JP2005004995A - Scanning type electron microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable to display as an image the energy distribution characteristics of signal electrons such as reflecting electrons and secondary electrons generated when primary electron beams are irradiated on a test piece. <P>SOLUTION: The voltage applied onto the signal electron detector 120, which measures the signal electrons 109, 110 emitted from the test piece 107 irradiated by the primary electron beams 104, is changed, and the energy distribution of the signal electrons is measured, and a color is assigned to each energy value. An image is displayed by the color corresponding to each energy value and the luminance corresponding to signal strength. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００２４】
これは、１枚の画像取得時に電子検出器１２０が検出した、電子の総電荷量に比例する値である。これにより、エネルギーＥ１における配色の変化率Ｃ（Ｅ１）は、次式で表される。ここでｋは通常、定数の１である。
【００２５】
【数２】

【００２６】
図５は、図２（ｄ）の信号スペクトルに対して、信号量の多い部分に色変化を多く付くように配色を分布させた例である。ここで、明暗を除いた基本色を２５６×５色使っていたとすると、互いに隣り合う各フレーム間の基本配色の変化は、通常２５６×５／Ｎとなる。これに、式（２）の値をかけて、エネルギーＥ１に対応するフレームの色変化の割合は、次式で表せる。
【００２７】
【数３】

【００２８】
図２（ｄ）において、試料の物質的な特長は、比較的高いエネルギーのａ，ｂ，ｃ，ｄ等の小さなピークに表れる。表示画像に試料物質の特徴を強調して表示するためにさまざまな方法が考えられるが、一例として、この信号電流スペクトルの対数をとり、これに対応させて画像表示をすることで、ａ，ｂ，ｃ，ｄ等の小さなピークを強調することができる。この状態を、図６に示す。図６において、実線が、破線で示す信号電流スペクトルの対数をとったスペクトルである。
【００２９】
また、ある特定のエネルギー値に電子信号を放出する物質の分布を確認したいといった用途に対しては、その様なエネルギー帯に赤等の目立つ色を対応させて表示することにより、目的の像観察をしやすくすることができる。
【００３０】
１フレームごとの画像を重ね合わせるとき、電極電圧変化他の要因で、一次電子線のスキャン領域が、わずかに移動することがある。したがって、画像を重ね合わせるときには、それぞれのフレームの画像の明るさの相関をとり、画像がマッチするように重ね合わせて行く。この場合、まず、電極電圧等を変化させずに二次電子、反射電子すべての信号を取り込んだ、基準と成る画像を最初に取得、保存しておき、相関のベースとなる画像をこの全電子信号を含んだ画像にすると相関がとりやすい。
【００３１】
図７は、バイアス電圧Ｖｂの値の変化を１フレーム毎ではなく、４フレーム毎に変化させている例である。このように１フレーム毎に電圧を変化させるのではなく、２フレーム毎、４フレーム毎等、数フレーム毎に電圧を変化させても、試料の物質的特徴を十分表現し得る。バイアス電圧Ｖｂを変化させなければ、一次電子線のスキャン領域が移動することもなくなるので、同一バイアス電圧で取得した数フレームの画像は、そのまま合成し得る。最後に１枚のカラー画像へ合成するときに、予めそれぞれの同一のＶｂで取得し合成した画像群を、その画素の明度の相関から合わせ位置を調節し、合成することも有効である。
【００３２】
さらに明度も、信号強度に対し、明暗を反転させて表示することもできる。このような操作は、入力装置１５４からの命令入力で、ＣＰＵ１５０による信号処理器１７８、画像積算器１５５等の制御によってさまざまに変え得る。
【００３３】
図８は、これら一連の作業をフローチャートにまとめたものである。
まず、フレーム数Ｎを決定する（ステップ３０１）。そして、バイアス電圧の初期値を設定し、電極に電圧を印加する（ステップ３０２）。この場合、一例として、すべての信号電子電流を取得する設定を初期値としておく。次に、このバイアス電圧設定条件のままで、基準となる画像を取得しておく（ステップ３０３）。この画像のフレーム数は、４から１６フレーム程度、多くても３２フレームもあれば十分である。
【００３４】
次に、主目的の画像の取得を開始する（ステップ３０４）。一次電子線を２次元的に走査し、１フレームの画像信号を検出し、保存する（ステップ３０５）。これを、フレーム毎にバイアス電圧を変化させながら設定したフレーム数だけ繰り返す（ステップ３０７、３０８）。前述のように、このバイアス電圧の変化を数フレーム毎に行ってもかまわない。信号取得が終了したら、取得したすべてのデータを保存しておく（ステップ３０９）。この場合、データとしては、１フレーム画面の画素数×フレーム数（Ｖｂ変化の段数に対応）だけある。
【００３５】
これらのデータから、各画素の信号スペクトルを取り出し、それを微分し、各エネルギー値に対する信号量を求める。これが、各色に対する明度となる（ステップ３１０）。各フレーム（Ｖｂ電圧：信号電子エネルギー）に配色をし、表示色を決定する。配色は、式（２）に示した方法を使って決定する（ステップ３１１）。次に、信号処理方法を指定する。物質の特徴を示す信号を強調するといったことが必要な場合、信号の対数をとるなどして、微小信号を強調する指示を入力する（ステップ３１２）。入力指示に従い、信号の補正を行う（ステップ３１３）。フレームごとの画像を作成する（ステップ３１４）。ステップ３０３で求めた基準画像に対して、マッチングを行い、各フレーム画像の位置を調節する（ステップ３１５）。調整後、それぞれのフレーム画像を合成する（ステップ３１６）。これで、１枚の観察画像が出来上がる。ステップ３１６では、所望のエネルギーの画像のみを表示するようにしてもかまわない。そうすることによって、特定エネルギー特性をもった試料上の個所の分布、面積比等をわかりやすく表示することができる。
【００３６】
図９は、本発明による走査形電子顕微鏡の他の実施例を示す概略図である。図９において、光軸上に二次電子１０９を透過できる多孔電極１１２と対向電極１１１、および該電極で発生する電界Ｅとほぼ直交する磁界Ｂを発生させる図１０に示した磁界発生用コイル２１３，２１４を配置して、二次電子１０９と反射電子１１０の軌道を偏向させる構成となっている。多孔電極１１２と対向電極１１１の電位差を±Ｖｅ（Ｖ）、磁界発生用コイル２１３，２１４の励磁電流をＩｂ（Ａ）、一次電子線の加速電圧をＶａｃｃ（Ｖ）、多孔電極１１２と対向電極１１１、および磁界発生用コイル２１３，２１４の形状で決まる定数をＫｅ，Ｋｂとしたとき、特許公報第３２９１８８０号記載のように、次式の関係を保つようにＩｂおよびＶｅを制御し、比例定数Ｋ１，Ｋ２は一次電子線に偏向作用を及ぼさない条件に設定する。
【００３７】
【数４】

【００３８】
多孔電極１１２を透過した二次電子１０９の軌道を見込む位置に二次電子検出器１２０配置して検出する。また、反射電子軌道は二次電子と分離され、その反射電子軌道上に反射電子を二次電子に変換する二次電子変換電極４４０を配置する。この電極に負の電圧を印加すると反射電子は電極に衝突して、電極表面からエネルギーの小さい二次電子を発生する。直交電磁界の強さは、一次電子線１０４に対して偏向作用を及ぼさないように設定されているが、一次電子線に比較してエネルギーの小さい二次電子４５０は、磁界よりも電界によって強く曲げられる。その結果、多孔電極側に強く偏向されて多孔電極１１２を透過し、多孔電極を見込む位置に配置された電子検出器１２０で検出される。
【００３９】
また、多孔電極１１２の下部に軸対称電極４４１を配置してこの電極に適当な負の電圧を印加すると、試料から発生した二次電子はこの軸対称電極を進行できずに試料側にはね返される。このように、軸対称電極４４１に印加する負電圧にしたがって、低エネルギー電子による信号が切り捨てられる。そして、エネルギーの高い反射電子のみが多孔電極上部に配置した変換電極４４０で二次電子４５０に変換される。この変換された二次電子４５０は、試料からの反射電子情報を反映しているため、この信号で像形成することは、試料からの反射電子信号で像形成することと等価となる。電子検出器１２０は、二次電子変換電極４４０で発生し、引き込まれる二次電子と、試料から放出され電磁界発生器によって偏向される二次電子を同じように検出できるため、電磁界発生器によって広い範囲に軌道分散（エネルギー分散）する反射電子、及び二次電子を高効率に検出することができる。
【００４０】
軸対称電極４４１に印加する負電圧は、図１における電子検出器１２０の正のバイアス電圧Ｖｂの逆の作用がある。したがって、図２（ａ）で示したＶｂの変化のように、可変電圧電源２０１から軸対称電極４４１に印加するバイアス電圧Ｖｂ’を、図１１（ａ）に示すように、試料画像の取り込み時にＮ段に分割し、１フレーム画像取り込みごとにＶｂ’を段階的に印加して行くようにする。こうすると図２（ｃ）で示したのと同様に、電子検出器１２０には、図１１（ｂ）に示したような信号電流が得られる。
【００４１】
図１２は、本発明による走査形電子顕微鏡の他の実施例を示す概略図である。この走査形電子顕微鏡は、図９の装置における反射電子および二次電子のエネルギーをフィルタリングする機能をより強化したものである。低エネルギーの二次電子が直交電磁界部に入射すると、電磁界によって偏向され、多孔電極１１２を通って電子検出器１２０に向かう。このとき、多孔電極１１２と電子検出器１２０との間に、多孔電極１１３があり、これに負電圧を印加して、ここを通過する二次電子をそのエネルギーで制限する。比較的エネルギーの高い反射電子も同様に、直交電磁界以内に設けた負電圧が印加できる多孔電極１１４を通過するときにフィルタリングされ多孔電極１１４の電位を越えるエネルギーを持った電子のみがここを通過する。
【００４２】
多孔電極１１３と１１４は同一の電源Ｖｂ’に接続されている。多孔電極１１４を通過した電子は、二次電子変換電極４４０に衝突し、二次電子４５０を発生する。この二次電子４５０も直交電磁界部の多孔電極１１２を通って電子検出器１２０へ達する。試料１０７と電子検出器１２０の間には、必ず負電位の多孔電極１１３もしくは１１４があるので、一次電子線１０４の照射によって試料１０７上で発生した二次電子１０９、および反射電子１１０は、この負電位を越えられるエネルギーを持つもののみが検出器１２０にて検出される。比較的高エネルギーの反射電子は、二次電子変換電極４４０に衝突して二次電子４５０を発生することで信号量を増幅することができる。
【００４３】
直交電磁界内の多孔電極１１４は、接地されている多孔電極１１７にはさまれており、一次電子線１０４が通る光軸中央部は、シールド筒１１６によって電磁シールドされている。したがって、多孔電極１１４の負電位は、一次電子線１０４の軌道に影響を与えることはない。この構造により、低エネルギー二次電子から高エネルギー反射電子まで連続的に確実にエネルギー分析することができる。さらに、取得する信号電子のエネルギーを変更するよう電極の電圧を変更しても、一次電子線の軌道にはなにも変化を出さず、影響を与えないので、画像フレームを重ねるときに像位置がずれるという恐れがない。低エネルギー電子の信号量をできるだけ増大させるためには、軸対称電極４４１には、数十Ｖの正電圧が印加されていることが望ましいが必ずしも不可欠ではない。
【００４４】
図１３は、本発明による走査形電子顕微鏡の他の実施例を示す概略図である。この走査形電子顕微鏡は、図９の電子検出器１２０の代わりにアレー状の電子検出器１２１を配置したものである。
【００４５】
アレー状の電子検出器１２１は、複数の検出器を一列に並べたようなものである。この検出器の列が、図１３において、軸方向、縦に並ぶように配置する。こうすることで、エネルギーの低い二次電子は、直交電磁界によってすぐに偏向され、アレー状の電子検出器１２１の下部で検出される。一方、エネルギーの高い反射電子等は、図１３において、アレー状の電子検出器１２１の上方で検出される。
【００４６】
このようにアレー状の電子検出器１２１を使うことによって、信号電子のエネルギー分布を、電極等の電圧を変化させずに、信号電子を検出する検出器要素の位置によって計測することができる。アレー状の電子検出器１２１のそれぞれの検出器の数がＭ個有った場合、Ｍ段階に信号電子のエネルギーを分析できる。信号変換器１６０では、これらＭ段の信号を並列で処理し、それぞれの検出器要素の信号ごとに色を割り当てる。これら各検出要素で検出した信号に色成分及び信号強度情報を付加して、スキャン信号に同期させて１枚の画像を仕上げる。この場合、１フレームの画像が既に複数色（Ｍ色）のカラー画像になっていることが、上述の図１及び図９の実施例と異なる。通常の走査形電子顕微鏡と同様に、この１フレームの画像を複数枚取得して、それらを重ね合わせノイズを低減することができる。
【００４７】
図１４は、アレー状電子検出器の拡大図である。図１４（ａ）に示すように、検出器の前面には、シンチレータ９０１とその背面に位置する光電面９０２があり、その後ろにダイノードアレー９０３がある。シンチレータ９０１には、バイアス電圧１５３が印加してあり、これにより、このシンチレータ９０１に入射した信号電子は加速され、シンチレータに衝突したときにシンチレータ９０１を発光させる。光電面９０２およびダイノードアレー９０３にも、図のように高電圧９０４が印加してある。電圧１５３および９０４は、数ｋＶから数十ｋＶが望ましい。ダイノードアレー９０３の背面には収集電極アレー９０５がある。また、ダイノードアレー９０３全体には、側面から磁場Ｂが印加されている。
【００４８】
図１５（ａ）は、図１４（ａ）の拡大断面図である。ダイノードアレー９０３は、抵抗体の中にチャンネルごとに二次電子増倍用の通路を設けてある。この場合、この通路がＭ個あり、Ｍ個のチャンネルを形成している。この抵抗体の表面と裏面に金属電極を蒸着し、この電極に電圧を印加することで、各チャンネルに均一に電圧が印加できる。図１４（ｂ）にダイノードアレー９０３を示す。
【００４９】
試料表面から発生した信号電子は、シンチレータ９０１に入射し、シンチレータ９０１を発光させる。その光が光電面９０１に入射すると、裏面から電子を発する。電子は、ダイノードに入るが、ここで、ダイノードには、側面から磁場が印加してあるので、直進できずチャネル側面に衝突する。このとき、複数個の二次電子が発生し、また加速される。この電子もまた磁場によって、偏向され、ダイノード壁面に衝突し、さらに多くの電子を発生させる。このようにして、電子電流が増倍されて行き、最後に電極９０５に達する。
【００５０】
図１５（ｂ）は、ダイノードに抵抗体ではなく、金属電極を使った場合の図である。いくつかに分割された電極に電圧が印加されており、この電極内間を電子が増倍されながら進み、最後に電極９０５に達する。図１４（ｃ）に、この電極が並んだダイノードアレー９０６を示す。図１５（ａ）および図１５（ｂ）は、共に図示していないが、光電面９０２からダイノードアレー９０３、電極アレー９０６までは、ガラス管等で密封されており、外部の影響を受けない構造にしておくことが望ましい。
【００５１】
図１６は、本発明を試料が傾斜できるタイプの走査形電子顕微鏡に適用した例を示す図である。検出器の部分は、図９、図１２及び図１３記載の構成を使用してもかまわない。
【００５２】
図９及び図１６で取得した１フレームごとの画像を重ね合わせるとき、図１の実施例の場合と同様に軸対称電極４４１の電圧変化他の要因で、一次電子線のスキャン領域が、わずかに移動することがある。したがって、画像を重ね合わせるときには、それぞれの画像の明るさの相関をとり、画像がマッチするように重ね合わせて行く。この場合、まず、電極電圧等を変化させずに二次電子、反射電子すべての信号を取り込んだ、基準と成る画像を最初に取得、保存しておき、相関のベースとなる画像をこの全電子信号を含んだ画像にすると相関がとりやすい。
【００５３】
図１７，図１８は、本発明の走査形電子顕微鏡で試料を測定した場合の表示画面例を説明する図である。
図１７は半導体基板（シリコンオキサイド）に設けられたフォトレジスト２２１２のホール２２１０を測定した例の説明図である。図１７（ａ）は測定対象の概略形状を示し、ホール開口部近辺に起伏２２１４があり、その開口部近辺の試料表面が負に帯電している状態を表している。図１７（ｂ）はこのホールを開口部方向から一次電子線で走査した像を示しており、ホールの帯電していない壁面の定在波２２２０、底の部分の正確な像情報が得られているが、帯電している試料開口部近辺の正確な像状態は得られていないことを示している。図１７（ｃ）は一次電子線で試料を走査し、高エネルギー反射電子信号による試料表面像を現しており、ホールの底の部分の像は得られていないが、試料開口部近辺の正確な起伏状態が得られていることを示している。
【００５４】
通常、一次電子線で試料を走査したことにより発生する二次電子信号は、試料の表面から放出されるエネルギーの低い（数エレクトロンボルト程度）電子であるため、試料の表面から放出され試料の凹凸状態を忠実に反映するため、電子線の試料材料内部での散乱の影響を受けず、高い空間分解能の情報を備える特徴を持っている。しかし、従来の低エネルギー二次電子信号による分析方法においては、試料表面が負に帯電（以下、チャージアップと表現する）していると、低エネルギー二次電子の上昇がチャージアップによって妨げられてしまい、このため、ホール開口部近辺の起伏、即ち試料表面の凹凸状態を忠実に反映することが出来なくなってしまう現象がある。この現象によって帯電している試料開口部近辺の正確な像情報が得られていないことを図１７（ｂ）の試料像は示している。これに対し図１７（ｃ）に示した試料像は、高エネルギー反射電子によるものであるが、低エネルギー二次電子では得られていない試料開口部近辺の正確な起伏状態が判明していることを示している。
【００５５】
以下、本発明の走査形電子顕微鏡において、高エネルギー反射電子により正確な試料像を検出することができる理由を述べる。従来の高エネルギー反射電子検出方法においては、エネルギーが高い高加速電圧の一次電子線で試料を走査しているので試料の深部に入り込み、これに対応して試料の深部からエネルギーが高い反射電子（ほぼ加速電圧と同じエネルギー）を発生させるものである。このため一次電子線の試料内部散乱の影響で高エネルギー反射電子の発生領域が広がり空間分解能は低下するが、その信号は試料表面の凹凸状態の他に組成情報を多く含む特徴を持っているため、従来方法においては主に試料内の組成情報を得るためにエネルギーが高い反射電子を検出していた。また、従来の高エネルギー反射電子検出方法として、低加速の一次電子線で試料を走査し、試料の表面近くで高エネルギー反射電子を発生させ、なるべく空間分解能を低下させずに高エネルギー反射電子を検出する方法も存在するが、従来例の方法では試料に一次電子線を照射することにより発生する低エネルギー二次電子と、高エネルギー反射電子を正確に分別して検出する手段がなく、高エネルギー反射電子信号としてとられた信号には低エネルギー二次電子が混入してしまっていたため、結果的に高い分解能を持つ高エネルギー反射電子検出方法は存在しなかった。
【００５６】
これに対し本発明の装置においては、電子源から試料までの光学系上に試料から生じた高エネルギー反射電子および低エネルギー二次電子を連続的に分離する電極を設けこの電極が発生する電界によって、または図１３に示した構成のように、これら試料から生じた高エネルギー反射電子および低エネルギー二次電子の軌道を分離する電磁界を設けることによって、それぞれのエネルギーに対応した位置で反射電子、および、二次電子をエネルギー別に連続的に検出することが出来るので、高エネルギー反射電子のみによる試料像の形成を始め、特定のエネルギーの信号電子のみによる試料画像を形成することを可能にしている。そして、本発明の一次電子線照射，高エネルギー反射電子検出方法においては、従来の高エネルギー反射電子の発生方法と異なり加速電圧を低く、即ちエネルギー状態を低くした場合においても、高エネルギー反射電子と低エネルギー二次電子をエネルギー別に連続的に分別して、比較的低いエネルギー状態の高エネルギー反射電子のみで試料像を形成することを可能にしている。
【００５７】
このため、加速電圧が低い一次電子線は試料表面の浅い部分にしか入り込まず、試料からの高エネルギー反射電子は浅い部分から放出されるようになるため、この高エネルギー反射電子の信号には試料の組成情報に対して、試料の凹凸状態の情報が多く含まれるので、この状態の高エネルギー反射電子の信号を検出することによって、従来の二次電子走査と同等の試料像を形成することを可能にしている。また、絶縁物等の観察において試料が負に帯電（チャージアップ）している場合においても、上述したようにエネルギーの低い二次電子はその発生過程で試料表面の帯電の影響を受けるため、低エネルギー二次電子信号には試料の凹凸情報が忠実に反映されなくなるが、二次電子に比較してエネルギーレベルの高い反射電子では、帯電の影響を受けないため、試料の帯電があっても試料の凹凸情報を安定して得られるようになる。
【００５８】
これから、本発明の一次電子線照射，高エネルギー反射電子検出方法により、試料表面の情報を、その表面が帯電していても正確に検出できることを、図１７（ｃ）の開口部近辺の試料像は示している。そして、本発明の走査形電子顕微鏡によれば、一次電子線照射に同期して、反射電子信号，二次電子信号をそれぞれエネルギー別に検出し、また、図１３のような構成を使うことによってそれぞれのエネルギーの電子を同時に検出できるので、試料が帯電しない状態で凹凸情報のみを高分解能に観察するための、低エネルギー二次電子の検出、および、組成情報を主に観察するため、また帯電している試料の凹凸観察のための、高エネルギー反射電子の検出、これら両方を同時に観察するための、低エネルギー二次電子から高エネルギー反射電子までの検出を連続的に可能にしている。
【００５９】
さらに、本発明の走査形電子顕微鏡によれば、高エネルギー反射電子信号による対象試料の像と、低エネルギー二次電子信号による対象試料の像を重ねあわせて試料像の情報を構築することを可能にしている。例えば、図１７（ｂ）の低エネルギー二次電子信号による対象試料の像は、ホールの開口部が帯電しているためその側面，底部しか正確な試料凹凸情報を得られていないが、図１７（ｃ）の高エネルギー反射電子信号によれば、開口部の正確な凹凸情報が得られているため、これらの試料像を重ねあわせること、即ち、ホールの内部を低エネルギー二次電子信号による試料像で、そして、その外部を高エネルギー反射電子による試料像を用いることにより、ホール全体の対象試料の情報を得ることが可能になる。さらにそれぞれの信号電子のエネルギーによって画像を色別に合成し１枚の画像を形成することができる。
【００６０】
図１７（ｄ）は、に全エネルギーの電子信号を合成した像の説明図である。図１７（ｄ）は、エネルギー別に色付けをしたカラー像となっている。図１７（ｄ）により、ホール内の側面、底部の凹凸情報と共に、ホール開口部の凹凸情報、および、レジスト表面の起伏の状態が同時に観察できると共に、それぞれが、二次電子や反射電子の信号電子エネルギーによって色分けされているので、レジスト表面の帯電のしやすさや、組成の違い等が、色の違いとして表示されている。
【００６１】
図１８は、半導体基板（シリコンオキサイド）に設けられたフォトレジスト２２１２のホール２２１０の断面を測定した例の説明図である。図１８（ａ）は測定対象の概略形状を示し、半導体基板（シリコンオキサイド）上に形成されたフォトレジスト中に、レジスト形成中に発生した定在波２２２０がいくつかの層状に存在していることを表している。尚、このフォトレジスト２２１２は帯電していない状態にある。
【００６２】
図１７（ｂ）は、このホール２２１０の断面を断面方向から一般的な一次電子線走査，低エネルギー二次電子検出方法で構成した試料像を示しており、断面形状の凹凸状態を忠実に反映し、かつ、高い空間分解能を持つ試料像が得られていることが示している。図１７（ｃ）は一次電子線走査，高エネルギー反射電子検出方法による試料像を示しているが、試料からの高エネルギー反射電子には対象試料中の組成情報が多く含まれるので、これを検出することによってこのフォトレジスト中にレジスト形成時に発生した定在波が、いくつかの層を形成して存在していることが示されている。これは、高エネルギー反射電子が低エネルギー二次電子と比較して試料の深部から発生し、この高エネルギー反射電子信号にはその組成の相違が現れるようになるためである。
【００６３】
そして、本発明の走査形電子顕微鏡によれば、一次電子線照射に同期して、高エネルギー反射電子信号から低エネルギー二次電子信号までそれぞれを連続的に明確に分離して同時に検出できるので、試料の凹凸情報と組成情報の両方を精密に対比して観察することが可能である。これにより、例えば試料がこわれやすく、電子線をあまり照射しないで試料の表面情報および組成情報を検出したい場合でも、一回の試料への一次電子線照射によって、凹凸情報と組成情報の両方を精密に得ることができるので、従来の複数回一次電子線を照射しなければ試料の表面情報と組成情報が得られない方法と比較して、試料へのダメージを最小限に抑えることができるので、広い範囲の試料測定アプリケーションに対応することができる。
【００６４】
さらに、本発明の走査形電子顕微鏡によれば、高エネルギー反射電子信号による対象試料の像と、低エネルギー二次電子信号による対象試料の像を重ねあわせて試料像の情報を構築することが可能になる。本実施例の図１８（ｂ）の低エネルギー二次電子信号によれば、正確な試料表面情報が得られ、図１８（ｃ）の高エネルギー反射電子信号によれば、レジストの組成状態の情報が得られているため、これら２つの試料像を重ねあわせることにより、試料の表面状態と組成状態を容易に比較して表示できる。また、表示するための信号処理方法として、単にそれぞれの画像の輝度調整のみでなく、それぞれの画像状態に応じて所定の色情報を付加することによって、試料の表面状態と組成状態を容易に比較して表示することが可能である。
【００６５】
図１８（ｄ）は、全エネルギーの電子信号を合成した像の説明図である。図１８（ｄ）では、エネルギー別に色付けをしたカラー像となっている。これにより、ホール内の正確な試料表面情報とレジストの組成状態の情報が同時に観察できると共に、それぞれが、二次電子や反射電子の信号電子エネルギーによって色分けされているので、組成の違い等が色の違いとして表示されている。
【００６６】
本発明の走査形電子顕微鏡による画像表示の他の例についてさらに説明する。図１９は、半導体基板（シリコンオキサイド）上の異物の画像例を示す図である。異物の部分が持つエネルギーの周辺の画像だけ表示したものが、図１９（ｂ）である。このように、表示するエネルギー範囲を限定することで、異物を特定しやすくなる。自動で画像処理により異物の位置を特定する場合にも、予め予想される異物のエネルギー範囲のデータを取得しておき、そのエネルギー範囲に着目し、その画像によって異物の位置を特定することで、より正確に異物を捉えることができる。特にこの方法は、異物の位置が見つかりにくい場合に有効である。低倍率で広い面積範囲にわたって目標の物体・異物の特性エネルギー範囲の画像を調べることにより、従来の画像認識の方法では、捕まえられなかった異物を捕まえることができる。
【００６７】
また、各エネルギー画面を合成した画像である図１９（ａ）では、異物を例えば赤系等の目立つ色で表示することで、人間にも確認しやすいように表示させることができる。図１９（ｃ）は、異物のエネルギー範囲以外のあるエネルギー範囲の画像を表示したものである。単純なモノクロ画像では確認しにくい、表面の組成の相違、小さな凹凸が黒点として確認される。
【００６８】
図２０は、ポリシリコンラインをエッチングした後、アッシングしたサンプルの画像を示している。ポリシリコンラインの左右に異物が付着していることが確認できる。図２０（ｂ）は、特に異物のみが発する信号電子のエネルギー範囲のみで作成した画像である。この部分に赤系等の目立つ配色を割り当て、図２０（ａ）に示すようにカラー画像を作成することにより、異物の存在やその位置がわかりやすい画像を作成できる。図２０（ｃ）は、異物のエネルギー範囲以外のあるエネルギー範囲の画像を表示したものである。単純なモノクロ画像では確認しにくい、表面の組成の相違、小さな凹凸が黒点として確認される。
【００６９】
図２１は、シリコン基板上の薄膜積層試料の断面の説明図である。図２１（ｂ）は、同一の試料断面をエネルギーの異なる信号電子を用いて形成した走査像である。信号電子のエネルギーによって走査像に現れる層が異なっている。これら信号電子のエネルギーの異なる各走査像にそれぞれ特定の色を割り当て合成することで、層毎に色の異なるカラー画像である図２１（ａ）が得られる。図２１（ａ）により、この１枚の画像で、各層の厚み、材料の混ざり具合、各層相互の関係等を一目で認識できる。
【００７０】
【発明の効果】
本発明によれば、観察試料の微細構造だけでなく、物質的な分布をもカラー表示で識別することが可能になる。
【図面の簡単な説明】
【図１】本発明による走査形電子顕微鏡の一実施例を示す概略図。
【図２】（ａ）は電子検出器に印加する電圧Ｖｂの変化の様子を示す図、（ｂ）は一次電子線のＹ方向の偏向走査信号の図、（ｃ）は１画像取得時の信号電子電流の平均推移を示す図、（ｄ）は信号電子のエネルギー分布を示す図、（ｅ）は信号電子のエネルギー分布に対応した配色分布とＲＧＢ成分の分布を示す図。
【図３】二次電子、反射電子のスペクトルの説明図。
【図４】電子信号曲線：ｆｓ（Ｅ）がＥ１，Ｅ１＋δの間で作る面積ΔＳの説明図。
【図５】信号量に比例して、色変化が大きくなるように配色を分布させた例を示す図。
【図６】信号電子のエネルギー分布で微小信号を強調した例を示す図。
【図７】バイアス電圧の変化を数フレーム毎に変化させる例を示す図。
【図８】本発明による分析信号の処理手順を示すフローチャート。
【図９】本発明による走査形電子顕微鏡の他の実施例を示す概略図。
【図１０】直交電磁界発生部の平面構成図。
【図１１】（ａ）は軸対称電極に印加するバイアス電圧Ｖｂ’の変化の様子を示す図、（ｂ）は１画像取得時の信号電子電流の平均推移を示す図。
【図１２】本発明による走査形電子顕微鏡の他の実施例を示す概略図。
【図１３】本発明による走査形電子顕微鏡の他の実施例を示す概略図。
【図１４】アレー状電子検出器の一実施例を示す図。
【図１５】アレー状電子検出器の拡大図。
【図１６】本発明を試料が傾斜できるタイプの走査形電子顕微鏡に適用した例を示す図。
【図１７】本発明の走査形電子顕微鏡で試料を測定した場合の表示画面例を示す図。
【図１８】本発明の走査形電子顕微鏡で試料を測定した場合の表示画面例を示す図。
【図１９】本発明により異物試料を観察した例を示す図。
【図２０】本発明により異物試料を観察した例を示す図。
【図２１】本発明により多層材料を観察した例を示す図。
【符号の説明】
１０１…陰極、１０２…第一陽極、１０３…第二陽極、１０４…一次電子線、１０５…収束レンズ、１０６、２０６…対物レンズ、１０７、２０７…試料、１０８…偏向コイル、１０９，４５０…二次電子、１１０…反射電子、１１１…対向電極、１１２…多孔電極、１１３、１１４…エネルギー制御用負電位多孔電極、１１７…接地電極、１１５…絞り装置、１１６…シールド筒、１２０…信号電子検出器、１２０…アレー状信号電子検出器、１２５…表示装置（ＣＲＴ・ＬＣＤ）、１４０…走査形電子顕微鏡制御システム、１５０…ＣＰＵ、１５１…可変電圧電源、１５２…記憶装置（メモリ、ハードディスク）、１５３…バイアス電源、１５４…入力装置、１５５…画像積算器、１５６…表示装置Ｉ／Ｆ、１６０…信号変換器、１７０…収束レンズ制御器、１７４…対物レンズ制御器、１７６…走査制御器、１７８…信号処理器、２１３，２１４…直交磁界発生コイル、４４０…二次電子変換電極、４４１…軸対称電極、９０１…シンチレータ、９０２…光電面、９０３…アレー状ダイノード、９０４…バイアス電圧、９０５…電極アレー、９０６…アレー状ダイノード、２２１２…フォトレジスト、２２１０…コンタクトホール、２２１４…フォトレジスト上の起伏、２２２０…定在波。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electron beam apparatus, and more particularly to a scanning electron microscope that detects signal electrons such as reflected electrons or secondary electrons generated from a sample and displays a sample scanning image based on the detected signal electrons.
[0002]
[Prior art]
The scanning electron microscope scans the surface of the sample for observing the accelerated primary electron beam in a two-dimensional manner, detects signal electrons such as reflected electrons or secondary electrons, and detects their signal intensity ( The signal current) is synchronized with the scanning signal, and is enlarged and displayed two-dimensionally on the display device as an image. The signal electrons are mostly secondary electrons with relatively low energy. However, not only the low-energy secondary electrons from the sample surface irradiated with the primary electron beam, but also the reflected electrons that are elastically reflected with almost the same energy as the primary electron beam, and the reflected electrons and the low-energy secondary electrons. Electrons with energy in the range between electrons are also emitted. Thus, the energy of the signal electrons is continuously distributed from 0 to the energy value of the primary electron beam, and the ratio of these distributions reflects the properties specific to the sample and its material. Conventional conventional scanning electron microscopes simply detect the sum of these signal electrons as a signal current or signal intensity without distinguishing these electrons, and display pixels on the display device according to the intensity. As an image. Further, there is a technique in which a backscattered electron detector and a low energy secondary electron detector are provided as in Patent Document 1, and each signal can be measured independently. Patent Document 1 describes that an image based on a reflected electron signal and a secondary electron signal, and an image obtained by synthesizing these images are displayed. In addition, it is also described that either a reflected electron signal or a secondary electron signal, or each detected signal level is converted into a color signal to be displayed on a display device and synthesized. As a result, it is possible to distinguish and display a slightly different portion as a color difference on the same sample depending on the reflected electron and secondary electron signals. In this case, there are two types of original images to be combined: a reflected electron signal image and a secondary electron signal image, and the combined image is a two-color display image.
[0003]
[Patent Document 1]
JP-A-7-192679
[0004]
[Problems to be solved by the invention]
When the reflected electron signal and the secondary electron signal are displayed in different colors, the amount of information is larger than that of a conventional monochrome image. However, the distribution characteristics of the signal electrons distributed continuously from 0 to the energy value of the primary electron beam, that is, the inherent characteristics of the sample cannot be displayed.
[0005]
An object of the present invention is to provide a scanning electron microscope capable of displaying an image reflecting the difference in characteristics of signal electrons such as reflected electrons and secondary electrons generated when a sample is irradiated with a primary electron beam.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, a function for identifying the energy value of the signal electrons is added to the portion of the signal electron detector that measures the signal electrons emitted from the sample by the irradiation of the primary electron beam. Then, the energy distribution of the signal electron intensity is measured, a color is assigned to each energy value, an image is configured with brightness corresponding to the signal intensity of each energy value, and an image of each energy value and a composite image thereof are obtained. Displayed.
[0007]
According to the present invention, the energy distribution / characteristics of signal electrons such as reflected electrons and secondary electrons generated when a sample is irradiated with a primary electron beam by a scanning electron microscope is faithfully displayed as a color image on a display device. Therefore, not only the two-dimensional fine surface structure of the sample but also information such as the difference and distribution of the sample substance can be displayed, observed and confirmed at the same time. Basically, electrons can be detected regardless of the energy state of the electrons. Therefore, when detecting backscattered electrons in a high energy state and examining the composition of the sample, high energy backscattered electrons and low energy secondary electrons Can be separated and detected continuously, and an accurate composition analysis can be performed. Therefore, not only can the low-energy secondary electron signal and the high-energy reflected electron signal be selectively detected or synthesized according to the purpose and the state of the sample, but also the difference in material properties of the sample can be expressed in color. Since these images can be observed as a single color image, an image having a larger amount of information than a monochrome image of a conventional scanning electron microscope can be provided, and the unevenness information and composition information can be confirmed with a single image. In addition, the state of the sample can be grasped sensorially and sensitively from the color tone.
[0008]
Also, in the past, materials that could not be identified without X-ray analysis etc. could now be predicted by scanning electron microscope images, greatly improving analysis time and efficiency. Can be made. In addition, when applied to semiconductor device manufacturing lines, the potential abnormality / defects of wiring, plugs, and hole bottoms can be displayed in different colors when observing the semiconductor substrate being manufactured, increasing the efficiency of defect analysis. Can do. In addition, even when there is a foreign substance on the surface of the substrate, the foreign substance can be displayed in a color different from that of a normal surface substance, so that the foreign substance can be easily found and the efficiency of foreign substance inspection, analysis, and analysis can be improved. In particular, when there are resist residues after etching, the resist residue is displayed in a color different from that of the substrate such as Si, so the presence or absence of residues can be checked immediately, and the distribution is also Since it is displayed clearly, the degree of good or bad can be grasped sensuously. Furthermore, the amount of residue can be quantitatively evaluated from the ratio of the distribution area by image processing. In addition, since information that could not be obtained conventionally can be displayed, it can be expected that a new discovery will be made from the image.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. In the following drawings, the same functional parts are denoted by the same reference numerals, and redundant description is omitted.
[0010]
FIG. 1 is a schematic view showing an embodiment of a scanning electron microscope according to the present invention. The primary electron beam 104 radiated from the cathode 101 by the voltage V1 applied to the cathode 101 and the first anode 102 is accelerated to the voltage Vacc applied to the second anode 103 and proceeds to the subsequent lens system. The primary electron beam 104 is focused as a minute spot on the sample 107 by the focusing lens 105 controlled by the focusing lens controller 170 in the scanning electron microscope control system 140 and the objective lens 106 controlled by the objective lens controller 174. The sample is scanned two-dimensionally by the two-stage deflection coil 108. The scanning signal of the deflection coil 108 is controlled by the CPU 150 via the scanning controller 176 according to the observation magnification designated by the input device 154.
[0011]
Secondary electrons 109 and reflected electrons 110 are emitted from the primary electron beam irradiation point of the sample 107. The secondary electrons 109 and the reflected electrons 110 travel upward while being spiraled under the influence of the magnetic field by the objective lens 106 and are captured by the electron detector 120. Signals from the electron detector 120 are input to a signal converter 160, where each signal is amplified with an arbitrary gain including zero and then converted to a digital signal. These signals are signal-processed by the signal processor 178 according to instructions from the CPU 150, and after that, or before the signal processing, the data signal is stored in the storage means 152 such as a memory. Then, using the backscattered electron, secondary electron signal, or processed signal stored in the storage unit 152, the CPU 150 transmits the backscattered electron image, secondary electron of the sample to the display device 125 such as a CRT via the interface 156. The image and the magnified sample image with the processed signal are displayed. Further, it has a function of displaying the sample images in real time while scanning the sample 107 without using the storage means.
[0012]
Here, by changing the voltage Vb applied to the signal detector 120 by the variable voltage power supply 151, the signal electron currents such as the secondary electrons 109 and the reflected electrons 110 detected by the signal detector 120 are limited. Yes. When the voltage of the variable voltage power supply 151 applied to the signal detector 120 is low, the low-energy secondary electrons 109 are not easily drawn, and only high-energy signal electrons such as the reflected electrons 110 are detected. Further, as the voltage Vb of the variable voltage power supply 151 applied to the signal detector 120 is increased, the amount of low energy secondary electrons taken in increases accordingly, and the ratio increases. Thus, the energy of the signal electrons entering the electron detector 120 is changed by means such as changing the voltage applied to the electron detector 120, and the energy of the signal electrons is controlled by the signal processor 178 and the CPU 150. Perform spectral analysis. Furthermore, according to the energy value and the intensity, the color and the brightness are respectively assigned, the images of the energy values and the images of the energy values are combined into one image and displayed in color.
[0013]
The voltage Vb applied to the electron detector 120 from the variable voltage power supply 151 is changed stepwise as shown in FIG. 2A during capturing of signals such as the secondary electrons 109 and the reflected electrons 110. This change is performed in synchronization with the deflection scanning signal of the primary electron beam as shown in FIG. In this case, one wavelength is changed in synchronization with a deflection scanning signal in the Y direction corresponding to one frame of an image. In the preparation of an observation image in the scanning electron microscope, the observation region is two-dimensionally scanned with the primary electron beam 104, and the intensity of signal electrons such as the secondary electrons 109 and the reflected electrons 110 generated from the sample 107 at that time is scanned. Corresponding to the above, it is reproduced on the display device 125 as a two-dimensional image. An image of one frame is created by scanning the primary electron beam 104 repeatedly in the X direction and two-dimensionally scanning it while shifting the scanning position in the Y direction. The deflection scanning control signals in the X and Y directions are sawtooth waves as shown in FIG. In this case, one peak of the sawtooth wave of the deflection scanning control signal in the Y direction corresponds to one frame. When creating an image, the observation area is scanned two-dimensionally at high speed, multiple image frames are acquired for the same area, and the images are combined to create an image with reduced charge-up effects and noise. Can be made.
[0014]
In the case of the present invention, specifically, for example, image capturing is started and a maximum voltage of Vb is applied to the electron detector 120. When the first one-frame image capturing is completed, the voltage Vb is decreased by one step, and the second frame image is captured. When the number of frames of the acquired image is N frames. The bias voltage Vb is divided into N stages from the maximum value to the minimum value, and the voltage is changed by one stage every time one frame image is acquired. The relationship between Vb and the deflection scanning signal in the Y direction, that is, the timing of image acquisition is shown in FIGS.
[0015]
FIG. 2C is obtained as an example of the intensity transition of the signal electrons such as the secondary electrons 109 and the reflected electrons 110 at this time. The vertical axis in FIG. 2C is the signal electron intensity Is. FIG. 2C may be regarded as a change in the bias voltage Vb of the total signal electron current for one frame image detected by the electron detector 120, or the signal current for each pixel assigned to the observation region. It may be considered that the change to the bias voltage Vb. When this is considered as a change of the signal current of one pixel with respect to the bias voltage Vb, such a signal spectrum exists for the number of pixels.
[0016]
When this signal spectrum is differentiated, an energy distribution of signal electrons as shown in FIG. 2D is obtained. The peak at the right end of the spectrum is a signal of the reflected electrons 110 that the primary electron beam is elastically reflected from the sample. The spectra of secondary electrons and reflected electrons are shown in ADRIANUS J. et al. Dekker: Solid physics (corona, Takayoshi Hashimoto, Masahide Kamiyama, page 458). This is shown in FIG. In FIG. 3, a small maximum inherent to the sample substance exists in the portion b. These correspond to primary electron beams that are inelastically reflected losing certain discrete energy before escaping from the surface. Most of the signal electrons are in a broad peak C with relatively low energy. The energy distribution of these electrons hardly depends on the energy of the primary electron beam. Even in actual measurement, a signal spectrum similar to this is obtained for a single metal sample.
[0017]
Colors such as purple, blue, green, yellow, and red are continuously assigned from the maximum value to the minimum value of the energy range of such a spectrum. Then, an image corresponding to each energy level is displayed in an assigned color, and those images are synthesized over all frames, thereby obtaining an observation image having a color expressed in a color corresponding to the energy of the signal electrons. it can. As a result, not only the two-dimensional surface structure can be represented in the observed image, but also the unique reflected electron energy value produced by the material corresponding to each pixel can be expressed in color, so that differences in material and material can be confirmed at the same time. Can do.
[0018]
FIG. 2E shows an example in which the signal electrons are continuously assigned from the maximum value to the minimum value in the order of shortest visible light color wavelengths such as purple, blue, sky blue, green, yellow, and red. When this is decomposed into three elements of the three primary colors RGB of the image display function, a distribution as shown in FIG. In FIG. 2 (e), each RGB value is independently changed from the maximum value to the minimum value, and a combination of these values enables color display of a plurality of colors. If each RGB value gradation is 16 gradations, in principle, a maximum of 16 × 16 × 16 = 4096 colors can be expressed. Further, if each RGB value gradation is 256 gradations, it is possible in principle to express 256 × 256 × 256 = 16,777,216 colors.
[0019]
In FIG. 2D, when the maximum value of the signal spectrum for all the pixels is assigned as the maximum value of lightness, and half of the value is assigned as the median value of lightness, FIG. The distribution of each gradation is shown. For example, in FIG. 2E, when the signal intensity corresponding to “green” is equal to or lower than the median value, the brightness of the pixel can be lowered by lowering the G: green gradation according to the ratio. When the lightness is maximum in purple near the maximum energy value, the lightness can be maximized by increasing the gradation of G: green to the maximum. For the other intermediate colors, the gradations of RGB are adjusted so that the brightness corresponds to the signal intensity of each energy. For example, when the signal intensity corresponding to green is the maximum, the brightness can be maximized by maximizing both the red: R and blue: B gradations.
[0020]
The image acquired in each frame is a part of the spectrum of signal electrons having an energy width obtained by dividing (dividing) the acceleration energy of the primary electron beam by the number of image frames (see FIG. 4). At this time, the color tone expressed in one frame is basically one color, and the brightness of the screen is determined by the amount of signal electrons corresponding to the scanning of the primary electron beam, and the brightness is brighter toward the white from the point where the grade is maximum. 256 gradations can be obtained, and 256 gradations can be obtained darker toward black. Therefore, from FIG. 2E, the number of colors that each pixel of each image frame can take is 256 × 5 colors × (256 × 2 gradations) = 655,360 colors. By overlapping these image frames, a maximum of 256 × 256 × 256 = 16,777,216 colors can be used.
[0021]
For image synthesis, addition for each corresponding pixel is desirable. When synthesizing each image frame to create one image, the tone values of the red, yellow, blue, RGB, or CMYK color elements of the corresponding pixels of each image frame are simply added, and the addition result is It is desirable to distribute evenly to each color and tone. For example, if the RGB values of each pixel of the image are added for synthesis and the maximum values are R: 4025, G: 3602, and B: 4226, the values of the individual pixels (Rij, Gij, Bij) If the result of simple addition (Rij, Gij, Bij) is Rij = Rij × 256/4625, Gij = Gij × 256/3602, Bij = Bij × 256/4226 it can. Various other color assignments may be devised. For example, the arrangement order of the energy from red to purple can be changed so that the signal on the high energy side corresponds to red and the signal on the low energy side corresponds to purple.
[0022]
In order to express changes effectively, it is also possible to make the distribution of the color scheme in the middle non-linear, for example, to distribute so that the color change is large on the low energy side where the signal change is large in FIG. It is. As shown in FIG. 4, the change in color scheme in a certain energy region is proportional to the area formed by the signal curve and the horizontal axis. Thereby, the change of the signal can be effectively expressed by the change of the color. The number of added image frames is N. As shown in FIG. 4, when ΔS is an area formed by the curve fs (E) of the electronic signal for a region from a certain energy E1 to E1 + δ, a change in color scheme is made proportional to ΔS. The area S created when the energy of the signal electrons is between “0” and the maximum value “Emax” is expressed by the following equation.
[0023]
[Expression 1]

[0024]
This is a value proportional to the total charge amount of electrons detected by the electron detector 120 when one image is acquired. Thereby, the color change rate C (E1) in the energy E1 is expressed by the following equation. Here, k is usually a constant 1.
[0025]
[Expression 2]

[0026]
FIG. 5 is an example in which the color scheme is distributed so that a large color change is applied to a portion with a large amount of signal with respect to the signal spectrum of FIG. Here, assuming that 256 × 5 basic colors excluding light and dark are used, the change in the basic color scheme between adjacent frames is usually 256 × 5 / N. The ratio of the color change of the frame corresponding to the energy E1 can be expressed by the following equation by multiplying this by the value of the equation (2).
[0027]
[Equation 3]

[0028]
In FIG. 2 (d), the material features of the sample appear in small peaks such as a, b, c, and d with relatively high energy. Various methods are conceivable for highlighting and displaying the characteristics of the sample substance on the display image. As an example, by taking the logarithm of this signal current spectrum and displaying the image corresponding to this, a, b , C, d, etc. can be emphasized. This state is shown in FIG. In FIG. 6, the solid line is a spectrum obtained by taking the logarithm of the signal current spectrum indicated by the broken line.
[0029]
For applications where you want to confirm the distribution of substances that emit an electronic signal at a specific energy value, display the target image by displaying a conspicuous color such as red in such an energy band. Can make it easier.
[0030]
When superimposing images for each frame, the scan region of the primary electron beam may move slightly due to changes in electrode voltage and other factors. Therefore, when the images are superimposed, the brightness of the images of the respective frames is correlated, and the images are superimposed so that the images match. In this case, first, a reference image obtained by capturing all the signals of secondary electrons and reflected electrons without changing the electrode voltage or the like is first acquired and stored, and the image serving as a base for correlation is obtained as the all electrons. If the image includes a signal, it is easy to correlate.
[0031]
FIG. 7 shows an example in which the change in the value of the bias voltage Vb is changed every four frames instead of every frame. In this way, the material characteristics of the sample can be sufficiently expressed by changing the voltage every several frames, such as every 2 frames, every 4 frames, etc., instead of changing the voltage every frame. If the bias voltage Vb is not changed, the scan region of the primary electron beam will not move, so that several frames of images acquired with the same bias voltage can be synthesized as they are. Finally, when compositing to one color image, it is also effective to synthesize an image group acquired and synthesized with the same Vb in advance by adjusting the alignment position based on the correlation of the brightness of the pixels.
[0032]
Furthermore, the brightness can also be displayed by reversing the brightness with respect to the signal intensity. Such an operation can be variously changed by controlling the signal processor 178, the image integrator 155, and the like by the CPU 150 by inputting a command from the input device 154.
[0033]
FIG. 8 summarizes the series of operations in a flowchart.
First, the number N of frames is determined (step 301). Then, an initial value of the bias voltage is set and a voltage is applied to the electrode (step 302). In this case, as an example, a setting for acquiring all signal electronic currents is set as an initial value. Next, a reference image is acquired under the bias voltage setting conditions (step 303). The number of frames of this image is about 4 to 16 frames, and at most 32 frames is sufficient.
[0034]
Next, acquisition of the main target image is started (step 304). The primary electron beam is scanned two-dimensionally, and an image signal of one frame is detected and stored (step 305). This is repeated for the set number of frames while changing the bias voltage for each frame (steps 307 and 308). As described above, the bias voltage may be changed every several frames. When the signal acquisition is completed, all acquired data is stored (step 309). In this case, the data includes only the number of pixels of one frame screen × the number of frames (corresponding to the number of steps of Vb change).
[0035]
From these data, the signal spectrum of each pixel is taken out and differentiated to obtain the signal amount for each energy value. This is the lightness for each color (step 310). Each frame (Vb voltage: signal electron energy) is colored to determine the display color. The color arrangement is determined using the method shown in the equation (2) (step 311). Next, a signal processing method is designated. When it is necessary to emphasize the signal indicating the characteristics of the substance, an instruction to enhance the minute signal is input by taking the logarithm of the signal (step 312). The signal is corrected in accordance with the input instruction (step 313). An image for each frame is created (step 314). Matching is performed on the reference image obtained in step 303, and the position of each frame image is adjusted (step 315). After the adjustment, the respective frame images are synthesized (step 316). Thus, one observation image is completed. In step 316, only an image having a desired energy may be displayed. By doing so, it is possible to display the distribution of the locations on the sample having specific energy characteristics, the area ratio, and the like in an easily understandable manner.
[0036]
FIG. 9 is a schematic view showing another embodiment of the scanning electron microscope according to the present invention. In FIG. 9, a magnetic field generating coil 213 shown in FIG. 10 that generates a porous electrode 112 capable of transmitting secondary electrons 109 on the optical axis, a counter electrode 111, and a magnetic field B substantially orthogonal to the electric field E generated at the electrode. , 214 are arranged to deflect the trajectories of the secondary electrons 109 and the reflected electrons 110. The potential difference between the porous electrode 112 and the counter electrode 111 is ± Ve (V), the excitation current of the magnetic field generating coils 213 and 214 is Ib (A), the acceleration voltage of the primary electron beam is Vacc (V), and the porous electrode 112 and the counter electrode 111, and constants determined by the shapes of the magnetic field generating coils 213 and 214 are Ke and Kb, and as described in Japanese Patent No. 3291880, Ib and Ve are controlled so as to maintain the relationship of K1 and K2 are set to conditions that do not exert a deflection action on the primary electron beam.
[0037]
[Expression 4]

[0038]
The secondary electron detector 120 is arranged and detected at a position where the trajectory of the secondary electrons 109 transmitted through the porous electrode 112 is expected. The reflected electron trajectory is separated from the secondary electrons, and a secondary electron conversion electrode 440 that converts the reflected electrons into secondary electrons is disposed on the reflected electron orbit. When a negative voltage is applied to the electrode, the reflected electrons collide with the electrode and generate secondary electrons with low energy from the electrode surface. The strength of the orthogonal electromagnetic field is set so as not to exert a deflection action on the primary electron beam 104. However, the secondary electron 450 having a lower energy than the primary electron beam is stronger by the electric field than the magnetic field. Bend. As a result, it is strongly deflected to the porous electrode side, passes through the porous electrode 112, and is detected by the electron detector 120 arranged at the position where the porous electrode is seen.
[0039]
Further, when an axially symmetric electrode 441 is disposed under the porous electrode 112 and an appropriate negative voltage is applied to this electrode, secondary electrons generated from the sample cannot be propagated through the axially symmetric electrode and rebounded to the sample side. . In this way, the signal due to the low energy electrons is discarded according to the negative voltage applied to the axisymmetric electrode 441. Then, only the high-energy reflected electrons are converted into secondary electrons 450 by the conversion electrode 440 disposed above the porous electrode. Since the converted secondary electrons 450 reflect the reflected electron information from the sample, forming an image with this signal is equivalent to forming an image with the reflected electron signal from the sample. The electron detector 120 can detect the secondary electrons generated and drawn in the secondary electron conversion electrode 440 and the secondary electrons emitted from the sample and deflected by the electromagnetic field generator in the same manner. Therefore, reflected electrons and secondary electrons that orbitally disperse (energy disperse) over a wide range can be detected with high efficiency.
[0040]
The negative voltage applied to the axisymmetric electrode 441 has the reverse effect of the positive bias voltage Vb of the electron detector 120 in FIG. Therefore, as shown in FIG. 2A, the bias voltage Vb ′ applied from the variable voltage power source 201 to the axially symmetric electrode 441 is changed when the sample image is captured as shown in FIG. Dividing into N stages, Vb ′ is applied step by step every time one frame image is captured. In this way, as shown in FIG. 2C, the signal current as shown in FIG. 11B is obtained in the electron detector 120.
[0041]
FIG. 12 is a schematic view showing another embodiment of the scanning electron microscope according to the present invention. This scanning electron microscope has an enhanced function of filtering the energy of reflected electrons and secondary electrons in the apparatus of FIG. When low energy secondary electrons enter the orthogonal electromagnetic field portion, they are deflected by the electromagnetic field and travel toward the electron detector 120 through the porous electrode 112. At this time, there is a porous electrode 113 between the porous electrode 112 and the electron detector 120, and a negative voltage is applied to the porous electrode 113 to limit secondary electrons passing therethrough with its energy. Similarly, reflected electrons having relatively high energy are filtered when passing through the porous electrode 114 to which a negative voltage provided within an orthogonal electromagnetic field can be applied, and only electrons having energy exceeding the potential of the porous electrode 114 pass through here. To do.
[0042]
The porous electrodes 113 and 114 are connected to the same power source Vb ′. The electrons that have passed through the porous electrode 114 collide with the secondary electron conversion electrode 440 and generate secondary electrons 450. The secondary electrons 450 also reach the electron detector 120 through the porous electrode 112 in the orthogonal electromagnetic field portion. Since there is always a negative potential porous electrode 113 or 114 between the sample 107 and the electron detector 120, the secondary electrons 109 and the reflected electrons 110 generated on the sample 107 by the irradiation of the primary electron beam 104 are Only those having energy that can exceed the negative potential are detected by the detector 120. The reflected electrons having relatively high energy collide with the secondary electron conversion electrode 440 and generate secondary electrons 450, thereby amplifying the signal amount.
[0043]
The porous electrode 114 in the orthogonal electromagnetic field is sandwiched between the grounded porous electrodes 117, and the central portion of the optical axis through which the primary electron beam 104 passes is electromagnetically shielded by the shield cylinder 116. Therefore, the negative potential of the porous electrode 114 does not affect the trajectory of the primary electron beam 104. With this structure, energy analysis can be continuously and reliably performed from low energy secondary electrons to high energy reflected electrons. Furthermore, changing the electrode voltage to change the energy of the signal electrons to be acquired does not change the trajectory of the primary electron beam and does not affect it. There is no fear of slipping. In order to increase the signal amount of low energy electrons as much as possible, it is desirable that a positive voltage of several tens of volts is applied to the axially symmetric electrode 441, but it is not indispensable.
[0044]
FIG. 13 is a schematic view showing another embodiment of the scanning electron microscope according to the present invention. In this scanning electron microscope, an array-shaped electron detector 121 is arranged instead of the electron detector 120 of FIG.
[0045]
The array-shaped electron detector 121 is like arranging a plurality of detectors in a line. In FIG. 13, the detector rows are arranged in the axial direction and vertically. By doing so, secondary electrons with low energy are immediately deflected by the orthogonal electromagnetic field and detected at the lower part of the array-shaped electron detector 121. On the other hand, reflected electrons having high energy are detected above the arrayed electron detector 121 in FIG.
[0046]
By using the array-like electron detector 121 in this way, the energy distribution of signal electrons can be measured by the position of the detector element that detects the signal electrons without changing the voltage of the electrodes or the like. When there are M detectors in each of the array-shaped electron detectors 121, the energy of signal electrons can be analyzed in M stages. The signal converter 160 processes these M-stage signals in parallel, and assigns a color to each detector element signal. Color components and signal intensity information are added to the signals detected by these detection elements, and one image is finished in synchronization with the scan signal. In this case, one frame image is already a color image of a plurality of colors (M colors), which is different from the above-described embodiments of FIGS. Similar to a normal scanning electron microscope, it is possible to obtain a plurality of images of one frame and overlay them to reduce noise.
[0047]
FIG. 14 is an enlarged view of the array electron detector. As shown in FIG. 14A, a scintillator 901 and a photocathode 902 located on the back surface of the scintillator 901 are disposed on the front surface of the detector, and a dynode array 903 is disposed behind the scintillator 901. A bias voltage 153 is applied to the scintillator 901, whereby signal electrons incident on the scintillator 901 are accelerated and cause the scintillator 901 to emit light when colliding with the scintillator. A high voltage 904 is also applied to the photocathode 902 and the dynode array 903 as shown. The voltages 153 and 904 are preferably several kV to several tens kV. On the back of the dynode array 903 is a collection electrode array 905. A magnetic field B is applied to the entire dynode array 903 from the side surface.
[0048]
Fig.15 (a) is an expanded sectional view of Fig.14 (a). The dynode array 903 is provided with a passage for secondary electron multiplication for each channel in the resistor. In this case, there are M passages, and M channels are formed. By depositing metal electrodes on the front and back surfaces of the resistor and applying a voltage to the electrodes, a uniform voltage can be applied to each channel. FIG. 14B shows a dynode array 903.
[0049]
Signal electrons generated from the sample surface enter the scintillator 901 and cause the scintillator 901 to emit light. When the light enters the photocathode 901, electrons are emitted from the back surface. The electrons enter the dynode. Here, since a magnetic field is applied to the dynode from the side surface, the electron cannot travel straight and collides with the side surface of the channel. At this time, a plurality of secondary electrons are generated and accelerated. These electrons are also deflected by the magnetic field and collide with the dynode wall surface to generate more electrons. In this way, the electron current is multiplied and finally reaches the electrode 905.
[0050]
FIG. 15B shows a case where a metal electrode is used for the dynode instead of a resistor. A voltage is applied to the electrodes divided into several parts, and the electrons progress while being multiplied between the electrodes, and finally reach the electrode 905. FIG. 14C shows a dynode array 906 in which the electrodes are arranged. Although neither FIG. 15A nor FIG. 15B is shown, the structure from the photocathode 902 to the dynode array 903 and the electrode array 906 is sealed with a glass tube or the like and is not affected by the outside. It is desirable to keep it.
[0051]
FIG. 16 is a diagram showing an example in which the present invention is applied to a scanning electron microscope of a type in which a sample can be tilted. For the detector portion, the configuration described in FIGS. 9, 12, and 13 may be used.
[0052]
When the images for each frame acquired in FIG. 9 and FIG. 16 are superimposed, the scan region of the primary electron beam is slightly changed due to the voltage change of the axially symmetrical electrode 441 and other factors as in the case of the embodiment of FIG. May move. Therefore, when the images are superimposed, the brightness of each image is correlated, and the images are superimposed so that the images match. In this case, first, a reference image obtained by capturing all the signals of secondary electrons and reflected electrons without changing the electrode voltage or the like is first acquired and stored, and the image serving as a base for correlation is obtained as the all electrons. If the image includes a signal, it is easy to correlate.
[0053]
17 and 18 are diagrams for explaining examples of display screens when a sample is measured with the scanning electron microscope of the present invention.
FIG. 17 is an explanatory diagram of an example in which a hole 2210 of a photoresist 2212 provided on a semiconductor substrate (silicon oxide) is measured. FIG. 17A shows a schematic shape of the measurement target, and shows a state in which there are undulations 2214 in the vicinity of the hole opening, and the sample surface in the vicinity of the opening is negatively charged. FIG. 17B shows an image obtained by scanning the hole with a primary electron beam from the direction of the opening, and the standing wave 2220 on the uncharged wall surface of the hole and accurate image information on the bottom portion are obtained. This shows that an accurate image state in the vicinity of the charged sample opening is not obtained. FIG. 17C shows a sample surface image obtained by scanning a sample with a primary electron beam and a high-energy reflected electron signal. An image of the bottom portion of the hole is not obtained, but an accurate image near the sample opening is obtained. It shows that the undulation state is obtained.
[0054]
Usually, secondary electron signals generated by scanning a sample with a primary electron beam are electrons with low energy (about several electron volts) emitted from the surface of the sample. In order to reflect the state faithfully, it is not affected by scattering of the electron beam inside the sample material, and has a feature of providing high spatial resolution information. However, in the conventional analysis method using low energy secondary electron signals, if the sample surface is negatively charged (hereinafter referred to as charge-up), the rise of low-energy secondary electrons is hindered by charge-up. Therefore, there is a phenomenon in which the undulations near the hole opening, that is, the uneven state of the sample surface cannot be accurately reflected. The sample image in FIG. 17B shows that accurate image information in the vicinity of the charged sample opening is not obtained due to this phenomenon. On the other hand, the sample image shown in FIG. 17C is based on high-energy reflected electrons, but an accurate undulation state near the sample opening that has not been obtained with low-energy secondary electrons has been found. Is shown.
[0055]
The reason why an accurate sample image can be detected by high-energy reflected electrons in the scanning electron microscope of the present invention will be described below. In the conventional high-energy backscattered electron detection method, the sample is scanned with a primary electron beam having a high energy and a high acceleration voltage. It generates almost the same energy as the acceleration voltage). For this reason, the region where high-energy reflected electrons are generated spreads due to the internal scattering of the primary electron beam and the spatial resolution is lowered, but the signal has a feature that contains a lot of composition information in addition to the uneven state of the sample surface. In the conventional method, reflected electrons having high energy are detected mainly to obtain composition information in the sample. In addition, as a conventional high-energy reflected electron detection method, a sample is scanned with a low-acceleration primary electron beam, high-energy reflected electrons are generated near the surface of the sample, and high-energy reflected electrons are detected without reducing the spatial resolution as much as possible. Although there is a method for detection, there is no means for accurately separating and detecting low energy secondary electrons generated by irradiating a sample with a primary electron beam and high energy reflected electrons in the conventional method. Since the low-energy secondary electrons have been mixed in the signal taken as the electronic signal, there was no high-energy backscattered electron detection method with high resolution as a result.
[0056]
On the other hand, in the apparatus of the present invention, an electrode for continuously separating high-energy reflected electrons and low-energy secondary electrons generated from the sample is provided on the optical system from the electron source to the sample, and the electric field generated by this electrode generates an electrode. Or by providing an electromagnetic field that separates the orbits of high-energy reflected electrons and low-energy secondary electrons generated from these samples as in the configuration shown in FIG. 13, reflected electrons at positions corresponding to the respective energies, Since secondary electrons can be detected continuously by energy, it is possible to form sample images using only signal electrons with a specific energy, starting with the formation of sample images using only high-energy reflected electrons. . In the primary electron beam irradiation and high energy backscattered electron detection method of the present invention, unlike the conventional high energy backscattered electron generation method, even when the acceleration voltage is low, that is, when the energy state is low, The low energy secondary electrons are continuously sorted according to energy, and it is possible to form a sample image only with high energy reflected electrons in a relatively low energy state.
[0057]
Therefore, the primary electron beam with a low accelerating voltage only enters the shallow part of the sample surface, and the high energy reflected electrons from the sample are emitted from the shallow part. Therefore, it is possible to form a sample image equivalent to the conventional secondary electron scanning by detecting a signal of high energy reflected electrons in this state. It is possible. Even when the sample is negatively charged (charged up) in the observation of an insulator or the like, since the secondary electrons with low energy are affected by the charging of the sample surface during the generation process as described above, The information on the unevenness of the sample is not faithfully reflected in the energy secondary electron signal. However, the reflected electrons with a higher energy level than the secondary electrons are not affected by charging, so the sample is charged even if the sample is charged. Can be obtained stably.
[0058]
From this, it can be seen that the information on the surface of the sample can be accurately detected by the primary electron beam irradiation and high energy backscattered electron detection method of the present invention even if the surface is charged. Shows. According to the scanning electron microscope of the present invention, the reflected electron signal and the secondary electron signal are detected for each energy in synchronism with the irradiation of the primary electron beam, and each of them is used by using the configuration as shown in FIG. Because it is possible to detect electrons with high energy at the same time, it is possible to detect low-energy secondary electrons and observe composition information mainly for observing only unevenness information with high resolution when the sample is not charged. Detection of high-energy reflected electrons for observing the unevenness of a sample, and detection from low-energy secondary electrons to high-energy reflected electrons for observing both of them simultaneously are enabled.
[0059]
Furthermore, according to the scanning electron microscope of the present invention, it is possible to construct the sample image information by superimposing the target sample image by the high energy reflected electron signal and the target sample image by the low energy secondary electron signal. I have to. For example, in the image of the target sample by the low energy secondary electron signal of FIG. 17B, since the opening of the hole is charged, accurate sample unevenness information can be obtained only at the side and bottom, but FIG. According to the high energy reflected electron signal of (c), accurate unevenness information of the opening is obtained. Therefore, these sample images are superimposed, that is, the inside of the hole is a sample by a low energy secondary electron signal. By using a sample image with high-energy reflected electrons on the outside of the image, it is possible to obtain information on the target sample of the entire hole. Furthermore, it is possible to form a single image by synthesizing images according to colors by the energy of each signal electron.
[0060]
FIG. 17D is an explanatory diagram of an image obtained by synthesizing the electronic signal of all energy. FIG. 17D shows a color image colored by energy. As shown in FIG. 17 (d), it is possible to simultaneously observe the unevenness information on the side surface and bottom of the hole, the unevenness information on the hole opening, and the undulation state of the resist surface. Since it is color-coded by electronic energy, the ease of charging the resist surface, the difference in composition, etc. are displayed as the difference in color.
[0061]
FIG. 18 is an explanatory diagram of an example in which the cross section of the hole 2210 of the photoresist 2212 provided on the semiconductor substrate (silicon oxide) is measured. FIG. 18A shows a schematic shape of a measurement target, and standing waves 2220 generated during resist formation are present in several layers in a photoresist formed on a semiconductor substrate (silicon oxide). Represents that. The photoresist 2212 is not charged.
[0062]
FIG. 17B shows a sample image in which the cross section of the hole 2210 is formed by a general primary electron beam scanning and low energy secondary electron detection method from the cross sectional direction, and faithfully reflects the uneven state of the cross sectional shape. In addition, it is shown that a sample image having a high spatial resolution is obtained. FIG. 17 (c) shows a sample image obtained by the primary electron beam scanning and high energy reflected electron detection method. Since the high energy reflected electrons from the sample contain a lot of composition information in the target sample, this is detected. Thus, it is shown that standing waves generated at the time of resist formation exist in this photoresist by forming several layers. This is because high-energy reflected electrons are generated from the deep part of the sample as compared with low-energy secondary electrons, and a difference in the composition appears in this high-energy reflected electron signal.
[0063]
And according to the scanning electron microscope of the present invention, in synchronization with the primary electron beam irradiation, each from the high energy reflected electron signal to the low energy secondary electron signal can be continuously and clearly separated and simultaneously detected, It is possible to accurately observe and compare both the unevenness information and the composition information of the sample. As a result, for example, even if the sample is easily broken and it is desired to detect the surface information and composition information of the sample without irradiating the electron beam very much, both the unevenness information and the composition information are accurately obtained by the primary electron beam irradiation to the sample once. Compared with the conventional method in which the surface information and composition information of the sample cannot be obtained unless the primary electron beam is irradiated multiple times, damage to the sample can be minimized. It can support a wide range of sample measurement applications.
[0064]
Furthermore, according to the scanning electron microscope of the present invention, it is possible to construct the sample image information by superimposing the target sample image by the high energy reflected electron signal and the target sample image by the low energy secondary electron signal. become. According to the low energy secondary electron signal of FIG. 18B of this example, accurate sample surface information can be obtained, and according to the high energy reflected electron signal of FIG. 18C, information on the composition state of the resist. Therefore, by superimposing these two sample images, the surface state and the composition state of the sample can be easily compared and displayed. In addition, as a signal processing method for display, not only the brightness adjustment of each image but also the addition of predetermined color information according to each image state makes it easy to compare the surface state and composition state of the sample. Can be displayed.
[0065]
FIG. 18D is an explanatory diagram of an image obtained by synthesizing all energy electronic signals. In FIG. 18D, a color image is colored according to energy. As a result, accurate sample surface information in the hole and information on the composition state of the resist can be observed at the same time, and each is color-coded by the signal electron energy of secondary electrons and reflected electrons. Is displayed as a difference.
[0066]
Another example of image display by the scanning electron microscope of the present invention will be further described. FIG. 19 is a diagram illustrating an example of an image of foreign matter on a semiconductor substrate (silicon oxide). FIG. 19B shows only an image around the energy of the foreign matter portion. Thus, it becomes easy to specify a foreign substance by limiting the energy range to display. Even when the position of a foreign object is automatically identified by image processing, data on the energy range of a foreign object that is expected in advance is acquired, and by paying attention to the energy range, the position of the foreign object is specified by the image, Foreign objects can be captured more accurately. This method is particularly effective when it is difficult to find the position of the foreign matter. By examining the image of the target object / foreign material characteristic energy range over a wide area range at a low magnification, the conventional image recognition method can catch foreign matter.
[0067]
Further, in FIG. 19A, which is an image obtained by combining the energy screens, the foreign matter can be displayed in a conspicuous color such as red, so that it can be displayed easily for human confirmation. FIG. 19C shows an image in a certain energy range other than the energy range of the foreign matter. Differences in the surface composition and small irregularities that are difficult to confirm in simple monochrome images are confirmed as black spots.
[0068]
FIG. 20 shows an image of a sample ashed after etching the polysilicon line. It can be confirmed that foreign matter is attached to the left and right sides of the polysilicon line. FIG. 20B is an image created only in the energy range of signal electrons generated by only foreign matters. By assigning a conspicuous color scheme such as red to this portion and creating a color image as shown in FIG. 20A, it is possible to create an image in which the presence and position of a foreign object can be easily understood. FIG. 20C shows an image in a certain energy range other than the energy range of the foreign matter. Differences in the surface composition and small irregularities that are difficult to confirm in simple monochrome images are confirmed as black spots.
[0069]
FIG. 21 is an explanatory diagram of a cross section of a thin film laminated sample on a silicon substrate. FIG. 21B is a scanning image in which the same sample cross section is formed using signal electrons having different energies. The layer that appears in the scanned image differs depending on the energy of the signal electrons. By assigning and synthesizing a specific color to each of the scanning images having different signal electron energies, a color image having a different color for each layer is obtained as shown in FIG. From FIG. 21A, it is possible to recognize at a glance the thickness of each layer, the mixing condition of materials, the relationship between layers, and the like from this single image.
[0070]
【The invention's effect】
According to the present invention, not only the fine structure of the observation sample but also the material distribution can be identified by color display.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an embodiment of a scanning electron microscope according to the present invention.
2A is a diagram showing a change in voltage Vb applied to an electron detector, FIG. 2B is a diagram of a deflection scanning signal in the Y direction of a primary electron beam, and FIG. 2C is a diagram when one image is acquired; The figure which shows the average transition of a signal electron current, (d) is a figure which shows the energy distribution of a signal electron, (e) is a figure which shows the color scheme distribution and RGB component distribution corresponding to the energy distribution of a signal electron.
FIG. 3 is an explanatory diagram of spectra of secondary electrons and reflected electrons.
FIG. 4 is an explanatory diagram of an area ΔS created by an electronic signal curve: fs (E) between E1 and E1 + δ.
FIG. 5 is a diagram illustrating an example in which a color arrangement is distributed so that a color change is increased in proportion to a signal amount;
FIG. 6 is a diagram showing an example in which a minute signal is emphasized by the energy distribution of signal electrons.
FIG. 7 is a diagram showing an example in which a change in bias voltage is changed every several frames.
FIG. 8 is a flowchart showing a processing procedure of an analysis signal according to the present invention.
FIG. 9 is a schematic view showing another embodiment of a scanning electron microscope according to the present invention.
FIG. 10 is a plan configuration diagram of an orthogonal electromagnetic field generation unit.
11A is a diagram showing a change in bias voltage Vb ′ applied to an axially symmetric electrode, and FIG. 11B is a diagram showing an average transition of signal electron current when one image is acquired.
FIG. 12 is a schematic view showing another embodiment of a scanning electron microscope according to the present invention.
FIG. 13 is a schematic view showing another embodiment of a scanning electron microscope according to the present invention.
FIG. 14 is a diagram showing an embodiment of an array-shaped electron detector.
FIG. 15 is an enlarged view of an array electron detector.
FIG. 16 is a diagram showing an example in which the present invention is applied to a scanning electron microscope of a type in which a sample can be tilted.
FIG. 17 is a diagram showing an example of a display screen when a sample is measured with the scanning electron microscope of the present invention.
FIG. 18 is a diagram showing an example of a display screen when a sample is measured with the scanning electron microscope of the present invention.
FIG. 19 is a diagram showing an example of observing a foreign material sample according to the present invention.
FIG. 20 is a diagram showing an example of observing a foreign material sample according to the present invention.
FIG. 21 is a diagram showing an example of observing a multilayer material according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 101 ... Cathode, 102 ... First anode, 103 ... Second anode, 104 ... Primary electron beam, 105 ... Converging lens, 106, 206 ... Objective lens, 107, 207 ... Sample, 108 ... Deflection coil, 109, 450 ... Two Secondary electron, 110 ... Reflected electron, 111 ... Counter electrode, 112 ... Porous electrode, 113, 114 ... Negative potential porous electrode for energy control, 117 ... Ground electrode, 115 ... Drawing device, 116 ... Shield tube, 120 ... Signal electron detection 120 ... array signal electron detector, 125 ... display device (CRT / LCD), 140 ... scanning electron microscope control system, 150 ... CPU, 151 ... variable voltage power supply, 152 ... storage device (memory, hard disk), 153: Bias power supply, 154: Input device, 155 ... Image accumulator, 156 ... Display device I / F, 160 ... Signal converter, 170 Converging lens controller, 174 ... Objective lens controller, 176 ... Scanning controller, 178 ... Signal processor, 213, 214 ... Orthogonal magnetic field generating coil, 440 ... Secondary electron conversion electrode, 441 ... Axisymmetric electrode, 901 ... Scintillator 902: Photocathode, 903 ... Array-like dynode, 904 ... Bias voltage, 905 ... Electrode array, 906 ... Array-like dynode, 2212 ... Photoresist, 2210 ... Contact hole, 2214 ... Unevenness on photoresist, 2220 ... Standing wave.

Claims (23)

An electron beam source, a scanning deflector that scans the sample with a primary electron beam emitted from the electron beam source, a signal electron detector that detects signal electrons emitted from the sample by electron beam irradiation, and an image display unit In a scanning electron microscope that displays a scanning image of a sample on the image display unit,
A scanning electron microscope characterized by measuring an energy distribution of the signal electrons, assigning a color and brightness according to the measured energy value and intensity thereof, and combining them into one image and displaying the color on the image display unit. . 2. The scanning electron microscope according to claim 1, wherein the energy distribution of the signal electrons is measured by stepwise changing the voltage applied to the signal electron detector in synchronization with the scanning of the primary electron beam by the scanning deflector. A scanning electron microscope characterized by: 2. The scanning electron microscope according to claim 1, further comprising a control electrode for limiting energy of signal electrons incident on the signal electron detector between a sample and the signal electron detector, and applying the control electrode to the control electrode. A scanning electron microscope characterized by measuring an energy distribution of signal electrons by changing a voltage stepwise in synchronization with scanning of the primary electron beam by the scanning deflector. 4. The scanning electron microscope according to claim 2, wherein when the number of frames of an acquired image is N (N is a positive integer), the stepwise change voltage is divided into N stages from a maximum value to a minimum value. A scanning electron microscope characterized by being changed by one step for each frame image acquisition. 4. The scanning electron microscope according to claim 2, wherein the voltage to be gradually changed is changed for each designated number of image frames. 5. The scanning electron microscope according to claim 4, wherein when the images for each frame are overlaid, the brightness of each frame image is correlated and the frame images are overlaid so that they match. electronic microscope. 6. The scanning electron microscope according to claim 5, wherein the images of a plurality of frames obtained by setting the stepwise changing voltage to the same voltage are combined as they are to form a combined image, and finally combined into a single color image. In this case, the scanning electron microscope is characterized in that the combined positions are adjusted based on the correlation of the brightness of the pixels of each of the combined images. 2. The scanning electron microscope according to claim 1, wherein a scanning image of a sample obtained by detecting signal electrons in a wide energy range by the signal electron detector is used as a reference, and a scanning image by signal electrons of each energy is used as the reference electron microscope. A scanning electron microscope characterized in that the position is adjusted and synthesized based on the correlation of brightness with a scanned image. 2. The scanning electron microscope according to claim 1, wherein an orthogonal electromagnetic field generator for generating an orthogonal electromagnetic field on the optical axis for deflecting the signal electrons toward the signal electron detector without exerting a deflection action on the primary electron beam. The scanning electron microscope is characterized in that the signal electron detector is an arrayed electron detector in which a plurality of detectors are arranged in the optical axis direction. 10. The scanning electron microscope according to claim 9, wherein the array-shaped electron detector includes a scintillator, a photocathode, a dynode array, and a collecting electrode array, and the dynode array is disposed in an integrated resistor. A scanning electron microscope, wherein channel holes are provided side by side for several minutes. 10. The scanning electron microscope according to claim 9, wherein the arrayed electron detector includes a scintillator, a photocathode, a dynode array, and a collecting electrode array, and the dynode array has channel holes corresponding to the number of poles. A scanning electron microscope comprising a plurality of electrodes arranged side by side. 2. The scanning electron microscope according to claim 1, wherein when colors are assigned according to the energy values of the signal electrons, the colors are assigned in order of visible light color wavelengths from the maximum value to the minimum value of the energy values. 13. The scanning electron microscope according to claim 12, wherein the color scheme is assigned so that the change in the color scheme of each energy region is proportional to the signal intensity of the signal electrons in each energy region. 2. The scanning electron microscope according to claim 1, wherein the brightness of the pixels is assigned according to the signal intensity at each energy value of the signal electrons, the maximum value of the signal intensity of the signal spectrum for all the pixels is assigned as the maximum value of the brightness, A scanning electron microscope characterized in that a value of 1/2 is assigned as a median brightness value. 2. The scanning electron microscope according to claim 1, wherein a logarithmic value of a signal intensity at each energy value of the signal electrons corresponds to lightness. 2. The scanning electron microscope according to claim 1, wherein when a color is assigned according to an energy value of the signal electrons, a specified color is assigned to a specific energy value. 2. The scanning electron microscope according to claim 1, wherein an image corresponding to one designated electron energy value is displayed or an image corresponding to a plurality of electron energy values is synthesized and displayed. A scanning type comprising: an electron beam source; a scanning deflector that scans the sample with a primary electron beam emitted from the electron beam source; and a signal electron detector that detects signal electrons emitted from the sample by electron beam irradiation In electron microscope,
A control electrode disposed between the signal electron detector and the sample, and a variable voltage power source for applying a voltage to the control electrode, and changing the voltage applied to the control electrode from the variable voltage power source A scanning electron microscope having a function of measuring an energy distribution of signal electrons detected by a signal electron detector. The scanning electron microscope according to claim 18,
It has a pair of electric field generating electrodes consisting of a porous electrode through which a positive voltage is applied and electrons can pass through the signal electron detector and an electrode to which a negative voltage is applied, and does not exert a deflection effect on the primary electron beam. An orthogonal electromagnetic field generator for generating an orthogonal electromagnetic field on the optical axis for deflecting signal electrons in the direction of the signal electron detector;
An electromagnetic shielding metal cylinder provided to surround the trajectory of the primary electron beam on the electron source side of the orthogonal electromagnetic field generation unit;
A first porous electrode to which a negative voltage is applied, provided in the vicinity of the sample side end portion of the metal cylinder, with a porous electrode having a ground potential sandwiched between the front and rear in the optical axis direction;
Providing a second porous electrode having the same potential as the first porous electrode between the porous electrode to which the positive voltage is applied and the signal electron detector;
A scanning electron microscope characterized in that the first and second porous electrodes are the control electrodes. 20. The scanning electron microscope according to claim 19, wherein color and brightness are respectively assigned according to the energy value and intensity of electrons detected by the electron detector, and are combined into one image and displayed in color. Shape electron microscope. Scanning and irradiating a sample with a primary electron beam;
Detecting signal electrons generated from the sample by irradiation of the primary electron beam according to energy in synchronization with the scanning;
A sample observation method characterized by assigning a color and brightness according to an energy value and intensity of detected signal electrons, and displaying a scan image of the sample in color. 23. The sample observation method according to claim 21, further comprising a step of creating a single image by combining a plurality of image frames, and the red, yellow, blue, RGB, or CMYK color elements of the corresponding pixels of each image frame. A sample observation method characterized in that gradation values are simply added and the addition result is equally distributed to each color and gradation. Scanning and irradiating a sample with a primary electron beam;
Detecting signal electrons generated from the sample by irradiation of the primary electron beam according to energy in synchronization with the scanning;
A sample observation method characterized by displaying a scanning image based on signal electrons having specific energy and specifying a position of a structure corresponding to the signal electrons.

Images