JP3978528B2

JP3978528B2 - Pattern defect inspection apparatus and laser microscope

Info

Publication number: JP3978528B2
Application number: JP10619198A
Authority: JP
Inventors: 治彦楠瀬; 米澤　　良
Original assignee: Lasertec Corp
Current assignee: Lasertec Corp
Priority date: 1998-04-16
Filing date: 1998-04-16
Publication date: 2007-09-19
Anticipated expiration: 2018-04-16
Also published as: JPH11304715A

Description

【０００１】
【発明の属する技術分野】
本発明は、フォトマスク、液晶パネル、カラーフィルタのような複数のパターンが透明基板に形成されている試料の欠陥を検査するのに好適な透過型欠陥検査装置に関するものである。
【０００２】
【従来の技術】
従来、ＬＳＩの製造においては、透明ガラス基板上に金属クロムの遮光パターンが形成されたフォトマスクを用い、投影光学系によりフォトマスクの像がウエハ上に縮小投影されている。従って、ＬＳＩの製造の歩留りを改善するためフォトマスクの欠陥を正確に検出できる欠陥検査装置の開発が強く要請されている。従来のフォトマスクの欠陥検査装置おいては、透過型顕微鏡の原理を用い、検査すべき試料の下側から集光レンズを介して試料に照明光を投射し、試料からの透過光を対物レンズを経てＣＣＤカメラのような画像検出器により撮像し、画像の振幅情報を利用して欠陥が検出されていた。
【０００３】
一方、ＬＳＩの線幅の微細化に伴い、その製造に用いられるフォトマスクとしてハーフトーン型の位相シフトマスクのような、振幅だけでなく振幅と位相の両方によりパターンを規定するフォトマスクが実用化されており、これらフォトマスクについても一層正確に欠陥検査できる検査装置の開発が強く要請されている。
【０００４】
【発明が解決しようとする課題】
ＬＳＩの線幅の微細化に伴い、フォトマスクのパターンも一層微細化しており、パターンサイズの微細化に応じてより微細な欠陥を正確に検出できることが要請されている。この課題を達成するためには欠陥検査装置の横方向の分解能を一層高くする必要がある。しかしながら、従来の透過型欠陥検査装置では、一層良好な性能の光学素子を用いても分解能を高くするには限界がある。
【０００５】
また、フォトマスクの欠陥として、例えばレジストの滓のような透明異物や半透明異物の付着による欠陥も多く存在する。しかしながら、従来の透過型欠陥検査装置はこのような透明欠陥に対する感度が低いため、本来検出されるべき欠陥を検出できない不具合も指摘されている。
【０００６】
また、ハーフトーン型位相シフトマスクの遮光パターンの透過率は、実際にパターンをウエハ上に投影する際の投影波長において約１０％程度に設定されているが、欠陥検査を行う際の検査波長における透過率は約５０％である。従って、遮光パターンが形成されている部分と形成されていない部分との間の透過光量比が小さいため検出される画像のコントラストが低く、検査精度に関して難点があった。
【０００７】
さらに、パターンの微細化に伴い、チイップサイズが増大する傾向にあり、欠陥検査すべき領域が一層拡大している。従って、検査速度すなわちスループットを一層高くすることも重要な課題になっている。
【０００８】
本発明の目的は、一層高い横方向分解能を達成できると共に透明欠陥も正確に検出でき、しかも検出感度が一層改善された透過型欠陥検査装置を提供することにある。
【０００９】
さらに、本発明の目的は、一層高い横方向分解能を達成できると共に一層高いスループットを達成できる透過型欠陥検査装置を提供することにある。
【００１０】
【課題を解決するための手段】
本発明によるパターン欠陥検査装置は、透明基板に形成されたパターンの欠陥を検査するパターン欠陥検査装置であって、光ビームを放出する光源装置と、光源装置からの光ビームを第１の方向に偏向するビーム偏向装置と、偏向された光ビームを集束して検査すべき試料に投射する第１の対物レンズと、検査すべき試料を支持する試料ステージと、前記試料を透過した光ビームを前記試料に向けて反射するミラーと、このミラーからの光ビームを再び集束して試料に投射する第２の対物レンズと、前記試料を２回透過した透過光を受光する光検出器と、この光検出器からの出力信号を処理して欠陥検出信号を発生する欠陥検出回路と、前記試料ステージを少なくとも前記第１の方向と直交する第２の方向に駆動するステージ駆動装置とを具え、
前記第２の対物レンズから出射し試料を２回透過した透過光を前記第１の対物レンズ及びビーム偏向装置を介して光検出器に入射させることを特徴とする。
【００１１】
本発明では、検査すべき試料を透過した透過光をミラーにより反射して再度試料に向けて投射し、試料を２回透過した光を光検出器に入射させるダブルパス方式を採用する。検査ビームが試料の同一の部分を２回透過するので、コントラストが一層増大し、ハーフトーン型の位相シフトマスクのような検査波長域における透過率が比較的高い遮光パターンが用いられている試料でも正確に欠陥検査することができる。さらに、例えばレジスト膜の滓の付着のような透明欠陥についても、検査ビームは透明欠陥を２回通過するので、透明欠陥により回折し又は散乱する光が増大する。このような光は光路外に出射して光学系の瞳に入らないため、最終的に光検出器に入射せず、この結果透明欠陥が存在する部分は周囲よりも暗く検出されることになる。従って、従来の欠陥検査装置では検出できなかった透明欠陥も明瞭に検出することができる。
【００１２】
本発明による透過型欠陥検査装置の好適例は、前記第２の対物レンズとミラーとの間に１／４波長板を配置し、光源装置とビーム偏向装置との間に偏光ビームスプリッタを配置し、光源装置から放出された検査ビームが偏光ビームスプリッタを透過し試料を２回透過した光は偏光ビームスプリッタにより反射するように構成したことを特徴とする。試料を２回透過した光の強度と遮光パターンで反射した光の強度が接近している場合、遮光パターンの形成部分と形成されていない部分との識別が困難になるおそれがある。このため、本例では、偏光を利用して試料からの透過光だけを光検出器に入射させる。本例では、試料を透過した光は位相板である１／４波長板を２回透過するので、その偏光面が９０°回転して試料から出射するので、偏光ビームスプリッタにより反射する。これに対して、試料表面で反射した光は１／４波長板を通過しないので、光源から出射した検査ビームと同一の偏光状態を維持し、偏光ビームスプリッタを透過する。この結果、検査すべき試料を２回透過した光だけを光検出器に入射させることができる。このように構成すれば、試料からの反射光による情報は全て除去され、試料からの透過光による情報だけを検出することができる。この結果、例えば遮光パターンの膜厚が不均一な場合、特に膜厚が規定の厚さよりも薄い場合欠陥として検出することができる。
【００１３】
本発明によるパターン欠陥検査装置の別の実施例は、前記光検出器が、共焦点光学系を構成するピンホール開口を有することを特徴とする。欠陥検査装置の光学系が共焦点光学系を構成すれば、光検出器にフレアが入射するのを一層有効に防止することができるので、欠陥により回折され又は散乱した光が光検出器に入射するのを一層有効に防止され、欠陥の存在を一層明瞭に検出することができる。
【００１４】
本発明による別のパターン欠陥検査装置は、透明基板に形成されたパターンの欠陥を検査するパターン欠陥検査装置であって、第１の方向に沿って整列した複数の光ビームを放出する光源装置と、これら複数の光ビームを集束して検査すべき試料に投射する第１の対物レンズと、検査すべき試料を支持する試料ステージと、前記試料ステージを前記第１の方向と直交する第２の方向に駆動するステージ駆動装置と、前記試料を透過した複数の光ビームを前記試料に向けて反射するミラーと、このミラーからの複数の光ビームを再び集束して試料に向けて投射する第２の対物レンズと、前記第１の方向と対応する方向に配列された複数の光検出素子を有し、各光検出素子が前記試料を２回透過した透過ビームをそれぞれ受光する光検出素子アレイと、前記光検出素子アレイからの出力信号に基づいて欠陥検出信号を発生する欠陥検出回路とを具えることを特徴とする。このように構成すれば、検査すべき試料は同時に複数の光ビームで走査されることになり、検査速度が一層速くなり、スループットを大幅に高くすることができる。尚、光源装置と試料との間の光路中にズームレンズを配置することにより、光ビーム間のピッチを調整することができるので、検査すべき試料のパターンが周期性を有する場合、検査ビーム間のピッチをパターンの周期に一致させることができる。
【００１５】
本発明によるパターン欠陥検査装置は、透明基板に形成されたパターンの欠陥を検査するパターン欠陥検査装置であって、第１の方向に沿って整列した複数の光ビームを放出する光源装置と、これら複数の光ビームを第１の方向と直交する第１の方向に偏向するビーム偏向装置と、前記複数の光ビームを集束して検査すべき試料に投射する第１の対物レンズと、検査すべき試料を支持する試料ステージと、前記試料を透過した複数の光ビームを前記試料に向けて反射するミラーと、このミラーからの複数の光ビームを再び集束して試料に向けて投射する第２の対物レンズと、前記光源装置とビーム偏向装置との間の光路中に配置したビームスプリッタと、前記第１の方向と対応する方向に配列された複数の光検出素子を有し、各光検出素子が前記試料を２回透過した透過ビームをそれぞれ受光する光検出素子アレイと、前記光検出素子アレイからの出力信号に基づいて欠陥検出信号を発生する欠陥検出回路とを具え、前記第２の対物レンズから出射し試料を２回透過した複数の透過ビームを前記第１の対物レンズ、ビーム偏向装置及びビームスプリッタを介して光検出素子アレイに入射させることを特徴とする。本例では、複数の光ビームをその配列方向と直交する方向にスキャンすることにより、試料を２次元的に走査する。尚、ビーム偏向装置を介して光検出素子アレイに入射させることにより試料からの透過光はビーム偏向装置によりデスキャンされるので、光検出素子アレイ上では静止した状態に維持されることになる。従って、偏光ビームスプリッタと光検出素子アレイとの間にズームレンズを配置することにより、試料からの透過ビームを各光検出素子にそれぞれ入射させることができる。
【００１６】
本発明による透過型欠陥検査装置の好適実施例は、前記光検出素子アレイを複数のフォトダイオードを有するフォトダイオードアレイで構成し、各フォトダイオードからの出力信号を並列に出力させ、各出力信号同士を比較することにより欠陥を検出することを特徴とする。この場合、リアルタイムで欠陥検査を行うことができ、スループットが大幅に向上する。
【００１７】
【発明の実施の形態】
図１は本発明によるパターン欠陥検査装置の一例の構成を示す線図である。レーザ光源１から検査ビームを放出する。この検査ビームは偏光ビームスプリッタ２を透過してビーム偏向装置であるポリゴンスキャナ３に入射する。ビーム偏向装置として、振動ミラー、ガルバノミラー等の種々のビーム偏向装置を用いることができる。ポリゴンスキャナ３は検査ビームを第１の方向（紙面内）に所定の周波数で周期的に偏向する。検査ビームは、さらにリレーレンズ４、高速ポジショナ５、リレーレンズ６、及びダイクロイックミラー７を経て第１の対物レンズ系８に入射する。この第１の対物レンズ系８は検査ビームを集束して検査すべき試料９に投射する。試料９は、Ｘ−Ｙ駆動機構を有する試料ステージ１０上に載置し、欠陥検査中第１の方向と直交する第２の方向に周期的に移動させる。従って、試料９は集束した検査ビームにより２次元的に走査されることになる。
【００１８】
本例において、検査すべき試料は透明なガラス基板上に金属クロムの遮光パターンが形成されているフォトマスクとする。フォトマスクに入射した光のうち遮光パターンが形成されている部分に入射した光は試料表面で反射し、パターンが形成されていない部分に入射した光は透過する。フォトマスクを透過した光は、板厚補正素子１１、第２の対物レンズ１２、１／４波長板１３、及びリレーレンズ１４を経て全反射ミラー１５に垂直に入射する。ミラー１５に入射した透過光は同一の光路を逆行し、再びリレーレンズ１４、１／４波長板１３、第２の対物レンズ系１２、及び板厚補正素子１１を経て試料９に入射する。第２の対物レンズ系１２は第１の対物レンズ系８とほぼ同一の焦点位置を有し、ミラー１５で反射した光を集束して試料９に投射する。尚、検査すべき試料の透明基板の厚さが異なる場合あるため、板厚補正素子１１を配置して第１の対物レンズ系と第２の対物レンズ系の焦点位置をほぼ一致させる。尚、例えば、０．１ｍｍ程度の透明基板の厚さのバラツキは、対物レンズ系のレンズ素子間の距離を調整して収差を低減することができる。
【００１９】
このように、検査ビームが試料を２回透過するダブルパス方式を利用することにより検査ビームが試料の同一部分を２回透過するので、コントラストが増大し、ハーフトーン型位相シフトマスクのような遮光パターンの透過率が大きな試料であって特に投影光の波長における透過率と検査ビームの波長における透過率とが相違するような試料でもパターンの欠陥を正確に検査することができる。
【００２０】
第２の対物レンズ系１２を出射し、再び試料９を透過した光は第１の対物レンズ系８により集光される。この透過ビームは１／４波長板１３を２回通過しているので、その偏光面は試料に入射する検査ビームの偏光面に対して９０°回転している。一方、試料９の遮光パターンにより反射し第１の対物レンズ８により集光される反射ビームは１／４波長板を通過していないので、その偏光面は試料に入射する検査ビームと同一である。
【００２１】
これら試料からの透過光及び反射光は第１の対物レンズにより集光され、ダイクロイックミラー７に入射し、その一部は反射して自動焦点光学装置１６に入射し、オートフォーカス用の信号が取り出される。この自動焦点光学装置１６は、対物レンズ非点収差素子を有する所謂ダブルフォーカルト法のような既知の自動焦点光学装置を用いることができ、その詳細な説明は省略する。この自動焦点光学装置１６からの出力信号に基づいて形成された駆動信号により、試料ステージ１０を対物レンズに光軸方向に沿って移動制御して検査中常時検査ビームを試料表面に合焦させることができる。
【００２２】
ダイクロイックミラー７を透過した光は高速ポジショナ５に入射する。この高速ポジショナ５は、２個の平行平面板を有し、これらの平行平面板をを回動させることにより光ビームを試料のＸ及びＹ方向に変位させることができ、従って例えば検査すべきフォトマスクのダイがＸ又はＹ方向に変位している場合、光ビームを高速で変位させることができる。
【００２３】
高速ポジショナ５を出射した光ビームはリレーレンズ４を経てポリゴンスキャナ３に入射してデスキャンされる。ポリゴンスキャナからの出射ビームは偏光ビームスプリッタ２に入射する。この偏光ビームスプリッタ２に入射する光のうち、フォトマスクの表面からの反射光はレーザ光源からの光ビームと同一の偏光面を有しているから透過し、フォトマスクからの透過光は偏光面が９０°回転しているので反射する。従って、フォトマスクからの反射と透過光は、この偏光ビームスプリッタ２により分離され、透過光を検査光学系に入射させることができる。
【００２４】
偏光ビームスプリッタ２により分離された試料からの透過光は、リレーレンズ１７を通過し、光検出器１８の前面に配置したピンホール１９を経て光検出器１８に入射する。この光検出器１８は、例えばフォトダイオードで構成することができる。光検出器に入射する光ビームはポリゴンスキャナ３によりデスキャンされているので、光検出器上では常時静止した状態で入射することになる。このように、光検出器１８の前面にピンホールを配置することにより、共焦点光学系が構成され、フレヤが除去され、解像度を一層高くすることができる。
【００２５】
光検出器１８からの出力信号は欠陥検出回路２０に供給する。図２は欠陥検出回路２０の一例の構成を示す回路図である。光検出器であるフォトダイオード１８からの出力信号をＡ／Ｄ変換器２１に供給してディジタル信号に変換してからメモリ２２に供給し、予め定めた時間経過してから順次出力する。そして、Ｄ／Ａ変換器に供給してアナログ信号に変換して差動増幅器２４の一方の入力端子に供給する。また、フォトダイオード１８の出力信号も差動増幅器２４の他方の端子に直接供給する。Ａ／Ｄ変換器２１、メモリ２２及びＤ／Ａ変換器２３は遅延回路を構成するものとし、その遅延時間は例えば検査すべきパターンの周期性を考慮して設定することができ、本例ではポリゴンスキャナ３の１ライン周期とする。従って、本例では互いに隣接する走査ライン毎に比較されることになる。差動増幅器２４の出力信号は比較回路２５の一方の入力端子に供給し、その他方の入力端子には基準電圧発生器２６からの所定の基準電圧を供給し、差動増幅器２４からの出力が基準電圧を超えるか否かを比較する。そして、基準電圧を超える場合欠陥検出信号を発生し、欠陥が存在していると判定する。尚、この欠陥検出回路は種々の型式のものを用いることができ、例えば検査すべきフォトマスク全体についての基準値をメモリに記憶しておき、光検出器の出力信号をメモリに記憶した基準値と直接比較することができる。また、検査すべき１個のダイ又はチイップのデータをメモリに記憶しておき、このデータと比較して欠陥検出信号を発生させることもできる。
【００２６】
図３はミラー１５の変形例を示す。上述した実施例では、ミラー１５として全面が反射性のミラーを用いたが、本例では反射面が全面ではなく、ポリゴンスキャナ３のビーム走査方向に延在する線状の反射面１５ａが形成されているミラーを用いる。この場合、試料９を透過した形成ビームは、線状のミラー面１５ａ上に沿って周期的に移動し、線状のミラー面に入射した光だけがミラー１５により反射され再び試料９に入射することになる。このように構成すれば、フレヤが一層大幅に除去され、コンフォーカリティを一層増強することができる。
【００２７】
さらに、本例では、ダイクロイックミラー７と第１の対物レンズ８との間の光路中に１／４波長板を挿脱自在に配置することができる。この場合、この１／４波長板が光路から除去されている場合試料９を２回透過した透過光だけが光検出器１８に入射する。一方、１／４波長板が光路中に配置されると、試料からの透過光は偏光ビームスプリッタ２を透過し光検出器１８に入射せず、試料９の表面で反射した反射光だけが偏光ビームスプリッタ２で反射し光検出器１８に入射する。このように構成すれば、１／４波長板を挿脱するだけで反射モード検査と透過モード検査とを切り換えることができる。
【００２８】
図１に示す欠陥検査装置は、光検出器１８から出力信号をクロック信号により一定の周波数でサンプリングして映像信号を発生させ、ポリゴンスキャナ３による走査を主走査と、ステージ１０をスキャン方向と直交する方向に移動させることによりレーザ顕微鏡を構成することができる。従って、前述した１／４波長板を挿脱自在に光路中に配置することにより試料の透過像及び反射像を選択的に撮像することができる。
【００２９】
図４は本発明による透過型欠陥検査装置の構成を示す。尚、図１で用いた構成要素と同一の構成要素には同一符号を付して説明する。本例では、マルチビーム照明方式を利用してスループットを大幅に改善する。レーザ光源１から発生したレーザビームを回折格子３０に入射させ、第１の方向すなわち紙面と直交する方向に整列した複数の光ビームに変換する。これら複数の光ビームは第１及び第２のリレーレンズ３１及び３２を経て偏光ビームスプリッタ２に入射し、この偏光ビームスプリッタ２を透過してポリゴンスキャナ３に入射する。ポリゴンスキャナ３は、入射した複数の光ビームを第１の方向と直交する第２の方向（紙面内方向）に所定の周波数で周期的に偏向する。ポリゴンスキャナ３で反射した複数の光ビームは第３のリレーレンズ４、高速ポジショナ５、第４のリレーレンズ６及びイクロイックミラー７を経て第１の対物レンズ８に入射する。第１の対物レンズ８は、入射した複数の光ビームを微小スポット状に集束して欠陥検査すべき試料９に投射する。従って、試料９上には複数の微小な光スポットが第１の方向と対応する方向に沿ってライン状に形成される。
【００３０】
試料９を透過した透過光は、板厚補正素子１１、第２の対物レンズ１２、１／４波長板１３及びリレーレンズ１４を経てミラー１５に垂直に入射する。ミラーに入射した複数の透過ビームは、光路を逆行し、再びリレーレンズ１４及び１／４波長板１４を経て第２の対物レンズ１３に入射し、再び微小スポット状に集束され、板厚補正素子１１を透過して試料９に入射する。
【００３１】
試料９を２回透過した光及び試料の表面で反射した光は第１の対物レンズにより集光され、光路を逆光してポリゴンスキャナ３に入射する。そして、ポリゴンスキャナ３によりデスキャンされて偏光ビームスプリッタ２に入射する。ここで、試料９の表面で反射した反射光は、１／４波長板を通過していないので、レーザ光源から出射した光と同一の偏光状態にあり、一方試料を２回透過した光は１／４波長板を２回通過しているので、その偏光面は光源からの出射ビームの偏光面に対して９０°回転している。この結果、試料からの反射光は偏光ビームスプリッタ２を透過し、試料からの透過光は偏光ビームスプリッタで反射し、試料からの反射光と透過光とが互いに分離される。
【００３２】
偏光ビームスプリッタ２で反射した試料からの複数の透過ビームはリレーレンズ１７を経て光検出器３３に入射する。ここで、光検出器３３に入射する光ビームは、ポリゴンスキャナによりデスキャンされているので、光検出器３３に対して静止した状態で入射する。本例では、光検出器３３は、複数の光ファイバと複数のフォトダイオードとの組合せにより構成する。複数の光ファイバの入射端をライン状に配列し、各光ファイバの出射端にはフォトダイオードをそれぞれ光学的に結合する。従って、この光検出器は、複数の受光素子がライン状に配列されたリニァイメージセンサと考えることができる。ライン状に配列された複数の光ファイバの入射端は第１の方向に対応する方向に配置する。従って、試料からの複数の透過ビームはそれぞれ対応する光ファイバに入射し、各フォトダイオードにそれぞれ入射し、電気信号に変換されて並列に出力される。このように構成することにより、共焦点光学系が構成されると共に、フォトダイオードアレイは任意の位置に配置できるので、光学系の設計の自由度が増大する。尚、試料９と光検出器３３との間の光路に配置したいずれかのリレーレンズをズームレンズで構成し、ズームレンズの倍率を調整することにより、試料からの複数の透過ビームのピッチを光ファイバアレイのピッチに整合させることができる。本例では、リレーレンズ１７をズームレンズで構成し、その倍率を調整して試料からの各透過ビームをそれぞれ対応する光ファイバに入射させる。
【００３３】
光検出器３３からの出力信号を並列に出力して電流−電圧変換増幅器アレイ３４にそれぞれ供給し、電圧信号に変換された各信号を比較回路３５に供給する。比較回路３５において、各光検出素子からの出力信号を比較し、例えば隣接する光検出素子間の出力信号同士を比較して欠陥検出信号を発生する。尚、欠陥検出は、隣接する素子からの出力信号を比較するだけでなく、１個おき又は２おき等の素子間の出力信号同士を比較することもできる。このように構成すれば、試料が同時に複数の光ビームで走査されると共に、光検出器からの出力信号を同時に並列に出力して欠陥検出を行うことができるので、欠陥検査時間が大幅に短縮し、スループットを大幅に改善することができる。
【００３４】
尚、本例では、ビーム偏向装置３と第１の対物レンズ８との間に第２の１／４波長板３６を光路に対して挿脱自在に配置して、試料からの透過光による欠陥検査と反射光による欠陥検査とを自由に切り換えられるように構成する。第２の１／４波長板３６が光路から除外されている場合、上述したように、試料からの透過光だけが光検出器に入射し、透過型の欠陥検査が行われる。一方、第２の１／４波長板３６を光路中に挿入すると、試料からの反射光はその偏光面がレーザ光源から出射した光に対して９０°回転し、偏光ビームスプリッタ２で反射する。これに対して、試料からの透過光は２個の１／４波長板をそれぞれ２回通過するので、その偏光面はレーザ光源から出射した光の偏光面と一致し、偏光ビームスプリッタ２を透過する。この結果、試料からの反射光だけが偏光ビームスプリッタ２により反射され光検出器に入射し、反射光による反射型の欠陥検査が行われることになる。このように、本例の欠陥検査装置は、第２の１／４波長板の光路への挿入を切り換えるだけで、透過型と反射型とを容易に切り換えることができ、欠陥検査装置の機能が大幅に増大する。尚、第２の１／４波長板は、偏光ビームスプリッタ２と試料９との間のいずれの位置にも配置することができる。
【００３５】
光源装置から発生する複数の光ビーム間のピッチは、用いる回折格子の条件により規定されるが、欠陥検査すべき試料の特性に応じて検査ビーム間のピッチを自在に設定することを希望する場合も多い。特に、試料に形成されている検査すべきパターンが周期性を有する場合、光源装置から発生する複数の検査ビームのピッチをパターンのピッチに整合させて欠陥検査することを望む場合がある。このような要求に適合させるため、光源装置と第１の対物レンズとの間にズームレンズ系を配置し、その倍率を調整することにより検査ビームのピッチを検査すべきパターンのピッチに整合させることができる。このように構成すれば、各検査ビームが各パターンの同一の部分を走査するので、光検出器からの出力信号を互いに比較するだけで欠陥の存在を見出すことができる。
【００３６】
さらに、本例では、ビーム偏向装置であるポリゴンスキャナ３と第１の対物レンズ８との間に、ノマルスキープリズム３７を光路に挿入可能に配置する。このノマルスキープリズムは第１の対物レンズと共に差分干渉光学系を構成する。従って、第２の１／４波長板３６を光路中に配置した反射型の検査モードにおいて、ノマルスキープリズム３７も光路中に配置すると、所定量だけ横ずらしされた像と横ずらしされていない像とが合成された差分干渉画像が形成される。この差分干渉画像を形成することにより、試料に存在する位相情報、例えば位相シフトマスクの位相シフタの形成の有無や表面の高さの差による干渉情報を電気信号として取り出すことができ、位相シフトマスクの検査に有用である。また、透過モードにおいて、ノルマルスキープリズムを光路中に配置することにより透過光の位相差による干渉情報を得ることができる。
【００３７】
図４に示す欠陥検査装置の光学系を利用して反射モードと透過モードとの間で切り換え可能なレーザ顕微鏡を構成することも可能である。レーザ顕微鏡として構成する場合、光検出器３３を各素子に蓄積された電荷を順次読み出して映像信号を発生するリニアイメージセンサで構成する。この場合、１／４波長板３６を光路に挿入又は取り出すだけで反射モードと透過モードとを切り換えることができる。従って、１個の光検出器を用いるだけで試料の透過像及び反射像の両方を撮像することができる。
【００３８】
図５は本発明による欠陥検査装置の光学系を利用したレーザ顕微鏡の構成を示す。本例では、図１に示す欠陥検査装置の光学系を利用して試料の反射像及び透過像を同時に撮像することができ、又は光路を切り換えることにより反射像又は透過像のいずれも撮像することができるレーザ顕微鏡について説明する。尚、図１で用いた構成要素と同一の構成要素には同一符号を付して説明する。レーザ光源１から発生したレーザ光、例えばP偏光したレーザ光は、第１の偏光ビームスプリッタ４０を透過し、１／２波長板及びファラディローテータ４２を経て第２の偏光ビームスプリッタ４３に入射する。１／２波長板４１を透過したレーザ光はファラディローテータ４２により元の偏光状態の光すなわちP偏光した光に変換されるので、第２の偏光ビームスプリッタ４３を第１の偏光面に設定することにより、入射したレーザ光は第２の偏光ビームスプリッタを透過する。この透過光はポリゴンスキャナ３により周期的に１方向に偏向され、第１の対物レンズ８を経て試料９に入射する。そして、試料９の表面で一部のレーザ光が反射し、残りのレーザ光は試料を透過する。試料９を透過したレーザ光は１／４波長板１３を経てミラー１５で反射し、再び１／４波長板１３を透過して試料９に入射し、再び試料を透過する。試料９の表面で反射した反射光及び試料９を２回透過した透過光は同一の光路を逆行し、ポリゴンスキャナ３によりデスキャンされ、第２の偏向ビームスプリッタ４３に入射する。
【００３９】
試料９を２回透過した透過光は１／４波長板１３を２回透過しているから、試料への入射光に対して偏光面が９０°回転しており、従って偏光ビームスプリッタ４３で反射する。偏光ビームスプタッタ４３で反射した試料からの反射光はリレーレンズ１７及びピンホール１８を経て第１の光検出器４４に入射する。第１の光検出器４４は、蓄積された電荷を駆動回路（図示せず）からの駆動信号に基づいて順次読み出して映像信号を発生する。従って、試料９の反射像が形成されることになる。
【００４０】
一方、試料９の表面で反射した反射光は偏光面が回転していないので、偏光ビームスプタッタ４３を透過する。そして、ファラディローテータ４２及び１／２波長板４１を通過して第１の偏光ビームスプリッタ４０に入射する。ファラディローテータ４２及び１／２波長板４１を通過することにより、試料からの反射光は偏光面が９０°回転しているので、この反射光は第１の偏光ビームスプリッタ４０で反射する。そして、リレーレンズ４５及びピンホール４６を経て第２の光検出器４７に入射する。第２の光検出器４７は、蓄積された電荷を駆動回路（図示せず）からの駆動信号に基づいて順次読み出して映像信号を発生する。従って、試料９の透過像が形成されることになる。このように構成すれば、試料の反射像及び透過像の両方を同時に撮像することができる。
【００４１】
尚、上述した実施例では、第２のビームスプリッタ４０を偏光ビームスプリッタで構成したが、入射する光のうち一部の光を反射し残りの光を透過するニュートラル形のビームスプリッタで構成することもできる。この場合、偏光変換光学系として機能する１／２波長板４１及びファラディローテータ４２は不要である。
【００４２】
図５に示すレーザ顕微鏡は、試料からの反射像及び透過像を同時に撮像することができるので、これらの反射光及び透過光を利用して欠陥検査装置としても用いることができる。すなわち、第１及び第２の光検出器４４及び４７の出力信号を信号処理回路に供給し、例えばこれらの信号の極性を互いに反転しレベル調整を行ってから加算することにより試料に形成されたパターンの欠陥を検出することができる。例えば、試料の表面にレジストのかすが残存している場合、光検出器４４に入射する試料からの反射光の光量が低下するため、加算された出力信号のレベルが基準のレベルよりも低下し、欠陥の存在を検出することができる。また、遮光パターンの膜厚が基準値よりも薄い場合透過光のレベルが基準値よりも高くなり、この結果加算された出力信号のレベルが基準レベルよりも上昇し、同様に欠陥の存在を検出することができる。勿論、上述した欠陥検査に加えて、試料からの反射光だけによる欠陥検査及び透過光だけによる欠陥検査も併せて同時に行うことができる。従って、本例の場合３種類の欠陥検査を行うことができる。さらに、本例においても、図４に示す実施例と同様にノマルスキープリズムを光路中に配置して差分干渉像を形成し、表面の高さの差による欠陥情報や透過光の位相差による欠陥情報を得ることもできる。従って、本例の欠陥検査装置は１個の検査装置で多種多様な欠陥検査を行うことができる利点が達成される。
【００４３】
本発明は上述した実施例だけに限定されず、種々の変形や変更が可能である。例えば、上述した図５に示したパターン欠陥検査装置及びレーザ顕微鏡は１本のレーザビームで試料を走査する構成としたが、勿論図４に示すように複数本のレーザビームを用いて試料を走査することもでき、この場合光検出器を複数の受光素子を有する光検出器で構成し、試料からの反射光又は透過光が対応する受光素子に入射するように構成する。
【図面の簡単な説明】
【図１】本発明による欠陥検査装置の一例の構成を示す線図である。
【図２】欠陥検査回路の一例の構成を示す回路図である。
【図３】ミラーの変形例を示す線図である。
【図４】本発明による欠陥検査装置の変形例を示す線図である。
【図５】本発明によるレーザ顕微鏡の一例を示す線図である。
【符号の説明】
１レーザ光源
２偏光ビームスプリッタ
３ビーム偏向装置
４４、６、１４、１７、３１、３２リレーレンズ
５高速ポジショナ
７ダイクロイックミラー
８第１の対物レンズ
９試料
１０試料ステージ
１１板厚補正素子
１２第２の対物レンズ
１３、３６１／４波長板
１５ミラー
１８光検出器
１９ピンホール
２０欠陥検出回路
３０回折格子[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a transmission type defect inspection apparatus suitable for inspecting a defect of a sample in which a plurality of patterns such as a photomask, a liquid crystal panel, and a color filter are formed on a transparent substrate.
[0002]
[Prior art]
Conventionally, in manufacturing an LSI, a photomask in which a light shielding pattern of metallic chromium is formed on a transparent glass substrate is used, and a photomask image is reduced and projected on a wafer by a projection optical system. Accordingly, there is a strong demand for the development of a defect inspection apparatus capable of accurately detecting photomask defects in order to improve the LSI manufacturing yield. In a conventional photomask defect inspection apparatus, using the principle of a transmission microscope, illumination light is projected onto a sample from the lower side of the sample to be inspected via a condenser lens, and the transmitted light from the sample is converted into an objective lens. Then, the image is picked up by an image detector such as a CCD camera, and the defect is detected using the amplitude information of the image.
[0003]
On the other hand, with the miniaturization of LSI line widths, photomasks that specify patterns not only with amplitude but also with amplitude and phase, such as halftone phase shift masks, are put into practical use as photomasks used in their production. Therefore, there is a strong demand for the development of an inspection apparatus that can inspect defects for these photomasks more accurately.
[0004]
[Problems to be solved by the invention]
With the miniaturization of LSI line widths, photomask patterns are further miniaturized, and it is demanded that finer defects can be accurately detected in accordance with the miniaturization of pattern size. In order to achieve this problem, it is necessary to further increase the lateral resolution of the defect inspection apparatus. However, in the conventional transmission type defect inspection apparatus, there is a limit to increase the resolution even if an optical element with better performance is used.
[0005]
In addition, as a defect of the photomask, there are many defects due to adhesion of transparent foreign matters such as resist wrinkles or semi-transparent foreign matters. However, since the conventional transmission type defect inspection apparatus has a low sensitivity to such a transparent defect, it has been pointed out that a defect that cannot detect a defect that should be detected originally is detected.
[0006]
Further, the transmittance of the light-shielding pattern of the halftone phase shift mask is set to about 10% at the projection wavelength when the pattern is actually projected onto the wafer, but at the inspection wavelength when performing the defect inspection. The transmittance is about 50%. Therefore, since the transmitted light amount ratio between the portion where the light shielding pattern is formed and the portion where the light shielding pattern is not formed is small, the contrast of the detected image is low, and there is a problem regarding the inspection accuracy.
[0007]
Further, as the pattern becomes finer, the chip size tends to increase, and the area for defect inspection is further expanded. Therefore, it is an important issue to further increase the inspection speed, that is, the throughput.
[0008]
An object of the present invention is to provide a transmission type defect inspection apparatus that can achieve higher lateral resolution, can accurately detect transparent defects, and has improved detection sensitivity.
[0009]
Furthermore, an object of the present invention is to provide a transmission type defect inspection apparatus that can achieve higher lateral resolution and higher throughput.
[0010]
[Means for Solving the Problems]
A pattern defect inspection apparatus according to the present invention is a pattern defect inspection apparatus for inspecting a defect of a pattern formed on a transparent substrate, and a light source device that emits a light beam and a light beam from the light source device in a first direction. A deflecting beam deflecting device; a first objective lens for focusing the deflected light beam onto a sample to be inspected; a sample stage for supporting the sample to be inspected; and a light beam transmitted through the sample as described above. A mirror that reflects toward the sample, a second objective lens that refocuss the light beam from the mirror and projects it onto the sample, and the sample Transmitted light transmitted twice , A defect detection circuit for processing a signal output from the photodetector to generate a defect detection signal, and driving the sample stage at least in a second direction orthogonal to the first direction A stage driving device that
The sample is emitted from the second objective lens Transmitted twice Transmitted light is incident on a photodetector through the first objective lens and a beam deflecting device.
[0011]
In the present invention, a double-pass method is adopted in which transmitted light that has passed through the sample to be inspected is reflected by a mirror and projected again toward the sample, and light that has passed through the sample twice is incident on the photodetector. Since the inspection beam is transmitted twice through the same part of the sample, the contrast is further increased, and even a sample using a light-shielding pattern with a relatively high transmittance in the inspection wavelength region such as a halftone phase shift mask is used. Defect inspection can be performed accurately. Furthermore, for a transparent defect such as a resist film flaw, for example, the inspection beam passes through the transparent defect twice, so that the light diffracted or scattered by the transparent defect increases. Since such light is emitted out of the optical path and does not enter the pupil of the optical system, it does not finally enter the photodetector, and as a result, the portion where the transparent defect exists is detected darker than the surroundings. . Therefore, it is possible to clearly detect a transparent defect that could not be detected by a conventional defect inspection apparatus.
[0012]
In a preferred example of the transmission defect inspection apparatus according to the present invention, a quarter-wave plate is disposed between the second objective lens and the mirror, and a polarization beam splitter is disposed between the light source device and the beam deflecting device. The inspection beam emitted from the light source device passes through the polarizing beam splitter and the light that has passed through the sample twice is reflected by the polarizing beam splitter. When the intensity of the light transmitted twice through the sample and the intensity of the light reflected by the light shielding pattern are close to each other, it may be difficult to distinguish between a portion where the light shielding pattern is formed and a portion where the light shielding pattern is not formed. For this reason, in this example, only the transmitted light from the sample is incident on the photodetector using polarized light. In this example, the light transmitted through the sample is transmitted through the quarter-wave plate, which is a phase plate, twice, so that the polarization plane is rotated by 90 ° and emitted from the sample, and is reflected by the polarizing beam splitter. On the other hand, since the light reflected by the sample surface does not pass through the quarter-wave plate, it maintains the same polarization state as the inspection beam emitted from the light source and passes through the polarizing beam splitter. As a result, only the light that has passed through the sample to be inspected twice can be incident on the photodetector. If comprised in this way, all the information by the reflected light from a sample will be removed, and only the information by the transmitted light from a sample can be detected. As a result, for example, when the film thickness of the light-shielding pattern is non-uniform, it can be detected as a defect, particularly when the film thickness is thinner than a prescribed thickness.
[0013]
Another embodiment of the pattern defect inspection apparatus according to the present invention is characterized in that the photodetector has a pinhole opening constituting a confocal optical system. If the optical system of the defect inspection apparatus constitutes a confocal optical system, it is possible to more effectively prevent flare from entering the photodetector, so that light diffracted or scattered by the defect enters the photodetector. This is more effectively prevented, and the presence of defects can be detected more clearly.
[0014]
According to the invention Another pattern defect inspection device , A pattern defect inspection apparatus for inspecting a pattern defect formed on a transparent substrate. A light source device that emits a plurality of light beams aligned along a first direction, a first objective lens that focuses the plurality of light beams onto a sample to be inspected, and supports the sample to be inspected A sample stage, A stage driving device for driving the sample stage in a second direction orthogonal to the first direction; A mirror that reflects a plurality of light beams transmitted through the sample toward the sample, and a sample by refocusing the plurality of light beams from the mirror Towards A second objective lens to project, and a plurality of light detection elements arranged in a direction corresponding to the first direction, each light detection element Transmitted beam transmitted twice And a defect detection circuit for generating a defect detection signal based on an output signal from the light detection element array. If comprised in this way, the sample which should be test | inspected will be scanned by a several light beam simultaneously, a test | inspection speed will become still faster and a throughput can be raised significantly. Since the pitch between the light beams can be adjusted by arranging a zoom lens in the optical path between the light source device and the sample, when the pattern of the sample to be inspected has periodicity, Can be made to coincide with the period of the pattern.
[0015]
According to the invention Pattern defect inspection system Is A pattern defect inspection apparatus for inspecting a pattern defect formed on a transparent substrate, A light source device that emits a plurality of light beams aligned along a first direction, a beam deflecting device that deflects the plurality of light beams in a first direction orthogonal to the first direction, and the plurality of light beams A first objective lens that focuses the light onto a sample to be inspected, a sample stage that supports the sample to be inspected, a mirror that reflects a plurality of light beams transmitted through the sample toward the sample, and Refocusing multiple light beams from the mirror into the sample Towards A second objective lens to project; The light source device And a beam splitter disposed in an optical path between the beam deflecting device and a plurality of photodetecting elements arranged in a direction corresponding to the first direction, and each photodetecting element includes the sample. Transmitted beam transmitted twice And a defect detection circuit for generating a defect detection signal based on an output signal from the photodetection element array, and from the second objective lens Multiple transmitted beams that exit and pass through the sample twice Is incident on the photodetecting element array via the first objective lens, the beam deflecting device, and the beam splitter. In this example, the sample is scanned two-dimensionally by scanning a plurality of light beams in a direction orthogonal to the arrangement direction. It is incident on the photodetection element array via the beam deflecting device By letting Since the transmitted light from the sample is descanned by the beam deflecting device, the light is kept stationary on the photodetecting element array. Therefore, by disposing the zoom lens between the polarization beam splitter and the light detection element array, the transmitted beam from the sample can be made incident on each light detection element.
[0016]
In a preferred embodiment of the transmission type defect inspection apparatus according to the present invention, the photodetecting element array is constituted by a photodiode array having a plurality of photodiodes, and output signals from the photodiodes are output in parallel. The defect is detected by comparing the two. In this case, defect inspection can be performed in real time, and the throughput is greatly improved.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram showing the configuration of an example of a pattern defect inspection apparatus according to the present invention. An inspection beam is emitted from the laser light source 1. The inspection beam passes through the polarization beam splitter 2 and enters the polygon scanner 3 which is a beam deflecting device. Various beam deflecting devices such as a vibrating mirror and a galvanometer mirror can be used as the beam deflecting device. The polygon scanner 3 periodically deflects the inspection beam in the first direction (in the paper) at a predetermined frequency. The inspection beam further enters the first objective lens system 8 via the relay lens 4, the high-speed positioner 5, the relay lens 6, and the dichroic mirror 7. This first objective lens system 8 focuses the inspection beam and projects it onto the sample 9 to be inspected. The sample 9 is placed on a sample stage 10 having an XY drive mechanism, and is periodically moved in a second direction orthogonal to the first direction during defect inspection. Therefore, the sample 9 is scanned two-dimensionally by the focused inspection beam.
[0018]
In this example, the sample to be inspected is a photomask in which a light shielding pattern of metallic chromium is formed on a transparent glass substrate. Of the light incident on the photomask, the light incident on the portion where the light shielding pattern is formed is reflected by the sample surface, and the light incident on the portion where the pattern is not formed is transmitted. The light transmitted through the photomask enters the total reflection mirror 15 through the plate thickness correction element 11, the second objective lens 12, the quarter wavelength plate 13, and the relay lens 14 perpendicularly. The transmitted light that has entered the mirror 15 travels in the same optical path and enters the sample 9 again through the relay lens 14, the quarter-wave plate 13, the second objective lens system 12, and the plate thickness correction element 11. The second objective lens system 12 has substantially the same focal position as the first objective lens system 8, focuses the light reflected by the mirror 15, and projects it onto the sample 9. Since the thickness of the transparent substrate of the sample to be inspected may be different, the plate thickness correcting element 11 is arranged to make the focal positions of the first objective lens system and the second objective lens system substantially coincide. For example, the variation in the thickness of the transparent substrate of about 0.1 mm can reduce the aberration by adjusting the distance between the lens elements of the objective lens system.
[0019]
In this way, since the inspection beam transmits the same part of the sample twice by using the double pass method in which the inspection beam transmits twice through the sample, the contrast is increased and a light-shielding pattern such as a halftone phase shift mask is obtained. It is possible to accurately inspect a pattern defect even in a sample having a large transmittance of the sample, and in particular, a sample in which the transmittance at the wavelength of the projection light is different from the transmittance at the wavelength of the inspection beam.
[0020]
The light emitted from the second objective lens system 12 and again transmitted through the sample 9 is condensed by the first objective lens system 8. Since this transmitted beam passes through the quarter-wave plate 13 twice, its polarization plane is rotated by 90 ° with respect to the polarization plane of the inspection beam incident on the sample. On the other hand, since the reflected beam reflected by the light-shielding pattern of the sample 9 and condensed by the first objective lens 8 does not pass through the quarter-wave plate, its polarization plane is the same as the inspection beam incident on the sample. .
[0021]
The transmitted light and reflected light from these samples are First And is incident on the dichroic mirror 7, a part of which is reflected and incident on the autofocus optical device 16, and an autofocus signal is taken out. As the autofocus optical device 16, a known autofocus optical device such as a so-called double focal method having an objective lens astigmatism element can be used, and detailed description thereof is omitted. By means of a drive signal formed based on the output signal from the autofocus optical device 16, the sample stage 10 is placed on the objective lens with the optical axis. Along the direction It is possible to focus the inspection beam on the sample surface at all times during the inspection by moving control.
[0022]
The light transmitted through the dichroic mirror 7 enters the high-speed positioner 5. This high-speed positioner 5 has two parallel flat plates, and by rotating these parallel flat plates, the light beam can be displaced in the X and Y directions of the sample. When the mask die is displaced in the X or Y direction, the light beam can be displaced at high speed.
[0023]
The light beam emitted from the high-speed positioner 5 enters the polygon scanner 3 through the relay lens 4 and is descanned. The outgoing beam from the polygon scanner enters the polarization beam splitter 2. Of the light incident on the polarization beam splitter 2, the reflected light from the surface of the photomask is transmitted because it has the same polarization plane as the light beam from the laser light source, and the transmitted light from the photomask is polarized. Is reflected by 90 °. Therefore, the reflected light and the transmitted light from the photomask are separated by the polarization beam splitter 2, and the transmitted light can be incident on the inspection optical system.
[0024]
The transmitted light from the sample separated by the polarization beam splitter 2 passes through the relay lens 17 and enters the photodetector 18 through the pinhole 19 disposed on the front surface of the photodetector 18. The photodetector 18 can be constituted by a photodiode, for example. Since the light beam incident on the photodetector is descanned by the polygon scanner 3, it is incident on the photodetector in a stationary state at all times. Thus, by disposing a pinhole on the front surface of the photodetector 18, a confocal optical system is configured, flare is removed, and resolution can be further increased.
[0025]
An output signal from the photodetector 18 is supplied to the defect detection circuit 20. FIG. 2 is a circuit diagram showing a configuration of an example of the defect detection circuit 20. An output signal from the photodiode 18 which is a photodetector is supplied to the A / D converter 21 and converted into a digital signal, and then supplied to the memory 22, and sequentially output after a predetermined time has elapsed. Then, it is supplied to a D / A converter, converted into an analog signal, and supplied to one input terminal of the differential amplifier 24. The output signal of the photodiode 18 is also supplied directly to the other terminal of the differential amplifier 24. The A / D converter 21, the memory 22, and the D / A converter 23 constitute a delay circuit, and the delay time can be set in consideration of, for example, the periodicity of the pattern to be inspected. One line cycle of the polygon scanner 3 is assumed. Therefore, in this example, comparison is made for each scanning line adjacent to each other. The output signal of the differential amplifier 24 is supplied to one input terminal of the comparison circuit 25, the predetermined reference voltage from the reference voltage generator 26 is supplied to the other input terminal, and the output from the differential amplifier 24 is supplied. Compare whether or not the reference voltage is exceeded. When the reference voltage is exceeded, a defect detection signal is generated, and it is determined that a defect exists. The defect detection circuit can be of various types. For example, a reference value for the entire photomask to be inspected is stored in a memory, and an output signal of the photodetector is stored in the memory. And can be directly compared. It is also possible to store data of one die or chip to be inspected in a memory and generate a defect detection signal in comparison with this data.
[0026]
FIG. 3 shows a modification of the mirror 15. In the embodiment described above, a mirror whose entire surface is reflective is used as the mirror 15, but in this example, the reflection surface is not the entire surface, and a linear reflection surface 15a extending in the beam scanning direction of the polygon scanner 3 is formed. Use the mirror. In this case, the formed beam transmitted through the sample 9 periodically moves along the linear mirror surface 15a, and only the light incident on the linear mirror surface is reflected by the mirror 15 and enters the sample 9 again. It will be. If comprised in this way, flare will be removed much more and confocality can be strengthened further.
[0027]
Furthermore, in this example, a quarter wavelength plate can be detachably disposed in the optical path between the dichroic mirror 7 and the first objective lens 8. In this case, when the quarter-wave plate is removed from the optical path, only the transmitted light that has passed through the sample 9 twice enters the photodetector 18. On the other hand, when the quarter-wave plate is disposed in the optical path, the transmitted light from the sample passes through the polarizing beam splitter 2 and does not enter the photodetector 18, and only the reflected light reflected from the surface of the sample 9 is polarized. The light is reflected by the beam splitter 2 and enters the photodetector 18. If comprised in this way, a reflection mode test | inspection and a transmission mode test | inspection can be switched only by inserting / removing a quarter wavelength plate.
[0028]
The defect inspection apparatus shown in FIG. 1 generates an image signal by sampling an output signal from a photodetector 18 at a constant frequency using a clock signal, scanning by the polygon scanner 3 is performed in the main scanning, and the stage 10 is orthogonal to the scanning direction. The laser microscope can be configured by moving it in the direction of movement. Therefore, the transmission image and the reflection image of the sample can be selectively picked up by disposing the above-described quarter wavelength plate in the optical path so as to be detachable.
[0029]
FIG. 4 shows the configuration of a transmission type defect inspection apparatus according to the present invention. In addition, the same code | symbol is attached | subjected and demonstrated to the component same as the component used in FIG. In this example, the throughput is greatly improved by using the multi-beam illumination method. The laser beam generated from the laser light source 1 is incident on the diffraction grating 30 and converted into a plurality of light beams aligned in the first direction, that is, the direction orthogonal to the paper surface. The plurality of light beams enter the polarization beam splitter 2 through the first and second relay lenses 31 and 32, pass through the polarization beam splitter 2, and enter the polygon scanner 3. The polygon scanner 3 periodically deflects a plurality of incident light beams at a predetermined frequency in a second direction (in-plane direction) perpendicular to the first direction. A plurality of light beams reflected by the polygon scanner 3 are incident on the first objective lens 8 through the third relay lens 4, the high-speed positioner 5, the fourth relay lens 6 and the ichroic mirror 7. The first objective lens 8 converges a plurality of incident light beams into a minute spot shape and projects it onto a sample 9 to be inspected for defects. Accordingly, a plurality of minute light spots are formed in a line shape on the sample 9 along a direction corresponding to the first direction.
[0030]
The transmitted light that has passed through the sample 9 enters the mirror 15 through the plate thickness correcting element 11, the second objective lens 12, the quarter wavelength plate 13, and the relay lens 14 perpendicularly. The plurality of transmitted beams incident on the mirror travels backward in the optical path, again enters the second objective lens 13 via the relay lens 14 and the quarter-wave plate 14, and is converged again into a minute spot, thereby obtaining a plate thickness correcting element. 11 is incident on the sample 9.
[0031]
The light transmitted through the sample 9 twice and the light reflected by the surface of the sample are collected by the first objective lens, and are incident on the polygon scanner 3 by being backlit on the optical path. Then, it is descanned by the polygon scanner 3 and enters the polarization beam splitter 2. Here, since the reflected light reflected by the surface of the sample 9 does not pass through the quarter-wave plate, it is in the same polarization state as the light emitted from the laser light source, while the light transmitted through the sample twice is 1 Since the light passes through the / 4 wavelength plate twice, its polarization plane is rotated by 90 ° with respect to the polarization plane of the outgoing beam from the light source. As a result, the reflected light from the sample is transmitted through the polarizing beam splitter 2, the transmitted light from the sample is reflected by the polarizing beam splitter, and the reflected light and the transmitted light from the sample are separated from each other.
[0032]
A plurality of transmitted beams from the sample reflected by the polarizing beam splitter 2 enter the photodetector 33 through the relay lens 17. Here, since the light beam incident on the photodetector 33 is descanned by the polygon scanner, it enters the photodetector 33 in a stationary state. In this example, the photodetector 33 is configured by a combination of a plurality of optical fibers and a plurality of photodiodes. The incident ends of the plurality of optical fibers are arranged in a line, and a photodiode is optically coupled to the output end of each optical fiber. Therefore, this photodetector can be considered as a linear image sensor in which a plurality of light receiving elements are arranged in a line. The incident ends of the plurality of optical fibers arranged in a line are arranged in a direction corresponding to the first direction. Accordingly, a plurality of transmitted beams from the sample are incident on the corresponding optical fibers, are incident on the respective photodiodes, are converted into electric signals, and are output in parallel. With this configuration, a confocal optical system is configured, and the photodiode array can be arranged at an arbitrary position, so that the degree of freedom in designing the optical system is increased. One of the relay lenses arranged in the optical path between the sample 9 and the light detector 33 is constituted by a zoom lens, and the magnification of the zoom lens is adjusted, so that the pitch of a plurality of transmitted beams from the sample can be adjusted to light. It can be matched to the pitch of the fiber array. In this example, the relay lens 17 is constituted by a zoom lens, and its magnification is adjusted so that each transmitted beam from the sample is incident on the corresponding optical fiber.
[0033]
Output signals from the photodetector 33 are output in parallel and supplied to the current-voltage conversion amplifier array 34, and the signals converted into voltage signals are supplied to the comparison circuit 35. In the comparison circuit 35, output signals from the respective photodetecting elements are compared, and for example, output signals between adjacent photodetecting elements are compared to generate a defect detection signal. The defect detection can not only compare output signals from adjacent elements but also compare output signals between elements such as every other element or every other element. With this configuration, the specimen can be scanned with a plurality of light beams simultaneously, and output signals from the photodetector can be simultaneously output in parallel to perform defect detection, greatly reducing the defect inspection time. In addition, the throughput can be greatly improved.
[0034]
In this example, a second quarter-wave plate 36 is detachably arranged with respect to the optical path between the beam deflecting device 3 and the first objective lens 8, and the defect due to the transmitted light from the sample. It is configured so that inspection and defect inspection by reflected light can be switched freely. When the second quarter-wave plate 36 is excluded from the optical path, only the transmitted light from the sample is incident on the photodetector as described above, and the transmission type defect inspection is performed. On the other hand, when the second quarter-wave plate 36 is inserted into the optical path, the reflected light from the sample is rotated by 90 ° with respect to the light emitted from the laser light source and reflected by the polarizing beam splitter 2. On the other hand, since the transmitted light from the sample passes through each of the two quarter wavelength plates twice, its polarization plane coincides with the polarization plane of the light emitted from the laser light source and passes through the polarization beam splitter 2. To do. As a result, only the reflected light from the sample is reflected by the polarization beam splitter 2 and enters the photodetector, and a reflection type defect inspection by the reflected light is performed. Thus, the defect inspection apparatus of this example can easily switch between the transmission type and the reflection type simply by switching the insertion of the second quarter-wave plate into the optical path. Increase significantly. The second quarter wave plate can be disposed at any position between the polarizing beam splitter 2 and the sample 9.
[0035]
The pitch between the multiple light beams generated from the light source device is defined by the conditions of the diffraction grating used, but when it is desired to freely set the pitch between the inspection beams according to the characteristics of the sample to be inspected for defects There are also many. In particular, when the pattern to be inspected formed on the sample has periodicity, it may be desired to inspect the defect by matching the pitch of the plurality of inspection beams generated from the light source device to the pattern pitch. In order to meet such requirements, a zoom lens system is disposed between the light source device and the first objective lens, and the magnification of the zoom lens system is adjusted to match the pitch of the inspection beam with the pitch of the pattern to be inspected. Can do. With this configuration, since each inspection beam scans the same portion of each pattern, the presence of a defect can be found by simply comparing output signals from the photodetector.
[0036]
Further, in this example, a Nomarski prism 37 is disposed between the polygon scanner 3 serving as a beam deflecting device and the first objective lens 8 so as to be inserted into the optical path. This Nomarski prism constitutes a differential interference optical system together with the first objective lens. Accordingly, in the reflection type inspection mode in which the second quarter-wave plate 36 is disposed in the optical path, when the Nomarski prism 37 is also disposed in the optical path, an image shifted laterally by a predetermined amount and an image not laterally shifted are obtained. Are combined to form a differential interference image. By forming this differential interference image, phase information existing in the sample, for example, interference information due to the presence or absence of the phase shifter of the phase shift mask and the difference in surface height can be extracted as an electrical signal. It is useful for inspection. Further, in the transmission mode, interference information based on a phase difference of transmitted light can be obtained by arranging a normal ski prism in the optical path.
[0037]
It is also possible to configure a laser microscope that can be switched between a reflection mode and a transmission mode by using the optical system of the defect inspection apparatus shown in FIG. When configured as a laser microscope, the photodetector 33 is configured by a linear image sensor that sequentially reads out the charges accumulated in each element and generates a video signal. In this case, it is possible to switch between the reflection mode and the transmission mode simply by inserting or removing the quarter-wave plate 36 into the optical path. Therefore, both a transmission image and a reflection image of the sample can be taken by using only one photodetector.
[0038]
FIG. 5 shows a configuration of a laser microscope using the optical system of the defect inspection apparatus according to the present invention. In this example, the reflected image and the transmitted image of the sample can be simultaneously captured using the optical system of the defect inspection apparatus shown in FIG. 1, or both the reflected image and the transmitted image are captured by switching the optical path. A laser microscope that can be used will be described. In addition, the same code | symbol is attached | subjected and demonstrated to the component same as the component used in FIG. Laser light generated from the laser light source 1, for example, P-polarized laser light, passes through the first polarizing beam splitter 40, and enters the second polarizing beam splitter 43 through the half-wave plate and the Faraday rotator 42. Since the laser beam that has passed through the half-wave plate 41 is converted by the Faraday rotator 42 into light in the original polarization state, that is, P-polarized light, the second polarization beam splitter 43 is set to the first polarization plane. Thus, the incident laser light is transmitted through the second polarization beam splitter. This transmitted light is periodically deflected in one direction by the polygon scanner 3 and enters the sample 9 through the first objective lens 8. Then, a part of the laser light is reflected on the surface of the sample 9, and the remaining laser light is transmitted through the sample. The laser beam that has passed through the sample 9 passes through the quarter-wave plate 13 and is reflected by the mirror 15 and then passes through the quarter-wave plate 13 again. The It enters the sample 9 and again passes through the sample. The reflected light reflected from the surface of the sample 9 and the transmitted light transmitted twice through the sample 9 are the same. The light path Reversely, it is descanned by the polygon scanner 3 and enters the second deflecting beam splitter 43.
[0039]
Since the transmitted light that has been transmitted through the sample 9 twice is transmitted through the quarter-wave plate 13 twice, the plane of polarization is rotated by 90 ° with respect to the light incident on the sample, and is therefore reflected by the polarizing beam splitter 43. To do. The reflected light from the sample reflected by the polarization beam splitter 43 is incident on the first photodetector 44 through the relay lens 17 and the pinhole 18. The first photodetector 44 sequentially reads the accumulated charges based on a drive signal from a drive circuit (not shown) to generate a video signal. Accordingly, a reflected image of the sample 9 is formed.
[0040]
On the other hand, the reflected light reflected by the surface of the sample 9 is transmitted through the polarization beam sputter 43 because the polarization plane is not rotated. Then, the light passes through the Faraday rotator 42 and the half-wave plate 41 and enters the first polarizing beam splitter 40. By passing through the Faraday rotator 42 and the half-wave plate 41, the reflected light from the sample has its polarization plane rotated by 90 °, and this reflected light is reflected by the first polarizing beam splitter 40. Then, the light enters the second photodetector 47 through the relay lens 45 and the pinhole 46. The second photodetector 47 sequentially reads the accumulated charges based on a drive signal from a drive circuit (not shown) to generate a video signal. Accordingly, a transmission image of the sample 9 is formed. If comprised in this way, both the reflected image and transmitted image of a sample can be imaged simultaneously.
[0041]
In the above-described embodiment, the second beam splitter 40 is configured by a polarization beam splitter. However, the second beam splitter 40 is configured by a neutral beam splitter that reflects part of incident light and transmits the remaining light. You can also. In this case, the half-wave plate 41 and the Faraday rotator 42 that function as a polarization conversion optical system are unnecessary.
[0042]
Since the laser microscope shown in FIG. 5 can simultaneously capture a reflected image and a transmitted image from a sample, it can also be used as a defect inspection apparatus using these reflected light and transmitted light. That is, the output signals of the first and second photodetectors 44 and 47 are supplied to the signal processing circuit, and for example, the polarities of these signals are inverted to adjust each other and then added to the sample. Pattern defects can be detected. For example, when resist residue remains on the surface of the sample, the amount of reflected light from the sample incident on the photodetector 44 decreases, so the level of the added output signal decreases below the reference level, The presence of a defect can be detected. In addition, when the thickness of the light shielding pattern is thinner than the reference value, the transmitted light level becomes higher than the reference value. As a result, the level of the added output signal rises above the reference level, and the presence of a defect is detected similarly. can do. Of course, in addition to the above-described defect inspection, a defect inspection using only reflected light from a sample and a defect inspection using only transmitted light can be simultaneously performed. Accordingly, in this example, three types of defect inspection can be performed. Further, in this example, similarly to the embodiment shown in FIG. 4, a Nomarski prism is arranged in the optical path to form a differential interference image, and defect information due to a difference in surface height and defect information due to a phase difference of transmitted light. You can also get Therefore, the defect inspection apparatus of this example achieves the advantage that a wide variety of defect inspections can be performed with one inspection apparatus.
[0043]
The present invention is not limited to the above-described embodiments, and various modifications and changes can be made. For example, the pattern defect inspection apparatus and laser microscope shown in FIG. 5 described above are configured to scan the sample with one laser beam, but of course, the sample is scanned using a plurality of laser beams as shown in FIG. In this case, the photodetector is composed of a photodetector having a plurality of light receiving elements, and the reflected light or transmitted light from the sample is made incident on the corresponding light receiving elements.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an example of a defect inspection apparatus according to the present invention.
FIG. 2 is a circuit diagram showing a configuration of an example of a defect inspection circuit.
FIG. 3 is a diagram showing a modification of the mirror.
FIG. 4 is a diagram showing a modification of the defect inspection apparatus according to the present invention.
FIG. 5 is a diagram showing an example of a laser microscope according to the present invention.
[Explanation of symbols]
1 Laser light source
2 Polarizing beam splitter
3 Beam deflector
4 4, 6, 14, 17, 31, 32 Relay lens
5 High-speed positioner
7 Dichroic mirror
8 First objective lens
9 samples
10 Sample stage
11 Thickness correction element
12 Second objective lens
13, 36 1/4 wave plate
15 Mirror
18 Photodetector
19 pinhole
20 Defect detection circuit
30 diffraction grating

Claims

A pattern defect inspection apparatus for inspecting a defect of a pattern formed on a transparent substrate, comprising: a light source device that emits a light beam; a beam deflection device that deflects the light beam from the light source device in a first direction; A first objective lens that focuses the projected light beam onto a sample to be inspected, a sample stage that supports the sample to be inspected, a mirror that reflects the light beam transmitted through the sample toward the sample, A second objective lens for refocusing the light beam from the mirror and projecting it onto the sample, a photodetector for receiving the transmitted light that has passed through the sample twice , and an output signal from the photodetector are processed. A defect detection circuit that generates a defect detection signal and a stage driving device that drives the sample stage in at least a second direction orthogonal to the first direction,
A pattern defect inspection apparatus, wherein transmitted light that has been emitted from the second objective lens and transmitted through the sample twice is incident on a photodetector through the first objective lens and a beam deflecting device.

A pattern defect inspection apparatus for inspecting a pattern defect formed on a transparent substrate,
A laser light source that emits a light beam in a first polarization state, a beam deflecting device that deflects the light beam from the laser light source in a first direction, and the deflected light beam is focused and projected onto a sample to be inspected. A first objective lens, a sample stage for supporting a sample to be inspected, a stage driving device for driving the sample stage in a second direction orthogonal to the first direction, and a light beam transmitted through the sample A mirror that reflects toward the sample, a second objective lens that refocuss the light beam from the mirror and projects it toward the sample, and a light that is disposed between the mirror and the sample and has passed twice A quarter-wave plate for converting the polarization state of the light from the first polarization state to the second polarization state, a photodetector for receiving the transmitted light that has passed through the sample twice , and the first objective lens and light detection And the first bias A polarization beam splitter that transmits light in a state and reflects light in a second polarization state; and a defect detection circuit that processes a signal output from the photodetector and generates a defect detection signal. A pattern defect inspection apparatus, wherein transmitted light that has been emitted from the objective lens and transmitted through the sample twice is incident on a photodetector through the first objective lens, a beam deflecting device, and a polarizing beam splitter.

The pattern defect inspection apparatus according to claim 1, wherein the photodetector has a pinhole opening constituting a confocal optical system.

A quarter wave plate is detachably disposed between the polarizing beam splitter and the sample, and is configured to selectively enter reflected light or transmitted light from the sample into the photodetector. The pattern defect inspection apparatus according to claim 2 or 3.

5. The pattern defect inspection apparatus according to claim 4, wherein an optical element for correcting a thickness of a transparent substrate of a sample to be inspected is disposed between the first objective lens and the second objective lens. .

5. The pattern defect inspection apparatus according to claim 4, wherein the mirror has a linear reflection surface, and the direction of the linear reflection surface coincides with the scanning direction of the light beam transmitted through the sample.

A pattern defect inspection apparatus for inspecting a defect of a pattern formed on a transparent substrate, wherein the light source apparatus emits a plurality of light beams aligned in a first direction, and the plurality of light beams are focused and inspected. A first objective lens that projects onto the sample to be tested; a sample stage that supports the sample to be inspected; a stage drive device that drives the sample stage in a second direction orthogonal to the first direction; and the sample A mirror for reflecting the plurality of light beams transmitted through the sample toward the sample , a second objective lens for refocusing the plurality of light beams from the mirror and projecting the sample toward the sample , and the first direction. have a corresponding plurality of which are arranged in a direction the light detecting element, and a light sensing element array for receiving the transmitted beam by each light detecting element is transmitted twice through the sample, respectively, the output signal from the photodetecting element array Based on the pattern defect inspection apparatus characterized by comprising a defect detection circuit for generating a defect detection signal.

A pattern defect inspection apparatus for inspecting defects of the formed on the transparent substrate pattern, a light source device which emits a plurality of light beams aligned along a first direction, a plurality of light beams first direction A beam deflecting device that deflects in a first direction orthogonal to the first direction, a first objective lens that focuses the plurality of light beams onto a sample to be inspected, a sample stage that supports the sample to be inspected, and A mirror that reflects a plurality of light beams transmitted through the sample toward the sample, a second objective lens that refocuses the plurality of light beams from the mirror and projects the light toward the sample, the light source device, and the beam A beam splitter disposed in the optical path between the deflecting device and a plurality of light detection elements arranged in a direction corresponding to the first direction, each light detection element transmitting through the sample twice the beam its A photodetecting element array for receiving, respectively, comprising a defect detection circuit for generating a defect detection signal based on the output signal from the photodetecting element array, and the sample is emitted from the second objective lens passes twice A pattern defect inspection apparatus, wherein a plurality of transmitted beams are incident on a light detection element array via the first objective lens, a beam deflecting device, and a beam splitter.

The beam splitter is composed of a polarizing beam splitter, and a quarter wavelength plate is disposed between the mirror and the sample, and only the transmitted light that has passed through the sample twice is incident on the photodetector array. The pattern defect inspection apparatus according to claim 8.

A quarter-wave plate is detachably disposed in the optical path between the polarizing beam splitter and the first objective lens, and the light reflected by the sample or the light transmitted through the sample twice is applied to the photodetecting element array. The pattern defect inspection apparatus according to claim 9, wherein the pattern defect inspection apparatus is configured to selectively enter the pattern defect.

8. The photodetecting element array is composed of a plurality of photodiode arrays, output signals from the respective photodiodes are output in parallel, and defects are detected by comparing the output signals with each other. 10. The pattern defect inspection apparatus according to any one of 9 to 9.

A relay lens is disposed between the photodetecting element array and the first objective lens, the relay lens is constituted by a zoom lens, and the light beam from the sample corresponds by adjusting the magnification of the zoom lens. The pattern defect inspection apparatus according to claim 8, wherein the pattern defect inspection apparatus is configured to be incident on a detection element.

9. The pattern defect inspection apparatus according to claim 8, wherein a Nomarski prism is detachably disposed in an optical path between the beam deflecting device and the first objective lens.

A laser light source that emits a light beam in a first polarization state, a beam deflecting device that deflects the light beam from the laser light source in a first direction, and the deflected light beam is focused and projected onto a sample to be inspected. A first objective lens; a sample stage for supporting a sample to be inspected; a stage driving device for driving the sample stage in at least a second direction orthogonal to the first direction; and a light beam transmitted through the sample A mirror that reflects the light beam toward the sample, a second objective lens that refocuss the light beam from the mirror and projects the light beam onto the sample, and is disposed between the mirror and the sample. A quarter-wave plate for converting the polarization state from the first polarization state to the second polarization state, and disposed in the optical path between the laser light source and the beam deflecting device, and the light in the first polarization state Transmitted and second polarized A first polarizing beam splitter for reflecting light, an optical path between the first photodetector for receiving the transmitted light from the sample which is reflected by the first polarized beam splitter, and the laser light source and the beam deflecting device Defect detection by processing a beam splitter disposed therein, a second photodetector for receiving reflected light from the sample reflected by the beam splitter, and output signals from the first and second photodetectors A pattern defect inspection apparatus comprising: a defect detection circuit that generates a signal.

The beam splitter includes a second polarization beam splitter that transmits light in the first polarization state and reflects light in the second polarization state, and is disposed between the second polarization beam splitter and the beam deflecting device. A polarization conversion optical system for converting the polarization state of the reflected light from the sample from the first polarization state to the second polarization state in the optical path, and the reflected light from the sample to the polarization conversion optical system and the second The pattern defect inspection apparatus according to claim 14, wherein the light is incident on the second photodetector through the polarizing beam splitter .

The pattern defect inspection apparatus according to claim 15 , wherein the polarization conversion optical system includes a half-wave plate and a Faraday rotator.

15. The pattern defect inspection apparatus according to claim 14, wherein the beam splitter is a neutral beam splitter that reflects a part of incident light and transmits the remaining light.

A light source device that emits a plurality of light beams aligned along a first direction, a beam deflecting device that deflects the plurality of light beams in a second direction orthogonal to the first direction, and the plurality of light beams A first objective lens that focuses the light onto a sample to be inspected, a sample stage that supports the sample to be inspected, a mirror that reflects a plurality of light beams transmitted through the sample toward the sample, and A second objective lens for refocusing a plurality of light beams from the mirror and projecting the same onto the sample; and a plurality of light detection elements arranged in a direction corresponding to the first direction. A photodetecting element array for receiving a transmitted beam that has passed through the sample twice; a signal processing circuit for forming a video signal based on an output signal from the photodetecting element array; and the light source device and the beam deflecting device. Placed between Is, comprising a beam splitter for separating the light beam from the light beam and the sample from the light source device, said second emitted from the objective lens transmitting the beam transmitted through the sample twice the first objective lens, the beam deflection device And a laser microscope that is incident on the photodetecting element array via a beam splitter.

19. The laser microscope according to claim 18, wherein a quarter-wave plate is disposed in an optical path between the mirror and the second objective lens, and the beam splitter is a polarization beam splitter.

Another quarter wavelength plate is detachably disposed in the optical path between the beam deflecting device and the first objective lens so that a transmission image or a reflection image of the sample can be selectively captured. The laser microscope according to claim 19.