JP2004271544A - Optical element, lens system, and projection aligner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element etc. which has a flat transmittance unevenness characteristic and exhibits excellent image formation performance in a stepper optical system. <P>SOLUTION: An antireflection film of a lens 10 arranged on the image side of a pupil surface is allowed to take the negative incident angle characteristic that the transmittance increases in accordance with an increase of incident angle, thereby, the extinction on the peripheral part due to lens etc. on the surroundings for example can be canceled, an illumination distribution on the pupil surface can be made approximately uniform and the resolution is prevented from causing a difference dependent on the incident direction of projection light. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

図１１は、λ_０＝１９３ｎｍにおける反射角度特性を示す。グラフからも明らかなように、実線で示す光学膜厚０．２９λ_０の第１の場合、反射率の変化幅Δが２％程度であり、一点鎖線で示す光学膜厚０．３０λ_０の第２の場合（第１実施例に対応）、反射率の変化幅Δが３％程度であり、点線で示す光学膜厚０．３１λ_０の第３の場合、反射率の変化幅Δが４％程度である。つまり、膜厚を若干変更することにより、変化幅Δすなわち補正量を制御可能であることがわかる。また、仮に補正量を超えるような透過率ムラがある場合でも、このような反射防止膜１１４を複数面に適用することにより透過率ムラを適切に補正できることが期待できる。なお、ここで複数面とは、着目レンズの他面に限らずレンズ系を構成する他のレンズの面も意味する。
【００５０】
〔第２実施形態〕
以下、本発明の第２実施形態である光学素子の製造方法及び装置について、図面に参照しつつ説明する。
【００５１】
図１２は、図１に示すレンズ１０等を製造するための装置を示すブロック図である。この装置４０は、レンズ１０の反射防止膜１４を製造するためのものであり、成膜装置本体４１と、その動作を制御する制御装置４５とを備える。
【００５２】
成膜装置本体４１は、レンズ本体１２の入出射面に多層膜からなる反射防止膜１４を形成する電子ビーム蒸着装置等の公知の成膜装置である。成膜装置本体４１は、レンズ本体１２を保持してこれを自転及び公転させるホルダ４１ａと、蒸発材料を選択的に切替可能な第１及び第２蒸発源４１ｃ，４１ｄと、両蒸発源４１ｃ，４１ｄの上方に配置されて両蒸発源４１ｃ，４１ｄからの蒸発物質の拡散方向を制御する絞り板４１ｆと、ホルダ４１ａや蒸発源４１ｃ，４１ｄの動作を制御する駆動制御装置４１ｈとを備える。この成膜装置本体４１では、ホルダ４１ａによってレンズ本体１２を自公転させることができ、さらに、絞り板４１ｆに設けた開口によって蒸発物質の拡散方向を制御することができるので、レンズ本体１２の中央と周辺とにバランス良い成膜が可能になり、レンズ本体１２の全面に亘って均一な膜厚の多層膜からなる反射防止膜１４を形成することができる（図１参照）。なお、両蒸発源４１ｃ，４１ｄは、駆動制御装置４１ｈに駆動されて蒸発物質を適当なタイミングで切替可能な構造に設計されており、屈折率の異なる２種以上の膜を順次積層することが可能になる。
【００５３】
制御装置４５は、ＣＰＵ４５ａ、入出力装置４５ｂ、記憶装置４５ｃ、表示装置４５ｄ、インターフェース４５ｅ等を備えるコンピュータである。ここで、ＣＰＵ４５ａは、入出力装置４５ｂ、記憶装置４５ｃ、表示装置４５ｄ、及びインターフェース４５ｅとの間で相互にデータの授受が可能になっている。また、ＣＰＵ４５ａは、入出力装置４５ｂすなわちオペレータからの指示等に基づいて、記憶装置４５ｃ等から所定のプログラムやデータを読み出し、これらプログラム及びデータに基づく各種処理を実行する。具体的には、ＡＲ膜設計プログラムを起動することにより、レンズ本体１２に形成すべき反射防止膜１４の膜構造の設計値を算出し、ＡＲ膜作製プログラムを起動することにより、成膜装置本体４１を動作させて上記設計値に対応する膜構造を有する反射防止膜１４を形成させる。なお、インターフェース４５ｅは、制御装置４５と成膜装置本体４１との間を取り持つ役割を有し、ＣＰＵ４５ａの指令を成膜装置本体４１側に伝えたり、成膜装置本体４１から出力された動作状態に関するデータをＣＰＵ４５ａに出力したりする。
【００５４】
図１３は、制御装置４５によって実行されるＡＲ膜設計プログラムの概要を簡単に説明するフローチャートである。まず、投影レンズを構成する各レンズのレンズデータを抽出する（ステップＳ１１）。なお、この投影レンズは、図３に例示するレンズ系１１０に限らず、様々なレンズ要素からなるものとすることができ、目的に応じた倍率、分解能等を有するように予め適宜光学設計されたものとすることができる。この際、投影レンズは、レンズに限らず平板ガラスを組み込んだものとすることができる。次に、入出力装置４５ｂや表示装置４５ｄを利用してオペレータからの指示を受け付け、自動設計と非自動設計のいずれが要求されたかが判断される（ステップＳ１２）。
【００５５】
ステップＳ１２で自動設計が選択された場合、投影レンズを構成する瞳面から像側の各レンズ要素における入射角度範囲を計算する（ステップＳ２１）。この入射角度範囲は、投影レンズについて光線追跡を行い、対象とするレンズ要素の各点を通過する各光束の入射角度範囲を計算し、中心からの距離と最大入射角との相関を表す入射角テーブルとして記憶装置４５ｃに保存される。
【００５６】
次に、ステップＳ２１で得た入射角テーブルから最大の入射角度を与える最大斜入射のレンズ要素を対象レンズとして選択する（ステップＳ２２）。ここで、対象レンズとは、図２に示す負の入射角特性を付与するレンズ要素であり、２以上とすることができる。この対象レンズによって、投影レンズを構成する他のレンズ等により形成される周辺部の減光を補償することがこの膜設計の目的である。
【００５７】
次に、ステップＳ２２で選択した対象レンズを除いた残りのレンズ要素等による斜入射の効果の総和を瞳面内透過率ムラとして評価する（ステップＳ２３）。具体的には、投影レンズについて光線追跡を行うことによって、各レンズ要素ごとに各点での平均入射角度を求め、この平均入射角度に対応する透過率の減少を瞳面上における２次元分布として計算し、このようにして得た透過率減少の総和として瞳面内透過率ムラを算出する。この際、残りのレンズ要素には、従来型の反射防止膜が形成されており、垂直入射で反射率がほぼ０％で最低となり比較的大きな入射角度まで低反射率が維持されるものとする。なお、対象レンズの一面のみに負の入射角特性を付与する場合、対象レンズの他面も瞳面内透過率ムラの評価対象となる。
【００５８】
図１４（ａ）は、瞳面内透過率ムラの評価例を瞳面における半径（ｒ）と透過率変動量（ΔＴ）との関係として表したグラフである。光軸が通る中心を基準として半径が増大するに従って透過率が減少していることがわかる。
【００５９】
図１３に戻って、次に対象レンズによる透過率補正目標量を算出する（ステップＳ２４）。これは、ステップＳ２３で得た瞳面内透過率ムラを解消するような高透過率フィルタの透過率分布の計算に対応し、透過率補正目標量と瞳面内透過率ムラとの積をとることによって瞳面に換算した場合における平坦な透過率分布を達成することができる。
【００６０】
図１４（ｂ）は、透過率補正目標量の計算例を瞳面における半径（ｒ）と透過率変動量（ΔＴ）との関係として表したグラフである。光軸が通る中心を基準として半径が増大するに従って透過率を減少させる必要があることがわかる。
【００６１】
図１３に戻って、次に対象レンズによる担当補正量を算出する（ステップＳ２５）。これは、ステップＳ２４で得た透過率補正目標量を対象レンズの面数に対応する負担分に分割したものであり、各面に形成される反射防止膜による透過率補正の目標量となっている。例えば、対象レンズが１つであり、その一対の光学面に形成する一対の反射防止膜の双方によって透過率補正を行う場合、各担当補正量は、ステップＳ２４で得た透過率補正目標量の平方根又は近似的に半分とする。もっとも、両反射防止膜による補正負担率は、上記に限らず適当な比率とできることは言うまでもない。
【００６２】
図１４（ｃ）は、担当補正量の計算例を瞳面における半径（ｒ）と透過率変動量（ΔＴ）との関係として表したグラフである。図１４（ｂ）の場合と比較すると、透過率の変化量が半分の値となっている。
【００６３】
図１３に戻って、次に対象レンズによる担当補正量を達成する反射防止膜の光学設計値を行う（ステップＳ２６）。具体的には、反射防止膜の初期条件として予め適当な膜構成、光学膜厚等の初期パラメータを設定する。これは、オペレータが入力してもよいが、制御装置４５側で使用波長を考慮して適宜選択したものとすることができる。次に、投影レンズについて光線追跡を行うことによって、対象レンズの各点での平均入射角度を求め、この平均入射角度に起因して反射防止膜によって発生する透過率の増加を、瞳面上に換算した２次元分布として計算し、このようにして得た透過率増加を達成補正量として算出する。このような達成補正量は、反射防止膜の初期パラメータを徐々に変更して新たな膜構成、光学膜厚等とした修正パラメータで繰返し計算され、目標値である担当補正量に最も近似する最適値が決定される。例えば達成補正量が、担当補正量に対して、予め定めた偏差量である２乗平均値（ＲＭＳ）以下に近似していれば処理を終了することができる。以上のような担当補正量の計算は、対象レンズの数やその面数に応じた回数だけ繰り返され、各反射防止膜による達成補正量を積算したものがステップＳ２４で得た透過率補正目標量となるように最適化のシミュレーションが繰り返される。
【００６４】
図１４（ｄ）は、達成補正量を積算値と瞳面内透過率ムラとを、瞳面における半径（ｒ）と透過率変動量（ΔＴ）との関係として表したグラフである。二点鎖線は瞳面内透過率ムラを示し、破線は、達成補正量の積算値を示す。実線は、反射防止膜の効果を示しており、二点鎖線と破線の積算値、すなわち達成補正量の積算値による瞳面内透過率ムラの補正後の透過特性を示す。このような補正後の透過特性は、投影レンズが半導体露光装置等に組み込まれるものである場合、その変動幅が３％以下であることが望ましい。
【００６５】
一方、図３のステップＳ１２で自動設計が選択されなかった場合、投影レンズを構成するいずれかのレンズ要素を対象レンズとして選択することオペレータに指示する（ステップＳ３１）。この際、瞳面内透過率ムラの補正を目的とするので、瞳面から像側で効果的と認められるレンズ要素が入出力装置４５ｂを介して選択される。
【００６６】
次に、ステップＳ３１で選択した対象レンズを除いた残りのレンズ要素等による斜入射の効果の総和を瞳面内透過率ムラとして評価する（ステップＳ３２）。この処理は、既に説明したステップＳ２３での処理と同様である。
【００６７】
次に、透過率補正目標量や対象レンズによる担当補正量を入力することをオペレータに指示する（ステップＳ３３）。ステップＳ２４，２５では、透過率補正目標量や担当補正量を投影レンズの設計値に基づいて計算したが、この場合、当業者であるオペレータの推測や直感に基づいて透過率補正目標量や担当補正量を人為的に設定させる。
【００６８】
最後に、対象レンズによる担当補正量を達成する反射防止膜の光学設計値を行う（ステップＳ３４）。この処理は、既に説明したステップＳ２６での処理と同様である。この処理において、対象レンズの数やその面数に応じた回数だけ担当補正量の計算が繰り返され、各反射防止膜による達成補正量を積算したものが透過率補正目標量となるように最適化のシミュレーションが繰り返される。
【００６９】
以上のような、反射防止膜の設計により、瞳面内透過率ムラの少ない投影レンズを実現することができる。このようにして得た反射防止膜の設計値は、記憶装置４５ｃに保管され、成膜装置本体４１による成膜工程の管理に利用される。
【００７０】
〔第３実施形態〕
以下、本発明の第３実施形態である投影露光装置について、図面に参照しつつ説明する。
【００７１】
図１５は、上述の第１実施形態等で構造や製造を説明したレンズを用いた投影露光装置の基本構造を示す。この投影露光装置は、フォトレジストでコートされたウェハー上にレチクルのパターンのイメージを投影するための、ステッパと呼ばれるような投影露光装置に特に応用される。
【００７２】
図１５に示すように、本実施形態の投影露光装置は少なくとも、▲１▼感光剤を塗布した基板（ウェハー）Ｗを表面３０１ａに置くことのできるウェハーステージ３０１，▲２▼露光光として用意された波長の真空紫外光を用意されたマスク（レチクルＲ）のパターンに照射する照明光学系１５０，▲３▼照明光学系１５０に露光光を供給するための光源１８０，▲４▼基板Ｗ上にマスクＲに形成されたパターンのイメージを投影するためのマスクＲが配置された最初の表面Ｐ１（物体面）と、基板Ｗの表面と一致させた二番目の表面Ｐ２（像面）との間に置かれ、基板Ｗ上にマスクＲのパターンを転写するための投影光学系４００，▲５▼投影露光装置の全系を統括的に制御して動作させる主制御部５００を含む。
【００７３】
ここで、ウェハーステージ３０１は、ステージ駆動系３００に駆動されて、基板Ｗを投影光学系４００に対して３次元的に移動させる。照明光学系１５０は、マスクＲと基板Ｗとの間の相対位置を調節するためのアライメント光学系１５１も含んでおり、マスクＲはウェハーステージ３０１の表面に対して平行に動くことのできるレチクルステージ２０１に配置される。レチクル交換系２００は、レチクルステージ２０１にセットされたレチクル（マスクＲ）を交換し運搬する。レチクル交換系２００は、ウェハーステージ３０１の表面３０１ａに対してレチクルステージ２０１を平行に動かすためのステージドライバーを含んでいる。投影光学系４００は、スキャンタイプの露光装置に応用されるアライメント光学系（不図示）を有している。
【００７４】
そして、本実施形態の投影露光装置は、第１実施形態等で構造や製造を説明したレンズを使用したものである。具体的には、図１５に示した投影露光装置は、照明光学系１５０の光学レンズ１５３、及び／又は投影光学系４００の光学レンズ４０１として、図１のレンズ１０又はこれに変更を加えたレンズを備えることが可能である。この場合、光学レンズ４０１によって透過率ムラの発生を防止するこことができ高い露光解像度を得ることができるので、大きなＮＡの投影露光装置において、高輝度で高精度の投影露光が可能になる。
【００７５】
以上実施形態に即して本発明を説明したが、本発明は、上記実施形態に限定されるものではない。例えば、上記実施形態では、反射防止膜１４，１５を３層構造としているが、これに限るものではなく、２層以下或いは４層以上とすることができる。その際、レンズ本体１２上に最初に形成する膜は、光学アドミッタンスの観点からすると低屈折率膜の成膜から開始する方が光学設計を通常簡単なものとするが、高屈折率膜の成膜から開始してその上に順次積層することも可能である。
【００７６】
【発明の効果】
以上の説明から明らかなように、本発明に係る光学素子によれば、垂直入射透過率に比較して斜入射透過率が相対的に高くなる負の特性を有する反射防止膜を組み込んでいるので、透過率ムラとりわけ瞳面内透過率ムラの発生を抑えることができ、良好な結像特性を有する投影レンズ等を提供することができる。
【００７７】
また、本発明に係るレンズ系によれば、着目するレンズ要素を構成する光学部材や他のレンズ要素によって生じた透過率ムラを補償してその分布を平坦化することができるので、瞳面内透過率ムラ等の透過率ムラの発生を抑えることができ、良好な結像特性を有する投影レンズ等を提供することができる。
【００７８】
また、本発明に係るレンズ系の設計方法によっても、着目するレンズ要素を構成する光学部材や他のレンズ要素によって生じた透過率ムラを補償してその分布を平坦化することができるので、瞳面内透過率ムラ等の透過率ムラの発生を抑えることができ、良好な結像特性を有する投影レンズ等を提供することができる。
【００７９】
また、本発明に係る投影露光装置によれば、紫外域で瞳面内透過率ムラ等の少ない良好な結像特性を有する投影光学系によって高精度の投影露光が可能になる。
【００８０】
また、本発明に係る別の投影露光装置によれば、紫外域で照度ムラの少ない良好な照明特性を有する照明光学系によって高精度の投影露光が可能になる。
【図面の簡単な説明】
【図１】第１実施形態の光学素子であるレンズの断面構造を説明する図である。
【図２】図１のレンズの透過率特性を概念的に説明するグラフである。
【図３】図１に示すレンズ１０の役割について説明する概念図である。
【図４】各実施例の反射防止膜の構成図である。
【図５】第１実施例の反射防止膜の１９３ｎｍでの反射角度特性である。
【図６】第１実施例の反射防止膜の１９３ｎｍでの透過角度特性である。
【図７】第２実施例の反射防止膜の１９３ｎｍでの反射角度特性である。
【図８】第２実施例の反射防止膜の１９３ｎｍでの透過角度特性である。
【図９】第３実施例の反射防止膜の１５７ｎｍでの反射角度特性である。
【図１０】第３実施例の反射防止膜の１５７ｎｍでの透過角度特性である。
【図１１】第４実施例の反射防止膜の１９３ｎｍでの反射角度特性である。
【図１２】図１に示すレンズを製造するための第２実施形態の装置を示すブロック図である。
【図１３】図１２に示す制御装置によって実行されるＡＲ膜設計プログラムを説明するフローチャートである。
【図１４】（ａ）〜（ｄ）は、図１３における処理の一部を視覚的に説明するグラフである。
【図１５】第３実施形態の投影露光装置の基本構成を示す構成図である。
【符号の説明】
１０…レンズ、 １０ａ…中心部分、 １０ｂ…周辺部分、 １２…レンズ本体、 １２ａ，１２ｂ…入出射面、 １４，１５…反射防止膜、 ４１…成膜装置本体、 ４１ｈ…駆動制御装置、 ４５…制御装置、 ４５ｅ…インターフェース、１１０ａ〜１１０ｄ…レンズ要素、ＩＰ…像面、ＯＡ…光軸、ＯＰ…物体面、Ｐ１…表面、Ｐ２…表面、ＰＰ…瞳面TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical element applied to an optical system of a projection exposure apparatus such as a semiconductor exposure apparatus, a lens system incorporating such an optical element, a design method thereof, and a projection exposure apparatus incorporating such an optical element. Things.
[0001]
[Prior art]
In recent years, in order to increase the degree of integration of semiconductor elements, there is an increasing demand for a high-resolution reduction projection type semiconductor exposure apparatus (stepper). Generally, the resolution R of photolithography is
R = k · λ / NA
Is represented by Here, k is a proportionality constant, and λ and NA are an exposure wavelength and a numerical aperture of the optical system, respectively.
[0002]
As is clear from the above resolution equation, one method of increasing the resolution of photolithography using a stepper is to shorten the wavelength of the light source. Recently, a stepper using a high-power laser as a light source capable of oscillating light in a shorter wavelength range than a conventionally used mercury lamp has begun to be put into practical use. The wavelength has been shortened from a KrF excimer laser (λ ≒ 248 nm) to an ArF excimer laser (λ ≒ 193 nm). ₂ There is a laser (λ ≒ 157 nm).
[0003]
In an optical system of a stepper used in such a short wavelength region, an antireflection film is formed on various optical element surfaces in order to reduce a light amount loss, a flare, a ghost, and the like due to surface reflection of an optical element such as a lens. Is common. At this time, if the optical thin film is formed of a film material having a large absorption or a low laser resistance with respect to light in such a short wavelength range, a loss of light amount due to absorption, film destruction due to absorption heat generation, a change in substrate surface, and the like are caused. This is a major disadvantage for steppers. For this reason, it is desirable that the film material used has low absorption and high laser resistance. Film materials that can be used at the laser wavelength are mainly magnesium fluoride (MgF ₂ ) Or silicon oxide (SiO ₂ ), But the types are limited. Similarly, the material of a substrate used for an optical element such as a lens is limited to a fluorine compound crystal such as fluorite or quartz glass. It is known that such a limitation on the substrate material and the film material becomes more significant as the wavelength of the light source becomes shorter. ₂ Only a part of the fluoride can be used at the wavelength, and it is not easy to shorten the wavelength of the stepper.
[0004]
On the other hand, according to the above-described resolution equation, another method of increasing the resolution of photolithography by a stepper is to increase the NA of the projection lens in the stepper optical system. Since NA is the sine (sin θ) of the maximum incident angle (θ) of the exposure light beam with respect to the radiation direction on the exposure target (such as a silicon wafer), increasing the NA implies the light on the surface of each lens element. This means that the light incident angle is also wider. That is, when the NA of the stepper optical system is increased, the antireflection film used in the stepper optical system needs to have an antireflection effect for a wider incident angle.
[0005]
By the way, in the stepper optical system, there is transmittance unevenness as a required performance. There are two types of transmittance unevenness, one of which is transmittance unevenness in the image plane, and the other is transmittance unevenness in the pupil. Both are desirably flat. For example, if the transmittance non-uniformity characteristic in the image plane is not flat, the exposure may be insufficient depending on the position of the image plane. Adversely affects the exposure resolution. It is generally difficult to produce a wide-incidence-angle anti-reflection film that satisfies the performance required for such a high NA, because the film material is limited. In particular, the reflectance at oblique incidence tends to increase ( Patent Document 1).
[0006]
In addition, the radius of curvature of the lens element tends to decrease with an increase in NA. Generally, the film thickness around the lens tends to be thinner than the lens vertex. In that case, the anti-reflection characteristics around the lens deteriorate, and the transmittance is more likely to further decrease.
[0007]
Due to the above situation, the general tendency is that the transmittance of light passing around the lens is lower than that of light passing through the center of the lens, and the transmittance of light obliquely incident is lower than that of vertically incident light. Occurs. This tendency results in a decrease in the transmittance around the image in the image plane as compared with the center of the image, and a decrease in the transmittance around the pupil relative to the center of the pupil in the pupil. That is, the illuminance around the exposure target decreases, and the exposure resolution at a high incident angle decreases.
[0008]
[Patent Document 1]
JP-A-9-329702
[Problems to be solved by the invention]
Among the transmittance unevenness of the stepper optical system as described above, the transmittance unevenness in the image plane can be corrected to some extent by controlling the unevenness of the illuminance by the illumination optical system. However, since it is necessary to perform the operation in the projection lens, there are many difficult points due to space limitations.
[0009]
The present invention has been made in view of such a conventional problem, and an object of the present invention is to provide an optical element and the like in a stepper optical system, in which transmittance unevenness characteristics are flat and exhibit good imaging performance. I do.
[0010]
[Means for solving the problem]
In order to solve the above-mentioned problems, an optical element according to a first aspect of the present invention includes an optical member having a light transmitting property, and an oblique incidence transmittance at a predetermined oblique incidence angle formed on a predetermined incident / exit surface of the optical member. And an antireflection film having an optical property that is higher than the normal incidence transmittance.
[0011]
Since the antireflection film provided on the optical element has optical characteristics such that the oblique incidence transmittance at a predetermined oblique incidence angle is higher than the normal incidence transmittance, the transmittance unevenness caused by the optical member and other optical elements is reduced. The distribution can be flattened by compensation. That is, in general, in a stepper optical system or the like, the transmittance of light passing around the lens tends to be lower than that of light passing through the center of the lens. By incorporating an antireflection film having a negative characteristic that is higher than that of the first embodiment, it is possible to suppress the occurrence of transmittance unevenness, particularly, the transmittance unevenness in the pupil plane, and to provide a projection lens or the like having good imaging characteristics. it can.
[0012]
An optical element according to a second aspect of the present invention is the optical element according to the first aspect, wherein the antireflection film has an oblique incidence angle when the predetermined oblique incidence angle is in a predetermined range of 30 ° or more. It has optical characteristics in which the transmittance is 2% or more higher than the normal incidence transmittance. In this case, the transmittance unevenness can be reliably corrected by the antireflection film.
[0013]
In an optical element according to a third aspect, in the optical element according to the first aspect, the optical member is a lens body. In this case, it is possible to effectively prevent dimming around the lens where the oblique incidence angle tends to be large.
[0014]
The optical element according to a fourth aspect is the optical element according to the first to third aspects, wherein the antireflection film includes a multilayer film in which a plurality of layers having different refractive indices are stacked, and the plurality of layers are formed. The difference between the oblique incidence transmittance and the normal incidence transmittance is adjusted by setting the optical film thickness. In this case, by the optical design of the multilayer film, optical characteristics having a relatively high oblique incidence transmittance can be easily given, and the degree of freedom of the correction range of the transmittance unevenness can be increased.
[0015]
Further, a lens system according to a fifth aspect includes a plurality of lens elements, and an antireflection film formed on a predetermined incident / exit surface of at least one of the plurality of lens elements. Transmittance adjusting means for adjusting a two-dimensional transmittance distribution of the lens element with respect to the transmitted light in accordance with the incident angle of the transmitted light.
[0016]
In the above lens system, the transmittance adjusting means adjusts the two-dimensional transmittance distribution of the transmitted light with respect to at least one lens element in accordance with the incident angle of the transmitted light. The unevenness in transmittance caused by the lens element can be compensated and its distribution can be flattened. Therefore, it is possible to suppress the occurrence of transmittance unevenness due to the lens system, in particular, the occurrence of transmittance unevenness in the pupil plane, and to provide a lens system such as a projection lens having good imaging characteristics.
[0017]
The lens system according to a sixth aspect of the present invention is the lens system according to the fifth aspect, wherein the transmittance adjusting means has an optical characteristic in which the oblique incidence transmittance at a predetermined oblique incidence angle is higher than the normal incidence transmittance. It is an antireflection film having: In this case, not only the reflection loss can be reduced by the unavoidable anti-reflection film, but also the function of adjusting the transmittance distribution is provided by the anti-reflection film, so that the configuration of the lens system can be simplified. A high-performance lens system can be easily provided. By appropriately adjusting the layer configuration of the antireflection film, various transmittance distributions can be formed with respect to the distribution of the incident angle.
[0018]
In a lens system according to a seventh aspect, in the lens system according to the sixth aspect, the at least one lens element is selected from one or more lens elements at which the oblique incident angle of transmitted light is greatest. In this case, since the transmittance distribution can be adjusted by the most effective lens element among the lens elements constituting the lens system, the design of the antireflection film is simplified.
[0019]
The lens system according to an eighth aspect is the lens system according to the sixth aspect, wherein the lens system is a projection lens, and the at least one lens element is closer to an exit side than a pupil plane of the projection lens. Placed in Since lens elements arranged on the exit side of the pupil plane of the projection lens generally tend to directly affect the transmittance unevenness in the pupil plane, such lens elements have an oblique incidence transmittance that is relatively high. By forming an antireflection film having characteristics, it is possible to effectively correct the transmittance unevenness in the pupil plane.
[0020]
Further, in the lens system according to the ninth aspect, in the lens system according to the eighth aspect, the flatness of the transmittance unevenness is within 3% in a variation width. In this case, the exposure using the projection lens becomes extremely uniform.
[0021]
A lens system designing method according to a tenth aspect of the present invention is the lens system designing method according to the fifth to ninth aspects, wherein at least one of the plurality of lens elements which is a determination target of transmittance distribution adjustment is determined. Selecting one target element, calculating an incident angle range of a light beam incident on the target element, and adjusting an optical characteristic of an antireflection film formed on the target element based on the incident angle range. Determining whether the adjustment amount of the transmittance distribution is within a predetermined range. Here, the “optical properties of the antireflection film” include various conditions such as the number of layers of the antireflection film and the optical film thickness.
[0022]
In the above-described lens system design method, by adjusting the optical characteristics of the antireflection film formed on the target element based on the incident angle range, it is determined whether or not the adjustment amount of the transmittance distribution is within a predetermined range. Since the determination is made, it is possible to design a lens system in which the distribution of the transmittance is flattened by compensating for the transmittance unevenness caused by the optical member constituting the lens element of interest and other lens elements. Therefore, it is possible to suppress the occurrence of transmittance unevenness due to the lens system, in particular, the occurrence of transmittance unevenness in the pupil plane, and to provide a lens system such as a projection lens having good imaging characteristics.
[0023]
The lens system designing method according to an eleventh aspect of the present invention is the lens system designing method according to the tenth aspect, wherein the adjustment amount of the transmittance distribution is different from the transmittance distribution by the other lens elements except the target element. Are set to approximate the amount that cancels out the effect on In this case, it is possible to provide a lens system such as a projection lens having good image forming characteristics and having little transmittance unevenness such as transmittance unevenness in the pupil plane as a whole.
[0024]
In a lens system designing method according to a twelfth aspect, in the lens system designing method according to the eleventh aspect, the step of selecting the target element includes the step of selecting a transmittance distribution among the lens elements constituting the lens system. This determines the lens element that has the greatest influence on the lens. In this case, since the transmittance distribution can be adjusted by the most effective lens element among the lens elements constituting the lens system, the design of the antireflection film is simplified.
[0025]
Further, a method for manufacturing a lens system according to a thirteenth invention manufactures a lens based on data determined by the method for designing a lens system according to the first to tenth inventions. In this case, a lens system such as a projection lens having good imaging characteristics can be provided.
[0026]
A projection exposure apparatus according to a fourteenth aspect of the present invention is an apparatus for projecting and exposing a pattern image of a mask onto a substrate using a projection optical system, and illuminating the mask with ultraviolet light such as vacuum ultraviolet as exposure light. And a projection optical system that includes the optical element according to the first to fourth inventions and forms a pattern image of the mask on a substrate.
[0027]
In the projection exposure apparatus, since the projection optical system for forming the pattern image of the mask on the substrate includes the optical elements according to the first to fourth aspects, a good pupil plane transmittance non-uniformity and the like in the ultraviolet region is reduced. High-precision projection exposure is made possible by a projection optical system having imaging characteristics.
[0028]
A projection exposure apparatus according to a fifteenth invention is an apparatus for projecting and exposing a pattern image of a mask onto a substrate using a projection optical system, and includes an optical element according to the first to fourth inventions, An illumination optical system for illuminating the mask with ultraviolet rays such as ultraviolet rays as exposure light, and a projection optical system for forming a pattern image of the mask on a substrate.
[0029]
In the projection exposure apparatus, since the illumination optical system that illuminates the mask with ultraviolet light as the exposure light includes the optical element according to the first to fourth inventions, the illumination optical system has good illumination characteristics with less illuminance unevenness in the ultraviolet region. This enables high-precision projection exposure.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
[First Embodiment]
Hereinafter, an optical element according to a first embodiment of the present invention will be described with reference to the drawings.
[0031]
FIG. 1 is a diagram illustrating a cross-sectional structure of a lens 10 that is an optical element according to the first embodiment. The lens 10 has a lens body 12 which is a lens-shaped optical member for ultraviolet light or the like, and antireflection films 14 and 15 formed on a pair of entrance / exit surfaces 12a and 12b of the lens body 12. . Here, the lens body 12 can have desired light-collecting characteristics with respect to incident light by setting the curvature of the entrance / exit surfaces 12a and 12b. In this case, the light beam L <b> 1 incident on the central portion 10 a of the lens 10 along the optical axis OA is incident perpendicularly on the antireflection film 14. On the other hand, the light beam L2 incident on the peripheral portion 10b of the lens 10 along the optical axis OA obliquely enters the antireflection film 14 at a large angle θ. Further, the light beam L2 that has passed through the anti-reflection film 14 enters the anti-reflection film 15 at a larger angle. That is, when the lens 10 is used for condensing, the light incident on the central portion 10a is almost vertically incident, and the light incident on the peripheral portion 10b is more likely to be obliquely incident.
[0032]
FIG. 2 is a graph illustrating transmittance characteristics of the lens 10 of FIG. In this graph, the horizontal axis indicates the incident angle θ, and the vertical axis indicates the transmittance T. The solid line shows the transmission characteristics of the lens 10 of the present embodiment, and the one-dot chain line shows the transmission characteristics of the lens of the comparative example provided with the conventional antireflection film. As is clear from the graph, the lens 10 of the embodiment has a structure in which the transmittance gradually increases as the incident angle increases. On the other hand, in the lens of the comparative example, the transmittance gradually decreases as the incident angle increases. In other words, this lens 10 is different from a normal lens, and the transmittance increases as the incident angle to the lens 10 increases, and it can be said that the lens 10 has a negative incident angle characteristic.
[0033]
Although the transmittance of the lens of the comparative example decreases as the incident angle to the lens increases, this is because the conventional antireflection film minimizes the reflectance at normal incidence. Is designed to maintain a low reflectance in the widest possible angle range. In other words, the conventional antireflection film is designed on the basis of normal incidence, and does not sufficiently consider under what conditions the target lens is actually used. Here, if an antireflection film whose transmittance does not depend on the incident angle, that is, an antireflection film having a constant reflectance over a wide incident angle range can be manufactured, the two-dimensional transmittance unevenness in the light flux passing through the lens is theoretically possible. Will not occur. However, it is practically difficult to realize such an antireflection film having no incident angle dependence without a decrease in transmittance. Particularly, in a lens system such as a projection optical system including a plurality of lens elements, if an anti-reflection film having no or little incidence angle dependence is formed on each lens element, transmission loss is extremely increased. become.
[0034]
On the other hand, in the present embodiment, when the light beam incident on the lens 10 is obliquely incident light, its transmittance is made larger than that in the case of vertically incident light. In other words, the dimming of the peripheral portion formed by a lens different from the lens 10 of the embodiment of interest and the luminance distribution of the light source, etc., is an anti-reflection property in which the transmittance increases at the periphery, that is, the transmittance decreases by oblique incidence. Compensation is performed by the lens 10 having a negative incident angle characteristic. Accordingly, in a lens system such as a projection optical system including a plurality of lens elements, the transmittance unevenness, that is, the transmittance unevenness in the pupil plane and the transmittance unevenness in the image plane can be achieved without substantially increasing the transmission loss of the lens system. Can be reliably prevented, and high-precision imaging, exposure, and the like can be performed.
[0035]
In the lens 10 as shown in FIG. 1, in order to realize a negative incident angle characteristic in which the transmittance is reduced by oblique incidence, the optical design values of the antireflection films 14 and 15 formed on the surface of the lens body 12 are realized. Is gradually optimized, for example, by simulation. Specifically, the transmittance of obliquely incident light is made larger than the transmittance of vertically incident light by appropriately adjusting the optical film thickness and the number of layers in each of the multilayer films constituting the antireflection films 14 and 15. The transmittance distribution with respect to the incident angle can be freely adjusted within a certain range. At this time, by calculating in advance the incident angle of the light beam incident on each part of the target lens 10, a desired two-dimensional transmittance distribution (specifically, a transmittance of approximately 100% around the lens 10). (Distribution indicating a transmittance reduction of several percent at the center of the lens), the antireflection films 14 and 15 can be designed.
[0036]
The lens body 12 of the lens 10 shown in FIG. 1 is produced by appropriately grinding and polishing various glass materials. When the light used is ultraviolet light, quartz glass or fluorite is used as the material. You. Further, the antireflection films 14 and 15 have a configuration in which a low refractive index layer and a high refractive index layer are sequentially laminated on the surface of the lens body 12.
[0037]
Here, the low-refractive-index layer refers to a layer having a refractive index lower than the refractive index of the lens body 12 and is made of magnesium fluoride (MgF ₂ ), Aluminum fluoride (AlF ₃ ), Sodium fluoride (NaF), lithium fluoride (LiF), calcium fluoride (CaF ₂ ), Barium fluoride (BaF ₂ ), Strontium fluoride (SrF ₂ ), Cryolite (Na ₃ AlF ₆ ), Thiolite (Na ₅ Al ₃ F ₁₆ ), Silicon oxide (SiO ₂ :) or a mixture thereof. Since the low refractive index layer is usually formed on the surface of the lens body 12, the low refractive index layer has two or more layers. In this case, the low-refractive-index layers may use the same type of low-refractive-index material, but a desired antireflection effect can be obtained even if different low-refractive-index materials are used. The high-refractive-index layer refers to a layer having a refractive index higher than the refractive index of the lens body 12, and when the used light is ultraviolet light, neodymium fluoride (NdF ₃ ), Lanthanum fluoride (LaF ₃ ), Gadolinium fluoride (GdF ₃ ), Dysprosium fluoride (DyF ₃ ), Yttrium fluoride (YF ₃ ), Lead fluoride (PbF ₂ ), Aluminum oxide (Al ₂ O ₃ ) Or a mixture thereof. When two or more high-refractive-index layers are used, each high-refractive-index layer may use the same kind of high-refractive-index material, but the desired antireflection effect can be obtained even when different high-refractive-index materials are used. Obtainable. These high and low refractive index films are formed by a known technique such as a vacuum deposition method, a sputtering method, and an ion plating method.
[0038]
FIG. 3 is a conceptual diagram illustrating the role of the lens 10 shown in FIG. The illustrated lens system 110 is a double-sided telecentric type projection lens that projects an object as an image having a desired magnification, and includes, for example, four lens elements 110a to 110d.
[0039]
As is clear from the figure, the two-dimensional positions of the lens elements 110a and 110b arranged on the object plane OP side of the pupil plane PP are close to the object plane OP, so that the two-dimensional positions of the object plane OP are different. High correlation with position. For example, consider a case where a two-dimensional transmittance distribution is formed in which light is increased or decreased in the peripheral portion due to the angle of incidence on the incident lens 110a facing the object plane OP. In this case, since such a two-dimensional transmittance distribution is directly reflected on the image plane IP, illuminance non-uniformity occurs in which light is increased or dimmed in a peripheral portion in the image plane IP.
[0040]
On the other hand, the two-dimensional positions of the lenses 110c and 110d arranged on the image plane IP side of the pupil plane PP are close to the image plane IP, so that the two-dimensional positions in the pupil plane PP, that is, the projected projections High correlation with the incident angle of light. For example, let us consider a case where a two-dimensional transmittance distribution is formed in which light is increased in the peripheral portion due to the angle of incidence on the exit lens 110d facing the image plane IP. In this case, since such a two-dimensional transmittance distribution is directly reflected on the pupil plane PP, the projection light increases as the incident angle increases with respect to the center light L11 along the optical axis OA, and the incident angle decreases. The illuminance non-uniformity at which the maximum outer edge light L21 becomes the maximum increase occurs. Conversely, it is assumed that a two-dimensional transmittance distribution is formed in which light is dimmed in the peripheral portion due to the angle of incidence on the exit lens 110d facing the image plane IP. In this case, as the incident angle increases with respect to the center light L11, the projection light decreases, and the illuminance non-uniformity in which the outer edge light L21 at which the incident angle becomes the maximum becomes the maximum dimming occurs.
[0041]
In summary, the lens arranged on the image side of the pupil plane PP typified by the entrance lens 110a generates in-image transmittance unevenness and is arranged on the object side of the pupil plane PP typified by the exit lens 110d. The generated lens causes transmittance unevenness in the pupil plane. Conversely, by setting the antireflection film such as the lens 110a disposed on the object side of the pupil plane PP to have a transmittance distribution as shown by a solid line in FIG. Can be canceled, and the illuminance distribution on the image plane IP can be made substantially uniform. In addition, the antireflection film such as the lens 110d disposed on the image side of the pupil plane PP has a transmittance distribution as shown by the solid line in FIG. Can be canceled, the illuminance distribution on the pupil plane PP can be made substantially uniform, and a difference in resolution depending on the incident direction of the projection light can be prevented.
[0042]
Hereinafter, specific examples will be described. In the following examples, an antireflection film 114 was formed on a flat substrate 112 as shown in FIG. 4 to simplify the evaluation of the transmittance distribution. The structure of the antireflection film 114 includes a first layer 114a having a low refractive index, a second layer 114b having a high refractive index, and a third layer 114c having a low refractive index, which are common to all the embodiments. A layer structure was adopted.
[0043]
[First embodiment]
Medium: air
Third layer: MgF ₂ (Optical film thickness 0.30λ ₀ )
Second layer: LaF ₃ (Optical film thickness 0.30λ ₀ )
First layer: MgF ₂ (Optical film thickness 0.30λ ₀ )
Substrate: quartz glass
Where λ ₀ Is the design center wavelength of the light used and can be set arbitrarily. ₀ = 193 nm. Quartz glass for substrate 112, MgF for first and third layers ₂ , And LaF of the second layer ₃ Have a refractive index of 1.55, 1.42, and 1.69, respectively.
[0044]
FIG. 5 shows the reflection angle characteristics at λ = 193 nm of the antireflection film 114 of the first embodiment, and FIG. 6 shows the transmission angle characteristics. As is apparent from FIG. 5, the reflectance of the light of λ = 193 nm is about 4% at the incident angle θ = 0 °, but is less than 1% near the incident angle θ = 50 °. FIG. 6 shows that the transmittance is about 96% at the incident angle θ = 0 °, and 99% or more near the incident angle θ = 50 °. When the incident angle θ is 30 ° or more, the transmittance is improved by about 2% or more as compared with the normal incidence. By incorporating the substrate 112 and the antireflection film 114 of the first embodiment into the lens system 110 as, for example, the exit lens 110d of FIG. 3, it is expected that the transmittance unevenness in the pupil plane is improved by about 3%.
[0045]
[Second embodiment]
Medium: air
Third layer: MgF ₂ (Optical film thickness 0.30λ ₀ )
Second layer: LaF ₃ (Optical film thickness 0.29λ ₀ )
First layer: MgF ₂ (Optical film thickness 0.30λ ₀ )
Substrate: fluorite
In the second embodiment, as in the first embodiment, λ ₀ = 193 nm, but the material of the substrate 112 is fluorite. Quartz glass for substrate 112, MgF for first and third layers ₂ , And LaF of the second layer ₃ Have a refractive index of 1.50, 1.42, and 1.69, respectively.
[0046]
FIG. 7 shows the reflection angle characteristics at λ = 193 nm of the antireflection film 114 of the second embodiment, and FIG. 8 shows the transmission angle characteristics. As is clear from FIG. 7, the reflectance of the light of λ = 193 nm is about 4% at the incident angle θ = 0 °, but is less than 1% near the incident angle θ = 50 °. From FIG. 8, it can be seen that the transmittance is about 96% at the incident angle θ = 0 °, and 99% or more near the incident angle θ = 50 °. When the incident angle θ is 30 ° or more, the transmittance is improved by about 2% or more as compared with the normal incidence. By incorporating the substrate 112 and the antireflection film 114 of the second embodiment into the lens system 110 as, for example, the exit lens 110d of FIG. 3, it can be expected that the transmittance unevenness in the pupil plane is improved by about 2%.
[0047]
[Third embodiment]
Medium: air
Third layer: MgF ₂ (Optical film thickness 0.30λ ₀ )
Second layer: LaF ₃ (Optical film thickness 0.27λ ₀ )
First layer: MgF ₂ (Optical film thickness 0.32λ ₀ )
Substrate: fluorite
In the third embodiment, λ ₀ = 157 nm. The material of the substrate 112 is fluorite. Fluorite, MgF ₂ , And LaF ₃ Have a refractive index of 1.56, 1.47, and 1.81, respectively.
[0048]
FIG. 9 shows the reflection angle characteristics of the antireflection film 114 of the third embodiment at λ = 157 nm, and FIG. 10 shows the transmission angle characteristics. As is clear from FIG. 9, the reflectance for light of λ = 157 nm is about 5% at the incident angle θ = 0 °, but is about 1% near the incident angle θ = 50 °. From FIG. 10, it can be seen that the transmittance is about 95% at the incident angle θ = 0 °, and is about 99% near the incident angle θ = 50 °. When the incident angle θ is 30 ° or more, the transmittance is improved by about 2% or more as compared with the normal incidence. By incorporating the substrate 112 and the antireflection film 114 of the third embodiment into the lens system 110 as, for example, the exit lens 110d of FIG. 3, it can be expected to improve the transmittance unevenness in the pupil plane by about 4%.
[0049]
[Fourth embodiment]
The fourth embodiment is a modification of the first embodiment, and the materials of the substrate and the first to third layers are the same as those of the first embodiment. In this case, the optical film thickness of each of the layers 114a, 114b, and 114c is similarly changed by a small amount in three stages, and the correction amount by the antireflection film 114 is adjusted. At this time, the setting of the optical film thickness of each layer 114a, 114b, 114c was as shown in Table 1 below.
[Table 1]

FIG. ₀ = 193 nm. As is clear from the graph, the optical film thickness indicated by the solid line is 0.29λ. ₀ In the first case, the change width Δ of the reflectivity is about 2%, and the optical film thickness 0.30λ ₀ In the second case (corresponding to the first embodiment), the change width Δ of the reflectivity is about 3%, and the optical film thickness 0.31λ shown by the dotted line. ₀ In the third case, the change width Δ of the reflectance is about 4%. That is, it is understood that the width of change Δ, that is, the correction amount can be controlled by slightly changing the film thickness. Even if there is uneven transmittance that exceeds the correction amount, it can be expected that the uneven transmittance can be appropriately corrected by applying such an antireflection film 114 to a plurality of surfaces. Here, the plurality of surfaces means not only the other surface of the lens of interest but also the surfaces of other lenses constituting the lens system.
[0050]
[Second embodiment]
Hereinafter, a method and an apparatus for manufacturing an optical element according to a second embodiment of the present invention will be described with reference to the drawings.
[0051]
FIG. 12 is a block diagram showing an apparatus for manufacturing the lens 10 and the like shown in FIG. This device 40 is for manufacturing the antireflection film 14 of the lens 10 and includes a film forming device main body 41 and a control device 45 for controlling the operation thereof.
[0052]
The film forming apparatus main body 41 is a known film forming apparatus such as an electron beam vapor deposition apparatus that forms the antireflection film 14 made of a multilayer film on the entrance / exit surface of the lens body 12. The film forming apparatus main body 41 holds the lens main body 12 and rotates and revolves the lens main body 12, first and second evaporation sources 41c and 41d capable of selectively switching the evaporation material, and both evaporation sources 41c and 41d. An aperture plate 41f is disposed above 41d to control the diffusion direction of the evaporating substance from both evaporation sources 41c and 41d, and a drive controller 41h to control the operation of the holder 41a and the evaporation sources 41c and 41d. In the film forming apparatus main body 41, the lens main body 12 can revolve around itself by the holder 41a, and the diffusion direction of the evaporated substance can be controlled by the opening provided in the aperture plate 41f. A well-balanced film can be formed on the entire surface of the lens body 12 and the antireflection film 14 having a uniform thickness can be formed over the entire surface of the lens body 12 (see FIG. 1). The two evaporation sources 41c and 41d are designed to be driven by the drive control device 41h so that the evaporation material can be switched at an appropriate timing, and two or more films having different refractive indexes can be sequentially laminated. Will be possible.
[0053]
The control device 45 is a computer including a CPU 45a, an input / output device 45b, a storage device 45c, a display device 45d, an interface 45e, and the like. Here, the CPU 45a can mutually exchange data with the input / output device 45b, the storage device 45c, the display device 45d, and the interface 45e. The CPU 45a reads out predetermined programs and data from the storage device 45c and the like based on instructions from the input / output device 45b, that is, the operator, and executes various processes based on these programs and data. Specifically, by activating the AR film design program, the design value of the film structure of the antireflection film 14 to be formed on the lens body 12 is calculated, and by activating the AR film production program, 41 is operated to form the antireflection film 14 having a film structure corresponding to the design value. The interface 45e has a role of interposing between the control device 45 and the film forming apparatus main body 41. For example, data related to the data is output to the CPU 45a.
[0054]
FIG. 13 is a flowchart for briefly explaining the outline of the AR film design program executed by the control device 45. First, lens data of each lens constituting the projection lens is extracted (step S11). The projection lens is not limited to the lens system 110 illustrated in FIG. 3, but may be composed of various lens elements, and is appropriately optically designed in advance so as to have a magnification, a resolution, and the like according to the purpose. Things. In this case, the projection lens is not limited to the lens, but may be a lens incorporating a flat glass. Next, an instruction from the operator is received using the input / output device 45b or the display device 45d, and it is determined which of automatic design and non-automatic design has been requested (step S12).
[0055]
When automatic design is selected in step S12, the incident angle range of each lens element on the image side from the pupil plane constituting the projection lens is calculated (step S21). For this incident angle range, ray tracing is performed on the projection lens, the incident angle range of each light beam passing through each point of the target lens element is calculated, and the incident angle representing the correlation between the distance from the center and the maximum incident angle The data is stored in the storage device 45c as a table.
[0056]
Next, the lens element having the maximum oblique incidence that gives the maximum incidence angle is selected as the target lens from the incidence angle table obtained in step S21 (step S22). Here, the target lens is a lens element that gives the negative incident angle characteristic shown in FIG. 2 and can be two or more. It is the purpose of this film design to compensate for the dimming of the peripheral part formed by other lenses or the like constituting the projection lens by the target lens.
[0057]
Next, the sum of the effects of oblique incidence by the remaining lens elements and the like excluding the target lens selected in step S22 is evaluated as transmittance variation in the pupil plane (step S23). Specifically, by performing ray tracing on the projection lens, the average incident angle at each point is determined for each lens element, and the decrease in transmittance corresponding to this average incident angle is defined as a two-dimensional distribution on the pupil plane. Then, the transmittance non-uniformity in the pupil plane is calculated as the sum of the transmittance decreases thus obtained. At this time, a conventional anti-reflection film is formed on the remaining lens elements, and the reflectance at normal incidence is almost 0%, which is the lowest, and the low reflectance is maintained up to a relatively large incident angle. . When a negative incident angle characteristic is given to only one surface of the target lens, the other surface of the target lens is also evaluated for the transmittance variation in the pupil plane.
[0058]
FIG. 14A is a graph showing an example of evaluating the transmittance unevenness in the pupil plane as a relationship between the radius (r) on the pupil plane and the transmittance variation (ΔT). It can be seen that the transmittance decreases as the radius increases with respect to the center through which the optical axis passes.
[0059]
Returning to FIG. 13, next, a transmittance correction target amount by the target lens is calculated (step S24). This corresponds to the calculation of the transmittance distribution of the high transmittance filter that eliminates the in-pupil transmittance unevenness obtained in step S23, and takes the product of the transmittance correction target amount and the in-pupil transmittance unevenness. As a result, a flat transmittance distribution when converted to the pupil plane can be achieved.
[0060]
FIG. 14B is a graph showing a calculation example of the transmittance correction target amount as a relationship between the radius (r) on the pupil plane and the transmittance variation (ΔT). It can be seen that it is necessary to decrease the transmittance as the radius increases with respect to the center through which the optical axis passes.
[0061]
Returning to FIG. 13, next, the assigned correction amount for the target lens is calculated (step S25). This is obtained by dividing the transmittance correction target amount obtained in step S24 into a portion corresponding to the number of surfaces of the target lens, and is a target amount of transmittance correction by an antireflection film formed on each surface. I have. For example, when the number of target lenses is one and the transmittance correction is performed by both of the pair of antireflection films formed on the pair of optical surfaces, each assigned correction amount is equal to the transmittance correction target amount obtained in step S24. Square root or approximately half. However, it goes without saying that the correction burden ratio by the two antireflection films is not limited to the above, but can be an appropriate ratio.
[0062]
FIG. 14C is a graph showing a calculation example of the assigned correction amount as a relationship between the radius (r) on the pupil plane and the transmittance variation (ΔT). Compared with the case of FIG. 14B, the change amount of the transmittance is a half value.
[0063]
Returning to FIG. 13, next, an optical design value of the antireflection film for achieving the assigned correction amount by the target lens is performed (step S26). More specifically, initial parameters such as an appropriate film configuration and an optical film thickness are set in advance as initial conditions of the antireflection film. This may be input by the operator, but may be appropriately selected in consideration of the wavelength used on the control device 45 side. Next, by performing ray tracing on the projection lens, the average incident angle at each point of the target lens is obtained, and the increase in transmittance generated by the anti-reflection film due to the average incident angle is displayed on the pupil plane. The calculated two-dimensional distribution is calculated, and the transmittance increase thus obtained is calculated as the achieved correction amount. Such an achieved correction amount is repeatedly calculated with correction parameters such as a new film configuration and an optical film thickness by gradually changing the initial parameters of the anti-reflection film, and is optimally approximated to the target correction amount in charge. The value is determined. For example, if the achieved correction amount is less than or equal to a root-mean-square value (RMS) that is a predetermined deviation amount from the assigned correction amount, the process can be ended. The calculation of the correction amount in charge as described above is repeated a number of times according to the number of target lenses and the number of surfaces thereof. The optimization simulation is repeated so that
[0064]
FIG. 14D is a graph showing the integrated value of the achieved correction amount and the transmittance variation in the pupil plane as a relationship between the radius (r) and the transmittance variation (ΔT) on the pupil plane. The two-dot chain line indicates the transmittance unevenness in the pupil plane, and the broken line indicates the integrated value of the achieved correction amount. The solid line shows the effect of the anti-reflection film, and shows the transmission characteristic after correcting the transmittance unevenness in the pupil plane by the integrated value of the two-dot chain line and the broken line, that is, the integrated value of the achieved correction amount. In the case where the projection lens is incorporated in a semiconductor exposure apparatus or the like, it is desirable that the transmission characteristics after such correction have a variation width of 3% or less.
[0065]
On the other hand, if automatic design is not selected in step S12 of FIG. 3, the operator is instructed to select any lens element constituting the projection lens as the target lens (step S31). At this time, since the objective is to correct the transmittance unevenness in the pupil plane, a lens element recognized as effective on the image side from the pupil plane is selected via the input / output device 45b.
[0066]
Next, the sum of the effects of oblique incidence due to the remaining lens elements and the like excluding the target lens selected in step S31 is evaluated as transmittance variation in the pupil plane (step S32). This processing is the same as the processing in step S23 described above.
[0067]
Next, the operator is instructed to input the transmittance correction target amount and the correction amount assigned by the target lens (step S33). In steps S24 and S25, the transmittance correction target amount and the charge correction amount are calculated based on the design value of the projection lens. In this case, the transmittance correction target amount and the charge correction amount are calculated based on the guess and intuition of an operator who is a person skilled in the art. The correction amount is set artificially.
[0068]
Finally, an optical design value of the antireflection film for achieving the assigned correction amount by the target lens is performed (step S34). This processing is the same as the processing in step S26 described above. In this process, the calculation of the correction amount in charge is repeated by the number of times according to the number of target lenses and the number of surfaces, and the sum of the correction amounts achieved by each anti-reflection film is optimized to become the transmittance correction target amount Is repeated.
[0069]
By designing the antireflection film as described above, it is possible to realize a projection lens with less transmittance unevenness in the pupil plane. The design value of the anti-reflection film obtained in this way is stored in the storage device 45c, and is used for the management of the film forming process by the film forming apparatus main body 41.
[0070]
[Third embodiment]
Hereinafter, a projection exposure apparatus according to a third embodiment of the present invention will be described with reference to the drawings.
[0071]
FIG. 15 shows a basic structure of a projection exposure apparatus using a lens whose structure and manufacturing have been described in the first embodiment and the like. The projection exposure apparatus is particularly applied to a projection exposure apparatus such as a stepper for projecting an image of a reticle pattern onto a wafer coated with a photoresist.
[0072]
As shown in FIG. 15, the projection exposure apparatus of this embodiment is provided as at least (1) a wafer stage 301 on which a substrate (wafer) W coated with a photosensitive agent can be placed on the surface 301a, and (2) exposure light. Optical system 150 that irradiates the pattern of the prepared mask (reticle R) with vacuum ultraviolet light having a different wavelength, (3) light source 180 for supplying exposure light to illumination optical system 150, (4) on substrate W Between the first surface P1 (object surface) on which the mask R for projecting the image of the pattern formed on the mask R is arranged, and the second surface P2 (image surface) matched with the surface of the substrate W The projection optical system 400 for transferring the pattern of the mask R onto the substrate W, and (5) a main control unit 500 for controlling and operating the entire system of the projection exposure apparatus.
[0073]
Here, the wafer stage 301 is driven by the stage drive system 300 to move the substrate W three-dimensionally with respect to the projection optical system 400. The illumination optical system 150 also includes an alignment optical system 151 for adjusting a relative position between the mask R and the substrate W. The mask R is a reticle stage that can move in parallel with the surface of the wafer stage 301. 201. The reticle exchange system 200 exchanges and transports the reticle (mask R) set on the reticle stage 201. Reticle exchange system 200 includes a stage driver for moving reticle stage 201 parallel to surface 301 a of wafer stage 301. The projection optical system 400 has an alignment optical system (not shown) applied to a scan type exposure apparatus.
[0074]
The projection exposure apparatus of this embodiment uses the lens whose structure and manufacture have been described in the first embodiment and the like. Specifically, the projection exposure apparatus shown in FIG. 15 uses the lens 10 of FIG. 1 or a modified lens thereof as the optical lens 153 of the illumination optical system 150 and / or the optical lens 401 of the projection optical system 400. Can be provided. In this case, since the transmittance unevenness can be prevented by the optical lens 401 and a high exposure resolution can be obtained, high-brightness and high-accuracy projection exposure can be performed in a projection exposure apparatus having a large NA.
[0075]
Although the present invention has been described with reference to the embodiment, the present invention is not limited to the above embodiment. For example, in the above embodiment, the antireflection films 14 and 15 have a three-layer structure, but are not limited to this, and may have two or less layers or four or more layers. At this time, from the viewpoint of optical admittance, it is usually easier to design an optical design of the first film formed on the lens body 12 from the formation of the low refractive index film. It is also possible to start with a film and stack sequentially on it.
[0076]
【The invention's effect】
As is apparent from the above description, the optical element according to the present invention incorporates the antireflection film having a negative characteristic in which the oblique incidence transmittance is relatively higher than the normal incidence transmittance. In addition, it is possible to suppress the occurrence of transmittance unevenness, in particular, the transmittance unevenness in the pupil plane, and to provide a projection lens or the like having good imaging characteristics.
[0077]
Further, according to the lens system according to the present invention, the distribution can be flattened by compensating for the transmittance non-uniformity caused by the optical member constituting the lens element of interest and other lens elements. The occurrence of transmittance unevenness such as transmittance unevenness can be suppressed, and a projection lens or the like having good imaging characteristics can be provided.
[0078]
Further, according to the lens system designing method according to the present invention, the transmittance unevenness caused by the optical members and other lens elements constituting the lens element of interest can be compensated and the distribution can be flattened. It is possible to suppress the occurrence of transmittance unevenness such as in-plane transmittance unevenness, and to provide a projection lens or the like having good imaging characteristics.
[0079]
Further, according to the projection exposure apparatus of the present invention, high-precision projection exposure can be performed by a projection optical system having good imaging characteristics with little unevenness in transmittance in a pupil plane in an ultraviolet region.
[0080]
Further, according to another projection exposure apparatus of the present invention, high-precision projection exposure can be performed by an illumination optical system having good illumination characteristics with less illuminance unevenness in an ultraviolet region.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a cross-sectional structure of a lens that is an optical element according to a first embodiment.
FIG. 2 is a graph conceptually illustrating transmittance characteristics of the lens of FIG.
FIG. 3 is a conceptual diagram illustrating a role of a lens 10 shown in FIG.
FIG. 4 is a configuration diagram of an antireflection film of each embodiment.
FIG. 5 is a reflection angle characteristic at 193 nm of the antireflection film of the first embodiment.
FIG. 6 shows transmission angle characteristics at 193 nm of the antireflection film of the first embodiment.
FIG. 7 shows reflection angle characteristics at 193 nm of the antireflection film of the second embodiment.
FIG. 8 shows transmission angle characteristics at 193 nm of the antireflection film of the second embodiment.
FIG. 9 shows reflection angle characteristics at 157 nm of the antireflection film of the third embodiment.
FIG. 10 shows transmission angle characteristics at 157 nm of the antireflection film of the third embodiment.
FIG. 11 shows reflection angle characteristics at 193 nm of the antireflection film of the fourth embodiment.
FIG. 12 is a block diagram showing an apparatus for manufacturing the lens shown in FIG. 1 according to a second embodiment.
13 is a flowchart illustrating an AR film design program executed by the control device shown in FIG.
FIGS. 14A to 14D are graphs for visually explaining a part of the processing in FIG. 13;
FIG. 15 is a configuration diagram illustrating a basic configuration of a projection exposure apparatus according to a third embodiment.
[Explanation of symbols]
Reference Signs List 10: lens, 10a: central portion, 10b: peripheral portion, 12: lens body, 12a, 12b: input / output surface, 14, 15: antireflection film, 41: film forming device main body, 41h: drive control device, 45: Control device, 45e interface, 110a to 110d lens element, IP image plane, OA optical axis, OP object plane, P1 surface, P2 surface, PP pupil surface

Claims (15)

A light-transmitting optical member;
An optical element formed on a predetermined entrance / exit surface of the optical member and having an antireflection film having optical characteristics such that an oblique incidence transmittance at a predetermined oblique incidence angle is higher than a normal incidence transmittance. The antireflection film has an optical characteristic in which the oblique incidence transmittance is 2% or more higher than the normal incidence transmittance when the predetermined oblique incidence angle is in a predetermined range of 30 ° or more. The optical element according to claim 1. The optical element according to claim 1, wherein the optical member is a lens body. The antireflection film includes a multilayer film in which a plurality of layers having different refractive indices are stacked, and a difference between oblique incidence transmittance and normal incidence transmittance is adjusted by setting an optical film thickness of the plurality of layers. The optical element according to claim 1, wherein the optical element is an optical element. A plurality of lens elements,
An anti-reflection film formed on a predetermined entrance / exit surface of at least one lens element of the plurality of lens elements; and a two-dimensional transmittance distribution for transmitted light with respect to the at least one lens element; A lens system comprising: a transmittance adjusting unit that adjusts according to an angle. 6. The lens system according to claim 5, wherein said transmittance adjusting means is an antireflection film having an optical characteristic such that an oblique incidence transmittance at a predetermined oblique incidence angle is higher than a normal incidence transmittance. 7. The lens system according to claim 6, wherein the at least one lens element is selected from one or more lens elements having a maximum oblique incident angle of transmitted light. 7. The lens system according to claim 6, wherein the lens system is a projection lens, and the at least one lens element is disposed closer to an exit side than a pupil plane of the projection lens. 9. The lens system according to claim 8, wherein the flatness of the transmittance unevenness is within 3% in a variation width. A method for designing a lens system according to any one of claims 5 to 9, wherein:
Selecting at least one target element to be determined for adjustment of transmittance distribution from the plurality of lens elements;
Calculating the incident angle range of the light beam incident on the target element,
Adjusting the optical characteristics of the antireflection film formed on the target element based on the incident angle range to determine whether the adjustment amount of the transmittance distribution is within a predetermined range. Design method. 11. The lens system according to claim 10, wherein the adjustment amount of the transmittance distribution is set to approximate an amount that cancels out an influence on the transmittance distribution by another lens element other than the target element. Design method. 12. The lens system according to claim 11, wherein the step of selecting the target element determines a lens element which has the greatest effect on transmittance distribution among lens elements constituting the lens system. Design method. A projection lens manufacturing method for manufacturing a lens based on data determined by the projection lens design method according to claim 1. An apparatus for projecting and exposing a pattern image of a mask onto a substrate using a projection optical system,
An illumination optical system that illuminates the mask with ultraviolet light as exposure light,
A projection exposure apparatus comprising: the optical element according to claim 1; and a projection optical system configured to form a pattern image of the mask on a substrate. An apparatus for projecting and exposing a pattern image of a mask onto a substrate using a projection optical system,
An illumination optical system including the optical element according to any one of claims 1 to 4, and illuminating the mask with ultraviolet light as exposure light.
A projection optical system for forming a pattern image of the mask on a substrate.

Images