JP4480357B2

JP4480357B2 - Plate silicon manufacturing equipment

Info

Publication number: JP4480357B2
Application number: JP2003194269A
Authority: JP
Inventors: 北斗山次; 万人五十嵐; 浩谷口
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 2003-07-09
Filing date: 2003-07-09
Publication date: 2010-06-16
Anticipated expiration: 2023-07-09
Also published as: JP2005029405A

Description

【０００１】
【発明の属する技術分野】
本発明は、多結晶シリコンウエハの製造装置に関する。本発明のシリコンウエハの製造装置は、角型ルツボおよび誘導加熱方式を備える熔融炉において、角型ルツボの開口部分に断熱材が配置されていることを特徴とする。
【０００２】
【従来の技術】
多結晶シリコンウエハは、鋳型に入ったシリコン融液を時間をかけて徐々に冷却し、得られた多結晶インゴットをブロック上に切り分けた後、さらに、そのブロックをスライスして製造しているため、スライスによるコストおよびシリコンの損失が大きい。かかる問題を解決し、低コストにて多結晶シリコンウエハの大量生産を可能とするために、スライス工程を必要としない板状シリコンの製造方法が知られている（特許文献１参照）。この製造方法は、原料シリコン融液に基板を浸漬し、基板上に板状シリコンを成長させる方法であり、製造装置は、板状シリコンが形成される主表面を有する基板と、融液を保持するルツボと、融液に接触した基板を融液から離すための可動部材と、可動部材を冷却するための冷却手段とを備える。
【０００３】
【特許文献１】
特開２００１−２４７３９６号公報
【０００４】
【発明が解決しようとする課題】
上記の方法で製造する板状シリコンは、主として角型であるため、装置の小型化および効率化を目的として、角型ルツボおよび高周波誘導加熱方式を採用している。しかしながら、角型ルツボおよび高周波誘導加熱方式では、角型ルツボの角部で磁束密度が高まるため、角部での過昇温が見られる一方、角型ルツボの開口部分における辺の中央部分では、十分に温度が上がりにくいため、角型ルツボの水平方向で温度分布の差が生じやすい。
【０００５】
したがって、角型ルツボの角部では、必要以上の過昇温により、炉材を損傷しやすく、一方、角型ルツボの開口部分における辺の中央部分では、融液の過冷却および凝固が発生しやすい。このような角型ルツボ内における温度分布の差は、角型ルツボの割れの原因になり、原料シリコンの熔融時および板状シリコンの製造時に、角型ルツボが割れるという現象が発生しやすい。
【０００６】
本発明の課題は、多結晶シリコンウエハの製造時における、角型ルツボの水平方向の温度分布の差を小さくすることにより、炉材の損傷、原料融液の過冷却、凝固および角型ルツボの割れなどの問題を回避することにある。また、容易に適用でき、コストが安く、既存の角型ルツボをそのまま使用して、上記の目的を達成することを解決すべき課題とする。
【０００７】
【課題を解決するための手段】
本発明の板状シリコン製造装置は、角型ルツボと誘導加熱コイルを備える装置であって、角型ルツボの開口部分の少なくとも一部に断熱材を有することを特徴とする。断熱材は、角型ルツボの開口部分における辺の中央部分に配置されている態様が好ましい。また、断熱材は、下部と上部を有し、下部と上部が異なる形状、もしくは、異なる材質を有するものが好ましい。さらに、断熱材は、角型ルツボの開口部分と接する面に凹凸を有するものが好適である。
【０００８】
【発明の実施の形態】
本発明の板状シリコン製造装置の典型的な例を図１に示す。この製造装置は、誘導加熱コイル１と角型ルツボ２を備え、角型ルツボ２の開口部分の少なくとも一部に断熱材５を有する。角型ルツボの開口部分の少なくとも一部に断熱材を配置することにより、角型ルツボの水平方向の温度分布を平坦に矯正し、既存の角型ルツボをそのまま使用して、炉材の損傷、原料融液の過冷却および角型ルツボの割れなどの問題を回避することができるため、適用が容易で、コストも安い。
【０００９】
角型ルツボとは、ルツボの開口部分の形状が角型であるものを指し、たとえば、図１に開口部分が長方形をした角型ルツボの例を示す。製造される板状シリコンの平面形状が主として長方形であるため、角型ルツボの開口部分も長方形であることが多い。しかし、必ずしも長方形の場合に限られるものではなく、角型ルツボの開口部分が正方形である場合、または、ひし形もしくは平行四辺形である場合などのほか、五角形あるいは六角形などの四角形以外の場合であっても、本発明は有効である。また、本発明で用いるルツボの開口部分の形状が「角型」であるとは、直線のみで構成されて、角部が頂点部分を持つものに限らず、角部が曲線で構成されたものも含まれる。
【００１０】
角型ルツボ２の開口部分の少なくとも一部に断熱材５が配置されている。図１に示す例では、長方形をした角型ルツボ２の開口部分において、１組の向かい合う２辺の中央部に、合計２個の断熱材５を配置している。角型ルツボ２内には、原料融液４が収容されており、原料融液４は、炉構成材３および角型ルツボ２を介して、誘導加熱コイル１により加熱され、融点以上に保持されている。また、このような構成を有する溶融炉は、チャンバ６内に配置され、安定した結晶成長を行なうために、融液温度の調節と、チャンバ内の雰囲気温度とを厳密に制御できるような構成を有している。
【００１１】
図２に、従来の溶融炉の例を示す。図２（ａ）は、熔融炉における角型ルツボ２２およびその周辺の構成を示す斜視図であり、ＩＩＢ−ＩＩＢで切断したときの右側断面図を、図２（ｂ）に示す。角型ルツボ２２の周囲には、炉構成材２３が形成され、角型ルツボ２２内には原料融液２４が収容されている。図２（ｂ）では、従来の溶融炉において、誘導加熱により角型ルツボ２２へ移動する熱量をＷ１、角型ルツボから炉構成材へ移動する熱量をＱ１、角型ルツボ２２から原料融液２４へ移動する熱量をＡ１、原料融液２４から外部へ移動する熱量をＢ１、角型ルツボの開口部分から外部へ移動する熱量をＦ１、角型ルツボ代表温度をＴ１として表している。
【００１２】
一方、図３に、本発明の溶融炉の例を示す。図３（ａ）は、溶融炉における角型ルツボ３２およびその周辺の構成を示す斜視図であり、ＩＩＩＢ−ＩＩＩＢで切断したときの右側断面図を、図３（ｂ）に示す。角型ルツボ３２の周囲には、炉構成材３３が形成され、角型ルツボ３２内には、原料融液３４が収容されている。また、角型ルツボ３２の開口部分には、向かい合う１組の辺上に断熱材３５が形成されている。図３（ｂ）では、本発明の溶融炉において、誘導加熱により角型ルツボ３２へ移動する熱量をＷ２、角型ルツボ３２から炉構成材３３へ移動する熱量をＱ２、角型ルツボ３２から収容された原料融液３４へ移動する熱量をＡ２、原料融液３４から外部へ移動する熱量をＢ２、角型ルツボ３２の開口部分からの断熱材３５へ移動する熱量をＦ２、断熱材３５から外部へ移動する熱量をＦ３、角型ルツボ３２の代表温度をＴ２、断熱材３５の代表温度をＴ３と表している。
【００１３】
本発明においては、従来と同様の融液温度管理を行ない、本発明の融液の状態を、従来の融液の状態と近いものになるように制御しているため、Ｂ１とＢ２は極めて近く、その差は無視できる。また、同様の理由で、Ａ１とＡ２もほぼ等しい。また、炉構成材も同一であるため、Ｑ１とＱ２もほぼ等しい。また、図２（ａ）に示す従来の溶融炉では、角型ルツボ２２の開口部分における角部（頂点部分）２２ａ付近は、誘導加熱コイルが弧を描いているため、磁束密度が高まり、角部２２ａで集中的な過熱が生じる。一方、開口部分における辺の中央部２２ｂ付近は、逆に十分温度が上がらず、角型ルツボ２２中に収容した原料融液２４の過冷却または凝固が発生しやすい。
【００１４】
図２（ｂ）に示す従来の角型ルツボにおける熱収支としては、流入している熱量はＷ１であり、流出している熱量はＡ１とＱ１とＦ１である。また、定常状態では、流入と流出の熱量は等しくなるため、以下の式が成り立つ。
Ｗ１＝Ａ１＋Ｑ１＋Ｆ１
一方、図３（ａ）に示す本発明の板状シリコン製造装置における角型ルツボ３２は、図２（ａ）に示す従来の角型ルツボ２２の開口部分に断熱材３５を配置したものに相当する。したがって、従来時および本発明適用時で加熱電力を等しくした場合を想定すると、図２（ｂ）における角型ルツボから外部への流出熱量Ｆ１と、図３（ｂ）における断熱材から外部への流出熱量Ｆ３との関係によって、系の状態は変化する。すなわち、Ｆ３がＦ１より大きい場合は、流出熱量が大きくなり、断熱材を配置した箇所の角型ルツボの温度は下がっていくことになる。逆に、Ｆ３がＦ１より小さい場合は、流出する熱量が小さくなり、断熱材を配置した箇所の角型ルツボの温度は上がっていくことになる。
【００１５】
したがって、適切な断熱材を適切な箇所に配置することで、角型ルツボの水平方向における温度分布は矯正され、前述したような角部のみの過熱、辺の中央部付近での原料融液の過冷却および凝固の発生を抑制できる。また、角型ルツボの開口部分に適切な断熱材を配置することにより、同一の加熱電力であっても、本発明適用時の角型ルツボの温度が高くなり、原料融液を同一の温度に設定した場合には、本発明適用時の方が加熱電力は少なくて済むという効果がある。角型ルツボの水平方向における温度の均一化という目的を達成する上では、Ｆ３がＦ１より大きくなるような断熱材を角型ルツボの角部に配置し、角部における温度を下げる方法も考えられるが、その場合には、角型ルツボからの流出熱量が大きくなるため、加熱電力の増大を招き、溶融炉における他の箇所の損傷が生じやすくなる。
【００１６】
さらに、熱の流れをより詳細に検討する。前述したように、定常状態において、図２（ｂ）に示す角型ルツボ２２に関する熱収支としては、つぎの式が成り立つ。
Ｗ１＝Ａ１＋Ｑ１＋Ｆ１
同様に、図３（ｂ）に示す本発明適用時における角型ルツボ３２に関する熱収支としては、流入熱量はＷ２であり、流出熱量はＡ２とＱ２とＦ２であるため、同様に、定常状態ではつぎの式が成り立つ。
Ｗ２＝Ａ２＋Ｑ２＋Ｆ２
また、Ｆ２は、角型ルツボから断熱材への熱伝導成分、および角型ルツボから断熱材への熱輻射成分により構成されているため、熱伝導成分をＭ２、熱輻射成分をＮ２で表すと、つぎの式で表すことができる。
Ｆ２＝Ｍ２＋Ｎ２
Ｍ２＝（Ｔ２−Ｔ３）／Ｒ２３
Ｎ２＝σ×｛ε２×（Ｔ２）⁴−ε３１×（Ｔ３）⁴｝
ここでＲ２３はルツボと断熱材間の熱抵抗、ε２は角型ルツボの放射率、ε３１は断熱材下面の放射率、σはステファンボルツマン定数である。
【００１７】
また、図３（ｂ）に示す、本発明適用時の断熱材の熱収支としては、流入熱量はＦ２、流出している熱量はＦ３であり、同様に、定常状態では流入熱量と流出熱量は等しくなるため、つぎの式が成り立つ。
Ｆ２＝Ｆ３
Ｆ３もＦ２と同様、断熱材から雰囲気ガスへの熱伝導成分、および断熱材から外部への熱輻射成分により構成されているが、一般的に高温状態での固体から気体への熱伝導成分は、熱輻射成分に比べ無視できるほど小さいため、Ｆ３は主として熱輻射成分で構成されており、つぎの式に近似できる。
Ｆ３＝σ×ε３２×（Ｔ３）⁴
ここでε３２は断熱材上面の放射率である。
【００１８】
前述したように、Ｆ３の値がＦ１と比べて小さくなるほど、断熱材を配置した箇所の角型ルツボの温度を上げる効果がある。したがって、角型ルツボの開口部分における辺の中央部分に断熱材を配置することにより、従来から解決すべき問題であった、辺の中央部分における過冷却および凝固を回避し、角型ルツボの水平方向における温度差を小さくすることができる。また、角型ルツボの開口部分における少なくとも一部に断熱材を配置することにより、角型ルツボおよび断熱材から外部への熱移動は抑制されるため、加熱電力を低く抑えることができる。
【００１９】
ここに、辺の中央部分とは、角型ルツボの開口部における角部を除く部分をいい、過冷却などの生じやすい範囲を指す。また、角型ルツボの開口部分に配置する断熱材は、角型ルツボの水平方向における温度差を小さくする効果を奏する点で、図１に示すように、角型ルツボの開口部分の上部に配置する態様のほか、溶融炉の仕様などに応じて、開口部分の内側または外側の側面に配置する態様も本発明に含まれる。同様に、１辺上に１個の断熱材を配置する態様のほか、１辺上に複数個の断熱材を配置する態様も本発明に含まれる。
【００２０】
断熱材は、下部と上部を有し、下部と上部が異なる材質を有する態様が好ましい。たとえば、断熱材から外部への熱移動を抑制するため、少なくとも断熱材の上部は、放射率が低い材質が望ましい。また、角型ルツボから断熱材への輻射成分による熱移動を抑制するため、少なくとも断熱材の下部は、反射率が高い材質が望ましい。さらに、角型ルツボから断熱材への伝導成分による熱移動を抑制するため、少なくとも角型ルツボの開口部と接する下部は、熱抵抗の大きい材質あるいは／および形状を有する断熱材が望ましい。断熱材の材料には、上記の放射率および熱抵抗のほかに、使用温度での耐熱性、および使用雰囲気での低反応性などが求められる。たとえば、黒鉛製の角型ルツボを用いたシリコン熔融炉においては、チタン、タングステン、クロムなどの高融点金属あるいはその合金、黒鉛繊維をフェルト加工し成形したもの、炭化珪素、酸化アルミニウムなどのセラミクス類の板、酸化アルミニウム繊維をフェルト加工し成形したもの、Ｃ／Ｃコンポジットと呼ばれる炭素繊維強化炭素複合材料、などが好適である。
【００２１】
断熱材は、図４（ａ）に示すように、角型ルツボ４２上に、単一層からなる断熱材４５ａを配置する態様であっても、本発明の顕著な効果を奏するが、角型ルツボから断熱材への熱移動、および断熱材から外部への熱移動を抑制するために、角型ルツボおよび断熱材の材質ならびに使用条件などに応じて、下部と上部が異なる形状を呈する断熱材を配置することもできる。たとえば、図４（ｂ）に示すように、角型ルツボ４２上に配置される断熱材が、上部４５ｂ１と下部４５ｂ２を有し、上部と下部の形状が異なる態様とすることができる。また、積層する断熱材層は、２層とする場合のほか、３以上とすることもできる。
【００２２】
さらに、図４（ｃ）に示すように、角型ルツボ４２上の断熱材４５ｃを、場所により厚みを変えて、断熱性を傾斜させた構造とすることができる。あるいは、図４（ｄ）に示すように、角型ルツボ４２上の断熱材が、上層４５ｄ１と下層４５ｄ２とからなり、上層と下層とで幅（奥行き）が異なる態様とすることもできる。この場合、図４（ｄ）に示すように、２層からなる態様のほか、３層以上からなる態様とすることも可能である。また、図４（ｅ）に示すように、角型ルツボ４２の開口部分と接する面に凹凸を有する断熱材４５ｅを配置することができる。あるいは、図４（ｆ）に示すように、上層４５ｆ１を下層４５ｆ２で支える橋渡し構造を有する断熱材を角型ルツボ４２上に配置することもできる。
【００２３】
同様に、角型ルツボについても、材質および構造を検討するべきであるが、角型ルツボの材質および構造の選択肢は現実には狭く、そのために多くの費用が発生するケースが多い。この点、材質または構造を改良した断熱材の設置は、容易かつ安価である。また、既存の溶融炉への適用も可能であるなどの利点がある。
【００２４】
【実施例】
実施例１
本実施例においては、図１に示すような、角型ルツボ２および誘導加熱コイル１を備える溶融炉により、板状シリコンを製造した。角型ルツボの斜視図を図５（ｂ）に示す。この角型ルツボ５２の外寸は、長辺６００ｍｍ、短辺３００ｍｍ、高さ２５０ｍｍであり、内寸は、長辺５５０ｍｍ、短辺２５０ｍｍ、深さ２００ｍｍであり、高純度黒鉛製のものを用いた。また、断熱材は、図４（ａ）に示すような、黒鉛繊維をフェルト加工し成形した、長さ１００ｍｍ、幅２０ｍｍ、厚み３ｍｍのものを用い、図５（ｂ）に示すように、断熱材５５を、角型ルツボ５２の開口部分における長辺の中央部分の２箇所に設置した。炉構成材は、アルミナ繊維を厚み２０ｍｍのブランケット状に成形したものを用い、角型ルツボの外周および底部に配置した。
【００２５】
つぎに、得られる板状シリコンの比抵抗が１Ω・ｃｍになるように、ボロン濃度を調整したシリコン原料を、図１に示すように、角型ルツボ２内に入れ、チャンバ６内を６．７×１０^-3Ｐａ程度まで減圧後、チャンバ６内にＡｒガスを導入して常圧にした。以後は、１０Ｌ／ｍｉｎでＡｒガスを常時流したままにした。ついで、チャンバ６内を、約１５００℃まで段階的に昇温して完全にシリコン原料を融解し、必要に応じて、さらに新たなシリコン原料を投入し、湯面を所定位置に設定した。その後、チャンバ６内を、角型ルツボ２の温度が１４５０℃になるまで降温し、３０分間そのまま保持して、チャンバ６内およびシリコン融液４の温度を安定化した。本実施例における断熱材の配置場所、形状、サイズおよび材質を表１に示す。
【００２６】
【表１】

【００２７】
また、チャンバ６内およびシリコン融液４の温度が安定した後、図５（ｂ）に示すように、４本の熱電対ＴＣ１〜ＴＣ４を用いて、シリコン融液５４を収容している角型ルツボ５２の各点の温度を測定し、最大温度差（温度差の最大値）を計算した。その結果を表２に示す。温度の制御はＴＣ２を用いて行ない、ＴＣ２の温度を、角型ルツボの代表温度とした。
【００２８】
【表２】

【００２９】
つぎに、浸漬機構部を動作させ、黒鉛製の結晶成長用下地基板をシリコン融液に浸漬し、板状シリコンを製造した。製造の際に、シリコン融液の飛沫および板状シリコンの破片が、角型ルツボの開口部分における熱電対付近に落下する現象が稀に見られたが、熱電対のうち断熱材の設置されていない箇所にあるＴＣ２と、ＴＣ３と、ＴＣ４の付近に落下した場合は、測定温度が大幅に変わるのが観察された。一方、断熱材の設置されている箇所であるＴＣ１付近に落下した場合には、測定温度は変化しなかった。つづいて、さらに段階的に降温し、シリコン融液の凝固が発生するときの、角型ルツボの代表温度を測定した。その結果を表３に示す。
【００３０】
【表３】

【００３１】
従来の角型ルツボでは、融解中あるいは融解後に割れることがあったことから、実験回数に対する角型ルツボの割れ回数を調査した。その結果を表３に示す。また、実験終了後、炉構成材を解体したところ、アルミナ繊維をブランケット状に成形した炉構成材の厚みが減少していた。これは、アルミナ繊維が高温下に長時間さらされることで、結晶化が進み、密度が上がり、一部が気化することで、炉構成材の体積が減少したことによるものと思われる。角型ルツボに収容された融液の温度管理を長期間に亘り正確に行なうためには、このような炉構成材の変質は望ましくない。炉構成材の厚みの減少は、特に角型ルツボの角部付近で顕著であることから、実験終了後に、角型ルツボの角部における炉構成材の厚みを測定した。その結果を表３に示す。
【００３２】
実施例２
黒鉛繊維をフェルト加工し成形した長さ２５０ｍｍ、幅２０ｍｍ、厚み２ｍｍの断熱材を用い、図４（ｃ）に示すように、場所により厚みを変えて断熱性に傾斜を持たせた形状とした断熱材４５ｃを用いた以外は実施例１と同様にして、シリコン原料を融解した。本実施例における断熱材の条件を表１に示す。その後、角型ルツボの温度が１４５０℃になるまで降温した。実施例１と同様に角型ルツボの温度を表２に示す。つぎに、段階的に降温し、凝固の発生を観察し、角型ルツボの割れを調査し、実験終了後、炉構成材の厚みを測定した。シリコン融液の凝固発生温度、ルツボの割れ回数および炉構成材の厚みを表３に示す。
【００３３】
実施例３
図４（ａ）に示すような、長さ２５０ｍｍ、幅２５ｍｍ、厚み１ｍｍのＣ／Ｃコンポジットと呼ばれる炭素繊維強化炭素複合材料を断熱材として用いた以外は実施例１と同様にして、原料シリコンを融解した。本実施例における断熱材の条件を表１に示す。その後、角型ルツボの温度が１４５０℃になるまで降温し、安定させた。このときの角型ルツボの温度を表２に示す。その後、実施例１と同様に、シリコン融液の凝固発生温度、ルツボの割れ回数および炉構成材の厚みを調査した。その結果を表３に示す。
【００３４】
実施例４
図４（ａ）に示すような、酸化アルミニウム繊維をフェルト加工し成形した、長さ２５０ｍｍ、幅２０ｍｍ、厚み２ｍｍのものを断熱材として用いたこと以外は実施例１と同様にして、原料シリコンを融解した。本実施例における断熱材の条件を表１に示す。その後、角型ルツボの温度が１４５０℃になるまで降温し、安定させた。このときの角型ルツボの温度を表２に示す。その後、実施例１と同様に、シリコン融液の凝固発生温度、ルツボの割れ回数および炉構成材の厚みを調査した。その結果を表３に示す。
【００３５】
実施例５
図４（ｂ）に示すような、黒鉛繊維をフェルト加工し成形した、長さ２５０ｍｍ、幅２０ｍｍ、厚み１ｍｍの下部断熱材の上に、黒鉛繊維をフェルト加工し成形した、長さ１００ｍｍ、幅１０ｍｍ、厚み３ｍｍの上部断熱材を積層したものを断熱材として用いた以外は実施例１と同様にして、原料シリコンを融解した。本実施例における断熱材の条件を表１に示す。その後、角型ルツボの温度が１４５０℃になるまで降温し、安定させた。このときの角型ルツボの温度を表２に示す。その後、実施例１と同様に、シリコン融液の凝固発生温度、ルツボの割れ回数および炉構成材の厚みを調査した。その結果を表３に示す。
【００３６】
実施例６
図４（ｄ）に示すような、酸化アルミニウム繊維をフェルト加工し成形した、長さ２５０ｍｍ、幅２５ｍｍ、厚み１ｍｍの下部断熱材の上に、黒鉛繊維をフェルト加工し成形した、長さ２５０ｍｍ、幅１５ｍｍ、厚み３ｍｍの上部断熱材を積層したものを断熱材として用いた以外は実施例１と同様にして、原料シリコンを融解した。本実施例における断熱材の条件を表１に示す。その後、角型ルツボの温度が１４５０℃になるまで降温し、安定させた。このときの角型ルツボの温度を表２に示す。その後、実施例１と同様に、シリコン融液の凝固発生温度、ルツボの割れ回数および炉構成材の厚みを調査した。その結果を表３に示す。
【００３７】
実施例７
実施例１で用いたルツボと同じ形状の角型ルツボに、図６（ａ）に示すように、断熱材６５を４箇所に配置した。断熱材６５は、いずれも黒鉛繊維をフェルト加工し成形したものであり、角型ルツボ６２の長辺の中央部分には、長さ２５０ｍｍ、幅２５ｍｍ、厚み３ｍｍの断熱材を配置し、短辺の中央部分には、長さ１２５ｍｍ、幅２０ｍｍ、厚み２ｍｍの断熱材を配置した。それ以外は、実施例１と同様にして、原料シリコンを融解した。本実施例における断熱材の条件を表１に示す。その後、角型ルツボの温度が１４５０℃になるまで降温し、安定させた。シリコン融液６４を収容している角型ルツボ６２の温度を表２に示す。その後、実施例１と同様に、シリコン融液の凝固発生温度、ルツボの割れ回数および炉構成材の厚みを調査した。その結果を表３に示す。
【００３８】
実施例８
図６（ｂ）に示すように、外寸が、縦４５０ｍｍ、横４５０ｍｍ、高さ５００ｍｍであり、内寸が、縦４００ｍｍ、横４００ｍｍ、深さ４００ｍｍの角型ルツボ６２の各辺に、断熱材６５を配置した。断熱材は、いずれもＣ／Ｃコンポジットと呼ばれる炭素繊維強化炭素複合材料を用い、形状は、図４（ａ）に示すように、長さ２５０ｍｍ、幅２５ｍｍ、厚み０．５ｍｍのものを用いた。それ以外は、実施例１と同様にして、原料シリコンを融解した。本実施例における断熱材の条件を表１に示す。その後、角型ルツボの温度が１４５０℃になるまで降温し、安定させた。このときの角型ルツボの温度を表２に示す。その後、実施例１と同様に、シリコン融液の凝固発生温度、ルツボの割れ回数および炉構成材の厚みを調査した。その結果を表３に示す。
【００３９】
実施例９
断熱材として、図４（ｅ）に示すような、長さ２５０ｍｍ、幅２５ｍｍ、厚み５ｍｍのチタン製の板を、凹凸面が角型ルツボの開口部分に接するように配置した。凹凸部は、凸部間の距離が２ｍｍ、凹部の深さが２．５ｍｍのものを用いた。それ以外は、実施例１と同様にして、原料シリコンを融解した。本実施例における断熱材の条件を表１に示す。その後、角型ルツボの温度が１４５０℃になるまで降温し、安定させた。このときの角型ルツボの温度を表２に示す。その後、実施例１と同様に、シリコン融液の凝固発生温度、ルツボの割れ回数および炉構成材の厚みを調査した。その結果を表３に示す。
【００４０】
実施例１０
図４（ｆ）に示すような、酸化アルミニウム繊維をフェルト加工し成形した、長さ１０ｍｍ、幅２５ｍｍ、厚み１ｍｍの下部断熱材４５ｆ２を２箇所に配置し、その上に、酸化アルミニウム製の長さ２５０ｍｍ、幅２０ｍｍ、厚み５ｍｍの板からなる上部断熱材４５ｆ１を配置した。それ以外は、実施例１と同様にして、原料シリコンを融解した。本実施例における断熱材の条件を表１に示す。その後、角型ルツボの温度が１４５０℃になるまで降温し、安定させた。このときの角型ルツボの温度を表２に示す。その後、実施例１と同様に、シリコン融液の凝固発生温度、ルツボの割れ回数および炉構成材の厚みを調査した。その結果を表３に示す。
【００４１】
比較例１
本比較例においては、図５（ａ）に示すように、断熱材を用いなかった以外は実施例１と同様にして、原料シリコンを融解した。その後、角型ルツボの温度が１４５０℃になるまで降温し、安定させた。そのときの角型ルツボの温度を表２に示す。その後、実施例１と同様に、シリコン融液の凝固発生温度、ルツボの割れ回数および炉構成材の厚みを調査した。その結果を表３に示す。
【００４２】
従来は、角型ルツボの開口部分における長辺の中央部分付近が、他の位置と比べて温度が低いため、凝固は主として長辺中央部付近から発生していた。しかし、表２の結果から明らかなとおり、従来技術を再現した比較例では、角型ルツボの最大温度差が７０℃であるのに対して、本発明では、温度差が１２〜２６℃に低下しており、角型ルツボの開口部分の少なくとも一部に断熱材を配置することにより、角型ルツボの水平方向の温度差を小さくできることがわかった。また、表３の結果から明らかなとおり、温度分布が矯正され、角型ルツボの長辺中央部分の温度が上昇して凝固しにくくなるため、凝固発生時の角型ルツボの代表温度が、比較例における場合よりも相対的に低くなっていることが観察された。
【００４３】
また、従来の角型ルツボでは、融解中あるいは融解後に割れることが多かったが、表３の結果から明らかなとおり、本発明によれば、角型ルツボの水平方向の温度差が緩和する結果、角型ルツボの割れ頻度が下がることがわかった。一方、表３の結果から明らかなとおり、溶融炉の角部の炉構成材の厚みは、本発明は比較例に比べて厚いことから、溶融炉の角部における過熱が抑制されていることがわかった。したがって、本発明によれば、融液の温度管理を長期間に亘り正確に行なうことができるものと予想された。
【００４４】
今回開示された実施の形態および実施例はすべての点で例示であって制限的なものではないと考えられるべきである。本発明の範囲は上記した説明ではなくて特許請求の範囲によって示され、特許請求の範囲と均等の意味および範囲内でのすべての変更が含まれることが意図される。
【００４５】
【発明の効果】
本発明によれば、角型ルツボの水平方向における温度差を小さくすることができるから、炉材の損傷、原料融液の過冷却および凝固ならびに角型ルツボの割れを効果的に抑制することができる。また、既存の炉を利用することができるため、適用が容易かつ安価である。
【図面の簡単な説明】
【図１】本発明の板状シリコン製造装置を示す斜視図である。
【図２】図２（ａ）は、従来の熔融炉における角型ルツボおよびその周辺の構成を示す斜視図であり、図２（ｂ）は、図２（ａ）におけるＩＩＢ−ＩＩＢで切断したときの右側断面図である。
【図３】図３（ａ）は、本発明の溶融炉における角型ルツボおよびその周辺の構成を示す斜視図であり、図３（ｂ）は、図３（ａ）におけるＩＩＩＢ−ＩＩＩＢで切断したときの右側断面図である。
【図４】本発明における断熱材の断面図である。
【図５】熱電対を取り付けた角型ルツボの斜視図である。
【図６】熱電対を取り付けた角型ルツボの斜視図である。
【符号の説明】
１誘導加熱コイル、２角型ルツボ、３炉構成材、４原料融液、５，３５，５５，６５断熱材、６チャンバ。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polycrystalline silicon wafer manufacturing apparatus. The silicon wafer manufacturing apparatus of the present invention is characterized in that, in a melting furnace having a square crucible and an induction heating method, a heat insulating material is disposed in an opening portion of the square crucible.
[0002]
[Prior art]
The polycrystalline silicon wafer is manufactured by gradually cooling the silicon melt contained in the mold over time, cutting the resulting polycrystalline ingot on the block, and then slicing the block. High cost and silicon loss due to slicing. In order to solve such a problem and enable mass production of a polycrystalline silicon wafer at low cost, a method for producing a plate-like silicon that does not require a slicing process is known (see Patent Document 1). This manufacturing method is a method in which a substrate is immersed in a raw material silicon melt to grow plate silicon on the substrate, and the manufacturing apparatus holds a substrate having a main surface on which plate silicon is formed, and the melt. And a movable member for separating the substrate in contact with the melt from the melt, and a cooling means for cooling the movable member.
[0003]
[Patent Document 1]
JP 2001-247396 A
[0004]
[Problems to be solved by the invention]
Since the plate-like silicon manufactured by the above method is mainly rectangular, a rectangular crucible and a high-frequency induction heating method are employed for the purpose of reducing the size and efficiency of the apparatus. However, in the square crucible and the high frequency induction heating method, the magnetic flux density is increased at the corners of the square crucible, so that overheating is observed at the corners, while at the central part of the side in the opening part of the square crucible, Since the temperature does not rise sufficiently, a difference in temperature distribution tends to occur in the horizontal direction of the square crucible.
[0005]
Therefore, at the corners of the square crucible, the furnace material is easily damaged by excessive heating, while the melt is overcooled and solidified at the center of the side of the opening of the square crucible. Cheap. Such a difference in temperature distribution in the square crucible causes cracking of the square crucible, and a phenomenon that the square crucible breaks easily when the raw material silicon is melted and the plate-like silicon is produced.
[0006]
The object of the present invention is to reduce the difference in the temperature distribution in the horizontal direction of the square crucible during the manufacture of the polycrystalline silicon wafer, thereby causing damage to the furnace material, supercooling of the raw material melt, solidification, and solidification of the square crucible. The problem is to avoid problems such as cracking. Further, it is an object to be solved to achieve the above object by using an existing square crucible as it is, which can be easily applied and is low in cost.
[0007]
[Means for Solving the Problems]
The plate-like silicon manufacturing apparatus of the present invention is an apparatus including a square crucible and an induction heating coil, and is characterized by having a heat insulating material in at least a part of the opening of the square crucible. The aspect in which the heat insulating material is arrange | positioned at the center part of the edge | side in the opening part of a square crucible is preferable. The heat insulating material preferably has a lower part and an upper part, and the lower part and the upper part have different shapes or different materials. Furthermore, it is preferable that the heat insulating material has irregularities on the surface in contact with the opening of the square crucible.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
A typical example of the plate-like silicon manufacturing apparatus of the present invention is shown in FIG. This manufacturing apparatus includes an induction heating coil 1 and a square crucible 2, and has a heat insulating material 5 in at least a part of the opening of the square crucible 2. By arranging a heat insulating material in at least a part of the opening of the square crucible, the horizontal temperature distribution of the square crucible is corrected to be flat, and the existing square crucible is used as it is. Since problems such as supercooling of the raw material melt and cracking of the square crucible can be avoided, the application is easy and the cost is low.
[0009]
The term “square crucible” refers to a crucible whose opening has a square shape. For example, FIG. 1 shows an example of a rectangular crucible having a rectangular opening. Since the planar shape of the silicon plate produced is mainly rectangular, the opening of the square crucible is often rectangular. However, it is not necessarily limited to the case of a rectangle, and when the opening of a square crucible is a square, or when it is a rhombus or a parallelogram, or other than a rectangle such as a pentagon or a hexagon. Even if it exists, this invention is effective. In addition, the shape of the opening of the crucible used in the present invention is “square”, which is composed of only a straight line, and is not limited to a corner having a vertex, but a corner composed of a curve. Is also included.
[0010]
A heat insulating material 5 is disposed in at least a part of the opening of the square crucible 2. In the example shown in FIG. 1, a total of two heat insulating materials 5 are arranged in the central portion of two sides facing each other in the opening portion of a rectangular crucible 2 having a rectangular shape. A raw material melt 4 is accommodated in the square crucible 2, and the raw material melt 4 is heated by the induction heating coil 1 through the furnace constituent material 3 and the square crucible 2, and is held above the melting point. ing. Further, the melting furnace having such a configuration is arranged in the chamber 6 and has a configuration capable of strictly controlling the melt temperature and the atmospheric temperature in the chamber in order to perform stable crystal growth. Have.
[0011]
FIG. 2 shows an example of a conventional melting furnace. Fig.2 (a) is a perspective view which shows the structure of the square crucible 22 and its periphery in a melting furnace, and the right side sectional view when cut | disconnected by IIB-IIB is shown in FIG.2 (b). A furnace component 23 is formed around the square crucible 22, and a raw material melt 24 is accommodated in the square crucible 22. In FIG. 2 (b), in a conventional melting furnace, the amount of heat transferred to the square crucible 22 by induction heating is W1, the amount of heat transferred from the square crucible to the furnace component is Q1, and the raw material melt 24 from the square crucible 22 is shown. The amount of heat transferred to A1 is indicated as A1, the amount of heat transferred from the raw material melt 24 to the outside as B1, the amount of heat transferred from the opening of the square crucible to the outside as F1, and the representative temperature of the square crucible as T1.
[0012]
On the other hand, FIG. 3 shows an example of the melting furnace of the present invention. FIG. 3A is a perspective view showing the configuration of the square crucible 32 and its surroundings in the melting furnace, and FIG. 3B shows a right side cross-sectional view taken along IIIB-IIIB. A furnace component 33 is formed around the square crucible 32, and a raw material melt 34 is accommodated in the square crucible 32. Further, in the opening portion of the square crucible 32, a heat insulating material 35 is formed on a pair of sides facing each other. 3B, in the melting furnace of the present invention, the amount of heat transferred to the square crucible 32 by induction heating is W2, the amount of heat transferred from the square crucible 32 to the furnace component 33 is Q2, and the amount of heat transferred from the square crucible 32 is accommodated. The amount of heat transferred to the raw material melt 34 is A2, the amount of heat transferred from the raw material melt 34 to the outside is B2, the amount of heat transferred to the heat insulating material 35 from the opening of the square crucible 32 is F2, and the heat amount from the heat insulating material 35 to the outside The amount of heat transferred to F3 is represented by F3, the representative temperature of the square crucible 32 is represented by T2, and the representative temperature of the heat insulating material 35 is represented by T3.
[0013]
In the present invention, the melt temperature is controlled in the same manner as in the prior art, and the melt state of the present invention is controlled to be close to that of the conventional melt, so B1 and B2 are extremely close to each other. The difference is negligible. For the same reason, A1 and A2 are substantially equal. Further, since the furnace constituent materials are the same, Q1 and Q2 are substantially equal. In the conventional melting furnace shown in FIG. 2A, the induction heating coil draws an arc in the vicinity of the corner (vertex portion) 22a in the opening of the square crucible 22, so that the magnetic flux density increases, Concentrated overheating occurs in the portion 22a. On the other hand, in the vicinity of the central portion 22b of the side of the opening, the temperature does not rise sufficiently, and overcooling or solidification of the raw material melt 24 stored in the square crucible 22 is likely to occur.
[0014]
As for the heat balance in the conventional square crucible shown in FIG. 2B, the amount of heat flowing in is W1, and the amount of heat flowing out is A1, Q1, and F1. In the steady state, the inflow and outflow heat amounts are equal, so the following equation is established.
W1 = A1 + Q1 + F1
On the other hand, the square crucible 32 in the plate-shaped silicon manufacturing apparatus of the present invention shown in FIG. 3 (a) is equivalent to the one in which the heat insulating material 35 is arranged in the opening portion of the conventional square crucible 22 shown in FIG. 2 (a). To do. Therefore, assuming the case where the heating power is made equal between the conventional case and the present invention, the amount of heat F1 flowing out from the square crucible in FIG. 2B to the outside and the heat insulating material in FIG. The state of the system changes depending on the relationship with the amount of heat released F3. That is, when F3 is larger than F1, the amount of heat that flows out increases, and the temperature of the square crucible at the location where the heat insulating material is disposed decreases. On the other hand, when F3 is smaller than F1, the amount of heat flowing out becomes small, and the temperature of the square crucible at the place where the heat insulating material is disposed increases.
[0015]
Therefore, by arranging an appropriate heat insulating material at an appropriate location, the temperature distribution in the horizontal direction of the square crucible is corrected, and only the corner portion is overheated as described above, the raw material melt near the center of the side. The occurrence of supercooling and solidification can be suppressed. Further, by arranging an appropriate heat insulating material in the opening portion of the square crucible, the temperature of the square crucible at the time of application of the present invention is increased even when the heating power is the same, and the raw material melt is kept at the same temperature. When set, there is an effect that less heating power is required when the present invention is applied. In order to achieve the object of uniforming the temperature in the horizontal direction of the square crucible, a method of lowering the temperature at the corner by arranging a heat insulating material such that F3 is larger than F1 at the corner of the square crucible can be considered. In this case, however, the amount of heat that flows out from the square crucible increases, leading to an increase in heating power and easily causing damage to other parts in the melting furnace.
[0016]
In addition, the heat flow will be examined in more detail. As described above, in the steady state, the following equation holds for the heat balance related to the square crucible 22 shown in FIG.
W1 = A1 + Q1 + F1
Similarly, as the heat balance regarding the square crucible 32 when the present invention is applied as shown in FIG. 3B, the inflow heat amount is W2 and the outflow heat amounts are A2, Q2, and F2, similarly, in the steady state, The following equation holds.
W2 = A2 + Q2 + F2
Further, F2 is composed of a heat conduction component from the square crucible to the heat insulating material and a heat radiation component from the square crucible to the heat insulating material. Therefore, the heat conduction component is represented by M2 and the heat radiation component is represented by N2. It can be expressed by the following equation.
F2 = M2 + N2
M2 = (T2-T3) / R23
N2 = σ × {ε2 × (T2)^Four-Ε31 × (T3)^Four}
Here, R23 is the thermal resistance between the crucible and the heat insulating material, ε2 is the emissivity of the square crucible, ε31 is the emissivity of the lower surface of the heat insulating material, and σ is the Stefan Boltzmann constant.
[0017]
In addition, as shown in FIG. 3B, the heat balance of the heat insulating material when the present invention is applied is that the inflow heat amount is F2 and the outflow heat amount is F3. Similarly, in the steady state, the inflow heat amount and the outflow heat amount are Since they are equal, the following equation holds:
F2 = F3
F3 is also composed of a heat conduction component from the heat insulating material to the atmosphere gas and a heat radiation component from the heat insulation material to the outside, as in F2, but generally a heat conduction component from a solid to a gas at a high temperature state is Since F3 is mainly composed of thermal radiation components, it can be approximated by the following equation.
F3 = σ × ε32 × (T3)^Four
Here, ε32 is the emissivity of the upper surface of the heat insulating material.
[0018]
As described above, the smaller the value of F3 compared to F1, the higher the temperature of the square crucible at the location where the heat insulating material is disposed. Therefore, by arranging a heat insulating material in the central part of the side of the opening part of the square crucible, it is possible to avoid overcooling and solidification in the central part of the side, which has been a problem to be solved in the past. The temperature difference in the direction can be reduced. Further, by disposing a heat insulating material at least at a part of the opening of the square crucible, heat transfer from the square crucible and the heat insulating material to the outside is suppressed, so that the heating power can be kept low.
[0019]
Here, the central portion of the side means a portion excluding the corner portion in the opening portion of the square crucible, and indicates a range in which overcooling or the like is likely to occur. In addition, the heat insulating material arranged in the opening portion of the square crucible has an effect of reducing the temperature difference in the horizontal direction of the square crucible, and is arranged above the opening portion of the square crucible as shown in FIG. In addition to the embodiment to be performed, an embodiment in which the opening portion is disposed on the inner side or the outer side surface according to the specifications of the melting furnace is included in the present invention. Similarly, in addition to a mode in which one heat insulating material is arranged on one side, a mode in which a plurality of heat insulating materials are arranged on one side is also included in the present invention.
[0020]
It is preferable that the heat insulating material has a lower part and an upper part, and the lower part and the upper part have different materials. For example, in order to suppress heat transfer from the heat insulating material to the outside, at least an upper portion of the heat insulating material is desirably a material having a low emissivity. In addition, in order to suppress heat transfer due to the radiation component from the square crucible to the heat insulating material, at least the lower part of the heat insulating material is desirably made of a material having high reflectance. Furthermore, in order to suppress heat transfer due to the conduction component from the square crucible to the heat insulating material, at least the lower part in contact with the opening of the square crucible is preferably a heat insulating material having a high thermal resistance and / or a shape. In addition to the above emissivity and thermal resistance, the heat insulating material is required to have heat resistance at the operating temperature and low reactivity in the operating atmosphere. For example, in silicon melting furnaces using graphite square crucibles, high melting point metals such as titanium, tungsten and chromium or alloys thereof, graphite fibers formed by felt processing, ceramics such as silicon carbide and aluminum oxide A plate made of felt, an aluminum oxide fiber formed by felting, a carbon fiber reinforced carbon composite material called a C / C composite, and the like are suitable.
[0021]
As shown in FIG. 4A, the heat insulating material has the remarkable effect of the present invention even when the heat insulating material 45a composed of a single layer is disposed on the square crucible 42. In order to suppress heat transfer from the heat insulating material to the heat insulating material and heat transfer from the heat insulating material to the outside, a heat insulating material having a different shape at the lower and upper parts depending on the material of the square crucible and the heat insulating material and usage conditions, etc. It can also be arranged. For example, as shown in FIG. 4B, the heat insulating material arranged on the square crucible 42 may have an upper part 45b1 and a lower part 45b2, and the upper and lower shapes may be different. Moreover, the heat insulating material layer to laminate | stack can also be made into 3 or more besides the case where it makes it 2 layers.
[0022]
Furthermore, as shown in FIG.4 (c), the heat insulating material 45c on the square crucible 42 can be made into the structure where the heat insulation property was inclined by changing thickness according to a place. Or as shown in FIG.4 (d), the heat insulating material on the square crucible 42 consists of the upper layer 45d1 and the lower layer 45d2, and it can also be set as the aspect from which a width | variety (depth) differs in an upper layer and a lower layer. In this case, as shown in FIG. 4 (d), in addition to the mode composed of two layers, it is possible to adopt a mode composed of three or more layers. Moreover, as shown in FIG.4 (e), the heat insulating material 45e which has an unevenness | corrugation in the surface which contact | connects the opening part of the square crucible 42 can be arrange | positioned. Alternatively, as shown in FIG. 4 (f), a heat insulating material having a bridging structure that supports the upper layer 45 f 1 with the lower layer 45 f 2 can be disposed on the square crucible 42.
[0023]
Similarly, the material and structure of the square crucible should be considered, but the choice of the material and structure of the square crucible is actually narrow, which often causes a lot of costs. In this respect, the installation of the heat insulating material improved in material or structure is easy and inexpensive. Further, there is an advantage that it can be applied to an existing melting furnace.
[0024]
【Example】
Example 1
In the present example, plate-like silicon was produced by a melting furnace having a square crucible 2 and an induction heating coil 1 as shown in FIG. A perspective view of the square crucible is shown in FIG. The outer dimensions of the square crucible 52 are 600 mm long, 300 mm short, and 250 mm high, and the internal dimensions are 550 mm long, 250 mm short, 200 mm deep, and are made of high-purity graphite. It was. Moreover, as shown in FIG. 5 (b), a heat insulating material having a length of 100 mm, a width of 20 mm, and a thickness of 3 mm formed by felting and molding graphite fiber as shown in FIG. The material 55 was installed in two places in the center part of the long side in the opening part of the square crucible 52. As the furnace constituent material, alumina fibers formed into a blanket shape having a thickness of 20 mm were used and arranged on the outer periphery and the bottom of a square crucible.
[0025]
Next, as shown in FIG. 1, a silicon raw material whose boron concentration is adjusted so that the specific resistance of the obtained plate-like silicon is 1 Ω · cm is placed in the square crucible 2 and the chamber 6 is filled with 6. 7 × 10^-3After reducing the pressure to about Pa, Ar gas was introduced into the chamber 6 to normal pressure. Thereafter, Ar gas was kept flowing constantly at 10 L / min. Next, the temperature inside the chamber 6 was raised stepwise to about 1500 ° C. to completely melt the silicon raw material, and if necessary, new silicon raw material was added to set the molten metal surface at a predetermined position. Thereafter, the temperature in the chamber 6 was lowered until the temperature of the square crucible 2 reached 1450 ° C., and maintained for 30 minutes, thereby stabilizing the temperature in the chamber 6 and the silicon melt 4. Table 1 shows the location, shape, size and material of the heat insulating material in this example.
[0026]
[Table 1]

[0027]
In addition, after the temperature of the chamber 6 and the silicon melt 4 is stabilized, as shown in FIG. 5B, the square type containing the silicon melt 54 using the four thermocouples TC1 to TC4. The temperature of each point of the crucible 52 was measured, and the maximum temperature difference (maximum temperature difference) was calculated. The results are shown in Table 2. The temperature was controlled using TC2, and the temperature of TC2 was set as the representative temperature of the square crucible.
[0028]
[Table 2]

[0029]
Next, the dipping mechanism was operated to immerse the base substrate for crystal growth made of graphite in the silicon melt to produce plate-like silicon. During manufacturing, a rare phenomenon was observed in which silicon melt droplets and plate-like silicon fragments dropped near the thermocouple at the opening of the square crucible, but insulation was installed in the thermocouple. When the TC2, TC3, and TC4 were dropped in the absence, the measured temperature was observed to change significantly. On the other hand, when it fell to TC1 vicinity which is the location in which the heat insulating material is installed, measurement temperature did not change. Subsequently, the temperature was lowered stepwise, and the representative temperature of the square crucible when the silicon melt solidified was measured. The results are shown in Table 3.
[0030]
[Table 3]

[0031]
Since the conventional square crucible sometimes cracked during or after melting, the number of cracks of the square crucible relative to the number of experiments was investigated. The results are shown in Table 3. Further, when the furnace constituent material was disassembled after the experiment was completed, the thickness of the furnace constituent material in which the alumina fibers were formed into a blanket shape was reduced. This is probably because the alumina fibers are exposed to a high temperature for a long time, so that the crystallization progresses, the density increases, and a part of the alumina fibers evaporates to reduce the volume of the furnace constituent material. In order to accurately control the temperature of the melt contained in the square crucible over a long period of time, such a change in the furnace components is not desirable. Since the decrease in the thickness of the furnace constituent material is remarkable particularly in the vicinity of the corner of the square crucible, the thickness of the furnace constituent material at the corner of the square crucible was measured after the experiment. The results are shown in Table 3.
[0032]
Example 2
Using a heat insulating material of 250 mm in length, 20 mm in width, and 2 mm in thickness formed by felting and processing graphite fiber, as shown in FIG. 4 (c), the thickness was changed depending on the location, and the heat insulating property was inclined. The silicon raw material was melted in the same manner as in Example 1 except that the heat insulating material 45c was used. Table 1 shows the heat insulating material conditions in this example. Thereafter, the temperature was lowered until the temperature of the square crucible reached 1450 ° C. As in Example 1, the temperature of the square crucible is shown in Table 2. Next, the temperature was lowered stepwise, the occurrence of solidification was observed, cracks in the square crucible were investigated, and the thickness of the furnace constituent material was measured after the experiment. Table 3 shows the solidification temperature of the silicon melt, the number of crucible cracks, and the thickness of the furnace components.
[0033]
Example 3
Raw material silicon as in Example 1 except that a carbon fiber reinforced carbon composite material called a C / C composite having a length of 250 mm, a width of 25 mm, and a thickness of 1 mm as shown in FIG. Was melted. Table 1 shows the heat insulating material conditions in this example. Thereafter, the temperature of the square crucible was lowered to 1450 ° C. and stabilized. The temperature of the square crucible at this time is shown in Table 2. Thereafter, as in Example 1, the solidification temperature of the silicon melt, the number of crucible cracks, and the thickness of the furnace components were investigated. The results are shown in Table 3.
[0034]
Example 4
As shown in FIG. 4 (a), raw material silicon was used in the same manner as in Example 1 except that an aluminum oxide fiber formed by felt processing and having a length of 250 mm, a width of 20 mm, and a thickness of 2 mm was used as a heat insulating material. Was melted. Table 1 shows the heat insulating material conditions in this example. Thereafter, the temperature of the square crucible was lowered to 1450 ° C. and stabilized. The temperature of the square crucible at this time is shown in Table 2. Thereafter, as in Example 1, the solidification temperature of the silicon melt, the number of crucible cracks, and the thickness of the furnace components were investigated. The results are shown in Table 3.
[0035]
Example 5
As shown in FIG. 4 (b), a graphite fiber is felt-processed and molded, and the graphite fiber is felt-processed and molded on a lower insulating material having a length of 250 mm, a width of 20 mm, and a thickness of 1 mm. Raw material silicon was melted in the same manner as in Example 1 except that a laminate of an upper heat insulating material having a thickness of 10 mm and a thickness of 3 mm was used as the heat insulating material. Table 1 shows the heat insulating material conditions in this example. Thereafter, the temperature of the square crucible was lowered to 1450 ° C. and stabilized. The temperature of the square crucible at this time is shown in Table 2. Thereafter, as in Example 1, the solidification temperature of the silicon melt, the number of crucible cracks, and the thickness of the furnace components were investigated. The results are shown in Table 3.
[0036]
Example 6
As shown in FIG. 4 (d), the aluminum oxide fiber was felt processed and molded, and the graphite fiber was felt processed and formed on the lower heat insulating material having a length of 250 mm, a width of 25 mm, and a thickness of 1 mm. Raw material silicon was melted in the same manner as in Example 1 except that a laminate of an upper heat insulating material having a width of 15 mm and a thickness of 3 mm was used as the heat insulating material. Table 1 shows the heat insulating material conditions in this example. Thereafter, the temperature of the square crucible was lowered to 1450 ° C. and stabilized. The temperature of the square crucible at this time is shown in Table 2. Thereafter, as in Example 1, the solidification temperature of the silicon melt, the number of crucible cracks, and the thickness of the furnace components were investigated. The results are shown in Table 3.
[0037]
Example 7
As shown in FIG. 6 (a), the heat insulating material 65 was arranged at four locations in the square crucible having the same shape as the crucible used in Example 1. Each of the heat insulating materials 65 is formed by felt-processing graphite fiber, and a heat insulating material having a length of 250 mm, a width of 25 mm, and a thickness of 3 mm is disposed in the central portion of the long side of the square crucible 62, and the short side A heat insulating material having a length of 125 mm, a width of 20 mm, and a thickness of 2 mm was disposed in the central portion of the. Otherwise, the raw material silicon was melted in the same manner as in Example 1. Table 1 shows the heat insulating material conditions in this example. Thereafter, the temperature of the square crucible was lowered to 1450 ° C. and stabilized. Table 2 shows the temperature of the square crucible 62 containing the silicon melt 64. Thereafter, as in Example 1, the solidification temperature of the silicon melt, the number of crucible cracks, and the thickness of the furnace components were investigated. The results are shown in Table 3.
[0038]
Example 8
As shown in FIG. 6B, the outer dimensions are 450 mm in length, 450 mm in width, and 500 mm in height, and the inner dimensions are 400 mm in length, 400 mm in width, and 400 mm in depth. Material 65 was placed. As the heat insulating material, a carbon fiber reinforced carbon composite material called C / C composite was used, and the shape was 250 mm long, 25 mm wide, and 0.5 mm thick as shown in FIG. . Otherwise, the raw material silicon was melted in the same manner as in Example 1. Table 1 shows the heat insulating material conditions in this example. Thereafter, the temperature of the square crucible was lowered to 1450 ° C. and stabilized. The temperature of the square crucible at this time is shown in Table 2. Thereafter, as in Example 1, the solidification temperature of the silicon melt, the number of crucible cracks, and the thickness of the furnace components were investigated. The results are shown in Table 3.
[0039]
Example 9
As a heat insulating material, a titanium plate having a length of 250 mm, a width of 25 mm, and a thickness of 5 mm as shown in FIG. 4E was disposed so that the uneven surface was in contact with the opening of the square crucible. The uneven part used the thing whose distance between convex parts is 2 mm, and the depth of a recessed part is 2.5 mm. Otherwise, the raw material silicon was melted in the same manner as in Example 1. Table 1 shows the heat insulating material conditions in this example. Thereafter, the temperature of the square crucible was lowered to 1450 ° C. and stabilized. The temperature of the square crucible at this time is shown in Table 2. Thereafter, as in Example 1, the solidification temperature of the silicon melt, the number of crucible cracks, and the thickness of the furnace components were investigated. The results are shown in Table 3.
[0040]
Example 10
As shown in FIG. 4 (f), a lower heat insulating material 45f2 having a length of 10 mm, a width of 25 mm, and a thickness of 1 mm, which is formed by felting and forming aluminum oxide fibers, is arranged in two locations, and an aluminum oxide length An upper heat insulating material 45f1 made of a plate having a thickness of 250 mm, a width of 20 mm, and a thickness of 5 mm was disposed. Otherwise, the raw material silicon was melted in the same manner as in Example 1. Table 1 shows the heat insulating material conditions in this example. Thereafter, the temperature of the square crucible was lowered to 1450 ° C. and stabilized. The temperature of the square crucible at this time is shown in Table 2. Thereafter, as in Example 1, the solidification temperature of the silicon melt, the number of crucible cracks, and the thickness of the furnace components were investigated. The results are shown in Table 3.
[0041]
Comparative Example 1
In this comparative example, as shown in FIG. 5A, raw material silicon was melted in the same manner as in Example 1 except that no heat insulating material was used. Thereafter, the temperature of the square crucible was lowered to 1450 ° C. and stabilized. Table 2 shows the temperature of the square crucible at that time. Thereafter, as in Example 1, the solidification temperature of the silicon melt, the number of crucible cracks, and the thickness of the furnace components were investigated. The results are shown in Table 3.
[0042]
Conventionally, since the temperature in the vicinity of the central portion of the long side in the opening portion of the square crucible is lower than that in other positions, solidification has occurred mainly from the vicinity of the central portion of the long side. However, as is apparent from the results in Table 2, in the comparative example reproducing the prior art, the maximum temperature difference of the square crucible is 70 ° C., whereas in the present invention, the temperature difference is reduced to 12 to 26 ° C. In addition, it has been found that the temperature difference in the horizontal direction of the square crucible can be reduced by disposing a heat insulating material in at least a part of the opening of the square crucible. In addition, as is clear from the results in Table 3, the temperature distribution is corrected and the temperature of the central part of the long side of the square crucible rises, making it difficult to solidify. Therefore, the representative temperature of the square crucible when solidification occurs is compared. It was observed that it was relatively lower than in the example.
[0043]
Further, in the conventional square crucible, it was often cracked during melting or after melting. As is apparent from the results of Table 3, according to the present invention, the horizontal temperature difference of the square crucible is alleviated. It was found that the cracking frequency of the square crucible decreased. On the other hand, as is apparent from the results in Table 3, the thickness of the furnace constituent material at the corner of the melting furnace is thicker than that of the comparative example, so that overheating at the corner of the melting furnace is suppressed. all right. Therefore, according to the present invention, it was expected that the temperature control of the melt can be accurately performed over a long period of time.
[0044]
It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
[0045]
【The invention's effect】
According to the present invention, since the temperature difference in the horizontal direction of the square crucible can be reduced, it is possible to effectively suppress damage to the furnace material, supercooling and solidification of the raw material melt, and cracking of the square crucible. it can. Moreover, since an existing furnace can be used, application is easy and inexpensive.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a plate-like silicon manufacturing apparatus of the present invention.
FIG. 2 (a) is a perspective view showing a configuration of a square crucible and its surroundings in a conventional melting furnace, and FIG. 2 (b) is cut along IIB-IIB in FIG. 2 (a). FIG.
FIG. 3 (a) is a perspective view showing a configuration of a square crucible and its surroundings in the melting furnace of the present invention, and FIG. 3 (b) is cut along IIIB-IIIB in FIG. 3 (a). FIG.
FIG. 4 is a cross-sectional view of a heat insulating material in the present invention.
FIG. 5 is a perspective view of a square crucible to which a thermocouple is attached.
FIG. 6 is a perspective view of a square crucible to which a thermocouple is attached.
[Explanation of symbols]
1 induction heating coil, 2 square crucible, 3 furnace components, 4 raw material melt, 5, 35, 55, 65 heat insulating material, 6 chambers.

Claims

A plate-like silicon manufacturing apparatus comprising an induction heating coil and the square crucible, have a heat insulating material on at least a portion of the opening portion of the squared crucible,
The amount of heat transferred to the outside of the square crucible directly from the corner of the opening in the square crucible or through the heat insulating material is directly from the center of the side in the opening of the square crucible. Alternatively, the heat insulating material is disposed so as to be larger than the amount of heat transferred to the outside of the square crucible through the heat insulating material .

The plate-shaped silicon manufacturing apparatus according to claim 1, wherein the heat insulating material is disposed at a central portion of a side of the opening portion of the square crucible.

The plate-shaped silicon manufacturing apparatus according to claim 1, wherein the heat insulating material is disposed at least at a central portion of a side of the opening portion of the square crucible.

The said heat insulating material has a lower part and an upper part, and the lower part and the upper part exhibit a different shape, The plate-shaped silicon manufacturing apparatus in any one of Claims 1-3 characterized by the above-mentioned.

The said heat insulating material has a lower part and an upper part, and the lower part and upper part have a different material, The plate-shaped silicon manufacturing apparatus in any one of Claims 1-4 characterized by the above-mentioned.

The plate-like silicon manufacturing apparatus according to claim 1 , wherein the heat insulating material has irregularities on a surface in contact with the opening of the square crucible.