JP3873568B2

JP3873568B2 - Silicon single crystal pulling device

Info

Publication number: JP3873568B2
Application number: JP2000071451A
Authority: JP
Inventors: 森林符; 吉亮坂本; 貴渡辺; 直樹小野; 康島貫
Original assignee: Sumco Corp
Current assignee: Sumco Corp
Priority date: 2000-03-15
Filing date: 2000-03-15
Publication date: 2007-01-24
Anticipated expiration: 2020-03-15
Also published as: JP2001261494A

Description

【０００１】
【発明の属する技術分野】
本発明は、チョクラルスキー法（ＣＺ法）により石英るつぼに貯留されたシリコン融液からシリコン単結晶を引上げる装置に関するものである。
【０００２】
【従来の技術】
図８に示すように、この種のシリコン単結晶引上げ装置では、チャンバ１内部にシリコン融液２を貯留する石英るつぼ３が設けられ、この石英るつぼ３は黒鉛サセプタ４に収容される。シリコン融液２は石英るつぼ３の周囲に配置した円筒状のヒータ５で所定温度に加熱制御され、このシリコン融液２からシリコン単結晶６が引上げられる。この引上げ装置は更にヒータ５の周囲に配置された円筒状の保温筒７と、この保温筒７の上部にアッパリング８を介して取付けられ石英るつぼ３と同軸に円筒状の熱遮蔽部材９とを備える。
この熱遮蔽部材９はヒータ５からの輻射熱を遮るとともに、チャンバ１内に供給されるアルゴンガスを通過させてシリコン融液４の表面に吹き付け、シリコン融液２から発生するＳｉＯガス又はＳｉＯ₂ガスを吹き流すものである。
【０００３】
従来、熱遮蔽部材９はアッパリング８上に載るフランジ部９ａと、このフランジ部９ａに連設し引上げられるシリコン単結晶６の周囲を包囲する円筒状の直胴部９ｂと、この直胴部９ｂの下端に連設され下方に向うに従って半径が小さくなるコーン部９ｃとを有する。この熱遮蔽部材９はカーボン、モリブデン、タングステン等の耐熱性部材により作られる。
この熱遮蔽部材９を用いて、単結晶中にベーカンシー点欠陥（vacancy point defect）を生じるような速度でシリコン単結晶を引上げた場合でも、引上げ方向の約１４００〜１０００℃の温度範囲は比較的長いため、単結晶内部で外方拡散（単結晶の内部から外側に向う拡散）や坂道拡散（高温側即ち下方に向う拡散）が促進されるため、その点欠陥の密度を低減する。ここで、べーカンシー点欠陥とは、一つのシリコン原子がシリコン結晶格子で正常的な位置の一つから離脱した点欠陥をいう。この結果、この単結晶から切り出したシリコンウェーハの表面に酸化膜を形成し、この酸化膜を介して直流電圧を印加したときの酸化膜の耐圧特性（Time Zero Dielectric Breakdown、ＴＺＤＢ）は比較的良好になる。
【０００４】
一方、本出願人は図９に示すように、熱遮蔽部材１０を備えた単結晶引上げ装置を提案した（特願平１１−１７７５３５）。図９において、図８と同一構成要素は同一符号で示している。この熱遮蔽部材１０は半径が下方に向けて漸次小さくなるテーパ状の円筒部材であり、その上端のフランジ部１０ａがアッパリング８を介して保温筒７の上部に取付けられる。熱遮蔽部材１０の下端１０ｂはシリコン融液２の表面近傍に位置し、熱遮蔽部材１０の下端面１０ｃは、半径方向内側から半径方向外側に上方に向けて傾斜して形成される。この下端面１０ｃの水平面に対する傾斜角θは３０度である。熱遮蔽部材１０は内部に炭素繊維からなる保温材１０ｅを充填したカーボン板１０ｆにより構成される。この熱遮蔽部材１０は、その下端部１０ｄが上部より厚肉な保温材１０ｅで形成されている。
この熱遮蔽部材１０を用いて、前述した速度とほぼ同一速度でシリコン単結晶を引上げた場合、シリコン単結晶とシリコン融液の固液界面近傍での単結晶中心位置及び単結晶外周面位置における結晶軸方向の温度勾配をそれぞれＧ₁（℃／ｍｍ）及びＧ₂（℃／ｍｍ）とするときに、両温度勾配の差（Ｇ₂−Ｇ₁）が１．３（℃／ｍｍ）程度以下で比較的小さいため、前述したベーカンシー点欠陥が単結晶中で三次元的に集まったベーカンシー固まり（vacancy agglomerates）が形成されにくくなる。このべーカンシー固まりには、ＣＯＰ(Crystal Originated Particles)やＦＰＤ(Flow Pattern Defect)等がある。ＣＯＰはＳＣ−１洗浄後にレーザパーティクルカウンタでパーティクルとしてカウントされた底の深いエッチピットであり、ＦＰＤはシリコン融液から引上げられたシリコン単結晶から切り出したシリコンウェーハを長時間化学エッチング（Seccoエッチング液）したときに現れる特異なフローパターンを呈する痕跡の源である。
【０００５】
【発明が解決しようとする課題】
しかし、図８に示す熱遮蔽部材９を用いた場合、シリコン単結晶とシリコン融液の固液界面近傍での上記両温度勾配の差（Ｇ₂−Ｇ₁）が２．０（℃／ｍｍ）程度以上で比較的大きくなるため、ＣＯＰ等の三次元欠陥であるベーカンシー固まりの密度が熱遮蔽部材１０を用いた場合より高くなる。このため、この単結晶から切り出したシリコンウェーハの表面に酸化膜を形成して、その耐圧を評価したときに酸化膜耐圧特性が悪化する不具合があった。
また図９に示す熱遮蔽部材１０を用いた場合、引上げ方向の約１４００〜１０００℃の温度範囲が比較的短いため、単結晶中のベーカンシー点欠陥の外方拡散や坂道拡散が十分に行われない。この結果、この単結晶から作られたシリコンウェーハの酸化膜耐圧特性が図８に示す熱遮蔽部材９を用いた場合より悪化する問題点があった。
【０００６】
本発明の目的は、シリコン単結晶のベーカンシー点欠陥のみならずベーカンシー固まりも低減し得るシリコン単結晶の引上げ装置を提供することにある。
本発明の別の目的は、シリコンウェーハにしたときの酸化膜耐圧特性を改善し得るシリコン単結晶の引上げ装置を提供することにある。
【０００７】
【課題を解決するための手段】
図１及び図２に示すように、石英るつぼ１３に貯留されたシリコン融液１２からシリコン単結晶２５を引上げる方法において、シリコン単結晶とシリコン融液の固液界面近傍での単結晶中心位置及び単結晶外周面位置における結晶軸方向の温度勾配をそれぞれＧ₁（℃／ｍｍ）及びＧ₂（℃／ｍｍ）とするとき、次の式（１）を満たし、かつ引上げに伴ってシリコン単結晶２５の中心及び外周面近傍の温度が１４００℃から１０００℃に降下するまでの時間が４００分以上となるように引上げるシリコン単結晶の引上げ方法である。
【０００８】
Ｇ₂−Ｇ₁≦１．３（℃／ｍｍ） …… （１）
上記引上げ方法によれば、両温度勾配の差（Ｇ₂−Ｇ₁）が１．３（℃／ｍｍ）程度以下で比較的小さいため、単結晶中のＣＯＰ等の三次元欠陥であるベーカンシー固まりの密度が低減する。また単結晶２５の外周面近傍の温度が１４００℃から１０００℃に降下するまでの時間が４００分以上と長いため、単結晶内部で外方拡散や坂道拡散が促進され、単結晶中のベーカンシー点欠陥の密度を低減する。
【０００９】
請求項１に係る発明は、チャンバ１１内に設けられシリコン融液１２が貯留された石英るつぼ１３と、この石英るつぼ１３の外周面を包囲しシリコン融液１２を加熱するヒータ１８と、シリコン融液１２から引上げられるシリコン単結晶２５の外周面を包囲しかつ下端がシリコン融液１２表面から間隔をあけて上方に位置しヒータ１８からの輻射熱を遮る円筒状の熱遮蔽部材３０とを備えたシリコン単結晶の引上げ装置の改良である。
その特徴ある構成は、熱遮蔽部材３０の基材３１の下部が下方に向うに従って半径が小さくなる第１アウタコーン３１ａに形成され、基材３１の上部が上方に向うに従って半径が大きくなる第２アウタコーン３１ｂに形成され、第１アウタコーン３１ａ及び基材３１の中間部３１ｃが下方に向うに従って半径が小さくなる第１インナコーン３２により覆われ、この第１インナコーン３２と第１アウタコーン３１ａ及び基材３１の中間部３１ｃとの間に第１保温材３３が充填され、第２アウタコーン３１ｂが上方に向うに従って半径が大きくなる第２インナコーン３４とこの第２インナコーン３４の下端に連設されかつ第２アウタコーン３１ｂの下端近傍に接続する底壁３６とにより覆われ、第２インナコーン３４及び底壁３６と第２アウタコーン３１ｂとの間に第２保温材３７が充填されたことにある。
請求項１に係る引上げ装置によれば、上記引上げ条件を実現でき、本発明の目的が達成される。
【００１０】
【発明の実施の形態】
次に本発明の実施の形態を図面に基づいて説明する。
図１及び図２に示すように、シリコン単結晶の引上げ装置２０のチャンバ１１内には、シリコン融液１２を貯留する石英るつぼ１３が設けられ、この石英るつぼ１３は黒鉛サセプタ１４に収容される。石英るつぼ１３の下面は上記黒鉛サセプタ１４を介して支軸１６の上端に固定され、この支軸１６の下部はるつぼ駆動手段１７に接続される（図１）。るつぼ駆動手段１７は図示しないが石英るつぼ１３を回転させる第１回転用モータと、石英るつぼ１３を昇降させる昇降用モータとを有し、これらのモータにより石英るつぼ１３が所定の方向に回転し得るとともに、上下方向に移動可能となっている。石英るつぼ１３の外周面は石英るつぼ１３から所定の間隔をあけてカーボンヒータ１８により包囲され、このヒータ１８は保温筒１９により包囲される。ヒータ１８は石英るつぼ１３に投入された高純度のシリコン多結晶を加熱・溶融してシリコン融液１２にする。
またチャンバ１１の上端には円筒状のケーシング２１が接続される。このケーシング２１には引上げ手段２２が設けられる。引上げ手段２２はケーシング２１の上端部に水平状態で旋回可能に設けられた引上げヘッド（図示せず）と、このヘッドを回転させる第２回転用モータ（図示せず）と、ヘッドから石英るつぼ１３の回転中心に向って垂下されたワイヤケーブル２３と、上記ヘッド内に設けられワイヤケーブル２３を巻取り又は繰出す引上げ用モータ（図示せず）とを有する。ワイヤケーブル２３の下端にはシリコン融液１２に浸してシリコン単結晶２５を引上げるための種結晶２４が取付けられる。
【００１１】
またケーシング２１の周壁にはチャンバ１１内にアルゴンガスのような不活性ガスを供給するための供給パイプ２７が接続される。またチャンバ１１の底壁には不活性ガスを排出するための排出パイプ２８の一端が接続され、この他端には図示しない真空ポンプが接続される。供給パイプ２７及び排出パイプ２８にはこれらのパイプ２７，２８を流れる不活性ガスの流量を調整する第１及び第２流量調整弁２７ａ，２８ａがそれぞれ設けられる。
また引上げ用モータの出力軸（図示せず）にはロータリエンコーダ（図示せず）が設けられ、るつぼ駆動手段１７には石英るつぼ１３内のシリコン融液１２の重量を検出する重量センサ（図示せず）と、支軸１６の昇降位置を検出するリニヤエンコーダ（図示せず）とが設けられる。ロータリエンコーダ、重量センサ及びリニヤエンコーダの各検出出力はコントローラ（図示せず）の制御入力に接続され、コントローラの制御出力は引上げ手段２２の引上げ用モータ及びるつぼ駆動手段の昇降用モータにそれぞれ接続される。またコントローラにはメモリ（図示せず）が設けられ、このメモリにはロータリエンコーダの検出出力に対するワイヤケーブル２３の巻取り長さ、即ちシリコン単結晶２５の引上げ長さが第１マップとして記憶され、重量センサの検出出力に対する石英るつぼ１３内のシリコン融液１２の液面レベルが第２マップとして記憶される。コントローラは重量センサの検出出力に基づいて石英るつぼ１３内のシリコン融液１２の液面を常に一定のレベルに保つように、るつぼ駆動手段１７の昇降用モータを制御するように構成される。
【００１２】
またシリコン単結晶２５の外周面と石英るつぼ１３の内周面との間にはシリコン単結晶２５を包囲する熱遮蔽部材３０が設けられる。図１に詳しく示すように、この熱遮蔽部材３０は、その基材３１の下部が下方に向うに従って半径が小さくなる第１アウタコーン３１ａに形成される。また基材３１の上部が上方に向うに従って半径が大きくなる第２アウタコーン３１ｂに形成される。基材３１の中間部３１ｃは両アウタコーン３１ａと３１ｂの間に設けられ、石英るつぼ１３と同軸に円筒状に形成される。中間部３１ｃはこの実施の形態では同一半径の円筒であるが、下方に向うに従って半径が小さくなるコーンでもよい。第１アウタコーン３１ａ及び中間部３１ｃは下方に向うに従って半径が小さくなる第１インナコーン３２により覆われ、第１インナコーン３２と第１アウタコーン３１ａ及び中間部３１ｃとの間には第１保温材３３が充填される。
また第２アウタコーン３１ｂは、上方に向うに従って半径が大きくなる第２インナコーン３４とこの第２インナコーン３４の下端に連設されかつ第２アウタコーン３１ｂの下端に接続する底壁３６とにより覆われる。この第２インナコーン３４及び底壁３６と第２アウタコーン３１ｂとの間には第２保温材３７が充填される。この第２アウタコーン３１ｂの上端には基材３１のフランジ部３１ｄが連設され、フランジ部３１ｄは保温筒１９の上部に設けられたアッパリング２６に取付けられる。フランジ部３１ｄをアッパリング２６に取付けることにより、第１アウタコーン３１ａの下端がシリコン融液１２の表面から所定の距離だけ上方に位置するようになる。第１アウタコーン３１ａ、中間部３１ｃ、第２アウタコーン３１ｂ及びフランジ部３１ｄは一体的に形成される。基材３１、両インナコーン３２，３４及び底壁３６はそれぞれカーボン、モリブデン、タングステンにより、或いは表面にＳｉＣがコーティングされたカーボン等により形成される。また両保温材３３，３７はフェルト状の炭素繊維により形成される。
【００１３】
シリコン単結晶２５の直径をＤとし、第１インナコーン３２の下端の半径をＲ₁とし、中間部３１ｃの半径をＲ₂とし、第２インナコーン３４の下端の半径をＲ₃とし、石英るつぼ１３の半径をＲ₄とするとき、(Ｄ／２)＜Ｒ₁＜Ｒ₃＜Ｒ₂＜Ｒ₄の関係を有するように形成される。この実施の形態では、第１アウタコーン３１ａの水平面とのなす角度をθ₁とし、第２アウタコーン３１ｂの水平面とのなす角度をθ₂とし、第２インナコーン３４と底壁３６とのなす角度をαとし、底壁３６と基材３１の中間部３１ｃとのなす角度をβとし、第１アウタコーン３１ａと第１インナコーン３２とのなす角度をγとし、第１インナコーン３２の内端面の高さをａとし、第２インナコーン３４の内端面の高さをｂとし、第１アウタコーン３１ａの下端から上端までの鉛直方向の距離をＬ₁とし、第１アウタコーン３１ａの下端から第１インナコーン３２の上端までの鉛直方向の距離をＬ₂とし、第１アウタコーン３１ａの下端から第２アウタコーン３１ｂの下端までの鉛直方向の距離をＬ₃とし、第１インナコーン３２の上端から第２アウタコーン３１ｂの下端までの鉛直方向の距離をＬ₄とするとき、次の式（２）〜（１２）を満たすように、熱遮蔽部材３０は構成される。
【００１４】
０度＜ θ₁ ≦ ５０度 …… （２）
０度＜ θ₂ ≦ ９０度 …… （３）
１０度 ≦ α ≦ ６０度 …… （４）
６０度 ≦ β ≦ １２０度 …… （５）
１０度 ≦ γ ≦ ６０度 …… （６）
０ｍｍ ≦ ａ ≦ １００ｍｍ …… （７）
０ｍｍ ≦ ｂ ≦ １００ｍｍ …… （８）
０ｍｍ ≦ Ｌ₁ ≦ １００ｍｍ …… （９）
１０ｍｍ ≦ Ｌ₂ ≦ ５００ｍｍ …… （１０）
３０ｍｍ ≦ Ｌ₃ ≦ ８００ｍｍ …… （１１）
１０ｍｍ ≦ Ｌ₄≦ ３００ｍｍ …… （１２）
このように構成されたシリコン単結晶の引上げ装置の動作を説明する。
シリコン単結晶２５をシリコン融液１２から所定の引上げ速度で引上げると、このシリコン単結晶とシリコン融液の固液界面近傍の温度分布は、シリコン融液１２からの輻射熱により第１保温材３３の温度が上昇しているため、シリコン単結晶２５からの急激な放熱は抑制され、シリコン単結晶２５の外周部の急激な温度低下を阻止できる。この固液界面近傍での単結晶中心位置及び単結晶外周面位置における結晶軸方向の温度勾配をそれぞれＧ₁（℃／ｍｍ）及びＧ₂（℃／ｍｍ）とするとき、両温度勾配の差（Ｇ₂−Ｇ₁）は１．３（℃／ｍｍ）以下となり、シリコン単結晶２５中の鉛直方向の温度勾配の径方向分布が略均一になる。この結果、ＣＯＰ等の三次元欠陥であるベーカンシー固まりの密度が低減する。なお、この両温度勾配の差（Ｇ₂−Ｇ₁）は、θ₁を２０〜４０度にし、θ₂を５０〜７０度にし、αを３０〜５０度にし、βを８０〜１００度にし、γを２０〜４０度にし、Ｌ₄を１００〜１５０ｍｍにすることにより、更に小さい１．０（℃／ｍｍ）以下にすることができる。またシリコン単結晶とシリコン融液の固液界面近傍とは、シリコン単結晶２５とシリコン融液１２の固液界面から結晶軸方向に０〜１０ｍｍ離れた位置をいう。
【００１５】
またシリコン単結晶２５が引上げられて、第１保温材３３と第２保温材３７の間の領域Ａ（図１）に達すると、底壁３６の存在によりこの領域Ａでは不活性ガスの流下によっても熱の移動が比較的少なく高温を維持する。また保温材３７の存在により、シリコン単結晶２５からの放熱は抑制される。このため、この領域Ａ及び第２インナコーン３７に接する単結晶２５の外周面の温度が降下しにくくなり、単結晶２５の中心及び外周面近傍の温度が１４００℃から１０００℃に降下するまでの時間が４００分以上、好ましくは４３０分以上かかるようになる。この結果、単結晶中のベーカンシー点欠陥の外方拡散や坂道拡散が促進され、ベーカンシー点欠陥密度が低減する。
【００１６】
【実施例】
次に本発明の実施例を比較例とともに詳しく説明する。
＜実施例１＞
図１及び図２に示すような直径(Ｄ)が１５５±５ｍｍのシリコン単結晶２５を引上げるためのシリコン単結晶の引上げ装置２０を用いた。この装置２０の熱遮蔽部材３０の各部位のサイズ及び角度は以下の通りである。第１インナコーン３２の下端の半径Ｒ₁は１００ｍｍであり、中間部３１ｃの半径Ｒ₂は１９５ｍｍであり、第２インナコーン３４の下端の半径Ｒ₃は１００ｍｍであり、石英るつぼ１３の半径Ｒ₄は２２０±５ｍｍであった。また第１アウタコーン３１ａの水平面とのなす角度θ₁は３０度であり、第２アウタコーン３１ｂの水平面とのなす角度θ₂は７５度であり、第２インナコーン３４と底壁３６とのなす角度αは５５度であり、底壁３６と基材３１の中間部３１ｃとのなす角度βは９０度であり、第１アウタコーン３１ａと第１インナコーン３２とのなす角度γは３５度であった。また第１インナコーン３２の内端面の高さａは１５ｍｍであり、第２インナコーン３４の内端面の高さｂは１０ｍｍであった。更に第１アウタコーン３１ａの下端から上端までの鉛直方向の距離Ｌ₁は３０ｍｍであり、第１アウタコーン３１ａの下端から第１インナコーン３２の上端までの鉛直方向の距離Ｌ₂は１１５ｍｍであり、第１アウタコーン３１ａの下端から第２アウタコーン３１ｂの下端までの鉛直方向の距離Ｌ₃は２５０ｍｍであり、第１インナコーン３２の上端から第２アウタコーン３１ｂの下端までの鉛直方向の距離Ｌ₄は１２５ｍｍであった。なお、熱遮蔽部材３０の基材３１、両インナコーン３２，３４及び底壁３６をそれぞれカーボンにより形成し、両保温材３３，３７をフェルト状の炭素繊維により形成した。
【００１７】
＜比較例１＞
図８に示すような実施例１と同一直径のシリコン単結晶６を引上げるためのシリコン単結晶の引上げ装置を用いた。このシリコン単結晶の引上げ装置にはフランジ部９ａ、直胴部９ｂ及びコーン部９ｃを有する熱遮蔽部材９が設けられる。直胴部９ｂの直径は４００ｍｍ、高さは３００ｍｍであった。またコーン部９ｃの上端の半径は２００ｍｍ、下端の半径は１０５ｍｍであり、高さは５５ｍｍであった。この熱遮蔽部材６の材質は実施例１の熱遮蔽部材の基材の材質と同一とした。この引上げ装置は上記のように熱遮蔽部材９の形状及びサイズを変更したことを除いて、実施例１の装置と同一とした。
【００１８】
＜比較例２＞
図９に示すような実施例１と同一直径のシリコン単結晶６を引上げるためのシリコン単結晶の引上げ装置を用いた。このシリコン単結晶の引上げ装置にはフランジ部１０ａ、下端面１０ｃ、下端部１０ｄ及びカーボン板１０ｆを有する熱遮蔽部材１０が設けられる。下端面１０ｃの水平面とのなす角度θは３０度であり、カーボン板１０ｆの上端半径は２０５ｍｍ、下端半径は１００ｍｍ、高さは３５０ｍｍであった。また下端部１０ｄの半径は２００ｍｍ、高さは１９５ｍｍであった。カーボン板１０ｆ及び保温材１０ｅの各材質は実施例１の熱遮蔽部材の基材及び保温材の各材質と同一とした。この引上げ装置は上記のように熱遮蔽部材９の形状及びサイズを変更したことを除いて、実施例１の装置と同一とした。
【００１９】
＜比較試験及び評価＞
(a) 熱履歴と温度勾配差
実施例１、比較例１及び比較例２の各引上げ装置でシリコン単結晶への輻射熱を考慮した熱伝導解析プログラムに基づいて、単結晶中の熱履歴及び固液界面近傍の温度勾配差の径方向変化状況をそれぞれシミュレーション計算して求めた。前者を図３に、後者を図４に示す。
図３において、たて軸はシリコン単結晶の外面近傍（Ｄ／２＝７７．５ｍｍ）の温度を示し、よこ軸は固液界面からの距離を示す。固液界面から３００ｍｍの高さの位置における単結晶の外面温度が、図９に示す比較例２では８００℃になるのに対して、図８に示す比較例１及び図２に示す実施例１では１０００℃及び９６０℃にそれぞれ維持され、単結晶が急激に冷却されていないことが確認された。
図４において、たて軸は径方向の各位置における単結晶の固液界面近傍（界面から１０ｍｍ）の温度勾配から単結晶中心位置の固液界面近傍（界面から１０ｍｍ）の温度勾配を差し引いた温度勾配差を示す。たて軸では２．００℃／ｍｍを基準として１００％としている。またよこ軸には比較例１の外周面位置での温度勾配の差を１００％としたときの実施例１及び比較例２のそれぞれの相対的な温度勾配の差を示す。単結晶の外周面位置において、図８に示す比較例１の温度勾配差が１００％のときに、図９に示す比較例２及び図２に示す実施例１ではそれぞれ約６７％及び約６２％に低下し、径方向の温度勾配変化が小さいことが確認された。
【００２０】
(b) ＣＯＰの数
実施例１、比較例１及び比較例２の各引上げ装置において、同一の条件でシリコン単結晶を引上げた。得られた３種類のシリコン単結晶から切出されたシリコンウェーハをラッピングし、面取り加工を施した後、鏡面研磨することにより、直径６インチで厚さ６５０±２５μｍの３種類のシリコンウェーハを用意した。
【００２１】
実施例１、比較例１及び比較例２の各シリコンウェーハの表面の直径１５０ｍｍの円内における０．１２μｍ以上のＣＯＰの数をレーザパーティクルカウンタ（ＫＬＡ-Ｔｅｎｃｏｒ社製、ＳＦＳ６２００）を用いて調べた。これらのそれぞれの平均値を表１に示す。
【００２２】
【表１】

【００２３】
表１から明らかなように、０．１２μｍ以上のＣＯＰの数が、比較例１のシリコンウェーハでは平均１．１／ｃｍ²であったのに対して、実施例１及び比較例２のシリコンウェーハではそれぞれ平均０．１個／ｃｍ²以下で少なかった。
【００２４】
(c) 酸化膜耐圧特性
ＣＯＰを測定したウェーハと同種の実施例１、比較例１及び比較例２の各シリコンウェーハについて酸化膜耐圧（ＴＺＤＢ）の測定を行った。測定したシリコンウェーハのうち、一部は６６％Ｏ₂雰囲気下、１０００℃で１５分間熱処理し、残りはその熱処理しなかった。この測定はウェーハ表面に厚さ２５ｎｍの酸化膜を形成し、その上に電極を形成して、１０ＭＶ／ｃｍの直流電圧を１００秒間印加した。印加した後、再度同様に電圧を印加し、電極に流れる電流量により、各点の酸化膜の破壊の有無を調べ、全点に対する破壊した点数から酸化膜の欠陥密度を算出した。図５（ａ）、図６（ａ）及び図７（ａ）に熱処理なしの実施例１のウェーハ、比較例１のウェーハ及び比較例２のウェーハの結果をそれぞれ示す。また図５（ｂ）、図６（ｂ）及び図７（ｂ）に熱処理した実施例１のウェーハ、比較例１のウェーハ及び比較例２のウェーハの結果をそれぞれ示す。図５〜図７において黒く塗りつぶした部分は酸化膜が破壊した部分である。
【００２５】
図８に示した引上げ装置で引上げた単結晶にはＣＯＰ等のベーカンシー固まりの三次元欠陥が多いため、この単結晶から切出された比較例１の「熱処理なし」（図６（ａ））のウェーハの酸化膜耐圧は低かった。またこのベーカンシー固まりのサイズが０．１２μｍ以上と大きいため、比較例１の「熱処理あり」（図６（ｂ））のウェーハの酸化膜耐圧は、熱処理によってもＣＯＰ等のベーカンシー固まり欠陥は消滅せず、やはり低かった。
一方、図９に示した引上げ装置で引上げた単結晶にはベーカンシー点欠陥が非常に多いため、この単結晶から切出された比較例２の「熱処理なし」（図７（ａ））のウェーハの酸化膜耐圧は非常に低かった。しかしこのベーカンシー点欠陥のサイズが０．１２μｍ未満で小さいため、比較例２の「熱処理あり」（図７（ｂ））のウェーハの酸化膜耐圧は、熱処理によってベーカンシー点欠陥が消滅し、向上した。
これらに対して、図１及び図２に示した引上げ装置で引上げた単結晶にはベーカンシー固まりの三次元欠陥もベーカンシー点欠陥も少ないため、この単結晶から切出された実施例１の「熱処理なし」（図５（ａ））のウェーハの酸化膜耐圧も、実施例１の「熱処理あり」（図５（ｂ））のウェーハの酸化膜耐圧も、高かった。これは図１に示す第１保温材３３によりＣＯＰ等のベーカンシー固まりの三次元欠陥が単結晶内に発生するのが抑制され、第２保温材３７で引上げられた単結晶を長時間保温するため、ベーカンシー点欠陥が殆ど消滅したためと考えられる。
【００２６】
【発明の効果】
以上述べたように、本発明によれば、単結晶中心位置及び単結晶外周面位置における結晶軸方向の温度勾配の差（Ｇ₂−Ｇ₁）が１．３（℃／ｍｍ）程度以下で比較的小さくなるため、ＣＯＰ等の三次元欠陥であるベーカンシー固まりの密度を小さくすることができ、また単結晶の外周面近傍の温度が１４００℃から１０００℃に降下するまでの時間を４００分以上と長くすることができるため、単結晶内部で外方拡散や坂道拡散が促進され、ベーカンシー点欠陥の密度を低減することができる。この結果、シリコン単結晶をシリコンウェーハにしたときの酸化膜耐圧特性を改善することができる。
【図面の簡単な説明】
【図１】本発明実施の形態のシリコン単結晶引上げ装置の熱遮蔽部材の要部断面図。
【図２】そのシリコン単結晶の引上げ装置の全体構成図。
【図３】実施例１，比較例１及び比較例２のシリコン単結晶の外面近傍の熱履歴を示す図。
【図４】実施例１，比較例１及び比較例２のシリコン単結晶の固液界面近傍の温度勾配差の径方向変化状況を示す図。
【図５】実施例１のシリコンウェーハに直流電圧を印加したときの酸化膜欠陥密度を示す図。
【図６】比較例１のシリコンウェーハに直流電圧を印加したときの酸化膜欠陥密度を示す図。
【図７】比較例２のシリコンウェーハに直流電圧を印加したときの酸化膜欠陥密度を示す図。
【図８】従来のシリコン単結晶の引上げ装置の全体構成図。
【図９】従来の別のシリコン単結晶の引上げ装置の全体構成図。
【符号の説明】
１１チャンバ
１２シリコン融液
１３石英るつぼ
１８ヒータ
２５シリコン単結晶
３０熱遮蔽部材
３１基材
３１ａ第１アウタコーン
３１ｂ第２アウタコーン
３１ｃ中間部
３２第１インナコーン
３３第１保温材
３４第２インナコーン
３６底壁
３７第２保温材[0001]
BACKGROUND OF THE INVENTION
The present invention pulls up a silicon single crystal from a silicon melt stored in a quartz crucible by the Czochralski method (CZ method). Dress Is related to the position.
[0002]
[Prior art]
As shown in FIG. 8, in this type of silicon single crystal pulling apparatus, a quartz crucible 3 for storing a silicon melt 2 is provided inside a chamber 1, and the quartz crucible 3 is accommodated in a graphite susceptor 4. The silicon melt 2 is heated and controlled at a predetermined temperature by a cylindrical heater 5 disposed around the quartz crucible 3, and the silicon single crystal 6 is pulled up from the silicon melt 2. This pulling device further includes a cylindrical heat insulating cylinder 7 disposed around the heater 5, a cylindrical heat shielding member 9 that is attached to the upper portion of the heat insulating cylinder 7 via an upper ring 8 and coaxial with the quartz crucible 3. Is provided.
The heat shielding member 9 shields the radiant heat from the heater 5 and allows the argon gas supplied into the chamber 1 to pass therethrough and spray it on the surface of the silicon melt 4 to generate SiO gas or SiO generated from the silicon melt 2. ₂ A gas is blown away.
[0003]
Conventionally, the heat shielding member 9 includes a flange portion 9a mounted on the upper ring 8, a cylindrical straight body portion 9b surrounding the silicon single crystal 6 connected to and pulled up from the flange portion 9a, and the straight body portion. 9b, and a cone portion 9c having a radius that decreases toward the bottom. The heat shielding member 9 is made of a heat resistant member such as carbon, molybdenum, tungsten.
Even when the silicon single crystal is pulled at such a rate that vacancy point defects are generated in the single crystal using the heat shielding member 9, the temperature range of about 1400 to 1000 ° C. in the pulling direction is relatively high. Since it is long, outward diffusion (diffusion from the inside of the single crystal toward the outside) and slope diffusion (diffusion toward the high temperature side, ie, downward) are promoted inside the single crystal, thereby reducing the density of point defects. Here, the vacancy point defect means a point defect in which one silicon atom is detached from one of normal positions in the silicon crystal lattice. As a result, an oxide film is formed on the surface of a silicon wafer cut out from this single crystal, and the withstand voltage characteristic (Time Zero Dielectric Breakdown, TZDB) of the oxide film when a DC voltage is applied through this oxide film is relatively good. become.
[0004]
On the other hand, the present applicant has proposed a single crystal pulling apparatus provided with a heat shielding member 10 as shown in FIG. 9 (Japanese Patent Application No. 11-177535). 9, the same components as those in FIG. 8 are denoted by the same reference numerals. The heat shield member 10 is a tapered cylindrical member whose radius gradually decreases downward, and a flange portion 10 a at the upper end thereof is attached to the upper portion of the heat retaining cylinder 7 via the upper ring 8. The lower end 10b of the heat shielding member 10 is located in the vicinity of the surface of the silicon melt 2, and the lower end surface 10c of the heat shielding member 10 is formed to be inclined upward from the radially inner side to the radially outer side. The inclination angle θ of the lower end surface 10c with respect to the horizontal plane is 30 degrees. The heat shielding member 10 is composed of a carbon plate 10f filled with a heat insulating material 10e made of carbon fiber. The heat shielding member 10 is formed of a heat insulating material 10e whose lower end portion 10d is thicker than the upper portion.
When the silicon single crystal is pulled up at substantially the same speed as described above using the heat shielding member 10, the single crystal center position and the single crystal outer peripheral surface position in the vicinity of the solid-liquid interface between the silicon single crystal and the silicon melt are used. G is the temperature gradient in the crystal axis direction. ₁ (° C / mm) and G ₂ (° C / mm), the difference between both temperature gradients (G ₂ -G ₁ ) Is about 1.3 (° C./mm) or less and is relatively small, it becomes difficult to form vacancy agglomerates in which the aforementioned vacancy point defects are collected three-dimensionally in a single crystal. The vacancy lump includes COP (Crystal Originated Particles) and FPD (Flow Pattern Defect). COP is a deep etch pit counted as particles by a laser particle counter after SC-1 cleaning, and FPD is a long-time chemical etching (Secco etching solution) of a silicon wafer cut out from a silicon single crystal pulled up from a silicon melt. ) Is a source of traces that exhibit a unique flow pattern.
[0005]
[Problems to be solved by the invention]
However, when the heat shielding member 9 shown in FIG. 8 is used, the difference between the temperature gradients in the vicinity of the solid-liquid interface between the silicon single crystal and the silicon melt (G ₂ -G ₁ ) Becomes relatively large at about 2.0 (° C./mm) or more, and therefore, the density of vacancy mass, which is a three-dimensional defect such as COP, becomes higher than when the heat shielding member 10 is used. For this reason, when an oxide film is formed on the surface of a silicon wafer cut out from the single crystal and the withstand voltage is evaluated, there is a problem that the oxide film withstand voltage characteristic deteriorates.
Further, when the heat shielding member 10 shown in FIG. 9 is used, since the temperature range of about 1400 to 1000 ° C. in the pulling direction is relatively short, the outward diffusion of the vacancy point defects in the single crystal and the hill diffusion are sufficiently performed. Absent. As a result, there is a problem that the oxide film withstand voltage characteristic of the silicon wafer made of this single crystal is worse than when the heat shielding member 9 shown in FIG. 8 is used.
[0006]
The object of the present invention is to pull up a silicon single crystal that can reduce not only the vacancy point defects of the silicon single crystal but also the vacancy mass. Dressing Is to provide a place.
Another object of the present invention is to pull up a silicon single crystal that can improve the oxide film breakdown voltage characteristics when formed into a silicon wafer. Dressing Is to provide a place.
[0007]
[Means for Solving the Problems]
Figure 1 and FIG. 2, in the method of pulling up the silicon single crystal 25 from the silicon melt 12 stored in the quartz crucible 13, the single crystal center position in the vicinity of the solid-liquid interface between the silicon single crystal and the silicon melt and The temperature gradient in the crystal axis direction at the position of the outer peripheral surface of the single crystal is represented by G ₁ (° C / mm) and G ₂ (° C./mm), the time until the temperature in the vicinity of the center and the outer peripheral surface of the silicon single crystal 25 drops from 1400 ° C. to 1000 ° C. with the pulling is 400 minutes. Pull up to be more Ru This is a method of pulling a recon single crystal.
[0008]
G ₂ -G ₁ ≦ 1.3 (℃ / mm) (1)
the above According to the pulling method, the difference between both temperature gradients (G ₂ -G ₁ ) Is about 1.3 (° C./mm) or less and is relatively small, the density of vacancy mass, which is a three-dimensional defect such as COP in the single crystal, is reduced. In addition, since the time until the temperature near the outer peripheral surface of the single crystal 25 drops from 1400 ° C. to 1000 ° C. is as long as 400 minutes or more, outward diffusion and slope diffusion are promoted inside the single crystal, and vacancy points in the single crystal Reduce the density of defects.
[0009]
Claim 1 The invention according to the present invention includes a quartz crucible 13 provided in the chamber 11 in which the silicon melt 12 is stored, a heater 18 that surrounds the outer peripheral surface of the quartz crucible 13 and heats the silicon melt 12, and the silicon melt 12. A silicon single crystal provided with a cylindrical heat shielding member 30 that surrounds the outer peripheral surface of the silicon single crystal 25 to be pulled up and has a lower end positioned above the surface of the silicon melt 12 so as to block radiation heat from the heater 18. It is an improvement of the pulling device.
The characteristic structure is formed in the first outer cone 31a whose radius decreases as the lower portion of the base material 31 of the heat shielding member 30 faces downward, and the radius increases as the upper portion of the base material 31 faces upward. The first outer cone 31a and the intermediate portion 31c of the base material 31 are covered with a first inner cone 32 having a radius that decreases downward, and the first inner cone 32, the first outer cone 31a, and the base material 31 are formed. The first heat insulating material 33 is filled between the intermediate portion 31c, the second inner cone 34 having a radius that increases as the second outer cone 31b faces upward, and the lower end of the second inner cone 34. 2 is covered with a bottom wall 36 connected to the vicinity of the lower end of the outer cone 31b, and the second inner cone 34 and the bottom wall 36 are connected to the second outer cone. The second heat insulator 37 between the emissions 31b are in fact filled.
Claim 1 According to the pulling device according to the above The pulling conditions can be realized and the object of the present invention is achieved.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
As shown in FIGS. 1 and 2, a quartz crucible 13 for storing a silicon melt 12 is provided in the chamber 11 of the silicon single crystal pulling apparatus 20, and the quartz crucible 13 is accommodated in a graphite susceptor 14. . The lower surface of the quartz crucible 13 is fixed to the upper end of the support shaft 16 via the graphite susceptor 14, and the lower portion of the support shaft 16 is connected to the crucible driving means 17 (FIG. 1). Although not shown, the crucible driving means 17 has a first rotating motor for rotating the quartz crucible 13 and a lifting motor for moving the quartz crucible 13 up and down, and the quartz crucible 13 can be rotated in a predetermined direction by these motors. At the same time, it is movable in the vertical direction. The outer peripheral surface of the quartz crucible 13 is surrounded by a carbon heater 18 at a predetermined interval from the quartz crucible 13, and the heater 18 is surrounded by a heat retaining cylinder 19. The heater 18 heats and melts high-purity silicon polycrystal charged in the quartz crucible 13 to form the silicon melt 12.
A cylindrical casing 21 is connected to the upper end of the chamber 11. The casing 21 is provided with a pulling means 22. The pulling means 22 is a pulling head (not shown) provided at the upper end of the casing 21 so as to be turnable in a horizontal state, a second rotating motor (not shown) for rotating the head, and a quartz crucible 13 from the head. And a pulling motor (not shown) that is provided in the head and winds or feeds the wire cable 23. A seed crystal 24 for pulling up the silicon single crystal 25 by dipping in the silicon melt 12 is attached to the lower end of the wire cable 23.
[0011]
A supply pipe 27 for supplying an inert gas such as argon gas into the chamber 11 is connected to the peripheral wall of the casing 21. One end of a discharge pipe 28 for discharging inert gas is connected to the bottom wall of the chamber 11, and a vacuum pump (not shown) is connected to the other end. The supply pipe 27 and the discharge pipe 28 are provided with first and second flow

rate adjusting valves

27a and 28a for adjusting the flow rate of the inert gas flowing through the

pipes

27 and 28, respectively.
A rotary encoder (not shown) is provided on the output shaft (not shown) of the pulling motor, and the crucible driving means 17 has a weight sensor (not shown) for detecting the weight of the silicon melt 12 in the quartz crucible 13. And a linear encoder (not shown) for detecting the raising / lowering position of the support shaft 16. The detection outputs of the rotary encoder, weight sensor and linear encoder are connected to the control input of a controller (not shown), and the control output of the controller is connected to the pulling motor of the pulling means 22 and the lifting motor of the crucible driving means. The In addition, the controller is provided with a memory (not shown), in which the winding length of the wire cable 23 with respect to the detection output of the rotary encoder, that is, the pulling length of the silicon single crystal 25 is stored as a first map. The liquid level of the silicon melt 12 in the quartz crucible 13 with respect to the detection output of the weight sensor is stored as a second map. The controller is configured to control the raising / lowering motor of the crucible driving means 17 so as to always keep the liquid level of the silicon melt 12 in the quartz crucible 13 at a constant level based on the detection output of the weight sensor.
[0012]
A heat shielding member 30 surrounding the silicon single crystal 25 is provided between the outer peripheral surface of the silicon single crystal 25 and the inner peripheral surface of the quartz crucible 13. As shown in detail in FIG. 1, the heat shielding member 30 is formed on a first outer cone 31 a whose radius decreases as the lower portion of the base material 31 faces downward. Further, it is formed on the second outer cone 31b whose radius increases as the upper portion of the base material 31 faces upward. An intermediate portion 31 c of the base material 31 is provided between the

outer cones

31 a and 31 b and is formed in a cylindrical shape coaxially with the quartz crucible 13. The intermediate portion 31c is a cylinder having the same radius in this embodiment, but may be a cone having a radius that decreases downward. The first outer cone 31a and the intermediate portion 31c are covered with a first inner cone 32 whose radius decreases as it goes downward, and the first heat insulating material 33 is interposed between the first inner cone 32 and the first outer cone 31a and the intermediate portion 31c. Is filled.
The second outer cone 31b is covered with a second inner cone 34 whose radius increases toward the upper side and a bottom wall 36 connected to the lower end of the second inner cone 34 and connected to the lower end of the second outer cone 31b. . A second heat insulating material 37 is filled between the second inner cone 34 and the bottom wall 36 and the second outer cone 31b. A flange portion 31d of the base material 31 is connected to the upper end of the second outer cone 31b, and the flange portion 31d is attached to an upper ring 26 provided at the upper portion of the heat retaining cylinder 19. By attaching the flange portion 31d to the upper ring 26, the lower end of the first outer cone 31a is positioned above the surface of the silicon melt 12 by a predetermined distance. The first outer cone 31a, the intermediate portion 31c, the second outer cone 31b, and the flange portion 31d are integrally formed. The base material 31, the

inner cones

32 and 34, and the bottom wall 36 are formed of carbon, molybdenum, tungsten, or carbon whose surface is coated with SiC. Both heat insulating

materials

33 and 37 are formed of felt-like carbon fibers.
[0013]
The diameter of the silicon single crystal 25 is D, and the radius of the lower end of the first inner cone 32 is R. ₁ And the radius of the intermediate part 31c is R ₂ And the radius of the lower end of the second inner cone 34 is R _Three And the radius of the quartz crucible 13 is R _Four (D / 2) <R ₁ <R _Three <R ₂ <R _Four It is formed to have the relationship of In this embodiment, the angle formed by the horizontal plane of the first outer cone 31a is θ ₁ And the angle between the second outer cone 31b and the horizontal plane is θ ₂ The angle between the second inner cone 34 and the bottom wall 36 is α, the angle between the bottom wall 36 and the intermediate portion 31c of the base 31 is β, and the first outer cone 31a and the first inner cone 32 are The angle formed is γ, the height of the inner end surface of the first inner cone 32 is a, the height of the inner end surface of the second inner cone 34 is b, and the vertical distance from the lower end to the upper end of the first outer cone 31a L ₁ And the vertical distance from the lower end of the first outer cone 31a to the upper end of the first inner cone 32 is L ₂ And the vertical distance from the lower end of the first outer cone 31a to the lower end of the second outer cone 31b is L _Three And the vertical distance from the upper end of the first inner cone 32 to the lower end of the second outer cone 31b is L _Four , The heat shielding member 30 is configured to satisfy the following expressions (2) to (12).
[0014]
0 degrees <θ ₁ ≦ 50 degrees (2)
0 degrees <θ ₂ ≦ 90 degrees (3)
10 degrees ≤ α ≤ 60 degrees (4)
60 degrees ≤ β ≤ 120 degrees ...... (5)
10 degrees ≤ γ ≤ 60 degrees ... (6)
0mm ≤ a ≤ 100mm (7)
0mm ≤ b ≤ 100mm (8)
0mm ≦ L ₁ ≦ 100mm (9)
10mm ≦ L ₂ ≦ 500mm (10)
30mm ≦ L _Three ≦ 800mm (11)
10mm ≦ L _Four ≦ 300mm (12)
The operation of the silicon single crystal pulling apparatus configured as described above will be described.
When the silicon single crystal 25 is pulled up from the silicon melt 12 at a predetermined pulling rate, the temperature distribution in the vicinity of the solid-liquid interface between the silicon single crystal and the silicon melt is changed to the first heat insulating material 33 by the radiant heat from the silicon melt 12. Therefore, rapid heat dissipation from the silicon single crystal 25 is suppressed, and a rapid temperature drop at the outer periphery of the silicon single crystal 25 can be prevented. The temperature gradient in the crystal axis direction at the single crystal center position and the single crystal outer peripheral surface position in the vicinity of the solid-liquid interface is expressed as G ₁ (° C / mm) and G ₂ (° C / mm), the difference between both temperature gradients (G ₂ -G ₁ ) Is 1.3 (° C./mm) or less, and the radial distribution of the temperature gradient in the vertical direction in the silicon single crystal 25 becomes substantially uniform. As a result, the density of vacancy clumps that are three-dimensional defects such as COP is reduced. The difference between the two temperature gradients (G ₂ -G ₁ ) Is θ ₁ Is set to 20 to 40 degrees, and θ ₂ To 50 to 70 degrees, α to 30 to 50 degrees, β to 80 to 100 degrees, γ to 20 to 40 degrees, L _Four By setting the thickness to 100 to 150 mm, it can be further reduced to 1.0 (° C./mm) or less. The vicinity of the solid-liquid interface between the silicon single crystal and the silicon melt refers to a position that is 0 to 10 mm away from the solid-liquid interface between the silicon single crystal 25 and the silicon melt 12 in the crystal axis direction.
[0015]
When the silicon single crystal 25 is pulled up to reach the region A (FIG. 1) between the first heat insulating material 33 and the second heat insulating material 37, the presence of the bottom wall 36 causes the inert gas to flow in the region A. However, heat transfer is relatively low and the high temperature is maintained. Further, the presence of the heat insulating material 37 suppresses heat radiation from the silicon single crystal 25. For this reason, it becomes difficult for the temperature of the outer peripheral surface of the single crystal 25 in contact with the region A and the second inner cone 37 to decrease, and the temperature near the center and the outer peripheral surface of the single crystal 25 decreases from 1400 ° C. to 1000 ° C. The time is 400 minutes or longer, preferably 430 minutes or longer. As a result, outward diffusion and slope diffusion of vacancy point defects in the single crystal are promoted, and vacancy point defect density is reduced.
[0016]
【Example】
Next, examples of the present invention will be described in detail together with comparative examples.
<Example 1>
A silicon single crystal pulling apparatus 20 for pulling a silicon single crystal 25 having a diameter (D) of 155 ± 5 mm as shown in FIGS. 1 and 2 was used. The size and angle of each part of the heat shielding member 30 of the apparatus 20 are as follows. The radius R of the lower end of the first inner cone 32 ₁ Is 100 mm and the radius R of the intermediate part 31c ₂ Is 195 mm, and the radius R of the lower end of the second inner cone 34 is _Three Is 100 mm and the radius R of the quartz crucible 13 _Four Was 220 ± 5 mm. Further, the angle θ formed with the horizontal plane of the first outer cone 31a ₁ Is 30 degrees, and the angle θ between the second outer cone 31b and the horizontal plane ₂ Is 75 degrees, the angle α formed by the second inner cone 34 and the bottom wall 36 is 55 degrees, the angle β formed by the bottom wall 36 and the intermediate portion 31c of the base material 31 is 90 degrees, and the first The angle γ formed by the outer cone 31a and the first inner cone 32 was 35 degrees. The height a of the inner end face of the first inner cone 32 was 15 mm, and the height b of the inner end face of the second inner cone 34 was 10 mm. Further, the vertical distance L from the lower end to the upper end of the first outer cone 31a. ₁ Is 30 mm, and the vertical distance L from the lower end of the first outer cone 31a to the upper end of the first inner cone 32 is ₂ Is 115 mm, and the vertical distance L from the lower end of the first outer cone 31a to the lower end of the second outer cone 31b _Three Is 250 mm, and the vertical distance L from the upper end of the first inner cone 32 to the lower end of the second outer cone 31b is _Four Was 125 mm. In addition, the base material 31, both the

inner cones

32 and 34, and the bottom wall 36 of the heat shielding member 30 were formed from carbon, and both the

heat insulating materials

33 and 37 were formed from felt-like carbon fibers.
[0017]
<Comparative Example 1>
A silicon single crystal pulling apparatus for pulling up the silicon single crystal 6 having the same diameter as that of Example 1 as shown in FIG. 8 was used. This silicon single crystal pulling apparatus is provided with a heat shielding member 9 having a flange portion 9a, a straight body portion 9b, and a cone portion 9c. The diameter of the straight body portion 9b was 400 mm and the height was 300 mm. Moreover, the radius of the upper end of the cone part 9c was 200 mm, the radius of the lower end was 105 mm, and the height was 55 mm. The material of the heat shielding member 6 was the same as the material of the base material of the heat shielding member of Example 1. This pulling apparatus was the same as the apparatus of Example 1 except that the shape and size of the heat shielding member 9 were changed as described above.
[0018]
<Comparative example 2>
A silicon single crystal pulling apparatus for pulling up the silicon single crystal 6 having the same diameter as in Example 1 as shown in FIG. 9 was used. This silicon single crystal pulling apparatus is provided with a heat shielding member 10 having a flange portion 10a, a lower end surface 10c, a lower end portion 10d, and a carbon plate 10f. The angle θ between the lower end surface 10c and the horizontal plane was 30 degrees, and the upper end radius of the carbon plate 10f was 205 mm, the lower end radius was 100 mm, and the height was 350 mm. The radius of the lower end 10d was 200 mm, and the height was 195 mm. Each material of the carbon plate 10f and the heat insulating material 10e was the same as each material of the base material and the heat insulating material of the heat shielding member of Example 1. This pulling apparatus was the same as the apparatus of Example 1 except that the shape and size of the heat shielding member 9 were changed as described above.
[0019]
<Comparison test and evaluation>
(a) Thermal history and temperature gradient difference
Based on the heat conduction analysis program in consideration of the radiant heat to the silicon single crystal in each pulling device of Example 1, Comparative Example 1 and Comparative Example 2, the diameter of the thermal history in the single crystal and the temperature gradient difference near the solid-liquid interface Each direction change situation was obtained by simulation calculation. The former is shown in FIG. 3, and the latter is shown in FIG.
In FIG. 3, the vertical axis indicates the temperature in the vicinity of the outer surface of the silicon single crystal (D / 2 = 77.5 mm), and the horizontal axis indicates the distance from the solid-liquid interface. The external surface temperature of the single crystal at a height of 300 mm from the solid-liquid interface is 800 ° C. in Comparative Example 2 shown in FIG. 9, whereas Comparative Example 1 shown in FIG. 8 and Example 1 shown in FIG. Then, the temperature was maintained at 1000 ° C. and 960 ° C., respectively, and it was confirmed that the single crystal was not rapidly cooled.
In FIG. 4, the vertical axis is obtained by subtracting the temperature gradient in the vicinity of the solid-liquid interface at the center of the single crystal (10 mm from the interface) from the temperature gradient in the vicinity of the solid-liquid interface of the single crystal at each radial position (10 mm from the interface). The temperature gradient difference is shown. The vertical axis is 100% based on 2.00 ° C./mm. Further, the horizontal axis shows the relative temperature gradient difference between Example 1 and Comparative Example 2 when the temperature gradient difference at the outer peripheral surface position of Comparative Example 1 is 100%. When the temperature gradient difference of Comparative Example 1 shown in FIG. 8 is 100% at the outer peripheral surface position of the single crystal, it is about 67% and about 62% in Comparative Example 2 shown in FIG. 9 and Example 1 shown in FIG. It was confirmed that the temperature gradient change in the radial direction was small.
[0020]
(b) Number of COPs
In each of the pulling apparatuses of Example 1, Comparative Example 1 and Comparative Example 2, the silicon single crystal was pulled under the same conditions. Three types of silicon wafers with a diameter of 6 inches and a thickness of 650 ± 25 μm are prepared by lapping, chamfering, and mirror polishing the silicon wafers cut from the three types of silicon single crystals obtained. did.
[0021]
The number of COPs of 0.12 μm or more in a circle having a diameter of 150 mm on the surface of each silicon wafer of Example 1, Comparative Example 1 and Comparative Example 2 was examined using a laser particle counter (manufactured by KLA-Tencor, SFS6200). . The average values of these are shown in Table 1.
[0022]
[Table 1]

[0023]
As is apparent from Table 1, the number of COPs of 0.12 μm or more averages 1.1 / cm for the silicon wafer of Comparative Example 1. ² In contrast, the silicon wafers of Example 1 and Comparative Example 2 each averaged 0.1 pieces / cm. ² Less in the following.
[0024]
(c) Oxide film breakdown voltage characteristics
The oxide film withstand voltage (TZDB) was measured for each of the silicon wafers of Example 1, Comparative Example 1 and Comparative Example 2 which was the same type as the wafer where COP was measured. Some of the measured silicon wafers are 66% O ₂ Under the atmosphere, heat treatment was performed at 1000 ° C. for 15 minutes, and the remainder was not heat-treated. In this measurement, an oxide film having a thickness of 25 nm was formed on the wafer surface, an electrode was formed thereon, and a DC voltage of 10 MV / cm was applied for 100 seconds. After the application, a voltage was again applied in the same manner, and the presence or absence of the oxide film at each point was examined by the amount of current flowing through the electrode, and the defect density of the oxide film was calculated from the number of points destroyed for all points. FIGS. 5A, 6A, and 7A show the results of the wafer of Example 1, the wafer of Comparative Example 1, and the wafer of Comparative Example 2 without heat treatment, respectively. 5B, 6B and 7B show the results of the heat-treated wafer of Example 1, the wafer of Comparative Example 1, and the wafer of Comparative Example 2, respectively. 5 to 7, black portions are portions where the oxide film is broken.
[0025]
Since the single crystal pulled by the pulling apparatus shown in FIG. 8 has many three-dimensional defects of vacancy mass such as COP, “no heat treatment” of Comparative Example 1 cut out from this single crystal (FIG. 6A) The oxide breakdown voltage of the wafer was low. Further, since the size of this vacancy mass is as large as 0.12 μm or more, the oxide film breakdown voltage of the wafer of Comparative Example 1 “with heat treatment” (FIG. 6B) is also eliminated by removing the vacancy mass defects such as COP by the heat treatment. It was still low.
On the other hand, since the single crystal pulled by the pulling apparatus shown in FIG. 9 has a large number of vacancy point defects, the wafer of “no heat treatment” (FIG. 7A) of Comparative Example 2 cut out from this single crystal. The breakdown voltage of the oxide film was very low. However, since the size of this vacancy point defect is less than 0.12 μm, the oxide film breakdown voltage of the wafer of “Compared with Example 2” (with heat treatment) (FIG. 7B) was improved by eliminating the vacancy point defect by the heat treatment. .
On the other hand, since the single crystal pulled by the pulling apparatus shown in FIGS. 1 and 2 has few three-dimensional defects and vacancy point defects in the vacancy mass, the “heat treatment of Example 1 cut out from this single crystal”. The oxide film withstand voltage of the wafer of “none” (FIG. 5A) and the oxide film withstand pressure of the wafer of “with heat treatment” in Example 1 (FIG. 5B) were also high. This is because the first heat insulating material 33 shown in FIG. 1 suppresses the generation of three-dimensional defects such as COP in the bakery lump in the single crystal, and the single crystal pulled up by the second heat insulating material 37 is kept warm for a long time. This is probably because vacancy point defects have almost disappeared.
[0026]
【The invention's effect】
As described above, according to the present invention, the temperature gradient difference (G) in the crystal axis direction at the single crystal center position and the single crystal outer peripheral surface position. ₂ -G ₁ ) Is relatively small at about 1.3 (° C./mm) or less, so the density of vacancy mass, which is a three-dimensional defect such as COP, can be reduced, and the temperature near the outer peripheral surface of the single crystal is 1400 ° C. Since the time until the temperature drops to 1000 ° C. can be increased to 400 minutes or more, outward diffusion and slope diffusion are promoted inside the single crystal, and the density of vacancy point defects can be reduced. As a result, it is possible to improve the oxide film breakdown voltage characteristics when a silicon single crystal is used as a silicon wafer.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a main part of a heat shielding member of a silicon single crystal pulling apparatus according to an embodiment of the present invention.
FIG. 2 is an overall configuration diagram of the silicon single crystal pulling apparatus.
FIG. 3 is a diagram showing thermal history in the vicinity of the outer surface of the silicon single crystals of Example 1, Comparative Example 1 and Comparative Example 2.
FIG. 4 is a diagram showing a radial change state of a temperature gradient difference in the vicinity of a solid-liquid interface of a silicon single crystal of Example 1, Comparative Example 1 and Comparative Example 2;
5 is a graph showing the oxide film defect density when a DC voltage is applied to the silicon wafer of Example 1. FIG.
6 is a graph showing an oxide film defect density when a DC voltage is applied to the silicon wafer of Comparative Example 1. FIG.
7 is a graph showing an oxide film defect density when a DC voltage is applied to the silicon wafer of Comparative Example 2. FIG.
FIG. 8 is an overall configuration diagram of a conventional silicon single crystal pulling apparatus.
FIG. 9 is an overall configuration diagram of another conventional silicon single crystal pulling apparatus.
[Explanation of symbols]
11 chambers
12 Silicon melt
13 Quartz crucible
18 Heater
25 Silicon single crystal
30 Heat shielding member
31 Substrate
31a First outer cone
31b 2nd outer cone
31c middle part
32 First Innakorn
33 1st heat insulating material
34 Second Innakorn
36 Bottom wall
37 Second heat insulating material

Claims

A quartz crucible (13) provided in the chamber (11) in which the silicon melt (12) is stored, and a heater (18) surrounding the outer peripheral surface of the quartz crucible (13) and heating the silicon melt (12) ), And surrounds the outer peripheral surface of the silicon single crystal (25) pulled up from the silicon melt (12), and the lower end is located above the surface of the silicon melt (12) and located above the heater (18). In a silicon single crystal pulling device comprising a cylindrical heat shielding member (30) that shields radiant heat from
The heat shielding member (30) is formed on a first outer cone (31a) having a radius that decreases as the lower portion of the base material (31) faces downward,
Formed on the second outer cone (31b), the radius of which increases as the upper portion of the base material (31) faces upward,
The intermediate portion (31c) of the first outer cone (31a) and the base material (31) is covered with a first inner cone (32) whose radius decreases as it goes downward,
A first heat insulating material (33) is filled between the first inner cone (32), the first outer cone (31a) and the intermediate portion (31c) of the base material (31),
The second outer cone (34b) is connected to the lower end of the second inner cone (34) and the lower end of the second inner cone (34b) and has a radius that increases as the second outer cone (31b) faces upward, and in the vicinity of the lower end of the second outer cone (31b). Covered with connecting bottom wall (36),
A silicon single crystal pulling apparatus, wherein a second heat insulating material (37) is filled between the second inner cone (34) and the bottom wall (36) and the second outer cone (31b).

The angle between the first outer cone (31a) and the horizontal plane is θ ₁ , the angle between the second outer cone (31b) and the horizontal plane is θ _2, and the second inner cone (34) and the bottom wall (36) are formed. An angle is α, an angle between the bottom wall (36) and the intermediate portion (31c) of the base material (31) is β, and an angle between the first outer cone (31a) and the first inner cone (32). Is γ, the height of the inner end surface of the first inner cone (32) is a, the height of the inner end surface of the second inner cone (34) is b, and from the lower end of the first outer cone (31a) the vertical distance to the upper end and L _1, the distance in the vertical direction to the upper end of the first In'nakon (32) and L ₂ from the lower end of the first Autakon (31a), said first Autakon (31a) bottom distance in the vertical direction to the lower end of the second Autakon (31b) and L ₃ from the second Autako from the upper end of the first In'nakon (32) When the distance in the vertical direction to the lower end of (31b) and L _4, pulling apparatus according to claim 1, wherein satisfying the following equation (2) to (12).
0 degrees <θ ₁ ≤ 50 degrees (2)
0 degrees <θ ₂ ≤ 90 degrees (3)
10 degrees ≤ α ≤ 60 degrees (4)
60 degrees ≤ β ≤ 120 degrees ...... (5)
10 degrees ≤ γ ≤ 60 degrees ... (6)
0mm ≤ a ≤ 100mm (7)
0mm ≤ b ≤ 100mm (8)
0mm ≦ L ₁ ≦ 100mm ...... (9)
10 mm ≦ L ₂ ≦ 500 mm (10)
30 mm ≦ L ₃ ≦ 800 mm (11)
10mm ≦ L ₄ ≦ 300mm (12)