JP5130334B2 - Square silica container for producing polycrystalline silicon ingot, porous silica plate and method for producing the same - Google Patents

Description

  The present invention relates to a square (square tank type) silica container for containing a silicon melt and then solidifying 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. Silica (silicon dioxide) containers and graphite containers are used as containers for containing a silicon melt and solidifying to produce a polycrystalline silicon ingot.

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.

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

  As described above, in a container for producing a polycrystalline silicon ingot by solidifying in a container, a release layer is generally formed on the inner surface in advance. 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, 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 these problems, and is capable of producing a polycrystalline silicon ingot having excellent releasability while suppressing impurity contamination to a silicon melt and a polycrystalline silicon ingot, and extremely low cost. An object of the present invention is to provide a rectangular silica container.

  Moreover, an object of this invention is to provide the porous silica board which comprises such a square silica container for polycrystalline silicon ingot manufacture, and its manufacturing method.

  The present invention has been made in order to solve the above-mentioned problems, and is a rectangular silica container for producing a polycrystalline silicon ingot by containing a silicon melt and then solidifying, and is a parallel plate shape made of porous silica. The bulk density of the surface portions of both parallel planes of the porous silica plate body is higher in the outer surface portion than in the inner surface portion of the square silica container. A rectangular silica container for producing a polycrystalline silicon ingot is provided.

  With such a silica container, the bulk density of the inner surface part of the container is made lower than the bulk density of the outer surface part, thereby suppressing impurity contamination in the contained silicon (silicon melt and polycrystalline silicon ingot). However, while maintaining the strength of the container itself, a low-cost rectangular silica container for producing a polycrystalline silicon ingot having excellent releasability can be obtained. Moreover, since the plates are combined, the container manufacturing cost can be remarkably reduced as compared with the single body.

In this case, 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 of the porous silica plate is deep from the inner and outer surfaces. The bulk density up to 3 mm preferably has a difference of 0.05 g / cm ³ or more.

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 of the porous silica plate is 3 mm deep from the inner and outer surfaces. If the bulk density has a difference of 0.05 g / cm ³ or more, the releasability can be improved without excessively reducing the strength of the inner surface portion of the container.

  The square silica container has an Al concentration of 5 to 500 wt. ppm, and the OH group concentration is 5 to 500 wt. Preference is given to ppm.

  By containing Al and OH groups in such a concentration in the square silica container, impurities contained in the contained silicon (silicon melt and polycrystalline silicon ingot) can be obtained even when an inexpensive raw material is used as a raw material for the silica container. Diffusion can be sufficiently prevented.

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.

  The concentration of each of Li, Na, and K contained in the square silica container is 5 wt. ppm or less, and each concentration of Ti, Cr, Fe, Ni, Cu, Zn, Au is 0.1 wt. It is preferably at most ppm.

  If the concentration of each of the metal elements contained in the rectangular silica container is set in this way, a rectangular silica container for producing a polycrystalline silicon ingot can be more effectively prevented from contaminating the silicon melt and the polycrystalline silicon ingot. can do.

Further, the present invention is a parallel flat plate-like porous silica plate made of porous silica, the bulk density is 1.60 to 2.20 g / cm ³ , and the surface portions of both parallel planes are respectively Provided is a porous silica plate having a difference of 0.05 g / cm ³ or more in terms of bulk density from the surface to a depth of 3 mm.

  Such porous silica plates can be combined to form a square silica container. The rectangular silica container is a low-cost polycrystalline silicon that has excellent releasability while maintaining the strength of the container itself while suppressing impurity contamination of the contained silicon (silicon melt and polycrystalline silicon ingot). It can be set as the square silica container for ingot manufacture.

  In this case, the porous silica plate has an Al concentration of 5 to 500 wt. ppm, and the OH group concentration is 5 to 500 wt. Preference is given to ppm.

  By including Al and OH groups in such a concentration in the porous silica plate, even when an inexpensive raw material is used as the raw material of the porous silica plate, it is accommodated when assembled into a rectangular silica container. Diffusion of impurities into silicon (silicon melt and polycrystalline silicon ingot) can be sufficiently prevented.

Moreover, it is preferable that a release accelerator for promoting release of polycrystalline silicon is contained in a part of at least one surface portion of both parallel planes. 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.

  Thus, if a release accelerator that promotes the release of polycrystalline silicon is contained in a part of at least one surface portion of both parallel planes of the porous silica plate, it is assembled into square silica. In the case of the container, the releasability can be increased more effectively and 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.

  The concentration of each of Li, Na and K contained in the porous silica plate is 5 wt. ppm or less, and each concentration of Ti, Cr, Fe, Ni, Cu, Zn, Au is 0.1 wt. It is preferably at most ppm. If the concentration of each of the metal elements contained in the porous silica plate is set in this way, impurity contamination to the silicon melt and polycrystalline silicon ingot is more effectively achieved when assembled into a rectangular silica container. A rectangular silica container for producing a polycrystalline silicon ingot that can be prevented can be obtained.

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 dehydrating and drying the mixed slurry in a mold to prepare a temporary molded body of a porous silica plate in a parallel plate shape, and the temporary molded body with an inert gas as a main component. In an atmosphere containing O ₂ gas, at a temperature of 1200 to 1500 ° C., it is heated and fired from one side of both parallel planes of the temporary molded body, and the bulk density of the surface portion on the heated side is Make the porous silica plate higher than the bulk density of the opposite surface part To provide a method of manufacturing a porous silica plate body characterized by comprising a formation step.

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. A step of introducing the mixed powder into a mold, and heating the mixture to 50 to 200 ° C. to melt the organic binder, thereby forming a temporary formed body of the porous silica plate into a parallel plate; And heating the temporary molded body from one side of both parallel planes of the temporary molded body at a temperature of 1200 to 1500 ° C. in an atmosphere mainly containing an inert gas and containing O ₂ gas. And the bulk density of the surface portion on the heated side is To provide a method of manufacturing a porous silica plate member which comprises a firing step to provide a highly porous silica plate member than the bulk density of the surface portion of the contralateral.

  The porous silica plates produced in this way can be combined to form a square silica container. Moreover, if it is the manufacturing method of said porous silica board, the square silica container which combined the manufactured porous silica board will suppress the impurity contamination to the silicon (silicon melt and polycrystalline silicon ingot) which accommodated. However, while maintaining the strength of the container itself, a low-cost rectangular silica container for producing a polycrystalline silicon ingot having excellent releasability can be obtained.

  In the method for producing a porous silica plate according to the present invention, before the firing step, at least one of a groove and a hole is formed in one of both parallel planes of the temporary molded body, and the firing step is performed. In the above, it is preferable to heat and fire from the side of the surface on which at least one of the groove and hole is formed.

  Thus, by heating and firing from the side of the surface on which at least one of the groove and the hole is formed, warping, bending and cracking are less likely to occur in the porous silica plate in the firing step.

  Moreover, it is preferable to add Al element to at least one of the first raw material powder, the second raw material powder, the mixed slurry, and the mixed powder.

  If it does in this way, Al element can be added to the porous silica board manufactured. As a result, in the rectangular silica container in which the produced porous silica plates are combined, impurity contamination of the contained silicon can be more effectively suppressed.

  Further, at least after the temporary forming step, a release accelerator that promotes the release of the polycrystalline silicon is provided on a surface opposite to the surface to be heated in the firing step of both parallel planes of the temporary molded body. It is preferable to add the release accelerator by adding the release accelerator by applying to at least a part and drying. Further, at least after the firing step, a release accelerator that promotes the release of polycrystalline silicon is a surface opposite to the surface heated in the firing step among the two parallel planes of the porous silica plate. It is also preferable to include the release accelerator by applying the release accelerator to at least a part of the release accelerator.

  By including the release accelerator in this manner, the release accelerator can be more efficiently contained in the porous silica plate.

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

  Thus, when the mold release accelerator is one or more of Ca, Sr, and Ba, in the rectangular silica container combined with the produced porous silica plate, the mold release property can be increased more effectively. 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.

  In the case of a rectangular silica container for producing a polycrystalline silicon ingot according to the present invention, impurities in the contained silicon can be obtained by making the bulk density of the inner surface portion of the container lower than the bulk density of the outer surface section and making it porous. A low-cost rectangular silica container for producing a polycrystalline silicon ingot can be obtained, which is excellent in releasability while maintaining the strength of the container itself while suppressing contamination.

In addition, such a rectangular silica container for producing a polycrystalline silicon ingot can be constructed by combining the silica plate materials according to the present invention, so that the container can be manufactured at a very low cost.
Moreover, if it is the manufacturing method of the porous silica board which concerns on this invention, such a silica board | plate material can be manufactured.

  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 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 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 groove | channel formed in the temporary molded object of a porous silica board, (a) is a top view, (b) is sectional drawing. It is the schematic which shows an example of the hole formed in the temporary molded object of a porous silica board, (a) is a top view, (b) is sectional drawing. 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.

  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.

  Thirdly, the above-described excellent mold releasability and prevention of impurity contamination are realized 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 a side wall part 11 and a bottom part 21. Moreover, the square silica container 10 according to the present invention is configured by combining parallel flat plate-like porous silica plates. Specifically, as shown in FIGS. 1 (a) and 1 (b), the four side walls 11 and the bottom 21 are each formed of a parallel flat plate-like porous silica plate, and according to the present invention. The square silica container 10 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, the shape for combination may be made in the peripheral part of flat plate shape. Moreover, as described later, the porous silica plate according to the present invention may have holes or grooves formed on the surface.

  FIG. 3A to FIG. 3C show examples of the shape of the porous silica plate that forms the side wall 11 of the square silica container 10.

  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 is substantially parallel. 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 porous silica plate shown in FIG. 3B corresponds to that of FIGS. 1A and 1B, and the shape of the porous silica plate shown in FIG. 2 corresponds to those of (a) and (b).

  Thus, the rectangular silica container 10 according to the present invention configured by combining the porous silica plates is a container for producing a rectangular polycrystalline silicon ingot by solidifying after containing the silicon melt. is there. 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. Compared with a cylindrical polycrystalline silicon ingot, the sliced wafer is converted into a solar cell. In this case, the light receiving area is not wasted, which is very suitable.

  Further, in the rectangular silica container 10 according to the present invention, the bulk density of the surface parts of both parallel planes of the porous silica plate is higher in the outer surface part than in the inner surface part of the rectangular silica container 10. That is, the porous silica plate body forming the side wall portion 11 has a higher bulk density in the surface portion corresponding to the side wall portion outer surface 13 than in the surface portion corresponding to the side wall portion inner surface 12. Further, the porous silica plate body forming the bottom portion 21 has a higher bulk density in the surface portion corresponding to the bottom outer surface 23 than in the surface portion corresponding to the bottom inner surface 22.

  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”. There is. Similarly, when a porous silica plate is assembled into a square silica container, the surface corresponding to the outer surface of the square silica container may be simply referred to as “the outer surface of the porous silica plate”.

  In order to improve releasability, the bulk density of the square silica container 10 is set as described above, and the amount of bubbles in the inner surface portion is increased (that is, the porosity is increased). 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.

Furthermore, the bulk density of each porous silica plate constituting the rectangular silica container 10 is 1.60 to 2.20 g / cm ³ , and the bulk density of the surface portions of both parallel planes of the porous silica plate is It is preferable to have a difference of 0.05 g / cm ³ or more with respect to the bulk density from each surface 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 . The difference in bulk density between the surface portions of both parallel planes of the porous silica plate is more preferably 0.1 g / cm ³ or more.

Further, in the porous silica plate body, the bulk density of the container surface portion is preferably in a 1.60~1.90g / cm ^3, be 1.65~1.85g / cm ³ further preferable. 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.

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.

The method for producing the porous silica plate according to the present invention 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. The silica raw material powder is sintered at 1200 to 1500 ° C., preferably 1300 to 1400 ° C., where the melting treatment is performed 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, the wet method) of the manufacturing method of the porous silica board 151 which concerns on this invention was shown in FIG.

  First, as shown to (a-1) of FIG. 7, 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 prepared before preparing a 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 that constitutes the porous silica plate 151 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 is 10 to 100 mPa · S at a shear rate of 1 to 10 / 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 151. Thereby, as described above, the movement 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 151, Diffusion can be prevented and the heat distortion resistance 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 151 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. 7, the mixed slurry 131 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 131.

  Specifically, the mixed slurry 131 is prepared 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) Although it can be performed through each sub-step such as vacuum degassing of the slurry, it is not limited to this.

(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 131 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% or more, the voids of the porous silica plate 151 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 151 can be improved. The mixing ratio of the second raw material powder is 50 wt. If it is% or less, the space | gap of the porous silica board 151 after shaping | molding and baking can fully be ensured, and a mold release property can be improved more. 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. % Is used as the mixed slurry 131. Care must be taken for impurity contamination during the production of the square silica container 10, and each concentration of Li, Na, K in the porous silica plate 151 is 5 wt. It is preferable to prepare the mixed slurry 131 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 131 as described above. In order to contain the Al element in the mixed slurry 131, 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. It can be carried out. The amount of Al to be added is such that the Al concentration in the porous silica plate 151 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 131 by adding the Al element to the water before mixing before preparing the mixed slurry 131. Good.

  Further, the mixed slurry 131 may further include a dispersant (for example, polyacrylate), an antifoaming agent (for example, polyethylene glycol), a lubricant (for example, stearic acid, wax), a binder (for example, polyethylene, A suitable amount of polypropylene, a polystyrene acrylic resin, a paraffin wax, an epoxy resin, methyl cellulose, ethyl cellulose, or the like can be mixed.

(3) Homogenous mixing of slurry The mixed slurry 131 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 131 is 1.6 to 2.1 g / cm ^3, preferably 1.7 to 2.0 g / cm ³ , and the viscosity is 300 to 300 at a shear rate of 1 to 10 / sec. It is preferable to set it as 3000 mPa * sec.

(4) Vacuum degassing of slurry The mixed slurry 131 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 131 in this way, the mixed slurry 131 is introduced into the mold as shown in FIG.

  Next, as shown in (a-4) of FIG. 7, the mixed slurry is dehydrated and dried in a mold to produce a porous silica plate temporary molded body 141 (temporary molding step). Specifically, the mixed slurry 131 contained in the mold is put in a clean oven, heated from room temperature to 5 to 20 ° C./hour, and then held at 50 to 200 ° C. for 10 to 100 hours to remove moisture. Evaporate and dry (casting). As the mold at this time, a porous ceramic mold such as gypsum or a porous plastic mold can be used.

At this time, it is preferable to form at least one of a groove and a hole in one of both parallel planes of the temporary molded body 141. 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 the temporary molding 141 once, you may form a groove | channel or a hole after that. FIG. 5A and FIG. 5B schematically show the case where the grooves 31 are formed in the temporary molded body of the porous silica plate. FIGS. 6A and 6B schematically show the case where the conical hole 32 is formed in the temporary molded body of the porous silica plate.
Here, the side of the surface on which at least one of the groove and the hole is formed becomes a surface to be heated in the firing step described later.

  In this way, the porous silica plate body 151 is fabricated and then fired to form the porous silica plate body 151 (firing step). In the present invention, both porous silica plate bodies 151 are formed. Of the parallel planes, it is preferable that at least a part of the surface portion that becomes the inner surface when assembled as the silica container 10 contains a release accelerator that promotes release of the polycrystalline silicon ingot. The mold release accelerator is contained after applying the mold release accelerator to at least a part of the surface opposite to the surface to be heated in the firing process of both parallel planes of the temporary molded body 141 after the temporary molding process. It can also be performed by drying, and, as will be described later, after the firing step, the mold release accelerator is placed on the opposite side of the surface parallel to the surface heated in the firing step of both parallel planes of the porous silica plate 151. It can also be performed by applying a mold release accelerator to at least a part of the surface. A specific method of containing the mold release accelerator will be described later.

After the temporary forming step, as shown in FIG. 7A-5, the porous silica plate temporary formed body 141 is fired to form a porous silica plate 151 (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 both parallel planes of the temporary molded body 141 of the porous silica plate, and the bulk density of the surface portion on the heated side is larger than the bulk density of the surface portion on the opposite side. A high porous silica plate 151 is used.

In this firing step, for example, a firing furnace such as a one-way heating electric furnace as shown in FIG. 9 can be used.
The one-way heating electric furnace 401 shown in FIG. 9 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 A heat-resistant belt conveyor 441 for conveying a temporary molded body 141 made of a porous silica plate.

The firing of the porous silica plate temporary molded body 141 using this firing furnace is performed as follows. First, a porous silica plate temporary molded body 141 is placed on a heat-resistant belt conveyor 441 and conveyed into a 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 raises the temperature 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 141. Subsequently, the temperature is increased from 1000 ° C. to 1200 to 1500 ° C. at 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 141 and the second raw material powder are sintered. Such heating is performed from one direction of the temporary molded body 141 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.

  In addition, when at least one of the groove and the hole is formed in the porous silica plate temporary molded body 141 as described above, it is fired by heating from the side of the surface on which at least one of the groove and the hole is formed. . If it does in this way, it will become difficult to generate | occur | produce a warp, a curvature, and a crack in a porous silica board in a baking process.

  Thus, since the porous silica plate body preform 141 is continuously heated and fired from one direction, the fired surface (heater side surface) of the porous silica plate body 151 has a high bulk density. The opposite surface has a lower bulk density.

  After firing, the porous silica plate 151 is carried out of the furnace by the heat resistant belt conveyor 441 and cooled.

  As described above, the porous silica plate body 151 is manufactured. As described above, in the present invention, when the porous silica plate body 151 is assembled as the silica container 10 out of the two parallel planes of the porous silica plate body 151, the porous silica plate body 151 is manufactured. It is preferable that a release accelerator for promoting the release of the polycrystalline silicon ingot is contained in at least a part of the surface portion serving as the surface. 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 forming step, it is applied to at least a part of the surface opposite to the surface heated in the firing step among both parallel planes of the temporary formed body 141. The mold release accelerator is added to at least a part of the surface opposite to the surface to be heated in the firing step of both parallel planes of the temporary molded body 141 by adding a mold release accelerator. A specific method will be exemplified and described.

For example, in the case of alkaline earth metal elements such as recrystallized type Ca, Sr, Ba, etc., chlorides, nitrates, carbonates, acetates, etc., which are these element compounds that are dissolved in water or alcohol, are selected, and the temporary molded body 141 is selected. Applying and drying by spraying, airbrushing, rollering, or brushing, etc. on the opposite side of the plane parallel to the surface heated in the firing step. Can do. The temporary molded body 141 to which the release accelerator is added is fired at 1200 to 1500 ° C. in an O ₂ gas-containing atmosphere mainly containing an inert gas 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 for containing a mold release accelerator, after the firing step, the surface on the opposite side to the surface heated in the firing step among the two parallel planes of the porous silica plate 151 A method of applying a mold release accelerator to at least a part of this will be described.

Instead of, or in addition to, the method of adding the release accelerator by application after the temporary molding step, the release accelerator is used as a firing step in both parallel planes of the porous silica plate 151 after the firing step. The release accelerator can be contained by applying (coating) at least a part of the surface opposite to the surface heated in step (b). The surface on the opposite side to the surface heated in the firing step of both parallel planes of the porous silica plate 151 after firing the mixed solution of at least one compound of alkaline earth metal elements such as Ca, Sr, Ba, etc. A coating process is performed by applying and drying at least a part of the film 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 the sintering process, so that the porous silica plate 151 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) 2nd aspect The outline of another example (2nd aspect, a dry process) of the manufacturing method of the square silica container 10 which concerns on this invention was shown in FIG.

  First, as shown to (b-1) of FIG. 8, 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), the first raw material powder, the second raw material powder, and the mixed powder 231 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) Al element to at least one. Thereby, Al element can be contained in the porous silica plate 251. Thereby, as described above, the movement 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 251; Diffusion can be prevented and the heat distortion resistance 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 251 after manufacture 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. 8, 1st raw material powder, 2nd raw material powder, and an organic binder are mixed, and the mixed powder 231 is produced. The second raw material powder may be mixed in the state of granules as described above to obtain a mixed powder 231.

  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 231 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 251 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 251 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 251 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, an Al element may be added to the mixed powder 231 instead of or in addition to adding the Al element to at least one of the first raw material powder and the second raw material powder. In this case, it is possible to use a method in which the mixed powder 231 is immersed and impregnated in an Al compound solution soluble in water or alcohol, and then pulled up at a constant speed and dried. The amount of Al to be added is such that the Al concentration in the porous silica plate 251 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. 8, the mixed powder 231 is introduced into the mold and heated to 50 to 200 ° C. to melt the organic binder. A temporary molded body 241 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 231 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 231 in the mold is pressed (pressed) and adjusted to a predetermined pressure of 0.1 to 1 MPa, and the temperature of the mixed powder 231 is increased until it reaches a predetermined temperature of 50 to 200 ° C. Then, it is held to a certain degree of compaction until the binder is welded. Subsequently, it is allowed to cool to room temperature to obtain a raw material porous silica plate temporary molded body 241.

At this time, it is preferable to form at least one of a groove and a hole in one of both parallel planes of the temporary molded body 241 of the porous silica substrate. This groove or hole can be formed, for example, by configuring the shape of the mold itself to form a groove or hole. Alternatively, the temporary molded body 241 may be once produced and then a groove or a hole may be formed.
Here, the side of the surface on which at least one of the groove and the hole is formed becomes a surface to be heated in the firing step described later.

  In this way, the porous silica plate body 241 is prepared and then fired to form the porous silica plate body 251 (firing step). In the present invention, both of the porous silica plate bodies 251 are used. Of the parallel planes, it is preferable that at least a part of the surface portion that becomes the inner surface when assembled as the silica container 10 contains a release accelerator that promotes release of the polycrystalline silicon ingot. Even in this embodiment, the release accelerator is heated in the firing step of the two parallel planes of the temporary molded body 241 after the temporary forming step in the same manner as in the first aspect. It can also be performed by applying it to at least a part of the surface opposite to the surface to be dried and drying it. As will be described later, after the firing step, the mold release accelerator is applied in parallel to the porous silica plate 251. 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 the planes.

Next, as shown in (b-5) of FIG. 8, the porous silica plate temporary molded body 241 is 1200 to 1500 in an atmosphere containing an inert gas as a main component and O ₂ gas. At a temperature of ° C., the porous molded body 241 is heated and fired from one side of both parallel planes 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 251 is manufactured. As in the first embodiment, 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 the 251 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.

After the silicon 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 of the polycrystalline silicon ingot with the rectangular silica container can be suppressed by controlling the bulk density, the polycrystalline silicon ingot can be easily taken out and the breakage can be prevented.
Thereafter, the taken polycrystalline silicon ingot is sliced to a predetermined thickness 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. 7 (first embodiment), a porous silica plate was produced as follows, and a square 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. Thus, a mixed slurry 131 was obtained.

  Next, the mixed slurry 131 was introduced into a plaster mold.

  Next, the mixed slurry 131 introduced into the mold was held at 100 ° C. for 10 hours in a clean oven, and then cooled to room temperature to prepare a parallel-plate-shaped porous silica plate temporary molding 141.

Next, the porous silica plate temporary molded body 141 was removed from the mold.
This porous silica plate temporary molded body 141 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 way, the porous silica plate body 151 was manufactured by firing the porous silica plate body temporary molded body 141.

  In addition, the dimension of the porous silica plate 151 was set to be 400 mm long × 400 mm wide × 15 mm thick.

  The peripheral portion of the parallel flat plate-like porous silica plate 151 manufactured 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 was applied to one entire surface portion of the temporary molded body 141 of the porous silica plate body, and unidirectional heating was performed using the surface opposite to this surface as a heating surface in the firing step.

(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 131.

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 131, and barium chloride is applied to the entire surface of one surface of the porous silica plate temporary molded body 141. Unidirectional heating was performed using the surface as the heating surface.

(Example 5)
In accordance with the method for producing a porous silica plate according to the present invention shown in FIG. 8 (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 231.

  Next, the mixed powder 231 introduced into the cylinder of the injection molding machine was injection-molded while being held at 100 ° C. in the cylinder to produce a temporary molded body 241 of a parallel flat plate-like porous silica plate.

  Next, this porous silica plate temporary molded body 141 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 way, the porous silica plate body 151 was manufactured by firing the porous silica plate body temporary molded body 141.

  In addition, the dimension of the porous silica plate 151 was set to be 400 mm long × 400 mm wide × 15 mm thick.

  The peripheral part of the parallel flat plate-like porous silica plate 151 manufactured in this way 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 one entire surface portion of the temporary molded body 241 of the porous silica plate body, and unidirectional heating was performed using the surface opposite to this 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 231.

(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 231, and barium chloride is applied to the entire surface of one surface of the temporary molded body 241 of the porous silica plate, and the opposite side to this surface is applied in the firing step. Unidirectional heating was performed using the surface 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 1.9 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 rectangular mold is kept in a clean oven at 150 ° C. for 5 hours, and then cooled to room temperature to produce a rectangular (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 porous silica substrate, and was subjected to infrared diffuse reflection spectrophotometry. 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)

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 concentrations 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.

  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 wall part, 12 ... Side wall part inner surface, 13 ... Side wall part outer surface,
21 ... Bottom part, 22 ... Bottom inner surface, 23 ... Bottom outer surface,
31 ... groove, 32 ... hole,
80 ... susceptor,
131 ... Mixed slurry, 141 ... Temporary molded article, 151 ... Porous silica plate,
231 ... Mixed powder, 241 ... Temporary molding, 251 ... Porous silica plate,
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 (21)

A rectangular silica container for producing a polycrystalline silicon ingot by solidifying after containing a silicon melt,
It is configured by combining parallel flat plate-like porous silica plates made of porous silica,
A square silica container for producing a polycrystalline silicon ingot, wherein the bulk density of the surface parts of both parallel planes of the porous silica plate is higher in the outer surface part than in the inner surface part of the square silica container. The bulk density of the porous silica plate is 1.60 to 2.20 g / cm ³ ,
The bulk density of the surface portions of both parallel planes of the porous silica plate 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. 2. A rectangular silica container for producing a polycrystalline silicon ingot according to 1.   The square silica container has an Al concentration of 5 to 500 wt. ppm, and the OH group concentration is 5 to 500 wt. The rectangular silica container for producing a polycrystalline silicon ingot according to claim 1 or 2, wherein the square silica container is ppm.   4. 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 square silica container for producing a polycrystalline silicon ingot according to any one of the above.   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 4, which is added at a concentration of ppm. 5. The release agent according to claim 4, 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. 5. A rectangular silica container for producing a polycrystalline silicon ingot according to 5.   The concentration of each of Li, Na, and K contained in the square silica container is 5 wt. ppm or less, and each concentration of Ti, Cr, Fe, Ni, Cu, Zn, Au is 0.1 wt. The rectangular silica container for producing a polycrystalline silicon ingot according to any one of claims 1 to 6, wherein the square silica container is not more than ppm. 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 porous silica plate, wherein the surface portions of both parallel planes have a difference of not less than 0.05 g / cm ^{3 in} terms of bulk density from each surface to a depth of 3 mm.   The porous silica plate has an Al concentration of 5 to 500 wt. ppm, and the OH group concentration is 5 to 500 wt. It is ppm, The porous silica plate body of Claim 8 characterized by the above-mentioned.   10. The porous material according to claim 8, wherein a release accelerator for promoting release of polycrystalline silicon is contained in a part of at least one surface portion of both parallel planes. 11. Silica plate.   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.   Each concentration of Li, Na, K contained in the porous silica plate is 5 wt. ppm or less, and each concentration of Ti, Cr, Fe, Ni, Cu, Zn, Au is 0.1 wt. The porous silica plate according to any one of claims 8 to 12, wherein the porous silica plate is at most ppm. 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 porous silica plate temporary molded body in a parallel plate shape; and
The temporary molded body is heated and fired from one side of both parallel planes of the temporary molded body at a temperature of 1200 to 1500 ° C. in an atmosphere containing an inert gas as a main component and O ₂ gas. And a baking step for forming a porous silica plate having a bulk density of the surface portion on the heated side higher than a bulk density of the surface portion on the opposite side, and a method for producing 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;
Temporary molding step of introducing the mixed powder into a mold and heating it to 50 to 200 ° C. to melt the organic binder, thereby forming a temporary molded body of the porous silica plate into a parallel plate,
The temporary molded body is heated and fired from one side of both parallel planes of the temporary molded body at a temperature of 1200 to 1500 ° C. in an atmosphere containing an inert gas as a main component and O ₂ gas. And a baking step for forming a porous silica plate having a bulk density of the surface portion on the heated side higher than a bulk density of the surface portion on the opposite side, and a method for producing a porous silica plate, .   Before the firing step, at least one of a groove and a hole is formed in one of both parallel planes of the temporary molded body, and in the firing step, at least one of the groove and the hole is formed. The method for producing a porous silica plate according to claim 14, wherein the method is fired by heating.   17. The Al element is added to at least one of the first raw material powder, the second raw material powder, the mixed slurry, and the mixed powder. 17. Method for producing a porous silica plate.   At least one of the surfaces on the opposite side of the surface to be heated in the firing step among the two parallel planes of the temporary molded body is added at least after the temporary molding step to promote the release of the polycrystalline silicon. The porous material according to any one of claims 14 to 17, wherein the release accelerator is contained by adding the release accelerator by applying to a part and drying. A method for producing a silica plate.   At least after the firing step, a release accelerator that promotes the release of polycrystalline silicon is included in at least one of the parallel planes of the porous silica plate opposite to the surface heated in the firing step. The method for producing a porous silica plate according to any one of claims 14 to 18, wherein the release accelerator is contained by applying the release accelerator to a part thereof. .   The method for producing a porous silica plate according to claim 18 or 19, 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 21. The method for producing a porous silica plate according to any one of claims 14 to 20, wherein the mixed slurry or the mixed powder is prepared using a granule.

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