JP4788029B2

JP4788029B2 - Semiconductor single crystal manufacturing apparatus and semiconductor single crystal manufacturing method using the same

Info

Publication number: JP4788029B2
Application number: JP2000263165A
Authority: JP
Inventors: 昌弘櫻田; 孝司水石; 泉布施川
Original assignee: Shin Etsu Handotai Co Ltd
Current assignee: Shin Etsu Handotai Co Ltd
Priority date: 2000-08-31
Filing date: 2000-08-31
Publication date: 2011-10-05
Anticipated expiration: 2020-08-31
Also published as: JP2002068887A

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。）により半導体単結晶を育成するための単結晶製造装置及びそれを用いた半導体単結晶の製造方法に関する。
【０００２】
【従来の技術】
従来、ＣＺ法により育成されたシリコン単結晶はシリコン半導体ウェーハに加工され、半導体素子の基板として数多く使用されている。しかし、この一方で半導体ウェーハに形成される集積回路は、集積回路の機能向上を目指し集積回路を構成する半導体素子の高密度化が進められ、集積回路の基板材料である半導体ウェーハ表層に形成される電子回路も微細化する一途をたどっている。また、このような基板ウェーハに形成させる電子回路の微細化に伴い、半導体素子を基板ウェーハ表層に形成する際に、ウェーハ表面に施される酸化膜は薄膜化する一方で、絶縁特性に優れリーク電流の少ないより高い信頼性を持った酸化膜を基板ウェーハ上に形成することが要求されるようになっている。そして、最近の研究によると、基板ウェーハに形成された酸化膜の電気的な耐圧特性（以下、酸化膜耐圧特性と称す）は、基板となる半導体単結晶の結晶育成時に形成、導入された結晶内の欠陥に大きく関係していることが判明している。
【０００３】
ＣＺ法により育成されたシリコン単結晶には、単結晶が育成された温度環境や引上速度等の育成条件の違いによって結晶内に取り込まれる欠陥に差異が生じ、形成される点欠陥が主として原子空孔（ベイキャンシー：Vacancy）となる領域（以下、Ｖ領域と称する。）と、同じく格子間シリコン原子（インタースティシアル・シリコン：Interstitial-Si）となる領域（以下、Ｉ領域と称する）とに大きく分けることができる。シリコン単結晶において、Ｖ領域は原子空孔、つまり結晶内のシリコン原子の不足により生じる凹部やボイド（穴）のようなものが多く存在する領域であり、これに対しＩ領域とは、格子間にシリコン原子が余分に存在することにより発生する転位や余分なシリコン原子のクラスターが多く存在する領域である。他方、Ｖ領域とＩ領域との間には、格子間に余分な原子や原子の不足がないか、あるいは極めて少ないニュートラル（Neutral）な領域（以下、Ｎ領域と称する）が存在する。
【０００４】
そして、最近の研究によれば、結晶内のＦＰＤ（Flow Pattern Defect）、ＬＳＴＤ（Laser Scattering Tomography Defect）、あるいはＣＯＰ（Crystal Originated Particle）等のグローンイン（Grown-in）欠陥は、あくまでも原子空孔や格子間シリコン原子が結晶内で過飽和な状態にある時に発生するものであり、多少の原子の偏りがあっても飽和以下であれば欠陥としては存在しないことがわかってきた。そして、この結晶に取り込まれる両点欠陥の濃度は、単結晶の引上速度（単結晶の成長速度）と育成単結晶と原料融液面の境界にあたる結晶成長界面近傍の温度勾配との関係から決まることが知られている。
【０００５】
また、Ｖ領域とＩ領域の間に存在するＮ領域には、ＯＳＦ（酸化誘起積層欠陥：Oxidation Induced Stacking Fault）と呼ばれる欠陥が高密度に発生する領域が存在することが確認されている。この酸化誘起積層欠陥が高密度に発生している領域は、引き上げられた単結晶をウェーハ状に加工した時にウェーハ面内にリング状に観察されることから、ＯＳＦリングあるいはＯＳＦリング領域と呼ばれている。
【０００６】
これら結晶成長起因の欠陥発生状況を、結晶成長速度を徐々に変化させて引き上げた単結晶について観察すると、例えば結晶成長速度が０．６ｍｍ／ｍｉｎ程度以上の比較的速い引上げ条件の領域では、空孔タイプの点欠陥が集合したボイド起因とされるＦＰＤ、ＬＳＴＤ、ＣＯＰ等のグローンイン欠陥が結晶径方向の全面に高密度に存在するＶ領域となり、これら欠陥が原因となってシリコン半導体ウェーハの酸化膜耐圧特性を低下させることになる。また、結晶の成長速度が０．６ｍｍ／ｍｉｎ程度以下の領域では結晶成長速度が低下するに従って格子間シリコン原子の発生が次第に優勢になり、またＯＳＦリングが徐々に縮小する第一の遷移領域が現れる。この第一の遷移領域においてＯＳＦリングの外側部分は低欠陥領域であるＮ領域であり、結晶成長速度が０．４ｍｍ／ｍｉｎ前後以下に低下したところでＯＳＦリングは結晶径方向の面内中心で凝集消滅し、ＯＳＦリングのないＮ領域となる。そして、さらに成長速度を遅くすると、そのＮ領域の外側において結晶の周辺部にＩ領域が形成される第二の遷移領域を経て結晶の軸断面全面がＩ領域となる。Ｉ領域は、転位ループ起因と考えられるＬＳＥＰＤ（Large Secco Etch Pit Defect）やＬＦＰＤ（Large Flow Pattern Defect）等の、Ｌ／Ｄ（Large Dislocation：格子間転位ループの略号）と呼ばれる欠陥が低密度に存在する領域であり、このようなＬ／Ｄ欠陥が半導体素子形成領域に存在すると、これが原因となって電流のリーク不良等、素子特性に大きな影響をおよぼす不良を誘発することになる。
【０００７】
このようなＣＺ法で育成されたシリコン単結晶の特性に配慮して、単結晶の育成時に結晶に取り込まれる欠陥を制御して酸化膜耐圧特性に優れた単結晶を育成するための方法が、特開平１１−７９８８９号公報に開示されている。この単結晶育成方法は、通常は結晶の生産性やＯＳＦの発生を考えてＶ領域が優勢となる育成条件を選択し結晶成長を行なうのに対し、Ｖ領域またはＩ領域のいずれでもない前記したＮ領域となるように単結晶の引上げを行なう。そして、このように単結晶をＮ領域となるように育成することによって、Ｖ領域またはＩ領域のどちらの欠陥も優勢ではない中間領域で単結晶が育成されることになり、結晶に欠陥が存在しないあるいは極力欠陥が抑制された極低欠陥の単結晶を得ることができ、ひいては、電流リークや酸化膜耐圧等の電気特性に優れた半導体ウェーハを得ることができる、というものである。
【０００８】
【発明が解決しようとする課題】
しかし、結晶の略全体がＮ領域で形成されるようにシリコン単結晶を育成するには、単結晶の育成速度を０．５ｍｍ／ｍｉｎ以下として結晶を引き上げる必要があり、通常の単結晶引上速度が１．０ｍｍ／ｍｉｎ程度であることを考えれば成長速度の低下が著しく、生産性の低下ひいては製造コストの高騰が必至である。
【０００９】
他方、特開２０００−３４１９２号公報には、引き上げられた単結晶の周囲を取り囲むように冷却筒を設けて雰囲気温度を制御するとともに結晶の冷却効果を高め、高速で単結晶育成を行なう装置が開示されている。しかし、該単結晶育成装置は、結晶成長速度の高速化には確かに効果を有しているが、低欠陥結晶を育成するのに必要な単結晶の引上軸方向の温度勾配をより適切に効率よく形成するには問題が残されていた。特に、Ｖ領域とＩ領域の中間領域であるＮ領域で単結晶を引き上げるためには、単結晶の成長条件がＶ領域やＩ領域で結晶を引き上げる場合に比べて厳しく、精密に育成環境を整える必要があった。また、Ｎ領域となるように単結晶を引き上げる場合にはＯＳＦリングの発生にも配慮する必要があり、結晶にＯＳＦリングが現れないで結晶の略全体にわたってＮ領域となるように結晶を引き上げるには、結晶引上軸方向の温度勾配を引上速度に合わせ所望の値に整えて結晶成長を行なうことが要求され、引上速度を高速化するに従って結晶周囲の温度条件をどのように整えるかが重要なポイントとなる。上記公報の技術では、冷却筒と融液表面との間に、円錐状の放熱抑制部材を２段に挿入されており、結晶半径方向の温度勾配の低減が図られているが、結晶引上軸方向の温度勾配制御効果は不十分と見られる。
【００１０】
本発明の課題は、ＣＺ法による半導体単結晶の育成において、原料融液より引き上げられた単結晶を冷却するにあたり、単結晶からの輻射熱を効率的に結晶育成炉の外部へ移送するとともに、単結晶の成長条件に合ったより好ましい冷却雰囲気を形成し、高い生産性で所望の品質を有する半導体単結晶を製造するための装置及び方法を提供することにある。
【００１１】
【課題を解決するための手段及び作用・効果】
本発明は、半導体単結晶の育成炉内においてルツボに収容した原料融液から、チョクラルスキー法により半導体単結晶を引き上げるようにした半導体単結晶の製造装置に係り、上記の課題を解決するため、その第一の態様は、
内部にルツボが配置される育成炉本体と、
該育成炉本体の上部に連通形態にて一体形成され、半導体単結晶の回収空間を形成する回収空間形成部と、
原料融液より引き上げられた半導体単結晶を囲繞するように配置された円筒状または円錐状の形状を有する結晶冷却筒と、
回収空間形成部に冷却媒体を還流することにより、該回収空間形成部を強制的に冷却する強制冷却機構とを有し、
結晶冷却筒は上部が回収空間形成部の下部に熱伝達可能に接続され、引き上げられた半導体単結晶の冷却により該結晶冷却筒の吸収した熱が、強制冷却機構により強制冷却される該回収空間形成部を経て育成炉外に排出されるとともに、該結晶冷却筒の原料融液直上に位置する下部側を黒鉛製冷却部とし、回収空間形成部に接続される上部側を金属製冷却部とし、
結晶冷却筒は、半導体単結晶の引上げ方向において、金属製冷却部の長さが黒鉛製冷却部の長さと等しいかあるいはそれよりも長いことを特徴とする。
【００１２】
結晶冷却筒は、ＣＺ法により半導体単結晶を育成するための単結晶製造装置に配設されるものであり、全体として円筒状または円錐状の形状を有し育成単結晶を囲繞するように配置されている。そして、上記本発明の第一の構成において結晶冷却筒は、引き上げられた単結晶からの輻射熱を効率よく育成炉外へ移送するために、冷却筒の上方は熱伝導率の高い金属製冷却部となし、原料融液面に近接する下部は黒鉛製冷却部となす。結晶冷却筒をこのような構造とすれば、結晶温度がある程度低下した、結晶成長界面から遠い位置では冷却速度が大きくなり、効率よく冷却が図られるのに対し、結晶成長界面付近では前記冷却温度勾配が小さい徐冷となり、結晶成長界面の方向の温度が安定するため結晶成長速度の高速化を図ることができる。また、強制冷却により冷却速度が相当大きくなる育成炉の回収空間形成部と、冷却速度の比較的小さい黒鉛製冷却部との間に、それらの中間の冷却速度となる金属製冷却部を配することで、結晶引上方向の温度勾配が最適化され、結晶内に取り込まれる欠陥濃度を適切に調整することができるため、安定して所望の品質を有する単結晶を育成することが可能となる。
【００１３】
なお、結晶冷却筒の金属製冷却部の上部は、冷却筒金属部からの熱を確実に育成炉へ伝えるために、回収空間形成部あるいは原料融液を収容している育成炉本体上部（以下、育成炉側係合部という）に対し、密接係合していることが望ましい。特に、冷却筒側係合部と育成炉と育成炉側係合部とは、より効率的に熱の伝達を行なうことができるよう、面接触で密着していることが望まれる。育成炉と冷却筒金属部を面接触で密着させておけば、冷却筒が育成結晶から吸収した熱を速やかに育成炉壁に伝達することができるようになり、結晶冷却筒の冷却効果が一層高められる。
【００１４】
なお、ＣＺ法による単結晶育成に用いられる単結晶製造装置の育成炉には、加熱ヒータ等から放射された輻射熱から育成炉壁を保護し一定温度に保つために単結晶育成炉の壁を二重構造とし、その隙間に水等による冷却媒体を還流させている構造を採用したものが多い。この構造によると、結晶冷却筒から伝達された熱は、製造装置の回収空間形成部あるいは育成炉本体の金属製の炉壁を介して炉壁を冷やすための冷却媒体に伝えられ、速やかに育成炉外部へと運ばれる。そして、育成炉の回収空間形成部が、そのような強制冷却構造を採用している場合、強制冷却機構を有さない上記構成の結晶冷却筒を追加装備するだけで、結晶内の欠陥が抑制された低欠陥結晶を高速で引き上げるための適切な冷却雰囲気を形成する機能を容易に付加することができる。該結晶冷却筒そのものは構造が比較的単純であり、製造装置への装着や取り外しが容易であるため、結晶製造装置の装備を、育成する単結晶の品質に適した装備へと速やかに変更することができ、ひいては効率的な製造装置運用を図ることが可能である。
【００１５】
次に、本発明に関連する半導体単結晶の製造装置は、
半導体単結晶の育成炉内においてルツボに収容した原料融液から、チョクラルスキー法により半導体単結晶を引き上げるようにした半導体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、
該育成炉本体の上部に連通形態にて一体形成され、半導体単結晶の回収空間を形成する回収空間形成部と、
円筒状または円錐状の形状をなし、原料融液より引き上げられた半導体単結晶を囲繞するように配置されるとともに上部が回収空間形成部に係合され、さらに、回収空間形成部に係合される上部が、引き上げられた半導体単結晶からの輻射熱を強制的に育成炉外へ移送するために内部に冷却媒体を還流する構造の強制冷却部とされ、また、原料融液直上に位置する下部が黒鉛製冷却部とされ、さらに、強制冷却部と黒鉛製冷却部との間に金属製冷却部を配した結晶冷却筒と、
を備えたことが想定される。
【００１６】
この構成では、第一の態様と異なり、回収空間形成部に係合される結晶冷却筒の上部そのものが強制冷却部とされている。そして、この場合においても、高温の原料融液からの冷却筒の保護と、結晶の引上軸方向に望ましい温度勾配を形成する観点において、冷却媒体を用いた強制冷却部の下方に熱伝導率の高い金属製冷却部を設け、さらに、その金属冷却部の下方には黒鉛から成る黒鉛製冷却部を設けるようにすることで、結晶内に欠陥の存在しないあるいは極力欠陥を抑えた単結晶を育成するのに望ましい結晶冷却温度雰囲気を、育成結晶周囲に形成することが可能となる。
【００１７】
従来、冷却筒は、全体がステンレス等の金属により、冷却媒体還流による一体の強制冷却部とされていることが多いが、シリコン融液の付着等により冷却筒下部が溶損すると、高価な強制冷却部の全体の交換を強いられるために不経済であった。そこで、この対応として冷却筒の下端に保護部材を設けたり、冷却筒と融液の距離を大きく取ることで冷却筒に原料融液が付着したり、あるいは融液に冷却筒が浸漬するのを防止してきたが、反面、冷却筒が結晶の成長界面から遠くなることでその効果を十分に発揮することができず、特に欠陥を抑制した高品質結晶の育成では結晶成長界面付近の温度分布を適切にコントロールする必要があり新たな冷却装置の検討が加えられていた。
【００１８】
これに対し上記本発明の結晶冷却筒は、原料融液面近くであっても効率よく最大限結晶からの輻射熱を吸収できるよう、強制冷却部の下部に金属製冷却部を配置して、その熱を強制冷却部へ移送する構造としているので、金属冷却部の冷却効果は衰えることなく、結晶育成全般にわたって安定した冷却効果を得ることが可能である。また、金属製冷却部の下には融液面直上に配置されている形で黒鉛製冷却部が設けられる。この黒鉛製冷却部は、金属製の冷却部に比べ融液あるいは育成結晶からの輻射熱を除去する効果が小さく、結晶周囲の融液温度の変化を小さく保ち結晶の育成を安定させると同時に、成長界面に近い結晶部位を必要以上に冷却することがないので、特に低欠陥結晶を育成する場合に適切な温度雰囲気を形成することが可能となる。
【００１９】
一方、黒鉛製冷却部の上端は、熱伝導の良好な金属製冷却部に接しているので、黒鉛製冷却部の温度が上がった場合でもその熱を速やかに金属製冷却部へ伝達することができ、ひいては安定した冷却効果を持続することができる。さらに、該結晶冷却筒は、上部に冷却媒体を用いて強制的に冷却を行なう強制冷却部、その下に密接に金属製冷却部、そして最下端に黒鉛製冷却部を有する三層から構成されており、冷却能力は冷却筒下方で低く上方に行くに従って徐々に冷却効果が高まる機構となっている。このような構造とすることにより、結晶引上軸方向の温度勾配に急激な温度変化を持った個所がなくなり、滑らかな引上軸方向の温度勾配を形成することでき、ひいては結晶に不要な熱的なストレスを加えることなく単結晶の育成を行なうことができるようになる。
【００２０】
さらに、結晶冷却筒の上部のみが強制冷却部とされ、その下側が金属製冷却部あるいは黒鉛製冷却部の配置により保護されているから、シリコン融液等の飛散・付着により高価な強制冷却部が破損する惧れがほとんどない。また、シリコン融液の付着しやすい結晶冷却筒の融液面直上部分はいわば消耗品的に取り扱うことができる安価な黒鉛製なので、万一破損しても経済的な損害はそれほど深刻とはならない。
【００２１】
なお、本発明の第１の態様及び第２の態様のいずれにおいても、結晶冷却筒の内表面には、溝あるいは凹凸を設け冷却筒内表面の面積を大きくして、冷却効果を高めることが可能である。冷却筒の内側表面に溝あるいは凹凸を付けることによって結晶からの輻射熱を受け取る面積を広くすれば、より冷却筒により育成炉の外部へ移送せされる熱量が大きくなり、育成単結晶の冷却効果を高めることができる。
【００２２】
また、本発明の結晶冷却筒の効果を高める方法として、冷却媒体を還流する強制冷却部や円筒あるいあは円錐形状の金属製の冷却筒部分の内表面に、黒鉛を塗布する等して表面を黒色化する黒化処理を施せば、さらに育成結晶と対峙する冷却筒の金属部分からの輻射熱の吸収効果が高まり、より速やかに結晶の熱を除去することが可能となる。
【００２３】
本発明の半導体単結晶の製造方法は、上記の半導体単結晶の製造装置を用い、ルツボに収容した原料融液から、チョクラルスキー法により半導体単結晶を引き上げて製造することを特徴とする。これによると、効率良く所望の育成単結晶を冷却する温度雰囲気を形成することができるとともに、結晶冷却筒の冷却効果もより一層高いものとなり単結晶育成時の引上速度の高速化を図ることが可能となる。また、本発明の結晶冷却筒を用いることにより結晶品質に合った適切な冷却温度雰囲気を形成することができるため、安定した品質の単結晶を容易に育成可能なものとなる。これによって、これまで製造の難しかった高品質結晶、特に育成時に導入される結晶欠陥を低密度に抑制した単結晶を高速で引き上げることが可能となり、低欠陥結晶の製造コストを低減が図られた。さらには、既存の単結晶製造装置であっても、育成単結晶を冷却するための複雑な結晶冷却機構を設けることなく効率の高い結晶冷却雰囲気を形成できるので、設備導入が容易になると同時に製造装置の装備変更も簡単であるため、製造装置の稼動率と作業性の向上に寄与することができる。
【００２４】
【発明の実施の形態】
以下に、本発明の実施の形態を、ＣＺ法によるシリコン半導体単結晶製造に適用した場合を例にとり、図面を参照しながら説明する。図１の単結晶製造装置１は、本発明の第二の態様に係る一例を示すものであり、その育成炉は、原料融液１４を内部に収容し、単結晶２３を引上育成するための育成炉本体２と、育成された単結晶を保持し取り出すための回収空間形成部４とから構成されている。そして、育成炉本体２と回収空間形成部４との各壁部は、単結晶育成時の加熱による高温から炉壁を保護するために、外壁２ａ，４ａと内壁２ｂ，４ｂとの二重構造とされ、両者の隙間には、冷却媒体を還流させて炉壁の温度が一定以上に上昇しないように保護するための強制冷却機構３が設けられている。本発明の単結晶製造装置では、比熱やコスト、取扱い易さ等を考えて冷却媒体として水を使用した。また、本実施形態において強制冷却機構３は、還流経路を銅パイプ等の金属パイプにて構成し、その一端側に冷却媒体入口３ａを、他端側に冷却媒体出口３ｂを形成している。なお、図１では強制冷却機構３は育成炉本体２にのみ設けているように描いているが、回収空間形成部４にも同様の構成の強制冷却機構を設けることができる。
【００２５】
育成炉本体２の中央部には、支持軸１３を介して内側が石英ルツボ１２ｂ、外側が黒鉛ルツボ１２ａとされたルツボ１２が配置され、支持軸１３の下端に取り付けられた非図示のルツボ駆動機構によって回転動かつ上下動自在とされている。また、ルツボ１２の外側周囲には、ルツボに充填された多結晶原料を融解し融液として保持するための加熱ヒータ１５が設けられている。さらに、その外側には黒鉛製の断熱材１６が置かれており、育成炉内の保温と加熱ヒータ１５からの高温の輻射熱から育成炉炉壁を保護する役目を果たしている。
【００２６】
一方、回収空間形成部４の上端には単結晶を引き上げるための非図示のワイヤー巻出し巻取り機構が取り付けられ、そこから巻き出されたワイヤー２２の先端には種結晶２１を保持するための種ホルダー２０が取り付けられている。この種ホルダー２０は、該ワイヤー巻出し巻取り機構によって回転及び上下動自在とされ、その先端には種結晶２１が取り付けられている。上記ワイヤー巻出し巻取り機構を駆動することによってワイヤー２２を巻き出し、種結晶２１を原料融液１４に浸漬する。そして、原料融液１４と種結晶２１の温度が安定したら、ワイヤー２２を回転させながら静かに巻き取ることで、種結晶２１の下方に単結晶２３を育成することができる。
【００２７】
なお、大直径あるいは長尺の単結晶棒を育成する場合は、図６に示すように、磁場発生装置３１，３１によって原料融液１４に磁場を印加することにより、ルツボ１２内での原料融液１４の対流を抑制することが有効である（いわゆるＭＣＺ法（Magnetic Field Applied Czochralski Method））。なお、図１と共通の部分には同一の符号を付与して詳細な説明を省略している（以降に説明する図７、図８、図９、図１０及び図１１についても同様）。
【００２８】
回収空間形成部４の下方には、育成炉本体２の原料融液面１４ａに向かって延伸する結晶冷却筒２５が装備されている。結晶冷却筒２５は、原料融液１４から引き上げられた単結晶２３を囲繞し、育成単結晶が適切な冷却速度で冷却されるよう、結晶周囲の温度雰囲気を所望の値とする働きをなす。この結晶冷却筒２５は、回収空間形成部４に接する上部が冷却媒体を還流して強制冷却する強制冷却部５とされ、強制冷却部５の下方には金属から成る金属製冷却部８が、さらに金属製冷却部８の下方に黒鉛製の黒鉛冷却部１０が配置された構造を有する。このうような構造を用いることによって冷却筒２５の冷却能力が高められ、引上速度を高速に保つとともに、所望の品質、特に低欠陥結晶の育成に必要とされる冷却温度雰囲気が形成される。なお、黒鉛製冷却部１０には原料融液１４の温度安定を図るために、その先端に板状の反射リング１１（例えば等方性黒鉛製である）を設けている。
【００２９】
金属冷却部８は、鉄、ニッケル、クロム、銅、チタン、モリブデン及びタングステンのいずれかを主成分とする金属（単体金属及び合金のいずれか）にて構成することができる。これらの金属は融点が高く熱伝導率も良好であるため、吸収した熱を速やかに育成炉や強制冷却部に伝え、単結晶の育成全般にわたり安定した高い除熱効果を維持できる。また、これら金属は機械的な強度も高く、さらには育成炉内の高温にも十分に耐えるので、変形や変質することなく長時間にわたって安全に使用することがきるものである。なお、耐久性の高い金属冷却部８をより安価に構成するには、鉄、ニッケル、クロム及び銅のいずれかを主成分とする金属からなる基材の表面を、チタン、モリブデン、タングステン及び白金族金属のいずれかを主成分とするライニング層で覆った構成とすることも有効である。例えば、鉄は高強度で安価であるが、耐食性には若干劣る。しかし、チタン、モリブデン、タングステンあるいは白金族金属からなる耐食性ライニングを施すことで、耐食性を補うことが可能となる。また、基材を銅で構成することは、熱伝達特性を高める上でより望ましい。
【００３０】
次に、強制冷却部５は、具体的には冷却媒体を還流するための強制冷却機構６を備えている。強制冷却機構６は、ここでも還流経路を銅パイプ等の金属パイプにて構成し、その一端側に冷却媒体入口６ａを、他端側に冷却媒体出口６ｂを形成している。なお、強制冷却機構６における冷却媒体の流通経路は、上記のように内壁と外壁との空間に別途金属パイプを配置して形成する態様のほか、内壁／外壁間の空間そのものを流通経路として使用するウォータージャケット型のものを採用してもよい。この場合、空間内に配置した仕切り板により適切な流通経路を画成することが可能である。また、回収空間形成部４に強制冷却機構を組み込む場合にも、同様にウォータージャケット型のものを採用することが可能である。
【００３１】
なお、単結晶育成時は育成炉内をアルゴン（以下、Ａｒと称する）ガス等の不活性で満たして操業が行なわれる。そこで、回収空間形成部４の上方にはガス導入管１９が設けられており、回収空間形成部４から不活性ガスが炉内に導入され、育成炉本体２の下部にある排ガス管１７から育成炉外へ排出される。育成炉内に流す不活性ガスの量と炉内の圧力は、ガス導入管１９に設けられた非図示のガス流量制御装置と、排ガス管１７上のコンダクタンスバルブ１８を用いて適宜調整される。
【００３２】
また、結晶冷却筒２５の内面側には、冷却筒内表面の面積を大きくし引き上げられ半導体単結晶からの輻射熱を効率よく吸収するための、溝及び／又は凹凸を１箇所以上設けることができる。結晶冷却筒２５の内部に形成する溝あるいは凹凸の数や形状は、必要とする冷却筒の冷却効果を検討して決めればよい。図２は、強制冷却部５及び金属製冷却部８に溝ないし凹凸を形成するいくつかの例を示すものである（いずれか一方のみに設けてもよいし、双方に設けてもいずれでもよい）。図２（ａ）は、筒状の強制冷却部５（金属製冷却部８）の内周面に、周方向の溝７（６７）を軸線方向に所定の間隔で複数刻設した態様を示す。図２（ｂ）は、同じく軸線方向の溝５７（７７）を周方向に所定の間隔で複数刻設した態様を示す。図２（ｃ）は、島状、例えば半球状の凸部６７（８７）を複数分散形成した態様を、同図（ｄ）は同じく凹部７７（９７）を複数分散形成した態様を示す。当然、（ａ）〜（ｄ）の２以上を組み合わせた方法でも問題はなく、例えば（ａ）及び（ｂ）を組み合わせた格子状の溝を刻設してもよい。また、図３に示すように、冷却筒の内周面に凸部として１又は複数のフィンを形成してもよい。図３（ａ）は、金属製冷却部８の内周面に沿うリング状のフィン９を、各々溶接部９ａにより軸線方向に所定の間隔で複数形成した例を示す。
【００３３】
なお、より大きな冷却効果を得る必要があれば、上記のような溝や凹凸を増やし、冷却筒内表面の面積を可能な限り大きなものとすればよい。例えば、図７の装置１００においては、金属製冷却部８の内周面に形成したフィン９の数を、図１の装置１よりも大きくしている。他方、それ程の効果を必要としない場合は、図１０の装置２５０のように、溝や凹凸を付けなくとも十分な効果を得ることができる。
【００３４】
また、上記以外に結晶冷却筒２５の効果を高める方法として、輻射熱を効率よく吸収するために、半導体結晶に向けた熱反射を抑制する熱反射抑制部を形成することができる。熱反射抑制部は、具体的には、領域の色調を黒色化させる黒化処理、及び半導体結晶からの輻射熱を乱反射させるために領域表面を粗化する表面粗化処理の少なくともいずれかを施して形成することができる。図３（ａ）は、金属製冷却部８の内面（フィン９を含む）に黒鉛塗布層８ｂ，９ｂを形成する黒化処理を施した例を、同図（ｃ）は、表面粗化処理としてショットブラストを施し、面粗し部８ｃ，９ｃを施した例を示す。
【００３５】
結晶冷却筒２５の金属製冷却部８と強制冷却部５、あるいは金属製冷却部８と黒鉛製冷却部１０とは、各々接続面が密着形態にて配置されていることが、金属製冷却部８から強制冷却部５への熱伝達効率を向上させる観点において望ましい。図４は、金属製冷却部８と強制冷却部５との接続形態のいくつかの例を示すものである。図４（ａ）では、強制冷却部５の下端面と金属製冷却部８の上端面とを突き合わせ（突き合わせ面は、密着性を高めるため研磨により平坦化しておくことが望ましい）、その突き合わせ縁を溶接部８ｅ，８ｆにより接続した例である。なお、突き合わせ面間にろう付け層８ｆを形成することも可能である。また、図４（ｂ）では、金属製冷却部８の上端縁から側方に延びる鍔状の接続部８ｃを形成して強制冷却部５の接合面に重ね合わせ、接続部８ｃを貫通する形で強制冷却部５側にボルト４０をねじ込んで締結した例である。さらに、図４（ｃ）は、強制冷却部５の下面側に開口する溝４１を形成し、ここに筒状の金属製冷却部８の上端部を圧入もしくは焼きバメ挿入した例である。
【００３６】
また、図５は、金属製冷却部８と黒鉛製冷却部１０との接続形態のいくつかの例を示す。いずれも、金属製冷却部８と黒鉛製冷却部１０とにそれぞれ面接触係合部８ｈ及び１０ｈを形成し、各係合面８ｉ，１０ｉにてそれらを面接触させつつ、係合保持手段により該面接触状態に保持させた構成を有する。図５（ａ）の構成では、金属製冷却部８の下端部に側方に突出する面接触係合部８ｈを形成する一方、黒鉛製冷却部１０の上端部に同じく側方に突出する面接触係合部１０ｈを形成し、黒鉛製冷却部１０側の面接触係合部１０ｈを金属製冷却部８側の面接触係合部８ｈに懸架させ、黒鉛製冷却部１０の自重により両係合部８ｈ、１０ｈの係合状態を維持する構成である。ここでは、面接触係合部８ｈは、金属製冷却部８の開口内縁にて周方向内向きに突出する鍔状に形成され、その上面が係合面８ｉとされる。また、面接触係合部１０ｈは黒鉛製冷却部１０の外周面上端部に外向きに突出する鍔状に形成され、その下面が係合面１０ｉとされている。組みつけの際には、黒鉛製冷却部１０を金属製冷却部８の内部に上部開口側から軸線方向に挿入し、面接触係合部１０ｈ，８ｈを係合面１０ｉ，８ｉにて面接触係合させる形とする。
【００３７】
一方、図５（ｂ）においては、金属製冷却部８の下端部と黒鉛製冷却部１０の上端部とをそれぞれ面接触係合部８ｈ，１０ｈとなし、それらの一方を他方の内側に軸線方向に挿入して、その接触周面をそれぞれ係合面８ｉ，１０ｉとするとともに、その状態で両者を締結部材にて締結した構造としている。この実施例では、締結部材は、面接触係合部８ｈ，１０ｈを半径方向に貫通するボルト４５と、これに螺合するナット４６とにより構成している。
【００３８】
次に、単結晶２３の引上げ方向において、金属製冷却部８の長さＬｍと黒鉛製冷却部１０の長さＬｃとは、例えば図８に示す装置１５０のように、金属製冷却部８の長さのほうを短くすることも可能であるが、原料融液面１４ａと育成炉本体の天井面との間の空間は限られおり、狭い育成炉内で効率的に結晶の冷却を行なうには、冷却能力の高い金属製冷却部８の面積を大きくすることが高い結晶冷却能力を得る上で有利である。従って、図１のように、金属製冷却部８の長さＬｍは黒鉛製冷却部１０の長さＬｃと等しいかそれ以上とすことが望ましい。黒鉛製冷却部１０の長さＬｃは結晶成長界面近傍の温度を安定させるため程度に留めておくのがよく、黒鉛製冷却部１０の長さＬｃに対し金属製冷却部８の長さＬｍを同じかあるいはそれ以上長くすることによって、より冷却能力の高い結晶冷却筒２５が得られるのである。
【００３９】
なお、図９に示すように、黒鉛製冷却部１０の先端側には、原料融液１４の保温と炉内のヒータ１５からの加熱によって原料融液１４に生ずる熱対流を安定させ、結晶成長界面付近での融液温度の変化をより安定的なものとするために、熱遮蔽リング３０を設けることができる。熱遮蔽リング３０は、図９（ｂ）に示すように、多孔質あるいは繊維質の断熱材からなる断熱層３０ｂを含んで構成される。これにより、原料融液１４からの輻射熱をより効果的に遮蔽し、融液の保温効果を高めて融液１４の温度変動をより小さくすることができる。特に、断熱層３０ｂを、カーボンファイバー製の繊維質断熱材等、断熱効果の高い材質にて構成すれば、より大きな保温効果が得られ、一層安定した結晶成長を行なうことができる。本実施例では、熱遮蔽リング３０の融液面１４ａに面する側を前述の反射リングと同様の等方性黒鉛板３０ａとなし、残部（すなわち、黒鉛製冷却部１０と等方性黒鉛板３０ａとの間に挟まれる部分）を、断熱層３０ｂとして構成している。
【００４０】
次に、図１１の単結晶製造装置３００は、本発明の第一の態様に係る一例を示すものである。単結晶製造装置３００においては、回収空間形成部４及び育成炉本体２とも、図１の単結晶製造装置と同様に壁部が二重構造となっており、回収空間形成部４にも強制冷却機構６が設けられている。また、結晶冷却筒２５からは強制冷却部が廃止されるとともに、その金属製冷却部８は回収空間形成部４の下部に熱伝達可能に接続されている。その接続形態は、図４に示す強制冷却部５との接続形態と同様のものが採用できる。これによる作用・効果は、図１の装置１と略同様である。なお、金属製冷却部８の上端を育成炉本体２の天井部に密接に係合しても同様の効果を得ることができる。また、結晶冷却筒２５の下部は図１と同様に黒鉛製冷却部１０とされている。このような構造とすることによって結晶成長界面近傍の雰囲気温度は安定し、融液の温度変動も小さく抑えることができるようになるので、結晶成長を妨げることなく順調な結晶育成を行なうことができる。さらに、黒鉛製冷却部１０の先端には、図９と同様の断熱リング３０が取り付けられている。
【００４１】
【実施例】
以下、本発明の単結晶製造装置によるシリコン単結晶の育成を実施例と比較例を挙げて具体的に説明するが、本発明はこれらに限定して解釈されるものではない。
【００４２】
（実施例１）
まず、結晶欠陥の少ないシリコン単結晶をできるだけ速い速度で引き上げるためにはどのような製造装置の構造とすべきか検討するために、単結晶製造装置の装備をいくつか変更しシリコン単結晶の育成を行なった。
【００４３】
単結晶の育成は、単結晶製造装置に下記Ａ〜Ｄのそれぞれ違った装備を施して、口径６０ｃｍの石英製ルツボにシリコン単結晶の原料である多結晶シリコンを１００ｋｇ充填しヒータを加熱して融解した後に、一定の直径を有する結晶定径部の直径が２００ｍｍのシリコン結晶を引き上げた。単結晶を育成するにあたっては、ルツボ回転や炉内に流すＡｒガスの量等の操業条件を調整し育成単結晶の酸素濃度が１９〜２０ｐｐｍａ（ＡＳＴＭ’７９規格による測定値）となるように調整を図り、結晶の引上速度を０．８ｍｍ／ｍｉｎの速度から単結晶の成長が進むに従って０．４ｍｍ／ｍｉｎまで次第に引上速度を遅くして、結晶のどの位置でＯＳＦリングが消え、無欠陥あるいは極めて欠陥密度の低いＮ領域となる部位が現れるかを確認した。単結晶製造装置は、育成単結晶の冷却雰囲気を形成する結晶冷却筒をＡ〜Ｄのような構造とした以外は、いずれも同じ構造の単結晶製造を用いて結晶の引上げを行なった。装備Ａ〜Ｄの詳細は、次の通りである。
【００４４】
１）装備Ａ（図１０に対応）：回収空間形成部４から冷却水により強制冷却する強制冷却部５を下垂し、その下方に円筒状のステンレス製金属製冷却部８を取り付け、さらに、その金属製冷却部８の下には高純度黒鉛を用いて作成した黒鉛製冷却部１０を設けた。なお、黒鉛製冷却部１０には反射リング１１を設けた。
２）装備Ｂ（図１に対応）：装備Ａと同じ構成の結晶冷却筒２５であるが、強制冷却部５と金属製冷却部８に、図２（ｂ）のような縦溝を刻み冷却筒内部２５の面積を増やし、さらに金属製冷却部８／強制冷却部５の輻射熱の反射を減らすために、各々内面に表面粗化処理を施した結晶冷却筒２５とした。
３）装備Ｃ（図７に対応）：装備Ｂに準ずるが、金属製冷却部８の長さＬｍを黒鉛製冷却部１０の長さＬｃの２倍にして冷却筒２５の冷却効率の向上を図った。
４）装備Ｄ（図９に対応）：装備Ｃに準ずるが、黒鉛製冷却部１０の先端に配置されていた反射リング１１を、さらに断熱効果の高い熱遮蔽リング３０に替え、融液の保温効果を高める構造とた。
【００４５】
以上の装備の単結晶装置を用いて育成した結晶を、結晶の引上軸中心に沿って縦割りにし、図１２に示すように、ＯＳＦリング結晶内の軸中心に向かって消滅している位置が結晶のどの位置にあるかを調べた。ＯＳＦリングの評価方法は、次の方法を用いて評価を行い、発生位置を確認した。
１）単結晶を引上軸方向に１０ｃｍ毎に切断した後にそれぞれを径中心から縦に割り、縦に割った面を結晶引上軸に沿ってスライスして厚さが２ｍｍ前後の観察用ウェーハを得た。
２）この観察用ウェーハに、窒素雰囲気および酸素雰囲気中で熱処理を加えた後に薬液で表面の酸化膜を除去し、Ｘ線トポグラフを用いてウェーハ表面を観察しＯＳＦの発生領域の確認を行なった。
３）この観察結果を元に、種結晶側の結晶先端１０ｃｍを除きＯＳＦリングが結晶中心に向かって消滅している位置を調べ、その結晶部位での引上速度を対比したところ表１に示す結果が得られた。
【００４６】
【表１】

【００４７】
上記の結果から、装備Ｄを用いた単結晶製造装置で引上速度が０．６５ｍｍ／ｍｉｎとなった時にＯＳＦリングが消滅していることから、この装備を用いて引上速度が０．６５ｍｍ前後となるように単結晶の育成を行なえば、欠陥の極めて少ない結晶を高速で引き上げられることを確認した。
【００４８】
（実施例２）
実施例１と同様に、口径６０ｃｍの石英ルツボに多結晶シリコンを１００ｋｇ充填し溶解した後に、定径部の直径が２００ｍｍのシリコン単結晶を引き上げた。この時の単結晶製造装置には装備Ｄの結晶冷却筒を取り付けた製造装置を用い、単結晶の引上速度が結晶定径部前半の１０ｃｍ位置で０．６４ｍｍ／ｍｉｎ、結晶成長が進むに従って徐々に引上速度を下げ、定径部の後半では０．６０ｍｍ／ｍｉｎの引上速度となるように操業条件を整えて単結晶を育成した（図１３：実線）。
【００４９】
育成されたシリコン単結晶には変形等を生じることもなく、略円柱状の単結晶を形成することができた。この単結晶をウェーハ状に加工して１ｃｍ単位で抜き取り、ＯＳＦの発生の有無と酸化膜耐圧特性の評価を行なった。この結果、結晶内にＯＳＦは観察されず、またＣモード酸化膜耐圧測定条件により酸化膜耐圧特性を評価したとこと良品率は１００％であり良好な結果を得ることができた。
【００５０】
なお、Ｃモード酸化膜耐圧測定条件は次の通りである。
１）酸化膜：２５ｎｍ２）測定電極：リンドープポリシリコン
３）電極面積：８ｍｍ^２３）判定電流：１ｍＡ／ｃｍ^２
４）８ＭＶ／ｃｍ以上の電圧を印加したときに、電流リークが発生しなかったものを良品と判定した。
【００５１】
（比較例）
次に、装備Ｄにおいて、結晶冷却筒２５を、全体が黒鉛にて構成された同じ寸法のものに替えて、シリコン単結晶の育成を行なった。単結晶の育成は、実施例と同様に口径６０ｃｍの石英ルツボに多結晶シリコンを１００ｋｇ充填し溶解した後で、原料融液から定径部の直径が２００ｍｍのシリコン単結晶の引き上げた。この単結晶製造装置の装備では、低欠陥結晶を０．６０ｍｍ／ｍｉｎ以上の高速で引き上げることは不可能であり、この装置によりＯＳＦリングの発生のない低欠陥結晶を育成できたのは、単結晶の結晶定径部前半の１０ｃｍ位置の引上速度を０．４７ｍｍ／ｍｉｎとし、それ以降、結晶成長が進むに従って徐々に引上速度を下げ定径部の後半で０．４３ｍｍ／ｍｉｎの引上速度となるように操業条件を整えて単結晶を育成時であった（図１３：破線）。この結果、本発明の装置を用いることにより引上速度が高められ、結晶定径部の製造時間を２７％も短縮できることを確認できた。
【００５２】
なお、本発明は上記した実施の形態に限定されるものではない。上記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無論である。
【００５３】
例えば、本発明の装置では磁場を印加しないで単結晶を育成するＣＺ法の単結晶製造装置を例に挙げて説明したが、原料融液に磁場を印加しながら単結晶を育成するＭＣＺ法を用いた単結晶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。また、本発明をシリコン以外の半導体単結晶の成長に利用可能なことは当然であり、ＣＺ法を用いた例えばＧａＡｓ結晶等の化合物半導体の育成に適用した場合でもその効果を十分に発揮することができる。
【図面の簡単な説明】
【図１】本発明の第二の態様に係る半導体単結晶の製造装置の一例を示す断面模式図。
【図２】結晶冷却筒に溝あるいは凹凸を施すいくつかの例を示す説明図。
【図３】金属製冷却部の内面にフィンを設ける例と、同じく黒化処理あるいは表面粗化処理を施す例を示す説明図。
【図４】金属製冷却部と強制冷却部との接続形態をいくつか例示して示す断面図。
【図５】金属製冷却部と黒鉛製冷却部との接続形態の一例を示す断面図。
【図６】図１の半導体単結晶の製造装置の第一変形例を示す断面模式図。
【図７】図１の半導体単結晶の製造装置の第二変形例を示す断面模式図。
【図８】図１の半導体単結晶の製造装置の第三変形例を示す断面模式図。
【図９】図１の半導体単結晶の製造装置の第四変形例を示す断面模式図。
【図１０】図１の半導体単結晶の製造装置の第五変形例を示す断面模式図。
【図１１】本発明の第一の態様に係る半導体単結晶の製造装置の一例を示す断面模式図。
【図１２】実施例１及び実施例２において、引上速度を徐々に低下させ、結晶のＮ領域が現れる位置の引上速度を求める方法を模式的に表した図。
【図１３】実施例２において、実施例と比較例との引上速度プロファイルを比較して示す図。
【符号の説明】
１，１００，１５０，２００，２５０，３００半導体単結晶の製造装置
２育成炉本体
３強制冷却機構
４回収空間形成部
５強制冷却部
６強制冷却機構
７溝部
８金属製冷却部
９フィン（凸部）
１０黒鉛製冷却部
１２ルツボ
１４原料融液
２５結晶冷却筒
３０熱遮蔽リング[0001]
[Technical field to which the invention belongs]
The present invention relates to a single crystal manufacturing apparatus for growing a semiconductor single crystal by the Czochralski method (hereinafter referred to as CZ method) and a method for manufacturing a semiconductor single crystal using the same.
[0002]
[Prior art]
Conventionally, a silicon single crystal grown by the CZ method is processed into a silicon semiconductor wafer and used in many cases as a substrate for semiconductor elements. However, on the other hand, the integrated circuit formed on the semiconductor wafer is formed on the surface layer of the semiconductor wafer, which is the substrate material of the integrated circuit, as the density of the semiconductor elements constituting the integrated circuit is increased to improve the function of the integrated circuit. Electronic circuits that are becoming more and more miniaturized. In addition, along with the miniaturization of electronic circuits formed on such substrate wafers, when forming semiconductor elements on the surface layer of a substrate wafer, the oxide film applied to the wafer surface is thinned, while having excellent insulating properties and leakage. There has been a demand for forming an oxide film with less current and higher reliability on a substrate wafer. According to recent research, the electrical breakdown voltage characteristics (hereinafter referred to as oxide breakdown voltage characteristics) of the oxide film formed on the substrate wafer are the crystals formed and introduced during the crystal growth of the semiconductor single crystal serving as the substrate. It has been found to be largely related to defects in the inside.
[0003]
A silicon single crystal grown by the CZ method has a difference in defects taken into the crystal due to differences in growth conditions such as the temperature environment and pulling speed at which the single crystal is grown, and the formed point defects are mainly atomic. A region (hereinafter referred to as V region) that becomes a vacancy (Vacancy) and a region (hereinafter referred to as I region) that also becomes an interstitial silicon atom (Interstitial-Si). It can be roughly divided. In a silicon single crystal, the V region is a region where there are many vacancies, that is, there are many recesses and voids (holes) caused by the shortage of silicon atoms in the crystal. In this region, there are many dislocations generated due to the presence of excess silicon atoms and clusters of excess silicon atoms. On the other hand, between the V region and the I region, there is a neutral region (hereinafter referred to as an N region) in which there are no extra atoms or shortages of atoms between the lattices, or very little.
[0004]
According to recent research, Grown-in defects such as FPD (Flow Pattern Defect), LSTD (Laser Scattering Tomography Defect), or COP (Crystal Originated Particle) in the crystal are not limited to atomic vacancies or It is generated when interstitial silicon atoms are in a supersaturated state in the crystal, and it has been found that even if there is a slight deviation of atoms, it does not exist as a defect if it is below saturation. The concentration of both-point defects taken into this crystal is based on the relationship between the pulling rate of the single crystal (single crystal growth rate) and the temperature gradient near the crystal growth interface, which is the boundary between the grown single crystal and the raw material melt surface. It is known to be decided.
[0005]
Further, it has been confirmed that in the N region existing between the V region and the I region, there is a region where defects called OSF (Oxidation Induced Stacking Fault) occur at high density. The region where the oxidation-induced stacking faults are generated at a high density is called an OSF ring or an OSF ring region because it is observed in a ring shape in the wafer surface when the pulled single crystal is processed into a wafer shape. ing.
[0006]
When the occurrence of defects due to crystal growth is observed for a single crystal pulled up by gradually changing the crystal growth rate, for example, in the region of a relatively fast pulling condition where the crystal growth rate is about 0.6 mm / min or more, it is empty. Grown-in defects such as FPD, LSTD, and COP, which are attributed to voids in which hole type point defects are gathered, become a V region existing at high density in the entire surface in the crystal diameter direction, and these defects cause oxidation of the silicon semiconductor wafer. The film withstand voltage characteristic is lowered. Further, in the region where the crystal growth rate is about 0.6 mm / min or less, the generation of interstitial silicon atoms becomes more dominant as the crystal growth rate decreases, and the first transition region where the OSF ring gradually shrinks appear. In this first transition region, the outer portion of the OSF ring is an N region which is a low defect region, and the OSF ring is agglomerated at the in-plane center in the crystal diameter direction when the crystal growth rate decreases to about 0.4 mm / min or less. It disappears and becomes an N region without an OSF ring. When the growth rate is further slowed down, the entire axial cross section of the crystal becomes the I region through the second transition region in which the I region is formed in the periphery of the crystal outside the N region. In the I region, defects called L / D (Large Dislocation: abbreviations for interstitial dislocation loops) such as LSEPD (Large Secco Etch Pit Defect) and LFPD (Large Flow Pattern Defect), which are thought to be caused by dislocation loops, have a low density. If such an L / D defect exists in the semiconductor element formation region, this causes a defect that greatly affects the element characteristics, such as a current leakage defect.
[0007]
In consideration of the characteristics of such a silicon single crystal grown by the CZ method, a method for growing a single crystal excellent in oxide film withstand voltage characteristics by controlling defects taken into the crystal during the growth of the single crystal, This is disclosed in Japanese Patent Application Laid-Open No. 11-79889. In this single crystal growth method, crystal growth is usually performed by selecting a growth condition in which the V region is dominant in consideration of crystal productivity and generation of OSF, whereas it is neither the V region nor the I region. The single crystal is pulled so as to be in the N region. Then, by growing the single crystal to be the N region in this way, the single crystal is grown in an intermediate region where neither the defect in the V region nor the I region is dominant, and there is a defect in the crystal. In other words, it is possible to obtain a single crystal having extremely low defects in which defects are suppressed as much as possible, and in turn, it is possible to obtain a semiconductor wafer having excellent electric characteristics such as current leakage and oxide film breakdown voltage.
[0008]
[Problems to be solved by the invention]
However, in order to grow a silicon single crystal so that substantially the entire crystal is formed in the N region, it is necessary to pull the crystal at a growth rate of the single crystal of 0.5 mm / min or less. Considering that the speed is about 1.0 mm / min, the growth rate is remarkably lowered, and the productivity is lowered and the manufacturing cost is inevitably increased.
[0009]
On the other hand, Japanese Patent Application Laid-Open No. 2000-34192 discloses an apparatus for growing a single crystal at a high speed by providing a cooling cylinder so as to surround the pulled single crystal to control the ambient temperature and enhancing the cooling effect of the crystal. It is disclosed. However, although the single crystal growth apparatus has an effect for increasing the crystal growth rate, the temperature gradient in the pulling axis direction of the single crystal necessary for growing the low defect crystal is more appropriate. However, there remains a problem in efficiently forming. In particular, in order to pull up a single crystal in the N region, which is an intermediate region between the V region and the I region, the growth conditions of the single crystal are stricter than in the case of pulling up the crystal in the V region and the I region, and a growth environment is prepared precisely. There was a need. Also, when pulling up the single crystal so as to be in the N region, it is necessary to consider the generation of the OSF ring. In order to pull up the crystal so that the entire region of the crystal becomes the N region without the OSF ring appearing in the crystal. Requires crystal growth with the temperature gradient in the crystal pulling axis direction adjusted to the pulling speed to the desired value, and how to adjust the temperature conditions around the crystal as the pulling speed is increased. Is an important point. In the technique of the above publication, a conical heat radiation suppressing member is inserted in two stages between the cooling cylinder and the melt surface to reduce the temperature gradient in the crystal radial direction. The axial temperature gradient control effect appears to be insufficient.
[0010]
An object of the present invention is to efficiently transfer radiant heat from a single crystal to the outside of a crystal growth furnace in cooling a single crystal pulled from a raw material melt in the growth of a semiconductor single crystal by the CZ method. An object of the present invention is to provide an apparatus and a method for producing a semiconductor single crystal having a desired quality with a high productivity by forming a more preferable cooling atmosphere suitable for crystal growth conditions.
[0011]
[Means for solving the problems and actions / effects]
  The present invention relates to a semiconductor single crystal manufacturing apparatus in which a semiconductor single crystal is pulled up by a Czochralski method from a raw material melt contained in a crucible in a semiconductor single crystal growth furnace. The first aspect is
  A growth furnace body in which a crucible is arranged;
  A recovery space forming part that is integrally formed in a communication form on the upper part of the growth furnace body and forms a recovery space of the semiconductor single crystal;
  A crystal cooling cylinder having a cylindrical or conical shape disposed so as to surround the semiconductor single crystal pulled up from the raw material melt;
A forced cooling mechanism for forcibly cooling the recovery space forming portion by returning the cooling medium to the recovery space forming portion;
The upper part of the crystal cooling cylinder is connected to the lower part of the recovery space forming part so that heat can be transferred, and the recovery space in which the heat absorbed by the crystal cooling cylinder is forcibly cooled by the forced cooling mechanism by cooling the pulled semiconductor single crystal. It is discharged to the outside of the growth furnace through the formation part, the lower side located immediately above the raw material melt of the crystal cooling cylinder is a graphite cooling part, and the upper side connected to the recovery space formation part is a metal cooling part ,
In the crystal cooling cylinder, the length of the metal cooling section is equal to or longer than the length of the graphite cooling section in the pulling direction of the semiconductor single crystal.It is characterized by that.
[0012]
The crystal cooling cylinder is arranged in a single crystal manufacturing apparatus for growing a semiconductor single crystal by the CZ method, and has a cylindrical or conical shape as a whole and is arranged so as to surround the grown single crystal. Has been. In the first configuration of the present invention, the crystal cooling cylinder is a metal cooling section having a high thermal conductivity above the cooling cylinder in order to efficiently transfer the radiant heat from the pulled single crystal to the outside of the growth furnace. The lower part close to the raw material melt surface is a graphite cooling part. When the crystal cooling cylinder has such a structure, the cooling temperature increases at a position far from the crystal growth interface where the crystal temperature has decreased to some extent, and the cooling temperature is increased near the crystal growth interface. Since the gradient is gradually cooled and the temperature in the direction of the crystal growth interface is stabilized, the crystal growth rate can be increased. In addition, a metal cooling unit having an intermediate cooling rate is disposed between the recovery space forming unit of the growth furnace in which the cooling rate is considerably increased by forced cooling and the graphite cooling unit having a relatively low cooling rate. As a result, the temperature gradient in the crystal pulling direction is optimized, and the defect concentration taken into the crystal can be adjusted appropriately, so that a single crystal having a desired quality can be stably grown. .
[0013]
The upper part of the metal cooling part of the crystal cooling cylinder is the upper part of the growth furnace main body (hereinafter referred to as the recovery space forming part or the raw material melt) in order to reliably transfer the heat from the cooling cylinder metal part to the growth furnace. It is desirable that they are closely engaged with each other. In particular, it is desirable that the cooling cylinder side engagement portion, the growth furnace, and the growth furnace side engagement portion are in close contact with each other so that heat can be transferred more efficiently. If the growth furnace and the cooling cylinder metal part are brought into close contact with each other by surface contact, the cooling cylinder can quickly transfer the heat absorbed from the growth crystal to the growth furnace wall, and the cooling effect of the crystal cooling cylinder is further enhanced. Enhanced.
[0014]
Note that the growth furnace of the single crystal production apparatus used for single crystal growth by the CZ method has two walls of the single crystal growth furnace in order to protect the growth furnace wall from radiant heat radiated from a heater or the like and keep it at a constant temperature. In many cases, a heavy structure is used, and a cooling medium such as water is refluxed in the gap. According to this structure, the heat transferred from the crystal cooling cylinder is transferred to the cooling medium for cooling the furnace wall through the recovery space forming part of the manufacturing apparatus or the metal furnace wall of the growth furnace body, and is quickly grown. Carried outside the furnace. And, when the recovery space forming part of the growth furnace adopts such a forced cooling structure, defects in the crystal can be suppressed only by additionally installing the crystal cooling cylinder having the above-mentioned configuration without the forced cooling mechanism. A function of forming an appropriate cooling atmosphere for pulling up the formed low defect crystal at high speed can be easily added. Since the crystal cooling cylinder itself has a relatively simple structure and can be easily attached to and detached from the production equipment, the equipment for the crystal production equipment is quickly changed to equipment suitable for the quality of the single crystal to be grown. As a result, it is possible to operate the manufacturing apparatus efficiently.
[0015]
  Next, in the present inventionRelatedSemiconductor single crystal manufacturing equipmentIs,
In a semiconductor single crystal manufacturing apparatus in which a semiconductor single crystal is pulled up by a Czochralski method from a raw material melt stored in a crucible in a semiconductor single crystal growth furnace,
  A growth furnace body in which a crucible is arranged;
  A recovery space forming part that is integrally formed in a communication form on the upper part of the growth furnace body and forms a recovery space of the semiconductor single crystal;
  It has a cylindrical or conical shape, is arranged so as to surround the semiconductor single crystal pulled up from the raw material melt, and the upper part is engaged with the recovery space forming part, and further is engaged with the recovery space forming part. The upper part is a forced cooling part having a structure in which a cooling medium is circulated in order to forcibly transfer the radiant heat from the pulled semiconductor single crystal to the outside of the growth furnace, and the lower part located immediately above the raw material melt Is a graphite cooling section, and further, a crystal cooling cylinder in which a metal cooling section is arranged between the forced cooling section and the graphite cooling section,
  HavingIs assumedThe
[0016]
In this configuration, unlike the first aspect, the upper part of the crystal cooling cylinder engaged with the recovery space forming part is the forced cooling part. Even in this case, in terms of protecting the cooling cylinder from the high-temperature raw material melt and forming a desirable temperature gradient in the crystal pulling axis direction, the thermal conductivity is below the forced cooling section using the cooling medium. By providing a high-temperature metal cooling part, and further providing a graphite cooling part made of graphite below the metal cooling part, a single crystal that has no defects in the crystal or suppresses defects as much as possible can be obtained. It is possible to form a crystal cooling temperature atmosphere desirable for growing around the grown crystal.
[0017]
Conventionally, a cooling cylinder is generally made of a metal such as stainless steel, and is often an integral forced cooling part by refluxing the cooling medium. However, if the lower part of the cooling cylinder melts down due to adhesion of silicon melt, etc. It was uneconomical to be forced to replace the entire cooling section. Therefore, as a countermeasure, a protective member is provided at the lower end of the cooling cylinder, or the distance between the cooling cylinder and the melt is increased so that the raw material melt adheres to the cooling cylinder, or the cooling cylinder is immersed in the melt. However, the cooling cylinder is far from the crystal growth interface, so the effect cannot be fully exerted. Especially in the growth of high-quality crystals with suppressed defects, the temperature distribution near the crystal growth interface is reduced. It was necessary to control appropriately, and the examination of a new cooling device was added.
[0018]
On the other hand, the crystal cooling cylinder of the present invention has a metal cooling part arranged below the forced cooling part so that it can efficiently absorb the radiant heat from the crystal even if it is close to the raw material melt surface. Since the heat is transferred to the forced cooling part, the cooling effect of the metal cooling part is not diminished, and a stable cooling effect can be obtained over the entire crystal growth. Further, a graphite cooling section is provided below the metal cooling section in a form arranged immediately above the melt surface. This graphite cooling part has a smaller effect of removing radiant heat from the melt or grown crystal than the metal cooling part, keeps the change in the melt temperature around the crystal small, stabilizes the growth of the crystal, and grows at the same time. Since the crystal part close to the interface is not cooled more than necessary, an appropriate temperature atmosphere can be formed particularly when growing a low defect crystal.
[0019]
On the other hand, the upper end of the graphite cooling unit is in contact with a metal cooling unit with good heat conduction, so even when the temperature of the graphite cooling unit rises, the heat can be quickly transferred to the metal cooling unit. And by extension, a stable cooling effect can be maintained. Further, the crystal cooling cylinder is composed of three layers having a forced cooling section forcibly cooling using a cooling medium at the top, a metal cooling section closely below it, and a graphite cooling section at the bottom end. The cooling capacity is low at the bottom of the cooling cylinder, and the cooling effect is gradually increased as it goes upward. By adopting such a structure, there is no place where the temperature gradient in the crystal pulling axis direction has a sudden temperature change, and a smooth temperature gradient in the pulling axis direction can be formed. Single crystal can be grown without applying additional stress.
[0020]
Further, only the upper part of the crystal cooling cylinder is a forced cooling part, and the lower side is protected by the arrangement of a metal cooling part or a graphite cooling part, so that an expensive forced cooling part is caused by scattering and adhesion of silicon melt or the like. There is almost no risk of damage. In addition, the portion immediately above the melt surface of the crystal cooling tube where the silicon melt easily adheres is made of cheap graphite that can be handled as a consumable item, so the economic damage will not be so serious even if it breaks. .
[0021]
In both the first and second aspects of the present invention, the cooling surface can be enhanced by providing grooves or irregularities on the inner surface of the crystal cooling cylinder to increase the area of the inner surface of the cooling cylinder. Is possible. If the area that receives the radiant heat from the crystal is increased by providing grooves or irregularities on the inner surface of the cooling cylinder, the amount of heat transferred to the outside of the growth furnace by the cooling cylinder increases and the cooling effect of the growing single crystal is increased. Can be increased.
[0022]
Further, as a method for enhancing the effect of the crystal cooling cylinder of the present invention, the surface is obtained by applying graphite or the like to the inner surface of the forced cooling part for refluxing the cooling medium or the cylindrical or conical metal cooling cylinder part. If the blackening treatment for blackening is performed, the effect of absorbing radiant heat from the metal portion of the cooling cylinder facing the grown crystal is further increased, and the heat of the crystal can be removed more rapidly.
[0023]
The method for producing a semiconductor single crystal according to the present invention is characterized in that the semiconductor single crystal is pulled up from the raw material melt contained in the crucible by the Czochralski method using the semiconductor single crystal production apparatus. According to this, a temperature atmosphere for efficiently cooling a desired grown single crystal can be formed, and the cooling effect of the crystal cooling cylinder can be further enhanced to increase the pulling speed during single crystal growth. Is possible. Further, by using the crystal cooling cylinder of the present invention, an appropriate cooling temperature atmosphere suitable for the crystal quality can be formed, so that a single crystal having a stable quality can be easily grown. This makes it possible to pull up high-quality crystals that have been difficult to manufacture, particularly single crystals that suppress crystal defects introduced at the time of growth at a low density, thereby reducing the manufacturing cost of low-defect crystals. . Furthermore, even with existing single crystal manufacturing equipment, it is possible to form a highly efficient crystal cooling atmosphere without providing a complicated crystal cooling mechanism for cooling the grown single crystal. Since the equipment can be easily changed, it can contribute to the improvement of the operating rate and workability of the manufacturing apparatus.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings, taking as an example the case of applying the present invention to the production of a silicon semiconductor single crystal by the CZ method. The single crystal manufacturing apparatus 1 of FIG. 1 shows an example according to the second aspect of the present invention, and the growth furnace accommodates the raw material melt 14 inside and pulls and grows the single crystal 23. And a recovery space forming part 4 for holding and taking out the grown single crystal. And each wall part of the growth furnace main body 2 and the collection | recovery space formation part 4 is a double structure of

outer wall

2a, 4a and

inner wall

2b, 4b in order to protect a furnace wall from the high temperature by the heating at the time of single crystal growth. The forced cooling mechanism 3 is provided in the gap between the two to protect the temperature of the furnace wall from rising above a certain level by refluxing the cooling medium. In the single crystal manufacturing apparatus of the present invention, water is used as a cooling medium in consideration of specific heat, cost, ease of handling, and the like. Further, in the present embodiment, the forced cooling mechanism 3 is configured such that the reflux path is formed of a metal pipe such as a copper pipe, and the cooling medium inlet 3a is formed on one end side and the cooling medium outlet 3b is formed on the other end side. In FIG. 1, the forced cooling mechanism 3 is illustrated as being provided only in the growth furnace main body 2, but the recovery space forming unit 4 can be provided with a forced cooling mechanism having a similar configuration.
[0025]
At the center of the growth furnace body 2, a crucible 12 having a quartz crucible 12 b on the inside and a graphite crucible 12 a on the outside via a support shaft 13 is arranged and a crucible drive (not shown) attached to the lower end of the support shaft 13. The mechanism is rotatable and vertically movable. A heater 15 for melting the polycrystalline raw material filled in the crucible and holding it as a melt is provided around the outer periphery of the crucible 12. Further, a heat insulating material 16 made of graphite is placed outside thereof, and plays a role of protecting the growth furnace wall from the heat retention in the growth furnace and high-temperature radiant heat from the heater 15.
[0026]
On the other hand, a wire unwinding / winding mechanism (not shown) for pulling up the single crystal is attached to the upper end of the recovery space forming portion 4, and the tip of the wire 22 unwound from there is used to hold the seed crystal 21. A seed holder 20 is attached. The seed holder 20 can be rotated and moved up and down by the wire unwinding / winding mechanism, and a seed crystal 21 is attached to the tip thereof. The wire unwinding mechanism is driven to unwind the wire 22 and immerse the seed crystal 21 in the raw material melt 14. When the temperature of the raw material melt 14 and the seed crystal 21 is stabilized, the single crystal 23 can be grown below the seed crystal 21 by gently winding the wire 22 while rotating the wire 22.
[0027]
When growing a large-diameter or long single crystal rod, as shown in FIG. 6, a magnetic field is applied to the raw material melt 14 by the

magnetic field generators

31 and 31, thereby melting the raw material in the crucible 12. It is effective to suppress the convection of the liquid 14 (so-called MCZ method (Magnetic Field Applied Czochralski Method)). In addition, the same code | symbol is attached | subjected to the part which is common in FIG. 1, and detailed description is abbreviate | omitted (it is the same also about FIG.7, FIG.8, FIG.9, FIG.10 and FIG.11 demonstrated later).
[0028]
A crystal cooling cylinder 25 extending toward the raw material melt surface 14a of the growth furnace body 2 is provided below the recovery space forming unit 4. The crystal cooling cylinder 25 surrounds the single crystal 23 pulled up from the raw material melt 14 and serves to set the temperature atmosphere around the crystal to a desired value so that the grown single crystal is cooled at an appropriate cooling rate. The crystal cooling cylinder 25 has an upper portion in contact with the recovery space forming unit 4 as a forced cooling unit 5 for refluxing the cooling medium and forcibly cooling it, and a metal cooling unit 8 made of metal below the forced cooling unit 5. Further, a graphite cooling part 10 made of graphite is arranged below the metal cooling part 8. By using such a structure, the cooling capacity of the cooling cylinder 25 is increased, the pulling speed is kept high, and a desired temperature, particularly a cooling temperature atmosphere necessary for growing a low defect crystal is formed. . The graphite cooling unit 10 is provided with a plate-like reflecting ring 11 (for example, made of isotropic graphite) at the tip thereof in order to stabilize the temperature of the raw material melt 14.
[0029]
The metal cooling part 8 can be comprised with the metal (any one of a single metal and an alloy) which has as a main component any one of iron, nickel, chromium, copper, titanium, molybdenum, and tungsten. Since these metals have a high melting point and good thermal conductivity, the absorbed heat can be quickly transferred to the growth furnace and forced cooling section, and a stable and high heat removal effect can be maintained throughout the growth of the single crystal. In addition, these metals have high mechanical strength and can sufficiently withstand the high temperatures in the growth furnace, so that they can be used safely for a long time without being deformed or altered. In addition, in order to construct the highly durable metal cooling unit 8 at a lower cost, the surface of a base material made of a metal mainly composed of iron, nickel, chromium, or copper is made of titanium, molybdenum, tungsten, and platinum. It is also effective to have a structure in which any of the group metals is covered with a lining layer having a main component. For example, iron has high strength and is inexpensive, but slightly inferior in corrosion resistance. However, it is possible to supplement the corrosion resistance by applying a corrosion-resistant lining made of titanium, molybdenum, tungsten, or a platinum group metal. Moreover, it is more desirable to configure the base material with copper in order to improve the heat transfer characteristics.
[0030]
Next, the forced cooling unit 5 is specifically provided with a forced cooling mechanism 6 for refluxing the cooling medium. In the forced cooling mechanism 6, the reflux path is also constituted by a metal pipe such as a copper pipe, and a cooling medium inlet 6 a is formed on one end side and a cooling medium outlet 6 b is formed on the other end side. The cooling medium flow path in the forced cooling mechanism 6 uses the space between the inner wall / outer wall itself as a flow path in addition to the mode in which the metal pipe is separately disposed in the space between the inner wall and the outer wall as described above. A water jacket type may be used. In this case, it is possible to define an appropriate distribution path by the partition plates arranged in the space. Also, when a forced cooling mechanism is incorporated in the recovery space forming unit 4, a water jacket type can be similarly employed.
[0031]
During the growth of the single crystal, the growth furnace is filled with an inert gas such as argon (hereinafter referred to as Ar) gas. Therefore, a gas introduction pipe 19 is provided above the recovery space forming section 4, and an inert gas is introduced into the furnace from the recovery space forming section 4 and grown from the exhaust gas pipe 17 at the lower part of the growth furnace body 2. It is discharged outside the furnace. The amount of inert gas flowing into the growth furnace and the pressure in the furnace are appropriately adjusted using a gas flow rate controller (not shown) provided in the gas introduction pipe 19 and a conductance valve 18 on the exhaust gas pipe 17.
[0032]
Further, one or more grooves and / or irregularities can be provided on the inner surface side of the crystal cooling cylinder 25 in order to efficiently absorb the radiant heat from the semiconductor single crystal that is pulled up by increasing the area of the inner surface of the cooling cylinder. . The number or shape of the grooves or irregularities formed inside the crystal cooling cylinder 25 may be determined by examining the cooling effect of the cooling cylinder that is required. FIG. 2 shows some examples of forming grooves or irregularities in the forced cooling section 5 and the metal cooling section 8 (may be provided in either one or both. ). FIG. 2A shows an embodiment in which a plurality of circumferential grooves 7 (67) are formed at predetermined intervals in the axial direction on the inner peripheral surface of the cylindrical forced cooling section 5 (metal cooling section 8). . FIG. 2B shows an aspect in which a plurality of axial grooves 57 (77) are formed at predetermined intervals in the circumferential direction. 2C shows an embodiment in which a plurality of island-shaped, for example, hemispherical convex portions 67 (87) are formed in a dispersed manner, and FIG. 2D shows an embodiment in which a plurality of concave portions 77 (97) are formed in a dispersed manner. Naturally, there is no problem even in a method in which two or more of (a) to (d) are combined. For example, a lattice-shaped groove in which (a) and (b) are combined may be formed. Moreover, as shown in FIG. 3, you may form a 1 or several fin as a convex part in the internal peripheral surface of a cooling cylinder. FIG. 3A shows an example in which a plurality of ring-shaped fins 9 along the inner peripheral surface of the metal cooling portion 8 are formed at predetermined intervals in the axial direction by the weld portions 9a.
[0033]
In addition, if it is necessary to obtain a greater cooling effect, the number of grooves and irregularities as described above may be increased to make the area of the inner surface of the cooling cylinder as large as possible. For example, in the apparatus 100 of FIG. 7, the number of fins 9 formed on the inner peripheral surface of the metal cooling section 8 is made larger than that of the apparatus 1 of FIG. On the other hand, in the case where such an effect is not required, a sufficient effect can be obtained without providing grooves or irregularities as in the device 250 of FIG.
[0034]
In addition to the above, as a method for enhancing the effect of the crystal cooling cylinder 25, a heat reflection suppressing portion that suppresses heat reflection toward the semiconductor crystal can be formed in order to efficiently absorb radiant heat. Specifically, the heat reflection suppression unit performs at least one of a blackening process for blackening the color tone of the area and a surface roughening process for roughening the area surface to diffusely reflect the radiant heat from the semiconductor crystal. Can be formed. FIG. 3A shows an example in which the blackening treatment for forming the graphite coating layers 8b and 9b is performed on the inner surface (including the fins 9) of the metal cooling section 8, and FIG. 3C shows the surface roughening treatment. As an example, shot blasting is performed and

surface roughening portions

8c and 9c are applied.
[0035]
The metal cooling unit 8 and the forced cooling unit 5 of the crystal cooling cylinder 25 or the metal cooling unit 8 and the graphite cooling unit 10 are arranged so that the connection surfaces are arranged in close contact with each other. It is desirable from the viewpoint of improving the heat transfer efficiency from 8 to the forced cooling section 5. FIG. 4 shows some examples of the connection form between the metal cooling section 8 and the forced cooling section 5. In FIG. 4A, the lower end surface of the forced cooling unit 5 and the upper end surface of the metal cooling unit 8 are abutted (the abutting surface is preferably flattened by polishing to improve adhesion), and the abutting edge Are connected by welding portions 8e and 8f. It is also possible to form a brazing layer 8f between the butted surfaces. Further, in FIG. 4 (b), a hook-like connection portion 8c extending laterally from the upper end edge of the metal cooling portion 8 is formed, overlapped with the joint surface of the forced cooling portion 5, and penetrates the connection portion 8c. This is an example in which the bolt 40 is screwed into the forced cooling section 5 and fastened. Further, FIG. 4C is an example in which a groove 41 opened on the lower surface side of the forced cooling unit 5 is formed, and the upper end portion of the cylindrical metal cooling unit 8 is press-fitted or shrink-fitted.
[0036]
FIG. 5 shows some examples of connection forms between the metal cooling section 8 and the graphite cooling section 10. In either case, the surface

contact engagement portions

8h and 10h are formed in the metal cooling portion 8 and the graphite cooling portion 10 respectively, and are brought into surface contact with each of the engagement surfaces 8i and 10i, and the engagement holding means. The surface contact state is maintained. In the configuration of FIG. 5A, a surface contact engaging portion 8 h that protrudes laterally is formed at the lower end portion of the metallic cooling portion 8, while a surface that also protrudes laterally at the upper end portion of the graphite cooling portion 10. A contact engagement portion 10h is formed, and the surface contact engagement portion 10h on the graphite cooling portion 10 side is suspended from the surface contact engagement portion 8h on the metal cooling portion 8 side, and both are engaged by the own weight of the graphite cooling portion 10. It is the structure which maintains the engagement state of

joint part

8h, 10h. Here, the surface contact engaging portion 8h is formed in a bowl shape protruding inward in the circumferential direction at the opening inner edge of the metal cooling portion 8, and the upper surface thereof is set as an engaging surface 8i. Further, the surface contact engaging portion 10h is formed in a bowl shape projecting outward at the upper end portion of the outer peripheral surface of the graphite cooling portion 10, and its lower surface is an engaging surface 10i. At the time of assembly, the graphite cooling part 10 is inserted into the metal cooling part 8 in the axial direction from the upper opening side, and the surface

contact engaging parts

10h, 8h are brought into surface contact with the engaging surfaces 10i, 8i. The shape is engaged.
[0037]
On the other hand, in FIG.5 (b), the lower end part of the metal cooling part 8 and the upper end part of the graphite cooling part 10 are each made into the surface

contact engaging part

8h and 10h, and one of them is an axis inside the other. Inserted in the direction, the contact peripheral surfaces are made into engagement surfaces 8i and 10i, respectively, and in this state, both are fastened by a fastening member. In this embodiment, the fastening member is constituted by a bolt 45 penetrating the surface

contact engaging portions

8h and 10h in the radial direction and a nut 46 screwed into the bolt 45.
[0038]
Next, in the pulling direction of the single crystal 23, the length Lm of the metal cooling unit 8 and the length Lc of the graphite cooling unit 10 are the same as those of the metal cooling unit 8 as in the apparatus 150 shown in FIG. Although it is possible to shorten the length, the space between the raw material melt surface 14a and the ceiling surface of the growth furnace body is limited, so that the crystal can be efficiently cooled in a narrow growth furnace. In order to obtain a high crystal cooling capacity, it is advantageous to increase the area of the metal cooling section 8 having a high cooling capacity. Therefore, as shown in FIG. 1, the length Lm of the metal cooling part 8 is preferably equal to or longer than the length Lc of the graphite cooling part 10. The length Lc of the graphite cooling section 10 is preferably kept to a level in order to stabilize the temperature in the vicinity of the crystal growth interface. The length Lm of the metal cooling section 8 is set to the length Lc of the graphite cooling section 10. By making it the same or longer, the crystal cooling cylinder 25 having a higher cooling capacity can be obtained.
[0039]
As shown in FIG. 9, on the tip side of the graphite cooling section 10, the heat convection generated in the raw material melt 14 due to the heat insulation of the raw material melt 14 and the heating from the heater 15 in the furnace is stabilized, and crystal growth is achieved. In order to make the change in the melt temperature near the interface more stable, a heat shielding ring 30 can be provided. As shown in FIG. 9B, the heat shielding ring 30 includes a heat insulating layer 30b made of a porous or fibrous heat insulating material. Thereby, the radiant heat from the raw material melt 14 can be shielded more effectively, the temperature retention effect of the melt can be enhanced, and the temperature fluctuation of the melt 14 can be further reduced. In particular, if the heat insulating layer 30b is made of a material having a high heat insulating effect such as a fibrous heat insulating material made of carbon fiber, a larger heat retaining effect can be obtained, and more stable crystal growth can be performed. In the present embodiment, the side facing the melt surface 14a of the heat shield ring 30 is the isotropic graphite plate 30a similar to the above-described reflection ring, and the remainder (that is, the cooling section 10 made of graphite and the isotropic graphite plate). The portion sandwiched between 30a and 30a is configured as a heat insulating layer 30b.
[0040]
Next, the single crystal manufacturing apparatus 300 of FIG. 11 shows an example according to the first aspect of the present invention. In the single crystal manufacturing apparatus 300, both the recovery space forming unit 4 and the growth furnace main body 2 have a double wall structure as in the single crystal manufacturing apparatus of FIG. A mechanism 6 is provided. Further, the forced cooling part is eliminated from the crystal cooling cylinder 25, and the metal cooling part 8 is connected to the lower part of the recovery space forming part 4 so as to be able to transfer heat. The connection form may be the same as the connection form with the forced cooling unit 5 shown in FIG. The operation and effect by this are substantially the same as those of the device 1 of FIG. Note that the same effect can be obtained even when the upper end of the metal cooling portion 8 is closely engaged with the ceiling portion of the growth furnace body 2. The lower part of the crystal cooling cylinder 25 is a graphite cooling unit 10 as in FIG. By adopting such a structure, the ambient temperature in the vicinity of the crystal growth interface can be stabilized, and the temperature fluctuation of the melt can be suppressed to be small, so that smooth crystal growth can be performed without hindering crystal growth. . Further, a heat insulating ring 30 similar to that shown in FIG. 9 is attached to the tip of the graphite cooling unit 10.
[0041]
【Example】
Hereinafter, the growth of a silicon single crystal by the single crystal production apparatus of the present invention will be specifically described with reference to examples and comparative examples, but the present invention is not construed as being limited thereto.
[0042]
(Example 1)
First, in order to examine what kind of manufacturing equipment structure should be used to pull up a silicon single crystal with few crystal defects at the fastest possible speed, the equipment of the single crystal manufacturing equipment has been changed to grow a silicon single crystal. I did it.
[0043]
Single crystal growth is carried out by applying the following equipment A to D to a single crystal manufacturing apparatus, filling a quartz crucible having a diameter of 60 cm with 100 kg of polycrystalline silicon, which is a raw material for silicon single crystal, and heating a heater. After melting, a silicon crystal having a constant diameter portion having a constant diameter of 200 mm was pulled up. When growing a single crystal, adjust the operating conditions such as crucible rotation and the amount of Ar gas flowing into the furnace so that the oxygen concentration of the grown single crystal is 19-20 ppma (measured value according to ASTM '79 standard). The crystal pulling speed was gradually decreased from 0.8 mm / min to 0.4 mm / min as the growth of the single crystal progressed, and the OSF ring disappeared at any position of the crystal. It was confirmed whether or not a defect or a portion that becomes an N region having a very low defect density appeared. The single crystal production apparatus pulled the crystal using single crystal production with the same structure except that the crystal cooling cylinder forming the cooling atmosphere of the grown single crystal had a structure such as AD. Details of the equipments A to D are as follows.
[0044]
1) Equipment A (corresponding to FIG. 10): A forced cooling part 5 forcibly cooling with cooling water is dropped from the recovery space forming part 4, and a cylindrical stainless steel metal cooling part 8 is attached below the forced cooling part 5. Below the metal cooling part 8, a graphite cooling part 10 made of high-purity graphite was provided. The graphite cooling unit 10 is provided with a reflection ring 11.
2) Equipment B (corresponding to FIG. 1): The crystal cooling cylinder 25 having the same configuration as the equipment A, however, the forced cooling part 5 and the metal cooling part 8 are cooled by cutting vertical grooves as shown in FIG. In order to increase the area of the cylinder interior 25 and further reduce the reflection of the radiant heat of the metal cooling section 8 / forced cooling section 5, a crystal cooling cylinder 25 having a surface roughening treatment applied to each inner surface was formed.
3) Equipment C (corresponding to FIG. 7): Although it is the same as Equipment B, the cooling efficiency of the cooling cylinder 25 is improved by making the length Lm of the metal cooling part 8 twice the length Lc of the cooling part 10 made of graphite. planned.
4) Equipment D (corresponding to FIG. 9): In accordance with equipment C, the reflective ring 11 arranged at the tip of the graphite cooling section 10 is replaced with a heat shielding ring 30 having a higher thermal insulation effect, and the temperature of the melt is kept. A structure that enhances the effect.
[0045]
The crystal grown using the single crystal apparatus having the above-mentioned equipment is vertically divided along the center of the crystal pulling axis, and as shown in FIG. 12, the position disappears toward the axis center in the OSF ring crystal. It was investigated where in the crystal. The evaluation method of the OSF ring was evaluated using the following method, and the generation position was confirmed.
1) An observation wafer having a thickness of about 2 mm obtained by cutting a single crystal every 10 cm in the pulling axis direction, dividing each of them vertically from the diameter center, and slicing the vertically divided plane along the crystal pulling axis. Got.
2) After heat-treating this observation wafer in a nitrogen atmosphere and an oxygen atmosphere, the oxide film on the surface was removed with a chemical solution, and the wafer surface was observed using an X-ray topograph to confirm the OSF generation region. .
3) Based on this observation result, the position where the OSF ring disappears toward the center of the crystal except for 10 cm of the crystal tip on the seed crystal side was examined, and the pulling speed at the crystal part was compared. Results were obtained.
[0046]
[Table 1]

[0047]
From the above results, since the OSF ring disappears when the pulling speed becomes 0.65 mm / min in the single crystal manufacturing apparatus using the equipment D, the pulling speed is 0.65 mm using this equipment. It was confirmed that if a single crystal was grown so as to be before and after, a crystal with very few defects could be pulled at a high speed.
[0048]
(Example 2)
Similarly to Example 1, 100 kg of polycrystalline silicon was filled in a quartz crucible having a diameter of 60 cm and dissolved, and then a silicon single crystal having a constant diameter portion of 200 mm was pulled up. As the single crystal manufacturing apparatus at this time, the manufacturing apparatus equipped with the crystal cooling cylinder of equipment D was used, and the pulling speed of the single crystal was 0.64 mm / min at the 10 cm position in the first half of the crystal constant diameter portion, and the crystal growth progressed. The pulling speed was gradually lowered, and the single crystal was grown by adjusting the operating conditions so that the pulling speed was 0.60 mm / min in the latter half of the constant diameter portion (FIG. 13: solid line).
[0049]
A substantially cylindrical single crystal could be formed without causing deformation or the like in the grown silicon single crystal. This single crystal was processed into a wafer shape and extracted in units of 1 cm, and the presence / absence of OSF generation and the oxide film withstand voltage characteristics were evaluated. As a result, OSF was not observed in the crystal, and when the oxide film breakdown voltage characteristics were evaluated under the C-mode oxide film breakdown voltage measurement conditions, the non-defective rate was 100%, and good results could be obtained.
[0050]
The C-mode oxide film withstand voltage measurement conditions are as follows.
1) Oxide film: 25 nm 2) Measuring electrode: Phosphorus-doped polysilicon
3) Electrode area: 8mm² 3) Determination current: 1 mA / cm²
4) When a voltage of 8 MV / cm or more was applied, a product in which no current leak occurred was determined as a good product.
[0051]
(Comparative example)
Next, in the equipment D, the crystal cooling cylinder 25 was changed to one having the same size and made entirely of graphite, and a silicon single crystal was grown. The growth of the single crystal was carried out by filling 100 kg of polycrystalline silicon in a quartz crucible having a diameter of 60 cm and dissolving the same, and then pulling up the silicon single crystal having a constant diameter portion of 200 mm from the raw material melt. With the equipment of this single crystal manufacturing apparatus, it is impossible to pull up a low defect crystal at a high speed of 0.60 mm / min or more, and this apparatus can grow a low defect crystal free from OSF rings. The pulling speed at the 10 cm position in the first half of the crystal constant diameter portion of the crystal is set to 0.47 mm / min. Thereafter, the pulling speed is gradually lowered as the crystal growth proceeds, and the pulling speed of 0.43 mm / min in the second half of the constant diameter portion. It was during the growth of the single crystal by adjusting the operating conditions so that the upper speed was reached (FIG. 13: broken line). As a result, it was confirmed that the pulling speed was increased by using the apparatus of the present invention, and the manufacturing time of the crystal constant diameter portion could be shortened by 27%.
[0052]
The present invention is not limited to the embodiment described above. The above-described embodiment is merely an example, and has substantially the same configuration as the technical idea described in the claims of the present invention, and any of the same effects can be obtained. Of course, it is included in the technical scope of the present invention.
[0053]
For example, in the apparatus of the present invention, the CZ method single crystal manufacturing apparatus for growing a single crystal without applying a magnetic field has been described as an example. However, the MCZ method for growing a single crystal while applying a magnetic field to a raw material melt is used. It goes without saying that the same effect can be obtained in the production of the single crystal used. In addition, it is natural that the present invention can be used for the growth of semiconductor single crystals other than silicon, and even when applied to the growth of compound semiconductors such as GaAs crystals using the CZ method, the effects can be sufficiently exerted. Can do.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing an example of a semiconductor single crystal manufacturing apparatus according to a second embodiment of the present invention.
FIGS. 2A and 2B are explanatory diagrams showing some examples of providing grooves or irregularities on the crystal cooling cylinder. FIGS.
FIG. 3 is an explanatory diagram showing an example in which fins are provided on the inner surface of a metal cooling section and an example in which blackening treatment or surface roughening treatment is performed.
FIGS. 4A and 4B are cross-sectional views illustrating some connection modes between a metal cooling unit and a forced cooling unit. FIGS.
FIG. 5 is a cross-sectional view showing an example of a connection form between a metal cooling section and a graphite cooling section.
6 is a schematic cross-sectional view showing a first modification of the semiconductor single crystal manufacturing apparatus of FIG. 1. FIG.
7 is a schematic cross-sectional view showing a second modification of the semiconductor single crystal manufacturing apparatus of FIG. 1. FIG.
8 is a schematic cross-sectional view showing a third modification of the semiconductor single crystal manufacturing apparatus of FIG. 1. FIG.
9 is a schematic cross-sectional view showing a fourth modification of the semiconductor single crystal manufacturing apparatus of FIG. 1. FIG.
10 is a schematic cross-sectional view showing a fifth modification of the semiconductor single crystal manufacturing apparatus of FIG. 1. FIG.
FIG. 11 is a schematic cross-sectional view showing an example of a semiconductor single crystal manufacturing apparatus according to the first embodiment of the present invention.
FIG. 12 is a diagram schematically showing a method for obtaining a pulling speed at a position where an N region of a crystal appears by gradually reducing the pulling speed in Example 1 and Example 2.
FIG. 13 is a diagram showing a comparison of pulling speed profiles between an example and a comparative example in Example 2.
[Explanation of symbols]
1,100,150,200,250,300 Semiconductor single crystal manufacturing equipment
2 Growth furnace body
3 Forced cooling mechanism
4 collection space formation part
5 Forced cooling section
6 Forced cooling mechanism
7 Groove
8 Metal cooling part
9 Fin (convex part)
10 Graphite cooling section
12 crucible
14 Raw material melt
25 Crystal cooling cylinder
30 heat shield ring

Claims

In a semiconductor single crystal manufacturing apparatus in which a semiconductor single crystal is pulled up by a Czochralski method from a raw material melt stored in a crucible in a semiconductor single crystal growth furnace,
A growth furnace body in which the crucible is disposed;
A recovery space forming part that is integrally formed in an upper part of the growth furnace main body in a communication form and forms a recovery space of the semiconductor single crystal;
A crystal cooling cylinder having a cylindrical or conical shape disposed so as to surround the semiconductor single crystal pulled up from the raw material melt;
A forced cooling mechanism for forcibly cooling the recovery space forming portion by refluxing the cooling medium to the recovery space forming portion;
The upper part of the crystal cooling cylinder is connected to the lower part of the recovery space forming part so that heat can be transferred, and the heat absorbed by the crystal cooling cylinder is forcibly cooled by the forced cooling mechanism by cooling the pulled semiconductor single crystal. It is discharged out of the growth furnace through the recovery space forming portion, and the lower side located immediately above the raw material melt of the crystal cooling cylinder is a graphite cooling portion, and the upper side connected to the recovery space forming portion is A metal cooling section ,
The apparatus for producing a semiconductor single crystal, wherein the crystal cooling cylinder has a length of the metal cooling section equal to or longer than a length of the graphite cooling section in the pulling direction of the semiconductor single crystal .

In the connection part between the metal cooling part and the growth furnace side of the crystal cooling cylinder, the connection surface on the metal cooling part side and the connection surface on the growth furnace side are arranged in close contact with each other. The apparatus for producing a semiconductor single crystal according to claim 1.

One or more grooves and / or irregularities are provided on the inner surface side of the crystal cooling cylinder to efficiently absorb the radiant heat from the semiconductor single crystal pulled up by increasing the area of the inner surface of the cooling cylinder. An apparatus for producing a semiconductor single crystal according to claim 1 or 2 .

The metallic cooling unit, iron, nickel, chromium, copper, titanium, according to any one of claims 1 to 3, characterized in that it is constituted by a metal mainly composed of one of molybdenum and tungsten Semiconductor single crystal manufacturing equipment.

The metal cooling section covers a base material made of a metal containing iron, nickel, chromium, or copper as a main component, and covers the base material surface, and includes any of titanium, molybdenum, tungsten, and a platinum group metal. The apparatus for producing a semiconductor single crystal according to claim 4 , further comprising a lining layer as a main component.

A heat reflection suppressing portion that suppresses heat reflection toward the semiconductor single crystal is formed at least in a region of the inner surface of the metal cooling portion facing the semiconductor single crystal pulled up. apparatus for manufacturing a semiconductor single crystal according to any one of claims 1 to 5.

The heat reflection suppressing portion is formed by performing at least one of a blackening process for blackening the color tone of the area and a surface roughening process for roughening the surface of the area to diffusely reflect radiant heat from the semiconductor crystal. The semiconductor single crystal manufacturing apparatus according to claim 6 , wherein the apparatus is a semiconductor single crystal.

A heat shielding ring is provided at the lower end of the graphite cooling part located immediately above the raw material melt surface to reflect the radiant heat from the raw material melt surface and to keep the crystal growth interface and the raw material melt near the crystal growth interface. apparatus for manufacturing a semiconductor single crystal according to any one of claims 1 to 7, characterized in that provided.

Using the apparatus for manufacturing a semiconductor single crystal according to any one of claims 1 to 8, the semiconductor single to the raw material melt accommodated in the crucible, characterized by producing by pulling the semiconductor single crystal by the Czochralski method Crystal production method.