JP2004198748A - Optical integrator, illumination optical device, exposure apparatus, and exposure method - Google Patents

Abstract

An optical integrator having a characteristic of minimizing the influence of a manufacturing error of a large number of minute refraction surfaces integrally formed by an etching process on an illuminance distribution.
A first optical member (8a) having a plurality of integrally formed first micro optical surfaces and an optically corresponding plurality of first micro optical surfaces are sequentially provided from a light incident side. And a second optical member (8b) having a plurality of second minute optical surfaces formed integrally with each other. The combined system of the first optical member and the second optical member has a rear focal point (85) in the Z direction at a predetermined distance behind the exit surface of the second optical member. The first optical member has a rear focal point (84) in the X direction in an optical path between the exit surface of the first optical member and the entrance surface of the second optical member.
[Selection diagram] FIG.

Description

【００２８】
表（１）、式（２）および式（３）を参照すると、第１部分系Ａにおける歪曲収差係数の非球面項Ｖ_aspA、および第２部分系Ｂにおける歪曲収差係数の非球面項Ｖ_aspBは、それぞれ次の式（５）および（６）で表わされる。
Ｖ_aspA＝０ （５）
Ｖ_aspB＝（γ−１）³・Δｎ・ｃ³・κ （６）
【００２９】
式（５）および（６）を参照すると、マイクロフライアイレンズＭＦの微小屈折面の面形状のばらつき（すなわち円錐係数κの変化）に起因する歪曲収差係数の非球面項の変化は、３次収差の範囲では第２部分系Ｂのみで発生することが分かる。次に、歪曲収差係数の非球面項の変化が照野Ｉにおける照度分布に与える影響を考える。第２部分系Ｂにおいて、曲率ｃと屈折率差Δｎとの間には、以下の式（７）に示す比例関係が成り立つ。
ｃ∝１／Δｎ （７）
【００３０】
３次収差の範囲では、照野Ｉにおける照度分布は、像高の二乗に比例して変化する。像高は、マイクロフライアイレンズＭＦの射出側の開口数ＮＡに比例する。したがって、式（５）〜（７）より、マイクロフライアイレンズＭＦの微小屈折面の面形状の変化に起因する歪曲収差の変化、ひいては照野（像面）Ｉ上での照度分布の変化の感度βは、以下の式（８）で表わされる。
β＝（γ−１）³・ＮＡ²／Δｎ² （８）
【００３１】
ちなみに、マイクロフライアイレンズＭＦが空気中に配置される場合、第２部分系Ｂを形成する光学材料の屈折率ｎとすれば、式（８）を次の式（８’）に示すように変形することができる。
β＝（γ−１）³・ＮＡ²／（ｎ−１）² （８’）
【００３２】
こうして、パラメータβの絶対値を小さくすることにより、マイクロフライアイレンズＭＦの微小屈折面の面形状のばらつきに起因する歪曲収差の変化を小さく抑えることができ、照野Ｉにおける照度分布が受ける影響を低減することができる。換言すれば、パラメータβの絶対値を小さくすることにより、たとえばエッチング加工により一体的に形成される多数の微小屈折面の製造誤差が照度分布に与える影響を小さく抑える特性を有するマイクロフライアイレンズ（オプティカルインテグレータ）ＭＦを実現することができる。
【００３３】
ところで、式（８’）を参照すると、マイクロフライアイレンズＭＦの微小屈折面の面形状のばらつきに起因する歪曲収差の変化を小さく抑えるためにパラメータβの絶対値を小さくするには、屈折力比γを１に近づければ良いことがわかる。しかしながら、単に屈折力比γを１に近づけると、マイクロフライアイレンズＭＦの射出面（すなわち第２部分系Ｂの射出面）におけるエネルギ密度が増大し、ひいては光エネルギ照射により第２部分系Ｂが破損する危険性が増大し、部品寿命が短くなる。
【００３４】
本発明では、具体的な実施形態を参照して後述するように、マイクロフライアイレンズＭＦ（第１部分系Ａと第２部分系Ｂとの合成系）が、第２部分系Ｂ（第２光学部材）の射出面よりも所定距離だけ後側に第１方向（光軸に垂直な面内において設定される所定の方向）に関する後側焦点を有する。また、第１部分系Ａ（第１光学部材）が、第１部分系Ａの射出面と第２部分系Ｂの入射面との間の光路中に第２方向（たとえば光軸に垂直な面内において第１方向と直交する方向）に関する後側焦点を有する。この場合、光軸を含む平面内において光軸対称な光学系であれば、前述の式（１）〜（８’）で述べた回転対称な光学系に関する議論と同様な議論が成立する。
【００３５】
本発明では、上述の構成を採用することにより、マイクロフライアイレンズＭＦの微小屈折面の面形状のばらつきに起因する歪曲収差の変化を小さく抑えるために屈折力比γを１に近づけても、マイクロフライアイレンズＭＦの射出面（すなわち第２部分系Ｂの射出面）を含む各光学面におけるエネルギ密度を小さく抑えることができ、ひいては光エネルギ照射による第２部分系Ｂや第１部分系Ａの破損を回避して十分に長い部品寿命を確保することができる。
【００３６】
また、式（８’）を参照すると、パラメータβの絶対値を小さくするには、第２部分系Ｂを形成する光学材料の屈折率ｎを大きくすれば良いことがわかる。ただし、光学材料の屈折率の増大に伴ってコストも増大し易いので、第２部分系Ｂのみに屈折率の高い光学材料を用いるのが現実的である。したがって、本発明では、第１部分系Ａ（第１光学部材）を形成する光学材料の屈折率ｎａよりも第２部分系Ｂ（第２光学部材）を形成する光学材料の屈折率ｎｂの方を大きく設定することが好ましい。
【００３７】
この場合、本発明の効果を良好に発揮するには、屈折率ｎａおよび屈折率ｎｂが０．０５≦ｎｂ−ｎａの条件を満足することが好ましい。具体的には、たとえば３００ｎｍ以下の波長を有する光に対して、第１部分系Ａを石英ガラスまたは蛍石で形成する場合、第２部分系Ｂを酸化マグネシウム、ルビー、サファイア、結晶水晶、または石英ガラスで形成することが好ましい。また、第１部分系Ａを蛍石で形成する場合、第２部分系Ｂを石英ガラスで形成することが好ましい。
【００３８】
本発明の実施形態を、添付図面に基づいて説明する。
図３は、本発明の実施形態にかかる照明光学装置を備えた露光装置の構成を概略的に示す図である。図３において、感光性基板であるウェハＷの法線方向に沿ってＺ軸を、ウェハ面内において図３の紙面に平行な方向にＹ軸を、ウェハ面内において図３の紙面に垂直な方向にＸ軸をそれぞれ設定している。なお、図３では、照明光学装置が輪帯照明を行うように設定されている。
【００３９】
図３の露光装置は、露光光（照明光）を供給するための光源１として、たとえば２４８ｎｍの波長の光を供給するＫｒＦエキシマレーザー光源または１９３ｎｍの波長の光を供給するＡｒＦエキシマレーザー光源を備えている。光源１からＺ方向に沿って射出されたほぼ平行な光束は、Ｘ方向に沿って細長く延びた矩形状の断面を有し、一対のレンズ２ａおよび２ｂからなるビームエキスパンダー２に入射する。各レンズ２ａおよび２ｂは、図３の紙面内（ＹＺ平面内）において負の屈折力および正の屈折力をそれぞれ有する。したがって、ビームエキスパンダー２に入射した光束は、図３の紙面内において拡大され、所定の矩形状の断面を有する光束に整形される。
【００４０】
整形光学系としてのビームエキスパンダー２を介したほぼ平行な光束は、折り曲げミラー３でＹ方向に偏向された後、回折光学素子４を介して、アフォーカルズームレンズ５に入射する。一般に、回折光学素子は、ガラス基板に露光光（照明光）の波長程度のピッチを有する段差を形成することによって構成され、入射ビームを所望の角度に回折する作用を有する。具体的には、回折光学素子４は、矩形状の断面を有する平行光束が入射した場合に、そのファーフィールド（またはフラウンホーファー回折領域）に円形状の光強度分布を形成する機能を有する。したがって、回折光学素子４を介した光束は、アフォーカルズームレンズ５の瞳位置に円形状の光強度分布、すなわち円形状の断面を有する光束を形成する。
【００４１】
なお、回折光学素子４は、照明光路から退避可能に構成されている。アフォーカルズームレンズ５は、アフォーカル系（無焦点光学系）を維持しながら所定の範囲で倍率を連続的に変化させることができるように構成されている。アフォーカルズームレンズ５を介した光束は、輪帯照明用の回折光学素子６に入射する。アフォーカルズームレンズ５は、回折光学素子４の発散原点と回折光学素子６の回折面とを光学的にほぼ共役に結んでいる。そして、回折光学素子６の回折面またはその近傍の面の一点に集光する光束の開口数は、アフォーカルズームレンズ５の倍率に依存して変化する。
【００４２】
輪帯照明用の回折光学素子６は、平行光束が入射した場合に、そのファーフィールドにリング状の光強度分布を形成する機能を有する。なお、回折光学素子６は、照明光路に対して挿脱自在に構成され、且つ４極照明用の回折光学素子６０や円形照明用の回折光学素子６１と切り換え可能に構成されている。回折光学素子６を介した光束は、ズームレンズ７に入射する。ズームレンズ７の後側焦点面の近傍には、光源側から順に第１フライアイ部材８ａと第２フライアイ部材８ｂとからなるマイクロフライアイレンズ８の入射面（すなわち第１フライアイ部材８ａの入射面）が位置決めされている。なお、マイクロフライアイレンズ８は入射光束に基づいて多数光源を形成する波面分割型のオプティカルインテグレータとして機能するが、その詳細な構成および作用については後述する。
【００４３】
上述したように、回折光学素子４を介してアフォーカルズームレンズ５の瞳位置に形成される円形状の光強度分布からの光束は、アフォーカルズームレンズ５から射出された後、様々な角度成分を有する光束となって回折光学素子６に入射する。したがって、回折光学素子６を介した光束は、ズームレンズ７の後側焦点面に（ひいてはマイクロフライアイレンズ８の入射面に）、たとえば光軸ＡＸを中心とした輪帯状の照野を形成する。
【００４４】
マイクロフライアイレンズ８の入射面に形成される輪帯状の照野の外径は、ズームレンズ７の焦点距離に依存して変化する。このように、ズームレンズ７は、回折光学素子６とマイクロフライアイレンズ８の入射面とを実質的にフーリエ変換の関係に結んでいる。マイクロフライアイレンズ８に入射した光束は二次元的に分割され、その後側焦点面には入射光束によって形成される照野と同じ輪帯状の多数光源（以下、「二次光源」という）が形成される。
【００４５】
マイクロフライアイレンズ８の後側焦点面に形成された輪帯状の二次光源からの光束は、コンデンサー光学系９の集光作用を受けた後、所定のパターンが形成されたマスクＭを重畳的に照明する。マスクＭのパターンを透過した光束は、投影光学系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。こうして、投影光学系ＰＬの光軸ＡＸと直交する平面（ＸＹ平面）内においてウェハＷを二次元的に駆動制御しながら一括露光またはスキャン露光を行うことにより、ウェハＷの各露光領域にはマスクＭのパターンが逐次露光される。
【００４６】
なお、一括露光では、いわゆるステップ・アンド・リピート方式にしたがって、ウェハの各露光領域に対してマスクパターンを一括的に露光する。この場合、マスクＭ上での照明領域の形状は正方形に近い矩形状となる。一方、スキャン露光では、いわゆるステップ・アンド・スキャン方式にしたがって、マスクおよびウェハを投影光学系に対して相対移動させながらウェハの各露光領域に対してマスクパターンをスキャン露光する。この場合、マスクＭ上での照明領域の形状は短辺と長辺との比がたとえば１：３の矩形状となる。
【００４７】
本実施形態では、アフォーカルズームレンズ５の倍率が変化すると、輪帯状の二次光源の中心高さ（円形状の中心線の光軸ＡＸからの距離）が変化することなく、その幅（外径（直径）と内径(直径)との差の１／２）だけが変化する。すなわち、アフォーカルズームレンズ５の倍率を変化させることにより、輪帯状の二次光源の大きさ（外径）およびその形状（輪帯比：内径／外径）をともに変更することができる。
【００４８】
また、ズームレンズ７の焦点距離が変化すると、輪帯状の二次光源の輪帯比が変化することなく、中心高さおよびその幅がともに変化する。すなわち、ズームレンズ７の焦点距離を変化させることにより、輪帯状の二次光源の輪帯比を変更することなくその外径を変更することができる。以上より、本実施形態では、アフォーカルズームレンズ５の倍率とズームレンズ７の焦点距離とを適宜変化させることにより、輪帯状の二次光源の外径を変化させることなくその輪帯比だけを変更することができる。
【００４９】
前述したように、回折光学素子６は、照明光路に対して挿脱自在に構成され、且つ４極照明用の回折光学素子６０や円形照明用の回折光学素子６１と切り換え可能に構成されている。以下、回折光学素子６に代えて回折光学素子６０を照明光路中に設定することによって得られる４極照明について説明する。４極照明用の回折光学素子６０は、平行光束が入射した場合に、そのファーフィールドに４点状の光強度分布を形成する機能を有する。したがって、回折光学素子６０を介した光束は、マイクロフライアイレンズ８の入射面に、たとえば光軸ＡＸを中心とした４つの円形状の照野からなる４極状の照野を形成する。その結果、マイクロフライアイレンズ８の後側焦点面にも、その入射面に形成された照野と同じ４極状の二次光源が形成される。
【００５０】
４極照明においても輪帯照明の場合と同様に、アフォーカルズームレンズ５の倍率を変化させることにより、４極状の二次光源の外径（４つの円形状の面光源に外接する円の直径）および輪帯比（４つの円形状の面光源に内接する円の直径／４つの円形状の面光源に外接する円の直径）をともに変更することができる。また、ズームレンズ７の焦点距離を変化させることにより、４極状の二次光源の輪帯比を変更することなくその外径を変更することができる。その結果、アフォーカルズームレンズ５の倍率とズームレンズ７の焦点距離とを適宜変化させることにより、４極状の二次光源の外径を変化させることなくその輪帯比だけを変更することができる。
【００５１】
次いで、回折光学素子４を照明光路から退避させるとともに、回折光学素子６または６０に代えて円形照明用の回折光学素子６１を照明光路中に設定することによって得られる円形照明について説明する。この場合、アフォーカルズームレンズ５には光軸ＡＸに沿って矩形状の断面を有する光束が入射する。アフォーカルズームレンズ５に入射した光束は、その倍率に応じて拡大または縮小され、矩形状の断面を有する光束のまま光軸ＡＸに沿ってアフォーカルズームレンズ５から射出され、回折光学素子６１に入射する。
【００５２】
ここで、円形照明用の回折光学素子６１は、回折光学素子４と同様に、矩形状の断面を有する平行光束が入射した場合に、ファーフィールドに円形状の光強度分布を形成する機能を有する。したがって、回折光学素子６１により形成された円形光束は、ズームレンズ７を介して、マイクロフライアイレンズ８の入射面において光軸ＡＸを中心とした円形状の照野を形成する。その結果、マイクロフライアイレンズ８の後側焦点面にも、光軸ＡＸを中心とした円形状の二次光源が形成される。この場合、アフォーカルズームレンズ５の倍率またはズームレンズ７の焦点距離を変化させることにより、円形状の二次光源の外径を適宜変更することができる。
【００５３】
図４は、本実施形態にかかるマイクロフライアイレンズの全体構成を概略的に示す斜視図である。また、図５は、本実施形態にかかるマイクロフライアイレンズの作用を説明する図である。図４を参照すると、本実施形態のマイクロフライアイレンズ８は、光源側に配置された第１フライアイ部材８ａとマスク側に配置された第２フライアイ部材８ｂとから構成されている。
【００５４】
第１フライアイ部材８ａの光源側の面および第２フライアイ部材８ｂの光源側の面には、Ｘ方向に沿って配列されたシリンドリカルレンズ群８１ａおよび８１ｂがそれぞれピッチｐ１で形成されている。一方、第１フライアイ部材８ａのマスク側の面および第２フライアイ部材８ｂのマスク側の面には、Ｚ方向に沿って配列されたシリンドリカルレンズ群８２ａおよび８２ｂがそれぞれピッチｐ２で形成されている。なお、図３では、図面の明瞭化のために、マイクロレンズアレイ８に形成されたシリンドリカルレンズの数を実際よりも非常に少なく表している。
【００５５】
マイクロフライアイレンズ８のＸ方向に関する屈折作用（すなわちＸＹ平面に関する屈折作用）に着目すると、光軸ＡＸに沿って入射した平行光束は、第１フライアイ部材８ａの光源側に形成されたシリンドリカルレンズ群８１ａによってＸ方向に沿ってピッチｐ１で波面分割される。そして、図５（ａ）に示すように、シリンドリカルレンズ群８１ａの微小屈折面９１ａに入射した平行光束は、微小屈折面９１ａで集光作用を受けた後、第１フライアイ部材８ａの射出面と第２フライアイ部材８ｂの入射面との間の光路中においてＸ方向に関する第１フライアイ部材８ａの後側焦点８４に集光する。後側焦点８４に一旦集光した発散光束は、第２フライアイ部材８ｂの光源側に形成されたシリンドリカルレンズ群８２ｂにおいて微小屈折面９１ａに対応する微小屈折面９２ａで集光作用を受けた後、第２フライアイ部材８ｂから射出される。
【００５６】
一方、マイクロフライアイレンズ８のＺ方向に関する屈折作用（すなわちＺＹ平面に関する屈折作用）に着目すると、光軸ＡＸに沿って入射した平行光束は、第１フライアイ部材８ａのマスク側に形成されたシリンドリカルレンズ群８２ａによってＺ方向に沿ってピッチｐ２で波面分割される。そして、図５（ｂ）に示すように、シリンドリカルレンズ群８２ａの微小屈折面９２ａに入射した平行光束は、微小屈折面９２ａで集光作用を受けた後、第２フライアイ部材８ｂのマスク側に形成されたシリンドリカルレンズ群８２ｂにおいて微小屈折面９２ａに対応する微小屈折面９２ｂで集光作用を受け、Ｚ方向に関するマイクロフライアイレンズ８の後側焦点８５に集光する。
【００５７】
次の表（２）に、本実施形態にかかるマイクロフライアイレンズ８の諸元の値を掲げる。表（２）において、ｍは光源からの光学面の順序を表わす面番号を、φｘはＸ方向に関する各光学面の屈折力（パワー）を、φｚはＺ方向に関する各光学面の屈折力を、ｄは各光学面の軸上間隔すなわち面間隔を、ｎは使用光に対する屈折率を、ｈｘはＸ方向に関する各光学面での光線高を、αｘはＸ方向に関する各光学面での傾角（当該面を通過した光線についての傾角）を、ｈｚはＺ方向に関する各光学面での光線高を、αｚはＺ方向に関する各光学面での傾角を、ＥｘはＸ方向に関する各光学面でのエネルギ密度比を、ＥｚはＺ方向に関する各光学面でのエネルギ密度比を、Ｅは各光学面でのエネルギ密度比をそれぞれ示している。
【００５８】
なお、エネルギ密度比Ｅｘ、ＥｚおよびＥは、第１面すなわち第１フライアイ部材８ａの入射面（マイクロフライアイレンズ８の入射面）におけるエネルギ密度を１に規格化したときの各光学面におけるエネルギ密度である。また、表（２）において、ｆｘはＸ方向に関するマイクロフライアイレンズ８の焦点距離を、ｆｚはＺ方向に関するマイクロフライアイレンズ８の焦点距離を、ｄｘはＸ方向に関するマイクロフライアイレンズ８のバックフォーカスを、ｄｚはＺ方向に関するマイクロフライアイレンズ８のバックフォーカスをそれぞれ示している。
【００５９】
【表２】

【００６０】
したがって、本実施形態では、Ｘ方向に関する第１フライアイ部材８ａの屈折力φ11、Ｘ方向に関する第２フライアイ部材８ｂの屈折力φ12、Ｘ方向に関する屈折力比γ１＝φ11／φ12、Ｚ方向に関する第１フライアイ部材８ａの屈折力φ21、Ｚ方向に関する第２フライアイ部材８ｂの屈折力φ22、およびＺ方向に関する屈折力比γ２＝φ21／φ22、Ｘ方向に関するパラメータβのファクター｜（γ１−１）³｜、およびＺ方向に関するパラメータβのファクター｜（γ２−１）³｜は、次の表（３）に示す通りになる。
【００６１】
【表３】
φ11＝０．５８８２３５
φ12＝０．５
γ１＝φ11／φ12＝１．１７６４７
φ21＝０．６６６６６３
φ22＝１
γ２＝φ21／φ22＝０．６６６６６３
｜（γ１−１）³｜＝０．００５５
｜（γ２−１）³｜＝０．０３７０３８
【００６２】
図６は、本実施形態の比較例にかかるマイクロフライアイレンズの作用を説明する図である。図６の比較例では、各光学面の軸上間隔すなわち面間隔ｄ、使用光に対する屈折率ｎ、Ｘ方向に関するマイクロフライアイレンズ（第１フライアイ部材１０８ａ＋第２フライアイ部材１０８ｂ）の焦点距離ｆｘ、Ｚ方向に関するマイクロフライアイレンズの焦点距離ｆｚを含む基本的なデータを図５の実施形態と同じに設定している。しかしながら、図６の比較例では、従来技術にしたがってマイクロフライアイレンズのＸ方向に関する後側焦点とＺ方向に関する後側焦点とを第２フライアイ部材１０８ｂの射出面よりも所定距離だけ後側においてほぼ一致させている点が図５の実施形態と相違している。
【００６３】
次の表（４）に、比較例にかかるマイクロフライアイレンズの諸元の値を掲げる。表（４）における表記は、表（２）の表記と同様である。
【００６４】
【表４】

【００６５】
したがって、図６の比較例では、Ｘ方向に関する第１フライアイ部材８ａの屈折力φ11、Ｘ方向に関する第２フライアイ部材８ｂの屈折力φ12、Ｘ方向に関する屈折力比γ１＝φ11／φ12、Ｚ方向に関する第１フライアイ部材８ａの屈折力φ21、Ｚ方向に関する第２フライアイ部材８ｂの屈折力φ22、およびＺ方向に関する屈折力比γ２＝φ21／φ22、Ｘ方向に関するパラメータβのファクター｜（γ１−１）³｜、およびＺ方向に関するパラメータβのファクター｜（γ２−１）³｜は、次の表（５）に示す通りになる。
【００６６】
【表５】
φ11＝０．２５３７３２
φ12＝０．５
γ１＝φ11／φ12＝０．５０７４６４
φ21＝０．５１４９３
φ22＝１
γ２＝φ21／φ22＝０．５１４９３
｜（γ１−１）³｜＝０．１１９４８５
｜（γ２−１）³｜＝０．１１４１３３
【００６７】
以上のように、本実施形態では、マイクロフライアイレンズ８（第１フライアイ部材８ａと第２フライアイ部材８ｂとの合成系）が、第２フライアイ部材８ｂの射出面よりも所定距離だけ後側にＺ方向に関する後側焦点８５を有する。また、第１フライアイ部材８ａが、第１フライアイ部材８ａの射出面と第２フライアイ部材８ｂの入射面との間の光路中にＸ方向に関する後側焦点８４を有する。
【００６８】
その結果、本実施形態では、第１フライアイ部材８ａの射出面および第２フライアイ部材８ｂの入射面においてエネルギ密度比がＥ≒８．５で最大値になっており、第２フライアイ部材８ｂの射出面においてエネルギ密度比がＥ≒７．０で最大値に近い値になっている。すなわち、本実施形態では、第１フライアイ部材８ａの射出面と第２フライアイ部材８ｂの入射面と第２フライアイ部材８ｂの射出面とでエネルギ密度の負担がある程度均等化されている。
【００６９】
これに対し、マイクロフライアイレンズのＸ方向に関する後側焦点とＺ方向に関する後側焦点とがほぼ一致する比較例では、第２フライアイ部材８ｂの射出面においてエネルギ密度比がＥ＝８．５で最大値になっており、他の光学面におけるエネルギ密度比はＥ＝１〜２．７程度で最大値よりもかなり小さい値になっている。すなわち、比較例では、エネルギ密度の負担が第２フライアイ部材８ｂの射出面（マイクロフライアイレンズの射出面）のみに集中している。
【００７０】
また、エネルギ密度比の最大値が互いに等しくなるように設定された本実施形態と比較例とを比べると、本実施形態におけるＸ方向に関するパラメータβのファクター｜（γ１−１）³｜は比較例におけるＸ方向に関するパラメータβのファクター｜（γ１−１）³｜の約１／２２になっており、本実施形態におけるＺ方向に関するパラメータβのファクター｜（γ２−１）³｜は比較例におけるＺ方向に関するパラメータβのファクター｜（γ２−１）³｜の約１／３になっている。
【００７１】
したがって、パラメータβの他のファクターＮＡ²および（ｎ−１）²が同じであれば、本実施形態では比較例に比して、マイクロフライアイレンズの微小屈折面の面形状のばらつきに起因する歪曲収差の変化を小さく抑えることができる。換言すれば、パラメータβの他のファクターＮＡ²および（ｎ−１）²が同じ場合、比較例において本実施形態と同等に歪曲収差の変化を小さく抑えるために屈折力比γ１およびγ２をさらに１に近づけると、第２フライアイ部材８ｂの射出面におけるエネルギ密度比が上述の最大値よりもさらに増大することになる。
【００７２】
以上のように、本実施形態では、マイクロフライアイレンズ８のＺ方向に関する後側焦点と第１フライアイ部材８ａのＸ方向に関する後側焦点とについて上述の構成を採用することにより、マイクロフライアイレンズ８の微小屈折面の面形状のばらつきに起因する歪曲収差の変化を小さく抑えるためにパラメータβのファクター｜（γ１−１）³｜および｜（γ２−１）³｜を小さく設定しても（屈折力比γ１およびγ２を１に近づけても）、マイクロフライアイレンズ８の射出面（すなわち第２フライアイ部材８ｂの射出面）を含む各光学面におけるエネルギ密度を小さく抑えることができ、ひいては光エネルギ照射による第２フライアイ部材８ｂおよび第１フライアイ部材８ａの破損を回避して十分に長い部品寿命を確保することができる。
【００７３】
なお、本実施形態において、第１フライアイ部材８ａの射出面と第２フライアイ部材８ｂの入射面と第２フライアイ部材８ｂの射出面とでエネルギ密度の負担をできるだけ均等化してエネルギ密度の最大値を小さく抑えるには、第１フライアイ部材８ａの射出面と第２フライアイ部材８ｂの入射面との中間面と第１フライアイ部材８ａの射出面との間の光路中に第１フライアイ部材８ａのＸ方向に関する後側焦点８４が存在するように構成すること、および第１フライアイ部材８ａの射出面におけるエネルギ密度と第２フライアイ部材８ｂの入射面におけるエネルギ密度とをほぼ同じに設定することが好ましい。
【００７４】
また、本実施形態において、マイクロフライアイレンズ８の微小屈折面の面形状のばらつきに起因する歪曲収差の変化を十分に小さく抑えるには、パラメータβのファクター｜（γ１−１）³｜および｜（γ２−１）³｜が次の条件式（ａ）および（ｂ）を満足することが好ましい。
｜（γ１−１）³｜＜０．１ （ａ）
｜（γ２−１）³｜＜０．１ （ｂ）
【００７５】
なお、本実施形態においては、マイクロフライアイレンズ８に平行光束が入射したときのＸ方向に関する集光点（Ｘ方向に関する光源形成点）８４とＺ方向に関する集光点（Ｚ方向に関する光源形成点）８５とが異なるが、集光点がＸ方向とＺ方向とで異なる構成がマスクＭ上（ひいてはウェハＷ上）での照度分布に与える影響を小さく抑えるために、第１フライアイ部材８ａのＸ方向に関する後側焦点８４とマイクロフライアイレンズ８のＺ方向に関する後側焦点８５との軸上距離を、マイクロフライアイレンズ８からの光をマスクＭへ導くための導光光学系（コンデンサー光学系９）の焦点距離の５％以下に設定することが好ましい。
【００７６】
ところで、スキャン露光型の露光装置の場合、マスクＭ上には細長い矩形状の照明領域が形成され、この矩形状の照明領域の短辺方向すなわち走査方向に沿ってマスクＭおよびウェハＷを投影光学系ＰＬに対して相対移動させることにより、マスクＭのパターンをウェハＷに投影露光することになる。この場合、マイクロフライアイレンズ８の射出側の開口数ＮＡを、走査方向よりも非走査方向（照明領域の長辺方向）の方に大きく設定するのが通常である。したがって、矩形状の照明領域の長辺方向がマイクロフライアイレンズ８におけるＺ方向に光学的に対応してマスクＭ上においてＹ方向に一致し、矩形状の照明領域の短辺方向がマイクロフライアイレンズ８におけるＸ方向に光学的に対応してマスクＭ上においてＸ方向に一致するように設定することが好ましい。
【００７７】
なお、上述の実施形態では、各微小屈折面が円筒面状に形成されたマイクロフライアイレンズに対して本発明を適用している。しかしながら、これに限定されることなく、一般に各微小屈折面が一方向にのみ曲率を有する曲面状（トーリック形状）に形成されたマイクロフライアイレンズに対して本発明を適用する変形例も可能である。
【００７８】
上述の実施形態にかかる露光装置では、照明光学装置によってマスク（レチクル）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、上述の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７のフローチャートを参照して説明する。
【００７９】
先ず、図７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、上述の実施形態の露光装置を用いて、マスク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。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。
【００８０】
また、上述の実施形態の露光装置では、プレート（ガラス基板）上に所定のパターン（回路パターン、電極パターン等）を形成することによって、マイクロデバイスとしての液晶表示素子を得ることもできる。以下、図８のフローチャートを参照して、このときの手法の一例につき説明する。図８において、パターン形成工程４０１では、上述の実施形態の露光装置を用いてマスクのパターンを感光性基板（レジストが塗布されたガラス基板等）に転写露光する、所謂光リソグラフィー工程が実行される。この光リソグラフィー工程によって、感光性基板上には多数の電極等を含む所定パターンが形成される。その後、露光された基板は、現像工程、エッチング工程、レジスト剥離工程等の各工程を経ることによって、基板上に所定のパターンが形成され、次のカラーフィルター形成工程４０２へ移行する。
【００８１】
次に、カラーフィルター形成工程４０２では、Ｒ（Red）、Ｇ（Green）、Ｂ（Blue）に対応した３つのドットの組がマトリックス状に多数配列されたり、またはＲ、Ｇ、Ｂの３本のストライプのフィルターの組を複数水平走査線方向に配列したカラーフィルターを形成する。そして、カラーフィルター形成工程４０２の後に、セル組み立て工程４０３が実行される。セル組み立て工程４０３では、パターン形成工程４０１にて得られた所定パターンを有する基板、およびカラーフィルター形成工程４０２にて得られたカラーフィルター等を用いて液晶パネル（液晶セル）を組み立てる。セル組み立て工程４０３では、例えば、パターン形成工程４０１にて得られた所定パターンを有する基板とカラーフィルター形成工程４０２にて得られたカラーフィルターとの間に液晶を注入して、液晶パネル（液晶セル）を製造する。
【００８２】
その後、モジュール組み立て工程４０４にて、組み立てられた液晶パネル（液晶セル）の表示動作を行わせる電気回路、バックライト等の各部品を取り付けて液晶表示素子として完成させる。上述の液晶表示素子の製造方法によれば、極めて微細な回路パターンを有する液晶表示素子をスループット良く得ることができる。
【００８３】
なお、上述の実施形態では、コンデンサー光学系９によって二次光源からの光を集光して重畳的にマスクＭを照明している。しかしながら、これに限定されることなく、コンデンサー光学系９とマスクＭとの間の光路中に、照明視野絞り（マスクブラインド）と、この照明視野絞りの像をマスクＭ上に形成するリレー光学系とを配置しても良い。この場合、コンデンサー光学系９は、二次光源からの光を集光して重畳的に照明視野絞りを照明することになり、リレー光学系は照明視野絞りの開口部（光透過部）の像をマスクＭ上に形成することになる。
【００８４】
また、上述の実施形態では、露光光としてＫｒＦエキシマレーザー光（波長：２４８ｎｍ）やＡｒＦエキシマレーザー光（波長：１９３ｎｍ）を用いているが、これに限定させることなく、たとえば３００ｎｍ以下の波長を有する露光光に対して本発明を適用することもできる。さらに、上述の実施形態では、照明光学装置を備えた投影露光装置を例にとって本発明を説明したが、マスク以外の被照射面を照明するための一般的な照明光学装置に本発明を適用することができることは明らかである。
【００８５】
【発明の効果】
以上説明したように、本発明のオプティカルインテグレータでは、第１光学部材と第２光学部材との合成系が第２光学部材の射出面よりも所定距離だけ後側に第１方向に関する後側焦点を有し、第１光学部材が第１光学部材の射出面と第２光学部材の入射面との間の光路中に第２方向に関する後側焦点を有する。この構成に基づいて、オプティカルインテグレータの微小屈折面の面形状のばらつきに起因する歪曲収差の変化を小さく抑えるために第１光学部材と第２光学部材との屈折力比γを１に近づけても、各光学面におけるエネルギ密度を小さく抑えることができ、ひいては光エネルギ照射による光学部材の破損を回避して十分に長い部品寿命を確保することができる。
【００８６】
すなわち、本発明のオプティカルインテグレータでは、たとえばエッチング加工により一体的に形成される微小屈折面の面形状のばらつきに起因する歪曲収差の変化を小さく抑え、ひいては被照射面における照度分布が受ける影響を低減することができる。したがって、本発明の照明光学装置では、微小屈折面の製造誤差が照度分布に与える影響が小さく抑えられたオプティカルインテグレータを用いて、所望の照明条件で被照射面を照明することができる。また、本発明の露光装置および露光方法では、所望の照明条件で被照射面を照明することのできる高性能な照明光学装置を用いて、良好な照明条件の下で良好な投影露光を行うことにより良好な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】本発明の基本的原理を説明する図である。
【図２】図１のマイクロフライアイレンズにおける光学的特性を説明する図である。
【図３】本発明の実施形態にかかる照明光学装置を備えた露光装置の構成を概略的に示す図である。
【図４】本実施形態にかかるマイクロフライアイレンズの全体構成を概略的に示す斜視図である。
【図５】本実施形態にかかるマイクロフライアイレンズの作用を説明する図である。
【図６】本実施形態の比較例にかかるマイクロフライアイレンズの作用を説明する図である。
【図７】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フローチャートである。
【図８】マイクロデバイスとしての液晶表示素子を得る際の手法のフローチャートである。
【符号の説明】
Ｓ，１ 光源
Ｃ１，Ｃ２，９ コンデンサー光学系
ＭＦ，８ マイクロフライアイレンズ
４ 回折光学素子
５ アフォーカルズームレンズ
６，６０，６１ 回折光学素子
７ ズームレンズ
８ａ 第１フライアイ部材
８ｂ 第２フライアイ部材
Ｍ マスク
ＰＬ 投影光学系
Ｗ ウェハ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical integrator, an illumination optical device, an exposure device, and an exposure method, and particularly to an illumination device suitable for an exposure device for manufacturing a micro device such as a semiconductor device, an imaging device, a liquid crystal display device, and a thin film magnetic head by a lithography process. The present invention relates to an optical device.
[0002]
[Prior art]
In a typical exposure apparatus of this type, a light beam emitted from a light source enters a fly-eye lens, and forms a secondary light source including a large number of light sources on a rear focal plane. The light flux from the secondary light source is restricted via an aperture stop arranged near the rear focal plane of the fly-eye lens, and then enters the condenser lens. The aperture stop limits the shape or size of the secondary light source to a desired shape or size according to a desired illumination condition (exposure condition).
[0003]
The light beam condensed by the condenser lens illuminates the mask on which the predetermined pattern is formed in a superimposed manner. The light transmitted through the mask pattern forms an image on the wafer via the projection optical system. Thus, the mask pattern is projected and exposed (transferred) on the wafer. The pattern formed on the mask is highly integrated, and it is indispensable to obtain a uniform illuminance distribution on the wafer in order to accurately transfer this fine pattern onto the wafer.
[0004]
[Problems to be solved by the invention]
In the exposure apparatus having the above configuration, it is necessary to set the number of minute lens elements constituting the fly-eye lens as large as possible in order to increase the uniformity of the illuminance distribution. Further, in order to avoid a loss of light amount in the aperture stop, it is necessary to form a secondary light source having a shape close to a desired shape. For this reason, for example, it is conceivable to set the size of the minute lens element constituting the fly-eye lens to be very small, that is, to use a micro fly-eye lens.
[0005]
Here, the fly-eye lens is configured by arranging a large number of lens elements vertically and horizontally and densely, whereas the micro-fly-eye lens is configured by integrally forming a large number of minute refraction surfaces. That is, a fly-eye lens is formed by combining and arranging a large number of single-polished lens elements, while a micro-fly-eye lens is formed by, for example, MEMS technology (lithography + etching) on a parallel flat glass plate. To form a large number of micro-refractive surfaces.
[0006]
Therefore, in the manufacture of a fly-eye lens, it is necessary to inspect the refraction surface shape of the polished lens element, select a lens element that satisfies the standard, and assemble using only the lens element having the refraction surface formed with high precision. it can. However, micro fly-eye lenses are required to manufacture all micro-refractive surfaces at the same time by etching, which makes it difficult to obtain a good surface shape compared to polishing. Is considerably lower.
[0007]
The present invention has been made in view of the above-described problems, and provides an optical integrator having a characteristic of minimizing the influence of manufacturing errors of a large number of minute refraction surfaces integrally formed by etching processing on the illuminance distribution. The purpose is to do. In addition, the present invention provides a high-performance illumination optical device capable of illuminating a surface to be illuminated under desired illumination conditions using an optical integrator in which the influence of a manufacturing error of a micro-refractive surface on an illuminance distribution is reduced. The purpose is to provide. Further, the present invention provides an exposure apparatus and an exposure apparatus capable of performing good projection exposure under good illumination conditions by using a high-performance illumination optical device capable of illuminating a surface to be irradiated under desired illumination conditions. The aim is to provide a method.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, in a first embodiment of the present invention, a first optical member having a plurality of first minute optical surfaces formed integrally in order from a light incident side; A wavefront splitting optical integrator comprising: a second optical member having a plurality of second minute optical surfaces integrally formed so as to optically correspond to the optical surface;
The combined system of the first optical member and the second optical member has a rear focal point in the first direction at a predetermined distance behind the exit surface of the second optical member,
The first optical member has a rear focal point in a second direction different from the first direction in an optical path between an exit surface of the first optical member and an entrance surface of the second optical member,
The optical integrator according to claim 1, wherein the first direction and the second direction are set in an in-plane direction perpendicular to an optical axis of a combined system of the first optical member and the second optical member. .
[0009]
According to a preferred aspect of the first aspect, the first optical member is provided between an intermediate surface between an exit surface of the first optical member and an entrance surface of the second optical member and an exit surface of the first optical member. Has a rear focus in the second direction in the optical path. In the first embodiment, it is preferable that the energy density at the exit surface of the first optical member and the energy density at the entrance surface of the second optical member are set to be substantially the same.
[0010]
According to a preferred mode of the first mode, a refractive power ratio γ1 = φ11 / φ11 between the refractive power φ11 of the first optical member in the first direction and the refractive power φ12 of the second optical member in the first direction. φ12 and a refractive power ratio γ2 = φ21 / φ22 between a refractive power φ21 of the first optical member in the second direction and a refractive power φ22 of the second optical member in the second direction are | (γ1-1 )^Three| <0.1, | (γ2-1)^Three| <0.1 is satisfied. In the first embodiment, it is preferable that the first direction and the second direction are substantially orthogonal to each other. Further, in the first embodiment, it is preferable that each minute optical surface is formed in a curved shape having a curvature in only one direction.
[0011]
Further, according to a preferred embodiment of the first mode, the refractive index of the optical material forming the second optical member is set to be larger than the refractive index of the optical material forming the first optical member. In this case, when the refractive index of the optical material forming the first optical member is na and the refractive index of the optical material forming the second optical member is nb, the condition of 0.05 ≦ nb−na is satisfied. Is preferred. In the first embodiment, the optical material used for light having a wavelength of 300 nm or less, the optical material forming the first optical member includes quartz glass or fluorite, and the optical material forming the second optical member is used. Preferably contains any one of magnesium oxide, ruby, sapphire, crystal quartz, and quartz glass. According to a preferred mode of the first mode, the first optical member and the second optical member have a refractive power in the first direction and a refractive power in the second direction, respectively.
[0012]
According to a second aspect of the present invention, there is provided an illumination optical device for illuminating an irradiation surface,
There is provided an illumination optical device including the optical integrator according to the first aspect.
[0013]
According to a preferred aspect of the second aspect, the optical system further includes a light guide optical system disposed in an optical path between the optical integrator and the irradiation surface, for guiding light from the optical integrator to the irradiation surface. The axial distance between the rear focal point in the first direction and the rear focal point in the second direction is 5% or less of the focal length of the light guiding optical system.
[0014]
According to a third aspect of the present invention, there is provided an illumination optical apparatus according to the second aspect, and a projection optical system for projecting and exposing a pattern of a mask disposed on the irradiation surface onto a photosensitive substrate. An exposure apparatus is provided.
[0015]
According to a preferred mode of the third mode, the illumination optical device forms a rectangular illumination region on the mask, and a long side direction of the rectangular illumination region optically corresponds to the first direction, The short side direction of the rectangular illumination area optically corresponds to the second direction. In this case, the pattern of the mask is projected and exposed on the photosensitive substrate by relatively moving the mask and the photosensitive substrate with respect to the projection optical system along a short side direction of the rectangular illumination region. Is preferred.
[0016]
According to a fourth aspect of the present invention, there is provided an exposure method comprising illuminating a mask via the illumination optical device of the second aspect, and projecting and exposing an image of a pattern formed on the illuminated mask onto a photosensitive substrate. Provide a way.
[0017]
According to a preferred aspect of the fourth aspect, a rectangular shape having a long side along a direction optically corresponding to the first direction and a short side along a direction optically corresponding to the second direction. Are formed on the mask. In this case, the pattern of the mask is projected and exposed on the photosensitive substrate by relatively moving the mask and the photosensitive substrate with respect to the projection optical system along a short side direction of the rectangular illumination region. Is preferred.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a diagram illustrating the basic principle of the present invention. Referring to FIG. 1, the light supplied from the light source S illuminates the micro fly's eye lens MF through the first condenser optical system C1. The micro fly's eye lens MF includes a first subsystem A and a second subsystem B in order from the light source S side. A large number of first minute refractive surfaces are integrally formed in the first partial system A, and a large number of second minute refractive surfaces are optically associated with the large number of first minute refractive surfaces in the second partial system B. Are integrally formed.
[0019]
Therefore, the light that has been wavefront-divided by each minute refraction surface of the micro fly's eye lens MF reaches the illumination field I on the irradiated surface via the second condenser optical system C2. Here, an optical conjugate relationship is established between the entrance surface A1 of the micro fly's eye lens MF (that is, the entrance surface of the first subsystem A) and the illumination field I. Therefore, the light intensity distribution in the area corresponding to each minute refraction surface on the incident surface A1 is enlarged and projected on the entire illumination field I. FIG. 1 schematically shows only light rays corresponding to one micro refraction surface. However, in practice, the entire illumination field I is illuminated in a superimposed manner through a number of micro refraction surfaces to thereby provide illumination. The uniformity of the illuminance distribution over the entire field I is obtained.
[0020]
In the illumination system shown in FIG. 1, there is an optical conjugate relationship between the entrance surface A1 of the micro fly's eye lens MF and the illumination field I, but the imaging system P (micro fly's eye lens MF + second condenser optical system C2) If the distortion of () changes, the imaging magnification changes with the image height, so that the illuminance distribution in the illumination field I changes. For example, according to the “Imaging Surface Illuminance Distribution of Photographic Lens” by Masayuki Isshiki (Optical Technology Contact Vol. 5, No. 11, p10-14, 1967), the image forming system P rotationally symmetrical with respect to the optical axis. It is known that when the distortion changes by D%, the illuminance at the illumination field (image plane of the imaging system P) I changes by about 4D%.
[0021]
As an evaluation method of aberration (including distortion) of the imaging system, an aberration evaluation method based on third-order aberration theory is known. The analysis of aberrations based on the third-order aberration theory has an advantage that visibility is good because calculation can be performed analytically, although there is an error due to approximation. The method of deriving the aberration coefficient based on the third-order aberration theory is described in detail, for example, in "Aberration Theory" by Yoshiya Matsui (Japan Opto-Mechatronics Association, 1989). Hereinafter, an imaging system interposed between the entrance surface A1 of the micro fly's eye lens MF and the illumination field I when the surface shape of the micro refraction surface of the micro fly's eye lens MF changes using the third-order aberration theory. Consider the change in the distortion of P.
[0022]
The surface shape of each micro-refractive surface in the micro fly's eye lens MF is defined as y, the height in the direction perpendicular to the optical axis, and the optical axis from the tangent plane at the vertex of the refractive surface to the position on the refractive surface at height y When the distance (sag amount) along the axis is x, the curvature is c, and the cone coefficient is κ, the following equation (1) is used.
x = (cy^Two) / [1+ ｛1- (κ + 1) c^Two・ Y^Two｝^1/2] (1)
[0023]
According to the third-order aberration theory, all aberration coefficients can be represented by the sum of a spherical term and an aspherical term. The variation in the surface shape during the manufacture of the micro fly's eye lens MF appears as a change in the curvature c and the cone coefficient κ in the above equation (1). At this time, the change in the curvature c affects the size of the illumination, but does not substantially affect the illumination unevenness. On the other hand, a change in the cone coefficient κ changes the aspherical term of the aberration coefficient, and affects illumination unevenness.
[0024]
According to "Aberration Theory" by Yoshiya Matsui mentioned above, the aspherical term V of the distortion aberration coefficient of the object image is obtained._aspIs generally represented by the following equation (2). In equation (2), h_iIs the ray height of the image paraxial trace value (the ray height when the object (image) paraxial ray is traced), and h_pIs the ray height of the pupil paraxial trace value (the ray height when the pupil paraxial ray is traced). Ψ is a coefficient represented by the following equation (3).
V_asp= H_i・ H_p ^Three・ Ψ (2)
Ψ = Δn · c^Three・ Κ (3)
[0025]
Here, Δn is the difference between the refractive index of the medium on the light incident side and the light exit side of the minute refraction surface, and is calculated from the refractive index n2 of the medium on the light exit side of the minute refraction surface. This is a value (n2-n1) obtained by subtracting the refractive index n1 of the medium. FIG. 2 is a diagram illustrating optical characteristics of the micro fly's eye lens of FIG. In FIG. 2, the refractive power (power) of the micro fly's eye lens MF is φ, the refractive power of the first subsystem A is φa, the refractive power of the second subsystem B is φb, and the first subsystem A and the second subsystem are The air-equivalent surface distance between the airplane B and the airplane B is represented by s.
[0026]
Therefore, if the refractive power φ of the micro fly's eye lens MF is normalized to 1, and the refractive power ratio φa / φb between the refractive power φa of the first subsystem A and the refractive power φb of the second subsystem B is γ, Equations (4a) to (4d) hold.
φ = 1 (4a)
φa = γ (4b)
φb = 1 (4c)
s = 1 (4d)
[0027]
The following table (1) shows paraxial tracking values at this time.
[Table 1]

[0028]
Referring to Tables (1), (2) and (3), the aspherical term V of the distortion aberration coefficient in the first subsystem A is shown._aspAAnd the aspherical term V of the distortion coefficient in the second subsystem B_aspBIs represented by the following equations (5) and (6), respectively.
V_aspA= 0 (5)
V_aspB= (Γ-1)^Three・ Δn ・ c^Three・ Κ (6)
[0029]
Referring to Equations (5) and (6), the change in the aspherical term of the distortion aberration coefficient due to the variation in the surface shape of the minute refraction surface of the micro fly's eye lens MF (that is, the change in the conical coefficient κ) is the third order It can be seen that the aberration occurs only in the second subsystem B in the range of aberration. Next, the influence of a change in the aspherical term of the distortion aberration coefficient on the illuminance distribution in the illumination field I will be considered. In the second subsystem B, a proportional relationship represented by the following equation (7) holds between the curvature c and the refractive index difference Δn.
c∝1 / Δn (7)
[0030]
In the range of the third-order aberration, the illuminance distribution in the illumination field I changes in proportion to the square of the image height. The image height is proportional to the numerical aperture NA on the exit side of the micro fly's eye lens MF. Therefore, from Expressions (5) to (7), the change in distortion due to the change in the surface shape of the minute refraction surface of the micro fly's eye lens MF, and the change in the illuminance distribution on the illumination field (image plane) I, can be calculated. The sensitivity β is represented by the following equation (8).
β = (γ-1)^Three・ NA^Two/ Δn^Two    (8)
[0031]
Incidentally, when the micro fly's eye lens MF is arranged in the air, assuming that the refractive index n of the optical material forming the second subsystem B is, the equation (8) is expressed as the following equation (8 ′). Can be transformed.
β = (γ-1)^Three・ NA^Two/ (N-1)^Two    (8 ')
[0032]
In this manner, by reducing the absolute value of the parameter β, it is possible to suppress a change in distortion due to a variation in the surface shape of the minute refraction surface of the micro fly's eye lens MF, and to influence the illuminance distribution in the illumination field I. Can be reduced. In other words, by reducing the absolute value of the parameter β, for example, a micro fly's eye lens having a characteristic of suppressing the influence of the manufacturing error of a large number of minute refraction surfaces formed integrally by etching processing on the illuminance distribution ( Optical integrator (MF) can be realized.
[0033]
By the way, referring to equation (8 '), in order to reduce the absolute value of the parameter β in order to reduce the change in distortion due to the variation in the surface shape of the micro-refractive surface of the micro fly's eye lens MF, the refractive power must be reduced. It can be seen that the ratio γ should be close to 1. However, simply bringing the refractive power ratio γ close to 1 increases the energy density at the exit surface of the micro fly's eye lens MF (that is, the exit surface of the second subsystem B), and eventually the second subsystem B is irradiated by light energy. The risk of breakage increases and component life is shortened.
[0034]
In the present invention, as described later with reference to a specific embodiment, the micro fly's eye lens MF (a composite system of the first partial system A and the second partial system B) is replaced with the second partial system B (second system). A rear focal point in the first direction (a predetermined direction set in a plane perpendicular to the optical axis) is located behind the exit surface of the optical member by a predetermined distance. Further, the first subsystem A (first optical member) is provided in the optical path between the exit surface of the first subsystem A and the entrance surface of the second subsystem B in a second direction (for example, a plane perpendicular to the optical axis). (In the direction perpendicular to the first direction). In this case, if the optical system is symmetric with respect to the optical axis in a plane including the optical axis, the same discussion as the discussion regarding the rotationally symmetric optical system described in the above-described equations (1) to (8 ') holds.
[0035]
In the present invention, by employing the above-described configuration, even if the refractive power ratio γ is brought close to 1 in order to suppress a change in distortion due to a variation in the surface shape of the minute refractive surface of the micro fly's eye lens MF, The energy density on each optical surface including the exit surface of the micro fly's eye lens MF (that is, the exit surface of the second subsystem B) can be reduced, and the second subsystem A and the first subsystem A by light energy irradiation can be reduced. , And a sufficiently long component life can be secured.
[0036]
Further, referring to the equation (8 '), it can be seen that the absolute value of the parameter β can be reduced by increasing the refractive index n of the optical material forming the second subsystem B. However, since the cost tends to increase with the increase in the refractive index of the optical material, it is practical to use an optical material having a high refractive index only for the second subsystem B. Therefore, in the present invention, the refractive index nb of the optical material forming the second subsystem B (second optical member) is greater than the refractive index na of the optical material forming the first subsystem A (first optical member). Is preferably set large.
[0037]
In this case, it is preferable that the refractive index na and the refractive index nb satisfy the condition of 0.05 ≦ nb−na in order to sufficiently exhibit the effects of the present invention. Specifically, for example, when the first subsystem A is formed of quartz glass or fluorite for light having a wavelength of 300 nm or less, the second subsystem B is formed of magnesium oxide, ruby, sapphire, crystal quartz, or It is preferable to form with quartz glass. When the first subsystem A is made of fluorite, the second subsystem B is preferably made of quartz glass.
[0038]
An embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 3 is a diagram schematically illustrating a configuration of an exposure apparatus including the illumination optical device according to the embodiment of the present invention. 3, the Z axis is along the normal direction of the wafer W as a photosensitive substrate, the Y axis is in the direction parallel to the plane of FIG. 3 in the wafer plane, and the Z axis is perpendicular to the plane of FIG. 3 in the wafer plane. The X axis is set in each direction. In FIG. 3, the illumination optical device is set to perform annular illumination.
[0039]
The exposure apparatus shown in FIG. 3 includes, as a light source 1 for supplying exposure light (illumination light), for example, a KrF excimer laser light source for supplying light having a wavelength of 248 nm or an ArF excimer laser light source for supplying light having a wavelength of 193 nm. ing. A substantially parallel light beam emitted from the light source 1 in the Z direction has a rectangular cross section elongated in the X direction, and enters a beam expander 2 including a pair of lenses 2a and 2b. Each of the lenses 2a and 2b has a negative refracting power and a positive refracting power, respectively, in the plane of FIG. 3 (in the YZ plane). Therefore, the light beam incident on the beam expander 2 is enlarged in the plane of FIG. 3 and shaped into a light beam having a predetermined rectangular cross section.
[0040]
The substantially parallel light beam passing through the beam expander 2 as a shaping optical system is deflected in the Y direction by the bending mirror 3 and then enters the afocal zoom lens 5 via the diffractive optical element 4. Generally, a diffractive optical element is formed by forming a step having a pitch on the order of the wavelength of exposure light (illumination light) on a glass substrate, and has a function of diffracting an incident beam to a desired angle. Specifically, the diffractive optical element 4 has a function of forming a circular light intensity distribution in its far field (or Fraunhofer diffraction region) when a parallel light beam having a rectangular cross section is incident. Therefore, the light beam having passed through the diffractive optical element 4 forms a circular light intensity distribution at the pupil position of the afocal zoom lens 5, that is, a light beam having a circular cross section.
[0041]
The diffractive optical element 4 is configured to be retractable from the illumination optical path. The afocal zoom lens 5 is configured to be able to continuously change magnification within a predetermined range while maintaining an afocal system (a non-focus optical system). The light beam having passed through the afocal zoom lens 5 enters a diffractive optical element 6 for annular illumination. The afocal zoom lens 5 optically connects the divergence origin of the diffractive optical element 4 and the diffractive surface of the diffractive optical element 6 almost optically conjugate. Then, the numerical aperture of the light beam condensed on one point of the diffractive surface of the diffractive optical element 6 or a surface in the vicinity thereof changes depending on the magnification of the afocal zoom lens 5.
[0042]
The diffractive optical element 6 for annular illumination has a function of forming a ring-shaped light intensity distribution in the far field when a parallel light beam enters. The diffractive optical element 6 is configured to be freely inserted into and removed from the illumination optical path, and is configured to be switchable between a diffractive optical element 60 for quadrupole illumination and a diffractive optical element 61 for circular illumination. The light beam having passed through the diffractive optical element 6 enters the zoom lens 7. In the vicinity of the rear focal plane of the zoom lens 7, the entrance surface of the micro fly's eye lens 8 composed of the first fly's eye member 8a and the second fly's eye member 8b in order from the light source side (that is, the first fly's eye member 8a Incident surface) is positioned. The micro fly's eye lens 8 functions as a wavefront splitting optical integrator that forms a large number of light sources based on the incident light beam, and its detailed configuration and operation will be described later.
[0043]
As described above, the luminous flux from the circular light intensity distribution formed at the pupil position of the afocal zoom lens 5 via the diffractive optical element 4 is emitted from the afocal zoom lens 5 and then has various angular components. And enters the diffractive optical element 6. Accordingly, the light beam having passed through the diffractive optical element 6 forms a ring-shaped illumination field around the optical axis AX on the rear focal plane of the zoom lens 7 (and thus on the entrance plane of the micro fly's eye lens 8). .
[0044]
The outer diameter of the annular illumination field formed on the entrance surface of the micro fly's eye lens 8 changes depending on the focal length of the zoom lens 7. As described above, the zoom lens 7 connects the diffractive optical element 6 and the incident surface of the micro fly's eye lens 8 substantially in a Fourier transform relationship. The light beam incident on the micro fly's eye lens 8 is two-dimensionally split, and a plurality of annular light sources (hereinafter, referred to as "secondary light sources") are formed on the rear focal plane in the same manner as the illumination field formed by the incident light beam. Is done.
[0045]
The light flux from the annular secondary light source formed on the rear focal plane of the micro fly's eye lens 8 is condensed by the condenser optical system 9 and then superimposed on the mask M on which a predetermined pattern is formed. To illuminate. The light flux transmitted through the pattern of the mask M forms an image of the mask pattern on the wafer W as a photosensitive substrate via the projection optical system PL. In this way, by performing collective exposure or scan exposure while controlling the wafer W two-dimensionally in a plane (XY plane) orthogonal to the optical axis AX of the projection optical system PL, each exposure area of the wafer W is masked. The M patterns are sequentially exposed.
[0046]
In the batch exposure, a mask pattern is collectively exposed to each exposure region of the wafer according to a so-called step-and-repeat method. In this case, the shape of the illumination area on the mask M is a rectangular shape close to a square. On the other hand, in scan exposure, according to a so-called step-and-scan method, a mask pattern is scanned and exposed on each exposure region of a wafer while the mask and wafer are relatively moved with respect to a projection optical system. In this case, the shape of the illumination area on the mask M is a rectangular shape having a ratio of the short side to the long side of, for example, 1: 3.
[0047]
In the present embodiment, when the magnification of the afocal zoom lens 5 changes, the center height (distance of the circular center line from the optical axis AX) of the annular secondary light source does not change, and its width (outside) does not change. Only one half of the difference between the diameter (diameter) and the inner diameter (diameter) changes. That is, by changing the magnification of the afocal zoom lens 5, both the size (outer diameter) of the annular secondary light source and its shape (ring ratio: inner diameter / outer diameter) can be changed.
[0048]
When the focal length of the zoom lens 7 changes, both the center height and the width change without changing the ring ratio of the ring-shaped secondary light source. That is, by changing the focal length of the zoom lens 7, the outer diameter of the secondary light source in the annular shape can be changed without changing the annular ratio. As described above, in the present embodiment, by appropriately changing the magnification of the afocal zoom lens 5 and the focal length of the zoom lens 7, only the annular ratio without changing the outer diameter of the annular secondary light source. Can be changed.
[0049]
As described above, the diffractive optical element 6 is configured so as to be freely inserted into and removed from the illumination optical path, and is configured to be switchable between the diffractive optical element 60 for quadrupole illumination and the diffractive optical element 61 for circular illumination. . Hereinafter, quadrupole illumination obtained by setting the diffractive optical element 60 in the illumination optical path instead of the diffractive optical element 6 will be described. The quadrupole illumination diffractive optical element 60 has a function of forming a four-point light intensity distribution in its far field when a parallel light beam enters. Therefore, the light beam having passed through the diffractive optical element 60 forms a quadrupole illumination field composed of, for example, four circular illumination fields centered on the optical axis AX on the incident surface of the micro fly's eye lens 8. As a result, a quadrupolar secondary light source is formed on the rear focal plane of the micro fly's eye lens 8 in the same manner as the illumination field formed on the incident plane.
[0050]
In the quadrupole illumination, as in the case of the annular illumination, by changing the magnification of the afocal zoom lens 5, the outer diameter of the quadrupolar secondary light source (the outer diameter of the circle circumscribing the four circular surface light sources) is changed. Both the diameter and the annular ratio (diameter of circle inscribed in four circular surface light sources / diameter of circle inscribed in four circular surface light sources) can be changed. Further, by changing the focal length of the zoom lens 7, the outer diameter of the quadrupole secondary light source can be changed without changing the annular ratio. As a result, by appropriately changing the magnification of the afocal zoom lens 5 and the focal length of the zoom lens 7, it is possible to change only the annular ratio without changing the outer diameter of the quadrupole secondary light source. it can.
[0051]
Next, circular illumination obtained by retracting the diffractive optical element 4 from the illumination optical path and setting a diffractive optical element 61 for circular illumination in the illumination optical path instead of the diffractive optical element 6 or 60 will be described. In this case, a light beam having a rectangular cross section is incident on the afocal zoom lens 5 along the optical axis AX. The light beam incident on the afocal zoom lens 5 is enlarged or reduced in accordance with the magnification, and is emitted from the afocal zoom lens 5 along the optical axis AX as a light beam having a rectangular cross section. Incident.
[0052]
Here, similarly to the diffractive optical element 4, the diffractive optical element 61 for circular illumination has a function of forming a circular light intensity distribution in the far field when a parallel light beam having a rectangular cross section is incident. . Therefore, the circular light beam formed by the diffractive optical element 61 forms a circular illumination field centered on the optical axis AX on the incident surface of the micro fly's eye lens 8 via the zoom lens 7. As a result, a circular secondary light source centered on the optical axis AX is also formed on the rear focal plane of the micro fly's eye lens 8. In this case, by changing the magnification of the afocal zoom lens 5 or the focal length of the zoom lens 7, the outer diameter of the circular secondary light source can be appropriately changed.
[0053]
FIG. 4 is a perspective view schematically showing the entire configuration of the micro fly's eye lens according to the present embodiment. FIG. 5 is a diagram illustrating the operation of the micro fly's eye lens according to the present embodiment. Referring to FIG. 4, the micro fly's eye lens 8 of the present embodiment includes a first fly's eye member 8a arranged on the light source side and a second fly's eye member 8b arranged on the mask side.
[0054]
Cylindrical lens groups 81a and 81b arranged along the X direction are formed on the light source side surface of the first fly eye member 8a and the light source side surface of the second fly eye member 8b, respectively, at a pitch p1. On the other hand, on the mask-side surface of the first fly-eye member 8a and the mask-side surface of the second fly-eye member 8b, cylindrical lens groups 82a and 82b arranged along the Z direction are formed at a pitch p2. I have. In FIG. 3, the number of cylindrical lenses formed in the microlens array 8 is much smaller than the actual number for clarity.
[0055]
Focusing on the refracting action of the micro fly's eye lens 8 in the X direction (that is, the refracting action on the XY plane), the parallel light beam incident along the optical axis AX is a cylindrical lens formed on the light source side of the first fly's eye member 8a. The group 81a divides the wavefront at a pitch p1 along the X direction. Then, as shown in FIG. 5A, the parallel light beam incident on the minute refraction surface 91a of the cylindrical lens group 81a undergoes a light condensing action on the minute refraction surface 91a, and then exits from the first fly-eye member 8a. In the optical path between the first fly-eye member 8a and the incident surface of the second fly-eye member 8b, the light is converged on the rear focal point 84 of the first fly-eye member 8a in the X direction. The divergent light beam once condensed on the rear focal point 84 is condensed by the minute refraction surface 92a corresponding to the minute refraction surface 91a in the cylindrical lens group 82b formed on the light source side of the second fly-eye member 8b. , From the second fly-eye member 8b.
[0056]
On the other hand, focusing on the refraction effect in the Z direction of the micro fly's eye lens 8 (that is, the refraction effect on the ZY plane), the parallel light beam incident along the optical axis AX is formed on the mask side of the first fly's eye member 8a. Wavefront division is performed at a pitch p2 along the Z direction by the cylindrical lens group 82a. Then, as shown in FIG. 5B, the parallel light beam incident on the minute refraction surface 92a of the cylindrical lens group 82a is condensed by the minute refraction surface 92a, and then the mask side of the second fly-eye member 8b. In the cylindrical lens group 82b formed as described above, the micro-refractive surface 92b corresponding to the micro-refractive surface 92a receives the light condensing action and condenses on the rear focal point 85 of the micro fly's eye lens 8 in the Z direction.
[0057]
Table 2 below summarizes the data values of the micro fly's eye lens 8 according to the present embodiment. In Table (2), m is a surface number representing the order of the optical surfaces from the light source, φx is the refractive power (power) of each optical surface in the X direction, φz is the refractive power of each optical surface in the Z direction, d is the on-axis spacing of each optical surface, that is, the surface spacing, n is the refractive index for the used light, hx is the ray height at each optical surface in the X direction, and αx is the tilt angle at each optical surface in the X direction ( Hz is the ray height at each optical surface in the Z direction, αz is the tilt angle at each optical surface in the Z direction, and Ex is the energy density at each optical surface in the X direction. Ez indicates the energy density ratio at each optical surface in the Z direction, and E indicates the energy density ratio at each optical surface.
[0058]
Note that the energy density ratios Ex, Ez, and E are calculated on the first surface, that is, on the optical surface when the energy density on the incident surface of the first fly-eye member 8a (the incident surface of the micro fly-eye lens 8) is normalized to 1. Energy density. In Table (2), fx is the focal length of the micro fly's eye lens 8 in the X direction, fz is the focal length of the micro fly's eye lens 8 in the Z direction, and dx is the back distance of the micro fly's eye lens 8 in the X direction. Focus indicates d, and dz indicates the back focus of the micro fly's eye lens 8 in the Z direction.
[0059]
[Table 2]

[0060]
Therefore, in the present embodiment, the refractive power φ11 of the first fly's eye member 8a in the X direction, the refractive power φ12 of the second fly's eye member 8b in the X direction, the refractive power ratio γ1 in the X direction = φ11 / φ12, and the refractive power in the Z direction. The refractive power φ21 of the first fly-eye member 8a, the refractive power φ22 of the second fly-eye member 8b in the Z direction, and the refractive power ratio γ2 = φ21 / φ22 in the Z direction, and the factor of the parameter β in the X direction | (γ1-1 )^Three| And the factor of the parameter β in the Z direction | (γ2-1)^Three| Is as shown in the following Table (3).
[0061]
[Table 3]
φ11 = 0.588235
φ12 = 0.5
γ1 = φ11 / φ12 = 1.17647
φ21 = 0.666663
φ22 = 1
γ2 = φ21 / φ22 = 0.666663
| (Γ1-1)^Three| = 0.0055
| (Γ2-1)^Three| = 0.037038
[0062]
FIG. 6 is a diagram illustrating the operation of the micro fly's eye lens according to the comparative example of the present embodiment. In the comparative example of FIG. 6, the on-axis spacing of each optical surface, that is, the surface spacing d, the refractive index n for the used light, and the focal length of the micro fly's eye lens (first fly's eye member 108a + second fly's eye member 108b) in the X direction. Basic data including the focal length fz of the micro fly's eye lens in the fx and Z directions are set to be the same as those in the embodiment of FIG. However, in the comparative example of FIG. 6, the rear focal point in the X direction and the rear focal point in the Z direction of the micro fly's eye lens are shifted a predetermined distance behind the exit surface of the second fly's eye member 108 b in accordance with the related art. The difference from the embodiment of FIG.
[0063]
Table 4 below summarizes the data values of the micro fly's eye lens according to the comparative example. The notation in Table (4) is the same as the notation in Table (2).
[0064]
[Table 4]

[0065]
Therefore, in the comparative example of FIG. 6, the refractive power φ11 of the first fly-eye member 8a in the X direction, the refractive power φ12 of the second fly-eye member 8b in the X direction, the refractive power ratio γ1 = φ11 / φ12 in the X direction, Z The refractive power φ21 of the first fly-eye member 8a in the direction, the refractive power φ22 of the second fly-eye member 8b in the Z direction, and the refractive power ratio γ2 = φ21 / φ22 in the Z direction, and the factor of the parameter β in the X direction | (γ1 -1)^Three| And the factor of the parameter β in the Z direction | (γ2-1)^Three| Is as shown in the following Table (5).
[0066]
[Table 5]
φ11 = 0.253732
φ12 = 0.5
γ1 = φ11 / φ12 = 0.507646
φ21 = 0.51493
φ22 = 1
γ2 = φ21 / φ22 = 0.51493
| (Γ1-1)^Three| = 0.119485
| (Γ2-1)^Three| = 0.114133
[0067]
As described above, in the present embodiment, the micro fly's eye lens 8 (combined system of the first fly's eye member 8a and the second fly's eye member 8b) is located at a predetermined distance from the exit surface of the second fly's eye member 8b. The rear side has a rear focal point 85 in the Z direction. The first fly-eye member 8a has a rear focal point 84 in the X direction in the optical path between the exit surface of the first fly-eye member 8a and the entrance surface of the second fly-eye member 8b.
[0068]
As a result, in the present embodiment, the energy density ratio at the exit surface of the first fly-eye member 8a and the entrance surface of the second fly-eye member 8b has a maximum value of E ≒ 8.5, and the second fly-eye member has a maximum value. At the exit surface of 8b, the energy density ratio is close to the maximum value when E ≒ 7.0. That is, in the present embodiment, the load of the energy density is equalized to some extent between the exit surface of the first fly-eye member 8a, the entrance surface of the second fly-eye member 8b, and the exit surface of the second fly-eye member 8b.
[0069]
On the other hand, in the comparative example in which the rear focal point in the X direction of the micro fly's eye lens substantially coincides with the rear focal point in the Z direction, the energy density ratio at the exit surface of the second fly's eye member 8b is E = 8.5. , And the energy density ratio on the other optical surfaces is about E = 1 to 2.7, which is considerably smaller than the maximum value. That is, in the comparative example, the load of the energy density is concentrated only on the emission surface of the second fly-eye member 8b (the emission surface of the micro fly-eye lens).
[0070]
Also, comparing the present embodiment in which the maximum values of the energy density ratios are set to be equal to each other and the comparative example, a factor | (γ1-1) of the parameter β in the X direction in the present embodiment^ThreeIs the factor of the parameter β in the X direction in the comparative example | (γ1-1)^ThreeIs approximately 1/22 of |, and the factor of the parameter β in the Z direction in the present embodiment | (γ2-1)^ThreeIs the factor of the parameter β in the Z direction in the comparative example | (γ2-1)^Three| Is about 1/3.
[0071]
Therefore, another factor NA of the parameter β^TwoAnd (n-1)^TwoIf the values are the same, in the present embodiment, a change in distortion due to a variation in the surface shape of the micro-refractive surface of the micro fly's eye lens can be suppressed smaller than in the comparative example. In other words, the other factor NA of the parameter β^TwoAnd (n-1)^TwoIn the comparative example, if the refractive power ratios γ1 and γ2 are further brought closer to 1 in the comparative example to suppress the change in distortion as small as in the present embodiment, the energy density ratio at the exit surface of the second fly-eye member 8b becomes Will be further increased from the maximum value.
[0072]
As described above, in the present embodiment, the micro fly-eye lens 8 employs the above-described configuration for the rear focal point in the Z direction of the micro fly's eye lens 8 and the rear focal point in the X direction of the first fly's eye member 8a. Factor | (γ1-1) of parameter β in order to reduce the change in distortion due to the variation in the surface shape of the minute refraction surface of lens 8^Three| And | (γ2-1)^ThreeIs small (even if the refractive power ratios γ1 and γ2 are close to 1), the energy density at each optical surface including the exit surface of the micro fly's eye lens 8 (that is, the exit surface of the second fly's eye member 8b) Can be kept small, and the second fly-eye member 8b and the first fly-eye member 8a can be prevented from being damaged by light energy irradiation, and a sufficiently long component life can be secured.
[0073]
In this embodiment, the load of the energy density is equalized as much as possible between the exit surface of the first fly-eye member 8a, the entrance surface of the second fly-eye member 8b, and the exit surface of the second fly-eye member 8b. In order to keep the maximum value small, it is necessary to place the first fly-eye member 8a in the optical path between the intermediate surface between the exit surface of the first fly-eye member 8a and the entrance surface of the second fly-eye member 8b and the exit surface of the first fly-eye member 8a. The rear focus 84 in the X direction of the fly-eye member 8a is configured to exist, and the energy density at the exit surface of the first fly-eye member 8a and the energy density at the entrance surface of the second fly-eye member 8b are substantially reduced. It is preferable to set the same.
[0074]
In the present embodiment, in order to sufficiently suppress the change in distortion due to the variation in the surface shape of the minute refraction surface of the micro fly's eye lens 8, the factor of the parameter β || (γ1-1)^Three| And | (γ2-1)^Three| Preferably satisfies the following conditional expressions (a) and (b).
| (Γ1-1)^Three| <0.1 (a)
| (Γ2-1)^Three| <0.1 (b)
[0075]
In the present embodiment, when a parallel light beam is incident on the micro fly's eye lens 8, a condensing point 84 in the X direction (light source forming point in the X direction) and a condensing point in the Z direction (light source forming point in the Z direction) 85), but in order to reduce the influence of the configuration in which the converging point is different in the X direction and the Z direction on the illuminance distribution on the mask M (hence, on the wafer W), the first fly-eye member 8a The axial distance between the rear focal point 84 in the X direction and the rear focal point 85 of the micro fly's eye lens 8 in the Z direction is determined by a light guiding optical system (condenser optics) for guiding the light from the micro fly's eye lens 8 to the mask M. It is preferable to set the focal length to 5% or less of the focal length of the system 9).
[0076]
In the case of a scanning exposure type exposure apparatus, an elongated rectangular illumination area is formed on the mask M, and the mask M and the wafer W are projected along the short side of the rectangular illumination area, that is, in the scanning direction. By relative movement with respect to the system PL, the pattern of the mask M is projected and exposed on the wafer W. In this case, the numerical aperture NA of the exit side of the micro fly's eye lens 8 is usually set to be larger in the non-scanning direction (longer side direction of the illumination area) than in the scanning direction. Therefore, the long side direction of the rectangular illumination area optically corresponds to the Z direction of the micro fly's eye lens 8 and coincides with the Y direction on the mask M, and the short side direction of the rectangular illumination area is the micro fly's eye. It is preferable that the lens 8 be set so as to correspond to the X direction on the mask M optically corresponding to the X direction.
[0077]
In the above-described embodiment, the present invention is applied to a micro fly's eye lens in which each minute refraction surface is formed in a cylindrical shape. However, the present invention is not limited to this, and a modification in which the present invention is applied to a micro fly's eye lens in which each minute refraction surface is generally formed in a curved surface shape (toric shape) having a curvature in only one direction is also possible. is there.
[0078]
In the exposure apparatus according to the above-described embodiment, a mask (reticle) is illuminated by an illumination optical device (illumination step), and a transfer pattern formed on the mask is exposed onto a photosensitive substrate using a projection optical system (exposure). Through the steps, a micro device (semiconductor element, imaging element, liquid crystal display element, thin film magnetic head, 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 above-described embodiment will be described with reference to the flowchart of FIG. Will be explained.
[0079]
First, in step 301 of FIG. 7, 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 above-described embodiment, the image of the pattern on the mask is sequentially exposed and transferred to each shot area on the wafer of the lot through the projection optical system. After that, 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 to form 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.
[0080]
In the exposure apparatus of the above-described embodiment, a liquid crystal display element as a micro device can be obtained by forming a predetermined pattern (circuit pattern, electrode pattern, etc.) on a plate (glass substrate). Hereinafter, an example of the technique at this time will be described with reference to the flowchart in FIG. 8, in a pattern forming step 401, a so-called photolithography step of transferring and exposing a mask pattern onto a photosensitive substrate (eg, a glass substrate coated with a resist) using the exposure apparatus of the above-described embodiment is performed. . By this photolithography process, a predetermined pattern including a large number of electrodes and the like is formed on the photosensitive substrate. After that, the exposed substrate undergoes various processes such as a developing process, an etching process, and a resist stripping process, so that a predetermined pattern is formed on the substrate, and the process proceeds to the next color filter forming process 402.
[0081]
Next, in a color filter forming step 402, a large number of sets of three dots corresponding to R (Red), G (Green), and B (Blue) are arranged in a matrix, or three sets of R, G, B Are formed in a horizontal scanning line direction to form a color filter. Then, after the color filter forming step 402, a cell assembling step 403 is performed. In the cell assembly step 403, a liquid crystal panel (liquid crystal cell) is assembled using the substrate having the predetermined pattern obtained in the pattern formation step 401, the color filter obtained in the color filter formation step 402, and the like. In the cell assembling step 403, for example, a liquid crystal is injected between the substrate having the predetermined pattern obtained in the pattern forming step 401 and the color filter obtained in the color filter forming step 402, and a liquid crystal panel (liquid crystal cell) is formed. ) To manufacture.
[0082]
Thereafter, in a module assembling step 404, components such as an electric circuit and a backlight for performing a display operation of the assembled liquid crystal panel (liquid crystal cell) are attached to complete a liquid crystal display element. According to the above-described method for manufacturing a liquid crystal display device, a liquid crystal display device having an extremely fine circuit pattern can be obtained with high throughput.
[0083]
In the above-described embodiment, the light from the secondary light source is condensed by the condenser optical system 9 to illuminate the mask M in a superimposed manner. However, without being limited to this, an illumination field stop (mask blind) and a relay optical system for forming an image of the illumination field stop on the mask M are provided in the optical path between the condenser optical system 9 and the mask M. May be arranged. In this case, the condenser optical system 9 condenses the light from the secondary light source and illuminates the illumination field stop in a superimposed manner, and the relay optical system sets the image of the opening (light transmission part) of the illumination field stop. Is formed on the mask M.
[0084]
In the above-described embodiment, the KrF excimer laser light (wavelength: 248 nm) or the ArF excimer laser light (wavelength: 193 nm) is used as the exposure light. The present invention can also be applied to exposure light. Further, in the above-described embodiment, the present invention has been described by taking the projection exposure apparatus having the illumination optical device as an example. However, the present invention is applied to a general illumination optical device for illuminating an irradiated surface other than a mask. Obviously you can.
[0085]
【The invention's effect】
As described above, in the optical integrator of the present invention, the combined system of the first optical member and the second optical member shifts the rear focal point in the first direction to the rear of the exit surface of the second optical member by a predetermined distance. A first optical member having a rear focal point in a second direction in an optical path between an exit surface of the first optical member and an entrance surface of the second optical member. Based on this configuration, even if the refractive power ratio γ between the first optical member and the second optical member is made close to 1, in order to suppress a change in distortion caused by a variation in the surface shape of the minute refraction surface of the optical integrator, In addition, the energy density on each optical surface can be suppressed to a small value, and the optical members can be prevented from being damaged by light energy irradiation, so that a sufficiently long component life can be secured.
[0086]
That is, in the optical integrator of the present invention, for example, a change in distortion due to a variation in the surface shape of the minute refraction surface formed integrally by etching is reduced, and the influence of the illuminance distribution on the irradiated surface is reduced. can do. Therefore, in the illumination optical device of the present invention, the illuminated surface can be illuminated under desired illumination conditions using the optical integrator in which the influence of the manufacturing error of the minute refraction surface on the illuminance distribution is reduced. Further, in the exposure apparatus and the exposure method of the present invention, good projection exposure is performed under favorable illumination conditions using a high-performance illumination optical device capable of illuminating a surface to be irradiated under desired illumination conditions. Thus, a better device can be manufactured.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a basic principle of the present invention.
FIG. 2 is a diagram illustrating optical characteristics of the micro fly's eye lens of FIG.
FIG. 3 is a diagram schematically illustrating a configuration of an exposure apparatus including an illumination optical device according to an embodiment of the present invention.
FIG. 4 is a perspective view schematically showing the entire configuration of the micro fly's eye lens according to the present embodiment.
FIG. 5 is a diagram illustrating the operation of the micro fly's eye lens according to the embodiment.
FIG. 6 is a diagram illustrating an operation of a micro fly's eye lens according to a comparative example of the embodiment.
FIG. 7 is a flowchart of a method for obtaining a semiconductor device as a micro device.
FIG. 8 is a flowchart of a method for obtaining a liquid crystal display element as a micro device.
[Explanation of symbols]
S, 1 Light source
C1, C2, 9 Condenser optical system
MF, 8 micro fly eye lens
4 Diffractive optical element
5 Afocal zoom lens
6,60,61 Diffractive optical element
7 Zoom lens
8a First fly eye member
8b 2nd fly eye member
M mask
PL projection optical system
W wafer

Claims (18)

A first optical member having a plurality of first minute optical surfaces formed integrally and a first optical member integrally formed so as to correspond optically to the plurality of first minute optical surfaces in order from the light incident side. A wavefront splitting type optical integrator comprising: a second optical member having a plurality of second minute optical surfaces;
The combined system of the first optical member and the second optical member has a rear focal point in the first direction at a predetermined distance behind the exit surface of the second optical member,
The first optical member has a rear focal point in a second direction different from the first direction in an optical path between an exit surface of the first optical member and an entrance surface of the second optical member,
The optical integrator according to claim 1, wherein the first direction and the second direction are set in an in-plane direction perpendicular to an optical axis of a combined system of the first optical member and the second optical member. The first optical member is disposed in an optical path between an intermediate surface between an exit surface of the first optical member and an entrance surface of the second optical member and an exit surface of the first optical member in a rearward direction in the second direction. The optical integrator according to claim 1, wherein the optical integrator has a side focus. The optical integrator according to claim 1, wherein an energy density at an exit surface of the first optical member and an energy density at an entrance surface of the second optical member are set to be substantially the same. The refractive power ratio γ1 = φ11 / φ12 between the refractive power φ11 of the first optical member in the first direction and the refractive power φ12 of the second optical member in the first direction, and the first optical power in the second direction. The refractive power ratio γ2 = φ21 / φ22 between the refractive power φ21 of the member and the refractive power φ22 of the second optical member in the second direction is:
| (Γ1-1) ³ | <0.1
| (Γ2-1) ³ | <0.1
The optical integrator according to any one of claims 1 to 3, wherein the following condition is satisfied. The optical integrator according to claim 1, wherein the first direction and the second direction are substantially orthogonal. The optical integrator according to any one of claims 1 to 5, wherein each minute optical surface is formed in a curved shape having a curvature only in one direction. The refractive index of the optical material forming the second optical member is set to be larger than the refractive index of the optical material forming the first optical member. Optical integrator according to the item. When the refractive index of the optical material forming the first optical member is na and the refractive index of the optical material forming the second optical member is nb,
0.05 ≦ nb-na
The optical integrator according to claim 7, wherein the following condition is satisfied. 9. The device according to claim 1, wherein the first optical member and the second optical member have a refractive power in the first direction and a refractive power in the second direction, respectively. 10. Optical integrator. Used for light having a wavelength of 300 nm or less,
The optical material forming the first optical member includes quartz glass or fluorite,
The optical material forming the second optical member includes any one of magnesium oxide, ruby, sapphire, crystal quartz, and quartz glass. The optical integrator according to 1. In an illumination optical device that illuminates a surface to be irradiated,
An illumination optical device comprising the optical integrator according to claim 1. A light guide optical system is disposed in an optical path between the optical integrator and the irradiated surface, and guides light from the optical integrator to the irradiated surface,
The illumination according to claim 11, wherein an axial distance between a rear focal point in the first direction and a rear focal point in the second direction is 5% or less of a focal length of the light guide optical system. Optical device. 13. An exposure apparatus, comprising: the illumination optical device according to claim 11; and a projection optical system for projecting and exposing a pattern of a mask disposed on the irradiation surface onto a photosensitive substrate. The illumination optical device forms a rectangular illumination area on the mask,
The long side direction of the rectangular illumination area optically corresponds to the first direction, and the short side direction of the rectangular illumination area optically corresponds to the second direction. 14. The exposure apparatus according to 13. The mask pattern and the photosensitive substrate are projected and exposed on the photosensitive substrate by relatively moving the mask and the photosensitive substrate with respect to the projection optical system along a short side direction of the rectangular illumination area. The exposure apparatus according to claim 14, wherein: An exposure method, comprising illuminating a mask via the illumination optical device according to claim 11, and projecting and exposing a pattern image formed on the illuminated mask onto a photosensitive substrate. A rectangular illumination region having a long side along a direction optically corresponding to the first direction and a short side along a direction optically corresponding to the second direction is formed on the mask. The exposure method according to claim 16, wherein: The mask pattern and the photosensitive substrate are projected and exposed on the photosensitive substrate by relatively moving the mask and the photosensitive substrate with respect to the projection optical system along a short side direction of the rectangular illumination area. The exposure method according to claim 17, wherein

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