JP3776073B2 - Semiconductor carrier lifetime measurement method and apparatus - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は，半導体の材料評価のために行われる半導体キャリアの寿命測定方法及びその装置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（以下，励起光という）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，前記励起光を照射した部分に測定電磁波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，例えば，特許文献１の図７や特許文献２の図１等に示されている。
ここで，キャリア濃度の高い低抵抗の半導体や低抵抗基板を有するエピタキシャルウェハ，或いは非常にライフタイムが短い半導体材料では，光励起による反射マイクロ波の変化が小さいため，その観測波形から感度よく（正確に）ライフタイムを算出するためには，観測波形の信号対ノイズ比（Ｓ／Ｎ比）を高める必要がある。このため，従来，反射マイクロ波のＳ／Ｎ比を高めるために，前記励起光の強度を高めることによって反射マイクロ波の信号強度（変化の大きさ）を高めることや，反射マイクロ波の信号を加算平均化処理することによってノイズ低減を図る等のＳ／Ｎ比向上対策がとられていた。
【０００３】
【特許文献１】
特開平７−２４０４５０号公報
【特許文献２】
特公昭６１−６０５７６４号公報
【０００４】
【発明が解決しようとする課題】
しかしながら，半導体に照射する前記励起光の強度を高めることは，半導体の元々のキャリア状態（平衡状態）からキャリア分布を著しく変化させることになり，高密度励起によるキャリア拡散の影響等の非線形特性が現れること等により正確なライフタイム値が算出できない場合が生じるという問題点があった。さらに，前記励起光の強度を高めることは，アニール等により被測定試料（半導体）を改質（破壊）してしまう恐れがあるという問題点もあった。
また，加算平均化処理を適用すると，ライフタイム測定に長時間を要してしまう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，マイクロ波光伝導減衰法に基づく半導体キャリアの寿命測定において，被測定試料の改質や測定時間の延長を生じさせることなく，高感度で観測波（マイクロ波の反射波又は透過波）の変化を測定できる半導体キャリアの寿命測定方法及びその装置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おける，前記半導体の前記パルス光の照射部に照射した所定の測定電磁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方法において，前記半導体における前記パルス光の照射部近傍に配置した電気光学素子に所定の測定光を照射し，該測定光の反射光又は透過光の変化を検出し，その検出結果に基づいて前記半導体のキャリアの寿命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。
これにより，マイクロ波等の前記測定電磁波の反射波或いは透過波の強度変化に応じて前記電気光学素子の屈折率が変化し，該屈折率の変化に応じて前記電気光学素子に照射した前記測定光の特性が変化する。即ち，前記電気光学素子に照射した後の前記測定光（透過光や反射光）の変化が前記測定電磁波の反射波或いは透過波の強度変化を表すことになる。従って，前記電気光学素子に照射した後の前記測定光の変化を検出することにより，測定対象となる前記半導体のキャリアの寿命を測定できる。このように，前記測定電磁波の変化を電気的にではなく光学的に検出することによって，前記測定電磁波の微小な変化を高感度で検出することが可能となる。
【０００６】
また，前記測定光の前記反射光又は透過光の変化の検出としては，該反射光又は透過光の偏光度合いの変化を検出することや，位相の変化を検出すること等が考えられる。
例えば，前記測定光の前記反射光又は透過光の位相の変化を検出する方法としては，光干渉法により検出すること等が考えられる。ここで，光干渉法としては，例えば，マイケルソン型光干渉系又はファブリペロー光干渉系等を用いる方法が考えられる。
また，前記測定光の前記反射光又は透過光の偏光度合いを検出する方法としては，前記反射光又は透過光を偏光板に通過させた後の光強度を検出することが考えられる。
【０００７】
また，本発明は，前記半導体キャリアの寿命測定方法を具現する半導体キャリアの寿命測定装置として捉えたものであってもよい。
即ち，半導体にパルス光を照射したときにおける，前記半導体に照射した所定の測定電磁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，前記パルス光の照射部の近傍に配置される電気光学素子と，前記電気光学素子に所定の測定光を照射する測定光照射手段と，前記電気光学素子に照射された前記測定光の反射光又は透過光を検出する光検出手段と，前記光検出手段の検出結果に基づいて前記半導体のキャリアの寿命を測定する寿命測定手段と，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。
【０００８】
【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の構成を表すブロック図，図２は本発明の実施例に係る半導体キャリアの寿命測定装置Ｘ１の構成を表すブロック図，図３は本発明の実施例に係る半導体キャリアの寿命測定装置Ｘ２の構成を表すブロック図である。
【０００９】
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，シリコンウェハ等の半導体を被検体（被測定試料）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），導波管（２），Ｅ−Ｈチューナ（３），導波管アンテナ（４），電気光学効果を有する電気光学結晶（６），励起光用のパルスレーザ（７），ミラー（８），半波長板（９），測定光用のレーザ（１０），ビームスプリッタ（１１），偏光板（１２），光検出器（１３），アンプ（１４），検波器（１５），及び計算機（１６）等を具備している。前記電気光学結晶（６）（前記電気光学素子の一例，例えば，ＬｉＮｂ０3結晶等）は，前記導波管アンテナ（４）の先端部に設けられた開口（スロット（４ａ））に，その結晶軸が前記レーザ（１０）から照射される測定光（レーザ光）の光軸（Ｚ軸）と略一致するよう設けられている。
前記パルスレーザ（７）が発光する励起光であるパルス光（例えば，波長５２３ｎｍ，パルス幅１０ｎｓ）は，前記ミラー（８）で反射され，前記導波管アンテナ（４）の上部に設けられた開口４ｂと，先端（下部）に設けられたの開口（スロット（４ａ），図１（ｂ）参照）を通過して被測定試料５に照射される。ここで，前記導波管アンテナ（４）は，その先端が被測定試料（６）表面に近接するよう配置される。
一方，前記マイクロ波発振器（１）により出力される測定電磁波であるマイクロ波（例えば，周波数１０ＧＨｚ）は，前記導波管（２），前記Ｅ−Ｈチューナ（３），及び前記導波管アンテナ（４）を経由し，前記導波管アンテナ（４）の先端の開口（スロット（４ａ））から被測定試料（５）に照射される。これにより，被測定試料（５）表面の前記パルス光が照射された位置（以下，測定部位という）に，前記マイクロ波も照射される。
また，前記レーザ（１０）（例えば，波長６８０ｎｍ，出力１ｍＷ）から出力される測定光（レーザ光）は，前記ビームスプリッタ（１１）で反射され，前記半波長板（９），前記導波管アンテナ（４）上部の開口（４ｂ），前記導波管アンテナ（４）を通過し，前記導波管アンテナ（４）先端の開口（４ａ）に設けられた前記電気光学結晶（６）を透過して（一部は反射する）被測定試料（５）の前記測定部位に照射される。ここで，前記レーザ（１０）による前記測定光は，前記電気光学結晶（６）のＸ軸（又はＹ軸）に対して前記測定光の偏光方向が４５°入射となるよう前記半波長板（９）によって偏光方向が調節される。
前記測定部位に照射された前記測定光（前記レーザ（１０）によるレーザ光）は，被測定試料（５）表面で反射し，その反射光が，前記電気光学結晶（６）を再度透過した後，該電気光学結晶（６）表面での前記測定光の一部の反射光とともに前記導波管アンテナ（４），その上部の開口（４ａ），前記半波長板（９），前記ビームスプリッタ（１１）を通過し，さらに，前記偏光板（１２）を通過して前記光検出器（１３）に入射する。これにより，前記光検出器（１３）に入射される前記測定光の反射光の強度が，前記光検出器（１３）により電気信号に変換され，該電気信号が前記アンプ（１４）で増幅された後，前記検波器（１５）でＡ／Ｄ変換されて，前記計算機（１６）に取り込まれる。
【００１０】
次に，図１に示した本測定装置Ｘの作用について説明する。
前記パルスレーザ（７）による前記測定部位へパルス光（前記励起光）を照射すると，前記測定部位の半導体キャリアが励起され，前記測定部位に照射した前記マイクロ波（測定電磁波）の反射波の強度が変化し，これによって前記マイクロ波の反射波により前記測定部位近傍に生じる電界の電界強度が変化する。この電界強度の変化を感度よく測定できれば，前記測定部位の半導体キャリアの寿命を正確に測定できることになる。
ここで，電気光学効果を有する電気光学結晶（６）は，該電気光学結晶（６）に加わる（該電気光学結晶（６）のまわりの）電界強度の変化に応じてその屈折率が変化することは周知である。
本測定装置Ｘでは，誘電率の高い（例えば，比誘電率＞４０）前記電気光学結晶（６）が前記測定部位に近接するので，該測定部位に照射された前記マイクロ波により生じる電界が前記電気光学結晶（６）近傍に集中する。従って，この電気光学結晶（６）近傍（即ち，前記測定部位の近傍）に生じる電界の電界強度の微小な変化に応じて感度よく前記電気光学結晶（６）の屈折率が変化する。また，前記電気光学結晶（６）を透過或いは反射した前記測定光は，電気光学効果（屈折率の変化）により，元の前記測定光とは異なる偏光面を有することとなり，その偏光度合い（偏光面の角度）は，前記電気光学結晶（６）近傍の電界強度に応じて変わる。従って，前記偏光板（１２）を通過後の前記測定光の強度は，前記偏光度合いに対応したものとなる。即ち，前記偏光板（１２）を通過後の前記測定光の強度が，前記電気光学結晶（６）近傍（即ち，前記測定部位近傍）の電界強度を表すことになり，前記パルス光照射のときに前記マイクロ波及び前記測定光を照射していれば，前記光検出器（１３）で検出される信号強度の変化を前記計算機（１６）で測定することにより，被測定試料（５）における半導体キャリアの寿命を光学系を用いて高感度で測定することが可能となる。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に前記測定光を照射して該測定光の前記電気光学結晶（６）における反射波及び透過波の偏光度合いの変化を測定する。
また，前記電気光学結晶（６）を，例えば０．１ｍｍ角程度と微細なものとすることにより，微小な領域の前記電界強度の変化をより高感度で検出することができる。
【００１１】
【実施例】
前記半導体キャリアの寿命測定装置Ｘは，前記電気光学結晶（６）への前記測定光の透過光の偏光度合いの変化を検出するものであったが，これに限るものでなく，前記測定光の透過光の位相変化を検出するものも考えられる。
図２は，前記前記半導体キャリアの寿命測定装置Ｘにおける前記測定光の位相の変化を，マイケルソン型干渉系を用いて検出する実施例の１つである半導体キャリアの寿命測定装置Ｘ１（以下，測定装置Ｘ１という）の構成を表すブロック図である。本測定装置Ｘ１における前記励起光（前記パルス光）に関する構成は前記測定装置Ｘと同じである。
図２に示すように，半導体キャリアの寿命測定装置Ｘ１では，前記レーザ（１０）により出力された前記測定光（レーザ光）は，ビームスプリッタ（１７）によって分岐され，その一方の分岐光は，前記導波管アンテナ（４）上部の開口４（ａ），前記導波管アンテナ（４）を通過して前記電気光学結晶（６）に照射され，該電気光学結晶（６）を透過した後に，被測定試料（５）に反射して前記ビームスプリッタ（１７）へ戻ってくる（以下，この光を測定反射光という）。そして，もう一方の分岐光は，ミラー（１８）に反射されて前記ビームスプリッタ（１７）に戻ってくる（以下，この光を参照光という）。これにより，前記測定反射光と前記参照光とが合流して干渉が生じ，合流した光（以下，干渉光という）が前記光検出器（１３）に入射されてその強度が前記測定装置Ｘと同様に，前記アンプ（１４），前記検波器（１５）を介して前記計算機（１６）に入力される。前記レーザ（１０）から出力された前記測定光が前記干渉光となるまでの光学系がマイケルソン型干渉系を構成している。
このような構成とすることにより，前記電気光学結晶（６）の屈折率の変化によって，前記測定反射光の光路長が変化してその位相が変化するため，前記干渉光の強度が，前記電気光学結晶（６）の屈折率の変化に応じて変化する。従って，前記光検出器（１３）で検出される信号強度の変化（前記干渉光の強度変化）を前記計算機（１６）で測定することにより，被測定試料（５）における半導体キャリアの寿命を光学系を用いて高感度で測定することが可能となる。なお，図２には示していないが，前記測定反射光の位相変化が前記干渉光の強度変化として顕著に表れるように，前記測定反射光と前記参照光との光路差が微動位置決め制御機構によって調節される。
【００１２】
また，図３は，前記前記半導体キャリアの寿命測定装置Ｘにおける前記測定光の位相の変化を，ファブリペロー干渉系を用いて検出する実施例の１つである半導体キャリアの寿命測定装置Ｘ２（以下，測定装置Ｘ２という）の構成を表すブロック図である。本測定装置Ｘ２における前記励起光（前記パルス光）に関する構成は前記測定装置Ｘと同じである。
図３（ａ）に示すように，半導体キャリアの寿命測定装置Ｘ２では，前記レーザ（１０）により出力された前記測定光（レーザ光）は，前記ビームスプリッタ（１１）によって反射され，前記導波管アンテナ（４）上部の開口４（ａ），前記導波管アンテナ（４）を通過して前記電気光学結晶（６）に照射される。該電気光学結晶（６）で反射した前記測定光（前記測定光の反射光）は，前記ビームスプリッタ（１１）を通過して前記光検出器（１３）に入射され，その強度が前記測定装置Ｘと同様に，前記アンプ（１４），前記検波器（１５）を介して前記計算機（１６）に入力される。また，本測定装置Ｘ２は，前記光検出器（１３）の測定値に応じて前記レーザ（１０）の出力波長（前記測定光の波長）を調節する波長コントローラ２０を具備している。
また，前記電気光学結晶（６）の前記測定光の照射面（上面）及びその裏面（下面）には，特定の波長λｘ（以下，反射波長λｘという）の光に対して高反射率（〜９５％）を有する誘電膜６ａがコーティングされている（図３（ｂ）参照）。これにより，前記電気光学結晶（６）に照射された前記測定光の前記電気光学結晶（６）内における波長が，前記反射波長λｘに近づくにつれて，上下の前記誘電膜６ａの間で多重反射する比率（前記測定光が前記電気光学結晶（６）内部で留まる比率）が高くなる。その結果，図３（ｃ）に示すように，前記電気光学結晶（６）内での前記測定光の波長λａが前記反射波長λｘに近づくにつれて，前記光検出器（１３）に入射される光（多重干渉光）の強度（受光強度）は急激に低下することになる。この多重干渉光の強度の変化率（低下率）は，前記誘電膜６ａの反射率が高いほど急激となる。このように，前記レーザ（１０）から出力された前記測定光が前記誘電膜６ａによって前記多重干渉光となるまでの光学系がファブリペロー干渉系を構成している。
【００１３】
ここで，前記電気光学結晶（６）内での前記測定光の波長λａは，前記電気光学結晶（６）の屈折率の変化によって微小変化する（位相も微小変化する）。従って，前記パルス光（前記励起光）の照射直後において，前記波長コントローラ２０により，記レーザ（１０）の出力波長（前記測定光の波長）の変化（即ち，前記電気光学結晶（６）内での前記測定光の波長λａの変化）に対して前記光検出器（１３）の検出値の変化が顕著（急激）となるように前記レーザ（１０）の出力波長（前記測定光の波長）を設定すれば，前記電気光学結晶（６）の屈折率のわずかな変化（即ち，前記測定光の波長λａ（或いは位相）のわずかな変化）に対して前記光検出器（１３）の検出値が大きく変化することとなり，感度よく前記電気光学結晶（６）の屈折率の変化（即ち，前記マイクロ波の反射波の強度の変化）を検出することが可能となる。従って，前記光検出器（１３）で検出される信号強度の変化（前記多重干渉光の強度変化）を前記計算機（１６）で測定することにより，被測定試料（５）における半導体キャリアの寿命を光学系を用いて高感度で測定することが可能となる。
前記波長コントローラ２０による前記測定光の波長設定は，例えば，前記パルス光（前記励起光）の照射直後において，記レーザ（１０）の出力波長（前記測定光の波長）を変化させたときに，前記光検出器（１３）の検出値（受光強度）が，その最大値ＶＨと最小値ＶＬとの略中間値（図３（ｂ）に黒丸印で示す点の値）となる波長に設定すること等が考えられる。
【００１４】
また，前記測定装置Ｘ，Ｘ１，Ｘ２は，半導体に照射したマイクロ波の反射波の強度変化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の強度変化を測定するものであってもよい。この場合，被測定試料（６）における前記測定部位の裏面側に，前記電気光学結晶（６）及び前記測定光による測定系を配置すればよい。
また，前記測定装置Ｘ，Ｘ１，Ｘ２では，マイクロ波の導波手段として前記導波管（３）及び前記導波管アンテナ４（導波管によるスロットアンテナ）を用いたが，同軸ケーブルやストリップ線路等を導波手段として用い，ループアンテナや平面アンテナ等をアンテナとして用いる等，種々のマイクロ波放射系を適用することも考えられる。
【００１５】
また，前記測定装置Ｘ，Ｘ１，Ｘ２では，前記測定光としてレーザ光（連続波）を用いたが，パルスレーザを用いてもよい。特に，マイクロ波の周期に比べてパルス幅の短いパルスレーザ光を前記測定光として用いれば，前記光検出器として前記マイクロ波の周波数の帯域を有する高速応答の（高価な）検出器を用いることなく前記測定電磁波の検出を行うことが可能となる。
即ち，前記マイクロ波の反射波の強度は，前記マイクロ波の発振周期と同周期で変動するので，例えば，前記マイクロ波の周波数が１０ＧＨｚである場合，前記光検出器（１３）で検出される前記測定光の強度は，０．１ｎｓの周期で変化することになる。一方，通常の（安価な）前記光検出器（光電変換器）の応答性は１ｎｓ程度であるため，前記レーザ光を連続照射しながらでは前記測定光の強度は測定できない。そこで，分周回路等によって生成された同期信号（前記マイクロ波の周期に同期した信号）を前記測定光出力用のパルスレーザに入力することにより，前記マイクロ波の周期に同期したパルス光（例えば，パルス幅１ｐｓ以下）を前記電気光学結晶（６）に照射する。これにより，前記光検出器（１３）により検出される光は，前記マイクロ波が一定の強度となっている瞬時のタイミングで前記電気光学結晶（６）に反射及び透過した光となるので，前記電気光学結晶（６）の屈折率の変化を測定できる。
【００１６】
【発明の効果】
以上説明したように，本発明によれば，マイクロ波光伝導減衰法に基く半導体キャリアの寿命測定において，測定部位のマイクロ波の強度を検出するための検出端が電気光学結晶であるので，これを微細にすることにより，非常に高感度で半導体キャリアの寿命測定を行うことができる。また，励起光（パルス光）の強度を上げたり，検出信号の加算平均化処理を行ったりする必要がないので，被測定試料の改質や測定時間の延長を生じさせることもない。
【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。
【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]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor carrier lifetime measuring method and apparatus for performing semiconductor material evaluation.
[0002]
[Prior art]
As semiconductor devices are highly integrated, it is important to manage the material properties of the semiconductors used in the devices. Semiconductor carrier lifetime (so-called lifetime) is an index of semiconductor material evaluation, and the microwave photoconductive decay method is widely used as the measurement method. This is because the semiconductor is irradiated with pulsed light (hereinafter referred to as pumping light) to generate photoexcited carriers (hereinafter referred to as pumped carriers) in the semiconductor, and then the rate of decrease is reduced by recombination of the excited carriers. This is a method for evaluating defects and contamination of semiconductor materials. Specifically, the reduction rate of the excited carrier is measured by irradiating the portion irradiated with the excitation light with microwaves as a measurement electromagnetic wave, and measuring the intensity change of the reflected wave or transmitted wave, thereby measuring the reflected wave or The lifetime of the semiconductor carrier (the time until the excited carriers disappear due to recombination) is measured from the time constant of the intensity change of the transmitted wave. The configuration of a general semiconductor carrier lifetime measuring apparatus based on this microwave photoconductive decay method is shown in FIG. 7 of
Here, in the case of an epitaxial wafer having a low-resistance semiconductor with a high carrier concentration, a low-resistance substrate, or a semiconductor material having a very short lifetime, the change in reflected microwave due to photoexcitation is small. In order to calculate the lifetime, it is necessary to increase the signal-to-noise ratio (S / N ratio) of the observed waveform. Therefore, conventionally, in order to increase the S / N ratio of the reflected microwave, the intensity of the reflected light is increased by increasing the intensity of the excitation light, or the reflected microwave signal is increased. Measures have been taken to improve the S / N ratio, such as reducing noise by performing an averaging process.
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 7-240450 [Patent Document 2]
Japanese Patent Publication No. 61-605764 [0004]
[Problems to be solved by the invention]
However, increasing the intensity of the excitation light that irradiates the semiconductor significantly changes the carrier distribution from the original carrier state (equilibrium state) of the semiconductor, and nonlinear characteristics such as the influence of carrier diffusion due to high-density excitation are present. There is a problem that an accurate lifetime value cannot be calculated due to the appearance. Furthermore, increasing the intensity of the excitation light has a problem that the sample to be measured (semiconductor) may be modified (destroyed) by annealing or the like.
In addition, when the averaging process is applied, it takes a long time to measure the lifetime.
Therefore, the present invention has been made in view of the above circumstances, and the object of the present invention is to modify the sample to be measured and extend the measurement time in measuring the lifetime of a semiconductor carrier based on the microwave photoconductive decay method. An object of the present invention is to provide a semiconductor carrier lifetime measurement method and apparatus capable of measuring changes in observation waves (microwave reflected waves or transmitted waves) with high sensitivity.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the present invention measures the change in the reflected wave or transmitted wave of a predetermined measurement electromagnetic wave irradiated to the pulsed light irradiation part of the semiconductor when the semiconductor is irradiated with the pulsed light. In the semiconductor carrier lifetime measurement method for measuring the lifetime of the semiconductor carrier, a predetermined measurement beam is irradiated to an electro-optic element disposed in the vicinity of the pulsed beam irradiation portion of the semiconductor, and the reflected or transmitted light of the measurement beam is transmitted. A semiconductor carrier lifetime measuring method, wherein a change in light is detected and the lifetime of the semiconductor carrier is measured based on the detection result.
As a result, the refractive index of the electro-optic element changes according to the intensity change of the reflected wave or transmitted wave of the measurement electromagnetic wave such as a microwave, and the measurement is performed when the electro-optic element is irradiated according to the change of the refractive index. The light characteristics change. That is, a change in the measurement light (transmitted light or reflected light) after irradiating the electro-optical element represents a change in the intensity of the reflected wave or transmitted wave of the measurement electromagnetic wave. Accordingly, the lifetime of the semiconductor carrier to be measured can be measured by detecting a change in the measurement light after irradiating the electro-optic element. Thus, by detecting the change of the measurement electromagnetic wave optically rather than electrically, it becomes possible to detect the minute change of the measurement electromagnetic wave with high sensitivity.
[0006]
Further, as the detection of the change in the reflected light or transmitted light of the measurement light, it is conceivable to detect a change in the degree of polarization of the reflected light or transmitted light, or to detect a change in phase.
For example, as a method of detecting a change in the phase of the reflected light or transmitted light of the measurement light, detection by an optical interferometry or the like can be considered. Here, as the optical interference method, for example, a method using a Michelson type optical interference system or a Fabry-Perot optical interference system can be considered.
Further, as a method for detecting the degree of polarization of the reflected light or transmitted light of the measurement light, it is conceivable to detect the light intensity after passing the reflected light or transmitted light through a polarizing plate.
[0007]
Further, the present invention may be a semiconductor carrier lifetime measuring apparatus that embodies the semiconductor carrier lifetime measuring method.
That is, in a semiconductor carrier lifetime measuring apparatus for measuring the lifetime of a semiconductor carrier by measuring a change in a reflected wave or transmitted wave of a predetermined measurement electromagnetic wave irradiated on the semiconductor when the semiconductor is irradiated with pulsed light. , An electro-optical element disposed in the vicinity of the pulsed light irradiation unit, measurement light irradiation means for irradiating the electro-optical element with predetermined measurement light, and reflected light of the measurement light irradiated on the electro-optical element Alternatively , a semiconductor carrier lifetime measurement comprising: a light detection means for detecting transmitted light; and a lifetime measurement means for measuring the lifetime of the semiconductor carrier based on a detection result of the light detection means. Device.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments and examples of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. It should be noted that the following embodiments and examples are examples embodying the present invention, and do not limit the technical scope of the present invention.
FIG. 1 is a block diagram showing the configuration of the semiconductor carrier lifetime measuring apparatus X according to the embodiment of the present invention. FIG. 2 is a block diagram showing the configuration of the semiconductor carrier lifetime measuring apparatus X1 according to the embodiment of the present invention. FIG. 3 is a block diagram showing the configuration of the semiconductor carrier lifetime measuring apparatus X2 according to the embodiment of the present invention.
[0009]
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. This measuring apparatus X is a semiconductor carrier lifetime measuring apparatus using a semiconductor such as a silicon wafer as an object (sample to be measured).
As shown in FIG. 1 (a), this measurement apparatus X has a microwave oscillator (1), a waveguide (2), an E-H tuner (3), a waveguide antenna (4), and an electro-optic effect. Electro-optic crystal (6), pulse laser (7) for excitation light, mirror (8), half-wave plate (9), laser for measurement light (10), beam splitter (11), polarizing plate (12) , A photodetector (13), an amplifier (14), a detector (15), a calculator (16), and the like. The electro-optic crystal (6) (an example of the electro-optic element, such as a LiNbO 3 crystal) is crystallized in an opening (slot (4a)) provided at the tip of the waveguide antenna (4). The axis is provided so as to substantially coincide with the optical axis (Z axis) of measurement light (laser light) emitted from the laser (10).
Pulse light (for example, wavelength 523 nm,
On the other hand, a microwave (for example, a frequency of 10 GHz) which is a measurement electromagnetic wave output from the microwave oscillator (1) is transmitted to the waveguide (2), the EH tuner (3), and the waveguide antenna. The sample to be measured (5) is irradiated from the opening (slot (4a)) at the tip of the waveguide antenna (4) via (4). Thereby, the microwave is also irradiated to a position (hereinafter referred to as a measurement site) where the pulsed light is irradiated on the surface of the sample to be measured (5).
Further, measurement light (laser light) output from the laser (10) (for example, wavelength 680 nm,
The measurement light irradiated to the measurement site (laser light by the laser (10)) is reflected on the surface of the sample to be measured (5), and the reflected light passes through the electro-optic crystal (6) again. The waveguide antenna (4), the upper opening (4a), the half-wave plate (9), the beam splitter (with the reflected light of a part of the measurement light on the surface of the electro-optic crystal (6)) 11), and further passes through the polarizing plate (12) and enters the photodetector (13). Thereby, the intensity of the reflected light of the measurement light incident on the photodetector (13) is converted into an electrical signal by the photodetector (13), and the electrical signal is amplified by the amplifier (14). After that, it is A / D converted by the detector (15) and is taken into the computer (16).
[0010]
Next, the operation of the measurement apparatus X shown in FIG. 1 will be described.
When pulsed light (excitation light) is irradiated onto the measurement site by the pulse laser (7), the semiconductor carrier at the measurement site is excited, and the intensity of the reflected wave of the microwave (measurement electromagnetic wave) irradiated to the measurement site As a result, the electric field strength of the electric field generated in the vicinity of the measurement site is changed by the reflected wave of the microwave. If this change in electric field intensity can be measured with high sensitivity, the lifetime of the semiconductor carrier at the measurement site can be accurately measured.
Here, the refractive index of the electro-optic crystal (6) having the electro-optic effect changes in accordance with the change in the electric field strength (around the electro-optic crystal (6)) applied to the electro-optic crystal (6). This is well known.
In this measurement apparatus X, since the electro-optic crystal (6) having a high dielectric constant (for example, relative dielectric constant> 40) is close to the measurement site, the electric field generated by the microwave irradiated to the measurement site is Concentrates near the electro-optic crystal (6). Accordingly, the refractive index of the electro-optic crystal (6) changes with high sensitivity in accordance with a minute change in the electric field strength of the electric field generated in the vicinity of the electro-optic crystal (6) (that is, near the measurement site). Further, the measurement light transmitted or reflected by the electro-optic crystal (6) has a polarization plane different from that of the original measurement light due to the electro-optic effect (change in refractive index). The angle of the surface changes according to the electric field strength in the vicinity of the electro-optic crystal (6). Therefore, the intensity of the measurement light after passing through the polarizing plate (12) corresponds to the degree of polarization. That is, the intensity of the measurement light after passing through the polarizing plate (12) represents the electric field intensity in the vicinity of the electro-optic crystal (6) (that is, in the vicinity of the measurement site). If the microwave and the measurement light are irradiated, the change in signal intensity detected by the photodetector (13) is measured by the computer (16), so that the semiconductor in the sample to be measured (5) is measured. The lifetime of the carrier can be measured with high sensitivity using an optical system. Usually, the pulsed light is irradiated while irradiating the microwave, and the measurement light is irradiated immediately after the pulsed light irradiation, and the polarization degree of the reflected wave and the transmitted wave of the measurement light in the electro-optic crystal (6). Measure changes.
Further, by making the electro-optic crystal (6) as fine as, for example, about 0.1 mm square, the change in the electric field strength in a minute region can be detected with higher sensitivity.
[0011]
【Example】
The semiconductor carrier lifetime measuring device X detects a change in the degree of polarization of the transmitted light of the measurement light to the electro-optic crystal (6), but is not limited to this. A device that detects a phase change of transmitted light is also conceivable.
FIG. 2 shows a semiconductor carrier lifetime measuring apparatus X1 (hereinafter, referred to as a semiconductor carrier lifetime measuring apparatus X1), which is one example of detecting a change in phase of the measurement light in the semiconductor carrier lifetime measuring apparatus X using a Michelson interference system. It is a block diagram showing the structure of measurement apparatus X1). The configuration related to the excitation light (the pulsed light) in the measurement apparatus X1 is the same as that of the measurement apparatus X.
As shown in FIG. 2, in the semiconductor carrier lifetime measuring apparatus X1, the measurement light (laser light) output from the laser (10) is branched by a beam splitter (17), and one of the branched lights is After irradiating the electro-optic crystal (6) through the opening 4 (a) and the waveguide antenna (4) above the waveguide antenna (4) and passing through the electro-optic crystal (6) Then, the light is reflected by the sample to be measured (5) and returns to the beam splitter (17) (hereinafter, this light is referred to as measurement reflected light). The other branched light is reflected by the mirror (18) and returns to the beam splitter (17) (hereinafter, this light is referred to as reference light). Thereby, the measurement reflected light and the reference light are merged to generate interference, and the merged light (hereinafter referred to as interference light) is incident on the photodetector (13) and the intensity thereof is the same as that of the measurement device X. Similarly, it is input to the computer (16) via the amplifier (14) and the detector (15). The optical system until the measurement light output from the laser (10) becomes the interference light constitutes a Michelson interference system.
With such a configuration, the optical path length of the measurement reflected light changes and its phase changes due to the change in the refractive index of the electro-optic crystal (6). It changes according to the change of the refractive index of the optical crystal (6). Therefore, the lifetime of the semiconductor carrier in the sample to be measured (5) is optically measured by measuring the change in signal intensity (intensity change in the interference light) detected by the photodetector (13) with the calculator (16). It becomes possible to measure with high sensitivity using the system. Although not shown in FIG. 2, the optical path difference between the measurement reflected light and the reference light is determined by the fine positioning control mechanism so that the phase change of the measurement reflected light is remarkably expressed as the intensity change of the interference light. Adjusted.
[0012]
FIG. 3 shows a semiconductor carrier lifetime measuring apparatus X2 (hereinafter referred to as one example) that detects a change in phase of the measurement light in the semiconductor carrier lifetime measuring apparatus X using a Fabry-Perot interference system. , Measuring device X2). The configuration related to the excitation light (the pulsed light) in the measurement apparatus X2 is the same as that of the measurement apparatus X.
As shown in FIG. 3A, in the semiconductor carrier lifetime measuring apparatus X2, the measurement light (laser light) output from the laser (10) is reflected by the beam splitter (11) and is guided by the waveguide. The electro-optic crystal (6) is irradiated through the opening 4 (a) at the top of the tube antenna (4) and the waveguide antenna (4). The measurement light reflected by the electro-optic crystal (6) (reflected light of the measurement light) passes through the beam splitter (11) and is incident on the photodetector (13), and its intensity is measured by the measurement device. Similarly to X, the signal is input to the computer (16) via the amplifier (14) and the detector (15). The measurement apparatus X2 further includes a
Also, the measurement light irradiation surface (upper surface) and the back surface (lower surface) of the electro-optic crystal (6) have a high reflectance (˜˜) with respect to light having a specific wavelength λx (hereinafter referred to as a reflection wavelength λx). 95%) is coated with a dielectric film 6a (see FIG. 3B). As a result, multiple reflections occur between the upper and lower dielectric films 6a as the wavelength in the electro-optic crystal (6) of the measurement light irradiated to the electro-optic crystal (6) approaches the reflection wavelength λx. The ratio (the ratio at which the measurement light stays inside the electro-optic crystal (6)) increases. As a result, as shown in FIG. 3C, the light incident on the photodetector (13) as the wavelength λa of the measurement light in the electro-optic crystal (6) approaches the reflection wavelength λx. The intensity (received light intensity) of (multiple interference light) will drop sharply. The rate of change (decrease rate) in the intensity of the multiple interference light becomes steeper as the reflectance of the dielectric film 6a increases. Thus, the optical system until the measurement light outputted from the laser (10) becomes the multiple interference light by the dielectric film 6a constitutes a Fabry-Perot interference system.
[0013]
Here, the wavelength λa of the measurement light in the electro-optic crystal (6) is slightly changed (the phase is also minutely changed) due to a change in the refractive index of the electro-optic crystal (6). Therefore, immediately after the irradiation with the pulsed light (excitation light), the
The wavelength setting of the measurement light by the
[0014]
The measuring devices X, X1, and X2 measure the intensity change of the reflected wave of the microwave irradiated to the semiconductor, but measure the intensity change of the transmitted wave of the microwave irradiated to the semiconductor. There may be. In this case, the electro-optic crystal (6) and the measurement system using the measurement light may be arranged on the back side of the measurement site in the sample to be measured (6).
In the measuring devices X, X1, and X2, the waveguide (3) and the waveguide antenna 4 (slot antenna by a waveguide) are used as microwave guiding means. It is also conceivable to apply various microwave radiation systems such as using a line or the like as a waveguide means and using a loop antenna or a planar antenna as an antenna.
[0015]
In the measuring devices X, X1, and X2, laser light (continuous wave) is used as the measurement light, but a pulse laser may be used. In particular, if a pulsed laser beam having a pulse width shorter than the period of the microwave is used as the measurement light, a high-speed (expensive) detector having a frequency band of the microwave is used as the photodetector. Therefore, it is possible to detect the measurement electromagnetic wave.
That is, the intensity of the reflected wave of the microwave fluctuates in the same period as the oscillation period of the microwave. Therefore, for example, when the frequency of the microwave is 10 GHz, it is detected by the photodetector (13). The intensity of the measurement light changes with a period of 0.1 ns. On the other hand, since the response property of the normal (inexpensive) photodetector (photoelectric converter) is about 1 ns, the intensity of the measurement light cannot be measured while continuously irradiating the laser beam. Therefore, by inputting a synchronization signal (a signal synchronized with the period of the microwave) generated by a frequency dividing circuit or the like to the pulse laser for outputting the measurement light, a pulsed light synchronized with the period of the microwave (for example, , A pulse width of 1 ps or less) is applied to the electro-optic crystal (6). As a result, the light detected by the photodetector (13) becomes light reflected and transmitted to the electro-optic crystal (6) at the instant when the microwave has a constant intensity. The change in the refractive index of the electro-optic crystal (6) can be measured.
[0016]
【The invention's effect】
As described above, according to the present invention, in the lifetime measurement of a semiconductor carrier based on the microwave photoconductive decay method, the detection end for detecting the microwave intensity at the measurement site is an electro-optic crystal. By miniaturizing, it is possible to measure the lifetime of semiconductor carriers with very high sensitivity. Further, since it is not necessary to increase the intensity of the excitation light (pulse light) or to perform the averaging process of the detection signals, the sample to be measured is not modified or the measurement time is not extended.
[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 intensity change 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 changes over time in measured values of semiconductor carrier lifetime with a semiconductor carrier lifetime measuring apparatus X according to an embodiment of the present invention, based on whether or not an oxidation process is performed on a semiconductor wafer after cleaning.
[Explanation of symbols]
DESCRIPTION OF
5a ... Opening 5b at the tip of the waveguide antenna ... Insulator 5c ... Connection line 6 to high-voltage power supply ... Silicon wafer 7 ... Transparent electrode 8 ... Amplifiers 9a, 9b ...
Claims (5)
前記半導体における前記パルス光の照射部近傍に配置した電気光学素子に所定の測定光を照射し，該測定光の反射光又は透過光の変化を検出し，その検出結果に基づいて前記半導体のキャリアの寿命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 for measuring the lifetime of the semiconductor carrier by measuring a change in reflected wave or transmitted wave of a predetermined measurement electromagnetic wave irradiated to the pulsed light irradiation part of the semiconductor when the semiconductor is irradiated with pulsed light In the life measurement method of
A predetermined measurement light is irradiated to an electro-optic element disposed in the vicinity of the pulsed light irradiation portion in the semiconductor, a change in reflected light or transmitted light of the measurement light is detected, and the semiconductor carrier is detected based on the detection result. A method for measuring the lifetime of a semiconductor carrier, comprising measuring the lifetime of a semiconductor carrier.
前記パルス光の照射部の近傍に配置される電気光学素子と，
前記電気光学素子に所定の測定光を照射する測定光照射手段と，
前記電気光学素子に照射された前記測定光の反射光又は透過光を検出する光検出手段と，
前記光検出手段の検出結果に基づいて前記半導体のキャリアの寿命を測定する寿命測定手段と，
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。In a semiconductor carrier lifetime measuring apparatus for measuring the lifetime of a semiconductor carrier by measuring a change in a reflected wave or transmitted wave of a predetermined measurement electromagnetic wave irradiated on the semiconductor when the semiconductor is irradiated with pulsed light,
An electro-optic element disposed in the vicinity of the pulsed light irradiation unit;
Measuring light irradiation means for irradiating the electro-optic element with predetermined measuring light;
A light detecting means for detecting reflected light or transmitted light of the measurement light irradiated on the electro-optic element;
A lifetime measuring means for measuring the lifetime of the carrier of the semiconductor based on the detection result of the light detecting means;
An apparatus for measuring a lifetime of a semiconductor carrier comprising:
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| JP5100986B2 (en) * | 2005-07-14 | 2012-12-19 | 株式会社神戸製鋼所 | Semiconductor carrier lifetime measuring device, semiconductor carrier lifetime measuring method |
| JP5308395B2 (en) * | 2010-04-28 | 2013-10-09 | 株式会社神戸製鋼所 | Semiconductor carrier lifetime measuring apparatus and method |
| US9201096B2 (en) | 2010-09-08 | 2015-12-01 | Dcg Systems, Inc. | Laser-assisted device alteration using synchronized laser pulses |
| JP5917218B2 (en) * | 2012-03-19 | 2016-05-11 | 八光オートメーション株式会社 | Internal defect inspection apparatus and internal defect inspection method |
| SG10201609595UA (en) * | 2012-05-16 | 2017-01-27 | Dcg Systems Inc | Laser-assisted device alteration using synchronized laser pulses |
| CN102980661B (en) * | 2012-11-07 | 2014-12-10 | 中国计量科学研究院 | Standard optical-fiber source device with changeable degree of polarization |
| WO2014160618A1 (en) | 2013-03-24 | 2014-10-02 | Dcg Systems, Inc. | Pulsed lada for acquisition of timing diagrams |
| TWI619954B (en) * | 2014-10-16 | 2018-04-01 | Ｄｃｇ系統公司 | Systems and method for laser voltage imaging |
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| CN107192933B (en) * | 2017-05-10 | 2019-07-23 | 西安工业大学 | A kind of semiconductor material carrier useful life measurement method |
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