JP3909675B2

JP3909675B2 - Silicon single crystal manufacturing apparatus and silicon single crystal manufacturing method using the same

Info

Publication number: JP3909675B2
Application number: JP2002092479A
Authority: JP
Inventors: 昌弘櫻田; 栄一飯野; 亮二星; 伸晃三田村; 泉布施川; 友彦太田
Original assignee: Shin Etsu Handotai Co Ltd
Current assignee: Shin Etsu Handotai Co Ltd
Priority date: 2001-04-20
Filing date: 2002-03-28
Publication date: 2007-04-25
Anticipated expiration: 2022-03-28
Also published as: JP2003002780A

Description

【０００１】
【発明が属する技術分野】
本発明は、チョクラルスキー法（以下、ＣＺ法と称する）によるシリコン単結晶の製造装置及びそれを用いたシリコン単結晶の製造方法に関する。
【０００２】
【従来の技術】
近年の半導体素子の高集積化や大型化により、半導体素子を構成する電子回路は微細化の一途をたどっている。このため、半導体素子形成の基板とされるシリコンウエーハへの高品質化の要求は高まる一方であり、これを満足するためシリコン単結晶の育成においても様々な対策が検討されている。特に、シリコンウエーハの材料として最も多く用いられているのがＣＺ法によって製造されたシリコン単結晶であり、結晶を育成する際に結晶内部に形成される結晶欠陥が、ウエーハ表面層に素子を構成した場合の特性に大きく影響することから、単結晶育成時に結晶内部に形成される結晶欠陥を低密度に抑えた引上方法が要望されている。
【０００３】
例えば、特開平１１−７９８８９号公報には、シリコン単結晶の育成時に結晶内に取り込まれる欠陥が存在しない、あるいは存在しても極低密度であるシリコン単結晶を育成する技術が開示されている。ＣＺ法によるシリコン単結晶の育成では、引上速度や結晶の冷却条件等により結晶内部に取り込まれるグローンイン欠陥（Grown−in Defect）と呼ばれる結晶成長時の熱履歴に起因する結晶欠陥に違いがあることがわかってきた。
【０００４】
シリコン単結晶の引上速度が比較的速い急冷の状態で単結晶を育成した場合には、単結晶育成時に結晶内部でシリコン原子に不足が生じ、シリコン格子点に空孔となる部分が発生する。この空孔が単結晶の冷却時に凝集し、単結晶をウエーハに加工した際にウエーハ表面に凹部あるいは穴のような形となって現れ、空孔（ボイド、穴）起因のグローンイン欠陥が優勢なシリコン単結晶となる。このような空孔型の点欠陥をベイカンシー（Vacancy：以下、Ｖとも略記する）と呼び、ベイカンシーが凝集して生じる点欠陥が優勢となるシリコン単結晶内部の領域を、Ｖ領域と呼んでいる。また、ベイカンシーに起因するグローンイン欠陥としては、ＦＰＤ（Flow Pattern Defects）、ＣＯＰ（Crystal Originated Particle）及びＬＳＴＤ（Laser Scattering Tomography Defects）等があり、シリコン単結晶をウエーハに加工した時に、ウエーハ表面に八面体のボイド状の点欠陥等として観察される。
【０００５】
これに対し、シリコン単結晶の引上速度を極力抑え、育成結晶を徐冷しながら引き上げた場合には、今度はシリコン単結晶の格子間に余分に存在するシリコン原子、すなわちインタースティシアル−シリコン（Interstitial−Si：以下、Ｉとも略記する）と呼ばれる点欠陥が優勢なシリコン単結晶が得られる。このようなシリコン単結晶の内部は、転位ループ起因と考えられるＬ／Ｄ（Large Dislocation：格子間転位ループの略号であり、ＬＳＰＤやＬＦＰＤ等の結晶欠陥の総称）と呼ばれている格子間型シリコン欠陥が低密度に存在するようになり、単結晶をウエーハ基板に加工して表層に半導体素子を形成した場合には、これら欠陥により電流リーク等の重大な不良を起こす原因にもなる。該インタースティシアル−シリコンが優勢となる結晶内部の領域を、Ｉ領域と呼んでいる。
【０００６】
そして、これらベイカンシーが優勢となるＶ領域や、インタースティシアル−シリコンが優勢であるＩ領域以外の中間の領域となる育成条件でシリコン単結晶を引き上げれば、シリコン原子間に原子の不足や余分な原子の存在しない、あるいは存在しても僅かであるニュートラル（Neutral、以下、Ｎと略記することがある）な状態でシリコン単結晶を育成することができる。このようなニュートラルな状態にある結晶内部の領域を、Ｎ領域と呼ぶ。
【０００７】
なお、シリコン単結晶の内部に形成されるＮ領域と前述のＶ領域との間には、ＯＳＦ（Oxidation Induced Stacking Fault、酸化誘起積層欠陥）と称される酸素起因の欠陥、あるいはその核が高密度に存在する領域があり、単結晶をウエーハ基板に加工した時にこの領域がリング状となって観察されることから、このＯＳＦあるいはＯＳＦとなる核が存在する領域を、ＯＳＦリングあるいはＯＳＦリング域と呼んでいる。
【０００８】
上述の特開平１１−７９８８９号公報では、結晶内部のグローンイン欠陥を極低密度に保って高品質のシリコン単結晶を得るために、単結晶の温度雰囲気を調整することにより、シリコン単結晶の内部に生ずるＯＳＦリングが結晶中心で閉じた、結晶全体がＮ領域となるような条件でシリコン単結晶を育成するようにしている。しかし、この特開平１１−７９８８９号公報に示されているような、単結晶全体あるいはその殆どをＮ領域と成して結晶成長を行う方法では、所望の結晶成長雰囲気を形成するために、シリコン融液面の上方に複雑な構造物を配置したり、あるいは単結晶の成長速度を０．５ｍｍ／ｍｉｎ程度以下の極めて低速に保つ必要がある。従って、結晶欠陥の少ない高品質な単結晶が得られるという利点はあるものの、装置構造が複雑で汎用性に欠けたり、結晶の生産性が低い等、生産効率の点では問題が多い。
【０００９】
【発明が解決しようとする課題】
通常の製造装置でＮ領域となるように結晶引上げを行なうには、引き上げられた結晶の冷却雰囲気が所望の値となるように調整し、結晶の引上速度を０．４ｍｍ／ｍｉｎ程度の低速に保って結晶育成を行っている。これは、一般的なシリコン単結晶引上速度が１．０ｍｍ／ｍｉｎ程度であることを考えれば、著しく生産性の劣った製造方法である。この引上速度を高めるための方法として、製造装置の上部に断熱特性を強化した構造物を配置し、結晶欠陥の低い単結晶を得るのに適した温度雰囲気に調整して結晶生産を行なう方法も検討されている。しかし、このような方法では、育成炉内の上部構造が複雑となり、装置のメンテナンスや汎用性を考えた場合に、作業効率を落とし生産性が低下したり、装置コストが割高になる等の問題が残されていた。また、結晶の成長速度を高めて、結晶欠陥の無いあるいは少ない高品質結晶を育成するには、更に結晶成長界面に近い部分での、単結晶の冷却効果を大きく保つ必要があることから、新たな装置構造の工夫が必要とされていた。
【００１０】
特に、直径が２００ｍｍφを超えるような大型の結晶では、その熱容量も大きくなることから装置を簡素化するとともに、いかに適切に育成結晶を冷却するかが課題とされている。この場合、得られるシリコン単結晶の特性に影響を及ぼす結晶欠陥の発生量が、育成結晶のどの温度域で積極的な冷却促進を行なうかにも極めて密接に関わっている。しかしながら、従来、この観点における課題解決と、装置構造の簡略化との両方を視野に入れた技術的な検討はなされてこなかった。
【００１１】
本発明は、上述した問題点に鑑みて成されたものであり、結晶欠陥の無いあるいは極めて少ない高品質のシリコン単結晶を育成するにあたり、シリコン融液から引き上げられた単結晶を適切かつ効率よく冷却して引上速度の向上を図るとともに、製造装置の構造を簡素なものとし、取り扱いが容易で汎用性の高い単結晶の製造装置、及びそれを用いたシリコン単結晶の製造方法を提供することを目的とする。
【００１２】
【課題を解決するための手段及び作用・効果】
本発明のシリコン単結晶製造装置は、シリコン単結晶の育成炉内においてルツボに収容したシリコン融液から、チョクラルスキー法によりシリコン単結晶を引き上げるようにしたシリコン単結晶の製造装置において、
内部にルツボが配置される育成炉本体と、
該育成炉本体内において、シリコン融液より引き上げられたシリコン単結晶を囲繞するように配置された結晶冷却筒と、
結晶冷却筒の下端部内周面に沿って、シリコン融液より引き上げられたシリコン単結晶の外周面に向けて突出する形態で設けられる炭素製の内周断熱材とを有し、
該内周断熱材が、シリコン単結晶の軸線方向においてその全体が、該シリコン単結晶の中心温度が１０００℃以上１２５０℃以下となる区間内に位置するように配置されていることを特徴とする。
【００１３】
また、本発明のシリコン単結晶の製造方法は、上記のシリコン単結晶の製造装置を用い、ルツボに収容したシリコン融液から、チョクラルスキー法によりシリコン単結晶を引き上げて製造することを特徴とする。
【００１４】
シリコン融液から単結晶を成長させる際に、結晶の成長速度を高めるためには、加熱ヒータやシリコン融液から単結晶への輻射熱を極力遮蔽して、育成結晶を効率的に冷却する必要がある。この理由から、シリコン単結晶の製造装置においては、育成結晶を取り囲むようにシリコン融液直上に結晶冷却筒を配設して、結晶からの輻射熱を除去すると同時に、加熱ヒータやシリコン融液からの輻射熱が結晶にあたらないように工夫することが有効である。しかし、シリコン融液面近くの結晶成長界面付近では、シリコン融液からの輻射熱を効率よく遮蔽することが難しく、特に欠陥を抑制した高品質結晶の育成では、結晶の冷却速度を精度よく所望の値に保つ必要があることから、結晶の成長速度を高めることが難しかった。
【００１５】
これに対し本発明の装置では、結晶冷却筒の下端部内周面に沿って、シリコン融液より引き上げられたシリコン単結晶の外周面に向けて突出する形態で、耐熱温度が高く断熱特性に優れた炭素製の内周断熱材を配置することにより、加熱ヒータやシリコン融液面からもたらされる輻射熱を遮蔽して、結晶高温部の冷却効率を高めることができる。また、このような位置に内周断熱材を配置することで、該位置での冷却筒と育成された単結晶との隙間が狭く保たれるため、シリコン融液側からの該隙間を介した輻射あるいは対流による熱伝達を抑制できるので、シリコン融液面から上方に離れた位置での結晶の冷却効果を高めることもできる。
【００１６】
結晶冷却筒は、冷却効率を高めるとともに耐熱性と機械構造的な強度を確保するために、少なくとも内周断熱材が設けられる下端部を黒鉛製とすることが望ましい。この場合、内周断熱材は該黒鉛製の結晶冷却筒下端部よりも気孔率の高い炭素材にて構成することが、断熱効果を高める上で望ましい。
【００１７】
そして、本発明では、上記内周断熱材が、シリコン単結晶の軸線方向においてその全体が、該シリコン単結晶の中心温度が１０００℃以上１２５０℃以下となる区間内に配置されていることがもう一つの大きな特徴である。具体的には、図３に示すように、内周断熱材（１５）の下縁（下端面）がシリコン単結晶の、空孔凝集による欠陥成長が始まると推定される１２５０℃よりも低い第一温度Ｔ１となる位置にあり、また、内周断熱材１５の上縁（上端面）がシリコン単結晶内の、欠陥成長が比較的不活発となる１０００℃よりも高い第二温度Ｔ２となる位置にあるようにする。なお、結晶冷却筒１３の下端部１３ａが内周断熱材１５の下端側に回りこんで配置されている場合は、該下端部１３ａは内周断熱材１５に属さないものとみなす。さらに、内周断熱材１５の上端側が結晶冷却筒１３と同材質の被覆材にて覆われている場合（図５（ａ）等）は、被覆材は内周断熱材１５に属さないものとみなす。
【００１８】
これにより、シリコン単結晶の電気的特性に悪影響を及ぼす欠陥形成を確実に抑制しつつ、成長速度を高めることが可能となる。この理由は、以下の通りである。ＣＺ法によるシリコン単結晶の育成においては経験的に、おおむね結晶温度が１２５０℃程度まで低下すると、空格子点や格子間シリコン原子が、グローンイン欠陥核となるための凝集を開始し、１０００℃〜１０５０℃付近で欠陥成長が収束に向かうものと推定されている。図４の（ａ）に示すように、この１０００℃〜１２５０℃の温度区間に、欠陥の成長が顕著となると考えられる温度区間τが存在する。そして、高品質のシリコン単結晶を得るには、上記温度区間τにシリコン単結晶が長時間留まらないよう、該温度区間τを通過するときの冷却速度を適度に大きくして、結晶中での欠陥成長を抑制することが重要である。
【００１９】
例えば、図４（ａ）において破線Ｂで示すように、温度区間τでの冷却速度が小さい場合、（ｃ）に示すように、系の温度が高いために、空孔が個々の欠陥核に急速に凝集して大きく成長し、シリコン単結晶の電気的特性に悪影響を及ぼす欠陥（以下、「悪質な欠陥」といい、本明細書にて単に「欠陥」という場合は、この「悪質な欠陥」を意味する）の個数は増加してしまう。しかし、１０００℃〜１２５０℃の温度区間に対応する位置に内周断熱材を配置することで、図４（ａ）の実線Ａで示すように上記温度区間τでの冷却速度を大きくできる。この場合、（ｂ）に示すように、過冷度が大きくなるために欠陥核Ｎの発生個数は多くなるが、系の温度が低下しているので、個々の欠陥核への空孔の凝集が抑えられ、欠陥の成長速度は小さくなる。従って、前記した悪質な欠陥の個数が減少し、高品質のシリコン単結晶が得られるものと考えられる。また、このような結晶冷却を行なうことによって結晶高温部での冷却が加速され、結晶成長速度も速めることができるようになる。
【００２０】
なお、内周断熱材の上縁位置が、シリコン単結晶の中心温度が１０００℃以下となる区間にまで上側に延長された場合、その延長区間では内周断熱材の保温材としての働きが顕著となり、そのため１０００℃〜１０５０℃近傍の、欠陥の成長が収束に向かう温度域での温度勾配が緩やかとなる。その結果、欠陥が活発に形成される温度区間において、シリコン単結晶は徐冷され、欠陥への空孔の凝集が継続し、欠陥サイズが粗大化するので、例えばデバイス化の際にその電気的特性の低下を招くことにつながる。他方、内周断熱材の下縁位置が、シリコン単結晶の中心温度が１２５０℃以上となる区間まで下側に延長された場合、内周断熱材の冷却効果により単結晶の径方向の温度分布が不均一となり、結晶内部に転位ループ起因と考えられる格子間型の欠陥が生じやすくなる。いずれの場合も、単結晶の軸断面において全面がＮ領域化した高品質の結晶を得る上では不利に作用する。
【００２１】
なお、上記効果を高めるために、内周断熱材の上縁位置はシリコン単結晶の中心温度が１０００℃以上１０５０℃以下となる区間内に位置し、同じく下縁位置はシリコン単結晶の中心温度が１１５０℃以上１２５０℃以下となる区間内に位置していることが望ましい。内周断熱材の軸方向寸法が短くなりすぎて、例えば上縁位置が、シリコン単結晶の中心温度が１０５０℃より高い区間に位置するか、あるいは下縁位置が、シリコン単結晶の中心温度が１１５０℃より低い区間に位置するようになると、欠陥形成が顕著となる温度区間τの全体を十分な冷却速度で冷却できなくなり、本発明の前記した効果の達成が困難となる。
【００２２】
【発明の実施の形態】
以下に、本発明の実施の形態を、添付図面を参照しながら、ＣＺ法を用いたシリコン単結晶の育成例を挙げて説明するが、本発明はこれらのみに限定されるものではない。図１は、本発明のシリコン単結晶の製造方法を実施するための、シリコン単結晶製造装置の一実施形態を示す概略断面図である。図１に示されるシリコン単結晶製造装置５０は、育成炉本体１と上部育成炉２から構成される。育成炉本体１の内部には、シリコン融液４を収容した石英製ルツボ５と、この石英製ルツボ５を保持し保護するために、黒鉛製ルツボ６が石英製ルツボ５の外側に配置されている。
【００２３】
そして、黒鉛製ルツボ６の外周には、石英製ルツボ５に収容された原料である多結晶シリコンを加熱し、溶融してシリコン融液４とするための黒鉛製の加熱ヒータ７が置かれている。シリコン単結晶の育成時には、電極から加熱ヒータに電力が供給され発熱し、多結晶シリコンを融解した後に、シリコン融液４の温度を所望の値に保持してシリコン単結晶３の成長を図るものである。
【００２４】
加熱ヒータ７と育成炉本体１の炉壁との間には、金属製の炉壁を保護し育成炉本体１の内部を効率的に保温するために炭素製の炉内断熱材８が置かれている。更に、育成炉本体１は、加熱ヒータ７からの輻射熱により、シリコン単結晶育成時に炉壁が必要以上に高温に加熱されることを防止する目的で、炉壁を二重構造とし、炉壁の隙間に冷却水を流して強制冷却を行いながらシリコン単結晶の育成を行なうような構造とされているものである。
【００２５】
一方、育成炉本体１の略中央に配置された黒鉛製ルツボ６は、底部を黒鉛製のルツボ支持軸１９によって支持されており、ルツボ支持軸１９の下端部に取り付けられた図示しないルツボ軸駆動機構によって、上下動及び回転動自在とされているものである。これによって単結晶育成時にシリコン融液４の液面を一定位置に保持したり、単結晶育成時にルツボ５，６を所望の方向や速さで回転させることができるようになっている。
【００２６】
装置内にて使用する炭素製の部材は、ルツボ６、加熱ヒータ７、後述のルツボ支持軸１９あるいは結晶冷却筒１３など、機械構造的な強度の求められる部分は緻密な黒鉛にて構成され、他方、上記の炉内断熱材８や、内周断熱材１５など、断熱性が要求される部材は、該黒鉛製の構造部材よりも気孔率の高い炭素材（以下、断熱性炭素材という）にて構成する。具体的には、炭素焼結体などの多孔質炭素材、あるいは繊維質炭素材、例えば炭素繊維をプリプレグ状あるいは不織布状に成型したものを採用することができる。
【００２７】
次に、シリコン単結晶３の育成時には、シリコン融液４から蒸発するＳｉＯ（一酸化珪素）等の酸化物が、育成炉の炉壁や炉内断熱材等の炉内部材に付着するのを防止するため、アルゴンガス等の不活性ガスを育成炉に流通しながら結晶成長を行なう必要がある。このため、育成炉本体１の底部には、不活性ガスを炉外へ排気するための排ガス管９と、育成炉内部の圧力を調整するための図示しない圧力制御装置が備えられており、シリコン単結晶の育成時には、この圧力制御装置によって炉内の圧力が所望の値に調整される。
【００２８】
一方、育成炉本体１の天井部には、シリコン融液４から引き上げられたシリコン単結晶３を収容し取出すための上部育成炉２が連通して設置されている。単結晶育成時にはこの上部育成炉２内でシリコン単結晶３を放冷し、取出し可能な温度となるまで結晶温度が低下したら、上部育成炉２の図示しないドアを開けてシリコン単結晶３を育成炉の外部へと移動させる。
【００２９】
育成炉本体２の天井部からは、シリコン融液４から引き上げられた単結晶３を囲繞するように結晶冷却筒１３がシリコン融液面に向かって配置され、その先端部の外周面には、シリコン融液４や加熱ヒータ７の輻射熱を効率的に反射してシリコン融液面を保温するための黒鉛製の断熱リング１４が取り付けられている（該断熱リング１４は省略してもよい）。シリコン単結晶３の育成時には、この結晶冷却筒１３によりシリコン単結晶３からの輻射熱が効率的に奪われることで、結晶成長速度を高めることができる。また、この結晶冷却筒１３には、上部育成炉２より冷却筒内部を伝ってシリコン融液面に下流する不活性ガスの整流作用もあり、融液面から放出される不純物を滞りなく炉外へ排出させるための役目も果たしている。なお、図２に示すように、結晶冷却筒１３の上部に、冷却媒体の流通により、強制的に結晶からの輻射熱を炉外へと排出する強制冷却筒１１を設け、冷却効果を更に高めることも可能である。結晶冷却筒１３は、伝熱性を高めるために、少なくとも下端部、本実施形態においてはその全体が黒鉛製とされている（ただし、強制冷却筒１１等との接続部をなす上端部を金属製としてもよい）。また、後述の内周断熱材１５等をなす断熱性炭素材よりも緻密なものが使用される。
【００３０】
図１に戻り、上部育成炉２には、育成炉の内部に不活性ガスを導入するためのガス導入管１０が備えられており、結晶成長作業の工程に合わせてガス導入管１０より育成炉へ不活性ガスが導入される。シリコン単結晶３の育成時には、この上部育成炉２から導入された不活性ガスが、結晶冷却筒１３の内部を下流しシリコン融液面を伝って育成炉本体１の底部にある排ガス管９から炉外へと排出される。これによって、シリコン融液から蒸発するＳｉＯ等の蒸発物を炉外へと除去している。
【００３１】
また、上部育成炉２の上方には、シリコン融液４からシリコン単結晶３を引き上げるための、ワイヤー１８を巻き出しあるいは巻き取る、図示しないワイヤー巻取り機構が備えられている。このワイヤー巻取り機構から巻き出された引上げワイヤー１８の先端部には種結晶ホルダー１８ａが取り付けられており、この種結晶ボルダー１８ａに種結晶１７を係止して、その先端をシリコン融液４の表面に接融し引き上げることによって、該種結晶１７の下方にシリコン単結晶３が育成される。
【００３２】
次に、図１あるいは図２に示すシリコン単結晶製造装置５０は、結晶冷却筒１３の下端部内周面に沿って、シリコン融液より引き上げられたシリコン単結晶３の外周面に向けて突出する形態で設けられる炭素製の内周断熱材１５を有している。内周断熱材１５は、前述の断熱性炭素材にて構成される。すでに図３を用いて説明した通り、該内周断熱材１５は、シリコン単結晶３の軸線Ｏの方向において該シリコン単結晶３の中心温度が１０００℃以上１２５０℃以下となる区間内に配置されている。このことによる作用・効果は既に説明済みである。
【００３３】
なお、図１に示すように、結晶冷却筒１３は、結晶の冷却効果を得るばかりではなく、育成された単結晶３の上方から結晶に沿って冷却筒１３内を流れる不活性ガスの整流を行なう作用もある。好ましくは、この整流作用を妨げないように、図５（ａ）に示すように、内周断熱材１５の上端面１５ａは、内周縁側が低くなる傾斜面とされているのがよい（ここでは、後述の黒鉛材１３ｂにより覆われているが、これは内周断熱材１５に属さないものとみなす）。このような傾斜を内周断熱材に設けることにより、冷却筒１３の内部を流れるアルゴン（Ａｒ）ガス等の不活性ガスを乱すことなく、スムーズに上方からシリコン融液面に向かって流すことができる。これにより、シリコン融液面から蒸発するＳｉＯ等の蒸発物を、滞りなく不活性ガスにより育成炉外部へと排出し、結晶に転位をもたらす可能性がある酸化物が、炉壁や炉内配置された部材等に付着することを防ぐことが可能とされる。なお、図５（ａ）では、内周断熱材１５の上端面１５ａに続く形で直立形態の内側壁面１５ｃを形成しているが、（ｂ）に示すように、内周断熱材１５を三角状断面とし、上端面１５ａを内周断熱材１５の下端部に至る傾斜面とすることもできる。
【００３４】
上記上端面１５ａの水平面とのなす角度（以下、傾斜角という）θは３０°〜７０°の範囲となるようにするのが好適である。傾斜角θが３０°以下の場合には、結晶冷却筒１３の上方から下流する不活性ガスが内周断熱材１５の上端面１５ａに当たり、流れが乱される可能性もあるし、反対に７０°以上の傾斜を付けた場合には、内周断熱材１５が冷却筒の上方に向けて延長され、適切な結晶冷却雰囲気を形成し難くなったり、内周断熱材が大型化するので、取り扱いが不便となる。なお、上端面１５ａは、図６に示すように曲面状に形成することも可能である。この場合の傾斜角度θは、内周断熱材１５の軸線を含む断面において、曲面状の上端面１５ａの上縁及び下縁とを結ぶ直線と水平面とのなす角度として定義する。
【００３５】
また、図５において、内周断熱材１５は、自身の内側壁面１５ｃと、引き上げられたシリコン単結晶３の定径部外周面３ｃとの距離ｄが２０ｍｍ以上５０ｍｍ以下となるように配置されているのが好ましい。距離ｄが５０ｍｍを超えると、内周断熱材１５の厚みが小さくなりすぎて断熱効果が弱まると同時に、シリコン融液面からの輻射熱が内周断熱材１５とシリコン単結晶３の隙間から直接結晶高温部に当たり、効果的に結晶を冷却することができなくなる。他方、距離ｄが２０ｍｍ以下になると、輻射熱の遮蔽効果は高まるものの、冷却筒の内部を流れる不活性ガスの流通路が狭められることになるので、結晶成長界面付近での不活性ガスの線速が高まり、結晶成長を阻害する可能性もある。なお、内周断熱材１５の半径方向における最大厚みは、該内周断熱材１５が十分な熱容量ひいては引き上げられるシリコン単結晶３に対する冷却能が十分に確保できるように、適宜、例えば４０ｍｍ以上に確保することが望ましい。また、この厚みの上限値は、シリコン単結晶３の定径部外周面３ｃとの距離ｄを２０ｍｍ以上確保できる範囲内にて適宜定まるものである。
【００３６】
次に、断熱性炭素材で構成された内周断熱材１５は、高い熱遮蔽効果を持つものであるが、脆く形が不安定で所望の形状に加工するのが難しく、更には、繊維状であるため、シリコン融液からの蒸発物が表面に付着し易い等の問題もある。これを補う方法として、図５（ａ）に示すように、内周断熱材１５の、結晶冷却筒の内側に露出する表面を黒鉛材１３ｂ（内周断熱材よりは緻密なもの）で被覆することが有効である。これにより、内周断熱材１５の取り扱いを容易にし作業性の向上も図ることができるし、ＳｉＯ等のシリコン融液からの蒸発物が、内周断熱材１５の繊維状の本体部分に付着するのを防止できる。また、該本体部分が崩れてシリコン融液に落下することも無くなるので、スリップ転位をもたらすなど結晶の成長を妨げたり、品質に影響を与えることも抑制できる。
【００３７】
そして、より好ましくは、上記の黒鉛材１３ｂの表面を、熱分解炭素あるいは炭化珪素でさらに被覆しておくのがよい。熱分解炭素あるいは炭化珪素で被覆した黒鉛材１３ｂを用いることによって、シリコン融液から蒸発したシリコンが黒鉛材１３ｂ表層付近に浸透し、炭化珪素が生成されることを抑制することができる。これにより、黒鉛材１３ｂの耐久性向上を図ることができる。また、炭化珪素生成に伴う黒鉛材１３ｂのヒビや亀裂等の発生がもたらす、黒鉛の原料融液への落下を防ぐ効果もあり、その結果、安定した結晶成長が達成できるものとなる。さらに、熱分解炭素あるいは炭化珪素で形成された被膜における鉄（Fe）濃度が、０．０５ｐｐｍ以下となるように、被膜を施すことにより、結晶に近接する内周断熱材１５または結晶冷却筒１３内周面から育成単結晶にもたらす鉄（Fe）汚染を確実に防止することができる。これにより、育成したシリコン単結晶をシリコンウエーハに加工した際に重金属、特に鉄（Fe）の汚染によって生じるキャリアライフタイムの低下が抑えられる。なお、被膜の鉄（Fe）濃度については、ＩＣＰ（Inductively Coupled Plasma）発光分析法により測定されるものである。また、結晶冷却筒１３を黒鉛製とする場合、その内周断熱材の形成されていない内周面１３ｊを、熱分解炭素あるいは炭化珪素で被覆しておけばより望ましい。
【００３８】
なお、内周断熱材１５を結晶冷却筒１３の先端に取り付けるためには、図７（ａ）に示すように、互いに重ねあわされた内周断熱材１５と結晶冷却筒１３の壁部とを、ボルト（もちろん、黒鉛等、必要な耐熱性を持った材料で構成する）等の締結部材３０で締結・固定する方法を例示できる。また、（ｂ）に示すように、結晶冷却筒１３の本体部にＬ字状に一体化された下端部１３ａに内周断熱材１５を乗せるのみの構造としてもよい。さらに、図７（ｃ）に示すように、内周断熱材１５（を覆う黒鉛材）側に形成された雄ねじ部１５ｍを、結晶冷却筒１３の内周面下端部に形成された雌ねじ部１３ｆに螺合させて固定する方法も可能である。
【００３９】
以下、装置５０を用いたシリコン単結晶の製造工程について、図１により説明する。まず、育成炉本体１の内部に置かれた石英製ルツボ６に多結晶シリコン塊を充填し、炉内をアルゴンガス等の不活性ガスで置換し満たした後、育成炉本体１の加熱ヒータ７を発熱させてシリコンの融点である１４２０℃以上に多結晶シリコンを加熱し、シリコン融液４とする。この時、育成炉の内部は、シリコン融液から蒸発するＳｉＯ等の蒸発物が低温度の炉内構造物に析出付着しないよう、不活性ガスを常時流しながら５００ｈＰａ程度以下の低圧に保って、蒸発物の炉外排出を促しつつ多結晶シリコンの融解を図る。これはシリコン単結晶３の育成に移行した時も継続され、単結晶育成中は不活性ガスを育成炉に流しながら低圧の状態に保って操業が行われる。
【００４０】
石英製ルツボ５に収容された全ての多結晶シリコンが溶解したら、シリコン融液４の温度を単結晶成長に適した温度に調整し、ワイヤー１８を巻き出して種結晶１７の先端部を融液表面に着液させる。そして、上部育成炉２から結晶冷却筒１３を伝って下流する不活性ガスの量と炉内圧力を育成条件に合わせ、黒鉛製ルツボ６と種結晶１７とを互いに反対方向に回転させながら、所望の速さでワイヤー１８を徐々に巻き上げることによって、種結晶１７の下方にシリコン単結晶３を成長させる。
【００４１】
種結晶１７の下方に所定径を有するシリコン単結晶３を形成するには、まず種結晶１７をシリコン融液４に着液させた時の熱衝撃によって生じたスリップ転位を除去するために、一旦、結晶径を細くして絞り部を作ることによってスリップ転位を除去する。絞り部の形成後は、所定の径となるまで径拡大を行い所望の径となったところで径拡大を止め、所望とする一定直径でシリコン単結晶３の育成を行なう。
【００４２】
一定径を持った定径部を所望長さ引き上げたならば、シリコン単結晶３をシリコン融液４から切り離した時に生じる温度変化によってスリップ転位がもたらされないよう、徐々に結晶径を小さくして縮径部を形成した後、シリコン単結晶３を融液から切り離し、静かにシリコン単結晶３を上部育成炉２まで巻き上げ常温付近まで冷却して育成を終える。
【００４３】
【実施例】
以下、本発明の効果を確認するために、以下の実験を行なった。
（実施例１：実験１）
本発明の装置を用いてシリコン単結晶を育成する際に、ＯＳＦリング域が閉じてＮ領域となるよう単結晶の引上げを行なうには、どのような製造条件で育成を行なえば適切なものであるかを確認するために、図１に示される装置５０を用いて引上速度を種々に変化させながらシリコン単結晶の育成を行った。
【００４４】
まず、口径が６０ｃｍの石英製ルツボに多結晶シリコンを１００ｋｇ入れて加熱溶融し、結晶軸方向が＜１００＞の種結晶をシリコン融液に着液させて直径２００ｍｍの単結晶を育成した。この際、内周断熱材すなわち冷却筒とシリコン融液面の隙間を５０ｍｍとして、引き上げられるシリコン単結晶の中心温度が、結晶冷却筒１３の下端位置で約１２５０℃、そこから上方１０ｃｍの位置で約１０００℃となるように（いずれもシミュレーションによる）、内周断熱材１５を配置して結晶育成を行った。この時、結晶と内周断熱材１５の隙間が３０ｍｍ程度になるように内周断熱材１５の厚みを調整して配置した。
【００４５】
シリコン単結晶の引上条件は、引上速度を結晶の定径部前半で０．７ｍｍ／ｍｉｎとして、徐々に引上速度を低下させていって定径部後半の尾部近くでは０．３ｍｍ／ｍｉｎとなるように漸減させた。その他、ルツボ回転数や炉内に流す不活性ガスの量等の育成条件は、シリコン単結晶に取り込まれる酸素濃度が１９〜２０ｐｐｍａ（ＡＳＴＭ（１９７９年）：Ｆ−１２１規定の測定値）となるように調整しながら育成を行った。
【００４６】
育成後の単結晶は、拡径部と縮径部を取り除いた後に定径部の先端から１０ｃｍ毎に切断し、結晶中心から縦割りにするとともに、ＯＳＦリング域が消えてＮ領域に達する引上速度を調べた。なお欠陥の識別は以下のようにして行なった。まず、単結晶定径部を約１０ｃｍ間隔で切断し、引上軸中心から縦割りにして厚さ２ｍｍ前後の長方形をしたウエーハ状の測定サンプルを作成した。この測定サンプルに、窒素雰囲気中で６００℃×２ｈｒ＋８００℃×４ｈｒ、そして、更に酸素雰囲気下で１０００℃×１６ｈｒの熱処理を施した後に、測定サンプル表面の酸化膜を薬液で除去し、Ｘ線トポグラフにより表面の欠陥を測定した。結果は、図８に示す通りである。これによると、引上速度が０．５１ｍｍ／ｍｉｎまで低下した部位でＯＳＦリング域が消え、引上速度が０．４８ｍｍ／ｍｉｎとなったところまでＮ領域となっていることがわかった。
【００４７】
（実施例１：実験２）
実験１と同じく石英製ルツボに多結晶原料１００ｋｇを仕込み融解して、同直径、同方位を有するシリコン単結晶を育成した。この時の単結晶を得るための操業条件は、単結晶定径部１０ｃｍ以降の定径部で、引上速度を０．４８〜０．５１ｍｍ／ｍｉｎの範囲に入るように調整した以外は試験１と同じ操業条件を採用し、酸素濃度や抵抗率は略同等になるように調整しながら結晶成長を行った。得られた単結晶の定径部先端から１０ｃｍを除いた部位から、シリコンウエーハ状の評価サンプルを作成するとともに、以下のようにして欠陥評価を行なった。
Ｖ領域における結晶欠陥の評価を行うため、Ｃモードでの酸化膜耐圧測定を行った（発明例）。なお、Ｃモード酸化膜耐圧の測定条件は次の通りである。
１）酸化膜厚：２５ｎｍ２）測定電極：リンドープ・ポリシリコン
３）電極面積：８ｍｍ^２４）判定電流：１ｍＡ／ｃｍ^２
５）良否判定：８ＭＶ／ｃｍ以上の耐圧を示したものを良品と判定。
この結果、略１００％の良品率を得られることがわかった。
【００４８】
つぎに、Ｉ領域において観察される結晶欠陥Ｌ／Ｄの評価を行うため、前記評価サンプルを弗酸と硝酸の混合液でエッチングし表面の加工歪みを取り除き、続いてＫ_２Ｃｒ_２Ｏ_７と弗酸と水の混合液でさらにセコ−エッチング（Secco etching）を施した後、前記評価サンプルの表面のＬ／Ｄに起因したピットを観察した。しかしながら、Ｌ／Ｄに起因した欠陥は観察されなかった。
Ｖ及びＩ領域における前記欠陥評価の結果より、結晶全域にわたって欠陥の極めて少ないＮ領域の単結晶が育成されたことを確認した。
【００４９】
一方、比較のため、シリコン単結晶製造装置の冷却筒先端部にある内周断熱材１５を取り除いた以外は、図１に示す製造装置と同じものを用いて、発明例と同じ条件で引上速度を調整しながら、直径２００ｍｍのシリコン単結晶を育成し、同様にＣモード酸化膜耐圧を測定した（比較例Ａ）。さらに、内周断熱材１５を、上縁位置でシリコン単結晶の中心温度が約８００℃となるように低温部まで延長した装置（比較例Ｂ）、逆に下縁位置でシリコン単結晶の中心温度が約１３５０℃となるように高温部まで延長した装置（比較例Ｃ）においても結晶育成を行った。その結果、Ｃモード酸化膜耐圧測定では、比較例Ａ及びＢでは良品率が５０〜７０％程度の値に留まり、比較例Ｃでは１００％に近い値となった。しかし、比較例Ｃから得られた単結晶において、Ｉ領域で観察される結晶欠陥Ｌ／Ｄの評価を行った結果、ウエーハ表面に低密度のＬ／Ｄに起因したビットが観察された。
【００５０】
また、比較例Ａで使用した装置により、実施例品と同程度の品質持つ単結晶、即ち全域がＮ領域となる単結晶を製造するには、どのような製造条件を用いれば好ましいかを、実験１と同様の引上速度の漸減実験を行って確認した。その結果、Ｎ領域となる引上速度域は、０．４４〜０．４６ｍｍ／ｍｉｎとかなり小さくなっていることがわかった。なお、図９に、発明例（実線）と比較例（破線）との適正引上速度の相違を視覚化して示している。
【００５１】
（実施例２：実験１）
図２に示す強制冷却機構をもった冷却筒を有するシリコン単結晶製造装置を用いて、実施例１の実験１と同じように多結晶シリコン１００ｋｇを石英製ルツボに仕込み、直径２００ｍｍのシリコン単結晶を製造し、ＯＳＦリング域が消滅し低欠陥領域であるＮ領域となる領域で単結晶を引き上げるための、引上条件の確認実験を行った。この際、内周断熱材すなわち冷却筒とシリコン融液面の隙間を５０ｍｍとして、引き上げられるシリコン単結晶の中心温度が、結晶冷却筒１３の下端位置で約１２５０℃、そこから上方１５ｃｍの位置で約１０００℃となるように（いずれもシミュレーションによる）、内周断熱材１５を配置して結晶育成を行った。この時、結晶と内周断熱材１５の隙間が３０ｍｍ程度になるように内周断熱材１５の厚みを調整して配置した。また、その他の酸素濃度等の結晶品質は、実施例１と略同等になるように操業条件を調整して、単結晶を育成している。
【００５２】
このシリコン単結晶に、実施例１の実験１と同様にして、ＯＳＦリング域とＮ領域となる部位の確認を行ったところ、図２の製造装置では、引上速度を０．５７〜０．５４ｍｍ／ｍｉｎの範囲となるように単結晶育成を行なえば、欠陥密度の低い酸化膜耐圧特性に優れたシリコンウエーハを得られることが判った。
【００５３】
（実施例２：実験２）
そして、図２の製造装置により、引き上げるシリコン単結晶の定径部先端から約１０ｃｍの位置で引上速度が０．５４〜０．５７ｍｍ／ｍｉｎの範囲となるように調整しながら、直径２００ｍｍのシリコン単結晶を育成した（発明例）。この単結晶の、定径部先端の約１０ｃｍを除いた部位から、実施例１の実験２と同様にシリコンウエーハを作製し、同じ条件でＣモード酸化膜耐圧を測定したところ、良品率は１００％に近い値となった。さらに、Ｉ領域で観察される結晶欠陥Ｌ／Ｄの評価を行った結果、Ｌ／Ｄに起因したビットは確認されず、結晶全域にわたって欠陥が抑制された高品質結晶が得られたことを確認した。
【００５４】
一方、比較のため、シリコン単結晶製造装置の冷却筒先端部にある内周断熱材を取り除いた以外は、図２に示す製造装置と同じものを用いて、発明例と同じ条件で引上速度を調整しながら、直径２００ｍｍのシリコン単結晶を育成し、同様にＣモード酸化膜耐圧を測定した（比較例Ｄ）。さらに、内周断熱材１５を、上縁位置でシリコン単結晶の中心温度が約８００℃となるように低温部まで延長した装置（比較例Ｅ）、逆に下縁位置でシリコン単結晶の中心温度が約１３５０℃となるように高温部まで延長した装置（比較例Ｆ）においても結晶育成を行った。その結果、Ｃモード酸化膜耐圧測定より、比較例Ｄ及びＥでは良品率が５０〜７０％前後の低い値を示し、比較例Ｆでは概ね１００％となった。しかし、比較例Ｆで製造したシリコン単結晶において、Ｉ領域で観察される結晶欠陥Ｌ／Ｄの評価を行った結果、ウエーハ表面に低密度のＬ／Ｄに起因したビットが観察された。
【００５５】
また、比較例Ｃで使用した装置により、実施例品と同程度の品質を持つ単結晶を製造するには、どのような製造条件を用いれば好ましいかを、実験１と同様の引上速度の漸減実験を行って確認したところ、高品質であるＮ領域となる引上速度域は、０．４９〜０．５２ｍｍ／ｍｉｎと小さくなっていることがわかった。
【００５６】
なお、本発明は上述した実施の形態に限定されるものではない。上述の実施の形態は単なる例示であり、本発明の特許請求の範囲に記載された技術的思想と実質的に同一な構成を有し、同様の効果を奏するものはいかなるものであっても、本発明の技術的範囲に包含されることは勿論である。例えば、本発明のシリコン単結晶の製造方法を、シリコン融液に磁場を印加することなくシリコン融液からシリコン単結晶を引き上げるＣＺ法を例に挙げて説明したが、単結晶製造装置の育成炉の外側に磁石を配置して、シリコン融液に磁場を印加しながらシリコン単結晶の育成を図るＭＣＺ法によるシリコン単結晶の製造においても、同様の効果が得られることは言うまでもない。
【００５７】
また、上記実施の形態においては、直径が２００ｍｍのシリコン単結晶を育成する場合を例に挙げて説明したが、本発明はこれに限定されるものではなく、直径が２００〜４００ｍｍ、あるはそれ以上の直径を有するシリコン単結晶の育成にも適用可能であり、より有効に作用し得る。
【図面の簡単な説明】
【図１】本発明のシリコン単結晶の製造装置の一例を示す全体模式図。
【図２】図１の製造装置の変形例を示す全体模式図。
【図３】内周断熱材の作用説明図。
【図４】内周断熱材が欠陥形成に及ぼす影響を概念的に説明する図。
【図５】内周断熱材の第一及び第二の変形例を示す拡大断面図。
【図６】同じく第三の変形例を示す拡大断面図。
【図７】結晶冷却筒への内周断熱材の取付構造をいくつか例示して示す模式図。
【図８】実施例１の実験１により得られたシリコン単結晶の引上速度プロファイル及び欠陥分布測定結果を示す図。
【図９】実施例１の実験２における発明例と比較例との適正引上速度の相違を視覚化して示す図。
【符号の説明】
１育成炉本体
４シリコン融液
５石英製ルツボ
６黒鉛製ルツボ
１３結晶冷却筒
１５内周断熱材
５０シリコン単結晶製造装置[0001]
[Technical field to which the invention belongs]
The present invention relates to an apparatus for producing a silicon single crystal by the Czochralski method (hereinafter referred to as CZ method) and a method for producing a silicon single crystal using the same.
[0002]
[Prior art]
With the recent high integration and large size of semiconductor elements, electronic circuits constituting the semiconductor elements have been increasingly miniaturized. For this reason, there is an increasing demand for high quality silicon wafers that are used as substrates for semiconductor element formation, and various measures are being studied in growing silicon single crystals to satisfy this demand. In particular, a silicon single crystal produced by the CZ method is most frequently used as a silicon wafer material, and crystal defects formed inside the crystal when the crystal is grown constitute an element in the wafer surface layer. Therefore, there is a demand for a pulling method in which crystal defects formed inside the crystal during single crystal growth are suppressed to a low density.
[0003]
For example, Japanese Patent Application Laid-Open No. 11-79889 discloses a technique for growing a silicon single crystal that does not have defects that are taken into the crystal when the silicon single crystal is grown, or that has an extremely low density even if it exists. . In the growth of a silicon single crystal by the CZ method, there is a difference in crystal defects caused by a thermal history during crystal growth called “Grown-in Defect” incorporated into the crystal depending on pulling speed, crystal cooling conditions, etc. I understand that.
[0004]
When a single crystal is grown in a rapidly cooled state where the pulling speed of the silicon single crystal is relatively fast, a shortage of silicon atoms occurs inside the crystal during single crystal growth, and a portion that becomes a vacancy is generated at the silicon lattice point. . These vacancies agglomerate when the single crystal is cooled, and when the single crystal is processed into a wafer, it appears in the shape of a recess or a hole on the wafer surface, and the grain-in defects due to vacancies (voids and holes) are dominant. It becomes a silicon single crystal. Such a vacancy-type point defect is called vacancy (hereinafter also abbreviated as V), and a region inside a silicon single crystal where point defects caused by vacancy aggregation are dominant is called a V region. . Grown-in defects caused by vacancy include FPD (Flow Pattern Defects), COP (Crystal Originated Particles), and LSTD (Laser Scattering Tomography Defects). When a silicon single crystal is processed into a wafer, It is observed as a void-like point defect of a face piece.
[0005]
On the other hand, when the pulling speed of the silicon single crystal is suppressed as much as possible and the grown crystal is pulled up while being slowly cooled, this time, silicon atoms existing between the lattices of the silicon single crystal, that is, interstitial-silicon A silicon single crystal having a dominant point defect called Interstitial-Si (hereinafter also abbreviated as I) is obtained. The inside of such a silicon single crystal is an interstitial type called L / D (Large Dislocation: an abbreviation of interstitial dislocation loop, which is a general term for crystal defects such as LSPD and LFPD) that is considered to be caused by a dislocation loop. Silicon defects are present at a low density, and when a single crystal is processed into a wafer substrate to form a semiconductor element on the surface layer, these defects may cause a serious defect such as current leakage. A region inside the crystal where the interstitial-silicon is dominant is called an I region.
[0006]
Then, if the silicon single crystal is pulled up under growth conditions that are intermediate regions other than the V region where vacancy predominates and the I region where interstitial-silicon predominates, a shortage or excess of atoms may occur between silicon atoms. It is possible to grow a silicon single crystal in a neutral state (Neutral, hereinafter sometimes abbreviated as “N”) in which no or a few atoms are present. A region inside the crystal in such a neutral state is called an N region.
[0007]
Note that oxygen-induced defects called OSF (Oxidation Induced Stacking Fault) or nuclei thereof are high between the N region formed inside the silicon single crystal and the above-described V region. There is a region that exists in the density, and when this single crystal is processed into a wafer substrate, this region is observed as a ring shape. Therefore, the region in which the OSF or OSF nucleus is present is defined as the OSF ring or OSF ring region. It is called.
[0008]
In the above-mentioned Japanese Patent Application Laid-Open No. 11-79889, in order to obtain a high-quality silicon single crystal while keeping the grown-in defects inside the crystal at an extremely low density, the temperature atmosphere of the single crystal is adjusted to adjust the inside of the silicon single crystal. The silicon single crystal is grown under such a condition that the OSF ring generated in (1) is closed at the crystal center and the entire crystal becomes the N region. However, in the method of crystal growth by forming the entire single crystal or most of it as an N region as shown in Japanese Patent Laid-Open No. 11-79889, silicon is formed in order to form a desired crystal growth atmosphere. It is necessary to arrange a complicated structure above the melt surface, or to keep the growth rate of the single crystal at an extremely low speed of about 0.5 mm / min or less. Therefore, although there is an advantage that a high-quality single crystal with few crystal defects can be obtained, there are many problems in terms of production efficiency, such as a complicated apparatus structure and lack of versatility and low crystal productivity.
[0009]
[Problems to be solved by the invention]
In order to perform crystal pulling so as to be in the N region with a normal manufacturing apparatus, the cooling atmosphere of the pulled crystal is adjusted to a desired value, and the crystal pulling speed is as low as about 0.4 mm / min. The crystal growth is carried out while maintaining the temperature. This is a manufacturing method that is remarkably inferior in productivity considering that the pulling speed of a general silicon single crystal is about 1.0 mm / min. As a method for increasing the pulling speed, a structure in which a structure with enhanced heat insulation properties is arranged in the upper part of the manufacturing apparatus and adjusted to a temperature atmosphere suitable for obtaining a single crystal having a low crystal defect, and crystal production is performed. Has also been considered. However, with such a method, the upper structure in the growth furnace becomes complicated, and when considering the maintenance and versatility of the equipment, problems such as reduced work efficiency and reduced productivity, and higher equipment costs, etc. Was left. In addition, in order to increase the growth rate of crystals and grow high-quality crystals with little or no crystal defects, it is necessary to keep the cooling effect of the single crystal at a portion closer to the crystal growth interface. The device structure must be devised.
[0010]
In particular, in the case of a large crystal having a diameter exceeding 200 mmφ, the heat capacity becomes large, so that the apparatus is simplified, and how to properly cool the grown crystal is a problem. In this case, the amount of crystal defects that affect the characteristics of the obtained silicon single crystal is very closely related to which temperature range of the grown crystal is actively promoted for cooling. Conventionally, however, no technical examination has been made in view of both the problem solving in this point of view and the simplification of the device structure.
[0011]
The present invention has been made in view of the above-mentioned problems. In growing a high-quality silicon single crystal having no or very few crystal defects, the single crystal pulled from the silicon melt is appropriately and efficiently produced. Provided is a single crystal manufacturing apparatus that is easy to handle and highly versatile, and a silicon single crystal manufacturing method using the same, while improving the pulling speed by cooling and simplifying the structure of the manufacturing apparatus For the purpose.
[0012]
[Means for solving the problems and actions / effects]
The silicon single crystal production apparatus of the present invention is a silicon single crystal production apparatus in which a silicon single crystal is pulled up by a Czochralski method from a silicon melt contained in a crucible in a silicon single crystal growth furnace.
A growth furnace body in which a crucible is arranged;
In the growth furnace body, a crystal cooling cylinder arranged so as to surround the silicon single crystal pulled up from the silicon melt,
Along with the inner peripheral surface of the lower end portion of the crystal cooling cylinder, it has a carbon inner peripheral heat insulating material provided in a form protruding toward the outer peripheral surface of the silicon single crystal pulled up from the silicon melt,
The inner peripheral heat insulating material is arranged so that the whole of the inner peripheral heat insulating material is located in a section where the central temperature of the silicon single crystal is 1000 ° C. or higher and 1250 ° C. or lower in the axial direction of the silicon single crystal. .
[0013]
In addition, the method for producing a silicon single crystal according to the present invention is characterized in that the silicon single crystal is pulled up and produced from the silicon melt contained in the crucible by the Czochralski method using the silicon single crystal production apparatus. To do.
[0014]
When growing a single crystal from a silicon melt, in order to increase the growth rate of the crystal, it is necessary to shield the radiant heat from the heater or the silicon melt to the single crystal as much as possible and cool the grown crystal efficiently. is there. For this reason, in a silicon single crystal manufacturing apparatus, a crystal cooling cylinder is disposed immediately above the silicon melt so as to surround the grown crystal to remove radiant heat from the crystal and at the same time from a heater or silicon melt. It is effective to devise so that radiant heat does not hit the crystal. However, in the vicinity of the crystal growth interface near the silicon melt surface, it is difficult to efficiently shield the radiant heat from the silicon melt. Especially in the growth of high quality crystals with suppressed defects, the cooling rate of the crystal can be accurately set as desired. Since it was necessary to keep the value, it was difficult to increase the crystal growth rate.
[0015]
On the other hand, in the apparatus of the present invention, it protrudes toward the outer peripheral surface of the silicon single crystal pulled up from the silicon melt along the inner peripheral surface of the lower end portion of the crystal cooling cylinder, and has a high heat resistance and excellent heat insulation characteristics. By arranging the inner peripheral heat insulating material made of carbon, it is possible to shield the radiant heat brought from the heater and the silicon melt surface, and to increase the cooling efficiency of the crystal high temperature portion. In addition, by arranging the inner peripheral heat insulating material at such a position, the gap between the cooling cylinder at this position and the grown single crystal is kept narrow, so the gap from the silicon melt side is interposed. Since heat transfer by radiation or convection can be suppressed, the cooling effect of the crystal at a position away from the silicon melt surface can be enhanced.
[0016]
In order to increase the cooling efficiency and to ensure heat resistance and mechanical structural strength, it is desirable that the crystal cooling cylinder is made of graphite at least at the lower end where the inner peripheral heat insulating material is provided. In this case, it is desirable that the inner peripheral heat insulating material is composed of a carbon material having a higher porosity than the lower end of the graphite crystal cooling cylinder.
[0017]
In the present invention, the inner peripheral heat insulating material as a whole in the axial direction of the silicon single crystal is disposed in a section where the center temperature of the silicon single crystal is 1000 ° C. or higher and 1250 ° C. or lower. It is one big feature. Specifically, as shown in FIG. 3, the lower edge (lower end surface) of the inner peripheral heat insulating material (15) is lower than 1250 ° C., which is estimated to start defect growth due to vacancy aggregation of silicon single crystal. At the position where the temperature is one temperature T1, the upper edge (upper end surface) of the inner peripheral heat insulating material 15 is the second temperature T2 higher than 1000 ° C. in the silicon single crystal where the defect growth becomes relatively inactive. Be in position. When the lower end portion 13 a of the crystal cooling cylinder 13 is disposed so as to wrap around the lower end side of the inner peripheral heat insulating material 15, the lower end portion 13 a is regarded as not belonging to the inner peripheral heat insulating material 15. Furthermore, when the upper end side of the inner peripheral heat insulating material 15 is covered with a covering material made of the same material as the crystal cooling cylinder 13 (FIG. 5A, etc.), the covering material does not belong to the inner peripheral heat insulating material 15. I reckon.
[0018]
This makes it possible to increase the growth rate while reliably suppressing the formation of defects that adversely affect the electrical characteristics of the silicon single crystal. The reason for this is as follows. In the growth of a silicon single crystal by the CZ method, empirically, when the crystal temperature is lowered to about 1250 ° C., vacancies and interstitial silicon atoms start to agglomerate to become grown-in defect nuclei. It is estimated that defect growth tends to converge around 1050 ° C. As shown in FIG. 4A, a temperature interval τ where defect growth is considered to be significant exists in the temperature interval of 1000 ° C. to 1250 ° C. In order to obtain a high-quality silicon single crystal, the cooling rate when passing through the temperature interval τ is appropriately increased so that the silicon single crystal does not stay in the temperature interval τ for a long time. It is important to suppress defect growth.
[0019]
For example, as shown by the broken line B in FIG. 4A, when the cooling rate in the temperature interval τ is low, the system temperature is high as shown in FIG. Defects that rapidly agglomerate and grow and have an adverse effect on the electrical properties of silicon single crystals (hereinafter referred to as “malicious defects”. The number of “)” increases. However, by disposing the inner peripheral heat insulating material at a position corresponding to the temperature interval of 1000 ° C. to 1250 ° C., the cooling rate in the temperature interval τ can be increased as shown by the solid line A in FIG. In this case, as shown in (b), since the degree of supercooling increases, the number of defect nuclei N generated increases, but the temperature of the system decreases, so that vacancies agglomerate into individual defect nuclei. And the defect growth rate is reduced. Therefore, it is considered that the number of the above-mentioned malicious defects is reduced and a high-quality silicon single crystal can be obtained. Further, by performing such crystal cooling, the cooling at the high temperature portion of the crystal is accelerated and the crystal growth rate can be increased.
[0020]
In addition, when the upper edge position of the inner peripheral heat insulating material is extended upward to a section where the center temperature of the silicon single crystal is 1000 ° C. or less, the function of the inner peripheral heat insulating material as a heat insulating material is remarkable in the extended section. Therefore, the temperature gradient in the temperature range near 1000 ° C. to 1050 ° C. toward the convergence of defect growth becomes gentle. As a result, in the temperature zone where defects are actively formed, the silicon single crystal is gradually cooled, vacancies agglomerate into the defects, and the defect size becomes coarser. This leads to deterioration of characteristics. On the other hand, when the lower edge position of the inner peripheral heat insulating material is extended downward to a section where the center temperature of the silicon single crystal is 1250 ° C. or more, the temperature distribution in the radial direction of the single crystal due to the cooling effect of the inner peripheral heat insulating material Becomes inhomogeneous and interstitial defects that are thought to be caused by dislocation loops are likely to occur inside the crystal. In either case, it is disadvantageous to obtain a high-quality crystal in which the entire surface is an N region in the axial section of the single crystal.
[0021]
In order to enhance the above effect, the upper edge position of the inner peripheral heat insulating material is located in a section where the center temperature of the silicon single crystal is 1000 ° C. or more and 1050 ° C. or less, and the lower edge position is also the center temperature of the silicon single crystal. It is desirable to be located in a section where 1150 ° C. or more and 1250 ° C. or less. The axial dimension of the inner peripheral heat insulating material becomes too short, for example, the upper edge position is located in a section where the center temperature of the silicon single crystal is higher than 1050 ° C., or the lower edge position is the center temperature of the silicon single crystal. If it is located in a section lower than 1150 ° C., it becomes impossible to cool the entire temperature section τ in which defect formation becomes remarkable at a sufficient cooling rate, and it becomes difficult to achieve the above-described effect of the present invention.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, taking examples of growing silicon single crystals using the CZ method, but the present invention is not limited to these. FIG. 1 is a schematic cross-sectional view showing an embodiment of a silicon single crystal manufacturing apparatus for carrying out the method for manufacturing a silicon single crystal of the present invention. A silicon single crystal manufacturing apparatus 50 shown in FIG. 1 includes a growth furnace main body 1 and an upper growth furnace 2. Inside the growth furnace main body 1, a quartz crucible 5 containing a silicon melt 4 and a graphite crucible 6 are arranged outside the quartz crucible 5 in order to hold and protect the quartz crucible 5. Yes.
[0023]
On the outer periphery of the graphite crucible 6, a graphite heater 7 for heating and melting polycrystalline silicon as a raw material contained in the quartz crucible 5 to form a silicon melt 4 is placed. Yes. When growing a silicon single crystal, electric power is supplied from an electrode to a heater to generate heat, and after melting polycrystalline silicon, the temperature of the silicon melt 4 is maintained at a desired value to grow the silicon single crystal 3 It is.
[0024]
Between the heater 7 and the furnace wall of the growth furnace body 1, a carbon furnace heat insulating material 8 is placed in order to protect the metal furnace wall and efficiently keep the inside of the growth furnace body 1 warm. ing. Furthermore, the growth furnace body 1 has a double-walled furnace wall for the purpose of preventing the furnace wall from being heated to an unnecessarily high temperature during silicon single crystal growth due to radiant heat from the heater 7. The silicon single crystal is grown while forced cooling is performed by flowing cooling water through the gap.
[0025]
On the other hand, the graphite crucible 6 disposed substantially at the center of the growth furnace body 1 is supported at the bottom by a graphite crucible support shaft 19, and a crucible shaft drive (not shown) attached to the lower end of the crucible support shaft 19. The mechanism is movable up and down and rotatable. As a result, the surface of the silicon melt 4 can be held at a fixed position during single crystal growth, and the crucibles 5 and 6 can be rotated at a desired direction and speed during single crystal growth.
[0026]
The parts made of carbon used in the apparatus, such as the crucible 6, the heater 7, the crucible support shaft 19 or the crystal cooling cylinder 13 to be described later, are required to have mechanical structural strength, and are made of dense graphite. On the other hand, a member requiring heat insulation, such as the above-mentioned furnace heat insulating material 8 and inner peripheral heat insulating material 15, is a carbon material having a higher porosity than the graphite structural member (hereinafter referred to as a heat insulating carbon material). It consists of. Specifically, a porous carbon material such as a carbon sintered body or a fibrous carbon material, for example, a carbon fiber molded into a prepreg shape or a nonwoven fabric shape can be employed.
[0027]
Next, when the silicon single crystal 3 is grown, the oxide such as SiO (silicon monoxide) evaporated from the silicon melt 4 adheres to the furnace wall such as the furnace wall of the growth furnace or the furnace heat insulating material. In order to prevent this, it is necessary to perform crystal growth while flowing an inert gas such as argon gas through the growth furnace. For this purpose, the bottom of the growth furnace body 1 is provided with an exhaust gas pipe 9 for exhausting the inert gas to the outside of the furnace, and a pressure control device (not shown) for adjusting the pressure inside the growth furnace. When the single crystal is grown, the pressure in the furnace is adjusted to a desired value by this pressure control device.
[0028]
On the other hand, an upper growth furnace 2 for accommodating and taking out the silicon single crystal 3 pulled up from the silicon melt 4 is installed in communication with the ceiling portion of the growth furnace body 1. When the single crystal is grown, the silicon single crystal 3 is allowed to cool in the upper growth furnace 2 and when the crystal temperature is lowered to a temperature at which it can be taken out, the door (not shown) of the upper growth furnace 2 is opened to grow the silicon single crystal 3. Move outside the furnace.
[0029]
From the ceiling portion of the growth furnace body 2, a crystal cooling cylinder 13 is arranged toward the silicon melt surface so as to surround the single crystal 3 pulled up from the silicon melt 4, and on the outer peripheral surface of the tip portion thereof, A heat insulating ring 14 made of graphite for efficiently reflecting the radiant heat of the silicon melt 4 and the heater 7 to keep the silicon melt surface warm is attached (the heat insulating ring 14 may be omitted). When the silicon single crystal 3 is grown, the crystal cooling cylinder 13 efficiently removes the radiant heat from the silicon single crystal 3, thereby increasing the crystal growth rate. The crystal cooling cylinder 13 also has a function of rectifying an inert gas downstream from the upper growth furnace 2 through the inside of the cooling cylinder and down to the silicon melt surface. It also plays the role of letting it discharge. As shown in FIG. 2, a forced cooling cylinder 11 that forcibly discharges radiant heat from the crystal to the outside of the furnace by the circulation of the cooling medium is provided at the top of the crystal cooling cylinder 13 to further enhance the cooling effect. Is also possible. The crystal cooling cylinder 13 is made of graphite at least at the lower end, in the present embodiment, in order to enhance heat transfer (however, the upper end forming the connection with the forced cooling cylinder 11 etc. is made of metal). As well). Further, a denser material than the heat insulating carbon material forming the inner peripheral heat insulating material 15 and the like described later is used.
[0030]
Returning to FIG. 1, the upper growth furnace 2 is provided with a gas introduction pipe 10 for introducing an inert gas into the inside of the growth furnace, and the growth furnace is adapted to the growth furnace from the gas introduction pipe 10 in accordance with the crystal growth operation process. An inert gas is introduced into the tank. During the growth of the silicon single crystal 3, the inert gas introduced from the upper growth furnace 2 flows from the exhaust pipe 9 at the bottom of the growth furnace main body 1 along the silicon melt surface downstream of the crystal cooling cylinder 13. It is discharged outside the furnace. As a result, evaporants such as SiO evaporating from the silicon melt are removed out of the furnace.
[0031]
Further, above the upper growth furnace 2, a wire winding mechanism (not shown) for unwinding or winding the wire 18 for pulling up the silicon single crystal 3 from the silicon melt 4 is provided. A seed crystal holder 18a is attached to the tip of the pulling wire 18 unwound from the wire winding mechanism. The seed crystal 17 is locked to the seed crystal boulder 18a, and the tip of the seed crystal holder 18a is attached to the silicon melt 4. The silicon single crystal 3 is grown below the seed crystal 17 by being melted and pulled up to the surface of the crystal.
[0032]
Next, the silicon single crystal manufacturing apparatus 50 shown in FIG. 1 or 2 projects toward the outer peripheral surface of the silicon single crystal 3 pulled up from the silicon melt along the inner peripheral surface of the lower end portion of the crystal cooling cylinder 13. It has the carbon inner peripheral heat insulating material 15 provided in the form. The inner periphery heat insulating material 15 is comprised with the above-mentioned heat insulating carbon material. As already described with reference to FIG. 3, the inner peripheral heat insulating material 15 is arranged in a section where the center temperature of the silicon single crystal 3 is 1000 ° C. or higher and 1250 ° C. or lower in the direction of the axis O of the silicon single crystal 3. ing. The actions and effects of this have already been explained.
[0033]
As shown in FIG. 1, the crystal cooling cylinder 13 not only obtains the cooling effect of the crystal, but also rectifies the inert gas flowing in the cooling cylinder 13 along the crystal from above the grown single crystal 3. There is also an action to perform. Preferably, as shown in FIG. 5 (a), the upper end surface 15a of the inner peripheral heat insulating material 15 is preferably an inclined surface with a lower inner peripheral edge side so as not to hinder this rectifying action (here) Then, it is covered with the graphite material 13b described later, but this is regarded as not belonging to the inner peripheral heat insulating material 15). By providing such an inclination in the inner peripheral heat insulating material, an inert gas such as argon (Ar) gas flowing inside the cooling cylinder 13 can be smoothly flowed from above toward the silicon melt surface without disturbing the inert gas. it can. As a result, SiO and other evaporates that evaporate from the silicon melt surface are exhausted to the outside of the growth furnace with an inert gas without delay, and oxides that may cause dislocations in the crystals are placed inside the furnace walls and furnaces. It can be prevented from adhering to the formed member or the like. 5A, the upright inner wall surface 15c is formed following the upper end surface 15a of the inner peripheral heat insulating material 15. However, as shown in FIG. 5B, the inner peripheral heat insulating material 15 is triangular. The upper end surface 15a may be an inclined surface that reaches the lower end portion of the inner peripheral heat insulating material 15.
[0034]
It is preferable that an angle θ (hereinafter referred to as an inclination angle) θ formed with the horizontal surface of the upper end surface 15a is in a range of 30 ° to 70 °. When the inclination angle θ is 30 ° or less, the inert gas downstream from the upper side of the crystal cooling cylinder 13 may hit the upper end surface 15a of the inner peripheral heat insulating material 15, and the flow may be disturbed. If the inclination is more than °°, the inner heat insulating material 15 is extended toward the upper side of the cooling cylinder, making it difficult to form an appropriate crystal cooling atmosphere, and the inner heat insulating material is enlarged. Is inconvenient. The upper end surface 15a can also be formed in a curved shape as shown in FIG. In this case, the inclination angle θ is defined as an angle between a horizontal line and a straight line connecting the upper edge and the lower edge of the curved upper end surface 15a in the cross section including the axis of the inner peripheral heat insulating material 15.
[0035]
In FIG. 5, the inner peripheral heat insulating material 15 is arranged so that the distance d between its inner wall surface 15c and the constant-diameter outer peripheral surface 3c of the pulled silicon single crystal 3 is 20 mm or more and 50 mm or less. It is preferable. When the distance d exceeds 50 mm, the thickness of the inner peripheral heat insulating material 15 becomes too small and the heat insulating effect is weakened. At the same time, the radiant heat from the silicon melt surface is directly crystallized from the gap between the inner peripheral heat insulating material 15 and the silicon single crystal 3. It hits the high temperature part and the crystal cannot be cooled effectively. On the other hand, when the distance d is 20 mm or less, although the shielding effect of radiant heat is enhanced, the flow path of the inert gas flowing inside the cooling cylinder is narrowed, so the linear velocity of the inert gas near the crystal growth interface is reduced. May increase and inhibit crystal growth. In addition, the maximum thickness in the radial direction of the inner peripheral heat insulating material 15 is appropriately set to, for example, 40 mm or more so that the inner peripheral heat insulating material 15 can sufficiently secure a sufficient heat capacity and thus a sufficient cooling capacity for the silicon single crystal 3 pulled up. It is desirable to do. Further, the upper limit value of the thickness is appropriately determined within a range in which a distance d with respect to the outer peripheral surface 3c of the constant diameter portion of the silicon single crystal 3 can be ensured by 20 mm or more.
[0036]
Next, the inner peripheral heat insulating material 15 made of a heat insulating carbon material has a high heat shielding effect, but it is brittle and unstable in shape and difficult to be processed into a desired shape. Therefore, there is a problem that the evaporated material from the silicon melt easily adheres to the surface. As a method of compensating for this, as shown in FIG. 5A, the surface of the inner peripheral heat insulating material 15 exposed inside the crystal cooling cylinder is covered with a graphite material 13b (which is denser than the inner peripheral heat insulating material). It is effective. Thereby, handling of the inner peripheral heat insulating material 15 can be facilitated and workability can be improved, and evaporated material from a silicon melt such as SiO adheres to the fibrous main body portion of the inner peripheral heat insulating material 15. Can be prevented. In addition, since the main body portion does not collapse and fall into the silicon melt, it is possible to suppress the growth of crystals such as causing slip dislocations or affecting the quality.
[0037]
More preferably, the surface of the graphite material 13b is further covered with pyrolytic carbon or silicon carbide. By using the graphite material 13b coated with pyrolytic carbon or silicon carbide, it is possible to prevent silicon evaporated from the silicon melt from penetrating into the vicinity of the surface of the graphite material 13b and generating silicon carbide. Thereby, durability improvement of the graphite material 13b can be aimed at. In addition, there is also an effect of preventing the graphite from falling into the raw material melt caused by the occurrence of cracks, cracks, etc. of the graphite material 13b due to the formation of silicon carbide. As a result, stable crystal growth can be achieved. Further, by applying a coating so that the iron (Fe) concentration in the coating formed of pyrolytic carbon or silicon carbide is 0.05 ppm or less, the inner peripheral heat insulating material 15 or the crystal cooling cylinder 13 close to the crystal. Iron (Fe) contamination brought from the inner peripheral surface to the grown single crystal can be reliably prevented. Thereby, when the grown silicon single crystal is processed into a silicon wafer, a decrease in carrier lifetime caused by contamination of heavy metals, particularly iron (Fe), can be suppressed. The iron (Fe) concentration of the coating is measured by ICP (Inductively Coupled Plasma) emission analysis. Further, when the crystal cooling cylinder 13 is made of graphite, it is more preferable that the inner peripheral surface 13j where the inner peripheral heat insulating material is not formed is covered with pyrolytic carbon or silicon carbide.
[0038]
In order to attach the inner peripheral heat insulating material 15 to the tip of the crystal cooling cylinder 13, as shown in FIG. 7A, the inner peripheral heat insulating material 15 and the wall portion of the crystal cooling cylinder 13 that are overlapped with each other are attached. A method of fastening and fixing with a fastening member 30 such as a bolt (of course, made of a material having necessary heat resistance such as graphite) can be exemplified. Moreover, as shown to (b), it is good also as a structure which only puts the inner periphery heat insulating material 15 on the lower end part 13a integrated in the L-shape at the main-body part of the crystal cooling cylinder 13. FIG. Further, as shown in FIG. 7 (c), the male screw portion 15m formed on the inner peripheral heat insulating material 15 (the covering graphite material) side is replaced with the female screw portion 13f formed on the lower end portion of the inner peripheral surface of the crystal cooling cylinder 13. It is also possible to fix by screwing to.
[0039]
A silicon single crystal manufacturing process using the apparatus 50 will be described below with reference to FIG. First, a quartz crucible 6 placed inside the growth furnace body 1 is filled with a polycrystalline silicon lump, and the inside of the furnace is filled with an inert gas such as argon gas, and then the heater 7 of the growth furnace body 1 is filled. The polycrystalline silicon is heated to 1420 ° C. or higher, which is the melting point of silicon, to obtain a silicon melt 4. At this time, the inside of the growth furnace is kept at a low pressure of about 500 hPa or less while constantly flowing an inert gas so that an evaporant such as SiO evaporated from the silicon melt does not precipitate and adhere to the low temperature furnace internal structure. The melting of polycrystalline silicon is promoted while encouraging evaporative discharge from the furnace. This is continued even when shifting to the growth of the silicon single crystal 3, and during the single crystal growth, the operation is performed while maintaining a low pressure state while flowing an inert gas through the growth furnace.
[0040]
When all the polycrystalline silicon contained in the quartz crucible 5 is dissolved, the temperature of the silicon melt 4 is adjusted to a temperature suitable for single crystal growth, the wire 18 is unwound and the tip of the seed crystal 17 is melted. Let the liquid adhere to the surface. Then, the amount of the inert gas downstream from the upper growth furnace 2 through the crystal cooling cylinder 13 and the pressure in the furnace are matched to the growth conditions, and the graphite crucible 6 and the seed crystal 17 are rotated in opposite directions to be desired. The silicon single crystal 3 is grown below the seed crystal 17 by gradually winding the wire 18 at a speed of
[0041]
In order to form the silicon single crystal 3 having a predetermined diameter below the seed crystal 17, first, in order to remove slip dislocation generated by thermal shock when the seed crystal 17 is deposited on the silicon melt 4, The slip dislocation is removed by reducing the crystal diameter and creating a constricted portion. After the narrowed portion is formed, the diameter is expanded until a predetermined diameter is reached, and when the desired diameter is reached, the diameter expansion is stopped and the silicon single crystal 3 is grown with a desired constant diameter.
[0042]
If the constant-diameter portion having a constant diameter is pulled up to a desired length, the crystal diameter is gradually reduced so that slip dislocation does not occur due to temperature changes that occur when the silicon single crystal 3 is separated from the silicon melt 4. After forming the reduced diameter portion, the silicon single crystal 3 is separated from the melt, and the silicon single crystal 3 is gently rolled up to the upper growth furnace 2 and cooled to near room temperature to complete the growth.
[0043]
【Example】
In order to confirm the effect of the present invention, the following experiment was conducted.
(Example 1: Experiment 1)
When growing the silicon single crystal using the apparatus of the present invention, it is appropriate to grow the single crystal so that the OSF ring region is closed and becomes the N region under what manufacturing conditions. In order to confirm whether or not there was, a silicon single crystal was grown using the apparatus 50 shown in FIG.
[0044]
First, 100 kg of polycrystalline silicon was put in a quartz crucible having a diameter of 60 cm, heated and melted, and a seed crystal having a crystal axis direction of <100> was deposited in the silicon melt to grow a single crystal having a diameter of 200 mm. At this time, the inner peripheral heat insulating material, that is, the clearance between the cooling cylinder and the silicon melt surface is set to 50 mm, and the center temperature of the silicon single crystal pulled up is about 1250 ° C. at the lower end position of the crystal cooling cylinder 13 and 10 cm upward from there. Crystal growth was performed by arranging the inner peripheral heat insulating material 15 so as to be about 1000 ° C. (both by simulation). At this time, the thickness of the inner peripheral heat insulating material 15 was adjusted and arranged so that the gap between the crystal and the inner peripheral heat insulating material 15 was about 30 mm.
[0045]
The pulling condition of the silicon single crystal is as follows: the pulling speed is 0.7 mm / min in the first half of the constant diameter portion of the crystal, and the pulling speed is gradually reduced to 0.3 mm / min near the tail in the second half of the constant diameter portion. It was gradually reduced to be min. In addition, the growth conditions such as the number of revolutions of the crucible and the amount of inert gas flowing into the furnace are such that the oxygen concentration taken into the silicon single crystal is 19 to 20 ppma (ASTM (1979): measured value specified in F-121). The training was carried out while adjusting.
[0046]
The single crystal after growth is cut every 10 cm from the tip of the constant diameter part after removing the enlarged diameter part and the reduced diameter part, and vertically split from the crystal center, and the OSF ring region disappears and reaches the N region. The upper speed was examined. Defects were identified as follows. First, a single crystal constant diameter portion was cut at an interval of about 10 cm, and a wafer-shaped measurement sample having a rectangular shape with a thickness of about 2 mm was created by dividing vertically from the center of the pulling axis. This measurement sample was subjected to a heat treatment of 600 ° C. × 2 hr + 800 ° C. × 4 hr in a nitrogen atmosphere and further 1000 ° C. × 16 hr in an oxygen atmosphere, and then the oxide film on the surface of the measurement sample was removed with a chemical solution. Were used to measure surface defects. The results are as shown in FIG. According to this, it was found that the OSF ring region disappeared at the portion where the pulling speed was reduced to 0.51 mm / min, and the region was the N region until the pulling speed reached 0.48 mm / min.
[0047]
(Example 1: Experiment 2)
As in Experiment 1, 100 kg of polycrystalline raw material was charged in a quartz crucible and melted to grow a silicon single crystal having the same diameter and orientation. The operating conditions for obtaining a single crystal at this time are the constant diameter portion after the single crystal constant diameter portion of 10 cm, and the test was conducted except that the pulling speed was adjusted to be in the range of 0.48 to 0.51 mm / min. The same operating conditions as in No. 1 were adopted, and crystal growth was performed while adjusting the oxygen concentration and resistivity to be substantially equal. A silicon wafer-like evaluation sample was prepared from a portion excluding 10 cm from the tip of the constant diameter portion of the obtained single crystal, and defect evaluation was performed as follows.
In order to evaluate crystal defects in the V region, an oxide film breakdown voltage measurement was performed in C mode (invention example). The measurement conditions for the C-mode oxide film breakdown voltage are as follows.
1) Oxide film thickness: 25 nm 2) Measuring electrode: Phosphorous doped polysilicon
3) Electrode area: 8mm² 4) Determination current: 1 mA / cm²
5) Pass / Fail Judgment: A product showing a breakdown voltage of 8 MV / cm or more is judged as a good product.
As a result, it was found that a non-defective product rate of approximately 100% can be obtained.
[0048]
Next, in order to evaluate the crystal defect L / D observed in the I region, the evaluation sample is etched with a mixed solution of hydrofluoric acid and nitric acid to remove the processing distortion on the surface.₂Cr₂O₇Further, Secco etching was performed with a mixed solution of hydrofluoric acid and water, and then pits due to L / D on the surface of the evaluation sample were observed. However, no defects due to L / D were observed.
From the result of the defect evaluation in the V and I regions, it was confirmed that a single crystal in the N region with very few defects was grown over the entire crystal region.
[0049]
On the other hand, for comparison, except that the inner peripheral heat insulating material 15 at the tip of the cooling cylinder of the silicon single crystal manufacturing apparatus was removed, the same manufacturing apparatus as shown in FIG. A silicon single crystal having a diameter of 200 mm was grown while adjusting the speed, and the C-mode oxide film withstand voltage was similarly measured (Comparative Example A). Furthermore, an apparatus (Comparative Example B) in which the inner peripheral heat insulating material 15 is extended to the low temperature portion so that the center temperature of the silicon single crystal is about 800 ° C. at the upper edge position, and conversely the center of the silicon single crystal at the lower edge position. Crystal growth was also performed in an apparatus (Comparative Example C) extended to the high temperature part so that the temperature was about 1350 ° C. As a result, in the C-mode oxide film breakdown voltage measurement, the non-defective product ratio remained at a value of about 50 to 70% in Comparative Examples A and B, and a value close to 100% in Comparative Example C. However, as a result of evaluating the crystal defect L / D observed in the I region in the single crystal obtained from Comparative Example C, a bit due to low density L / D was observed on the wafer surface.
[0050]
Further, in order to produce a single crystal having the same quality as that of the example product by the apparatus used in Comparative Example A, that is, a single crystal in which the entire region is an N region, what production conditions are preferably used, It was confirmed by conducting a gradual decrease experiment of the pulling speed similar to Experiment 1. As a result, it was found that the pulling speed region that becomes the N region is considerably small, 0.44 to 0.46 mm / min. In FIG. 9, the difference in the appropriate pulling speed between the invention example (solid line) and the comparative example (broken line) is visualized.
[0051]
(Example 2: Experiment 1)
Using a silicon single crystal manufacturing apparatus having a cooling cylinder having a forced cooling mechanism shown in FIG. 2, 100 kg of polycrystalline silicon was charged into a quartz crucible as in Experiment 1 of Example 1, and a silicon single crystal having a diameter of 200 mm was obtained. Then, an experiment for confirming the pulling condition was performed to pull up the single crystal in the region which becomes the N region, which is the low defect region, with the OSF ring region disappearing. At this time, the inner peripheral heat insulating material, that is, the clearance between the cooling cylinder and the silicon melt surface is set to 50 mm, and the center temperature of the silicon single crystal pulled up is about 1250 ° C. at the lower end position of the crystal cooling cylinder 13 and 15 cm above. Crystal growth was performed by arranging the inner peripheral heat insulating material 15 so as to be about 1000 ° C. (both by simulation). At this time, the thickness of the inner peripheral heat insulating material 15 was adjusted and arranged so that the gap between the crystal and the inner peripheral heat insulating material 15 was about 30 mm. Further, the single crystal is grown by adjusting the operating conditions so that other crystal qualities such as oxygen concentration are substantially the same as in Example 1.
[0052]
When the silicon single crystal was checked for the OSF ring region and the N region in the same manner as in Experiment 1 of Example 1, in the manufacturing apparatus of FIG. It has been found that if a single crystal is grown so as to be in the range of 54 mm / min, a silicon wafer having a low defect density and excellent oxide breakdown voltage characteristics can be obtained.
[0053]
(Example 2: Experiment 2)
Then, while adjusting the pulling speed to be in the range of 0.54 to 0.57 mm / min at a position of about 10 cm from the tip of the constant diameter portion of the silicon single crystal to be pulled up by the manufacturing apparatus of FIG. A silicon single crystal was grown (invention example). A silicon wafer was produced from the portion of the single crystal excluding about 10 cm at the tip of the constant diameter portion in the same manner as in Experiment 2 of Example 1, and when the C-mode oxide film breakdown voltage was measured under the same conditions, the yield rate was 100. It became a value close to%. Furthermore, as a result of evaluating the crystal defect L / D observed in the I region, it was confirmed that a high-quality crystal in which defects were suppressed throughout the entire crystal was obtained without confirming the bit due to L / D. did.
[0054]
On the other hand, for comparison, except that the inner peripheral heat insulating material at the tip of the cooling cylinder of the silicon single crystal manufacturing apparatus was removed, the same speed as the manufacturing apparatus shown in FIG. A silicon single crystal having a diameter of 200 mm was grown while adjusting the C-mode oxide breakdown voltage (Comparative Example D). Furthermore, a device (Comparative Example E) in which the inner peripheral heat insulating material 15 is extended to the low temperature portion so that the center temperature of the silicon single crystal is about 800 ° C. at the upper edge position, conversely, the center of the silicon single crystal at the lower edge position. Crystal growth was also performed in an apparatus (Comparative Example F) extended to the high temperature part so that the temperature was about 1350 ° C. As a result, according to the C-mode oxide film breakdown voltage measurement, the non-defective product ratio showed a low value of around 50 to 70% in Comparative Examples D and E, and it was almost 100% in Comparative Example F. However, as a result of evaluating the crystal defect L / D observed in the I region in the silicon single crystal manufactured in Comparative Example F, a bit due to low density L / D was observed on the wafer surface.
[0055]
In addition, in order to produce a single crystal having the same quality as that of the example product using the apparatus used in Comparative Example C, it is determined what production conditions are preferable for the pulling speed similar to that in Experiment 1. As a result of conducting a gradual reduction experiment, it was found that the pulling speed range, which is the high quality N region, was as small as 0.49 to 0.52 mm / min.
[0056]
The present invention is not limited to the embodiment described above. The above-described embodiment is merely an example, and any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and has the same effect can be used. Of course, it is included in the technical scope of the present invention. For example, the method for producing a silicon single crystal according to the present invention has been described by taking as an example the CZ method of pulling up the silicon single crystal from the silicon melt without applying a magnetic field to the silicon melt. It goes without saying that the same effect can be obtained also in the production of a silicon single crystal by the MCZ method in which a magnet is disposed outside the silicon melt and a silicon single crystal is grown while applying a magnetic field to the silicon melt.
[0057]
In the above embodiment, the case where a silicon single crystal having a diameter of 200 mm is grown is described as an example. However, the present invention is not limited to this, and the diameter is 200 to 400 mm. The present invention can be applied to the growth of a silicon single crystal having the above diameter, and can work more effectively.
[Brief description of the drawings]
FIG. 1 is an overall schematic view showing an example of an apparatus for producing a silicon single crystal according to the present invention.
2 is an overall schematic view showing a modification of the manufacturing apparatus of FIG.
FIG. 3 is a diagram for explaining the action of an inner peripheral heat insulating material.
FIG. 4 is a diagram conceptually illustrating the influence of an inner peripheral heat insulating material on defect formation.
FIG. 5 is an enlarged cross-sectional view showing first and second modifications of the inner peripheral heat insulating material.
FIG. 6 is an enlarged sectional view showing a third modified example.
FIGS. 7A and 7B are schematic views illustrating some examples of a structure for attaching an inner peripheral heat insulating material to a crystal cooling cylinder. FIGS.
8 is a graph showing the pulling speed profile and defect distribution measurement result of the silicon single crystal obtained by Experiment 1 of Example 1. FIG.
FIG. 9 is a diagram visualizing the difference in the appropriate pulling speed between the invention example and the comparative example in Experiment 2 of Example 1.
[Explanation of symbols]
1 Growing furnace body
4 Silicon melt
5 Quartz crucible
6 Graphite crucible
13 Crystal cooling cylinder
15 Inner peripheral insulation
50 Silicon single crystal manufacturing equipment

Claims

In the silicon single crystal manufacturing apparatus in which the silicon single crystal is pulled up by the Czochralski method from the silicon melt contained in the crucible in the silicon single crystal growth furnace,
A growth furnace body in which the crucible is disposed;
In the growth furnace body, a crystal cooling cylinder arranged so as to surround the silicon single crystal pulled up from the silicon melt,
Along with the inner peripheral surface of the lower end portion of the crystal cooling cylinder, it has a graphite inner peripheral heat insulating material provided in a form protruding toward the outer peripheral surface of the silicon single crystal pulled up from the silicon melt,
The inner peripheral heat insulating material is disposed so that a distance between its inner wall surface and the outer peripheral surface of the constant diameter portion of the pulled silicon single crystal is 20 mm or more and 50 mm or less, and in the axial direction of the silicon single crystal An apparatus for producing a silicon single crystal, characterized in that the whole is disposed so as to be located in a section where the center temperature of the silicon single crystal is 1000 ° C. or higher and 1250 ° C. or lower.

At least the lower end portion of the crystal cooling cylinder is made of graphite, and the inner peripheral heat insulating material is made of a carbon material having a higher porosity than the lower end portion of the crystal cooling cylinder made of graphite. Item 2. An apparatus for producing a silicon single crystal according to Item 1.

3. The apparatus for producing a silicon single crystal according to claim 1, wherein an upper end surface of the inner peripheral heat insulating material is an inclined surface having a lower inner peripheral edge side. 4.

4. The apparatus for producing a silicon single crystal according to claim 3, wherein an angle between the inclined surface and a horizontal plane is 30 [deg.] To 70 [deg.].

The inner circumferential insulation, the crystal cooling cylinder apparatus for producing a silicon single crystal according to surface exposed to the inside to any one of claims 1 to 4, characterized in that coated with graphite material.

6. The apparatus for producing a silicon single crystal according to claim 5 , wherein the surface of the graphite material is further coated with pyrolytic carbon or silicon carbide.

The crystal cooling cylinder is made of graphite, and the inner peripheral surface which is not formed in the inner peripheral thermal insulation, claims 1, characterized in that those coated with pyrolytic carbon or silicon carbide 6 The manufacturing apparatus of the silicon single crystal of any one of these.

The apparatus for producing a silicon single crystal according to claim 6 or 7 , wherein an iron (Fe) concentration in the film formed of the pyrolytic carbon or the silicon carbide is 0.05 ppm or less.

The silicon single crystal manufacturing apparatus according to any one of claims 1 to 8 , wherein the silicon single crystal is pulled up and manufactured from a silicon melt contained in the crucible by a Czochralski method. A method for producing a silicon single crystal.