JP5604366B2 - Square silica composite container for manufacturing silicon ingot, porous silica composite plate and method for manufacturing the same - Google Patents

Description

  The present invention relates to a rectangular (rectangular tank) container for producing a polycrystalline silicon ingot by solidifying a silicon melt.

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

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

  In silica rectangular containers by integral molding and firing of silica raw material powders, especially large-sized silica rectangular containers with one side of the square container exceeding 30 cm, have poor dimensional accuracy due to large thermal deformation and thermal shrinkage in the molding and firing processes. Only obtained. In addition, there is a problem that costs are increased because the molding process and the firing process are batch-type. (For example, see Patent Documents 1-6.)

In rectangular containers made from materials other than silica, such as silicon carbide SiC, silicon nitride Si ₃ N ₄ , silicon oxynitride SiO _x N _y (x> 0, y> 0), carbon C, etc., Li , Na, K, and other alkali metal elements, Ti, Cr, Fe, Ni, Cu, Zn, Zr, Au, Ag, Au, and other transition metal elements are contained in a high concentration. When the metal is melted and solidified, there is a problem that these impurity metal elements move and diffuse to silicon metal (silicon melt and silicon ingot) and contaminate the silicon metal. (For example, refer to Patent Documents 3 and 7-12.)

JP 2002-362932 A JP 2004-131380 A JP 2009-269992 A JP 2010-52996 A JP 2010-83699 A JP 2010-280529 A JP 2005-125380 A JP 2009-274905 A JP 2009-215137 A JP 2010-77003 A JP 2010-77005 A JP 2010-208866 A

  The present invention has been made in view of the above problems, and provides a rectangular container for producing a silicon ingot that suppresses impurity contamination of a silicon melt and a polycrystalline silicon ingot, has excellent releasability, and is extremely low cost. The purpose is to do.

  Another object of the present invention is to provide a porous silica composite plate constituting such a square silica composite container for manufacturing a silicon ingot and a method for manufacturing the same.

  The present invention has been made to solve the above problems, and is a container for solidifying a silicon melt to produce a polycrystalline silicon ingot, wherein at least a surface layer portion is made of silica glass and an inner portion is silica. There is provided a rectangular silica composite container for producing a silicon ingot, which is a rectangular container configured by combining parallel plate-like porous silica composite plates made of a heat-resistant substance having a higher melting point.

  Such a rectangular silica composite container increases the amount of bubbles contained in the internal part made of a heat-resistant substance of the porous silica composite plate constituting the container (that is, increases the porosity), and the porous silica composite container The strength of the inner portion of the silica composite plate can be reduced, and as a result, the polycrystalline silicon ingot can be easily removed from the rectangular silica composite container containing the manufactured polycrystalline silicon ingot without damaging it. be able to. Further, since silica glass on the inner surface of the container contacts the manufactured silicon, impurity contamination from the container to the manufactured silicon can be suppressed. In addition, since such a rectangular silica composite container is a combination of plates, the manufacturing cost of the container can be remarkably reduced as compared with a single body, and the dimensional accuracy can be improved even with a large rectangular container.

  In this case, it is preferable that the porous silica composite plate is made of silica glass at least from the surfaces of both parallel planes to a depth of 1 mm, and at least 3 mm in thickness of the inner part is made of the heat-resistant substance. .

  If it is the square silica composite container comprised from such a porous silica composite board, mold release property can be improved more effectively.

  The heat-resistant substance is preferably one or more of a single element substance having a melting point of 2000 ° C. or higher, an oxide, a composite oxide, a nitride, an acid nitride, a carbide, and a boride.

  With such a heat-resistant substance, the difference in melting point from silica is sufficient, and the porosity of the inner part of the porous silica composite plate can be increased more effectively.

In addition, the heat-resistant substance is C, Al ₂ O ₃ , BeO, MgO, ThO ₂ , ZrO ₂ , CaZrO ₃ , MgAl ₂ O ₄ , YAlO ₃ , SiON, AlN, BN, Si ₃ N ₄ , TiN, SiC, It is preferably at least one of TiC, WC, ZrC, TiB ₂ and ZrB ₂ .

  By using these materials as the heat-resistant substance, the porosity of the inner part of the porous silica composite plate can be increased more effectively.

  The Al concentration in the silica glass of the surface layer portion of the porous silica composite plate is 3 to 300 wt. ppm, and the OH group concentration is 5 to 500 wt. Preference is given to ppm.

  With a square silica composite container composed of a porous silica composite plate containing Al and OH groups in the surface portion silica glass at such a concentration, even when using an inexpensive raw material, the purity is somewhat low. Diffusion of impurities into the contained silicon can be sufficiently prevented.

  Moreover, it is preferable that a release accelerator for promoting release of the polycrystalline silicon ingot is contained in the silica glass of the surface layer portion of the porous silica composite plate.

  Thus, if the release accelerator is contained in the silica glass of the surface layer portion of the porous silica composite plate, the release property can be further improved.

  The present invention also relates to a parallel flat plate-like porous silica composite plate having at least a surface layer portion made of silica glass for constituting a container for producing a polycrystalline silicon ingot by solidifying a silicon melt. The porous silica is characterized in that a portion from the surface of both parallel planes to a depth of at least 1 mm is made of silica glass, and an inner portion is made of a heat-resistant material having a melting point higher than that of silica. A composite plate is provided.

  Such porous silica composite plates can be combined to form a square silica composite container. The rectangular silica composite container is sufficiently prevented from contaminating impurities contained in silicon, has excellent releasability, and can be a very low-cost rectangular silica composite container for producing a silicon ingot.

In this case, the heat-resistant substance is C, Al ₂ O ₃ , BeO, MgO, ThO ₂ , ZrO ₂ , CaZrO ₃ , MgAl ₂ O ₄ , YAlO ₃ , SiON, AlN, BN, Si ₃ N ₄ , TiN, SiC , TiC, WC, ZrC, TiB ₂ , and ZrB ₂ are preferably used.

  By using these materials as heat-resistant substances, the porosity of the inner part of the porous silica composite plate can be increased more effectively.

  Moreover, Al concentration in the silica glass of the said surface layer part is 3-300 wt. ppm, and the OH group concentration is 5 to 500 wt. Preference is given to ppm.

  If it is a porous silica composite plate containing Al and OH groups at such a concentration, even if a low-purity, inexpensive raw material is used, a combination of the porous silica composite plate and In this case, it is possible to sufficiently prevent the diffusion of impurities into the accommodated silicon.

  Moreover, it is preferable that the silica glass of the said surface layer part contains the mold release accelerator which accelerates | stimulates the mold release of the said polycrystal silicon ingot.

  Thus, if the release accelerator is contained in the silica glass of the surface layer portion of the porous silica composite plate, the release property can be further improved.

  Further, each concentration of Li, Na, K in the silica glass of the surface layer portion is 30 wt. ppm, and each concentration of Ti, Cr, Fe, Ni, Cu, Zn, Zr, Mo, Ag, Au is 3 wt. It is preferably at most ppm.

  If the impurity concentration in the silica glass of the surface layer portion of the silica glass of the porous silica composite plate is such a concentration, to the manufactured silicon when the porous silica composite plate is combined into a square silica composite container Impurity contamination from the container can be more effectively suppressed.

  In addition, the present invention produces a parallel flat plate-like porous silica composite plate having at least a surface layer portion made of silica glass for constituting a rectangular container for producing a polycrystalline silicon ingot by solidifying a silicon melt. A method of producing at least a silica powder as a first raw material powder, a step of producing a powder comprising a heat-resistant substance having a melting point higher than that of silica as a second raw material powder, and an electric heating furnace Replacing the inside of the melting vessel disposed therein with an inert gas atmosphere containing any one or more of nitrogen, neon, argon, and krypton, while maintaining the inside of the melting vessel in the inert gas atmosphere, The supply position of the raw material powder is supplied as the center side in the melting container, and the first raw material powder is supplied outside the supply position of the second raw material powder in the melting container. And melting and softening the first raw material powder by heating the temperature of the melting container to 1700 ° C. or higher while maintaining the pressure of the inert gas atmosphere in the melting container at atmospheric pressure or higher. A step of forming silica glass, and a step of continuously drawing out a composite of the fused and softened silica glass and the heat-resistant substance from the lower part of the melting container into a parallel plate shape through a shape forming tool; Cutting the composite of the drawn and melted and softened silica glass and the heat-resistant substance with a predetermined size and grinding to produce a parallel flat plate-like porous silica composite plate. The manufacturing method of the porous silica composite board characterized by including is provided.

  According to such a production method, it is possible to produce a parallel flat plate-like porous silica composite plate made of a heat-resistant substance having at least a surface layer portion made of silica glass and an inner portion having a melting point higher than that of silica. Such porous silica composite plates can be combined to form a square silica composite container. The rectangular silica composite container is sufficiently prevented from contaminating impurities contained in silicon, has excellent releasability, and can be a very low-cost rectangular silica composite container for producing a silicon ingot.

  In this case, the first raw material powder has a particle size of 5 to 1000 μm and a silica purity of 99.99 wt. It is preferable that it is the silica powder which is% or more.

  If the first raw material powder is such a silica powder, the porous silica glass constituting the surface layer portion of the porous silica composite plate can be formed with sufficient purity.

The second raw material powder has a particle size of 5 to 1000 μm, and C, Al ₂ O ₃ , BeO, MgO, ThO ₂ , ZrO ₂ , CaZrO ₃ , MgAl ₂ O ₄ , YAlO ₃ , SiON, AlN , BN, Si ₃ N ₄ , TiN, SiC, TiC, WC, ZrC, TiB ₂ , and ZrB ₂ are preferable.

  If the second raw material powder is such, the porosity of the inner part of the porous silica composite plate can be increased more effectively.

  Moreover, it is preferable to add a mold release accelerator for promoting mold release of the polycrystalline silicon ingot to the first raw material powder.

  Moreover, it is preferable to apply a mold release accelerator for promoting mold release of the polycrystalline silicon ingot to the surface of the produced porous silica composite plate.

  By these methods, a release accelerator can be contained in the silica glass of the surface layer portion of the porous silica composite plate, and as a result, the release property of silicon can be further improved.

  The rectangular silica composite container for manufacturing a silicon ingot according to the present invention can be easily removed from the rectangular silica composite container containing the manufactured polycrystalline silicon ingot without damaging the polycrystalline silicon ingot. Impurity contamination from the container to the silicon can be suppressed. In addition, since such a rectangular silica composite container is a combination of plates, the manufacturing cost of the container can be remarkably reduced as compared with a single body, and the dimensional accuracy can be improved even with a large rectangular container.

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

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

It is a schematic sectional drawing which shows typically the structure of the porous silica composite board which concerns on this invention. It is a figure which shows an example of the square silica composite container which concerns on this invention, (a) is a schematic top view, (b) is a schematic sectional drawing. It is a figure which shows another example of the square silica composite container which concerns on this invention, (a) is a schematic top view, (b) is a schematic sectional drawing. It is a figure which shows another example of the square silica composite container which concerns on this invention, (a) is a schematic top view, (b) is a schematic sectional drawing. It is a figure which shows another example of the square silica composite container which concerns on this invention, (a) is a schematic top view, (b) is a schematic sectional drawing. It is a figure which shows the example of installation of the square silica composite container which concerns on this invention, (a) is a schematic top view, (b) is a schematic sectional drawing. It is a schematic sectional drawing which shows an example of the apparatus used for manufacture of the porous silica composite board which concerns on this invention. It is a schematic sectional drawing which shows an example of the apparatus used for manufacture of the porous silica composite board which concerns on this invention from another angle.

  In the present invention, for example, a rectangular silica composite container for producing a 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 composite container having excellent releasability (improvement of releasability). In other words, after the polycrystalline silicon ingot is manufactured by solidification of the silicon melt contained in the rectangular silica composite container, the polycrystalline silicon ingot is easily removed from the rectangular silica composite container.

  Secondly, a rectangular silica composite container capable of preventing impurity contamination. This means that various impurity metal elements contained in the rectangular silica composite 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.

  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 rectangular silica composite container, the cost of parts can be reduced and an inexpensive silica raw material can be used, and the silica raw material can be continuously melted and molded in a relatively short time. To reduce energy consumption.

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

  FIG. 2 shows an outline of an example of a square silica composite container for producing a silicon ingot according to the present invention. As illustrated in FIGS. 2A and 2B, the shape of the silica container 10 according to the present invention is a square shape (also called a square tank shape or a box shape). The square silica composite container 10 includes a side part (side wall part) 11 and a bottom part 21. Moreover, the square silica composite container 10 according to the present invention is configured by combining parallel flat plate-like porous silica composite plates. Specifically, as shown in FIGS. 2 (a) and 2 (b), the four side portions 11 and the one bottom portion 21 are each composed of a parallel flat plate-like porous silica composite plate, The rectangular silica composite container 10 is configured by combining these.

  The method for combining the porous silica composite plates constituting the rectangular silica composite container 10 according to the present invention is not particularly limited, but it is preferable that the porous silica composite plates do not fall inward when combined. For example, as shown in FIG. 2, each combination portion of the parallel flat plate-like porous silica composite plate body can be combined with the inclined surfaces facing each other (grinding (ground glass bonding) type). .

The rectangular silica composite container 10 according to the present invention is further made of a heat-resistant substance having at least a surface layer portion made of silica glass and an inner portion having a melting point higher than that of silica. is there. FIG. 1 is a schematic cross-sectional view schematically showing the structure of a porous silica composite plate according to the present invention. In the porous silica composite plate 100, the surface layer portions 111 and 112 are made of silica glass, and the inner portion 113 is a porous material made of a heat resistant material having a melting point higher than that of silica. That is, the portions from the surfaces 101 and 102 of both parallel planes to a predetermined depth (T ₁ , T ₂ ) are made of silica glass, and the predetermined thickness (T ₃ ) of the inner portion 113 is a refractory material. Consists of. Preferably, T ₁ and T ₂ are each 1 mm or more, and T ₃ is 3 mm or more.

The heat-resistant substance constituting the inner portion 113 of the porous silica composite plate body 100 is any one of a single element substance, an oxide, a composite oxide, a nitride, an acid nitride, a carbide, and a boride having a melting point of 2000 ° C. or higher. One or more are preferable. Specifically, this heat-resistant substance is C, Al ₂ O ₃ , BeO, MgO, ThO ₂ , ZrO ₂ , CaZrO ₃ , MgAl ₂ O ₄ , YAlO ₃ , SiON, AlN, BN, Si ₃ N ₄ , TiN. , SiC, TiC, WC, ZrC, TiB ₂ , and ZrB ₂ . If the inner portion 113 is made of such a heat-resistant substance, the difference in melting point from silica is sufficient, and the porosity of the inner portion of the porous silica composite plate can be increased more effectively.

  3 to 5 show an outline of another example of the square silica composite container 10 according to the present invention.

  In FIG. 3, the outline of another example of the square silica composite container for silicon ingot manufacture which concerns on this invention was shown. As shown in FIG. 3 (a) and FIG. 3 (b), each combination portion of the parallel flat plate-like porous silica composite plate can be formed so as to be fitable, and can be combined (fit type).

  In addition, each side and bottom of the square are not limited to being assembled with one porous silica composite plate, but each side with a plurality of porous silica composite plates as shown in FIGS. And the bottom can be configured. In this case, the rectangular container is composed of a porous silica composite plate having eight side portions 11a and 11b and two bottom portions 21a and 21b each having a parallel plate shape.

  As described above, the porous silica composite plate according to the present invention has a parallel plate shape. However, in the description of the present invention, the parallel plate shape is two flat surfaces having a large area among the surfaces of the plate shape. It means that the surface is substantially parallel. However, as illustrated in FIGS. 2 to 5, a shape for combination may be formed in the peripheral portion of the flat plate shape.

FIG. 6 shows an installation example of the square silica composite container 10 according to the present invention. In FIG. 6, an example in which the square silica composite container 10 is configured by a combination of the combination types as illustrated in FIG. 2 is shown as a representative, but other combinations, for example, configurations as illustrated in FIGS. Also good.
As shown in FIG. 6, the porous silica composite plate constituting the square silica composite container 10 can be fixed by a susceptor 80 made of carbon or the like.

  Thus, the rectangular silica composite container 10 according to the present invention, which is a container for solidifying a silicon melt to produce a rectangular polycrystalline silicon ingot, is configured by combining porous silica composite plates. Yes. Therefore, the manufacturing cost can be significantly reduced as compared with the case where the entire container is manufactured integrally. In addition, in the case where the entire container is manufactured integrally, only thermal deformation and thermal shrinkage in the molding process and baking process are large, so that only those with poor dimensional accuracy can be obtained. In the present invention, for example, the dimension of one side is 50 cm. Even if it is a large-sized square container exceeding the above, the dimensional accuracy can be improved.

  Moreover, from the square silica composite container according to the present invention, a polycrystalline silicon ingot can be produced as a square. If the manufactured polycrystalline silicon ingot is rectangular, this can be sliced to obtain a rectangular polycrystalline silicon wafer, compared to a case where a wafer obtained by slicing a cylindrical polycrystalline silicon ingot is used as a solar cell. Therefore, the light receiving area is not wasted, which is very suitable.

  Further, as described above, the present invention provides a porous silica composite plate having at least a surface layer portion made of silica glass and an inner portion made of a heat resistant material having a melting point higher than that of silica. The strength of the inner part of the silica composite plate is set low. In the case of producing a polycrystalline silicon ingot by solidifying the silicon melt in such a square silica composite container, the strength of the container itself is appropriately maintained. It becomes possible to manufacture a polycrystalline silicon ingot having a predetermined shape.

  On the other hand, when the polycrystalline silicon ingot is peeled off from the container, the strength of the inner part of the porous silica composite plate is weak, and the surface part of the polycrystalline silicon ingot is easily lost without causing microcracks on the surface. The polycrystalline silicon ingot can be taken out. In addition, since the strength of the inner portion of the porous silica composite plate is weak, if necessary, the rectangular silica composite container can be easily broken and the polycrystalline silicon ingot can be removed from the container.

  Further, since silica glass on the inner surface of the container contacts the manufactured silicon, impurity contamination from the container to the manufactured silicon can be suppressed.

  Further, in the rectangular silica composite container of the present invention, in order to further improve the release property of the polycrystalline silicon ingot, the release of the polycrystalline silicon ingot is promoted to the silica glass of the surface layer portion of the porous silica composite plate. It is preferable that an accelerator is contained.

  Examples of the release accelerator that can be used in the present invention include alkaline earth metal elements such as calcium Ca, strontium Sr, and barium Ba, and compounds such as sulfates, chlorides, carbonates, halides, and the like. It can be contained in the square silica composite container 10 in the form.

  Manufacturing by containing Ca, Sr, and Ba in the inner surface portion of the square silica composite container 10 so that the silicon melt is accommodated in the square silica composite container 10 and gradually cooled and solidified to obtain a polycrystalline silicon ingot. In the process, the inner surface layer of the square silica composite container 10 can be transferred from silica glass to a microcrystalline phase such as cristobalite or opal, thereby generating microcracks. As a result, since the fusion between the cooled and solidified polycrystalline silicon ingot and the inner surface of the rectangular silica composite container 10 can be reduced, the polycrystalline silicon ingot can be removed when removing the polycrystalline silicon ingot from the rectangular silica composite container 10. It is possible to remove the silicon ingot without damaging the surface or forming irregularities or progressive cracks on the surface portion of the polycrystalline silicon ingot.

  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 used in the present invention because it has less diffusion contamination into the polycrystalline silicon ingot.

  Of the inner surface portion of the square silica composite container 10, the range in which the release accelerator is contained may be at least a part of the inner surface portion of the square silica composite container 10. The entire inner surface portion up to a height at which the melt is accommodated and solidified is more preferable, and the entire inner surface portion of the square silica composite container 10 is further preferable.

  Examples of the method for containing the release accelerator in the inner surface portion of the square silica composite container include a method by coating (coating) the surface of the porous silica composite plate constituting the square silica composite container, and a porous silica composite plate. There is a method of adding (doping) the raw material powder during body production. From the viewpoint of cost, a method of applying an aqueous solution such as barium sulfate or barium chloride to the inner surface of the square silica composite container and drying it is effective at low cost.

As the coating concentration of the mold release accelerator, when an alkaline earth metal element such as Ca, Sr or Ba is used as the mold release accelerator, the total value of alkaline earth metal elements such as Ca, Sr or Ba is 50 to 50. It is preferably set to 5000 [mu] g / cm ² (inner surface 1 cm ² per 50~5000μg prismatic silica composite container), and even more preferably from 100-1000 / cm ^2.

  The square silica composite container 10 has an Al concentration (Al element concentration) of 3 to 300 wt. ppm, and the OH group concentration is 5 to 500 wt. Preference is given to ppm. In order to prevent impurity contamination, it is preferable that the square silica composite container 10 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 20 to 200 wt. More preferably, it is ppm.

  When these Al and OH groups reduce the carrier lifetime of the impurity metal element in the porous silica composite plate, particularly polycrystalline silicon under light irradiation, or when the polycrystalline silicon ingot is used as a solar cell material, Migration and diffusion in silica of alkali metal elements such as Li, Na, K, etc. and transition metal elements such as Ti, Cr, Fe, Ni, Cu, Zn, Zr, Mo, Ag, Au, which are considered to reduce the conversion efficiency To prevent. 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.

The Al concentration is 3 wt. If it is ppm or more, a sufficient impurity contamination preventing effect is recognized. On the other hand, the Al concentration is 300 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 composite plate at a high temperature will not be too low. 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, the inclusion of a high concentration of OH groups is considered to facilitate the deformation of the porous silica composite 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 glass located on the surface layer side of the porous silica composite plate constituting the square silica composite container 10 is SiO ₂ 99.9 to 99.999 wt. %, It is possible to produce a rectangular silica composite 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 each concentration of Li, Na, and K is 30 wt. ppm, and each concentration of Ti, Cr, Fe, Ni, Cu, Zn, Zr, Mo, Ag, Au is 3 wt. When the content is less than or equal to ppm, by incorporating an appropriate amount of Al and OH groups at the same time when producing a porous silica composite plate, the rectangular silica composite container of the present invention can sufficiently prevent process contamination of the polycrystalline silicon ingot. And can be manufactured. In this way, if the polycrystalline silicon ingot is sufficiently prevented from being contaminated with a process, when a solar power generation device (solar cell) is manufactured, its photoelectric conversion efficiency can be significantly increased.

  A method for producing the porous silica composite plate as described above will be described with reference to the drawings.

(1) Preparation and preparation of raw material powder First, silica powder and heat-resistant substance powder are prepared as raw material powder.

  Silica powder is produced as the first raw material powder. The first raw material powder has a particle size of 5 to 1000 μm and a silica purity of 99.99 wt. The silica powder is preferably at least%. In addition, this particle size range is 99 wt.% In the particle size range of 5 to 1000 μm in the silica powder of the first raw material powder. % Of silica powder is included.

  High-purity silica raw material powder (high-purity quartz powder, high-purity natural quartz powder, ultra-high-purity synthetic silica glass powder such as silica purity of 99.9999% or more) It is not always necessary to use it. In the present invention, as described above, for example, the silica purity is 99.99 wt. % Or more is sufficient, and it is preferable to use silica raw material powder having relatively low purity.

  From the viewpoint of reducing impurities, the silica purity of the first raw material powder is 99.99 wt. % Or more is more preferable. In particular, each concentration of Li, Na, K is 30 wt. ppm, and each concentration of Ti, Cr, Fe, Ni, Cu, Zn, Zr, Mo, Ag, Au is 3 wt. It is preferable to set it as ppm or less.

  As the first raw material powder, it is preferable to use low-cost crystalline natural quartz powder, but it is not necessarily limited to the case where only crystalline natural quartz powder is used. For example, crystalline natural quartz powder may be used as the main raw material (for example, 50% or more by weight), and amorphous silica powder (fused natural quartz glass powder, synthetic silica glass powder) or the like may be mixed to obtain the raw material powder. Moreover, the particle size of the silica raw material powder is preferably a raw material powder having a relatively large particle size of 5 to 1000 μm as described above, but is not necessarily limited to the case of using only that. For example, a raw material powder having a particle size of 5 to 1000 μm mixed with a synthetic silica glass powder having a particle size of about 0.1 to 5 μm, which is highly active, or a higher type Silica powder may be mixed to make raw material powder.

  The production of the first raw material powder can be produced, for example, by crushing and sizing the quartzite lump 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 the 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, for example, 5 to 1000 μm 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 heated to 800 to 1100 ° C. For about 1 to 100 hours. However, in a 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 raw material powder obtained after the above steps is crystalline silica powder. From the viewpoint of cost, it is preferable to use such natural crystalline silica powder as the main raw material powder.

  Moreover, in order to improve the heat-resistant deformation property of the porous silica composite plate, it is preferable to contain Al (aluminum element) in the raw material powder. The method of adding Al to the raw material powder is not particularly limited. For example, an aluminum compound (aluminum nitrate, aluminum carbonate, aluminum chloride, etc.) is directly mixed with the raw material powder, or dissolved and mixed in water or alcohol, and then the raw material is mixed. Can be mixed into powder. As described above, the amount of Al to be added is such that the Al concentration of the silica glass in the surface layer portion of the porous silica composite plate to be produced is 3 to 300 wt. It is preferable to make it ppm, and 10 to 100 wt. It is more preferable to adjust to ppm.

  Furthermore, a mold release accelerator can be added (doping) to the surface layer portion of the porous silica composite plate to be produced by adding a mold release accelerator to the first raw material powder. When Ba is contained as a mold release accelerator, 100 to 2000 wt. It is preferable to add so that it may become the range of ppm.

As the second raw material powder, a powder made of a heat-resistant substance having a melting point higher than that of silica is prepared. Since this heat-resistant substance is a material for the internal portion of the porous silica composite plate, it is preferable to use a material having a melting point of 2000 ° C. or higher as described above. As the heat-resistant material of the raw material powder, single element material such as carbon C, alumina Al ₂ O ₃ , beryllia BeO, magnesia MgO, tria ThO ₂ , oxide such as zirconia ZrO ₂ , CaZrO ₃ , MgAl ₂ O ₄ , YAlO Composite oxides such as _3; oxynitrides such as SiON; nitrides such as AlN, BN, Si ₃ N ₄ and TiN; carbides such as SiC, TiC, WC and ZrC; borides such as TiB ₂ and ZrB ₂ A powder containing any one or more of them is preferable. The purity of the second raw material powder is 99 wt. % Or more, preferably 99.9 wt. % Or more is more preferable. With such purity, it is possible to sufficiently suppress the diffusion of impurities to the surface of the porous silica composite plate after production.

  The production of the second raw material powder can be performed by various known methods.

  The second raw material powder preferably has a particle size of 5 to 1000 μm, and more preferably 50 to 500 μm. The particle size range of the second raw material powder is 99 wt. It means that a powder composed of at least% heat-resistant substance is included.

(2) Electric furnace for heat treatment of raw material powder Next, an electric heating furnace in which the first raw material powder and the second raw material powder are charged and heat-treated will be described. A schematic cross-sectional view of the electric heating furnace is shown in FIGS. FIG. 8 is a cross-sectional view when viewed from a direction perpendicular to FIG. The electric heating furnace 300 needs to have a structure necessary for setting the supply positions of the first raw material powder and the second raw material powder to predetermined positions when the raw material powder is supplied into the melting container. There is.

  The electric heating furnace includes a first raw material powder supply port 303a, a second raw material powder supply port 303b, and a melting container for melting and softening both raw material powders through the supply ports. (A refractory metal crucible such as molybdenum or tungsten is preferable, but not limited thereto) 308, heating means for heating the melting vessel 308 (electric resistance heating, high frequency induction heating, etc. are available methods) 307, A heat insulating material 309 that blocks the release of heat generated by the heating means 307, and a shape forming tool having a substantially rectangular opening (a high melting point metal tool such as molybdenum or tungsten is preferable, but not limited thereto. 312, atmosphere gas supply in the melting container for adjusting the atmosphere gas in the melting container 308, the atmosphere outside the melting container 308 among the exhaust port 302 and the electric heating furnace. Melting vessel outside atmosphere gas supply for adjusting the air gas, from the exhaust port 305 and the like. 7 and 8, the first raw material powder supply port 303a is configured to surround the second raw material powder supply port 303b.

  A porous silica composite plate body take-out chamber 313 is arranged at the lower part of the electric heating furnace 300, and a porous silica composite plate take-out chamber atmosphere gas supply, an exhaust port 314, a porous silica composite plate body drawing roller 316, and the like. Has been placed. An opening / closing plate 322 at the bottom of the melting vessel that can move in the direction of the arrow 323 is provided below the shape forming tool 312.

  The basic structure and operating conditions of this electric heating furnace are shown in documents such as JP-A-1-320234, JP-A-2-296740, and JP-A-6-24785. However, conventional electric furnaces such as those described in these documents are designed to produce transparent rod-like or tubular silica glass that does not contain bubbles, and parallel that contains bubbles as in the present invention. This is different from an electric heating furnace structure for producing a flat porous silica composite plate. The first difference is the shape of the electric heating furnace and the shape of the melting vessel. The electric heating furnace 300 that can be used in the present invention preferably has a substantially cylindrical shape or a substantially elliptical column shape together with the melting vessel 308 in order to produce a parallel flat plate-like porous silica composite plate. The second difference is the type and pressure of the atmospheric gas when heating the silica raw material powder. In the present invention, an inert gas containing at least one of nitrogen, neon, argon, and krypton is set to a pressure of atmospheric pressure or higher in order to contain bubbles in the porous silica composite plate. These gases are inert gases having a larger molecular radius than hydrogen or helium. The third difference is the shape of the shape forming tool for forming the fused silica body. In the present invention, the shape of the opening of the shape forming tool 312 is substantially rectangular as described above in order to form the fused silica body into a parallel plate shape.

(3) Melting and forming of raw material powder The porous silica composite plate of the present invention is produced using the electric heating furnace shown in FIGS. Specifically, it is performed as follows.

(A) Atmospheric gas adjustment in melting container First, the inside of the melting container 308 disposed in the electric heating furnace 300 is replaced with an inert gas atmosphere containing at least one of nitrogen, neon, argon, and krypton. Nitrogen gas is 80 vol. % Or more is preferable. In order to extend the life of the container under high temperature, hydrogen gas is added in an amount of 1 to 4 vol. % May be used in combination.

(B) Atmospheric gas adjustment in the electric heating furnace (outside of the melting vessel) In the electric heating furnace, the outside of the melting vessel 308 is also preferably replaced with an inert gas such as nitrogen, neon, argon, krypton, etc. . Nitrogen gas is 80 vol. % Or more is preferable. In order to extend the life of the melting vessel 308 and the heating means 307 at a high temperature, hydrogen gas is added at 1 to 4 vol. % May be used in combination.

(C) Supplying the first raw material powder and the second raw material powder to the melting container in the electric heating furnace while maintaining the inside of the melting container 308 in the above inert gas atmosphere, the first raw material powder and the second raw material Powder is fed into the melting vessel 308.
At this time, the supply position of the second raw material powder 306b is supplied as the center side in the melting container 308, and the first raw material powder 306a is placed outside the supply position of the second raw material powder 306b in the melting container 308. Supply. Such raw material powder is supplied from the first raw material powder supply port 303a and the second raw material powder supply port 303b arranged in the upper part of the electric heating furnace 300 shown in FIGS. It can be performed by supplying the powder 306a and the second raw material powder 306b, respectively.

(D) Melting and softening by heating to raw material powder Next, the temperature of the melting vessel 308 is heated to 1700 ° C. or higher while maintaining the pressure of the inert gas atmosphere in the melting vessel 308 at atmospheric pressure or higher. The raw material powder 306a is melted. Thereby, the first raw material powder becomes a fused silica glass body 321a. On the other hand, the second raw material powder 306b has a higher melting point than the first raw material powder 306a made of silica, and in particular, has a melting point of 2000 ° C. or higher. Therefore, the second raw material powder 306b is hardly softened and hardly sintered. Therefore, the heat-resistant substance 321b having a high degree of shape retention is obtained from the raw material powder. However, depending on the type of heat-resistant substance (for example, Si ₃ N ₄ which is a heat-resistant substance having a relatively low melting point), it is relatively soft.

  By using a powder made of a heat-resistant substance having a higher melting point than silica as the second raw material powder as described above, the degree of sintering of the second raw material powder in this heating step can be reduced, The amount of bubbles contained in the inner portion of the porous silica composite plate after production can be increased (that is, the porosity can be increased). Therefore, the strength of the inner part of the manufactured porous silica composite plate can be set low.

  Further, as described above, when the first raw material powder contains a mold release accelerator, when the first raw material powder 306a is melted and softened in this step, the peripheral silica glass body in the melting vessel 308 is used. 321a contains a lot of mold release accelerator.

(E) Molding of melted and softened porous silica composite plate Next, a composite of melted and softened silica glass 321a and heat-resistant substance 321b is formed into a parallel plate through the shape forming tool 312 from the lower part of the melting vessel 308. And continuously drawn out (in the direction of arrow 317).
As described above, the shape forming tool 312 and the opening / closing plate 322 for forming a composite of the silica glass 321a and the heat-resistant material 321b are arranged at the bottom of the melting vessel 308. The shape forming tool 312 is in close contact with the plug. When the raw material powder is sufficiently heated and becomes a composite of the softened silica glass and the heat-resistant substance, the opening / closing plate 322 is moved in the lateral direction. At this time, by controlling the amount of movement of the opening / closing plate 322 in the lateral direction, the gap size of the shape forming tool 312 and the gas pressure in the melting vessel 308, the parallel-plate-shaped porous silica composite plate 315 having a predetermined size is formed. It can be taken out. The dimensional accuracy of the porous silica composite plate 315 controls the temperature of the melting vessel 308, the atmospheric gas pressure, the position adjustment of the opening / closing plate 322, the gap size of the shape forming tool 312, the drawing speed of the porous silica composite plate 315, and the like. It can be increased by doing. Further, the bulk density (g / cm ³ ) of the porous silica composite plate 315 is determined based on the average particle size, particle size range and particle size distribution setting of the first raw material powder and the second raw material powder, It can be controlled to a predetermined value by adjusting the gas type, gas pressure and the like.

(F) Finishing of porous silica composite plate and application of mold release accelerator Parallel plate-like porous silica composite plate 315 continuously produced from the lower part of the electric heating furnace has a predetermined length. Disconnect when it reaches. Next, if necessary, the end of the porous silica composite plate is cut, ground, and polished to obtain a porous silica composite plate having a shape and size that can be used for an assembled square silica composite container for producing a silicon ingot. .

  By applying (coating) to at least a part of the surface of the porous silica composite plate thus obtained, a mold release accelerator can be contained. If the release accelerator is a water-soluble substance, an aqueous solution of the release accelerator can be contained on the surface of the porous silica composite plate by spray coating or the like and then dried, etc. If it is an insoluble substance, it can be contained by mixing fine particles of a release accelerator with a solvent, spray-coating the surface in the same manner, and drying.

For example, when an alkaline earth metal element such as Ca, Sr, or Ba is used as a mold release accelerator, at least a part of a mixed solution of at least one compound of Ca, Sr, and Ba is used as at least a part of the porous silica composite plate. The coating process is carried out by applying a spray method, an air brush method, or the like on the surface of the substrate and drying it. When only Ba is contained, the range of 200 to 4000 μg / cm ² is preferable when it is applied (coated) to the silica glass surface portion.

  In addition, when the release accelerator is contained in the surface portion of the porous silica composite plate body by the above-described application, it is preferably performed after combining the porous silica composite plate body to form a square silica composite container. .

  The OH group concentration contained in the porous silica composite plate can be adjusted by selecting the type of raw material powder, changing the raw material powder drying step, and the atmosphere, temperature, and time conditions of the melting step. Thereby, 5-500 wt. It is preferable to make it contain by the density | concentration of ppm, 20-200 wt. More preferably, it is in the range of ppm.

  The parallel flat plate-like porous silica composite plates produced as described above are combined in a susceptor 80 made of carbon or the like, for example, as shown in FIG. When the whole is heated in such an arrangement, the silica glass portions of the porous silica composite plate are welded together, and the square silica composite container 10 can be easily integrated.

Furthermore, a method as described in JP-T-2008-511527 may be used alone or in an auxiliary manner. That is, an aqueous slurry containing amorphous SiO ₂ particles is placed at the joint of each porous silica composite plate, and the slurry is solidified by drying and heating, whereby the porous silica composite plates are bonded together. You may join.

  An example of a method for producing a polycrystalline silicon ingot using the rectangular silica composite container for producing a silicon ingot according to the present invention will be described.

  First, molten silicon as a raw material is put into a square silica composite container according to the present invention. Next, the molten silicon is heated and kept at a predetermined temperature.

  After the silicon melt is solidified by cooling to produce a polycrystalline silicon ingot, the polycrystalline silicon ingot is taken out from the square silica composite container. As described above, in the present invention, by configuring the inner part of the porous silica composite plate constituting the square silica composite container with a heat-resistant substance, the amount of contained bubbles is larger than the surface layer part (that is, Increasing the porosity), the strength of the inner part of the porous silica composite plate is set low. Thus, by setting the strength of the container to be moderately low and making it easy to break, the polycrystalline silicon ingot can be easily taken out, and damage to the polycrystalline silicon ingot can be prevented.

  Thereafter, the taken polycrystalline silicon ingot is sliced to a predetermined thickness and polished to obtain a polycrystalline silicon substrate.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to the examples.
Example 1
In accordance with the method for producing a porous silica composite plate according to the present invention, a porous silica composite plate was produced as follows, and a square silica composite container was further produced.

First, a first raw material powder was produced. 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 range of 50 to 500 μm and a silica purity of 99.99 wt. % And a total weight of 40 kg of silica powder (natural quartz powder). The average particle size (particle size value at 50% of the mass-based cumulative distribution, D ₅₀ ) of this first raw material powder was 220 μm. Next, aluminum nitrate was added to the first raw material powder as an aqueous solution and dried.

As the second raw material powder, a purity of 99.99 wt. % Alumina Al ₂ O ₃ powder was prepared. At this time, the particle size range was 30 to 300 μm, and the average particle size was 95 μm.

  Next, using this first raw material powder and second raw material powder, a porous silica composite plate was produced by an electric heating furnace (high frequency induction heating) shown in FIGS. The atmosphere gas was a nitrogen atmosphere containing 3% hydrogen (nitrogen 97%).

  The dimensions of the porous silica composite plate were 200 mm long x 400 mm wide x 10 mm thick.

  The peripheral portion of the parallel flat plate-like porous silica composite plate produced in this way was processed, and 10 pieces were combined to form a square silica composite container 10 as shown in FIG. The dimension of the square silica composite container after the combination was 400 × 400 × 400 mm in height. The mold release accelerator was not applied to the inner surface portion of this square silica composite container.

(Example 2)
A porous silica composite plate was produced in substantially the same manner as in Example 1, and a square silica composite container was produced. However, the following conditions were changed. The first raw material powder was produced in substantially the same manner as in Example 1, but the average particle size was 210 μm. As the second raw material powder, a zirconia ZrO ₂ powder was prepared (particle size range 30 to 300 μm, average particle size 100 μm).

(Example 3)
A porous silica composite plate was produced in substantially the same manner as in Example 1, and a square silica composite container was produced. However, the following conditions were changed. That is, spinel MgAl ₂ O ₄ powder was prepared as the second raw material powder (particle size range 30 to 300 μm, average particle size 110 μm).

Example 4
A porous silica composite plate was manufactured by substantially the same process as in Example 1, and a square silica composite container was manufactured. However, the following conditions were changed.
The silica purity of the first raw material powder is 99.999 wt. %. The particle size range of the first raw material powder was 100 to 700 μm, and the average particle size was 350 μm. Further, the amount of aluminum nitrate added to the first raw material powder was reduced, and the amount of Al added was reduced.
The purity of 99.9 wt. % Magnesia MgO powder was prepared (particle size range 30-300 μm, average particle size 105 μm).

(Example 5)
A porous silica composite plate was manufactured by substantially the same process as in Example 1, and a square silica composite container was manufactured. However, the following conditions were changed.
The silica purity of the first raw material powder is 99.999 wt. %. The particle size range of the first raw material powder was 100 to 700 μm, and the average particle size was 360 μm. Moreover, Al was added to the first raw material powder by aluminum chloride, but the amount of Al added was reduced.
Al ₂ O ₃ powder was produced as the second raw material powder (purity 99.9 wt.%, Particle size range 30 to 300 μm, average particle size 100 μm).
Moreover, Ba application | coating (concentration 1000 microgram / cm < ² >) was performed to the square silica composite container inner surface.

(Example 6)
In accordance with substantially the same process as in Example 1, a porous silica composite plate was manufactured as follows, and a square silica composite container was further manufactured.
The silica purity of the first raw material powder is 99.9 wt. %. The particle size range of the first raw material powder was 100 to 700 μm, and the average particle size was 340 μm. Moreover, Al was added to the first raw material powder by aluminum chloride to increase the amount of Al added.
Al ₂ O ₃ powder was produced as the second raw material powder (purity 99.9 wt.%, Particle size range 30 to 300 μm, average particle size 110 μm).

(Comparative Example 1)
A silica plate was manufactured as follows, and a rectangular silica container was further manufactured.
Only high-purity natural quartz powder (silica purity 99.9999 wt.%, Particle size range 50-500 μm, average particle size 210 μm) was used as the raw material powder. The molten gas atmosphere was He 100%. The same electric heating furnace as in Example 1 was used, but only one kind of raw material powder was used.
Moreover, Al was not added to the raw material powder.
The obtained silica plate was transparent silica glass, and the density was 2.2 (g / cm ³ ).

(Comparative Example 2)
Compared to Comparative Example 1, the following conditions were changed to produce a silica plate, and a square silica container was further produced.
The particle size range of the raw material powder was 100 to 700 μm, and the average particle size was 350 μm. In addition, the atmosphere gas of the electric heating furnace was changed to He95 vol. %, H _{2 5} vol. %.
As in Comparative Example 1, the obtained silica plate was a transparent silica glass.

(Comparative Example 3)
Compared to Comparative Example 1, the following conditions were changed to produce a silica plate, and a square silica container was further produced.
The silica purity of the raw material powder is 99.99 wt. % Compared with Comparative Example 1. The particle size range of the raw material powder was 50 to 500 μm, and the average particle size was 200 μm. Also, aluminum nitrate was added to the raw material powder and dried. In addition, the atmospheric gas was changed to He 70 vol. %, H ₂ 30 vol. %.
As in Comparative Example 1, the obtained silica plate was a transparent silica glass.

[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 composite plate and square silica composite container were evaluated as follows.

(A) Measurement of particle size range of 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).

(B) Measurement of average particle size of each raw material powder:
Using a plurality of powder sieves, the particle size distribution was measured according to the screening method (JIS R1639-1). As a sieve, a standard sieve of JIS Z 8801 was used.
In addition to the above sieving method, particle size distribution measurement was performed according to laser diffraction and scattering methods (also JIS R 1639-1). From these two types of data, the correlation between the particle diameter (μm) and the mass-based cumulative distribution (wt.%) Was determined. Finally, 50 wt. The particle diameter (D ₅₀ ) in% cumulative mass value was shown as the average particle diameter.

(C) Metal element concentration analysis:
First, a sample was prepared by cutting out a silica sample piece from the surface layer position of the porous silica composite plate and dissolving it in a hydrofluoric acid aqueous solution. Using this sample, the metal element concentration analysis was performed when the concentration of the metal element contained was relatively low. Plasma emission analysis (ICP-AES, Inductively Coupled Plasma-Atomic Emission Spectroscopy) or plasma mass spectrometry (ICP-MS, Inductively Coupled Plasma-Mass Spectroscopy was performed, and when the concentration of the metal element contained was relatively high, it was performed by atomic absorption spectrophotometry (AAS, Atomic Absorption Spectroscopy).

(D) OH group concentration measurement:
From the surface layer portion of the porous silica composite plate, approximately 30 mm × 30 mm × thickness 1 mm (however, the thickness of the comparative silica plate was 9 mm), a double-sided mirror finish sample was prepared, and the infrared absorption spectrophotometry was performed. It was. The conversion to the OH group concentration follows the literature.
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.

(E) Effect of preventing diffusion of impurities from the rectangular silica composite container to the 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 380 mm × 380 mm × 240 mm. Next, a silicon piece was sampled at a depth of 3 mm from the surface of the ingot, and this was treated with an acidic solution to obtain a solution sample, and then analyzed for Na concentration by ICP-AES. The effect of preventing impurity diffusion from the rectangular silica composite container into the polycrystalline silicon ingot was evaluated based on 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)

(F) Releasability 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 composite container and the welded portions of the four side walls and the bottom corner were cut with a cutter. The four side walls and the bottom plate of the square silica composite container were peeled off. Thereafter, the releasability was evaluated by measuring the depth of the unevenness and cracks remaining on the surface of the ingot from the position in contact with the inner surface of the square silica composite 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)

(G) Manufacturing cost (relative) evaluation:
The manufacturing cost of the square silica composite container was examined.
The standard was Comparative Example 1, and the total costs of the entire manufacturing process such as the raw material costs and adjustment costs of the silica powder and the heat-resistant substance, the melting and sintering costs, etc. were relatively evaluated.
Cost is very low ◎ (30% or less)
Low cost ○ (about 30-50%)
Medium cost △ (about 50-90%)
Cost is high × (Comparative Example 1 is 100%)

  The production conditions, measured physical property values, and evaluation results of each porous silica composite plate and square silica composite container produced in Examples 1 to 6 and Comparative Examples 1 to 3 are summarized and shown in Tables 1 to 3 below. .

  As can be seen from Tables 1 to 3, in Examples 1 to 6 according to the method for producing a silica container according to the present invention, a rectangular silica composite container for producing a silicon ingot having excellent releasability and low impurity contamination is reduced. It was possible to manufacture at a 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 composite container for producing a silicon ingot according to the present invention,
11, 11a, 11b ... side,
21, 21a, 21b ... bottom,
80 ... susceptor,
100 ... porous silica composite plate according to the present invention,
101, 102 ... surface, 111, 112 ... surface layer portion, 113 ... inner portion,
300 ... Electric heating furnace,
302 ... atmosphere gas supply in the melting container, exhaust port,
303a ... First raw material powder supply port, 303b ... Second raw material powder supply port,
305 ... Gas supply outside the melting container, exhaust port,
306a ... first raw material powder, 306b ... second raw material powder,
307 ... Heating means (induction coil, resistance heating body, etc.),
308 ... melting container,
309 ... heat insulation,
312 ... Shape forming tool,
313: Porous silica composite plate take-out chamber,
314... Porous silica composite plate take-out indoor atmosphere gas supply, exhaust port,
315 ... manufactured porous silica composite plate,
316 ... porous silica composite plate drawing roller,
317 ... porous silica composite plate body drawing direction,
321a ... fused silica glass body, 321b ... heat-resistant substance,
322: Opening / closing plate, 323: Opening / closing plate moving direction.

Claims (16)

A container for solidifying a silicon melt to produce a polycrystalline silicon ingot,
At least a surface layer portion is made of silica glass, and an inner portion is a rectangular container composed of a combination of parallel plate-like porous silica composite plates made of a heat-resistant material having a melting point higher than that of silica. Square silica composite container for silicon ingot production.   The porous silica composite plate is characterized in that a portion from the surfaces of both parallel planes to a depth of at least 1 mm is made of silica glass and an inner portion is made of the heat-resistant substance at a thickness of at least 3 mm. Item 2. A rectangular silica composite container for manufacturing a silicon ingot according to Item 1.   The heat-resistant substance is at least one of a single element substance having a melting point of 2000 ° C or higher, an oxide, a composite oxide, a nitride, an acid nitride, a carbide, and a boride. A rectangular silica composite container for producing a silicon ingot according to claim 2. The heat-resistant substance is C, Al ₂ O ₃ , BeO, MgO, ThO ₂ , ZrO ₂ , CaZrO ₃ , MgAl ₂ O ₄ , YAlO ₃ , SiON, AlN, BN, Si ₃ N ₄ , TiN, SiC, TiC, The rectangular silica composite container for producing a silicon ingot according to any one of claims 1 to 3, wherein the rectangular silica composite container is one or more of WC, ZrC, TiB ₂ , and ZrB ₂ .   The Al concentration in the silica glass of the surface layer portion of the porous silica composite plate is 3 to 300 wt. ppm, and the OH group concentration is 5 to 500 wt. The square silica composite container for producing a silicon ingot according to any one of claims 1 to 4, wherein the composite is a ppm.   6. The mold release accelerator for promoting mold release of the polycrystalline silicon ingot is contained in the silica glass of the surface layer portion of the porous silica composite plate body. The square silica composite container for producing a silicon ingot according to one item.   A parallel flat plate-like porous silica composite plate having at least a surface layer portion made of silica glass for constituting a container for producing a polycrystalline silicon ingot by solidifying a silicon melt, and surfaces of both parallel planes A porous silica composite plate characterized in that at least a portion up to a depth of 1 mm is made of silica glass, and at least a thickness of 3 mm of the inner portion is made of a heat resistant material having a melting point higher than that of silica. The heat-resistant substance is C, Al ₂ O ₃ , BeO, MgO, ThO ₂ , ZrO ₂ , CaZrO ₃ , MgAl ₂ O ₄ , YAlO ₃ , SiON, AlN, BN, Si ₃ N ₄ , TiN, SiC, TiC, The porous silica composite plate according to claim 7, which is at least one of WC, ZrC, TiB ₂ , and ZrB ₂ .   The Al concentration in the silica glass of the surface layer portion is 3 to 300 wt. ppm, and the OH group concentration is 5 to 500 wt. It is ppm, The porous silica composite board of Claim 7 or Claim 8 characterized by the above-mentioned.   The porous glass according to any one of claims 7 to 9, wherein a release accelerator that promotes release of the polycrystalline silicon ingot is contained in the silica glass of the surface layer portion. Silica composite plate.   Each concentration of Li, Na, K in the silica glass of the surface layer portion is 30 wt. ppm, and each concentration of Ti, Cr, Fe, Ni, Cu, Zn, Zr, Mo, Ag, Au is 3 wt. The porous silica composite plate according to any one of claims 7 to 10, wherein the porous silica composite plate is not more than ppm. A method for producing a parallel flat plate-like porous silica composite plate having at least a surface layer portion made of silica glass for constituting a rectangular container for producing a polycrystalline silicon ingot by solidifying a silicon melt, at least,
Producing silica powder as the first raw material powder;
Producing a powder composed of a heat-resistant substance having a higher melting point than silica as the second raw material powder;
A step of replacing the inside of the melting vessel disposed in the electric heating furnace with an inert gas atmosphere containing any one or more of nitrogen, neon, argon, and krypton;
While maintaining the inside of the melting container in the inert gas atmosphere, the supply position of the second raw material powder is supplied as the center side in the melting container, and the first raw material powder is supplied to the first in the melting container. Supplying the outside of the supply position of the second raw material powder;
While maintaining the pressure of the inert gas atmosphere in the melting container at atmospheric pressure or higher, the temperature of the melting container is heated to 1700 ° C. or higher to melt and soften the first raw material powder to form silica glass. Process,
A step of continuously pulling out a composite of the fused, softened silica glass and the heat-resistant substance while forming a parallel plate shape from a lower part of the melting container through a shape forming tool;
Cutting the composite of the drawn fused and softened silica glass and the heat-resistant substance with a predetermined size and grinding to produce a parallel flat plate-like porous silica composite plate;
A method for producing a porous silica composite plate, comprising:   The first raw material powder has a particle size of 5 to 1000 μm and a silica purity of 99.99 wt. The method for producing a porous silica composite plate according to claim 12, wherein the silica powder is at least%. The second raw material powder has a particle size of 5 to 1000 μm, and C, Al ₂ O ₃ , BeO, MgO, ThO ₂ , ZrO ₂ , CaZrO ₃ , MgAl ₂ O ₄ , YAlO ₃ , SiON, AlN, BN The porous material according to claim 12, which is a powder containing at least one of Si ₃ N ₄ , TiN, SiC, TiC, WC, ZrC, TiB ₂ , and ZrB _2. A method for producing a silica composite plate.   The porous silica composite plate according to any one of claims 12 to 14, wherein a release accelerator for promoting release of the polycrystalline silicon ingot is added to the first raw material powder. Body manufacturing method.   The mold release accelerator which accelerates | stimulates the mold release of the said polycrystal silicon ingot is apply | coated to the surface of the said manufactured porous silica composite board body, The Claim 12 thru | or 15 characterized by the above-mentioned. A method for producing a porous silica composite plate.

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