JP2011126735A - Mold release agent composition for silicon casting, method for preparing the same and method for manufacturing silicon casting mold - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mold release agent composition for silicon casting capable of forming a mold release agent layer free of adhesion to melted and solidified metallic silicon, a method for preparing the same and a method for manufacturing a silicon casting mold. <P>SOLUTION: The mold release agent composition for silicon casting is prepared by suspending and dispersing silicon dioxide particles having an average particle diameter of 0.05-10 μm in a liquid and slurrying those. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a mold release agent composition for silicon casting, which is applied to a mold for silicon casting and, in particular, is fired to form a release agent layer, a preparation method thereof, and a method for manufacturing a mold for silicon casting.

  Silicon is an element classified as a semi-metal, and is used in various fields as an element having properties different from those of general metals. For example, metallurgical and metallic uses that are introduced into molten iron as a deoxidizer component or added as a major component of aluminum alloys for the purpose of removing oxygen atoms in iron In addition to a method and a method of using a silicone compound in which various organic functional groups are added to a siloxane bond in which silicon and oxygen are bonded, there are a method of using silicon as an important industrial method of using silicon.

  Among these uses, metallurgical and metallic usage methods and usage methods as silicone compounds are rarely used as silicon elements alone, but as semiconductor materials are used as silicon alone, In other words, the use is premised on use as highly purified silicon. This semiconductor application is further divided into applications such as wafers for semiconductor devices such as LSI, wafers for solar cells, sputter league targets, and reflective insulation for high-purity atmosphere furnaces. Among these, except for LSI wafers, which are limited to the method of use as single crystal silicon, the present invention can be used in a crystalline form of polycrystalline silicon.

  The method for producing polycrystalline silicon is usually produced by casting silicon into a mold. As for the casting method of polycrystalline silicon, a crucible made of a heat-resistant material such as graphite or silica is used, and a substance as a release agent is attached in a layered manner to the crucible side where molten silicon contacts. Is widely used.

For example, Japanese Patent Application Laid-Open No. 10-182133 (Patent Document 1) discloses a technique of using SiC or C as a mold release agent on the inner wall of a graphite crucible.
In Japanese Patent Laid-Open No. 2002-292449 (Patent Document 2), a method of applying a base material made of silicon nitride and a mixed material in which silicon nitride and silicon dioxide are mixed at a weight ratio of 28:72 to 75:25 in an overlapping manner. Is disclosed.
JP 2004-291027 A (Patent Document 3) contains silicon nitride and amorphous fine silica obtained by heat treatment by injecting silicon tetrachloride into a high-temperature flame of hydrogen gas and oxygen gas. A technique is disclosed in which fine silica mixed with silicon nitride in an amount of 10 to 90% by weight is used as a release agent.
Japanese Patent Laid-Open No. 2006-334671 (Patent Document 4) discloses a method of applying a material containing silicon nitride and silicon dioxide by a plasma spraying method to form a release agent layer.

  Thus, in the prior art, silicon nitride and silicon dioxide are mainly used as the release agent component. Of these, silicon nitride is a heat-resistant material and functions as a main component of the release agent. On the other hand, silicon dioxide has a property of gradually dissolving in molten silicon, and has an affinity for molten silicon, so that it firmly adheres during solidification of the molten silicon, and has a property as a binder rather than a releasability. It is a material to be demonstrated. Nevertheless, silicon dioxide is actively used as a release agent component in the above prior art because the silicon nitride layer that is the original release agent is brittle, due to mechanical action and thermal fluctuations. Since it is easy to peel from the crucible, the purpose was mainly as a binder for suppressing the peeling.

  Silicon dioxide, which functions as a binder, has a binder function when mixed with a release agent (heat-resistant material) in relation to a release agent component as an effective heat-resistant material such as silicon nitride or silicon carbide. It can be confirmed by the above-mentioned prior art that the change is large. For example, in Japanese Patent Application Laid-Open No. 2004-291027 (Patent Document 3), amorphous silica having an average particle diameter of 0.05 μm produced by an oxyhydrogen combustion method is used instead of the conventional silicon dioxide having an average particle diameter of about 20 μm. By doing so, it is supposed that fine silica is surrounded around coarse silicon nitride and induces an effect that silicon nitride adheres firmly.

  By the way, since silicon dioxide is dissolved in molten silicon, the silicon dioxide serving as the binder component is melted in the molten silicon. For this reason, the heat-resistant material such as silicon nitride and silicon carbide as the release component that is in contact with the silicon dioxide melts the silicon dioxide as the binder component, and the heat-resistant material becomes a binderless state. The part moves as a powder into molten silicon, and after silicon is solidified, it is mixed as solid impurities in the silicon. If the solid impurities do not affect the use of the melted and solidified silicon, the release agent layer composed of the above-mentioned “release component (heat-resistant material) + silicon dioxide as the binder component” is effective. If the use of solidified silicon is a problem where the presence of solid impurities in silicon is a problem, the release agent is "release component (heat-resistant material) + silicon dioxide as binder component". The mold layer is not a good mold release agent.

  From the above, if a heat-resistant substance such as silicon nitride or silicon carbide is not used as a release agent component, and silicon dioxide as a binder becomes a release agent layer as it is, contamination of impurities can be essentially prevented. However, in the conventional technology, when a release agent layer is formed with silicon dioxide as the main component of the release agent, the release agent layer is fixed to the molten and solidified silicon, and separation from silicon is not possible. It was possible.

  Furthermore, as shown in FIG. 1, the release agent layer 2 mainly composed of silicon dioxide formed on the surface of the crucible 1 not only adheres to the molten and solidified silicon 3, but the release agent layer 2 As a result, the molten and solidified silicon 3 adheres to the crucible 1 and, due to the difference in thermal expansion between the crucible material and the silicon, causes internal stress during cooling. And crack 4 was generated, and the ingot was broken.

Japanese Patent Laid-Open No. 10-182133 JP 2002-292449 A JP 2004-291027 A JP 2006-334671 A

  The present invention has been made in view of the above circumstances, and does not contain a heat-resistant substance such as silicon nitride or silicon carbide, which has been conventionally used as a mold release component, and contains only silicon dioxide as a mold release component. Even so, a release agent composition for silicon casting that can form a release agent layer that can be cast without the metal silicon being fixed to the crucible, a method for preparing the release agent composition, and a silicon casting using the release agent composition It aims at providing the manufacturing method of the casting mold.

  As a result of intensive investigations to achieve the above object, the present inventor turned silicon dioxide particles having a specific average particle diameter, preferably solid amorphous silicon dioxide particles having no pores, into a liquid such as water. A release agent composition (slurry) obtained by suspending and dispersing and mixing is applied to a silicon casting mold and baked to prevent the release agent from adhering to molten and solidified metallic silicon. The inventors have found that a layer can be formed, and have made the present invention.

Accordingly, the present invention provides the following mold release agent composition for silicon casting, a method for preparing the same, and a method for producing a mold for silicon casting.
Claim 1:
A release agent composition for silicon casting, characterized in that silicon dioxide particles having an average particle diameter of 0.05 to 10 μm are suspended and dispersed in a liquid and slurried.
Claim 2:
The mold release agent composition according to claim 1, wherein the ratio Sb / Sc of the specific surface area Sc and the BET specific surface area Sb calculated from the particle diameter of the silicon dioxide particles is in the range of 0.5-4.
Claim 3:
The release agent composition according to claim 1 or 2, wherein the silicon dioxide particles are amorphous.
Claim 4:
A method for preparing a release agent composition for casting silicon, wherein the silicon dioxide particles are suspended and dispersed in a liquid and then mixed to form a slurry.
Claim 5:
A mold release agent composition according to any one of claims 1 to 3 is applied to a silicon casting mold and then fired to form a mold release agent layer on the mold surface. Mold manufacturing method.
Claim 6:
2. A mold release agent containing silicon nitride is applied in advance to a silicon casting mold and then fired to form a silicon nitride release agent layer on the mold surface, and then overlaid on the silicon nitride release agent layer. After applying the release agent composition according to any one of claims 1 to 3, firing to form a silicon dioxide release agent layer, thereby forming two or more release agent layers on the mold surface. A method for producing a silicon casting mold.

  ADVANTAGE OF THE INVENTION According to this invention, the mold release agent composition for silicon casting which can form the mold release agent layer which does not adhere to the molten and solidified metal silicon, its preparation method, and the manufacturing method of a silicon casting mold can be provided.

It is a partial expanded sectional view which shows a state when silicon | silicone is fuse | melted with the crucible which has the conventional mold release agent layer. It is an optical microscope photograph of the surface after the silicon melting use of the release agent layer of the present invention. It is an optical microscope photograph of the cross section of the crucible which has a mold release agent layer of this invention. It is a partial expanded sectional view which shows a state when silicon | silicone is fuse | melted with the crucible which has a mold release agent layer of this invention.

  The release agent composition of the present invention is characterized in that silicon dioxide particles having an average particle size of 0.05 to 10 μm are suspended and dispersed in a liquid and mixed to form a slurry.

  Examples of the silicon dioxide particles used in the present invention include various types of silicon dioxide particles such as fine particles (powder particles) obtained by pulverizing quartz and fumed silicon dioxide produced by oxidizing a silicon compound.

  Here, as described above, the molten silicon wets well with silicon dioxide, and depending on the release agent conditions, it firmly adheres during solidification. Therefore, conventionally, a release agent mainly composed of silicon dioxide is used for melting silicon. Could not be used as a mold release agent. That is, at 1450 ° C., which is the melting temperature of silicon exposed when silicon is melted, is a temperature at which silicon dioxide as a release agent sinters, so that silicon dioxide in the release agent layer is strongly sintered, It was in a state where the crucible material such as silicon dioxide or carbon material was fixed. If silicon is melted in a crucible in which such a release agent layer is formed, the "crucible-release agent layer-melted / solidified silicon" is fixed, so that the silicon ingot was broken during the solidification of silicon. .

  As a result of the study by the present inventor as a countermeasure against such a sticking phenomenon, the silicon dioxide particles have a particle diameter of 0.05 to 10 μm and a specific surface area value Sc calculated from the particle diameter, and a BET specific surface area meter. The ratio Sb / Sc to the specific surface area value Sb measured in (5) is in the range of 0.5 to 4, and the amorphous silicon dioxide particles are stirred well with a dispersion medium such as water together with an appropriate binder component, Applying and drying to a crucible (mold) in a slurry state, and then using a release agent layer formed by firing and processing at 1450 ° C. or higher, no sticking phenomenon between the crucible and metal silicon occurs. Even if the sticking phenomenon occurs, casting can be achieved without collapsing to such an extent that the release agent layer and the crucible impair the function.

  That is, the release agent composition containing the silicon dioxide particles of the present invention is released by firing after applying the release agent slurry and raising the temperature to 1450 ° C. or higher, which is the melting point of the metal silicon actually used. The release agent layer has a large and small number of pores in the agent layer. FIG. 2 is a photograph taken by an optical microscope of the surface of the release agent layer of the present invention after silicon melting use, and FIG. 3 shows a crucible 1 having the release agent layer 5 (thickness w = about 200 μm) of the present invention. As shown in the optical micrograph of the cross section, the presence of a large number of pores as described above causes the strength of the release agent layer to be moderately weakened, and the release agent layer collapses with a slight load application. This will be explained with reference to FIG. 4. When the silicon 3 is melted in the crucible 1 having the silicon dioxide release agent layer 5 of the present invention, the mold release agent even if the silicon and silicon dioxide are fixed during solidification of the molten silicon. Since the strength of the layer 5 is moderately weak, only a part of the release agent layer in the vicinity of silicon, in particular, only the part of the release agent layer in contact with silicon collapses, so that other parts of the release agent layer Cracks do not occur in the crucible body.

In the present invention, silicon dioxide particles having an average particle diameter of 0.05 to 10 μm, preferably 0.1 to 2.5 μm, as a condition for forming a release agent layer having a large and small pores therein. Is used. Silicon dioxide particles within this particle size range are exposed to high temperatures under the firing and melting temperature of metal silicon, so that the silicon dioxide particles sinter, but if the particle size is too small, the sintering becomes too dense. As a result, the ratio of the pores in the release agent layer is lowered, so that the release agent layer and silicon may be fixed. Further, if the particle size is too large, the bubbles in the release agent layer are enlarged, and silicon penetrates into the bubbles, and the release agent layer and silicon may be fixed in the same manner. In this case, if the silicon dioxide particles are crystalline, the silicon dioxide particles are sintered while maintaining the crystallinity, and the movement speed of the silicon dioxide particles during the sintering is lower than that of the amorphous one, so that the sintering is difficult. Moreover, since the proportion of pores in the silicon dioxide sintered layer (release agent layer) may be lowered, the silicon dioxide particles are preferably amorphous. Due to the presence of pores in the release agent layer, the strength of the release agent layer is moderately weakened, and only the release agent layer collapses when the silicon release crucible is separated, so that the silicon release crucible does not adhere.
In addition, although the particle diameter of a silicon dioxide particle can be measured by an electron microscope image or a centrifugal sedimentation type particle size distribution measurement, it is a value obtained from an electron microscope image in the present invention.

  In addition, the silicon dioxide particles of the present invention are spherical, and the ratio Sb / Sc between the specific surface area value Sc calculated from the particle diameter and the specific surface area value Sb measured with a BET specific surface area meter is 0.5 to 4, In particular, it should be in the range of 0.8-2. This is because it is desirable that the silicon dioxide particles used do not have many open pores in the particles. If the pores are widely present in the silicon dioxide particles, the effective size of the silicon dioxide particles decreases due to expansion of the pores inside the particles when exposed to a high temperature under the silicon melting temperature, and the above particles This is because the same result as when the diameter is small is obtained. Therefore, it is preferable that the silicon dioxide particles have a solid spherical shape. A commercial item can be used for such a silicon dioxide particle, for example, brand name: Admafine SO-C5, SO-E1, SO-E2 (made by Admatechs Co., Ltd.) etc. can be used.

  The content ratio of silicon dioxide particles in the composition (slurry) of the present invention is not particularly limited, but is preferably 5 to 50% by mass, more preferably 20 to 40% by mass with respect to the total solid content of the slurry.

  The release agent composition of the present invention is generated when water is slurried with respect to silicon dioxide particles, liquids such as alcohols such as water, ethanol and butyl alcohol, binder components such as polyvinyl alcohol (PVA) and cellulose, and slurry. After appropriately adding a surfactant or the like to defoam bubbles, the mixture is sufficiently stirred using a mixer such as a ball mill, kneader, screw stirrer, etc., and this slurry is applied by brush or spraying. A mold release agent layer is formed by applying to the inner wall of the crucible (mold) by application. It is preferable to appropriately adjust the viscosity of the slurry and the concentration of the surfactant or the like depending on what method is selected as the coating method.

  Since the crucible immediately after the slurry is applied is wet with the liquid component of the slurry, a step of holding it at an intermediate temperature of about 50 to 200 ° C. for an appropriate time is taken for the purpose of drying it. Since the release agent layer is not wet by this step, a desired release agent layer thickness is obtained by, for example, applying a slurry on the release agent layer by overcoating.

  Since the silicon dioxide release agent layer of the present invention is in contact with molten silicon as described above, the release agent layer gradually dissolves in silicon and gradually decreases in thickness. Therefore, in the present invention, it is necessary to determine the thickness of the release agent layer on the assumption that the release agent layer thickness decreases. In this regard, according to the study of the present inventor, although depending on the melting time and the melting temperature, the thickness of the release agent layer is preferably 30 μm or more, desirably 100 μm or more, particularly 400 μm or more. Further, if the thickness of the release agent layer is too thick, it becomes uneconomical to use the release agent unnecessarily. Therefore, it is usually sufficient that the thickness is 1 mm, preferably 500 μm or less, particularly 450 μm. The following is preferable. If the melting time is extremely long and it is unclear how much the release agent component silicon dioxide dissolves in silicon, make the release agent layer thick enough and use a release agent layer other than silicon dioxide. The layer on the crucible side is coated with a release agent containing, for example, silicon nitride as a main component, and dried to form a silicon nitride release agent layer. The release agent composition containing the silicon dioxide particles of the present invention can be applied again to form a silicon dioxide release agent layer.

  Furthermore, as described above, the release agent layer of the present invention has a structure having many fine pores. Since the pores are fine, the molten silicon does not enter the pores and is in contact with the silicon dioxide only on the surface of the release agent layer. Since these pores are basically open pores, if molten silicon penetrates into the pores, the silicon penetrates the entire release agent layer, and the role of the release agent layer is no longer fulfilled. In the present invention, since the pores are fine, the effect as a release agent layer can be exhibited without the penetration of silicon.

When a desired release agent layer can be formed, the crucible coated with the release agent layer is fired. The main purpose of firing is to remove the binder component and organic material component of the release agent layer from the release agent layer by evaporation, oxidation reaction, etc., and to treat at a high temperature of 400 to 1200 ° C. for 10 minutes to 2 hours. Is good. In this case, when the crucible material is made of a substance that is not oxidized at the processing temperature, for example, an oxide such as silicon carbide, alumina, or silicon dioxide, the processing atmosphere can be an oxidizing atmosphere such as the atmosphere. In the case of a material that is oxidized at a firing temperature such as graphite, it is preferable to fire in an inert atmosphere such as argon or nitrogen.
The crucible having the silicon dioxide release agent layer thus fired can be suitably used particularly for melting metal silicon.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not restrict | limited to the following Example. In addition, in the following example, a part represents a mass part.

[Example 1]
Average particle diameter 0.5 μm, BET specific surface area Sb 5.5 m ² / g, ratio of specific surface area value Sc 5.2 m ² / g calculated from the particle size and specific surface area value Sb measured by BET specific surface area meter Sb / Sc Amorphous silicon dioxide powder (trade name: Admafine SO-E2, manufactured by Admatechs Co., Ltd.) 1 part, PVA 1.8 parts, water 1.8 parts and butyl alcohol 0.001 Part was placed in a resin ball mill, and this ball mill was rotated for 5 hours to prepare a slurry mainly composed of silicon dioxide.
This slurry was applied to the entire inner wall of the silica crucible with a brush and dried in a dryer at 50 ° C. for 1 hour. When the thickness of the release agent layer after drying was measured, it was 100 μm. This coating and drying were repeated 4 times to form a release agent layer having a thickness of 400 μm on the inner wall of the silica crucible.
This crucible with a release agent layer was placed in an electric furnace and baked in air at 1000 ° C. for 2 hours. The release agent layer after firing peeled off the release agent silica when rubbed with a fingertip, but the release agent and crucible were not peeled off.

After putting silicon into the crucible, the silicon was melted at 1500 ° C. in an electric furnace, and then the crucible was gradually lowered in the furnace to solidify the silicon from the bottom of the crucible.
When the crucible was taken out after cooling the electric furnace, the crucible was cracked, but no fusion between the crucible and silicon occurred.

[Example 2]
Amorphous silicon dioxide powder (trade name: Admafine SO-E1, manufactured by Admatechs Co., Ltd.) having an average particle size of 0.25 μm, specific surface area Sb16 m ² / g, and Sb / Sc of 1.6 is used. A slurry was prepared by the same treatment as in Example 1 except that coating, drying, and baking were performed in the same manner. The thickness of the release agent layer was 420 μm.
When this was used to melt and solidify silicon in the same manner as in Example 1, the crucible had cracks, but no fusion between the crucible and silicon occurred.

[Example 3]
Amorphous silicon dioxide powder having an average particle diameter of 2.2 μm, a specific surface area Sb of 1.9 m ² / g, and Sb / Sc of 1.6 (trade name: Admafine SO-C5, manufactured by Admatechs) A slurry was prepared by the same treatment as in Example 1 except that was used, and coating, drying, and firing were performed in the same manner. The thickness of the release agent layer was 420 μm.
When this was used to melt and solidify silicon in the same manner as in Example 1, the crucible had cracks, but no fusion between the crucible and silicon occurred.

[Comparative Example 1]
Average particle size 0.02 μm, specific surface area Sb 90 m ² / g, ratio Sb / Sc of specific surface area value Sc calculated from the particle size and specific surface area value Sb measured by BET specific surface area meter is 0.7, 1 part of crystalline silicon dioxide powder (trade name: Aerosil 90, manufactured by Evonik Co., Ltd.), 1.8 parts of PVA, 1.8 parts of water and 0.001 part of butyl alcohol are placed in a resin ball mill. A slurry containing silicon dioxide as a main component was prepared by rotating for 5 hours.
This slurry was applied to the entire inner wall of the silica crucible with a brush and dried in a dryer at 50 ° C. for 1 hour. It was 80 micrometers when the thickness of the mold release agent layer was measured after drying. This coating and drying were repeated 5 times to form a release agent layer having a thickness of 400 μm on the inner wall of the silica crucible.
This crucible with a release agent layer was placed in an electric furnace and baked in air at 1000 ° C. for 2 hours. The release agent layer after firing peeled off the release agent silica when rubbed with a fingertip, but the release agent and crucible were not peeled off.

After putting silicon into the crucible, the silicon was melted at 1500 ° C. in an electric furnace, and then the crucible was gradually lowered in the furnace to solidify the silicon from the bottom of the crucible.
When the crucible was taken out after cooling the electric furnace, about 30% of the interface between the crucible and silicon was fused.

DESCRIPTION OF SYMBOLS 1 Crucible 2 Conventional release agent layer 3 Metallic silicon 4 Crack 5 Release agent layer of this invention

Claims (6)

  A release agent composition for silicon casting, characterized in that silicon dioxide particles having an average particle size of 0.05 to 10 μm are suspended and dispersed in a liquid to form a slurry.   The mold release agent composition according to claim 1, wherein the ratio Sb / Sc of the specific surface area Sc and the BET specific surface area Sb calculated from the particle diameter of the silicon dioxide particles is in the range of 0.5-4.   The release agent composition according to claim 1 or 2, wherein the silicon dioxide particles are amorphous.   A method for preparing a release agent composition for casting silicon, wherein the silicon dioxide particles are suspended and dispersed in a liquid and then mixed to form a slurry.   A mold release agent composition according to any one of claims 1 to 3 is applied to a silicon casting mold and then fired to form a mold release agent layer on the mold surface. Mold manufacturing method.   2. A mold release agent containing silicon nitride is applied in advance to a silicon casting mold and then fired to form a silicon nitride release agent layer on the mold surface, and then overlaid on the silicon nitride release agent layer. After applying the release agent composition according to any one of claims 1 to 3, firing to form a silicon dioxide release agent layer, thereby forming two or more release agent layers on the mold surface. A method for producing a silicon casting mold characterized by the above.