WO2011074321A1 - 太陽電池用多結晶シリコン及びその製造方法 - Google Patents
太陽電池用多結晶シリコン及びその製造方法 Download PDFInfo
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- WO2011074321A1 WO2011074321A1 PCT/JP2010/068511 JP2010068511W WO2011074321A1 WO 2011074321 A1 WO2011074321 A1 WO 2011074321A1 JP 2010068511 W JP2010068511 W JP 2010068511W WO 2011074321 A1 WO2011074321 A1 WO 2011074321A1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D25/00—Special casting characterised by the nature of the product
- B22D25/02—Special casting characterised by the nature of the product by its peculiarity of shape; of works of art
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- the present invention relates to polycrystalline silicon for solar cells and a method for producing the same.
- Solar cells are a type of semiconductor that can directly convert light energy into electricity. It has attracted attention as a clean power generation method because it can generate electricity without emitting carbon dioxide and harmful exhaust gas, which cause global warming, and it has begun to spread as a power source for general households.
- Solar cells can be classified into several types depending on the semiconductor used as the substrate, but can be broadly classified into silicon and compound systems. Currently, the majority of solar cells supplied to the market are silicon-based. Silicon-based solar cells are further divided into a single crystal type and a polycrystalline type, but the polycrystalline type is the mainstream because it is advantageous for cost reduction.
- a casting method in which molten silicon is grown and solidified with a mold is known.
- a quartz crucible or a graphite crucible is used as the mold.
- a mold release agent made of silicon nitride Si 3 N 4 is generally applied to the inner surface of the mold. Is.
- the mold release agent is used to prevent impurities such as Fe, C, Al and Ca contained in the mold release agent from diffusing into the silicon and reducing the purity of the silicon during the production of polycrystalline silicon. It is desirable to use a high-purity material that does not contain impurities. Among impurities, Fe has a large diffusion constant into silicon, and thus it is particularly desirable to remove it from the mold release agent.
- Patent Document 1 a mixture obtained by adding water to a silicon nitride release agent powder is kneaded by a ball mill and stirred using a Teflon (registered trademark) coated magnetic stirrer.
- Teflon registered trademark
- an object of the present invention is to provide polycrystalline silicon in which a region having a short carrier lifetime on the surface layer caused by Fe is substantially eliminated, and a method for producing such polycrystalline silicon.
- One of the other issues is to provide
- the present inventor has conducted extensive research to solve the above-mentioned problems. As a result, it is not sufficient to simply suppress the Fe concentration in the release agent, and it is important to control the thickness of the release agent applied to the mold. Only when the Fe concentration in the silicon nitride mold release agent and the thickness of the mold release agent applied to the mold satisfy a predetermined relationship, the region having a short lifetime of the surface layer caused by Fe disappears substantially. I found it.
- the Fe concentration in the release agent is x (atomic ppm), and the thickness of the release agent applied to the mold is y ( ⁇ m), x ⁇ It was found that when polycrystalline silicon was produced in a mold coated with a release agent under conditions satisfying 5.0, 20 ⁇ y ⁇ 100, and x ⁇ y ⁇ 100, a region having a good lifetime was rapidly expanded. . In the polycrystalline silicon obtained by the production method, the Fe concentration on the outermost surface becomes 1 atomic ppm or less in a state where the surface is unpolished, and typically falls below the lower limit of detection (10 ppb or less).
- the present invention provides a method for producing polycrystalline silicon, which comprises applying a mold release agent obtained by mixing a binder and a solvent to silicon nitride powder to a mold, and solidifying molten silicon in the mold.
- a mold release agent obtained by mixing a binder and a solvent to silicon nitride powder to a mold
- solidifying molten silicon in the mold When the concentration of Fe contained as impurities in the silicon nitride powder is x (atomic ppm) and the thickness of the release agent applied to the mold is y ( ⁇ m), x ⁇ 5.0, 20 ⁇ y ⁇ 100 And x ⁇ y ⁇ 100.
- the Fe concentration in the silicon nitride powder is reduced through a step of bringing hydrochloric acid or aqua regia into contact with the silicon nitride powder.
- x ⁇ y ⁇ 30 In one embodiment of the method for producing polycrystalline silicon according to the present invention, x ⁇ y ⁇ 30.
- the temperature of hydrochloric acid or aqua regia is 60-100 ° C.
- the present invention provides polycrystalline silicon in which the carrier lifetime of the crystal face in contact with the release agent is 5 ⁇ sec or more.
- polycrystalline silicon in which a region having a short lifetime of the surface layer due to Fe contained as impurities in the release agent is substantially eliminated can be obtained, so that the material yield is good and the conversion efficiency is high.
- a solar cell can be manufactured.
- the release agent used in the present invention can be produced by using silicon nitride powder as a material and mixing it in a solution composed of a binder and a solvent to form a slurry, but it is contained in commercially available silicon nitride powder. Since the Fe concentration is high (typically 10 ppm or more), it cannot be used directly in the present invention. Therefore, it is first necessary to reduce the Fe concentration in the silicon nitride powder.
- hydrochloric acid or aqua regia capable of effectively dissolving iron and the silicon nitride powder are brought into contact with each other. And the said contact is performed in grinders, such as a ball mill using a grinding medium which does not use Fe as a material and / or Fe, and a vibration mill. With such a configuration, the Fe concentration can be reduced to a desired level in a shorter time.
- the agglomeration of the silicon nitride powder can be easily solved, so that the contact efficiency between the Fe component and the acid mixed in the silicon nitride powder is increased, and the Fe component Melting out will be performed efficiently.
- the silicon nitride powder to be used is preferably smaller in particle size because the contact efficiency is higher.
- the median particle size (d50) is preferably 1 ⁇ m or less.
- a grinding medium not containing Fe As a material in order to prevent secondary contamination.
- nylon, PVC, PP, PE, ABS, or other resins or balls made of silicon nitride are used. can do.
- a resin even if a resin component is mixed in the silicon nitride powder, it volatilizes in the subsequent annealing step, so that there is an effect of suppressing secondary contamination.
- ultrasonic waves are superior to ball mills in that there is no fear of secondary contamination.
- the ultrasonic wave and the ball mill may be used alone or in combination. What is necessary is just to set suitably the time required in order to melt
- Hydrochloric acid or aqua regia may be used as an aqueous solution at room temperature (15 to 25 ° C.), but it is desirable to use it as a heated aqueous solution at about 60 to 100 ° C., preferably 80 to 100 ° C. from the viewpoint of Fe dissolution performance.
- the acid concentration in the aqueous solution is desirably 2 to 30% by mass, preferably 5 to 20% by mass in hydrochloric acid for efficient Fe dissolution. The upper limit is determined because the dissolution rate decreases even if the concentration is too high.
- the target Fe concentration in the silicon nitride powder is 5.0 atomic ppm or less at the stage after this post-treatment.
- the Fe concentration in the silicon nitride powder is preferably 3.0 atomic ppm or less, more preferably 1.0 atomic ppm or less, and even more preferably 0.5 atomic ppm or less.
- the silicon nitride powder is mixed with a conventional binder and solvent to prepare a release agent.
- the binder include, but are not limited to, PVA (polyvinyl alcohol), PVB (polyvinyl butyral), MC (methyl cellulose), CMC (carboxymethyl cellulose), EC (ethyl cellulose), HPC (hydroxypropyl cellulose), wax, and starch.
- PVA polyvinyl alcohol
- PVB polyvinyl butyral
- MC methyl cellulose
- CMC carboxymethyl cellulose
- EC ethyl cellulose
- HPC hydroxypropyl cellulose
- wax hydroxypropyl cellulose
- starch starch
- PVA polyvinyl alcohol
- the solvent include, but are not limited to, water and alcohol, and water is preferable because of easy handling.
- the mixing ratio of the silicon nitride powder, the binder and the solvent is not particularly limited and may be appropriately set in consideration of the viscosity at the time of coating.
- the binder is 100 g and the solvent is 100 g with respect to 100 g of the silicon nitride powder. be able to.
- the release agent is applied to the inner surface of a mold having an appropriate shape and size.
- the release agent is preferably applied with a uniform thickness.
- the mold is not limited, but generally a quartz crucible or a graphite crucible can be used. Examples of the application method include application by spray, spatula, and brush, but there is no particular limitation. If the thickness of the mold release agent applied to the mold is too thin, it will not serve as a mold release agent, and conversely if it is too thick, it will be easy to peel from the mold. Therefore, the thickness of the release agent applied to the mold needs to be 20 to 100 ⁇ m, and preferably 30 to 80 ⁇ m.
- the Fe concentration in the silicon nitride powder used for the release agent is x (atomic ppm) and the thickness of the release agent applied to the mold is y ( ⁇ m)
- x ⁇ y ⁇ 100 It is important to apply the release agent under the following conditions. If xxy> 100, there will be an adverse effect on the lifetime due to the diffusion of Fe from the release agent into the silicon. On the other hand, when x ⁇ y ⁇ 100, a region having a good lifetime is suddenly expanded. It is important to control the thickness of the release agent simultaneously with the reduction of the Fe concentration in the silicon nitride powder.
- the mold is annealed to remove the solvent and binder.
- Annealing may be performed by any method known to those skilled in the art.
- the annealing may be performed by heating the mold to 850 to 950 ° C. in the atmosphere, holding the temperature for 3 to 5 hours, and then cooling the mold. Can do.
- the solvent and binder are removed from the release agent by evaporation or thermal decomposition due to the high temperature during heating.
- a method for producing polycrystalline silicon using the mold obtained as described above is not limited, but includes a casting method in which high-purity silicon is melted and poured into a mold and grown and solidified in the mold. It is done.
- a Siemens method is known as a method for obtaining high-purity silicon.
- a metal silicon raw material having a purity of about 97% is chlorinated and then purified and reduced to obtain high purity silicon of 11N or higher.
- Polycrystals can be grown by putting raw materials in a crucible and solidifying in one direction from the bottom of the crucible. Specifically, the molten sample is sequentially solidified in one direction from the bottom of the container by moving a mold containing molten silicon in a furnace having an appropriate temperature gradient or lowering the temperature of the furnace.
- the decrease in the lifetime of the surface layer due to the impurity Fe contained in the release agent is substantially eliminated, and the region having a good lifetime is dramatically expanded.
- an area of 1 ⁇ sec or less exists from the contact surface of the polycrystalline release agent to about 2 cm, but 5 ⁇ sec or more is typical also in the contact surface of the polycrystalline release agent according to the present invention. Can be obtained.
- the Fe concentration in the silicon nitride powder used for the release agent is measured by ICP-MS in accordance with JISK0133-2007.
- ICP-MS of type 7500CS manufactured by Agilent was used.
- the thickness of the mold release agent applied to the mold was determined by measuring the weight of the mold before applying the mold release agent and the weight after evaporating the solvent and binder after applying the mold release agent.
- the weight of silicon is calculated, and the weight is measured by the following formula: weight of coated silicon nitride (g) /3.44 (g / cm 3 ) / surface area of crucible inner surface (cm 2 ).
- Silicon lifetime is measured by a chemical passivation method using iodine.
- the measurement procedure is as follows. The grown crystal is cut into a wafer, and the surface is lapped with sandpaper of # 600, and then etched with hydrofluoric acid to obtain a mirror surface. Put the crystals in a plastic bag and fill the crystal surface with iodine methanol solution so that it is thin and almost uniform.
- the lifetime was measured by the micro PCD method, and the apparatus used was measured using WT2000 manufactured by SEMI LAB. The measurement method was specifically carried out by the method described in SEMI MF1535-1106.
- Example 1 (comparative example)> 200 g of silicon nitride powder (SN-E10 manufactured by Ube Industries, specific surface area: 9 to 13 m 2 / g, Fe concentration ⁇ 100 ppm, median particle size: about 0.5 ⁇ m) was prepared. When the Fe concentration in the powder sample was measured, it was 10.0 atomic ppm. This was mixed with 200 mL of PVA and 200 mL of water to prepare a slurry-like mold release agent in which silicon nitride was uniformly dispersed.
- silicon nitride powder SN-E10 manufactured by Ube Industries, specific surface area: 9 to 13 m 2 / g, Fe concentration ⁇ 100 ppm, median particle size: about 0.5 ⁇ m
- This mold release agent is uniformly applied to the inner surface of a quartz crucible (Glassman (trade name) crucible manufactured by Covalent Materials, purity: 99% by mass (SiO 2 ), shape: inner dimensions of width 190 mm ⁇ depth 190 mm ⁇ height 300 mm) It was applied with a brush. Thereafter, the quartz crucible coated with the release agent was baked in the atmosphere at 950 ° C. for 3 hours to remove PVA and water. At this time, the thickness of the release agent applied to the quartz crucible was 50 ⁇ m.
- the silicon chunk raw material was charged into the quartz crucible coated with the release agent obtained above.
- the crucible charged with the raw material was placed in a Bridgman furnace, heated to 1500 ° C. under reduced pressure in an argon atmosphere to completely dissolve the silicon, and then subjected to unidirectional solidification to produce polycrystalline silicon.
- the growth rate was 10 mm / hr, the growth time was 15 hours, and the temperature drop time was 12 hours.
- the obtained polycrystalline silicon was taken out, it was vertically split with a band saw, and after lapping with # 600 sandpaper, the surface was etched with hydrofluoric acid, and then the in-plane measurement of lifetime was performed using the iodine passivation method described above. However, it was less than 1 ⁇ sec at the bottom and side portions in contact with the crucible.
- Example 2 (comparative example)> The silicon nitride powder is immersed in hydrochloric acid (10% by mass) at 20 ° C. and washed by stirring with a Teflon (registered trademark) coated magnetic stirrer for 5 hours, and then immersed in ultrapure water to remove the supernatant. Post-processing was performed multiple times. The Fe concentration in the silicon nitride powder after the treatment was 5.0 atomic ppm. Otherwise, a release agent was prepared in the same manner as in Example 1. The release agent was applied to the quartz crucible and the polycrystalline silicon was produced under the same conditions as in Example 1. As a result, the lifetime of silicon was less than 1 ⁇ sec.
- Example 3 (comparative example)> A release agent was prepared, a release agent was applied to the quartz crucible, and polycrystalline silicon was produced under the same conditions as in Example 1 except that the thickness of the release agent applied to the quartz crucible was 20 ⁇ m. As a result, the lifetime of silicon was less than 1 ⁇ sec.
- Example 4 (comparative example)> A release agent was prepared, a release agent was applied to the quartz crucible, and polycrystalline silicon was manufactured under the same conditions as in Example 2 except that the thickness of the release agent applied to the quartz crucible was 10 ⁇ m. As a result, the crystal fixed to the crucible and crystal cracking occurred. It could not be evaluated as a crystal.
- Example 5 (comparative example)> The silicon nitride powder was immersed in hydrochloric acid (10% by mass) at 80 ° C. and ultrasonically stirred to wash for 1 hour, after which the supernatant was removed, washed with ultrapure water, and removal of the supernatant was repeated 5 times.
- the Fe concentration in the silicon nitride powder after the treatment was 1.0 atomic ppm.
- a release agent was prepared in the same manner as in Example 1.
- the release agent was applied to the quartz crucible under the same conditions as in Example 1 except that the thickness of the release agent applied to the quartz crucible was 200 ⁇ m. As a result, the lifetime of silicon was less than 1 ⁇ sec.
- Example 6 (Invention)> The silicon nitride powder was immersed in hydrochloric acid (10% by mass) at 80 ° C. and ultrasonically stirred to wash for 1 hour, after which the supernatant was removed, washed with ultrapure water, and removal of the supernatant was repeated 5 times.
- the Fe concentration in the silicon nitride powder after the treatment was 1.0 atomic ppm.
- a release agent was prepared in the same manner as in Example 1. Further, except that the thickness of the release agent applied to the quartz crucible was set to 100 ⁇ m, the release agent was applied to the quartz crucible and the polycrystalline silicon was manufactured under the same conditions as in Example 1. As a result, the lifetime of the silicon in contact with the release agent was 5 ⁇ sec.
- Example 7 (Invention)> The release agent was prepared, the release agent was applied to a quartz crucible, and polycrystalline silicon was produced under the same conditions as in Example 6 except that the time of ultrasonic stirring was doubled. As a result, the Fe concentration in the silicon nitride powder was 0.5 atomic ppm, and the lifetime of silicon in contact with the release agent was 25 ⁇ sec.
- Example 8 (Invention)> Except that the thickness of the release agent applied to the quartz crucible was 50 ⁇ m, the release agent dispersion was prepared, the release agent was applied to the quartz crucible, and the polycrystalline silicon was grown in the same manner as in Example 6. did. As a result, the lifetime of the silicon in contact with the release agent was 25 ⁇ sec.
- Example 9 (Invention example)> A mixture of 200 g of silicon nitride powder and 400 mL of hydrochloric acid (10% by mass) at 60 ° C. is kneaded in a ball mill ( ⁇ 240 mm ⁇ H220 mm nylon pot) containing 1200 nylon balls ( ⁇ 10 mm) at a rotational speed of 72 rpm for 3 hours. did. Then, it filtered using the membrane made from Teflon (trademark), the silicon nitride powder after filtration, and 800 mL of ultrapure water were mixed, and it put into the pot made from nylon, and wash-processed at the rotation speed of 72 rpm for 30 minutes.
- the process from filtration to ultrapure water washing was repeated and carried out 5 times in total.
- the Fe concentration in the powder sample after the treatment was 2.0 atomic ppm.
- a release agent was prepared under the same conditions as in Example 1. Further, except that the thickness of the release agent applied to the quartz crucible was 50 ⁇ m, the release agent was applied to the quartz crucible and the polycrystalline silicon was produced under the same conditions as in Example 1. As a result, the lifetime of the silicon in contact with the release agent was 5 ⁇ sec.
- Example 10 A mixture of 200 g of silicon nitride powder and 400 mL of hydrochloric acid (10% by mass) at 60 ° C. is kneaded in a ball mill ( ⁇ 240 mm ⁇ H220 mm nylon pot) containing 1200 nylon balls ( ⁇ 10 mm) at a rotational speed of 72 rpm for 3 hours. did. Then, it filtered using the membrane made from a Teflon (trademark), the silicon nitride powder after filtration, and 800 mL of ultrapure water were mixed, and it put into the pot made from nylon, and wash-processed at the rotation speed of 72 rpm for 30 minutes.
- the process from filtration to ultrapure water washing was repeated and carried out 5 times in total.
- the treated silicon nitride was further immersed in hydrochloric acid (10%) at 100 ° C. and subjected to ultrasonic cleaning, followed by the same post-treatment as above (filtering and ultrapure water cleaning were performed 5 times).
- the Fe concentration in the silicon nitride powder thus obtained was 0.1 atomic ppm.
- a release agent dispersion was prepared in the same manner as in Example 1. Further, except that the thickness of the release agent applied to the quartz crucible was set to 100 ⁇ m, the release agent was applied to the quartz crucible and the polycrystalline silicon was manufactured in the same manner as in Example 1. As a result, the lifetime of the silicon in contact with the release agent was 150 ⁇ sec, which was the same value as the lifetime inside the crystal.
- Example 11 (comparative example)> A mixture of 200 g of silicon nitride powder and 400 mL of hydrochloric acid (10% by mass) at 60 ° C. is kneaded in a ball mill ( ⁇ 240 mm ⁇ H220 mm nylon pot) containing 1200 nylon balls ( ⁇ 10 mm) at a rotational speed of 72 rpm for 3 hours. did. Then, it filtered using the membrane made from Teflon (trademark), the silicon nitride powder after filtration, and 800 mL of ultrapure water were mixed, and it put into the pot made from nylon, and wash-processed at the rotation speed of 72 rpm for 30 minutes.
- the process from filtration to ultrapure water washing was repeated and carried out 5 times in total.
- the Fe concentration in the powder sample after the treatment was 2.0 atomic ppm.
- a release agent was prepared under the same conditions as in Example 1. Further, except that the thickness of the release agent applied to the quartz crucible was 70 ⁇ m, the release agent was applied to the quartz crucible and the polycrystalline silicon was manufactured under the same conditions as in Example 1. As a result, the lifetime of the silicon in contact with the release agent was 1 ⁇ sec.
- Table 1 summarizes the above results. As can be seen from Table 1, in the case satisfying all of x ⁇ 5.0, 20 ⁇ y ⁇ 100, and x ⁇ y ⁇ 100, the lifetime of the polycrystalline silicon is drastically improved.
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Abstract
Description
本発明において使用する離型剤は窒化ケイ素粉末を材料とし、これをバインダー及び溶媒からなる溶液中に混合してスラリー状にすることで製造可能であるが、市販されている窒化ケイ素粉末では含有するFe濃度が高い(10ppm以上であるのが典型的である。)ので、本発明に直接使用することはできない。そこで、窒化ケイ素粉末中のFe濃度を低減することがまず必要となる。
離型剤の調製後は、適当な形状及び寸法をもつ鋳型の内面に離型剤を塗布する。離型剤は均一な厚みで塗布することが好ましい。鋳型としては、限定的ではないが、一般に石英坩堝や黒鉛坩堝を使用することができる。塗布の方法としては、スプレー、へら、及び刷毛による塗布が挙げられるが特に制限はない。鋳型に塗布する離型剤の厚みは、薄すぎると離型剤としての役目を果たさず、逆に厚すぎると鋳型から剥離しやすくなる。従って、鋳型に塗布する離型剤の厚みは20~100μmとすることが必要であり、30~80μmとするのが好ましい。
上記のようにして得た鋳型を用いて多結晶シリコンを製造する方法としては、限定的ではないが、高純度のシリコンを溶融して鋳型に注ぎ、鋳型内で育成・凝固させるキャスト法が挙げられる。高純度のシリコンを得る方法としては例えばシーメンス法が知られている。この方法は、純度97%程度の金属シリコン原料を塩化した後、精製・還元することで、11N以上の高純度シリコンを得るというものである。多結晶は坩堝に原料を入れ、坩堝の底から一方向に凝固を実施することで育成することができる。具体的には、適当な温度勾配をもった炉内で溶融シリコンを入れた鋳型を移動する又は炉の温度を下げることで、容器の底から順次溶融試料を一方方向に凝固させる方法である。
本発明において使用される各種の特性値は以下の方法で測定することにする。
窒化ケイ素粉末(宇部興産社製SN-E10、比表面積:9~13m2/g、Fe濃度<100ppm、中央粒径:約0.5μm)を200g用意した。当該粉末試料中のFe濃度を測定したところ、10.0原子ppmであった。これを200mLのPVA及び200mLの水と混合し、窒化ケイ素が均一に分散したスラリー状の離型剤を調製した。この離型剤を石英坩堝(コバレントマテリアル社製グラッサン(商品名)ルツボ、純度:99質量%(SiO2)、形状:内側の寸法で幅190mm×奥行き190mm×高さ300mm)の内面に均一に刷毛により塗布した。その後、離型剤を塗布した石英坩堝を大気中で950℃×3時間焼成し、PVA及び水を除去した。このとき、石英坩堝に塗布した離型剤の厚みは50μmであった。
窒化ケイ素粉末を、20℃の塩酸(10質量%)中に浸漬してテフロン(登録商標)コート磁気撹拌子により5時間撹拌することにより洗浄し、その後超純水中に浸漬し、上澄み除去を複数回実施する後処理をした。処理後の窒化ケイ素粉末中のFe濃度は5.0原子ppmであった。その他は、例1と同様にして離型剤を調製した。また、離型剤の石英坩堝への塗布及び多結晶シリコンの製造も例1と同様の条件で実施した。その結果、シリコンのライフタイムは1μsec未満であった。
石英坩堝に塗布した離型剤の厚みを20μmとした他は、例1と同様の条件で離型剤の調製、離型剤の石英坩堝への塗布、及び多結晶シリコンの製造を実施した。その結果、シリコンのライフタイムは1μsec未満であった。
石英坩堝に塗布した離型剤の厚みを10μmとした他は、例2と同様の条件で離型剤の調製、離型剤の石英坩堝への塗布、及び多結晶シリコンの製造を実施した。その結果、結晶が坩堝に固着し、結晶割れが生じた。結晶として評価できなかった。
窒化ケイ素粉末を80℃の塩酸(10質量%)中に浸漬して超音波撹拌することにより1時間洗浄し、その後上澄みを除去し、超純水で洗浄、上澄みの除去を5回繰り返した。処理後の窒化ケイ素粉末中のFe濃度は1.0原子ppmであった。その他は、例1と同様にして離型剤を調製した。また、石英坩堝に塗布した離型剤の厚みを200μmとした他は、離型剤の石英坩堝への塗布を例1と同様の条件で実施した。その結果、シリコンのライフタイムは1μsec未満であった。
窒化ケイ素粉末を80℃の塩酸(10質量%)中に浸漬して超音波撹拌することにより1時間洗浄し、その後上澄みを除去し、超純水で洗浄、上澄みの除去を5回繰り返した。処理後の窒化ケイ素粉末中のFe濃度は1.0原子ppmであった。その他は、例1と同様にして離型剤を調製した。また、石英坩堝に塗布した離型剤の厚みを100μmとした他は、離型剤の石英坩堝への塗布及び多結晶シリコンの製造を例1と同様の条件で実施した。その結果、離型剤と接触した部分のシリコンのライフタイムは5μsecであった。
超音波撹拌の時間を2倍にした他は、例6と同様の条件で離型剤の調製、離型剤の石英坩堝への塗布、及び多結晶シリコンの製造を実施した。その結果、窒化ケイ素粉末中のFe濃度は0.5原子ppm、離型剤と接した部分のシリコンのライフタイムは25μsecとなった。
石英坩堝に塗布した離型剤の厚みを50μmとした他は、例6と同様の方法で離型剤分散液の調製、離型剤の石英坩堝への塗布、及び多結晶シリコンの育成を実施した。その結果、離型剤と接した部分のシリコンのライフタイムは25μsecであった。
窒化ケイ素粉末200gと60℃の塩酸(10質量%)400mLの混合物を、ナイロン製のボール(Φ10mm)を1200個入れたボールミル(Φ240mm×H220mmのナイロン製ポット)で3時間72rpmの回転数で混練した。その後、テフロン(登録商標)製のメンブレンを用いてろ過し、ろ過後の窒化珪素粉末と超純水800mLを混合してナイロン製のポットに入れ、30分間72rpmの回転数で洗浄処理した。ろ過から超純水洗浄までの工程は繰り返して行い、合計で5回実施した。処理後の粉末試料中のFe濃度は2.0原子ppmであった。その他は、例1と同様の条件で離型剤を調製した。また、石英坩堝に塗布した離型剤の厚みを50μmとした他は、離型剤の石英坩堝への塗布及び多結晶シリコンの製造を例1と同様の条件で実施した。その結果、離型剤と接した部分のシリコンのライフタイムは5μsecとなった。
窒化ケイ素粉末200gと60℃の塩酸(10質量%)400mLの混合物を、ナイロン製のボール(Φ10mm)を1200個入れたボールミル(Φ240mm×H220mmのナイロン製ポット)で3時間72rpmの回転数で混練した。その後、テフロン(登録商標)製のメンブレンを用いてろ過し、ろ過後の窒化珪素粉末と超純水800mLを混合してナイロン製のポットに入れ、30分間72rpmの回転数で洗浄処理した。ろ過から超純水洗浄までの工程は繰り返して行い、合計で5回実施した。上記処理した窒化ケイ素をさらに、100℃の塩酸(10%)中に浸漬して超音波洗浄を行い、上記同様の後処理(ろ過及び超純水洗浄を5回実施)をした。これにより得られた窒化ケイ素粉末中のFe濃度は0.1原子ppmであった。その他は、例1と同様にして離型剤分散液を調製した。また、石英坩堝に塗布した離型剤の厚みを100μmとした他は、離型剤の石英坩堝への塗布及び多結晶シリコンの製造を例1と同様の方法で実施した。その結果、離型剤と接した部分のシリコンのライフタイムは150μsecであり、結晶内部のライフタイムと同様な値となった。
窒化ケイ素粉末200gと60℃の塩酸(10質量%)400mLの混合物を、ナイロン製のボール(Φ10mm)を1200個入れたボールミル(Φ240mm×H220mmのナイロン製ポット)で3時間72rpmの回転数で混練した。その後、テフロン(登録商標)製のメンブレンを用いてろ過し、ろ過後の窒化珪素粉末と超純水800mLを混合してナイロン製のポットに入れ、30分間72rpmの回転数で洗浄処理した。ろ過から超純水洗浄までの工程は繰り返して行い、合計で5回実施した。処理後の粉末試料中のFe濃度は2.0原子ppmであった。その他は、例1と同様の条件で離型剤を調製した。また、石英坩堝に塗布した離型剤の厚みを70μmとした他は、離型剤の石英坩堝への塗布及び多結晶シリコンの製造を例1と同様の条件で実施した。その結果、離型剤と接した部分のシリコンのライフタイムは1μsecとなった。
Claims (7)
- 窒化ケイ素粉末にバインダー及び溶媒を混合してできた離型剤を鋳型に塗布し、該鋳型内で溶融シリコンを凝固させることを含む多結晶シリコンの製造方法であって、窒化ケイ素粉末中に不純物として含まれるFe濃度をx(原子ppm)とし、鋳型に塗布した離型剤の厚みをy(μm)とすると、x≦5.0、20≦y≦100、及びx×y≦100を満たすことを特徴とする多結晶シリコンの製造方法。
- 窒化ケイ素粉末中のFe濃度は、塩酸又は王水と窒化ケイ素粉末とを接触させる工程を経て低減されており、当該工程は超音波中及び/又はFeを材料としない粉砕媒体を用いた粉砕機中で行われる請求項1記載の製造方法。
- x≦1.0である請求項1又は2記載の製造方法。
- 30≦y≦80である請求項1~3何れか一項記載の製造方法。
- x×y≦30である請求項1~4何れか一項記載の製造方法。
- 塩酸又は王水は温度が60~100℃である請求項2~5何れか一項記載の製造方法。
- 離型剤と接触した結晶面のキャリアライフタイムが5μsec以上である多結晶シリコン。
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WO2015017098A1 (en) * | 2013-07-31 | 2015-02-05 | Christoph Sachs | Use of silicon nitride as a substrate and a coating material for the rapid solidification of silicon |
JP2018065710A (ja) * | 2016-10-18 | 2018-04-26 | 信越化学工業株式会社 | 多結晶シリコン塊、多結晶シリコン棒、および単結晶シリコンの製造方法 |
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