JP2004006756A - Lifetime measuring instrument for semiconductor carrier and its method - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は，半導体の材料評価の指標として用いる半導体キャリアの寿命測定装置及びその方法に関するものである。
【０００２】
【従来の技術】
半導体デバイスの高集積化に伴い，デバイスに使用される半導体の材料特性の管理が重要となっている。半導体の材料評価の指標として，半導体のキャリア寿命（いわゆるライフタイム）があり，その測定方法として，マイクロ波光伝導減衰法が普及している。これは，半導体にパルス光を照射することによって半導体内に光励起キャリア（以下，励起キャリアという）を生成させ，その後に励起キャリアが再結合することによって減少する減少速度をもって半導体材料の欠陥や汚染の評価を行う方法である。励起キャリアの減少速度の測定は，具体的には，パルス光を照射した部分に測定光としてマイクロ波を照射し，その反射波或いは透過波の強度変化を測定することにより，前記反射波或いは透過波の強度変化の時定数から半導体キャリアの寿命（励起キャリアが再結合により消失するまでの時間）を測定する。このマイクロ波光伝導減衰法に基づく一般的な半導体キャリアの寿命測定装置の構成は，特許文献１の図７に示されている。
一般に，半導体の表面には結晶性不整が存在し，これにより励起キャリアが半導体表面で再結合するいわゆる表面再結合が生じる。該表面再結合は，前記マイクロ波光伝導減衰法による測定値に悪影響を及ぼすため，これを防止する必要がある。通常は，被測定物である半導体の事前の熱処理によって試料表面に酸化膜を形成させ，前記表面再結合の発生を抑制した後に半導体キャリアの寿命測定を行う。しかしながら，測定前に熱処理工程を実行することは多大な手間と時間とを要する上，あまり高温に加熱すると半導体自体の性能劣化も懸念される。
この問題を解決するため，特許文献１には，半導体表面全体にコロナ放電によって電荷層を生成することにより，前記表面再結合を抑制できる状態とした後に前記マイクロ波光伝導減衰法によって半導体キャリアの寿命測定を行う方法が示されている。
【０００３】
【特許文献１】
特開平７−２４０４５０号公報
【０００４】
【発明が解決しようとする課題】
しかしながら，半導体表面に形成される自然酸化膜のような絶縁層の下では，コロナ放電により生成される電荷層は放電しやすく，その帯電効果が長時間持続しない。このため，特許文献１に示される方法では，半導体キャリアの寿命測定中に前記表面再結合が生じてしまい，精度のよい半導体キャリアの寿命測定が行えないという問題点があった。さらに，コロナ放電工程（半導体表面の帯電工程）と半導体キャリアの寿命測定工程との間に時間間隔をおけない等，測定工程上の制約も大きい。
また，コロナ放電による帯電効果を持続させるためには，測定前に予め半導体表面に絶縁層を形成する工程が必要となり，測定前にこのような工程を行うことは手間と時間とを要するという問題点があった。
従って，本発明は上記事情に鑑みてなされたものであり，その目的とするところは，加熱等による半導体自体の性能劣化を極力防止するとともに，余分な前処理工程を行う手間や時間を要することなく励起キャリアの表面再結合を抑制する半導体キャリアの寿命測定装置及びその方法を提供することにある。
【０００５】
【課題を解決するための手段】
上記目的を達成するために本発明は，半導体にパルス光を照射したときに，前記半導体に照射した所定の測定波の反射波或いは透過波の変化を測定することにより前記半導体のキャリアの寿命を測定する半導体キャリアの寿命測定装置において，前記測定波を前記半導体の表面へ導く導波管と，前記導波管の前記半導体に近接する部分又はその近傍に設けられ，少なくとも前記測定波の反射波或いは透過波の変化の測定中に所定の電圧が印加されてコロナ放電する第１の電極と，を具備してなることを特徴とする半導体キャリアの寿命測定装置である。
このように，測定対象となる半導体に近接する位置でコロナ放電を行いながらマイクロ波等の測定波の反射波又は透過波を測定することにより，測定中は半導体の測定波照射部分の帯電状態が維持され，事前の加熱処理工程を設ける等の余分な手間や時間を要することなく励起キャリアの表面再結合を抑制することができる。
【０００６】
また，前記半導体における前記測定波が照射される部分の裏面に近接して設けられ，少なくとも前記測定波の反射波或いは透過波の変化の測定中に所定の電圧が印加されてコロナ放電する第２の電極を具備するものも考えられる。
これにより，半導体の裏面側の表面再結合も抑制できるのでより効果的である。
【０００７】
また，前記半導体の表面に所定の光を照射する光照射手段と，前記光照射手段の光照射により前記半導体に発生する光電圧を測定する光電圧測定手段と，測定された前記光電圧の極性に基づいて前記第１の電極及び／又は第２の電極に印加する電圧の極性を設定する極性設定手段と，を具備するものも考えられる。
これにより，半導体表面に照射した光により発生する光電圧に基づいて，半導体がＮ型であるかＰ型であるかを判別し，これによってコロナ放電用電極に印加する電圧の極性を半導体の型（ＮｏｒＰ）に適した極性に設定すれば，より効果的に励起キャリアの表面再結合を抑制することができる。
【０００８】
また，本発明は，前記半導体キャリアの寿命測定装置による測定を，半導体キャリアの寿命測定方法として捉えてもよい。
即ち，半導体にパルス光を照射したときに，前記半導体に照射した所定の測定波の反射波或いは透過波の変化を測定することにより前記半導体キャリアの寿命を測定する半導体キャリアの寿命測定方法において，前記測定波を前記半導体の表面へ導く導波管の，前記半導体に近接する部分又はその近傍に設けられた第１の電極に，所定の電圧を印加してコロナ放電を行いながら前記測定波の反射波或いは透過波の変化を測定することを特徴とする半導体キャリアの寿命測定方法である。
【０００９】
また，前記半導体における前記測定波が照射される部分の裏面に近接して設けられた第２の電極に，所定の電圧を印加してコロナ放電を行いながら前記測定波の反射波或いは透過波の変化を測定することである。
【００１０】
更に，前記半導体の表面に所定の光を照射することにより前記半導体に発生する光電圧を測定し，測定した前記光電圧の極性に基づいて前記第１の電極及び／又は第２の電極に印加する電圧の極性を設定することである。
【００１１】
また，前記パルス光の照射前に，予め前記半導体の表面を酸化する所定の酸化工程を有してもよい。この酸化工程としては，前記半導体のオゾンとの接触工程，加熱した過酸化水素水中への前記半導体の浸漬工程，酸化プラズマの前記半導体への照射工程，塩酸或いは硫酸中への前記半導体の浸漬工程，加熱水蒸気による前記半導体の加熱工程，陽極酸化工程等が考えられる。
前記半導体のオゾンとの接触工程としては，オゾン水を前記半導体に吹き付ける工程やオゾン水に前記半導体を浸漬させる工程，或いはオゾンを前記半導体に直接吹き付ける工程等が考えられる。ここで，オゾンとの接触工程に用いるオゾン水の濃度，接触時の温度，接触時間等の条件は一律に決定できないが，前記半導体の表面状態やライフタイム測定に要求される精度等に応じて適当な条件とすればよい。
これにより，半導体表面の自然酸化膜が薬品洗浄等によって除去されることにより，コロナ放電による帯電効果が弱くなり，そのままでは表面再結合の抑制効果が下がる場合でも，非常に短時間のうちに半導体表面に酸化膜が生成され，本発明を適用することが可能となる。
【００１２】
【発明の実施の形態】
以下添付図面を参照しながら，本発明の実施の形態及び実施例について説明し，本発明の理解に供する。尚，以下の実施の形態及び実施例は，本発明を具体化した一例であって，本発明の技術的範囲を限定する性格のものではない。
ここに，図１は本発明の実施の形態に係る半導体キャリアの寿命測定装置Ｘの構成図，図２は本発明の実施の形態に係る半導体キャリアの寿命測定装置Ｘによりパルス光照射のときに照射したマイクロ波の反射波の強度変化の測定結果を表すグラフ，図３は本発明の実施の形態に係る半導体キャリアの寿命測定装置Ｘによる半導体キャリアの寿命測定値の経時変化を洗浄後半導体ウェハに対する酸化処理の有無で比較した表，図４は本発明の実施の形態に係る半導体キャリアの寿命測定装置Ｘにより洗浄直後のウェハと洗浄後にオゾンによる酸化工程を経た後のウェハとについてマイクロ波の反射波の強度変化の測定した結果を表すグラフである。
【００１３】
まず，図１を用いて本発明の実施の形態に係る半導体キャリアの寿命測定装置Ｘ（以下，測定装置Ｘと略称する）の構成について説明する。本測定装置Ｘは，シリコンウェハを被検体とする半導体キャリアの寿命測定装置である。
図１（ａ）に示すように，本測定装置Ｘは，マイクロ波発振器（１），サーキュレータ（２），導波管（３），Ｅ−Ｈチューナ（４），透明電極（７），増幅器（８），マイクロ波検出器（１０），高圧電源（１１），パルスレーザ（１２），計算機（１３）等を具備している。
前記パルスレーザ（１２）が発光するパルス光（波長５２３ｎｍ，パルス幅１０ｎｓ）は，ミラー（２１）により前記導波管（５）の一端の直管部分である導波管アンテナ（５）内に導かれ，その開口部（５ａ）から被測定試料であるシリコンウェハ（６）の表面に照射される。
また，前記マイクロ波発振器（１）により発生したマイクロ波は，前記サーキュレータ（２）を経由して前記導波管（３）内を通り，前記導波管（３）の途中に設けられた前記Ｅ−Ｈチューナ（４）を経由して前記導波管アンテナ（５）の先端の開口部（５ａ）から前記シリコンウェハ（６）に照射される。これにより，前記シリコンウェハ（６）表面の前記パルス光が照射された位置に，前記マイクロ波も照射される。そして，前記シリコンウェハ（６）からの反射マイクロ波は，前記導波管アンテナ（５）の開口部（５ａ）から前記導波管（５）内を通り，前記Ｅ−Ｈチューナ（４）を経由して前記サーキュレータ（２）に戻る。該サーキュレータ（２）に戻った前記反射マイクロ波の強度が，前記マイクロ波検出器（１０）によって検出され，検出値が前記計算機（１３）に取り込まれる。これにより，前記パルス光照射のときに前記マイクロ波を照射していれば，該マイクロ波の反射波の強度変化を前記計算機（１３）によって測定できる。通常は，前記マイクロ波を照射しながら前記パルス光を照射し，該パルス光照射直後の前記マイクロ波の反射波の強度変化を測定する。
【００１４】
本測定装置Ｘの特徴は，前記導波管アンテナ（５）の開口部（５ａ）付近に，高電圧を印加することによってコロナ放電する電極であるコロナワイヤ（９ａ）（前記第１の電極の一例）が設けられている点である。更に，前記シリコンウェハ（６）の前記マイクロ波が照射される部分の裏面に近接する位置にも，同様に高電圧の印加でコロナ放電する別のコロナワイヤ（９ｂ）（前記第２の電極の一例）が設けられていることも特徴の１つである。前記コロナワイヤ９ａ，９ｂとしては，例えば，線径０．１ｍｍのタングステンワイヤ等を用いればよい。
図１（ｂ）は，前記導波管アンテナ（５）の先端の開口部（５ａ）を拡大して示した図である。前記導波管アンテナ（５）は，角型管であり，その開口部（５ａ）の対向する２つの面それぞれの一部が切り欠かれ，該切り欠かれた部分それぞれに所定の絶縁体（５ｂ）が設けられている。そして，前記コロナワイヤ（９ａ）は，対向する２つの前記絶縁体（５ｂ）に渡らせて前記開口部（５ａ）の中央を横断するように取り付けられている（図１（ｂ）には，前記絶縁体（５ｂ）の一方のみが図示されている）。また，前記コロナワイヤ（９ａ）は，接続線（５ｃ）により，前記高圧電源（１１）に接続される。これにより，前記コロナワイヤ（９ａ）と前記導波管アンテナ（５）とが絶縁される。裏面側の前記コロナワイヤ（９ｂ）も，同様に，所定の取り付け部材（２３）と絶縁して取り付けられている。
また，前記パルスレーザ（１２）によるパルス光は，ビームスプリッタ（２２）により分岐され，前記透明電極（７）を介して前記シリコンウェハ（６）表面の前記マイクロ波が照射される位置とは別の位置にも照射され，該照射によって前記シリコンウェハ（６）に発生する光電圧を前記透明電極（７）によって検出し，該光電圧の検出値が前記増幅器を介して前記計算機（１３）に取り込まれる。これにより，前記シリコンウェハ（６）に発生する前記光電圧が前記計算機（１３）によって測定される。ここで，前記パルスレーザ（１２）及び前記ビームスプリッタ（２２）が前記光照射手段の一例，前記透明電極（７），前記増幅器（８），及び前記計算機（１３）が前記光電圧測定手段の一例である。
【００１５】
次に，本測定装置Ｘの動作について説明する。
まず，前記パルスレーザ（１２）により前記シリコンウェハ（６）表面に前記パルス光を照射する。これにより，前記シリコンウェハ（６）における前記パルス光を照射した部分が励起される。このとき，前記ビームスプリッタ（２２）による前記パルス光の分岐光も前記シリコンウェハ（６）表面に照射され，前記分岐光により前記シリコンウェハ（６）表面に発生した前記光電圧を前記透明電極（７）を介して前記計算機（１３）により測定する。
次に，前記計算機（１３）により，前記光電圧の極性に基づいて前記高圧電源（１１）による前記コロナワイヤ（９ａ，９ｂ）への印加電圧の極性が設定される（前記極性設定手段の一例）。
さらに，前記マイクロ波発振器（１）により前記シリコンウェハ（６）表面に前記マイクロ波を照射するとともに，前記コロナワイヤ（９ａ，９ｂ）に前記高電圧電源（１１）によって高電圧を印加しながら，前記反射マイクロ波の強度変化を前記計算機（１３）によって測定する。
【００１６】
図２（ａ１），（ｂ１）は，前記計算機（１３）により測定された前記反射マイクロ波の強度変化を表すグラフであり，縦軸が前記マイクロ波の強度，横軸が時間軸を表す。ここで，太い実線で示すグラフｇａ１，ｇｂ１は，前記コロナワイヤ（９ａ，９ｂ）に＋４ｋＶを印加した場合を表し，細い実線で表すグラフｇａ２，ｇｂ２は，同−４ｋＶを印加した場合，破線で表すグラフｇａ３，ｇｂ３は，電圧を印加しない（印加電圧＝０Ｖ）場合をそれぞれ表す。
また，図２（ａ２），（ｂ２）は，同じく前記ウェハ（６）表面の前記光電圧のグラフであり，縦軸が前記光電圧，横軸が時間軸を表す。
また，図２（ａ１），（ａ２）は，測定した前記シリコンウェハ（６）が，Ｎ型半導体である場合であり，図２（ｂ１）（ｂ２）は，同Ｐ型半導体である場合である。
図２（ａ１）に示すＮ型半導体のグラフｇａ３に示すように，前記コロナワイヤ（９ａ，９ｂ）に電圧を印加しない場合には，前記パルス光照射直後に生じる前記反射マイクロ波の強度のピークが低く，ごく短時間で元のレベルへ戻ってしまう。これは，マイクロ波照射により生じた励起キャリアが，通常の半導体内部の再結合により消失するのにくわえ，前記表面結合により急速に消失するためである。このように，前記表面結合が急速に進行する状態では正確に半導体キャリアの寿命を測定できない。これは，図２（ｂ１）に示すＰ型半導体のグラフｇｂ３（印加電圧＝０Ｖ）においても同様である。
これに対し，グラフｇａ１に示すように，Ｎ型半導体において前記コロナワイヤ（９ａ，９ｂ）に＋４ｋＶを印加した場合には，前記パルス光照射直後に生じる前記反射マイクロ波の強度にピークが高く，その後，徐々に強度が低下していく。これは，これは，前記コロナワイヤ（９ａ，９ｂ）に電圧を印加した場合，これがコロナ放電して発生したイオンが前記シリコンウェハ（６）表面に付着し帯電するため，励起キャリアの前記表面再結合が抑制されるためである。半導体キャリアの寿命は，前記反射マイクロ波のピーク時の値が，その１／ｅの値になるまでの時間（いわゆる時定数）に基づいて求められる。
このように，前記シリコンウェハ（６）に近接する位置でコロナ放電を行いながら前記反射マイクロ波を測定することにより，事前の加熱処理工程を設ける等の余分な手間や時間を要することなく前記表面再結合を抑制することができる。さらに，前記コロナワイヤ（９ａ）が前記導波管アンテナ（５）（前記導波管（３）の一部）の先端部分（前記シリコンウェハ（６）に近接する部分）に設けられるので，発生したイオンが前記マイクロ波の照射部以外に逃げないように集中させることができ，前記マイクロ波の照射部を効率的に帯電させることができる。しかも，前記導波管アンテナ（５）は，前記マイクロ波照射に必要なものであり，これを前記コロナワイヤ（９ａ）の取り付け部材として兼用させることで構造がシンプルとなる。ここで，前記コロナワイヤ（９ａ）は，前記導波管アンテナ（５）の先端の近傍（即ち，前記シリコンウェハ（６）に近接する部分又はその近傍）であれば，他の位置に，或いは他の構造で取り付けてもかまわない。もちろん，前記導波管アンテナ（５）以外により支持する構造としてもかまわない。また，前記シリコンウェハ（６）の一方の面のみでコロナ放電を行っても前記表面結合を抑制する効果はあるが，本実施の形態のように表裏両面で行ったほうがより効果的である。
【００１７】
一方，図２（ａ１）のグラフｇａ２に示すように，Ｎ型半導体において前記コロナワイヤ（９ａ，９ｂ）に−４ｋＶを印加した場合には，前記パルス光照射直後に生じる前記反射マイクロ波の強度のピークは，電圧印加を行わない場合よりは高いが，＋４ｋＶを印加した場合よりも低い。
これに対し，図２（ｂ１）のグラフｇｂ１，ｇｂ２に示すように，Ｐ型半導体においては，前記コロナワイヤ（９ａ，９ｂ）に＋４ｋＶを印加した場合（ｇｂ１）よりも，−４ｋＶを印加した場合の方が，前記パルス光照射直後に生じる前記反射マイクロ波の強度のピークは高い，即ち，前記表面再結合の抑制効果が高い。これは，前記コロナワイヤ（９ａ，９ｂ）への印加電圧の極性は，測定対象となる半導体の少数キャリアを表面から遠ざける働きを有する極性とする方が，前記表面再結合の抑制効果が高いことを示している。そこで，図２（ａ２），（ｂ２）に示すように，前記シリコンウェハ（６）表面で発生する前記光電圧が，Ｎ型とＰ型とで逆極性であることを利用し，前記光電圧に基づいて前記コロナワイヤ（９ａ，９ｂ）への印加電圧の極性を設定する。これにより，より効果的に前記表面再結合を抑制できる。
【００１８】
ところで，図２に示したグラフは，前記コロナワイヤ（９ａ，９ｂ）のコロナ放電による前記表面再結合の抑制は，前記シリコンウェハ（６）の表面に自然酸化膜を有する場合のものであるが，薬品洗浄等によって前記シリコンウェハ（６）表面の自然酸化膜が除去された直後には，コロナ放電による帯電効果が弱く，前記表面再結合の抑制効果も下がる。
図３は，洗浄した後に大気中に放置した前記シリコンウェハ（６）を，本測定装置Ｘを用いて，所定の経過時間ごと（洗浄直後，２時間後，１日後，２日後，３日後，４日後，７日後）にそのシリコンウェハ（６）について半導体キャリアの寿命を測定したデータの表である。ここで，表の上段は，洗浄後の前記シリコンウェハ（６）をそのまま大気中に放置した場合のデータであり，下段は，洗浄後の前記シリコンウェハ（６）を温度７０℃に加熱した過酸化水素水（濃度５０％）に２時間浸漬させる酸化工程を経た後に，大気中に放置した場合のデータである。ここで，測定対象とした前記シリコンウェハ（６）の半導体キャリアの寿命は，５９０〜６１０μｓ程度であるものとする。
【００１９】
図３からわかるように，洗浄後の前記シリコンウェハ（６）をそのまま放置した場合，適正な測定結果が得られるまでに洗浄後４日以上の経過が必要であることがわかる。
一方，前記過酸化水素水に浸漬させた場合には，洗浄から２時間後には，適正な測定結果が得られており，７日経過時点でもその効果は持続している。
このように，前記過酸化水素水への浸漬により，測定対象となる半導体表面の酸化膜が薬品洗浄等により除去された場合であっても，非常に短時間のうちに本発明に係る半導体キャリアの寿命予測装置及び方法を適用することが可能となる。また，７０℃程度の過酸化水素水への浸漬では，半導体自体の性能劣化の問題もない。
【００２０】
一方，図４（ａ），（ｂ）は，ＨＦ洗浄した直後のＰ型の前記シリコンウェハ（６）と，ＨＦ洗浄後にオゾンに接触させる酸化工程を経た後のＰ型の前記シリコンウェハ（６）とのそれぞれについて，本測定装置Ｘを用いて，前記計算機（１３）により測定された前記反射マイクロ波の強度変化を表すグラフであり，縦軸が前記マイクロ波の強度，横軸が時間軸を表す。
ここで用いた，オゾンに接触させる酸化工程は，オゾン水（濃度１５ｍｇ／ｌ）に３０分間浸漬させる工程である。
図４（ａ），（ｂ）の比較からわかるように，ＨＦ洗浄後は，ウェハ表面に絶縁層（酸化膜）が形成されていないため，コロナ放電で生成されたイオンはウェハ表面で帯電維持されず，ライフタイム測定値は，表面再結合の影響で実際よりも短くなる。これに対し，オゾン水への浸漬工程を経たウェハの表面には，酸化膜（絶縁膜）が形成されるため，表面再結合が抑止され，イオンがウェハ表面で維持される。その結果，ライフタイム測定値が長くなり，これは，ウェハのバルクライフタイムを反映することになる。
このように，ウェハ表面に酸化膜（絶縁膜）を形成するための酸化工程としては，前述した前記過酸化水素水に浸漬させる工程の他に，オゾンに接触させる工程も有効である。
表面結合を抑制するためのオゾン水への浸漬条件は，オゾン水の濃度，時間，温度の他，ウェハの特性（不純物濃度，ライフタイム等），表面状態（表面粗さ等）及びライフタイム測定に要求される精度にも依存するため，一律に定めることはできないが，このような酸化工程に要する時間や手間を考慮すると，濃度約１０ｍｇ／ｌ以下の常温のオゾン水に，２０分以上浸漬させることが好ましいと考えられる。もちろん，オゾン水への浸漬に限らず，例えば，オゾン水をウェハに対して噴霧する等の処理であってもよい。
【００２１】
【実施例】
前記半導体キャリアの寿命測定装置Ｘは，半導体に照射したマイクロ波の反射波を測定するものであったが，半導体に照射したマイクロ波の透過波を測定するものであってもよい。この場合，前記シリコンウェハ（６）の裏面側に，前記マイクロ波の透過波を導く導波管を設け，該導波管内で前記マイクロ波の透過波を測定するよう構成することが考えられる。
また，測定対象となる半導体表面の自然酸化膜が薬品洗浄等により除去されている場合の半導体の酸化工程としては，前述したオゾンへの接触や過酸化水素水への浸漬が好適であると考えられるが，この他にも，酸化プラズマの半導体への照射や，塩酸或いは硫酸中への半導体の浸漬，加熱水蒸気による半導体の加熱等の酸化工程，陽極酸化工程等も考えられる。
【００２２】
【発明の効果】
以上説明したように，本発明によれば，測定対象となる半導体に近接する位置でコロナ放電を行いながら，パルス光照射部分に照射した測定波の反射波又は透過波を測定することにより，測定中は半導体の測定波照射部分の帯電状態が維持され，事前の加熱処理工程を設ける等の余分な手間や時間を要することなく励起キャリアの表面再結合を抑制することができる。
更に，コロナ放電を行う電極が測定波を半導体表面に導く導波管の先端部分（半導体に近接する部分）又はその近傍に設けられるので，コロナ放電により発生したイオンを測定波の照射部以外に逃げないように集中させることができ，測定波の照射部を効率的に帯電させることができる。しかも，導波管は，測定波照射に必要なものであるため，これをコロナ放電用電極の取り付け部材として兼用すれば構造がシンプルとなる上，導波管がアースとなることでコロナ放電の安定化が図れる。。
また，半導体の測定波照射部分の表裏両面でコロナ放電を行えば，より効果的に励起キャリアの表面再結合を防止できる。
また，半導体表面に照射した光により発生する光電圧に基づいて，半導体がＮ型であるかＰ型であるかを判別し，これによりコロナ放電用電極に印加する電圧の極性を半導体の型（ＮｏｒＰ）に適した極性に設定すれば，より効果的に励起キャリアの表面再結合を抑制することができる。このように，励起キャリアの表面再結合が抑制されるので，精度よく半導体キャリアの寿命を測定できる。
そして，測定前に，予め前記半導体の表面を酸化する酸化工程，例えば，加熱した過酸化水素水中への前記半導体の浸漬工程等を行うことにより，半導体表面の自然酸化膜が薬品洗浄等によって除去されている場合でも，非常に短時間のうちに半導体表面に酸化膜を生成できので，短時間のうちに本発明を適用することが可能となる。
【図面の簡単な説明】
【図１】本発明の実施の形態に係る半導体キャリアの寿命測定装置Ｘの構成図。
【図２】本発明の実施の形態に係る半導体キャリアの寿命測定装置Ｘによりパルス光照射のときに照射したマイクロ波の反射波の強度変化の測定結果を表すグラフ。
【図３】本発明の実施の形態に係る半導体キャリアの寿命測定装置Ｘによる半導体キャリアの寿命測定値の経時変化を洗浄後半導体ウェハに対する酸化処理の有無で比較した表。
【図４】本発明の実施の形態に係る半導体キャリアの寿命測定装置Ｘにより洗浄直後のウェハと洗浄後にオゾンによる酸化工程を経た後のウェハとについてマイクロ波の反射波の強度変化の測定した結果を表すグラフ。
【符号の説明】
１…マイクロ波発振器
２…サーキュレータ
３…導波管
４…Ｅ−Ｈチューナ
５…導波管アンテナ（導波管の一部）
５ａ…導波管アンテナの先端の開口部
５ｂ…絶縁体
５ｃ…高圧電源への接続線
６…シリコンウェハ
７…透明電極
８…増幅器
９ａ，９ｂ…コロナワイヤ
１０…マイクロ波検出器
１１…高圧電源
１２…パルスレーザ
１３…計算機
２１…ミラー
２２…ビームスプリッタ
２３…コロナワイヤの取り付け部材[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an apparatus and a method for measuring the life of a semiconductor carrier used as an index of semiconductor material evaluation.
[0002]
[Prior art]
With the high integration of semiconductor devices, it has become important to control the material properties of semiconductors used in the devices. As an index of semiconductor material evaluation, there is a carrier lifetime (so-called lifetime) of a semiconductor, and as a measuring method, a microwave photoconductive decay method is widely used. This is because, by irradiating a semiconductor with pulsed light, photoexcited carriers (hereinafter referred to as "excited carriers") are generated in the semiconductor, and then the defects and contamination of the semiconductor material are reduced at a decreasing rate by the recombination of the excited carriers. It is a method of performing an evaluation. Specifically, the measurement of the rate of decrease of the excited carriers is performed by irradiating a portion of the irradiated portion of the pulsed light with a microwave as measurement light and measuring the intensity change of the reflected or transmitted wave to obtain the reflected or transmitted wave. The lifetime of the semiconductor carrier (the time until the excited carrier disappears by recombination) is measured from the time constant of the intensity change of the wave. The configuration of a general semiconductor carrier lifetime measuring apparatus based on the microwave photoconductive decay method is shown in FIG.
In general, crystalline irregularities exist on the surface of a semiconductor, which causes so-called surface recombination in which excited carriers recombine on the semiconductor surface. The surface recombination has an adverse effect on the value measured by the microwave photoconductive decay method, and it is necessary to prevent this. Normally, an oxide film is formed on the surface of a sample by prior heat treatment of a semiconductor to be measured, and the lifetime of the semiconductor carrier is measured after suppressing the occurrence of the surface recombination. However, performing the heat treatment step before the measurement requires a great deal of time and labor, and if the temperature is too high, the performance of the semiconductor itself may be deteriorated.
In order to solve this problem, Patent Document 1 discloses that a charge layer is generated on the entire semiconductor surface by corona discharge so that the surface recombination can be suppressed and then the lifetime of the semiconductor carrier is reduced by the microwave photoconductive decay method. A method for performing the measurement is shown.
[0003]
[Patent Document 1]
JP-A-7-240450
[0004]
[Problems to be solved by the invention]
However, under an insulating layer such as a natural oxide film formed on a semiconductor surface, a charge layer generated by corona discharge is easily discharged, and its charging effect does not last for a long time. For this reason, the method disclosed in Patent Document 1 has a problem that the surface recombination occurs during the measurement of the life of the semiconductor carrier, and the life of the semiconductor carrier cannot be accurately measured. Furthermore, there is a large restriction in the measurement process, such as no time interval between the corona discharge process (the process of charging the semiconductor surface) and the process of measuring the lifetime of the semiconductor carrier.
In addition, in order to maintain the charging effect by corona discharge, a step of forming an insulating layer on the semiconductor surface before measurement is required, and performing such a step before measurement requires time and effort. There was a point.
Therefore, the present invention has been made in view of the above circumstances, and its purpose is to minimize the performance deterioration of the semiconductor itself due to heating or the like and to require time and labor for performing an extra pre-processing step. It is an object of the present invention to provide an apparatus and a method for measuring the lifetime of a semiconductor carrier, which suppresses surface recombination of excited carriers without using the same.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a method for measuring the change in the reflected or transmitted wave of a predetermined measurement wave applied to a semiconductor when the semiconductor is irradiated with pulsed light, thereby extending the lifetime of the carrier of the semiconductor. In a device for measuring the life of a semiconductor carrier to be measured, a waveguide for guiding the measurement wave to the surface of the semiconductor and a portion of the waveguide close to the semiconductor or at or near the semiconductor, and at least a reflected wave of the measurement wave Alternatively, there is provided a semiconductor carrier lifetime measuring apparatus, comprising: a first electrode to which a predetermined voltage is applied during measurement of a change in a transmitted wave to perform corona discharge.
In this way, by measuring the reflected or transmitted wave of a measurement wave such as a microwave while performing corona discharge at a position close to the semiconductor to be measured, the charged state of the portion irradiated with the measurement wave of the semiconductor during measurement is measured. It is maintained, and the surface recombination of the excited carriers can be suppressed without requiring extra labor and time such as providing a preliminary heat treatment step.
[0006]
Also, a second voltage is provided in close proximity to the back surface of a portion of the semiconductor to which the measurement wave is irradiated, and a predetermined voltage is applied at least during measurement of a change in a reflected wave or a transmitted wave of the measurement wave to perform a corona discharge. It is also conceivable to provide an electrode having the above structure.
This is more effective because surface recombination on the back surface side of the semiconductor can also be suppressed.
[0007]
A light irradiating means for irradiating the surface of the semiconductor with predetermined light; a light voltage measuring means for measuring a light voltage generated in the semiconductor by light irradiation of the light irradiating means; a polarity of the measured light voltage; And a polarity setting means for setting the polarity of the voltage applied to the first electrode and / or the second electrode based on the above.
Thus, it is determined whether the semiconductor is N-type or P-type based on the light voltage generated by the light applied to the semiconductor surface, and the polarity of the voltage applied to the corona discharge electrode is determined by the type of the semiconductor. By setting the polarity suitable for (NorP), surface recombination of excited carriers can be more effectively suppressed.
[0008]
In the present invention, the measurement by the semiconductor carrier life measuring device may be regarded as a semiconductor carrier life measuring method.
That is, when the semiconductor is irradiated with pulsed light, a semiconductor carrier lifetime measuring method for measuring the lifetime of the semiconductor carrier by measuring a change in a reflected or transmitted wave of a predetermined measurement wave applied to the semiconductor. A predetermined voltage is applied to a portion of the waveguide that guides the measurement wave to the surface of the semiconductor near the semiconductor or to a first electrode provided near the semiconductor, and a corona discharge is performed while applying a predetermined voltage. This is a method for measuring the life of a semiconductor carrier, which measures a change in a reflected wave or a transmitted wave.
[0009]
In addition, a predetermined voltage is applied to a second electrode provided in proximity to a back surface of a portion of the semiconductor to which the measurement wave is irradiated, and a corona discharge is applied to the second electrode to generate a reflected or transmitted wave of the measurement wave. Is to measure change.
[0010]
Further, a light voltage generated in the semiconductor by irradiating the surface of the semiconductor with predetermined light is measured, and applied to the first electrode and / or the second electrode based on the measured polarity of the light voltage. This is to set the polarity of the applied voltage.
[0011]
The method may further include a predetermined oxidation step of oxidizing the surface of the semiconductor before the irradiation with the pulse light. The oxidizing step includes a step of contacting the semiconductor with ozone, a step of immersing the semiconductor in a heated hydrogen peroxide solution, a step of irradiating the semiconductor with oxidizing plasma, and a step of immersing the semiconductor in hydrochloric acid or sulfuric acid. And a step of heating the semiconductor with heated steam, an anodic oxidation step, and the like.
Examples of the step of contacting the semiconductor with ozone include a step of spraying ozone water on the semiconductor, a step of immersing the semiconductor in ozone water, and a step of directly spraying ozone on the semiconductor. Here, the conditions such as the concentration of ozone water used in the contact step with ozone, the temperature at the time of contact, the contact time, etc. cannot be determined uniformly, but depending on the surface condition of the semiconductor and the accuracy required for lifetime measurement, etc. Appropriate conditions may be set.
As a result, the natural oxide film on the semiconductor surface is removed by chemical cleaning or the like, so that the charging effect due to corona discharge is weakened. An oxide film is generated on the surface, and the present invention can be applied.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments and examples of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention. The following embodiments and examples are mere examples embodying the present invention, and do not limit the technical scope of the present invention.
Here, FIG. 1 is a configuration diagram of a semiconductor carrier lifetime measuring apparatus X according to an embodiment of the present invention, and FIG. FIG. 3 is a graph showing the measurement results of the intensity change of the reflected microwave of the irradiated microwave. FIG. 3 is a graph showing the change over time of the measured value of the lifetime of the semiconductor carrier by the semiconductor carrier lifetime measuring apparatus X according to the embodiment of the present invention. FIG. 4 shows a comparison between a wafer immediately after cleaning by a semiconductor carrier lifetime measuring apparatus X according to the embodiment of the present invention and a wafer after passing through an oxidation step using ozone after cleaning. It is a graph showing the measurement result of the intensity change of the reflected wave.
[0013]
First, the configuration of a semiconductor carrier lifetime measuring apparatus X (hereinafter, abbreviated as measuring apparatus X) according to an embodiment of the present invention will be described with reference to FIG. The present measuring device X is a device for measuring the life of a semiconductor carrier using a silicon wafer as a subject.
As shown in FIG. 1A, the measuring apparatus X includes a microwave oscillator (1), a circulator (2), a waveguide (3), an EH tuner (4), a transparent electrode (7), an amplifier. (8), a microwave detector (10), a high voltage power supply (11), a pulse laser (12), a computer (13) and the like.
The pulse light (wavelength: 523 nm, pulse width: 10 ns) emitted by the pulse laser (12) is introduced into a waveguide antenna (5) which is a straight tube portion at one end of the waveguide (5) by a mirror (21). The sample is guided and radiated from the opening (5a) to the surface of the silicon wafer (6) as the sample to be measured.
The microwave generated by the microwave oscillator (1) passes through the waveguide (3) via the circulator (2), and is provided in the middle of the waveguide (3). The silicon wafer (6) is irradiated from the opening (5a) at the tip of the waveguide antenna (5) via the EH tuner (4). Thereby, the microwave is also applied to the position on the surface of the silicon wafer (6) where the pulse light is applied. The reflected microwave from the silicon wafer (6) passes through the waveguide (5) from the opening (5a) of the waveguide antenna (5) and passes through the EH tuner (4). Then, the flow returns to the circulator (2). The intensity of the reflected microwave returned to the circulator (2) is detected by the microwave detector (10), and the detected value is taken into the computer (13). Thereby, if the microwave is irradiated at the time of the pulse light irradiation, the computer (13) can measure a change in the intensity of the reflected wave of the microwave. Usually, the pulse light is irradiated while irradiating the microwave, and the intensity change of the reflected wave of the microwave immediately after the pulse light irradiation is measured.
[0014]
The characteristic of the measuring apparatus X is that a corona wire (9a) (corresponding to the first electrode) is an electrode that performs a corona discharge by applying a high voltage near the opening (5a) of the waveguide antenna (5). An example) is provided. Furthermore, another corona wire (9b) (corresponding to the second electrode), which similarly performs corona discharge by applying a high voltage, is also provided at a position near the back surface of the portion of the silicon wafer (6) where the microwave is irradiated. Is one of the features. As the corona wires 9a and 9b, for example, a tungsten wire having a wire diameter of 0.1 mm may be used.
FIG. 1B is an enlarged view of an opening (5a) at the tip of the waveguide antenna (5). The waveguide antenna (5) is a rectangular tube, and a part of each of two opposing surfaces of an opening (5a) is cut out, and a predetermined insulator ( 5b) is provided. The corona wire (9a) is attached so as to extend across two opposing insulators (5b) and to cross the center of the opening (5a). Only one of the insulators (5b) is shown). The corona wire (9a) is connected to the high-voltage power supply (11) by a connection line (5c). Thereby, the corona wire (9a) and the waveguide antenna (5) are insulated. Similarly, the corona wire (9b) on the back side is attached insulated from a predetermined attachment member (23).
The pulse light from the pulse laser (12) is split by a beam splitter (22), and is separated from a position on the surface of the silicon wafer (6) where the microwave is irradiated via the transparent electrode (7). And a light voltage generated on the silicon wafer (6) by the irradiation is detected by the transparent electrode (7), and the detected value of the light voltage is sent to the computer (13) via the amplifier. It is captured. Thereby, the light voltage generated on the silicon wafer (6) is measured by the computer (13). Here, the pulse laser (12) and the beam splitter (22) are examples of the light irradiating means, and the transparent electrode (7), the amplifier (8), and the calculator (13) are the light voltage measuring means. This is an example.
[0015]
Next, the operation of the measuring apparatus X will be described.
First, the surface of the silicon wafer (6) is irradiated with the pulse light by the pulse laser (12). This excites the portion of the silicon wafer (6) irradiated with the pulse light. At this time, the branch light of the pulse light by the beam splitter (22) is also applied to the surface of the silicon wafer (6), and the light voltage generated on the surface of the silicon wafer (6) by the branch light is converted to the transparent electrode ( It is measured by the computer (13) via 7).
Next, the polarity of the voltage applied to the corona wires (9a, 9b) by the high-voltage power supply (11) is set by the computer (13) based on the polarity of the light voltage (an example of the polarity setting means). ).
Further, while irradiating the microwave to the surface of the silicon wafer (6) by the microwave oscillator (1) and applying a high voltage to the corona wires (9a, 9b) by the high voltage power supply (11), The intensity change of the reflected microwave is measured by the computer (13).
[0016]
2 (a1) and 2 (b1) are graphs showing the change in the intensity of the reflected microwave measured by the computer (13), wherein the vertical axis represents the intensity of the microwave and the horizontal axis represents the time axis. Here, the graphs ga1 and gb1 shown by thick solid lines show the case where +4 kV is applied to the corona wires (9a and 9b), and the graphs ga2 and gb2 shown by thin solid lines show the cases where -4 kV is applied. Graphs ga3 and gb3 represent cases where no voltage is applied (applied voltage = 0 V), respectively.
2 (a2) and (b2) are graphs of the photovoltage on the surface of the wafer (6), wherein the vertical axis represents the photovoltage and the horizontal axis represents the time axis.
2 (a1) and (a2) show the case where the measured silicon wafer (6) is an N-type semiconductor, and FIGS. 2 (b1) and (b2) show the case where the measured silicon wafer (6) is the same P-type semiconductor. is there.
As shown in the graph ga3 of the N-type semiconductor shown in FIG. 2 (a1), when no voltage is applied to the corona wires (9a, 9b), the peak of the intensity of the reflected microwave generated immediately after the irradiation of the pulsed light. And return to the original level in a very short time. This is because the excited carriers generated by the microwave irradiation disappear quickly due to recombination inside the normal semiconductor and rapidly disappear due to the surface coupling. As described above, the life of the semiconductor carrier cannot be accurately measured in a state where the surface bonding proceeds rapidly. The same applies to the graph gb3 (applied voltage = 0 V) of the P-type semiconductor shown in FIG.
On the other hand, as shown in a graph ga1, when +4 kV is applied to the corona wires (9a, 9b) in the N-type semiconductor, the intensity of the reflected microwave generated immediately after the irradiation of the pulse light has a high peak, Thereafter, the strength gradually decreases. This is because, when a voltage is applied to the corona wires (9a, 9b), ions generated by the corona discharge adhere to the surface of the silicon wafer (6) and become charged, so that the surface of the excited carrier is recharged. This is because binding is suppressed. The lifetime of the semiconductor carrier is determined based on the time (so-called time constant) until the value at the peak of the reflected microwave reaches its value of 1 / e.
As described above, by measuring the reflected microwave while performing corona discharge at a position close to the silicon wafer (6), the surface of the surface can be reduced without requiring extra labor and time such as providing a preliminary heat treatment step. Recombination can be suppressed. Further, since the corona wire (9a) is provided at a tip portion (a portion close to the silicon wafer (6)) of the waveguide antenna (5) (a part of the waveguide (3)), generation of the corona wire (9a) occurs. The collected ions can be concentrated so as not to escape to portions other than the microwave irradiation portion, and the microwave irradiation portion can be charged efficiently. Moreover, the waveguide antenna (5) is necessary for the microwave irradiation, and the structure is simplified by using the waveguide antenna (5) as a mounting member for the corona wire (9a). Here, if the corona wire (9a) is near the tip of the waveguide antenna (5) (that is, at or near the silicon wafer (6)), it is located at another position or Other structures can be used. Needless to say, a structure supporting other than the waveguide antenna (5) may be used. In addition, although corona discharge is performed only on one surface of the silicon wafer (6), the surface bonding can be suppressed. However, it is more effective to perform corona discharge on both surfaces as in the present embodiment.
[0017]
On the other hand, as shown in a graph ga2 of FIG. 2 (a1), when -4 kV is applied to the corona wires (9a, 9b) in the N-type semiconductor, the intensity of the reflected microwave generated immediately after the irradiation of the pulsed light. Is higher than when no voltage is applied, but lower than when +4 kV is applied.
On the other hand, as shown in the graphs gb1 and gb2 in FIG. 2 (b1), in the case of the P-type semiconductor, −4 kV was applied to the corona wires (9a, 9b) compared to the case where +4 kV was applied (gb1). In the case, the peak of the intensity of the reflected microwave generated immediately after the irradiation of the pulse light is higher, that is, the effect of suppressing the surface recombination is higher. This is because the effect of suppressing the surface recombination is higher when the polarity of the voltage applied to the corona wires (9a, 9b) is such that the minority carrier of the semiconductor to be measured is moved away from the surface. Is shown. Therefore, as shown in FIGS. 2 (a2) and (b2), the optical voltage generated on the surface of the silicon wafer (6) has the opposite polarity between the N type and the P type, and The polarity of the voltage applied to the corona wires (9a, 9b) is set based on Thereby, the surface recombination can be suppressed more effectively.
[0018]
Meanwhile, in the graph shown in FIG. 2, the suppression of the surface recombination due to the corona discharge of the corona wires (9a, 9b) is performed when the silicon wafer (6) has a natural oxide film on its surface. Immediately after the natural oxide film on the surface of the silicon wafer (6) is removed by chemical cleaning or the like, the charging effect by corona discharge is weak, and the effect of suppressing the surface recombination is also reduced.
FIG. 3 shows that the silicon wafer (6) which has been washed and left in the air is measured at predetermined time intervals (immediately after cleaning, after 2 hours, after 1 day, after 2 days, after 3 days) using the measuring apparatus X. It is a table of the data which measured the life of the semiconductor carrier about the silicon wafer (6 days after 4 days, after 7 days). Here, the upper part of the table shows data when the silicon wafer (6) after cleaning is left in the air as it is, and the lower part shows the temperature when the silicon wafer (6) after cleaning is heated to 70 ° C. This is data obtained when the device is left in the air after an oxidation process of immersing it in hydrogen oxide water (concentration: 50%) for 2 hours. Here, it is assumed that the life of the semiconductor carrier of the silicon wafer (6) to be measured is about 590 to 610 μs.
[0019]
As can be seen from FIG. 3, when the silicon wafer (6) after the cleaning is left as it is, it is necessary to pass at least four days after the cleaning until an appropriate measurement result is obtained.
On the other hand, when immersed in the hydrogen peroxide solution, an appropriate measurement result was obtained two hours after the washing, and the effect was maintained even after seven days.
As described above, even if the oxide film on the semiconductor surface to be measured is removed by the chemical cleaning or the like by the immersion in the hydrogen peroxide solution, the semiconductor carrier according to the present invention can be obtained in a very short time. Can be applied. Further, immersion in a hydrogen peroxide solution at about 70 ° C. does not cause a problem of performance deterioration of the semiconductor itself.
[0020]
On the other hand, FIGS. 4 (a) and 4 (b) show the P-type silicon wafer (6) immediately after the HF cleaning and the P-type silicon wafer (6) after an oxidation step of contacting with ozone after the HF cleaning. ) Is a graph showing the intensity change of the reflected microwave measured by the calculator (13) using the present measuring apparatus X, the vertical axis being the intensity of the microwave, and the horizontal axis being the time axis. Represents
The oxidation step of contacting with ozone used here is a step of immersion in ozone water (concentration: 15 mg / l) for 30 minutes.
As can be seen from the comparison between FIGS. 4A and 4B, after the HF cleaning, since the insulating layer (oxide film) is not formed on the wafer surface, the ions generated by the corona discharge maintain the charge on the wafer surface. However, the measured lifetime is shorter than the actual value due to the effect of surface recombination. On the other hand, since an oxide film (insulating film) is formed on the surface of the wafer that has undergone the immersion step in ozone water, surface recombination is suppressed and ions are maintained on the wafer surface. As a result, the measured lifetime is increased, which reflects the bulk lifetime of the wafer.
As described above, as an oxidation step for forming an oxide film (insulating film) on the wafer surface, a step of contacting with ozone is also effective in addition to the above-described step of immersion in the hydrogen peroxide solution.
Conditions for immersion in ozone water to suppress surface bonding include ozone water concentration, time, temperature, wafer characteristics (impurity concentration, lifetime, etc.), surface condition (surface roughness, etc.) and lifetime measurement However, considering the time and labor required for such an oxidation step, it can be immersed in ozone water at a normal temperature of about 10 mg / l or less for 20 minutes or more. It is considered preferable to have Of course, the process is not limited to immersion in ozone water, but may be, for example, a process of spraying ozone water onto the wafer.
[0021]
【Example】
The semiconductor carrier lifetime measuring apparatus X measures a reflected wave of a microwave applied to a semiconductor, but may also measure a transmitted wave of a microwave applied to a semiconductor. In this case, it is conceivable that a waveguide for guiding the microwave transmission wave is provided on the back surface side of the silicon wafer (6), and the microwave transmission wave is measured in the waveguide.
In addition, when the natural oxide film on the surface of the semiconductor to be measured is removed by chemical cleaning or the like, the above-mentioned contact with ozone or immersion in hydrogen peroxide is considered to be suitable as the semiconductor oxidation step. However, in addition to this, an oxidizing process such as irradiation of the semiconductor with an oxidizing plasma, immersion of the semiconductor in hydrochloric acid or sulfuric acid, heating of the semiconductor with heated steam, and an anodic oxidation process are also conceivable.
[0022]
【The invention's effect】
As described above, according to the present invention, while performing corona discharge at a position close to a semiconductor to be measured, a reflected wave or a transmitted wave of a measurement wave applied to a pulsed light irradiation portion is measured, thereby performing measurement. During the measurement, the charged state of the portion irradiated with the measurement wave of the semiconductor is maintained, and the surface recombination of the excited carriers can be suppressed without requiring extra labor and time such as providing a preliminary heat treatment step.
In addition, since the corona discharge electrode is provided at or near the tip of the waveguide (a part close to the semiconductor) that guides the measurement wave to the semiconductor surface, the ions generated by the corona discharge can be applied to the part other than the part irradiated with the measurement wave. It is possible to concentrate so as not to escape, and it is possible to efficiently charge the irradiation part of the measurement wave. In addition, since the waveguide is necessary for the irradiation of the measurement wave, it can be used as a mounting member for the corona discharge electrode, which simplifies the structure. Stabilization can be achieved. .
Further, if corona discharge is performed on both the front and back surfaces of the portion of the semiconductor irradiated with the measurement wave, surface recombination of the excited carriers can be more effectively prevented.
Further, it is determined whether the semiconductor is N-type or P-type based on the light voltage generated by the light applied to the surface of the semiconductor, whereby the polarity of the voltage applied to the corona discharge electrode is determined by the type of semiconductor ( By setting the polarity suitable for (NorP), surface recombination of excited carriers can be suppressed more effectively. As described above, the surface recombination of the excited carriers is suppressed, so that the lifetime of the semiconductor carriers can be accurately measured.
Before the measurement, a natural oxide film on the semiconductor surface is removed by chemical cleaning or the like by performing an oxidation step of oxidizing the surface of the semiconductor in advance, for example, a step of immersing the semiconductor in a heated hydrogen peroxide solution. Even if it is performed, an oxide film can be formed on the semiconductor surface in a very short time, so that the present invention can be applied in a short time.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a semiconductor carrier lifetime measuring apparatus X according to an embodiment of the present invention.
FIG. 2 is a graph showing a measurement result of a change in intensity of a reflected wave of a microwave irradiated at the time of pulse light irradiation by the semiconductor carrier lifetime measuring apparatus X according to the embodiment of the present invention.
FIG. 3 is a table comparing the change over time of the measured value of the lifetime of the semiconductor carrier by the semiconductor carrier lifetime measuring apparatus X according to the embodiment of the present invention with and without the oxidation treatment of the semiconductor wafer after cleaning.
FIG. 4 shows the results of measuring the change in the intensity of the reflected microwaves of a wafer immediately after cleaning and a wafer that has undergone an oxidation step using ozone after cleaning using the semiconductor carrier lifetime measuring apparatus X according to the embodiment of the present invention. A graph representing.
[Explanation of symbols]
1. Microwave oscillator
2. Circulator
3. Waveguide
4: EH tuner
5. Waveguide antenna (part of waveguide)
5a: Opening at the tip of waveguide antenna
5b ... insulator
5c ... connection line to high voltage power supply
6. Silicon wafer
7 ... Transparent electrode
8 ... Amplifier
9a, 9b ... corona wire
10 ... Microwave detector
11 ... High voltage power supply
12 ... Pulse laser
13 ... Calculator
21 ... Mirror
22 ... Beam splitter
23 ... Corona wire mounting member
Claims (8)
前記測定波を前記半導体の表面へ導く導波管と，
前記導波管の前記半導体に近接する部分又はその近傍に設けられ，少なくとも前記測定波の反射波或いは透過波の変化の測定中に所定の電圧が印加されてコロナ放電する第１の電極と，
を具備してなることを特徴とする半導体キャリアの寿命測定装置。A semiconductor carrier lifetime measuring device for measuring the lifetime of the semiconductor carrier by measuring a change in a reflected or transmitted wave of a predetermined measurement wave applied to the semiconductor when the semiconductor is irradiated with pulsed light.
A waveguide for guiding the measurement wave to the surface of the semiconductor;
A first electrode provided at or near a portion of the waveguide close to the semiconductor and subjected to corona discharge by applying a predetermined voltage at least during measurement of a change in a reflected wave or a transmitted wave of the measurement wave;
An apparatus for measuring the life of a semiconductor carrier, comprising:
前記光照射手段の光照射により前記半導体に発生する光電圧を測定する光電圧測定手段と，
測定された前記光電圧の極性に基づいて前記第１の電極及び／又は第２の電極に印加する電圧の極性を設定する極性設定手段と，
を具備してなる請求項１又は２のいずれかに記載の半導体キャリアの寿命測定装置。Light irradiating means for irradiating predetermined light to the surface of the semiconductor;
Light voltage measurement means for measuring a light voltage generated in the semiconductor by light irradiation of the light irradiation means;
Polarity setting means for setting the polarity of the voltage applied to the first electrode and / or the second electrode based on the measured polarity of the light voltage;
The device for measuring the life of a semiconductor carrier according to claim 1, further comprising:
前記測定波を前記半導体の表面へ導く導波管の，前記半導体に近接する部分又はその近傍に設けられた第１の電極に，所定の電圧を印加してコロナ放電を行いながら前記測定波の反射波或いは透過波の変化を測定することを特徴とする半導体キャリアの寿命測定方法。A semiconductor carrier lifetime measurement method for measuring the lifetime of the semiconductor carrier by measuring a change in a reflected or transmitted wave of a predetermined measurement wave applied to the semiconductor when the semiconductor is irradiated with pulsed light.
A predetermined voltage is applied to a portion of the waveguide that guides the measurement wave to the surface of the semiconductor or a first electrode provided in the vicinity of the semiconductor or in the vicinity thereof, and a corona discharge is performed while applying a predetermined voltage. A method for measuring the lifetime of a semiconductor carrier, comprising measuring a change in a reflected wave or a transmitted wave.
測定した前記光電圧の極性に基づいて前記第１の電極及び／又は第２の電極に印加する電圧の極性を設定する請求項４又は５のいずれかに記載の半導体キャリアの寿命測定方法。Measuring a photovoltage generated in the semiconductor by irradiating a predetermined light on the surface of the semiconductor;
The method according to claim 4, wherein the polarity of the voltage applied to the first electrode and / or the second electrode is set based on the measured polarity of the photovoltage.
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