a container capable of producing a polycrystalline silicon ingot with crystal grains as uniform in size and crystal axis orientation as possible. That is, to improve the crystal quality of the polycrystalline silicon ingot to be manufactured.

  Fourthly, it is possible to realize the above-described excellent mold release property, prevention of impurity contamination, and improvement of crystal quality of the manufactured polycrystalline silicon ingot at low cost. This means that, for the production of a square silica container, the cost of parts is reduced, and an inexpensive silica raw material can be used, and the melting and sintering temperature of the silica raw material is performed at a relatively low temperature. It is to reduce the energy consumption when manufacturing the square silica container.

  Hereinafter, although the present invention is explained in detail, referring to drawings, the present invention is not limited to these.

  FIG. 1 shows an outline of an example of a rectangular silica container for producing a polycrystalline silicon ingot according to the present invention. 1A is a schematic top view, and FIG. 1B is a schematic cross-sectional view.

  As shown in FIGS. 1 (a) and 1 (b), the shape of the silica container 10 according to the present invention is a square (also called a square tank type). The square silica container 10 includes side portions (also referred to as side wall portions) and a bottom portion, and is configured by combining parallel flat plate-like porous silica plates. Specifically, as shown in FIG. 1 (a) and FIG. 1 (b), four side portions and one bottom portion each form a porous silica plate body (in the present specification, (Also referred to as “side plate”) 11 and porous silica plate 21 (also referred to as “bottom plate” in the present specification) 21 forming the bottom are respectively formed of parallel flat plate-like porous silica plates. The rectangular silica container 10 according to the invention is configured by combining these.

  The method for combining the porous silica plates constituting the rectangular silica container 10 according to the present invention is not particularly limited, but it is preferable that the porous silica plates do not fall inward when combined. For example, as shown in FIG. 1, the parallel flat porous silica plates can be combined such that each inclined portion is an inclined surface and the inclined surfaces face each other (grinding (ground glass bonding) type).

  FIG. 2 shows an outline of another example of a rectangular silica container for producing a polycrystalline silicon ingot according to the present invention. FIG. 2A is a schematic top view, and FIG. 2B is a schematic cross-sectional view. As shown in FIG. 2, each combination portion of the parallel flat plate-like porous silica plates can be formed so as to be fitable, and can be combined (fit type).

  As described above, the porous silica plate according to the present invention has a parallel plate shape. In the description of the present invention, the parallel plate shape is two flat surfaces having a large area among the flat plate-shaped surfaces. Means substantially parallel. However, as will be described later, holes or grooves may be formed on the surface of the plate, and in the description of the present invention, the parallel plate shape is a shape in which such holes or grooves are formed. Including. Moreover, the shape for a combination may be made in the peripheral part of flat plate shape.

3A to 3C show examples of the shape of the side plate 11.
The porous silica plate according to the present invention has a shape as shown in FIG. 3A, that is, a surface that becomes the inner surface 12 when the rectangular silica container 10 is assembled, and an outer surface when the rectangular silica container 10 is assembled. The surface to be 13 has a substantially parallel shape. In addition, as described above, a shape for combination may be formed in the peripheral portion of the flat plate shape. The shape of the side plate body 11 shown in FIG. 3B corresponds to that of FIGS. 1A and 1B, and the shape of the side plate body 11 shown in FIG. 2 corresponds to those of (a) and (b).

  As described above, the rectangular silica container 10 according to the present invention configured by combining the porous silica plates is a container for solidifying the silicon melt to produce a rectangular polycrystalline silicon ingot. Therefore, compared with the case where the whole container is manufactured integrally, the manufacturing cost can be significantly reduced. Also, if the manufactured polycrystalline silicon ingot is rectangular, it can be sliced to obtain a rectangular polycrystalline silicon wafer, and when a wafer obtained by slicing a cylindrical polycrystalline silicon ingot is used as a solar cell. In comparison, there is no waste of light receiving area, which is very suitable.

  In the rectangular silica container 10 according to the present invention, the bulk density of the surface parts of both parallel planes in the porous silica plate forming at least the side part of the rectangular silica container is more than the outer surface part than the inner surface part of the rectangular silica container. Is high. That is, the side plate 11 has a higher bulk density in the surface portion corresponding to the side outer surface 13 than in the surface portion corresponding to the side inner surface 12.

  Further, as shown in FIGS. 1B and 2B, the rectangular silica container 10 according to the present invention has grooves or holes 31 formed at predetermined intervals on the inner surface portion of the bottom plate 21 of the rectangular silica container. It has a plurality. In FIG. 1 (a) and FIG. 2 (a), the grooves or holes of the bottom plate body 21 of the square silica container are omitted for easy viewing of the drawings. At least a part of the side surface of the groove or hole 31 is formed as an inclined surface having an angle of 15 to 60 ° with respect to the vertical direction (direction perpendicular to the surface of the bottom plate 21).

  In the description of the present invention, when the porous silica plate is assembled into a square silica container, the surface corresponding to the inner surface of the square silica container is simply referred to as “the inner surface of the porous silica plate”. May be expressed. Similarly, the surface corresponding to the outer surface of the rectangular silica container when the porous silica sheet is assembled into a rectangular silica container can be simply expressed as “the outer surface of the porous silica sheet”.

  In order to improve the releasability, the bulk density of the side plate 11 among the porous silica plates constituting the rectangular silica container 10 is set as described above, and the amount of bubbles in the inner surface portion is increased (that is, the pores) Increase the rate). By increasing the amount of bubbles in this manner, the fusion (adhesion) of the polycrystalline silicon ingot with the rectangular silica container 10 when the silicon melt is solidified is suppressed, and the polycrystalline silicon ingot is removed from the rectangular silica container 10. It becomes easy to remove without being damaged. Moreover, since the bulk density on the outside is high, the strength of the container can be kept sufficiently.

  Among the porous silica plates constituting the rectangular silica container 10, and also for the bottom plate 21, the surface density corresponding to the bottom outer surface 23 is higher in bulk density than the surface corresponding to the bottom inner surface 22. If it is made higher, it is preferable because the releasability can be further improved. However, in order to favorably promote the growth of a seed crystal, which will be described later, it may be preferable to reduce the surface roughness of the grooves and holes for seed crystal growth so as to have a smooth surface. In such a case, it is possible to set the bulk density of the inner portion only in the bottom plate body 21, or the bulk density of the inner and outer surface portions of the bottom plate body 21 may be the same.

Further, the bulk density of each porous silica plate constituting the square silica container 10 is 1.60 to 2.20 g / cm ³ , and at least the side portion of the porous silica plate constituting the square silica container 10 is used. The bulk density of the surface portions of both parallel planes of the plate body 11 preferably has a difference of 0.05 g / cm ³ or more with respect to the bulk density from the inner and outer surfaces to a depth of 3 mm. In this way, it is possible to improve the releasability without excessively reducing the strength of the inner surface portion of the container.

The bulk density of the porous silica plate is more preferably in the range of 1.70 to 2.00 g / cm ³ . Further, the difference in bulk density between the surface portions of both parallel planes of the side plate 11 is more preferably 0.1 g / cm ³ or more.

Moreover, it is preferable that the bulk density of the container inner surface part of the side plate body 11 of the square silica container 10 is 1.60 to 1.90 g / cm ^3, and is 1.65 to 1.85 g / cm ³ . More preferably. If the bulk density of the inner portion of the container is 1.90 g / cm ³ or less, the fusion between the polycrystalline silicon ingot and the square silica container 10 will not be too strong, and sufficient release properties can be provided. it can. On the other hand, if the bulk density is 1.60 g / cm ³ or more, the releasability can be further improved, and the strength of the inner portion of the container is not excessively lowered.

  As described above, the inner surface portion of the bottom plate of the rectangular silica container according to the present invention has a plurality of grooves or holes at a predetermined interval. At least a part of the side surface of the groove or hole is formed as an inclined surface having an angle of 15 to 60 ° with respect to a direction perpendicular to the surface of the bottom plate. The groove or hole of the bottom plate 21 of the rectangular silica container 10 according to the present invention will be described in more detail with reference to FIGS.

  FIG. 5 shows an outline of a case where a groove is formed in the bottom plate 21 as an example of the shape of the porous silica plate (bottom plate 21) forming the bottom of the rectangular silica container 10 according to the present invention. FIG. 5A is a top view of the bottom plate 21, and FIG. 5B is a cross-sectional view of the bottom plate 21. Reference numeral 22 denotes an inner surface of the bottom plate 21. FIG. 5A and FIG. 5B show a case where the groove 31 a is formed in the inner surface portion of the bottom plate 21. In this case, at least a part of the side surface of the groove 31 a needs to be formed with an inclined surface that forms an angle of 15 to 60 ° with respect to a direction perpendicular to the surface of the bottom plate 21. Due to the presence of such a groove 31a, when producing a polycrystalline silicon ingot by solidifying from a silicon melt using the rectangular silica container according to the present invention, the size of each crystal grain of the polycrystalline silicon ingot is appropriately set. In addition, the crystal axis orientation of each crystal grain can be adjusted in a certain direction.

Furthermore, the shape of the groove 31a is preferably V-shaped, that is, a V-shaped groove.
Moreover, it is preferable that the vertical wall along the direction perpendicular | vertical to a part surface exists in the side surface of the groove | channel 31a. The depth of the vertical wall (length in the direction perpendicular to the surface) is more preferably 3 to 20 mm. Moreover, it is preferable that the width | variety of the groove | channel 31a is 5-20 mm.
When the groove 31a is designed in this way, the size of each crystal grain and the crystal axis orientation of each crystal grain of the polycrystalline silicon ingot can be more reliably aligned.

  Each of FIGS. 6 to 8 schematically shows a case where a hole is formed in the bottom plate 21 as an example of the shape of the bottom plate 21 constituting the rectangular silica container according to the present invention. 6 (a), 7 (a), and 8 (a) are top views of the bottom plate body 21, and FIGS. 6 (b), 7 (b), and 8 (b) are bottom plates. 3 is a cross-sectional view of a body 21. FIG. Reference numeral 22 denotes an inner surface of the bottom plate 21.

FIG. 6A and FIG. 6B show a case where a pyramidal hole 31 b is formed in the inner surface portion of the bottom plate 21.
FIG. 7A and FIG. 7B show a case where a conical hole 31 c is formed in the inner surface portion of the bottom plate 21.
8A and 8B show a case where conical holes 31d are densely formed in the inner surface portion of the bottom plate 21. FIG.

  The hole formed in the bottom plate 21 is preferably a pyramid shape or a cone shape as illustrated in FIGS. 9 to 12, but is not limited thereto. However, it is necessary that at least a part of the side surface of the hole is formed with an inclined surface having an angle of 15 to 60 ° with respect to a direction perpendicular to the surface of the bottom plate 21. The pyramid shape and the cone shape as the shape of the hole are not limited to a geometrically accurate shape, and may be similar, for example, the shape of the opening is an ellipse. Further, the pyramid shape is not limited to the quadrangular pyramid shown in FIG.

It is preferable that a vertical wall along a direction perpendicular to the partial surface exists on the side surface of the hole. The depth of the vertical wall (length in the direction perpendicular to the surface) is more preferably 3 to 20 mm.
As for the dimension of the opening part of a hole, it is preferable that the minimum length is 5-20 mm. Here, the minimum length of the opening of the hole is the interval between the parallel lines having the minimum width in contact with the shape of the opening. For example, in the case of the quadrangular pyramid hole 31b as shown in FIG. 6, the opening is a square, and the minimum length of the opening is the length of one side. In the case of the conical holes 31c and 31d as shown in FIGS. 7 and 8, the opening is a circle, and the minimum length of the opening is a diameter.

  Due to the presence of such holes, when manufacturing a polycrystalline silicon ingot by solidifying from a silicon melt using the square silica container according to the present invention, the size of each crystal grain of the polycrystalline silicon ingot is appropriately set. In addition, the crystal axis orientation of each crystal grain can be adjusted in a certain direction.

  The grooves or holes formed in the plate body (bottom plate body) 21 forming the bottom of the rectangular silica container 10 according to the present invention are formed at a predetermined interval. The term “interval” used herein refers to an interval between representative positions such as the deepest part of a groove or a hole. For example, as shown in FIG. 8, the openings of adjacent grooves or holes may be in contact with each other.

9 to 12 show schematic cross-sectional views of the cross-sectional shape of the grooves or holes formed in the plate body (bottom plate body) 21 forming the bottom of the rectangular silica container 10 according to the present invention.
As described above, the groove or hole 31 formed in the bottom plate 21 constituting the rectangular silica container according to the present invention has at least a part of the side surface of the groove or hole 15 to 15 in the direction perpendicular to the surface. It is necessary to form the inclined surface 32 having an angle of 60 °. That is, the slope 32 has an angle (crossing angle θ) with the vertical direction of 15 to 60 °. Here, the angle formed with respect to the vertical direction of the inclined surface 32 is an angle formed by the cross-sectional shape of the inclined surface 32 with respect to the vertical direction as illustrated in FIGS. 9 to 12.
The angle of the inclined surface 32 with respect to the vertical direction is more preferably 30 ° or more and less than 50 °.
Further, as described above, the vertical wall 33 is preferably present in the groove or hole 31 (see FIGS. 10 and 12). Moreover, as shown in FIG.11 and FIG.12, the flat bottom 34 may exist.

FIG. 4 shows an installation example of the square silica container 10 according to the present invention. FIG. 4A is a schematic top view, and FIG. 4B is a schematic cross-sectional view.
As shown in FIG. 4, the porous silica plate constituting the rectangular silica container 10 can be fixed by a susceptor 80 made of carbon or the like.

  In the present invention, a release accelerator that promotes the release of the polycrystalline silicon ingot is contained in at least a part of the inner surface portion of the square silica container 10, that is, a part of the inner surface portion of the porous silica plate. It is preferable.

  As the mold release accelerator used in the rectangular silica container 10 according to the present invention, the following three types can be used.

First, the recrystallization type, that is, the releasability is improved by finely recrystallizing the inner surface portion of the silica container 10. Specific examples that are particularly suitable for the present invention include alkaline earth metal elements Ba, Ca, and Sr. Of these, Ba is the most preferable. In addition, mullite 3Al ₂ O ₃ .2SiO _{2 to} 2Al ₂ O ₃ .SiO ₂ , spinel MgAl ₂ O _{4 and the} like can be mentioned.

Secondly, the mold release property is improved by reacting with silica at a high temperature such as 1400 ° C. or higher to foam the silica. Specific examples include silicon carbide SiC and silicon nitride Si ₃ N ₄ .

Third, non-reactive type, that is, release property is improved by not reacting with silica or silicon at a high temperature such as 1400 ° C. or higher. Specifically, mention may be made of carbon C, zirconia ZrO _2, beryllia BeO, magnesia MgO, calcia CaO, thoria ThO _2, tungsten W or the like.

Of these three types of mold release accelerators, the recrystallization type is most preferably used in the present invention. In this case, one or more of Ca, Sr, and Ba is formed on at least a part of the inner surface portion of the square silica container 10, that is, a part of the inner surface portion of the porous silica plate, from the inner surface to a depth of 2 mm. , 50 to 5000 wt. It is preferable that it is added at a concentration of ppm. 50 wt. If it is ppm or more, an improvement in releasability is recognized, and 5000 wt. If it is less than or equal to ppm, it is preferable that sufficient release properties are recognized and the polycrystalline silicon ingot is not contaminated with the release agent. The total value of each element is 300 to 3000 wt. A range of ppm is more preferred. Further, at least one of Ca, Sr, and Ba as a release accelerator is applied to at least a part of the inner surface portion of the square silica container 10 at a concentration of 50 to 5000 μg / cm ² as a total value of each element. It is also preferable that 50 [mu] g / cm ² or more in the improvement of releasability if is recognized, if 5000 [mu] g / cm ² or less, while observed sufficient releasability, and contaminating the polycrystalline silicon ingot with a release agent also It is preferable because it disappears. The total value of each element is more preferably in the range of 300 to 3000 μg / cm ² .

  By containing the recrystallization type, particularly Ca, Sr, and Ba in the inner surface portion of the rectangular silica container 10 in this way, the silicon melt is accommodated in the rectangular silica container 10 and gradually cooled and solidified. In the process of producing a crystalline silicon ingot, the inner surface layer of the square silica container 10 can be transferred from silica glass to a microcrystalline phase such as cristobalite or opal, thereby causing the generation of microcracks. As a result, since the fusion between the cooled and solidified polycrystalline silicon ingot and the inner surface of the rectangular silica container 10 can be reduced, the polycrystalline silicon ingot is removed when removing the polycrystalline silicon ingot from the rectangular silica container 10. It can be removed without breaking or forming irregularities on the surface portion of the polycrystalline silicon ingot or causing progressive cracks.

  Compared with alkali metal elements such as Li, Na, K, etc., the alkaline earth metal elements Ca, Sr, Ba have a correlation with the segregation coefficient, and are applied to the polycrystalline silicon ingot produced by solidification from the melt. Incorporation is small, that is, process contamination of the polycrystalline silicon ingot can be reduced. In particular, Ba is most preferable as a mold release accelerator because it has less diffusion contamination into the polycrystalline silicon ingot.

  Of the inner surface portion of the rectangular silica container 10, the range in which the mold release accelerator is contained may be at least part of the inner surface portion of the rectangular silica container 10 as described above. More preferably, the entire inner surface portion up to a height at which the silicon melt is accommodated and solidified is more preferable, and the entire inner surface portion of the square silica container 10 is more preferable.

  The square silica container 10 has an Al concentration (Al element concentration) of 5 to 500 wt. ppm, and the OH group concentration is 5 to 500 wt. Preference is given to ppm. In order to prevent impurity contamination, the rectangular silica container 10 preferably contains an OH group simultaneously with the Al element. Al concentration is 10-100 wt. More preferably, it is ppm, and the OH group concentration is 30 to 300 wt. More preferably, it is ppm.

  These Al and OH groups are converted when impurity metal elements in the porous silica plate, especially when the carrier lifetime of polycrystalline silicon under light irradiation is reduced or when a polycrystalline silicon ingot is used as a solar cell material. It prevents migration and diffusion in the silica of alkali metal elements such as Li, Na and K which are considered to reduce the efficiency and transition metal elements such as Ti, Cr, Fe, Ni, Cu, Zn, Mo and Au. The details of the mechanism are unknown, but by replacing the Al atom with the Si atom, the cation (cation) of the impurity metal element is incorporated from the difference in coordination number, and the charge balance in the silica glass network is maintained. Therefore, it is presumed to prevent adsorption and diffusion. In addition, it is presumed that the OH group has an effect of adsorbing or preventing diffusion of these impurity metal elements by substitution of hydrogen ions and impurity metal ions.

Al concentration is 5 wt. If it is ppm or more, a sufficient impurity contamination preventing effect is recognized. On the other hand, the Al concentration is 500 wt. If it is less than or equal to ppm, contamination of the polycrystalline silicon ingot to be produced by Al or Al ₂ O ₃ itself can be suppressed.

  Further, the concentration of OH groups is 5 wt. If it is ppm or more, a sufficient impurity contamination preventing effect is recognized. On the other hand, the OH group concentration is 500 wt. If it is ppm or less, the viscosity of the porous silica plate at a high temperature will not be excessively lowered. The OH group serves as a silica glass network structure of Si and O, that is, a terminal portion (network terminator) of the glass network. For this reason, it is considered that the inclusion of a high concentration of OH groups tends to cause deformation of the porous silica plate at a high temperature.

The effect of preventing contamination of impurities by Al and OH groups is recognized to some extent with either one of Al or OH groups, but the combination of these two types greatly improves the effect. Thereby, the purity of the silica powder used as the raw material of the porous silica plate constituting the square silica container 10 is SiO ₂ 99.9 to 99.999 wt. %, It is possible to produce a rectangular silica container 10 that matches the purpose of the present invention. More specifically, for example, the purity of the silica raw material powder (SiO ₂ purity) is 99.99 wt. %, And the concentration of each of Li, Na, and K is 5 wt. ppm or less, and each concentration of Ti, Cr, Fe, Ni, Cu, Zn, Au is 0.1 wt. When the content is less than or equal to ppm, it is possible to produce a polycrystalline silicon ingot with sufficient prevention of process contamination by containing appropriate amounts of Al and OH groups simultaneously. Thus, in the polycrystalline silicon ingot in which the process contamination is sufficiently prevented, the size of each crystal grain is more uniform. If a solar power generation device (solar cell) is manufactured from such a polycrystalline silicon ingot, its photoelectric conversion efficiency can be significantly increased.

FIG. 13 shows a schematic cross-sectional view of still another embodiment of the square silica container according to the present invention.
In this embodiment, a plate material 41 in which a plurality of round or square through holes 42 are formed at a predetermined interval is disposed at a position higher than the bottom plate 21 constituting the square silica container 10.

A top view of such a plate 41 is shown in FIG.
The through hole 42 can be rectangular as shown in FIG. In this case, it can also be referred to as a through groove. Moreover, it can also arrange | position like FIG.17 (b).
Further, the through-hole 42 may be circular as shown in FIG. 17C and square as shown in FIG.
The side walls of these through-holes 42 are preferably vertical walls and should not have a taper angle.

  As the material of the plate material 41, heat-resistant ceramics can be used, but a silica glass material is preferable. However, in this case, it is not necessarily limited to those made of porous silica, and for example, a transparent to translucent silica glass material can be used.

  In order to arrange the plate material 41 at a position higher than the bottom plate 21 constituting the rectangular silica container 10, a spacer 51 or the like can be used.

With such a plate material 41, it is possible to manufacture a polycrystalline silicon ingot having a more uniform crystal axis orientation and crystal grain size.
FIG. 19 schematically shows the state of crystal growth when a polycrystalline silicon ingot is manufactured using the square silica container 10 provided with the plate material 41. For ease of viewing, the grooves or holes of the bottom plate 21 and the through holes of the plate 41 are not shown in FIG. Since the plate material 41 can narrow the crystal growth direction for the polycrystals grown from the bottom plate 21 constituting the square silica container 10, the polycrystalline silicon ingot having a more uniform crystal axis orientation and crystal grain size can be obtained. It can be manufactured.
Such a plate 41 can be called a necking plate in the sense of narrowing the crystal growth direction.

A method for producing the porous silica plate as described above will be described.
First, in order to reduce costs during production, high-purity silica raw material powder (high-purity quartz powder, high-purity quartz powder, ultra-high-purity synthetic silica glass powder) as in the past is not necessarily used. Silica purity SiO ₂ 99.9 to 99.999 wt. % Of relatively low purity silica raw material powder is preferably used.

In addition, it is not a melting process under an extremely high temperature (estimated temperature is 2000 to 2300 ° C.) by a conventional carbon electrode discharge heating and melting method (arc melting method), but in a furnace having heating means from one direction. Melt processing. The silica raw material powder is sintered at a treatment temperature of 1200 to 1500 ° C., preferably 1300 to 1400 ° C., to produce a porous silica plate. Subsequently, a silica container is manufactured by combining these plate bodies. The atmosphere during firing is mainly composed of an inert gas such as N ₂ gas, He gas, Ar gas, and O ₂ gas is preferably 1 to 30 vol. % Gas atmosphere. In terms of cost, N ₂ gas is most preferably an inert gas.

  Therefore, silica raw powder is not limited to low-cost crystalline natural quartz powder. For example, amorphous silica powder (fused natural quartz glass powder, synthetic silica glass powder) and crystalline natural quartz powder are mixed to form raw material powder. To do. Further, the silica raw material powder having a large particle size, for example, a raw material powder having a relatively large particle size of 0.03 to 3 mm as well as a highly active fine particle size of 0.1 to 10 μm. It is preferable to mix two kinds of synthetic silica glass raw materials into raw powder.

  Hereinafter, the method for producing the porous silica plate according to the present invention will be described more specifically with reference to the drawings.

(I) 1st aspect The outline of an example (1st aspect, a wet method) of the manufacturing method of the porous silica board which concerns on this invention was shown in FIG.

  First, as shown to (a-1) of FIG. 14, raw material powder is produced. Specifically, silica powder having a particle size of 0.03 to 3.0 mm and silica powder having a particle size of 0.1 to 10 μm are prepared as the first raw material powder. Each of the first raw material powder and the second raw material powder may be adjusted before preparing the mixed slurry described later.

Among these, the first raw material powder is a main constituent material of the porous silica plate constituting the rectangular silica container 10 (see FIGS. 1 and 2) according to the present invention. As the first raw material powder, high purity silica raw material powder (high purity quartz powder, high purity quartz powder, ultra high purity synthetic silica glass powder) is not used, and silica purity SiO ₂ 99.9 to 99.999 wt. % Of relatively low purity silica powder raw material is preferably used. This first raw material powder can be produced, for example, by pulverizing and sizing the silica mass as follows, but is not limited thereto.

  First, a natural silica stone block (naturally produced crystal, quartz, quartzite, siliceous rock, opal stone, etc.) having a diameter of about 10 to 100 mm is heated in a temperature range of 600 to 1000 ° C. for about 1 to 10 hours in an air atmosphere. To do. Next, the natural silica mass is put into water, taken out after rapid cooling, and dried. This process facilitates the subsequent crushing and sizing process using a crusher or the like, but the process may proceed to the crushing process without performing the heating and quenching process.

  Next, the natural silica mass is pulverized and sized by a crusher or the like, and the particle size is adjusted to 0.03 to 3 mm, preferably 0.1 to 1 mm, to obtain natural silica powder.

Next, this natural silica powder is put into a rotary kiln composed of a silica glass tube having an inclination angle, and the inside of the kiln is made into an atmosphere containing hydrogen chloride (HCl) or chlorine (Cl ₂ ) gas, and is kept at 700 to 1100 ° C. For about 1 to 100 hours. However, in a polycrystalline silicon ingot manufacturing application that does not require high purity, the process may proceed to the next process without performing this high-purification process.

  The first raw material powder obtained after the above steps is crystalline silica powder. From the viewpoint of cost, such natural crystalline silica powder is preferably used as the first raw material powder.

As described above, the particle size of the first raw material powder is 0.03 to 3 mm, preferably 0.1 to 1 mm.
The silica purity of the first raw material powder is 99.9 wt. % Or more, preferably 99.99 wt. % Or more is more preferable. In particular, the concentration of each of Li, Na, and K is 5 wt. ppm or less, and the concentration of each of Ti, Cr, Fe, Ni, Cu, Zn, and Au is 0.1 wt. It is preferable to set it as ppm or less. Moreover, if it is the manufacturing method of the square silica container which concerns on this invention, the silica purity of 1st raw material powder will be 99.999 wt. Even if it has a relatively low purity of not more than%, the manufactured rectangular silica container can sufficiently prevent impurity contamination of the silicon melt and polycrystalline silicon ingot. Therefore, a rectangular silica container for producing a polycrystalline silicon ingot can be produced at a lower cost than before.

  As the first raw material powder, it is sufficient that the particle diameter is 0.03 to 3 mm, and amorphous fused natural quartz glass powder, synthetic silica glass powder, etc. are used in place of or mixed with the above crystalline silica powder. May be. Such a vitreous silica powder can reduce the firing temperature, which may be advantageous in terms of cost.

  The second raw material powder is a material constituting the porous silica plate of the rectangular silica container 10 according to the present invention together with the first raw material powder.

As the second raw material powder, silica glass powder having a particle size of 0.1 to 10 μm, preferably 0.2 to 5 μm, preferably spherical silica glass is prepared. The spherical silica glass can be produced by a wet sol-gel method (alkoxide method) and a dry melting method (spraying method). Alternatively, as an alternative material, a silica glass fine powder, so-called soot powder, is produced by flame hydrolysis of a silicon compound raw material such as silicon tetrachloride (SiCl ₄ ). The particle size of the soot powder in this case is 0.1 to 10 μm, preferably 0.2 to 5 μm, as described above.

  The silica purity of the second raw material powder is also 99.9 wt. % Or more, preferably 99.99 wt. % Or more is more preferable. In particular, the concentration of each of Li, Na, and K is 5 wt. ppm or less, and the concentration of each of Ti, Cr, Fe, Ni, Cu, Zn, and Au is 0.1 wt. It is preferable to set it as ppm or less. Silica glass powder or soot powder produced by the above sol-gel method or thermal spraying method is preferable because it can be easily obtained with high purity.

After producing the second raw material powder, before producing a mixed slurry to be described later, it is possible to produce a granule having a particle diameter of 5 to 500 μm formed by the aggregation of the second raw material powder from the second raw material powder. it can. Thus, it is preferable to use the second raw material powder as a granule because the second raw material powder can be handled easily.
In order to make the second raw material powder into granules, for example, the following procedure can be used.

  First, an organic binder having a melting point of 200 ° C. or lower, for example, a paraffin binder (melting point 40 to 70 ° C.) or a stearic acid binder (melting point 70 to 150 ° C.) is added to the second raw material powder in a weight ratio of 1 to 10 wt. % Preferably 2 to 5 wt. % Pure water is added so that the viscosity value at a shear rate of 1 to 10 / sec is 10 to 100 mPa · sec (about 10 to 40% as a moisture content), and then the mesh filter is set to 20 to 30 μm. Foreign matter is removed to prepare a slurry (suspension) for preparing granules.

  This granule-prepared mixed slurry is dried to produce a binder-coated granule. The method of drying the mixed slurry is not particularly limited, and for example, it can be put into a spray dryer (spray dryer) to produce granules of the second raw material powder having a binder coated on the surface. This spray dryer has a cylindrical hopper-type chamber, an apparatus (atomizer) for spraying the granule preparation mixed slurry installed at the upper part of the chamber, a hot air supply duct installed at the side of the chamber, and the lower part of the chamber It consists of a granule collection port installed in the. The temperature of the air flowing out from the hot air supply duct needs to be set higher than the melting point of the binder to be used, and is set in the range of 100 to 250 ° C. The granules produced in this way are aggregates of second raw material powders whose surfaces are coated with a binder, and can be set to a predetermined average particle size in the range of 5 to 500 μm.

  The first raw material powder and the second raw material powder are produced as described above. In the present invention, Al element is added to at least one of the first raw material powder, the second raw material powder, and a mixed slurry obtained by mixing the first raw material powder, the second raw material powder, and water, which will be described later (doping). ) Thereby, Al element can be contained in the porous silica plate. Thereby, as described above, migration and diffusion of alkali metal elements such as Li, Na and K and transition metal elements such as Ti, Cr, Fe, Ni, Cu, Zn, Mo and Au in the porous silica plate. Can be prevented, and the heat-resistant deformation property of the square silica container 10 can be improved.

  In order to add Al element to at least one of the first raw material powder and the second raw material powder, the raw material powder is immersed and impregnated in an Al compound solution soluble in water or alcohol, and then pulled up at a constant rate. A method such as drying can be used. The amount of Al to be added is such that the Al concentration in the porous silica plate of the square silica container 10 after manufacture is 5 to 500 wt. ppm, and 10 to 100 wt. It is preferable to make it ppm.

  Next, as shown to (a-2) of FIG. 14, the mixed slurry containing 1st raw material powder, 2nd raw material powder, and water is produced. The second raw material powder can be mixed in the state of granules as described above to form a mixed slurry.

  Specifically, the preparation of this mixed slurry is as follows: (1) mixing of the first raw material powder and second raw material powder, (2) preparation of the mixed slurry, (3) homogeneous mixing of the slurry, 4) It can be performed through each sub-step such as vacuum degassing of the slurry, but is not limited thereto.

(1) Mixing of first raw material powder and second raw material powder First, the first raw material powder is used as a main raw material, and the second raw material powder is preferably 5 wt. % To 50 wt. %, More preferably 10-30 wt. Mix evenly in the range of%. The mixing ratio of the raw material powder here determines the mixing ratio of the first raw material powder and the second raw material powder when the mixed slurry is produced. In order to reduce the manufacturing cost, it is necessary to increase the ratio of the first raw material powder to the second raw material powder as much as possible. The mixing ratio of the second raw material powder is 5 wt. If it is at least%, voids in the porous silica plate after molding and firing are reduced and the density is sufficiently high. As a result, the dimensional accuracy and heat resistance of the porous silica plate can be improved. The mixing ratio of the second raw material powder is 50 wt. If it is% or less, sufficient voids in the porous silica plate after molding and firing can be secured, and the releasability can be further improved. As a mixing method, when the amount is relatively small, a V-type mixer can be used, but it is not limited to this method.

(2) Preparation of slurry (mixed aqueous solution) The mixed powder of the first raw material powder and the second raw material powder prepared above was used as a main raw material at 95 to 80 wt. %, Pure water 5-20 wt. % To make a mixed slurry. Care must be taken for impurity contamination during the production of the square silica container 10, and the concentration of Li, Na, K in the porous silica plate is 5 wt. Preferably, the mixed slurry is prepared so as to be equal to or lower than ppm. More preferably, it is at most ppm.

  In the present invention, it is preferable to add Al element to at least one of the first raw material powder, the second raw material powder, and the mixed slurry as described above. In order to contain the Al element in the mixed slurry, it is performed by dissolving and mixing an Al compound soluble in water or alcohol, for example, any one of a small amount of aluminum nitrate, aluminum carbonate, and aluminum chloride in pure water or alcohol. be able to. The amount of Al to be added is such that the Al concentration in the porous silica plate of the square silica container 10 after manufacture is 5 to 500 wt. ppm, and 10 to 100 wt. It is preferable to make it ppm.

  Instead of adding the Al element in the mixed slurry state, the Al element may be added to the mixed slurry by adding the Al element to the water before mixing before preparing the mixed slurry.

  The mixed slurry may further include a dispersant (for example, polyacrylate), an antifoaming agent (for example, polyethylene glycol), a lubricant (for example, stearic acid, wax), and a binder (for example, polyethylene, polypropylene) as necessary. Polyesterene acrylic resin, paraffin wax, epoxy resin, methyl cellulose, ethyl cellulose) and the like can be mixed in an appropriate amount.

(3) Homogenous mixing of slurry The mixed slurry is put into a ball mill composed of a cylindrical silica glass container and silica glass balls, and mixed for 1 to 2 hours. The density (specific gravity) of the prepared mixed slurry is 1.6 to 2.1 g / cm ^3, preferably 1.7 to 2.0 g / cm ³ , and the viscosity is 300 to 3000 mPa at a shear rate of 1 to 10 / sec. -It is preferable to set to sec.

(4) Vacuum degassing of slurry The mixed slurry is placed in a silica glass chamber, and vacuum degassing is performed at room temperature at a vacuum degree of 10 ⁴ Pa or less for 5 to 30 minutes. However, this treatment may not be performed depending on the use of the manufactured square silica container.

  After preparing the mixed slurry in this way, the mixed slurry is introduced into the mold as shown in FIG.

  Next, as shown in FIG. 14A-4, the mixed slurry is dehydrated and dried in a mold to produce a porous silica plate temporary molded body (temporary molding step). Specifically, the mixed slurry contained in the mold is put in a clean oven, heated from room temperature to 5 to 20 ° C./hour, and then kept at 50 to 200 ° C. for 10 to 100 hours to evaporate moisture. Let dry (casting). As the mold at this time, a porous ceramic mold such as gypsum or a porous plastic mold can be used.

About a bottom part board body, a temporary forming process is performed as follows.
A groove or a hole for favorably promoting the growth of the seed crystal is formed in one of both parallel planes of the temporary molded body of the bottom plate. The grooves or holes formed in the temporary molded body of the bottom plate body have the shapes and intervals as described above with reference to FIGS. 5 to 12 in the bottom plate body after firing.

  This groove or hole can be formed, for example, by configuring the shape of the mold itself to form a groove or hole. Moreover, after producing a temporary molded object once, you may form a groove | channel or a hole by grinding the surface after that.

Here, the surface opposite to the surface on which the groove or hole for favorably promoting the growth of the seed crystal is formed is a surface heated in the firing step.
However, grooves or holes may be formed on a surface opposite to the surface on which the grooves or holes are formed for another purpose. This groove or hole is for making it difficult for warpage, bending and cracking in the firing process, and the shape, interval, and the like can be set as necessary. The heating surface in the firing step is the surface on the side where such grooves or holes are formed.

On the other hand, about a side part board body, a temporary forming process is performed as follows.
Unlike the temporary molded body of the bottom plate, it is not necessary to form a groove or hole for favorably promoting seed crystal growth. However, it is preferable to form a groove or a hole in one of the parallel planes of the temporary molded body to make it difficult for warpage, bending and cracking in the firing process.
Here, the side of the surface on which the groove or hole is formed is a surface that is heated in the firing step described later.

  In this way, after preparing a temporary molded body of the porous silica plate, it is fired to obtain a porous silica plate (firing step). In the present invention, both parallel planes of the porous silica plate are used. Among them, it is preferable to include a release accelerator that promotes release of the polycrystalline silicon ingot in at least a part of the surface portion that becomes the inner surface when the silica container 10 is assembled. The content of the release accelerator is applied to at least a part of the surface opposite to the surface heated in the firing step among the two parallel planes of the temporary molded body after the temporary molding step, It can also be performed by drying, and, as will be described later, after the firing step, the mold release accelerator on the opposite side of the surface heated in the firing step of both parallel planes of the porous silica plate body It can also be carried out by applying a release accelerator to at least a part. A specific method of containing the mold release accelerator will be described later.

After the temporary forming step, as shown in FIG. 14 (a-5), the temporary formed body of the porous silica plate is fired to form a porous silica plate (firing step). This firing step is performed at a temperature of 1200 to 1500 ° C. in an atmosphere containing an inert gas as a main component and an O ₂ gas. Furthermore, it heats and bakes from one side among the both parallel planes of the temporary molded body of the porous silica plate, and the bulk density of the surface portion on the heated side is higher than the bulk density of the surface portion on the opposite side. A porous silica plate is used.

For this firing step, for example, a firing furnace such as a one-way heating electric furnace as shown in FIG. 16 can be used.
The one-way heating electric furnace 401 shown in FIG. 16 includes, for example, an upper heat insulating material 411 and a lower heat insulating material 412 made of a high-purity alumina board, a heater 421 made of molybdenum disilicide, an air inlet 431, an air outlet 432, a porous Heat-resistant belt conveyor 441 etc. which convey the temporary molded object of a quality silica board.

In order to perform firing of the temporary molded body of the porous silica plate using this firing furnace, the following is performed. First, the porous silica plate temporary molded body 141 that has been subjected to the temporary molding process is placed on a heat-resistant belt conveyor 441 and conveyed into the one-way heating electric furnace 401. Next, using the intake port 431 and the exhaust port 432, the inside of the furnace is O ₂ (oxygen) gas containing an inert gas such as N ₂ (nitrogen) gas, He (helium) gas, or Ar (argon) gas as a main component. The atmosphere is contained. Next, the heater 421 is heated from room temperature to 1000 ° C. at 50 ° C./hour to 500 ° C./hour to oxidize, burn, and remove organic substances such as a binder contained in the temporary molded body. Next, from 1000 ° C. to 1200 to 1500 ° C., the temperature is increased from 20 ° C./hour to 200 ° C./hour, and subsequently at a predetermined temperature in the range of 1200 to 1500 ° C., preferably 1250 to 1350 ° C., for 1 to 10 hours. The first raw material powder in the temporary molded body and the second raw material powder are sintered. Such heating is performed from one direction of the temporary molded body by the heater 421. The firing atmosphere is most preferably N ₂ gas as an inert gas in terms of cost.

The O ₂ gas content in the firing step is 1 to 30 vol. For the purpose of oxidizing and removing various organic substances (binder, dispersant, antifoaming agent, lubricant, binder, etc.). % Is preferred. O ₂ gas content is 1 vol. If it is% or more, the organic binder can be removed more effectively. The O ₂ gas content is 30 vol. If it is% or less, it is sufficient for removing the organic binder, and the consumption of the heater material can be reduced, and the cost of gas for firing can be suppressed, which is industrially preferable.

  At this time, the bottom plate body is heated from the surface opposite to the surface on which grooves or holes for favorably promoting the growth of seed crystals are formed. When a groove or hole for making it difficult for warpage, bending or cracking is formed, the surface on the groove or hole side becomes a heating surface.

  On the other hand, the side plate is heated and fired from the side of the surface on which the groove or hole is formed when a groove or hole for preventing warpage, bending or cracking is formed.

  Thus, since the porous silica plate body is continuously heated and fired from one direction, the fired surface (heater side surface) of the porous silica plate body has a higher bulk density and the opposite surface. Bulk density decreases.

  After firing, the porous silica plate is carried out of the furnace by the heat-resistant belt conveyor 441 and cooled.

  As described above, the porous silica plate body is manufactured. As described above, in the present invention, of the two parallel planes of the porous silica plate body, It is preferable that a release accelerator for promoting release of the polycrystalline silicon ingot is contained in at least a part of the surface portion. However, when it is desired to avoid contamination of silicon contained in the rectangular silica container 10 as much as possible, it is not necessary to include a mold release accelerator.

  As a specific method of containing a mold release accelerator, first, after the temporary molding step, the mold release is performed on at least a part of the surface opposite to the surface heated in the firing step among the two parallel planes of the temporary molded body. Apply accelerator and dry. Hereinafter, a specific method for incorporating a mold release accelerator will be described as an example.

For example, in the case of alkaline earth metal elements such as recrystallized type Ca, Sr, Ba, etc., chloride, nitrate, carbonate, acetate, etc., which are these element compounds dissolved in water or alcohol, are selected, Spray method, air brush method, roller method, or brush coating method on the surface of both parallel planes opposite to the surface heated in the firing process (the surface where grooves or holes are formed in the bottom plate) The addition treatment can be carried out by coating and drying. The temporary molded body to which the release accelerator has been added is fired at 1200 to 1500 ° C. in an O ₂ gas-containing atmosphere containing an inert gas as a main component in the firing step. These mold release accelerators are contained at least 2 mm thick on the surface by the firing step. The content concentration is 50 to 5000 wt. As the total value of alkaline earth metal elements of Ca, Sr, and Ba. ppm, preferably 100 to 1000 wt. More preferably, it is ppm.

  As another specific method of including a mold release accelerator, after the firing step, the two parallel planes of the porous silica plate are separated into at least a part of the surface opposite to the surface heated in the firing step. A method performed by applying a mold accelerator will be described.

Instead of adding the release accelerator before the firing step, a release accelerator can be contained by applying (coating) to at least a part of the porous silica plate after the firing step. The surface opposite to the surface heated in the firing step among the two parallel planes of the porous silica plate after firing the mixed solution of at least one compound of alkaline earth metal elements such as Ca, Sr and Ba ( In the bottom plate body, the coating treatment is performed by applying and drying at least a part of a surface on which grooves or holes are formed by a spray method, an air brush method or the like. The coating concentration, Ca, Sr, it is preferable that the 50~5000μg / cm ² as an alkaline earth metal element sum of such Ba, and even more preferably from 100-1000 / cm ^2.

  The OH group concentration is adjusted by selecting the type of the first raw material powder and changing the atmosphere, temperature, and time conditions of the drying process and sintering process, and the porous silica plate body has 5 to 500 wt. It is preferable to contain at a concentration of ppm. Also, 30 to 300 wt. More preferably, it is in the range of ppm.

(II) Second Aspect FIG. 15 shows an outline of another example (second aspect, dry method) of the method for producing the square silica container 10 according to the present invention.

  First, as shown to (b-1) of FIG. 15, raw material powder is produced. Specifically, silica powder having a particle size of 0.03 to 3.0 mm and silica powder having a particle size of 0.1 to 10 μm are prepared as the first raw material powder. These raw material powders can be produced in the same manner as in the first embodiment.

  After producing the second raw material powder, before producing the mixed powder to be described later, it is possible to produce a granule having a particle size of 5 to 500 μm in which the second raw material powder is aggregated from the second raw material powder. What can be done is the same as in the first embodiment. Thus, it is preferable to use the second raw material powder as a granule because the second raw material powder can be handled easily.

  In this embodiment (second aspect), at least the first raw material powder, the second raw material powder, and the mixed powder obtained by mixing the first raw material powder, the second raw material powder, and the organic binder described later are used. It is preferable to add (doping) one Al element. Thereby, Al element can be contained in the porous silica plate. Thereby, as described above, migration and diffusion of alkali metal elements such as Li, Na and K and transition metal elements such as Ti, Cr, Fe, Ni, Cu, Zn, Mo and Au in the porous silica plate. Can be prevented, and the heat-resistant deformation property of the square silica container 10 can be improved.

  In order to add Al element to at least one of the first raw material powder and the second raw material powder, the raw material powder is immersed and impregnated in an Al compound solution soluble in water or alcohol, and then pulled up at a constant rate. A method such as drying can be used. The amount of Al to be added is such that the Al concentration in the porous silica plate after production is 5 to 500 wt. It is preferable to make it ppm, and 10 to 100 wt. It is more preferable to adjust to ppm.

  Next, as shown to (b-2) of FIG. 15, 1st raw material powder, 2nd raw material powder, and an organic binder are mixed, and mixed powder is produced. The second raw material powder can be mixed in the state of granules as described above to obtain a mixed powder.

  In this mixing, the first raw material powder is the main raw material and the second raw material powder is preferably 5 wt. % To 50 wt. %, More preferably 10-30 wt. Mix evenly in the range of%. The ratio of the organic binder in the mixed powder is 1 to 10 wt. % Is preferable.

  In order to reduce the manufacturing cost, it is necessary to increase the ratio of the first raw material powder to the second raw material powder as much as possible. The mixing ratio of the second raw material powder is 5 wt. If it is at least%, voids in the porous silica plate after molding and firing are reduced and the density is sufficiently high. As a result, the dimensional accuracy and heat resistance of the porous silica plate can be improved. The mixing ratio of the second raw material powder is 50 wt. If it is% or less, sufficient voids in the porous silica plate after molding and firing can be secured, and the releasability can be further improved. As a mixing method, when the amount is relatively small, a V-type mixer can be used, but it is not limited to this method.

  As described above, instead of or in addition to adding Al element to at least one of the first raw material powder and the second raw material powder, Al element may be added to the mixed powder. In this case, it is possible to use a method of immersing and impregnating the mixed powder in an Al compound solution soluble in water or alcohol, and then lifting and drying at a constant speed. The amount of Al to be added is such that the Al concentration in the porous silica plate of the square silica container 10 after manufacture is 5 to 500 wt. ppm, and 10 to 100 wt. It is preferable to make it ppm.

  Next, as shown in (b-3) and (b-4) of FIG. 15, the mixed powder is introduced into the mold and heated to 50 to 200 ° C. to melt the organic binder. A temporary molded body of a porous silica plate is produced. As a manufacturing method, a hot press method, an injection molding method, or the like can be used.

  Specifically, first, the mixed powder is introduced into the mold and formed into a predetermined shape in accordance with the shape of the inner wall portion. Next, the mixed powder in the mold is pressurized (pressed) and adjusted to a predetermined pressure of 0.1 to 1 MPa, and the temperature of the mixed powder is increased until it reaches a predetermined temperature of 50 to 200 ° C., Hold until compacted to some extent and the binder is welded. Next, the mixture is allowed to cool to room temperature to obtain a temporary molded body of a raw material porous silica plate.

About a bottom part board body, a temporary forming process is performed as follows.
A groove or a hole for favorably promoting the growth of the seed crystal is formed in one of both parallel planes of the temporary molded body of the bottom plate. The groove or hole formed in the temporary molded body of the bottom plate body has the shape and interval as described above in the bottom plate body after firing.

  This groove or hole can be formed, for example, by configuring the shape of the mold itself to form a groove or hole. Moreover, after producing a temporary molded object once, you may form a groove | channel or a hole after that.

Here, the surface opposite to the surface on which the groove or hole is formed is a surface heated in the firing step.
However, the groove or hole may be formed on the surface opposite to the surface on which the groove or hole is formed. This groove or hole is for making it difficult for warpage, bending and cracking in the firing process, and the shape, interval, and the like can be set as necessary. The heating surface in the firing step is the surface on the side where such grooves or holes are formed.

On the other hand, about a side part board body, a temporary forming process is performed as follows.
Unlike the temporary molded body of the bottom plate, it is not necessary to form grooves or holes. However, it is preferable to form a groove or a hole in one of the parallel planes of the temporary molded body to make it difficult for warpage, bending and cracking in the firing process.
Here, the side of the surface on which the groove or hole is formed is a surface that is heated in the firing step described later.

  In this way, after preparing a temporary molded body of the porous silica plate, it is fired to obtain a porous silica plate (firing step). In the present invention, both parallel planes of the porous silica plate are used. Among them, it is preferable to include a release accelerator that promotes release of the polycrystalline silicon ingot in at least a part of the surface portion that becomes the inner surface when the silica container 10 is assembled. Similarly to the first aspect, after the temporary molding step, the mold release accelerator is a surface opposite to the surface heated in the firing step among the two parallel planes of the temporary molded body (in the bottom plate body, the groove or It can be carried out by applying to at least a part of the surface on which the hole is formed and drying. In addition, after the firing step, at least a part of the surface opposite to the surface heated in the firing step among the parallel planes of the porous silica plate (the surface on which grooves or holes are formed in the bottom plate) It can also be carried out by applying a mold release accelerator.

Next, as shown in (b-5) of FIG. 15, the porous silica plate temporary molded body was 1200 to 1500 ° C. in an atmosphere mainly containing an inert gas and containing O ₂ gas. At this temperature, it is heated and fired from one side of both parallel planes of the temporary molded body to obtain a porous silica plate (firing step).
This step can be performed in the same manner as the firing step of the first aspect described above.

  As described above, the porous silica plate is produced. As in the first aspect, the release accelerator is contained in the porous silica plate after the firing step. It can also carry out by apply | coating a mold release accelerator to at least one part of the surface on the opposite side to the surface heated in the baking process among both parallel planes.

  For example, as shown in FIG. 4, the parallel flat porous silica plates manufactured as described above are combined in a susceptor 80 made of carbon or the like to form a square silica container 10. In this case, it arrange | positions so that the one where the density of a porous silica board body may come outside. When the whole is heated in such an arrangement, the porous silica plates are welded together, and the square silica container 10 can be easily integrated.

An example of a method for producing a polycrystalline silicon ingot using the rectangular silica container for producing a polycrystalline silicon ingot according to the present invention will be described.
First, molten silicon as a raw material is put into a rectangular silica container according to the present invention. Next, the molten silicon is heated and kept at a predetermined temperature.

  Next, cooling proceeds from the bottom of the rectangular silica container to grow silicon crystals. The state of crystal growth at the bottom of the container at this time will be described with reference to FIG.

  In FIG. 18 (a), the angle (crossing angle θ) formed by the inclined surface with respect to the vertical direction, such as a groove or a hole in the bottom of the rectangular silica container according to the present invention, is in the range of 15 to 60 °. The case is schematically illustrated. In this case, at the initial stage of cooling from the bottom of the container, the deepest part of the groove or hole is most easily cooled from the shape of the groove or hole. Therefore, first, crystal growth starts from the solid seed crystal 301 in the deepest part of the groove or hole. As shown in FIG. 18A, when the crossing angle θ is in the range of 15 to 60 °, even if a plurality of crystals grow from the seed crystal 301, single crystallization (in the entire polycrystalline silicon ingot is performed in the growth process). Easy to be polycrystalline). This phenomenon is more pronounced when vertical walls are also present in the grooves or holes.

  On the other hand, as schematically shown in FIG. 18B, when the crossing angle θ is smaller than 15 °, a plurality of crystals grow from the seed crystal 301 and expand as they are to form a polycrystalline body with small crystal grains. End up.

After the silicon melt is solidified to produce a polycrystalline silicon ingot, the polycrystalline silicon ingot is taken out from the square silica container. In the present invention, since the fusion between the polycrystalline silicon ingot and the rectangular silica container can be suppressed by controlling the bulk density of the rectangular silica container, it is easy to take out the polycrystalline silicon ingot and prevent breakage. it can.
Thereafter, the taken polycrystalline silicon ingot is sliced to a predetermined thickness and polished to obtain a polycrystalline silicon substrate.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to these.
Example 1
According to the method for producing a porous silica plate according to the present invention shown in FIG. 14 (first embodiment), a porous silica plate was produced as follows, and a rectangular silica container was further produced.

First, the first raw material powder was produced as follows.
50 kg of natural silica was prepared, heated in an air atmosphere at 1000 ° C. for 10 hours, put into a water tank containing pure water, and rapidly cooled. This was dried and then pulverized using a crusher to obtain a particle size of 0.1 to 1.0 mm and a silica (SiO ₂ ) purity of 99.99 wt. % And a total weight of 40 kg of silica powder (natural silica powder).

  Moreover, the 2nd raw material powder was produced as follows and this was made into the state of a granule.

  As the second raw material powder, spherical amorphous silica powder was produced by a melting method. The particle size was 0.2-5 μm and the weight was 10 kg.

  The second raw material powder produced in this way was used as a binder-coated granule as follows. 50 g of paraffinic binder (melting point 55 ° C.), 50 g of stearic acid binder (melting point 100 ° C.) and 2.5 kg of pure water are mixed with 10 kg of the second raw material powder to produce a mixed slurry for forming granules. did. This mixed slurry was dried by a spray dryer to prepare a binder-coated granule. The granule diameter of the binder-coated second raw material powder was 10 to 100 μm, and the average was 50 μm.

  Next, using a V-type mixer, the first raw material powder 85 wt. % Of granular second raw material powder at 15 wt. % Were uniformly dry mixed.

10 parts by weight of pure water and a small amount of a dispersant (ammonium polyacrylate) are mixed with 90 parts by weight of the mixed powder of the first raw material powder and the granular second raw material powder to form a slurry. . Next, the slurry was uniformly mixed for 1 hour in a ball mill composed of a cylindrical silica glass container and silica glass balls. A suitable amount of pure water is added to the uniformly mixed slurry so that the viscosity is about 500 to 1000 mPa · sec at a shear rate of 1.8 to 1.9 g / cm ³ and 1 to 10 / sec. did. Next, this slurry was put in a container, placed in a silica glass chamber, and vacuum degassed for 3 minutes at a vacuum of 10 ⁴ Pa at room temperature. In this way, a mixed slurry was obtained.

Next, the mixed slurry was introduced into a gypsum mold.
At this time, the bottom plate body is formed by introducing the mixed slurry into a plaster mold capable of forming a plurality of conical holes on one surface of the cast body after casting. went. The size of the conical hole formed here was 10 mm in diameter, the angle between the side surface (slope) and the direction perpendicular to the surface of the temporary molded body was 45 °, and the interval was 15 mm.

  Next, the mixed slurry introduced into the mold was held in a clean oven at 100 ° C. for 10 hours, and then cooled to room temperature to prepare a parallel plate-like porous silica plate temporary molding.

Next, the temporary molded body of the porous silica plate was removed from the mold.
This porous silica plate temporary compact was placed in a one-way heating electric furnace 401 as shown in FIG.

  Then, oxygen 20 vol. %, Nitrogen 80 vol. In an atmosphere of 100%, the temperature was raised from room temperature to 1000 ° C. at a heating rate of 500 ° C./hour over about 2 hours, raised to 1350 ° C. at a heating rate of 200 ° C./hour, and then at 1350 ° C. Hold for 3 hours. In this manner, the porous silica plate body was manufactured by firing the temporary molded body of the porous silica plate body.

  The dimensions of the porous silica plate were such that the length was 400 mm × width 400 mm × thickness 15 mm.

  The peripheral part of the parallel flat plate-like porous silica plate produced in this way was processed, and five pieces were combined as shown in FIG.

(Example 2)
A square silica container was produced in the same manner as in Example 1. However, barium chloride is applied to the entire surface of the porous silica plate body in which a plurality of conical holes are formed, and one-way heating is performed using the surface opposite to this surface as a heating surface in the firing step. went.

(Example 3)
A square silica container was produced in the same manner as in Example 1. However, a small amount of aluminum chloride AlCl ₃ was mixed with the mixed slurry.

Example 4
A square silica container was produced in the same manner as in Example 1. However, a small amount of aluminum chloride AlCl ₃ is mixed into the mixed slurry, and barium chloride is applied to the entire surface portion where a plurality of conical holes are formed in the temporary molded body of the porous silica plate, and this surface is used in the firing step. One-way heating was performed using the opposite surface as the heating surface.

(Example 5)
According to the method for producing a porous silica plate according to the present invention shown in FIG. 15 (second embodiment), a porous silica plate was produced as follows, and a square silica container was further produced.

  First, the first raw material powder and the second raw material powder were produced in the same manner as in Example 1. The second raw material powder was made into granules in the same manner as in Example 1.

  Next, using a V-type mixer, the first raw material powder 85 wt. % Of granular second raw material powder at 15 wt. % Were uniformly dry mixed.

  A small amount of an organic binder was mixed into the mixed powder of the first raw material powder and the granular second raw material powder to obtain a mixed powder.

  Next, while holding the mixed powder introduced into the cylinder of the injection molding machine at 100 ° C. in the cylinder, it is injection-molded into another ceramic mold and temporarily formed into a parallel flat porous silica plate The body was made. At this time, with respect to the bottom plate body, the mixed powder was introduced into a ceramic mold frame capable of forming a plurality of conical holes to prepare a temporary molded body. The dimensions and spacing of the conical holes formed here were 10 mm in diameter, 45 ° in angle, and 15 mm apart as in Example 1.

  Next, the temporary molded body of the porous silica plate was placed in a one-way heating electric furnace 401 as shown in FIG.

  Then, oxygen 20 vol. %, Nitrogen 80 vol. In an atmosphere of 100%, the temperature was raised from room temperature to 1000 ° C. at a heating rate of 500 ° C./hour over about 2 hours, raised to 1350 ° C. at a heating rate of 200 ° C./hour, and then at 1350 ° C. Hold for 3 hours. In this manner, the porous silica plate body was manufactured by firing the temporary molded body of the porous silica plate body.

  The dimensions of the porous silica plate were such that the length was 400 mm × width 400 mm × thickness 15 mm.

  The peripheral part of the parallel flat plate-like porous silica plate thus manufactured was processed, and five pieces were combined to form a square silica container 10.

(Example 6)
A square silica container was produced in the same manner as in Example 5. However, barium chloride was applied to the entire surface of one surface of the temporary molded body of the porous silica plate, and one-way heating was performed using the surface opposite to this surface as a heating surface in the firing step.

(Example 7)
A square silica container was produced in the same manner as in Example 5. However, a small amount of aluminum chloride AlCl ₃ was mixed with the mixed powder.

(Example 8)
A square silica container was produced in the same manner as in Example 5. However, a small amount of aluminum chloride AlCl ₃ is mixed with the mixed powder, and barium chloride is applied to the entire surface of one surface of the porous silica plate temporary body, and the surface opposite to this surface is applied in the firing step. Unidirectional heating was performed as the heating surface.

(Comparative Example 1)
A square silica container was produced as follows.

First, the first raw material powder was produced as follows.
50 kg of natural silica was prepared, heated in an air atmosphere at 1000 ° C. for 10 hours, put into a water tank containing pure water, and rapidly cooled. After dried, triturated with crusher performs high purification treatment, particle size 0.1 to 1.0 mm, silica (SiO ₂₎ purity 99.999wt. % And a total weight of 40 kg of silica powder (natural silica powder).

  Moreover, the 2nd raw material powder was produced as follows and this was made into the state of a granule.

  As the second raw material powder, spherical amorphous silica powder was produced by a melting method. The particle size was 0.2-5 μm and the weight was 10 kg.

  The second raw material powder produced in this way was used as a binder-coated granule as follows. 50 g of paraffinic binder (melting point 55 ° C.), 50 g of stearic acid binder (melting point 100 ° C.) and 2.5 kg of pure water are mixed with 10 kg of the second raw material powder to produce a mixed slurry for forming granules. did. This mixed slurry was dried by a spray dryer to prepare a binder-coated granule. The granule diameter of the second raw material powder coated with the binder was 10 to 100 μm, and the average was 50 μm.

  Next, using a V-type mixer, the first raw material powder 60 wt. % Of the second raw material powder in the form of granules is 40 wt. % Were uniformly dry mixed.

A small amount of 10 parts by weight of pure water and a dispersing agent (ammonium polyacrylate) were mixed with 90 parts by weight of the mixed powder of the first raw material powder and the granular second raw material powder to form a slurry. Next, the slurry was uniformly mixed for 1 hour in a ball mill composed of a cylindrical silica glass container and silica glass balls. An appropriate amount of pure water was added to the uniformly mixed slurry so that the density was 1.8 to 2.0 g / cm ³ and the viscosity was about 500 to 1000 mPa · sec at a shear rate of 1 to 10 / sec. . Next, this slurry was put in a container, placed in a silica glass chamber, and vacuum degassed for 3 minutes at a vacuum of 10 ⁴ Pa at room temperature. In this way, a mixed slurry was obtained.

  Next, the mixed slurry was introduced into a square mold that can be shaped like a square (square tank).

  Next, the mixed slurry introduced into the square formwork is kept in a clean oven at 150 ° C. for 5 hours and then cooled to room temperature to produce a square (square tank-shaped) porous silica substrate temporary molded body. did.

  Next, a temporary molded body of a porous silica substrate was placed in an electric resistance heating furnace made of a heat-resistant material of a high-purity alumina board having a furnace size of 1 m × 1 m × 1 m and equipped with a molybdenum disilicide heater. And oxygen 20 vol. %, Nitrogen 80 vol. %, The temperature was increased from room temperature to 1000 ° C. at a heating rate of 500 ° C./hour over about 2 hours, and the temperature was increased from 1400 ° C. at a heating rate of 200 ° C./hour at 1400 ° C. Hold for 3 hours. In this way, the porous silica-based temporary molded body was fired to produce a square silica container.

  The dimensions of the porous silica substrate were such that the inner dimensions were width 400 mm × depth 400 mm × height 400 mm, and the thickness was 15 mm.

(Comparative Example 2)
A square silica container was produced as follows.

  First, the first raw material powder and the second raw material powder were produced in the same manner as in Comparative Example 1. Further, the second raw material powder was made into granules in the same manner as in Comparative Example 1.

  Next, using a V-type mixer, the first raw material powder 60 wt. % Of the second raw material powder in the form of granules is 40 wt. % Were uniformly dry mixed.

  A small amount of an organic binder was mixed into the mixed powder of the first raw material powder and the granular second raw material powder to obtain a mixed powder.

  Next, the mixed powder was introduced into the square formwork.

  Next, the mixed powder introduced into the square formwork is kept in a clean oven at 500 ° C. for 5 hours, and then cooled to room temperature to produce a square (rectangular tank-shaped) porous silica substrate temporary molded body. did.

  Next, a temporary molded body of a porous silica substrate was placed in an electric resistance heating furnace made of a heat-resistant material of a high-purity alumina board having a furnace size of 1 m × 1 m × 1 m and equipped with a molybdenum disilicide heater. And oxygen 20 vol. %, Nitrogen 80 vol. %, The temperature was increased from room temperature to 1000 ° C. at a heating rate of 500 ° C./hour over about 2 hours, and the temperature was increased from 1400 ° C. at a heating rate of 200 ° C./hour at 1400 ° C. Hold for 5 hours. In this way, the porous silica-based temporary molded body was fired to produce a square silica container.

[Evaluation Methods in Examples and Comparative Examples]
The physical properties and characteristics of the raw material powder used in each Example and Comparative Example, and the produced porous silica plate and square silica container were evaluated as follows.
Bulk density measurement method:
A plate-like sample of 50 mm × 50 mm × 3 mm was cut out from the surface portion of the porous silica plate, and the weight (g) of the sample was measured.
Next, the volume of the sample (cm ³ ) was determined by immersing the sample in a water tank containing pure water and measuring the weight loss of the sample. The bulk density (g / cm ³ ) was calculated from these two values.

Particle size measurement method for each raw material powder:
Two-dimensional shape observation and area measurement of each raw material powder were performed with an optical microscope or an electron microscope. Next, assuming that the shape of the particle is a perfect circle, the diameter was calculated from the area value. This method was repeated statistically to obtain a value within the range of the particle size (in this range, 99 wt.% Or more of the raw material powder was included).

Metal element concentration analysis:
A sample sample was prepared by cutting a silica sample piece from a predetermined position and dissolving it with a hydrofluoric acid aqueous solution. In particular, in the concentration analysis of the mold release accelerator, a plurality of 20 mm × 20 mm × 2 mm samples were cut out from the inner surface layer portion of the square silica container to obtain a silica sample piece for analysis. When the concentration of the contained metal element is relatively low, plasma emission spectrometry (ICP-AES, Inductively Coupled Plasma-Atomic Emission Spectroscopy) or plasma mass spectrometry (ICP-MS, Inductively Coupled Plasma, When the element concentration was relatively high, it was performed by atomic absorption spectrophotometry (AAS, Atomic Absorption Spectroscopy).

OH group concentration measurement:
A powdery sample having a particle size of 10 to 100 μm was prepared from a rectangular silica container, and the infrared diffuse reflection spectrophotometry was performed. Conversion to the OH group concentration follows the literature below.
Dodd, D.D. M.M. and Fraser, D.A. B. (1966) Optical determination of OH in fused silica. Journal of Applied Physics, vol. 37, P.I. 3911.

Anti-diffusion effect from rectangular silica container to polycrystalline silicon ingot:
Si purity 99.99999999 wt. % High-purity silicon melt was charged and cooled to room temperature to prepare a polycrystalline silicon ingot having dimensions of 400 mm × 400 mm × 300 mm. Next, a silicon piece was sampled at a position 5 mm deep from the surface of the ingot, and this was treated with an acidic solution to obtain a solution-like sample, and then Na concentration analysis was performed by ICP-AES. The effect of preventing impurity diffusion from the rectangular silica container to the polycrystalline silicon ingot was evaluated by the Na concentration value.
High impurity diffusion prevention effect ○ (Na concentration is less than 10wt.ppb)
During impurity diffusion prevention effect Δ (Na concentration is 10 wt. Ppb or more and less than 100 wt. Ppb)
Small impurity diffusion prevention effect × (Na concentration is 100wt.ppb or more)

Release property evaluation:
A polycrystalline silicon ingot was prepared in the same manner as described above, and then the four side wall corners of the square silica container and the welded portions of the four side walls and the bottom corner were cut with a cutter, and the square silica was cut from the ingot. The four side walls and bottom plate of the container were peeled off. The releasability was evaluated by measuring the depth of unevenness and cracks remaining on the surface of the ingot from the position in contact with the inner surface of the square silica container to the inner direction with a scale.
Good releasability ○ (depth less than 2mm)
Moderate releasability △ (depth 2mm or more and less than 5mm)
Good releasability × (depth 5mm or more)

Quality evaluation of polycrystalline silicon ingot:
The produced polycrystalline silicon ingot was sliced and the cross section was observed.
From the viewpoint of the size of the crystal grains and the uniformity in the crystal growth direction, the evaluation was made in comparison with the prior art (comparative example 1 as a standard).
Good quality ○ (Crystal grain size 5-50mm occupies 70% or more of the total area, and the crystal orientation of the grown crystal is aligned in a certain direction)
Medium quality △ (crystal grain size 5-50mm is about 30-70% of the total area, and the crystal orientation of the grown crystal is at an intermediate level)
Poor quality × (same as conventional)

Manufacturing cost (relative) evaluation:
The manufacturing cost of the square silica container was examined.
The standard was Comparative Example 1, and the total values of the silica raw material powder cost, the powder molding cost, the fired cost of the molded body and the like were relatively evaluated.
Low cost ○ (50% or less)
Medium cost △ (about 50-90%)
Cost is high × (Comparative Example 1 is 100%)

  The production conditions, measured physical property values, and evaluation results of the respective square silica containers produced in Examples 1 to 8 and Comparative Examples 1 and 2 are summarized and shown in Tables 1 to 6 below. Table 6 shows the impurity transition metal element concentration (unit: wt.ppb) of the porous silica plate of each example and the porous silica substrate of each comparative example.

As can be seen from Tables 1 to 6, Examples 1 to 8 according to the method for producing a silica container according to the present invention.
Then, a rectangular silica container for producing a polycrystalline silicon ingot having excellent releasability could be produced at a low cost. Moreover, in Examples 1-8, the polycrystalline silicon ingot with which the magnitude | size of the crystal grain and the crystal axis direction were equal was able to be manufactured.

  The present invention is not limited to the above embodiment. The above embodiment is merely an example, and the present invention has the same configuration as that of the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

10 ... Square silica container for producing a polycrystalline silicon ingot according to the present invention,
11 ... side plate, 12 ... side inner surface, 13 ... side outer surface,
21 ... Bottom plate body, 22 ... Bottom inner surface, 23 ... Bottom outer surface,
31 ... groove or hole, 31a ... groove, 31b ... pyramid shaped hole,
31c, 31d ... conical hole, 32 ... slope, 33 ... vertical wall, 34 ... flat bottom,
41 ... Plate material in which through holes are formed, 42 ... Through holes, 51 ... Spacers,
80 ... susceptor,
301 ... Seed crystal,
401 ... one-way heating electric furnace, 411 ... upper heat insulating material, 412 ... lower heat insulating material,
421 ... heater, 431 ... intake port, 432 ... exhaust port,
441 ... A heat-resistant belt conveyor.

Claims (19)

A rectangular silica container for solidifying a silicon melt to produce a polycrystalline silicon ingot,
It is configured by combining parallel flat plate-like porous silica plates made of porous silica,
The bulk density of the surface portions of both parallel planes in the porous silica plate forming at least the side of the square silica container is higher in the outer surface portion than the inner surface portion of the square silica container,
The inner surface portion of the porous silica plate forming the bottom of the square silica container has a plurality of grooves or holes at predetermined intervals,
A rectangular silica container for producing a polycrystalline silicon ingot, characterized in that at least a part of a side surface of the groove or hole is formed as an inclined surface having an angle of 15 to 60 ° with respect to the vertical direction. The bulk density of the porous silica plate is 1.60 to 2.20 g / cm ³ ,
The difference in bulk density between the surface portions of both parallel planes in the porous silica plate forming at least the side of the rectangular silica container is 0.05 g / cm ³ or more with respect to the bulk density from the inner and outer surfaces to a depth of 3 mm The rectangular silica container for producing a polycrystalline silicon ingot according to claim 1, wherein   3. The release accelerator for promoting release of the polycrystalline silicon ingot is contained in at least a part of the inner surface portion of the square silica container. A rectangular silica container for producing a polycrystalline silicon ingot as described.   One or more of Ca, Sr, and Ba as the mold release accelerator are 50 to 5000 wt. As a total value of each element in a depth of 2 mm from the inner surface of the square silica container. The rectangular silica container for producing a polycrystalline silicon ingot according to claim 3, wherein the rectangular silica container is added at a concentration of ppm. 4. The release agent according to claim 3, wherein at least one of Ca, Sr, and Ba is applied at a concentration of 50 to 5000 μg / cm ² as a total value of each element. 4. A rectangular silica container for producing a polycrystalline silicon ingot according to 4. A parallel flat plate-like porous silica plate made of porous silica,
The bulk density is 1.60 to 2.20 g / cm ³ ;
A part of at least one surface portion of both parallel planes has a plurality of grooves or holes at a predetermined interval,
A porous silica plate, wherein at least a part of a side surface of the groove or hole is formed as an inclined surface having an angle of 15 to 60 ° with respect to a direction perpendicular to the surface.   The porous silica plate according to claim 6, wherein the shape of the groove or hole is a V shape in the case of a groove, and a conical shape or a pyramid shape in the case of a hole.   The porous silica plate according to claim 6 or 7, wherein a vertical wall along a direction perpendicular to a part of the surface is present on a side surface of the groove or hole.   The dimension of the opening of the groove or hole has a width of 5 to 20 mm in the case of a groove, and a minimum length of 5 to 20 mm in the case of a hole. The porous silica plate according to claim 1.   10. The mold release accelerator for promoting mold release of polycrystalline silicon is contained in a part of the surface portion in which the groove or hole is formed. 11. 2. The porous silica plate described in 1.   One or more of Ca, Sr, and Ba as the release accelerator are 50 to 5000 wt. The porous silica plate according to claim 10, wherein the porous silica plate is added at a concentration of ppm. The one or more of Ca, Sr, and Ba as the mold release accelerator are applied at a concentration of 50 to 5000 μg / cm ² as a total value of each element. 11. A porous silica plate according to item 11. A method for producing a parallel flat plate-like porous silica plate made of porous silica,
Producing silica powder having a particle size of 0.03 to 3.0 mm as the first raw material powder;
Producing silica powder having a particle size of 0.1 to 10 μm as the second raw material powder;
Producing a mixed slurry containing the first raw material powder, the second raw material powder, and water;
The mixed slurry is dehydrated and dried in a mold, and a temporary molding step for producing a temporary molded body of a porous silica plate having a plurality of grooves or holes at a predetermined interval on one surface portion of both parallel planes;
The temporary molded body is heated from a surface opposite to the surface on which the grooves or holes are formed at a temperature of 1200 to 1500 ° C. in an atmosphere containing an inert gas as a main component and O ₂ gas. A method for producing a porous silica plate, comprising: a firing step to form a porous silica plate. A method for producing a parallel flat plate-like porous silica plate made of porous silica,
Producing silica powder having a particle size of 0.03 to 3.0 mm as the first raw material powder;
Producing silica powder having a particle size of 0.1 to 10 μm as the second raw material powder;
Mixing the first raw material powder, the second raw material powder and an organic binder to produce a mixed powder;
Porous silica having a plurality of grooves or holes at predetermined intervals on one surface portion of both parallel planes by introducing the mixed powder into a mold and heating to 50 to 200 ° C. to melt the organic binder A step of producing a temporary molded body of the plate,
The temporary molded body is heated from a surface opposite to the surface on which the grooves or holes are formed at a temperature of 1200 to 1500 ° C. in an atmosphere containing an inert gas as a main component and O ₂ gas. A method for producing a porous silica plate, comprising: a firing step to form a porous silica plate.   At least after the temporary forming step, a release accelerator for promoting the release of polycrystalline silicon is applied to at least a part of the surface where the groove or hole is formed in both parallel planes of the temporary molded body, and then dried. The method for producing a porous silica plate according to claim 13 or 14, wherein the mold release accelerator is added by adding the mold release accelerator.   At least after the firing step, a mold release accelerator for promoting mold release of polycrystalline silicon is used, and the mold release accelerator is formed on at least a part of the surface of the temporary molded body where the groove or hole is formed. The method for producing a porous silica plate according to any one of claims 13 to 15, wherein the mold release accelerator is contained by applying a release agent.   The method for producing a porous silica plate according to claim 15 or 16, wherein the release accelerator is one or more of Ca, Sr, and Ba.   Before producing the mixed slurry or the mixed powder, a granule having a particle diameter of 5 to 500 μm formed by collecting the second raw material powder is produced from the second raw material powder, and the second raw material powder The method for producing a porous silica plate according to any one of claims 13 to 17, wherein the mixed slurry or the mixed powder is prepared using a granule.   A rectangular silica container comprising a porous silica plate manufactured by the method for manufacturing a porous silica plate according to any one of claims 13 to 18 in a bottom portion to form a rectangular silica container. Production method.

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