JP3965325B2

JP3965325B2 - Microstructure observation method and defect inspection apparatus

Info

Publication number: JP3965325B2
Application number: JP2002154896A
Authority: JP
Inventors: 啓志村
Original assignee: Hitachi High Technologies Corp
Current assignee: Hitachi High Tech Corp
Priority date: 2002-05-29
Filing date: 2002-05-29
Publication date: 2007-08-29
Anticipated expiration: 2022-05-29
Also published as: JP2003344306A

Description

【０００１】
【発明の属する技術分野】
本発明は、微細構造の観察方法、およびそれを実現する高分解能な顕微鏡の光学系、特に半導体製造工程やフラットパネルディスプレイの製造工程などにおいて微細パターンの欠陥および異物等の観察や検査に用いる高分解能光学系と、これを用いた欠陥検査装置に関する。
【０００２】
【従来の技術】
半導体製造工程やフラットパネルディスプレイの製造工程などにおいて、光学顕微鏡を用いた微細パターンの欠陥および異物等の観察や検査が行われている。近年、半導体デバイスの集積度の向上に伴い、顕微鏡光学系の高性能化が必要となってきた。
【０００３】
光学顕微鏡の分解能を上げる方法としては、結像に使用する光の波長の短波長化と、対物レンズの高開口数（ＮＡ）化，結像系の伝達関数（ＭＴＦ）の高域を持ち上げる超解像技術を用いる方法などがある。これらのうち、短波長化と高ＮＡ化は直接的な方法であるが、実用上はいずれについても様々な制約があり、実現できない場合がある。そこで、波長とＮＡを変えずに微細構造を高いコントラストで観察できる方法、すなわち結像系のＭＴＦの高域を持ち上げる超解像技術が注目されている。
【０００４】
超解像技術の一例として、偏光状態を制御することでＭＴＦを改善する方法が特開２０００−１５５０９９に示されている。直線偏光で試料を照明し、試料からの反射光をアナライザを通して結像系に導く方法と、楕円偏光で試料を照明し、試料からの反射光のうち偏光ビームスプリッタで反射された直線偏光成分のみを結像系に導く方法が示されている。前者では、試料上の直線状パターンの方向に対する試料を照明する直線偏光の方位とアナライザの方位を最適化することで、試料上のパターンによる高次回折光と０次光との光量比を調整している。０次光の光量を減らすことで高域のＭＴＦが改善されるとともに、パターンのある部分と無い部分の光量差を減らすことが可能になり、微細パターンが見やすくなり、また、観察像を用いた欠陥検査の性能を向上させることができる。照明系の結像系の光路の分離に無偏光ビームスプリッタを用いる必要があるため、光の利用効率が低く、像が暗くなるという欠点はあるが、試料での反射時の偏光の変化が顕著に現われるため、大きなＭＴＦ改善効果を得ることができる。後者の方法では、試料上の直線状パターンの方向に対する試料を照明する楕円偏光の方位と楕円率を最適化することで、同様のＭＴＦ改善効果が得られる。直線偏光照明を用いる系よりも光の利用効率を高くとることが可能で、明るい像を得ることができる。なお、この系では、直線偏光照明を実現することもできる。しかし、その場合には、試料からの反射光が結像系に戻らないため、ＭＴＦ改善効果が最も大きくなる直線偏光照明で像を観察することはできない。
【０００５】
この方法を実現する系の基本構成のうち後者の楕円偏光照明を用いる場合の例を図４および図５に示す。光源８からでた光は、凹面鏡とレンズ９を介して開口絞り１１に達し、さらにレンズと波長選択フィルタ１２，視野絞り１３を経て偏光ビームスプリッタ１５に入射する。偏光ビームスプリッタ１５を透過した直線偏光は、λを波長として、λ／２板１６，λ／４板１７を通って楕円偏光となり、対物レンズ２０によって試料１に照射される。λ／４板１７を回転させることによって楕円偏光の長軸の方向を制御し、λ／２板１６を回転させることによって楕円偏光の楕円率を制御することができる。試料１で反射された光は、対物レンズ２０，λ／４板１７，λ／２板１６を経て再び偏光ビームスプリッタ１５に入射し、ｓ偏光成分だけが反射され、結像レンズ３０とズームレンズ５０からなる結像系に導かれる。この系では、試料１を円偏光照明するように２枚の波長板の角度を決めた場合には、試料面で反射する際に偏光状態が変化しなかった成分だけが、偏光ビームスプリッタ１５で反射されて結像系に導かれる。
【０００６】
一方、試料１を楕円偏光照明するように２枚の波長板の角度を決めた場合には、試料１で反射する際に偏光状態が変化した成分の一部も偏光ビームスプリッタ１５で反射されて結像系に導かれる。一般的に直線状のパターンで回折された光は偏光状態が変化する場合があるが、０次光は変化しない。そこで、楕円偏光照明することによって回折光成分が強調され、結像系に導かれる。その結果、高域のＭＴＦが改善された像を得ることが可能になる。
【０００７】
【発明が解決しようとする課題】
従来例で説明した直線偏光照明や楕円偏光照明を用いる方法は、高域のＭＴＦを改善できる有効な方法である。しかし、大きなＭＴＦ改善効果を得るためには、試料上のパターンの方位によって照明光の偏光の方位を変える必要があり、条件設定が煩雑であるという問題点があった。また、試料上に方位の異なるパターンが混在する場合に、すべてのパターンについて同等のＭＴＦ改善効果を得ることが難しいという問題があった。これは、ＭＴＦの改善効果が等方的でなく、照明光の偏光方向と試料上のパターンの方向との関係に依存するからである。そこで、本発明の目的は、試料上のパターンの方向に依存せず高域でのＭＴＦ改善効果が得られる方法および装置を提供することにある。
【０００８】
また、楕円偏光照明を用いる方法は、光の利用効率が高く、かつＭＴＦ改善効果も得られる優れた方式ではあるが、直線偏光照明を用いる方法との共存が難しいという問題があった。直線偏光照明を用いる方法は、光の利用効率が低く像が暗くなるため、常用するには問題がある。しかし、楕円偏光照明の場合より大きなＭＴＦ改善効果が得られるため、必要な時には使用できることが望ましい。ところが、照明系の結像系の光路の分離に用いるビームスプリッタ等に求められる特性が異なるため、ひとつの光学系で両方を実現することが非常に困難である。そこで、本発明の他の目的は、必要に応じて照明光の偏光状態を直線偏光にも切り替えられるような光学系を実現することにある。
【０００９】
【課題を解決するための手段】
本発明の実施態様においては、試料に照明光を照射する照明手段と、照明された試料の像を結像させる結像手段と、前記試料の像を撮像する撮像手段と、取得された画像を予め記憶しておいた画像と比較して前記試料の欠陥を検出する欠陥検出手段と、該欠陥検出手段で検出した欠陥を表示する表示手段を備えた欠陥検査装置において、結像手段が、λを波長として対物レンズとλ／４板とλ／２板と、λ／４板とλ／２板とを個別に光路に対して出し入れする波長板切り替え手段と、部分偏光ビームスプリッタとアナライザと結像レンズを具備するものである。
【００１０】
試料上のパターンの方位によらずＭＴＦ改善効果をえるために、円偏光照明下でＭＴＦ改善効果を得る方法を提供する。具体的には、照明系と結像系の光路の分離に部分偏光ビームスプリッタを用い、これにλ／４板を加えて試料を円偏光で照明し、部分偏光ビームスプリッタ直後の結像系にアナライザを追加する。試料で反射された際に偏光が変化して生じた成分は、部分偏光ビームスプリッタにｐ偏光として入射するため、一部が反射されて結像系に導かれる。結像系のアナライザの方位を調整することで、この成分を必要な量だけ結像系に導くことが可能になり、ＭＴＦ改善効果を得ることが可能になる。さらに、本発明では、必要に応じて偏光ビームスプリッタとアナライザの間に位相補償板を追加する。部分偏光ビームスプリッタで反射されたｐ偏光成分とｓ偏光成分をアナライザで加算する際の互いの位相差を、位相補償板で調整することで、さらにＭＴＦ改善効果を大きくすることが可能になる。
【００１１】
また、本発明では、単一の光学系で簡単な切り替えによって、従来の楕円偏光照明系と上述の円偏光照明、もっとも大きなＭＴＦ改善効果が得られる直線偏光照明のすべてを実現する方法を提供する。具体的には、照明系と結像系の光路の分離に部分偏光ビームスプリッタを用い、これに個別に出し入れ可能にしたλ／２板とλ／４板を加えて試料を任意の偏光状態の光で照明し、部分偏光ビームスプリッタ直後の結像系にアナライザを追加する。従来の楕円偏光照明方式と互換の系を実現する場合には、部分偏光ビームスプリッタで反射された光のうちｓ偏光成分のみが結像系に導かれるようにアナライザの方位を設定する。それ以外の場合には、アナライザの方位を調整することでＭＴＦ改善効果の程度を調整することができる。さらに、直線偏光照明を用いた場合には、試料で反射された際に偏光が変化して生じた成分は、部分偏光ビームスプリッタにｓ偏光として入射するため、ほとんど全てが反射されて結像系に導かれる。この成分に関しては、無偏光ビームスプリッタを用いた場合と比べると、約２倍の効率で結像系に導かれるため、従来の直線偏光照明による方法よりさらに大きなＭＴＦ改善効果を得ることが可能になる。
【００１２】
【発明の実施の形態】
本発明の微細構造観察方法を用いた光学欠陥検査装置の実施例を図１に示す。円偏光照明を用いる例である。試料１はチャック２に真空吸着されており、このチャック２は、θステージ３，Ｚステージ４，Ｙステージ５，Ｘステージ６上に搭載されている。試料１の上方に配置されている光学系１１１は、試料１に形成されているパターンの外観検査を行うために試料１の光学像を撮像するものであり、主に照明光学系と試料１の像を作り撮像する結像光学系及び、焦点検出光学系４５で構成されている。照明光学系に配置された光源８はインコヒーレント光源であり、例えばキセノンランプである。
【００１３】
光源８からでた光は、レンズ９を介して開口絞り１１の開口部を透過し、さらにレンズと波長選択フィルタ１２を経て視野絞り１３に到達する。この波長選択フィルタ１２は試料１の分光反射率を考慮し、高解像度の試料１の像を検出するために照明波長域を限定するものであり、例えば干渉フィルタを配置する。視野絞り１３を透過した光は、光路分離部２１０に入射する。
【００１４】
光路分離部２１０は、部分偏光ビームスプリッタ２００（例えば、Ｔｐ：Ｒｐ＝６：４，Ｔｓ／Ｒｓ＜０.０５)とλ／４板１７，位相補償板２２０，アナライザ２２から構成されており、光源８から試料１に向かう照明光の光路と試料１から撮像素子へ向かう光路を分離する。その機能は図２に示す。光路分離部２１０に入射した照明光（ランダム偏光）は、部分偏光ビームスプリッタ２００を透過率Ｔｐ(〜０.６）だけ透過してｐ偏光の直線偏光となる。さらにλ／４板１７によって円偏光となって対物レンズ２０を経て試料１に照射される。試料１に照明された光は、試料１上で反射，散乱，回折され、対物レンズ２０のＮＡ以内の光は再び対物レンズ２０に入射し、λ／４板１７を通り、部分偏光ビームスプリッタ２００で反射され、アナライザ２２に入射する。試料で反射された光のうち反射時に回転方向が逆になった成分（正反射成分、すなわち０次光成分）は、λ／４板１７で直線偏光となり、部分偏光ビームスプリッタ２００にｓ偏光として入射し、ほとんどロスなく反射される。
【００１５】
一方、試料で反射された光のうち反射時に回転方向が変わらなかった成分（反射光の偏光状態の変化によって生じた成分、すなわち高次回折光の一部）は、λ／４板１７で直線偏光となり、部分偏光ビームスプリッタ２００にｐ偏光として入射し、反射率Ｒｐで反射される。（普通の偏光ビームスプリッタではＲｐ〜０なので、この成分は結像系には到達しない）これらの成分は、位相補償板２２０で互いの位相差を調整された後、アナライザ２２に入射し、その方位で決まる比率で合成（加算）され結像光学系に導かれる。位相補償板２２０の位相補償量およびアナライザ２２の方位は、高次回折光が０次光より効率良く結像系に導かれるように決める。円偏光の回転方向が反射時に変わらなかった高次回折光成分も結像光学系に取り込むことができるので、高域のＭＴＦを改善することが可能になる。また、位相補償板で円偏光の回転方向が反射時に反転した成分と変わらなかった成分との位相差を最適化し、アナライザの方位を調整することで、結像光学系へ導かれる光中のこれらの成分の割合を調整することができるので、高域のＭＴＦの改善度合いの調整も可能である。
【００１６】
アナライザ２２を透過した光は、結像レンズ３０とズームレンズ５０からなる結像光学系を介して、イメージセンサ７０の受光面に試料１の像を形成する。イメージセンサ７０はリニアセンサやＴＤＩイメージセンサ或いはエリアセンサ（ＴＶカメラ）等が用いられる。また、試料からの反射光の一部は、例えばダイクロイックミラー等の光分割手段２５によって焦点検出光学系４５に導かれ、自動焦点合せを行うための信号検出に用いられる。
【００１７】
焦点検出光は、結像レンズ４０で試料１の高さ情報を有した光学像をセンサ４１上に形成し、このセンサ出力の信号は、焦点検出信号処理回路９０に入力される。焦点検出信号処理回路９０は試料１の高さと対物レンズ２０の焦点位置のズレ量を検出し、ＣＰＵ７５に焦点ズレ量のデータを送る。この焦点ズレ量に応じて、ＣＰＵ７５からステージ制御部８０にＺステージ４を駆動させる指令を行い、所定パルスをステージ制御部８０からＺステージ４に送り、自動焦点合わせが行われる。
【００１８】
また、検出光学系のイメージセンサ７０で検出した試料１の光学像の画像データは、画像処理回路７１に入力されて処理が行われ、欠陥判定回路７２で欠陥部の判定が行われる。その結果は、ディスプレイなどの表示手段に表示されるとともに、通信手段を介して、ワークステーションやデータサーバなどの外部記憶・制御装置へ送信される。
【００１９】
検出した画像データから欠陥部の判定を行うイメージセンサ７０から欠陥判定回路７２までの一連の画像処理の具体的な処理の方法としては、例えば、特開平２−１７０２７９号公報または特開平３−３３６０５号公報などに記載されているように、隣接チップの対応する画像データ同士を比較することにより行う方法や、隣接チップの対応する画像データ同士を比較する方法、隣接するパターンの画像データ同士を比較する方法，設計データと画像データ同士を比較する方法等がある。
【００２０】
試料１のＸＹ方向への移動は、ステージ制御部８０でＸステージ６及びＹステージ５の動きを２次元的に制御して行う。また、θステージ３は、ＸＹステージ６及び５の運動方向と試料１に形成されたパターンのθアライメントを行うときに用いれらる。
【００２１】
次に、円偏光照明や楕円偏光照明が可能な光学系において、直線偏光照明を実現する際の照明系と結像系の光路分離部２１０の実施例を図２に示す。
【００２２】
この実施例では、光路分離部２１０は、部分偏光ビームスプリッタ２００（例えば、Ｔｐ：Ｒｐ＝６：４，Ｔｓ／Ｒｓ＜０.０５）と、それぞれ出し入れ可能なλ／２板１６とλ／４板１７，位相補償板２２０，アナライザ２２から構成される。
【００２３】
直線偏光照明を用いて像観察を行う場合には、図に示すように光路にλ／２板１６を挿入し、λ／４板１７を外す。部分偏光ビームスプリッタ２００に入射した照明光（ランダム偏光）は、Ｔｐ(〜０.６）だけ透過してｐ偏光となり、λ／２板１６で試料上のパターンに合わせて偏光の方位を変えられたあと、対物レンズ２０を経て試料に入射する。試料で反射された光のうち偏光方向が変化しなかった成分は、λ／２板１６で元の偏光方向に戻され、部分偏光ビームスプリッタ２００にｐ偏光として入射し、反射率Ｒｐ(〜０.４）で反射される。
【００２４】
一方、試料で反射された光のうち反射光の偏光方向が回転したことによって生じた成分は、λ／２板１６で元の偏光と直行する直線偏光となり、部分偏光ビームスプリッタ２００にｓ偏光として入射し、ほとんどロスなく反射される。これらの成分は、位相補償板２２０で互いの位相差を調整された後、アナライザ２２に入射し、その方位で決まる比率で合成（加算）され結像光学系に導かれる。反射時に偏光方向が変化することによって生じた成分を効率よく結像光学系に取り込むことができるので、従来の楕円偏光照明を用いる方法だけでなく、同様に直線偏光照明による像観察が可能な無偏光ビームスプリッタ用いる方法と比べても、より大きなＭＴＦ改善効果が得られる。
【００２５】
また、位相補償板で反射時に偏光方向が変わらなかった成分と反射時に偏光方向が変化することによって生じた成分の位相差を最適化し、アナライザの方位を調整することで、結像光学系へ導かれる光中のこれらの成分の割合を調整することができるので、ＭＴＦ改善効果のさらなる強調や調整が可能である。
【００２６】
また、図１に示した円偏光照明を用いる方式に切り替えるには、光路にλ／４板１７を挿入し、λ／２板１６を外せばよい。さらに従来の楕円偏光照明を用いる方法と互換性をとるためには、光路にλ／２板１６とλ／４板１７の両方を挿入し、部分偏光ビームスプリッタで反射された光のうちｓ偏光成分のみが結像系に導かれるようにアナライザの方位を設定すればよい。このように、簡単な切り替えで、必要に応じて観察条件を変えることが可能になる。
【００２７】
なお、これらの実施例では、光路分離部２１０に位相補償板２２０が入る例を示したが、これは必須ではない。位相補償板２２０無しでもこの系は成立し、円偏光照明下で高域でのＭＴＦ改善の効果が得られる。また、部分偏光ビームスプリッタ２００の特性の例として、Ｔｐ：Ｒｐ＝６：４，Ｔｓ／Ｒｓ＜０.０５という数字を示したが、これらも必須の条件ではない。ｐ偏光成分が一部反射されるものであれば良い。
【００２８】
上記のように、円偏光照明の場合でも高域でのＭＴＦ改善効果が得られるので、試料上のパターン方向に依存しない高分解能像観察、および、高感度な欠陥検出が可能になる。また、必要に応じて、簡単な切り替えで直線偏光照明と円偏光照明、楕円偏光照明を使い分けることが可能になるので、より多様な試料への対応が可能になる。
【００２９】
【発明の効果】
本発明によれば、試料上のパターンの方向に依存せず高域でのＭＴＦ改善効果が得られる。また、必要に応じて照明光の偏光状態を直線偏光にも切り替えられるような光学系を実現できる。
【図面の簡単な説明】
【図１】欠陥検査装置の構成を示す縦断面図。
【図２】円偏光照明を用いる場合の光路分離部の構成を示す縦断面図。
【図３】直線偏光照明と円偏光照明および楕円偏光照明を切り替えて用いる場合の光路分離部の構成を示す縦断面図。
【図４】従来の欠陥検査装置の光学系の構成を示す縦断面図。
【図５】従来の欠陥検査装置における光路分離部の構成を示す縦断面図。
【符号の説明】
１…試料、８…光源、１６…λ／２板、１７…λ／４板、２０…対物レンズ、２２…アナライザ、３０…結像レンズ、５０…ズームレンズ、７０…イメージセンサ、７１…画像処理回路、７２…欠陥判定回路、２００…部分偏光ビームスプリッタ、２１０…光路分離部、２２０…位相補償板。[0001]
BACKGROUND OF THE INVENTION
The present invention is a method for observing a fine structure, and a high-resolution microscope optical system that realizes the same, and particularly for high-definition observation and inspection of fine pattern defects and foreign matters in a semiconductor manufacturing process and a flat panel display manufacturing process. The present invention relates to a resolution optical system and a defect inspection apparatus using the same.
[0002]
[Prior art]
In a semiconductor manufacturing process, a flat panel display manufacturing process, and the like, observation and inspection of fine pattern defects and foreign matters using an optical microscope are performed. In recent years, it has become necessary to improve the performance of microscope optical systems as the degree of integration of semiconductor devices increases.
[0003]
Methods for increasing the resolution of the optical microscope include shortening the wavelength of light used for imaging, increasing the numerical aperture (NA) of the objective lens, and increasing the high frequency of the transfer function (MTF) of the imaging system. There are methods using a resolution technique. Of these, shortening the wavelength and increasing the NA are direct methods, but there are various restrictions in practical use, and there are cases where it cannot be realized. Therefore, a method that can observe a fine structure with high contrast without changing the wavelength and NA, that is, a super-resolution technique that raises the high region of the MTF of the imaging system has been attracting attention.
[0004]
As an example of the super-resolution technique, Japanese Patent Laid-Open No. 2000-155099 discloses a method for improving MTF by controlling the polarization state. Illuminate the sample with linearly polarized light, guide the reflected light from the sample to the imaging system through the analyzer, and illuminate the sample with elliptically polarized light, and only the linearly polarized component reflected by the polarizing beam splitter from the reflected light from the sample A method is shown for guiding to the imaging system. In the former, by adjusting the direction of linearly polarized light that illuminates the sample with respect to the direction of the linear pattern on the sample and the direction of the analyzer, the light quantity ratio between the higher-order diffracted light and the 0th-order light by the pattern on the sample is adjusted. ing. By reducing the amount of zero-order light, the high-frequency MTF is improved, and the difference in the amount of light between the part with and without the pattern can be reduced, making it easy to see the fine pattern and using the observation image. The performance of defect inspection can be improved. Since it is necessary to use a non-polarizing beam splitter to separate the optical path of the imaging system of the illumination system, there are drawbacks in that the light utilization efficiency is low and the image becomes dark, but the change in polarization during reflection on the sample is significant. Therefore, a large MTF improvement effect can be obtained. In the latter method, the same MTF improvement effect can be obtained by optimizing the orientation and ellipticity of elliptically polarized light that illuminates the sample with respect to the direction of the linear pattern on the sample. It is possible to obtain higher light use efficiency than a system using linearly polarized illumination, and a bright image can be obtained. In this system, linearly polarized illumination can be realized. However, in this case, since the reflected light from the sample does not return to the imaging system, the image cannot be observed with linearly polarized illumination that maximizes the MTF improvement effect.
[0005]
An example of using the latter elliptically polarized illumination in the basic configuration of the system realizing this method is shown in FIGS. Light from the light source 8 reaches the aperture stop 11 through the concave mirror and the lens 9, and further enters the polarization beam splitter 15 through the lens, the wavelength selection filter 12, and the field stop 13. The linearly polarized light transmitted through the polarizing beam splitter 15 is converted into elliptically polarized light through the λ / 2 plate 16 and the λ / 4 plate 17 with λ as a wavelength, and is irradiated onto the sample 1 by the objective lens 20. By rotating the λ / 4 plate 17, the direction of the major axis of the elliptically polarized light can be controlled, and by rotating the λ / 2 plate 16, the ellipticity of the elliptically polarized light can be controlled. The light reflected by the sample 1 passes through the objective lens 20, the λ / 4 plate 17, and the λ / 2 plate 16 and again enters the polarization beam splitter 15, and only the s-polarized component is reflected, and the imaging lens 30 and the zoom lens are reflected. 50 to the imaging system. In this system, when the angle of the two wave plates is determined so as to illuminate the sample 1 with circularly polarized light, only the component whose polarization state has not changed when reflected on the sample surface is reflected by the polarization beam splitter 15. Reflected and guided to the imaging system.
[0006]
On the other hand, when the angle of the two wave plates is determined so that the sample 1 is elliptically polarized, a part of the component whose polarization state has changed when reflected by the sample 1 is also reflected by the polarization beam splitter 15. Guided to the imaging system. In general, the light diffracted in a linear pattern may change the polarization state, but the zero-order light does not change. Therefore, the diffracted light component is enhanced by elliptical illumination and guided to the imaging system. As a result, it is possible to obtain an image with improved high-frequency MTF.
[0007]
[Problems to be solved by the invention]
The method using the linearly polarized illumination or the elliptically polarized illumination described in the conventional example is an effective method that can improve the high-frequency MTF. However, in order to obtain a large MTF improvement effect, it is necessary to change the direction of polarization of illumination light depending on the direction of the pattern on the sample, and there is a problem that the condition setting is complicated. In addition, when patterns with different orientations coexist on the sample, there is a problem that it is difficult to obtain the same MTF improvement effect for all patterns. This is because the improvement effect of MTF is not isotropic and depends on the relationship between the polarization direction of the illumination light and the direction of the pattern on the sample. SUMMARY OF THE INVENTION An object of the present invention is to provide a method and apparatus capable of obtaining an MTF improvement effect in a high range without depending on the direction of a pattern on a sample.
[0008]
In addition, the method using elliptically polarized illumination is an excellent method with high light utilization efficiency and an MTF improvement effect, but has a problem that coexistence with the method using linearly polarized illumination is difficult. The method using linearly polarized illumination has a problem in regular use because the light use efficiency is low and the image becomes dark. However, since a larger MTF improvement effect can be obtained than in the case of elliptically polarized illumination, it is desirable that it can be used when necessary. However, since the characteristics required for the beam splitter used for separating the optical path of the imaging system of the illumination system are different, it is very difficult to realize both with one optical system. Accordingly, another object of the present invention is to realize an optical system that can switch the polarization state of illumination light to linearly polarized light as required.
[0009]
[Means for Solving the Problems]
In an embodiment of the present invention, an illuminating unit that irradiates the sample with illumination light, an imaging unit that forms an image of the illuminated sample, an imaging unit that captures the image of the sample, and the acquired image In a defect inspection apparatus comprising a defect detection means for detecting a defect of the sample in comparison with an image stored in advance, and a display means for displaying the defect detected by the defect detection means, the imaging means includes λ A wavelength plate switching means for individually moving the objective lens, the λ / 4 plate, the λ / 2 plate, the λ / 4 plate and the λ / 2 plate into and out of the optical path, the partial polarization beam splitter and the analyzer. An image lens is provided.
[0010]
In order to obtain the MTF improvement effect regardless of the orientation of the pattern on the sample, a method for obtaining the MTF improvement effect under circularly polarized illumination is provided. Specifically, a partially polarized beam splitter is used to separate the optical path between the illumination system and the imaging system, and a λ / 4 plate is added to illuminate the sample with circularly polarized light. Add an analyzer. The component generated by changing the polarization when reflected by the sample is incident on the partially polarized beam splitter as p-polarized light, and thus a part of the component is reflected and guided to the imaging system. By adjusting the orientation of the analyzer of the imaging system, this component can be guided to the imaging system by a necessary amount, and an MTF improvement effect can be obtained. Furthermore, in the present invention, a phase compensator is added between the polarizing beam splitter and the analyzer as necessary. By adjusting the phase difference between the p-polarized component and the s-polarized component reflected by the partially polarized beam splitter by the analyzer using the phase compensator, it is possible to further increase the MTF improvement effect.
[0011]
The present invention also provides a method for realizing all of the conventional elliptically polarized illumination system, the above-mentioned circularly polarized illumination system, and the linearly polarized illumination system that can obtain the greatest MTF improvement effect by simple switching with a single optical system. . Specifically, a partial polarization beam splitter is used to separate the optical path of the illumination system and the imaging system, and a λ / 2 plate and a λ / 4 plate, which can be put in and out individually, are added to the specimen so that the sample has an arbitrary polarization state. Illuminate with light and add an analyzer to the imaging system immediately after the partially polarized beam splitter. When realizing a system compatible with the conventional elliptically polarized illumination system, the analyzer orientation is set so that only the s-polarized component of the light reflected by the partially polarized beam splitter is guided to the imaging system. In other cases, the degree of the MTF improvement effect can be adjusted by adjusting the orientation of the analyzer. Further, when linearly polarized illumination is used, since the component generated by the change in polarization when reflected by the sample is incident on the partially polarized beam splitter as s-polarized light, almost all is reflected and the imaging system is reflected. Led to. Since this component is led to the imaging system with about twice the efficiency compared to the case of using a non-polarizing beam splitter, it is possible to obtain a greater MTF improvement effect than the conventional linear polarization illumination method. Become.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of an optical defect inspection apparatus using the microstructure observation method of the present invention is shown in FIG. This is an example using circularly polarized illumination. The sample 1 is vacuum-adsorbed on the chuck 2, and the chuck 2 is mounted on the θ stage 3, the Z stage 4, the Y stage 5, and the X stage 6. The optical system 111 disposed above the sample 1 captures an optical image of the sample 1 in order to inspect the appearance of the pattern formed on the sample 1, and mainly includes the illumination optical system and the sample 1. An imaging optical system that forms and captures an image and a focus detection optical system 45 are included. The light source 8 disposed in the illumination optical system is an incoherent light source, for example, a xenon lamp.
[0013]
The light emitted from the light source 8 passes through the opening of the aperture stop 11 through the lens 9, and further reaches the field stop 13 through the lens and the wavelength selection filter 12. The wavelength selection filter 12 considers the spectral reflectance of the sample 1 and limits the illumination wavelength region in order to detect an image of the sample 1 with high resolution. For example, an interference filter is disposed. The light transmitted through the field stop 13 enters the optical path separation unit 210.
[0014]
The optical path separation unit 210 includes a partial polarization beam splitter 200 (for example, Tp: Rp = 6: 4, Ts / Rs <0.05), a λ / 4 plate 17, a phase compensation plate 220, and an analyzer 22. The optical path of illumination light from the light source 8 toward the sample 1 and the optical path from the sample 1 toward the image sensor are separated. Its function is shown in FIG. Illumination light (random polarization) incident on the optical path separation unit 210 passes through the partial polarization beam splitter 200 by the transmittance Tp (˜0.6) and becomes p-polarized linearly polarized light. Further, the sample 1 is irradiated with the λ / 4 plate 17 through the objective lens 20 as circularly polarized light. The light illuminated on the sample 1 is reflected, scattered, and diffracted on the sample 1, and the light within the NA of the objective lens 20 enters the objective lens 20 again, passes through the λ / 4 plate 17, and passes through the partial polarization beam splitter 200. And is incident on the analyzer 22. Of the light reflected by the sample, the component whose rotation direction is reversed at the time of reflection (regular reflection component, that is, the 0th-order light component) becomes linearly polarized light by the λ / 4 plate 17 and is converted into s-polarized light by the partial polarization beam splitter 200. Incident and reflected with almost no loss.
[0015]
On the other hand, a component of the light reflected by the sample whose rotation direction did not change at the time of reflection (a component generated by a change in the polarization state of the reflected light, that is, a part of higher-order diffracted light) is linearly polarized by the λ / 4 plate 17. Then, it enters the partially polarized beam splitter 200 as p-polarized light, and is reflected at the reflectance Rp. (This component does not reach the imaging system because it is Rp˜0 in a normal polarization beam splitter.) After these components are adjusted in phase difference by the phase compensator 220, they enter the analyzer 22, They are combined (added) at a ratio determined by the azimuth and guided to the imaging optical system. The phase compensation amount of the phase compensation plate 220 and the orientation of the analyzer 22 are determined so that the high-order diffracted light is guided to the imaging system more efficiently than the 0th-order light. Since the high-order diffracted light component whose rotational direction of the circularly polarized light does not change at the time of reflection can also be taken into the imaging optical system, it is possible to improve the high-frequency MTF. In addition, the phase compensation plate optimizes the phase difference between the component whose circular polarization is rotated during reflection and the component that did not change at the time of reflection, and adjusts the azimuth of the analyzer. Since the ratio of these components can be adjusted, the improvement degree of the high frequency MTF can also be adjusted.
[0016]
The light transmitted through the analyzer 22 forms an image of the sample 1 on the light receiving surface of the image sensor 70 through an imaging optical system including the imaging lens 30 and the zoom lens 50. As the image sensor 70, a linear sensor, a TDI image sensor, an area sensor (TV camera), or the like is used. Further, a part of the reflected light from the sample is guided to the focus detection optical system 45 by a light splitting means 25 such as a dichroic mirror and used for signal detection for automatic focusing.
[0017]
The focus detection light forms an optical image having the height information of the sample 1 on the sensor 41 by the imaging lens 40, and the sensor output signal is input to the focus detection signal processing circuit 90. The focus detection signal processing circuit 90 detects the amount of deviation between the height of the sample 1 and the focal position of the objective lens 20 and sends data on the amount of focus deviation to the CPU 75. In accordance with the amount of focus shift, the CPU 75 instructs the stage control unit 80 to drive the Z stage 4 and sends a predetermined pulse from the stage control unit 80 to the Z stage 4 to perform automatic focusing.
[0018]
Further, the image data of the optical image of the sample 1 detected by the image sensor 70 of the detection optical system is input to the image processing circuit 71 and processed, and the defect determination circuit 72 determines the defective portion. The result is displayed on a display means such as a display and transmitted to an external storage / control device such as a workstation or a data server via a communication means.
[0019]
As a specific processing method of a series of image processing from the image sensor 70 for determining the defective portion based on the detected image data to the defect determination circuit 72, for example, Japanese Patent Laid-Open No. 2-170279 or Japanese Patent Laid-Open No. 3-33605. As described in the Gazette, etc., a method of comparing adjacent image data of adjacent chips, a method of comparing corresponding image data of adjacent chips, and comparing image data of adjacent patterns And a method of comparing design data and image data.
[0020]
The movement of the sample 1 in the XY directions is performed by two-dimensionally controlling the movement of the X stage 6 and the Y stage 5 by the stage controller 80. The θ stage 3 is used when θ alignment of the movement direction of the XY stages 6 and 5 and the pattern formed on the sample 1 is performed.
[0021]
Next, FIG. 2 shows an embodiment of the optical path separation unit 210 of the illumination system and the imaging system when realizing linearly polarized illumination in an optical system capable of circularly polarized illumination and elliptically polarized illumination.
[0022]
In this embodiment, the optical path separation unit 210 includes a partial polarization beam splitter 200 (for example, Tp: Rp = 6: 4, Ts / Rs <0.05), and a λ / 2 plate 16 and a λ / 4 that can be taken in and out, respectively. The plate 17, the phase compensation plate 220, and the analyzer 22 are included.
[0023]
When image observation is performed using linearly polarized illumination, the λ / 2 plate 16 is inserted into the optical path and the λ / 4 plate 17 is removed as shown in the figure. Illumination light (random polarization) incident on the partial polarization beam splitter 200 is transmitted by Tp (˜0.6) to become p-polarized light, and the polarization direction can be changed in accordance with the pattern on the sample by the λ / 2 plate 16. After that, it enters the sample through the objective lens 20. The component of the light reflected by the sample whose polarization direction has not changed is returned to the original polarization direction by the λ / 2 plate 16 and is incident on the partial polarization beam splitter 200 as p-polarized light, and the reflectance Rp (˜0). Reflected in 4).
[0024]
On the other hand, the component generated by the rotation of the polarization direction of the reflected light of the light reflected from the sample becomes linearly polarized light that is orthogonal to the original polarized light by the λ / 2 plate 16 and is converted into s-polarized light by the partial polarization beam splitter 200. Incident and reflected with almost no loss. These components are adjusted in phase difference with each other by the phase compensation plate 220, then enter the analyzer 22, and are combined (added) at a ratio determined by the azimuth and guided to the imaging optical system. Since the component generated by the change in the polarization direction during reflection can be efficiently taken into the imaging optical system, not only the conventional method using elliptically polarized illumination but also the image observation using linearly polarized illumination is possible. Compared with a method using a polarizing beam splitter, a larger MTF improvement effect can be obtained.
[0025]
In addition, the phase compensation plate optimizes the phase difference between the component whose polarization direction did not change during reflection and the component caused by the change in polarization direction during reflection, and adjusted the orientation of the analyzer, leading to the imaging optical system. Since the ratio of these components in the light to be burned can be adjusted, it is possible to further emphasize and adjust the MTF improvement effect.
[0026]
In order to switch to the method using the circularly polarized illumination shown in FIG. 1, the λ / 4 plate 17 is inserted into the optical path and the λ / 2 plate 16 is removed. Furthermore, in order to be compatible with the conventional method using elliptically polarized illumination, both the λ / 2 plate 16 and the λ / 4 plate 17 are inserted in the optical path, and the s-polarized light out of the light reflected by the partial polarization beam splitter. The orientation of the analyzer may be set so that only the components are guided to the imaging system. In this way, the observation conditions can be changed as necessary by simple switching.
[0027]
In these embodiments, an example in which the phase compensation plate 220 is inserted in the optical path separation unit 210 is shown, but this is not essential. Even without the phase compensator 220, this system is established, and the effect of improving the MTF in the high band can be obtained under circularly polarized illumination. In addition, as an example of the characteristics of the partial polarization beam splitter 200, the number Tp: Rp = 6: 4, Ts / Rs <0.05 is shown, but these are not essential conditions. Any p-polarized component may be reflected.
[0028]
As described above, even in the case of circularly polarized illumination, an effect of improving the MTF at a high frequency can be obtained, so that high-resolution image observation independent of the pattern direction on the sample and highly sensitive defect detection can be performed. Further, if necessary, it is possible to selectively use linearly polarized illumination, circularly polarized illumination, and elliptically polarized illumination by simple switching, so that it is possible to deal with a wider variety of samples.
[0029]
【The invention's effect】
According to the present invention, the effect of improving the MTF at a high frequency can be obtained without depending on the direction of the pattern on the sample. In addition, an optical system that can switch the polarization state of illumination light to linearly polarized light as required can be realized.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a configuration of a defect inspection apparatus.
FIG. 2 is a longitudinal sectional view showing a configuration of an optical path separation unit when circularly polarized illumination is used.
FIG. 3 is a longitudinal sectional view showing a configuration of an optical path separation unit when switching between linearly polarized illumination, circularly polarized illumination, and elliptically polarized illumination.
FIG. 4 is a longitudinal sectional view showing a configuration of an optical system of a conventional defect inspection apparatus.
FIG. 5 is a longitudinal sectional view showing a configuration of an optical path separation unit in a conventional defect inspection apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Sample, 8 ... Light source, 16 ... (lambda) / 2 board, 17 ... (lambda) / 4 board, 20 ... Objective lens, 22 ... Analyzer, 30 ... Imaging lens, 50 ... Zoom lens, 70 ... Image sensor, 71 ... Image Processing circuit 72... Defect determination circuit 200. Partial polarization beam splitter 210 210 Optical path separation unit 220 Phase compensation plate

Claims

In a method of observing a fine pattern formed on a sample surface with light, illumination light having a substantially circular polarization state is irradiated on the sample surface through an objective lens, and the light reflected by the sample is λ / 4 plate with λ as a wavelength. A fine structure observing method, characterized in that the image is guided to an imaging optical system through a partial polarization beam splitter and an analyzer, and an image formed by the imaging optical system is observed or imaged.

In a method of observing a fine pattern formed on a sample surface with light, illumination light having a substantially linear polarization state is irradiated onto the sample surface through an objective lens, and the light reflected by the sample is λ / 2 plate with λ as a wavelength. A method for observing a fine structure, characterized in that the image is guided to an imaging optical system through a partial polarization beam splitter and an analyzer, and an image formed by the imaging optical system is observed or captured.

A phase compensation element is provided between the partial polarization beam splitter and the analyzer, and the phase difference between the s-polarized component and the p-polarized component reflected by the partial polarization beam splitter is adjusted and guided to the imaging optical system. The microstructure observation method according to claim 1 or 2.

An illumination unit that irradiates the sample with illumination light, an imaging unit that forms an image of the illuminated sample, an imaging unit that captures the image of the sample, and an image in which the acquired image is stored in advance In a defect inspection apparatus comprising a defect detection means for detecting a defect of the sample by comparison and a display means for displaying a defect detected by the defect detection means, the illumination means converts the illumination light in a substantially circular polarization state into an objective lens A defect inspecting device comprising: a circularly polarized light generating means incident on the light source, and the imaging means having an objective lens, a λ / 4 plate, a partial polarization beam splitter, an analyzer, and an imaging lens with λ as a wavelength. apparatus.

An illumination unit that irradiates the sample with illumination light, an imaging unit that forms an image of the illuminated sample, an imaging unit that captures the image of the sample, and an image in which the acquired image is stored in advance In a defect inspection apparatus comprising a defect detection means for detecting a defect of the sample by comparison and a display means for displaying a defect detected by the defect detection means, the illumination means converts illumination light in a substantially linear polarization state into an objective lens Defect inspection, characterized in that it comprises linearly polarized light generating means to be incident on the image forming means, and the imaging means comprises an objective lens, a λ / 2 plate, a partial polarization beam splitter, an analyzer, and an imaging lens with λ as a wavelength. apparatus.

An illumination unit that irradiates the sample with illumination light, an imaging unit that forms an image of the illuminated sample, an imaging unit that captures the image of the sample, and an image in which the acquired image is stored in advance In a defect inspection apparatus comprising a defect detection means for detecting a defect of the sample by comparison and a display means for displaying a defect detected by the defect detection means, the imaging means has an objective lens and λ / 4 plates, λ / 2 plates, λ / 4 plates and λ / 2 plates are individually provided in and out of the optical path, wave plate switching means, a partial polarization beam splitter, an analyzer, and an imaging lens. Defect inspection equipment.

7. The defect inspection apparatus according to claim 4, wherein the imaging unit includes a phase compensation unit.