JP3632241B2

JP3632241B2 - Position detection device

Info

Publication number: JP3632241B2
Application number: JP13678395A
Authority: JP
Inventors: 直正白石
Original assignee: Nikon Corp
Current assignee: Nikon Corp
Priority date: 1995-06-02
Filing date: 1995-06-02
Publication date: 2005-03-23
Anticipated expiration: 2020-03-23
Also published as: JPH08327318A

Description

【０００１】
【産業上の利用分野】
本発明は、例えば半導体素子等を製造する際にマスクパターンを感光性の基板上に露光するフォトリソグラフィ工程で使用される露光装置に適用されるマスクパターンと感光性基板の相対的な位置合わせ技術に関し、特に感光基板上のマークパターンの検出技術に関するものである。
【０００２】
【従来の技術】
例えば半導体素子、液晶表示素子、薄膜磁気ヘッド、撮像素子（ＣＣＤ）、又は光磁気ディスク等を製造するためのフォトリソグラフィ工程では、転写用のパターンが形成されたフォトマスク又はレチクル（以下、まとめて「レチクル」という）の像を、投影光学系を介した投影露光法、あるいはプロキシミティ露光法により、フォトレジストが塗布されたウエハ、又はガラスプレート等の感光基板上に転写する露光装置が使用されている。
【０００３】
このような露光装置においては、露光に先立ってレチクルとウエハとの位置合わせ（アライメント）を高精度に行う必要がある。このアライメントを行うために、ウエハ上には以前の工程で形成（露光転写）された位置検出マーク（アライメントマ−ク）が形成されており、このアライメントマ−クの位置を検出することで、ウエハ（ウエハ上の回路パターン）の正確な位置を検出することができる。
【０００４】
アライメントマークの検出方法としては、例えばレーザビームスキャン方式、レーザ干渉式等のレーザ光の散乱、回折光を検出するものがある。しかしながら、レーザ光は単色性が強く、フォトレジスト表面とマーク表面との多重干渉等の悪影響により、位置検出精度が悪化する恐れがある。
これに対して、ランプ等を光源としてアライメントマークをブロードバンドな光束で照明し、その像を結像光学系を介して撮像し、その画像信号に基づいて位置検出を行なう方式（以後「結像式位置検出」と称す）は、フォトレジスト等の悪影響を受けにくいというメリットがある。
【０００５】
【発明が解決しようとする課題】
近年、半導体集積回路等の微細化に伴い、成膜工程後であってフォトリソグラフィ工程前に、ウエハ表面を平坦化する工程が導入されるようになった。これには、回路パターンが形成される生成膜の厚さを均一化して素子特性を改善する効果と、フォトリソグラフィ工程においてウエハ表面の凹凸が転写パターンの線幅誤差に与える悪影響を改善する効果がある。
【０００６】
しかしながら、ウエハ表面のアライメントマーク部での凹凸変化や反射率変化を基に位置検出を行なう方式においては、平坦化工程によりアライメントマーク部での凹凸変化が著しく減少するため、アライメントマークを検出できなくなる恐れがある。特に不透明な生成膜（金属や半導体膜）に対する工程では、アライメントマークは一様な反射率の不透明膜で被われる。このため、位置検出はマークの凹凸変化のみに頼ることになり、不透明な生成膜は平坦化が最も問題となる工程である。
【０００７】
本発明は上述の問題点を鑑みてなされたもので、凹凸変化（段差）の極めて小さい位置検出マークであっても精度良く確実にその位置を検出できる位置検出装置を提供することを目的とする。
【０００８】
【課題を解決するための手段】
本発明は、所定の波長域の照明光（例えば広帯域光、又は多波長光）で基板上の位置検出マークを照射する照明光学系と、その位置検出マークから発生する光を入射して撮像素子上にその位置検出マークの像を形成する結像光学系とを備え、撮像素子から出力される画像信号に基づいてその位置検出マークの位置を検出する装置に適用されるものである。
【０００９】
そして本発明では、位置検出マークに対して実質的に光学的フーリエ変換の関係となる照明光学系中の第１面（瞳面）上での照明光を、照明光学系の光軸を中心とするほぼ輪帯状の第１領域内に制限する光束制限部材と、位置検出マークに対して実質的に光学的フーリエ変換の関係となる結像光学系中の第２面（瞳面）上の、第１領域と結像関係となるほぼ輪帯状の第２領域とそれ以外の領域とにそれぞれ分布する結像光束の位相を異ならせる位相差部材とを設ける。
【００１０】
または、照明光学系中の第１面上での照明光を、その光軸を中心とするほぼ輪帯状の第１領域内に制限する光束制限部材と、結像光学系中の第２面上に分布する、位置検出マークからの０次光とそれ以外の光の位相を異ならせる位相差部材とを設けるようにしてもよい。
あるいは、照明光学系中の第１面上での照明光、又は２次光源（面光源）の強度分布を、輪帯状の第１領域で他の領域よりも高める光学部材と、結像光学系中の第２面上の、第１領域と結像関係となるほぼ輪帯状の第２領域とそれ以外の領域とにそれぞれ分布する結像光束の位相を異ならせる位相差部材とを設けるようにしてもよい。
【００１１】
もしくは、照明光学系の実質的な瞳面上の、輪帯状の第１領域内に分布する照明光束を透過せしめる絞り部材と、結像光学系中の第２面上の、第１領域と結像関係となるほぼ輪帯状の第２領域とそれ以外の領域とにそれぞれ分布する結像光束の位相を異ならせる位相差部材とを設けるようにしてもよい。
または、照明光学系の実質的な瞳面上に、その光軸を中心とするほぼ輪帯状の２次光源（もしくは、その瞳面上の光軸を中心とするほぼ輪帯状の領域内に複数の光源像）を形成する部材と、結像光学系の実質的な瞳面上の、その２次光源と結像関係となるほぼ輪帯状の領域とそれ以外の領域とにそれぞれ分布する結像光束の位相を異ならせる位相差部材とを設けるようにしてもよい。
【００１２】
あるいは、照明光学系の実質的な瞳面上での光強度分布を、照明光学系の光軸を中心とするほぼ輪帯状の領域でその内側の領域よりも高める光学部材と、結像光学系の実質的な瞳面上の、その内側領域と結像関係となるほぼ円形の領域とそれ以外の領域とにそれぞれ分布する結像光束の位相を異ならせる位相差部材とを設けるようにしてもよい。
【００１３】
また、結像光学系中の第２面上の輪帯状の領域内に分布する結像光束、即ちその第２面上に分布する０次光を減光する部材を有することが望ましい。この減光部材は、位相差部材と一体に形成してもよいし、位相差部材に近接して配置しても、あるいは位相差部材とほぼ共役な面（瞳共役面）内に配置してもよい。
さらに位相差部材は、第２領域内に分布する結像光束とそれ以外の領域内に分布する結像光束との間に、ほぼ（２ｍ＋１）π／２±π／４［ｒａｄ］（ｍは整数）の位相差を与えることが望ましい。このとき、第２領域内に分布する結像光束の位相とそれ以外の領域内に分布する結像光束の位相のどちらをシフトさせてもよい。また、両光束の位相シフト量をそれぞれ異ならせて前述の位相差を与えるようにしてもよい。
【００１４】
また、照明光のうち画像信号の形成に寄与する光束の波長域中の最短波長をλ１、最長波長をλ２、位置検出マークの周期をＰとすると、輪帯状の第１領域の外半径ｒｏ、及び内半径ｒｉは、
ｒｉ≧λ２／（２×Ｐ）
ｒｏ−ｒｉ≦λ１／Ｐ
の関係を満たすことが望ましい。また、結像光学系の開口数ＮＡｏは、
ＮＡｏ≧ｒｏ＋λ２／Ｐ
の関係を満たすことが望ましい。
【００１５】
さらに、結像光学系の光路に対して位相差部材を挿脱可能に保持する部材を設けると良い。さらにこのとき、照明光学系の光路に対して光束制限部材（又は光学部材、絞り部材、２次光源（光源像）形成部材）を挿脱可能に保持する部材も設けると良い。
また、撮像素子上に指標マークの像を形成する像形成手段を設け、撮像素子から出力される画像信号に基づいて位置検出マークの像と指標マークの像との位置ずれを検出するようにしても良い。この像形成手段は、指標マークを有する指標板と、基板上に照射される照明光とは異なる光ビームで指標板を照射する照明系と、指標マークから発生した光を入射してその像を撮像素子上に形成する結像系とを有することが望ましい。特に指標板を、結像光学系中の基板と実質的に共役な面に配置し、結像光学系によって、位置検出マークの像を指標板上に形成するとともに、この位置検出マークの像と指標マークの像とを撮像素子上に形成するようにしても良い。
【００１６】
さらに、例えば照明光学系の光路に対する光束制限部材（又は光学部材等）の挿脱、又は交換に伴う、撮像素子に入射する位置検出マークからの結像光束の光量変化に応じて、指標マークを照明する光ビームの強度の調整する部材を設けることが望ましい。一例としては、照明光路からの光束制限部材の退出に連動して、その光ビームの強度を高くする。この調整部材は、光ビームを射出する光源に供給する電力（電流、電圧）を変化させるもの、あるいは透過率が異なる複数の減光フィルターをそれぞれ交換してビーム光路に配置するもの等でよい。
【００１７】
また、照明光学系中の第１面上での照明光（又は２次光源）の強度分布を、輪帯状の第１領域で他の領域よりも高める光学部材は、他の領域での光強度をほぼ零にするように、他の領域をほぼ覆う遮光部を持つ絞り部材でも良い。
さらに光学部材は、輪帯状の第１領域の外半径と内半径の少なくとも一方を変化させる強度分布変更部材を有することが望ましい。この強度分布変更部材は、輪帯状の開口の外半径と内半径の少なくとも一方が異なる複数の絞り部材と、この複数の絞り部材の１つを照明光学系の光路中に配置するように複数の絞り部材を保持する部材とを持つようにしても良い。さらに位相差部材は、第１領域の外半径と内半径の少なくとも一方の変化に応じて、輪帯状の第２領域の半径方向の幅と位置との少なくとも一方を変化させることが望ましい。
【００１８】
また、前述した輪帯状の第１領域（２次光源）の外半径や内半径（即ち半径方向の幅や位置）、照明光の強度分布の変更は、例えば液晶素子、又はエレクトロクロミック素子で作られた開口絞りを瞳面に配置する、あるいは開口部の外半径と内半径の少なくとも一方が異なる複数の絞り部材をそれぞれ交換して光路中に配置可能に構成することで実現できる。あるいは、可変開口絞りを瞳面に配置してその開口径を任意に変更可能（又は開口径が異なる複数の開口絞りをそれぞれ交換して光路中に配置可能）として外半径を変更するようにし、かつ互いに直径が異なる複数の円形の遮光板をそれぞれ交換して光路中に配置可能に構成して内半径を変更するようにしてもよい。
【００１９】
さらに、前述した輪帯状の第２領域の外半径や内半径（即ち半径方向の位置や幅）の変更は、例えば輪帯状の位相シフター（誘電体膜等）、あるいは輪帯状の凹部（又は凸部）の半径方向の位置と幅の少なくとも一方が異なる複数の透明基板をそれぞれ交換して光路中に配置可能に構成することで実現できる。尚、輪帯状の位相シフターを設ける代わりに、輪帯状の第２領域以外に位相シフターを設けるようにしてもよい。または、光学的な厚さはほぼ同一で、直径が異なる複数の円形透明板をそれぞれ交換して光路中に配置可能に構成するだけでもよい。但し、前述した第１領域の外半径を変更するときは、その変更された第１領域と結像関係となる第２領域内の結像光束とその外側の結像光束との間に位相差を付与できないが、その変更により像コントラストや忠実性が、所望の位置検出精度を得られない程度に劣化しなければ何ら問題ない。尚、像コントラストや忠実性の劣化が問題になるときは、例えば可変開口絞りによって第２領域の外側に分布する結像光束を遮光するようにしてもよい。
【００２０】
【作用】
ほぼ平坦な被検物上の「段差」部のみを検出する光学系としては、「暗視野顕微鏡」や「位相差顕微鏡」が知られている。暗視野顕微鏡は、結像光学系の瞳面（被検物に対するフーリエ変換面）に遮光領域を設け、被検物（例えばウエハ上の位置検出マーク）への照明光の照射によってその被検物から発生する反射回折光のうち、０次回折光（正反射光）を遮光し、高次回折光（及び散乱光）のみによる像を形成するものである。このうち０次回折光は、被検物の凹凸や反射率変化に関する情報をほとんど含まないが、高次（１次以上）の回折光はこれらの情報を含んでいる。従って暗視野顕微鏡では、０次回折光が遮光され、高次回折光のみにより像が形成されるため、通常の（明視野の）顕微鏡よりも明瞭に（高コントラストで）段差を可視化することが可能となる。
【００２１】
これに対して位相差顕微鏡は、結像光学系の瞳面に、０次回折光と他の次数の回折光（及び散乱光）との間に位相差を与えて透過せしめる位相差フィルターを設けたものである。低段差のマークパターンから発生する高次（１次以上）回折光の光量は極めて僅かであるが、位相差顕微鏡では光量の多い０次回折光も像形成に寄与させることができるため、暗視野顕微鏡よりも明るい（強度の大きい）像を得ることができる。尚、０次回折光と他の次数の回折光との強度比が極端に大きいと像コントラストが低下するため、０次回折光を減光することもある。
【００２２】
しかしながら、従来の位相差顕微鏡をウエハ上の位置検出マークの検出に用いると、像形成に不要な０次回折光だけでなく、他の次数の回折光（像形成に寄与する有益な回折光）に対しても位相差の付加や減光効果が及んでしまい、像のコントラストや忠実性が劣化するという問題がある。
そこで本発明では、ウエハ等の基板上の位置検出マークには通常、その位置検出方向にある一定の周期性（周期Ｐ）があることに着目し、その周期性により生じる０次以外の回折光が極力、位相差部材の影響を受けないように、その位相差部材、及び照明光学系の２次光源（照明光学系の瞳面での照明光束分布、又は照明光の強度分布）の形状を設定したので、０次回折光のみに対して重点的に位相差を付加する、さらには減光することができる。
【００２３】
即ち本発明では、位置検出マークに対して実質的に光学的フーリエ変換の関係となる照明光学系中の第１面（瞳面）での照明光束を、光軸を中心とするほぼ輪帯状の第１領域内に制限し、かつ位置検出マークに対して実質的に光学的フーリエ変換の関係となる結像光学系中の第２面（瞳面）上の、第１領域と結像関係となるほぼ輪帯状の第２領域とそれ以外の領域とにそれぞれ分布する結像光束の位相を異ならせる、換言すればその第２面上に分布する位置検出マークからの０次光とそれ以外の光とでその位相を異ならせるようにした。
【００２４】
または、照明光学系中の第１面上での照明光（又は２次光源、面光源）の強度分布を、輪帯状の第１領域で他の領域よりも高める、あるいは照明光学系の実質的な瞳面上の、輪帯状の第１領域内に分布する照明光束を透過せしめる、もしくは照明光学系の実質的な瞳面上に、その光軸を中心とするほぼ輪帯状の２次光源（面光源）を形成する、または照明光学系の実質的な瞳面上の、その光軸を中心とするほぼ輪帯状の領域内に複数の光源像を形成するようにしてもよい。また、照明光学系の実質的な瞳面上での光強度分布を、照明光学系の光軸を中心とするほぼ輪帯状の領域でその内側の領域よりも高め、かつ結像光学系の実質的な瞳面上の、その内側領域と結像関係となるほぼ円形の領域とそれ以外の領域とにそれぞれ分布する結像光束の位相を異ならせるようにしてもよい。
【００２５】
このため、凹凸変化（段差）の極めて小さい位置検出マークに対しても、確実に（高コントラストな像で）位置検出を行なうことが可能となる。尚、前述の第１及び第２領域や２次光源（面光源）の形状は輪帯（円環）状であるとしたが、例えば矩形、正方形、又は多角形（特に正多角形）としても良い。さらに、照明光学系中の第１面（瞳面）上の第１領域を部分的に遮光（又は減光）する、即ち第１領域を複数の部分領域（その形状は任意で良く、例えば円弧、円形、又は直線状等として構わない）から構成しても良い。これに対応して結像光学系中の第２面（瞳面）上の第２領域を、その第１領域と同一の形状としても良いし、あるいはその第１領域と結像関係となる複数の部分領域をほぼ含む輪帯、矩形、又は多角形状等としても良い。
【００２６】
また、結像光学系中の第２面上の輪帯状の領域内に分布する結像光束、即ちその第２面上に分布する０次回折光を減光する部材を設ける。これにより、位置検出マークからの０次回折光と他の次数の回折光との強度比を小さくすることができ、位置検出マークの像をより高いコントラストで検出することができる。
さらに、照明光のうち画像信号の形成に寄与する光束の波長域中の最短波長をλ１、最長波長をλ２、位置検出マークの周期をＰとすると、輪帯状の第１領域の外半径ｒｏ、及び内半径ｒｉを、
ｒｉ≧λ２／（２×Ｐ）
ｒｏ−ｒｉ≦λ１／Ｐ
なる関係を満足するように設定する。また、結像光学系の開口数ＮＡｏを、
ＮＡｏ≧ｒｏ＋λ２／Ｐ
なる関係を満足するように設定する。このため、低段差の位置検出マークの像をより高いコントラストで検出することができる。
【００２７】
さらに、結像光学系内の第２面（瞳面）、又はその共役面に、結像光学系の開口数ＮＡｏを変化させるための可変開口絞り（ＮＡ絞り）を、位相差部材と機械的に干渉しないように設けると良い。これにより、位置検出マークの周期が変化しても、前述の条件を満足するように、結像光学系の開口数をその周期に対応した値に設定することができ、常にそのマーク像を高いコントラストで検出できる。尚、可変開口絞りは結像光学系の瞳面、又はその共役面から光軸方向にずらして配置しても構わない。
【００２８】
また、結像光学系の光路に対して位相差部材を挿脱可能に保持する部材を設ける。このため、明視野検出との切り替えを行うことができ、位置検出マークの段差量に応じて位相差部材の有無を選択してそのマーク像を検出できる。従って、位置検出マークの段差量に依らず、常に高いコントラストのマーク像を得ることができ、位置検出精度を向上させることができる。
【００２９】
さらに、照明光学系の光路に対して光束制限部材（又は光学部材、絞り部材、２次光源形成部材）を挿脱可能に保持する部材も設ける。このため、輪帯照明と通常照明とを切り替えることができ、位置検出マークが低段差でない場合にはその反射率が低くても、通常照明によってそのマーク像を確実に検出することができる。
【００３０】
また、照明光学系中の第１面上での照明光（２次光源、面光源）の強度分布を、輪帯状の第１領域で他の領域よりも高める光学部材は、輪帯状の第１領域の外半径と内半径の少なくとも一方を変化させる強度分布変更部材を有する。このため、位置検出マークの周期が変化しても、前述の条件式を満足するように、輪帯状の第１領域の外半径と内半径の少なくとも一方をその周期に対応した値に設定することができる。従って、位置検出マークの周期に依らず、常に高いコントラストのマーク像を得ることができる。尚、輪帯状の第１領域の外半径や内半径は、位置検出マークの周期の変化に連動して変更する必要はなく、その変化により像コントラストや忠実性が、所望の位置検出精度を得られない程度に劣化したときのみ、その外半径や内半径を変更するようにしても良い。
【００３１】
さらに位相差部材は、第１領域の外半径と内半径の少なくとも一方の変化に応じて、輪帯状の第２領域の半径方向の幅と位置の少なくとも一方を変化させる。このため、位置検出マークの周期に応じて輪帯状の第１領域の外半径と内半径の少なくとも一方が変化しても、常に０次回折光のみに対して位相差を付与して撮像素子に入射させることができる。尚、結像光学系の輪帯状の第２領域の幅や位置は、輪帯状の第１領域の外半径や内半径（位置検出マークの周期）の変化に連動して変更する必要はなく、その変化により像コントラストや忠実性が、所望の位置検出精度を得られない程度に劣化したときのみ、その位相シフト部の幅や位置を変更するだけでも良い。また、第１領域の外半径及び内半径の変化に連動して第２領域の外半径と内半径の両方を変更する必要はなく、例えば第２領域の内半径のみを変更するだけでもよい。
【００３２】
【実施例】
図１〜図６を参照して本発明の実施例について説明する。図１は、本実施例の位置検出装置の概略的な全体構成を示す。図１において、ハロゲンランプ等の光源１を発したブロードバンドな照明光束（広帯域光）はコンデンサーレンズ２、及び波長選択素子（シャープカットフィルター、又は干渉フィルター等）３を経て照明視野絞り４に入射する。
【００３３】
波長選択素子３は、後述するウエハ１０上に塗布されたフォトレジスト（露光波長は例えば３６５ｎｍ、又は２４８ｎｍ）に対して、非感光な波長域（例えば波長５５０ｎｍ〜７５０ｎｍ）の光束のみを透過させる。ただし本発明を、フォトレジストで覆われていない基板の位置検出装置、例えば露光、現像処理後のウエハ上の、回路パターンと転写したレジストパターンとの重ね合わせ位置検出装置に適用するのであれば、フォトレジストの感光を防ぐ必要はないので、より短波長の（露光波長に近い）光束も使用することができる。
【００３４】
照明視野絞り４を透過した光束は、リレーレンズ５を経て本発明の照明光束制限部材（開口絞り）６に入射する。さらに照明光は、ビームスプリッター８、及び対物レンズ群９を介して、位置検出マーク１１が形成されたウエハ１０に入射する。照明光束制限部材６は、ウエハ１０の表面（位置検出マーク１１）に対して、対物レンズ群９とビームスプリッター８を介して、光学的にフーリエ変換の関係となっている面（以後「照明系瞳面」と略す）に配置されている。すなわち、照明光束制限部材６内の所定点の、照明光学系（１〜５、８、９）の光軸ＡＸＩからの位置ずれ量は、その所定点を通過する照明光束の、ウエハ１０の表面に対する入射角の正弦に比例する。
【００３５】
ここで、照明光束制限部材６は輪帯開口を有し、その輪帯開口の中心が照明光学系の光軸ＡＸＩと一致するように可動部材７に保持されている。この可動部材７は、例えばターレット板、又はスライダーであり、照明光学系の光路に対して照明光束制限部材６を挿脱可能としている。従って、本実施例では可動部材７によって輪帯照明と通常照明とを切り替えることができ、位置検出マーク１１の段差量（及び／又は微細度（周期、線幅等））に応じていずれか一方を選択できるようになっている。例えば、低段差の位置検出マーク、及び高段差の微細な位置検出マークでは輪帯照明が選択されて照明光束制限部材６が光路中に挿入され、高段差の粗い位置検出マークでは通常照明が選択されて照明光束制限部材６が光路外に待避される。
【００３６】
また、照明視野絞り４は一連の光学系５〜９を介して、ウエハ１０の表面（位置検出マーク１１）と実質的に共役（結像関係）となっており、照明視野絞り４の透過部の形状、大きさに応じて、ウエハ１０上での照明範囲を制限することができる。照明視野絞り４は、例えば複数の可動ブレードからなり、位置検出マーク１１の大きさや形状に応じて、その複数の可動ブレードによって規定される開口部の大きさや形状を変化させることでウエハ１０上での照明範囲を変更することができる。
【００３７】
ウエハ１０は、２次元移動可能なウエハステージ１２に載置され、このウエハステージ１２の端部にはレーザ干渉計１５からのレーザビームを反射するミラー１４が固定されている。ウエハステージ１２（ウエハ１０）のＸ、Ｙ方向の位置はレーザ干渉計１５によって、例えば０．０１μｍ程度の分解能で常時検出される。さらにウエハステージ１２には、ベースライン計測等に用いられる基準マークが形成された基準板１３が設けられている。
【００３８】
さて、ウエハ１０（位置検出マーク１１）で反射した光束は、対物レンズ群９、及びビームスプリッター８を介して、本発明の位相差部材（位相差フィルター）１６に至る。位相差フィルター１６は、ウエハ１０の表面（位置検出マーク１１）に対して、対物レンズ群９とビームスプリッター８を介して、光学的にフーリエ変換の関係となっている面（以後「結像系瞳面」と略す）に配置されている。即ち、位相差フィルター１６内の所定点の、結像光学系の光軸ＡＸからの位置ずれ量は、その所定点を通過する光束（結像光束）の、ウエハ１０の表面に対する射出角の正弦に比例する。
【００３９】
位相差フィルター１６の具体的な構成については後で詳しく説明するが、位相差フィルター１６はその中心が結像光学系の光軸ＡＸと一致するように可動部材１７に保持されている。この可動部材１７は、例えばターレット板、又はスライダーであり、結像光学系の光路に対して位相差フィルター１６を挿脱可能としている。従って、本実施例では可動部材１７によって明視野検出との切り替えを行うことができ、位置検出マーク１１の段差量に応じていずれか一方を選択できるようになっている。例えば、低段差の位置検出マークでは位相差フィルター１６が光路中に挿入され、高段差の位置検出マークでは明視野検出が選択されて位相差フィルター１６が光路外に待避される。
【００４０】
ここで、光学的なフーリエ変換の関係を図２を用いて説明するが、図２では１枚のレンズ９’で表される対物レンズ群９（焦点距離をｆとする）の一方の焦点面に、ウエハ１０を配置すれば、他方の焦点面が「光学的なフーリエ変換面（瞳面）」ＦＰとなる。そして、ウエハ１０上での入射、及び射出角度がθである光束はそれぞれフーリエ変換面（瞳面）ＦＰ上の、光軸ＡＸからｆ・ｓｉｎθだけ離れた位置を通ることになる。
【００４１】
図２では、対物レンズ群９を１枚のレンズ９’で表しているが、これが複数枚から成るレンズ系であっても本質的には何ら変わりはなく、複数枚のレンズの合成焦点面にウエハ１０を配置すれば、他方の焦点面がフーリエ変換面（瞳面）となる。そして、対物レンズ群９と瞳面との間にビームスプリッター８を配することで、送光側（照明系）瞳面と受光側（結像系）瞳面とを分離することが可能となる。また、この分離された２つの瞳面は共にウエハ１０に対するフーリエ変換面である、即ち照明系瞳面と結像系瞳面とはウエハ１０、対物レンズ群９、及びビームスプリッター８を介して実質的に共役（結像関係）となっている。
【００４２】
位相差フィルター１６を通過した結像光束は、レンズ系１８、及びビームスプリッター１９を経て、指標板２４上に位置検出マーク１１の像を形成する。一方、指標板２４は、指標板照明用光学系２０〜２３によっても照明される。この指標板照明用光学系は、発光ダイオード等の光源２０、コンデンサーレンズ２１、指標板照明視野絞り２２、及びリレーレンズ２３からなる。指標板照明視野絞り２２は、リレーレンズ２３、及びビームスプリッター１９を介して指標板２４と共役、ひいてはウエハ１０の表面と共役になっている。さらに指標板２４には、後述するように位置検出マーク１１の検出に際して使用される基準指標（指標マーク）が形成されている。指標板照明視野絞り２２は、指標板２４上の基準指標のみが光源２０からの照明光で照射されるように、その基準指標と結像関係になる領域に開口を有する。
【００４３】
指標板照明用光学系２０〜２３はこの基準指標を照明するためのものであるので、光源２０からの照明光は、位置検出マーク１１を照射する光源１からの照明光と異なり、単色光でもよい。また、光源２０からの照明光はウエハ１０上に照射されないため、その波長がフォトレジストの感光波長であっても構わない。そこで、本実施例では発光ダイオードである光源２０の波長を５００ｎｍ程度とし、ビームスプリッター１９の反射面をダイクロイックミラーとすることで、ウエハ１０からの結像光束及び指標用照明光の利用効率を高める（即ち光量損失を抑える）ことができる。尚、本実施例では照明視野絞り４によってウエハ１０上での照明範囲が制限されるので、位置検出マーク１１の像が基準指標に重畳して形成されることはない。
【００４４】
指標板２４上に形成される位置検出マーク１１の像と基準指標の像はそれぞれリレーレンズ２５、２７によってＣＣＤ等の撮像素子２８上に結像される。画像処理系２９は、撮像素子２８からの出力信号を基に、前述の基準指標像と位置検出マーク１１の像との位置関係（位置ずれ量）を算出する。位置検出マーク１１の像位置は、当然ながらレーザ干渉計１５によって規定される直交座標系ＸＹ上での位置検出マーク１１の位置を反映したものであるから、これにより位置検出マーク１１の位置検出が可能となる。即ち、画像処理系２９で算出される位置ずれ量と干渉計１５から出力される座標位置とによって位置検出マーク１１の位置が求められる。
【００４５】
ここで、例えば可動部材７による照明光束制限部材６の挿脱、又は交換に伴い、撮像素子２８に入射する、位置検出マーク１１からの結像光束の光量が変化する。このため、撮像素子２８上でそのマーク像と基準指標像の各強度（明るさ）が異なることになり、その強度差が大きくなると、画像処理系２９での位置ずれ検出精度が悪化する恐れがある。そこで本実施例では、撮像素子２８上に結像される位置検出マーク１１の像と基準指標の像の各強度が常にほぼ等しくなるように、その結像光束の光量変化に応じて、基準指標を照明する、光源２０からの照明光の強度を調整可能に構成する。本実施例では、光源（発光ダイオード）２０への注入電流を調節してその発光強度を調整するものとし、例えば照明光学系の光路から照明光束制限部材６を退出させたときは、光源２０の発光強度を高くする。尚、光源２０と指標板２４との間に、透過率が異なる複数の減光フィルターを保持する部材（ターレット板、スライダー等）に設け、この保持部材を駆動して、複数の減光フィルターをそれぞれ交換してその光路中に配置するように構成してもよい。図示していないが、照明光束制限部材６や位相差フィルター１６の挿脱、又は交換は、入力装置（キーボード等）からの情報（位置検出マーク１１の周期や段差量等）に基づいて、図１の装置全体を統括制御するコントローラが自動的に行うようになっている。さらにコントローラは、照明光束制限部材６や位相差フィルター１６の種類や有無に応じて光源２０の発光強度を調整する。
【００４６】
ところで、開口絞り２６はウエハ１０に対して実質的に光学的なフーリエ変換の関係となる結像光学系（９〜２７）中の面（位相差フィルター１６と共役（結像関係）の面）に配置され、結像光学系の開口数を制限するものである。本実施例では、開口絞り２６によって結像光学系の開口数を任意に変更できるものとする。また、図１では指標板２４を結像光学系の光路中に配置したが、指標板２４をその光路外に配置し、結像系を介して撮像素子２８上に基準指標の像を形成するように構成してもよい。例えば、指標板２４の代わりに撮像素子２８を配置し、かつ指標板照明視野絞り２２の代わりに指標板２４を配置すれば、リレーレンズ２５、２７が不要となって装置全体を小型化できる。このとき、基準指標以外からの光が撮像素子２８に入射しないように、指標板２４上の、基準指標以外の領域は遮光しておくと良い。また、開口絞り２６は位相差フィルター１６と機械的に干渉しないようにそれに近接して配置すれば良い。
【００４７】
ここで、位置検出マーク１１の形状、指標板２４、指標板照明視野絞り２２、及び照明視野絞り４の各透過部の形状、及び撮像素子２８上に形成される像の強度分布の一例を、図３、図４を用いて説明する。図４（Ａ）は位置検出マーク１１の上面図を示し、図４（Ｂ）はその位置計測方向（図４（Ａ）中のＸ方向）の断面図を示す。即ち、本実施例ではウエハ１０の表面に、Ｘ方向に周期Ｐで配列される３本の帯状凹部からなる位置検出マーク１１を形成している。また、ウエハ１０の表面には図４（Ｂ）に示すようにフォトレジスト１０’が塗布されている。
【００４８】
照明視野絞り４は、図３（Ａ）に示すように、ウエハ１０上での照明領域を制限する四角形の透過部４Ｍ以外は、全て遮光部（斜線部）となっている。そして、この透過部４Ｍがウエハ１０上に投影され、位置検出マーク１１を含む部分領域のみを照明する。この照明領域は、図４（Ｂ）中のマーク領域Ｍ（Ｘ方向の幅Ｗ）に相当し、図３（Ｃ）に示す指標板２４上のマーク像領域ＭＩにも相当する。すなわち、指標板２４上のマーク像領域ＭＩ内に位置検出マーク１１の像が形成される。
【００４９】
一方、指標板照明視野絞り２２も図３（Ｂ）に示すように、２つの四角形の透過部４Ｌ、４Ｒ以外は、全て遮光部（斜線部）となっている。この透過部４Ｌ、４Ｒからの透過光は、図３（Ｃ）に示す指標板２４上の矩形領域（透過部）ＬＩ、ＲＩを照明する。そしてこの矩形領域ＬＩ、ＲＩ内にはそれぞれ遮光部である前述の基準指標（バーマーク）２４Ｌ、２４Ｒが形成されている。
【００５０】
以上のことから、撮像素子２８上に形成される像強度分布は図４（Ｃ）のようになる。即ち、光源（ハロゲンランプ）１からの照明光で照射された位置検出マーク１１の像ＩＭを中心として、その左右に光源（発光ダイオード）２０からの照明光で照射された基準指標２４Ｌ、２４Ｒの像（暗像）ＩＬ、ＩＲが形成される。前述したように、位置検出マーク１１の像ＩＭと基準指標２４Ｌ、２４Ｒの像ＩＬ、ＩＲ上との明るさがあまり異なると、両像の位置ずれの検出精度が悪化する恐れがあるので、光源（発光ダイオード）２０への注入電流を調節して、両像がほぼ等しい強度となるように調整する機構（不図示）が設けられている。
【００５１】
また、図４（Ｂ）の断面図において、位置検出マーク１１の左右の領域Ｌ、Ｒを平坦な領域としたが、この領域Ｌ、Ｒの状態は位置検出マーク１１の位置検出には全く影響を与えない（照明光で照明されていない）ので、ここに回路パターン等が存在しても全く問題はない。
画像処理系２９は、撮像素子２８からの出力される図４（Ｃ）の如き光量信号を基に、位置検出マーク１１の像ＩＭと基準指標２４Ｌ、２４Ｒの像ＩＬ、ＩＲとの位置関係を算出する。この算出過程は、従来の結像式位置検出で一般に行なわれている処理と全く同様である。例えば、所定のスライスレベルＳＬでの光量信号のスライス位置（Ｌｏ、Ｌｉ、Ｍ_１〜Ｍｎ、Ｒｉ、Ｒｏ）に基づいて位置検出を行なってもよいし、あるテンプレート信号とマーク部の光量信号の相関を基に位置検出を行なってもよい。
【００５２】
また、これらの位置検出に先立ち、検出位置の基準となる基準指標２４Ｌ、２４Ｒの、ウエハ１０（ウエハステージ１２）に対する位置関係を計測しておく必要がある。これも従来から知られているベースラインチェックと呼ばれる処理であり、本実施例に於ても従来と基本的に同様である。即ち、ウエハステージ１２上に固設される基準板１３の表面に、位置検出マーク１１と同一形状の基準マークを形成しておき、位置検出マーク１１の検出に先立ち、ウエハステージ１２を駆動してこの基準マークを対物レンズ群９の下に移動し、この基準マークと基準指標２４Ｌ、２４Ｒとの位置関係を検出する。同時に、このときのウエハステージ１２の位置（ウエハステージ１２上のミラー１４の位置）をレーザ干渉計１５で計測する。この干渉計１５の出力値と上記検出値（画像処理系２９で検出される位置関係）の和を「ベースライン量」として記憶する。そして、位置検出マーク１１の計測時の干渉計１５の出力値と、前述の光量信号から求めた位置検出マーク１１と基準指標２４Ｌ、２４Ｒとの位置関係との和から「ベースライン量」を差し引いた値が、位置検出マーク１１の基準マークに対する位置となるわけである。
【００５３】
また、本発明を投影露光装置の位置検出系（アライメント系）に適用する場合には、以上の位置検出値と、投影露光装置内に記憶された露光ショットの配列データとを基に、ウエハ上の各ショット領域を不図示の投影光学系の下に移動し、重ね合わせ露光を行なう。
次に、本実施例の照明光束制限部材６、及び位相差フィルター１６について、周期８μｍの位置検出マーク１１を波長域５５０〜７５０ｎｍの照明光束で照射してその位置検出することを前提として説明する。
【００５４】
図５（Ａ）、（Ｂ）はそれぞれこの条件に適した照明光束制限部材６、位相差フィルター１６の構成の一例を示す。各図中のＵ軸、Ｖ軸方向は、それぞれ図４（Ａ）に示した位置検出マーク１１のＸ軸、Ｙ軸方向に等しいが、照明光束制限部材６、及び位相差フィルター１６はそれぞれ位置検出マーク１１に対する光学的なフーリエ変換面（瞳面）に配置されるので、慣例に従ってＵ軸、Ｖ軸と表す。
【００５５】
図５（Ａ）に示すように照明光束制限部材６は、遮光性基板上に、照明光学系（１〜９）の光軸（Ｕ軸とＶ軸の交点）を中心として内半径ｒｉが０．１６（単位は開口数、即ち半径ｒｉの円上の所定点を通過した光束の位置検出マーク１１への入射角の正弦、以下も同様）、外半径ｒｏが０．２０である円環（輪帯）状の透過部Ｉが形成されたものである。照明光束制限部材６としては、金属遮光板上の特定個所に輪帯開口を開けたもの、又はガラス等の透明基板上に金属等で遮光膜を形成し、特定個所の遮光膜を除去したものを使用する。
【００５６】
一方、位相差フィルター１６は、照明光束制限部材６上の輪帯透光部Ｉと共役な位置に、その輪帯透光部Ｉと結像関係となる輪帯形状の位相差付加部Ｓ（図中斜線部）が形成されたものとなっている。図６は、図５（Ｂ）のＵ軸での断面図である。図６に示すように位相差フィルター１６は、ガラス等の透明基板１６Ａの表面に、金属薄膜Ｓｏ及び誘電体膜Ｓ１を積層して形成したものであり、金属薄膜Ｓｏによって透過光を減光し、かつ誘電体膜Ｓ１によってその透過光の位相をシフトさせる。従って、位相差付加部Ｓとそれ以外の領域とにそれぞれ分布する位置検出マーク１１からの結像光束の位相が互いに異なる、即ち両光束の間に所定の位相差が与えられることになる。このような構成は、従来の位相差顕微鏡での位相差フィルター、あるいは最近フォトリソグラフィ工程で使用され始めた「ハーフトーン位相シフトレチクル」と同様であり、それらの各種製法を用いて製造することができる。
【００５７】
また、金属薄膜Ｓｏ及び誘電体膜Ｓ１により透過光に与えられる位相差（他の部分の透過光との位相差）はπ／２［ｒａｄ］（即ち１／４波長）程度が最適であるので、誘電体膜Ｓ１の厚さはその屈折率をｎとしてλ／（４（ｎ−１））程度とする。このとき、λは照明光のうち結像に寄与する光束の中心波長（図６の例では６５０ｎｍ）である。但し、位相差付加部Ｓの位相差量（位相シフト量）に多少の誤差があっても位置検出マーク１１の像コントラストは急激には低下しないので、位相差付加部Ｓの透過光に与えるべき位相差はπ／２±π／４［ｒａｄ］の範囲であれば、精度良く位置検出可能な、比較的良好なコントラストの像を得ることができる。また、特にこの位相差がπ／２±π／６［ｒａｄ］程度に抑えられれば、より良好なコントラストの像を得ることができる。
【００５８】
ここで、結像に寄与する光束の波長域が狭い（即ち照明光が実質的に単色に近い）場合には、誘電体膜Ｓ１の厚さは（２ｋ＋１）λ／（４（ｎ−１））（位相差は（２ｋ＋１）π／４［ｒａｄ］）（但しｋは自然数）であってもよい。これに対して結像に寄与する光束の波長域が広い場合、中心波長以外の波長に対しては、ｋが大きいほど位相差が（２ｋ＋１）π／４［ｒａｄ］（最適条件）からずれるので、誘電体膜Ｓ１の厚さはλ／（４（ｎ−１））とするのが良い。このような条件の位相差フィルター１６を使用すると、位置検出マーク１１の凹部が明るく凸部が暗い、明瞭なコントラストを持ったマーク像を得ることができる。
【００５９】
また、位相差フィルターとして、位相差付加部Ｓに金属薄膜Ｓｏのみを形成し、他の部分に誘電体膜Ｓ１を形成する構成としてもしても良い。この場合、０次光の位相は他の次数の回折光に対してπ／２［ｒａｄ］進んだものとなるので、位置検出マーク１１の像は図６の位相差フィルター１６の使用時とは異なり、位置検出マーク１１の凹部が暗く凸部が明るい像となる。但し、像のコントラストはいずれの場合にも同等で、かつ高いことは勿論である。
【００６０】
さらに、位相差付加部Ｓは必ずしも減光作用を有している必要はなく、この場合には金属薄膜Ｓｏを付加しなくてもよい。また、位相差を付加するために誘電体膜Ｓ１を形成する代わりに、透明基板１６Ａをエッチングにより掘り込んでも良い。
また、位相差付加部Ｓの大きさは、照明光束制限部材６上の輪帯透過部Ｉよりも多少大きくなるように、内半径ｒｉ’を０．１５、外半径ｒｏ’を０．２１とした。これは、位置検出マーク１１からの０次回折光が位相差フィルター１６上で若干広がることを考慮して、より確実に０次回折光に前述の位相差を付加するためである。また、結像光学系の開口数ＮＡｏ（結像系瞳面の半径）は０．３０であるものとした。尚、図１では実際の開口数を規定する開口絞り２６が、位相差フィルター１６と同一位置ではなく、その共役位置に配置されているが、ここでの開口数ＮＡｏは、開口絞り２６の開口数が対物レンズ群９の開口数よりも小さく絞られている場合には、開口絞り２６の開口数（実効的な開口数）を表すことになる。また、照明光束制限部材６の外周の半径は照明光学系の開口数（照明系瞳面の半径）に比べて十分に大きく、輪帯透光部Ｉの外側に分布する透過光は当然ながら位置検出マーク１１には達しない。
【００６１】
図５（Ｂ）に、図５（Ａ）の照明光束制限部材６上の輪帯透光部Ｉを透過した照明光の照射により、位置検出マーク１１から発生した１つの１次回折光の、位相差フィルター１６上での分布（図中の２つの破線円で囲まれた領域Ｄ）を示す。尚、位置検出マーク１１からの回折光のうち０次回折光は、輪帯透光部Ｉと共役な（かつそれよりも一回り大きい）位相差付加部Ｓ上に分布し、金属薄膜Ｓｏによって減光され、かつ誘電体膜Ｓ１によって位相差が付加される。もちろん実際には、これ以外の次数の回折光も分布しているが、ここでは位置検出マーク１１の像の形成に支配的な０次及び１次の回折光についてのみ考察する。
【００６２】
ところで、図５（Ｂ）に示すように１次回折光の一部は位相差付加部Ｓで減光されることになるが、本実施例では図５（Ａ）に示したように輪帯透過部Ｉの内半径ｒｉ、及び外半径ｒｏが適切に定められているので、位相差付加部Ｓによる１次回折光の減光、及び位相差の付加は最小限に抑えられている。以下、この理由を説明する。
【００６３】
まず、位相差付加部Ｓの内周及び外周とＵ軸との交点のＵ座標はそれぞれｒｉ’、ｒｏ’（及び−ｒｉ’、−ｒｏ’）となる。一方、１次回折光が分布する領域Ｄの境界（２つの破線円）とＵ軸との交点のＵ座標をＤｐｉ、Ｄｐｏ，Ｄｍｉ、Ｄｍｏと定めると、これらの値は、
Ｄｐｉ＝λ／Ｐ＋ｒｉ、Ｄｐｏ＝λ／Ｐ＋ｒｏ
Ｄｍｉ＝λ／Ｐ−ｒｉ、Ｄｍｏ＝λ／Ｐ−ｒｏ
となる。
【００６４】
このとき、特にＤｐｉの値がｒｏ’よりも小さい、あるいはＤｍｏの値が−ｒｉ’よりも小さいと、位相差付加部Ｓによる１次回折光の減光の度合いが大きくなることは図５（Ｂ）から明らかである。また、Ｄｍｉの値がｒｉ’よりも大きくても、同様に減光の度合いが大きくなる。
図５（Ａ）の例においては、位置検出マーク１１の周期Ｐは８μｍ、輪帯透過部Ｉの内半径ｒｉが０．１６、外半径ｒｏが０．２０であり、照明光の波長λの範囲は最短波長λ１が５５０ｎｍ、最長波長λ２が７５０ｎｍであるので、Ｄｐｉの最小値はλ＝λ１のときに、
Ｄｐｉ＝λ１／Ｐ＋ｒｉ＝０．２３（１）
となってｒｏ’（＝０．２１）より大きく、Ｄｍｏの最小値はλ＝λ１のときに、
Ｄｍｏ＝λ１／Ｐ−ｒｏ＝−０．１３（２）
となって−ｒｉ’（＝−０．１５）より大きい。
【００６５】
さらに、Ｄｍｉの最大値はλ＝λ２のときに、
Ｄｍｉ＝λ２／Ｐ−ｒｉ＝−０．０７（３）
となってｒｉ’（＝０．１５）より小さい。
従って、位相差付加部Ｓによる１次回折光の減光の度合いは小さくなるが、このための条件を一般化すると、
Ｄｐｉ＝λ１／Ｐ＋ｒｉ≧ｒｏ’ （４）
Ｄｍｏ＝λ１／Ｐ−ｒｏ≧−ｒｉ’ （５）
Ｄｍｉ＝λ２／Ｐ−ｒｉ≦ｒｉ’ （６）
となる。
【００６６】
また、位相差付加部Ｓの外半径ｒｏ’は輪帯透過部Ｉの外半径ｒｏよりも大きく、位相差付加部Ｓの内半径ｒｉ’は輪帯透過部Ｉの内半径ｒｉよりも小さいので、上記不等式（４）〜（６）は、
Ｄｐｉ＝λ１／Ｐ＋ｒｉ≧ｒｏ（７）
Ｄｍｏ＝λ１／Ｐ−ｒｏ≧−ｒｉ（８）
Ｄｍｉ＝λ２／Ｐ−ｒｉ≦ｒｉ（９）
としても良い。特に不等式（７）、（８）は共に、
ｒｏ−ｒｉ≦λ１／Ｐ（１０）
と等価であり、不等式（９）は、
ｒｉ≧λ２／（２×Ｐ）（１１）
と等価である。
【００６７】
従って、一般に輪帯透過部Ｉの内半径ｒｉ及び外半径ｒｏが不等式（１０）、（１１）を満たすとき、位相差付加部Ｓによる１次回折光の減光の度合いを極めて小さくできることになる。
ところで、結像光学系の開口数ＮＡｏの値によっては、位相差付加部Ｓによる減光のみでなく、開口数ＮＡｏによる制限によって１次回折光が遮光されてしまう恐れもある。これを避けるためには、Ｄｐｏ＝λ／Ｐ＋ｒｏの値が前述した開口数ＮＡｏ以下であることが望ましい。Ｄｐｏの最大値は、λ＝λ２のときにλ２／Ｐ＋ｒｏとなるので、開口数ＮＡｏは、
ＮＡｏ≧λ２／Ｐ＋ｒｏ（１２）
の関係を満たすことが望ましい。
【００６８】
以上の説明では、０次回折光に対して片側（＋Ｕ方向）に発生する１次回折光のみに着目して説明したが、反対方向（−Ｕ方向）に発生する１次回折光についても全く同様であり、上記条件（不等式）に変わりはない。また、位置検出マーク１１の周期Ｐや照明光束の波長域（λ１、λ２）も、上記の値に限らず、他の条件であってもこれらの条件（不等式）が成立する。
【００６９】
次に、本実施例の位置検出装置の効果について、凹凸変化（段差）が極めて小さい位置検出マークの像のシミュレーション結果を基に説明する。
図７は、本実施例の位置検出装置により得られる、段差５ｎｍの位置検出マーク像のシミュレーション結果を示す。マーク形成条件は、周期が１２μｍで、凹部幅と凸部幅が等しく、マーク表面の材質は一様で（屈折率は３．５５）、その上に屈折率が１．６８であるフォトレジストが厚さ１μｍで塗布されているものとした。尚、照明光の波長域は５５０ｎｍ（＝λ１）から７５０ｎｍ（＝λ２）であり、照明光束制限部材６上の輪帯透過部Ｉの内半径、外半径はそれぞれ前述の条件（不等式）に従い、
ｒｉ＝０．１０≧λ２／（２×Ｐ）＝０．７５０／２４＝０．０３１
ｒｏ＝０．１４
（ｒｏ−ｒｉ＝０．０４≦λ１／Ｐ＝０．５５０／１２＝０．０４６）
とした。
【００７０】
また、位相差フィルター１６の構成は図６の通りであり、その位相差付加部Ｓの内半径、外半径はそれぞれ輪帯透過部Ｉの内半径ｒｉ、外半径ｒｏと等しくし、結像光学系の開口数ＮＡｏは前述の条件（不等式）に従い、
ＮＡｏ＝０．２２≧λ２／Ｐ＋ｒｏ＝０．７５０／１２＋０．１４＝０．２０３とした。
【００７１】
さらに、位相差付加部Ｓの透過率は１％とし、誘電体膜Ｓ１は、照明光の中心波長６５０ｎｍに対してπ／２［ｒａｄ］の位相差を付加するように、屈折率を１．５、厚さを３２５ｎｍとした。
図７に示した像強度分布は、位置検出マーク１１の１周期分であり、横軸の位置０はマーク（凹部）の中心を示し、±Ｐ／４の破線はマークのエッジ（凹部と凸部の境界）を示す。また、縦軸の強度分布は一周期の像強度の最大値が１となるように規格化してある。
【００７２】
さらに図８には、図７とほぼ同一の条件で、開口数ＮＡｏのみを０．１８とし、前述した開口数ＮＡｏの条件式（１２）を満たさない場合のシミュレーション結果を示す。この図８のマーク像は、図７に示した像に比べてやや暗部（マークのエッジ部分）のシャープさが劣るものの、エッジ位置、即ちマーク位置を検出するのに十分なコントラストを有している。従って、本実施例による前述の条件式（１０）〜（１２）のうち、開口数ＮＡｏの条件式（１２）については必ずしもこれを厳密に満たす必要はないことが分かる。
【００７３】
同様に図９には、図７の条件とほぼ同一の条件で、輪帯透過部Ｉの外半径ｒｏのみを０．１８とし、前述した外半径ｒｏの条件式（１０）を満たさない場合のシミュレーション結果を示す。この場合、図７、図８に示した像に比べて像コントラストの劣化が顕著であり、従ってこのような像に基づいた位置検出では良好な検出精度を得ることができないことが分かる。
【００７４】
さらに図１０には、図７の条件とほぼ同一の条件で、輪帯透過部Ｉの内半径ｒｉを０．０２、外半径ｒｏを０．０６とし、前述した外半径ｒｏの条件式（１０）は満たすものの、内半径ｒｉの条件式（１１）は満たさない場合のシミュレーション結果を示す。この場合、像のコントラストは高いものの、マークエッジだけでなく凹部の中心にも若干の暗部が生じて像の忠実度が低下し、これが位置検出に悪影響を及ぼす恐れがあるので、位置検出に使用することは難しい。
【００７５】
図１１には、図７〜図１０と異なり、照明光束制限部材６上の輪帯透過部Ｉが光軸を中心とする円形（通常のσ絞り）であり、位相差フィルター１６上の位相差付加部Ｓも光軸を中心とする円形である場合のシミュレーション結果を示す。尚、このときの透過部Ｉ、位相差付加部Ｓの半径は共に０．６６（σ値としては０．３）とした。波長域、開口数、その他の条件は、図７の条件と同一である。この場合の像も、図１０と同様に像の忠実度が低下したものとなり、位置検出に使用することは難しい。
【００７６】
図１２には、比較のために、照明光束制限部材６の輪帯透過部Ｉ、及び位相差フィルター１６上の位相差付加部Ｓの形状が、本発明の条件を満たす図７の例と同一であるが、位相差付加部Ｓの透過率が０％（位相差付加部Ｓが遮光部）である、即ち暗視野顕微鏡によるマーク像を示す。尚、図１２だけは比較が容易なように、縦軸のスケールを図７と同一に設定してある。このような暗視野顕微鏡によっても、低段差の位置検出マークの像に明暗変化（コントラスト）が生じるものの、その強度は本発明の位置検出装置での像強度（図７）の１／５程度であってそのマーク像は暗く、従って撮像素子２８から出力される画像信号もＳ／Ｎ比の悪いものとなる。
【００７７】
さらに図１３には、通常（明視野）の顕微鏡による像を示す。σ絞りの半径は０．１７６（σ値としては０．８）であり、当然ながら位相差付加部Ｓは設けない。その他の条件は図７の条件と同一である。図１３から明らかなように、低段差（５ｎｍ）の位置検出マークに対して明視野顕微鏡を使用すると、像に明暗変化（コントラスト）が殆どなく、位置検出は不可能なことがわかる。
【００７８】
以上のように、図９〜図１３に示した各像に比べて図７、図８に示した本発明の位置検出装置による像は、コントラストが十分であるばかりでなく、その明暗部がそれぞれマークの凹部、凸部と一致しているため、このようなマーク像を用いて確実な位置検出を行なうことができる。
尚、前述の実施例における照明光束制限部材６及び位相差フィルター１６は、段差の小さな位置検出マークの検出に極めて有効であることは前述の通りであるが、段差の大きな（例えば１００ｎｍ以上）の位置検出マークに対しては、従来の位置検出装置でも十分な検出精度が得られるので、段差の大きなマークを検出する際には、照明光束制限部材６及び位相差フィルター１６を、交換機構（可動部材）７及び１７を用いて光路外へ待避させるようにしてもよい。また、ガラス基板からなる位相差フィルター１６（又は照明光束制限部材６）の待避により、光学系の収差状態が変動する恐れがある場合は、その待避時に、位相差フィルター１６（又は照明光束制限部材６）の代わりにそれと同等な光学的厚さを有する透明部材を挿入する必要がある。これは、交換機構７、１７にそれぞれその透明部材を保持させておけば、簡単に交換を行なうことができる。
【００７９】
また、前述のシミュレーションでは段差５ｎｍの位置検出マークを想定したが、これ程には低段差でないマーク、例えば数十ｎｍ程度の段差を持つマークに対しては、図６に示した、減光及び位相差の付加を行う位相差フィルター以外にも、位相差のみを付加して減光を行わない位相差フィルターを用いることができる。図１４は、段差４０ｎｍの位置検出マークに対してこのような位相差フィルターを用いた場合のシミュレーション結果を示す。なおこのときの、照明光束制限部材６上の輪帯透過部Ｉ、及び位相差フィルター１６上の位相差付加部Ｓの形状は、図７の例と同一である。図１４から明らかなように、段差がある程度大きい位置検出マークに対しては、位相差付加部Ｓの透過率が高くとも（さほど減光しなくても）十分にコントラストの高い像が得られる。
【００８０】
従って、図６の位相差フィルター１６と位相差の付加のみを行なう位相差フィルター（ないしは比較的高い透過率を有する位相差フィルター）とを交換機構１７に保持させておき、位置検出マークの段差量に応じて、その２つの位相差フィルターを交換して結像光路中に配置するようにしてもよい。尚、より低段差のマークに対しては、透過率の低い位相差フィルターを選択して装填する。
【００８１】
図１５には、比較のために、図１３と同一条件の明視野顕微鏡を用いて段差４０ｎｍの位置検出マークを検出した場合のシミュレーション結果を示す。図１５から明らかなように、段差が４０ｎｍであっても明視野顕微鏡ではまだ十分なコントラストを得ることができず、図１４に示した本発明による像とのコントラストの差は明らかである。
【００８２】
ところで、前述の実施例では、照明光束制限部材６が形成する輪帯状の２次光源、即ち輪帯透過部Ｉの内半径や外半径、その輪帯透過部Ｉと共役な位相差フィルター１６上の位相差付加部Ｓの内半径や外半径、及び結像光学系の開口数は、照明光束の波長域（λ１〜λ２）により決定されるとしたが、例えば位置検出マーク１１と撮像素子２８との間にシャープカットフィルター等の波長選択素子を挿入する場合、または撮像素子２８の分光感度が照明光束の波長域よりも狭い場合などは、これらを考慮して、すなわち位置検出マーク１１の画像信号の形成に実際に寄与する波長域に基づいて、各値を決定することになる。
【００８３】
また、前述の実施例で用いた照明光束制限部材６は、照明系瞳面上に分布する光束のうち輪帯透過部Ｉ内の光束のみを透過し、それ以外は遮光して輪帯状の２次光源を形成するものであったが、照明系瞳面上の輪帯領域に、例えば光ファイバー、又は凹型円錐プリズムと凸型円錐プリズムとを組み合わせたもの等を用いて照明光束を集光させて２次光源を形成するようにしても良い。この場合、光量損失が大幅に低減されるという利点が得られる。
【００８４】
さらに、光源１からの光を入射して、照明系瞳面上に複数の光源像を形成するオプチカルインテグレータ（例えばフライアイレンズ）を設けるようにしてもよい。この場合、位置検出マーク１１上での照明光の照度均一性が大幅に向上するという利点が得られる。但し、照明系瞳面上に輪帯状の２次光源を形成するために、例えばフライアイレンズの射出側面、又は入射側面近傍に、輪帯開口を持つ開口絞り（図５（Ａ））を配置することになる。また、光量損失を最小限に抑えるために、光源１とフライアイレンズとの間に、前述の凹型及び凸型円錐プリズム、又は輪帯状の射出端を持つ光ファイバーを配置する、あるいは光源１とフライアイレンズとの間に配置されるインプットレンズの収差を利用することにより、フライアイレンズの入射面上での照明光の強度分布を、光軸を中心とする輪帯領域で他の領域よりも高くすることが好ましい。
【００８５】
さらに、輪帯透過部Ｉの外半径と内半径の少なくとも一方が異なる、換言すれば輪帯透過部Ｉの半径方向の幅（輪帯比）と位置の少なくとも一方が異なる複数の開口絞りを交換機構７に設け、この複数の開口絞りをそれぞれ交換して照明光路中に配置するように構成しても良い。この場合、位置検出マーク１１の微細度（周期Ｐ）の変化に応じて、前述の条件式（１０）、（１１）を満足する、その周期に最適な開口絞りを選択して照明光路に配置することができる。従って、位置検出マーク１１の周期に依らず、常に高いコントラストのマーク像を得ることができる。また、直径が異なる複数の円形遮光板、及び円形開口の直径が異なる複数の絞り部材（σ絞り）を交換機構７に設け、円形遮光板によって輪帯透過部Ｉの内半径を、σ絞りによってその外半径を規定するように構成し、円形遮光板とσ絞りとの組み合わせによって照明系瞳面上での輪帯状の２次光源（照明光束分布、又は光強度分布）の半径方向の幅や位置を変更するようにしてもよい。ここで、複数のσ絞りを交換機構７に設ける代わりに、光源１と交換機構７との間にズームレンズ系を配置する、または円形遮光板に近接して可変開口絞り（虹彩絞り）を配置し、このズームレンズ系、または虹彩絞りによって照明光の光束径（大きさ）、即ち輪帯透過部Ｉの外半径を任意に変更するように構成してもよい。
【００８６】
また、複数の開口絞りを有する交換機構７の代わりに、例えば液晶素子、又はエレクトロクロミック素子で作られた開口絞りを照明系瞳面に配置するようにしても良い。この場合、照明系瞳面上の透過部Ｉの形状、大きさ、及び位置を任意に変更することが可能となる。さらに、凹状円錐プリズムと凸型円錐プリズムとを組み合わせて、照明系瞳面上に前述の条件式（１０）、（１１）を満足する輪帯状の照明光束分布（又は光強度分布）を形成するようにしても良い。このとき、この２つのプリズムを光軸方向に相対移動可能に構成して、その輪帯状の照明光束分布（光強度分布）の半径方向の位置を変更するようにしてもよい。また、光源１とこの２つのプリズムとの間にズームレンズ系を配置して、光源側の円錐プリズムに入射する照明光束の径（大きさ）を変化させるようにし、その輪帯状の照明光束分布（光強度分布）の半径方向の幅を変更するようにしても良い。
【００８７】
尚、輪帯透過部Ｉ（２次光源）の外半径や内半径は、位置検出マーク１１の周期の変化に連動して変更する必要はなく、その変化により像コントラストや忠実性が、所望の位置検出精度を得られない程度に劣化したときのみ、その外半径や内半径を変更するようにしても良い。
また、像コントラストや忠実性を多少劣化させても所望の位置検出精度が得られるのであれば、照明系瞳面上の輪帯透過部Ｉ以外の領域に分布する照明光束を完全に遮光しなくてもよい。即ち、照明系瞳面上での輪帯領域以外の領域を減光部としてもよく、要は照明系瞳面上の照明光（２次光源）の強度分布を、光軸を中心とする輪帯領域で他の領域よりも高くすればよい。一例としては、照明系瞳面上での光強度分布が輪帯領域で他の領域よりも高くなるように、光源１と照明系瞳面との間に配置される少なくとも１つのレンズ系、例えば図１のリレーレンズ５の収差を調整すればよい。このとき、収差の補正量が異なる複数のリレーレンズをそれぞれ交換して照明光路中に配置して、照明系瞳面上での光強度分布を変更するようにしてもよい。
【００８８】
さらに照明光源１として、半導体レーザ等のレーザを用いてもよい。この場合も照明光束としてはある程度の波長域を有することが望ましいので、多波長で発振するレーザ、例えば色素レーザを使用するか、異なる波長で発振する複数個のレーザを使用すると良い。
また、位相差フィルター１６はその位相差付加部Ｓに、結像光束（０次光）を減光する部材（金属薄膜Ｓｏ）が一体に形成されるものとしたが、例えば輪帯状の金属薄膜（減光部）を持つ透明基板を、位相差フィルター１６に近接して配置する、あるいは位相差フィルター１６とほぼ共役な面（瞳共役面）に配置するようにしてもよい。
【００８９】
さらに、照明系瞳面上の輪帯透過部Ｉの外半径と内半径の少なくとも一方の変化に連動して、結像系瞳面上の位相差付加部Ｓの外半径と内半径の少なくとも一方を変化させるように構成してもよい。例えば、位相差付加部Ｓの外半径と内半径の少なくとも一方が異なる、換言すれば位相差付加部Ｓの半径方向の幅（輪帯比）と位置の少なくとも一方が異なる複数の位相差フィルターを交換機構１７に設け、この複数の位相差フィルターをそれぞれ交換して結像光路中に配置するように構成すればよい。この場合、前述の如く位置検出マーク１１の周期に応じて輪帯透過部Ｉの外半径と内半径の少なくとも一方が変化しても、この変化後の輪帯透過部Ｉに最適な位相差フィルターを選択して結像光路に配置することができる。従って、常に０次回折光のみに位相差を付加して撮像素子２８に入射させることができる。尚、結像系瞳面上の位相差付加部Ｓの幅や位置は、照明系瞳面上の輪帯透過部Ｉの外半径や内半径の変化に連動して変更する必要はなく、その変化により像コントラストや忠実性が、所望の位置検出精度を得られない程度に劣化したときのみ、その遮光幅や位置を変更するだけでも良い。
【００９０】
また、前述の如く外半径及び／又は内半径が異なる位相差付加部を持つ、複数の位相差フィルターの代わりに、例えば光学的な厚さはほぼ同一で、直径が異なる複数の円形透明板を交換機構１７に設け、この複数の円形透明板をそれぞれ交換して結像光路中に配置可能に構成するだけでもよい。但し、照明系瞳面上の輪帯透過部Ｉの外半径を変更するときは、その変更された輪帯透過部と結像関係となる輪帯領域内の結像光束とその外側の結像光束との間に位相差を付加できないが、その変更により像コントラストや忠実性が、所望の位置検出精度を得られない程度に劣化しなければ何ら問題ない。尚、像コントラストや忠実性の劣化が問題になるときは、例えば開口絞り２６によってその輪帯領域の外側に分布する結像光束の少なくとも一部を遮光するようにしてもよい。このとき、前述の不等式（１２）をほぼ満足する（結像光学系の開口数ＮＡｏの変更に伴う像コントラストや忠実性の劣化が実用上問題とならない）範囲内で開口絞り２６の開口径を変更することが望ましい。
【００９１】
また、前述の輪帯透過部Ｉ及び位相差付加部Ｓは共にその形状が輪帯（円環）状であるとしたが、例えば矩形、正方形、又は多角形（特に正多角形）としても良い。さらに、照明系瞳面上の輪帯透過部Ｓを部分的に遮光（又は減光）する、即ち輪帯透過部Ｉを複数の部分透光部（その形状は任意で良く、例えば円弧、円形、又は直線状等として構わない）から構成しても良い。これに対応して結像系瞳面上の位相差付加部Ｓを、その輪帯透過部Ｉと同一の形状としても良いし、あるいはその部分透光部と結像関係となる複数の部分領域をほぼ含む輪帯、矩形、又は多角形状等としても良い。尚、照明系瞳面上の輪帯透過部Ｉを正方形とする場合は、その正方形透過部の内側エッジと光軸との距離を前述の内半径ｒｉ、その外側エッジと光軸との距離を前述の外半径ｒｏと見做して、前述の条件式（１０）、（１１）を満足するように各値を決定すれば良い。但し、結像光学系の開口数ＮＡｏについては前述の条件式（１２）から決定される開口数よりも大きくしておくことが望ましい。
【００９２】
尚、以上の実施例では半導体基板上のマークの位置を検出する装置を前提に説明を行ったが、本発明はフォトリソグラフィ工程で使用される各種装置（露光装置等）以外に、他の用途の光学装置に対しても応用することが可能である。例えば、目視検査、観察に使用される一般の光学顕微鏡に対して本発明を適用すれば、上記と同様に低段差パターンに対して高コントラストな像を得ることができる。さらには、生物顕微鏡のように透過照明を使用する顕微鏡に対しても本発明を適用して同様の効果を得ることができる。
【００９３】
【発明の効果】
以上のように本発明によれば、平坦化工程等により凹凸変化（段差）が極めて小さくなる位置検出マークであっても、十分にコントラストの高いマーク像を得ることができる。従って、高いコントラストの像強度分布を用いてそのマーク位置の検出を高精度に行なうことができる。
【００９４】
また、表面段差、又は光束の位相変化が少ない各種パターンの像を従来よりも高いコントラストで検出可能な光学装置（光学顕微鏡等）を実現できる。
【図面の簡単な説明】
【図１】本発明の実施例による位置検出装置の概略的な全体構成を示す図。
【図２】本発明における光学的なフーリエ変換の関係の説明に供する図。
【図３】（Ａ）は照明視野絞りの構成を示す図、（Ｂ）は指標板用照明視野絞りの構成を示す図、（Ｃ）は指標板の構成を示す図。
【図４】（Ａ）、（Ｂ）は位置検出マークの具体的な構成を示す図、（Ｃ）は撮像素子上に形成される像強度分布を示す図。
【図５】（Ａ）は照明光束制限部材の具体的な構成を示す図、（Ｂ）は位相差フィルターの具体的な構成を示す図。
【図６】本発明の一実施例による位相差フィルターの断面図。
【図７】本発明の実施例による位置検出装置で得られる低段差の位置検出マークの像のシミュレーション結果を示す図。
【図８】図７のシミュレーション条件のうち結像光学系の開口数のみを変更して得られる低段差の位置検出マークの像のシミュレーション結果を示す図。
【図９】図７のシミュレーション条件のうち照明系瞳面上の輪帯透過部の外半径のみを変更して得られる低段差の位置検出マークの像のシミュレーション結果を示す図。
【図１０】図７のシミュレーション条件のうち照明系瞳面上の輪帯透過部の内半径のみを変更して得られる低段差の位置検出マークの像のシミュレーション結果を示す図。
【図１１】照明系瞳面上の透過部、及び結像系瞳面上の位相差付加部をそれぞれ円形としたときに得られる低段差の位置検出マークの像のシミュレーション結果を示す図。
【図１２】図７のシミュレーション条件のうち結像系瞳面上の位相差付加部の透過率のみを変更して０％とした、所謂暗視野顕微鏡で得られる低段差の位置検出マークの像のシミュレーション結果を示す図。
【図１３】明視野顕微鏡で得られる低段差の位置検出マークの像のシミュレーション結果を示す図。
【図１４】結像系瞳面上の位相差付加部の透過率が１００％であるときに得られる低段差の位置検出マークの像のシミュレーション結果を示す図。
【図１５】明視野顕微鏡で得られる比較的高段差の位置検出マークの像のシミュレーション結果を示す図。
【符号の説明】
４照明視野絞り
６照明光束制限部材
１６位相差フィルター
２２指標板照明視野絞り
２４指標板
２８撮像素子
２９画像処理系[0001]
[Industrial application fields]
The present invention relates to a relative alignment technique between a mask pattern and a photosensitive substrate applied to an exposure apparatus used in a photolithography process for exposing the mask pattern onto a photosensitive substrate, for example, when manufacturing a semiconductor element or the like. In particular, the present invention relates to a technique for detecting a mark pattern on a photosensitive substrate.
[0002]
[Prior art]
For example, in a photolithography process for manufacturing a semiconductor element, a liquid crystal display element, a thin film magnetic head, an imaging device (CCD), a magneto-optical disk, etc., a photomask or reticle (hereinafter collectively referred to as a transfer pattern) is formed. An exposure apparatus that transfers an image of a “reticle” onto a photosensitive substrate such as a wafer coated with a photoresist or a glass plate by a projection exposure method using a projection optical system or a proximity exposure method is used. ing.
[0003]
In such an exposure apparatus, it is necessary to perform alignment (alignment) between the reticle and the wafer with high accuracy prior to exposure. In order to perform this alignment, a position detection mark (alignment mark) formed in the previous process (exposure transfer) is formed on the wafer, and by detecting the position of this alignment mark, An accurate position of the wafer (circuit pattern on the wafer) can be detected.
[0004]
As an alignment mark detection method, for example, there is a laser beam scanning method, a laser interference method, or the like that detects scattering of laser light or diffracted light. However, the laser beam has strong monochromaticity, and the position detection accuracy may deteriorate due to adverse effects such as multiple interference between the photoresist surface and the mark surface.
On the other hand, a method of illuminating an alignment mark with a broadband light beam using a lamp or the like as a light source, picking up an image through an imaging optical system, and performing position detection based on the image signal (hereinafter referred to as “imaging type”). (Referred to as “position detection”) has the advantage of being less susceptible to adverse effects of photoresist and the like.
[0005]
[Problems to be solved by the invention]
In recent years, with the miniaturization of semiconductor integrated circuits and the like, a process for flattening the wafer surface has been introduced after the film forming process and before the photolithography process. This has the effect of improving the device characteristics by making the thickness of the generated film on which the circuit pattern is formed uniform, and the effect of improving the adverse effect of the irregularities on the wafer surface on the line width error of the transfer pattern in the photolithography process. is there.
[0006]
However, in the method of detecting the position based on the unevenness change or reflectance change at the alignment mark portion on the wafer surface, the unevenness change at the alignment mark portion is remarkably reduced by the flattening process, so that the alignment mark cannot be detected. There is a fear. In particular, in a process for an opaque generated film (metal or semiconductor film), the alignment mark is covered with an opaque film having a uniform reflectance. For this reason, the position detection relies only on the unevenness of the mark, and the flattening of the opaque generated film is the most problematic process.
[0007]
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a position detection device that can accurately and reliably detect a position detection mark even with a position detection mark having extremely small unevenness (step). .
[0008]
[Means for Solving the Problems]
The present invention relates to an illumination optical system that irradiates a position detection mark on a substrate with illumination light (for example, broadband light or multi-wavelength light) in a predetermined wavelength range, and an image sensor that receives light generated from the position detection mark. An image forming optical system for forming an image of the position detection mark on the image pickup system is applied to an apparatus for detecting the position of the position detection mark based on an image signal output from the image sensor.
[0009]
In the present invention, the illumination light on the first surface (pupil plane) in the illumination optical system that has a substantially optical Fourier transform relationship with the position detection mark is centered on the optical axis of the illumination optical system. On the second surface (pupil surface) in the imaging optical system that is substantially in a relationship of optical Fourier transform with respect to the position detection mark; A phase difference member is provided for differentiating the phases of the imaged light fluxes distributed in the substantially annular zone-like second region that has an imaging relationship with the first region and the other regions.
[0010]
Alternatively, a light flux limiting member that limits illumination light on the first surface in the illumination optical system to a substantially annular first region centered on the optical axis, and on the second surface in the imaging optical system A phase difference member that makes the phases of the zero-order light from the position detection mark and the other light different from each other may be provided.
Alternatively, an optical member that increases the intensity distribution of the illumination light on the first surface in the illumination optical system or the secondary light source (surface light source) over the other region in the ring-shaped first region, and the imaging optical system A phase difference member for differentiating the phases of the imaged light fluxes distributed in the substantially annular zone-like second region having an image-formation relationship with the first region and the other regions on the second surface is provided. May be.
[0011]
Alternatively, a diaphragm member that transmits the illumination light beam distributed in the annular first region on the substantial pupil plane of the illumination optical system and the first region on the second surface in the imaging optical system are connected. You may make it provide the phase difference member which makes the phase of the imaging light beam each distributed in the substantially annular zone 2nd area | region used as an image relationship, and the area | region other than that differ.
Alternatively, a substantially annular secondary light source centered on the optical axis on the substantial pupil surface of the illumination optical system (or a plurality of secondary light sources in an approximately annular region centered on the optical axis on the pupil surface). Of the light source image) and the image formed on the substantial pupil plane of the image forming optical system and distributed in a substantially ring-shaped region having an image forming relationship with the secondary light source and other regions. You may make it provide the phase difference member which changes the phase of a light beam.
[0012]
Alternatively, an optical member that increases the light intensity distribution on the substantial pupil plane of the illumination optical system in a substantially ring-shaped area centered on the optical axis of the illumination optical system, as compared with the inner area, and the imaging optical system A phase difference member for differentiating the phases of the imaged light fluxes distributed in the substantially circular area that is in an imaging relationship with the inner area and the other areas on the substantial pupil plane of Good.
[0013]
It is also desirable to have a member that diminishes the imaging light beam distributed in the annular zone on the second surface in the imaging optical system, that is, the 0th-order light distributed on the second surface. This dimming member may be formed integrally with the phase difference member, arranged close to the phase difference member, or arranged in a plane substantially conjugate with the phase difference member (pupil conjugate plane). Also good.
Further, the phase difference member is approximately (2m + 1) π / 2 ± π / 4 [rad] (m is between the imaging light beam distributed in the second region and the imaging light beam distributed in the other region. It is desirable to give an integer phase difference. At this time, either the phase of the imaging light beam distributed in the second region or the phase of the imaging light beam distributed in the other region may be shifted. Further, the above-described phase difference may be given by changing the phase shift amounts of the two light beams.
[0014]
Further, if the shortest wavelength in the wavelength range of the luminous flux contributing to the formation of the image signal in the illumination light is λ1, the longest wavelength is λ2, and the period of the position detection mark is P, the outer radius ro of the annular zone-shaped first region, And the inner radius ri is
ri ≧ λ2 / (2 × P)
ro-ri ≦ λ1 / P
It is desirable to satisfy the relationship. The numerical aperture NAo of the imaging optical system is
NAo ≧ ro + λ2 / P
It is desirable to satisfy the relationship.
[0015]
Furthermore, it is preferable to provide a member for holding the phase difference member so that it can be inserted into and removed from the optical path of the imaging optical system. Further, at this time, a member for holding the light flux limiting member (or the optical member, the diaphragm member, the secondary light source (light source image) forming member) so as to be detachable with respect to the optical path of the illumination optical system may be provided.
Further, an image forming means for forming an image of the index mark is provided on the image sensor, and a position shift between the image of the position detection mark and the image of the index mark is detected based on an image signal output from the image sensor. Also good. The image forming means includes an indicator plate having an indicator mark, an illumination system that irradiates the indicator plate with a light beam different from the illumination light irradiated on the substrate, and light generated from the indicator mark is incident on the image. It is desirable to have an imaging system formed on the image sensor. In particular, the index plate is disposed on a surface substantially conjugate with the substrate in the imaging optical system, and an image of the position detection mark is formed on the index plate by the imaging optical system. An image of the index mark may be formed on the image sensor.
[0016]
Further, for example, the index mark is set according to the change in the light amount of the imaged light beam from the position detection mark incident on the image sensor when the light beam limiting member (or optical member or the like) is inserted into or removed from the optical path of the illumination optical system. It is desirable to provide a member for adjusting the intensity of the light beam to be illuminated. As an example, the intensity of the light beam is increased in conjunction with the withdrawal of the light beam limiting member from the illumination optical path. This adjusting member may be one that changes the power (current, voltage) supplied to the light source that emits the light beam, or one that replaces a plurality of neutral density filters with different transmittances and that is arranged in the beam optical path.
[0017]
In addition, the optical member that enhances the intensity distribution of the illumination light (or secondary light source) on the first surface in the illumination optical system more than the other areas in the ring-shaped first area is a light intensity in the other areas. A diaphragm member having a light-shielding portion that substantially covers the other region may be used so that the value is substantially zero.
Furthermore, the optical member desirably has an intensity distribution changing member that changes at least one of the outer radius and the inner radius of the annular zone-shaped first region. The intensity distribution changing member includes a plurality of aperture members having at least one of an outer radius and an inner radius of the annular aperture, and a plurality of aperture members arranged in the optical path of the illumination optical system. You may make it have a member holding an aperture member. Furthermore, it is desirable that the phase difference member changes at least one of the radial width and position of the annular zone-shaped second region in accordance with a change in at least one of the outer radius and the inner radius of the first region.
[0018]
In addition, the change in the outer radius and inner radius (that is, the width and position in the radial direction) of the ring-shaped first region (secondary light source) and the intensity distribution of the illumination light described above can be made using, for example, a liquid crystal element or an electrochromic element. This can be realized by arranging the aperture stop on the pupil plane, or by replacing a plurality of aperture members having at least one of the outer radius and the inner radius of the aperture so as to be arranged in the optical path. Alternatively, a variable aperture stop is arranged on the pupil plane, and the aperture diameter can be arbitrarily changed (or a plurality of aperture stops having different aperture diameters can be replaced and arranged in the optical path), and the outer radius is changed, In addition, a plurality of circular light shielding plates having different diameters may be exchanged to be arranged in the optical path so as to change the inner radius.
[0019]
Furthermore, the change of the outer radius and the inner radius (that is, the position and width in the radial direction) of the annular zone-shaped second area described above is performed by, for example, an annular zone phase shifter (dielectric film, etc.), or an annular zone-like recess (or a convex portion). This can be realized by exchanging a plurality of transparent substrates having at least one of a radial position and a width of each portion, and arranging them in the optical path. Instead of providing an annular zone phase shifter, a phase shifter may be provided in areas other than the annular zone second region. Alternatively, a plurality of circular transparent plates having substantially the same optical thickness and different diameters may be exchanged so that they can be arranged in the optical path. However, when the outer radius of the first area is changed, the phase difference between the imaging light beam in the second area and the imaging light beam outside the second area, which is in an imaging relationship with the changed first area. However, there is no problem if the image contrast and fidelity are not deteriorated to such an extent that the desired position detection accuracy cannot be obtained. When image contrast or fidelity degradation becomes a problem, for example, the imaging light flux distributed outside the second region may be shielded by a variable aperture stop.
[0020]
[Action]
As an optical system for detecting only a “step” portion on a substantially flat test object, a “dark field microscope” and a “phase contrast microscope” are known. In the dark field microscope, a light shielding region is provided on the pupil plane (Fourier transform plane for the test object) of the imaging optical system, and the test object is irradiated with illumination light on the test object (for example, a position detection mark on the wafer). Among the reflected diffracted light generated from the light, the 0th-order diffracted light (regularly reflected light) is shielded to form an image using only the higher-order diffracted light (and scattered light). Among these, the 0th-order diffracted light contains almost no information on the unevenness of the test object and the reflectance change, but the higher-order (first-order or higher) diffracted light contains such information. Therefore, in the dark field microscope, the 0th-order diffracted light is shielded and an image is formed only by the high-order diffracted light, so that the step can be visualized more clearly (with high contrast) than a normal (bright-field) microscope. Become.
[0021]
On the other hand, the phase-contrast microscope is provided with a phase-difference filter that transmits a phase difference between zero-order diffracted light and other orders of diffracted light (and scattered light) on the pupil plane of the imaging optical system. Is. Although the amount of high-order (first-order or higher) diffracted light generated from a low-level mark pattern is very small, a zero-order diffracted light with a large amount of light can contribute to image formation in a phase contrast microscope, and thus a dark field microscope. A brighter (higher intensity) image can be obtained. Note that if the intensity ratio between the 0th-order diffracted light and the other-order diffracted light is extremely large, the image contrast is lowered, and therefore the 0th-order diffracted light may be dimmed.
[0022]
However, when a conventional phase-contrast microscope is used to detect a position detection mark on a wafer, not only zero-order diffracted light unnecessary for image formation but also other orders of diffracted light (beneficial diffracted light that contributes to image formation). On the other hand, there is a problem in that the addition of a phase difference and the dimming effect are exerted, and the contrast and fidelity of the image are deteriorated.
Therefore, in the present invention, it is noted that a position detection mark on a substrate such as a wafer usually has a certain periodicity (period P) in the position detection direction, and diffracted light other than the 0th order generated by the periodicity. The shape of the phase difference member and the secondary light source of the illumination optical system (the illumination light flux distribution on the pupil plane of the illumination optical system, or the intensity distribution of the illumination light) is minimized so that the phase difference member is not affected as much as possible. Since it is set, it is possible to add a phase difference with respect to only the 0th-order diffracted light and further reduce the light.
[0023]
That is, in the present invention, the illumination light beam on the first surface (pupil surface) in the illumination optical system that has a substantially optical Fourier transform relationship with respect to the position detection mark is substantially ring-shaped around the optical axis. The first region and the imaging relationship on the second surface (pupil plane) in the imaging optical system that is limited within the first region and has a substantially optical Fourier transform relationship with the position detection mark. The phase of the imaging light flux distributed in each of the substantially annular second region and the other regions is different, in other words, the zero-order light from the position detection mark distributed on the second surface and the other The phase was changed with light.
[0024]
Alternatively, the intensity distribution of the illumination light (or the secondary light source or the surface light source) on the first surface in the illumination optical system is made higher than the other regions in the ring-shaped first region, or the illumination optical system substantially An illumination light beam distributed in the first annular region on the pupil plane, or a substantially annular secondary light source centered on the optical axis on the substantial pupil surface of the illumination optical system ( (Surface light source) may be formed, or a plurality of light source images may be formed in a substantially annular zone centered on the optical axis on the substantial pupil plane of the illumination optical system. In addition, the light intensity distribution on the substantial pupil plane of the illumination optical system is higher than the inner region in a substantially ring-shaped region centered on the optical axis of the illumination optical system, and the image forming optical system substantially The phases of the imaged light fluxes distributed in the substantially circular region that is in an image formation relationship with the inner region on the typical pupil surface and the other regions may be made different from each other.
[0025]
For this reason, position detection can be performed reliably (with a high-contrast image) even for position detection marks with extremely small unevenness (steps). The first and second regions and the secondary light source (surface light source) are in the shape of a ring (annular), but may be rectangular, square, or polygonal (especially regular polygon). good. Further, the first region on the first surface (pupil surface) in the illumination optical system is partially shielded (or dimmed), that is, the first region may be a plurality of partial regions (the shape may be arbitrary, for example, an arc , Circular, linear, etc.). Correspondingly, the second region on the second surface (pupil surface) in the imaging optical system may have the same shape as the first region, or a plurality of images having an imaging relationship with the first region. It is good also as a ring zone, a rectangle, or a polygonal shape etc. which substantially contain these partial areas.
[0026]
Further, there is provided a member for dimming the imaging light beam distributed in the annular zone on the second surface in the imaging optical system, that is, the 0th-order diffracted light distributed on the second surface. Thereby, the intensity ratio between the 0th-order diffracted light from the position detection mark and the diffracted light of other orders can be reduced, and the image of the position detection mark can be detected with higher contrast.
Further, if the shortest wavelength in the wavelength range of the light beam contributing to the formation of the image signal in the illumination light is λ1, the longest wavelength is λ2, and the period of the position detection mark is P, the outer radius ro of the annular zone-shaped first region, And the inner radius ri
ri ≧ λ2 / (2 × P)
ro-ri ≦ λ1 / P
To satisfy the relationship. Also, the numerical aperture NAo of the imaging optical system is
NAo ≧ ro + λ2 / P
To satisfy the relationship. For this reason, the image of the position detection mark of a low level | step difference can be detected with higher contrast.
[0027]
Further, a variable aperture stop (NA stop) for changing the numerical aperture NAo of the image forming optical system is provided on the second surface (pupil surface) in the image forming optical system, or a conjugate surface thereof, and the retardation member and the mechanical surface. It is good to provide it so as not to interfere with. As a result, even if the period of the position detection mark changes, the numerical aperture of the imaging optical system can be set to a value corresponding to the period so as to satisfy the above-described condition, and the mark image is always high. It can be detected by contrast. The variable aperture stop may be arranged so as to be shifted from the pupil plane of the imaging optical system or its conjugate plane in the optical axis direction.
[0028]
In addition, a member for holding the phase difference member so as to be detachable with respect to the optical path of the imaging optical system is provided. For this reason, switching to bright field detection can be performed, and the mark image can be detected by selecting the presence or absence of a phase difference member in accordance with the level difference of the position detection mark. Therefore, it is possible to always obtain a high-contrast mark image regardless of the step amount of the position detection mark, and to improve the position detection accuracy.
[0029]
Further, a member for holding the light flux limiting member (or the optical member, the diaphragm member, the secondary light source forming member) so as to be detachable with respect to the optical path of the illumination optical system is also provided. For this reason, it is possible to switch between the annular illumination and the normal illumination, and when the position detection mark is not a low step, even if the reflectance is low, the mark image can be reliably detected by the normal illumination.
[0030]
In addition, the optical member that increases the intensity distribution of the illumination light (secondary light source, surface light source) on the first surface in the illumination optical system in the first annular region is higher than the other regions. An intensity distribution changing member that changes at least one of the outer radius and the inner radius of the region is provided. For this reason, even if the period of the position detection mark changes, at least one of the outer radius and the inner radius of the ring-shaped first region is set to a value corresponding to the period so as to satisfy the conditional expression described above. Can do. Therefore, it is possible to always obtain a high contrast mark image regardless of the period of the position detection mark. It is not necessary to change the outer radius and the inner radius of the ring-shaped first region in conjunction with the change in the period of the position detection mark, and the change causes the image contrast and fidelity to obtain the desired position detection accuracy. The outer radius and the inner radius may be changed only when the deterioration is not possible.
[0031]
Furthermore, the phase difference member changes at least one of the radial width and position of the annular zone-shaped second region in accordance with a change in at least one of the outer radius and the inner radius of the first region. For this reason, even if at least one of the outer radius and the inner radius of the ring-shaped first region changes according to the period of the position detection mark, a phase difference is always given only to the 0th-order diffracted light and incident on the image sensor. Can be made. Note that the width and position of the ring-shaped second region of the imaging optical system do not need to be changed in conjunction with the change in the outer radius or inner radius (period of the position detection mark) of the ring-shaped first region, Only when the image contrast and fidelity are deteriorated to such an extent that the desired position detection accuracy cannot be obtained, the width and position of the phase shift unit may be changed. In addition, it is not necessary to change both the outer radius and the inner radius of the second region in conjunction with changes in the outer radius and the inner radius of the first region, and for example, only the inner radius of the second region may be changed.
[0032]
【Example】
Embodiments of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic overall configuration of the position detection apparatus of the present embodiment. In FIG. 1, a broadband illumination light beam (broadband light) emitted from a light source 1 such as a halogen lamp is incident on an illumination field stop 4 through a condenser lens 2 and a wavelength selection element (such as a sharp cut filter or an interference filter) 3. .
[0033]
The wavelength selection element 3 transmits only a light beam in a non-photosensitive wavelength region (for example, a wavelength of 550 nm to 750 nm) with respect to a photoresist (exposure wavelength is, for example, 365 nm or 248 nm) applied on the wafer 10 described later. However, if the present invention is applied to a position detection device for a substrate not covered with a photoresist, for example, a position detection device for overlaying a circuit pattern and a transferred resist pattern on a wafer after exposure and development processing, Since it is not necessary to prevent the photoresist from being exposed, a light beam having a shorter wavelength (close to the exposure wavelength) can also be used.
[0034]
The light beam transmitted through the illumination field stop 4 enters the illumination light beam limiting member (aperture stop) 6 of the present invention through the relay lens 5. Further, the illumination light enters the wafer 10 on which the position detection mark 11 is formed via the beam splitter 8 and the objective lens group 9. The illumination light beam limiting member 6 is optically Fourier-transformed with respect to the surface of the wafer 10 (position detection mark 11) via the objective lens group 9 and the beam splitter 8 (hereinafter referred to as “illumination system”). (Abbreviated as “pupil plane”). That is, the positional deviation amount of the predetermined point in the illumination light beam limiting member 6 from the optical axis AXI of the illumination optical system (1 to 5, 8, 9) is the surface of the wafer 10 of the illumination light beam passing through the predetermined point. Is proportional to the sine of the angle of incidence.
[0035]
Here, the illumination light flux limiting member 6 has an annular opening, and is held by the movable member 7 so that the center of the annular opening coincides with the optical axis AXI of the illumination optical system. The movable member 7 is, for example, a turret plate or a slider, and the illumination light beam limiting member 6 can be inserted into and removed from the optical path of the illumination optical system. Accordingly, in the present embodiment, the annular illumination and the normal illumination can be switched by the movable member 7, and either one is selected according to the step amount (and / or the fineness (cycle, line width, etc.) of the position detection mark 11. Can be selected. For example, the annular illumination is selected for the low level position detection mark and the high level fine position detection mark, and the illumination light beam limiting member 6 is inserted into the optical path, and the normal illumination is selected for the high level rough position detection mark. Thus, the illumination light flux limiting member 6 is retracted outside the optical path.
[0036]
Further, the illumination field stop 4 is substantially conjugated (imaging relationship) with the surface (position detection mark 11) of the wafer 10 through a series of optical systems 5 to 9, and a transmission part of the illumination field stop 4 is provided. The illumination range on the wafer 10 can be limited according to the shape and size of the wafer 10. The illumination field stop 4 is composed of, for example, a plurality of movable blades, and changes the size and shape of the opening defined by the plurality of movable blades on the wafer 10 according to the size and shape of the position detection mark 11. The illumination range can be changed.
[0037]
The wafer 10 is placed on a wafer stage 12 that can move two-dimensionally, and a mirror 14 that reflects the laser beam from the laser interferometer 15 is fixed to the end of the wafer stage 12. The position of the wafer stage 12 (wafer 10) in the X and Y directions is always detected by the laser interferometer 15 with a resolution of about 0.01 μm, for example. Further, the wafer stage 12 is provided with a reference plate 13 on which reference marks used for baseline measurement and the like are formed.
[0038]
The light beam reflected by the wafer 10 (position detection mark 11) reaches the phase difference member (phase difference filter) 16 of the present invention via the objective lens group 9 and the beam splitter 8. The phase difference filter 16 is optically Fourier-transformed on the surface of the wafer 10 (position detection mark 11) via the objective lens group 9 and the beam splitter 8 (hereinafter referred to as “imaging system”). (Abbreviated as “pupil plane”). That is, the positional deviation amount of the predetermined point in the phase difference filter 16 from the optical axis AX of the imaging optical system is the sine of the exit angle of the light beam (imaging light beam) passing through the predetermined point with respect to the surface of the wafer 10. Is proportional to
[0039]
Although the specific configuration of the phase difference filter 16 will be described in detail later, the phase difference filter 16 is held by the movable member 17 so that the center thereof coincides with the optical axis AX of the imaging optical system. The movable member 17 is, for example, a turret plate or a slider, and the phase difference filter 16 can be inserted into and removed from the optical path of the imaging optical system. Therefore, in the present embodiment, the bright member detection can be switched by the movable member 17 and either one can be selected according to the step amount of the position detection mark 11. For example, the phase difference filter 16 is inserted into the optical path for the low step position detection mark, and the bright field detection is selected for the high step position detection mark, and the phase difference filter 16 is retracted outside the optical path.
[0040]
Here, the relationship of the optical Fourier transform will be described with reference to FIG. 2. In FIG. 2, one focal plane of the objective lens group 9 (focal length is f) represented by one lens 9 ′. If the wafer 10 is arranged, the other focal plane becomes an “optical Fourier transform plane (pupil plane)” FP. Then, the light fluxes having the incident and exit angles θ on the wafer 10 pass through positions on the Fourier transform plane (pupil plane) FP that are separated from the optical axis AX by f · sin θ.
[0041]
In FIG. 2, the objective lens group 9 is represented by a single lens 9 ′. However, even if this is a lens system composed of a plurality of lenses, there is essentially no change, and the objective focal point group 9 has a combined focal plane of a plurality of lenses. When the wafer 10 is disposed, the other focal plane becomes a Fourier transform plane (pupil plane). Then, by arranging the beam splitter 8 between the objective lens group 9 and the pupil plane, it is possible to separate the light transmitting side (illumination system) pupil plane and the light receiving side (imaging system) pupil plane. . The two separated pupil planes are Fourier transform planes for the wafer 10, that is, the illumination system pupil plane and the imaging system pupil plane are substantially passed through the wafer 10, the objective lens group 9, and the beam splitter 8. Therefore, it is conjugate (image formation relationship).
[0042]
The imaging light beam that has passed through the phase difference filter 16 forms an image of the position detection mark 11 on the index plate 24 through the lens system 18 and the beam splitter 19. On the other hand, the indicator plate 24 is also illuminated by the indicator plate illumination optical systems 20-23. The index plate illumination optical system includes a light source 20 such as a light emitting diode, a condenser lens 21, an index plate illumination field stop 22, and a relay lens 23. The index plate illumination field stop 22 is conjugated with the index plate 24 via the relay lens 23 and the beam splitter 19 and thus conjugated with the surface of the wafer 10. Further, the index plate 24 is formed with a reference index (index mark) used when detecting the position detection mark 11 as described later. The indicator plate illumination field stop 22 has an opening in a region that has an imaging relationship with the reference indicator so that only the reference indicator on the indicator plate 24 is irradiated with illumination light from the light source 20.
[0043]
Since the index plate illumination optical systems 20 to 23 are for illuminating the reference index, the illumination light from the light source 20 is different from the illumination light from the light source 1 that irradiates the position detection mark 11 and may be monochromatic light. Good. Moreover, since the illumination light from the light source 20 is not irradiated on the wafer 10, the wavelength may be the photosensitive wavelength of the photoresist. Therefore, in this embodiment, the wavelength of the light source 20 which is a light emitting diode is set to about 500 nm, and the reflection surface of the beam splitter 19 is a dichroic mirror, thereby increasing the utilization efficiency of the imaging light flux from the wafer 10 and the indicator illumination light. (That is, light loss is suppressed). In the present embodiment, the illumination range on the wafer 10 is limited by the illumination field stop 4, so that the image of the position detection mark 11 is not superimposed on the reference index.
[0044]
An image of the position detection mark 11 and a reference index image formed on the index plate 24 are formed on an image sensor 28 such as a CCD by relay lenses 25 and 27, respectively. The image processing system 29 calculates the positional relationship (position shift amount) between the reference index image and the image of the position detection mark 11 based on the output signal from the image sensor 28. Since the image position of the position detection mark 11 naturally reflects the position of the position detection mark 11 on the orthogonal coordinate system XY defined by the laser interferometer 15, the position detection mark 11 is thereby detected. It becomes possible. That is, the position of the position detection mark 11 is obtained from the positional deviation amount calculated by the image processing system 29 and the coordinate position output from the interferometer 15.
[0045]
Here, for example, with the insertion / removal or replacement of the illumination light beam limiting member 6 by the movable member 7, the light quantity of the imaging light beam from the position detection mark 11 that enters the image sensor 28 changes. For this reason, the respective intensities (brightness) of the mark image and the reference index image are different on the image sensor 28, and if the intensity difference becomes large, the positional deviation detection accuracy in the image processing system 29 may be deteriorated. is there. Therefore, in this embodiment, the reference index is changed according to the change in the amount of light of the imaged light beam so that the intensities of the image of the position detection mark 11 and the reference index image formed on the image sensor 28 are always substantially equal. The intensity of the illumination light from the light source 20 can be adjusted. In this embodiment, the light emission intensity is adjusted by adjusting the injection current to the light source (light emitting diode) 20. For example, when the illumination light beam limiting member 6 is withdrawn from the optical path of the illumination optical system, Increase emission intensity. A member (turret plate, slider, etc.) for holding a plurality of neutral density filters having different transmittances is provided between the light source 20 and the indicator plate 24, and the plurality of neutral density filters are provided by driving the holding member. Each may be exchanged and arranged in the optical path. Although not shown, the insertion / removal or replacement of the illumination light flux limiting member 6 or the phase difference filter 16 is based on information from the input device (keyboard or the like) (period of the position detection mark 11 or the amount of steps). A controller that performs overall control of the entire apparatus is automatically performed. Further, the controller adjusts the light emission intensity of the light source 20 according to the type and presence of the illumination light beam limiting member 6 and the phase difference filter 16.
[0046]
By the way, the aperture stop 26 is a surface in the imaging optical system (9 to 27) that has a substantially optical Fourier transform relationship with respect to the wafer 10 (a surface that is conjugate (imaging relationship) with the phase difference filter 16). And restricts the numerical aperture of the imaging optical system. In this embodiment, it is assumed that the numerical aperture of the imaging optical system can be arbitrarily changed by the aperture stop 26. In FIG. 1, the index plate 24 is arranged in the optical path of the imaging optical system. However, the index plate 24 is arranged outside the optical path, and an image of the reference index is formed on the image sensor 28 via the imaging system. You may comprise as follows. For example, if the image sensor 28 is disposed instead of the index plate 24 and the index plate 24 is disposed instead of the index plate illumination field stop 22, the relay lenses 25 and 27 are not required, and the entire apparatus can be downsized. At this time, an area other than the reference index on the index plate 24 is preferably shielded so that light from other than the reference index does not enter the image sensor 28. The aperture stop 26 may be disposed close to the phase difference filter 16 so as not to mechanically interfere.
[0047]
Here, an example of the shape of the position detection mark 11, the shape of each transmission part of the indicator plate 24, the indicator plate illumination field stop 22, and the illumination field stop 4, and the intensity distribution of the image formed on the image sensor 28, This will be described with reference to FIGS. 4A shows a top view of the position detection mark 11, and FIG. 4B shows a cross-sectional view in the position measurement direction (X direction in FIG. 4A). That is, in the present embodiment, the position detection mark 11 composed of three strip-shaped concave portions arranged in the X direction with a period P is formed on the surface of the wafer 10. Further, a photoresist 10 'is applied to the surface of the wafer 10 as shown in FIG.
[0048]
As shown in FIG. 3A, the illumination field stop 4 is a light-shielding portion (shaded portion) except for the rectangular transmission portion 4M that limits the illumination area on the wafer 10. The transmissive part 4M is projected onto the wafer 10 and illuminates only the partial area including the position detection mark 11. This illumination area corresponds to the mark area M (width W in the X direction) in FIG. 4B, and also corresponds to the mark image area MI on the indicator plate 24 shown in FIG. That is, an image of the position detection mark 11 is formed in the mark image area MI on the index plate 24.
[0049]
On the other hand, as shown in FIG. 3B, the indicator plate illumination field stop 22 is also a light shielding portion (shaded portion) except for the two rectangular transmission portions 4L and 4R. The transmitted light from the transmission parts 4L and 4R illuminates rectangular areas (transmission parts) LI and RI on the indicator plate 24 shown in FIG. In the rectangular areas LI and RI, the above-described reference indicators (bar marks) 24L and 24R, which are light shielding portions, are formed, respectively.
[0050]
From the above, the image intensity distribution formed on the image sensor 28 is as shown in FIG. That is, the reference indicators 24L and 24R irradiated with the illumination light from the light source (light emitting diode) 20 on the left and right sides of the image IM of the position detection mark 11 irradiated with the illumination light from the light source (halogen lamp) 1. Images (dark images) IL and IR are formed. As described above, if the brightness of the image IM of the position detection mark 11 and the images IL and IR of the reference indicators 24L and 24R is very different, the detection accuracy of the positional deviation between the two images may be deteriorated. (Light-emitting diode) A mechanism (not shown) is provided that adjusts the injection current to 20 to adjust both images to have substantially the same intensity.
[0051]
In the cross-sectional view of FIG. 4B, the left and right regions L and R of the position detection mark 11 are flat regions. The state of these regions L and R has no influence on the position detection of the position detection mark 11. (Not illuminated with illumination light), there is no problem even if a circuit pattern or the like is present here.
The image processing system 29 determines the positional relationship between the image IM of the position detection mark 11 and the images IL and IR of the reference indicators 24L and 24R based on the light amount signal output from the image sensor 28 as shown in FIG. calculate. This calculation process is exactly the same as the processing generally performed in the conventional imaging type position detection. For example, the slice position (Lo, Li, M) of the light quantity signal at a predetermined slice level SL ₁ (Mn, Ri, Ro), position detection may be performed, or position detection may be performed based on a correlation between a certain template signal and a light amount signal of a mark portion.
[0052]
Prior to these position detections, it is necessary to measure the positional relationship of the reference indices 24L and 24R serving as the reference for the detection positions with respect to the wafer 10 (wafer stage 12). This is also a conventionally known process called baseline check, and this embodiment is basically the same as the conventional process. That is, a reference mark having the same shape as the position detection mark 11 is formed on the surface of the reference plate 13 fixed on the wafer stage 12, and the wafer stage 12 is driven prior to the detection of the position detection mark 11. The reference mark is moved below the objective lens group 9, and the positional relationship between the reference mark and the reference indicators 24L and 24R is detected. At the same time, the position of the wafer stage 12 (the position of the mirror 14 on the wafer stage 12) at this time is measured by the laser interferometer 15. The sum of the output value of the interferometer 15 and the detected value (the positional relationship detected by the image processing system 29) is stored as a “baseline amount”. Then, the “baseline amount” is subtracted from the sum of the output value of the interferometer 15 at the time of measurement of the position detection mark 11 and the positional relationship between the position detection mark 11 and the reference indicators 24L and 24R obtained from the light quantity signal. This value is the position of the position detection mark 11 relative to the reference mark.
[0053]
In addition, when the present invention is applied to a position detection system (alignment system) of a projection exposure apparatus, on the wafer based on the above position detection values and exposure shot arrangement data stored in the projection exposure apparatus. Each shot area is moved under a projection optical system (not shown) to perform overlay exposure.
Next, the illumination light beam limiting member 6 and the phase difference filter 16 according to the present embodiment will be described on the assumption that the position detection mark 11 having a period of 8 μm is irradiated with the illumination light beam having a wavelength region of 550 to 750 nm to detect the position. .
[0054]
FIGS. 5A and 5B show examples of configurations of the illumination light beam limiting member 6 and the phase difference filter 16 that are suitable for this condition, respectively. The U-axis and V-axis directions in each figure are the same as the X-axis and Y-axis directions of the position detection mark 11 shown in FIG. 4A, respectively, but the illumination light beam limiting member 6 and the phase difference filter 16 are each in position. Since it is arranged on the optical Fourier transform plane (pupil plane) with respect to the detection mark 11, it is expressed as U axis and V axis according to the custom.
[0055]
As shown in FIG. 5A, the illumination light flux limiting member 6 has an inner radius ri of 0 on the light-shielding substrate with the optical axis (intersection of the U axis and V axis) of the illumination optical system (1-9) as the center. .16 (the unit is the numerical aperture, that is, the sine of the incident angle of the light beam that has passed through a predetermined point on the circle of radius ri to the position detection mark 11, and so on), and the outer ring with an outer radius ro of 0.20 An annular zone-shaped transmission part I is formed. Illumination light flux limiting member 6 has a ring opening at a specific location on a metal light-shielding plate, or a light-shielding film formed of metal or the like on a transparent substrate such as glass, and the light-shielding film at a specific location is removed. Is used.
[0056]
On the other hand, the phase difference filter 16 is located at a position conjugate with the annular light transmitting portion I on the illumination light flux restricting member 6 and has an annular shape phase difference adding portion S (image forming relationship with the annular light transmitting portion I). A hatched portion in the figure is formed. FIG. 6 is a cross-sectional view taken along the U axis in FIG. As shown in FIG. 6, the phase difference filter 16 is formed by laminating a metal thin film So and a dielectric film S1 on the surface of a transparent substrate 16A such as glass, and the transmitted light is attenuated by the metal thin film So. The phase of the transmitted light is shifted by the dielectric film S1. Accordingly, the phases of the imaged light beams from the position detection marks 11 distributed in the phase difference adding portion S and the other regions are different from each other, that is, a predetermined phase difference is given between the two light beams. Such a configuration is the same as a phase difference filter in a conventional phase contrast microscope or a “halftone phase shift reticle” that has recently begun to be used in a photolithography process, and can be manufactured by using these various manufacturing methods. it can.
[0057]
In addition, the phase difference given to the transmitted light by the metal thin film So and the dielectric film S1 (the phase difference from the transmitted light of other portions) is optimally about π / 2 [rad] (that is, ¼ wavelength). The thickness of the dielectric film S1 is about λ / (4 (n−1)) where n is the refractive index. In this case, λ is the center wavelength of the luminous flux that contributes to image formation in the illumination light (650 nm in the example of FIG. 6). However, even if there is a slight error in the phase difference amount (phase shift amount) of the phase difference adding unit S, the image contrast of the position detection mark 11 does not drop sharply, so it should be given to the transmitted light of the phase difference adding unit S. If the phase difference is in the range of π / 2 ± π / 4 [rad], it is possible to obtain an image with a relatively good contrast that enables accurate position detection. In particular, if this phase difference is suppressed to about π / 2 ± π / 6 [rad], an image with better contrast can be obtained.
[0058]
Here, when the wavelength region of the light beam contributing to the imaging is narrow (that is, the illumination light is substantially monochromatic), the thickness of the dielectric film S1 is (2k + 1) λ / (4 (n−1)). ) (The phase difference is (2k + 1) π / 4 [rad]) (where k is a natural number). On the other hand, when the wavelength range of the light beam contributing to the imaging is wide, the phase difference shifts from (2k + 1) π / 4 [rad] (optimum condition) as k increases with respect to wavelengths other than the center wavelength. The thickness of the dielectric film S1 is preferably λ / (4 (n−1)). When the phase difference filter 16 under such conditions is used, it is possible to obtain a mark image with clear contrast in which the concave portion of the position detection mark 11 is bright and the convex portion is dark.
[0059]
Further, as the phase difference filter, only the metal thin film So may be formed in the phase difference adding portion S, and the dielectric film S1 may be formed in other portions. In this case, the phase of the 0th-order light is advanced by π / 2 [rad] with respect to the diffracted light of other orders, so the image of the position detection mark 11 is different from that when the phase difference filter 16 of FIG. 6 is used. In contrast, the concave portion of the position detection mark 11 is dark and the convex portion is a bright image. However, the contrast of the image is the same and high in any case.
[0060]
Furthermore, the phase difference adding portion S does not necessarily have a dimming action, and in this case, the metal thin film So may not be added. Further, instead of forming the dielectric film S1 in order to add a phase difference, the transparent substrate 16A may be dug by etching.
Further, the inner radius ri ′ is 0.15 and the outer radius ro ′ is 0.21 so that the phase difference adding portion S is slightly larger than the annular transmission portion I on the illumination light flux limiting member 6. did. This is because the above-described phase difference is more reliably added to the 0th-order diffracted light in consideration that the 0th-order diffracted light from the position detection mark 11 slightly spreads on the phase difference filter 16. In addition, the numerical aperture NAo (radius of the imaging system pupil plane) of the imaging optical system is 0.30. In FIG. 1, the aperture stop 26 that defines the actual numerical aperture is not located at the same position as the phase difference filter 16 but at its conjugate position. The numerical aperture NAo here is the aperture of the aperture stop 26. When the numerical aperture is set smaller than the numerical aperture of the objective lens group 9, the numerical aperture (effective numerical aperture) of the aperture stop 26 is represented. Further, the radius of the outer periphery of the illumination light beam limiting member 6 is sufficiently larger than the numerical aperture of the illumination optical system (radius of the illumination system pupil plane), and the transmitted light distributed outside the annular light transmitting portion I is naturally positioned. The detection mark 11 is not reached.
[0061]
FIG. 5B shows the position of one first-order diffracted light generated from the position detection mark 11 by irradiation of illumination light transmitted through the annular light transmitting portion I on the illumination light flux limiting member 6 in FIG. The distribution on the phase difference filter 16 (region D surrounded by two broken circles in the figure) is shown. Of the diffracted light from the position detection mark 11, the 0th-order diffracted light is distributed on the phase difference adding portion S conjugate with (and slightly larger than) the annular light transmitting portion I and reduced by the metal thin film So. The phase difference is added by the dielectric film S1. Of course, other orders of diffracted light are actually distributed, but only the 0th and 1st order diffracted lights dominant in the formation of the image of the position detection mark 11 will be considered here.
[0062]
Incidentally, a part of the first-order diffracted light is attenuated by the phase difference adding unit S as shown in FIG. 5B, but in this embodiment, as shown in FIG. Since the inner radius ri and the outer radius ro of the part I are appropriately determined, the attenuation of the first-order diffracted light and the addition of the phase difference by the phase difference adding unit S are minimized. Hereinafter, the reason will be described.
[0063]
First, U coordinates of intersections between the inner and outer circumferences of the phase difference adding unit S and the U axis are ri ′ and ro ′ (and −ri ′ and −ro ′), respectively. On the other hand, if the U coordinate of the intersection of the boundary (two dashed circles) where the first-order diffracted light is distributed and the U axis is defined as Dpi, Dpo, Dmi, Dmo, these values are
Dpi = λ / P + ri, Dpo = λ / P + ro
Dmi = λ / P-ri, Dmo = λ / P-ro
It becomes.
[0064]
At this time, especially when the value of Dpi is smaller than ro ′ or the value of Dmo is smaller than −ri ′, the degree of attenuation of the first-order diffracted light by the phase difference adding unit S increases as shown in FIG. ) Is clear. Even if the value of Dmi is larger than ri ′, the degree of dimming is similarly increased.
In the example of FIG. 5A, the period P of the position detection mark 11 is 8 μm, the inner radius ri of the annular transmission part I is 0.16, the outer radius ro is 0.20, and the wavelength λ of the illumination light is Since the shortest wavelength λ1 is 550 nm and the longest wavelength λ2 is 750 nm, the minimum value of Dpi is λ = λ1.
Dpi = λ1 / P + ri = 0.23 (1)
And is larger than ro ′ (= 0.21), and the minimum value of Dmo is λ = λ1.
Dmo = λ1 / P-ro = −0.13 (2)
And greater than -ri '(= -0.15).
[0065]
Furthermore, the maximum value of Dmi is λ = λ2.
Dmi = λ2 / P-ri = −0.07 (3)
And is smaller than ri '(= 0.15).
Therefore, the degree of attenuation of the first-order diffracted light by the phase difference adding unit S is reduced, but if the conditions for this are generalized,
Dpi = λ1 / P + ri ≧ ro ′ (4)
Dmo = λ1 / P−ro ≧ −ri ′ (5)
Dmi = λ2 / P−ri ≦ ri ′ (6)
It becomes.
[0066]
Further, the outer radius ro ′ of the phase difference adding portion S is larger than the outer radius ro of the annular transmission portion I, and the inner radius ri ′ of the phase difference adding portion S is smaller than the inner radius ri of the annular transmission portion I. And the above inequalities (4) to (6) are
Dpi = λ1 / P + ri ≧ ro (7)
Dmo = λ1 / P−ro ≧ −ri (8)
Dmi = λ2 / P−ri ≦ ri (9)
It is also good. In particular, both inequalities (7) and (8)
ro-ri ≦ λ1 / P (10)
And the inequality (9) is
ri ≧ λ2 / (2 × P) (11)
Is equivalent to
[0067]
Therefore, generally, when the inner radius ri and the outer radius ro of the annular transmission part I satisfy the inequalities (10) and (11), the degree of attenuation of the first-order diffracted light by the phase difference adding part S can be made extremely small.
By the way, depending on the value of the numerical aperture NAo of the imaging optical system, the first-order diffracted light may be shielded not only by the light attenuation by the phase difference adding unit S but also by the restriction by the numerical aperture NAo. In order to avoid this, it is desirable that the value of Dpo = λ / P + ro is equal to or less than the numerical aperture NAo described above. Since the maximum value of Dpo is λ2 / P + ro when λ = λ2, the numerical aperture NAo is
NAo ≧ λ2 / P + ro (12)
It is desirable to satisfy the relationship.
[0068]
In the above description, only the first-order diffracted light generated on one side (+ U direction) with respect to the 0th-order diffracted light has been described. However, the same applies to the first-order diffracted light generated in the opposite direction (−U direction). The above condition (inequality) remains unchanged. Further, the period P of the position detection mark 11 and the wavelength range (λ1, λ2) of the illumination light beam are not limited to the above values, and these conditions (inequalities) are satisfied even under other conditions.
[0069]
Next, the effect of the position detection apparatus according to the present embodiment will be described based on a simulation result of an image of a position detection mark with extremely small unevenness (step).
FIG. 7 shows a simulation result of a position detection mark image having a level difference of 5 nm obtained by the position detection apparatus of the present embodiment. As for the mark forming conditions, a photoresist having a period of 12 μm, the width of the concave portion and the width of the convex portion are equal, the material of the mark surface is uniform (refractive index is 3.55), and the refractive index is 1.68. It was assumed that it was applied with a thickness of 1 μm. The wavelength range of the illumination light is 550 nm (= λ1) to 750 nm (= λ2), and the inner radius and the outer radius of the annular transmission part I on the illumination light flux limiting member 6 are in accordance with the above-described conditions (inequality), respectively.
ri = 0.10 ≧ λ2 / (2 × P) = 0.750 / 24 = 0.031
ro = 0.14
(Ro-ri = 0.04 ≦ λ1 / P = 0.550 / 12 = 0.046)
It was.
[0070]
The configuration of the phase difference filter 16 is as shown in FIG. 6. The inner radius and the outer radius of the phase difference adding portion S are equal to the inner radius ri and the outer radius ro of the annular transmission portion I, respectively. The numerical aperture NAo of the system follows the above-mentioned condition (inequality),
NAo = 0.22 ≧ λ2 / P + ro = 0.750 / 12 + 0.14 = 0.203.
[0071]
Further, the transmittance of the phase difference adding portion S is 1%, and the dielectric film S1 has a refractive index of 1. to add a phase difference of π / 2 [rad] with respect to the center wavelength 650 nm of the illumination light. 5. The thickness was 325 nm.
The image intensity distribution shown in FIG. 7 is for one period of the position detection mark 11, the position 0 on the horizontal axis indicates the center of the mark (recess), and the dashed line ± P / 4 indicates the edge of the mark (recess and protrusion). Part boundary). The intensity distribution on the vertical axis is standardized so that the maximum value of the image intensity in one period is 1.
[0072]
Further, FIG. 8 shows a simulation result in the case where only the numerical aperture NAo is set to 0.18 under substantially the same conditions as in FIG. 7 and the above-described conditional expression (12) of the numerical aperture NAo is not satisfied. Although the mark image of FIG. 8 is slightly inferior to the sharpness of the dark part (edge part of the mark) as compared with the image shown in FIG. 7, it has sufficient contrast to detect the edge position, that is, the mark position. Yes. Therefore, it can be understood that among the conditional expressions (10) to (12) according to the present embodiment, the conditional expression (12) of the numerical aperture NAo does not necessarily have to be strictly satisfied.
[0073]
Similarly, FIG. 9 shows a case in which only the outer radius ro of the annular transmission part I is set to 0.18 under substantially the same conditions as in FIG. 7, and the conditional expression (10) for the outer radius ro described above is not satisfied. The simulation result is shown. In this case, it is understood that the image contrast is significantly deteriorated as compared with the images shown in FIGS. 7 and 8, and therefore it is not possible to obtain a good detection accuracy by position detection based on such an image.
[0074]
Further, in FIG. 10, the inner radius ri of the annular transmission part I is 0.02 and the outer radius ro is 0.06 under substantially the same conditions as in FIG. ) Shows a simulation result in a case where the conditional expression (11) of the inner radius ri is not satisfied but is satisfied. In this case, although the contrast of the image is high, a slight dark area is generated not only at the mark edge but also at the center of the recess, which reduces the fidelity of the image and this may adversely affect the position detection. Difficult to do.
[0075]
In FIG. 11, unlike FIGS. 7 to 10, the annular transmission part I on the illumination light flux limiting member 6 has a circular shape (normal σ stop) centered on the optical axis, and the phase difference on the phase difference filter 16. The simulation result in the case where the additional portion S is also a circle centered on the optical axis is shown. The radii of the transmission part I and the phase difference adding part S at this time were both 0.66 (σ value is 0.3). The wavelength range, numerical aperture, and other conditions are the same as those in FIG. The image in this case also has a reduced image fidelity as in FIG. 10, and is difficult to use for position detection.
[0076]
In FIG. 12, for comparison, the shapes of the annular transmission part I of the illumination light flux limiting member 6 and the phase difference adding part S on the phase difference filter 16 are the same as the example of FIG. 7 that satisfies the conditions of the present invention. However, the transmittance of the phase difference adding portion S is 0% (the phase difference adding portion S is a light shielding portion), that is, a mark image by a dark field microscope is shown. In FIG. 12, the scale of the vertical axis is set to be the same as that in FIG. 7 so that the comparison is easy. Even with such a dark field microscope, although the image of the position detection mark having a low step changes in contrast (contrast), its intensity is about 1/5 of the image intensity (FIG. 7) of the position detection apparatus of the present invention. Therefore, the mark image is dark, so that the image signal output from the image sensor 28 also has a poor S / N ratio.
[0077]
Further, FIG. 13 shows a normal (bright field) microscope image. The radius of the σ stop is 0.176 (0.8 as the σ value), and of course the phase difference adding unit S is not provided. Other conditions are the same as those in FIG. As can be seen from FIG. 13, when a bright field microscope is used for a position detection mark with a low step (5 nm), there is almost no change in contrast (contrast) in the image and position detection is impossible.
[0078]
As described above, the images obtained by the position detection device of the present invention shown in FIGS. 7 and 8 are not only sufficiently contrasted with the images shown in FIGS. Since it coincides with the concave and convex portions of the mark, such a mark image can be used for reliable position detection.
As described above, the illumination light beam limiting member 6 and the phase difference filter 16 in the above-described embodiment are extremely effective for detecting a position detection mark having a small step, but have a large step (for example, 100 nm or more). For position detection marks, sufficient detection accuracy can be obtained even with a conventional position detection device. Therefore, when detecting a mark with a large level difference, the illumination light beam limiting member 6 and the phase difference filter 16 are replaced with an exchange mechanism (movable). (Members) 7 and 17 may be used to retract outside the optical path. Further, when there is a possibility that the aberration state of the optical system may fluctuate due to retraction of the phase difference filter 16 (or illumination light flux limiting member 6) made of a glass substrate, the phase difference filter 16 (or illumination light flux restriction member) is saved during the retraction. Instead of 6), it is necessary to insert a transparent member having an optical thickness equivalent to that. This can be easily exchanged by holding the transparent members in the exchange mechanisms 7 and 17, respectively.
[0079]
In the above-described simulation, a position detection mark having a level difference of 5 nm is assumed. However, for a mark that is not so low, for example, a mark having a level difference of about several tens of nm, the dimming and level shown in FIG. In addition to the phase difference filter that adds the phase difference, a phase difference filter that adds only the phase difference and does not attenuate the light can be used. FIG. 14 shows a simulation result when such a phase difference filter is used for a position detection mark having a step of 40 nm. At this time, the shapes of the annular transmission part I on the illumination light flux limiting member 6 and the phase difference adding part S on the phase difference filter 16 are the same as in the example of FIG. As can be seen from FIG. 14, an image with sufficiently high contrast can be obtained for a position detection mark having a certain level difference even if the transmittance of the phase difference adding portion S is high (even if the light is not so dimmed).
[0080]
Therefore, the phase difference filter 16 of FIG. 6 and a phase difference filter (or a phase difference filter having a relatively high transmittance) that only adds a phase difference are held in the exchange mechanism 17 so that the step amount of the position detection mark is increased. Accordingly, the two phase difference filters may be exchanged and arranged in the imaging optical path. For lower level marks, a phase difference filter with low transmittance is selected and loaded.
[0081]
For comparison, FIG. 15 shows a simulation result when a position detection mark having a step of 40 nm is detected using a bright field microscope under the same conditions as in FIG. As is clear from FIG. 15, even with a step of 40 nm, a bright field microscope still cannot obtain a sufficient contrast, and the contrast difference from the image according to the present invention shown in FIG. 14 is clear.
[0082]
By the way, in the above-mentioned embodiment, the annular secondary light source formed by the illumination light flux limiting member 6, that is, the inner radius and the outer radius of the annular transmission portion I, the phase difference filter 16 conjugate with the annular transmission portion I is provided. The inner and outer radii of the phase difference adding section S and the numerical aperture of the imaging optical system are determined by the wavelength range (λ1 to λ2) of the illumination light beam. For example, the position detection mark 11 and the image sensor 28 are used. When a wavelength selection element such as a sharp cut filter is inserted between the two, or when the spectral sensitivity of the image sensor 28 is narrower than the wavelength range of the illumination light beam, these are taken into consideration, that is, the image of the position detection mark 11 Each value is determined based on the wavelength region that actually contributes to signal formation.
[0083]
Also, the illumination light beam limiting member 6 used in the above-described embodiment transmits only the light beam in the annular transmission part I among the light beams distributed on the illumination system pupil plane, and shields the other light beams so as to shield the annular 2 The secondary light source was formed, but the illumination light flux was condensed using, for example, an optical fiber or a combination of a concave conical prism and a convex conical prism in the annular zone on the illumination system pupil plane. A secondary light source may be formed. In this case, there is an advantage that the light quantity loss is greatly reduced.
[0084]
Furthermore, an optical integrator (for example, a fly-eye lens) that enters light from the light source 1 and forms a plurality of light source images on the illumination system pupil plane may be provided. In this case, there is an advantage that the illuminance uniformity of the illumination light on the position detection mark 11 is greatly improved. However, in order to form an annular secondary light source on the pupil plane of the illumination system, for example, an aperture stop (FIG. 5 (A)) having an annular aperture is arranged on the exit side or near the entrance side of the fly-eye lens. Will do. In order to minimize light loss, the above-described concave and convex conical prisms or optical fibers having an annular exit end are disposed between the light source 1 and the fly-eye lens, or the light source 1 and the fly-eye lens are disposed. By using the aberration of the input lens placed between the eye lens, the intensity distribution of the illumination light on the entrance surface of the fly-eye lens can be reduced more in the annular zone around the optical axis than in other regions. Higher is preferred.
[0085]
Further, a plurality of aperture stops in which at least one of the outer radius and the inner radius of the annular transmission portion I is different, in other words, at least one of the radial width (annular ratio) and the position of the annular transmission portion I is changed. The mechanism 7 may be provided so that the plurality of aperture stops are respectively exchanged and arranged in the illumination optical path. In this case, according to the change in the fineness (period P) of the position detection mark 11, an aperture stop that satisfies the conditional expressions (10) and (11) described above and that is optimal for the period is selected and arranged in the illumination optical path. can do. Accordingly, it is possible to obtain a mark image with high contrast at all times regardless of the period of the position detection mark 11. Further, a plurality of circular light shielding plates having different diameters and a plurality of diaphragm members (σ diaphragms) having different diameters of the circular openings are provided in the exchange mechanism 7, and the inner radius of the annular transmission part I is reduced by the circular light shielding plates by the σ diaphragm. The outer radius is defined, and the radial width of the annular secondary light source (illumination light flux distribution or light intensity distribution) on the pupil plane of the illumination system is determined by the combination of the circular light shielding plate and the σ stop. The position may be changed. Here, instead of providing a plurality of σ stops in the replacement mechanism 7, a zoom lens system is disposed between the light source 1 and the replacement mechanism 7, or a variable aperture stop (iris stop) is disposed in the vicinity of the circular light shielding plate. In addition, the light beam diameter (size) of the illumination light, that is, the outer radius of the annular transmission part I may be arbitrarily changed by the zoom lens system or the iris diaphragm.
[0086]
Further, instead of the exchange mechanism 7 having a plurality of aperture stops, for example, an aperture stop made of a liquid crystal element or an electrochromic element may be arranged on the illumination system pupil plane. In this case, the shape, size, and position of the transmission part I on the illumination system pupil plane can be arbitrarily changed. Further, the annular conical prism and the convex conical prism are combined to form a ring-shaped illumination light flux distribution (or light intensity distribution) that satisfies the conditional expressions (10) and (11) above on the illumination system pupil plane. You may do it. At this time, the two prisms may be configured to be relatively movable in the optical axis direction, and the radial position of the annular illumination light beam distribution (light intensity distribution) may be changed. Also, a zoom lens system is arranged between the light source 1 and the two prisms so as to change the diameter (size) of the illumination light beam incident on the conical prism on the light source side, and the annular illumination light beam distribution thereof. The width in the radial direction of (light intensity distribution) may be changed.
[0087]
Note that the outer radius and inner radius of the annular transmission part I (secondary light source) do not need to be changed in conjunction with the change in the period of the position detection mark 11, and the image contrast and fidelity can be changed by the change. The outer radius and the inner radius may be changed only when the position detection accuracy is deteriorated to such an extent that it cannot be obtained.
Also, if the desired position detection accuracy can be obtained even if the image contrast and fidelity are somewhat degraded, the illumination light flux distributed in the area other than the annular transmission part I on the illumination system pupil plane is not completely shielded. May be. In other words, a region other than the annular zone region on the illumination system pupil plane may be used as the dimming unit. In short, the intensity distribution of the illumination light (secondary light source) on the illumination system pupil plane is a ring centered on the optical axis. What is necessary is just to make it higher than another area | region in a strip | belt area | region. As an example, at least one lens system disposed between the light source 1 and the illumination system pupil plane so that the light intensity distribution on the illumination system pupil plane is higher in the annular zone than in other areas, for example, What is necessary is just to adjust the aberration of the relay lens 5 of FIG. At this time, a plurality of relay lenses having different aberration correction amounts may be exchanged and arranged in the illumination optical path to change the light intensity distribution on the illumination system pupil plane.
[0088]
Further, a laser such as a semiconductor laser may be used as the illumination light source 1. Also in this case, since it is desirable that the illumination light beam has a certain wavelength range, it is preferable to use a laser that oscillates at multiple wavelengths, for example, a dye laser, or a plurality of lasers that oscillate at different wavelengths.
Further, in the phase difference filter 16, a member (metal thin film So) for reducing the imaging light beam (0th order light) is integrally formed in the phase difference adding portion S. The transparent substrate having (attenuating portion) may be disposed close to the phase difference filter 16 or may be disposed on a plane (pupil conjugate plane) substantially conjugate with the phase difference filter 16.
[0089]
Further, in conjunction with the change of at least one of the outer radius and the inner radius of the annular transmission part I on the illumination system pupil plane, at least one of the outer radius and the inner radius of the phase difference adding section S on the imaging system pupil plane. You may comprise so that may be changed. For example, a plurality of phase difference filters in which at least one of the outer radius and the inner radius of the phase difference adding unit S is different, in other words, at least one of the radial width (ring zone ratio) and the position of the phase difference adding unit S is different. The exchange mechanism 17 may be provided so that the plurality of phase difference filters are respectively exchanged and arranged in the imaging optical path. In this case, even if at least one of the outer radius and the inner radius of the annular transmission portion I changes according to the period of the position detection mark 11 as described above, the optimum phase difference filter for the annular transmission portion I after this change. Can be selected and placed in the imaging optical path. Accordingly, it is possible to always add only the 0th-order diffracted light to the image pickup element 28 with a phase difference. Note that the width and position of the phase difference adding portion S on the imaging system pupil plane need not be changed in conjunction with changes in the outer radius and inner radius of the annular transmission portion I on the illumination system pupil plane. Only when the image contrast or fidelity is deteriorated to such an extent that the desired position detection accuracy cannot be obtained due to the change, the light shielding width and position may be changed.
[0090]
Further, instead of a plurality of phase difference filters having phase difference adding portions having different outer radii and / or inner radii as described above, for example, a plurality of circular transparent plates having substantially the same optical thickness and different diameters are used. The exchange mechanism 17 may be provided so that the plurality of circular transparent plates are respectively exchanged and arranged in the imaging optical path. However, when the outer radius of the annular transmission part I on the illumination system pupil plane is changed, the imaging light beam in the annular region that forms an imaging relationship with the changed annular transmission part and the imaging outside the outer zone Although no phase difference can be added to the light beam, there is no problem if the image contrast and fidelity are not deteriorated to such an extent that the desired position detection accuracy cannot be obtained. When deterioration of image contrast or fidelity becomes a problem, for example, the aperture stop 26 may block at least a part of the imaging light beam distributed outside the annular region. At this time, the aperture diameter of the aperture stop 26 is set within a range that substantially satisfies the inequality (12) described above (deterioration of image contrast and fidelity associated with a change in the numerical aperture NAo of the imaging optical system is not a problem in practice). It is desirable to change.
[0091]
In addition, although the above-described annular zone transmitting portion I and phase difference adding portion S are both in the shape of an annular zone (ring), for example, they may be rectangular, square, or polygonal (especially regular polygons). . Further, the annular transmission part S on the illumination system pupil plane is partially shielded (or dimmed), that is, the annular transmission part I has a plurality of partial transparent parts (the shape may be arbitrary, for example, an arc, a circle, etc. Or a straight line or the like). Correspondingly, the phase difference adding portion S on the imaging system pupil plane may have the same shape as that of the annular transmission portion I, or a plurality of partial regions having an imaging relationship with the partial light transmission portion. It is good also as a ring zone, a rectangle, or a polygonal shape etc. When the annular transmission part I on the illumination system pupil plane is a square, the distance between the inner edge of the square transmission part and the optical axis is the inner radius ri, and the distance between the outer edge and the optical axis is the same. Each value may be determined so as to satisfy the above-described conditional expressions (10) and (11), considering the aforementioned outer radius ro. However, it is desirable that the numerical aperture NAo of the imaging optical system be larger than the numerical aperture determined from the conditional expression (12).
[0092]
In the above embodiment, the description has been made on the assumption that the apparatus detects the position of the mark on the semiconductor substrate. However, the present invention is not limited to various apparatuses (exposure apparatus, etc.) used in the photolithography process. The present invention can also be applied to other optical devices. For example, if the present invention is applied to a general optical microscope used for visual inspection and observation, a high-contrast image can be obtained for a low step pattern as described above. Furthermore, the same effect can be obtained by applying the present invention to a microscope using transmitted illumination such as a biological microscope.
[0093]
【The invention's effect】
As described above, according to the present invention, a mark image having a sufficiently high contrast can be obtained even with a position detection mark in which the unevenness change (step) is extremely reduced by a flattening process or the like. Accordingly, the mark position can be detected with high accuracy using a high contrast image intensity distribution.
[0094]
In addition, it is possible to realize an optical device (such as an optical microscope) that can detect images of various patterns with little surface step or light phase change with higher contrast than conventional ones.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic overall configuration of a position detection apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining the relationship of optical Fourier transform in the present invention.
3A is a diagram showing a configuration of an illumination field stop, FIG. 3B is a diagram showing a configuration of an indicator plate illumination field stop, and FIG. 3C is a diagram showing a configuration of an indicator plate.
4A and 4B are diagrams illustrating a specific configuration of a position detection mark, and FIG. 4C is a diagram illustrating an image intensity distribution formed on an image sensor.
5A is a diagram illustrating a specific configuration of an illumination light beam limiting member, and FIG. 5B is a diagram illustrating a specific configuration of a phase difference filter.
FIG. 6 is a sectional view of a phase difference filter according to an embodiment of the present invention.
FIG. 7 is a diagram showing a simulation result of an image of a position detection mark with a low step obtained by the position detection device according to the embodiment of the present invention.
8 is a diagram showing a simulation result of an image of a low step position detection mark obtained by changing only the numerical aperture of the imaging optical system in the simulation conditions of FIG.
9 is a view showing a simulation result of an image of a low step position detection mark obtained by changing only the outer radius of the annular transmission part on the illumination system pupil plane in the simulation conditions of FIG. 7;
10 is a diagram showing a simulation result of an image of a low step position detection mark obtained by changing only the inner radius of the annular transmission part on the illumination system pupil plane in the simulation conditions of FIG. 7;
FIG. 11 is a diagram showing a simulation result of an image of a low step position detection mark obtained when each of a transmission part on the illumination system pupil plane and a phase difference addition part on the imaging system pupil plane is circular.
12 is an image of a low step position detection mark obtained by a so-called dark field microscope, in which only the transmittance of the phase difference adding portion on the imaging system pupil plane is changed to 0% among the simulation conditions of FIG. The figure which shows the simulation result.
FIG. 13 is a view showing a simulation result of an image of a low-level position detection mark obtained by a bright field microscope.
FIG. 14 is a diagram showing a simulation result of an image of a low step position detection mark obtained when the transmittance of the phase difference adding unit on the imaging system pupil plane is 100%.
FIG. 15 is a diagram illustrating a simulation result of an image of a position detection mark having a relatively high step obtained by a bright field microscope.
[Explanation of symbols]
4 Illumination field stop
6 Illumination beam limiting member
16 Phase difference filter
22 Indicator plate illumination field stop
24 Indicator board
28 Image sensor
29 Image processing system

Claims

An illumination optical system that irradiates a position detection mark on a substrate with illumination light in a predetermined wavelength range, and imaging optics that forms an image of the position detection mark on an image sensor by incidence of light generated from the position detection mark An apparatus for detecting the position of the position detection mark based on an image signal output from the image sensor,
The illumination light beam on the first surface in the illumination optical system that has a substantially optical Fourier transform relationship with respect to the position detection mark is a first ring-shaped first beam centered on the optical axis of the illumination optical system. A light flux limiting member for limiting within the region;
A substantially annular second region having an imaging relationship with the first region on the second surface in the imaging optical system having a substantially optical Fourier transform relationship with respect to the position detection mark, and the second region A position detection device comprising: a phase difference member that changes a phase of an imaging light beam distributed to each other region.

The apparatus according to claim 1, further comprising a member for dimming an imaging light beam distributed in the second region.

The retardation member is disposed on the second surface in the imaging optical system, and is approximately (2m + 1) π / 2 ± π / 4 between the imaging light fluxes distributed in the second region and the other regions. The apparatus according to claim 1, wherein the optical filter provides a phase difference of [rad] (m is an integer).

Outer radius of the ring-shaped first region, where λ1 is the shortest wavelength in the wavelength region of the luminous flux contributing to the formation of the image signal in the illumination light, λ2 is the longest wavelength, and P is the period of the position detection mark. ro and inner radius ri are
ri ≧ λ2 / (2 × P)
ro-ri ≦ λ1 / P
The apparatus according to claim 1, wherein the relationship is satisfied.

Assuming that the outer radius of the ring-shaped first region is ro, the period of the position detection mark is P, and the longest wavelength in the wavelength range of the luminous flux contributing to the formation of the image signal of the illumination light is λ2. The numerical aperture NAo of the image optical system is
NAo ≧ ro + λ2 / P
The device according to claim 1, wherein the relationship is satisfied.

The apparatus according to claim 1, further comprising: a member that holds the phase difference member in a removable manner with respect to an optical path of the imaging optical system.

The apparatus according to claim 6, further comprising a member that removably holds the light flux limiting member with respect to the optical path of the illumination optical system.

Image forming means for forming an index mark image on the image sensor, and detecting a positional shift between the position detection mark image and the index mark image based on an image signal output from the image sensor An apparatus according to any one of claims 1 to 7, characterized in that

The image forming unit includes an index plate having the index mark, an illumination system that irradiates the index plate with a light beam different from the illumination light, and light generated from the index mark is incident on the image to capture the image. 9. An apparatus as claimed in claim 8, including an imaging system formed thereon.

The index plate is disposed on a surface substantially conjugate with the substrate in the imaging optical system, and the imaging optical system forms an image of the position detection mark on the index plate and The apparatus according to claim 9, wherein an image of a detection mark and an image of the index mark are formed on the image sensor.

The illumination system includes a member that adjusts an intensity of a light beam that illuminates the index mark according to a change in a light amount of an imaging light beam incident on the image sensor from the position detection mark. Item 9. The device according to Item 9 or 10.

An illumination optical system that irradiates a position detection mark having periodicity on the substrate with illumination light in a predetermined wavelength range, and forms an image of the position detection mark on an image sensor by incidence of light generated from the position detection mark An apparatus for detecting the position of the position detection mark based on an image signal output from the imaging device,
The illumination light beam on the first surface in the illumination optical system that has a substantially optical Fourier transform relationship with respect to the position detection mark is in a substantially annular zone centered on the optical axis of the illumination optical system. A light flux limiting member for limiting to
If the phase of the zero-order light from the position detection mark distributed on the second surface in the imaging optical system, which has a substantially optical Fourier transform relationship with respect to the position detection mark, is different from that of the other light. A position detection device comprising: a phase difference member to be moved.

The apparatus according to claim 12, further comprising a member that attenuates zero-order light from the position detection mark.

The retardation member is disposed on the second surface in the imaging optical system, and is approximately (2m + 1) π / 2 ± π / 4 [between the zero-order light from the position detection mark and the other light. The apparatus according to claim 12, wherein the optical filter provides a phase difference of rad] (m is an integer).

Out of the illumination light, if the shortest wavelength in the wavelength range of the luminous flux contributing to the formation of the image signal is λ1, the longest wavelength is λ2, and the period of the position detection mark is P, the outer radius ro of the ring-shaped region, And the inner radius ri is
ri ≧ λ2 / (2 × P)
ro-ri ≦ λ1 / P
The apparatus according to claim 12, wherein the relationship is satisfied.

If the outer radius of the annular zone is ro, the period of the position detection mark is P, and the longest wavelength in the wavelength range of the luminous flux contributing to the formation of the image signal of the illumination light is λ2, the imaging optics The numerical aperture NAo of the system is
NAo ≧ ro + λ2 / P
The device according to claim 12, wherein the relationship is satisfied.

An illumination optical system that irradiates a position detection mark on a substrate with illumination light in a predetermined wavelength range, and imaging optics that forms an image of the position detection mark on an image sensor by incidence of light generated from the position detection mark An apparatus for detecting the position of the position detection mark based on an image signal output from the image sensor,
The intensity distribution of the illumination light on the first surface in the illumination optical system that has a substantially optical Fourier transform relationship with respect to the position detection mark is substantially the same as the optical axis of the illumination optical system. An optical member that is higher than the other regions in the first zone of the annular zone;
A substantially annular second region having an imaging relationship with the first region on the second surface in the imaging optical system having a substantially optical Fourier transform relationship with respect to the position detection mark, and the second region A position detection device comprising: a phase difference member that changes a phase of an imaging light beam distributed to each other region.

The apparatus according to claim 17, further comprising a member for dimming an imaging light beam distributed in the second region.

The retardation member is disposed on the second surface in the imaging optical system, and is approximately (2m + 1) π / 2 ± π / 4 between the imaging light fluxes distributed in the second region and the other regions. The apparatus according to claim 17 or 18, wherein the apparatus is an optical filter that gives a phase difference of [rad] (m is an integer).

Outer radius of the ring-shaped first region, where λ1 is the shortest wavelength in the wavelength region of the luminous flux contributing to the formation of the image signal in the illumination light, λ2 is the longest wavelength, and P is the period of the position detection mark. ro and inner radius ri are
ri ≧ λ2 / (2 × P)
ro-ri ≦ λ1 / P
The apparatus according to claim 17, wherein the relationship is satisfied.

Assuming that the outer radius of the ring-shaped first region is ro, the period of the position detection mark is P, and the longest wavelength in the wavelength range of the luminous flux contributing to the formation of the image signal of the illumination light is λ2. The numerical aperture NAo of the image optical system is
NAo ≧ ro + λ2 / P
The device according to claim 17, wherein the relationship is satisfied.

The optical member includes a diaphragm member having a light shielding portion that substantially covers the other area so that light intensity in the other area on the first surface is substantially zero. The apparatus in any one of -21.

23. The apparatus according to claim 17, wherein the optical member includes an intensity distribution changing member that changes at least one of an outer radius and an inner radius of the ring-shaped first region.

The intensity distribution changing member includes a plurality of diaphragm members having at least one of an outer radius and an inner radius of a ring-shaped opening, and one of the plurality of diaphragm members arranged in an optical path of the illumination optical system. 24. The apparatus according to claim 23, further comprising a member that holds a plurality of throttle members.

The phase difference member changes at least one of a radial width and a position of the ring-shaped second region in accordance with a change in at least one of an outer radius and an inner radius of the first region. An apparatus according to any one of claims 17 to 24.

An illumination optical system that irradiates a position detection mark on a substrate with illumination light in a predetermined wavelength range, and imaging optics that forms an image of the position detection mark on an image sensor by incidence of light generated from the position detection mark An apparatus for detecting the position of the position detection mark based on an image signal output from the image sensor,
A diaphragm member that transmits an illumination light beam distributed in a substantially annular first region centered on the optical axis of the illumination optical system on a substantial pupil plane of the illumination optical system;
The phase of the imaged light fluxes distributed in the substantially annular zone-like second region that has an imaging relationship with the first region and the other regions on the substantial pupil plane of the imaging optical system are different. A position detection device comprising a phase difference member.

An illumination optical system that irradiates a position detection mark on a substrate with illumination light in a predetermined wavelength range, and imaging optics that forms an image of the position detection mark on an image sensor by incidence of light generated from the position detection mark An apparatus for detecting the position of the position detection mark based on an image signal output from the image sensor,
A secondary light source forming member for forming a substantially annular secondary light source centered on the optical axis of the illumination optical system on a substantial pupil plane of the illumination optical system;
A phase difference member that makes the phases of imaging light fluxes distributed in a substantially annular area and an area other than the secondary light source on the substantial pupil plane of the imaging optical system different from each other. And a position detecting device.

An illumination optical system that irradiates a position detection mark on a substrate with illumination light in a predetermined wavelength range, and imaging optics that forms an image of the position detection mark on an image sensor by incidence of light generated from the position detection mark An apparatus for detecting the position of the position detection mark based on an image signal output from the image sensor,
An optical member that increases the light intensity distribution on the substantial pupil plane of the illumination optical system in a substantially ring-shaped region centering on the optical axis of the illumination optical system, as compared with the inner region;
A phase difference member for differentiating the phases of the imaging light fluxes distributed in a substantially circular area having an imaging relationship with the inner area on the substantial pupil plane of the imaging optical system and the other areas; A position detection device comprising the position detection device.

The apparatus according to any one of claims 1 to 28, wherein the illumination optical system includes a light source that emits broadband light or multi-wavelength light as the illumination light.