JP4685231B2 - Silicon wafer manufacturing method - Google Patents

Description

【００５１】
図３３及び表１から明らかなように、ピークでの酸素析出物の濃度は、温度上昇率に大きく影響されない。
【００５２】
図３４は、本発明の一実施形態に従い熱処理時間を変えながら図５のＲＴＡ工程を行った後、ピークでの酸素析出物の濃度変化を測定して示したグラフである。比較のために、他の工程条件を一定にした。すなわち、窒素ガス及びアルゴンガスの混合比を５：５に、温度上昇率は５０℃／秒に、急速熱処理のアニーリング温度は１２５０℃に、そして温度下降率は３３℃／秒に設定した。また、後続熱処理は、前述したように、全てのウェーハに対して８００℃で４時間、１６００℃で１６時間、窒素雰囲気下で行った。その結果を下記表２に示す。
【表２】

【００５３】
図３４及び表２から明らかなように、ピークでの酸素析出物の濃度はアニーリング時間に大きく影響されない。また、ピークでの酸素析出物の濃度を少なくとも１０⁹／ｃｍ³にするためには、本発明のアニーリング時間を少なくとも５秒間以上行わなければならない。
【００５４】
図３５は、本発明の一実施形態に従い熱処理温度を変えながら図５のＲＴＡ工程を行った後、ピークでの酸素析出物の濃度変化を測定して示したグラフである。比較のために、他の工程条件を一定にした。すなわち、窒素ガス及びアルゴンガスの混合比を５：５に、温度上昇率は５０℃／秒に、急速熱処理のアニーリング時間は１０℃に、そして温度下降率は３３℃／秒に設定した。また、後続熱処理は、前述したように、全てのウェーハに対して８００℃で４時間、１６００℃で１６時間、窒素雰囲気下で行った。その結果を下記表２に示す。
【表３】

【００５５】
図３５及び表３から明らかなように、ピークでの酸素析出物の濃度はアニーリング温度に大きく影響されない。また、ピークでの酸素析出物の濃度を少なくとも１０⁹／ｃｍ³にするためには、本発明のアニーリング温度を少なくとも１２５０℃にしなければならない。しかし、アニーリング温度及びアニーリング時間は酸素析出物の濃度と密接な関係にある。図３４の結果を考慮するとき、同一の酸素析出物の濃度を得るためには、アニーリング温度が高ければアニーリング時間は相対的に短くでき、逆に、アニーリング温度が低ければアニーリング時間は相対的に長くできる。
【００５６】
図３６は、本発明の一実施形態に従い温度下降率を変えながら図５のＲＴＡ工程を行った後、ピークでの酸素析出物の濃度変化を測定して示したグラフである。比較のため、他の工程条件を一定にした。すなわち、窒素ガス及びアルゴンガスの混合比を５：５に、温度上昇率は５０℃／秒に、急速熱処理のアニーリング温度は１２５０℃に、そしてアニーリング時間は１０秒に設定した。また、後続熱処理は、前述したように、全てのウェーハに対して８００℃で４時間、１６００℃で１６時間、窒素雰囲気下で行った。その結果を下記表４に示す。
【表４】

【００５７】
図３６及び表４から明らかなように、ピークでの酸素析出物の濃度は、温度下降率に大きく影響されない。また、温度下降率が大きくなるにつれて、ピークでの酸素析出物の濃度が少し増大することが分かる。
【００５８】
図１０は、本発明の一実施形態に従いＲＴＡ工程を行った後に熱処理を行い、このときの酸素析出物の濃度プロファイルを示したものである。図１０において、▲１▼は窒素ガス雰囲気、▲２▼は窒素ガス及びアルゴンガスの混合ガス雰囲気、▲３▼は窒素ガス及び水素ガスの混合ガス雰囲気、▲４▼はアルゴンガス雰囲気、▲５▼は水素ガス雰囲気下で各々図５のＲＴＡ工程を行い、次に熱処理を行って形成された酸素析出物の濃度プロファイルである。
【００５９】
比較のために、急速熱処理は１２５０℃の温度で１０秒間行ったし、後続する熱処理は、前述したように、全てのウェーハに対して８００℃で４時間、１６００℃で１６時間、窒素雰囲気下で行った。その結果を下記表５に示す。
【表５】

【００６０】
図１１は、アルゴンガス雰囲気下で図５のＲＴＡ工程を行うに従い、シリコンウェーハの表面近傍でのＣＯＰの分解過程を説明するための図である。一般的に、チョクラルスキー法によるインゴット成長時に形成されるＣＯＰは、割れた８面体のボイド状であり、ボイド２０の内壁側にはシリコン酸化膜２２が形成されている。アルゴンガスまたは水素ガスなど、図５のＲＴＡ工程中にウェーハの表面にインタスティシャルシリコン注入効果をもつガスの雰囲気下では、表面近傍のＣＯＰが分解される現象が起こる。
【００６１】
分解のメカニズムについてもう少し詳しく説明すると、インゴット成長時にインゴット内に含まれる初期酸素濃度Ｏ_iは、冷却が進むに従い、その冷却温度での溶解度以上に過泡化される。したがって、ウェーハにおいても、初期酸素濃度は一定の濃度の溶解度線（図１１のＳ）以上に過泡化されるが、ウェーハの表面では、ウェーハ表面への拡散によって初期酸素濃度が溶解度線（図１１のＳ）以下になる。このため、ウェーハのバルク領域では過泡化された初期酸素がボイド２０内に供給されてシリコン酸化膜２２を形成するのに対し、ウェーハの表面近傍（すなわち、溶解度線と初期酸素の濃度線との交差点″Ｔ″以下の深さ）では初期酸素の濃度が溶解度線以下になるため、ボイド２０内のシリコン酸化膜２０から酸素が離脱されると共に、インタスティシャルシリコン注入効果によりボイドにシリコンが供給されながらボイドが次第に小さくなり、結局、それが消滅する。
【００６２】
このようなＣＯＰの分解効果により、後述するように、本発明による急速熱処理過程の適用対象となるウェーハの範囲がさらに広くなる。また、このようなＣＯＰの分解は、表５に示したように、アルゴンガスに比べて水素ガスの方がより効果的である。
【００６３】
図１２ないし図１６は、図１０の各場合に対して図５のＲＴＡ工程を行い、次に熱処理工程を行って形成された酸素析出物の分布を示した写真である。特に、図１２は窒素ガスを使用した場合であり、図１３はアルゴンガスを使用した場合であり、図１４は水素ガスを使用した場合であり、図１５は窒素ガス及びアルゴンガスの混合ガスを使用した場合であり、図１６は窒素ガス及び水素ガスの混合ガスを使用した場合である。また、各図において、左側はウェーハの前面であり、右側はウェーハの背面である。
【００６４】
図１７ないし図２１は、図１０の各場合に対して図５のＲＴＡ工程を行い、次に熱処理を行って形成された、酸素析出物の存在しないウェーハ前面近傍のデヌードゾーンの深さを示した写真である。特に、図１７は窒素ガスを使用した場合であり、図１８はアルゴンガスを使用した場合であり、図１９は水素ガスを使用した場合であり、図２０は窒素ガス及びアルゴンガスの混合ガスを使用した場合であり、図２１は窒素ガス及び水素ガスの混合ガスを使用した場合である。表５から明らかなように、窒素ガスを使用した場合には、デヌードゾーンがほとんど確保されない。
【００６５】
図２２Ａないし図２４Ｂは、アズ−グロウン（as-grown）状態のＣＯＰの形状及び図５のＲＴＡ工程を行った後の変化された形状を各々示した図である。特に、図２２Ａ及び図２２Ｂは窒素ガス雰囲気下でＲＴＡ工程を行った場合であり、図２３Ａ及び図２３Ｂは、窒素ガス及びアルゴンガスの混合ガス雰囲気下でＲＴＡ工程を行った場合であり、図２４Ａ及び図２４Ｂは、窒素ガス及び水素ガスの混合ガス雰囲気下でＲＴＡ工程を行った場合である。表５から明らかなように、窒素雰囲気下ではＣＯＰの分解が起こらないのに対し、アルゴンガス及び水素ガスの混合ガス雰囲気下ではＣＯＰの分解がよく起こる。特に、水素ガスの雰囲気下では、ＣＯＰが完全に分解されることが分かる。したがって、アズ−グロウン状態でＣＯＰを小さくすれば、図５の急速熱処理中にＣＯＰが完全に分解されることが分かる。
【００６６】
[ウェーハの用意]
本発明は、シリコンウェーハに対して図５の急速熱処理を行うことにより、後続する熱処理によって形成される酸素析出物の分布を制御することに係り、以下では、このような本発明の急速熱処理を行える段階と、その適用対象となるウェーハの用意について説明する。
【００６７】
図２５は、本発明の一実施形態によりシリコンウェーハを用意する工程を示した工程手順図であって、特に、結晶成長（Ｓ１０）後の一般的なウェーハリング過程を示したものである。一般的な半導体ウェーハリング方法は、１９８６年ウルフ（Ｓ．Ｗｏｌｆ）及びタウバー（Ｒ．Ｎ．Ｔａｕｂｅｒ）氏により作成されたテキストブック"Ｓｉｌｉｃｏｎ Ｐｒｏｃｅｓｓｉｎｇ ｆｏｒ ｔｈｅ ＶＬＳＩ Ｅｒａ，Ｖｏｌｕｍｅ １，Ｐｒｏｃｅｓｓ Ｔｅｃｈｎｏｌｏｇｙ"の１章の１〜３５頁に詳細に開示されている。図２５を参照し、半導体ウェーハのウェーハリング過程を簡単に調べてみると、チョクラルスキープーラを用いてインゴットを形成する結晶成長工程（Ｓ１０）後に、このインゴットをウェーハ状に切断する切断工程（Ｓ１２）がなされる。次に、切断された各インゴットを角取りしたり、あるいは表面をエッチングするエッチング工程（Ｓ１４）がなされる。次に、表面に対する第１洗浄工程（Ｓ１６）が行われた後にドナーキーリング工程（Ｓ１８）がなされる。次に、半導体素子が形成されるウェーハの前面をポリシングするポリシング工程（Ｓ２０）及び第２洗浄工程（Ｓ２２）がなされ、最後に、ウェーハのパッケージング工程（Ｓ２４）がなされる。
【００６８】
本発明の図５のＲＴＡ工程は、ドナーキーリング段階（Ｓ１８）で行われる。もちろん、本発明の熱処理段階を別途に行っても良いが、コストの節減の点から、ドナーキーリング段階で行うことが好ましい。一般的に、ドナーキーリングとは、シリコンインゴット中に含まれた酸素が後続する半導体素子の製造中にイオンの形で存在してイオン注入された不純物に対しドナーとして働くことがあるため、これを防止すべく、ウェーハリング中に予め熱処理を行って酸素析出物にする過程を言う。これは、通常、ＲＴＡ装備を用い、７００℃で３０秒間行われる。
【００６９】
図２７は、前記結晶成長工程（Ｓ１０）がなされる装置として、従来のチョクラルスキープーラを示した概略図である。これを参照すれば、チョクラルスキープーラ１００は、炉、結晶引き上げメカニズム、環境制御器及びコンピュータを利用した制御システムを含む。前記チョクラルスキープーラは、一般的に、ホットゾーンとも呼ばれる。また、このホットゾーンは、ヒーター１０４、石英製の坩堝１０６、黒鉛製のサセプタ１０８及び示したように第１方向１１２に回転する回転軸１１０を含む。
【００７０】
冷却などの外部冷却手段により、ジャケットまたは冷却ポート１３２の冷却がなされる。熱遮断体１１４が付加的な熱分布を提供する。また、加熱パック１０２が熱吸収物質１１６により充填され、かつ、付加的な熱分布を提供する。
【００７１】
前記結晶引き上げメカニズムは、示したように、第１方向１１２の反対方向である第２方向１２２に回転自在な結晶引き上げ軸１２０を含む。前記結晶引き上げ軸１２０は、その端部に、結晶ホルダ１２０ａを含む。前記結晶ホルダ１２０ａはシード結晶１２４をホールドし、坩堝１０６内の溶融物１２６から引き上げられてインゴット１２８を形成する。
【００７２】
前記環境制御システムは、チャンバ密封体１３０、冷却ジャケット１３２及び図示しない他の流動制御器及び真空排気システムを含む。コンピュータを利用した制御システムは、前記ヒーター、プーラ及び他の電気的及び機械的な要素を制御するために用いられる。
【００７３】
単結晶シリコンインゴットを成長させるために、前記シード結晶１２４はシリコン溶融物１２６と接触し、かつ、軸方向（上側）に向けて次第に引き上げられる。単結晶シリコンとしての前記シリコン溶融物１２６の冷却及び固相化は、インゴット１２８と溶融物１２６との境界１３１で起こる。図２７に示したように、前記境界１３１は、前記溶融物１２６に対して盛り上がっている。
【００７４】
一方、本発明による急速熱処理工程を利用し、図４でのように制御された酸素析出物の濃度プロファイルが得られるシリコンウェーハは、大きく３種類に大別できる。すなわち、ウェーハの半径方向の全体に渡ってインタスティシャル集塊及びベーカンシ集塊が形成されない無欠陥のパーフェクトウェーハ、ベーカンシ集塊がウェーハの中心部から一定の半径内のベーカンシ−リッチ領域にのみ形成されており、ベーカンシ領域の外側にはインタスティシャル集塊及びベーカンシ集塊が存在しないセミパーフェクトウェーハ、ウェーハの全体に渡ってインタスティシャル集塊は存在せず、ベーカンシ集塊だけが存在するウェーハである。しかし、本発明の適用対象となるウェーハは必ずしもこれに限定されるとは限らず、本発明の原理が適用できるものなら、いずれも適用対象になる。すなわち、本発明は、前述したように、所定のシリコンウェーハに対して図５のＲＴＡ工程を行い、次に熱処理を行って図４のような酸素析出物の濃度プロファイルを得ることである。また、ＣＯＰが、ウェーハのバルク領域内には存在するが、デヌードゾーンには存在しないシリコンウェーハを具現することでもある。
【００７５】
シリコンウェーハでの欠陥を防止するために、結晶成長時に高純度のインゴットを製作するための各種多様な研究がなされてきている。特に、シード結晶の引き上げ速度及びホットゾーン構造での温度勾配を制御する技術はよく知られている。ヴォロンコフ（Ｖｏｒｏｎｋｏｖ）による"Ｔｈｅ Ｍｅｃｈａｎｉｚｍ ｏｆ Ｓｗｉｒｌ Ｄｅｆｅｃｔｓ Ｆｏｒｍａｔｉｏｎ ｉｎ Ｓｉｌｉｃｏｎ "[Ｊｏｕｒｎａｌ ｏｆ Ｃｒｙｓｔａｌ Ｇｒｏｗｔｈ，Ｖｏｌ．５９，１９８２，ｐｐ．６２５−６４３]には、インゴットの引き上げ速度（Ｖ）及びインゴット−溶融物の接触面での温度勾配（Ｇ）の制御に関する技術が開示されている。この技術を適用した、本発明者により１９９６年１１月２５日から２９日にかけて開かれたシリコン物質に対する向上された科学技術に対する第２次国際シンポジウム（Ｓｅｃｏｎｄ Ｉｎｔｅｒｎａｔｉｏｎａｌ Ｓｙｍｐｏｓｉｕｍ ｏｎ Ａｄｖａｎｃｅｄ Ｓｃｉｅｎｃｅ ａｎｄ Ｔｅｃｈｎｏｌｏｇｙ ｏｆ Ｓｉｌｉｃｏｎ Ｍａｔｅｒｉａｌ）で発表された論文"Ｅｆｆｅｃｔ ｏｆ Ｃｒｙｓｔａｌ Ｄｅｆｅｃｔｓ ｏｎ Ｄｅｖｉｃｅ Ｃｈａｒａｃｔｅｒｉｓｔｉｃｓ"によれば、Ｇに対するＶの比（以下、Ｖ／Ｇと称する）が臨界点以上であればベーカンシ−リッチ領域が形成され、臨界点以下であればインタスティシャル−リッチ領域が形成される。
【００７６】
図２６は、シリコンインゴットでの相対的な点欠陥分布及びＶ／Ｇの関係を示した概念図である。これを参照すれば、インゴット成長時にＶ／Ｇが臨界点（Ｖ／Ｇ^＊ ）以上のときにはベーカンシ−リッチ領域が形成され、臨界ベーカンシ濃度（Ｃｖ^＊ ）以上のときにはベーカンシ集塊が形成される。そして臨界インタスティシャル濃度（ＣI ^＊ ）以上のときにはインタスティシャル集塊が形成される。また、図２６において、（Ｖ／Ｇ）_Ｂ ^＊ はインタスティシャルシリコンと関わったリングであるＢ−バンドを表わし、（Ｖ／Ｇ）_Ｐ ^＊ はＯ．Ｓ．ＦリングであるＰ−バンドを表わす。
【００７７】
本発明の適用対象となるウェーハは、インゴット成長時にＶ／Ｇが前記Ｂ−バンド及びＰ−バンド間に存在する無欠陥のパーフェクトウェーハ、前記Ｐ−バンドを含むセミパーフェクトウェーハ及び臨界ベーカンシ濃度に該当する（Ｖ／Ｇ）^*以上でベーカンシ集塊がウェーハの全体に渡って形成されるウェーハなどである。
【００７８】
一方、本発明の適用対象となるウェーハのパーフェクトウェーハ及びセミパーフェクトウェーハに関しては、本発明者により出願された米国特許第０８／９８９，５９１号及びそれに対するＣＩＰ出願である第０９／３２０，２１０号及び第０９／３２０，１０２号に開示されている。また、これは出願書と共に結合される参証とし、それについての詳細な説明は省略する。
【００７９】
図２８は、本発明者により発明されて前記ＣＩＰ出願に開示されたチョクラルスキープーラを示した概略図であって、図２７と比較し、熱遮断体２１４を改良したものである。図２８を参照すれば、チョクラルスキープーラ２００は、炉、結晶引き上げメカニズム、環境制御器及びコンピュータを利用した制御システムを含む。また、前記ホットゾーン炉は、ヒーター２０４、坩堝２０６、サセプタ２０８及び図示したように、第１方向２１２に回転する回転軸２１０を含む。冷却ジャケット２３２及び熱遮断体２１４が付加的な熱分布を提供する。また、加熱パック２０２が熱吸収物質２１６により充填されて付加的な熱分布を提供する。
【００８０】
前記結晶引き上げメカニズムは、示されたように、第１方向２１２の反対方向である第２方向２２２に回転自在な結晶引き上げ軸２２０を含む。前記結晶引き上げ軸２２０は、その端部に、結晶ホルダ２２０ａを含む。前記結晶ホルダ２２０ａはシード結晶２２４をホールドしており、坩堝２０６内の溶融物２２６から引き上げられてインゴット２２８を形成する。
【００８１】
前記環境制御システムは、チャンバ密封体２３０、冷却ジャケット２３２及び図示しない他の流動制御器及び真空排気システムを含む。コンピュータを利用した制御システムは前記ヒーター、プーラ及び他の電気的及び機械的な要素を制御するために用いられる。単結晶シリコンインゴットを成長させるために、前記シード結晶２２４はシリコン溶融物２２６と接触し、軸方向（上側）に次第に引き上げられる。単結晶シリコンとしての前記シリコン溶融物２２６の冷却及び固相化は、インゴット２２８及び溶融物２２６間の境界２３１で起こる。これは、図２７と比較して熱遮断ハウジング２３４をさらに含んで、より精度良いＶ／Ｇの調節が可能である。
【００８２】
図２９は、本発明の一実施形態に従い改良されたチョクラルスキープーラを示した概略図であり、図３０は、その改良された要部を示したものである。ここで、図２８と同一の構成要素については、その説明を省略する。すなわち、その改良は、図３０に示したように、熱遮断ハウジング３００の形状が変わったことと、熱遮断弁３６０がさらに設けられたことである。前記熱遮断ハウジング３００は、９０°だけ回転された台形であって、垂直した内部熱遮断ハウジング壁３１０及び外部熱遮断ハウジング壁３３０、前記内部熱遮断ハウジング壁３１０及び外部熱遮断ハウジング壁３３０間を連結すると共に、外側方向に上向き傾斜した熱遮断ハウジング蓋部３４０及び前記内部熱遮断ハウジング壁３１０及び外部熱遮断ハウジング壁３３０間を連結すると共に、外側方向に下向き傾斜した熱遮断ハウジング底３２０を含むリング状をしている。
【００８３】
前記リング状の熱遮断ハウジング３００内には、熱を吸収できる熱吸収物質が満たされ、この熱遮断ハウジング３００はカーボンフェライト製である。
【００８４】
前記熱遮断ハウジング３００の熱遮断ハウジング蓋部３４０及び前記冷却ジャケット２３２の間に、前記引き上げられるインゴットを取り囲む熱遮断板３６０が設けられ、この熱遮断ハウジング３００は、支持部材３５０により加熱パック２０２の上側に固定される。
【００８５】
図２９に示したチョクラルスキープーラの構造は、基本的に、成長されるインゴットの冷却速度を高めることができる。一般的に、結晶成長されたインゴット内にあるボイドの大きさは、シリコン溶融物とインゴットとの接触面で形成される初期ベーカンシ濃度の平方根に比例するが、インゴットの冷却速度の平方根には反比例する。一方、図１１で述べたように、インゴット内に存在するボイドを一定の大きさ以下に形成すると、たとえ、結晶成長時にインゴット内にボイドが形成されるとしても、本発明の急速熱処理工程によりデヌードゾーンにはボイドが存在しない。
【００８６】
したがって、この本発明の目的に応じてインゴット内に形成されるボイドを小さくするためには、インゴットの冷却速度は上げる必要がある。一方、インゴットの冷却速度が高くなると、引き上げられるインゴットの中心軸に沿って温度勾配（Ｇｃ）が大きくなり、所定の欠陥分布をもつようにＶ／Ｇを一定値にする場合、インゴットの引き上げ速度も高くなる。
【００８７】
本発明では、インゴット軸の温度が、前記インゴット−溶融物境界でのインゴット軸の温度からインゴットの成長段階に該当する一定の温度に達するまで、前記インゴットの冷却速度が少なくても１．４°ｋ／分以上になるように、前記熱遮断ハウジング３００の内部熱遮断ハウジング壁３１０及び外部熱遮断ハウジング壁３３０の長さ"ａ"及び"ｃ"、熱遮断ハウジング蓋部３４０の傾斜角β、熱遮断ハウジング底３２０の傾斜角α、前記インゴット２２８から内部熱遮断ハウジング壁３１０までの距離"ｄ"、前記坩堝２０６から外部熱遮断ハウジング壁３３０までの距離"ｆ"、前記内部熱遮断ハウジング壁３１０から外部熱遮断ハウジング壁３３０までの距離"ｅ"及び前記熱遮断弁３６０の配列が選択される。
【００８８】
図２９のプーラでは、成長されるインゴットの冷却速度が大きいために引き上げ速度を極めて大きく、例えば、約０．５０ｍｍ／分〜１．００ｍｍ／分にでき、その結果、インゴットの生産性が向上される。加えて、図２８で製作されるパーフェクトウェーハやセミパーフェクトウェーハのためのインゴット成長時の工程マージンもさらに大きく確保できる。
【００８９】
【発明の効果】
以上述べたように、本発明によれば、ウェーハの表面近傍にデヌードゾーンが十分確保されていると共に、ウェーハのバルク領域内で十分なゲッタリング効果が得られるように酸素析出物が分布されたシリコンウェーハを形成できる。
【００９０】
さらに、ウェーハの表面近傍にデヌードゾーンが十分確保されていると共に、ウェーハのバルク領域内で十分なゲッタリング効果が得られるように欠陥分布を自由に制御できる。加えて、本発明のプーラを使用すると、成長されるインゴットの急速冷却が可能なので、インゴット内のボイドを小さくできる。
【００９１】
以上、本発明を望ましい実施形態を例にとって詳細に説明したが、本発明はこれらの実施形態に限定されるものではなく、本発明の技術的な思想範囲内であれば、当分野における通常の知識を有した者にとって各種の変形が可能である。
【００９２】
また、以上の実施形態は本発明を思想を単に例示的に示したものに過ぎず、本発明の思想内で各種の変形例が可能である。特に、急速熱処理工程の温度、時間、冷却速度、ガスの混合比などを多様に設定でき、ウェーハの用意段階でも各種のプーラの構造が可能である。
【図面の簡単な説明】
【図１】 シリコンウェーハの表面近傍に形成される従来のＭＯＳトランジスタの構造を示した断面図である。
【図２】 従来のシリコンウェーハに対する酸素析出物の濃度プロファイルを示した図である。
【図３】 従来の他のシリコンウェーハに対する酸素析出物の濃度プロファイルを示した図である。
【図４】 本発明の一実施形態によるシリコンウェーハに対する酸素析出物の濃度プロファイルを概略的に示した図である。
【図５】 本発明の一実施形態により行われるＲＴＡ工程のタイムチャートである。
【図６】 窒素ガス雰囲気下で図５のＲＴＡ工程を行った後の点欠陥の濃度プロファイルを示した図である。
【図７】 アルゴンガス雰囲気下で図５のＲＴＡ工程を行った後の点欠陥の濃度プロファイルを示した図である。
【図８】 水素ガス雰囲気下で図５のＲＴＡ工程を行った後の点欠陥の濃度プロファイルを示した図である。
【図９】 窒素ガス及びアルゴンガスの混合ガス雰囲気下で、混合比を変えながら図５のＲＴＡ工程を行った後のベーカンシ濃度プロファイルを示した図である。
【図１０】 本発明によるＲＴＡ工程を行った後、後続熱処理による酸素析出物の濃度プロファイルを示した図である。
【図１１】 アルゴンガス雰囲気下で図５のＲＴＡ工程を行うに従い、シリコンウェーハの表面近傍でのＣＯＰの分解過程を説明するための図である。
【図１２】 窒素ガス雰囲気下で図５のＲＴＡ工程を行った後、後続熱処理により形成された酸素析出物の分布を示した写真である。
【図１３】 アルゴンガス雰囲気下で図５のＲＴＡ工程を行った後、後続熱処理によって形成された酸素析出物の分布を示した写真である。
【図１４】 水素ガス雰囲気下で図５のＲＴＡ工程を行った後、後続熱処理により形成された酸素析出物の分布を示した写真である。
【図１５】 窒素ガス及びアルゴンガスの混合ガス雰囲気下で図５のＲＴＡ工程を行った後、後続熱処理により形成された酸素析出物の分布を示した写真である。
【図１６】 窒素ガス及び水素ガスの混合ガス雰囲気下で図５のＲＴＡ工程を行った後、後続熱処理により形成された酸素析出物の分布を示した写真である。
【図１７】 窒素ガス雰囲気下で図５のＲＴＡ工程を行った後、後続熱処理により形成されたデヌードゾーンの深さを示した写真である。
【図１８】 アルゴンガス雰囲気下で図５のＲＴＡ工程を行った後、後続熱処理により形成されたデヌードゾーンの深さを示した写真である。
【図１９】 水素ガス雰囲気下で図５のＲＴＡ工程を行った後、後続熱処理により形成されたデヌードゾーンの深さを示した写真である。
【図２０】 窒素ガス及びアルゴンガスの混合ガス雰囲気下で図５のＲＴＡ工程を行った後、後後続熱処理により形成されたデヌードゾーンの深さを示した写真である。
【図２１】 窒素ガス及び水素ガスの混合ガス雰囲気下で図５のＲＴＡ工程を行った後、後続熱処理により形成されたデヌードゾーンの深さを示した写真である。
【図２２】 図２２Ａは、アズ−グロウン状態のＣＯＰの形状を示した写真であり、図２２Ｂは、これを窒素ガス雰囲気下で図５のＲＴＡ工程を行った後の変化された形状を示した写真である。
【図２３】 図２３Ａは、アズ−グロウン状態のＣＯＰの形状を示した写真であり、図２３Ｂは、これを窒素ガス及びアルゴンガスの混合ガス雰囲気下で図５のＲＴＡ工程を行った後の変化された形状を示した写真である。
【図２４】 図２４Ａは、アズ−グロウン状態のＣＯＰの形状を示した写真であり、図２４Ｂは、これを窒素ガス及び水素ガスの混合ガス雰囲気下で図５のＲＴＡ工程を行った後の変化された形状を示した写真である。
【図２５】 本発明の一実施形態による工程過程を示した工程手順図である。
【図２６】 シリコンインゴットでの相対的な点欠陥分布及びＶ／Ｇの関係を示した概念図である。
【図２７】 従来のチョクラルスキープーラを示した概略図である。
【図２８】 本願発明者により発明された従来のチョクラルスキープーラを示した概略図である。
【図２９】 本発明の一実施形態によって改良されたチョクラルスキープーラを示した概略図である。
【図３０】 図２９のチョクラルスキープーラの要部を示した図である。
【図３１】 本発明の一実施形態により窒素ガス及びアルゴンガスの流量を変えながら図５のＲＴＡ工程を行った後のピークでの酸素析出物の濃度変化を測定したグラフである。
【図３２】 本発明の一実施形態により窒素ガス及びアルゴンガスの混合比を変えながら図５のＲＴＡ工程を行った後のピークでの酸素析出物の濃度変化を測定したグラフである。
【図３３】 本発明の一実施形態により温度上昇率を変えながら図５のＲＴＡ工程を行った後のピークでの酸素析出物の濃度変化を測定したグラフである。
【図３４】 本発明の一実施形態により熱処理時間を変えながら図５のＲＴＡ工程を行った後のピークでの酸素析出物の濃度変化を測定したグラフである。
【図３５】 本発明の一実施形態により熱処理温度を変えながら図５のＲＴＡ工程を行った後のピークでの酸素析出物の濃度変化を測定したグラフである。
【図３６】 本発明の一実施形態により温度下降率を変えながら図５のＲＴＡ工程を行った後のピークでの酸素析出物の濃度変化を測定したグラフである。
【符号の説明】
１０ シリコン基板
１０ａ バルク領域
１０ｂ デヌードゾーン
１２ ソース領域
１４ ドレイン領域
１６ ゲート絶縁膜
１８ ゲート電極
２０ ボイド
２２ シリコン酸化膜
１００、２００ チョクラルスキープーラ
１０２、２０２ 加熱パック
１０４、２０４ ヒーター
１０６、２０６ 坩堝
１０８、２０８ サセプタ
１１０、２１０ 回転軸
１１２、２１２ 第１方向
１１４、２１４ 熱遮断体
１１６、２１６ 熱吸収物質
１２０、２２０ 結晶引き上げ軸
１２０ａ、２２０ａ 結晶ホルダ
１２２、２２２ 第２方向
１２４、２２４ シード結晶
１２６、２２６ 溶融物
１２８、２２８ インゴット
１３０、２３０ チャンバ密封体
１３１、２３１ インゴット−溶融物境界
１３２、２３２ 冷却ジャケット
２３４、３００ 熱遮断ハウジング
３１０ 内部熱遮断ハウジング壁
３２０ 熱遮断ハウジング底
３３０ 外部熱遮断ハウジング壁
３４０ 熱遮断ハウジング蓋部
３５０ 支持部材
３６０ 熱遮断弁[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a silicon wafer with controlled defect distribution, its manufacturing process and a Czochralski puller for the production of single crystal silicon ingots for the formation of these wafers. In particular, the present invention relates to a heat treatment process for controlling the distribution of nucleation centers of oxygen precipitates serving as a gettering site, and a wafer preparation process for performing this process.
[0002]
[Prior art]
  Single crystal silicon, which is a starting material for manufacturing a semiconductor element, is generally formed into a cylindrical ingot by a crystal growth method called a Czochralski (CZ) method. The ingot-shaped single crystal silicon is manufactured as a wafer through a wafer ring process such as cutting, etching, cleaning, and polishing. The Czochralski method is to perform crystal growth while bringing a single crystal seed crystal into contact with a silicon melt and then slowly pulling it up. Since the silicon melt is contained in a quartz crucible, it contains various impurities, particularly oxygen. At the temperature of the silicon melt, oxygen penetrates into the crystal lattice until it reaches a concentration determined by the solubility of oxygen in silicon corresponding to the temperature of the melt and the actual separation factor of oxygen in solid-phased silicon. To do. Thus, the concentration of oxygen that has penetrated into the silicon ingot during crystal growth is a typical temperature during the fabrication of subsequent integrated circuits, which is much greater than the oxygen solubility in solid phase silicon corresponding to this temperature. On the other hand, as the crystal grows and cools, the solubility of oxygen in the crystal suddenly drops.As a result, oxygen is supersaturated in the cooled ingot, and these form void-like crystal defects called D-defects in the ingot.
[0003]
  like thisThe D-defect causes a pit-like COP (Crystal Originated Precipitate) having a {111} plane on the wafer surface through a wafer ring process such as ingot cutting, polishing, and cleaning. In addition, these are gradually increased by the cleaning and oxidation processes repeatedly performed during the fabrication of the subsequent integrated circuit elements, and the number thereof is increased rapidly.FIG. 1 is a view showing a cross section of a conventional MOS transistor. By referring to this, the wafer surfaceCOPExists in the channel region between the source region 12 and the drain region 14 formed near the surface of the silicon substrate 10, for example, between the gate electrode 18 and the silicon substrate 10. In addition to this, the gate insulating film 16 to be insulated is broken, and in addition, the refresh characteristics in the memory element are also deteriorated.. Further, when such a COP on the wafer surface exists in the field oxide film that separates the active region of the semiconductor element, impurity ions implanted during the ion implantation process penetrate into the bulk region below the field oxide film, and as a result. In this case, poor element isolation due to channeling is caused.
[0004]
On the other hand, oxygen precipitates formed in the bulk region of the wafer (10a in FIG. 1) by the subsequent heat treatment act as a leakage current source, but are intrinsic capable of trapping undesirable metal contaminants during subsequent semiconductor device fabrication. Also acts as a gettering site. Therefore, if the oxygen concentration in the ingot is sufficiently high, the amount of oxygen precipitates that are intrinsic gettering sites will increase and the gettering performance will be improved. On the other hand, if the oxygen concentration is not sufficient, oxygen precipitation will occur. No object is formed and gettering performance is lost. For this reason, it is necessary to adjust so that an appropriate amount of oxygen precipitates is distributed in the bulk region of the wafer.
[0005]
  On the other hand, oxygen precipitates are distributed as a whole from the front surface to the back surface of a wafer that has been ingot-grown by a conventional general method and that has been subjected to wafer ringing. In particular, until reaching a certain depth (10b in FIG. 1) from the front surface of the wafer where the active region of the semiconductor device is formed.Oxygen related defects, ie voids, COP,A denuded zone 10b layer free from dislocation, stacking faults, oxygen precipitates, etc. must be secured. However, the wafer manufactured by the conventional method has a problem that oxygen precipitates are distributed to the vicinity of the surface and this acts as a leakage current source.
[0006]
  Therefore, in order to form intrinsic gettering in the bulk region of the wafer while securing a sufficient denuded zone near the surface of the wafer, a high oxygen concentration, for example, an initial oxygen concentration of 13 ppma (parts per million) has been conventionally used. atom) or more, by performing heat treatment at a low temperature-high temperature-low temperature for a long time, oxygen precipitates are formed in the bulk region of the wafer.In addition, a technique has been used in which oxygen precipitates in the vicinity of the wafer surface are decomposed to ensure a clean denuded zone.FIG. 2 is a graph showing a concentration profile of oxygen precipitates from the front surface to the back surface of a semiconductor wafer heat-treated by such a conventional technique.
[0007]
  According to FIG. 2, it is possible to achieve both intrinsic gettering in the bulk region and securing a sufficient denuded zone near the wafer surface by the conventional technique. However, since the heat treatment process is performed for a long time at a high temperature, the wafer characteristics are deteriorated.For example, slippage and sintering distortion occur, and the cost increases. Also, in this case, metal contaminants trapped by oxygen precipitates in the bulk region, particularly iron (Fe), etc., are released again toward the denuded zone on the wafer surface by a subsequent process, and this is a source of leakage. There is a problem of acting as.
[0008]
FIG. 3 is a graph showing an extracted concentration profile of oxygen precipitates formed by another conventional method disclosed in FIG. 1A of US Pat. No. 5,401,669. That is, FIG. 3 shows a concentration profile according to the wafer depth of oxygen precipitates formed by performing a rapid thermal processing (RTA) step in a nitrogen atmosphere and then performing the thermal processing. However, as is apparent from FIG. 3, this method can hardly obtain a denuded zone from the surface of the wafer, and there is almost no oxygen precipitate in the bulk region, so that a sufficient gettering effect can be obtained. Absent.
[0009]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide a silicon wafer having a defect distribution controlled so as to obtain a sufficient gettering effect in a bulk region of the wafer while a sufficient denuded zone is secured near the surface of the wafer. That is.
[0010]
Another object of the present invention is to provide a silicon wafer manufacturing method capable of controlling a defect distribution so as to obtain a sufficient gettering effect in the bulk region of the wafer while a sufficient denuded zone is secured in the vicinity of the wafer surface. Is to provide.
[0011]
Still another object of the present invention is to provide a Czochralski puller for manufacturing a single crystal silicon ingot capable of rapid cooling to manufacture a silicon wafer according to the present invention.
[0012]
[Means for Solving the Problems]
  The method for producing a silicon wafer of the present invention comprises a step of preparing a silicon wafer,
The wafer is subjected to a rapid heating / cooling process in a mixed gas atmosphere of a gas having a vacancy injection effect and a gas having an interstitial silicon injection effect on the wafer surface, thereby following the rapid heating / rapid cooling process. A nucleation center that serves as a place where oxygen precipitates grow during the heat treatment is generated, and a concentration profile of the nucleation center from the front surface to the back surface of the wafer generated thereby is a predetermined depth from the front surface and the back surface. In the bulk region between the first peak and the second peak, respectively, and is maintained below the critical value before reaching the first peak and the second peak from the front and back, respectively. A rapid heating / cooling treatment step that makes the concentration profile of the production center concave,
The mixed gas is nitrogen gas + argon gas, or nitrogen gas + hydrogen gas,
The critical value is an equilibrium concentration at a standby temperature after the rapid heating / cooling treatment.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Preparation of wafers to which the present invention is applied, and silicon wafer products in which the idea of the invention is more concentrated, a rapid heat treatment process in the manufacturing process of silicon wafers, and a "heat treatment stage for wafers" resulting from the subsequent heat treatment The steps and the “wafer preparation step” for the apparatus will be described sequentially.
[0028]
[Heat treatment for wafers]
FIG. 4 is a diagram schematically illustrating a concentration profile of oxygen precipitates on a silicon wafer to be formed according to an embodiment of the present invention. As shown in FIG. 2 and FIG. 3, according to the present invention, compared to the concentration profile of oxygen precipitates in a silicon wafer formed by a conventional technique, the wafer has a certain depth from the front and back surfaces of the wafer. The reaching denuded zone is sufficiently secured, and a double peak having the maximum peak value is formed at the boundary between each denuded zone and the bulk region. In addition, the concentration of oxygen precipitates in the bulk region between the double peaks exists to such an extent that the gettering effect of the metal contaminant can be sufficiently exhibited.
[0029]
FIG. 5 is a time chart of an RTA process performed according to an embodiment of the present invention. As the RTA equipment to which the present invention is applied, an ordinary commercialized equipment can be used. Hereinafter, a rapid thermal process in the RTA equipment will be examined. First, a silicon wafer to which the present invention is applied is brought into an RTA equipment maintained at, for example, about 700 ° C. and waited (I). Next, the temperature in the RTA equipment is rapidly increased, for example, to 1250 ° C. at a rate of 50 ° C./min (II). Next, the temperature of 1250 ° C. is maintained for a certain time, for example, 10 seconds (III). Next, the temperature is rapidly cooled to a standby temperature at a rate of 33 ° C./min (IV). Next, the wafer is unloaded (V). By performing the rapid heat treatment as shown in FIG. 5, oxygen precipitate nucleation centers having a controlled distribution are obtained. On the other hand, as described in the explanation of FIG. 11, voids or COPs existing on the surface of the wafer are obtained. The decomposition effect is obtained.
[0030]
Although the temperature conditions shown in FIG. 5 exemplarily illustrate an embodiment of the present invention, as will be described later, in the present invention, the type of atmospheric gas for rapid thermal processing, the flow rate of the atmospheric gas, The mixing ratio, the rate of temperature increase until the rapid heat treatment stage, the annealing temperature and annealing time in the rapid heat treatment stage, the temperature decrease rate from the rapid heat treatment stage (that is, the cooling rate), etc. act as important factors. The rapid heat treatment in the present invention is performed at a temperature of at least 1150 ° C. or more for at least 5 seconds. For example, heat treatment is performed at 1150 ° C. for at least about 30 seconds, and heat treatment is performed at 1250 ° C. for at least about 5 seconds to 10 seconds. On the other hand, the cooling rate is at least 30 ° C./second or more.
[0031]
As a gas for performing the rapid thermal processing of the present invention, basically, a gas having a vacancy injection effect on the surface of the wafer exposed to the gas atmosphere during the rapid thermal processing and an interstitial silicon injection effect on the surface of the wafer. It is possible to use a mixed gas obtained by mixing gases having a certain ratio. In this embodiment, nitrogen gas is used as a representative example of a gas having a bakery injection effect, and argon gas and hydrogen gas are used as representative examples of a gas having an interstitial silicon injection effect.
[0032]
FIG. 6 is a diagram showing concentration profiles of point defects of baked silicon and interstitial silicon after performing the RTA process of FIG. 5 in a nitrogen gas atmosphere, and FIG. 7 is a diagram in an argon gas atmosphere. FIG. 5 is a diagram showing a concentration profile of point defects after performing the RTA process 5. FIG. 8 is a diagram showing a concentration profile of point defects after the RTA process of FIG. 5 is performed in a hydrogen gas atmosphere.
[0033]
6 to 8, (1) is the concentration profile of the vacancy point defect after performing the RTA process of FIG. 5 in an inert gas atmosphere, and (2) is the RTA of FIG. 5 under the respective gas conditions. The concentration profile of the interstitial point defect after the process is performed, and (3) is the concentration profile of the bakery point defect after the RTA process of FIG. 5 is performed under each gas condition.
[0034]
It can be seen that the concentration of vacancy point defects after performing the RTA process in an inert gas atmosphere is low on the front and back surfaces of the wafer and rises in the vicinity of the bulk region of the wafer. Generally, when the temperature is rapidly increased up to (a) in FIG. 5 in an inert gas atmosphere, the equilibrium concentration corresponding to the temperature of the vacancy existing as a point defect in the wafer increases. At this time, since the mobility of vacancy is low in the bulk region of the wafer, the vacancy concentration is kept lower than the equilibrium concentration. On the other hand, since the movement of vacancy is active in the surface area of the wafer, the equilibrium concentration is maintained almost the same. Conversely, interstitial silicon increases in vacancy concentration as temperature rises rapidly, and at the same time, the equilibrium concentration corresponding to that temperature decreases due to Frenkel recombination. At this time, the interstitial existing in the bulk region of the wafer is maintained at a higher concentration than the equilibrium concentration because of its low mobility as in the case of vacancy, but is close to the equilibrium concentration on the surface of the wafer as in the case of vacancy.
[0035]
Next, when the temperature in (a) is maintained for a certain period of time until it reaches (b) in FIG. 5, diffusion occurs so that both vacancy and interstitial are maintained at equilibrium concentrations. Next, when this temperature is rapidly cooled to (c), the interstitial point defect with a large diffusion coefficient becomes the same as the new equilibrium concentration corresponding to the lowered temperature, but in the case of a vacancy with a small diffusion coefficient, it is supersaturated in the wafer. Is done. At this time, the supersaturation degree is large in the bulk region of the wafer, whereas the mobility of the vacancy is large in the vicinity of the wafer surface, so that it immediately approaches a new equilibrium concentration corresponding to the lowered temperature.
[0036]
For this reason, as shown in FIGS. 6 to 8, the vacancy concentration profile after the rapid heat treatment of FIG. 5 is performed in an inert gas atmosphere.
[0037]
On the other hand, as shown in FIG. 6, when the RTA process of FIG._ThreeN_Four), The concentration of vacancy is lowered. On the other hand, a vacancy injection effect occurs near the surface of the wafer, and the concentration of vacancy increases. For this reason, the vacancy concentration profile under an inert gas atmosphere has a shape opposite to that of (1).
[0038]
On the other hand, as shown in FIGS. 7 and 8, when the RTA process of FIG. 5 is performed in an argon gas or hydrogen gas atmosphere, the concentration of bakery decreases over the entire wafer due to the interstitial silicon implantation effect. Especially, near the surface of the wafer, the recombination of vacancy silicon and interstitial silicon occurs abruptly due to the interstitial silicon injection effect, and the vacancy concentration is maintained at a specific critical value that is the equilibrium concentration at the corresponding temperature. .
[0039]
On the other hand, in the embodiment of the present invention, the RTA process of FIG. 5 is performed in an atmosphere of nitrogen gas and argon gas, or a mixed gas of nitrogen gas and hydrogen gas. By combining the vacancy concentration profiles of FIG. 8, the vacancy concentration profiles in these mixed gas atmospheres can be found. As shown in FIG. 9, the vacancy concentration profile under such a mixed gas atmosphere shows a first peak and a second peak at a predetermined depth from the front and back surfaces of the silicon wafer, respectively. It can be seen that before reaching the first peak and the second peak, it is maintained below a certain critical value, that is, below the equilibrium concentration at the corresponding temperature. The concentration profile of vacancy in the bulk region between the first peak and the second peak has a raised shape.
[0040]
Here, the vacancy concentration profile as shown in FIG. 9 is obtained because the RTA process of FIG. 5 is performed in a mixed gas atmosphere of a gas having a vacancy silicon injection effect and a gas having an interstitial silicon injection effect. is there. Comparing the concentration profile of vacancy silicon due to the vesicle silicon injection effect under nitrogen gas and the concentration profile of interstitial silicon due to the interstitial silicon injection effect under argon gas or hydrogen gas on a logarithmic scale, The vacancy silicon concentration profile from the front and back surfaces of the wafer to the bulk region is less steep than the interstitial silicon concentration profile. However, this becomes steep above a certain depth from the wafer surface. Therefore, the denuded zone is formed in the vicinity of the surface within a certain depth from the front and back of the wafer, where interstitial silicon is recombined with vacancy silicon and vacancy silicon is specified. Is maintained below the critical value of, i.e., the equilibrium concentration at the temperature. This is the position at which the difference between the concentration value of the vacancy silicon and the concentration value of the interstitial silicon becomes the maximum after the concentration of the vacancy silicon rapidly increases above the equilibrium concentration value while deviating from the denuded zone, that is, A peak (a first peak and a second peak) is formed where the vacancy silicon concentration profile is steeper than the interstitial silicon concentration profile. Next, the concentration of the baked silicon gradually decreases toward the bulk region, and as a result, the concentration profile of the baked silicon between the first peak and the second peak becomes a raised shape.
[0041]
On the other hand, vacancy point defects in the wafer are formed as oxygen precipitates by heat treatment repeatedly performed during the manufacture of subsequent semiconductor elements. That is, the vacancy point defect becomes a nucleation center of oxygen precipitates formed by the subsequent heat treatment. Accordingly, when the bakery concentration is high, the concentration of oxygen precipitates formed is also high. For this reason, the shape of the oxygen precipitate concentration profile can be easily inferred through the vacancy concentration profile in the wafer.
[0042]
There is the following relationship between the vacancy concentration and the oxygen precipitates.
Si (silicon substrate) + xO_i+ YV_Si⇔SiO₂(Oxygen precipitate) + Si_I(Interstitial silicon) + σ
[0043]
Here, bakery silicon V_SiConcentration and initial oxygen concentration O_iIf is high, the reaction proceeds to the right, resulting in an increase in the concentration of oxygen precipitates. Here, σ is a constant.
[0044]
On the other hand, in the embodiment of the present invention, heat treatment was performed after the RTA process of FIG. 5 was completed, and the formation state of oxygen precipitates was measured. Here, in general, the heat treatment is set in a manner similar to the condition in which oxygen precipitates are formed in consideration of the heat treatment step repeatedly performed during the manufacture of the semiconductor element. In this embodiment, for comparison, after the RTA process of FIG. 5 was performed, all wafers were heat-treated in a nitrogen atmosphere for 4 hours at a temperature of 800 ° C. and for 16 hours at a temperature of 1600 ° C. .
[0045]
In order to investigate the influence of the mixed gas used in the present invention, the flow rate and the mixing ratio of the mixed gas used during the RTA process of FIG. 5 were changed. FIG. 9 is a schematic diagram showing a vacancy concentration profile after performing the RTA process of FIG. 5 while changing the mixing ratio in an atmosphere of nitrogen gas and argon mixed gas, and FIG. 31 shows the flow rate of the argon and nitrogen mixed gas. FIG. 32 is a graph showing changes in the concentration of oxygen precipitates at the peak due to the mixing ratio of the argon and nitrogen mixed gas.
[0046]
In FIG. 9, (a) shows the case where the mixing ratio of nitrogen gas and argon gas is 7: 3, (b) shows the case where it is 5: 5, and (c) is the opposite of (a). Represents the case of 3: 7. Here, it can be seen that as the mixing ratio of nitrogen gas increases, the peak of the vacancy concentration profile gradually moves toward the wafer surface, and the concentration value at the peak also increases. On the other hand, it can be seen that as the mixing ratio of nitrogen gas increases, the denuded zone in which oxygen precipitates are not formed by the subsequent heat treatment also decreases rapidly.
[0047]
FIG. 31 shows a mixture of argon and nitrogen under the same conditions as the RTA process of FIG. 5, that is, temperature increase rate 50 ° C./second, annealing temperature 1250 ° C., annealing time 10 seconds, temperature decrease rate 33 ° C./second The RTA process is performed while changing the gas flow rate to 1/1, 2/2, 3/3, 4/4, and 5/5 liters / minute, and then heat treatment in a nitrogen atmosphere is performed at 800 ° C. for 4 hours. It shows the measurement of the concentration of oxygen precipitates at the peak after 16 hours at 1600 ° C. Here, it can be seen that the concentration of oxygen precipitates increases as the flow rate of the mixed gas increases.
[0048]
FIG. 32 shows an argon / nitrogen gas mixing ratio of 3/1, 2.5 / 1.5, 2/2, 1.5 / 2.5 under the same conditions as the RTA process of FIG. Perform RTA process while changing to 1/3 liter / min, then measure oxygen precipitate concentration at peak after heat treatment at 800 ° C for 4 hours and 1600 ° C for 16 hours under nitrogen gas atmosphere It is shown. Here, it can be seen that the concentration of oxygen precipitates increases as the mixing ratio of nitrogen gas increases at the same mixed gas flow rate (4 liters / minute).
[0049]
In the present invention, the process conditions of the RTA process, that is, the ratio and flow rate of the mixed gas, the temperature increase rate, the annealing temperature and time, and the temperature decrease rate can be adjusted in various ways. The size of the bakery concentration value in the region, the vacancy concentration value in the bulk region, the size of the denuded zone, and the like are considered.
[0050]
FIG. 33 is a graph showing changes in the concentration of oxygen precipitates at the peak after performing the RTA process of FIG. 5 while changing the temperature increase rate according to an embodiment of the present invention. Other process conditions were kept constant for comparison. That is, the mixing ratio of nitrogen gas and argon gas was set to 5: 5, the annealing temperature for rapid thermal processing was set to 1250 ° C., the annealing time was set to 10 seconds, and the temperature decrease rate was set to 33 ° C./second. Further, as described above, the subsequent heat treatment was performed on all wafers at 800 ° C. for 4 hours and at 1600 ° C. for 16 hours in a nitrogen atmosphere. The results are shown in Table 1 below.
[Table 1]

[0051]
As apparent from FIG. 33 and Table 1, the concentration of oxygen precipitates at the peak is not greatly affected by the rate of temperature increase.
[0052]
FIG. 34 is a graph obtained by measuring the concentration change of oxygen precipitates at the peak after performing the RTA process of FIG. 5 while changing the heat treatment time according to an embodiment of the present invention. Other process conditions were kept constant for comparison. That is, the mixing ratio of nitrogen gas and argon gas was set to 5: 5, the temperature increase rate was set to 50 ° C./second, the annealing temperature for rapid thermal processing was set to 1250 ° C., and the temperature decrease rate was set to 33 ° C./second. Further, as described above, the subsequent heat treatment was performed on all wafers at 800 ° C. for 4 hours and at 1600 ° C. for 16 hours in a nitrogen atmosphere. The results are shown in Table 2 below.
[Table 2]

[0053]
As apparent from FIG. 34 and Table 2, the concentration of oxygen precipitates at the peak is not greatly affected by the annealing time. The concentration of oxygen precipitates at the peak is at least 10⁹/ Cm^ThreeIn order to achieve this, the annealing time of the present invention must be at least 5 seconds.
[0054]
FIG. 35 is a graph obtained by measuring the concentration change of oxygen precipitates at the peak after performing the RTA process of FIG. 5 while changing the heat treatment temperature according to an embodiment of the present invention. Other process conditions were kept constant for comparison. That is, the mixing ratio of nitrogen gas and argon gas was set to 5: 5, the temperature increase rate was set to 50 ° C./second, the annealing time for rapid heat treatment was set to 10 ° C., and the temperature decrease rate was set to 33 ° C./second. Further, as described above, the subsequent heat treatment was performed on all wafers at 800 ° C. for 4 hours and at 1600 ° C. for 16 hours in a nitrogen atmosphere. The results are shown in Table 2 below.
[Table 3]

[0055]
As is clear from FIG. 35 and Table 3, the concentration of oxygen precipitates at the peak is not greatly affected by the annealing temperature. The concentration of oxygen precipitates at the peak is at least 10⁹/ Cm^ThreeIn order to achieve this, the annealing temperature of the present invention must be at least 1250 ° C. However, the annealing temperature and annealing time are closely related to the concentration of oxygen precipitates. When considering the results of FIG. 34, in order to obtain the same oxygen precipitate concentration, the annealing time can be relatively short when the annealing temperature is high, and conversely, the annealing time is relatively low when the annealing temperature is low. Can be long.
[0056]
FIG. 36 is a graph obtained by measuring the concentration change of oxygen precipitates at the peak after performing the RTA process of FIG. 5 while changing the temperature decrease rate according to an embodiment of the present invention. Other process conditions were made constant for comparison. That is, the mixing ratio of nitrogen gas and argon gas was set to 5: 5, the rate of temperature increase was set to 50 ° C./second, the annealing temperature for rapid thermal processing was set to 1250 ° C., and the annealing time was set to 10 seconds. Further, as described above, the subsequent heat treatment was performed on all wafers at 800 ° C. for 4 hours and at 1600 ° C. for 16 hours in a nitrogen atmosphere. The results are shown in Table 4 below.
[Table 4]

[0057]
As is clear from FIG. 36 and Table 4, the concentration of oxygen precipitates at the peak is not greatly affected by the temperature decrease rate. Moreover, it turns out that the density | concentration of the oxygen precipitate in a peak increases a little as the temperature fall rate becomes large.
[0058]
FIG. 10 shows a concentration profile of oxygen precipitates at the time of heat treatment after the RTA process according to an embodiment of the present invention. In FIG. 10, (1) is a nitrogen gas atmosphere, (2) is a mixed gas atmosphere of nitrogen gas and argon gas, (3) is a mixed gas atmosphere of nitrogen gas and hydrogen gas, (4) is an argon gas atmosphere, (5) ▼ is a concentration profile of oxygen precipitates formed by performing the RTA process of FIG. 5 in a hydrogen gas atmosphere and then performing a heat treatment.
[0059]
For comparison, rapid thermal processing was performed at a temperature of 1250 ° C. for 10 seconds, and the subsequent thermal processing was performed at 800 ° C. for 4 hours and 1600 ° C. for 16 hours in a nitrogen atmosphere as described above. I went there. The results are shown in Table 5 below.
[Table 5]

[0060]
FIG. 11 is a diagram for explaining the COP decomposition process in the vicinity of the surface of the silicon wafer as the RTA process of FIG. 5 is performed under an argon gas atmosphere. Generally, the COP formed during ingot growth by the Czochralski method is a cracked octahedral void, and a silicon oxide film 22 is formed on the inner wall side of the void 20. Under the atmosphere of a gas having an interstitial silicon injection effect on the wafer surface during the RTA process of FIG. 5, such as argon gas or hydrogen gas, a phenomenon occurs in which COP near the surface is decomposed.
[0061]
Explaining the decomposition mechanism in more detail, the initial oxygen concentration O contained in the ingot during ingot growth is_iAs cooling progresses, it becomes excessively foamed beyond its solubility at the cooling temperature. Accordingly, even in the wafer, the initial oxygen concentration is excessively bubbled above the solubility curve having a constant concentration (S in FIG. 11). However, on the wafer surface, the initial oxygen concentration is increased by the diffusion to the wafer surface. 11 S) or less. For this reason, in the bulk region of the wafer, the excessively bubbled initial oxygen is supplied into the void 20 to form the silicon oxide film 22, whereas the vicinity of the wafer surface (that is, the solubility line and the initial oxygen concentration line) At a depth of less than or equal to the intersection “T”), the initial oxygen concentration is below the solubility line, so that oxygen is released from the silicon oxide film 20 in the void 20 and silicon is contained in the void due to the interstitial silicon implantation effect. While being supplied, the void gradually becomes smaller and eventually disappears.
[0062]
Due to the COP decomposition effect, as described later, the range of wafers to which the rapid thermal process according to the present invention is applied is further expanded. Further, as shown in Table 5, hydrogen gas is more effective for decomposition of COP than argon gas.
[0063]
12 to 16 are photographs showing the distribution of oxygen precipitates formed by performing the RTA process of FIG. 5 for each case of FIG. 10 and then performing a heat treatment process. 12 shows a case where nitrogen gas is used, FIG. 13 shows a case where argon gas is used, FIG. 14 shows a case where hydrogen gas is used, and FIG. 15 shows a mixed gas of nitrogen gas and argon gas. FIG. 16 shows a case where a mixed gas of nitrogen gas and hydrogen gas is used. In each figure, the left side is the front side of the wafer, and the right side is the back side of the wafer.
[0064]
17 to 21 show the depth of the denuded zone in the vicinity of the front surface of the wafer without oxygen precipitates formed by performing the RTA process of FIG. 5 for each case of FIG. 10 and then performing a heat treatment. It is the photograph shown. 17 shows a case where nitrogen gas is used, FIG. 18 shows a case where argon gas is used, FIG. 19 shows a case where hydrogen gas is used, and FIG. 20 shows a mixed gas of nitrogen gas and argon gas. FIG. 21 shows a case where a mixed gas of nitrogen gas and hydrogen gas is used. As apparent from Table 5, when nitrogen gas is used, a denuded zone is hardly secured.
[0065]
22A to 24B are diagrams showing the shape of the COP in the as-grown state and the changed shape after the RTA process of FIG. 5 is performed. In particular, FIGS. 22A and 22B show the case where the RTA process is performed in a nitrogen gas atmosphere, and FIGS. 23A and 23B show the case where the RTA process is performed in a mixed gas atmosphere of nitrogen gas and argon gas. 24A and 24B show the case where the RTA process is performed in a mixed gas atmosphere of nitrogen gas and hydrogen gas. As is clear from Table 5, COP decomposition does not occur in a nitrogen atmosphere, whereas COP decomposition often occurs in a mixed gas atmosphere of argon gas and hydrogen gas. In particular, it can be seen that COP is completely decomposed in an atmosphere of hydrogen gas. Therefore, it can be seen that if the COP is reduced in the as-grown state, the COP is completely decomposed during the rapid heat treatment of FIG.
[0066]
[Wafer preparation]
The present invention relates to controlling the distribution of oxygen precipitates formed by the subsequent heat treatment by performing the rapid heat treatment of FIG. 5 on the silicon wafer. The steps that can be performed and the preparation of the wafer to be applied will be described.
[0067]
FIG. 25 is a process procedure diagram illustrating a process of preparing a silicon wafer according to an embodiment of the present invention, and particularly illustrates a general wafer ring process after crystal growth (S10). A general semiconductor wafering method is described in Chapter 1 of a textbook “Silicon Processing for the VLSI Era, Volume 1, Process Technology” created by S. Wolf and RN Tauber in 1986. 1 to 35 pages. Referring to FIG. 25, when the wafer ringing process of the semiconductor wafer is briefly examined, after the crystal growth process (S10) for forming the ingot using the Czochralski puller, the cutting process for cutting the ingot into a wafer ( S12) is performed. Next, an etching step (S14) is performed in which each cut ingot is rounded or the surface is etched. Next, after the first cleaning process (S16) is performed on the surface, a donor keying process (S18) is performed. Next, a polishing process (S20) and a second cleaning process (S22) for polishing the front surface of the wafer on which the semiconductor elements are formed are performed, and finally a wafer packaging process (S24) is performed.
[0068]
The RTA process of FIG. 5 of the present invention is performed in the donor keying step (S18). Of course, the heat treatment step of the present invention may be performed separately, but it is preferably performed in the donor keying step from the viewpoint of cost saving. In general, donor keying refers to the fact that oxygen contained in a silicon ingot exists in the form of ions during the manufacture of a subsequent semiconductor device and may act as a donor for implanted ions. In order to prevent this, it refers to a process in which heat treatment is performed in advance during wafer ring to form oxygen precipitates. This is typically done at 700 ° C. for 30 seconds using RTA equipment.
[0069]
FIG. 27 is a schematic view showing a conventional Czochralski puller as an apparatus for performing the crystal growth step (S10). Referring to this, the Czochralski puller 100 includes a furnace, a crystal pulling mechanism, an environmental controller, and a control system using a computer. The Czochralski puller is generally called a hot zone. The hot zone also includes a heater 104, a quartz crucible 106, a graphite susceptor 108, and a rotating shaft 110 that rotates in a first direction 112 as shown.
[0070]
The jacket or cooling port 132 is cooled by external cooling means such as cooling. A heat shield 114 provides additional heat distribution. Also, the heating pack 102 is filled with a heat absorbing material 116 and provides additional heat distribution.
[0071]
As shown, the crystal pulling mechanism includes a crystal pulling shaft 120 that is rotatable in a second direction 122 that is opposite to the first direction 112. The crystal pulling shaft 120 includes a crystal holder 120a at its end. The crystal holder 120 a holds the seed crystal 124 and is pulled up from the melt 126 in the crucible 106 to form an ingot 128.
[0072]
The environmental control system includes a chamber seal 130, a cooling jacket 132, and other flow controllers and evacuation systems not shown. A computer based control system is used to control the heater, puller and other electrical and mechanical elements.
[0073]
In order to grow a single crystal silicon ingot, the seed crystal 124 comes into contact with the silicon melt 126 and is gradually pulled up in the axial direction (upper side). The cooling and solidification of the silicon melt 126 as single crystal silicon occurs at the boundary 131 between the ingot 128 and the melt 126. As shown in FIG. 27, the boundary 131 is raised with respect to the melt 126.
[0074]
On the other hand, silicon wafers that can obtain the concentration profile of oxygen precipitates controlled as shown in FIG. 4 using the rapid thermal processing process according to the present invention can be roughly classified into three types. That is, a defect-free perfect wafer in which interstitial agglomerates and vacancy agglomerates are not formed over the entire radial direction of the wafer, and vacancy agglomerates are formed only in a vacancy-rich region within a certain radius from the center of the wafer. The semi-perfect wafer where no interstitial agglomerates and vacancy agglomerates are present outside the bakery region, and there is no interstitial agglomeration over the entire wafer, and there are only vacancy agglomerates. It is. However, the wafer to which the present invention is applied is not necessarily limited to this, and any wafer that can apply the principle of the present invention can be applied. That is, as described above, the present invention is to perform the RTA process of FIG. 5 on a predetermined silicon wafer and then perform a heat treatment to obtain a concentration profile of oxygen precipitates as shown in FIG. In addition, the COP may be a silicon wafer that exists in the bulk region of the wafer but does not exist in the denuded zone.
[0075]
In order to prevent defects in silicon wafers, various studies have been conducted to produce high-purity ingots during crystal growth. In particular, techniques for controlling the seed crystal pulling rate and the temperature gradient in the hot zone structure are well known. "The Mechanizm of Swirl Defects Formation in Silicon" by Voronkov, [Journal of Crystal Growth, Vol. 59, 1982, pp. 625-643] discloses a technique related to the control of the ingot pulling speed (V) and the temperature gradient (G) at the contact surface of the ingot-melt. Second International Symposium on Advanced Science and Technology of Silicon Material for Advanced Science and Technology for Silicon Materials Opened from November 25th to 29th, 1996 by the Inventor by Applying this Technology According to the paper “Effect of Crystal Defects on Device Characteristics” published in Japan, if the ratio of V to G (hereinafter referred to as V / G) is above the critical point, a vacancy-rich region is formed and below the critical point. If so, an interstitial-rich region is formed.
[0076]
  FIG. 26 is a conceptual diagram showing a relative point defect distribution and V / G relationship in a silicon ingot. Referring to this, V / G is the critical point (V / G during ingot growth).^* ), A vacancy-rich region is formed and the critical vacancy concentration (Cv)^* ) At the above time, a vacancy agglomerate is formed. And critical interstitial concentration (CI^* ) Interstitial agglomerates are formed at the above times. In FIG. 26, (V / G)_B ^* B-Bang is a ring related to interstitial siliconDo(V / G)_P ^* Is O. S. P-van which is F ringDoRepresent.
[0077]
The wafer to which the present invention is applied corresponds to a defect-free perfect wafer in which V / G exists between the B-band and P-band during ingot growth, a semi-perfect wafer including the P-band, and a critical vacancy concentration. Yes (V / G)^*Thus, a wafer or the like in which a vacancy agglomerate is formed over the entire wafer.
[0078]
On the other hand, regarding perfect wafers and semi-perfect wafers to which the present invention is applied, U.S. patent application Ser. No. 08 / 989,591 filed by the present inventor and the corresponding CIP application No. 09 / 320,210. And 09 / 320,102. In addition, this is a reference combined with the application, and a detailed description thereof is omitted.
[0079]
FIG. 28 is a schematic view showing the Czochralski puller invented by the present inventor and disclosed in the CIP application, and is an improvement of the heat shield 214 compared to FIG. Referring to FIG. 28, the Czochralski puller 200 includes a furnace, a crystal pulling mechanism, an environmental controller, and a control system using a computer. The hot zone furnace includes a heater 204, a crucible 206, a susceptor 208, and a rotating shaft 210 that rotates in a first direction 212 as shown. A cooling jacket 232 and a heat shield 214 provide additional heat distribution. Also, the heating pack 202 is filled with a heat absorbing material 216 to provide additional heat distribution.
[0080]
As shown, the crystal pulling mechanism includes a crystal pulling shaft 220 that is rotatable in a second direction 222 that is opposite to the first direction 212. The crystal pulling shaft 220 includes a crystal holder 220a at its end. The crystal holder 220 a holds the seed crystal 224 and is pulled up from the melt 226 in the crucible 206 to form an ingot 228.
[0081]
The environmental control system includes a chamber seal 230, a cooling jacket 232, and other flow controllers and evacuation systems not shown. A computer based control system is used to control the heater, puller and other electrical and mechanical elements. In order to grow a single crystal silicon ingot, the seed crystal 224 comes into contact with the silicon melt 226 and is gradually pulled up in the axial direction (upper side). Cooling and solidification of the silicon melt 226 as single crystal silicon occurs at the boundary 231 between the ingot 228 and the melt 226. This further includes a heat shield housing 234 as compared with FIG. 27, so that the V / G can be adjusted more accurately.
[0082]
FIG. 29 is a schematic view showing an improved Czochralski puller according to an embodiment of the present invention, and FIG. 30 shows an improved main part thereof. Here, the description of the same components as those in FIG. 28 is omitted. That is, as shown in FIG. 30, the improvement is that the shape of the heat shut-off housing 300 is changed and a heat shut-off valve 360 is further provided. The heat shield housing 300 has a trapezoidal shape rotated by 90 °, and includes a vertical inner heat shield housing wall 310 and an outer heat shield housing wall 330, and a space between the inner heat shield housing wall 310 and the outer heat shield housing wall 330. A heat shield housing lid 340 that is inclined upward in the outward direction and connects between the internal heat shield housing wall 310 and the external heat shield housing wall 330 and includes a heat shield housing bottom 320 that is inclined downward in the outward direction. It has a ring shape.
[0083]
The ring-shaped heat shield housing 300 is filled with a heat absorbing material capable of absorbing heat, and the heat shield housing 300 is made of carbon ferrite.
[0084]
A heat shield plate 360 is provided between the heat shield housing cover 340 and the cooling jacket 232 of the heat shield housing 300 to surround the ingot to be pulled up. The heat shield housing 300 is attached to the heating pack 202 by a support member 350. Fixed to the upper side.
[0085]
The structure of the Czochralski puller shown in FIG. 29 can basically increase the cooling rate of the grown ingot. In general, the size of the void in the crystal-grown ingot is proportional to the square root of the initial vacancy concentration formed at the contact surface between the silicon melt and the ingot, but inversely proportional to the square root of the cooling rate of the ingot. To do. On the other hand, as described with reference to FIG. 11, if the void existing in the ingot is formed below a certain size, even if the void is formed in the ingot during crystal growth, the rapid heat treatment process of the present invention is used. There are no voids in the nude zone.
[0086]
Therefore, in order to reduce the void formed in the ingot according to the object of the present invention, it is necessary to increase the cooling rate of the ingot. On the other hand, when the cooling rate of the ingot increases, the temperature gradient (Gc) increases along the central axis of the ingot to be pulled up. When V / G is set to a constant value so as to have a predetermined defect distribution, the ingot pulling rate is increased. Also gets higher.
[0087]
In the present invention, the temperature of the ingot shaft is at least 1.4 ° until the temperature of the ingot shaft reaches a certain temperature corresponding to the growth stage of the ingot from the temperature of the ingot shaft at the ingot-melt boundary. k / min or more, the lengths “a” and “c” of the inner heat shield housing wall 310 and the outer heat shield housing wall 330 of the heat shield housing 300, the inclination angle β of the heat shield housing lid 340, The angle of inclination α of the heat shield housing bottom 320, the distance “d” from the ingot 228 to the internal heat shield housing wall 310, the distance “f” from the crucible 206 to the external heat shield housing wall 330, the internal heat shield housing wall The distance “e” from 310 to the external heat isolation housing wall 330 and the arrangement of the heat isolation valves 360 are selected.
[0088]
In the puller of FIG. 29, since the cooling rate of the ingot to be grown is large, the pulling rate can be extremely high, for example, about 0.50 mm / min to 1.00 mm / min. As a result, the productivity of the ingot is improved. The In addition, it is possible to further secure a process margin when growing an ingot for the perfect wafer or semi-perfect wafer manufactured in FIG.
[0089]
【The invention's effect】
As described above, according to the present invention, an oxygen precipitate is distributed so that a denuded zone is sufficiently secured near the surface of the wafer and a sufficient gettering effect is obtained in the bulk region of the wafer. A silicon wafer can be formed.
[0090]
Further, a sufficient denuded zone is secured in the vicinity of the wafer surface, and the defect distribution can be freely controlled so that a sufficient gettering effect is obtained in the bulk region of the wafer. In addition, when the puller of the present invention is used, the ingot to be grown can be rapidly cooled, so that the void in the ingot can be reduced.
[0091]
The present invention has been described in detail with reference to the preferred embodiments. However, the present invention is not limited to these embodiments, and is within the scope of the technical idea of the present invention. Various modifications are possible for a knowledgeable person.
[0092]
In addition, the above embodiments are merely illustrative of the idea of the present invention, and various modifications are possible within the concept of the present invention. In particular, the temperature, time, cooling rate, gas mixing ratio, and the like of the rapid heat treatment process can be set in various ways, and various puller structures are possible even at the wafer preparation stage.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing the structure of a conventional MOS transistor formed near the surface of a silicon wafer.
FIG. 2 is a view showing a concentration profile of oxygen precipitates on a conventional silicon wafer.
FIG. 3 is a diagram showing a concentration profile of oxygen precipitates with respect to another conventional silicon wafer.
FIG. 4 is a view schematically showing a concentration profile of oxygen precipitates on a silicon wafer according to an embodiment of the present invention.
FIG. 5 is a time chart of an RTA process performed according to an embodiment of the present invention.
6 is a diagram showing a concentration profile of point defects after performing the RTA process of FIG. 5 in a nitrogen gas atmosphere.
7 is a diagram showing a concentration profile of point defects after performing the RTA process of FIG. 5 in an argon gas atmosphere.
8 is a diagram showing a concentration profile of point defects after performing the RTA process of FIG. 5 in a hydrogen gas atmosphere.
FIG. 9 is a diagram showing a vacancy concentration profile after performing the RTA process of FIG. 5 while changing the mixing ratio in a mixed gas atmosphere of nitrogen gas and argon gas.
FIG. 10 is a diagram showing a concentration profile of oxygen precipitates by a subsequent heat treatment after performing an RTA process according to the present invention.
11 is a diagram for explaining a COP decomposition process in the vicinity of the surface of a silicon wafer as the RTA process of FIG. 5 is performed under an argon gas atmosphere.
12 is a photograph showing a distribution of oxygen precipitates formed by subsequent heat treatment after performing the RTA process of FIG. 5 in a nitrogen gas atmosphere.
13 is a photograph showing a distribution of oxygen precipitates formed by subsequent heat treatment after performing the RTA process of FIG. 5 in an argon gas atmosphere.
14 is a photograph showing a distribution of oxygen precipitates formed by subsequent heat treatment after performing the RTA process of FIG. 5 in a hydrogen gas atmosphere.
15 is a photograph showing the distribution of oxygen precipitates formed by subsequent heat treatment after performing the RTA process of FIG. 5 in a mixed gas atmosphere of nitrogen gas and argon gas.
16 is a photograph showing a distribution of oxygen precipitates formed by subsequent heat treatment after performing the RTA process of FIG. 5 in a mixed gas atmosphere of nitrogen gas and hydrogen gas.
17 is a photograph showing the depth of a denuded zone formed by subsequent heat treatment after performing the RTA process of FIG. 5 under a nitrogen gas atmosphere.
18 is a photograph showing the depth of a denuded zone formed by subsequent heat treatment after performing the RTA process of FIG. 5 under an argon gas atmosphere.
19 is a photograph showing the depth of a denuded zone formed by subsequent heat treatment after performing the RTA process of FIG. 5 under a hydrogen gas atmosphere.
20 is a photograph showing the depth of a denuded zone formed by a subsequent subsequent heat treatment after performing the RTA process of FIG. 5 in a mixed gas atmosphere of nitrogen gas and argon gas.
FIG. 21 is a photograph showing the depth of a denuded zone formed by subsequent heat treatment after performing the RTA process of FIG. 5 in a mixed gas atmosphere of nitrogen gas and hydrogen gas.
22A is a photograph showing the shape of the COP in the as-grown state, and FIG. 22B shows the changed shape after the RTA process of FIG. 5 is performed in a nitrogen gas atmosphere. It is a photograph.
23A is a photograph showing the shape of a COP in an as-grown state, and FIG. 23B is a view after performing the RTA process of FIG. 5 in a mixed gas atmosphere of nitrogen gas and argon gas. It is the photograph which showed the changed shape.
24A is a photograph showing the shape of a COP in an as-grown state, and FIG. 24B is a view after performing the RTA process of FIG. 5 in a mixed gas atmosphere of nitrogen gas and hydrogen gas. It is the photograph which showed the changed shape.
FIG. 25 is a process flowchart showing a process according to an embodiment of the present invention.
FIG. 26 is a conceptual diagram showing a relative point defect distribution and V / G relationship in a silicon ingot.
FIG. 27 is a schematic view showing a conventional Czochralski puller.
FIG. 28 is a schematic view showing a conventional Czochralski puller invented by the present inventor.
FIG. 29 is a schematic diagram illustrating a Czochralski puller improved according to an embodiment of the present invention.
30 is a view showing a main part of the Czochralski puller of FIG. 29. FIG.
FIG. 31 is a graph obtained by measuring a change in concentration of oxygen precipitates at a peak after performing the RTA process of FIG. 5 while changing the flow rates of nitrogen gas and argon gas according to an embodiment of the present invention.
32 is a graph obtained by measuring a change in concentration of oxygen precipitates at a peak after performing the RTA process of FIG. 5 while changing the mixing ratio of nitrogen gas and argon gas according to an embodiment of the present invention.
FIG. 33 is a graph obtained by measuring a change in concentration of oxygen precipitates at a peak after performing the RTA process of FIG. 5 while changing the rate of temperature increase according to an embodiment of the present invention.
FIG. 34 is a graph obtained by measuring a change in concentration of oxygen precipitates at a peak after performing the RTA process of FIG. 5 while changing the heat treatment time according to an embodiment of the present invention.
FIG. 35 is a graph obtained by measuring a change in concentration of oxygen precipitates at a peak after performing the RTA process of FIG. 5 while changing the heat treatment temperature according to an embodiment of the present invention.
36 is a graph obtained by measuring a change in concentration of oxygen precipitates at a peak after performing the RTA process of FIG. 5 while changing the temperature decrease rate according to an embodiment of the present invention.
[Explanation of symbols]
10 Silicon substrate
10a Bulk region
10b Denud zone
12 Source region
14 Drain region
16 Gate insulation film
18 Gate electrode
20 voids
22 Silicon oxide film
100, 200 Czochralski Pula
102, 202 Heated pack
104, 204 heater
106,206 crucible
108, 208 Susceptor
110, 210 Rotating shaft
112, 212 1st direction
114, 214 Heat shield
116, 216 Heat absorption material
120, 220 Crystal pulling shaft
120a, 220a Crystal holder
122, 222 Second direction
124, 224 seed crystal
126, 226 Melt
128, 228 ingot
130, 230 Chamber seal
131,231 Ingot-melt interface
132, 232 Cooling jacket
234, 300 Heat insulation housing
310 Internal heat shield housing wall
320 Heat insulation housing bottom
330 External heat shield housing wall
340 Heat shut-off housing lid
350 Support member
360 Thermal shut-off valve

Claims (20)

Preparing a silicon wafer;
By performing the rapid thermal processing in a mixed gas atmosphere of a gas having a gas and interstitial silicon injection effect with Bekanshi injection effect of the wafer in the surface of the wafer, subsequent to the rapid thermal processing A nucleation center that serves as a place where oxygen precipitates grow during the heat treatment is generated, and a concentration profile of the nucleation center from the front surface to the back surface of the wafer generated thereby is a predetermined depth from the front surface and the back surface. In the bulk region between the first peak and the second peak, respectively, and is maintained below the critical value before reaching the first peak and the second peak from the front and back, respectively. A rapid heating / cooling treatment step that makes the concentration profile of the production center concave,
The mixed gas is nitrogen gas + argon gas, or nitrogen gas + hydrogen gas,
The silicon wafer manufacturing method, wherein the critical value is an equilibrium concentration at a standby temperature after the rapid heating / cooling treatment . The rapid thermal processing stage of claim 1, wherein, after the rapid heating and rapid cooling process step, the concentration profile of Bekanshi to the back from the front of the wafer, the first peak each in a predetermined depth from the front and rear And a second peak, maintained below a critical value before reaching the first peak and the second peak from the front surface and the rear surface, respectively, and the concentration profile of vacancy is concave in the bulk region between the first peak and the second peak. A method for producing a silicon wafer, comprising: The concentration profile of oxygen precipitates from the front surface to the back surface of the wafer has a first peak and a second peak at a predetermined depth from the front surface and the back surface, respectively, after the rapid heating / rapid cooling treatment step according to claim 1 or 2. A denuded zone is formed before reaching the first and second peaks from the front and back surfaces, respectively, and the oxygen precipitate concentration profile is concave in the bulk region between the first and second peaks. A method of manufacturing a silicon wafer, comprising a heat treatment step.   The silicon wafer production according to claim 3, wherein a peak value of the first peak and the second peak of the oxygen precipitate and a concentration value of the bulk region are controlled by adjusting a mixing ratio of the mixed gas. Method.   4. The method of manufacturing a silicon wafer according to claim 3, wherein a depth of the denuded zone is controlled by adjusting a mixing ratio of the mixed gas. 6. The method for producing a silicon wafer according to claim 4, wherein, in addition to adjusting the mixing ratio of the mixed gas, the temperature and time of the rapid heating / rapid cooling treatment stage are further adjusted. 4. The method for producing a silicon wafer according to claim 1, wherein the rapid heating / rapid cooling treatment step includes rapid cooling of at least 30 [deg.] C./second or more. 8. The method of manufacturing a silicon wafer according to claim 7, wherein the rapid heating / cooling treatment stage is performed at a temperature of at least 1150 [deg.] C. or more. The method of claim 8, wherein the rapid heating / cooling treatment step is performed for at least 5 seconds. 9. The method of manufacturing a silicon wafer according to claim 8, wherein the rapid heating / cooling treatment stage is performed at a temperature of at least 1150 [deg.] C. for 30 seconds or more. 9. The method of manufacturing a silicon wafer according to claim 8, wherein the rapid heating / cooling treatment stage is performed at a temperature of 1250 [deg.] C. or more for 10 seconds or more. The method for manufacturing a silicon wafer according to claim 3, wherein the heat treatment step after the rapid heating / rapid cooling treatment step is performed at 800 ° C to 1000 ° C for 4 to 20 hours.   4. The method for producing a silicon wafer according to claim 3, wherein the concentration profile of the oxygen precipitate is symmetric with respect to the center of the silicon wafer.   4. The method of manufacturing a silicon wafer according to claim 3, wherein the depth of the denuded zone is secured in a range of 10 [mu] m to 40 [mu] m from the surface of the wafer.   4. The method of manufacturing a silicon wafer according to claim 3, wherein the depth of the denuded zone is secured in a range of 20 [mu] m to 40 [mu] m from the surface of the wafer. 4. The method for producing a silicon wafer according to claim 3, wherein the concentration of oxygen precipitates at the first peak and the second peak is at least 1 × 10 9 / cm ³ or more. The method for producing a silicon wafer according to claim 3, wherein the concentration of oxygen precipitates in the bulk region between the first peak and the second peak is at least 1 x 10 8 / cm ³ or more. 4. The method of manufacturing a silicon wafer according to claim 1, wherein the rapid heating / cooling treatment stage is performed at a donor keying stage of a wafer ring process of the silicon wafer. The silicon wafer according to claim 1, further comprising a step of polishing a front surface of the wafer on which an active region of a semiconductor device is formed after the rapid heating / cooling treatment step. Production method.   4. The method for manufacturing a silicon wafer according to claim 3, wherein COP further exists only in a bulk region between the first peak and the second peak due to the subsequent heat treatment step.

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