JP2004342341A - Mirror electron microscope, and pattern defect inspection device using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-resolution mirror electron microscope for separating irradiating electron beams and imaging electron beams at a low aberration. <P>SOLUTION: An E×B deflector 3 as a separator is arranged near by an imaging face 304 of imaging electron beams 302 to eliminate the effect of the deflector 3 on the electron beam 302. The aberration generated from the deflector 3 to irradiation electron beams 301 is corrected by arranging another E×B deflector for correcting aberration 4 between an irradiation system condenser lens 2 and the E×B deflector 3 and by operating it. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

なお、上式で、ｅ／ｍは、比電荷である。
電界Ｅによる偏向と磁界Ｂによる偏向が打ち消しあう条件、
【００１９】
【数２】

を、Ｗｉｅｎ条件と呼び、図２でＷｉｅｎ条件に設定されたＥ×Ｂ偏向器に上方から入射した電子線は直進し、下方から入射した電子線はθ_Ｅ＋θ_Ｍ＝２θ_Ｅの偏向を受ける。Ｗｉｅｎ条件で、ｅ（Ｖ_０＋ΔＶ）のエネルギーの電子線の偏向量Δｙは、Ｅ×Ｂ偏向器の偏向色収差となり、次式で近似される。
【００２０】
【数３】

また、Ｗｉｅｎ条件で反対方向から入射した場合の偏向量Δｙ’は、上式の括弧内を加算して、
【００２１】
【数４】

となり、Ｗｉｅｎ条件で反対方向から入射した電子線は直進する電子線より約３倍の色収差をもつことになることがわかる。
【００２２】
ここで、電子レンズの物面上の１点からあらゆる方向に出射した電子線は像面上の１点に集束するので、Ｅ×Ｂ偏向器が電子レンズの物面上にある場合には、Ｅ×Ｂ偏向器の色収差によって偏向角度のずれが生じても像面では１点に集束するので、偏向収差は発生しないと考えられる。
【００２３】
ＬＥＥＭ（Ｌｏｗ Ｅｎｅｒｇｙ Ｅｌｅｃｔｒｏｎ Ｍｉｃｒｏｓｃｏｐｙ）と呼ばれる二次電子を二次元結像させる従来装置では、ビームセパレータとしてＥ×Ｂ偏向器を用い、Ｅ×Ｂ偏向器を結像系の対物レンズ像面すなわち中間レンズの物面近傍に配置することにより、中間レンズ以降への収差の影響を最小にする構成としていた。しかし、結像対物レンズの像面と照射系のクロスオーバ位置は一致しないので、この構成では照射電子線に対する収差が大きくなる。二次電子を結像する方式では二次電子の放出角度分布が照射電子線の入射条件にあまり依存しないので、照射系の収差が大きくても二次電子像への影響がなかったものと推定される。ミラー電子顕微鏡については、この構成では試料を平行照射できなくなるので所望の性能を達成することができない。
【００２４】
そこで、Ｅ×Ｂ偏向器を次のような構成とした。Ｅ×Ｂ偏向器の配置は照射系のクロスオーバ位置か、結像系の像面（ミラー像面）位置近傍とし、収差が発生したもう一方の光学系内に、もうひとつＥ×Ｂ偏向器を配置して、逆方向に動作させることにより、セパレータで発生した色収差を補正する構成とした。図３に示すように、Ｅ×Ｂ偏向器Ｌ及びＥ×Ｂ偏向器Ｕが、像面上からそれぞれＬ_Ｌ及びＬ_Ｕ離れて配置する２つのＥ×Ｂ偏向器の像面上の色収差を逆向きに等しくなるように動作させる。ここで、θ_Ｌ、θ_Ｕを、それぞれ、偏向器Ｌの色収差Δｙ_Ｌ＝θ_ＬＬ_Ｌ（ΔＶ／２Ｖ_０）、偏向器Ｕの色収差Δｙ_Ｕ＝θ_ＵＬ_Ｕ（ΔＶ／２Ｖ_０）で与えられる偏向角とすると、Δｙ_Ｌ＝Δｙ_Ｕ、すなわち、
Ｌ_Ｌθ_Ｌ＝Ｌ_Ｕθ_Ｕ ．．．．．．．．．．．（３）
となるように、Ｅ×Ｂ偏向器の強度を調整すれば、像面上の色収差は補正できると考えられる。
【００２５】
具体的な構成は、以下のようにした。すなわち、図４に示すように、照射系のクロスオーバ位置すなわち対物レンズの焦点面近傍にセパレータとして動作するＥ×Ｂ偏向器を配置して、照射系の収差を最小にする。結像系で発生した収差は、結像系像面位置とＥ×Ｂ偏向器の間にもうひとつ収差補正用のＥ×Ｂ偏向器を配置、動作させて補正する構成とした。
【００２６】
あるいは、図５に示すように、セパレータ用のＥ×Ｂ偏向器は、結像電子線（反射電子線）に対してＷｉｅｎ条件となるように動作させ、結像系の像面位置に配置させる。すなわち、ミラー電子による結像電子線はＥ×Ｂ偏向器を直進して、収差も最小条件となるようにする。照射電子線（入射電子線）に対してＥ×Ｂ偏向器は偏向器として動作し、照射系のクロスオーバとＥ×Ｂ偏向器は離れてしまうので、Ｅ×Ｂ偏向器により照射系で発生する収差を補正するためにもうひとつの収差補正用のＥ×Ｂ偏向器を照射レンズとＥ×Ｂ偏向器の間に配置させることにより、色収差を補正する構成とした。この場合、Ｗｉｅｎ条件で動作するセパレータ用のＥ×Ｂ偏向器は照射系に対して電子線を偏向させる偏向器として動作するので、色収差は直進する電子線の場合より約３倍大きくなる。ここで、θ_Ｌ、θ_Ｕを、それぞれ、偏向器Ｌの色収差Δｙ_Ｌ＝３θ_ＬＬ_Ｌ（ΔＶ／２Ｖ_０）、偏向器Ｕの色収差Δｙ_Ｕ＝θ_ＵＬ_Ｕ（ΔＶ／２Ｖ_０）で与えられる偏向角とすると、Δｙ_Ｌ＝Δｙ_Ｕ、すなわち、
３Ｌ_Ｌθ_Ｌ＝Ｌ_Ｕθ_Ｕ ．．．．．．．．．．（４）
となるように、Ｅ×Ｂ偏向器の強度を調整すれば、クロスオーバ上の色収差は補正できる。
【００２７】
また、試料が傾斜した場合にも常に試料に垂直に照射電子線を照射できるように、結像レンズの像面近傍に偏向器を配置して、試料照射角度を調整できる構成とした。
【００２８】
以下、本発明の代表的な構成例を述べる。
【００２９】
（１）電子源から出射した照射電子線を照射レンズにより対物レンズの焦点面に結像させて、前記照射電子線の加速電圧と略等しい電位もしくは負の電位に印加された試料に照射する第１の電子光学系と、前記第１の電子光学系により前記試料に衝突せずに前記試料の表面付近で引き戻された電子によって形成される反射電子線を投影拡大して試料像を投影結像させる第２の電子光学系と、前記対物レンズにより前記試料の投影像が形成されるミラー像面近傍に配置され、前記照射電子線と前記反射電子線とを分離するためのビームセパレータとを有し、かつ、前記ビームセパレータで発生した収差を補正するための偏向器を前記第１の電子光学系に設けてなることを特徴とするミラー電子顕微鏡。
【００３０】
（２）電子源から出射した照射電子線を照射レンズにより対物レンズの焦点面に結像させて、前記照射電子線の加速電圧と略等しい電位もしくは負の電位に印加された試料に照射する第１の電子光学系と、前記第１の電子光学系により前記試料に衝突せずに前記試料の表面付近で引き戻された電子によって形成される反射電子線を投影拡大して試料像を投影結像させる第２の電子光学系と、前記対物レンズの焦点面近傍に配置され、前記照射電子線と前記反射電子線とを分離するためのビームセパレータとを有し、かつ、前記ビームセパレータで発生した収差を補正するための偏向器を前記第２の電子光学系に設けてなることを特徴とするミラー電子顕微鏡。
【００３１】
（３）電子源と、前記電子源から出射した照射電子線を照射レンズにより対物レンズの焦点面に結像させて、前記照射電子線の加速電圧と略等しい電位もしくは負の電位を印加された試料に２次元的な広がりを有する面状の前記照射電子線を照射する照射手段と、前記照射手段により前記試料に衝突せずに前記試料の表面付近で引き戻されたミラー電子によって形成される反射電子線を投影拡大して試料像を投影結像させる結像手段と、前記対物レンズにより前記試料の投影像が形成されるミラー像面近傍に配置され、前記照射電子線と前記反射電子線とを分離するためのビームセパレータとを有し、かつ、前記照射電子線の前記ビームセパレータと前記照射レンズとの間に、前記ビームセパレータで発生した収差を補正するための偏向器を設けたことを特徴とするミラー電子顕微鏡。
【００３２】
（４）電子源と、前記電子源から出射した照射電子線を照射レンズにより対物レンズの焦点面に結像させて、前記照射電子線の加速電圧と略等しい電位もしくは負の電位を印加された試料に２次元的な広がりを有する面状の照射電子線を照射する照射手段と、前記照射手段により前記試料に衝突せずに前記試料の表面付近で引き戻された電子によって形成される反射電子線を投影拡大して試料像を投影結像させる結像手段と、前記対物レンズの焦点面近傍に配置され、前記照射電子線と前記反射電子線とを分離するビームセパレータとを有し、かつ、前記反射電子線の前記ビームセパレータと、前記対物レンズにより前記試料の投影像が形成される対物レンズ像面との間に、前記ビームセパレータで発生した収差を補正するための偏向器を設けたことを特徴とするミラー電子顕微鏡。
【００３３】
（５）前記ミラー電子顕微鏡において、前記ビームセパレータは、前記照射電子線と前記反射電子線とを分離する機能に重畳して、偏向器の強度を調整することにより、前記照射電子線を前記試料に垂直に照射し得る機能を有することを特徴とするミラー電子顕微鏡。
【００３４】
（６）電子源から出射した照射電子線を照射レンズにより対物レンズの焦点面に結像させて、前記照射電子線の加速電圧と略等しい電位もしくは負の電位を印加された前記試料に２次元的な広がりを有する面状の照射電子線を照射する照射手段と、前記照射手段により前記試料に衝突せずに前記試料の表面付近で引き戻された電子によって形成される反射電子線を投影拡大して試料像を投影結像させる結像手段とを備えたミラー電子顕微鏡において、前記対物レンズにより前記試料の投影像が形成されるミラー像面近傍に偏向支点を有する偏向器を設置して、前記偏向器の強度を調整することにより、前記照射電子線を前記試料に垂直に照射し得るよう構成したことを特徴とするミラー電子顕微鏡。
【００３５】
（７）電子源と、前記電子源から出射した照射電子線を照射レンズにより対物レンズの焦点面に結像させて、前記照射電子線の加速電圧と略等しい電位もしくは負の電位を印加された前記試料に２次元的な広がりを有する面状の照射電子線を照射する照射手段と、前記照射手段により前記試料に衝突せずに前記試料の表面付近で引き戻された電子によって形成される反射電子線を投影拡大して試料像を投影結像させる結像手段と、前記対物レンズにより前記試料の投影像が形成されるミラー像面近傍に配置され、前記照射電子線と前記反射電子線を分離するためのビームセパレータと、前記照射電子線の前記ビームセパレータと前記照射レンズとの間に配置され、前記ビームセパレータで発生した収差を補正するための偏向器と、前記面状の照射電子線を、前記試料表面の複数の照射領域に順次照射し、前記試料に衝突せずに前記試料の表面付近で引き戻された電子を結像せしめて、前記複数の照射領域の全域もしくは一部の拡大電子像を順次形成する手段と、形成された前記複数の照射領域の拡大電子像を電気的な画像信号に変換する手段と、前記複数の照射領域についての画像信号同士を比較して、前記試料に形成されたパターン欠陥を検出する手段とを具備することを特徴とするパターン欠陥検査装置。
【００３６】
（８）電子源と、前記電子源から出射した照射電子線を照射レンズにより対物レンズの焦点面に結像させて、前記照射電子線の加速電圧と略等しい電位もしくは負の電位を印加された前記試料に２次元的な広がりを有する面状の照射電子線を照射する照射手段と、前記照射手段により前記試料に衝突せずに前記試料の表面付近で引き戻された電子によって形成される反射電子線を投影拡大して試料像を投影結像させる結像手段と、前記照射電子線の前記対物レンズの焦点面近傍に配置され、前記照射電子線と前記反射電子線を分離するためのビームセパレータと、前記反射電子線の前記ビームセパレータと前記照射レンズとの間に配置され、前記ビームセパレータで発生した収差を補正するための偏向器と、前記面状の照射電子線を、前記試料表面の複数の照射領域に順次照射し、前記試料に衝突せずに前記試料の表面付近で引き戻された電子を結像せしめて、前記複数の照射領域の全域もしくは一部の拡大電子像を順次形成する手段と、形成された前記複数の照射領域の拡大電子像を電気的な画像信号に変換する手段と、前記複数の照射領域についての画像信号同士を比較して、前記試料に形成されたパターン欠陥を検出する手段とを具備することを特徴とするパターン欠陥検査装置。
【００３７】
【発明の実施の形態】
以下に、本発明の実施例について、図面を参照して詳細に説明する。
【００３８】
（実施例１）
図１は、実施例１の動作を説明するための構成を示したものである。セパレータとしてＥ×Ｂ偏向器３を結像電子線３０２の結像面（ミラー像面）３０４近傍に配置させる。この配置では、照射電子線３０１に対してＥ×Ｂ偏向器で収差が発生する。この収差を補正するために照射系コンデンサレンズ２とＥ×Ｂ偏向器３の間にもうひとつ収差補正用のＥ×Ｂ偏向器４を配置させる構成とする。
【００３９】
コンデンサレンズ２と対物レンズの間にはビームセパレータとしてＥ×Ｂ偏向器３が配置されており、電子源１より放出された照射電子線３０１は、Ｅ×Ｂ偏向器３によりウェハ７に垂直な光軸に偏向される。Ｅ×Ｂ偏向器３により偏向された照射電子線３０１は、コンデンサレンズ２により対物レンズの焦点面３０３の近傍に集束され、試料上７をほぼ平行に照射される。
【００４０】
試料７には、電子線の加速電圧Ｖ_０とほぼ等しいか、わずかに高い負の電位Ｖ_Ｓが試料７に印加されている。試料７に対向する円孔電極４１には、電圧Ｖ_ｒが印加されている。円孔電極４１と試料７との間に生ずる電界によって面状の照射電子線３０１の大部分が試料７に衝突する直前で引き戻され、ミラー電子となり、試料７の形状や電位、磁界などを反映した方向や強度を持って上がってくる。
【００４１】
このミラー電子による結像電子線３０２は、対物レンズ６により投影されてミラー像を対物レンズ６によるミラー像面位置３０４に結ぶ。Ｅ×Ｂ偏向器３はこのミラー像面３０４近傍に配置され、このＥ×Ｂ偏向器３は、結像電子線にはＷｉｅｎ条件で作用する。したがって、結像電子線３０２に対してはＥ×Ｂ偏向器３は偏向作用を持たず、ミラー像面位置３０４近傍に配置されるので偏向収差も発生しない。この対物レンズ６によるミラー像は、中間レンズ１３および投影レンズ１４により投影され、シンチレータ１５上に拡大されたミラー電子像が形成される。このミラー電子はシンチレータ１５により光に変換され、光学レンズ１６あるいは光ファイバー束３３によりＣＣＤカメラ１７上に投影され、ＣＣＤカメラ１７により電気信号に変換され、モニタ２２によりミラー像が表示される。
【００４２】
この構成では、照射電子線３０１のクロスオーバ位置とＥ×Ｂ偏向器３の位置が離れているので、照射電子線３０１に対してＥ×Ｂ偏向器３の収差が発生する。この収差を補正するために、照射系のコンデンサレンズ２とＥ×Ｂ偏向器３の間に収差補正用のＥ×Ｂ偏向器４を配置させる。
【００４３】
Ｅ×Ｂ偏向器３を光軸垂直方向から見た断面は、図６に示す８極電磁極構造であり、各電磁極５１はパーマロイなどの磁性体で構成されている。各電磁極に電位を与えることによって電極として動作し、各電磁極にＮ回巻かれているコイル５３に電流を流すことによって磁極として動作する。
【００４４】
図６に示す電圧配分で各電磁極に電圧Ｖｘを印加すると電子は、ｘ方向に偏向作用を受ける。また、図７に示すような電流配分で電流Ｉｙを各コイルに流すと、図３の紙面の裏側から表へ運動する電子はｘ方向の正方向、紙面の表から裏側へ運動する電子はｘ方向の負方向へ偏向作用を受ける。各電極の電圧および電流配分は実際の電磁極形状に電位あるいは磁位を与えた電磁界計算により均一な電磁界が発生するように最適化されており、例えば、図中のα＝０．４１４に設定している。また、図８に示すような、電圧配分あるいは電流配分で電磁極５１を動作させると、この８個の電磁極は非点収差補正器としても動作する。
【００４５】
図９は、Ｅ×Ｂ偏向器３の光軸を含む断面図である。Ｅ×Ｂ偏向器をビームセパレータとして用いる場合、電子線偏向角は二つの光学系が互いに干渉しない配置関係を考慮すると、３０度以上は曲げる必要がある。照射電子線３０１を３０度偏向しても電磁極に当たらないようにするためには、開口部の直径を電磁極長さより大きくしなければならないが、開口を広げると偏向させる電圧を増加させなければならないので、電磁極５１形状は電子軌道にほぼ沿った末広がりの円錐形状とした。また、電磁極の上下にはシールド電磁極５４を設け、電磁界の滲みだしを抑えるとともに、電界と磁界が同一の空間で作用するようにして、空間内で常にＷｉｅｎ条件が成り立つ完全なＥ×Ｂ偏向器として動作するようにした。
【００４６】
この二つのＥ×Ｂ偏向器の強度比の配分について以下に説明する。Ｅ×Ｂ偏向器３は結像電子線３０２に対しては、Ｗｉｅｎ条件で動作し、照射電子線３０１に対しては偏向器として動作する。すなわち、照射系と結像系が２θ_１の角度で互いに傾斜しているとすると、Ｅ×Ｂ偏向器３は、照射電子線に対してＥ×Ｂ偏向器３を構成する電界偏向器でθ_１、磁界偏向器でθ_１の角度で同じ方向に作用するように動作し、結像電子線に対してＥ×Ｂ偏向器３を構成する電界偏向器でθ_１、磁界偏向器でθ_１の角度で反対方向に作用するように動作する。
【００４７】
Ｅ×Ｂ偏向器４は、照射電子線に対してＥ×Ｂ偏向器４を構成する電界偏向器でθ_２、磁界偏向器でθ_２の角度で反対方向に作用するＷｉｅｎ条件で動作するように動作する。照射電子線３０１のＥ×Ｂ偏向器３の焦点面上までの光路長をＬ_Ｌと置き、Ｅ×Ｂ偏向器４から焦点面上までの光路長をＬ_Ｕと置くと、（４）式でθ_Ｕをθ_２、θ_Ｌをθ_１で置き換えて（４）式が成り立つようにθ_２の強度を設定すれば、焦点面上で照射電子線３０１の色収差を概ね補正できる。
【００４８】
上記の動作を実行する制御部２８の機能について、以下に説明する。Ｅ×Ｂ偏向器３に供給する電圧Ｖｘと電子線の偏向角θ_１との関係は電子線がＥ×Ｂ偏向器３に入射するエネルギー、電子源に印加する加速電圧Ｖ_０に依存するので、あらかじめ電子線の軌道計算結果や実験から求めた所望の偏向角に対するＶ_０とＶｘの関係が制御部２８にインプットされている。Ｅ×Ｂ偏向器３に供給するコイル電流ＩｙとＶｘのＷｉｅｎ条件が成り立つ強度関係は、電子線の軌道計算結果から求めた値があらかじめ制御部２８にインプットされているか、表示装置２２の画像上で試料上の偏向量が完全にキャンセルするようにマニュアルあるいは自動的に設定される。加速電圧Ｖ_０が一定の条件では、Ｗｉｅｎ条件が成り立つＶｘとＩｙの強度比は一定であるので、ＶｘとＩｙの強度比を一定にしたまま変化させることによって、Ｗｉｅｎ条件を保持したまま入射電子線に対する偏向角を変化させる制御が可能である。このようにして、制御部２８からセパレータ用Ｅ×Ｂ偏向器電源３１へ供給するＶｘとＩｙを制御することにより、Ｅ×Ｂ偏向器３で偏向する偏向角θ_１を制御することができる。
【００４９】
また、Ｅ×Ｂ偏向器４に供給する電圧Ｖｘ’と電子線偏向角θ_２との関係も、あらかじめ電子線の軌道計算結果や実験から求めた所望の偏向角に対する加速電圧Ｖ_０とＶｘ’の関係が制御部２８にインプットされている。Ｅ×Ｂ偏向器４に供給するコイル電流Ｉｙ’とＶｘ’のＷｉｅｎ条件が成り立つ強度関係は、電子線の軌道計算結果から求めた値があらかじめ制御部２８にインプットされているか、表示装置２２の画像上で試料上の偏向量が完全にキャンセルするようにマニュアルあるいは自動的に設定される。加速電圧Ｖ_０が一定の条件では、Ｗｉｅｎ条件が成り立つＶｘ’とＩｙ’の強度比は一定であるので、Ｖｘ’とＩｙ’の強度比を一定にしてＷｉｅｎ条件を保持したまま、θ_２を変化させることが可能である。このようにして、制御部２８から収差補正用Ｅ×Ｂ偏向器電源３２へ供給するＶｘ’とＩｙ’を制御することにより、Ｅ×Ｂ偏向器４で偏向する偏向角θ_２を制御することができる。
【００５０】
制御部２８は、セパレータ用Ｅ×Ｂ偏向器電源３１を通じて、照射系と結像系の傾斜角２θ_１と加速電圧Ｖ_０の関係が成り立つように、Ｅ×Ｂ偏向器３の各電磁極に電圧Ｖｘ、αＶｘ、−αＶｘ、および−Ｖｘを供給し、コイル電流Ｉｙ、αＩｙ、−αＩｙ、および−Ｉｙを供給する。
【００５１】
また、制御部２８は（４）式の演算を行い、（４）式が成り立つような偏向角θ_２と加速電圧Ｖ０の関係が成り立つように、収差補正用Ｅ×Ｂ偏向器電源３２を通じてＥ×Ｂ偏向器４の各電磁極に電圧Ｖｘ’、αＶｘ’、−αＶｘ’、および−Ｖｘ’を供給し、コイル電流Ｉｙ’、αＩｙ’、−αＩｙ’、および−Ｉｙ’を供給する。このような動作を行うことによって、セパレータ用のＥ×Ｂ偏向器３で発生した収差を収差補正用Ｅ×Ｂ偏向器４で補正することができる。
【００５２】
なお、上記の動作は、Ｅ×Ｂ偏向器３およびＥ×Ｂ偏向器４のｘ方向の偏向方向について説明したが、ｙ方向への偏向成分の補正についても８極の電磁極にｙ方向の偏向成分の電圧あるいは電流を供給することによって同様の手順で行うことができる。例えば、Ｅ×Ｂ偏向器に周辺の磁界レンズからの磁束の漏れが生じている場合には、このようなｙ方向の電磁界を重畳させる回転補正が必要である。
【００５３】
また、図７においては、各コイルの巻き数は等しくＮ回としたが、磁極に流す電流Ｉとの関係がＮＩが一定になる範囲で電流ＩおよびＮを変化させても良い。
【００５４】
照射系のクロスオーバの収差が補正されているかどうかは、クロスオーバの大きさを計測する手段があれば達成される。例えば、このクロスオーバが試料上で再びスポットになるように対物レンズを動作させて、試料上を走査する手段を設け、試料に電子線を衝突させて発生した二次電子を検出してＳＥＭ像を取得できるような手段を設ければ、ＳＥＭ像の分解能を評価することによってクロスオーバの大きさを計測することができる。
【００５５】
または、このクロスオーバが対物レンズの焦点面に形成されて、試料を平行照射できるが、このクロスオーバの大きさが試料を照射する電子線の平行度に関係し、クロスオーバが大きくなるほど平行度が劣化するが、この照射電子線の平行度は結像電子線の電子線回折像を観察することにより確認することができる。すなわち、試料として鏡面状の試料を置けば、照射電子線が鏡面反射して試料の構造を含まないミラー電子として結像電子線となり、ミラー電子の電子線回折像が対物レンズ像面に形成されるが、この電子線回折像を中間レンズ及び投影レンズにより拡大して、シンチレータ１５上に投影して、ＣＣＤカメラ１７で観察する。この電子線回折像が一番小さくなるように、収差補正用Ｅ×Ｂ偏向器４に供給する電圧Ｖｘ’及び電流Ｉｙ’を、Ｗｉｅｎ条件を保持したまま、調整することによって、照射系クロスオーバを最小にすることができる。
【００５６】
（実施例２）
図１０は、第２の実施例の動作を説明するための構成を示したものである。本実施例では、照射系のクロスオーバ位置３０３近傍にセパレータ用のＥ×Ｂ偏向器３を配置して、照射系の収差を最小にする。結像系で発生した収差は、結像系像面位置３０４とＥ×Ｂ偏向器３の間にもうひとつＥ×Ｂ偏向器４を配置、動作させて補正する構成とした。
【００５７】
セパレータとして動作するＥ×Ｂ偏向器３は、照射電子線に対してＥ×Ｂ偏向器３を構成する電界偏向器でθ_１、磁界偏向器でθ_１の角度で同じ方向に作用するように動作し、結像電子線に対してＥ×Ｂ偏向器３を構成する電界偏向器でθ１、磁界偏向器でθ_１の角度で反対方向に作用するように動作する。Ｅ×Ｂ偏向器３の配置は照射電子線３０１のクロスオーバ位置に配置されるので、照射系に対する色収差は発生しない。結像電子線３０２に対しては、Ｅ×Ｂ偏向器３の収差が発生するので、Ｅ×Ｂ偏向器３と対物レンズによるミラー像面３０３の間に収差補正用のＥ×Ｂ偏向器４を配置する。結像電子線３０２に対しては、Ｅ×Ｂ偏向器３はＷｉｅｎ条件で動作するので、照射電子線３０１のＥ×Ｂ偏向器３の焦点面上までの光路長をＬ_Ｌと置き、Ｅ×Ｂ偏向器４から焦点面上までの光路長をＬ_Ｕと置くと、（３）式が成り立つように、Ｅ×Ｂ偏向器４を構成する電界偏向器で偏向させるθ_２、磁界偏向器で偏向させる角度θ_２を設定することによって、像面上の色収差を補正することが可能となる。
【００５８】
（実施例３）
図１１は、第３の実施例の動作を説明するための構成を示したものである。
【００５９】
本実施例では、セパレータとしてＥ×Ｂ偏向器３を結像電子線の結像面３０４近傍に配置させる。この配置では、照射レンズに対してＥ×Ｂ偏向器で収差が発生する。この収差を補正するために、照射系コンデンサレンズ２とＥ×Ｂ偏向器３の間にもうひとつ収差補正用のＥ×Ｂ偏向器４を配置させる構成とした。また、本実施例では、結像系は正立とし、照射系は傾斜する構成とした。
【００６０】
Ｅ×Ｂ偏向器３は照射電子線３０１に対しては、Ｗｉｅｎ条件で動作し、結像電子線３０２に対しては偏向器として動作する。すなわち、照射系と結像系が２θ_１の角度で互いに傾斜しているとすると、Ｅ×Ｂ偏向器３は、照射電子線に対してＥ×Ｂ偏向器３を構成する電界偏向器でθ_１、磁界偏向器でθ_１の角度で反対の方向に作用するＷｉｅｎ条件で動作し、結像電子線に対してＥ×Ｂ偏向器３を構成する電界偏向器でθ_１、磁界偏向器でθ_１の角度で同じ方向に作用する偏向器として動作する。Ｅ×Ｂ偏向器４は、照射電子線に対してＥ×Ｂ偏向器４を構成する電界偏向器でθ_２、磁界偏向器でθ_２の角度で反対方向に作用するＷｉｅｎ条件で動作するように動作する。照射電子線３０１のＥ×Ｂ偏向器３の焦点面上までの光路長をＬ_Ｌと置き、Ｅ×Ｂ偏向器４から焦点面上までの光路長をＬ_Ｕと置くと、（３）式が成り立つようにθ_２の強度を設定すれば、焦点面上で照射電子線３０１の色収差を概ね補正できる。制御部２８は、（３）式が成り立つように演算を行い、セパレータＥ×Ｂ偏向器電源３１および収差補正用Ｅ×Ｂ偏向器電源３２に供給する電圧および電流を制御する。
【００６１】
（実施例４）
図１２は、実施例４の動作を説明するための構成を示したものである。
本実施例では照射系のクロスオーバ位置にＥ×Ｂ偏向器を配置して、照射系の収差を最小にする。結像系で発生した収差は、結像系像面位置とＥ×Ｂ偏向器の間にもうひとつＥ×Ｂ偏向器を配置、動作させて補正する構成とした。また、本実施例では、実施例３と同様に、結像系は正立とし、照射系は傾斜する構成とした。
【００６２】
Ｅ×Ｂ偏向器３は照射電子線３０１に対しては、Ｗｉｅｎ条件で動作し、結像電子線３０２に対しては偏向器として動作する。すなわち、照射系と結像系が２θ_１の角度で互いに傾斜しているとすると、Ｅ×Ｂ偏向器３は、照射電子線に対してＥ×Ｂ偏向器３を構成する電界偏向器でθ_１、磁界偏向器でθ_１の角度で反対の方向に作用するＷｉｅｎ条件で動作し、結像電子線に対してＥ×Ｂ偏向器３を構成する電界偏向器でθ_１、磁界偏向器でθ_１の角度で同じ方向に作用する偏向器として動作する。Ｅ×Ｂ偏向器４は、照射電子線に対してＥ×Ｂ偏向器４を構成する電界偏向器でθ_２、磁界偏向器でθ_２の角度で反対方向に作用するＷｉｅｎ条件で動作するように動作する。結像電子線３０２のＥ×Ｂ偏向器３の焦点面上までの光路長をＬ_Ｌと置き、Ｅ×Ｂ偏向器４から焦点面上までの光路長をＬ_Ｕと置くと、（４）式が成り立つようにθ_２の強度を設定すれば、ミラー像面上で結像電子線３０２の色収差を概ね補正できる。制御部２８は、（４）式が成り立つように演算を行い、セパレータＥ×Ｂ偏向器電源３１および収差補正用Ｅ×Ｂ偏向器電源３２に供給する電圧および電流を制御する。
【００６３】
（実施例５）
図１３は、第５の実施例を示し、ウェハが傾斜した場合にも、試料に垂直に電子線が入射するための偏向器を設けたものである。ｚ方向を光軸に取り、通常はｚ＝０のｘｙ平面内にある試料表面が、ｘ方向にθだけ傾斜しているとすると、試料７と円孔電極４１間の距離をＬ_０と置けば、電界強度のｚ方向成分Ｅｚおよびｘ方向成分Ｅｘは、それぞれ、Ｅｚ≒Ｅ、Ｅｘ≒（１−ｚ／Ｌ_０）Ｅで与えられる。
【００６４】
ｘ方向およびｚ方向について運動方程式を解けば、電子線が試料に一番近づく条件で試料にほぼ垂直に入射する条件、すなわちｚ方向の速度が０で、ｘ方向の速度成分も０になるような条件は、円孔電極４１を通過する角度βが、
【００６５】
【数５】

をおおむね満たすことであることがわかる。
【００６６】
さらに、円孔電極４１の焦点距離ｆ＝４Ｌ_０と置けば、円孔電極４１に入射する電子線の角度β_２を２ｓｉｎθ（≒２θ）だけ傾ければ良いことがわかる。
【００６７】
そこで、たとえば、円孔電極４１の上方にアライナ４２を配置して、試料がｘ方向にθ傾いた場合には、２θだけ傾斜するように作用させれば、常に試料に垂直に電子線を照射することができる。ここでアライナ４２の配置が対物レンズによって投影されるミラー像面３０２近傍にあれば、物面上の１点からあらゆる方向に出た電子線は像面上の１点に集束するので、アライナ４２により試料上の照射角度が変化しても、常に同一の視野を照射することができる。このアライナ４２はミラー像面３０２近傍にあるひとつのアライナ４２であってもよいし、上下２つのアライナにより構成され、アライナの仮想偏向支点がミラー像面３０２近傍にあるように上下のアライナの偏向比率を調整する構成でもよい。
【００６８】
また、対物レンズによって投影されるミラー像面３０２近傍に照射電子線３０１と結像電子線３０２を分離するセパレータとしてＥ×Ｂ偏向器３が配置されている場合には、電界と磁界が反対方向に同じ力が作用するＷｉｅｎ条件に加えてアライナとして作用する成分を重畳させることにより、上記の機能を実現することができる。
【００６９】
ただし、このアライナ４２は、照射ビームと結像ビームとで同じ方向に作用するように静電型のアライナを用いるほうが望ましい。すなわち、図１４は、静電型のアライナを示し、図１５は、磁界型のアライナを用いた場合の照射電子線および結像電子線の軌道を示したものであるが、磁界型アライナでは、アライナより上方の入射電子線と反射電子線の軌道が一致しなくなるので、アライナを動作させることにより、アライナより上方の電子光学系の再調整が必要になってしまうからである。図１６を用いて、調整手順を説明する。
【００７０】
セパレータとしてＥ×Ｂ偏向器３を結像電子線３０２の結像面３０４近傍に配置させる。この配置では、照射電子線３０１に対してＥ×Ｂ偏向器で収差が発生する。この収差を補正するために照射系コンデンサレンズ２とＥ×Ｂ偏向器３の間にもうひとつ収差補正用のＥ×Ｂ偏向器４を配置させる構成とする。Ｅ×Ｂ偏向器３の各電磁極にはセパレータとして、図６および図７に示されるようなＷｉｅｎ条件を満足する供給電圧Ｖｘとコイル電流Ｉｙに加えて、照射電子線３０１を試料に対し垂直に照射させる偏向電圧が供給される。静電偏向器には、試料傾斜角調整用電源（図示してない）から垂直照射調整用の電圧が供給される。
【００７１】
試料７の傾斜分布は、あらかじめ観察前に試料内の数点以上の位置について、高さ測定器２６や電子線による合焦点レンズ強度などの高さ計測手段を用いて、面内の傾斜分布を算出する。観察時には、この検査位置座標に対応した試料傾斜データに基づいて、制御部２８で試料傾斜角θが算出され、対物レンズ出射時の傾斜角２θを計算する。本実施例ではＥ×Ｂ偏向器３は対物レンズ６の上方に配置されているので、対物レンズ倍率より対物レンズ出射角θに対応する偏向角θ’を算出し、偏向角θ’に相当する偏向電圧を、Ｗｉｅｎ条件を満足する供給電圧Ｖｘに重畳して、各電磁極に供給する。以上のように制御することにより、試料面内で常に試料に垂直に電子線を照射することが可能となる。
【００７２】
（実施例６）
図１７に示す本実施例は、ミラー電子顕微鏡を高速ウェハ検査に適用した構成である。
【００７３】
電子光学系１０１において、電子源１より放出された電子線は、コンデンサレンズ２により収束され試料上をほぼ平行に照射される。電子源１には、Ｚｒ／Ｏ／Ｗ型のショットキー電子源を用いた。大電流ビーム（例えば、１．５μＡ）で、かつエネルギー幅が１．５ｅＶの均一な面状電子線を安定に形成できる。
【００７４】
セパレータとしてＥ×Ｂ偏向器３を結像電子線３０２の結像面３０４近傍に配置させる。この配置では、照射電子線３０１に対してＥ×Ｂ偏向器で収差が発生する。この収差を補正するために照射系コンデンサレンズ２とＥ×Ｂ偏向器３の間にもうひとつ収差補正用のＥ×Ｂ偏向器４を配置させる構成とする。
【００７５】
電子線は、Ｅ×Ｂ偏向器３によりウェハ７に垂直な光軸に偏向される。Ｅ×Ｂ偏向器３は上方からの電子線に対してのみ偏向作用を持つ。Ｅ×Ｂ偏向器３より偏向された電子線は、対物レンズ６により試料（ウェハ）表面に垂直な方向に面状の電子線が形成される。Ｅ×Ｂ偏向器４よりセパレータＥ×Ｂ偏向器３の偏向収差が補正されるので、対物レンズ６の焦点面上には微細なクロスオーバが形成されるので、平行性の良い照射電子線３０１を試料に照射できる。
【００７６】
試料室１０２内の試料移動ステージ８に搭載された試料（ウェハ）７には、電子線の加速電圧とほぼ等しいか、わずかに高い負の電位が試料印加電源９によって印加されており、ウェハ７の表面には形成された半導体パターン形状や帯電の状態を反映した電界が形成されている。この電界によって面状電子線の大部分がウェハ７に衝突する直前で引き戻され、ウェハ７のパターン情報を反映した方向や強度を持って上がってくる。
【００７７】
引き戻された電子線は、対物レンズ６により収束作用を受け、ビームセパレータとしての偏向器３は下方から進行した電子線に対しては偏向作用を持たないので、そのまま垂直に上昇し、対物レンズ６、中間レンズ１３、投影レンズ１４により投影拡大されて、シンチレータ１５、光学レンズ１６、ＣＣＤ１７よりなる画像検出部上にウェハ７表面の画像を結像させる。また、対物レンズ６、あるいは中間レンズ１３により形成される電子線回折像面上にコントラストアパーチャ１２を配置して、像のコントラストが調整される。
【００７８】
これにより、ウェハ７表面の局部的な帯電電位の変化や凹凸等の構造の違いが画像として形成される。収差を補正することにより、平行性の良い照射電子線３０１を照射でき、高分解能なミラー像を形成することができるので、１００ｎｍ以下の帯電電位の変化や凹凸等の構造の違いを検出することが可能となる。この画像は電気信号に変換され画像処理部１０４に送られる。
【００７９】
画像処理部１０４は、画像信号記憶部１８及び１９、演算部２０、欠陥判定部２１より構成されている。画像記憶部１８と１９は同一パターンの隣接部の画像を記憶するようになっており、両者の画像を演算部２０で演算して両画像の異なる場所を検出する。この結果を欠陥判定部２１により欠陥として判定しその座標を記憶する。なお、取り込まれた画像信号はモニタ２２により画像表示される。
【００８０】
半導体ウェハ７表面上に形成された同一設計パターンを有する隣接チップＡ、Ｂ間でのパターンの比較検査をする場合には、先ず、チップＡ内の被検査領域についての電子線画像信号を取り込んで、記憶部１８内に記憶させる。次に、隣接するチップＢ内の上記と対応する被検査領域についての画像信号を取り込んで、記憶部１９内に記憶させながら、それと同時に、記憶部１８内の記憶画像信号と比較する。さらに、次のチップＣ内の対応する被検査領域についての画像信号を取得し、それを記憶部１８に上書き記憶させながら、それと同時に、記憶部１９内のチップＢ内の被検査領域についての記憶画像信号と比較する。このような動作を繰り返して、全ての被検査チップ内の互いに対応する被検査領域についての画像信号を順次記憶させながら、比較して行く。
【００８１】
上記の方法以外に、予め、標準となる良品（欠陥のない）試料についての所望の検査領域の電子線画像信号を記憶部１８内に記憶させておく方法を採ることも可能である。その場合には、予め制御計算機２９に上記良品試料についての検査領域および検査条件を入力しておき、これらの入力データに基づき上記良品試料についての検査を実行し、所望の検査領域についての取得画像信号を記憶部１８内に記憶する。次に、検査対象となるウェハ７をステージ８上にロードして、先と同様の手順で検査を実行する。
【００８２】
そして、上記と対応する検査領域についての取得画像信号を記憶部１９内に取り込むと同時に、この検査対象試料についての画像信号と先に記憶部１８内に記憶された上記良品試料についての画像信号とを比較する。これにより上記検査対象試料の上記所望の検査領域についてのパターン欠陥の有無を検出する。なお、上記標準（良品）試料としては、上記検査対象試料とは別の予めパターン欠陥が無いことが判っているウェハを用いても良いし、上記検査対象試料表面の予めパターン欠陥が無いことが判っている領域（チップ）を用いても良い。例えば、半導体試料（ウェハ）表面にパターンを形成する際、ウェハ全面にわたり下層パターンと上層パターン間での合わせずれ不良が発生することがある。このような場合には、比較対象が同一ウェハ内あるいは同一チップ内のパターン同士であると、上記のようなウェハ全面にわたり発生した不良（欠陥）は見落とされてしまう。
【００８３】
しかし、本実施例によれば、予め良品（無欠陥）であることが判っている領域の画像信号を記憶しておき、この記憶画像信号と検査対象領域の画像信号とを比較するので、上記したようなウェハ全面にわたり発生した不良をも精度良く検出することができる。
【００８４】
記憶部１８、１９内に記憶された両画像信号は、それぞれ演算部２０内に取り込まれ、そこで、既に求めてある欠陥判定条件に基づき、各種統計量（具体的には、画像濃度の平均値、分散等の統計量）、周辺画素間での差分値等が算出される。これらの処理を施された両画像信号は、欠陥判定部２１内に転送されて、そこで比較されて両画像信号間での差信号が抽出される。これらの差信号と、既に求めて記憶してある欠陥判定条件とを比較して欠陥判定がなされ、欠陥と判定されたパターン領域の画像信号とそれ以外の領域の画像信号とが分別される。
【００８５】
装置各部の動作命令および動作条件は、制御計算機２９から入出力される。制御計算機２９には、予め電子線発生時の加速電圧、電子線偏向幅・偏向速度、試料ステージ移動速度、画像検出素子からの画像信号取り込みタイミング等々の諸条件が入力されている。ビーム制御系２８は、制御計算機２９からの指令を受けて、ステージ位置測定器２７、試料高さ測定器２６からの信号を基にして補正信号を生成し、電子線が常に正しい位置に照射されるように対物レンズ電源２５や走査信号発生器２４に補正信号を送る。ステージ制御系３０は、制御計算機２９から指令を受けて試料移動ステージ８を制御する。
【００８６】
検査時には、試料（半導体ウェハ）７を搭載したステージ８はｘ方向に一定速度で連続移動する。ステージ８は連続移動しているので、電子線は照射系偏向器５によってステージ８の移動に追従して偏向走査させる。
【００８７】
電子線の照射領域あるいは照射位置は、ステージ８に設けられたステージ位置測定器２７、試料高さ測定器２６等により常時モニタされる。これらのモニタ情報が制御計算機２９に転送されて詳細に位置ずれ量が把握され、かつこの位置ずれ量はビーム制御系２８によって正確に補正される。これにより、パターンの比較検査に必要な正確な位置合わせが高速・高精度で行われ得る。
【００８８】
また、半導体ウェハ７の表面高さを、電子線以外の手段でリアルタイムに測定し、電子線を照射するための対物レンズ６や結像レンズ１１の焦点距離をダイナミックに補正する。電子線以外の手段としては、例えば、レーザ干渉方式や反射光の位置変化を計測する方式等による光学式の高さ測定器２６である。これにより、常に被検査領域の表面に焦点のあった電子線像を形成することができる。また、予め検査前にウェハ７の反りを測定しておき、その測定データを基に上記の焦点距離補正をするようにして、実検査時にはウェハ７の表面高さ測定を行う必要がないようにしてもよい。
【００８９】
以上で述べた検査方法および検査装置により、収差が補正された平行性の良い照射電子線３０１を照射でき、高分解能なミラー像を形成することができるので、ウェハ７の表面の電位および形状の情報を反映した画像を形成し、対応するパターン領域についての画像信号を比較検査することによって、１００ｎｍ以下のパターン欠陥の有無を検出することが可能となった。これにより、従来の電子線による検査装置と比べ非常に高速かつ高分解能な検査が可能になった。
【００９０】
【発明の効果】
本発明によれば、照射電子線および反射電子線に対して発生する収差を最小にすることにより、高分解能なミラー電子顕微鏡の構成を実現させるとともに、このミラー電子顕微鏡を用いて、ウェハ上に形成されたパターンにおける欠陥部分を、高分解能でかつ高速で検出する欠陥検査装置を実現する。
【図面の簡単な説明】
【図１】本発明の第１の実施例になるミラー電子顕微鏡の構成を示す図。
【図２】Ｅ×Ｂ偏向器の動作を説明する図。
【図３】Ｅ×Ｂ偏向器の収差補正を説明する図。
【図４】Ｅ×Ｂ偏向器の収差補正の構成（１）を説明する図。
【図５】Ｅ×Ｂ偏向器の収差補正の構成（２）を説明する図。
【図６】８極型Ｅ×Ｂ偏向器の電圧配分の例（１）を説明する図。
【図７】８極型Ｅ×Ｂ偏向器の電流配分の例（２）を説明する図。
【図８】８極型Ｅ×Ｂ偏向器の非点収差補正を説明する図。
【図９】８極型Ｅ×Ｂ偏向器の断面図。
【図１０】本発明の第２の実施例の構成を説明する図。
【図１１】本発明の第３の実施例の構成を説明する図。
【図１２】本発明の第４の実施例の構成を説明する図。
【図１３】本発明の第５の実施例を説明する図。
【図１４】本発明の第５の実施例による静電偏向器の動作を説明する図。
【図１５】本発明の第５の実施例による磁界偏向器の動作を説明する図。
【図１６】本発明の第５の実施例の構成を説明する図。
【図１７】本発明の第６の実施例の構成を説明する図。
【符号の説明】
１…電子源、２…コンデンサレンズ、３…Ｅ×Ｂ偏向器、４…Ｅ×Ｂ偏向器、５…照射系偏向器、６…対物レンズ、７…試料（ウェハ）、８…ウェハ移動ステージ、１０…結像系偏向器、１２…コントラストアパーチャ、１３…中間レンズ、１４…投影レンズ、１５…シンチレータ、１６…光学レンズ、１７…ＣＣＤ、１８…画像記憶部、１９…画像記憶部、２０…演算部、２１…欠陥判定部、２２…モニタ、２３…加速電源、２４…走査信号発生器、２５…対物レンズ電源、２６…試料高さ測定器、２７…ステージ位置測定器、２８…ビーム制御系、２９…制御計算機、３０…ステージ制御系、３１…セパレータ用Ｅ×Ｂ偏向器電源、３２…収差補正用Ｅ×Ｂ偏向器電源、３３…光ファイバー束、４１…円孔電極、４２…アアライナ、５１…電磁極、５２…ボビン、５３…コイル、５４…シールド、１０１…電子光学系、１０２…試料室、１０４…画像処理部、２０１…電子銃、２０２…コンデンサレンズ、２０３…アライナ、３０１…照射電子線、３０２…結像電子線、３０３…照射系クロスオーバ、３０４…ミラー像面。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a pattern defect inspection apparatus for inspecting a pattern defect formed on a semiconductor wafer using a mirror electron microscope or a mirror electron microscope for observing a surface state of a sample (such as a semiconductor sample).
[0002]
[Prior art]
In the process of manufacturing a semiconductor device, as a method of detecting a defect of a circuit pattern formed on a wafer by a comparative inspection of an image, a sample is irradiated with an electron beam and a minute etching residue or a minute residue having a resolution lower than that of an optical microscope is obtained. It is utilized for detecting pattern defects and detecting electrical defects such as non-opening failure of minute conduction holes.
[0003]
Here, in a method using a scanning electron microscope that scans a point-like electron beam on a sample, there is a limit in obtaining a practical inspection speed, so that a semiconductor wafer is irradiated with a rectangular electron beam. There has been proposed an apparatus for performing high-speed inspection by a so-called projection method, such as forming reflected electrons, secondary electrons, or electrons reflected without being irradiated onto a wafer due to formation of a reverse electric field by a lens (for example, Patent Document 1). 1).
[0004]
In addition, in this projection system, a report is also made on a negative sample applied voltage for accelerating secondary electrons emitted from the sample and an imaging resolution of the secondary electrons (for example, see Non-Patent Document 1).
[0005]
[Patent Document 1]
JP-A-7-249393
[Non-patent document 1]
LSI Testing Symposium / Proceedings of 1999, P.S. 142, FIG.
[0006]
[Problems to be solved by the invention]
However, the projection method of reflected electrons and secondary electrons has the following problems.
[0007]
In the projection method, an electron beam having a larger current can be irradiated at a time than in the SEM method, and images can be acquired at a time. Therefore, it can be expected that an image can be formed at an ultra-high speed as compared with the SEM method. However, the emission angle distribution of the secondary electrons is spread over a wide angle, and the energy is also spread at about 1 to 10 eV. It can be easily understood from the above-mentioned conventional technique (Non-Patent Document 1) that sufficient resolution cannot be obtained unless most of the secondary electrons are cut when forming an enlarged image of a sample by forming such electrons. You can judge. According to this, when the sample applied voltage is −5 kV, the resolution is approximately 0.2 μm.
[0008]
Then, not all the emitted secondary electrons can be used for image formation. For example, in the calculation of the cited document, a beam having an opening angle of 1.1 mrad or less is used on the image plane after passing through the objective lens. . The secondary electrons within the range of the opening angle are only about 10% of the whole. Furthermore, the energy width of the secondary electrons used for imaging is calculated at 1 eV, but the energy width of the emitted secondary electrons is actually emitted with a width of several eV or more. Side tails exist up to about 50 eV. When only electrons having an energy width of at most 1 eV are extracted from the secondary electrons having such a wide energy distribution, the number is further reduced to a fraction.
[0009]
As described above, it is difficult to secure the S / N ratio of an image even when attempting to form an image by irradiating a large current using an electron beam as an area beam because the ratio of electrons that can actually contribute to image formation is low. Therefore, it is impossible to reduce the inspection time as much as expected. Similarly, in the case of using the backscattered electrons, the emission amount is smaller by two orders of magnitude than the irradiation beam current, and it is difficult to achieve both high resolution and high speed as in the case of the secondary electrons.
[0010]
By using mirror electrons (retracted electrons) that reflect without hitting the sample immediately before the sample instead of secondary electrons and reflected electrons, defect detection is performed by detecting disturbance caused by a defect and detecting potential. be able to. As shown in the figure, when the pattern is negatively charged, the equipotential surface formed immediately above the sample acts on the incident electrons like a convex mirror, returning the orbit of the mirror electrons. On the other hand, when the pattern is more positively charged, the equipotential surface formed directly on the sample acts as a concave mirror for incident electrons. As described above, the trajectory of the mirror electrons is changed by the lens formed immediately above the sample, but if the focus condition of the imaging lens is adjusted, most of these mirror electrons can be used for image formation. That is, if mirror electrons are used, an image having a high S / N ratio can be obtained, and a reduction in inspection time can be expected.
[0011]
The device configuration for imaging mirror electrons includes an irradiation electron lens that irradiates the sample with an incident electron beam, an imaging lens that images electrons reflected from the sample, and a separator that separates the irradiation electron beam from the imaging electron beam. It is composed of A similar device configuration is described in the above-described conventional example in which secondary electrons and reflected electrons are imaged. That is, an E × B deflector that operates with an electric field and a magnetic field orthogonal to each other is used as the irradiation lens, the imaging lens, and the separator. Electrons that have passed through the E × B deflector generate aberrations such as chromatic aberration. Here, in an apparatus for imaging secondary electrons, the distribution of secondary electrons emitted from the sample does not depend much on the irradiation angle of the irradiation electron beam, and therefore the incident angles of the irradiation electron beams may not be uniform. Therefore, regarding the arrangement of the E × B deflector, if it is arranged at a position where the aberration with respect to the imaging electron beam is minimized, for example, it is arranged near the image plane position of the imaging electron, the aberration with respect to the imaging electron beam will be reduced. Minimized and a high-resolution image is obtained. With this arrangement, even if a large aberration occurs in the irradiation electron beam, it does not affect the secondary electron beam. Therefore, the conventional configuration does not consider minimizing the aberration of the irradiation electron beam.
[0012]
However, in a device configuration for imaging mirror electrons, it is necessary to minimize the aberration that occurs when both the irradiation electron beam and the imaging electron beam pass through a separator such as an E × B deflector.
[0013]
In order to obtain a high-resolution mirror electron image, it is necessary to irradiate the sample with an electron beam that is substantially parallel to the sample. For this purpose, a sample can be irradiated with a substantially parallel electron beam by forming an image of the irradiated electron beam near the focal plane of the objective lens. Therefore, if an E × B deflector for separating the irradiation electron beam and the imaging electron beam is arranged near the focal plane of the objective lens, the aberration with respect to the irradiation electron beam is minimized. However, in this arrangement, the aberration generated in the E × B deflector becomes large with respect to the imaging electron beam, so that there is a problem that high-resolution imaging cannot be performed even if the irradiation electron beam is optimized.
[0014]
The present invention has been made by paying attention to the above-described points, and realizes the configuration of a high-resolution mirror electron microscope by minimizing aberrations generated for the irradiation electron beam and the reflected electron beam, It is an object of the present invention to provide a defect inspection apparatus that detects a defective portion in a pattern formed on a wafer at high resolution and at high speed by using the mirror electron microscope.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, an E × B deflector is employed as a beam separator. In the E × B deflector, an electron beam incident from one side goes straight and an electron beam incident from the other side is deflected. It has the following characteristics.
[0016]
Hereinafter, the basic configuration of the present invention will be described.
[0017]
The E × B deflector is a deflector that operates by operating the electric field and the magnetic field orthogonally and superimposedly. Acceleration voltage V ₀ Deflection angle θ at which the electron beam is deflected by a parallel plate electrode type electrostatic deflector having a length of 2 l and an interval d shown in FIG. _E And the deflection angle θ deflected by the uniform magnetic deflector having a length of 2 l _M Are given by the following equations, respectively.
[0018]
(Equation 1)

In the above equation, e / m is a specific charge.
A condition in which the deflection by the electric field E and the deflection by the magnetic field B cancel each other,
[0019]
(Equation 2)

Is referred to as the Wien condition, and the electron beam incident from above on the E × B deflector set in the Wien condition in FIG. _E + Θ _M = 2θ _E To be deflected. Under Wien conditions, e (V ₀ The deflection amount Δy of the electron beam having the energy of + ΔV) becomes the deflection chromatic aberration of the E × B deflector and is approximated by the following equation.
[0020]
[Equation 3]

In addition, the deflection amount Δy ′ when incident from the opposite direction under the Wien condition is obtained by adding the values in parentheses in the above equation,
[0021]
(Equation 4)

It can be seen that the electron beam incident from the opposite direction under the Wien condition has about three times the chromatic aberration as the electron beam traveling straight.
[0022]
Here, since the electron beam emitted from one point on the object surface of the electron lens in all directions converges to one point on the image surface, when the E × B deflector is on the object surface of the electron lens, Even if the deviation of the deflection angle occurs due to the chromatic aberration of the E × B deflector, it converges to one point on the image plane, and it is considered that no deflection aberration occurs.
[0023]
In a conventional apparatus called LEEM (Low Energy Electron Microscopy) for two-dimensional imaging of secondary electrons, an E × B deflector is used as a beam separator, and the E × B deflector is connected to an objective lens image plane of an imaging system, that is, an intermediate lens. In this case, the arrangement near the object surface minimizes the influence of aberration on the intermediate lens and the subsequent lenses. However, since the image plane of the imaging objective lens does not coincide with the crossover position of the irradiation system, aberrations with respect to the irradiation electron beam are increased in this configuration. In the secondary electron imaging method, the secondary electron emission angle distribution does not depend much on the incident conditions of the irradiation electron beam, so it is estimated that the secondary electron image was not affected even if the irradiation system aberration was large. Is done. With this configuration, the mirror electron microscope cannot achieve the desired performance because the sample cannot be irradiated in parallel.
[0024]
Therefore, the E × B deflector has the following configuration. The E × B deflector is located at the crossover position of the irradiation system or in the vicinity of the image plane (mirror image plane) position of the imaging system, and another E × B deflector is provided in the other optical system where the aberration has occurred. Are arranged and operated in the opposite direction to correct the chromatic aberration generated in the separator. As shown in FIG. 3, the E × B deflector L and the E × B deflector U are respectively L from the image plane. _L And L _U The two E × B deflectors arranged apart are operated so that the chromatic aberrations on the image plane are equal in the opposite directions. Where θ _L , Θ _U Is the chromatic aberration Δy of the deflector L, respectively. _L = Θ _L L _L (ΔV / 2V ₀ ), Chromatic aberration Δy of deflector U _U = Θ _U L _U (ΔV / 2V ₀ ), Δy _L = Δy _U That is,
L _L θ _L = L _U θ _U . . . . . . . . . . . (3)
It is considered that the chromatic aberration on the image plane can be corrected by adjusting the intensity of the E × B deflector such that
[0025]
The specific configuration was as follows. That is, as shown in FIG. 4, an E × B deflector that operates as a separator is arranged near the crossover position of the irradiation system, that is, near the focal plane of the objective lens, to minimize the aberration of the irradiation system. The aberration generated in the imaging system is corrected by disposing and operating another E × B deflector for aberration correction between the image plane position of the imaging system and the E × B deflector.
[0026]
Alternatively, as shown in FIG. 5, the E × B deflector for the separator is operated so as to satisfy the Wien condition with respect to the imaging electron beam (reflected electron beam), and is arranged at the image plane position of the imaging system. . That is, the imaging electron beam generated by the mirror electrons travels straight through the E × B deflector so that the aberration is also minimized. The E × B deflector operates as a deflector for the irradiation electron beam (incident electron beam), and the crossover of the irradiation system and the E × B deflector are separated from each other. To correct the chromatic aberration, another E × B deflector for correcting the aberration is disposed between the irradiation lens and the E × B deflector to correct the chromatic aberration. In this case, since the E × B deflector for the separator that operates under the Wien condition operates as a deflector that deflects the electron beam with respect to the irradiation system, the chromatic aberration is about three times larger than that of the electron beam that goes straight. Where θ _L , Θ _U Is the chromatic aberration Δy of the deflector L, respectively. _L = 3θ _L L _L (ΔV / 2V ₀ ), Chromatic aberration Δy of deflector U _U = Θ _U L _U (ΔV / 2V ₀ ), Δy _L = Δy _U That is,
3L _L θ _L = L _U θ _U . . . . . . . . . . (4)
By adjusting the intensity of the E × B deflector so as to obtain the following formula, the chromatic aberration on the crossover can be corrected.
[0027]
A deflector is arranged near the image plane of the imaging lens so that the sample irradiation angle can be adjusted so that the sample can always be irradiated with the irradiation electron beam vertically even when the sample is tilted.
[0028]
Hereinafter, a typical configuration example of the present invention will be described.
[0029]
(1) The irradiation electron beam emitted from the electron source is formed into an image on the focal plane of the objective lens by the irradiation lens, and is irradiated on the sample applied to a potential substantially equal to the acceleration voltage of the irradiation electron beam or a negative potential. And projecting and enlarging a reflected electron beam formed by electrons drawn back near the surface of the sample without colliding with the sample by the first electron optical system and the first electron optical system to project and form a sample image. A second electron optical system to be formed, and a beam separator disposed near a mirror image plane on which a projection image of the sample is formed by the objective lens, for separating the irradiation electron beam and the reflected electron beam. A mirror electron microscope, wherein a deflector for correcting aberration generated in the beam separator is provided in the first electron optical system.
[0030]
(2) forming an image of the irradiation electron beam emitted from the electron source on the focal plane of the objective lens by the irradiation lens, and irradiating the sample applied with a potential substantially equal to the acceleration voltage of the irradiation electron beam or a negative potential. And projecting and enlarging a reflected electron beam formed by electrons drawn back near the surface of the sample without colliding with the sample by the first electron optical system and the first electron optical system to project and form a sample image. A second electron optical system to be provided, and a beam separator arranged near the focal plane of the objective lens for separating the irradiation electron beam and the reflected electron beam, and generated by the beam separator. A mirror electron microscope, wherein a deflector for correcting aberration is provided in the second electron optical system.
[0031]
(3) An electron source and an irradiation electron beam emitted from the electron source were imaged on a focal plane of an objective lens by an irradiation lens, and a potential substantially equal to the acceleration voltage of the irradiation electron beam or a negative potential was applied. Irradiation means for irradiating the sample with the planar irradiation electron beam having a two-dimensional spread, and reflection formed by mirror electrons pulled back near the surface of the sample without colliding with the sample by the irradiation means Image forming means for projecting and enlarging an electron beam to project and form a sample image, and arranged near a mirror image plane on which a projected image of the sample is formed by the objective lens, and the irradiation electron beam and the reflected electron beam A beam separator for separating the irradiation electron beam, and between the beam separator and the irradiation lens of the irradiation electron beam, a deflector for correcting aberration generated in the beam separator. Mirror electron microscope, characterized in that digit.
[0032]
(4) An electron source and an irradiation electron beam emitted from the electron source are imaged on a focal plane of an objective lens by an irradiation lens, and a potential substantially equal to the acceleration voltage of the irradiation electron beam or a negative potential is applied. Irradiating means for irradiating a sample with a planar irradiation electron beam having a two-dimensional spread, and a reflected electron beam formed by electrons returned near the surface of the sample by the irradiation means without colliding with the sample Imaging means for projecting and projecting a sample image by projecting and enlarging, and a beam separator arranged near the focal plane of the objective lens and separating the irradiation electron beam and the reflected electron beam, and A deflector for correcting aberration generated in the beam separator is provided between the beam separator of the reflected electron beam and an objective lens image plane on which a projection image of the sample is formed by the objective lens. Mirror electron microscope, characterized in that the.
[0033]
(5) In the mirror electron microscope, the beam separator overlaps a function of separating the irradiation electron beam and the reflected electron beam, and adjusts the intensity of a deflector, thereby changing the irradiation electron beam to the sample. A mirror electron microscope having a function of irradiating light vertically.
[0034]
(6) The irradiation electron beam emitted from the electron source is imaged on the focal plane of the objective lens by the irradiation lens, and a two-dimensional image is applied to the sample to which a potential substantially equal to the acceleration voltage of the irradiation electron beam or a negative potential is applied. Irradiating means for irradiating a planar irradiating electron beam having a general spread, and projecting and enlarging a reflected electron beam formed by electrons returned near the surface of the sample without colliding with the sample by the irradiating means. A mirror electron microscope having an image forming means for projecting and forming a sample image by setting a deflector having a deflection fulcrum near a mirror image plane on which a projected image of the sample is formed by the objective lens; A mirror electron microscope characterized in that the sample is irradiated with the irradiation electron beam vertically by adjusting the intensity of a deflector.
[0035]
(7) An electron source and an irradiation electron beam emitted from the electron source are imaged on a focal plane of an objective lens by an irradiation lens, and a potential substantially equal to the acceleration voltage of the irradiation electron beam or a negative potential is applied. Irradiating means for irradiating the sample with a planar irradiation electron beam having a two-dimensional spread, and reflected electrons formed by electrons returned near the surface of the sample without colliding with the sample by the irradiating means. Imaging means for projecting and enlarging a line to project and form a sample image, and being arranged near a mirror image plane on which a projection image of the sample is formed by the objective lens, separating the irradiation electron beam and the reflected electron beam A beam separator for arranging the irradiation electron beam between the beam separator and the irradiation lens, and a deflector for correcting aberration generated in the beam separator; A plurality of irradiation areas on the sample surface are sequentially irradiated with an electron beam to form an image of electrons pulled back near the surface of the sample without colliding with the sample, thereby forming an image of all or one of the plurality of irradiation areas. Means for sequentially forming an enlarged electronic image of the portion, means for converting the formed enlarged electronic image of the plurality of irradiation areas into an electric image signal, and comparing image signals of the plurality of irradiation areas with each other. Means for detecting a pattern defect formed on the sample.
[0036]
(8) An electron source and an irradiation electron beam emitted from the electron source are imaged on a focal plane of an objective lens by an irradiation lens, and a potential substantially equal to the acceleration voltage of the irradiation electron beam or a negative potential is applied. Irradiating means for irradiating the sample with a planar irradiation electron beam having a two-dimensional spread, and reflected electrons formed by electrons returned near the surface of the sample without colliding with the sample by the irradiating means. Imaging means for projecting and enlarging a line to project and form a sample image, and a beam separator disposed near the focal plane of the objective lens for the irradiation electron beam, for separating the irradiation electron beam and the reflected electron beam A deflector disposed between the beam separator of the reflected electron beam and the irradiation lens for correcting aberrations generated in the beam separator; and By sequentially irradiating a plurality of irradiation regions on the surface, the electrons drawn back near the surface of the sample without colliding with the sample are imaged, and an enlarged electron image of the whole or a part of the plurality of irradiation regions is sequentially formed. Means for forming, means for converting the formed enlarged electronic images of the plurality of irradiation areas into electrical image signals, and comparing the image signals for the plurality of irradiation areas with each other to form on the sample A pattern defect inspection device, comprising: means for detecting a pattern defect.
[0037]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0038]
(Example 1)
FIG. 1 shows a configuration for explaining the operation of the first embodiment. The E × B deflector 3 as a separator is arranged near an image forming plane (mirror image plane) 304 of the image forming electron beam 302. In this arrangement, aberration is generated for the irradiation electron beam 301 by the E × B deflector. In order to correct this aberration, another E × B deflector 4 for aberration correction is arranged between the irradiation system condenser lens 2 and the E × B deflector 3.
[0039]
An E × B deflector 3 is disposed as a beam separator between the condenser lens 2 and the objective lens, and the irradiation electron beam 301 emitted from the electron source 1 is perpendicular to the wafer 7 by the E × B deflector 3. Deflected to the optical axis. The irradiation electron beam 301 deflected by the E × B deflector 3 is focused by the condenser lens 2 near the focal plane 303 of the objective lens, and irradiates the sample 7 almost in parallel.
[0040]
Sample 7 has an acceleration voltage V of the electron beam. ₀ Or slightly higher negative potential V _S Is applied to the sample 7. A voltage V is applied to the circular electrode 41 facing the sample 7. _r Is applied. Most of the planar irradiation electron beam 301 is pulled back immediately before colliding with the sample 7 due to the electric field generated between the circular hole electrode 41 and the sample 7 and becomes mirror electrons, reflecting the shape, potential, magnetic field, etc. of the sample 7. It comes up with the direction and strength that you did.
[0041]
The electron beam 302 formed by the mirror electrons is projected by the objective lens 6 to form a mirror image at a mirror image plane position 304 of the objective lens 6. The E × B deflector 3 is disposed in the vicinity of the mirror image plane 304, and the E × B deflector 3 acts on the imaging electron beam under the Wien condition. Therefore, the E × B deflector 3 has no deflecting effect on the imaging electron beam 302 and is disposed near the mirror image plane position 304, so that no deflection aberration occurs. The mirror image by the objective lens 6 is projected by the intermediate lens 13 and the projection lens 14, and an enlarged mirror electronic image is formed on the scintillator 15. The mirror electrons are converted into light by the scintillator 15, projected on the CCD camera 17 by the optical lens 16 or the optical fiber bundle 33, converted into electric signals by the CCD camera 17, and the mirror image is displayed by the monitor 22.
[0042]
In this configuration, since the crossover position of the irradiation electron beam 301 is far from the position of the E × B deflector 3, aberration of the E × B deflector 3 occurs with respect to the irradiation electron beam 301. In order to correct this aberration, an E × B deflector 4 for correcting aberration is arranged between the condenser lens 2 of the irradiation system and the E × B deflector 3.
[0043]
A cross section of the E × B deflector 3 viewed from the direction perpendicular to the optical axis has an eight-pole electromagnetic pole structure shown in FIG. 6, and each of the electromagnetic poles 51 is made of a magnetic material such as permalloy. It operates as an electrode by applying a potential to each electromagnetic pole, and operates as a magnetic pole by passing a current through a coil 53 wound N times around each electromagnetic pole.
[0044]
When a voltage Vx is applied to each of the electromagnetic poles according to the voltage distribution shown in FIG. 6, the electrons are deflected in the x direction. When a current Iy is applied to each coil with a current distribution as shown in FIG. 7, electrons moving from the back side of the drawing to the front in FIG. 3 are positive in the x direction, and electrons moving from the front to the back of the drawing are x. It is deflected in the negative direction. The distribution of the voltage and current of each electrode is optimized so that a uniform electromagnetic field is generated by an electromagnetic field calculation in which a potential or magnetic potential is applied to the actual electromagnetic pole shape. For example, α = 0.414 in the figure Is set to When the electromagnetic poles 51 are operated by voltage distribution or current distribution as shown in FIG. 8, these eight electromagnetic poles also operate as astigmatism correctors.
[0045]
FIG. 9 is a sectional view including the optical axis of the E × B deflector 3. When an E × B deflector is used as a beam separator, the electron beam deflection angle needs to be bent by 30 degrees or more in consideration of an arrangement relationship in which the two optical systems do not interfere with each other. In order to prevent the irradiation electron beam 301 from hitting the electromagnetic pole even when it is deflected by 30 degrees, the diameter of the opening must be larger than the length of the electromagnetic pole. However, if the opening is widened, the voltage to be deflected must be increased. Therefore, the shape of the electromagnetic pole 51 is a divergent conical shape almost along the electron trajectory. Further, shield electromagnetic poles 54 are provided above and below the electromagnetic poles to suppress the bleeding of the electromagnetic field, and to make the electric and magnetic fields act in the same space. It operates as a B deflector.
[0046]
The distribution of the intensity ratio between the two E × B deflectors will be described below. The E × B deflector 3 operates under the Wien condition for the imaging electron beam 302 and operates as a deflector for the irradiation electron beam 301. That is, the irradiation system and the imaging system are 2θ ₁ When the E × B deflector 3 is inclined with respect to the irradiation electron beam, the E × B deflector 3 becomes ₁ , With magnetic field deflector θ ₁ And act on the same direction at an angle of .theta. With the electric field deflector constituting the E.times.B deflector 3 for the imaging electron beam. ₁ , With magnetic field deflector θ ₁ Operate in the opposite direction at an angle of.
[0047]
The E × B deflector 4 is an electric field deflector constituting the E × B deflector 4 with respect to the irradiation electron beam, and θ ₂ , With magnetic field deflector θ ₂ To operate under the Wien condition acting in the opposite direction at an angle of. The optical path length of the irradiation electron beam 301 up to the focal plane of the E × B deflector 3 is represented by L _L And the optical path length from the E × B deflector 4 onto the focal plane is L _U Then, in equation (4), θ _U To θ ₂ , Θ _L To θ ₁ So that equation (4) holds true ₂ , The chromatic aberration of the irradiation electron beam 301 can be substantially corrected on the focal plane.
[0048]
The function of the control unit 28 that executes the above operation will be described below. The voltage Vx supplied to the E × B deflector 3 and the deflection angle θ of the electron beam ₁ Is related to the energy of the electron beam incident on the E × B deflector 3 and the acceleration voltage V applied to the electron source. ₀ Depends on the electron beam trajectory calculation result or the desired deflection angle obtained from experiments in advance. ₀ And Vx are input to the control unit 28. The relationship between the intensity of the coil current Iy supplied to the E × B deflector 3 and the Wien condition of Vx is satisfied, based on whether the value obtained from the calculation result of the trajectory of the electron beam is input to the control unit 28 in advance, or on the image of the display device 22. Is set manually or automatically so that the amount of deflection on the sample is completely canceled. Acceleration voltage V ₀ Is constant, the intensity ratio between Vx and Iy that satisfies the Wien condition is constant. Therefore, by changing the intensity ratio between Vx and Iy constant, the deflection angle with respect to the incident electron beam while maintaining the Wien condition is maintained. Can be changed. In this way, by controlling Vx and Iy supplied from the control unit 28 to the separator E × B deflector power supply 31, the deflection angle θ deflected by the E × B deflector 3 is controlled. ₁ Can be controlled.
[0049]
Further, the voltage Vx ′ supplied to the E × B deflector 4 and the electron beam deflection angle θ ₂ And the acceleration voltage V for a desired deflection angle obtained in advance from the results of electron beam trajectory calculations and experiments. ₀ The relationship between Vx ′ and Vx ′ is input to the control unit 28. The relationship between the intensity of the coil current Iy ′ to be supplied to the E × B deflector 4 and the Wien condition of Vx ′ is satisfied. The value obtained from the calculation result of the trajectory of the electron beam is input to the control unit 28 in advance or the display device 22 It is set manually or automatically so that the deflection amount on the sample is completely canceled on the image. Acceleration voltage V ₀ Is constant, the intensity ratio between Vx ′ and Iy ′ that satisfies the Wien condition is constant. Therefore, the intensity ratio between Vx ′ and Iy ′ is kept constant, and ₂ Can be changed. By controlling Vx ′ and Iy ′ supplied from the control unit 28 to the aberration correcting E × B deflector power supply 32 in this manner, the deflection angle θ deflected by the E × B deflector 4 ₂ Can be controlled.
[0050]
The control unit 28 controls the tilt angle 2θ between the irradiation system and the imaging system through the separator E × B deflector power supply 31. ₁ And acceleration voltage V ₀ The voltages Vx, αVx, −αVx, and −Vx are supplied to the respective electromagnetic poles of the E × B deflector 3 so that the following relationship holds, and the coil currents Iy, αIy, −αIy, and −Iy are supplied.
[0051]
Further, the control unit 28 calculates the expression (4) and calculates the deflection angle θ such that the expression (4) holds. ₂ And the acceleration voltage V0, the voltages Vx ′, αVx ′, −αVx ′, and −Vx ′ are supplied to the respective electromagnetic poles of the E × B deflector 4 through the E × B deflector power supply 32 for aberration correction. Then, coil currents Iy ′, αIy ′, −αIy ′, and −Iy ′ are supplied. By performing such an operation, the aberration generated by the E × B deflector 3 for the separator can be corrected by the E × B deflector 4 for aberration correction.
[0052]
Although the above operation has been described with respect to the deflection directions of the XB deflector 3 and the XB deflector 4 in the x direction, the correction of the deflection component in the y direction is also performed by the eight electromagnetic poles in the y direction. The same procedure can be performed by supplying the voltage or current of the deflection component. For example, when a magnetic flux leaks from a peripheral magnetic lens in the E × B deflector, rotation correction for superimposing such an electromagnetic field in the y direction is necessary.
[0053]
Further, in FIG. 7, the number of turns of each coil is set equal to N, but the currents I and N may be changed within a range in which the relation with the current I flowing through the magnetic pole is constant.
[0054]
Whether or not the crossover aberration of the irradiation system has been corrected can be achieved by means of measuring the magnitude of the crossover. For example, the objective lens is operated so that this crossover becomes a spot again on the sample, a means for scanning the sample is provided, and secondary electrons generated by colliding an electron beam with the sample are detected, and an SEM image is obtained. Is provided, the magnitude of the crossover can be measured by evaluating the resolution of the SEM image.
[0055]
Alternatively, the crossover is formed on the focal plane of the objective lens, and the sample can be irradiated in parallel. The magnitude of the crossover is related to the parallelism of the electron beam irradiating the sample, and the larger the crossover, the more the parallelism. However, the degree of parallelism of the irradiation electron beam can be confirmed by observing the electron diffraction image of the imaging electron beam. In other words, if a mirror-like sample is placed as a sample, the irradiated electron beam is specularly reflected and becomes an image-forming electron beam as mirror electrons not including the structure of the sample, and an electron beam diffraction image of the mirror electrons is formed on the image plane of the objective lens. However, the electron beam diffraction image is enlarged by an intermediate lens and a projection lens, projected on the scintillator 15, and observed by the CCD camera 17. By adjusting the voltage Vx ′ and the current Iy ′ supplied to the aberration correcting E × B deflector 4 so as to minimize the electron beam diffraction image while maintaining the Wien condition, the irradiation system crossover Can be minimized.
[0056]
(Example 2)
FIG. 10 shows a configuration for explaining the operation of the second embodiment. In this embodiment, the E × B deflector 3 for the separator is arranged near the crossover position 303 of the irradiation system to minimize the aberration of the irradiation system. The aberration generated in the imaging system is corrected by arranging and operating another E × B deflector 4 between the image plane position 304 of the imaging system and the E × B deflector 3.
[0057]
The E × B deflector 3 operating as a separator is an electric field deflector constituting the E × B deflector 3 for the irradiation electron beam and θ ₁ , With magnetic field deflector θ ₁ And act on the imaging electron beam in the same direction at an angle of θ1 with an electric field deflector constituting the E × B deflector 3 and θ with a magnetic field deflector. ₁ Operate in the opposite direction at an angle of. Since the E × B deflector 3 is disposed at the crossover position of the irradiation electron beam 301, no chromatic aberration occurs with respect to the irradiation system. Since the E × B deflector 3 generates an aberration with respect to the imaging electron beam 302, the E × B deflector 4 for aberration correction is disposed between the E × B deflector 3 and a mirror image plane 303 formed by the objective lens. Place. Since the E × B deflector 3 operates under the Wien condition with respect to the imaging electron beam 302, the optical path length of the irradiation electron beam 301 to the focal plane of the E × B deflector 3 is represented by L. _L And the optical path length from the E × B deflector 4 onto the focal plane is L _U Is deflected by the electric field deflector constituting the E × B deflector 4 so that the equation (3) holds. ₂ , Angle θ to be deflected by magnetic field deflector ₂ , It is possible to correct chromatic aberration on the image plane.
[0058]
(Example 3)
FIG. 11 shows a configuration for explaining the operation of the third embodiment.
[0059]
In the present embodiment, the E × B deflector 3 as a separator is arranged near the imaging plane 304 of the imaging electron beam. In this arrangement, aberration is generated by the E × B deflector with respect to the irradiation lens. In order to correct this aberration, another E × B deflector 4 for correcting aberration is arranged between the irradiation system condenser lens 2 and the E × B deflector 3. In this embodiment, the imaging system is erected and the irradiation system is inclined.
[0060]
The E × B deflector 3 operates under the Wien condition for the irradiation electron beam 301 and operates as a deflector for the imaging electron beam 302. That is, the irradiation system and the imaging system are 2θ ₁ When the E × B deflector 3 is inclined with respect to the irradiation electron beam, the E × B deflector 3 becomes ₁ , With magnetic field deflector θ ₁ Is operated under the Wien condition acting in the opposite direction at an angle of θ. ₁ , With magnetic field deflector θ ₁ Act as a deflector acting in the same direction at an angle of. The E × B deflector 4 is an electric field deflector constituting the E × B deflector 4 with respect to the irradiation electron beam, and θ ₂ , With magnetic field deflector θ ₂ To operate under the Wien condition acting in the opposite direction at an angle of. The optical path length of the irradiation electron beam 301 up to the focal plane of the E × B deflector 3 is represented by L _L And the optical path length from the E × B deflector 4 onto the focal plane is L _U Then, θ is set so that equation (3) holds. ₂ , The chromatic aberration of the irradiation electron beam 301 can be substantially corrected on the focal plane. The control unit 28 performs an operation so that the equation (3) holds, and controls the voltage and current supplied to the separator E × B deflector power supply 31 and the aberration correction E × B deflector power supply 32.
[0061]
(Example 4)
FIG. 12 shows a configuration for explaining the operation of the fourth embodiment.
In this embodiment, an E × B deflector is arranged at the crossover position of the irradiation system to minimize the aberration of the irradiation system. The aberration generated in the imaging system is corrected by arranging and operating another E × B deflector between the image plane position of the imaging system and the E × B deflector. In the present embodiment, as in the third embodiment, the imaging system is erected and the irradiation system is inclined.
[0062]
The E × B deflector 3 operates under the Wien condition for the irradiation electron beam 301 and operates as a deflector for the imaging electron beam 302. That is, the irradiation system and the imaging system are 2θ ₁ When the E × B deflector 3 is inclined with respect to the irradiation electron beam, the E × B deflector 3 becomes ₁ , With magnetic field deflector θ ₁ Is operated under the Wien condition acting in the opposite direction at an angle of θ. ₁ , With magnetic field deflector θ ₁ Act as a deflector acting in the same direction at an angle of. The E × B deflector 4 is an electric field deflector constituting the E × B deflector 4 with respect to the irradiation electron beam, and θ ₂ , With magnetic field deflector θ ₂ To operate under the Wien condition acting in the opposite direction at an angle of. The optical path length of the imaging electron beam 302 up to the focal plane of the E × B deflector 3 is represented by L _L And the optical path length from the E × B deflector 4 onto the focal plane is L _U Then, θ is set so that equation (4) holds. ₂ , The chromatic aberration of the imaging electron beam 302 can be substantially corrected on the mirror image plane. The control unit 28 performs an operation so that the expression (4) is satisfied, and controls the voltage and current supplied to the separator E × B deflector power supply 31 and the aberration correction E × B deflector power supply 32.
[0063]
(Example 5)
FIG. 13 shows a fifth embodiment, in which a deflector for allowing an electron beam to be incident on a sample vertically even when the wafer is tilted is provided. Assuming that the z direction is taken as the optical axis and the surface of the sample, which is usually in the xy plane at z = 0, is inclined by θ in the x direction, the distance between the sample 7 and the circular hole electrode 41 is L. ₀ , The z-direction component Ez and the x-direction component Ex of the electric field intensity are Ez ≒ E and Ex ≒ (1−z / L ₀ ) Given by E.
[0064]
If the equations of motion are solved in the x and z directions, the condition that the electron beam enters the sample almost perpendicularly under the condition that it is closest to the sample, that is, the velocity in the z direction is 0 and the velocity component in the x direction is also 0 Is that the angle β passing through the circular electrode 41 is
[0065]
(Equation 5)

Is generally satisfied.
[0066]
Further, the focal length f of the circular hole electrode 41 is 4L. ₀ Is the angle β of the electron beam incident on the circular electrode 41. ₂ Is inclined by 2 sin θ (≒ 2θ).
[0067]
Therefore, for example, when the aligner 42 is disposed above the circular hole electrode 41 and the sample is inclined by θ in the x direction, the electron beam is always irradiated vertically to the sample by acting so as to incline by 2θ. can do. Here, if the arrangement of the aligner 42 is in the vicinity of the mirror image plane 302 projected by the objective lens, the electron beam emitted from one point on the object plane in all directions converges to one point on the image plane. Thus, even if the irradiation angle on the sample changes, the same field of view can always be irradiated. The aligner 42 may be a single aligner 42 near the mirror image plane 302 or may be composed of two upper and lower aligners. The ratio may be adjusted.
[0068]
When the E × B deflector 3 is disposed near the mirror image plane 302 projected by the objective lens as a separator for separating the irradiation electron beam 301 and the imaging electron beam 302, the electric field and the magnetic field are in opposite directions. The above function can be realized by superimposing a component acting as an aligner in addition to the Wien condition under which the same force acts on.
[0069]
However, it is desirable to use an electrostatic aligner for the aligner 42 so that the irradiation beam and the imaging beam act in the same direction. That is, FIG. 14 shows an electrostatic aligner, and FIG. 15 shows trajectories of an irradiation electron beam and an imaging electron beam when a magnetic field type aligner is used. In the magnetic field type aligner, This is because the trajectories of the incident electron beam and the reflected electron beam above the aligner do not coincide with each other, so that by operating the aligner, it is necessary to readjust the electron optical system above the aligner. The adjustment procedure will be described with reference to FIG.
[0070]
The E × B deflector 3 is disposed as a separator in the vicinity of the imaging plane 304 of the imaging electron beam 302. In this arrangement, aberration is generated for the irradiation electron beam 301 by the E × B deflector. In order to correct this aberration, another E × B deflector 4 for aberration correction is arranged between the irradiation system condenser lens 2 and the E × B deflector 3. Each of the electromagnetic poles of the E × B deflector 3 serves as a separator, in addition to the supply voltage Vx and the coil current Iy satisfying the Wien condition as shown in FIGS. Is supplied with a deflection voltage. A voltage for vertical irradiation adjustment is supplied to the electrostatic deflector from a power supply (not shown) for adjusting the sample tilt angle.
[0071]
The inclination distribution of the sample 7 is determined in advance by using a height measuring device 26 or a height measuring means such as a focusing lens intensity using an electron beam at a plurality of positions in the sample before observation. calculate. At the time of observation, the control unit 28 calculates the sample tilt angle θ based on the sample tilt data corresponding to the inspection position coordinates, and calculates the tilt angle 2θ at the time of emission from the objective lens. In this embodiment, since the E × B deflector 3 is disposed above the objective lens 6, a deflection angle θ ′ corresponding to the exit angle θ of the objective lens is calculated from the magnification of the objective lens, and corresponds to the deflection angle θ ′. The deflection voltage is superimposed on the supply voltage Vx that satisfies the Wien condition and supplied to each electromagnetic pole. By performing the control as described above, it is possible to always irradiate the sample with the electron beam vertically within the sample plane.
[0072]
(Example 6)
The present embodiment shown in FIG. 17 has a configuration in which a mirror electron microscope is applied to high-speed wafer inspection.
[0073]
In the electron optical system 101, the electron beam emitted from the electron source 1 is converged by the condenser lens 2 and irradiated substantially parallel on the sample. As the electron source 1, a Zr / O / W type Schottky electron source was used. A uniform planar electron beam having a large current beam (for example, 1.5 μA) and an energy width of 1.5 eV can be stably formed.
[0074]
The E × B deflector 3 is disposed as a separator in the vicinity of the imaging plane 304 of the imaging electron beam 302. In this arrangement, aberration is generated for the irradiation electron beam 301 by the E × B deflector. In order to correct this aberration, another E × B deflector 4 for aberration correction is arranged between the irradiation system condenser lens 2 and the E × B deflector 3.
[0075]
The electron beam is deflected by the E × B deflector 3 to an optical axis perpendicular to the wafer 7. The E × B deflector 3 has a deflecting effect only on an electron beam from above. The electron beam deflected by the E × B deflector 3 is formed into a planar electron beam by the objective lens 6 in a direction perpendicular to the sample (wafer) surface. Since the deflection aberration of the separator ExB deflector 3 is corrected by the ExB deflector 4, a fine crossover is formed on the focal plane of the objective lens 6. Can be applied to the sample.
[0076]
To the sample (wafer) 7 mounted on the sample moving stage 8 in the sample chamber 102, a negative potential substantially equal to or slightly higher than the accelerating voltage of the electron beam is applied by the sample application power supply 9, and the wafer 7 An electric field reflecting the shape of the formed semiconductor pattern and the state of charging is formed on the surface of. Due to this electric field, most of the planar electron beam is pulled back immediately before colliding with the wafer 7 and rises in a direction and intensity reflecting the pattern information of the wafer 7.
[0077]
The retracted electron beam is converged by the objective lens 6, and the deflector 3 as a beam separator has no deflecting effect on the electron beam traveling from below. The image is projected and enlarged by the intermediate lens 13 and the projection lens 14 to form an image of the surface of the wafer 7 on an image detection unit including the scintillator 15, the optical lens 16 and the CCD 17. Further, the contrast of the image is adjusted by disposing the contrast aperture 12 on the electron beam diffraction image plane formed by the objective lens 6 or the intermediate lens 13.
[0078]
As a result, a structural change such as a local change in the charged potential and unevenness on the surface of the wafer 7 is formed as an image. By correcting the aberration, it is possible to irradiate the irradiation electron beam 301 with good parallelism and to form a high-resolution mirror image. Therefore, it is possible to detect a change in the charging potential of 100 nm or less and a difference in structure such as unevenness. Becomes possible. This image is converted into an electric signal and sent to the image processing unit 104.
[0079]
The image processing unit 104 includes image signal storage units 18 and 19, a calculation unit 20, and a defect determination unit 21. The image storage units 18 and 19 store images of adjacent portions of the same pattern, and the two images are calculated by the calculation unit 20 to detect different locations of the two images. The result is determined as a defect by the defect determination unit 21 and its coordinates are stored. The captured image signal is displayed on the monitor 22 as an image.
[0080]
When performing a comparative inspection of patterns between adjacent chips A and B having the same design pattern formed on the surface of the semiconductor wafer 7, first, an electron beam image signal for a region to be inspected in the chip A is fetched. , In the storage unit 18. Next, an image signal of the inspection area corresponding to the above in the adjacent chip B is fetched and stored in the storage unit 19, and at the same time, compared with the stored image signal in the storage unit 18. Further, while acquiring an image signal for the corresponding inspection area in the next chip C and storing the image signal in the storage section 18 by overwriting, at the same time, storing the image signal for the inspection area in the chip B in the storage section 19 Compare with the image signal. By repeating such an operation, comparison is performed while sequentially storing the image signals of the corresponding test areas in all the test chips.
[0081]
In addition to the above method, it is also possible to adopt a method in which an electron beam image signal of a desired inspection area for a standard non-defective (no defect) sample is stored in the storage unit 18 in advance. In this case, the inspection area and the inspection conditions for the non-defective sample are previously input to the control computer 29, and the inspection for the non-defective sample is executed based on the input data, and the acquired image for the desired inspection area is obtained. The signal is stored in the storage unit 18. Next, the wafer 7 to be inspected is loaded on the stage 8, and the inspection is performed in the same procedure as above.
[0082]
Then, at the same time as capturing the acquired image signal of the inspection area corresponding to the above into the storage unit 19, the image signal of the inspection target sample and the image signal of the non-defective sample previously stored in the storage unit 18 are obtained. Compare. Thus, the presence or absence of a pattern defect in the desired inspection area of the inspection target sample is detected. In addition, as the standard (non-defective) sample, a wafer different from the inspection target sample, which is known in advance to have no pattern defect, may be used. A known area (chip) may be used. For example, when a pattern is formed on the surface of a semiconductor sample (wafer), a misalignment failure between the lower layer pattern and the upper layer pattern may occur over the entire surface of the wafer. In such a case, if the objects to be compared are patterns in the same wafer or in the same chip, the above-described defects (defects) generated over the entire surface of the wafer are overlooked.
[0083]
However, according to the present embodiment, the image signal of the area known to be good (no defect) is stored in advance, and the stored image signal is compared with the image signal of the inspection target area. Such a defect occurring over the entire surface of the wafer can be accurately detected.
[0084]
The two image signals stored in the storage units 18 and 19 are respectively fetched into the calculation unit 20, where various statistics (specifically, the average value of the image density) are based on the defect determination conditions already obtained. , A statistic such as variance), a difference value between neighboring pixels, and the like. The two image signals that have been subjected to these processes are transferred to the defect determination unit 21, where they are compared and a difference signal between the two image signals is extracted. These difference signals are compared with the defect determination conditions that have already been obtained and stored, and defect determination is performed, and the image signal of the pattern area determined to be defective and the image signal of the other area are separated.
[0085]
Operation commands and operation conditions of each unit of the device are input and output from the control computer 29. Various conditions such as an acceleration voltage at the time of generation of an electron beam, an electron beam deflection width / deflection speed, a sample stage moving speed, and a timing of capturing an image signal from an image detection element are input to the control computer 29 in advance. The beam control system 28 receives a command from the control computer 29, generates a correction signal based on signals from the stage position measuring device 27 and the sample height measuring device 26, and irradiates the electron beam to a correct position at all times. The correction signal is sent to the objective lens power supply 25 and the scanning signal generator 24 as described above. The stage control system 30 controls the sample moving stage 8 in response to a command from the control computer 29.
[0086]
At the time of inspection, the stage 8 on which the sample (semiconductor wafer) 7 is mounted continuously moves at a constant speed in the x direction. Since the stage 8 is continuously moving, the electron beam is deflected and scanned by the irradiation system deflector 5 following the movement of the stage 8.
[0087]
The irradiation area or irradiation position of the electron beam is constantly monitored by a stage position measuring device 27, a sample height measuring device 26, and the like provided on the stage 8. These pieces of monitor information are transferred to the control computer 29, and the positional deviation amount is grasped in detail. The positional deviation amount is accurately corrected by the beam control system 28. Thus, accurate positioning required for pattern comparison inspection can be performed at high speed and high accuracy.
[0088]
Further, the surface height of the semiconductor wafer 7 is measured in real time by means other than the electron beam, and the focal length of the objective lens 6 and the imaging lens 11 for irradiating the electron beam is dynamically corrected. The means other than the electron beam is, for example, an optical height measuring device 26 using a laser interference method or a method for measuring a change in the position of reflected light. This makes it possible to always form an electron beam image focused on the surface of the region to be inspected. Further, the warpage of the wafer 7 is measured in advance before the inspection, and the focal length is corrected based on the measured data so that the surface height of the wafer 7 need not be measured during the actual inspection. You may.
[0089]
The inspection method and the inspection apparatus described above can irradiate the irradiation electron beam 301 with good parallelism with the aberration corrected, and form a high-resolution mirror image. By forming an image reflecting the information and comparing and inspecting the image signal of the corresponding pattern area, it is possible to detect the presence or absence of a pattern defect of 100 nm or less. As a result, a very high-speed and high-resolution inspection can be performed as compared with a conventional electron beam inspection apparatus.
[0090]
【The invention's effect】
According to the present invention, it is possible to realize a configuration of a high-resolution mirror electron microscope by minimizing aberrations generated with respect to the irradiation electron beam and the reflected electron beam, and to use the mirror electron microscope on a wafer. A defect inspection apparatus that detects a defective portion in a formed pattern at high resolution and at high speed is realized.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a mirror electron microscope according to a first embodiment of the present invention.
FIG. 2 is a diagram illustrating the operation of an E × B deflector.
FIG. 3 is a view for explaining aberration correction of an E × B deflector.
FIG. 4 is a diagram illustrating a configuration (1) of aberration correction of an E × B deflector.
FIG. 5 is a diagram illustrating a configuration (2) of aberration correction of an E × B deflector.
FIG. 6 is a view for explaining an example (1) of voltage distribution of an 8-pole E × B deflector.
FIG. 7 is a view for explaining an example (2) of current distribution of an 8-pole E × B deflector.
FIG. 8 is a view for explaining astigmatism correction of an 8-pole E × B deflector.
FIG. 9 is a sectional view of an 8-pole type E × B deflector.
FIG. 10 is a diagram illustrating a configuration of a second example of the present invention.
FIG. 11 is a view for explaining the configuration of a third embodiment of the present invention.
FIG. 12 is a view for explaining the configuration of a fourth embodiment of the present invention.
FIG. 13 is a view for explaining a fifth embodiment of the present invention.
FIG. 14 is a view for explaining the operation of the electrostatic deflector according to the fifth embodiment of the present invention.
FIG. 15 is a diagram illustrating the operation of a magnetic field deflector according to a fifth embodiment of the present invention.
FIG. 16 is a view for explaining the configuration of a fifth embodiment of the present invention.
FIG. 17 is a view for explaining the configuration of a sixth embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Electron source, 2 ... Condenser lens, 3 ... ExB deflector, 4 ... ExB deflector, 5 ... Irradiation system deflector, 6 ... Objective lens, 7 ... Sample (wafer), 8 ... Wafer moving stage Reference numeral 10: imaging system deflector, 12: contrast aperture, 13: intermediate lens, 14: projection lens, 15: scintillator, 16: optical lens, 17: CCD, 18: image storage unit, 19: image storage unit, 20 Calculation unit 21, Defect determination unit 22, Monitor 23, Acceleration power supply 24, Scanning signal generator 25, Objective lens power supply 26, Sample height measuring instrument 27, Stage position measuring instrument 28, Beam Control system, 29: control computer, 30: stage control system, 31: E × B deflector power supply for separator, 32: E × B deflector power supply for aberration correction, 33: optical fiber bundle, 41: circular electrode, 42 ... A aligner, 51 ... Magnetic pole, 52: bobbin, 53: coil, 54: shield, 101: electron optical system, 102: sample chamber, 104: image processing unit, 201: electron gun, 202: condenser lens, 203: aligner, 301: irradiation electron beam Reference numeral 302 denotes an imaging electron beam, 303 denotes an irradiation system crossover, and 304 denotes a mirror image plane.

Claims (19)

An irradiation electron beam emitted from an electron source is imaged on a focal plane of an objective lens by an irradiation lens, and a first electron beam is applied to a sample applied to a potential substantially equal to the acceleration voltage of the irradiation electron beam or a negative potential. An optical system for projecting and enlarging a reflected electron beam formed by electrons pulled back near the surface of the sample without colliding with the sample by the first electron optical system, and projecting and forming a sample image. An electron optical system and a beam separator for separating the irradiation electron beam and the reflected electron beam, which is disposed near a mirror image plane on which a projection image of the sample is formed by the objective lens, and A mirror electron microscope, wherein a deflector for correcting aberration generated in the beam separator is provided in the first electron optical system. An irradiation electron beam emitted from an electron source is imaged on a focal plane of an objective lens by an irradiation lens, and a first electron beam is applied to a sample applied to a potential substantially equal to the acceleration voltage of the irradiation electron beam or a negative potential. An optical system for projecting and enlarging a reflected electron beam formed by electrons pulled back near the surface of the sample without colliding with the sample by the first electron optical system, and projecting and forming a sample image. An electron optical system, and a beam separator disposed near the focal plane of the objective lens for separating the irradiation electron beam and the reflected electron beam, and corrects aberration generated by the beam separator. A mirror electron microscope, wherein a deflector is provided in the second electron optical system. The mirror electron microscope according to claim 1, wherein the beam separator is an E × B deflector in which an electric field and a magnetic field intersect. The mirror electron microscope according to claim 3, wherein the deflector is an E × B deflector in which an electric field and a magnetic field intersect. An electron source and an irradiation electron beam emitted from the electron source are imaged on a focal plane of an objective lens by an irradiation lens, and a sample to which a potential substantially equal to the acceleration voltage of the irradiation electron beam or a negative potential is applied is applied. Irradiating means for irradiating the planar irradiation electron beam having a dimensional spread, and a reflected electron beam formed by mirror electrons pulled back near the surface of the sample without colliding with the sample by the irradiation means. Imaging means for projecting and projecting a sample image by projecting and enlarging, and being arranged near a mirror image plane on which a projection image of the sample is formed by the objective lens, and separating the irradiation electron beam and the reflected electron beam And a deflector for correcting aberrations generated in the beam separator is provided between the beam separator and the irradiation lens of the irradiation electron beam. Mirror electron microscope characterized and. The mirror electron microscope according to claim 5, wherein the beam separator is an E × B deflector in which an electric field and a magnetic field intersect. The mirror electron microscope according to claim 5, wherein the deflector is an E × B deflector in which an electric field and a magnetic field intersect. An electron source and an irradiation electron beam emitted from the electron source are imaged on a focal plane of an objective lens by an irradiation lens, and a sample to which a potential substantially equal to the acceleration voltage of the irradiation electron beam or a negative potential is applied is applied. An irradiation unit for irradiating a planar irradiation electron beam having a dimensional spread, and a reflected electron beam formed by electrons returned near the surface of the sample without colliding with the sample by the irradiation unit, is projected and enlarged. Imaging means for projecting and imaging a sample image, and a beam separator disposed near the focal plane of the objective lens for separating the irradiation electron beam and the reflected electron beam, and A deflector for correcting aberration generated in the beam separator is provided between the beam separator of the line and an objective lens image plane on which a projection image of the sample is formed by the objective lens. Mirror electron microscope according to claim. The mirror electron microscope according to claim 8, wherein the beam separator is an E × B deflector in which an electric field and a magnetic field intersect. The mirror electron microscope according to claim 8, wherein the deflector is an E × B deflector in which an electric field and a magnetic field intersect. The beam separator has a function of superimposing the irradiation electron beam and the reflected electron beam on a function of separating the irradiation electron beam and the reflected electron beam, and adjusting the intensity of the deflector, so that the irradiation electron beam can be irradiated to the sample vertically. The mirror electron microscope according to claim 6 or 9, wherein: The irradiation electron beam emitted from the electron source is imaged on the focal plane of the objective lens by the irradiation lens, and two-dimensionally spreads on the sample to which a potential substantially equal to the acceleration voltage of the irradiation electron beam or a negative potential is applied. Irradiating means for irradiating a planar irradiating electron beam having: and a sample image obtained by projecting and enlarging a reflected electron beam formed by electrons returned near the surface of the sample without colliding with the sample by the irradiating means. And an image forming means for projecting an image of the sample, a deflector having a deflection fulcrum near a mirror image plane on which the projection image of the sample is formed by the objective lens, A mirror electron microscope characterized in that the sample is configured to be able to irradiate the sample with the irradiation electron beam vertically by adjusting the intensity. The mirror electron microscope according to claim 12, wherein the deflector is an electric field type deflector or an E × B deflector in which an electric field and a magnetic field intersect. An electron source and an irradiation electron beam emitted from the electron source are imaged on a focal plane of an objective lens by an irradiation lens, and the specimen to which a potential substantially equal to the acceleration voltage of the irradiation electron beam or a negative potential is applied. An irradiation unit for irradiating a planar irradiation electron beam having a two-dimensional spread, and a reflected electron beam formed by electrons returned near the surface of the sample without colliding with the sample by the irradiation unit, is projected. Imaging means for enlarging and projecting a sample image, and arranged near a mirror image plane on which a projected image of the sample is formed by the objective lens, for separating the irradiation electron beam and the reflected electron beam A beam separator; a deflector disposed between the beam separator for the irradiation electron beam and the irradiation lens; and a deflector for correcting aberration generated by the beam separator; Line, sequentially irradiating a plurality of irradiation areas on the sample surface, image the electrons pulled back near the surface of the sample without colliding with the sample, image the whole or a part of the plurality of irradiation areas Means for sequentially forming an enlarged electronic image, means for converting the formed enlarged electronic images of the plurality of irradiation regions into electrical image signals, and comparing image signals for the plurality of irradiation regions with each other, Means for detecting a pattern defect formed on the sample. The mirror electron microscope according to claim 14, wherein the beam separator is an E × B deflector in which an electric field and a magnetic field intersect. 16. The pattern defect inspection apparatus according to claim 14, wherein the deflector is an E × B deflector in which an electric field and a magnetic field intersect. An electron source and an irradiation electron beam emitted from the electron source are imaged on a focal plane of an objective lens by an irradiation lens, and the specimen to which a potential substantially equal to the acceleration voltage of the irradiation electron beam or a negative potential is applied. An irradiation unit for irradiating a planar irradiation electron beam having a two-dimensional spread, and a reflected electron beam formed by electrons returned near the surface of the sample without colliding with the sample by the irradiation unit, is projected. Imaging means for projecting and imaging a sample image by enlarging, and a beam separator arranged near the focal plane of the objective lens for the irradiation electron beam, for separating the irradiation electron beam and the reflected electron beam, A deflector arranged between the beam separator for reflected electron beams and the irradiation lens, for correcting aberrations generated in the beam separator, and applying the planar irradiation electron beam to the sample surface. By sequentially irradiating a plurality of irradiation regions and imaging electrons pulled back near the surface of the sample without colliding with the sample, an enlarged electron image of the whole or a part of the plurality of irradiation regions is sequentially formed. Means for converting the formed enlarged electron images of the plurality of irradiation areas into electrical image signals, and comparing the image signals for the plurality of irradiation areas with each other to determine a pattern defect formed on the sample. A pattern defect inspection apparatus comprising: means for detecting a pattern defect. The mirror electron microscope according to claim 17, wherein the beam separator is an E × B deflector in which an electric field and a magnetic field intersect. 19. The pattern defect inspection apparatus according to claim 17, wherein the deflector is an E × B deflector in which an electric field and a magnetic field intersect.

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