JP2004207521A - Optical characteristic measuring method, exposure method, and device manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure an optical characteristic of a projection optical system with the good accuracy and reproducibility in a short time. <P>SOLUTION: A light exposure is altered within a scope of at least an appropriate light exposure or below, while sequentially transferring a measuring pattern disposed on a reticle R to a wafer W disposed on an image plane side of a projection optical system PL to form a first region composed of a plurality of block regions on the wafer. Next, of the plurality of block regions, information regarding at least a part of the plurality of block regions which become a boundary in which an image of the measuring pattern starts emerging is detected. In this case, as the information regarding at least a part of the plurality of block regions which become a boundary in which the image of the measuring pattern starts emerging is detected, even if the light exposure made, while it is altered within a scope of at least the appropriate light exposure or below, it does not hinder the detection in particular. The optical characteristic of the projection optical system PL is acquired based on the detected results. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０１２９】
本実施形態の場合、前述した区画領域のサイズと計測用パターンＭＰ_nのウエハ上のサイズとの関係から容易に想像されるように、パターン出現区画領域において、計測用パターンＭＰ_nは、区画領域ＤＡ_i,jと中心を同じくし、該区画領域ＤＡ_i,jをほぼ６０％に縮小した範囲（領域）に存在することとなる。
【０１３０】
かかる点を考慮すると、上記の指定範囲として、例えば区画領域ＤＡ_i,j（ｉ＝１〜Ｍ、ｊ＝１〜Ｎ）と中心を同じくし、その領域を縮小した範囲をスコア算出に用いることができる。但し、その縮小率Ａ（％）は以下のように制限される。
【０１３１】
まず、下限については、範囲が狭すぎるとスコア算出に用いる領域が、パターン部分のみになってしまい、そうするとパターン出現部でもばらつきが小さくなってパターン有無判別には利用できなくなる。この場合には、上述のパターンの存在範囲から明らかなように、Ａ＞６０％である必要がある。また、上限については、当然１００％以下だが、検出誤差などを考慮して１００％より小さい比率にすべきである。これより、縮小率Ａは、６０％＜Ａ＜１００％に定める必要がある。
【０１３２】
本実施形態の場合、パターン部が区画領域の約６０％を占めているため、スコア算出に用いる領域（指定範囲）の区画領域に対する比を上げるほどＳ／Ｎ比が上がるものと予想される。
【０１３３】
しかるに、スコア算出に用いる領域内でのパターン部と非パターン部の領域サイズが同じになれば、パターン有無判別のＳ／Ｎ比を最大にすることができる。本実施形態では、幾つかの比率を実験的に確認した結果、例えばＡ＝９０％との場合に最も安定した結果が得られたので、Ａ＝９０％という比率を採用するものとする。勿論Ａは、９０％に限定されるものではなく、計測用パターンＭＰ_nとステップピッチＳＰによって決定されるウエハ上の区画領域とを考慮して、区画領域に対する計測用パターンＭＰ_nの像が占める割合を考慮して定めれば良い。また、スコア算出に用いる指定範囲は、区画領域と中心を同じくする領域に限定されるものではなく、計測用パターンＭＰ_nの像が区画領域内のどの位置に存在するかを考慮して定めれば良い。
【０１３４】
従って、ステップ５２０では、前記撮像データファイルから、各区画領域ＤＡ_i,jの前記指定範囲内の撮像データを抽出し、上式（１）を用いて、各区画領域ＤＡ_i,j（ｉ＝１〜Ｍ、ｊ＝１〜Ｎ）のスコアＥ_i,jを算出する。
【０１３５】
上記の方法で求めたスコアＥは、パターンの有無具合を数値として表しているので、所定の閾値で二値化することによってパターン有無の判別を自動的にかつ安定して行うことが可能である。
【０１３６】
そこで、次のステップ５２２（図１１）において、区画領域ＤＡ_i,j毎に上で求めたスコアＥ_i,jと所定の閾値ＳＨとを比較して、各区画領域ＤＡ_i,jにおける計測用パターンＭＰの像の有無を検出し、検出結果としての判定値Ｆ_i,j（ｉ＝１〜Ｍ、ｊ＝１〜Ｎ）を図示しない記憶装置に保存する。すなわち、このようにして、スコアＥ_i,jに基づいて、区画領域ＤＡ_i,j毎に計測用パターンＭＰ_nの像の形成状態を検出する。なお、像の形成状態としては、種々のものが考えられるが、本実施形態では、上述の如く、スコアＥがパターンの有無具合を数値として表すものであるという点に基づいて、区画領域内にパターンの像が形成されているか否かに着目することとしたものである。
【０１３７】
ここでは、スコアＥ_i,jが閾値ＳＨ以上の場合には、計測用パターンＭＰ_nの像が形成されていると判断し、検出結果としての判定値Ｆ_i,jを「０」とする。一方、スコアＥ_i,jが閾値ＳＨ未満の場合には、計測用パターンＭＰ_nの像が形成されていないと判断し、検出結果としての判定値Ｆ_i,jを「１」とする。図１３には、この検出結果の一例がテーブルデータとして示されている。この図１３は、前述の図９に対応するものである。
【０１３８】
図１３において、例えば、Ｆ_12,16は、ウエハＷ_TのＺ軸方向の位置がＺ₁₂で、露光エネルギ量がＰ₁₆のときに転写された計測用パターンＭＰ_nの像の形成状態の検出結果を意味し、一例として、図１３の場合には、Ｆ_12,16は、「１」という値になっており、計測用パターンＭＰ_nの像が形成されていないと判断されたことを示している。
【０１３９】
なお、閾値ＳＨは、予め設定されている値であり、オペレータが図示しない入出力装置を用いて変更することも可能である。
【０１４０】
次のステップ５２４では、上述の検出結果に基づいて、フォーカス位置毎にパターンの像が形成されている区画領域の数を求める。すなわち、フォーカス位置毎に判定値「０」の区画領域が何個あるかを計数し、その計数結果をパターン出現数Ｔ_i（ｉ＝１〜Ｍ）とする。この際に、周囲の領域と異なる値を持ついわゆる跳び領域は無視する。例えば、図１３の場合には、ウエハＷ_Tのフォーカス位置がＺ₁ではパターン出現数Ｔ₁＝８、Ｚ₂ではＴ₂＝１１、Ｚ₃ではＴ₃＝１４、Ｚ₄ではＴ₄＝１６、Ｚ₅ではＴ₅＝１６、Ｚ₆ではＴ₆＝１３、Ｚ₇ではＴ₇＝１１、Ｚ₈ではＴ₈＝８、Ｚ₉ではＴ₉＝５、Ｚ₁₀ではＴ₁₀＝３、Ｚ₁₁ではＴ₁₁＝２、Ｚ₁₂ではＴ₁₂＝２、Ｚ₁₃ではＴ₁₃＝２である。このようにして、フォーカス位置とパターン出現数Ｔ_iとの関係を求めることができる。
【０１４１】
なお、上記の跳び領域が生ずる原因として、計測時の誤認識、レーザのミスファイヤ、ゴミ、ノイズ等が考えられるが、このようにして生じた跳び領域がパターン出現数Ｔ_iの検出結果に与える影響を軽減するために、フィルタ処理を行っても良い。このフィルタ処理としては、例えば評価する区画領域を中心とする３×３の区画領域のデータ（判定値Ｆ_i,j）の平均値（単純平均値又は重み付け平均値）を求めることが考えられる。なお、フィルタ処理は、形成状態の検出処理前のデータ（スコアＥ_i,j）に対して行っても勿論良く、この場合には、より有効に跳び領域の影響を軽減できる。
【０１４２】
次のステップ５２６では、パターン出現数からベストフォーカス位置を算出するためのｎ次の近似曲線（例えば４〜６次曲線）を求める。
【０１４３】
具体的には、上記ステップ５２４で検出されたパターンの出現数を、横軸をフォーカス位置とし、縦軸をパターン出現数Ｔ_iとする座標系上にプロットする。この場合、図１４に示されるようになる。ここで、本実施形態の場合、ウエハＷ_Tの露光にあっては、各区画領域ＤＡ_i,jを同一の大きさとし、かつ、行方向で隣接する区画領域間の露光エネルギの差を一定値（＝ΔＰ）とし、列方向で隣接する区画領域間のフォーカス位置の差を一定値（＝ΔＺ）としたので、パターン出現数Ｔ_iが露光エネルギ量に比例するものとして扱うことができる。すなわち、図１９において、縦軸は露光エネルギ量Ｐであると考えることもできる。
【０１４４】
上記のプロット後、各プロット点をカーブフィットすることによりｎ次の近似曲線（最小自乗近似曲線）を求める。これにより、例えば図１９に点線で示されるような曲線Ｐ＝ｆ（Ｚ）が求められる。
【０１４５】
図１１に戻り、次のステップ５２８では、上記曲線Ｐ＝ｆ（Ｚ）の極値（極大値又は極小値）の算出を試みるとともに、その結果に基づいて極値が存在するか否かを判断する。そして、極値が算出できた場合には、ステップ５３０に移行して極値におけるフォーカス位置を算出して、その算出結果を光学特性の一つである最良フォーカス位置とするとともに、該最良フォーカス位置を図示しない記憶装置に保存する。
【０１４６】
一方、上記ステップ５２８において、極値が算出されなかった場合には、ステップ５３２に移行して、ウエハＷの位置変化（Ｚの変化）に対応する曲線Ｐ＝ｆ（Ｚ）の変化量が最も小さいフォーカス位置の範囲を算出し、その範囲の中間の位置を最良フォーカス位置として算出し、その算出結果を最良フォーカス位置とするとともに、該最良フォーカス位置を図示しない記憶装置に保存する。すなわち、曲線Ｐ＝ｆ（Ｚ）の最も平坦な部分に基づいてフォーカス位置を算出する。
【０１４７】
ここで、このステップ５３２のようなベストフォーカス位置の算出ステップを設けたのは、計測用パターンＭＰの種類やレジストの種類その他の露光条件によっては、例外的に上述の曲線Ｐ＝ｆ（Ｚ）が明確なピークを持たないような場合があるのでこのような場合にも、ベストフォーカス位置をある程度の精度で算出できるようにしたものである。
【０１４８】
次のステップ５３４において、前述のカウンタｎを参照して、全ての評価点対応領域ＤＢ₁〜ＤＢ₅について処理が終了したか否かを判断する。ここでは、評価点対応領域ＤＢ₁についての処理が終了しただけであるため、このステップ５３４における判断は否定され、ステップ５３６に進んでカウンタｎをインクリメント（ｎ←ｎ＋１）した後、図１０のステップ５０２に戻り、評価点対応領域ＤＢ₂がアライメント検出系ＡＳで検出可能となる位置に、ウエハＷ_Tを位置決めする。
【０１４９】
そして、上述したステップ５０４〜５３４までの処理（判断を含む）を再度行い、上述した評価点対応領域ＤＢ₁の場合と同様にして、評価点対応領域ＤＢ₂について最良フォーカス位置を求める。
【０１５０】
そして、評価点対応領域ＤＢ₂について最良フォーカス位置の算出が終了すると、ステップ５３４で全ての評価点対応領域ＤＢ₁〜ＤＢ₅について処理が終了したか否かを再度判断するが、ここでの判断は否定される。以後、ステップ５３４における判断が肯定されるまで、上記ステップ５０２〜５３６の処理（判断を含む）が繰り返される。これにより、他の評価点対応領域ＤＢ₃〜ＤＢ₉について、前述した評価点対応領域ＤＢ₁の場合と同様にして、それぞれ最良フォーカス位置が求められることとなる。
【０１５１】
このようにして、ウエハＷ_T上の全ての評価点対応領域ＤＢ₁〜ＤＢ₉について最良フォーカス位置の算出、すなわち投影光学系ＰＬに関して照明領域ＩＡＲと共役な露光領域内で９つの計測用パターンＭＰ₁〜ＭＰ₉の投影位置となる計測点（評価点）での最良フォーカス位置の算出がなされると、ステップ５３４での判断が肯定され、ステップ５３８に移行して、上で求めた最良フォーカス位置データに基づいて他の光学特性を算出する。
【０１５２】
例えば、このステップ５３８では、一例として、評価点対応領域ＤＢ₁〜ＤＢ₉における最良フォーカス位置のデータに基づいて、投影光学系ＰＬの像面湾曲を算出する。また、前述した露光領域内の各計測点（評価点）での焦点深度などを求めても良い。
【０１５３】
ここで、本実施形態では、説明の簡略化のため、投影光学系ＰＬの視野内の各評価点に対応するレチクルＲ_T上の領域に計測用パターンとして前述のパターンＭＰ_nのみが形成されていることを前提として、説明を行った。しかし、本発明がこれに限定されないことは勿論である。例えば各評価点に対応するレチクルＲ_T上の領域の近傍に、前述したステップピッチＳＰの整数倍、例えば８倍、１２倍などの間隔の所定領域に周期方向が異なるＬ／Ｓパターンや、ピッチが異なるＬ／Ｓパターンなど複数種類の計測用パターンをそれぞれ配置しても良い。このようにすると、例えば、各評価点に対応する位置に近接して配置された周期方向が直交する１組のＬ／Ｓパターンを計測用パターンとして得られた最良フォーカス位置から各評価点における非点収差を求めることができる。さらに、投影光学系ＰＬの視野内の各評価点について、上述のようにして算出された非点収差に基づいて最小二乗法による近似処理を行うことにより非点収差面内均一性を求めるとともに、非点収差面内均一性と像面湾曲とから総合焦点差を求めることも可能となる。
【０１５４】
そして、上述のようにして求められた投影光学系ＰＬの光学特性データは、図示しない記憶装置に保存されるとともに、不図示の表示装置の画面上に表示される。これにより、図１１のステップ５３８の処理、すなわち図５のステップ４５６の処理を終了し、一連の光学特性の計測処理を終了する。
【０１５５】
次に、デバイス製造の場合における、本実施形態の露光装置１００による露光動作を説明する。
【０１５６】
前提として、上述のようにして決定された投影光学系ＰＬの光学特性、例えば最良フォーカス位置の情報、あるいはこれに加えて像面湾曲の情報が、不図示の入出力装置を介して主制御装置２８に入力されているものとする。
【０１５７】
例えば、像面湾曲の情報が入力されている場合には、主制御装置２８は、露光に先立って、この光学特性データに基づいて、図示しない結像特性補正コントローラに指示し、例えば投影光学系ＰＬの少なくとも１つの光学素子（本実施形態では、レンズエレメント）の位置（他の光学素子との間隔を含む）あるいは傾斜などを変更することにより、その像面湾曲が補正されるように投影光学系ＰＬの結像特性を可能な範囲で補正する。なお、投影光学系ＰＬの結像特性の調整に用いる光学素子は、レンズエレメントなどの屈折光学素子だけでなく、例えば凹面鏡などの反射光学素子、あるいは投影光学系ＰＬの収差（ディストーション、球面収差など）、特にその非回転対称成分を補正する収差補正板などでも良い。さらに、投影光学系ＰＬの結像特性の補正方法は光学素子の移動に限られるものではなく、例えば光源１を制御して照明光ＩＬの中心波長を僅かにシフトさせる方法、又は投影光学系ＰＬの一部で屈折率を変化させる方法などを単独、あるいは光学素子の移動との組み合わせで採用しても良い。
【０１５８】
そして、主制御装置２８からの指示に応じて、不図示のレチクルローダにより転写対象となる所定の回路パターン（デバイスパターン）が形成されたレチクルＲがレチクルステージＲＳＴ上にロードされる。同様に、不図示のウエハローダにより、ウエハＷがウエハテーブル１８上にロードされる。
【０１５９】
次に、主制御装置２８により、不図示のレチクルアライメント検出系、ウエハテーブル１８上の基準マーク板ＦＰ、アラインメント検出系ＡＳ等を用いて、レチクルアラインメント、ベースライン計測などの準備作業が所定の手順で行われ、これに続いてＥＧＡ（エンハンスト・グローバル・アラインメント）方式などのウエハアライメントが行われる。なお、上記のレチクルアライメント、ベースライン計測等の準備作業については、例えば特開平７−１７６４６８号公報（対応米国特許第５，６４６，４１３号）に詳細に開示され、また、これに続くＥＧＡについては、特開昭６１−４４４２９号公報（対応米国特許第４，７８０，６１７号）に詳細に開示されているので、ここではこれ以上の詳細説明は省略する。
【０１６０】
上記のウエハアライメントが終了すると、以下のようにしてステップ・アンド・スキャン方式の露光動作が行われる。
【０１６１】
まず、主制御装置２８は、レチクルＲとウエハＷ、すなわちレチクルステージＲＳＴとＸＹステージ２０とのＹ軸方向の相対走査を開始する。両ステージＲＳＴ、２０がそれぞれの目標走査速度に達し、等速同期状態に達すると、照明系ＩＯＰからの紫外パルス光によってレチクルＲのパターン領域が照明され始め、走査露光が開始される。上記の相対走査は、主制御装置２８が、前述したレーザ干渉計２６及びレーザ干渉計１４の計測値をモニタしつつ、レチクルステージ駆動部（不図示）及び駆動系２２を制御することにより行われる。
【０１６２】
主制御装置２８は、特に上記の走査露光時には、レチクルステージＲＳＴのＹ軸方向の移動速度ＶｒとＸＹステージ２０のＹ軸方向の移動速度Ｖｗとが、投影光学系ＰＬの投影倍率（１／４倍あるいは１／５倍）に応じた速度比に維持されるように同期制御を行う。また、主制御装置２８は、走査露光中に、フォーカスセンサＡＦＳによって検出されたウエハＷのＺ軸方向の位置情報に基づき、前述の照明領域ＩＡＲと共役な露光領域内で、前述した光学特性補正後の投影光学系ＰＬの像面の焦点深度の範囲内にウエハＷ（ショット領域）表面が収まるように、駆動系２２を介してウエハテーブル１８をＺ軸方向及び傾斜方向に駆動し、ウエハＷのフォーカス・レベリング制御を行う。なお、本実施形態では、ウエハＷの露光動作に先立って、前述した各評価点における最良フォーカス位置に基づいて投影光学系ＰＬの像面を算出し、この像面がフォーカスセンサＡＦＳの検出基準となるようにフォーカスセンサＡＦＳの光学的なキャリブレーション（例えば、受光系５０ｂ内に配置される平行平面板の傾斜角度の調整など）が行われている。勿論、光学的なキャリブレーションを必ずしも行う必要はなく、例えば先に算出した像面とフォーカスセンサＡＦＳの検出基準との偏差に応じたオフセットを考慮して、フォーカスセンサＡＦＳの出力に基づいてウエハＷ表面を像面に一致させるフォーカス動作（及びレベリング動作）を行うようにしても良い。また、ウエハＷの移動の代わりに、あるいはこれと組み合わせて、レチクルＲと投影光学系ＰＬの光学素子との少なくとも一方を移動してフォーカス・レベリング制御を行っても良い。
【０１６３】
そして、レチクルＲのパターン領域の異なる領域が紫外パルス光で逐次照明され、パターン領域全面に対する照明が完了することにより、ウエハＷ上の第１ショット領域の走査露光が終了する。これにより、レチクルＲのパターンが投影光学系ＰＬを介して第１ショット領域に縮小転写される。
【０１６４】
上述のようにして、第１ショット領域の走査露光が終了すると、主制御装置２８により、駆動系２２を介してＸＹステージ２０がＸ、Ｙ軸方向にステップ移動され、第２ショット領域の露光のための走査開始位置（加速開始位置）に移動される。
【０１６５】
そして、主制御装置２８により、上述と同様に各部の動作が制御され、ウエハＷ上の第２ショット領域に対して上記と同様の走査露光が行われる。
【０１６６】
このようにして、ウエハＷ上のショット領域の走査露光とショット間のステッピング動作とが繰り返し行われ、ウエハＷ上の露光対象ショットの全てにレチクルＲのパターンが順次転写される。
【０１６７】
ウエハＷ上の全露光対象ショットへのパターン転写が終了すると、次のウエハと交換され、上記と同様にアライメント、露光動作が繰り返される。
【０１６８】
以上詳細に説明したように、本実施形態の露光装置１００によると、投影光学系の光学特性計測に際し、主制御装置２８は、計測用パターンＭＰ_n（ｎ＝１〜９）と枠パターンＡＰとが形成されたレチクルＲ_Tを、投影光学系の物体面側に配置されたレチクルステージＲＳＴ上に搭載し、投影光学系ＰＬの像面側に配置されたウエハＷ_T上に照射される照明光ＩＬのエネルギ量（露光量）Ｐを適正露光量以下の範囲内で変更しながら、かつウエハＷ_Tの投影光学系ＰＬの光軸方向に関する位置（Ｚ）を変更し、ウエハＷ_T上に計測用パターンＭＰ_nをステップ・アンド・リピート方式（ステップピッチＳＰ）で順次転写する（ステップ４０８〜４２４）。これにより、ウエハＷ_T上には、マトリックス状に配置された複数（Ｍ×Ｎ個）の区画領域（仮想の区画領域）ＤＡ_i,j（ｉ＝１〜Ｍ、ｊ＝１〜Ｎ）から成る全体として矩形の第１領域ＤＣ_nが形成される。この場合、適正露光量以下の範囲内で露光量を変更しながら露光が行われるので、前述した適性露光量以上の範囲で露光を行う場合に比べて、露光時間の短縮が可能となる。また、パターン線幅差が露光に与える影響が低減されている。また、第１領域ＤＣ_nは、区画領域相互間の境界に従来のような枠線が存在しないＮ行Ｍ列のマトリックス状配置の複数の区画領域（計測用パターンの像が投影された領域）によって構成される。
【０１６９】
次いで、主制御装置２８は、レチクルＲ_Tを移動し、レチクルＲ_TとウエハＷ_Tとを所定の位置関係に設定して、枠パターンＡＰを過露光となる露光量でウエハＷ_T上に転写する。これにより、ウエハＷ_T上の各第１領域ＤＣ_nの周囲に過露光の第２領域ＤＤ_nがそれぞれ形成される（ステップ４２８、４３０）。すなわち、ウエハＷ_T上には、第１領域ＤＣ_nとこの外枠領域を形成する第２領域ＤＤ_nとから成る評価点対応領域ＤＢ_nが形成される。
【０１７０】
そして、ウエハＷ_Tの現像後に、主制御装置２８は、ＦＩＡ系のアライメントセンサから成るアライメント検出系ＡＳを用いてウエハＷ_T上の評価点対応領域ＤＢ_nを撮像する（ステップ５０４）。次いで、主制御装置２８は、取り込んだレジスト像の撮像データに基づき、評価点対応領域ＤＢ_nの輪郭（矩形の外枠ＤＢＦ）を検出する（ステップ５０６、５０８）。
【０１７１】
次に、主制御装置２８は、既知の設計上の位置関係を考慮し、検出した外枠ＤＢＦを基準として評価点対応領域ＤＢ_nを構成する複数の区画領域ＤＡ_i,jのうち、第２領域ＤＤ_nを除く第１領域ＤＣ_nを構成するＭ×Ｎ個の区画領域それぞれの位置を算出する（ステップ５１８）。この算出は、外枠内の区画領域の数及び配置の情報に基づいて行われる。本実施形態では、外枠ＤＢＦを基準として設計値に基づき複数の区画領域の位置を算出するので、その複数の区画領域のほぼ正確な位置を求めることが可能となる。
【０１７２】
次いで、主制御装置２８は、前記撮像データに基づき、第１領域ＤＣ_nを構成するＭ×Ｎ個の区画領域の中から、計測用パターンの像が出現し始める境界となる複数の区画領域に関する情報を検出する。具体的には、第１領域ＤＣ_nを構成するＭ×Ｎ個の区画領域における像の形成状態（計測用パターンの像が出現しているか否か）を画像処理の手法、前述の各区画領域ＤＡ_i,jのスコアＥ_i,jと閾値ＳＨとを比較した二値化の手法により検出し（ステップ５２０、５２２）、その結果、パターンが出現しているとされた区画領域ＤＡ_i,jの数をフォーカス位置毎に計数し（ステップ５２４）、そのパターンの出現数を、横軸をフォーカス位置とし、縦軸をパターン出現数とする座標系上にプロットして、各プロット点をカーブフィットすることによりｎ次の近似曲線（最小自乗近似曲線）を求める。この場合、この近似曲線が、計測用パターンの像が出現し始める境界となる複数の区画領域に関する情報、具体的には計測用パターンの像が出現し始める境界となる複数の区画領域の配置情報に他ならない。
【０１７３】
すなわち、本実施形態では、過露光により計測用パターンの像が消失し始める境界となる区画領域を検出対象とせず、計測用パターンの像が出現し始める境界となる複数の区画領域の少なくとも一部に関する情報を検出するので、前述の如く、適正露光量以下の範囲で露光量を変化させながら露光を行っても、特に支障なく検出を行うことが可能となる。
【０１７４】
そして、検出された計測用パターンの像が出現し始める境界となる複数の区画領域の少なくとも一部に関する情報、すなわち前述のｎ次の近似曲線に基づいて、投影光学系の光学特性を求める（ステップ５３０〜５３８）。本実施形態では、客観的かつ定量的な上記のスコアＥ_i,j、すなわち画像のコントラストの指標値を用いた検出結果に基づいて最良フォーカス位置などの投影光学系ＰＬの光学特性を求めているため、短時間で精度良く最良フォーカス位置などを求めることが可能となる。従って、この最良フォーカス位置に基づいて決定される光学特性の計測精度及び計測結果の再現性を向上させることができるとともに、結果的に光学特性計測のスループットを向上させることが可能となる。また、従来の寸法を計測する方法に比べて、計測用パターンを小さくすることができるため、レチクルのパターン領域内に多くの計測用パターンを配置することが可能となる。従って、評価点の数を増加させることができるとともに、各評価点間の間隔を狭くすることができ、結果的に光学特性計測の計測精度を向上させることが可能となる。さらに、最適露光量以下の範囲で露光量を変化させているので、例えばレジスト像を計測対象とする場合に、レジストの特性によって計測結果が殆ど左右されない。
【０１７５】
また、本実施形態の場合、隣接する区画領域間に枠線が存在しないので、像形成状態の検出対象である複数の区画領域（主として計測用パターンの像が出現した区画領域）において、計測用パターンの像のコントラストが枠線の干渉に起因して低下することがない。このため、それらの複数の区画領域の撮像データとしてパターン部と非パターン部のＳ／Ｎ比の良好なデータを得ることができる。従って、区画領域毎の計測用パターンＭＰ_nの形成状態を精度、再現性良く検出することが可能となる。しかも、像の形成状態を客観的、定量的なスコアＥ_i,jを閾値ＳＨと比較してパターンの有無情報（二値化情報）に変換して検出するので、区画領域毎の計測用パターンＭＰ_nの形成状態を、再現性良く検出することができるとともに、パターン有無の判別を自動的にかつ安定して行うことができる。従って、本実施形態では、二値化に際して、閾値は一つだけで足り、複数の閾値を設定しておいて閾値毎にパターンの有無具合を判別するような場合に比べて、像の形成状態の検出に要する時間を短縮することができるとともに、その検出アルゴリズムも簡略化することができる。
【０１７６】
また、本実施形態では、上述の如く、像の形成状態をパターンの有無情報（二値化情報）に変換して検出するので、レチクルＲ_Tのパターン領域ＰＡ内に計測用パターンＭＰ_n以外のパターン（例えば、比較用の基準パターンや、位置決め用マークパターン等）を配置する必要がない。
【０１７７】
また、本実施形態に係る光学特性計測方法によると、統計処理による近似曲線の算出という客観的、かつ確実な方法を基礎として最良フォーカス位置を算出しているので、安定して高精度かつ確実に光学特性を計測することができる。なお、近似曲線の次数によっては、その変曲点、あるいはその近似曲線と所定のスライスレベルとの複数の交点等に基づいて最良フォーカス位置を算出することは可能である。
【０１７８】
また、本実施形態の露光装置１００では、前述の光学特性計測方法により精度良く計測された投影光学系ＰＬの光学特性を考慮して最適な転写が行えるように投影光学系ＰＬが露光に先立って調整され、その調整された投影光学系ＰＬを介してレチクルＲに形成されたパターンがウエハＷ上に転写される。更に、上述のようにして決定された最良フォーカス位置を考慮して露光の際のフォーカス制御目標値の設定が行われるので、デフォーカスによる色むらの発生を効果的に抑制することができる。従って、本実施形態に係る露光方法によると、微細パターンをウエハ上に高精度に転写することが可能となる。
【０１７９】
なお、上記実施形態で説明した光学特性計測方法は、一実施形態に過ぎず、本発明の光学特性計測方法がこれに限定されないことは勿論である。例えば、上記実施形態では、マトリックス状に配置された複数の区画領域ＤＡ_i,jから成る全体として矩形の第１領域ＤＣ_nをウエハＷ_T上に形成した後、第１領域の周囲に過露光の第２領域ＤＤ_nを形成するものとしたが、第２領域ＤＤ_nを形成した後、第１領域ＤＣ_nを形成しても良い。かかる場合には、例えば感光剤として、化学増幅型レジストなどの高感度レジストを用いる場合に、検出対象である計測用パターンの像の形成（転写）から現像までの時間を短くできるので、より望ましい。
【０１８０】
また、上記実施形態では、評価点対応領域ＤＢ_nを構成する第２領域ＤＤ_nが矩形枠状である場合について説明したが、本発明がこれに限定されるものではない。すなわち、第２領域は、その外縁が少なくとも第１領域を構成する各区画領域の位置算出の基準にできれば良いので、矩形枠状の一部の例えばコ字状（Ｕ字状）部分、あるいはＬ字状部分であっても良い。この場合、第１領域とその外側の第２領域とで構成される評価点対応領域は、全体として矩形の領域となる。
【０１８１】
また、前述の第２領域、すなわち矩形枠状の領域、あるいはその一部の領域を形成する方法は、上記実施形態で説明した方法に限らず、例えば、露光装置１００のレチクルステージＲＳＴ上に例えば矩形枠状の光透過部から成るパターン（第２領域ＤＤ_nと同様の形状のパターン）あるいはその一部のパターンなどが形成されたレチクルを搭載し、そのレチクルのパターンを１回の走査露光で、投影光学系ＰＬの像面側に配置されたウエハ上に転写して、過露光の第２領域をウエハ上に形成することとしても良い。あるいは、前述の計測用パターンをステップ・アンド・リピート方式又はステップ・アンド・スキャン方式で、過露光となる露光量でウエハ上に転写して前述の第２領域ＤＤ_nを形成しても良い。この他、、計測用パターンが完全に含まれる区画領域ＤＡ_i,jに対応するサイズの矩形の開口パターンが形成されたレチクルをレチクルステージＲＳＴ上に搭載して、ステップ・アンド・リピート方式又はステップ・アンド・スキャン方式で、その開口パターンを過露光の露光エネルギ量でウエハ上に転写することにより、過露光の第２領域をウエハ上に形成することとしても良い。また、例えば上記の開口パターンを用いてステップ・アンド・スティッチ方式で露光を行い、ウエハ上に開口パターンの複数の像を隣接してあるいは繋ぎ合わせて形成することによって、過露光の第２領域をウエハ上に形成しても良い。この他、レチクルステージＲＳＴを静止させた状態でそのレチクルステージＲＳＴ上に搭載されたレチクルに形成された開口パターンを照明光で照明しながらウエハＷ（ウエハテーブル１８）を所定方向に移動して過露光の第２領域を形成しても良い。いずれにしても、上記実施形態と同様に、過露光の第２領域の存在により、その第２領域の外縁をＳ／Ｎ比の良好な検出信号に基づいて精度良く検出することが可能となる。
【０１８２】
なお、上記実施形態では、計測用パターンＭＰ_nの像の形成状態を、スコアＥ_i,jと閾値ＳＨとを比較してパターンの有無情報（二値化情報）に変換して検出する場合について説明したが、本発明がこれに限定されるものではない。上記実施形態では、評価点対応領域ＤＢ_nの外枠ＤＢＦを精度良く検出し、この外枠を基準として各区画領域ＤＡ_i,jを演算により算出するので、各区画領域の位置を正確に求めることができる。従って、この正確に求められた各区画領域に対してテンプレートマッチングを行うこととしても良い。このようにすれば、短時間にテンプレートマッチングを行うことができる。この場合、テンプレートパターンとして、例えば像が出現した区画領域あるいは像が出現しなかった区画領域の撮像データを用いることができる。このようにしても、客観的、定量的な相関値の情報が区画領域毎に得られるので、得られた情報を、所定の閾値と比較することにより、計測用パターンＭＰ_nの形成状態を二値化情報（像の有無情報）に変換して、上記実施形態と同様に像の形成状態を精度、再現性良く検出することができる。
【０１８３】
また、過露光の第２領域は、必ずしもなくても良い。かかる場合であっても、第１領域の輪郭が矩形の外枠となり、第１領域内の最外周部に位置する区画領域（以下、「外縁部区画領域」と呼ぶ）の一部には、パターン像が形成されない領域が存在するので、上記実施形態と同様の手法により、その外枠の一部、すなわち第１領域とその外側の領域の境界線をＳ／Ｎ比良く検出することが可能となり、その境界線を基準として設計値に基づき他の区画領域（第１領域を構成する各区画領域）の位置を算出することができ、他の区画領域のほぼ正確な位置を求めることが可能である。同様に、過露光の第２領域は、上記実施形態のような矩形枠状あるいはその一部のような形状に限定されるものではない。例えば、第２領域の形状は、第１領域との境界線（内縁）のみが矩形枠状の形状を有し、外縁は任意形状であっても良い。これらの場合にも、第１領域内の複数の区画領域それぞれの位置をほぼ正確に知ることができるので、例えばそれぞれの区画領域に対して、上記実施形態と同様のスコア（像のコントラストの指標値）を用いた方法、あるいはテンプレートマッチング法を適用して像の形成状態を検出することにより、上記実施形態と同様に、パターン像の形成状態を短時間で検出することが可能になる。
【０１８４】
そして、その検出結果に基づいて投影光学系の光学特性を求めることにより、客観的かつ定量的な像のコントラスト又は相関値を用いた検出結果に基づいて光学特性が求めることができる。従って、上記実施形態と同等の効果を得ることができる。
【０１８５】
また、上記実施形態では、各区画領域の検出の基準となる外枠ＤＢＦの検出、及び各区画領域の像の形成状態の検出にＦＩＡ系のアライメントセンサを用いるものとしたが、本発明がこれに限定されるものではない。すなわち、外枠ＤＢＦあるいは上述した前記外縁部区画領域と第２領域の境界線の検出、及び各区画領域の像の形成状態の検出の少なくとも一方に、ＳＥＭ（走査型電子顕微鏡）などの他の撮像装置（画像計測装置）を用いても良い。かかる場合であっても、第２領域の外枠又は内縁部を基準として、第１領域内の各区画領域の位置を精度良く求めることが可能である。
【０１８６】
また、上記実施形態では、図３に示されるように、遮光部から成るパターン領域ＰＡの内部に光透過部によって計測用パターンＭＰ_nが形成された場合について説明したが、これに限らず、図３の場合と反対に、開口パターンの内部に遮光部によって形成される残しパターン（すなわち、両側が光透過部となる複数のライン部）によって計測用パターンＭＰ_nを形成しても良い。残しパターンによって計測用パターンを形成する場合には、ウエハにはその表面にネガ型レジストによって感光層を形成すれば良い。このようにすることにより、上記実施形態と同様に適正露光量以下の範囲で露光量を変化させても、前述と同様に転写像の出現し始める境界となる区画領域を精度良く検出することができ、結果的に上記実施形態と同等の効果を得ることができる。更に、上記実施形態ではレチクルのパターン領域ＰＡを遮光部としたが、パターン領域ＰＡは光透過部でも良く、この場合には、計測用パターンＭＰ_nの周囲の部分のみを遮光部とするとともに、転写に際して、照明領域をその遮光部部分のみに制限すれば良い。
【０１８７】
なお、上記実施形態では、レチクルＲ_T上の計測用パターンＭＰ_nとして１種類のＬ／Ｓパターン（マルチバーパターン）を用いる場合について説明したが、本発明がこれに限定されないことは言うまでもない。計測用パターンとしては、周期方向が異なる少なくとも２種類のＬ／Ｓパターンや、孤立線やコンタクトホールなどを用いても良い。計測用パターンＭＰ_nとしてＬ／Ｓパターンを用いる場合には、デューティ比及び周期方向は、任意で良い。また、計測用パターンＭＰ_nとして周期パターンを用いる場合、その周期パターンは、Ｌ／Ｓパターンだけではなく、例えばドットマークを周期的に配列したパターンでも良い。これは、像の線幅等を計測する従来の方法とは異なり、像の形成状態をスコア（コントラスト）で検出しているからである。
【０１８８】
また、上記実施形態では、１種類のスコアに基づいて最良フォーカス位置を求めているが、これに限らず、複数種類のスコアを設定しこれらに基づいて、それぞれ最良フォーカス位置を求めても良く、あるいはこれらの平均値（あるいは重み付け平均値）に基づいて最良フォーカス位置を求めても良い。
【０１８９】
また、上記実施形態では、像の形成状態の検出に１種類の閾値を用いているが、これに限らず、複数の閾値を用いても良い。複数の閾値を求める場合、それぞれの閾値を、スコアと比較することで、区画領域の像の形成状態を検出することとしても良い。この場合、例えば第１の閾値での検出結果から最良フォーカス位置が算出困難な場合に、第２の閾値での形成状態の検出を行い、その検出結果から最良フォーカス位置を求めることなどが可能となる。
【０１９０】
また、予め複数の閾値を設定しておき、閾値毎に最良フォーカス位置を求め、それらの平均値（単純平均値あるいは重み付け平均値）を最良フォーカス位置としても良い。例えば、各閾値に応じて、露光エネルギ量Ｐが極値を示すときのフォーカス位置を順次算出する。そして、各フォーカス位置の平均値を最良フォーカス位置とする。なお、露光エネルギ量Ｐとフォーカス位置Ｚとの関係を示す近似曲線と適当なスライスレベル（露光エネルギ量）との２つの交点（フォーカス位置）を求め、両交点の平均値を、各閾値毎に算出し、それらの平均値（単純平均値あるいは重み付け平均値）を最良フォーカス位置としても良い。
【０１９１】
あるいは、各閾値毎に最良フォーカス位置を算出し、閾値と最良フォーカス位置との関係において、閾値の変動に対して、最良フォーカス位置の変化が最も小さい区間における最良フォーカス位置の平均値（単純平均値あるいは重み付け平均値）を最良フォーカス位置としても良い。
【０１９２】
また、上記実施形態では、予め設定されている値を閾値として用いているが、これに限定されるものではない。例えば、ウエハＷ_T上の計測用パターンＭＰ_nが転写されていない領域を撮像し、得られたスコアを閾値としても良い。
【０１９３】
さらに、例えば前述の第１領域と第２領域とで、アライメント検出系ＡＳによる画像の取り込み回数を異ならせても良く、このようにすることにより計測時間の短縮などを図ることができる。
【０１９４】
なお、上記実施形態の露光装置１００では、主制御装置２８は、図示しない記憶装置に格納されている処理プログラムに従って、前述した投影光学系の光学特性の計測を行うことにより、計測処理の自動化を実現することができる。勿論、この処理プログラムは、他の情報記録媒体（ＣＤ−ＲＯＭ、ＭＯ等）に保存されていても良い。さらに、計測を行う時に、図示しないサーバから処理プログラムをダウンロードしても良い。また、計測結果を、図示しないサーバに送付したり、インターネットやイントラネットを介して電子メール及びファイル転送により、外部に通知することも可能である。
【０１９５】
なお、上記実施形態では、計測用パターンＭＰ_nをウエハＷ_T上の各区画領域ＤＡ_i,jに転写した後、現像後にウエハＷ_T上の各区画領域ＤＡ_i,jに形成されるレジスト像をアライメント検出系ＡＳによって撮像し、その撮像データに対して画像処理を行う場合について説明したが、本発明に係る光学特性の計測方法はこれに限定されるものではない。例えば、撮像の対象は、露光の際にレジストに形成された潜像であっても良く、上記像が形成されたウエハを現像し、さらにそのウエハをエッチング処理して得られる像（エッチング像）などに対して行っても良い。また、ウエハなどの物体上における像の形成状態を検出するための感光層は、フォトレジストに限らず、光（エネルギ）の照射によって像（潜像及び顕像）が形成されるものであれば良い。例えば、感光層は、光記録層、光磁気記録層などであっても良く、従って、感光層が形成される物体もウエハ又はガラスプレート等に限らず、光記録層、光磁気記録層などが形成可能な板等であっても良い。
【０１９６】
また、オペレータなどが介在することなく、前述の計測結果（最良フォーカス位置など）に基づいて投影光学系ＰＬの光学特性を調整することができる。すなわち、露光装置に自動調整機能を持たせることが可能となる。
【０１９７】
また、上記実施形態では、パターンの転写の際に変更される露光条件が、投影光学系の光軸方向に関するウエハＷ_Tの位置及びウエハＷ_Tの面上に照射されるエネルギビームのエネルギ量（露光ドーズ量）である場合について説明したが、本発明がこれに限定されるものではない。例えば、投影光学系の光軸方向に関するウエハＷ_Tの位置に限らず、例えば、照明条件（マスクの種別を含む）、投影光学系の結像特性など露光に関連する全ての構成部分の設定条件などの何れかを露光条件の１つとして変化させても良い。また、必ずしも２種類の露光条件を変更しながら露光を行う必要もない。すなわち、一種類の露光条件、すなわち、適正露光量以下の範囲内で露光量を変更しながら計測用マスクのパターンを感光物体上の複数の領域に転写し、その転写像の形成状態を検出する場合であっても、上記実施形態と同様のスコアを用いたコントラスト計測、あるいはテンプレートマッチングの手法により、その検出を迅速に行うことができるという効果がある。
【０１９８】
また、上記実施形態において、最良フォーカス位置とともに最良露光量を決定することができる。すなわち、露光エネルギ量を高エネルギ量側にも設定して、上記実施形態と同様の処理を行い、露光エネルギ量毎に、その像が検出されたフォーカス位置の幅を求め、該幅が最大となるときの露光エネルギ量を算出し、その場合の露光量を最良露光量とする。
【０１９９】
また、上記実施形態では、一例として、区画領域内の指定範囲のピクセル値の分散（又は標準偏差）を、スコアＥとして採用するものとしたが、本発明がこれに限定されるものではなく、区画領域内又はその一部（例えば、前述の指定範囲）のピクセル値の加算値、微分総和値をスコアＥとしても良い。
【０２００】
また、上記実施形態では、各区画領域ＤＡ_i,jの計測用パターンの像の有無を、スコアを閾値と比較することで検出するものとしたが、この代わりに、次のようにして、前述の図１４の曲線Ｐ＝ｆ（Ｚ）と同様の近似曲線を算出しても良い。
【０２０１】
すなわち、前述の外枠検出及びその検出結果を利用した各区画領域の位置の算出により、撮像データ上における第１領域ＤＣ_nの範囲を求める。そして、この第１領域ＤＣ_nに対応する撮像データの所定方向、例えば前述のマトリックスの行方向（Ｘ軸方向）のピクセル列毎のピクセルデータの加算値（Ｘ軸方向の走査線上の輝度値の積算信号）の分布状況を検出する。そして、このようにして得られたピクセル列毎のピクセルデータ（ピクセル値）の加算値の分布曲線における各ピーク点を見つけると、このピーク点が、計測用パターンの像が出現し始める境界となる区画領域の位置に相当する。
【０２０２】
次に、このピーク点をカーブフィットすることによりｎ次の近似曲線（最小自乗近似曲線）を求める。これにより、例えば図１４の曲線Ｐ＝ｆ（Ｚ）と同様の形状の近似曲線を得ることができる。この場合、所定方向のピクセル列毎のピクセルデータの加算値の分布状況を算出するという簡単な画像処理により、前述の区画領域毎の像の形成状態（例えば有無検出）の検出結果と実質的に等価な分布状況のデータを得ることができる。従って、客観的かつ定量的な撮像データを用いて、前述の区画領域毎の像の形成状態（例えば有無検出）の検出結果を得る場合と同程度の検出精度及び再現性で、より簡易な手法により像の形成状態を検出することができる。
【０２０３】
そして、上記の近似曲線を用いて、上記実施形態と同様の処理を行うことにより、投影光学系ＰＬの光学特性、例えばベストフォーカス位置などを求めることとすれば良い。このようにしても、上記実施形態と同様に、客観的かつ定量的な撮像データを用いた検出結果に基づいて光学特性が求められるため、従来の方法と比較して光学特性を精度及び再現性良く計測することができる。
【０２０４】
さらに、上記実施形態では、結像特性補正コントローラを介して投影光学系ＰＬの結像特性を調整するものとしたが、例えば、結像特性補正コントローラだけでは結像特性を所定の許容範囲内に制御することができないときなどは、投影光学系ＰＬの少なくとも一部を交換しても良いし、あるいは投影光学系ＰＬの少なくとも１つの光学素子を再加工（非球面加工など）しても良い。また、特に光学素子がレンズエレメントであるときはその偏芯を変更しても良く、あるいは光軸を中心として回転させても良い。このとき、露光装置１００のアライメントセンサを用いてレジスト像などを検出する場合、主制御装置２８はディスプレイ（モニタ）への警告表示、あるいはインターネット又は携帯電話などによって、オペレータなどにアシストの必要性を通知しても良いし、投影光学系ＰＬの交換箇所や再加工すべき光学素子など、投影光学系ＰＬの調整に必要な情報を一緒に通知すると良い。これにより、光学特性の計測などの作業時間だけでなく、その準備期間も短縮でき、露光装置の停止期間の短縮、すなわち稼働率の向上を図ることが可能となる。また、本実施形態では計測用パターンを静止露光方式でウエハに転写するものとしたが、静止露光方式の代わりに、あるいはそれに加えて走査露光方式で、上記実施形態と全く同様に少なくとも１つの露光条件を変えながら計測用パターンをウエハに転写することでダイナミックな光学特性を求めるようにしても良い。
【０２０５】
また、上記実施形態では、評価点対応領域ＤＢ_nを構成するＮ×Ｍ個の区画領域ＤＡ_i,jを全て露光するものとしたが、Ｎ×Ｍ個の区画領域の少なくとも１個、すなわち曲線Ｐ＝ｆ（Ｚ）の決定に明らかに寄与しない露光条件が設定される区画領域（例えば、図９で左上隅及び左下隅に位置する区画領域など）についてはその露光を行わなくても良く、評価点対応領域ＤＢ_nは、全体として矩形（マトリックス）となっていなくても良い。
【０２０６】
また、上記実施形態ではアライメント検出系ＡＳで撮像されるレジスト像の画像信号を走査線毎に積算しても良い。また、上記実施形態では１つの評価点対応領域ＤＢ_nの全体を一括で撮像するものとしたが、例えば１つの評価点対応領域ＤＢ_nを複数回に分けて撮像しても良い。さらに、各撮像時にウエハを位置決めすることなく連続移動しても良く、これにより計測時間の短縮を図ることが可能となる。このとき、例えば区画領域ＤＡ_i,j毎に複数回撮像してその画像データを加算しても良い。
【０２０７】
さらに、本発明が適用される露光装置の光源は、ＫｒＦエキシマレーザやＡｒＦエキシマレーザに限らず、Ｆ₂レーザ（波長１５７ｎｍ）、あるいは他の真空紫外域のパルスレーザ光源であっても良い。この他、露光用照明光として、例えば、ＤＦＢ半導体レーザ又はファイバーレーザから発振される赤外域、又は可視域の単一波長レーザ光を、例えばエルビウム（又はエルビウムとイッテルビウムの両方）がドープされたファイバーアンプで増幅し、非線形光学結晶を用いて紫外光に波長変換した高調波を用いても良い。また、紫外域の輝線（ｇ線、ｉ線等）を出力する超高圧水銀ランプ等を用いても良い。この場合には、ランプ出力制御、ＮＤフィルタ等の減光フィルタ、光量絞り等によって露光エネルギの調整を行えば良い。また、ＥＵＶ光、Ｘ線、あるいは電子線及びイオンビームなどの荷電粒子線を露光ビームとして用いる露光装置に本発明を適用しても良い。
【０２０８】
なお、上記実施形態では、本発明がステップ・アンド・スキャン方式の縮小投影露光装置に適用された場合について説明したが、本発明の適用範囲がこれに限定されないのは勿論である。すなわち、ステップ・アンド・リピート方式、ステップ・アンド・スティッチ方式又はプロキシミティ方式などの露光装置、あるいはミラープロジェクション・アライナー、及びフォトリピータなどにも好適に適用することができる。さらに、例えば国際公開ＷＯ９９／４９５０４号などに開示される、投影光学系ＰＬとウエハとの間に液体が満たされる液浸露光装置にも本発明は好適に適用することができる。
【０２０９】
さらに、投影光学系ＰＬは、屈折系、反射屈折系、及び反射系のいずれでもよいし、縮小系、等倍系、及び拡大系のいずれでも良い。
【０２１０】
さらに、本発明は、半導体素子の製造に用いられる露光装置だけでなく、液晶表示素子、プラズマディスプレイなどを含むディスプレイの製造に用いられる、デバイスパターンをガラスプレート上に転写する露光装置、薄膜磁気へッドの製造に用いられる、デバイスパターンをセラミックウエハ上に転写する露光装置、撮像素子（ＣＣＤなど）、有機ＥＬ、マイクロマシン、及びＤＮＡチップなどの製造、さらにはマスク又はレチクルの製造に用いられる露光装置などにも適用することができる。
【０２１１】
《デバイス製造方法》
次に、上記説明した露光装置及び方法を使用したデバイスの製造方法の実施形態を説明する。
【０２１２】
図１５には、デバイス（ＩＣやＬＳＩ等の半導体チップ、液晶パネル、ＣＣＤ、薄膜磁気ヘッド、ＤＮＡチップ、マイクロマシン等）の製造例のフローチャートが示されている。図１５に示されるように、まず、ステップ３０１（設計ステップ）において、デバイスの機能・性能設計（例えば、半導体デバイスの回路設計等）を行い、その機能を実現するためのパターン設計を行う。引き続き、ステップ３０２（マスク製作ステップ）において、設計した回路パターンを形成したマスクを製作する。一方、ステップ３０３（ウエハ製造ステップ）において、シリコン等の材料を用いてウエハを製造する。
【０２１３】
次に、ステップ３０４（ウエハ処理ステップ）において、ステップ３０１〜ステップ３０３で用意したマスクとウエハを使用して、後述するように、リソグラフィ技術によってウエハ上に実際の回路等を形成する。次いで、ステップ３０５（デバイス組立ステップ）において、ステップ３０４で処理されたウエハを用いてデバイス組立を行う。このステップ３０５には、ダイシング工程、ボンディング工程、及びパッケージング工程（チップ封入）等の工程が必要に応じて含まれる。
【０２１４】
最後に、ステップ３０６（検査ステップ）において、ステップ３０５で作製されたデバイスの動作確認テスト、耐久性テスト等の検査を行う。こうした工程を経た後にデバイスが完成し、これが出荷される。
【０２１５】
図１６には、半導体デバイスの場合における、上記ステップ３０４の詳細なフロー例が示されている。図１６において、ステップ３１１（酸化ステップ）においてはウエハの表面を酸化させる。ステップ３１２（ＣＶＤステップ）においてはウエハ表面に絶縁膜を形成する。ステップ３１３（電極形成ステップ）においてはウエハ上に電極を蒸着によって形成する。ステップ３１４（イオン打込みステップ）においてはウエハにイオンを打ち込む。以上のステップ３１１〜ステップ３１４それぞれは、ウエハ処理の各段階の前処理工程を構成しており、各段階において必要な処理に応じて選択されて実行される。
【０２１６】
ウエハプロセスの各段階において、上述の前処理工程が終了すると、以下のようにして後処理工程が実行される。この後処理工程では、まず、ステップ３１５（レジスト形成ステップ）において、ウエハに感光剤を塗布する。引き続き、ステップ３１６（露光ステップ）において、上記各実施形態の露光装置及び露光方法によってマスクの回路パターンをウエハに転写する。次に、ステップ３１７（現像ステップ）においては露光されたウエハを現像し、ステップ３１８（エッチングステップ）において、レジストが残存している部分以外の部分の露出部材をエッチングにより取り去る。そして、ステップ３１９（レジスト除去ステップ）において、エッチングが済んで不要となったレジストを取り除く。
【０２１７】
これらの前処理工程と後処理工程とを繰り返し行うことによって、ウエハ上に多重に回路パターンが形成される。
【０２１８】
以上のような、本実施形態のデバイス製造方法を用いれば、露光ステップで、上記実施形態の露光装置及び露光方法が用いられるので、前述した光学特性計測方法で精度良く求められた光学特性を考慮して調整された投影光学系を介して高精度な露光が行われ、高集積度のデバイスを生産性良く製造することが可能となる。
【０２１９】
【発明の効果】
以上説明したように、本発明に係る光学特性計測方法によれば、短時間で、精度及び再現性良く投影光学系の光学特性を求めることができるという効果がある。
【０２２０】
また、本発明に係る露光方法によれば、高精度な露光を実現できるという効果がある。
【０２２１】
また、本発明に係るデバイス製造方法によれば、高集積度のデバイスを製造することができるという効果がある。
【図面の簡単な説明】
【図１】本発明の一実施形態の露光装置の概略構成を示す図である。
【図２】図１の照明系ＩＯＰの具体的構成の一例を説明するための図である。
【図３】投影光学系の光学特性の計測に用いられるレチクルの一例を示す図である。
【図４】光学特性の計測方法を説明するためのフローチャート（その１）である。
【図５】光学特性の計測方法を示すフローチャート（その２）である。
【図６】区画領域の配列を説明するための図である。
【図７】ウエハＷ_T上に第１領域ＤＣ_nが形成された状態を示す図である。
【図８】ウエハＷ_T上に評価点対応領域ＤＢ_nが形成された状態を示す図である。
【図９】ウエハＷ_Tを現像後にＷ_T上に形成された評価点対応領域ＤＢ₁のレジスト像の一例を示す図である。
【図１０】図５のステップ４５６（光学特性の算出処理）の詳細を示すフローチャート（その１）である。
【図１１】図５のステップ４５６（光学特性の算出処理）の詳細を示すフローチャート（その２）である。
【図１２】ステップ５１８の処理により第１領域ＤＣ_nを構成する各区画領域ＤＡ_i,jが求められた様子を示す図である。
【図１３】検出結果の一例を示すテーブルデータ形式の図である。
【図１４】パターン出現数（露光エネルギ量）とフォーカス位置との関係を示す図である。
【図１５】本発明に係るデバイス製造方法の実施形態を説明するためのフローチャートである。
【図１６】図１５のステップ３０４における処理のフローチャートである。
【符号の説明】
ＤＡ_i,j…区画領域、ＤＢ_n…評価点対応領域（所定領域）、ＩＬ…エネルギビーム、ＭＰ_n…計測用パターン、ＰＬ…投影光学系、Ｒ…レチクル（マスク）、Ｗ…ウエハ（感光物体）、Ｗ_T…ウエハ（感光物体）。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical property measuring method, an exposure method, and a device manufacturing method, and more particularly, to an optical property measuring method for measuring optical properties of a projection optical system, and taking into account optical properties measured by the optical property measuring method. The present invention relates to an exposure method for performing exposure using a projection optical system adjusted by the method, and a device manufacturing method using the exposure method.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in a lithography process for manufacturing a semiconductor element, a liquid crystal display element, or the like, a resist or the like is applied to a pattern formed on a mask or a reticle (hereinafter, collectively referred to as a “reticle”) via a projection optical system. 2. Description of the Related Art An exposure apparatus is used for transferring an image onto a substrate such as a wafer or a glass plate (hereinafter, also appropriately referred to as a “wafer”). In recent years, as this type of apparatus, from the viewpoint of emphasizing throughput, a step-and-repeat type reduced projection exposure apparatus (so-called “stepper”) or a step-and-scan type scanning type apparatus which is an improvement on this stepper has been used. 2. Description of the Related Art A sequentially moving type exposure apparatus such as an exposure apparatus is relatively frequently used.
[0003]
In addition, semiconductor elements (integrated circuits) and the like are becoming highly integrated year by year. Accordingly, projection exposure apparatuses, which are apparatuses for manufacturing semiconductor elements and the like, require higher resolution, that is, transfer of finer patterns with high precision. It has come to be required. In order to improve the resolving power of a projection exposure apparatus, it is necessary to improve the optical performance of the projection optical system, and it is necessary to accurately measure and evaluate the optical characteristics (including the imaging characteristics) of the projection optical system. It is important.
[0004]
The accurate measurement of the optical characteristics of the projection optical system, for example, the image plane of the pattern, is based on the premise that the optimum focus position (best focus position) at each evaluation point (measurement point) in the field of view of the projection optical system can be accurately measured. Become.
[0005]
As a method of measuring the best focus position in a conventional projection exposure apparatus, a so-called CD / focus method and a so-called SMP focus measurement method have been mainly used. In the former CD / focus method, for example, a test pattern such as a line and space pattern is transferred to a test wafer at a plurality of wafer positions in the optical axis direction of the projection optical system. Then, the line width value of the resist image (transferred pattern image) obtained by developing the test wafer is measured using a scanning electron microscope (SEM) or the like, and the line width value and the projection optical system are measured. The best focus position is determined based on a correlation with the wafer position in the optical axis direction (hereinafter, also appropriately referred to as “focus position”). In the latter SMP focus measurement method, a resist image of a wedge mark is formed on a wafer at a plurality of focus positions, and a change in a line width value of the resist image due to a difference in the focus position is amplified to a dimensional change in a longitudinal direction. The length of the resist image in the longitudinal direction is measured using a mark detection system such as an alignment system of the exposure apparatus. Then, the best focus position is detected (calculated) based on the correlation between the focus position and the length of the resist image (see Patent Documents 1 and 2).
[0006]
For various test patterns, astigmatism, field curvature, and the like, which are optical characteristics of the projection optical system, are measured based on the best focus position obtained as described above.
[0007]
However, in the above-described CD / focus method, for example, in order to measure the line width value of a resist image by SEM, it is necessary to strictly adjust the focus of SEM, and the measurement time per point is extremely long. It took several hours to several tens of hours to perform the measurement at. Further, it is expected that a test pattern for measuring the optical characteristics of the projection optical system will be miniaturized, and the number of evaluation points in the field of view of the projection optical system will also increase. Therefore, the conventional measurement method using the SEM has a disadvantage that the throughput until a measurement result is obtained is significantly reduced. Also, higher levels of measurement error and reproducibility of measurement results have been required, and it has become difficult to cope with the conventional measurement methods. Further, as an approximation curve indicating the correlation between the focus position and the line width value, an approximation curve of the fourth order or higher is used to reduce the error. There was a constraint that a width value had to be determined. The difference between the line width value at the focus position (including both the + direction and the − direction with respect to the optical axis direction of the projection optical system) deviated from the best focus position and the line width value at the best focus position is an error. Is required to be 10% or more in order to reduce the value, but it has become difficult to satisfy this condition.
[0008]
In addition, in the above-described SMP focus measurement method, since the measurement is usually performed with monochromatic light, the influence of interference varies depending on the shape of the resist image, which may lead to a measurement error (dimensional offset). Furthermore, in order to measure the length of the resist image of the wedge-shaped mark by image processing, it is necessary to capture in detail information up to both ends in the longitudinal direction where the resist image becomes thinnest. However, there is a problem that the resolution of a camera or the like is not yet sufficient. In addition, since the test pattern is large, it has been difficult to increase the number of evaluation points in the field of view of the projection optical system.
[0009]
In addition, in order to mainly improve the above-mentioned drawbacks of the CD / focus method, a wafer on which a pattern is transferred by test exposure is developed, and a resist image of a pattern formed on the wafer after the development is captured. There is also known an invention in which pattern matching with a predetermined template is performed by using the method and the best exposure condition such as a best focus position is determined based on the result (see Patent Documents 3 and 4). According to the inventions disclosed in Patent Documents 3 and 4, the resolution of the current image capturing device (such as a CCD camera) such as the SMP measurement method is insufficient, and the number of evaluation points within the field of view of the projection optical system is low. There is no inconvenience that the increase is difficult.
[0010]
[Patent Document 1]
Patent No. 2580668
[Patent Document 2]
Patent No. 2712330
[Patent Document 3]
JP-A-11-233434
[Patent Document 4]
WO 02/29870 pamphlet
[Problems to be solved by the invention]
However, when the template matching method is adopted and automated, a frame (pattern) serving as a reference for matching is usually formed on a wafer together with a pattern in order to facilitate the template matching. is there.
[0011]
However, in the method of determining the best exposure condition using template matching as described in Patent Documents 3 and 4, etc., a variety of process conditions include a reference for template matching formed near a pattern. When the image is captured by an image processing type wafer alignment system such as an FIA (field image alignment) system alignment sensor due to the presence of a frame, the contrast of the pattern portion is significantly reduced and measurement becomes difficult. was there.
[0012]
In particular, in the method described in Patent Document 4, the presence or absence of the image of the measurement pattern is detected for each divided area based on the result of the pattern matching described above, and the image of the pattern is detected based on the presence / absence information. Since a partition area (vanishing point) serving as a boundary of disappearance is detected, the exposure amount is changed in a range from near the optimum exposure amount of the resist to overexposure (overdose). In this case, even if the line width of the measurement pattern is slightly changed, the optimum exposure amount largely changes. In other words, since the line width difference of the measurement pattern greatly affects the exposure, the optimum exposure condition is determined. It was accompanied by difficulties. For example, when a resist image is to be measured, the measurement result tends to be greatly affected by the type of the resist. In addition, in the case of measuring the optical characteristics of the projection optical system, exposure is performed by a static exposure method. In this case, exposure is performed by taking a certain amount of time for exposure in the above-described overexposure range. As a result, it took some time. Exposure may be performed by a scanning exposure method.However, in order to achieve exposure in the overexposure range, the exposure must be performed at a low moving speed of the reticle and the wafer with respect to the illumination light. Therefore, it took a long time for measurement and was not always satisfactory in terms of throughput.
[0013]
The present invention has been made under such circumstances, and a first object of the present invention is to provide an optical characteristic measuring method capable of measuring optical characteristics of a projection optical system in a short time with high accuracy and reproducibility. It is in.
[0014]
A second object of the present invention is to provide an exposure method capable of realizing highly accurate exposure.
[0015]
A third object of the present invention is to provide a device manufacturing method capable of improving the productivity of a highly integrated device.
[0016]
[Means for Solving the Problems]
The invention according to claim 1 is an optical characteristic measuring method for measuring an optical characteristic of a projection optical system for projecting a pattern on a first surface onto a second surface, wherein the exposure amount is within a range of an appropriate exposure amount or less. Changing the at least one exposure condition, sequentially transferring the measurement pattern arranged on the first surface to the photosensitive object arranged on the second surface side of the projection optical system. A first step of forming a first area composed of a plurality of divided areas on the photosensitive object; and at least one of the plurality of divided areas serving as a boundary where an image of the measurement pattern starts to appear among the plurality of divided areas. An optical characteristic measuring method comprising: a second step of detecting information on a part; and a third step of obtaining an optical characteristic of the projection optical system based on the detection result.
[0017]
In this specification, “exposure conditions” include all conditions related to exposure, such as illumination conditions (including the type of mask), exposure conditions in a narrow sense such as an exposure dose on an image plane, and optical characteristics of a projection optical system. It also means a broadly defined exposure condition including a setting condition of a component. Further, “changing the exposure amount within the range of the appropriate exposure amount or less” means that the appropriate exposure amount (resist sensitivity, etc.) according to the irradiation characteristic curve of the photosensitive agent (resist, etc.) that forms the photosensitive layer of the photosensitive object. This means that the exposure amount is changed from a small range to an appropriate exposure amount.
[0018]
According to this, as an exposure condition, the measurement pattern arranged on the first surface (object surface) is changed to the second surface (image) of the projection optical system while changing the exposure amount at least within a range not more than the appropriate exposure amount. The first area including a plurality of divided areas is formed on the photosensitive object by sequentially transferring the light to the photosensitive object arranged on the (surface) side (first step). In this case, the transfer of the measurement pattern is realized by exposure such as a step-and-repeat method or a step-and-scan method. The exposure is performed while changing the exposure time, so that the exposure time can be reduced as compared with the case where the exposure is performed in the range equal to or more than the appropriate exposure amount described above. Further, the influence of the pattern line width difference on exposure is reduced.
[0019]
Next, information on at least a part of the plurality of divided regions that are boundaries between which the image of the measurement pattern starts to appear among the plurality of divided regions is detected (second step). That is, the section area serving as the boundary where the image of the measurement pattern starts to disappear due to overexposure is not set as a detection target, and information regarding at least a part of the plurality of section areas serving as the boundary where the image of the measurement pattern starts appearing is detected. Therefore, even when the exposure is performed while changing the exposure amount within the range of the appropriate exposure amount or less, the detection can be performed without any particular problem.
[0020]
Here, the detection of the image formation state may be performed on the latent image formed on the photosensitive object without developing the photosensitive object, or after the development of the photosensitive object on which the image is formed, The processing may be performed on an image formed on an object (resist image) or an image obtained by etching a photosensitive object on which a resist image is formed (etched image). Here, the photosensitive layer for detecting the state of image formation on the photosensitive object is not limited to the photoresist, and may be any as long as images (latent image and visible image) are formed by irradiation of light (energy). . For example, the photosensitive layer may be an optical recording layer, a magneto-optical recording layer, or the like. Therefore, the object on which the photosensitive layer is formed is not limited to a wafer or a glass plate, and the optical recording layer and the magneto-optical recording layer are formed. A possible plate or the like may be used.
[0021]
For example, when detecting the image formation state with respect to a resist image, an etching image, and the like, not only a microscope such as an SEM but also an alignment detection system of an exposure apparatus, for example, an image of an alignment mark is formed on an image sensor. An image processing type alignment detection system, that is, a so-called FIA (Field Image Alignment) type alignment sensor can be used. Further, when the formation state of an image is detected for a latent image, an FIA system or the like can be used.
[0022]
In any case, the image formation state can be detected by an image processing method. For example, the pattern image formation state can be detected in a short time by detecting the contrast of the image in the detection target area. become.
[0023]
Then, the optical characteristics of the projection optical system are obtained based on the detection result, that is, information on at least a part of the plurality of divided areas that are boundaries where the image of the detected measurement pattern starts to appear (third step). Here, since the optical characteristics are obtained based on the detection result using the objective and quantitative image contrast, the optical characteristics can be measured with higher accuracy and reproducibility than the conventional method. Further, since the measurement pattern can be made smaller as compared with the conventional method of measuring dimensions, it is possible to arrange many measurement patterns in the pattern region of the mask. Therefore, the number of evaluation points can be increased, and the interval between the evaluation points can be narrowed. As a result, the measurement accuracy of the optical characteristic measurement can be improved. Further, when a resist image is to be measured, the measurement result hardly depends on the characteristics of the resist.
[0024]
Therefore, according to the optical characteristic measuring method of the first aspect, the optical characteristics of the projection optical system can be measured in a short time, reliably, with high accuracy and reproducibility. In particular, when a measurement pattern is transferred onto a photosensitive object by a scanning exposure method, high-speed scanning exposure can be performed and throughput can be improved.
[0025]
In this case, as in the optical characteristic measuring method according to claim 2, the measurement pattern is a blank pattern in which a pattern is formed by a light transmitting portion in a light shielding portion, and the photosensitive object has a positive type on its surface. The photosensitive layer may be formed of a resist.
[0026]
In this case, as in the optical characteristic measuring method according to claim 3, prior to the second step, at least a part of a periphery of a region on the photosensitive object serving as the first region is overexposed to a second region. The method further comprises: detecting a part of the outline of the second region, and using the detection result to form a plurality of at least some of the plurality of divided regions. Detecting the state of formation of the image of the measurement pattern in the partitioned area.
[0027]
In this case, the fourth step can be performed after the first step. However, as in the optical characteristic measuring method according to claim 4, the fourth step is performed prior to the first step. It can also be done.
[0028]
In each of the optical characteristic measuring methods according to the third and fourth aspects, various methods of forming the second region are conceivable. For example, as in the optical characteristic measuring method according to the fifth aspect, in the fourth step, the second step is performed in the fourth step. The second area may be formed by transferring a predetermined pattern arranged on one surface onto the photosensitive object arranged on the second surface side of the projection optical system.
[0029]
In this case, as in the optical characteristic measuring method according to claim 6, the first area is a rectangular area as a whole, and the predetermined pattern is a pattern having a rectangular frame shape or a partial shape thereof. In the fourth step, the predetermined pattern arranged on the first surface is transferred onto the photosensitive object arranged on the second surface side of the projection optical system by a scanning exposure method. Can be.
[0030]
In each of the optical characteristic measuring methods according to the third to fifth aspects, as in the optical characteristic measuring method according to the seventh aspect, in the fourth step, the measurement pattern arranged on the first surface is converted into the measurement pattern. The second region can be formed by sequentially transferring the photosensitive object disposed on the second surface side of the projection optical system at an exposure amount that causes overexposure.
[0031]
In the optical characteristic measuring method according to the first aspect, as in the optical characteristic measuring method according to the eighth aspect, the measurement pattern is a remaining pattern in which a pattern is formed by a light shielding part in a light transmitting part. The photosensitive object may have a photosensitive layer formed on its surface by a negative resist.
[0032]
In the optical characteristic measuring method according to any one of the first to eighth aspects, as in the optical characteristic measuring method according to the ninth aspect, in the second step, at least a part of the plurality of divided regions constituting the first region. The state of image formation in the plurality of divided areas may be determined by detecting a representative value of pixel data of each of the divided areas obtained by imaging as a determination value.
[0033]
In this case, as in the optical characteristic measuring method according to claim 10, the representative value is at least one of an addition value, a differential sum value, a variance, and a standard deviation of pixel data in at least a part of each of the divided regions. It can be.
[0034]
In the present specification, the sum of the pixel values, the differential sum, the variance, or the standard deviation of the pixel values used as the representative values will be referred to as “score” or “contrast index value” as appropriate.
[0035]
As in each of the optical characteristic measuring methods according to the ninth and tenth aspects, as in the optical characteristic measuring method according to the eleventh aspect, when detecting the formation state of the image, a representative value related to pixel data of each of the divided areas is determined. The binarization can be performed by comparing with a predetermined threshold.
[0036]
In the optical characteristic measuring method according to any one of claims 1 to 8, as in the optical characteristic measuring method according to claim 12, in the second step, at least a part of the plurality of divided regions constituting the first region. And the boundary area where the image of the measurement pattern starts to appear based on the distribution of the added value of the pixel value for each pixel row in the predetermined direction in the imaging data, using the imaging data corresponding to the plurality of division areas. Can be detected.
[0037]
In each of the optical characteristic measuring methods according to the first to twelfth aspects, as in the optical characteristic measuring method according to the thirteenth aspect, in the first step, as the exposure condition, the exposure condition is related to an optical axis direction of the projection optical system. The measurement pattern is sequentially transferred onto the photosensitive object while also changing the position of the photosensitive object, and the third step is a boundary where an image of the measurement pattern detected in the second step starts to appear. Determining a best focus position based on a correlation between an energy amount of an exposure energy beam corresponding to information on at least a part of the plurality of partitioned regions and a position of the photosensitive object in an optical axis direction of the projection optical system. can do.
[0038]
The invention according to claim 14 is an exposure method for irradiating a mask with an energy beam for exposure and transferring a pattern formed on the mask onto a photosensitive object via a projection optical system. A step of adjusting the projection optical system in consideration of the optical characteristics measured by the optical characteristic measurement method according to any one of 13; and a step of adjusting the projection optical system on the mask via the adjusted projection optical system. Transferring a pattern onto the photosensitive object.
[0039]
According to this, the projection optical system is adjusted so that optimum transfer can be performed in consideration of the optical characteristics of the projection optical system measured by each of the optical characteristic measurement methods according to claims 1 to 13, and the adjustment is performed. Since the pattern formed on the mask is transferred onto the object via the projection optical system, the fine pattern can be transferred onto the photosensitive object with high accuracy.
[0040]
According to a fifteenth aspect of the present invention, there is provided a device manufacturing method including a lithography step, wherein the lithography step uses the exposure method according to the fourteenth aspect.
[0041]
According to this, a fine pattern can be accurately transferred onto a photosensitive object by the exposure method according to claim 14 in a lithography process, and as a result, the productivity (including the yield) of a highly integrated device is obtained. Can be improved.
[0042]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
[0043]
FIG. 1 shows a schematic configuration of an exposure apparatus 100 according to an embodiment suitable for carrying out the optical characteristic measuring method and the exposure method according to the present invention. The exposure apparatus 100 is a step-and-scan type reduction projection exposure apparatus (a so-called scanning stepper (also called a scanner)).
[0044]
The exposure apparatus 100 projects an illumination system IOP, a reticle stage RST holding a reticle R as a mask, and a pattern image formed on the reticle R onto a wafer W as an object coated with a photosensitive agent (photoresist). A projection optical system PL, an XY stage 20 that holds a wafer W and moves on a two-dimensional plane (within an XY plane), a drive system 22 that drives the XY stage 20, and a control system for these components. This control system is mainly composed of a main controller 28 composed of a microcomputer (or a workstation) for controlling the whole apparatus.
[0045]
As shown in FIG. 2, the illumination system IOP includes a light source 1, a beam shaping optical system 2, an energy rough adjuster 3, an optical integrator (homogenizer) 4, an illumination system aperture stop plate 5, a beam splitter 6, a first relay. A lens 7A, a second relay lens 7B, a reticle blind 8 (including a fixed reticle blind 8A and a movable reticle blind 8B in this embodiment) as a field stop, a mirror M for bending an optical path, and the like are provided. In addition, as the optical integrator 4, a fly-eye lens, a rod type (internal reflection type) integrator, a diffractive optical element, or the like can be used. In the present embodiment, since a fly-eye lens is used as the optical integrator 4, it is also referred to as a fly-eye lens 4 below.
[0046]
Here, each component of the illumination system IOP will be described. As the light source 1, a KrF excimer laser (oscillation wavelength 248 nm), an ArF excimer laser (oscillation wavelength 193 nm), or the like is used. The light source 1 is actually installed on a floor surface in a clean room in which the exposure apparatus main body is installed, or on a room (service room) having a low degree of cleanness different from the clean room, and is connected via a drawing optical system (not shown). Connected to the incident end of the beam shaping optical system 2.
[0047]
The beam shaping optical system 2 shapes the cross-sectional shape of the laser beam LB pulsed from the light source 1 so as to efficiently enter a fly-eye lens 4 provided behind the optical path of the laser beam LB. For example, it is composed of a cylinder lens, a beam expander (both not shown), and the like.
[0048]
The energy rough adjuster 3 is disposed on the optical path of the laser beam LB behind the beam shaping optical system 2. Here, a plurality of energy rough adjusters 3 (e.g. 6), ND filters (only two ND filters 32A and 32D are shown in FIG. 2) are arranged, and the rotating plate 31 is rotated by a drive motor 33, so that the incident laser beam The transmittance for LB can be switched from 100% in geometric progression in a plurality of steps. Drive motor 33 is controlled by main controller 28.
[0049]
The fly-eye lens 4 is disposed on the optical path of the laser beam LB behind the energy coarse adjuster 3, and has a large number of point light sources (light source images) on its emission-side focal plane to illuminate the reticle R with a uniform illuminance distribution. , Ie, a secondary light source. Hereinafter, the laser beam emitted from the secondary light source is referred to as “illumination light IL”.
[0050]
An illumination system aperture stop plate 5 made of a disc-shaped member is arranged near the exit-side focal plane of the fly-eye lens 4. The illumination system aperture stop plate 5 is provided at substantially equal angular intervals, for example, an aperture stop composed of a normal circular aperture, an aperture stop composed of a small circular aperture, and a small coherence factor σ value (small σ stop); A ring-shaped aperture stop (ring-shaped stop) for annular illumination, and a modified aperture stop in which a plurality of apertures are eccentrically arranged for the modified light source method (only two of these aperture stops are shown in FIG. 2). Etc.) are arranged. The illumination system aperture stop plate 5 is configured to be rotated by a driving device 51 such as a motor controlled by the main controller 28, so that one of the aperture stops is selectively placed on the optical path of the illumination light IL. Is set to Instead of the aperture stop plate 5 or in combination therewith, for example, a plurality of diffractive optical elements that are exchangeably arranged in the illumination optical system, a prism (cone prism, polyhedron, movable along the optical axis of the illumination optical system) An optical unit including at least one of a prism and a zoom optical system is disposed between the light source 1 (specifically, the energy rough adjuster 3) and the optical integrator 4, and the optical integrator 4 is a fly-eye lens. When the optical integrator 4 is an internal reflection type integrator, the intensity distribution of the illumination light IL on the incident surface is variable, and the incident angle range of the illumination light IL with respect to the incident surface is variable. The light amount distribution of the illumination light IL on the pupil plane (the size and shape of the secondary light source), that is, the light amount loss accompanying the change of the illumination condition is suppressed. Rukoto is desirable.
[0051]
A beam splitter 6 having a small reflectance and a large transmittance is arranged on the optical path of the illumination light IL behind the illumination system aperture stop plate 5, and the reticle blind 8 is interposed on the optical path behind the first. A relay optical system including a relay lens 7A and a second relay lens 7B is arranged.
[0052]
The fixed reticle blind 8A constituting the reticle blind 8 is disposed on a surface slightly defocused from a conjugate plane with respect to the pattern surface of the reticle R, and has a rectangular illumination area (this embodiment) on which illumination light IL is irradiated on the reticle R. In the embodiment, a rectangular opening defining the X-axis direction as the longitudinal direction and the center thereof coincides with the optical axis of the illumination optical system is formed. In addition, an opening having a variable position and width in a direction corresponding to the scanning direction (in the present embodiment, the Y-axis direction, which is the horizontal direction in the drawing of FIGS. 1 and 2) is provided near the fixed reticle blind 8A. A movable reticle blind 8B is provided, and at the start and end of the scanning exposure, the illumination area is further limited via the movable reticle blind 8B, thereby preventing unnecessary portions from being exposed. Further, the width of the opening of the movable reticle blind 8B is variable also in the direction corresponding to the non-scanning direction orthogonal to the scanning direction, and the width of the opening in the non-scanning direction of the illumination area is changed according to the pattern of the reticle R to be transferred onto the wafer. The width can be adjusted.
[0053]
A bending mirror M that reflects the illumination light IL that has passed through the second relay lens 7B toward the reticle R is disposed on the optical path of the illumination light IL behind the second relay lens 7B that constitutes the relay optical system. .
[0054]
On the other hand, on the light path reflected by the beam splitter 6, an integrator sensor 53 composed of a photoelectric conversion element is disposed via a condenser lens 52. As the integrator sensor 53, for example, a PIN photodiode having sensitivity in the deep ultraviolet region and having a high response frequency for detecting pulse light emission of the light source unit 1 can be used. The correlation coefficient (or correlation function) between the output DP of the integrator sensor 53 and the illuminance (intensity) of the illumination light IL on the surface of the wafer W is obtained in advance and stored in a memory inside the main controller 28. ing.
[0055]
The operation of the illumination system IOP configured as described above will be briefly described. The laser beam LB pulse-emitted from the light source 1 enters the beam shaping optical system 2 where the laser beam LB is efficiently transmitted to the rear fly-eye lens 4. After its cross-sectional shape is shaped so as to be incident well, it is incident on the energy rough adjuster 3. Then, the laser beam LB transmitted through any of the ND filters of the energy rough adjuster 3 enters the fly-eye lens 4. Thus, the above-mentioned secondary light source is formed on the exit-side focal plane of the fly-eye lens 4. The illumination light IL emitted from the secondary light source passes through one of the aperture stops on the illumination system aperture stop plate 5 and thereafter reaches a beam splitter 6 having a large transmittance and a small reflectance. The illumination light IL transmitted through the beam splitter 6 passes through the opening of the reticle blind 8 via the first relay lens 7A, passes through the second relay lens 7B, and the optical path is bent vertically downward by the mirror M. Thereafter, a rectangular illumination area on reticle R held on reticle stage RST is illuminated with a uniform illuminance distribution.
[0056]
On the other hand, the illumination light IL reflected by the beam splitter 6 is received by an integrator sensor 53 via a condenser lens 52, and a photoelectric conversion signal of the integrator sensor 53 is transmitted to a peak hold circuit and an A / D converter (not shown). The output is supplied to the main controller 28 as an output DP (digit / pulse).
[0057]
Returning to FIG. 1, the reticle stage RST is arranged below the illumination system IOP in FIG. The reticle R is mounted on the reticle stage RST, and is held by suction via a vacuum chuck (not shown). The reticle stage RST can be finely driven in a horizontal plane (XY plane) by a reticle stage driving unit (not shown), and has a predetermined stroke in a scanning direction (here, the Y-axis direction which is the horizontal direction in FIG. 1). It is designed to be scanned in a range. The position of the reticle stage RST during the scanning is measured by an external laser interferometer 14 via a movable mirror 12 fixed on the reticle stage RST, and the measured value of the laser interferometer 14 is supplied to a main controller 28. It is supposed to be. Note that the end surface of reticle stage RST may be mirror-finished to form a reflection surface of laser interferometer 14 (corresponding to the reflection surface of movable mirror 12 described above).
[0058]
The projection optical system PL is arranged below the reticle stage RST in FIG. 1 so that the direction of the optical axis AXp is the Z-axis direction orthogonal to the XY plane. Here, as the projection optical system PL, a refracting optical system which is a double-sided telecentric reduction system and includes a plurality of lens elements (not shown) having a common optical axis AXp in the Z-axis direction is used. Specific plural lenses among the lens elements are controlled by an imaging characteristic correction controller (not shown) based on a command from the main controller 28, and optical characteristics (including imaging characteristics) of the projection optical system PL, for example, magnification. , Distortion, coma, curvature of field, and the like can be adjusted.
[0059]
The projection magnification of the projection optical system PL is, for example, 1/4 (or 1/5). Therefore, when the reticle R is illuminated with the uniform illuminance by the illumination light IL as described above, a part of the pattern in the illumination area on the reticle R is reduced by the projection optical system PL, and the photoresist is applied. The image is projected on the wafer W, and a reduced image of the pattern is formed on the wafer W.
[0060]
The XY stage 20 is actually two-dimensionally movable on a base (not shown) by, for example, a linear motor. A wafer table 18 is mounted on the XY stage 20, and a wafer W is held on the wafer table 18 by vacuum suction or the like via a wafer holder (not shown).
[0061]
The wafer table 18 minutely drives a wafer holder that holds the wafer W in the Z-axis direction and the tilt direction with respect to the XY plane, and is also called a Z-tilt stage. A movable mirror 24 is provided on the upper surface of the wafer table 18, and the position of the wafer table 18 in the XY plane is measured by projecting a laser beam onto the movable mirror 24 and receiving the reflected light. A laser interferometer 26 is provided to face the reflecting surface of the movable mirror 24. Actually, the moving mirror is provided with an X moving mirror having a reflecting surface orthogonal to the X axis and a Y moving mirror having a reflecting surface orthogonal to the Y axis. Although an X laser interferometer for measuring the direction position and a Y laser interferometer for measuring the Y direction position are provided, these are representatively shown as a movable mirror 24 and a laser interferometer 26 in FIG. The X laser interferometer and the Y laser interferometer are multi-axis interferometers having a plurality of measurement axes, and in addition to the X and Y positions of the wafer table 18, rotation (yaw (θz rotation which is rotation about the Z axis)) , Pitching (θx rotation around the X axis) and rolling (θy rotation around the Y axis) can also be measured. Therefore, in the following description, it is assumed that the position of the wafer table 18 in the directions of five degrees of freedom of X, Y, θz, θy, and θx is measured by the laser interferometer 26. Further, instead of the movable mirror 24, the end surface of the wafer table 18 may be mirror-finished and used as a reflection surface.
[0062]
The measurement value of the laser interferometer 26 is supplied to a main controller 28, and the main controller 28 controls the XY stage 20 via the drive system 22 based on the measurement value of the laser interferometer 26, so that the wafer table 18 (Including θz rotation) in the XY plane is controlled.
[0063]
Further, the position and the amount of tilt in the Z-axis direction of the surface of the wafer W can be determined, for example, from the oblique incidence type multi-point focal position detection system having the light transmission system 50a and the light reception system 50b disclosed in Japanese Patent Application Laid-Open No. 6-283403. Is measured by the focus sensor AFS. The measurement value of the focus sensor AFS is also supplied to the main controller 28. The main controller 28 moves the wafer table 18 via the drive system 22 in the Z direction, the θx direction, and the θy based on the measurement value of the focus sensor AFS. In the direction of the optical axis of the projection optical system PL to control the position and inclination of the wafer W.
[0064]
In this way, the position and orientation of the wafer W in the directions of five degrees of freedom of X, Y, Z, θx, and θy are controlled via the wafer table 18. The remaining error of θz (yaw) is corrected by rotating at least one of reticle stage RST and wafer table 18 based on yaw information of wafer table 18 measured by laser interferometer 26.
[0065]
On the wafer table 18, a reference plate FP whose surface is the same as the surface of the wafer W is fixed. On the surface of the reference plate FP, various reference marks including a reference mark used for so-called baseline measurement of an alignment detection system described later are formed.
[0066]
Further, in the present embodiment, an off-axis type alignment detection system AS as a mark detection system for detecting an alignment mark formed on the wafer W is provided on a side surface of the projection optical system PL. As an example of the alignment detection system AS, a kind of an image processing type alignment sensor of an image processing method of illuminating a mark with broadband (broadband) light such as a halogen lamp and measuring a mark position by processing the mark image. The FIA (Field Image Alignment) system is used, and it is possible to measure the position of the reference mark on the reference plate FP and the alignment mark on the wafer W in the X and Y two-dimensional directions.
[0067]
The alignment control device 16 A / D-converts the information DS from the alignment detection system AS, calculates the digitized waveform signal, and calculates the position information of the mark with respect to the detection center of the alignment detection system AS. At this time, the measurement value of the laser interferometer 26 is also supplied to the alignment control device 16, and the alignment control device 16 converts the calculated position information of the mark into the stage coordinates defined by the length measurement axis of the laser interferometer 26. The position information on the system is converted, and the conversion result, that is, the coordinate value of the mark is supplied to the main controller 28.
[0068]
The alignment detection system AS includes, in addition to the above-described FIA system, an alignment sensor that irradiates a target with coherent detection light and detects scattered light or diffracted light generated from the target, and two diffraction lights generated from the target. Various alignment sensors such as an alignment sensor that detects light by interference with light (for example, the same order) can be used alone or in an appropriate combination.
[0069]
Further, in the exposure apparatus 100 of the present embodiment, although not shown, above the reticle R, for example, the projection optical system PL disclosed on Japanese Patent Laid-Open No. A pair of reticle alignments composed of a TTR (Through The Reticle) alignment system using light of an exposure wavelength for simultaneously observing a reticle mark or a reference mark on the reticle stage RST (both not shown) and a mark on the reference plate FP. A detection system is provided. The detection signals of these reticle alignment detection systems are supplied to main controller 28 via alignment controller 16.
[0070]
Next, an example of a reticle used for measuring the optical characteristics of the projection optical system according to the present invention will be described.
[0071]
FIG. 3 shows a reticle R used for measuring the optical characteristics of the projection optical system. _T An example is shown. FIG. 3 shows a reticle R _T 2 is a plan view as viewed from a pattern surface side (a lower surface side in FIG. 1). As shown in FIG. 3, reticle R _T In the figure, a pattern area PA made of a light shielding member such as chrome is formed in the center of a glass substrate 42 as a substantially rectangular mask substrate. A rectangular area IAR indicated by a dotted line in FIG. 3 is the above-described illumination area whose center coincides with the optical axes of the illumination optical system and the projection optical system. In FIG. 3, the reticle R _T Are arranged such that the center of the pattern area PA substantially coincides with the center of the illumination area IAR. Inside this illumination area IAR, its center (that is, reticle R _T (A reticle center) and eight peripheral portions of the center at a total of nine locations, for example, a measurement pattern MP composed of a line and space pattern (L / S pattern). ₁ ~ MP ₉ Are formed respectively. In this case, the measurement pattern MP _Four And MP ₆ Is the central measurement pattern MP _Five Are located at the same distance (for example, about 500 μm) on one side and the other side in the X-axis direction. Also, the measurement pattern MP ₁ And MP ₇ Is the measurement pattern MP _Four Are formed at positions separated by the same distance (about 300 μm) on one side and the other side in the Y-axis direction. Also, the measurement pattern MP _Two And MP ₈ Is the measurement pattern MP _Five Are formed at positions separated by the same distance (about 300 μm) on one side and the other side in the Y-axis direction. Also, the measurement pattern MP _Three And MP ₉ Is the measurement pattern MP ₆ Are formed at positions separated by the same distance (about 300 μm) on one side and the other side in the Y-axis direction with respect to.
[0072]
Measurement pattern MP _n In each of (n = 1 to 9), for example, the X-axis direction is a periodic direction, and five line patterns having a line width of about 1.3 μm and a length of about 12 μm are arranged at a pitch of about 2.6 μm. It is composed of a multi-bar pattern. Measurement pattern MP _n Is a blank pattern in which the line portion is formed of the light transmitting portion.
[0073]
In the present embodiment, the above-described measurement pattern MP _n As is clear from the arrangement, 24 measurement patterns can be arranged between the measurement patterns adjacent to each other in the X-axis direction with an arrangement pitch of 20 μm, and the measurement patterns adjacent to each other in the Y-axis direction can be arranged. Between them, the arrangement pitch is also 20 μm, and 14 measurement patterns can be arranged. In this case, the step pitch of the wafer W is set to 5 μm, and the reticle R is formed by a step-and-repeat method (or a step-and-scan method). _T Is transferred onto the wafer W, as can be understood from the above description of the configuration of the measurement pattern, the measurement pattern MP falls within about 60% of the area of 5 μm square (shot area) on the wafer W. _n Is formed.
[0074]
A pair of reticle alignment marks RM1 and RM2 are formed on both sides of the pattern area PA passing through the reticle center in the X-axis direction.
[0075]
Further, at a position separated by a predetermined distance L1 (L1 is, for example, 40 mm) from the reticle center of the pattern area PA to the + Y side, nine rectangles of a matrix arrangement of 3 rows and 3 columns centered on the position (point). A frame pattern AP formed by the frame-shaped light transmitting portion is formed. Each light transmitting portion constituting the frame pattern AP has a rectangular frame-shaped pattern (hereinafter, referred to as a 20 μm) having a predetermined width surrounding a rectangular region of 460 μm (length in the X-axis direction) × 260 μm (length in the Y-axis direction). , For convenience). The center-to-center distance between adjacent rectangular patterns is about 500 μm in the X-axis direction and about 300 μm in the Y-axis direction.
[0076]
Reticle R _T Although each of the above patterns actually has the dimensional relationship as described above, FIG. 3 illustrates the size and dimensional relationship as different from the actual size for convenience of illustration.
[0077]
Next, a method for measuring the optical characteristics of the projection optical system PL in the exposure apparatus 100 of the present embodiment will be described with reference to FIGS. 4 and 5, which show simplified processing algorithms of the CPU in the main controller 28, and Description will be made with reference to other drawings as appropriate.
[0078]
First, in step 402 of FIG. 4, the reticle R is placed on the reticle stage RST via a reticle loader (not shown). _T Is loaded, and the wafer W is loaded through a wafer loader (not shown). _T Is loaded on the wafer table 18.
[0079]
In the next step 404, reticle R _T Preparatory work such as alignment with the projection optical system PL and setting of a reticle blind is performed. Specifically, first, the midpoint of a pair of fiducial marks (not shown) formed on the surface of the fiducial plate FP provided on the wafer table 18 substantially coincides with the optical axis of the projection optical system PL. The XY stage 20 is moved via the drive system 22 while monitoring the measurement result of the laser interferometer 26. Then, reticle R _T The position of reticle stage RST is adjusted via a reticle stage drive unit (not shown) based on the measurement value of laser interferometer 14 so that the center of reticle (reticle center) substantially matches the optical axis of projection optical system PL. . At this time, for example, the relative position between the reticle alignment marks RM1 and RM2 and the corresponding reference mark is detected by the reticle alignment detection system (not shown) via the projection optical system PL. A reticle stage driving unit (not shown) based on the detection result of the relative position detected by the reticle alignment detection system, so that the relative position error between the reticle alignment marks RM1 and RM2 and the corresponding reference mark is minimized. The position of the reticle stage RST in the XY plane is adjusted via. Thereby, the reticle R _T (Reticle center) exactly coincides with the optical axis of the projection optical system PL, and the reticle R _T Also accurately coincides with the coordinate axes of the rectangular coordinate system defined by the length measurement axes of the laser interferometer 26.
[0080]
Note that reticle R _T When the width of the illumination area IAR is larger than the width of the pattern area PA in the non-scanning direction (X-axis direction), the illumination system is set so that the width of the illumination area IAR is substantially equal to or less than the width of the pattern area PA. The opening width of the movable reticle blind 8B in the IOP in the non-scanning direction is adjusted.
[0081]
When the predetermined preparation work is completed in this way, the process proceeds to the next step 408, where the target value of the exposure energy amount is initialized. That is, the initial value “1” is set in the counter j and the target value P of the exposure energy amount is set. _j To P ₁ (J ← 1). In the present embodiment, the counter j sets the target value of the exposure energy amount and sets the wafer W during the exposure. _T Is also used to set the movement target position in the row direction. In the present embodiment, the wafer W _T A positive resist is applied to the surface of the substrate. For example, the exposure energy amount is set to P around a value smaller than the known optimum exposure amount for the positive resist by a predetermined amount. ₁ From P in ΔP increments _N (For example, N = 23) (P _j = P ₁ ~ P _{twenty three} ). In this case, the exposure amount P _N Is almost the same as the above-mentioned optimum exposure amount.
[0082]
In the next step 410, the wafer W _T The target value of the focus position (position in the Z-axis direction) is initialized. That is, the initial value “1” is set in the counter i and the wafer W _T Focus position target value Z _i To Z ₁ (I ← 1). In the present embodiment, the counter i is _T The target value of the focus position is set, and the wafer W at the time of exposure is set. _T Is also used to set the movement target position in the column direction. In the present embodiment, for example, the wafer W is centered on a known best focus position (design value or the like) relating to the projection optical system PL. _T The focus position of ₁ To Z in ΔZ increments _M (For example, M = 13) (Z _i = Z ₁ ~ Z ₁₃ ).
[0083]
Therefore, in the present embodiment, the wafer W in the optical axis direction of the projection optical system PL is _T Position and wafer W _T While changing the amount of energy of the illumination light IL illuminated above, the measurement pattern MP _n (N = 1 to 9) for the wafer W _T N × M (for example, 23 × 13 = 299) exposures are performed for sequential transfer to the upper side. Wafer W corresponding to each evaluation point in the field of view of projection optical system PL _T Upper area (hereinafter referred to as “evaluation point corresponding area”) DB ₁ ~ DB ₉ Of the first area DC to be described later ₁ ~ DC ₉ (See FIGS. 7 and 8) include N × M measurement patterns MP. _n Will be transferred.
[0084]
Here, the evaluation point corresponding area DB _n First area DC in (n = 1 to 9) _n In the present embodiment, each evaluation point corresponding area DB _n Is the above-mentioned N × M measurement patterns MP _n Is transferred to a rectangular first area DC _n And a rectangular frame-shaped second region DD surrounding the first region. _n (See FIG. 8).
[0085]
In addition, this evaluation point corresponding area DB _n (That is, the first area DC _n ) Correspond to a plurality of evaluation points whose optical characteristics are to be detected in the field of view of the projection optical system PL.
[0086]
Here, although the description is before and after, for convenience, the measurement pattern MP _n Wafer W to which is transferred _T Each first area DC above _n Will be described with reference to FIG. As shown in FIG. 6, in the present embodiment, M × N (= 13 × 23 = 299) virtual partitioned areas DA arranged in a matrix of M rows and N columns (13 rows and 23 columns) _{i, j} (I = 1 to M, j = 1 to N) and the measurement pattern MP _n Are transferred respectively, and these measurement patterns MP _n Are respectively transferred to the M × N divided areas DA _{i, j} 1st area DC which consists of _n Is wafer W _T Formed on top. Note that the virtual partitioned area DA _{i, j} Are arranged such that the + X direction is the row direction (j increasing direction) and the + Y direction is the column direction (i increasing direction), as shown in FIG. The subscripts i and j and M and N used in the following description have the same meaning as described above.
[0087]
Returning to FIG. 4, in the next step 412, the wafer W _T Each evaluation point corresponding area DB above _n Virtual partitioned area DA within _{i, j} (Here DA _1,1 (See FIG. 7)) _n XY stage 20 (wafer W) via drive system 22 while monitoring the measurement value of laser interferometer 26 at the positions where the images of _T Move).
[0088]
In the next step 414, the wafer W _T Target value Z at which the focus position is set _i (In this case Z ₁ The wafer table 18 is minutely driven in the Z-axis direction (and the tilt direction) while monitoring the measurement value from the focus sensor AFS so as to coincide with (2).
[0089]
In the next step 416, exposure is performed. At this time, the wafer W _T The target value (in this case, P ₁ The exposure amount control is performed so that As a method of controlling the amount of exposure energy, for example, the following first to third methods can be used alone or in an appropriate combination.
[0090]
That is, as a first method, the energy amount of the illumination light IL given to the image plane (wafer plane) by maintaining the pulse repetition frequency constant and changing the transmittance of the laser beam LB using the energy coarse adjuster 3 To adjust. As a second method, by maintaining the pulse repetition frequency constant and giving an instruction to the light source 1 to change the energy per pulse of the laser beam LB, the illumination light IL given to the image plane (wafer plane) is changed. Adjust the amount of energy. As a third method, the transmittance of the laser beam LB and the energy per pulse of the laser beam LB are kept constant, and the illumination light IL applied to the image plane (wafer plane) by changing the pulse repetition frequency. Adjust the energy amount of.
[0091]
As a result, as shown in FIG. _T Each first area DC above _n Area DA _1,1 Each for measurement pattern MP _n Is transferred.
[0092]
Returning to FIG. 4, when the exposure in step 416 is completed, the process proceeds to the next step 420. In this step 420, the wafer W _T The target value of the focus position is Z _M By judging whether or not this is the case, it is determined whether or not exposure in a predetermined Z range has been completed. Here, the first target value Z ₁ Since the exposure in the step (i) has only been completed, the process proceeds to step 422, and the counter i is incremented by one (i ← i + 1). Thereby, the wafer W _T ΔZ is added to the target value of the focus position. Here, the target value of the focus position is Z _Two (= Z ₁ + ΔZ). Thereafter, the process returns to step 412.
[0093]
In this step 412, the wafer W _T Each first area DC above _n Area DA _2,1 Measurement pattern MP _n Wafers W at the positions where the images of _T The XY stage 20 is moved in a predetermined direction (in this case, the −Y direction) within the XY plane by a predetermined step pitch SP so that is positioned. Here, in the present embodiment, the step pitch SP is set to, for example, about 5 μm.
[0094]
In the next step 414, the wafer W _T Is the target value (in this case, Z _Two The wafer table 18 is step-moved by ΔZ in the direction of the optical axis AXp so as to coincide with the above. _T Each first area DC above _n Area DA _2,1 Measurement pattern MP _n Are transferred respectively. Here, the partition area DA _2,1 Is an imaginary partitioned area whose one side length matches the above step pitch SP, and each first area DC _n Area DA _1,1 And partition area DA _2,1 There is no frame line at the boundary with. Partition area DA described above _1,1 And other partitioned areas DA to be described later. _{i, j} (I = 3 to M, j = 1 to N) also correspond to the partitioned area DA _1,1 This is a virtual partitioned area similar to.
[0095]
Thereafter, until the determination in step 420 is affirmed, that is, the wafer W set at that time is set. _T The target value of the focus position is Z _M The loop processing (including the determination) of steps 420 → 422 → 412 → 414 → 416 is repeated until it is determined that. Thereby, the wafer W _T Each first area DC above _n Area DA _{i, 1} (I = 3 to M) for the measurement pattern MP _n Are respectively transcribed. However, also in this case, no border line exists at the boundary between the adjacent partitioned areas as described above.
[0096]
On the other hand, the partition area DA _{M, 1} Is completed, and if the determination in step 420 is affirmative, the process proceeds to step 424 where the target value of the exposure energy amount set at that time is P _N It is determined whether or not this is the case. Here, the target value of the exposure energy amount set at that time is P ₁ Therefore, the determination in step 424 is denied, and the process proceeds to step 426.
[0097]
In step 426, the counter j is incremented by 1 (j ← j + 1). Thereby, ΔP is added to the target value of the exposure energy amount. Here, the target value of the exposure energy amount is P _Two (= P ₁ + ΔP). Thereafter, the process returns to step 410.
[0098]
In step 410, the wafer W _T After the target value of the focus position is initialized, the loop processing (including the determination) of steps 412 → 414 → 416 → 420 → 422 is repeated. The processing of this loop is performed until the determination in step 420 is affirmed, that is, the target value P of the exposure energy amount. _Two Predetermined wafer W _T Focus position range (Z ₁ ~ Z _M This is repeated until the exposure for ()) is completed. Thereby, the wafer W _T Each first area DC above _n Area DA _{i, 2} (I = 1 to M) for the measurement pattern MP _n Are respectively transcribed. However, also in this case, no border line exists at the boundary between the adjacent partitioned areas as described above.
[0099]
On the other hand, the target value P of the exposure energy amount _Two Predetermined wafer W _T Focus position range (Z ₁ ~ Z _M When the exposure of ()) is completed, the determination in step 420 is affirmed, and the flow shifts to step 424 where the target value of the set exposure energy amount is P. _N It is determined whether or not this is the case. In this case, the target value of the exposure energy amount is P _Two Therefore, the determination in step 424 is denied, and the process proceeds to step 426. In step 426, the counter j is incremented by one. Thereby, ΔP is added to the target value of the exposure energy amount. Here, the target value of the exposure energy amount is P _Three Is changed to Thereafter, the process returns to step 410, and thereafter, the same processing (including determination) as described above is repeated.
[0100]
Thus, the range of the predetermined exposure energy amount (P ₁ ~ P _N When the exposure of ()) is completed, the determination in step 424 is affirmed, and the flow shifts to step 428 in FIG. Thereby, the wafer W _T Each first area DC above _n As shown in FIG. 7, N × M (23 × 13 = 299 as an example) measurement patterns MP with different exposure conditions _n Is formed. In practice, as described above, the wafer W _T Measurement pattern MP on top _n When the transferred image (latent image) is formed, N × M (for example, 23 × 13 = 299) virtual partitioned areas DA including the transferred image therein are provided. _{i, j} Each first area DC consisting of _n Is formed, but in the above description, the first region DC is used to make the description easy to understand. _n Is the wafer W _T An explanation method as if it is above is adopted.
[0101]
In step 428 of FIG. _T Each rectangular pattern forming the upper frame pattern AP is _T Each evaluation point corresponding area DB formed above _n First area DC _n Reticle R so that it exactly matches the contour of _T And wafer W _T Are moved (positioned) as follows.
[0102]
That is, first, based on the measurement value of the laser interferometer 14, the reticle stage RST is moved via the reticle stage driving unit (not shown) in the -Y direction by the above-described distance L1 (L1 is, for example, 40 mm). Thus, the center of the frame pattern AP substantially coincides with the optical axis of the projection optical system PL, and the rotation angle of the frame pattern AP accurately coincides with the coordinate axis of the rectangular coordinate system defined by the length measurement axis of the laser interferometer 26. . Next, while monitoring the measurement result of the laser interferometer 26, the wafer W _T Upper first area DB _Five The XY stage 20 is moved to a position where the center of the XY line substantially coincides with the optical axis of the projection optical system PL. At this time, the wafer W _T Is prevented from occurring before and after the movement.
[0103]
Reticle R as described above _T And wafer W _T Is completed, the process proceeds to the next step 430 to execute exposure. At this time, the wafer W _T Exposure amount control is performed so that the exposure energy amount (integrated exposure amount) at the above one point becomes a value larger by a predetermined amount than the known optimum exposure amount.
[0104]
Thereby, the wafer W _T Above, a rectangular (rectangular) first area DC as shown in FIG. _n And a rectangular frame-shaped second region DD surrounding the second region DD _n Evaluation point corresponding area DB consisting of _n (N = 1 to 9) latent images are formed. In this case, the second area DD _n Are clearly in an overexposure (overdose) state.
[0105]
Thus, the wafer W _T When the exposure for is completed, the process proceeds to step 450 in FIG. In this step 450, the wafer W is transferred via a wafer unloader (not shown). _T Is unloaded from above the wafer table 18 and the wafer W is _T Is transported to a coater / developer (not shown) connected inline to the exposure apparatus 100.
[0106]
Wafer W for the above coater / developer _T After the transfer of the wafer W, the process proceeds to step 452, where the wafer W _T Wait for the development to finish. During the waiting time in this step 452, the wafer W _T Is developed. Upon completion of this development, the wafer W _T Above, a rectangular (rectangular) first area DC as shown in FIG. _n And a rectangular frame-shaped second region DD surrounding the second region DD _n Evaluation point corresponding area DB consisting of _n (N = 1 to 9) resist images are formed, and the wafer W on which the resist images are formed _T Is a sample for measuring the optical characteristics of the projection optical system PL. FIG. 9 shows the wafer W _T Evaluation point corresponding area DB formed above ₁ Is shown as an example.
[0107]
In FIG. 9, the evaluation point corresponding area DB ₁ Is the second area DD ₁ N × M = 23 × 13 = 299 partitioned areas DA inside _{i, j} (I = 1 to M, j = 1 to N) are arranged, and it is illustrated as if a resist image of a partition frame exists between adjacent partitioned areas. This is done for clarity. However, in practice, there is no resist image of a partition frame between adjacent partitioned areas. By eliminating the frame in this manner, it is possible to prevent a decrease in the contrast of the pattern portion due to interference caused by the frame when capturing an image using an FIA-based alignment sensor, which has conventionally been a problem.
[0108]
In this case, the measurement pattern MP composed of a multi-bar pattern between adjacent partitioned areas is used. _n Let L be the distance between the resist images of FIG. _n The other measurement pattern MP _n The distance is set to such an extent that the presence of the image does not affect the image. This distance L is determined by the resolution of an imaging device (in this embodiment, an alignment detection system AS (an FIA alignment sensor)) for imaging a partitioned area. _f , The contrast of the image of the measurement pattern _f , The process factor determined by the process including the reflectivity and the refractive index of the resist _f , The detection wavelength of the alignment detection system AS (the alignment sensor of the FIA system) is λ _f If, for example, L = f (C _f , R _f , P _f , Λ _f ).
[0109]
Note that the process factor P _f Affects the contrast of the image, so the function L = f ′ (C _f , R _f , Λ _f ) May be used to define the distance L.
[0110]
Further, as can be seen from FIG. 9, the rectangular (rectangular) first region DC ₁ Frame-shaped second area DD surrounding ₁ Does not have a pattern. In this case, the second area DD ₁ The pattern portion in the partitioned area where the measurement pattern image is formed is a portion where the resist is at least partially removed, and the other portions are portions where the resist remains. Of these, the second area DD ₁ Since the exposure energy for overexposure was set during the exposure, the resist was completely removed. The reason for this is to improve the contrast of the outer frame portion at the time of detecting the outer frame, which will be described later, and to increase the S / N ratio of the detection signal.
[0111]
In the waiting state of the step 452, the wafer W is notified by a notification from the control system of the coater / developer (not shown). _T Is completed, the process proceeds to step 454, where an instruction is issued to a wafer loader (not shown), and the wafer W _T Is loaded onto the wafer table 18 again, and the process proceeds to a subroutine for calculating the optical characteristics of the projection optical system in step 456 (hereinafter, also referred to as an “optical characteristic measurement routine”).
[0112]
In this optical characteristic measurement routine, first, in step 502 of FIG. _T Upper evaluation point corresponding area DB _n Wafer W at a position where the resist image can be detected by alignment detection system AS. _T To move. This movement, that is, positioning, is performed by controlling the XY stage 20 via the drive system 22 while monitoring the measurement value of the laser interferometer 26. Here, it is assumed that the counter n has been initialized to n = 1. Therefore, here, the wafer W shown in FIG. _T Upper evaluation point corresponding area DB ₁ Wafer W at a position where the resist image can be detected by alignment detection system AS. _T Is positioned. In the following description of the optical characteristic measurement routine, the evaluation point corresponding area DB _n The resist image of “Evaluation point corresponding area DB” _n ".
[0113]
In the next step 504, the wafer W _T Upper evaluation point corresponding area DB _n (Here, DB ₁ ) Is captured using the alignment detection system AS, and the captured data is captured. The alignment detection system AS divides the resist image into pixels of an image pickup device (CCD or the like) of its own, and converts the density of the resist image corresponding to each pixel into 8-bit digital data (pixel data). 28. That is, the imaging data is composed of a plurality of pixel data. Here, it is assumed that the value of the pixel data increases as the density of the resist image increases (closes to black).
[0114]
In the next step 506, the evaluation point corresponding area DB from the alignment detection system AS _n (Here, DB ₁ The image data of the resist image formed in the step (1) is arranged and an image data file is created.
[0115]
In the next step 508, the evaluation point corresponding area DB _n (Here, DB ₁ ) Is detected. The detection of the outer frame is performed by, for example, the following A. ~ D. It is performed as follows.
[0116]
A. First, the evaluation point corresponding area DB _n (Here, DB ₁ )) Using the pixel row information in the vertical direction (direction substantially parallel to the Y axis) passing near the center of the image described in a. ~ C. Boundary detection is performed according to the following procedure, and the evaluation point corresponding area DB _n Approximate positions of the upper side and lower side of are detected.
a. First, linear pixel row data (pixel row data) for boundary detection is extracted from the above-described imaging data file. An intersection (that is, a point where the threshold t crosses the waveform data) between the waveform data corresponding to the pixel row data and a predetermined threshold t (threshold level line) is obtained. In this case, the intersection is actually detected by scanning the pixel column from outside to inside. Therefore, at least two intersections are detected.
b. Next, the pixel row is scanned bidirectionally from the position of each obtained intersection, the maximum value and the minimum value of the pixel value near each intersection are obtained, and the average value of the obtained maximum value and the minimum value is calculated. Then, this is set as a new threshold value t ′. In this case, since there are at least two intersections, a new threshold value t 'is also obtained for each intersection.
c. Next, an intersection between the threshold value t 'and the waveform data (that is, a point where the threshold value t' crosses the waveform data) is determined between the maximum value and the minimum value for each of the obtained intersection points, and each of the obtained points is obtained. The position of (pixel) is defined as a boundary position. That is, the boundary position (in this case, the evaluation point corresponding area DB _n (Approximate positions of the upper side and the lower side).
[0117]
B. Next, by using the pixel row information in the horizontal direction slightly below the upper side and slightly above the lower side obtained as described above, A. The boundary detection is performed in the same manner as described above, and two points on each of the left side and the right side are detected.
[0118]
C. Next, using the obtained vertical pixel row information slightly to the right of the left side and slightly to the left of the right side, the above A.P. The boundary detection is performed in the same manner as described above, and two points on each of the upper and lower sides are detected.
[0119]
D. Next, B. And C.I. The position information of the four vertices of the rectangular outer frame DBF (see FIG. 9) is calculated by a predetermined calculation using the position information of the eight points detected in step (1).
[0120]
E. FIG. Next, by using the obtained position information (coordinates) of the four vertices, a rectangle approximation operation using the least squares method is performed to obtain the evaluation point corresponding region DB including the rotation. _n Is calculated.
[0121]
As described above, the evaluation point corresponding area DB _n Is calculated (detected), in the next step 518, based on the detected outer frame DBF, the first area DC _n Is estimated, and the estimated contour is equally divided using the known number of partitioned areas in the vertical direction = M = 13 and the number of partitioned areas in the horizontal direction = N = 23. DA _{i, j} (I = 1 to 13, j = 1 to 23) are obtained. That is, each section area is determined based on the outer frame DBF.
[0122]
FIG. 12 shows the first area DC obtained in this manner. _n Areas DA that configure _{i, j} (I = 1 to 13, j = 1 to 23) are shown.
[0123]
Returning to FIG. 10, in the next step 520, each partitioned area DA _{i, j} For (i = 1 to M, j = 1 to N), a representative value (hereinafter, also appropriately referred to as “score”) regarding the pixel data is calculated.
[0124]
Below, score E _{i, j} The calculation method of (i = 1 to M, j = 1 to N) will be described in detail.
[0125]
Usually, in a captured measurement target, there is a contrast difference between a pattern portion and a non-pattern portion. Only the pixels having the non-pattern area luminance exist in the area where the pattern does not appear, while the pixels having the pattern area luminance and the pixels having the non-pattern area luminance coexist in the area where the pattern appears. . Therefore, as a representative value (score) for determining the presence / absence of a pattern, a variation in pixel value within each partitioned area can be used.
[0126]
In the present embodiment, as an example, the variance (or standard deviation) of the pixel values in the specified range in the defined area is adopted as the score E.
[0127]
S is the total number of pixels within the specified range, and I is the luminance value of the kth pixel. _k Then, the score E can be expressed by the following equation (1).
[0128]
(Equation 1)

[0129]
In the case of the present embodiment, the size of the above-described divided area and the measurement pattern MP _n As can be easily imagined from the relationship with the size on the wafer, the measurement pattern MP _n Is the partition area DA _{i, j} And the center of the area DA _{i, j} Exists in a range (region) reduced to approximately 60%.
[0130]
In consideration of such a point, for example, the specified area _{i, j} (I = 1 to M, j = 1 to N), the center is the same, and a reduced area of the area can be used for score calculation. However, the reduction rate A (%) is limited as follows.
[0131]
First, as for the lower limit, if the range is too narrow, the area used for calculating the score is only the pattern portion, and if this is the case, the variation also becomes small in the pattern appearance portion, making it unusable for pattern presence / absence discrimination. In this case, it is necessary that A> 60%, as is apparent from the above-described pattern existence range. Although the upper limit is naturally 100% or less, the upper limit should be smaller than 100% in consideration of a detection error and the like. Thus, the reduction ratio A needs to be set to 60% <A <100%.
[0132]
In the case of the present embodiment, since the pattern portion occupies about 60% of the defined area, it is expected that the S / N ratio will increase as the ratio of the area (designated range) used for score calculation to the defined area increases.
[0133]
However, if the area size of the pattern part and the non-pattern part in the area used for score calculation become the same, the S / N ratio of the pattern presence / absence determination can be maximized. In the present embodiment, as a result of experimentally confirming some ratios, for example, the most stable result was obtained when A = 90%, the ratio A = 90% is adopted. Of course, A is not limited to 90%, and the measurement pattern MP _n The pattern MP for measurement with respect to the divided area is determined in consideration of the divided area on the wafer determined by the step pitch SP. _n May be determined in consideration of the ratio occupied by the image. Further, the designated range used for calculating the score is not limited to an area having the same center as the divided area, and the measurement pattern MP _n May be determined in consideration of where in the partitioned area the image is located.
[0134]
Therefore, in step 520, the respective segment areas DA are read from the image data file. _{i, j} The imaging data within the specified range is extracted, and each divided area DA is extracted using the above equation (1). _{i, j} Score E of (i = 1 to M, j = 1 to N) _{i, j} Is calculated.
[0135]
Since the score E obtained by the above method represents the presence or absence of a pattern as a numerical value, it is possible to automatically and stably determine the presence or absence of a pattern by binarizing it with a predetermined threshold. .
[0136]
Therefore, in the next step 522 (FIG. 11), the partition area DA _{i, j} Score E obtained above for each _{i, j} Is compared with a predetermined threshold value SH. _{i, j} The presence or absence of an image of the measurement pattern MP in the above, and a determination value F as a detection result _{i, j} (I = 1 to M, j = 1 to N) are stored in a storage device (not shown). That is, in this way, the score E _{i, j} Based on the partition area DA _{i, j} Measurement pattern MP for each _n Is detected. Note that various image forming states are conceivable, but in the present embodiment, as described above, the score E indicates the presence or absence of a pattern as a numerical value, and the The focus is on whether or not an image of a pattern is formed.
[0137]
Here, the score E _{i, j} Is greater than or equal to the threshold SH, the measurement pattern MP _n Is determined to be formed, and a determination value F as a detection result is determined. _{i, j} Is set to “0”. On the other hand, score E _{i, j} Is less than the threshold value SH, the measurement pattern MP _n Is not formed, and the determination value F as a detection result is determined. _{i, j} Is “1”. FIG. 13 shows an example of this detection result as table data. FIG. 13 corresponds to FIG. 9 described above.
[0138]
In FIG. 13, for example, F _12,16 Is the wafer W _T Is in the Z-axis direction ₁₂ And the exposure energy amount is P ₁₆ Measurement pattern MP transferred at the time of _n Means the detection result of the image formation state, and as an example, in FIG. _12,16 Has a value of “1”, and the measurement pattern MP _n Is determined not to have been formed.
[0139]
The threshold value SH is a preset value and can be changed by an operator using an input / output device (not shown).
[0140]
In the next step 524, based on the above-described detection results, the number of divided areas where a pattern image is formed for each focus position is determined. That is, for each focus position, the number of partitioned areas having the determination value “0” is counted, and the counting result is used as the pattern appearance number T _i (I = 1 to M). At this time, a so-called jump area having a different value from the surrounding area is ignored. For example, in the case of FIG. _T Focus position of Z ₁ Then the pattern appearance number T ₁ = 8, Z _Two Then T _Two = 11, Z _Three Then T _Three = 14, Z _Four Then T _Four = 16, Z _Five Then T _Five = 16, Z ₆ Then T ₆ = 13, Z ₇ Then T ₇ = 11, Z ₈ Then T ₈ = 8, Z ₉ Then T ₉ = 5, Z _Ten Then T _Ten = 3, Z ₁₁ Then T ₁₁ = 2, Z ₁₂ Then T ₁₂ = 2, Z ₁₃ Then T ₁₃ = 2. Thus, the focus position and the number of pattern appearances T _i You can ask for the relationship.
[0141]
The jump region may be caused by misrecognition during measurement, laser misfire, dust, noise, or the like. _i Filter processing may be performed to reduce the influence on the detection result. As this filter processing, for example, data of a 3 × 3 section area centered on the section area to be evaluated (judgment value F _{i, j} ) May be calculated (simple average or weighted average). Note that the filter processing is performed on the data (score E) before the formation state detection processing. _{i, j} ) May be performed, and in this case, the effect of the jump area can be more effectively reduced.
[0142]
In the next step 526, an nth order approximate curve (for example, a 4th to 6th order curve) for calculating the best focus position from the number of pattern appearances is obtained.
[0143]
More specifically, the horizontal axis represents the focus position, and the vertical axis represents the pattern appearance number T. _i Is plotted on a coordinate system. In this case, the result is as shown in FIG. Here, in the case of the present embodiment, the wafer W _T In the exposure of _{i, j} Are the same size, the difference between the exposure energies between the adjacent divided areas in the row direction is a constant value (= ΔP), and the difference between the focus positions between the adjacent divided areas in the column direction is a constant value (= ΔZ). , The number of pattern appearances T _i Can be treated as being proportional to the amount of exposure energy. That is, in FIG. 19, the vertical axis can be considered to be the exposure energy amount P.
[0144]
After the above plotting, an nth-order approximate curve (least squares approximate curve) is obtained by curve fitting each plot point. Thereby, for example, a curve P = f (Z) shown by a dotted line in FIG. 19 is obtained.
[0145]
Returning to FIG. 11, in the next step 528, calculation of an extreme value (maximum value or minimum value) of the curve P = f (Z) is attempted, and it is determined whether or not an extreme value exists based on the result. I do. If the extreme value can be calculated, the process proceeds to step 530 to calculate the focus position at the extreme value, and to use the result of calculation as the best focus position, which is one of the optical characteristics. Is stored in a storage device (not shown).
[0146]
On the other hand, if the extreme value has not been calculated in step 528, the process proceeds to step 532, where the change amount of the curve P = f (Z) corresponding to the change in the position of the wafer W (change in Z) is the smallest. The range of the small focus position is calculated, the middle position of the range is calculated as the best focus position, the calculation result is set as the best focus position, and the best focus position is stored in a storage device (not shown). That is, the focus position is calculated based on the flattest part of the curve P = f (Z).
[0147]
Here, the step of calculating the best focus position as in step 532 is exceptionally provided depending on the type of the measurement pattern MP, the type of resist, and other exposure conditions, as described above with the curve P = f (Z). May not have a clear peak, so that even in such a case, the best focus position can be calculated with a certain degree of accuracy.
[0148]
In the next step 534, referring to the aforementioned counter n, all the evaluation point corresponding areas DB ₁ ~ DB _Five It is determined whether or not the processing has been completed for. Here, the evaluation point corresponding area DB ₁ Since the processing of step 534 has only been completed, the determination in step 534 is denied, the processing proceeds to step 536, and the counter n is incremented (n ← n + 1). Thereafter, the processing returns to step 502 in FIG. _Two At a position where the wafer W can be detected by the alignment detection system AS. _T Position.
[0149]
Then, the processing (including determination) of steps 504 to 534 described above is performed again, and the above-described evaluation point corresponding area DB ₁ In the same manner as in the case of _Two For the best focus position.
[0150]
And evaluation point corresponding area DB _Two When the calculation of the best focus position is completed for all the evaluation point corresponding areas DB in step 534 ₁ ~ DB _Five It is determined again whether or not the processing has been completed, but this determination is denied. Thereafter, the processing (including the determination) of steps 502 to 536 is repeated until the determination in step 534 is affirmed. Thereby, another evaluation point corresponding area DB _Three ~ DB ₉ The evaluation point corresponding area DB described above ₁ In the same manner as in the above case, the best focus position is obtained.
[0151]
Thus, the wafer W _T All evaluation point corresponding area DB above ₁ ~ DB ₉ Of the best focus position, that is, nine measurement patterns MP in the exposure area conjugate with the illumination area IAR with respect to the projection optical system PL. ₁ ~ MP ₉ When the best focus position at the measurement point (evaluation point) at which the projection position is obtained is determined, the determination in step 534 is affirmed, and the flow shifts to step 538, based on the best focus position data obtained above. Calculate other optical characteristics.
[0152]
For example, in this step 538, as an example, the evaluation point corresponding area DB ₁ ~ DB ₉ The field curvature of the projection optical system PL is calculated based on the data of the best focus position in. Further, the depth of focus at each measurement point (evaluation point) in the above-described exposure area may be obtained.
[0153]
Here, in the present embodiment, for simplicity of description, the reticle R corresponding to each evaluation point in the field of view of the projection optical system PL. _T The above pattern MP is used as a measurement pattern in the upper area. _n The description has been made on the assumption that only the first electrode is formed. However, it goes without saying that the present invention is not limited to this. For example, reticle R corresponding to each evaluation point _T In the vicinity of the upper region, there are a plurality of types of L / S patterns having different periodic directions and L / S patterns having different pitches in a predetermined region having an interval of an integral multiple of the above-described step pitch SP, for example, 8 times or 12 times. Each of the measurement patterns may be arranged. In this way, for example, a set of L / S patterns arranged in close proximity to the position corresponding to each evaluation point and having a periodic direction orthogonal to each other is obtained from the best focus position obtained as a measurement pattern and the non- Point aberration can be determined. Further, for each evaluation point in the field of view of the projection optical system PL, an astigmatism in-plane uniformity is obtained by performing an approximation process by the least square method based on the astigmatism calculated as described above, It is also possible to obtain the total focus difference from the astigmatism in-plane uniformity and the field curvature.
[0154]
The optical characteristic data of the projection optical system PL obtained as described above is stored in a storage device (not shown) and displayed on a screen of a display device (not shown). As a result, the process of step 538 in FIG. 11, that is, the process of step 456 in FIG. 5, ends, and a series of optical characteristic measurement processes ends.
[0155]
Next, an exposure operation by the exposure apparatus 100 of the present embodiment in the case of device manufacturing will be described.
[0156]
As a premise, the optical characteristics of the projection optical system PL determined as described above, for example, information on the best focus position, or information on the curvature of field in addition to the information, are transmitted to the main controller via an input / output device (not shown). 28.
[0157]
For example, when information on the curvature of field is input, the main controller 28 instructs an imaging characteristic correction controller (not shown) based on the optical characteristic data before the exposure, for example, before the exposure. By changing the position (including the distance from another optical element) or the inclination of at least one optical element (lens element in the present embodiment) of the PL, the projection optics is corrected so that its field curvature is corrected. The imaging characteristics of the system PL are corrected within a possible range. The optical elements used for adjusting the imaging characteristics of the projection optical system PL are not only refractive optical elements such as lens elements, but also reflective optical elements such as concave mirrors, or aberrations (distortion, spherical aberration, etc.) of the projection optical system PL. ), Especially an aberration correction plate for correcting the non-rotationally symmetric component may be used. Further, the method of correcting the image forming characteristics of the projection optical system PL is not limited to the movement of the optical element. For example, the method of controlling the light source 1 to slightly shift the center wavelength of the illumination light IL, or the method of correcting the projection optical system PL The method of changing the refractive index in a part of the method may be used alone or in combination with the movement of the optical element.
[0158]
Then, in response to an instruction from main controller 28, reticle R on which a predetermined circuit pattern (device pattern) to be transferred is formed by reticle loader (not shown) is loaded onto reticle stage RST. Similarly, the wafer W is loaded on the wafer table 18 by a wafer loader (not shown).
[0159]
Next, the main controller 28 uses a reticle alignment detection system (not shown), a reference mark plate FP on the wafer table 18, an alignment detection system AS, and the like to perform a preparation operation such as reticle alignment and baseline measurement in a predetermined procedure. Subsequently, wafer alignment such as an EGA (Enhanced Global Alignment) method is performed. The above-mentioned preparation work such as reticle alignment and baseline measurement is disclosed in detail, for example, in JP-A-7-176468 (corresponding US Pat. No. 5,646,413). Is disclosed in detail in JP-A-61-44429 (corresponding to U.S. Pat. No. 4,780,617), and will not be described in further detail here.
[0160]
When the above wafer alignment is completed, the exposure operation of the step-and-scan method is performed as follows.
[0161]
First, main controller 28 starts relative scanning of reticle R and wafer W, ie, reticle stage RST and XY stage 20, in the Y-axis direction. When the two stages RST and 20 reach their respective target scanning speeds and reach a constant speed synchronization state, the pattern area of the reticle R starts to be illuminated by the ultraviolet pulse light from the illumination system IOP, and scanning exposure is started. The relative scanning is performed by the main controller 28 controlling the reticle stage driving unit (not shown) and the driving system 22 while monitoring the measured values of the laser interferometer 26 and the laser interferometer 14 described above. .
[0162]
Main controller 28 determines that the moving speed Vr of reticle stage RST in the Y-axis direction and the moving speed Vw of XY stage 20 in the Y-axis direction particularly at the time of the scanning exposure described above are the projection magnification (倍率) of projection optical system PL. (Or 1/5 times). Further, the main controller 28 performs the above-described optical characteristic correction within the exposure area conjugate with the above-mentioned illumination area IAR based on the position information in the Z-axis direction of the wafer W detected by the focus sensor AFS during the scanning exposure. The wafer table 18 is driven via the drive system 22 in the Z-axis direction and the tilt direction so that the surface of the wafer W (shot area) falls within the range of the depth of focus of the image plane of the later projection optical system PL. Focus leveling control. Note that, in the present embodiment, prior to the exposure operation of the wafer W, the image plane of the projection optical system PL is calculated based on the above-described best focus position at each evaluation point, and this image plane is used as a detection reference of the focus sensor AFS. Optical calibration of the focus sensor AFS (for example, adjustment of the inclination angle of a plane-parallel plate disposed in the light receiving system 50b) is performed so as to be as follows. Of course, it is not always necessary to perform optical calibration, and for example, taking into account an offset corresponding to a deviation between the previously calculated image plane and the detection reference of the focus sensor AFS, the wafer W is output based on the output of the focus sensor AFS. A focus operation (and a leveling operation) for matching the surface to the image plane may be performed. Further, instead of or in combination with the movement of the wafer W, at least one of the reticle R and the optical element of the projection optical system PL may be moved to perform focus / leveling control.
[0163]
Then, the different areas of the pattern area of the reticle R are sequentially illuminated with the ultraviolet pulse light, and the illumination of the entire pattern area is completed, thereby completing the scanning exposure of the first shot area on the wafer W. Thereby, the pattern of the reticle R is reduced and transferred to the first shot area via the projection optical system PL.
[0164]
As described above, when the scanning exposure of the first shot area is completed, the XY stage 20 is step-moved in the X and Y axes directions by the main controller 28 via the drive system 22 so that the exposure of the second shot area is performed. Is moved to the scanning start position (acceleration start position).
[0165]
Then, the operation of each section is controlled by the main controller 28 in the same manner as described above, and the same scanning exposure as described above is performed on the second shot area on the wafer W.
[0166]
In this manner, the scanning exposure of the shot area on the wafer W and the stepping operation between shots are repeatedly performed, and the pattern of the reticle R is sequentially transferred to all the exposure target shots on the wafer W.
[0167]
When the pattern transfer to all the shots to be exposed on the wafer W is completed, the wafer is replaced with the next wafer, and the alignment and exposure operations are repeated in the same manner as described above.
[0168]
As described in detail above, according to the exposure apparatus 100 of the present embodiment, when measuring the optical characteristics of the projection optical system, the main control device 28 _n (N = 1 to 9) and reticle R on which frame pattern AP is formed _T Is mounted on a reticle stage RST arranged on the object plane side of the projection optical system, and a wafer W arranged on the image plane side of the projection optical system PL _T While changing the energy amount (exposure amount) P of the illumination light IL irradiated upward within a range not more than the appropriate exposure amount, the wafer W _T The position (Z) of the projection optical system PL in the optical axis direction is changed, and the wafer W _T Measurement pattern MP on top _n Are sequentially transferred by a step-and-repeat method (step pitch SP) (steps 408 to 424). Thereby, the wafer W _T On the top, a plurality (M × N) of partitioned areas (virtual partitioned areas) DA arranged in a matrix _{i, j} (I = 1 to M, j = 1 to N) and the first rectangular area DC as a whole _n Is formed. In this case, since the exposure is performed while changing the exposure amount within the range of the appropriate exposure amount or less, the exposure time can be reduced as compared with the case where the exposure is performed in the range of the appropriate exposure amount or more. Further, the influence of the pattern line width difference on exposure is reduced. Also, the first area DC _n Is composed of a plurality of divided regions (regions on which the images of the measurement patterns are projected) arranged in a matrix of N rows and M columns in which no border line exists between the divided regions as in the related art.
[0169]
Next, main controller 28 controls reticle R _T Move the reticle R _T And wafer W _T Are set in a predetermined positional relationship, and the frame pattern AP is exposed with an overexposure amount of the wafer W. _T Transfer to the top. Thereby, the wafer W _T Each first area DC above _n Over-exposed second area DD around _n Are formed respectively (steps 428, 430). That is, the wafer W _T Above, the first area DC _n And a second area DD forming the outer frame area _n Evaluation point corresponding area DB consisting of _n Is formed.
[0170]
Then, the wafer W _T After the development, the main controller 28 uses the alignment detection system AS including the FIA-based alignment sensor to _T Upper evaluation point corresponding area DB _n Is imaged (step 504). Next, the main controller 28 determines the evaluation point corresponding area DB based on the captured image data of the resist image. _n (Rectangular outer frame DBF) is detected (steps 506 and 508).
[0171]
Next, main controller 28 considers the known positional relationship in design and sets evaluation point corresponding area DB based on detected outer frame DBF as a reference. _n A plurality of partitioned areas DA _{i, j} Of the second region DD _n 1st area DC excluding _n Are calculated (step 518). This calculation is performed based on information on the number and arrangement of the divided areas in the outer frame. In the present embodiment, since the positions of the plurality of partitioned areas are calculated based on the design values based on the outer frame DBF, it is possible to obtain substantially accurate positions of the plurality of partitioned areas.
[0172]
Next, the main control device 28 controls the first area DC based on the imaging data. _n Is detected from among the M × N pieces of the divided areas forming the boundary, a plurality of pieces of the divided areas serving as boundaries where the image of the measurement pattern starts to appear. Specifically, the first area DC _n The image formation state (whether or not the image of the measurement pattern has appeared) in the M × N divided areas constituting the image data is determined by the image processing method, _{i, j} Score E of _{i, j} And the threshold SH are detected by a binarization method (steps 520 and 522), and as a result, the divided area DA in which the pattern appears to have appeared _{i, j} Is counted for each focus position (step 524), and the number of appearances of the pattern is plotted on a coordinate system where the horizontal axis is the focus position and the vertical axis is the number of pattern appearances, and each plot point is curve-fitted. By doing so, an nth-order approximate curve (least squares approximate curve) is obtained. In this case, the approximation curve is information on a plurality of partitioned areas serving as boundaries at which the image of the measurement pattern starts to appear, and specifically, arrangement information of a plurality of partitioned areas serving as boundaries at which the image of the measurement pattern starts to appear. Nothing else.
[0173]
That is, in the present embodiment, at least a part of the plurality of divided regions that are boundaries that start the appearance of the image of the measurement pattern is not set as the detection target as the boundary region that is the boundary where the image of the measurement pattern starts to disappear due to overexposure. As described above, even if the exposure is performed while changing the exposure amount within a range equal to or less than the appropriate exposure amount, the detection can be performed without any particular problem.
[0174]
Then, the optical characteristics of the projection optical system are obtained based on the information on at least a part of the plurality of divided areas which are boundaries where the detected image of the measurement pattern starts to appear, that is, the aforementioned n-th approximate curve (step). 530-538). In this embodiment, the objective and quantitative score E _{i, j} That is, since the optical characteristics of the projection optical system PL such as the best focus position are obtained based on the detection result using the index value of the contrast of the image, the best focus position and the like can be obtained with high accuracy in a short time. . Therefore, the measurement accuracy of the optical characteristics determined based on the best focus position and the reproducibility of the measurement results can be improved, and as a result, the throughput of the optical characteristics measurement can be improved. Further, since the measurement pattern can be made smaller as compared with the conventional method of measuring dimensions, it becomes possible to arrange a large number of measurement patterns in the pattern area of the reticle. Therefore, the number of evaluation points can be increased, and the interval between the evaluation points can be narrowed. As a result, the measurement accuracy of the optical characteristic measurement can be improved. Further, since the exposure amount is changed within the range equal to or less than the optimum exposure amount, for example, when a resist image is to be measured, the measurement result is hardly influenced by the characteristics of the resist.
[0175]
Further, in the case of the present embodiment, since there is no frame line between the adjacent divided areas, a plurality of divided areas (mainly, the divided areas where the image of the measurement pattern appears) for which the image forming state is to be detected are measured. The contrast of the pattern image does not decrease due to the interference of the frame lines. For this reason, it is possible to obtain, as the imaging data of the plurality of divided areas, data having a good S / N ratio between the pattern portion and the non-pattern portion. Therefore, the measurement pattern MP for each partitioned area _n Can be detected with high accuracy and reproducibility. Moreover, an objective and quantitative score E is used to determine the state of image formation. _{i, j} Is compared with the threshold value SH and converted into the presence / absence information of the pattern (binary information) and detected. _n Can be detected with good reproducibility, and the presence or absence of a pattern can be automatically and stably determined. Therefore, in the present embodiment, when binarizing, only one threshold is sufficient, and compared to a case where a plurality of thresholds are set and the presence or absence of a pattern is determined for each threshold, the image forming state Can be shortened and the detection algorithm can be simplified.
[0176]
Further, in the present embodiment, as described above, since the image formation state is converted into the presence / absence information of the pattern (binary information) and detected, the reticle R _T Measurement pattern MP in the pattern area PA _n There is no need to arrange other patterns (for example, a reference pattern for comparison, a mark pattern for positioning, etc.).
[0177]
In addition, according to the optical characteristic measurement method according to the present embodiment, since the best focus position is calculated based on an objective and reliable method of calculating an approximate curve by statistical processing, stable high accuracy and reliability are ensured. Optical characteristics can be measured. Note that, depending on the order of the approximate curve, it is possible to calculate the best focus position based on the inflection point or a plurality of intersections between the approximate curve and a predetermined slice level.
[0178]
In addition, in the exposure apparatus 100 of the present embodiment, the projection optical system PL is subjected to exposure prior to exposure so that optimal transfer can be performed in consideration of the optical characteristics of the projection optical system PL accurately measured by the above-described optical characteristic measurement method. The adjusted pattern formed on the reticle R is transferred onto the wafer W via the adjusted projection optical system PL. Furthermore, since the focus control target value at the time of exposure is set in consideration of the best focus position determined as described above, it is possible to effectively suppress the occurrence of color unevenness due to defocus. Therefore, according to the exposure method according to the present embodiment, a fine pattern can be transferred onto a wafer with high accuracy.
[0179]
Note that the optical characteristic measuring method described in the above embodiment is merely an embodiment, and the optical characteristic measuring method of the present invention is not limited to this. For example, in the above embodiment, a plurality of partitioned areas DA arranged in a matrix _{i, j} As a whole, a first rectangular region DC _n The wafer W _T After forming on the second area DD over-exposed around the first area _n Is formed, but the second region DD is formed. _n After forming the first region DC _n May be formed. In such a case, for example, when a high-sensitivity resist such as a chemically amplified resist is used as the photosensitive agent, the time from the formation (transfer) of the image of the measurement pattern to be detected to the development can be shortened. .
[0180]
In the above embodiment, the evaluation point corresponding area DB _n Region DD that constitutes _n Is a rectangular frame, but the present invention is not limited to this. That is, since the second region only needs to be such that its outer edge can be used as a reference for calculating the position of at least each of the divided regions constituting the first region, a part of the rectangular frame, for example, a U-shaped (U-shaped) portion or an L-shaped portion is formed. It may be a letter-shaped part. In this case, the evaluation point corresponding area including the first area and the second area outside the first area is a rectangular area as a whole.
[0181]
Further, the method of forming the above-described second region, that is, the rectangular frame-shaped region or a part of the region is not limited to the method described in the above embodiment, and may be, for example, on the reticle stage RST of the exposure apparatus 100. A pattern composed of a rectangular frame-shaped light transmitting portion (second region DD _n A reticle on which a pattern having the same shape as that of the reticle) or a part of the reticle pattern is formed is mounted, and the pattern of the reticle is formed on a wafer arranged on the image plane side of the projection optical system PL by one scanning exposure The transfer may be performed to form a second overexposed area on the wafer. Alternatively, the above-described measurement pattern is transferred onto the wafer by an exposure amount that causes overexposure by the step-and-repeat method or the step-and-scan method, and the second region DD is transferred. _n May be formed. In addition, the divided area DA completely including the measurement pattern _{i, j} Is mounted on the reticle stage RST, and the opening pattern is exposed to overexposure energy by a step-and-repeat method or a step-and-scan method. The second region of overexposure may be formed on the wafer by transferring onto the wafer. In addition, for example, by performing exposure by the step-and-stitch method using the above-described opening pattern and forming a plurality of images of the opening pattern adjacent to or joined to each other on the wafer, the second region of overexposure is formed. It may be formed on a wafer. In addition, while the reticle stage RST is stationary, the wafer W (wafer table 18) is moved in a predetermined direction while illuminating an opening pattern formed on the reticle mounted on the reticle stage RST with illumination light. A second region for exposure may be formed. In any case, as in the above embodiment, the presence of the overexposed second region makes it possible to accurately detect the outer edge of the second region based on a detection signal having a good S / N ratio. .
[0182]
In the above embodiment, the measurement pattern MP _n The formation state of the image of _{i, j} A case has been described in which the data is compared with the threshold value SH and converted to pattern presence / absence information (binary information) and detected, but the present invention is not limited to this. In the above embodiment, the evaluation point corresponding area DB _n Is accurately detected, and each of the divided areas DA is determined based on the outer frame DBF. _{i, j} Is calculated by calculation, the position of each partitioned area can be accurately obtained. Therefore, the template matching may be performed on each of the precisely determined divided areas. By doing so, template matching can be performed in a short time. In this case, as the template pattern, for example, imaging data of a partitioned area where an image has appeared or a partitioned area where no image has appeared can be used. Even in this case, objective and quantitative information of the correlation value is obtained for each sectioned area. By comparing the obtained information with a predetermined threshold value, the measurement pattern MP _n Is converted into binary information (image presence / absence information), and the image formation state can be detected with high accuracy and reproducibility as in the above embodiment.
[0183]
Further, the second region of overexposure is not necessarily required. Even in such a case, the outline of the first area is a rectangular outer frame, and a part of the outermost peripheral area in the first area (hereinafter referred to as “outer edge area”) includes: Since there is an area where no pattern image is formed, it is possible to detect a part of the outer frame, that is, the boundary between the first area and the area outside the area, with a good S / N ratio by the same method as in the above embodiment. Then, the position of another partitioned area (each of the partitioned areas constituting the first area) can be calculated based on the design value based on the boundary line, and an almost accurate position of the other partitioned area can be obtained. It is. Similarly, the second region of overexposure is not limited to a rectangular frame or a part thereof as in the above embodiment. For example, as for the shape of the second region, only the boundary (inner edge) with the first region may have a rectangular frame shape, and the outer edge may have an arbitrary shape. Also in these cases, since the positions of the plurality of divided areas in the first area can be almost accurately known, for example, for each of the divided areas, the same score (index of the contrast of the image) Value), or by applying the template matching method to detect the image formation state, it is possible to detect the pattern image formation state in a short time as in the above embodiment.
[0184]
Then, by obtaining the optical characteristics of the projection optical system based on the detection result, it is possible to obtain the optical characteristics based on the objective and quantitative detection result using the image contrast or correlation value. Therefore, the same effect as in the above embodiment can be obtained.
[0185]
In the above-described embodiment, the FIA-based alignment sensor is used for detecting the outer frame DBF as a reference for detecting each of the divided areas and for detecting the image formation state of each of the divided areas. However, the present invention is not limited to this. That is, at least one of the detection of the boundary between the outer frame DBF or the outer edge section area and the second area and the detection of the image formation state of each section area is performed by another method such as SEM (scanning electron microscope). An imaging device (image measuring device) may be used. Even in such a case, it is possible to accurately determine the position of each partitioned area in the first area based on the outer frame or inner edge of the second area.
[0186]
Further, in the above embodiment, as shown in FIG. 3, the measurement pattern MP is provided inside the pattern area PA including the light-shielding portion by the light transmitting portion. _n However, the present invention is not limited to this. In contrast to the case of FIG. 3, the remaining pattern formed by the light shielding portion inside the opening pattern (that is, a plurality of line portions having light transmitting portions on both sides) ) By the measurement pattern MP _n May be formed. When a measurement pattern is formed by using the remaining pattern, a photosensitive layer may be formed on the surface of the wafer by using a negative resist. In this manner, even when the exposure amount is changed in a range equal to or less than the appropriate exposure amount in the same manner as in the above-described embodiment, it is possible to accurately detect the section area serving as the boundary where the transfer image starts to appear as described above. As a result, the same effect as the above embodiment can be obtained. Further, in the above-described embodiment, the pattern area PA of the reticle is used as the light-shielding part. However, the pattern area PA may be a light-transmitting part. _n Only the surrounding area may be used as a light-shielding portion, and at the time of transfer, the illumination area may be limited to only the light-shielding portion.
[0187]
In the above embodiment, the reticle R _T Upper measurement pattern MP _n As described above, the case where one type of L / S pattern (multi-bar pattern) is used has been described, but it goes without saying that the present invention is not limited to this. As the measurement pattern, at least two types of L / S patterns having different periodic directions, an isolated line, a contact hole, or the like may be used. Measurement pattern MP _n When the L / S pattern is used, the duty ratio and the period direction may be arbitrary. Also, the measurement pattern MP _n When a periodic pattern is used, the periodic pattern may be not only an L / S pattern but also a pattern in which dot marks are periodically arranged, for example. This is because, unlike the conventional method of measuring the line width or the like of an image, the state of image formation is detected by a score (contrast).
[0188]
Further, in the above embodiment, the best focus position is obtained based on one type of score. However, the present invention is not limited to this. A plurality of types of scores may be set and the best focus position may be obtained based on these. Alternatively, the best focus position may be obtained based on these average values (or weighted average values).
[0189]
In the above-described embodiment, one type of threshold is used for detecting the state of image formation. However, the present invention is not limited to this, and a plurality of thresholds may be used. When a plurality of threshold values are obtained, each threshold value may be compared with a score to detect the image formation state of the partitioned area. In this case, for example, when it is difficult to calculate the best focus position from the detection result at the first threshold, the formation state is detected at the second threshold, and the best focus position can be obtained from the detection result. Become.
[0190]
Alternatively, a plurality of thresholds may be set in advance, the best focus position may be determined for each threshold, and their average value (simple average value or weighted average value) may be used as the best focus position. For example, the focus position when the exposure energy amount P shows an extreme value is sequentially calculated according to each threshold value. Then, the average value of each focus position is set as the best focus position. Note that two intersections (focus positions) between an approximate curve indicating the relationship between the exposure energy amount P and the focus position Z and an appropriate slice level (exposure energy amount) are obtained, and an average value of both intersection points is calculated for each threshold value. Calculated values and their average value (simple average value or weighted average value) may be used as the best focus position.
[0191]
Alternatively, the best focus position is calculated for each threshold value, and in the relationship between the threshold value and the best focus position, the average value of the best focus position in the section where the change in the best focus position is the smallest (simple average value) Alternatively, a weighted average value may be used as the best focus position.
[0192]
In the above embodiment, a preset value is used as the threshold, but the present invention is not limited to this. For example, wafer W _T Upper measurement pattern MP _n May be imaged in an area where is not transferred, and the obtained score may be used as a threshold.
[0193]
Further, for example, the number of times the image is taken in by the alignment detection system AS may be made different between the first area and the second area. By doing so, the measurement time can be reduced.
[0194]
In the exposure apparatus 100 of the above embodiment, the main controller 28 measures the optical characteristics of the projection optical system described above according to a processing program stored in a storage device (not shown), thereby automating the measurement process. Can be realized. Of course, this processing program may be stored in another information recording medium (CD-ROM, MO, etc.). Further, when performing the measurement, a processing program may be downloaded from a server (not shown). It is also possible to send the measurement result to a server (not shown), or to notify the outside of the measurement result by e-mail and file transfer via the Internet or an intranet.
[0195]
In the above embodiment, the measurement pattern MP _n The wafer W _T Upper section area DA _{i, j} To the wafer W after development. _T Upper section area DA _{i, j} Although the description has been given of the case where the resist image formed in the image is captured by the alignment detection system AS and the image data is subjected to image processing, the method for measuring the optical characteristics according to the present invention is not limited to this. For example, the object to be imaged may be a latent image formed on a resist at the time of exposure, and an image (etched image) obtained by developing the wafer on which the image is formed and further etching the wafer. It may be performed for such as. In addition, the photosensitive layer for detecting the state of image formation on an object such as a wafer is not limited to a photoresist, but may be any as long as images (latent image and visible image) are formed by irradiation of light (energy). good. For example, the photosensitive layer may be an optical recording layer, a magneto-optical recording layer, and the like. Therefore, the object on which the photosensitive layer is formed is not limited to a wafer or a glass plate, but may be an optical recording layer, a magneto-optical recording layer, or the like. It may be a plate that can be formed.
[0196]
Further, the optical characteristics of the projection optical system PL can be adjusted based on the above-described measurement results (such as the best focus position) without the intervention of an operator or the like. That is, the exposure apparatus can have an automatic adjustment function.
[0197]
Further, in the above embodiment, the exposure condition changed at the time of pattern transfer is the same as the wafer W in the optical axis direction of the projection optical system. _T Position and wafer W _T Although the description has been given of the case where the energy amount (exposure dose) of the energy beam applied to the surface is described, the present invention is not limited to this. For example, the wafer W in the optical axis direction of the projection optical system _T Not only the position of the exposure condition but also any of the setting conditions of all the components related to the exposure such as the illumination condition (including the type of the mask) and the imaging characteristics of the projection optical system are changed as one of the exposure conditions. May be. Further, it is not always necessary to perform exposure while changing two types of exposure conditions. That is, the pattern of the measurement mask is transferred to a plurality of regions on the photosensitive object while changing the exposure amount within a range of one type of exposure condition, that is, the appropriate exposure amount or less, and the formation state of the transferred image is detected. Even in this case, there is an effect that the detection can be performed quickly by the method of the contrast measurement using the same score as in the above embodiment or the template matching technique.
[0198]
In the above embodiment, the best exposure amount can be determined together with the best focus position. That is, the exposure energy amount is also set on the high energy amount side, the same processing as in the above embodiment is performed, and for each exposure energy amount, the width of the focus position where the image is detected is obtained, and the width is determined as the maximum. Is calculated, and the exposure amount in that case is set as the best exposure amount.
[0199]
Further, in the above embodiment, as an example, the variance (or standard deviation) of the pixel values in the specified range in the defined area is adopted as the score E, but the present invention is not limited to this. The score E may be the sum of the pixel values in the divided area or a part thereof (for example, the specified range described above) and the differential sum.
[0200]
Further, in the above embodiment, each partitioned area DA _{i, j} The presence or absence of the image of the measurement pattern is detected by comparing the score with a threshold value. Instead, the same as the curve P = f (Z) in FIG. An approximate curve may be calculated.
[0201]
That is, by detecting the outer frame and calculating the position of each partitioned area using the detection result, the first area DC on the imaging data is obtained. _n Find the range of Then, the first area DC _n Is detected, for example, the distribution state of the sum of pixel data (integrated signal of luminance values on scanning lines in the X-axis direction) of each pixel column in the row direction (X-axis direction) of the above-described matrix is detected. I do. When each peak point in the distribution curve of the added value of the pixel data (pixel value) for each pixel row obtained as described above is found, the peak point becomes a boundary where the image of the measurement pattern starts to appear. It corresponds to the position of the partitioned area.
[0202]
Next, an nth-order approximation curve (least square approximation curve) is obtained by curve fitting this peak point. Thereby, for example, an approximate curve having the same shape as the curve P = f (Z) in FIG. 14 can be obtained. In this case, the detection result of the image formation state (for example, presence / absence detection) of each of the above-described divided areas is substantially obtained by a simple image processing of calculating the distribution state of the added value of the pixel data for each pixel row in the predetermined direction. Data of an equivalent distribution situation can be obtained. Therefore, a simpler method with the same level of detection accuracy and reproducibility as the case of using the objective and quantitative imaging data to obtain a detection result of the image formation state (for example, presence / absence detection) of each of the above-described divided areas. Thus, the state of image formation can be detected.
[0203]
Then, by performing the same processing as in the above embodiment using the above-described approximate curve, the optical characteristics of the projection optical system PL, for example, the best focus position may be obtained. Even in this case, similarly to the above-described embodiment, since the optical characteristics are determined based on the detection result using the objective and quantitative imaging data, the optical characteristics can be compared with the conventional method in accuracy and reproducibility. You can measure well.
[0204]
Further, in the above embodiment, the imaging characteristic of the projection optical system PL is adjusted via the imaging characteristic correction controller. However, for example, only the imaging characteristic correction controller sets the imaging characteristic within a predetermined allowable range. When the control cannot be performed, at least a part of the projection optical system PL may be replaced, or at least one optical element of the projection optical system PL may be reworked (aspherical processing or the like). In particular, when the optical element is a lens element, its eccentricity may be changed, or it may be rotated about the optical axis. At this time, when detecting a resist image or the like using the alignment sensor of the exposure apparatus 100, the main control device 28 displays a warning on a display (monitor) or informs the operator or the like of necessity of assistance to the operator through the Internet or a mobile phone. The notification may be made, or information necessary for adjusting the projection optical system PL, such as a replacement portion of the projection optical system PL and an optical element to be reworked, may be notified together. As a result, not only the operation time for measuring the optical characteristics and the like but also the preparation period can be shortened, and the stop period of the exposure apparatus can be shortened, that is, the operation rate can be improved. Further, in this embodiment, the measurement pattern is transferred to the wafer by the static exposure method. However, instead of or in addition to the static exposure method, at least one exposure method is used in the scanning exposure method just as in the above embodiment. Dynamic optical characteristics may be obtained by transferring the measurement pattern to the wafer while changing the conditions.
[0205]
In the above embodiment, the evaluation point corresponding area DB _n N × M partitioned areas DA _{i, j} Are exposed, at least one of the N × M divided areas, that is, a divided area in which exposure conditions that do not clearly contribute to the determination of the curve P = f (Z) are set (for example, in FIG. The exposure area need not be exposed for the division areas located at the upper left corner and the lower left corner, and the evaluation point corresponding area DB _n Need not be a rectangle (matrix) as a whole.
[0206]
In the above embodiment, the image signal of the resist image picked up by the alignment detection system AS may be integrated for each scanning line. In the above embodiment, one evaluation point corresponding area DB _n Is imaged collectively, for example, one evaluation point corresponding area DB _n May be imaged in a plurality of times. Furthermore, the wafer may be moved continuously without positioning at the time of each imaging, thereby making it possible to reduce the measurement time. At this time, for example, the partition area DA _{i, j} The image data may be added a plurality of times each time and the image data is added.
[0207]
Further, the light source of the exposure apparatus to which the present invention is applied is not limited to a KrF excimer laser or an ArF excimer laser, _Two A laser (wavelength: 157 nm) or another pulsed laser light source in the vacuum ultraviolet region may be used. In addition, a fiber doped with, for example, erbium (or both erbium and ytterbium) is used as the illumination light for exposure, for example, a single-wavelength laser beam in the infrared or visible range oscillated from a DFB semiconductor laser or a fiber laser. A harmonic that has been amplified by an amplifier and wavelength-converted to ultraviolet light using a nonlinear optical crystal may be used. Further, an ultra-high pressure mercury lamp or the like that outputs an ultraviolet bright line (g line, i line, etc.) may be used. In this case, the exposure energy may be adjusted by lamp output control, a dimming filter such as an ND filter, a light amount aperture, and the like. Further, the present invention may be applied to an exposure apparatus that uses a charged particle beam such as an EUV light, an X-ray, or an electron beam and an ion beam as an exposure beam.
[0208]
In the above embodiment, the case where the present invention is applied to the step-and-scan type reduction projection exposure apparatus has been described, but the scope of the present invention is not limited to this. That is, the present invention can be suitably applied to an exposure apparatus such as a step-and-repeat method, a step-and-stitch method or a proximity method, a mirror projection aligner, and a photo repeater. Further, the present invention can be suitably applied to an immersion exposure apparatus disclosed in, for example, International Publication WO99 / 49504, in which a liquid is filled between a projection optical system PL and a wafer.
[0209]
Further, the projection optical system PL may be any one of a refraction system, a catadioptric system, and a reflection system, and may be any one of a reduction system, an equal magnification system, and an enlargement system.
[0210]
Furthermore, the present invention is not limited to an exposure apparatus used for manufacturing a semiconductor element, but also an exposure apparatus used for manufacturing a display including a liquid crystal display element and a plasma display, which transfers a device pattern onto a glass plate, and a thin film magnet. Exposure equipment used in the manufacture of masks, reticle used in the manufacture of exposure devices for transferring device patterns onto ceramic wafers, imaging devices (such as CCDs), organic ELs, micromachines, and DNA chips, as well as masks or reticles It can also be applied to devices and the like.
[0211]
《Device manufacturing method》
Next, an embodiment of a device manufacturing method using the above-described exposure apparatus and method will be described.
[0212]
FIG. 15 shows a flowchart of an example of manufacturing devices (semiconductor chips such as ICs and LSIs, liquid crystal panels, CCDs, thin-film magnetic heads, DNA chips, micromachines, etc.). As shown in FIG. 15, first, in step 301 (design step), a function / performance design of a device (for example, a circuit design of a semiconductor device) is performed, and a pattern design for realizing the function is performed. Subsequently, in step 302 (mask manufacturing step), a mask on which the designed circuit pattern is formed is manufactured. On the other hand, in step 303 (wafer manufacturing step), a wafer is manufactured using a material such as silicon.
[0213]
Next, in step 304 (wafer processing step), actual circuits and the like are formed on the wafer by lithography using the mask and the wafer prepared in steps 301 to 303, as described later. Next, in step 305 (device assembly step), device assembly is performed using the wafer processed in step 304. Step 305 includes processes such as a dicing process, a bonding process, and a packaging process (chip encapsulation) as necessary.
[0214]
Finally, in step 306 (inspection step), inspections such as an operation confirmation test and a durability test of the device manufactured in step 305 are performed. After these steps, the device is completed and shipped.
[0215]
FIG. 16 shows a detailed flow example of step 304 in the case of a semiconductor device. In FIG. 16, in step 311 (oxidation step), the surface of the wafer is oxidized. In step 312 (CVD step), an insulating film is formed on the wafer surface. In step 313 (electrode forming step), electrodes are formed on the wafer by vapor deposition. In step 314 (ion implantation step), ions are implanted into the wafer. Each of the above steps 311 to 314 constitutes a pre-processing step in each stage of wafer processing, and is selected and executed according to a necessary process in each stage.
[0216]
In each stage of the wafer process, when the above-described pre-processing step is completed, the post-processing step is executed as follows. In this post-processing step, first, in step 315 (resist forming step), a photosensitive agent is applied to the wafer. Subsequently, in step 316 (exposure step), the circuit pattern of the mask is transferred to the wafer by the exposure apparatus and the exposure method of each of the above embodiments. Next, in Step 317 (development step), the exposed wafer is developed, and in Step 318 (etching step), the exposed members other than the portion where the resist remains are removed by etching. Then, in step 319 (resist removing step), unnecessary resist after etching is removed.
[0219]
By repeating these pre-processing and post-processing steps, multiple circuit patterns are formed on the wafer.
[0218]
As described above, if the device manufacturing method of the present embodiment is used, the exposure apparatus and the exposure method of the above embodiment are used in the exposure step, so that the optical characteristics accurately determined by the optical characteristic measurement method described above are taken into account. High-precision exposure is performed via the projection optical system adjusted as described above, and a device with a high degree of integration can be manufactured with high productivity.
[0219]
【The invention's effect】
As described above, according to the optical characteristic measuring method of the present invention, there is an effect that the optical characteristics of the projection optical system can be obtained in a short time with high accuracy and reproducibility.
[0220]
Further, according to the exposure method of the present invention, there is an effect that highly accurate exposure can be realized.
[0221]
Further, according to the device manufacturing method of the present invention, there is an effect that a highly integrated device can be manufactured.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a schematic configuration of an exposure apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining an example of a specific configuration of the illumination system IOP of FIG.
FIG. 3 is a diagram illustrating an example of a reticle used for measuring optical characteristics of a projection optical system.
FIG. 4 is a flowchart (part 1) for describing a method for measuring optical characteristics.
FIG. 5 is a flowchart (part 2) illustrating a method for measuring optical characteristics.
FIG. 6 is a diagram for explaining the arrangement of partitioned areas.
FIG. 7 shows a wafer W _T Above the first area DC _n It is a figure showing the state where was formed.
FIG. 8 shows a wafer W _T Evaluation point corresponding area DB on top _n It is a figure showing the state where was formed.
FIG. 9 shows a wafer W _T After development _T Evaluation point corresponding area DB formed above ₁ FIG. 3 is a diagram showing an example of a resist image of FIG.
FIG. 10 is a flowchart (part 1) showing details of step 456 (processing for calculating optical characteristics) in FIG. 5;
FIG. 11 is a flowchart (part 2) showing details of step 456 (optical characteristic calculation processing) in FIG. 5;
FIG. 12 is a diagram illustrating a first area DC according to the processing of step 518; _n Areas DA that configure _{i, j} It is a figure which shows a mode that was calculated.
FIG. 13 is a diagram of a table data format showing an example of a detection result.
FIG. 14 is a diagram showing a relationship between the number of pattern appearances (exposure energy amount) and a focus position.
FIG. 15 is a flowchart illustrating an embodiment of a device manufacturing method according to the present invention.
FIG. 16 is a flowchart of a process in step 304 of FIG. 15;
[Explanation of symbols]
DA _{i, j} … Partitioned area, DB _n ... Evaluation point corresponding area (predetermined area), IL ... Energy beam, MP _n … Measurement pattern, PL… projection optical system, R… reticle (mask), W… wafer (photosensitive object), W _T ... wafer (photosensitive object).

Claims (15)

An optical characteristic measuring method for measuring an optical characteristic of a projection optical system that projects a pattern on a first surface onto a second surface,
Changing the exposure amount within a range equal to or less than the appropriate exposure amount, while changing at least one exposure condition, the measurement pattern arranged on the first surface to the second surface side of the projection optical system. A first step of sequentially transferring to the arranged photosensitive object to form a first area including a plurality of divided areas on the photosensitive object;
A second step of detecting information on at least a part of the plurality of divided regions that are boundaries between which the image of the measurement pattern starts to appear among the plurality of divided regions;
A third step of obtaining optical characteristics of the projection optical system based on the detection result. 2. The measurement pattern is a blank pattern in which a pattern is formed by a light transmitting part in a light shielding part, and a photosensitive layer is formed on a surface of the photosensitive object by a positive resist. The optical characteristic measuring method according to 1. Prior to the second step, further including a fourth step of forming a second area of overexposure in at least a part of a periphery of the area on the photosensitive object to be the first area,
The second step is a step of detecting a part of an outline of the second area, and forming an image of a measurement pattern in at least a part of the plurality of divided areas using the detection result. 3. The method for measuring optical characteristics according to claim 2, further comprising a step of detecting a state. The method according to claim 3, wherein the fourth step is performed prior to the first step. In the fourth step, a predetermined pattern arranged on the first surface is transferred onto the photosensitive object arranged on a second surface side of the projection optical system to form the second region. The optical characteristic measuring method according to claim 3 or 4, wherein The first region is a rectangular region as a whole,
The predetermined pattern is a pattern having a rectangular frame shape or a partial shape thereof, and in the fourth step, the predetermined pattern arranged on the first surface is placed on a second surface side of the projection optical system. The method according to claim 5, wherein the image is transferred onto the arranged photosensitive object by a scanning exposure method. In the fourth step, the measurement pattern arranged on the first surface is sequentially transferred onto the photosensitive object arranged on the second surface side of the projection optical system at an exposure amount that causes overexposure, and The optical characteristic measuring method according to claim 3, wherein a second region is formed. 2. The measurement pattern is a remaining pattern in which a pattern is formed by a light shielding portion in a light transmitting portion, and a photosensitive layer is formed on the surface of the photosensitive object by a negative resist. The optical characteristic measuring method according to 1. In the second step, an image formation state in at least some of the plurality of divided areas constituting the first area is represented by a representative value relating to pixel data of each of the divided areas obtained by imaging. The optical characteristic measuring method according to claim 1, wherein the optical characteristic is detected as a determination value. The optical characteristic measuring method according to claim 9, wherein the representative value is at least one of an added value, a differential sum, a variance, and a standard deviation of pixel data in at least a part of each of the divided areas. The optical characteristic measuring method according to claim 9, wherein when detecting the image formation state, a representative value of pixel data of each of the divided areas is compared with a predetermined threshold to binarize. In the second step, image data corresponding to at least a part of the plurality of divided areas constituting the first area is used, and a pixel value of each pixel row in a predetermined direction in the imaged data is used. The optical characteristic measuring method according to claim 1, wherein a section area serving as a boundary at which an image of the measurement pattern starts to appear is detected based on a distribution of the added values. In the first step, the measurement pattern is sequentially transferred onto the photosensitive object while changing the position of the photosensitive object in the optical axis direction of the projection optical system as the exposure condition,
In the third step, the energy amount of the exposure energy beam corresponding to the information regarding at least a part of the plurality of divided areas serving as boundaries where the image of the measurement pattern detected in the second step starts to appear and the projection optical system 13. The optical characteristic measuring method according to claim 1, wherein a best focus position is determined based on a correlation with a position of the photosensitive object in an optical axis direction of a system. An exposure method of irradiating a mask with an energy beam for exposure, and transferring a pattern formed on the mask onto a photosensitive object via a projection optical system,
A step of adjusting the projection optical system in consideration of the optical characteristics measured by the optical characteristic measurement method according to any one of claims 1 to 13;
Transferring the pattern formed on the mask onto the photosensitive object via the adjusted projection optical system. A device manufacturing method including a lithography step,
15. A device manufacturing method, wherein the lithography step uses the exposure method according to claim 14.

Images