JP2004170869A - Imaging optical system, exposure apparatus and exposure method - Google Patents

Abstract

A reflection type imaging optical system which has a relatively small number of reflecting surfaces and has a sufficiently large effective image forming area and an image-side numerical aperture which is well corrected for aberrations with respect to, for example, EUV light. system.
A reflective imaging optical system including a plurality of reflecting mirrors (M1 to M6) and forming an image of a first surface (M) on a second surface (W). A first reflection imaging optical system (M1 to M4) for forming an intermediate image on the first surface and a second reflection imaging optical system (M5, M6) for forming an image of the intermediate image on the second surface. ), The plurality of reflecting mirrors are arranged in a space between the first surface and the second surface, the entrance pupil is located on the opposite side of the imaging optical system across the first surface, and the Petzval sum The absolute value is 0.0002 (mm ^-1 ) or less.
[Selection] Fig. 18

Description

【００２３】
図２は、先行特許出願の第２実施例にかかる結像光学系の像高２５．５ｍｍに対応する透過波面の形状を示す図である。図３は、先行特許出願の第２実施例にかかる結像光学系の像高２６ｍｍに対応する透過波面の形状を示す図である。図４は、先行特許出願の第２実施例にかかる結像光学系の像高２６．５ｍｍに対応する透過波面の形状を示す図である。なお、第２実施例にかかる結像光学系のさらに詳細な構成については、先行特許出願における関連の記載を参照することができる。
【００２４】
一般に、光学系の透過波面をツェルニケ多項式により級数展開することができる。以下、ツェルニケ多項式について基本的な事項を簡単に説明する。ツェルニケ多項式の表現では、座標系として極座標（ρ，θ）を用い、直交関数系としてツェルニケの円筒関数を用いる。すなわち、透過波面Ｗ（ρ，θ）は、ツェルニケの円筒関数Ｚｉ（ρ，θ）を用いて、次の式（ｃ）に示すように展開される。
【００２５】
【数２】

【００２６】
ここで、Ｃ_ｉは、ツェルニケ多項式の各項の係数である。以下、ツェルニケ多項式の各項の関数系Ｚｉ（ρ，θ）のうち、第１項〜第３６項にかかる関数Ｚ１〜Ｚ３６を、次の表（２）に示す。
【００２７】
【表２】

【００２８】
図５は、ツェルニケ多項式の第１項に対応する透過波面の形状を模式的に示す図である。図６は、ツェルニケ多項式の第２項に対応する透過波面の形状を模式的に示す図である。図７は、ツェルニケ多項式の第３項に対応する透過波面の形状を模式的に示す図である。図８は、ツェルニケ多項式の第４項に対応する透過波面の形状を模式的に示す図である。図９は、ツェルニケ多項式の第５項に対応する透過波面の形状を模式的に示す図である。図１０は、ツェルニケ多項式の第６項に対応する透過波面の形状を模式的に示す図である。図１１は、ツェルニケ多項式の第７項に対応する透過波面の形状を模式的に示す図である。図１２は、ツェルニケ多項式の第８項に対応する透過波面の形状を模式的に示す図である。図１３は、ツェルニケ多項式の第９項に対応する透過波面の形状を模式的に示す図である。
【００２９】
図２〜図４を参照すると、先行特許出願の第２実施例にかかる結像光学系の透過波面の形状において、ツェルニケ多項式の第５項に対応する透過波面の形状（図９を参照）の成分が支配的であることが明らかである。図９に示す波面形状は、収差論では非点収差（ａｓｔｉｇｍａｔｉｓｍ）と呼ばれる成分に対応している。収差論によれば、非点収差は、メリジオナル像面とサジタル像面とが乖離することにより発生する。同じく収差論によれば、メリジオナル像面とサジタル像面とはペッツバール像面上で一致し、メリジオナル像面とサジタル像面とは３：１の割合でペッツバール像面から乖離する。このため、ペッツバール像面と実際の像面（メリジオナル像面とサジタル像面との中間面）との乖離が大きいほど、非点収差は大きくなると言われている。すなわち、図２〜図４に示す波面は、このペッツバール像面と実際の像面との乖離に起因するものであることが予想される。
【００３０】
さて、ペッツバール像面と実際の像面との乖離は、ペッツバール像面が平面状になっていないことに起因するものと予想される。ペッツバール像面が平面状でない場合、ＥＵＶ光用の投影光学系のように非球面を多用した結像光学系では特に、実際の像面を平面状にするために実際の像面とペッツバール像面との乖離が大きくなる。以上の考察より、ペッツバール像面を平面に近付けることにより、非点収差の発生を良好に抑えることができ、ひいては十分に収差補正された良好な結像性能を得ることができることが予想される。
【００３１】
ペッツバール像面を平面に近付けるには、ペッツバール和（すなわち光学系の各レンズ（または各反射鏡）のパワーの和）を零に近付ければ良いことが知られている。反射光学系の場合、ペッツバール和ρは、一般に下記の式（ｄ）により定義される。なお、式（ｄ）において、Σはすべての反射鏡に関する総和記号である。また、曲率半径は、凹面反射鏡の場合には正の値をとり、凸面反射鏡の場合には負の値をとる。
ρ＝Σ｛２／（各反射鏡の曲率半径）｝ （ｄ）
【００３２】
先行特許出願の第２実施例にかかる結像光学系では、式（ｄ）により求まるペッツバール和は約０．０００３８（ｍｍ^−１）である。本件出願の発明者は、入射瞳が物体面を挟んで結像光学系の反対側に位置するような反射型の結像光学系について多数の設計解を試行した結果、ペッツバール和の値が０．０００２（ｍｍ^−１）以下であれば、非点収差がある程度良好に補正された設計解が得られること、ペッツバール和の値が０．０００１（ｍｍ^−１）以下であれば、非点収差が非常に良く補正された設計解が得られることを見出した。なお、反射型の結像光学系では、光軸上において反射面が切り欠かれた反射鏡が存在するが、この場合は反射面を延長した光軸上の仮想反射面に基づいてペッツバール和が算出されることになる。
【００３３】
一般の光学系においてペッツバール和を小さく抑えるには、下記の技法を用いるのが一般的であり、本発明の場合も例外ではない。図１４は、凸レンズと凹レンズと凸レンズとの組み合わせからなる、トリプレットと呼ばれる３枚レンズの結像光学系の模式図である。さて、屈折型の結像光学系においてペッツバール和が零ということは、すべてのレンズについてパワーの単純和が零ということであるが、光学系全体では正のパワーを持たなければ結像系は成り立たない。したがって、光学系中の凸レンズは、同じ曲率半径であっても、光束に対して正のパワーの影響をより大きく作用させるために、光束径のできるだけ大きな個所に配置することが望ましい。逆に、光学系の中の凹レンズは、同じ曲率半径であっても、光束に対して負のパワーの影響をより小さく作用させるために、光束径のできるだけ小さな個所に配置することが望ましい。そこで、ペッツバール和を零に近付けるには、図１４（ｂ）に示すようなパワー配置よりも図１４（ａ）に示すようなパワー配置が望ましく、光学系中において光束が極端にくびれるような（光束径の変化にメリハリを付けるような）設計が望ましい。
【００３４】
ところで、たとえばＥＵＶＬ露光装置に本発明の結像光学系を搭載する場合、次の条件式（１）を満足することが望ましい。なお、条件式（１）において、Ｄｏは結像光学系の入射瞳とマスク面（物体面；第１面）との間隔であり、Ｈｏはマスク面における最大物体高であり、ＮＡｏは結像光学系のマスク側の開口数である。
Ｄｏ＞Ｈｏ／（２×ＮＡｏ） （１）
【００３５】
露光装置では、結像光学系（投影光学系）の入射瞳の位置に、実質的な面光源が形成されることになり、ひいてはフライアイミラーの射出面が配置されることになる。このとき、マスクに入射する照明光の開口数は仕様により決められているので、結像光学系の入射瞳とマスク面との間隔Ｄｏが小さくて条件式（１）を満足しない場合には、フライアイミラーの外径が小さくなりすぎて、その製造が困難になるので好ましくない。
【００３６】
以上のように、本発明の結像光学系では、入射瞳が物体面を挟んで結像光学系の反対側に位置するとともに、ペッツバール和の絶対値が所定値以下に抑えられているので、反射面の枚数が比較的少ない構成にもかかわらず、たとえばＥＵＶ光に対して良好に収差補正され、且つ十分に大きな有効結像領域および像側開口数を確保することができる。特に、本発明の結像光学系を露光装置に適用する場合、結像光学系の入射瞳がマスク面を挟んで結像光学系の反対側に位置しているので、照明系の射出瞳と結像光学系の入射瞳とを光学的に共役に配置するための集光反射光学系の配置が不要になり、照明系の射出瞳と結像光学系の入射瞳とを単に一致させるだけでよいため、照明系の構成が簡素化されるだけでなく、集光反射光学系に起因する光量損失および収差発生を回避して、マスクパターンを感光性基板上に忠実に且つ高スループットで転写することができる。また、本発明の結像光学系を露光装置または露光方法に用いることにより、露光光としてＥＵＶ光を使用して、マスクパターンを感光性基板上に忠実に且つ高スループットで転写することができ、ひいては良好な露光条件のもとで高精度なマイクロデバイスを製造することができる。
また、本発明の露光装置では、投影光学系の入射瞳位置を第１面よりも投影光学系の反対側に設定して照明光学系の構成の簡素化をはかり、かつマスクから投影光学系へ向かう光束と投影光学系の光軸との間の空間に光路偏向鏡を配置して、照明光学系と投影光学系との光路分離を容易にしている。
【００３７】
本発明の実施形態を、添付図面に基づいて説明する。
図１５は、本発明の実施形態にかかる露光装置の全体構成を概略的に示す図である。また、図１６は、ウェハ上に形成される円弧状の露光領域（すなわち実効露光領域）と光軸との位置関係を示す図である。さらに、図１７は、図１５の光源および照明光学系の内部構成を概略的に示す図である。図１５において、投影光学系の光軸方向すなわち感光性基板であるウェハの法線方向に沿ってＺ軸を、ウェハ面内において図１５の紙面に平行な方向にＹ軸を、ウェハ面内において図１５の紙面に垂直な方向にＸ軸をそれぞれ設定している。
【００３８】
図１５の露光装置は、露光光を供給するための光源として、たとえばレーザプラズマ光源１を備えている。光源１から射出された光は、波長選択フィルタ（不図示）を介して、照明光学系２に入射する。ここで、波長選択フィルタは、光源１が供給する光から、所定波長（たとえば１３．４ｎｍまたは１１．５ｎｍ）のＥＵＶ光だけを選択的に透過させ、他の波長光の透過を遮る特性を有する。波長選択フィルタを透過したＥＵＶ光３は、照明光学系２および光路偏向鏡としての平面反射鏡４を介して、転写すべきパターンが形成された反射型のマスク（レチクル）Ｍを照明する。マスクＭは、そのパターン面がＸＹ平面に沿って延びるように、Ｙ方向に沿って移動可能なマスクステージ５によって保持されている。そして、マスクステージ５の移動は、レーザー干渉計６により計測されるように構成されている。
【００３９】
照明されたマスクＭのパターンからの光は、反射型の投影光学系（結像光学系）ＰＬを介して、感光性基板であるウェハＷ上にマスクパターンの像を形成する。すなわち、ウェハＷ上には、図１６に示すように、たとえばＹ軸に関して対称な細長い円弧状の露光領域（すなわち静止露光領域）が形成される。図１６を参照すると、光軸ＡＸを中心とした半径φを有する円形状の領域（イメージサークル）ＩＦ内において、このイメージサークルＩＦに接するようにＸ方向の長さがＬＸでＹ方向の長さがＬＹの円弧状の実効露光領域ＥＲが設定されている。
【００４０】
ウェハＷは、その露光面がＸＹ平面に沿って延びるように、Ｘ方向およびＹ方向に沿って二次元的に移動可能なウェハステージ７によって保持されている。なお、ウェハステージ７の移動は、マスクステージ５と同様に、レーザー干渉計８により計測されるように構成されている。こうして、マスクステージ５およびウェハステージ７をＹ方向に沿って移動させながら、すなわち投影光学系ＰＬに対してマスクＭおよびウェハＷをＹ方向に沿って相対移動させながらスキャン露光（走査露光）を行うことにより、ウェハＷの１つの露光領域にマスクＭのパターンが転写される。
【００４１】
このとき、投影光学系ＰＬの投影倍率（転写倍率）が１／４である場合、ウェハステージ７の移動速度をマスクステージ５の移動速度の１／４に設定して同期走査を行う。また、ウェハステージ７をＸ方向およびＹ方向に沿って二次元的に移動させながら走査露光を繰り返すことにより、ウェハＷの各露光領域にマスクＭのパターンが逐次転写される。
【００４２】
また、図１７を参照すると、レーザプラズマ光源１では、レーザ光源１１から発した光（非ＥＵＶ光）がレンズ１２を介して気体ターゲット１３上に集光する。ここで、たとえばキセノン（Ｘｅ）からなる高圧ガスがノズル１４より供給され、ノズル１４から噴射されたガスが気体ターゲット１３を形成する。気体ターゲット１３は、集光されたレーザ光によりエネルギーを得てプラズマ化し、ＥＵＶ光を発する。なお、気体ターゲット１３は、楕円反射鏡１５の第１焦点に位置決めされている。したがって、レーザプラズマ光源１から放射されたＥＵＶ光は、楕円反射鏡１５の第２焦点に集光する。一方、発光を終えたガスはダクト１６を介して吸引されて外部へ導かれる。
【００４３】
楕円反射鏡１５の第２焦点に集光したＥＵＶ光は、一対のフライアイミラー１７ａおよび１７ｂからなるインテグレータ１７に導かれる。一対のフライアイミラー１７ａおよび１７ｂとして、たとえば特開平１１−３１２６３８号公報において本出願人が開示したフライアイミラーを用いることができる。ただし、同公報の実施例では、第１フライアイミラーに平行光束が入射するように構成しているが、図１７では第１フライアイミラー１７ａに発散光束が入射するように設定している。この場合、中央よりも周辺の要素ミラーほど大きくチルトさせることにより、第１フライアイミラー１７ａの各要素ミラーで反射された光束が第２フライアイミラー１７ｂの対応する要素ミラーに入射し且つ第２フライアイミラー１７ｂの各要素ミラーで反射された光束がマスクＭ上において互いに重なり合うように構成すれば、原理は同公報に開示した通りである。なお、フライアイミラーのさらに詳細な構成および作用については、たとえば特開平１１−３１２６３８号公報における関連の記載を参照することができる。
【００４４】
こうして、第２フライアイミラー１７ｂの反射面の近傍、すなわちインテグレータ１７の射出面の近傍には、所定の形状を有する実質的な面光源が形成される。ここで、実質的な面光源は、前述したように、照明光学系２の射出瞳位置またはその近傍、すなわち投影光学系ＰＬの入射瞳と光学的に共役な面またはその近傍に形成される。実質的な面光源からの光は、平面反射鏡４により偏向された後、マスクＭにほぼ平行に且つ近接して配置された視野絞り１８を介して、マスクＭ上に細長い円弧状の照明領域を形成する。
【００４５】
以下、第１実施例および第２実施例を参照して、投影光学系ＰＬの具体的な構成について説明する。各実施例において、投影光学系ＰＬは、光軸に関して回転対称な非球面状の反射面を有する６つの反射鏡Ｍ１〜Ｍ６により構成されている。また、各実施例において、投影光学系ＰＬは、ウェハ側（像像）にほぼテレセントリックな光学系である。さらに、各実施例において、非球面は、光軸に垂直な方向の高さをｙとし、非球面の頂点における接平面から高さｙにおける非球面上の位置までの光軸に沿った距離（サグ量）をｚとし、頂点曲率半径をｒとし、円錐係数をκとし、ｎ次の非球面係数をＣ_ｎ としたとき、以下の数式（ｅ）で表される。
【００４６】
【数３】
ｚ＝（ｙ^２／ｒ）／｛１＋（１−ｙ^２／ｒ^２）^１／２｝＋Ｃ_４・ｙ^４＋Ｃ_６・ｙ^６＋Ｃ_８・ｙ^８＋Ｃ_１０・ｙ^１０＋・・・ （ｅ）
【００４７】
［第１実施例］
図１８は、本実施形態の第１実施例にかかる投影光学系の構成を示す図である。図１８を参照すると、第１実施例の投影光学系では、マスクＭからの光は、第１凹面反射鏡Ｍ１の反射面、第２凸面反射鏡Ｍ２の反射面、開口絞りＡＳ、第３凸面反射鏡Ｍ３の反射面、および第４凹面反射鏡Ｍ４の反射面で順次反射された後、マスクパターンの中間像を形成する。そして、マスクパターン中間像からの光は、第５凸面反射鏡Ｍ５の反射面および第６凹面反射鏡Ｍ６の反射面で順次反射された後、ウェハＷ上にマスクパターンの縮小像（二次像）を形成する。すなわち、第１実施例の投影光学系では、マスクＭからウェハＷへ光軸ＡＸに沿って、第２凸面反射鏡Ｍ２、第４凹面反射鏡Ｍ４、第１凹面反射鏡Ｍ１、第３凸面反射鏡Ｍ３、第６凹面反射鏡Ｍ６、および第５凸面反射鏡Ｍ５の順に配置されている。また、第１実施例では、反射鏡Ｍ１〜Ｍ４はマスクＭのパターンの中間像を形成するための第１反射結像光学系を構成し、反射鏡Ｍ５およびＭ６は中間像の像をウェハＷ上に形成するための第２反射結像光学系を構成している。さらに、第１実施例では、すべての反射鏡Ｍ１〜Ｍ６はマスクＭとウェハＷとの間の空間に配置されている。
【００４８】
次の表（３）に、第１実施例にかかる投影光学系の諸元の値を掲げる。表（３）において、λは露光光の波長を、βは投影倍率を、ＮＡは像側（ウェハ側）開口数を、ＮＡｏは物体側（マスク側）開口数を、ＨｏはマスクＭ上における最大物体高を、Ｄｏは入射瞳とマスク面との間隔を、φはウェハＷ上でのイメージサークルＩＦの半径（最大像高）を、ＬＸは実効露光領域ＥＲのＸ方向に沿った寸法を、ＬＹは実効露光領域ＥＲのＹ方向に沿った寸法をそれぞれ表している。
【００４９】
また、面番号は像面であるウェハ面から物体面であるマスク面へ光線が逆行する方向に沿ったウェハ側からの反射面の順序を、ｒは各反射面の頂点曲率半径（ｍｍ）を、ｄは各反射面の軸上間隔すなわち面間隔（ｍｍ）をそれぞれ示している。なお、面間隔ｄは、反射される度にその符号を変えるものとする。そして、光線の入射方向にかかわらずウェハ側に向かって凸面の曲率半径を正とし、凹面の曲率半径を負としている。上述の表記は、以降の表（４）においても同様である。
【００５０】
【表３】

【００５１】
［第２実施例］
図１９は、本実施形態の第２実施例にかかる投影光学系の構成を示す図である。図１９を参照すると、第２実施例の投影光学系では、マスクＭからの光は、第１凹面反射鏡Ｍ１の反射面、第２凸面反射鏡Ｍ２の反射面、開口絞りＡＳ、第３凸面反射鏡Ｍ３の反射面、および第４凹面反射鏡Ｍ４の反射面で順次反射された後、マスクパターンの中間像を形成する。そして、マスクパターン中間像からの光は、第５凸面反射鏡Ｍ５の反射面および第６凹面反射鏡Ｍ６の反射面で順次反射された後、ウェハＷ上にマスクパターンの縮小像（二次像）を形成する。すなわち、第２実施例の投影光学系では、マスクＭからウェハＷへ光軸ＡＸに沿って、第４凹面反射鏡Ｍ４、第２凸面反射鏡Ｍ２、第３凸面反射鏡Ｍ３、第１凹面反射鏡Ｍ１、第６凹面反射鏡Ｍ６、および第５凸面反射鏡Ｍ５の順に配置されている。また、第２実施例においても第１実施例と同様に、反射鏡Ｍ１〜Ｍ４はマスクＭのパターンの中間像を形成するための第１反射結像光学系を構成し、反射鏡Ｍ５およびＭ６は中間像の像をウェハＷ上に形成するための第２反射結像光学系を構成している。さらに、第２実施例においても第１実施例と同様に、すべての反射鏡Ｍ１〜Ｍ６はマスクＭとウェハＷとの間の空間に配置されている。次の表（４）に、第２実施例にかかる投影光学系の諸元の値を掲げる。
【００５２】
【表４】

【００５３】
第１実施例では、ペッツバール和が−０．００００１４（ｍｍ^−１）であり、その絶対値が０．０００１（ｍｍ^−１）よりも小さく抑えられているので、透過波面のＲＭＳが０．００２３〜０．００７４という極めて小さな値になり、非点収差を含む諸収差が非常に良好に補正されていることがわかる。また、第２実施例では、ペッツバール和が０．００００２８（ｍｍ^−１）であり、その絶対値が０．０００１（ｍｍ^−１）よりも小さく抑えられているので、透過波面のＲＭＳが０．００７２〜０．０１３２という十分に小さな値になり、非点収差を含む諸収差が良好に補正されていることがわかる。
【００５４】
このように、上述の各実施例では、波長が１３．４ｎｍのＥＵＶ光に対して、０．２６の像側開口数を確保するとともに、ウェハＷ上において諸収差が良好に補正された２６ｍｍ×２ｍｍの円弧状の実効露光領域を確保することができる。したがって、ウェハＷにおいて、たとえば２６ｍｍ×３３ｍｍの大きさを有する各露光領域に、マスクＭのパターンを走査露光により高解像で転写することができる。
【００５５】
また、上述の各実施例では、投影光学系が反射面の枚数の比較的少ない構成を有するので、すなわち６つの反射鏡により構成されているので、反射面における光量損失を良好に抑えて、スループットの高い投影露光が可能である。さらに、上述の各実施例では、投影光学系の入射瞳がマスク面を挟んで投影光学系の反対側に位置しているので、照明系の射出瞳と投影光学系の入射瞳とを光学的に共役に配置するための集光反射光学系の配置が不要になり、照明系の射出瞳と投影光学系の入射瞳とを単に一致させるだけでよい。その結果、照明系の構成が簡素化されるだけでなく、集光反射光学系に起因する光量損失および収差発生を回避して、マスクパターンを感光性基板上に忠実に且つ高スループットで転写することができる。さらに、上述の各実施例では、条件式（１）を満足しているので、フライアイミラー（１７ａ，１７ｂ）の外径が小さくなり過ぎることなく、その製造が容易である。
【００５６】
また、第２実施例では、図１９に示すように、各反射鏡において反射面が光軸ＡＸと交わる原点の近傍を光束が通過することがないので、原点を含む中央領域を切り欠く必要のある反射鏡が存在しない。すなわち、第２実施例では、すべての反射鏡の反射面の原点を残すことができるので、各反射鏡の反射面形状の計測が容易になり、ひいては各反射鏡の反射面の加工が容易になる。
【００５７】
なお、上述の各実施例では、マスクパターンの縮小像をウェハ上に形成しているが、物体面と像面とを逆に設定して拡大結像光学系として用いることもできる。この場合、射出瞳が像面を挟んで結像光学系の反対側に位置することになり、ペッツバール和の絶対値は不変である。また、物体面と像面とを逆に設定した拡大結像光学系において条件式（１）に対応する条件は、次の式（２）で表わされる。なお、条件式（２）において、Ｄｉは結像光学系の射出瞳と像面との間隔であり、Ｈｉは像面における最大像高であり、ＮＡｉは結像光学系の像側の開口数である。
Ｄｉ＞Ｈｉ／（２×ＮＡｉ） （２）
【００５８】
なお、光路偏向鏡としての平面反射鏡４において、マスクから投影光学系へ向かう光束に近い側の端面形状はほぼ楕円形状の一部であることが好ましい。これにより、マスクから投影光学系へ向かう光束のけられを防ぐことができる。
また、上述の実施形態では、光路偏向鏡としての平面反射鏡４は、第１面と投影光学系との間の空間に位置決めされていたが、投影光学系の内部または投影光学系を通り抜けた反対側に位置決めされてもよい。この場合、投影光学系を構成する光学部材に切り欠きや穴を設けておくことが好ましい。
また、上述の実施形態では、光路偏向鏡としての平面反射鏡４の反射面が、マスクから投影光学系へ向かう光束に向けられていたが、この平面反射鏡４の反射面の向きをマスクから投影光学系へ向かう光束とは反対側に向けても良い。
また、上述の実施形態では、光路偏向鏡としての平面反射鏡４における反射率を向上させるために、光路偏向鏡へ向かう光束と前記光路偏向鏡の反射面とのなす角度を小さく設定していたが、この角度を９０度に近い角度にしても良い。これは、平面反射鏡４の反射面の反射率が４５度近傍で最悪値となり、この角度から離れるにしたがって反射率が向上するためである。
また、上述の実施形態では、光路偏向鏡として、平面反射鏡４を用いたが、その代わりに、所定のパワーを持たせても良い。
また、上述の実施形態では、マスクＭに近接して視野絞り１８を配置していたが、特開２０００−９１２２０号公報に開示されるような視野絞り１８をマスクＭ上に投影するための再結像光学系を設けても良い。
また、上述の実施形態において、イングレータ１７と光路偏向鏡４との間に別の光路偏向鏡を設けて、インテグレータ１７をマスクＭ面を含む面とウェハＷ面を含む面との間の空間に位置させても良い。これにより、マスクステージおよびウェハステージの構成が簡易となる利点がある。このとき、上記別の光路偏向鏡では垂直入射に近い入射角であることが好ましい。
また、光路偏向鏡に、特開２０００−１００６８５号に開示される光量検出器を設けて露光量制御を行っても良い。これにより、露光量制御の高精度化を図ることができる。
また、上述の実施形態においては、楕円反射鏡１５の第２焦点を一対のフライアイミラー１７ａおよび１７ｂに近づけているが、この第２焦点、すなわちＥＵＶ光の集光点を一対のフライアイミラー１７ａおよび１７ｂから離す構成が好ましい。これにより、ＥＵＶ光の集光点の近傍にピンホールを設けた仕切り部材を配置することが容易となり、この仕切り部材によって、光源側の雰囲気と装置本体側の雰囲気とを分離することが容易となる。
【００５９】
上述の実施形態にかかる露光装置では、照明系によってマスクを照明し（照明工程）、投影光学系を用いてマスクに形成された転写用のパターンを感光性基板に露光する（露光工程）ことにより、マイクロデバイス（半導体素子、撮像素子、液晶表示素子、薄膜磁気ヘッド等）を製造することができる。以下、本実施形態の露光装置を用いて感光性基板としてのウェハ等に所定の回路パターンを形成することによって、マイクロデバイスとしての半導体デバイスを得る際の手法の一例につき図２０のフローチャートを参照して説明する。
【００６０】
先ず、図２０のステップ３０１において、１ロットのウェハ上に金属膜が蒸着される。次のステップ３０２において、そのｌロットのウェハ上の金属膜上にフォトレジストが塗布される。その後、ステップ３０３において、本実施形態の露光装置を用いて、マスク（レチクル）上のパターンの像がその投影光学系を介して、その１ロットのウェハ上の各ショット領域に順次露光転写される。
【００６１】
その後、ステップ３０４において、その１ロットのウェハ上のフォトレジストの現像が行われた後、ステップ３０５において、その１ロットのウェハ上でレジストパターンをマスクとしてエッチングを行うことによって、マスク上のパターンに対応する回路パターンが、各ウェハ上の各ショット領域に形成される。その後、更に上のレイヤの回路パターンの形成等を行うことによって、半導体素子等のデバイスが製造される。上述の半導体デバイス製造方法によれば、極めて微細な回路パターンを有する半導体デバイスをスループット良く得ることができる。
【００６２】
なお、上述の実施形態では、ＥＵＶ光を供給するための光源としてレーザプラズマ光源を用いているが、これに限定されることなく、他の適当な光源を用いることもできる。また、上述の本実施形態では、ＥＵＶＬ露光装置の投影光学系に対して本発明を適用しているが、これに限定されることなく、他の一般的な結像光学系に対して本発明を適用することもできる。
【００６３】
【発明の効果】
以上説明したように、本発明の結像光学系では、入射瞳が物体面を挟んで結像光学系の反対側に位置するとともに、ペッツバール和の絶対値が所定値以下に抑えられているので、反射面の枚数が比較的少ない構成にもかかわらず、たとえばＥＵＶ光に対して良好に収差補正され、且つ十分に大きな有効結像領域および像側開口数を確保することができる。
【００６４】
特に、本発明の結像光学系を露光装置に適用する場合、結像光学系の入射瞳がマスク面を挟んで結像光学系の反対側に位置しているので、照明系の射出瞳と結像光学系の入射瞳とを光学的に共役に配置するための集光反射光学系の配置が不要になり、照明系の射出瞳と結像光学系の入射瞳とを単に一致させるだけでよい。その結果、照明系の構成が簡素化されるだけでなく、集光反射光学系に起因する光量損失および収差発生を回避して、マスクパターンを感光性基板上に忠実に且つ高スループットで転写することができる。
【００６５】
また、本発明の結像光学系を露光装置または露光方法に用いることにより、露光光としてＥＵＶ光を使用して、マスクパターンを感光性基板上に忠実に且つ高スループットで転写することができ、ひいては良好な露光条件のもとで高精度なマイクロデバイスを製造することができる。
【図面の簡単な説明】
【図１】先行特許出願の第２実施例にかかる結像光学系の構成を概略的に示す図である。
【図２】先行特許出願の第２実施例にかかる結像光学系の像高２５．５ｍｍに対応する透過波面の形状を示す図である。
【図３】先行特許出願の第２実施例にかかる結像光学系の像高２６ｍｍに対応する透過波面の形状を示す図である。
【図４】先行特許出願の第２実施例にかかる結像光学系の像高２６．５ｍｍに対応する透過波面の形状を示す図である。
【図５】ツェルニケ多項式の第１項に対応する透過波面の形状を模式的に示す図である。
【図６】ツェルニケ多項式の第２項に対応する透過波面の形状を模式的に示す図である。
【図７】ツェルニケ多項式の第３項に対応する透過波面の形状を模式的に示す図である。
【図８】ツェルニケ多項式の第４項に対応する透過波面の形状を模式的に示す図である。
【図９】ツェルニケ多項式の第５項に対応する透過波面の形状を模式的に示す図である。
【図１０】ツェルニケ多項式の第６項に対応する透過波面の形状を模式的に示す図である。
【図１１】ツェルニケ多項式の第７項に対応する透過波面の形状を模式的に示す図である。
【図１２】ツェルニケ多項式の第８項に対応する透過波面の形状を模式的に示す図である。
【図１３】ツェルニケ多項式の第９項に対応する透過波面の形状を模式的に示す図である。
【図１４】凸レンズと凹レンズと凸レンズとの組み合わせからなる、トリプレットと呼ばれる３枚レンズの結像光学系の模式図である。
【図１５】本発明の実施形態にかかる露光装置の構成を概略的に示す図である。
【図１６】ウェハ上に形成される円弧状の露光領域（すなわち実効露光領域）と光軸との位置関係を示す図である。
【図１７】図１５の光源および照明光学系の内部構成を概略的に示す図である。
【図１８】本実施形態の第１実施例にかかる投影光学系の構成を示す図である。
【図１９】本実施形態の第２実施例にかかる投影光学系の構成を示す図である。
【図２０】マイクロデバイスとしての半導体デバイスを得る際の手法の一例について、そのフローチャートを示す図である。
【符号の説明】
１ レーザプラズマ光源
２ 照明光学系
５ マスクステージ
７ ウェハステージ
１１ レーザ光源
１３ 気体ターゲット
１４ ノズル
１５ 楕円反射鏡
１７ａ，１７ｂ フライアイミラー
１８ 視野絞り
Ｍ マスク
ＰＬ 投影光学系（結像光学系）
Ｗ ウェハ
Ｍ１〜Ｍ６ 反射鏡
ＡＳ 開口絞り[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an imaging optical system, an exposure apparatus, and an exposure method, and more particularly to a reflection-type imaging optical system suitable for a projection exposure apparatus used for manufacturing a semiconductor integrated circuit.
[0002]
[Prior art]
In this type of exposure apparatus, further improvement in resolution is required with miniaturization of a circuit pattern to be transferred, and shorter wavelength light is used as exposure light. In the present specification, “light” means not only “light” in a narrow sense that can be seen with the eyes, but also “light” in a broad sense including from infrared rays to X-rays having a wavelength shorter than 1 mm among electromagnetic waves. I do. In recent years, an exposure apparatus using EUV (Extreme UltraViolet) light having a wavelength of about 5 to 40 nm (hereinafter, referred to as an “EUVL (Extreme UltraViolet Lithography) exposure apparatus”) has been proposed as a next-generation apparatus.
[0003]
In such a very short wavelength region of EUV light, since there is no substance having a sufficient transmittance as a refractive optical member, a reflective projection optical system (imaging optical system) including only reflective optical members is required. Will be used. Conventionally, various types of optical systems have been proposed as projection optical systems for EUV light. The resolution limit line width in the EUVL exposure apparatus is expressed by the following equation (a) according to the laws of physics. In equation (a), λ is the wavelength of the exposure light, NA is the image-side numerical aperture of the projection optical system, and k is a constant that depends on the environment such as the characteristics of the device and the light-receiving resin.
Resolution limit line width = k × λ / NA (a)
[0004]
According to the laws of physics, k is at least 0.25, but it is appropriate to consider k to be about 0.4 in consideration of practicality as an apparatus. At present, the wavelength of EUV light expected to be used in the EUVL exposure apparatus is 13.4 nm, and the target minimum line width is assumed to be about 50 nm. Therefore, referring to the equation (a), the image-side numerical aperture NA of the projection optical system required to achieve the minimum line width of 50 nm is about 0.11, as shown in the following equation (b).
(Equation 1)
Required NA> k × λ / (minimum line width) = 0.4 × 13.4 / 50 = 0.11 (b)
[0005]
Further, the image-side numerical aperture NA required for the projection optical system applicable to the next-generation EUVL exposure apparatus targeting a minimum line width of 30 nm is 0.18 or more. However, in the prior art, a projection optical system for a EUVL exposure apparatus which has a practically-sized static exposure area and a large image-side numerical aperture of NA = 0.1 to 0.18 and is sufficiently aberration-corrected Have been little proposed. This is because conventionally, the minimum line width targeted by the EUVL exposure apparatus has been assumed to be about 100 nm. However, for example, JP-A-10-90602 and JP-A-9-213332 disclose a reflection type having an image-side numerical aperture of NA = 0.1 to 0.18 and having a sufficiently corrected aberration. A projection optical system is disclosed.
[0006]
By the way, in the EUVL exposure apparatus, since a reflection type mask is used instead of a transmission type mask, it is necessary to make illumination light obliquely enter the mask. This is because, when illumination light is vertically incident on a reflective mask, the optical path of the illumination light incident on the mask and the optical path of the illumination light reflected by the mask and traveling toward the projection optical system overlap, and the illumination for illuminating the mask is performed. This is because the optical member of the system blocks the optical path of the projection optical system, or the optical member of the projection optical system blocks the optical path of the illumination system. The conventional projection optical system disclosed in the above publication is configured such that the entrance pupil is located closer to the projection optical system than the object plane (mask plane).
[0007]
[Patent Document 1]
JP-A-10-90602
[Patent Document 2]
JP-A-9-213332
[0008]
[Problems to be solved by the invention]
Generally, in order to transfer a mask pattern onto a surface to be exposed efficiently without distortion, it is necessary to optically conjugate the exit pupil of the illumination system and the entrance pupil of the projection optical system. Therefore, it is necessary to configure the illumination system in consideration of the position of the entrance pupil of the projection optical system. The present applicant optically configures the entrance pupil of the illumination system and the entrance pupil of the projection optical system optically because the entrance pupil is located closer to the projection optical system than the mask surface in the conventional projection optical system. Focusing on the necessity of interposing a reflection optical system having a light condensing function between a mask and a surface light source in order to achieve conjugate, the specification and drawings of Japanese Patent Application No. 2001-305521 (hereinafter simply referred to as “prior patent application”) ") Is proposed in which the entrance pupil is located on the opposite side of the projection optical system with respect to the mask plane.
[0009]
In particular, when a spheroidal mirror is used as an intervening condensing and reflecting optical system, the imaging relationship between two focal points has no aberration, but the imaging relationship between a point slightly out of focus and its conjugate point is Causes a very large aberration. That is, there is no problem when a point light source is formed on the exit pupil of the illumination system, but in the case of an exposure apparatus in which a substantial surface light source is formed on the exit pupil of the illumination system, the problem is caused by the spheroidal mirror. The illumination light for illuminating the mask will be distorted. As a result, the surface light source image formed on the pupil plane of the projection optical system is also distorted, so that the mask pattern cannot be transferred onto the surface to be exposed without distortion.
[0010]
In the projection optical system (imaging optical system) proposed in the above-mentioned prior patent application, the entrance pupil is located on the opposite side of the projection optical system with respect to the mask surface, so that the light is collected between the mask and the surface light source. There is no need to interpose a light reflection optical system. As a result, not only can the configuration of the illumination system be simplified, but also the mask pattern can be faithfully transferred to the surface to be exposed based on good imaging performance. It should be noted that the projection optical system in which the entrance pupil is located closer to the projection optical system than the mask plane, and the projection optical system in which the entrance pupil is located on the opposite side of the projection optical system across the mask plane, are more detailed. For the operation and effect, reference can be made to the related description in the prior patent application.
[0011]
By the way, especially in a projection optical system mounted on an EUVL exposure apparatus, it is required that aberration is extremely small. Specifically, in a general imaging optical system, if the RMS (root mean square) of the wavefront is about 1/14 of the wavelength of the used light, it is recognized that there is almost no influence of aberration. . On the other hand, in the projection optical system for EUV light, the RMS of the wavefront is required to be within about 1/30 to 1/100 of the wavelength of the used light (EUV light). In the invention according to the above-mentioned prior patent application, if the exposure wavelength is 13.4 nm, the RMS of the wavefront in the first embodiment is 0.0057 to 0.0110, which substantially satisfies the required aberration level. However, the RMS of the wavefront in the second embodiment is 0.0096 to 0.0375, which does not satisfy the strictest required level.
[0012]
The second embodiment is inferior to the first embodiment from the viewpoint of aberration correction mainly because the number of reflecting surfaces (the number of reflecting mirrors) constituting the imaging optical system is smaller than that of the first embodiment. That's why. More specifically, while the imaging optical system of the first embodiment uses eight reflecting surfaces, the imaging optical system of the second embodiment uses only six reflecting surfaces. In the example, sufficient aberration correction is not achieved as compared with the first embodiment. However, in the EUVL exposure apparatus, in particular, the reflectivity per reflection surface is extremely low at about 70%. Therefore, from the viewpoint of avoiding a light amount loss and improving the throughput, a sufficiently large still exposure area (effective imaging area) and image side are required. In addition to ensuring a numerical aperture, the number of reflecting surfaces constituting the projection optical system is severely limited.
[0013]
The present invention has been made in view of the above-described problem, and has a sufficiently large effective imaging area, for example, in which aberrations are well corrected for EUV light despite a configuration in which the number of reflecting surfaces is relatively small. It is another object of the present invention to provide a reflection type imaging optical system having an image-side numerical aperture. It is another object of the present invention to provide an exposure apparatus and an exposure method that can transfer a mask pattern onto a photosensitive substrate with high fidelity via an imaging optical system of the present invention.
[0014]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, according to a first embodiment of the present invention, there is provided a reflective imaging optical system including a plurality of reflecting mirrors and forming an image of a first surface on a second surface.
A first reflective imaging optical system for forming an intermediate image of the first surface, and a second reflective imaging optical system for forming an image of the intermediate image on the second surface;
The plurality of reflecting mirrors are arranged in a space between the first surface and the second surface,
An entrance pupil is located on the opposite side of the imaging optical system across the first surface;
The absolute value of Petzval sum is 0.0002 (mm ^-1 2.) An imaging optical system characterized by the following.
[0015]
According to a preferred mode of the first embodiment, the absolute value of the Petzval sum is 0.0001 (mm ^-1 ) When the distance between the entrance pupil and the first surface is Do, the maximum object height on the first surface is Ho, and the numerical aperture on the first surface side of the imaging optical system is NAo, Do> It is preferable to satisfy the condition of Ho / (2 × NAo).
[0016]
According to a second embodiment of the present invention, there is provided a reflection-type imaging optical system including six aspherical reflecting mirrors and forming an image on a first surface on a second surface.
An entrance pupil is located on the opposite side of the imaging optical system across the first surface;
A first reflecting mirror M1, a second reflecting mirror M2, a third reflecting mirror M3, a fourth reflecting mirror M4, a fifth reflecting mirror M5, and a sixth reflecting mirror M6 in the order of incidence of light from the first surface side; ,
The second reflecting mirror M2, the fourth reflecting mirror M4, the first reflecting mirror M1, the third reflecting mirror M3, and the sixth reflecting mirror M6 along the optical axis from the first surface to the second surface. , And the fifth reflecting mirror M5 in this order.
[0017]
According to a third embodiment of the present invention, there is provided a reflection-type imaging optical system including six aspherical reflecting mirrors and forming an image on a first surface on a second surface.
An entrance pupil is located on the opposite side of the imaging optical system across the first surface;
A first reflecting mirror M1, a second reflecting mirror M2, a third reflecting mirror M3, a fourth reflecting mirror M4, a fifth reflecting mirror M5, and a sixth reflecting mirror M6 in the order of incidence of light from the first surface side; ,
The fourth reflecting mirror M4, the second reflecting mirror M2, the third reflecting mirror M3, the first reflecting mirror M1, and the sixth reflecting mirror M6 along the optical axis from the first surface to the second surface. , And the fifth reflecting mirror M5 in this order.
[0018]
According to a fourth aspect of the present invention, there is provided an illumination system for illuminating a mask set on the first surface, and a illuminating system for projecting and exposing a pattern of the mask onto a photosensitive substrate set on the second surface. An exposure apparatus comprising the imaging optical system according to any one of the first to third embodiments is provided.
[0019]
In a fifth embodiment of the present invention, the mask set on the first surface is illuminated, and the pattern of the mask is set on the second surface via the imaging optical system of the first to third embodiments. An exposure method characterized by performing projection exposure on a reactive substrate.
According to a sixth aspect of the present invention, there is provided an exposure apparatus which illuminates a mask set on a first surface and forms an image of the mask on a photosensitive substrate set on a second surface.
An illumination optical system that guides radiation from the light source to the mask,
A projection optical system for forming an image of the mask on the second surface,
The illumination optical system includes an optical path deflecting mirror,
The optical path deflecting mirror is positioned in a space between a light beam from the mask toward the projection optical system and an optical axis of the projection optical system. According to a preferred aspect of the sixth aspect, only one of the optical path deflecting mirrors is arranged in a space between a light beam from the mask toward the projection optical system and an optical axis of the projection optical system. preferable.
According to another preferred aspect of the sixth aspect, it is preferable that an angle formed between a light beam directed to the optical path deflector and a reflection surface of the optical path deflector is 15 degrees or less. Thereby, the reflectance at the optical path deflecting mirror can be increased, and the throughput can be further improved.
According to still another preferred aspect of the sixth aspect, it is preferable that the optical path deflecting mirror is positioned in a space between the first surface and the projection optical system.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, prior to the description of the operation of the present invention, the optical system proposed in the above-mentioned prior patent application, particularly, the imaging optical system according to the second embodiment will be considered in more detail. FIG. 1 is a view schematically showing a configuration of an imaging optical system according to a second embodiment of the prior patent application. In the imaging optical system of FIG. 1, light from a reticle (mask) R is sequentially reflected by a first reflecting mirror M26, a second reflecting mirror M25, an aperture stop AS, a third reflecting mirror M24, and a fourth reflecting mirror M23. After that, an intermediate image of the reticle pattern is formed. Then, the light from the reticle pattern intermediate image is sequentially reflected by the fifth reflecting mirror M22 and the sixth reflecting mirror M21, and then forms a reduced image of the reticle pattern on the wafer W.
[0021]
Table (1) below gives the values of the specifications of the imaging optical system shown in FIG. In Table (1), λ represents the wavelength of the exposure light, NA represents the numerical aperture on the image side (wafer side), and Y represents the range of the image height in the exposure area. The surface number indicates the order of the reflecting surfaces from the wafer side along the direction in which the light rays go from the wafer surface to the reticle surface, r indicates the vertex radius of curvature (mm) of each reflecting surface, and d indicates the axis of each reflecting surface. The upper distance, that is, the surface distance (mm) is shown. It should be noted that the sign of the surface distance d changes each time it is reflected. The radius of curvature of the convex surface toward the wafer is set to be positive and the radius of curvature of the concave surface is set to be negative regardless of the incident direction of the light beam. The aspheric surface is represented by the following equation (e).
[0022]
[Table 1]
(Main specifications)
λ = 13.4 nm
NA = 0.18
Y = 25.5 mm to 26.5 mm

[0023]
FIG. 2 is a diagram showing a shape of a transmitted wavefront corresponding to an image height of 25.5 mm of the imaging optical system according to the second example of the prior patent application. FIG. 3 is a diagram illustrating a shape of a transmitted wavefront corresponding to an image height of 26 mm of the imaging optical system according to the second example of the prior patent application. FIG. 4 is a diagram illustrating a shape of a transmitted wavefront corresponding to an image height of 26.5 mm of the imaging optical system according to the second example of the prior patent application. For a more detailed configuration of the imaging optical system according to the second example, reference can be made to the related description in the prior patent application.
[0024]
In general, the transmitted wavefront of an optical system can be series-expanded by a Zernike polynomial. Hereinafter, the basic items of the Zernike polynomial will be briefly described. In the expression of the Zernike polynomial, polar coordinates (ρ, θ) are used as a coordinate system, and a Zernike cylindrical function is used as an orthogonal function system. That is, the transmitted wavefront W (ρ, θ) is developed as shown in the following equation (c) using the Zernike cylindrical function Zi (ρ, θ).
[0025]
(Equation 2)

[0026]
Where C _i Is the coefficient of each term of the Zernike polynomial. Hereinafter, in the functional system Zi (ρ, θ) of each term of the Zernike polynomial, functions Z1 to Z36 relating to the first to thirty-sixth terms are shown in the following Table (2).
[0027]
[Table 2]

[0028]
FIG. 5 is a diagram schematically illustrating the shape of the transmitted wavefront corresponding to the first term of the Zernike polynomial. FIG. 6 is a diagram schematically illustrating the shape of the transmitted wavefront corresponding to the second term of the Zernike polynomial. FIG. 7 is a diagram schematically illustrating the shape of the transmitted wavefront corresponding to the third term of the Zernike polynomial. FIG. 8 is a diagram schematically showing the shape of the transmitted wavefront corresponding to the fourth term of the Zernike polynomial. FIG. 9 is a diagram schematically illustrating the shape of the transmitted wavefront corresponding to the fifth term of the Zernike polynomial. FIG. 10 is a diagram schematically showing the shape of the transmitted wavefront corresponding to the sixth term of the Zernike polynomial. FIG. 11 is a diagram schematically showing the shape of the transmitted wavefront corresponding to the seventh term of the Zernike polynomial. FIG. 12 is a diagram schematically illustrating the shape of the transmitted wavefront corresponding to the eighth term of the Zernike polynomial. FIG. 13 is a diagram schematically illustrating the shape of the transmitted wavefront corresponding to the ninth term of the Zernike polynomial.
[0029]
Referring to FIGS. 2 to 4, in the shape of the transmitted wavefront of the imaging optical system according to the second embodiment of the prior patent application, the shape of the transmitted wavefront corresponding to the fifth term of the Zernike polynomial (see FIG. 9) is shown. It is clear that the components are dominant. The wavefront shape shown in FIG. 9 corresponds to a component called astigmatism (astigmatism) in aberration theory. According to the theory of aberrations, astigmatism is caused by the separation between the meridional image plane and the sagittal image plane. According to the aberration theory, the meridional image plane and the sagittal image plane coincide with each other on the Petzval image plane, and the meridional image plane and the sagittal image plane deviate from the Petzval image plane at a ratio of 3: 1. For this reason, it is said that the larger the difference between the Petzval image plane and the actual image plane (the intermediate plane between the meridional image plane and the sagittal image plane), the greater the astigmatism. That is, the wavefronts shown in FIGS. 2 to 4 are expected to be caused by the difference between the Petzval image plane and the actual image plane.
[0030]
The difference between the Petzval image plane and the actual image plane is expected to be due to the Petzval image plane not being planar. When the Petzval image plane is not planar, especially in an imaging optical system that uses many aspherical surfaces, such as a projection optical system for EUV light, the actual image plane and the Petzval image plane are used to make the actual image plane planar. And the deviation from. From the above considerations, it is expected that by bringing the Petzval image plane closer to a plane, the occurrence of astigmatism can be satisfactorily suppressed, and, consequently, good imaging performance with sufficient aberration correction can be obtained.
[0031]
It is known that the Petzval image plane can be made closer to a plane by bringing the Petzval sum (that is, the sum of the power of each lens (or each reflecting mirror) of the optical system) closer to zero. In the case of a reflection optical system, the Petzval sum ρ is generally defined by the following equation (d). In the equation (d), Σ is a sum symbol for all the reflecting mirrors. The radius of curvature takes a positive value in the case of a concave reflecting mirror, and takes a negative value in the case of a convex reflecting mirror.
ρ = {2 / (radius of curvature of each reflecting mirror)} (d)
[0032]
In the imaging optical system according to the second embodiment of the prior patent application, the Petzval sum obtained by the equation (d) is about 0.00038 (mm). ^-1 ). The inventor of the present application has conducted a number of design solutions for a reflection type imaging optical system in which the entrance pupil is located on the opposite side of the imaging optical system across the object plane, and as a result, the value of Petzval sum is 0. .0002 (mm ^-1 ), It is possible to obtain a design solution in which astigmatism has been corrected to some extent, and the Petzval sum is 0.0001 (mm ^-1 ) It has been found that a design solution in which astigmatism is very well corrected can be obtained if: In the reflection type imaging optical system, there is a reflector whose reflection surface is cut off on the optical axis. In this case, the Petzval sum is calculated based on the virtual reflection surface on the optical axis obtained by extending the reflection surface. It will be calculated.
[0033]
In order to suppress the Petzval sum in a general optical system, the following technique is generally used, and the present invention is not an exception. FIG. 14 is a schematic diagram of a three-lens imaging optical system called a triplet, which is a combination of a convex lens, a concave lens, and a convex lens. By the way, the zero Petzval sum in a refraction-type imaging optical system means that the simple sum of power is zero for all lenses, but the imaging system can be established unless the optical system has positive power. Absent. Therefore, even if the convex lens in the optical system has the same radius of curvature, it is desirable to arrange the convex lens at a position where the diameter of the light beam is as large as possible in order to make the influence of the positive power more exert on the light beam. Conversely, it is desirable that the concave lens in the optical system be disposed at a place where the diameter of the light beam is as small as possible so that the influence of the negative power on the light beam is reduced even if the radius of curvature is the same. Therefore, in order to make the Petzval sum close to zero, a power arrangement as shown in FIG. 14A is more preferable than a power arrangement as shown in FIG. 14B, and a light beam is extremely constricted in the optical system ( A design that makes the change in the beam diameter sharper is desirable.
[0034]
Incidentally, for example, when the imaging optical system of the present invention is mounted on an EUVL exposure apparatus, it is desirable to satisfy the following conditional expression (1). In the conditional expression (1), Do is the distance between the entrance pupil of the imaging optical system and the mask surface (object surface; first surface), Ho is the maximum object height on the mask surface, and NAo is the image formation. The numerical aperture on the mask side of the optical system.
Do> Ho / (2 × NAo) (1)
[0035]
In the exposure apparatus, a substantial surface light source is formed at the position of the entrance pupil of the imaging optical system (projection optical system), and thus the exit surface of the fly-eye mirror is disposed. At this time, since the numerical aperture of the illumination light incident on the mask is determined by the specification, if the distance Do between the entrance pupil of the imaging optical system and the mask surface is small and does not satisfy the conditional expression (1), The outside diameter of the fly-eye mirror is too small, which makes it difficult to manufacture, which is not preferable.
[0036]
As described above, in the imaging optical system of the present invention, the entrance pupil is located on the opposite side of the imaging optical system across the object plane, and the absolute value of the Petzval sum is suppressed to a predetermined value or less. Despite the configuration having a relatively small number of reflection surfaces, for example, aberrations can be satisfactorily corrected for, for example, EUV light, and a sufficiently large effective imaging region and image-side numerical aperture can be secured. In particular, when the image forming optical system of the present invention is applied to an exposure apparatus, the entrance pupil of the image forming optical system is located on the opposite side of the image forming optical system across the mask surface, so that the light exit pupil of the illumination system is There is no need to dispose a converging / reflecting optical system to optically conjugate the entrance pupil of the imaging optical system, and simply align the exit pupil of the illumination system with the entrance pupil of the imaging optical system. This not only simplifies the configuration of the illumination system, but also avoids the loss of light amount and aberration caused by the converging / reflecting optical system, and transfers the mask pattern onto the photosensitive substrate with high fidelity and high throughput. be able to. Further, by using the imaging optical system of the present invention in an exposure apparatus or an exposure method, a mask pattern can be faithfully transferred onto a photosensitive substrate with high throughput using EUV light as exposure light, As a result, a highly accurate microdevice can be manufactured under favorable exposure conditions.
Further, in the exposure apparatus of the present invention, the position of the entrance pupil of the projection optical system is set on the opposite side of the projection optical system with respect to the first surface to simplify the configuration of the illumination optical system, and to move from the mask to the projection optical system. An optical path deflecting mirror is arranged in a space between the incoming light beam and the optical axis of the projection optical system to facilitate the optical path separation between the illumination optical system and the projection optical system.
[0037]
An embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 15 is a diagram schematically showing an overall configuration of an exposure apparatus according to the embodiment of the present invention. FIG. 16 is a diagram showing a positional relationship between an arc-shaped exposure region (that is, an effective exposure region) formed on a wafer and an optical axis. FIG. 17 is a diagram schematically showing an internal configuration of the light source and the illumination optical system of FIG. 15, the Z axis is set along the optical axis direction of the projection optical system, that is, the normal direction of the wafer as the photosensitive substrate, the Y axis is set in a direction parallel to the plane of FIG. The X-axis is set in a direction perpendicular to the paper surface of FIG.
[0038]
The exposure apparatus of FIG. 15 includes, for example, a laser plasma light source 1 as a light source for supplying exposure light. The light emitted from the light source 1 enters the illumination optical system 2 via a wavelength selection filter (not shown). Here, the wavelength selection filter has a characteristic of selectively transmitting only EUV light of a predetermined wavelength (for example, 13.4 nm or 11.5 nm) from light supplied by the light source 1 and blocking transmission of light of other wavelengths. . The EUV light 3 transmitted through the wavelength selection filter illuminates a reflection type mask (reticle) M on which a pattern to be transferred is formed via an illumination optical system 2 and a plane reflection mirror 4 as an optical path deflecting mirror. The mask M is held by a mask stage 5 that can move in the Y direction so that the pattern surface extends along the XY plane. The movement of the mask stage 5 is configured to be measured by the laser interferometer 6.
[0039]
The illuminated light from the pattern of the mask M forms an image of the mask pattern on the wafer W as a photosensitive substrate via a reflective projection optical system (imaging optical system) PL. That is, on the wafer W, for example, an elongated circular arc-shaped exposure region (that is, a stationary exposure region) symmetric with respect to the Y axis is formed as shown in FIG. Referring to FIG. 16, in a circular area (image circle) IF having a radius φ around the optical axis AX, the length in the X direction is LX and the length in the Y direction is in contact with the image circle IF. Is set to an effective exposure area ER in an arc shape of LY.
[0040]
The wafer W is held by a wafer stage 7 that can move two-dimensionally in the X direction and the Y direction so that the exposure surface extends along the XY plane. The movement of the wafer stage 7 is configured to be measured by the laser interferometer 8 as in the case of the mask stage 5. Thus, scan exposure (scan exposure) is performed while moving the mask stage 5 and the wafer stage 7 along the Y direction, that is, while relatively moving the mask M and the wafer W relative to the projection optical system PL along the Y direction. Thereby, the pattern of the mask M is transferred to one exposure area of the wafer W.
[0041]
At this time, if the projection magnification (transfer magnification) of the projection optical system PL is １ ／, the moving speed of the wafer stage 7 is set to １ ／ of the moving speed of the mask stage 5 to perform synchronous scanning. Further, by repeating the scanning exposure while moving the wafer stage 7 two-dimensionally in the X direction and the Y direction, the pattern of the mask M is sequentially transferred to each exposure area of the wafer W.
[0042]
Referring to FIG. 17, in the laser plasma light source 1, light (non-EUV light) emitted from the laser light source 11 is focused on the gas target 13 via the lens 12. Here, a high-pressure gas made of, for example, xenon (Xe) is supplied from the nozzle 14, and the gas injected from the nozzle 14 forms the gas target 13. The gas target 13 obtains energy from the condensed laser light, turns it into plasma, and emits EUV light. Note that the gas target 13 is positioned at the first focal point of the elliptical reflecting mirror 15. Therefore, the EUV light emitted from the laser plasma light source 1 is focused on the second focal point of the elliptical reflecting mirror 15. On the other hand, the gas that has finished emitting light is sucked through the duct 16 and guided to the outside.
[0043]
The EUV light focused on the second focal point of the elliptical reflecting mirror 15 is guided to an integrator 17 including a pair of fly-eye mirrors 17a and 17b. As the pair of fly-eye mirrors 17a and 17b, for example, a fly-eye mirror disclosed by the present applicant in Japanese Patent Application Laid-Open No. H11-312638 can be used. However, in the embodiment of the publication, the parallel light beam is configured to be incident on the first fly-eye mirror, but in FIG. 17, the divergent light beam is configured to be incident on the first fly-eye mirror 17a. In this case, the light flux reflected by each element mirror of the first fly-eye mirror 17a enters the corresponding element mirror of the second fly-eye mirror 17b by tilting the element mirror of the first fly-eye mirror 17a to be larger than that of the second element. If the light beams reflected by the element mirrors of the fly-eye mirror 17b are configured to overlap each other on the mask M, the principle is as disclosed in the publication. For a more detailed configuration and operation of the fly-eye mirror, reference can be made to, for example, the related description in JP-A-11-312638.
[0044]
Thus, a substantial surface light source having a predetermined shape is formed near the reflection surface of the second fly-eye mirror 17b, that is, near the emission surface of the integrator 17. Here, as described above, the substantial surface light source is formed at or near the exit pupil position of the illumination optical system 2, that is, at or near a plane optically conjugate with the entrance pupil of the projection optical system PL. After being deflected by the plane reflecting mirror 4, the light from the substantial surface light source passes through the field stop 18 arranged almost in parallel with and close to the mask M, and forms an elongated arc-shaped illumination area on the mask M. To form
[0045]
Hereinafter, a specific configuration of the projection optical system PL will be described with reference to the first embodiment and the second embodiment. In each embodiment, the projection optical system PL includes six reflecting mirrors M1 to M6 each having an aspherical reflecting surface that is rotationally symmetric with respect to the optical axis. In each embodiment, the projection optical system PL is an optical system that is almost telecentric on the wafer side (image image). Further, in each embodiment, the height of the aspheric surface in the direction perpendicular to the optical axis is defined as y, and the distance along the optical axis from the tangent plane at the vertex of the aspheric surface to a position on the aspheric surface at height y ( The sag amount) is z, the vertex radius of curvature is r, the cone coefficient is κ, and the nth order aspherical coefficient is C _n Is represented by the following equation (e).
[0046]
[Equation 3]
z = (y ² / R) / ｛1+ (1-y ² / R ² ) ^1/2 ｝ + C ₄ ・ Y ⁴ + C ₆ ・ Y ⁶ + C ₈ ・ Y ⁸ + C ₁₀ ・ Y ¹⁰ + ... (e)
[0047]
[First embodiment]
FIG. 18 is a diagram illustrating a configuration of a projection optical system according to Example 1 of the present embodiment. Referring to FIG. 18, in the projection optical system of the first embodiment, the light from the mask M is reflected on the reflecting surface of the first concave reflecting mirror M1, the reflecting surface of the second convex reflecting mirror M2, the aperture stop AS, and the third convex surface. After being sequentially reflected by the reflecting surface of the reflecting mirror M3 and the reflecting surface of the fourth concave reflecting mirror M4, an intermediate image of the mask pattern is formed. Then, the light from the mask pattern intermediate image is sequentially reflected by the reflecting surface of the fifth convex reflecting mirror M5 and the reflecting surface of the sixth concave reflecting mirror M6, and then is reduced on the wafer W (secondary image). ) Is formed. That is, in the projection optical system of the first embodiment, the second convex reflecting mirror M2, the fourth concave reflecting mirror M4, the first concave reflecting mirror M1, and the third convex reflecting mirror are arranged along the optical axis AX from the mask M to the wafer W. The mirror M3, the sixth concave reflecting mirror M6, and the fifth convex reflecting mirror M5 are arranged in this order. In the first embodiment, the reflection mirrors M1 to M4 constitute a first reflection imaging optical system for forming an intermediate image of the pattern of the mask M, and the reflection mirrors M5 and M6 convert the image of the intermediate image to the wafer W. A second reflection / imaging optical system to be formed thereon is configured. Further, in the first embodiment, all the reflecting mirrors M1 to M6 are arranged in a space between the mask M and the wafer W.
[0048]
Table 3 below summarizes the data values of the projection optical system according to the first example. In Table (3), λ represents the wavelength of the exposure light, β represents the projection magnification, NA represents the numerical aperture on the image side (wafer side), NAo represents the numerical aperture on the object side (mask side), and Ho represents the numerical aperture on the mask M. The maximum object height, Do is the distance between the entrance pupil and the mask surface, φ is the radius of the image circle IF (maximum image height) on the wafer W, and LX is the dimension of the effective exposure area ER along the X direction. , LY represent the dimensions of the effective exposure area ER along the Y direction.
[0049]
Further, the surface number indicates the order of the reflecting surfaces from the wafer side along the direction in which the light ray goes backward from the wafer surface as the image surface to the mask surface as the object surface, and r indicates the vertex radius of curvature (mm) of each reflecting surface. , D denote the on-axis spacing of each reflecting surface, that is, the surface spacing (mm). It should be noted that the sign of the surface distance d changes each time it is reflected. The radius of curvature of the convex surface toward the wafer is set to be positive and the radius of curvature of the concave surface is set to be negative regardless of the incident direction of the light beam. The above notation is the same in the following Table (4).
[0050]
[Table 3]

[0051]
[Second embodiment]
FIG. 19 is a diagram illustrating a configuration of a projection optical system according to Example 2 of the present embodiment. Referring to FIG. 19, in the projection optical system of the second embodiment, the light from the mask M is reflected by the reflecting surface of the first concave reflecting mirror M1, the reflecting surface of the second convex reflecting mirror M2, the aperture stop AS, and the third convex surface. After being sequentially reflected by the reflecting surface of the reflecting mirror M3 and the reflecting surface of the fourth concave reflecting mirror M4, an intermediate image of the mask pattern is formed. Then, the light from the mask pattern intermediate image is sequentially reflected by the reflecting surface of the fifth convex reflecting mirror M5 and the reflecting surface of the sixth concave reflecting mirror M6, and then is reduced on the wafer W (secondary image). ) Is formed. That is, in the projection optical system of the second embodiment, the fourth concave reflecting mirror M4, the second convex reflecting mirror M2, the third convex reflecting mirror M3, and the first concave reflecting mirror are arranged along the optical axis AX from the mask M to the wafer W. The mirror M1, the sixth concave reflecting mirror M6, and the fifth convex reflecting mirror M5 are arranged in this order. Also, in the second embodiment, similarly to the first embodiment, the reflecting mirrors M1 to M4 constitute a first reflecting imaging optical system for forming an intermediate image of the pattern of the mask M, and the reflecting mirrors M5 and M6. Constitutes a second reflection imaging optical system for forming an intermediate image on the wafer W. Further, in the second embodiment, as in the first embodiment, all the reflecting mirrors M1 to M6 are arranged in the space between the mask M and the wafer W. Table 4 below summarizes the data values of the projection optical system according to the second example.
[0052]
[Table 4]

[0053]
In the first embodiment, the Petzval sum is −0.000014 (mm). ^-1 ), Whose absolute value is 0.0001 (mm ^-1 ), The RMS of the transmitted wavefront becomes an extremely small value of 0.0023 to 0.0074, and it can be seen that various aberrations including astigmatism are corrected very well. In the second embodiment, the Petzval sum is 0.000028 (mm). ^-1 ), Whose absolute value is 0.0001 (mm ^-1 ), The RMS of the transmitted wavefront becomes a sufficiently small value of 0.0072 to 0.0132, and it can be seen that various aberrations including astigmatism are well corrected.
[0054]
As described above, in each of the above-described embodiments, for EUV light having a wavelength of 13.4 nm, an image-side numerical aperture of 0.26 is secured, and various aberrations on the wafer W are corrected to 26 mm × A 2 mm arc-shaped effective exposure area can be secured. Therefore, the pattern of the mask M can be transferred to each exposure region having a size of, for example, 26 mm × 33 mm on the wafer W with high resolution by scanning exposure.
[0055]
Further, in each of the above-described embodiments, since the projection optical system has a configuration with a relatively small number of reflecting surfaces, that is, is constituted by six reflecting mirrors, the light amount loss on the reflecting surface can be suppressed favorably, and the throughput can be reduced. Projection exposure is possible. Further, in each of the above embodiments, since the entrance pupil of the projection optical system is located on the opposite side of the projection optical system with respect to the mask surface, the exit pupil of the illumination system and the entrance pupil of the projection optical system are optically connected. Therefore, it is not necessary to dispose a converging / reflecting optical system for conjugate arrangement, and the exit pupil of the illumination system and the entrance pupil of the projection optical system need only be made to coincide with each other. As a result, not only the configuration of the illumination system is simplified, but also the loss of the light amount and the occurrence of aberration caused by the light collecting and reflecting optical system are avoided, and the mask pattern is faithfully transferred onto the photosensitive substrate with high throughput. be able to. Further, in each of the above embodiments, since the conditional expression (1) is satisfied, the outer diameter of the fly-eye mirror (17a, 17b) does not become too small, and the manufacture thereof is easy.
[0056]
In the second embodiment, as shown in FIG. 19, since the light flux does not pass near the origin where the reflecting surface intersects the optical axis AX in each reflecting mirror, it is necessary to cut out the central region including the origin. There is no reflector. That is, in the second embodiment, since the origins of the reflecting surfaces of all the reflecting mirrors can be left, measurement of the reflecting surface shapes of the respective reflecting mirrors is facilitated and processing of the reflecting surfaces of the respective reflecting mirrors is facilitated. Become.
[0057]
In each of the above-described embodiments, the reduced image of the mask pattern is formed on the wafer. However, the object plane and the image plane can be set to be opposite to each other and used as an enlarged imaging optical system. In this case, the exit pupil is located on the opposite side of the imaging optical system across the image plane, and the absolute value of the Petzval sum is unchanged. The condition corresponding to the conditional expression (1) in the magnified imaging optical system in which the object plane and the image plane are set oppositely is represented by the following expression (2). In conditional expression (2), Di is the distance between the exit pupil of the imaging optical system and the image plane, Hi is the maximum image height on the image plane, and NAi is the numerical aperture on the image side of the imaging optical system. It is.
Di> Hi / (2 × NAi) (2)
[0058]
In the plane reflecting mirror 4 as an optical path deflecting mirror, it is preferable that the end face shape on the side close to the light beam going from the mask to the projection optical system is a part of an almost elliptical shape. Thereby, it is possible to prevent the light flux from traveling from the mask to the projection optical system.
Further, in the above-described embodiment, the plane reflecting mirror 4 as the optical path deflecting mirror is positioned in the space between the first surface and the projection optical system, but has passed through the inside of the projection optical system or through the projection optical system. It may be positioned on the opposite side. In this case, it is preferable to provide notches or holes in the optical member constituting the projection optical system.
In the above-described embodiment, the reflecting surface of the plane reflecting mirror 4 as an optical path deflecting mirror is directed to the light beam traveling from the mask to the projection optical system. However, the direction of the reflecting surface of the plane reflecting mirror 4 is changed from the mask. The light beam may be directed to the side opposite to the light beam directed to the projection optical system.
Further, in the above-described embodiment, in order to improve the reflectance of the plane reflecting mirror 4 as the optical path deflecting mirror, the angle formed between the light beam going to the optical path deflecting mirror and the reflection surface of the optical path deflecting mirror is set small. However, this angle may be set to an angle close to 90 degrees. This is because the reflectance of the reflecting surface of the plane reflecting mirror 4 has the worst value near 45 degrees, and the reflectance increases as the angle increases.
In the above-described embodiment, the plane reflecting mirror 4 is used as the optical path deflecting mirror. However, a predetermined power may be provided instead.
In the above-described embodiment, the field stop 18 is arranged close to the mask M. However, the field stop 18 for projecting the field stop 18 onto the mask M as disclosed in JP-A-2000-91220 is disclosed. An imaging optical system may be provided.
In the above-described embodiment, another optical path deflecting mirror is provided between the integrator 17 and the optical path deflecting mirror 4, and the integrator 17 is provided in a space between the surface including the mask M surface and the surface including the wafer W surface. It may be located. Thereby, there is an advantage that the configurations of the mask stage and the wafer stage are simplified. At this time, it is preferable that the angle of incidence of the another optical path deflecting mirror is close to normal incidence.
Further, the light path deflector may be provided with a light amount detector disclosed in JP-A-2000-100385 to control the exposure amount. Thereby, high precision of the exposure amount control can be achieved.
In the above-described embodiment, the second focal point of the elliptical reflecting mirror 15 is brought closer to the pair of fly-eye mirrors 17a and 17b. A configuration remote from 17a and 17b is preferred. This makes it easy to arrange a partition member provided with a pinhole in the vicinity of the focal point of the EUV light. This partition member makes it easy to separate the atmosphere on the light source side from the atmosphere on the apparatus main body side. Become.
[0059]
In the exposure apparatus according to the above-described embodiment, the mask is illuminated by the illumination system (illumination step), and the transfer pattern formed on the mask is exposed to the photosensitive substrate using the projection optical system (exposure step). Microdevices (semiconductor elements, imaging elements, liquid crystal display elements, thin-film magnetic heads, etc.) can be manufactured. Hereinafter, an example of a method for obtaining a semiconductor device as a micro device by forming a predetermined circuit pattern on a wafer or the like as a photosensitive substrate using the exposure apparatus of the present embodiment will be described with reference to the flowchart in FIG. Will be explained.
[0060]
First, in step 301 of FIG. 20, a metal film is deposited on one lot of wafers. In the next step 302, a photoresist is applied on the metal film on the l lot of wafers. Thereafter, in step 303, using the exposure apparatus of the present embodiment, an image of the pattern on the mask (reticle) is sequentially exposed and transferred to each shot area on the wafer of the lot through the projection optical system. .
[0061]
Thereafter, in step 304, the photoresist on the one lot of wafers is developed, and in step 305, the resist on the one lot of wafers is etched using the resist pattern as a mask, thereby forming a pattern on the mask. A corresponding circuit pattern is formed in each shot area on each wafer. Thereafter, a device such as a semiconductor element is manufactured by forming a circuit pattern of an upper layer and the like. According to the above-described semiconductor device manufacturing method, a semiconductor device having an extremely fine circuit pattern can be obtained with high throughput.
[0062]
In the above-described embodiment, a laser plasma light source is used as a light source for supplying EUV light. However, the present invention is not limited to this, and another appropriate light source may be used. In the above-described embodiment, the present invention is applied to the projection optical system of the EUVL exposure apparatus. However, the present invention is not limited to this, and the present invention may be applied to other general imaging optical systems. Can also be applied.
[0063]
【The invention's effect】
As described above, in the imaging optical system of the present invention, the entrance pupil is located on the opposite side of the imaging optical system across the object plane, and the absolute value of the Petzval sum is suppressed to a predetermined value or less. In spite of the configuration in which the number of reflecting surfaces is relatively small, aberration can be satisfactorily corrected for, for example, EUV light, and a sufficiently large effective image forming area and image-side numerical aperture can be secured.
[0064]
In particular, when the image forming optical system of the present invention is applied to an exposure apparatus, the entrance pupil of the image forming optical system is located on the opposite side of the image forming optical system across the mask surface, so that the light exit pupil of the illumination system is There is no need to dispose a converging / reflecting optical system to optically conjugate the entrance pupil of the imaging optical system, and simply align the exit pupil of the illumination system with the entrance pupil of the imaging optical system. Good. As a result, not only the configuration of the illumination system is simplified, but also the loss of the light amount and the occurrence of aberration caused by the light collecting and reflecting optical system are avoided, and the mask pattern is faithfully transferred onto the photosensitive substrate with high throughput. be able to.
[0065]
Further, by using the imaging optical system of the present invention in an exposure apparatus or an exposure method, a mask pattern can be faithfully transferred onto a photosensitive substrate with high throughput using EUV light as exposure light, As a result, a highly accurate microdevice can be manufactured under favorable exposure conditions.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a configuration of an imaging optical system according to a second embodiment of the prior patent application.
FIG. 2 is a diagram illustrating a shape of a transmitted wavefront corresponding to an image height of 25.5 mm of an imaging optical system according to a second example of the prior patent application.
FIG. 3 is a diagram showing a shape of a transmitted wavefront corresponding to an image height of 26 mm of an imaging optical system according to a second embodiment of the prior patent application.
FIG. 4 is a diagram showing a shape of a transmitted wavefront corresponding to an image height of 26.5 mm of an imaging optical system according to a second example of the prior patent application.
FIG. 5 is a diagram schematically showing a shape of a transmitted wavefront corresponding to a first term of a Zernike polynomial.
FIG. 6 is a diagram schematically illustrating a shape of a transmitted wavefront corresponding to a second term of a Zernike polynomial.
FIG. 7 is a diagram schematically showing a shape of a transmitted wavefront corresponding to a third term of a Zernike polynomial.
FIG. 8 is a diagram schematically showing the shape of a transmitted wavefront corresponding to the fourth term of the Zernike polynomial.
FIG. 9 is a diagram schematically showing the shape of a transmitted wavefront corresponding to the fifth term of the Zernike polynomial.
FIG. 10 is a diagram schematically showing the shape of a transmitted wavefront corresponding to the sixth term of the Zernike polynomial.
FIG. 11 is a diagram schematically showing the shape of a transmitted wavefront corresponding to the seventh term of the Zernike polynomial.
FIG. 12 is a diagram schematically showing the shape of a transmitted wavefront corresponding to the eighth term of the Zernike polynomial.
FIG. 13 is a diagram schematically showing the shape of a transmitted wavefront corresponding to the ninth term of the Zernike polynomial.
FIG. 14 is a schematic diagram of a three-lens imaging optical system called a triplet, which is a combination of a convex lens, a concave lens, and a convex lens.
FIG. 15 is a view schematically showing a configuration of an exposure apparatus according to an embodiment of the present invention.
FIG. 16 is a diagram illustrating a positional relationship between an optical axis and an arc-shaped exposure region (ie, an effective exposure region) formed on a wafer.
17 is a diagram schematically showing an internal configuration of a light source and an illumination optical system of FIG.
FIG. 18 is a diagram showing a configuration of a projection optical system according to Example 1 of the present embodiment.
FIG. 19 is a diagram showing a configuration of a projection optical system according to a second example of the present embodiment.
FIG. 20 is a flowchart showing an example of a technique for obtaining a semiconductor device as a micro device.
[Explanation of symbols]
1 laser plasma light source
2 Illumination optical system
5 Mask stage
7 Wafer stage
11 Laser light source
13 Gas target
14 nozzles
15 Elliptical reflector
17a, 17b Fly eye mirror
18 Field stop
M mask
PL projection optical system (imaging optical system)
W wafer
M1-M6 reflector
AS aperture stop

Claims (11)

In a reflective imaging optical system including a plurality of reflecting mirrors and forming an image of the first surface on the second surface,
A first reflective imaging optical system for forming an intermediate image of the first surface, and a second reflective imaging optical system for forming an image of the intermediate image on the second surface;
The plurality of reflecting mirrors are arranged in a space between the first surface and the second surface,
An entrance pupil is located on the opposite side of the imaging optical system across the first surface;
An imaging optical system, wherein the absolute value of the Petzval sum is 0.0002 (mm ^-1 ) or less. The imaging optical system according to claim 1, wherein the absolute value of the Petzval sum is 0.0001 (mm- ¹ ) or less. When the distance between the entrance pupil and the first surface is Do, the maximum object height on the first surface is Ho, and the numerical aperture on the first surface side of the imaging optical system is NAo,
Do> Ho / (2 × NAo)
The imaging optical system according to claim 1, wherein the following condition is satisfied. In a reflection type imaging optical system including six aspherical reflecting mirrors and forming an image of a first surface on a second surface,
An entrance pupil is located on the opposite side of the imaging optical system across the first surface;
A first reflecting mirror M1, a second reflecting mirror M2, a third reflecting mirror M3, a fourth reflecting mirror M4, a fifth reflecting mirror M5, and a sixth reflecting mirror M6 in the order of incidence of light from the first surface side; ,
The second reflecting mirror M2, the fourth reflecting mirror M4, the first reflecting mirror M1, the third reflecting mirror M3, and the sixth reflecting mirror M6 along the optical axis from the first surface to the second surface. , And the fifth reflecting mirror M5 in this order. In a reflection type imaging optical system including six aspherical reflecting mirrors and forming an image of a first surface on a second surface,
An entrance pupil is located on the opposite side of the imaging optical system across the first surface;
A first reflecting mirror M1, a second reflecting mirror M2, a third reflecting mirror M3, a fourth reflecting mirror M4, a fifth reflecting mirror M5, and a sixth reflecting mirror M6 in the order of incidence of light from the first surface side; ,
The fourth reflecting mirror M4, the second reflecting mirror M2, the third reflecting mirror M3, the first reflecting mirror M1, and the sixth reflecting mirror M6 along the optical axis from the first surface to the second surface. , And the fifth reflecting mirror M5 in this order. 6. An illumination system for illuminating a mask set on the first surface, and projecting and exposing a pattern of the mask onto a photosensitive substrate set on the second surface. An exposure apparatus comprising: the imaging optical system according to any one of the above items. A mask set on the first surface is illuminated, and a pattern of the mask is set on the photosensitive substrate set on the second surface via the imaging optical system according to claim 1. An exposure method characterized by performing projection exposure to light. An exposure apparatus that illuminates a mask set on a first surface and forms an image of the mask on a photosensitive substrate set on a second surface,
An illumination optical system that guides radiation from the light source to the mask,
A projection optical system for forming an image of the mask on the second surface,
The illumination optical system includes an optical path deflecting mirror,
An exposure apparatus, wherein the optical path deflecting mirror is positioned in a space between a light beam from the mask toward the projection optical system and an optical axis of the projection optical system. 9. The exposure according to claim 8, wherein only one optical path deflecting mirror is disposed in a space between a light beam from the mask toward the projection optical system and an optical axis of the projection optical system. apparatus. 10. The exposure apparatus according to claim 8, wherein an angle formed between a light beam directed to the optical path deflecting mirror and a reflecting surface of the optical path deflecting mirror is 15 degrees or less. The exposure apparatus according to any one of claims 8 to 10, wherein the optical path deflector is positioned in a space between the first surface and the projection optical system.

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