JP2006334671A - Method for manufacturing silicon casting mold - Google Patents

Method for manufacturing silicon casting mold Download PDF

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JP2006334671A
JP2006334671A JP2006259486A JP2006259486A JP2006334671A JP 2006334671 A JP2006334671 A JP 2006334671A JP 2006259486 A JP2006259486 A JP 2006259486A JP 2006259486 A JP2006259486 A JP 2006259486A JP 2006334671 A JP2006334671 A JP 2006334671A
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mold
silicon
release material
silicon nitride
silicon dioxide
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JP4884150B2 (en
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Muneyoshi Yamatani
宗義 山谷
Yohei Sakai
洋平 坂井
Yoshiharu Hasegawa
義治 長谷川
Satoshi Kawamura
聡 川村
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Kyocera Corp
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<P>PROBLEM TO BE SOLVED: To provide a silicon casting mold which solves the problem that the mold releasing agent is exfoliated and the mold can not be reused by the sticking of the mold releasing agent to the mold, when molten silicon is poured into the mold, when the molten silicon is solidified later, or when silicon raw material being put in the mold is melted, and in which the consumption of graphite by oxidation is reduced in the case of using graphite as mold material. <P>SOLUTION: In the method for making the silicon casting mold on the inner surface of which the mold releasing agent is coated, the mold releasing agent containing silicon nitride and silicon dioxide is coated by plasma thermal spray method. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

本発明はシリコン鋳造用鋳型の製造方法に関するものである。 The present invention relates to a method for manufacturing a silicon casting mold.

従来から太陽電池を形成するための半導体基板の一種として多結晶シリコンが用いられている。このような多結晶シリコンは、高温度で加熱溶融させたシリコン融液を鋳型内に注湯して凝固させることによって形成したり、シリコン原料を鋳型内に入れて一旦溶解した後に再び凝固させることによって形成している。   Conventionally, polycrystalline silicon has been used as a kind of semiconductor substrate for forming solar cells. Such polycrystalline silicon can be formed by pouring and solidifying a silicon melt that has been heated and melted at a high temperature in a mold, or by solidifying the silicon raw material once dissolved in the mold. Is formed by.

このような鋳型としては、通常、分割可能な黒鉛製鋳型の内表面に離型材を塗布したものが用いられ、離型材としてはシリコンの窒化物である窒化シリコン（Ｓｉ3Ｎ4）が用いられる。一般に、窒化シリコン、炭化珪素、酸化珪素等の粉末を適当なバインダーと溶剤とから構成される溶液中に混合して攪拌してスラリーとし、これを鋳型内壁に塗布若しくはスプレー等の手段でコーティングすることが公知の技術として知られている（例えば、15th Photovoltaic Specialists Conf. (1981), P576〜P580, "A NEW DIRECTIONAL SOLIDIFICATION TECHNIQUE FORPOLYCRYSTALLINE SOLAR GRADE SILICON"を参照）。 As such a mold, a detachable graphite mold having an inner surface coated with a release material is usually used, and silicon nitride (Si 3 N 4 ), which is a silicon nitride, is used as the mold release material. . In general, powders such as silicon nitride, silicon carbide, and silicon oxide are mixed in a solution composed of a suitable binder and solvent and stirred to form a slurry, which is coated on the inner wall of the mold by means such as coating or spraying. it known as known techniques (e.g., 15 th Photovoltaic Specialists Conf. ( 1981), see P576~P580, "a NEW DIRECTIONAL SOLIDIFICATION tECHNIQUE FORPOLYCRYSTALLINE SOLAR GRADE SILICON").

ところが、窒化シリコンを黒鉛製鋳型の内表面に塗布してシリコンを鋳造する場合、窒化シリコン膜は脆弱であることから、シリコン融液を注湯する際に、またその後の凝固の際に、窒化シリコン膜が破損して鋳型にシリコン融液が接触し、鋳型がシリコンの鋳塊に付着して脱型する際にシリコンの鋳塊に欠けが発生するという問題があった。また、鋳型内に入れたシリコン原料を溶解する際に、窒化シリコン膜が破損するという問題があった。   However, when silicon nitride is applied to the inner surface of a graphite mold and silicon is cast, the silicon nitride film is fragile. Therefore, when silicon melt is poured, and during subsequent solidification, nitriding is performed. There was a problem that when the silicon film was broken and the silicon melt contacted the mold and the mold adhered to the silicon ingot and removed from the mold, the silicon ingot was chipped. Further, there is a problem that the silicon nitride film is damaged when the silicon raw material put in the mold is melted.

また、二酸化シリコン（ＳｉＯ2）を黒鉛製鋳型の内表面に塗布してシリコンを鋳造することも提案されているが、二酸化シリコンを離型材として用いる場合、二酸化シリコンは黒鉛と付着性がよく、また二酸化シリコンとシリコンの鋳塊も付着性がよいために、二酸化シリコンが鋳型に付着して鋳型の再使用ができなくなったり、鋳型が離型材を介してシリコンの鋳塊に付着し、脱型するときにシリコンの鋳塊の一部に欠けが発生するという問題があった。 In addition, it has also been proposed to cast silicon by applying silicon dioxide (SiO 2 ) to the inner surface of a graphite mold, but when silicon dioxide is used as a release material, silicon dioxide has good adhesion to graphite, In addition, since silicon dioxide and silicon ingots have good adhesion, silicon dioxide adheres to the mold and the mold cannot be reused, or the mold adheres to the silicon ingot via a mold release material, and demolding When doing so, there was a problem that a part of the silicon ingot was chipped.

このような問題を解決するために、特開平７−２０６４１９号公報では、一層目に二酸化シリコンを塗布し、二層目に二酸化シリコンと窒化シリコンの混合物を塗布し、さらに三層目に窒化シリコンを塗布することが提案されている。   In order to solve such problems, Japanese Patent Laid-Open No. 7-206419 discloses that silicon dioxide is applied to the first layer, a mixture of silicon dioxide and silicon nitride is applied to the second layer, and silicon nitride is applied to the third layer. It has been proposed to apply.

ところが、このように離型材を三層構造に塗布すると、それぞれの層に対応する離型材を調合して塗布しなければならず、離型材の塗布と調合に手間が掛かるという問題があった。   However, when the release material is applied to the three-layer structure in this way, it is necessary to prepare and apply the release materials corresponding to the respective layers, and there is a problem that it takes time to apply and prepare the release material.

そこで、本発明者らは、二酸化シリコンと窒化シリコンの混合比率を最適化した離型材を提案した（特開平９−１７５８０９号公報）。   Therefore, the present inventors have proposed a release material in which the mixing ratio of silicon dioxide and silicon nitride is optimized (Japanese Patent Laid-Open No. 9-175809).

しかしながら、この技術によると離型材を塗布する基材がグラファイト材である場合、離型材中の二酸化シリコンと黒鉛が部分的に接触しているため、シリコンの融点である１４２０℃付近での使用中に黒鉛が酸化されてしまい、基材の損傷を早めるという問題がある。これは離型材と鋳型基材の接触力を増加させる目的で提案されている二酸化シリコン単独層を塗布する際にもっとも顕著である。   However, according to this technique, when the base material to which the release material is applied is a graphite material, silicon dioxide and graphite in the release material are in partial contact with each other, so that it is in use at around 1420 ° C. which is the melting point of silicon. There is a problem in that graphite is oxidized and the damage to the substrate is accelerated. This is most noticeable when a silicon dioxide single layer proposed for the purpose of increasing the contact force between the mold release material and the mold substrate is applied.

また、スラリー状の離型材を作製して鋳型に塗布するためには、水やアルコール等の溶剤と塗布成形用バインダー、さらには流動性を高めるための添加材等を適宜、混合して攪拌するのが普通である。成形用バインダーの中で最も利用されている物質としてＰＶＡ（ポリビニルアルコール）がある。ＰＶＡは接着性に優れることから、粉体の接着・結合に適してしている。   In addition, in order to prepare a slurry-like release material and apply it to the mold, a solvent such as water or alcohol, a binder for coating molding, and an additive for increasing fluidity are appropriately mixed and stirred. Is normal. PVA (polyvinyl alcohol) is the most used substance among the molding binders. Since PVA is excellent in adhesiveness, it is suitable for adhesion and bonding of powders.

成形（塗布）後は、その後の加熱や融液との接触中に熱分解生成物が融液中に混入するのを防ぐために、酸化雰囲気中で６００℃程度の温度で脱脂することが通常行なわれている。ＰＶＡは３００℃付近で急激に熱分解を起こしてＣＯ等にガス化する結果、９０％程度までは急速に除去することができるが、残り１０％は５００℃以上の温度に加熱してもなかなか除去されず、カーボン残渣として残ってしまうことが多い。   After molding (coating), degreasing is usually performed in an oxidizing atmosphere at a temperature of about 600 ° C. in order to prevent thermal decomposition products from being mixed into the melt during subsequent heating or contact with the melt. It is. PVA undergoes rapid thermal decomposition at around 300 ° C and gasifies to CO etc. As a result, it can be rapidly removed up to about 90%, but the remaining 10% can be easily heated to a temperature of 500 ° C or higher. It is often not removed and remains as a carbon residue.

また、離型材をカーボン系離型材に塗布した場合、酸化雰囲気中で高温脱脂を行なうと、離型材が酸化するため、消耗が進む結果、耐久性が落ち、結果的にシリコン鋳塊の製作コストを増大させるという問題がある。   In addition, when a release material is applied to a carbon-based release material, if the high-temperature degreasing is performed in an oxidizing atmosphere, the release material will oxidize, resulting in a decrease in durability, resulting in the production cost of the silicon ingot. There is a problem of increasing.

一方、脱脂を不活性雰囲気中で実施すると、有機高分子の熱分解反応が急速に進行する結果、水素原子が引き抜かれてＣＨが直線状に並び、それが環状になってベンゼンその他環状化合物になる。さらに、脱水素反応を繰り返して大きく縮合して炭素の多い煤へと成長してしまう。一旦、煤として安定化してしまうと熱分解で除去することは困難であるため、離型材中や離型材表面に付着したままシリコン融液と接触することになる。融液と接触した煤あるいは融液中に溶け込んだ炭素は、太陽電池特性を低下させるばかりでなく、析出して鋳塊をスライスする際に加工不良を生む原因になる場合が多い。ＰＶＡに変わる有機バインダーは種々存在するが、塗布性や接着性を兼ね備えたものはない。また、離型材としての充分な強度を有し、且つ有機バインダーを使用することがなく、また離型材塗布時間を短縮する有効な方法はない。   On the other hand, when degreasing is performed in an inert atmosphere, the thermal decomposition reaction of the organic polymer proceeds rapidly. As a result, hydrogen atoms are extracted and CH is arranged in a straight line, which becomes cyclic and becomes benzene or other cyclic compounds. Become. In addition, the dehydrogenation reaction is repeated and condensed to grow into carbon-rich soot. Once stabilized as soot, it is difficult to remove by thermal decomposition, so that it comes into contact with the silicon melt while adhering to the mold release material or the mold release material surface. The soot in contact with the melt or the carbon dissolved in the melt not only deteriorates the solar cell characteristics, but often causes a processing defect when it precipitates and slices the ingot. There are various organic binders that can be used instead of PVA, but none has both coating properties and adhesiveness. Further, it has sufficient strength as a release material, does not use an organic binder, and there is no effective method for shortening the release material application time.

本発明は、このような従来技術の問題点に鑑みてなされたものであり、鋳型内にシリコン融液を注湯する際、その後の凝固する際、或いは鋳型に入れたシリコン原料を溶解する際に、離型材が剥離したり、離型材が鋳型に付着して鋳型が再使用できなくなったり、鋳型材を黒鉛にした場合の酸化消耗を抑えたシリコン鋳造用鋳型を提供することを目的とする。   The present invention has been made in view of such problems of the prior art, and when pouring a silicon melt into a mold, when solidifying thereafter, or when melting a silicon raw material put in the mold Another object is to provide a casting mold for silicon casting in which the mold release material is peeled off, the mold release material adheres to the mold and the mold cannot be reused, or the mold material is made of graphite and the oxidation consumption is suppressed. .

また、鋳型の内表面に窒化シリコンと二酸化シリコンを含有したものをプラズマ溶射機を用いてコーティングすることにより、シリコンの鋳塊が鋳型に付着することによって発生するシリコンの欠けを防止すると共に、従来使用していた有機バインダーを除去する脱バインダー工程を省略し、シリコン鋳塊の作製コストを削減したシリコン鋳造方法を提供することを目的とする。   In addition, by coating the inner surface of the mold containing silicon nitride and silicon dioxide using a plasma spraying machine, silicon chipping caused by adhesion of the silicon ingot to the mold can be prevented. An object of the present invention is to provide a silicon casting method that eliminates the binder removal step of removing the organic binder that has been used and reduces the production cost of the silicon ingot.

上記目的を達成するため、本発明に係るシリコン鋳造鋳型の製造方法では、鋳型の内表面に離型材を塗布したシリコン鋳造用鋳型において、前記材として、窒化シリコンと二酸化シリコンを含有したものをプラズマ溶射法で塗布する上記シリコン鋳造用鋳型の製造方法では、前記窒化シリコンと二酸化シリコンの混合比が１：９から９：１であることが望ましい。   In order to achieve the above object, in a method for producing a silicon casting mold according to the present invention, a silicon casting mold in which a mold release material is applied to the inner surface of a mold, the material containing silicon nitride and silicon dioxide as a plasma is used as the material. In the method for producing a silicon casting mold applied by spraying, it is desirable that the mixing ratio of silicon nitride and silicon dioxide is 1: 9 to 9: 1.

また、上記シリコン鋳造用鋳型の製造方法では、前記窒化シリコンと二酸化シリコンの混合材料の厚みが２０μｍ以上であることが望ましい。   In the method for manufacturing a silicon casting mold, the thickness of the mixed material of silicon nitride and silicon dioxide is preferably 20 μm or more.

また、上記シリコン鋳造用鋳型の製造方法では、前記鋳型の本体が黒鉛からなることが望ましい。   In the method for manufacturing a silicon casting mold, it is preferable that the main body of the mold is made of graphite.

以上のように、本発明に係るシリコン鋳造用鋳型の製造方法によれば、離型材として、窒化シリコンと二酸化シリコンを含有したものをプラズマ溶射法で塗布することから、鋳型がシリコンの鋳塊に付着することによって発生するシリコンの欠けを防止することができると共に、従来使用していた有機バインダーを除去する脱バインダー工程を省略することができ、シリコン鋳塊の製作コストを低減することができる。   As described above, according to the method for producing a casting mold for silicon casting according to the present invention, as a release material, a material containing silicon nitride and silicon dioxide is applied by a plasma spraying method. The chipping of silicon generated by the adhesion can be prevented, and the binder removal step for removing the organic binder that has been conventionally used can be omitted, so that the production cost of the silicon ingot can be reduced.

以下、本発明を添付図面に基づき詳細に説明する。図１は、本発明に係るシリコン鋳造用鋳型に用いられる鋳型の一例を示す図である。   Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a view showing an example of a mold used for a silicon casting mold according to the present invention.

鋳型１は例えば黒鉛などから成り、一つの底部材１ａと四つの側部材１ｂを組み合わせた分割と組み立てが可能な分割型鋳型などで構成される。なお、底部材１ａと側部材１ｂは、ボルト（不図示）などで固定することによって分割可能に組み立てられたり、底部材１ａと側部材１ｂが丁度嵌まる枠部材（不図示）で固定することによって分割可能に組み立てられる。   The mold 1 is made of, for example, graphite, and is composed of a split mold that can be divided and assembled by combining one bottom member 1a and four side members 1b. The bottom member 1a and the side member 1b are assembled so as to be separable by fixing with bolts (not shown) or the like, or fixed with a frame member (not shown) in which the bottom member 1a and the side member 1b just fit. Is assembled in a separable manner.

鋳型１の内表面には、底部材１ａや側部材１ｂを何回も繰り返して使用することができるように離型材２が塗布される。このような離型材２としては、窒化シリコン（Ｓｉ3Ｎ4）からなる下地材料を塗布した上に窒化シリコン（Ｓｉ3Ｎ4）と二酸化シリコン（ＳｉＯ2）を２８：７２〜７５：２５の重量比率で混合した混合材料を塗布する。窒化シリコンの粉体、および窒化シリコンと二酸化シリコンの粉体をポリビニルアルコール水溶液で混ぜ合わせて鋳型１の内面に塗布する。窒化シリコンと二酸化シリコンをポリビニルアルコール水溶液などで混合することによって、粉体である窒化シリコンと二酸化シリコンがスラリー状となり、黒鉛製の鋳型１に塗布しやすくなる。 The mold release material 2 is applied to the inner surface of the mold 1 so that the bottom member 1a and the side member 1b can be used repeatedly. As such a mold release material 2, a base material made of silicon nitride (Si 3 N 4 ) is applied, and then silicon nitride (Si 3 N 4 ) and silicon dioxide (SiO 2 ) are 28:72 to 75:25. A mixed material mixed in a weight ratio is applied. Silicon nitride powder and silicon nitride and silicon dioxide powder are mixed with an aqueous polyvinyl alcohol solution and applied to the inner surface of the mold 1. By mixing silicon nitride and silicon dioxide with an aqueous polyvinyl alcohol solution or the like, powdered silicon nitride and silicon dioxide become a slurry and can be easily applied to the graphite mold 1.

窒化シリコンの粉体としては、０．４〜０．６μｍ程度の平均粒径を有するものが用いられる。また、二酸化シリコンの粉体としては、２０μｍ程度の平均粒径を有するものが用いられる。このような窒化シリコンと二酸化シリコンを濃度が５〜１５重量％程度のポリビニルアルコール水溶液に混合してスラリー状とし、へらや刷毛などで鋳型１の内表面に塗布する。その状態で自然乾燥又はホットプレートに載せて乾燥させて鋳型１内にシリコン融液を注湯する。   As the silicon nitride powder, one having an average particle diameter of about 0.4 to 0.6 μm is used. As the silicon dioxide powder, one having an average particle diameter of about 20 μm is used. Such silicon nitride and silicon dioxide are mixed in a polyvinyl alcohol aqueous solution having a concentration of about 5 to 15% by weight to form a slurry, which is applied to the inner surface of the mold 1 with a spatula or a brush. In that state, the silicon melt is poured into the mold 1 by natural drying or drying by placing on a hot plate.

離型材２中の窒化シリコンと二酸化シリコンとの混合材料の混合比率は、重量比率で２８：７２〜７５：２５の間に調整したものを使用する。しかしながら、窒化シリコンの重量比率が２８％に近づく程、離型材２と鋳型１の反応が顕著になるため、鋳型材１の上に窒化シリコンからなる下地材料を０.０４ｇ／ｃｍ2以上塗布して耐酸化層とし、その上に窒化シリコンと二酸化シリコンとの混合材料を０.０４ｇ／ｃｍ2以上塗布する。下地材料と混合材料との単位面積当りの塗布重量が０.０４ｇ／ｃｍ2未満である場合には離型材層２としての強度が保てなくなったり、混合材料中の二酸化シリコン（ＳｉＯ2）と鋳型１中の黒鉛とが部分的に融着したりする。 The mixing ratio of the mixed material of silicon nitride and silicon dioxide in the release material 2 is adjusted to a weight ratio of 28:72 to 75:25. However, as the weight ratio of silicon nitride approaches 28%, the reaction between the mold release material 2 and the mold 1 becomes more prominent. Therefore, a base material made of silicon nitride is applied to the mold material 1 by 0.04 g / cm 2 or more. Then, 0.04 g / cm 2 or more of a mixed material of silicon nitride and silicon dioxide is applied thereon. Or not be maintained, the strength of the releasing agent layer 2 when the coating weight per unit area of the base material and the mixed material is less than 0.04 g / cm 2, silicon dioxide in the mixed material as (SiO 2) The graphite in the mold 1 is partially fused.

シリコン融液の注湯と凝固は、例えば鋳型１の内面に離型材２を塗布して乾燥させた後に、鋳型１を７．０〜９．０Ｔｏｒｒに減圧したアルゴン（Ａｒ）雰囲気中に置き、鋳型１をシリコン融液と同程度か若干低い温度で加熱してシリコン融液を注湯する。また鋳型１内にシリコン原料を入れ、直接溶解してもよい。しかる後、鋳型１の底部から徐々に降温させてシリコン融液を鋳型の底部から徐々に凝固させる。最後に鋳型１を分割してシリコンの鋳塊を取り出すことにより完成する。   For the silicon melt pouring and solidification, for example, the mold release material 2 is applied to the inner surface of the mold 1 and dried, and then the mold 1 is placed in an argon (Ar) atmosphere reduced to 7.0 to 9.0 Torr. The mold 1 is heated at a temperature similar to or slightly lower than the silicon melt to pour the silicon melt. Alternatively, a silicon raw material may be placed in the mold 1 and dissolved directly. Thereafter, the temperature is gradually lowered from the bottom of the mold 1 to gradually solidify the silicon melt from the bottom of the mold. Finally, the mold 1 is divided to complete the silicon ingot.

次ぎに、本発明に係るシリコン鋳造用鋳型の一実施形態を説明する。この発明では、離型材２として窒化シリコンからなる下地材料と、窒化シリコンと二酸化シリコンを２８：７２〜７５：２５の重量比率で混合した混合材料と、窒化シリコンからなる表面材料とを重ねて塗布する下地材料と混合材料との上に、さらに窒化シリコンからなる表面材料を０．０４ｇ／ｃｍ2以上塗布して耐酸素溶出層とする。表面材料の塗布量が少ないとシリコン融液と混合材料中の二酸化シリコンとの接触が盛んになって融液中の酸素濃度が増加する。融液中の酸素はウエハーにした後のデバイス工程における種々の処理工程において析出物として顕在化して品質に影響を及ぼすことから、酸素濃度を適度に最適化する。 Next, an embodiment of a silicon casting mold according to the present invention will be described. In the present invention, a base material made of silicon nitride, a mixed material in which silicon nitride and silicon dioxide are mixed at a weight ratio of 28:72 to 75:25, and a surface material made of silicon nitride are applied in an overlapping manner as the release material 2. Further, 0.04 g / cm 2 or more of a surface material made of silicon nitride is applied on the base material and the mixed material to form an oxygen-resistant elution layer. When the coating amount of the surface material is small, the contact between the silicon melt and silicon dioxide in the mixed material becomes active and the oxygen concentration in the melt increases. Oxygen in the melt is manifested as precipitates in various processing steps in the device process after forming the wafer and affects the quality, so that the oxygen concentration is appropriately optimized.

次ぎに、本発明に係るシリコン鋳造用鋳型の製造方法を説明する。鋳型１の内表面には、離型材２がプラズマ溶射法を用いてコーティングされる。プラズマ溶射機は、プラズマ流中に各種粉末材料を送って溶融噴射して皮膜を形成する装置である。溶射温度は３２０００°Ｋに及ぶプラズマ気流中の１００００℃前後の温度帯を使用して溶射粒子の噴射速度はマッハ１に達しており、この結果極めて高品質で緻密な皮膜層が形成される。   Next, a method for producing a silicon casting mold according to the present invention will be described. A mold release material 2 is coated on the inner surface of the mold 1 using a plasma spraying method. The plasma spraying machine is an apparatus for forming a film by sending various powder materials into a plasma stream and melt-spraying them. The spraying temperature of the sprayed particles reaches Mach 1 using a temperature range of about 10,000 ° C. in a plasma airflow of 32000 ° K. As a result, a very high quality and dense coating layer is formed.

しかしながら、窒化シリコンは約１９００℃（１ａｔｍ、ｉｎ Ｎ2）で昇華分解してしまうため、単体では液相を作らずに溶射による皮膜層を形成することができない。そこで、比較的低温でガラス層を形成する二酸化シリコンを焼結助剤として混合することにより、窒化シリコン粉体は溶融した二酸化シリコン中に溶け込んだ状態で鋳型１の基材に融着して急速に冷却されることにより固着する。 However, since silicon nitride undergoes sublimation decomposition at about 1900 ° C. (1 atm, in N 2 ), a coating layer by thermal spraying cannot be formed without forming a liquid phase by itself. Therefore, by mixing silicon dioxide that forms a glass layer at a relatively low temperature as a sintering aid, the silicon nitride powder is rapidly melted and fused to the base material of the mold 1 while being dissolved in the molten silicon dioxide. It is fixed by being cooled.

シリコン融液の注湯と凝固は、例えば鋳型の内面に離型材２を塗布して乾燥させた後に、鋳型１を７．０〜９．０Ｔｏｒｒに減圧したアルゴン（Ａｒ）雰囲気中に置き、鋳型１をシリコン融液と同程度か若干低い温度で加熱してシリコン融液を注湯する。また、鋳型１内にシリコン原料を入れ、直接溶解してもよい。しかる後、鋳型１の底部から徐々に降温させてシリコン融液を鋳型１の底部から徐々に凝固させる。最後に鋳型１を分割してシリコンの鋳塊を取り出すことにより完成する。   For the pouring and solidification of the silicon melt, for example, the mold release material 2 is applied to the inner surface of the mold and dried, and then the mold 1 is placed in an argon (Ar) atmosphere reduced to 7.0 to 9.0 Torr. 1 is heated at a temperature similar to or slightly lower than the silicon melt to pour the silicon melt. Alternatively, a silicon raw material may be placed in the mold 1 and dissolved directly. Thereafter, the temperature is gradually lowered from the bottom of the mold 1 to gradually solidify the silicon melt from the bottom of the mold 1. Finally, the mold 1 is divided to complete the silicon ingot.

平均粒径０．５μｍの窒化シリコン粉末を秤量して８．７％のポリビニルアルコール水溶液で攪拌混合してスラリー状にした離型材を得た。その離型材を黒鉛製鋳型の内表面に刷毛で塗布してホットプレートに載せて乾燥した（下地材料）。単位面積当りの塗布重量は０、０．０２、０．０４、０．２ｇ／ｃｍ2と変化させた。その後下地材料の上に平均粒径０．５μｍの窒化シリコン粉末と平均粒径２０μｍの二酸化シリコン粉末を秤量して８．７％のポリビニルアルコール水溶液で攪拌混合してスラリー状にして得た離型材を刷毛で塗布してホットプレートに載せて乾燥した（混合材料）。乾燥終了後、鋳型を８．０Ｔｏｒｒに減圧したアルゴン雰囲気中に置き、黒鉛ヒータを使って１０００℃に加熱した状態で鋳型内にシリコン融液６８ｋｇを注湯して７時間かけて徐々に凝固させた。冷却後固化したシリコンの鋳塊を鋳型から取り出し、離型材と鋳型の付着の有無、シリコンの鋳塊と鋳型の付着の有無について調べた。その結果を表１に示す。

Figure 2006334671
A silicon nitride powder having an average particle size of 0.5 μm was weighed and stirred and mixed with an 8.7% aqueous polyvinyl alcohol solution to obtain a release material in a slurry form. The release material was applied to the inner surface of the graphite mold with a brush, placed on a hot plate and dried (underlying material). The coating weight per unit area was changed to 0, 0.02, 0.04, and 0.2 g / cm 2 . Thereafter, a release material obtained by weighing silicon nitride powder having an average particle size of 0.5 μm and silicon dioxide powder having an average particle size of 20 μm on the base material and stirring and mixing with an 8.7% aqueous polyvinyl alcohol solution to form a slurry. Was applied with a brush and placed on a hot plate and dried (mixed material). After drying, the mold is placed in an argon atmosphere with a reduced pressure of 8.0 Torr, and 68 kg of silicon melt is poured into the mold while being heated to 1000 ° C. using a graphite heater and gradually solidified over 7 hours. It was. After cooling, the solidified silicon ingot was taken out of the mold, and the presence or absence of adhesion between the release material and the mold and the presence or absence of adhesion between the silicon ingot and the mold were examined. The results are shown in Table 1.
Figure 2006334671

表１に示すように、下地材料の単位面積当り塗布重量がない場合（条件No.１、５、９、１３、１７、２１、２５、２９）には全ての条件で鋳型材表面酸化が観察された。また、下地材料、混合材料共に単位面積当り塗布重量が少ない場合には（条件No.１、５、９、１３)では、融液の鋳型材への融着が見られ離型材としての機能を有していないことが判った。また、混合材料の単位面積当り塗布重量が少ない場合（条件No.１〜１６）には、離型材が鋳型から剥離してしまい離型材強度そのものに問題があることが判った。結論として所定条件（No.１９、２０、２３、２４、２７、２８、３１、３２）で使用することが望ましいことが判った。   As shown in Table 1, when there is no coating weight per unit area of the base material (conditions No. 1, 5, 9, 13, 17, 21, 25, 29), the surface oxidation of the mold material was observed under all conditions. It was done. In addition, when the coating weight per unit area is small for both the base material and the mixed material (conditions Nos. 1, 5, 9, and 13), the melt can be fused to the mold material and function as a mold release material. It turns out that it does not have. Moreover, when the coating weight per unit area of the mixed material is small (conditions No. 1 to 16), it has been found that the release material peels off from the mold and there is a problem with the release material strength itself. As a conclusion, it has been found that it is desirable to use it under predetermined conditions (No. 19, 20, 23, 24, 27, 28, 31, 32).

平均粒径０．５μｍの窒化シリコン粉末を秤量して８．７％のポリビニルアルコール水溶液で攪拌混合してスラリー状にした離型材を得た。その離型材を黒鉛製鋳型の内表面に刷毛で塗布してホットプレートに載せて乾燥した（下地材料）。単位面積当りの塗布重量は０．０４ｇ／ｃｍ2とした。その後、下地材料の上に平均粒径０．５μｍの窒化シリコン粉末と平均粒径２０μｍの二酸化シリコン粉末を秤量して８．７％のポリビニルアルコール水溶液で攪拌混合してスラリー状にして得た離型材を刷毛で塗布してホットプレートに載せて乾燥した（混合材料）。さらに１、２層の上に平均粒径０．５μｍの窒化シリコン粉末を秤量して８．７％のポリビニルアルコール水溶液で攪拌混合してスラリー状にして得た離型材を刷毛で塗布してホットプレートに載せて乾燥した（表面材料）。表面材料の単位面積当りの塗布重量を０、０．０４、０．１、０．２ｇ／ｃｍ2と変化させた。乾燥終了後、鋳型を８．０Ｔｏｒｒに減圧したアルゴン雰囲気中に置き、黒鉛ヒータを使って１０００℃に加熱した状態で鋳型内にシリコン融液６８ｋｇを注湯して７時間かけて徐々に凝固させた。冷却後固化したシリコンの鋳塊を鋳型から取り出し、離型材と鋳型の付着の有無、シリコンの鋳塊と鋳型の付着の有無について調べた後、太陽電池を作製して変換効率を調べた。その結果を図２と表２に示す。

Figure 2006334671
A silicon nitride powder having an average particle size of 0.5 μm was weighed and stirred and mixed with an 8.7% aqueous polyvinyl alcohol solution to obtain a release material in a slurry form. The release material was applied to the inner surface of the graphite mold with a brush, placed on a hot plate and dried (underlying material). The coating weight per unit area was 0.04 g / cm 2 . Thereafter, a silicon nitride powder having an average particle size of 0.5 μm and a silicon dioxide powder having an average particle size of 20 μm were weighed on the base material, and stirred and mixed with an 8.7% aqueous polyvinyl alcohol solution to obtain a slurry. The mold was applied with a brush and placed on a hot plate and dried (mixed material). Further, a silicon nitride powder having an average particle diameter of 0.5 μm is weighed on the first and second layers, and a release material obtained by stirring and mixing with an 8.7% aqueous polyvinyl alcohol solution to form a slurry is applied with a brush and heated. Placed on plate and dried (surface material). The coating weight per unit area of the surface material was changed to 0, 0.04, 0.1, and 0.2 g / cm 2 . After drying, the mold is placed in an argon atmosphere with a reduced pressure of 8.0 Torr, and 68 kg of silicon melt is poured into the mold while being heated to 1000 ° C. using a graphite heater and gradually solidified over 7 hours. It was. After cooling, the solidified silicon ingot was taken out of the mold and examined for the presence of the release material and the mold and the presence of the silicon ingot and the mold, and then a solar cell was fabricated and the conversion efficiency was examined. The results are shown in FIG.
Figure 2006334671

図２と表２から明らかなように、表面材料の単位面積当りの塗布重量が０ｇ／ｃｍ2の場合には明らかに変換効率が低下するが、０．０４ｇ／ｃｍ2以上の塗布条件にすると変換効率の低下は殆ど見られない。 As is apparent from FIG. 2 and Table 2, the conversion efficiency is clearly reduced when the coating weight per unit area of the surface material is 0 g / cm 2 , but when the coating condition is 0.04 g / cm 2 or more. There is almost no decrease in conversion efficiency.

平均粒径０．５μｍの窒化シリコン粉末と平均粒径２０μｍの二酸化シリコン粉末を秤量し混合重量比にして１：９〜９：１の比率で作製した粉末をプラズマ溶射機で黒鉛製の鋳型材にコーティングした。皮膜厚みは１０、２５、４０、７５μｍになるように調整した。鋳型を８．０Ｔｏｒｒに減圧したアルゴン雰囲気中に置き、黒鉛ヒータを使って１０００℃に加熱した状態で鋳型内にシリコン融液７０ｋｇを注湯して７時間かけて徐々に凝固させた。冷却後固化したシリコンの鋳塊を鋳型から取り出し、離型材と鋳型の付着の有無、シリコンの鋳塊と鋳型の付着の有無について調べた。その結果を表３に示す。

Figure 2006334671
A powder prepared by weighing a silicon nitride powder having an average particle diameter of 0.5 μm and a silicon dioxide powder having an average particle diameter of 20 μm in a mixing weight ratio of 1: 9 to 9: 1 is formed by a plasma spraying machine using a graphite mold material. Coated. The film thickness was adjusted to 10, 25, 40, and 75 μm. The mold was placed in an argon atmosphere with a reduced pressure of 8.0 Torr, and 70 kg of silicon melt was poured into the mold in a state heated to 1000 ° C. using a graphite heater, and gradually solidified over 7 hours. After cooling, the solidified silicon ingot was taken out of the mold, and the presence or absence of adhesion between the release material and the mold and the presence or absence of adhesion between the silicon ingot and the mold were examined. The results are shown in Table 3.
Figure 2006334671

二酸化シリコンの混合比に拘わらず、コート層の厚みが１０μｍのものは鋳型材とシリコンが融着してしまうために使用できない。しかしながら、２５μｍ以上の厚みがあれば、窒化シリコンと二酸化シリコンを１：９から９：１の割合で混合したものを溶射コーティングすることで充分離型材としての機能を有することが分かった。コート層と離型材の付着力の観点からは窒化シリコン：二酸化シリコンの比率が７：３で最も付着性が良い結果が得られているが、二酸化シリコン比率が１０％以上あれば充分な付着力を有することが分かった。   Regardless of the mixing ratio of silicon dioxide, a coating layer having a thickness of 10 μm cannot be used because the mold material and silicon are fused. However, when the thickness is 25 μm or more, it has been found that a mixture of silicon nitride and silicon dioxide in a ratio of 1: 9 to 9: 1 has a function as a charge / separation mold material by thermal spray coating. From the viewpoint of the adhesion between the coating layer and the release material, the best adhesion was obtained when the ratio of silicon nitride: silicon dioxide was 7: 3. However, if the silicon dioxide ratio is 10% or more, sufficient adhesion is obtained. It was found to have

本発明に係るシリコン鋳造用鋳型の一例を示す図である。It is a figure which shows an example of the casting mold for silicon which concerns on this invention. 本発明に係るシリコン鋳造用鋳型の実験結果を示す図である。It is a figure which shows the experimental result of the casting mold for silicon which concerns on this invention.

符号の説明Explanation of symbols

１・・・鋳型、２・・・離型材 1 ... mold, 2 ... release material

Claims (4)

鋳型の内表面に離型材を塗布するシリコン鋳造用鋳型の製造方法において、前記離型材として、窒化シリコンと二酸化シリコンを含有したものをプラズマ溶射法で塗布することを特徴とするシリコン鋳造用鋳型の製造方法。 In a method for manufacturing a silicon casting mold in which a mold release material is applied to the inner surface of a mold, a silicon casting mold characterized in that a silicon nitride and silicon dioxide containing material is applied as a mold release material by plasma spraying. Production method. 前記窒化シリコンと二酸化シリコンの混合比が１：９から９：１であることを特徴とする請求項１に記載のシリコン鋳造用鋳型の製造方法。 2. The method for producing a silicon casting mold according to claim 1, wherein the mixing ratio of silicon nitride and silicon dioxide is 1: 9 to 9: 1. 前記窒化シリコンと二酸化シリコンの混合材料の厚みが２０μｍ以上であることを特徴とする請求項１又は請求項２に記載のシリコン鋳造用鋳型の製造方法。 3. The method for producing a silicon casting mold according to claim 1, wherein a thickness of the mixed material of silicon nitride and silicon dioxide is 20 μm or more. 4. 前記鋳型の本体が黒鉛からなることを特徴とする請求項１、請求項２、又は請求項３に記載のシリコン鋳造用鋳型の製造方法。 4. The method for producing a silicon casting mold according to claim 1, wherein the main body of the mold is made of graphite.
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