JP4192038B2 - Surface shape and / or film thickness measuring method and apparatus - Google Patents

Description

、ここでＣ ( Ｄ ) は強度値の平均値、 k _u は照射される光の波数の上限値、 k ₁ は照射される光の波数の下限値、Ｒ、Ｓは装置と測定対象の物性により決まるパラメータ、αは空気の屈折率、および、ｋは角波数、ｎ _ｓ は膜屈折率、Ｄは透明膜の膜厚に基づいて前記第４の過程で実測により求めた強度値の平均値から透明膜の膜厚を求める第５の過程と、
前記求めた強度値群から直流成分を除去して交流成分のみを求め、当該交流成分を２乗してプラス側に強調した特性値群を取得する第６の過程と、
前記特性値群から包絡線となる特性関数を求め、この特性関数に基づいて前記測定対象面と参照面との距離に関連するピーク位置情報を求める第７の過程と、
前記求めたピーク位置情報に基づいて、測定対象面の表面高さを求める第８の過程と、
前記第５の過程で求めた透明膜の膜厚と、前記第８の過程で求めた測定対象面の表面高さとから透明膜の表面高さを求める第９の過程と
を備えたことを特徴とするものである。
【００１２】
（作用・効果） 請求項１に記載の発明によれば、白色光源から発生した白色光を測定対象面と参照面とに照射する。透明膜の表面および表面側と接合している物体の表面である測定対象面と参照面とでそれぞれ反射した白色光の光路差に応じて干渉した干渉縞が発生する。ここで、測定対象面と参照面との距離を変動させることにより、それぞれの光路差を変化させて干渉縞を変化させながら所定間隔で連続して複数枚の測定対象面の画像を取得し、画像ごとの各画素における干渉光の強度値群の変化を求める。この強度値群の変化から平均値を求める。次に、測定対象物と同じ対象物について予め求めた干渉光の強度値の平均値と透明膜の相関関係に基づいて、実測によって求まった強度値群の平均値から透明膜の膜厚を求める。また、同時に取得した強度値群から包絡線に相当する特性値群を取得し、この特性値群の示す波形データから特性関数を求める。この特性関数からは、測定対象面と参照面との距離に関連するピーク位置情報が求められ、このピーク位置情報に基づいて、測定対象面の表面高さが求められる。求まった測定対象面の表面高さと実測により求めた透明膜の膜厚を利用する。つまり、それぞれの値を加算することによって透明膜の表面高さが求められる。すなわち、干渉光の強度値群の平均値を利用することにより、正確に透明膜の膜厚を求めることができ、この透明膜の膜厚を利用することによって、透明膜の表面高さもより正確にもとめることができる。
【００１３】
また、請求項２に記載の発明は、請求項１に記載の表面形状および／または膜厚測定方法において、前記第９の過程で求める透明膜の表面高さ（ｈ）は、透明膜の膜厚（Ｄ）と透明膜の屈折率（ｎ）の関係から予め求めた透明膜の膜厚の補正量を含む膜厚ｆ（ｎ，Ｄ）を前記第８の過程で求めた測定対象面の表面高さ（ｈａ）に加算して求めた値であることを特徴とするものである。
【００１４】
また、請求項３に記載の発明は、請求項２に記載の表面形状および／または膜厚測定方法において、前記透明膜の補正量を含む透明膜の膜厚ｆ（ｎ，Ｄ）は、ｆ（ｎ，Ｄ）＝ｎ×Ｄの関係式で表されることを特徴とするものである。
【００１５】
（作用・効果）請求項２および請求項３に記載の発明によれば、透明膜の表面高さ（ｈ）は、透明膜の膜厚（Ｄ）と透明膜の屈折率（ｎ）とから求まる透明膜の膜厚の補正量を含む透明膜の膜厚ｆ（ｎ，Ｄ）が測定対象面の表面高さ（ｈ）に加算される（請求項２）。このときの補正量を含む透明膜の膜厚f（ｎ，Ｄ）は、f（ｎ，Ｄ）＝ｎ×Ｄの関係式で表すことができる（請求項３）。したがって、透明膜の表面高さをより一層に精度よく求めることができる。
【００１６】
また、請求項４に記載の発明は、請求項１ないし請求項３のいずれかに記載の表面形状および／または膜厚測定方法において、前記第７の過程で求める特性関数は、包絡線または２乗包絡線であることを特徴とするものである。
【００１７】
（作用・効果）請求項４に記載の発明によれば、特性関数として、包絡線または２乗包絡線が利用される。したがって、干渉縞波形のノイズ成分を除去した状態でピーク位置情報を求めることができる。したがって、測定対象面の表面高さを精度よく求めることができ、ひいては、透明膜の表面高さも精度よく求めることができる。
【００１８】
また、請求項５に記載の発明は、請求項１ないし請求項４のいずれかに記載の表面形状および／または膜厚測定方法において、前記特性関数は、帯域通過型標本化定理に基づいて求めることを特徴とするものである。
【００１９】
（作用・効果）請求項５に記載の発明によれば、帯域通過型標本化定理を利用することによって、サブナイキストのサンプリング間隔で取得された特性値群から特性関数を容易に復元することができる。
【００２０】
また、請求項６に記載の発明は、請求項２ないし請求項５のいずれかに記載の表面形状および／または膜厚測定方法において、前記透明膜の膜厚の補正量を規定するためのパラメータとして、反射率が既知の測定対象物の試料を用いて装置パラメータを予め求めておくことを特徴とするものである。
【００２１】
また、請求項７に記載の発明は、請求項２ないし請求項６のいずれかに記載の表面形状および／または膜厚測定方法において、前記透明膜の膜厚の補正量を規定するためのパラメータとして、膜厚が既知の測定対象物の試料を用いて装置パラメータを予め求めておくことを特徴とするものである。
【００２２】
（作用・効果）請求項６および請求項７に記載の発明によれば、測定対象物の表面が透明膜で覆われているので、その透明膜の膜厚の補正量を規定するのに反射率が既知の透明膜および測定対象物のそれぞれの試料を用いて（請求項６）、または膜厚が既知の透明膜の試料を用いて（請求項７）装置パラメータを予め求めておくことにより、透明膜の膜厚、測定対象面の高さ、および透明膜の表面高さをより一層精度よく求めることができる。
【００２３】
また、請求項８に記載の発明は、請求項１ないし請求項７のいずれかに記載の表面形状および／または膜厚測定方法において、前記第１の過程の前に、さらに前記白色光源からの白色光の周波数帯域を特定周波数帯域に制限する過程を備えたことを特徴とするものである。
【００２４】
また、請求項９に記載の発明は、請求項８に記載の表面形状および／または膜厚測定方法において、異なる複数の特定周波数帯域を用いること特徴とするものである。
【００２５】
（作用・効果）請求項８および請求項９に記載の発明によれば、白色光の周波数帯域を特定周波数帯域に制限することにより、測定対象面からの反射光をより精度よく検出することができる。なお、異なる複数の特定周波数帯域を用いることが好ましい（請求項９）。すなわち、強度値の平均値から透明膜の膜厚を求める第５の過程において、一般には、複数の膜厚の候補値が存在する。対象の膜厚値が十分に狭い範囲内に存在することが既知の場合には、一義的に透明膜の膜厚を特定できるが、それが不可能な場合には、複数の特定周波数帯域を用いて透明膜の膜厚の候補を求め、全ての帯域に共通する膜厚の候補を選択することで、精度よく透明膜の膜厚を特定することができる。
【００２６】
また、請求項１０に記載の発明は、透明膜で覆われた測定対象面と参照面とに照射する白色光を発生させる白色光源と、前記測定対象面と参照面との距離を変動させる変動手段と、前記白色光が照射された測定対象面と参照面との距離の変動に伴って測定対象面と参照面とから反射して同一光路を戻る反射光によって干渉縞の変化を生じさせるとともに前記測定対象面を撮像する撮像手段と、前記撮像された測定対象面上の複数の特定箇所における干渉光の強度値を取り込むサンプリング手段と、前記サンプリング手段によって取り込まれた特定箇所ごとの複数個の強度値である各干渉光強度値群を記憶する記憶手段と、前記記憶手段に記憶された各干渉光強度値群に基づいて特定箇所の透明膜の表面高さ、測定対象面の表面高さ、および透明膜の膜厚の少なくともいずれか一つを求める演算手段とを備えた表面形状および／または膜厚測定装置において、
前記白色光源から発生した白色光の周波数帯域を特定周波数帯域に制限する周波数帯域制限手段を備え、
前記サンプリング手段は、前記変動手段による前記測定対象面と参照面との距離の変動に伴って測定対象面と参照面とから反射して同一光路を戻る反射光によって生じた干渉縞の変化に応じた特定箇所の干渉光の強度値を、前記特定周波数帯域の帯域幅に応じたサンプリング間隔で順次取込み、
前記記憶手段は、前記サンプリング間隔で取り込まれた複数個の強度値である干渉光強度値群を記憶し、
前記演算手段は、測定対象面の特定箇所の透明膜の表面高さ、測定対象面の表面高さ、および／または透明膜の膜厚の少なくともいずれか一つを以下の処理にしたがって求める
（１）前記記憶手段に記憶された各画素における干渉光から干渉光強度値群の変化を求め、
（２）前記求めた干渉光の強度値群の変化の平均値を求め、
（３）測定対象物と同じ対象物について予め求めた干渉光の強度値の平均値と透明膜の膜厚の相関関係による式

、ここでＣ ( Ｄ ) は強度値の平均値、 k _u は照射される光の波数の上限値、 k ₁ は照射される光の波数の下限値、Ｒ、Ｓは装置と測定対象の物性により決まるパラメータ、αは空気の屈折率、および、ｋは角波数、ｎ _ｓ は膜屈折率、Ｄは透明膜の膜厚基づいて実測により求めた強度値の平均値から透明膜の膜厚を求め、
（４）前記強度値群から直流成分を除去して交流成分のみを求め、当該交流成分を２乗してプラス側に強調した特性値群を求め、当該特性値から包絡線となる特性関数を求め
（５）前記特性関数に基づいて測定対象面と参照面との距離に関連するピーク位置情報を求め、
（６）前記求めたピーク位置情報に基づいて、測定対象面の表面高さを求め、
（７）前記求めた透明膜の膜厚と、測定対象面の表面高さから透明膜の表面高さを求めることを特徴とするものである。
【００２７】
（作用・効果）白色光源は、透明膜で覆われた測定対象面と参照面とに白色光を照射する。変動手段は、測定対象面と参照面との距離とを変動させる。撮像手段は、白色光が照射された測定対象面と参照面との相対的距離の変動に伴って発生する干渉縞の変化とともに前記測定対象面を撮像する。サンプリング手段は、撮像された測定対象面上の複数の特定箇所における干渉光の強度値を取り込む。記憶手段は、サンプリング手段によって取り込まれた特定箇所ごとの複数個の強度値である各干渉光強度値群を記憶する。演算手段は、記憶手段に記憶された各画素における実測による干渉光強度値群から干渉光の強度値の変化を求め、この強度値群の平均値を求める。次に、測定対象物と同じ対象物から予め求めた干渉光の強度値群の平均値と透明膜の膜厚の相関関係に基づいて実測により求めた強度値群の平均値から透明膜の膜厚を求める。同時に、強度値群から包絡線に相当する特性値群を求めて特性関数を作成し、この特定関数に基づいて測定対象面と参照面との距離に関連するピーク位置情報を求める。ピーク位置情報に基づいて測定対象面の表面高さが求められる。これら求めた透明膜の膜厚と測定対象面の表面高さとを利用する。つまり、それぞれの値を加算することによって、透明膜の表面高さを求めることができる。すなわち、請求項１に記載の方法を好適に実現することができる。
【００２８】
また、請求項１１に記載の発明は、請求項１０に記載の表面形状および／または膜厚測定装置において、前記演算手段は、さらに透明膜の膜厚と透明膜の屈折率とに基づいて透明膜の表面高さを補正演算処理することを特徴とするものである。
【００２９】
（作用・効果）請求項１１に記載の発明によれば、演算処理手段で、さらに透明膜の膜厚と透明膜の屈折率に基づいて透明膜の表面高さを補正演算することにより、透明膜の表面高さをより精度よく求めることができる。すなわち、請求項２および請求項３に記載の方法を好適に実現することができる。
【００３０】
また、請求項１２に記載の発明は、請求項１０または請求項１１に記載の表面形状および／または膜厚測定装置において、前記周波数帯域制限手段は、前記白色光源から前記撮像手段までの光路に取り付けられる、特定周波数帯域の白色光だけを通過させるバンドパスフィルタであることを特徴とするものである。
【００３１】
（作用・効果）請求項１２に記載の発明によれば、白色光源から撮像手段までの光路に取り付けられたバンドパスフィルタは、特定周波数帯域の白色光のみを通過させる。これにより、撮像手段では、特定周波数帯域の白色光による干渉縞および測定対象面が撮像される。したがって、装置構成を簡素化することができるとともに、任意の周波数帯域を通過させるバンドパスフィルタを利用することによって、特定周波数帯域を任意の周波数帯域にすることもできる。
【００３２】
また、請求項１３に記載の発明は、請求項１０または請求項１１に記載の表面形状および／または膜厚測定装置において、前記周波数帯域制限手段は、前記白色光源から発せられた白色光の周波数帯域を特定周波数帯域にまで狭める、前記白色光源から前記撮像手段までの光学系であることを特徴とするものである。
【００３３】
（作用・効果）請求項１３に記載の発明によれば、白色光源から撮像手段までの光学系は、白色光源から発生した白色光が撮像手段に届くまでの間に、その白色光の周波数帯域を特定周波数帯域にまで狭める。これにより、撮像手段では、特定周波数帯域の白色光による干渉縞および測定対象面が撮像される。したがって、装置構成をより簡素化することができる。
【００３４】
また、請求項１４に記載の発明は、請求項１０または請求項１１に記載の表面形状および／または膜厚測定装置において、前記周波数帯域制限手段は、特定周波数帯域の白色光を感知する前記撮像手段の周波数感度であることを特徴とするものである。
【００３５】
（作用・効果）請求項１４に記載の発明によれば、撮像手段は、その周波数特性によって、特定周波数帯域の白色光による干渉縞および測定対象面を撮像する。したがって、装置構成をより簡素化することができる。
【００３６】
【発明の実施の形態】
以下、図面を参照して本発明の実施例について具体的に説明をする。
図１は、本発明の実施例に係る表面形状測定装置の概略構成を示す図である。
【００３７】
この表面形状測定装置は、半導体ウエハ、ガラス基板や金属基板などの測定対象物３０の表面を覆った透明膜３１および透明膜３１の裏面側と接合している測定対象物３０に形成された微細なパターンに、特定周波数帯域の白色光を照射する光学系ユニット１と、光学系ユニット１を制御する制御系ユニット２とを備えて構成されている。
【００３８】
光学系ユニット１は、測定対象面３０Ａ、３１Ａおよび参照面１５に照射する白色光を発生させる白色光源１０と、白色光源１０から白色光を平行光にするコリメートレンズ１１と、特定周波数帯域の白色光だけを通過させるバンドパスフィルタ１２と、バンドパスフィルタ１２を通過してきた白色光を測定対象物３０の方向に反射する一方、測定対象物３０の方向からの白色光を通過させるハーフミラー１３と、ハーフミラー１３で反射されてきた白色光を集光する対物レンズ１４と、対物レンズ１４を通過してきた白色光を、参照面１５へ反射させる参照光と、測定対象面３０Ａ、３１Ａへ通過させる測定光とに分けるとともに、参照面１５で反射してきた参照光と測定対象面３０Ａ、３１Ａで反射してきた測定光とを再びまとめて、干渉縞を発生させるビームスプリッタ１７と、参照面１５で参照光を反射させるために設けられたミラー１６と、参照光と測定光とがまとめられた白色光を結像する結像レンズ１８と、干渉縞とともに測定対象面３０Ａを撮像するＣＣＤカメラ１９とを備えて構成されている。
【００３９】
白色光源１０は、例えば白色光ランプなどであり、比較的広い周波数帯域の白色光を発生させる。この白色光源１０から発生された白色光は、コリメートレンズ１１によって平行光とされ、バンドパスフィルタ１２に入射する。
【００４０】
バンドパスフィルタ１２は、特定周波数帯域の白色光だけを通過させるためのフィルタであり、白色光源１０からＣＣＤカメラ１９までの光路に取り付けられる。好ましくは、白色光源１０からの白色光が参照面１５への参照光と測定対象面３０Ａの測定光に分かれる位置までの間の光路に取り付けられる。この実施例では、例えばコリメートレンズ１１と、ハーフミラー１３との間の光路に取り付けられている。バンドパスフィルタ１２としては、例えば中心波長が６００ｎｍの帯域通過型光学干渉フィルタなどを利用する。このバンドパスフィルタ１２を通過した白色光は、その周波数帯域が狭められ、特定周波数帯域の白色光だけがバンドパスフィルタ１２を通過する。
【００４１】
ハーフミラー１３は、バンドパスフィルタ１２を通過してきた特定周波数帯域の白色光を測定対象物３０の方向に向けて反射する一方、測定対象物３０の方向から戻ってきた白色光を通過させるものである。このハーフミラー１３で反射された特定周波数帯域の白色光は、対物レンズ１４に入射する。
【００４２】
対物レンズ１４は、入射してきた白色光を焦点Ｐに向けて集光するレンズである。この対物レンズ１４によって集光される白色光は、参照面１５を通過し、ビームスプリッタ１７に到達する。
【００４３】
ビームスプリッタ１７は、対物レンズ１４で集光される白色光を、参照面１５で反射させるために、ビームスプリッタ１７の例えば上面で反射させる参照光と、測定対象面３０Ａ、３１Ａで反射させるために、ビームスプリッタ１７を通過させる測定光とに分けるとともに、それら参照光と測定光とを再びまとめることによって、干渉縞を発生させるものである。ビームスプリッタ１７に達した白色光は、ビームスプリッタ１７の上面で反射された参照光と、ビームスプリッタ１７を通過する測定光とに分けられ、その参照光は参照面１５に達し、その測定光は透明膜３１で覆われた測定対象物３０の透明３１膜の表面、および透明膜の裏面と接合した測定対象物３０の表面である測定対象面３０Ａに達する。
【００４４】
参照面１５には、参照光をビームスプリッタ１７の方向に反射させるためのミラー１６が取り付けられており、このミラー１６によって反射された参照光は、ビームスプリッタ１７に達し、さらに、この参照光はビームスプリッタ１７によって反射される。
【００４５】
ビームスプリッタ１７を通過した測定光は、焦点ＰおよびＰ’に向けて集光され、測定対象面３０Ａ，３１Ａ上で反射する。この反射した２つの測定光は、ビームスプリッタ１７に達して、そのビームスプリッタ１７を通過する。
【００４６】
ビームスプリッタ１７は、参照光と測定光とを再びまとめる。このとき、参照面１５とビームスプリッタ１７との間の距離Ｌ１と、ビームスプリッタ１７と測定対象面３０Ａ、３１Ａとの間の距離Ｌ２との、距離の違いによって光路差が生じる。この光路差に応じて、参照光と測定光とは干渉し合うことで、干渉縞が生じる。この干渉縞が生じた状態の白色光は、ハーフミラー１３を通過し、結像レンズ１８によって結像されて、ＣＣＤカメラ１９に入射する。
【００４７】
ＣＣＤカメラ１９は、干渉縞が生じた状態の白色光とともに、測定光によって映し出される測定対象面３０Ａ，３１Ａの焦点Ｐ、Ｐ’付近の画像を撮像する。この撮像した画像データは、制御系ユニット２によって収集される。また、後述で明らかになるが、本願発明の変動手段に相当する制御系ユニット２の駆動部２４によって、例えば光学系ユニット１が上下左右に変動される。特に、光学系ユニット１が上下方向に駆動されることによって、距離Ｌ１と距離Ｌ２との距離が変動される。これにより、距離Ｌ１と距離Ｌ２との距離の差に応じて、干渉縞が徐々に変化する。ＣＣＤカメラ１９によって、後述する所定のサンプリング間隔ごとに、干渉縞の変化とともに測定対象面３０Ａ、３１Ａの画像が撮像され、その画像データが制御系ユニット２によって収集される。ＣＣＤカメラ１９は、本発明における撮像手段に相当する。
【００４８】
制御系ユニット２は、表面形状測定装置の全体を統括的に制御や、所定の演算処理を行うためのＣＰＵ２０と、ＣＰＵ２０によって逐次収集された画像データやＣＰＵ２０での演算結果などの各種のデータを記憶するメモリ２１と、サンプリング間隔やその他の設定情報を入力するマウスやキーボードなどの入力部２２と、測定対象面３０Ａの画像などを表示するモニタ２３と、ＣＰＵ２０の指示に応じて光学系ユニット１を上下左右に駆動する例えば３軸駆動型のサーボモータなどの駆動機構で構成される駆動部２４とを備えるコンピュータシステムで構成されている。なお、ＣＰＵ２０は、本発明におけるサンプリング手段および演算手段に、メモリ２１は本発明における記憶手段に、駆動部２５は本発明における変動手段にそれぞれ相当する。
【００４９】
ＣＰＵ２０は、いわゆる中央処理装置であって、ＣＣＤカメラ１９、メモリ２１及び駆動部２４を制御するとともに、ＣＣＤカメラ１９で撮像した干渉縞を含む測定対象面３０Ａの画像データに基づいて、測定対象物３０の特定箇所の透明膜３１の表面高さ、測定対象物３０の表面高さ、および透明膜３１の膜厚Ｄとを求める演算処理を行う。この処理については後で詳細に説明する。さらに、ＣＰＵ２０には、モニタ２３と、キーボードやマウスなどの入力部２２とが接続されており、操作者は、モニタ２３に表示される操作画面を観察しながら、入力部２２から各種の設定情報の入力を行う。また、モニタ２３には、測定対象面３０Ａの測定終了後に、測定対象面３０Ａ、３１Ａの表面高さ、透明膜３１の膜厚Ｄ、および測定対象面の凹凸形状などを数値や画像として表示される。
【００５０】
駆動部２４は、光学系ユニット１内の参照面１５とビームスプリッタ１７との間の固定された距離Ｌ１と、ビームスプリッタ１７と測定対象面３０Ａとの間の可変の距離Ｌ２との距離の差を変化させるために、光学系ユニット１を直交３軸方向に変動させる装置であり、ＣＰＵ２０からの指示によって光学系ユニット１をＸ，Ｙ，Ｚ軸方向に駆動する例えば３軸駆動型のサーボモータを備える駆動機構で構成されている。なお、駆動部２４は、本発明における変動手段に相当し、本発明における相対的距離とは、参照面１５から測定対象面３０Ａまでの距離すなわち距離Ｌ１および距離Ｌ２を示す。本実施例では、光学系ユニット１を動作させるが、例えば測定対象物３０が載置される図示していないテーブルを直交３軸方向に変動させるようにしてもよい。
【００５１】
以下、本実施例の特徴部分である表面形状測定装置全体で行なわれる処理を図２のフローチャートを参照しながら具体的に説明する。
【００５２】
[第１実施例]
本実施例では、中心周波数が６００ｎｍのバンドパスフィルタ１２を挿入し、測定対象物３０であるＳｉ基板の表面に透明膜３１として約０．４５μｍの酸化膜（ＳｉＯ₂）を形成したものを用いて測定した場合を例に採って説明する。なお、図７は、バンドパスフィルタ１２を通過した白色光の波長スペクトルの分布を示した図である。
【００５３】
＜ステップＳ１＞ 条件設定
光学系ユニットをｚ軸方向に移動させるための走査速度や走査レンジなどの種々の条件設定や、測定対象と同じ対象物の試料を用いて干渉光の強度値の平均値と透明膜３１の膜厚の相関関係を予め求め、その関係式等を入力設定する。
【００５４】
本実施例の場合、種々の条件として、例えばバンドパスフィルタ１２によって特定周波数帯域が制限された白色光の中心周波数を６００ｎｍとする。
【００５５】
干渉光の強度値の平均値と透明膜３１の膜厚の相関関係による関係式は、次のようにして求まる。
【００５６】
透明膜内を透過する白色光および測定対象面３０Ａで反射する白色光（反射光）は、その透明膜内で多重に反射する。しかし、本実施例では、この多重反射による干渉光の強度が十分に小さいことから無視し、測定対象面３０Ａで１回反射した場合を仮定している。このときの観測輝度ｇ（強度値）は、次式で表される。
【００５７】
【数１】

【００５８】
ここで、ｚｐは測定対象面３０Ａの表面高さ、Ｄは透明膜３１の膜厚、α＝２ｋ（空気の屈折率＝１と仮定する）、ｋは角波数、ｎｓは膜屈折率、ｋｌは照射される光の波数の下限値、ｋｕは照射される光の波数の上限値、Ｐ，Ｑ，Ｒ，Ｓは装置と対象膜物性により決まるパラメータである。
【００５９】
上記式（１）から求まる強度値ｇの交流成分（ＡＣ成分）をｆ、直流成分（ＤＣ成分）をＣとすると、各成分は次式で表すことができる。
【００６０】
【数２】

【００６１】
【数３】

【００６２】
すなわち、式（３）において、右辺にはピーク高さｚｐが含まれず、透明膜の膜厚Ｄの未知のパラメータである。したがって、強度値の実測値Ｃ（Ｄ）が与えられると、膜厚Ｄが求まることが分かる。
【００６３】
また、装置条件と透明膜の膜厚の条件が与えられると、強度値の平均値Ｃと膜厚Ｄとの関係は図３および図４（図３のレンジ拡大図）のように求めることができる。求められた強度値の平均値Ｃと透明膜の膜厚Ｄの関係を図３および図４に示すように直線近似し、制御系ユニット２のメモリ２１などに予め設定保存しておく。
【００６４】
なお、図３および図４において、強度平均曲線は、照明光の波長λ、透明膜の屈折率をｎとした場合、（λ／２）／ｎの周期を持つ。本実施例では、略２００ｎｍの周期である。
【００６５】
＜ステップＳ２＞ 測定データ取得
光学系ユニット１は、白色光源１０から発生される白色光をバンドパスフィルタ１２によって特定周波数帯域に制限した白色光を測定対象面３０Ａ、３１Ａおよび参照面１５に照射する。このバンドパスフィルタ１２または後述する測定光および参照光に分けるまでの光学系によって特定周波数に制限するまでが、本発明における請求項８に記載の第１の過程の前の過程に相当する。
【００６６】
また、ＣＰＵ２０は、予め所定の測定場所に移動された光学系ユニット１をｚ軸方向に移動を開始させるための変動開始の指示を駆動部２４に与える。駆動部２４は、図示しないステッピングモータなどの駆動系を駆動して、光学系ユニット１をｚ軸方向に予め決められた距離だけ移動させる。これにより、参照面１５と測定対象面３０Ａとの距離が変動される。この過程が本発明における第１の過程に相当する。
【００６７】
ＣＰＵ２０は、光学系ユニット１がサンプリング間隔だけ移動するたびに、ＣＣＤ１９で撮像される干渉縞を含む測定対象面３０Ａ、の画像データを収集して、メモリ２１に順次記憶する。光学系ユニット１が予め決められた距離だけ移動することで、メモリ２１には光学系ユニット１の移動距離およびサンプリング間隔によって決まる複数枚の画像データが記憶される。この過程が本発明における第２の過程に相当する。
【００６８】
＜ステップＳ３＞ 特定箇所の干渉光強度値群を取得
例えば、操作者がモニタ２３に表示される測定対象面３０Ａを観察しながら、その測定対象面３０Ａ、３１Ａの高さを測定したい複数の特定箇所を入力部２２から入力する。ＣＰＵ２０は、入力された複数の特定箇所を把握して、測定対象面３０Ａを撮像した画像上の前記複数の特定箇所に相当する画素の濃度値すなわち特定箇所における干渉光の強度値を、複数枚の画像データからそれぞれ取込む。これにより、各特定箇所における複数個の強度値（干渉光強度値群）が得られる。この過程が、本発明における第３の過程に相当する。
【００６９】
＜ステップＳ４＞ 強度値群から平均値を求める
ＣＰＵ２０は、図５に示すように、離散的に取得した特定箇所における干渉光強度値群に基づいて、干渉光の強度値を求める。なお、この過程が本発明における第４の過程に相当する。
【００７０】
＜ステップＳ５＞ 透明膜の膜厚を求める
ステップＳ４で求めた強度値の平均値を予め設定入力した式（３）の直線近似式を利用して透明膜３１の膜厚Ｄを求める。
【００７１】
本実施例では、強度値の平均値が７１．５となったので、この強度値の平均値から、図３の関係を使って膜厚Ｄが０．４〜０．５μｍの間と仮定すると、膜厚Ｄが０．４６μｍと求められる。
【００７２】
なお、この過程が、本発明における第５の過程に相当する。
【００７３】
＜ステップＳ６＞ 強度値の平均値から特性値を求める
ＣＰＵ２０は、ステップＳ４で干渉光強度値群に基づいて求めた干渉光の強度値の平均値を利用し、干渉光強度値群の各強度値から平均値を減算した各値（調整値群）を求める。つまり、図６に示すように、干渉縞波形から直流成分を除去し、交流成分のみを残す。
【００７４】
調整値をさらに２乗し、強度値をプラス側に強調した特性値を求める。なお、ステップＳ６は、本発明における第６の過程に相当する。
【００７５】
＜ステップＳ７＞ ピーク位置の取得
ＣＰＵ２０は、ステップＳ６で求まる特性値群と利用し、２乗包絡線または包絡線である特性関数を作成する。この作成としては、例えば帯域通過型標本化定理によって波形を復元してもよいし、バンドパスフィルタによって特性値を平準化して求めるようにしてもよい。この作成した特性関数から特性値がピークとなる箇所を読み取る。つまり、測定対象面３０Ａのピーク位置として取得画像の枚数目（数値）を読み取る。
【００７６】
＜ステップＳ８ａ＞ 表面形状の測定
ＣＰＵ２０は、求めたピーク位置が撮像された画像の枚数目の値（数値）に予め設定した既知の標本点間隔の積をとることによって測定対象面３０Ａの表面高さを求める。ステップＳ８のここまでが、本発明における第８の過程に相当する。
【００７７】
次に、この測定対象面３０Ａの表面高さにステップＳ５で求めた透明膜３１の膜厚Ｄを加算することにより、透明膜３１の表面高さを求める。なお、ステップＳ８は、本発明における第９の過程に相当する。
【００７８】
＜ステップＳ９＞ 全特定箇所が終了？
ＣＰＵ２０は、全ての特定箇所が終了するまで、ステップＳ３〜Ｓ８の処理を繰り返し行い、全ての特定箇所の高さを求める。
【００７９】
＜ステップＳ１０＞ 表示
ＣＰＵ２０は、モニタ２３に透明膜３１の特定箇所の透明膜３１の表面高さや測定対象面３０Ａの表面高さ、膜厚Ｄの情報を表示したり、それら各特定箇所の高さの情報に基づいた３次元または２次元の画像を表示したりする。操作者は、これらの表示を観察することで、測定対象物３０の測定対象面３０Ａや透明膜３１の表面３１Ａの凹凸形状を把握することができる。
【００８０】
ところで、図３および図４に示すように、Ｃ（Ｄ）は、白色光（照明光）波長λ、透明膜３１の屈折率ｎとして（λ／２）／ｎの周期を持つ。本実施例では、約２００ｎｍの周期である。
【００８１】
したがって、強度値の平均値Ｃが与えられた時、一般に、複数の透明膜３１の膜厚Ｄの候補が存在ずる。対象の膜厚Ｄの値が十分に狭い範囲に存在することが既知の場合には、一義的に膜厚Ｄを決定できる。
【００８２】
なお、上述のように一義的に膜厚を求めづらい場合には、異なる複数の特定周波数帯域の波長で同様の測定を行い、複数の測定結果から共通する膜厚Ｄの候補を選択することで、一義的に透明膜３１の膜厚Ｄを決定できる。
【００８３】
上述した実施例によれば、透明膜３１で覆われた測定対象物３０と同じ対象物の干渉光の強度値の平均値と透明膜３１の膜厚Ｄの相関関係による式（３）を予め求めて設定入力し、実測によって求めた強度値を、この式（３）に代入して演算処理することによって、透明膜３１の膜厚Ｄを精度よく求めることができる。また、干渉光の強度値群から包絡線に相当する特性値群を取得し、この特性値群の示す波形データから特性関数としての２乗包絡線を求める。この２乗包絡線のピーク位置情報を求め、このピーク位置情報に基づいて、測定対象面３０Ａの特定箇所の表面高さが求められる。この求まる測定対象面３０Ａの表面高さと透明膜３１の膜厚Ｄの加算から透明膜３１の表面高さを求めることができる。つまり、透明膜３１の凹凸形状を、透明膜３１の膜厚Ｄと測定対象面３０Ａの表面高さから測定することができる。
【００８４】
[第２実施例]
本実施例では、透明膜表面での反射光の影響により発生するピーク位置のズレ量を厳密に補正し、透明膜３１の表面高さを正しく求める場合について説明する。
【００８５】
以下、原理について説明する。
【００８６】
上記式（２）の強度値ｇの交流成分をｆとして表した式（２）をｃｏｓ関数と振幅成分の積として変形する。
【００８７】
ｆ（ｚ；ｚｐ，Ｄ）＝ｍ（ｚ；ｚｐ，Ｄ）cos｛β（ｚ−ｚｐ）＋Ａ（ｚ）｝…（４）
【００８８】
包絡線関数ｒの２乗を次式（５）により定義する。
ｒ（ｚ；ｚｐ，Ｄ）= [ｍ（ｚ；ｚｐ，Ｄ）]² … （５）
【００８９】
この式（５）から求まるピーク位置ｚｐは、透明膜の影響によって正確な値ではなくズレ量を含んだピーク位置ｚｐ’である。
【００９０】
式（２）によると、ピーク位置情報ｚｐは、ｚ−ｚｐの関係でしか現れていない。したがって、ｚｐの値が変化した場合に、関数ｆ自体は変形せずに、ピーク位置がｚ軸方向に平行移動することを意味する。その結果、２乗包絡線関数自体も同じ特性を有することになる。
【００９１】
よって、ｚｐ＝０のときにおける２乗包絡線関数ｒのピーク位置ｚｐ’（０）は、真のピーク位置ｚｐ＝０からのズレ量であり、ｚｐが０以外の場合のズレ量と同一である。つまり、ｚｐ−ｚｐ’＝０−ｚｐ’（０）の関係となる。したがって、ズレ量を含まない真のピーク位置は次式（６）で表される。
【００９２】
ｚｐ＝ｚｐ’―ｚｐ’（０） … （６）
【００９３】
このことから、上記式（６）において右辺第２項は、透明膜３１の膜厚Ｄが既知の場合、補正項として予め求めておくことができる。すなわち、ｚｐ＝０のときのｆをｆ０と、ｒをｒ０と定義すると、上記式（４）および（５）は次式（７）および（８）として表すことができ、式（７）および（８）がズレ量を補正したピーク位置を求める演算式となる。
【００９４】
【数４】

【００９５】
ｒ０（ｚ；Ｄ）= [ｍ（ｚ；０，Ｄ）]² … （８）
【００９６】
上記式において、膜厚Ｄが既知の場合、ｒ０はｚのみの関数となるので、ピーク位置ｚｐ’（０）を求めることができるのである。
【００９７】
透明膜３１の表面高さのズレ量は、透明膜３１の膜厚Ｄと透明膜の屈折率ｎとの関係に依存することが分かる。したがって、求めるべき真の透明膜３１の表面高さｈは、ｈ＝ｈａ＋ｆ（ｎ，Ｄ）の関係で表すことができる。ここで、ｈａは、実測によって求まる測定対象面３０Ａの表面高さ、ｆ（ｎ，Ｄ）は膜厚の補正量を含む透明膜の膜厚（以下、適宜に「補正量」という）である。
【００９８】
また、補正量ｆ（ｎ，Ｄ）は、近似的にはｎ×Ｄの積算により求めることもできる。このことは、発明者達の実験シミュレーションによって以下のように確認されている。
なお、透明膜と測定対象面の複数の組み合わせにおいて、以下の表１に示す３通りについて実験シミュレーションを行った。
【００９９】
【表１】

【０１００】
上記の表１の条件によって行った実験シミュレーションの結果を示す図８〜 １０における透明膜３１の膜厚Ｄと補正量の関係は、測定対象面３０Ａの表面３０Ａからの反射光が実験例１から実験例３のように強くなるにつれて補正量ｆ（ｎ，Ｄ）＝ｎ×Ｄの関係に近似することが分かった。
【０１０１】
次に、本実施例の表面形状測定装置全体で行なわれる処理を図２のフローチャートを参照しながら具体的に説明する。なお、本実施例では、第１実施例と共通する処理（ステップＳ１〜ステップＳ６）につていの説明は省略する。
【０１０２】
＜ステップＳ７＞ ピーク位置の取得
ＣＰＵ２０は、ステップＳ６で求まる特性値群と利用し、包絡線または２乗包絡線である特性関数を作成する。この作成としては、例えば帯域通過型標本化定理によって波形を復元してもよいし、バンドパスフィルタによって特性値を平準化して求めるようにしてもよい。この作成した特性関数から特性値がピークとなる箇所を読み取る。つまり、測定対象面３０Ａのピーク位置として取得画像の枚数目（数値）を読み取る。
【０１０３】
＜ステップＳ８ｂ＞ 表面形状の測定
ＣＰＵ２０は、実測によって求まったピーク位置を利用して測定対象面３０Ａの表面高さを求める。測定対象面３０Ａの表面高さは、例えば、ピーク位置の撮像された画像の枚数目の数値と標本点間隔の積算処理により求める。
【０１０４】
次に、実測により求まった測定対象面３０Ａの表面高さに対してピーク位置のズレ量によって影響する透明膜３１の表面高さのズレ量を補正する。つまり、予め求めた補正量ｆ（ｎ，Ｄ）を測定対象面３０Ａの表面高さに加算することにより、真の透明膜３１の表面高さを求める。なお、ステップＳ８ｂは、本発明における第９の過程および請求項２に記載の方法に相当する。
【０１０５】
以下、ステップＳ９およびステップＳ１０は、第１実施例のステップＳ９およびステップＳ１０と同じ処理であるので、ここでの具体的な説明は省略する。
【０１０６】
以上のように、測定対象面３０Ａを覆う透明膜３１の影響によるピーク位置のズレ量を補正することによって、正確な透明膜３１の表面高さを求めることができる。
【０１０７】
本発明は上述した実施例のものに限らず、次のように変形実施することもできる。
（１）上記各実施例では、測定対象面３０Ａの画像データを撮像した後で、特定箇所の干渉光の強度値を取得するように構成したが、本発明はこれに限定されるものではなく、例えば、撮像した画像上の特定箇所に相当する画素における強度値をリアルタイムに取得して、それら干渉光の強度値を順次メモリ２１に記憶するように構成することもできる。
【０１０８】
（２）上記各実施例では、白色光源から発せられた白色光の周波数帯域を、バンドパスフィルタ１１によって特定周波数帯域に帯域制限したが、本発明はこれに限定されるものではなく、白色光源からの白色光が撮像手段であるＣＣＤカメラ１９までの光学系（光源、レンズ、各ミラーを含む）によって白色光源からの白色光の周波数帯域が帯域制限されることを利用して、その周波数帯域を予め把握しておき、その帯域制限された周波数帯域を本発明における特定周波数帯域とすることもできる。
【０１０９】
（３）上記各実施例では、撮像手段であるＣＣＤカメラ１９の周波数特性によって制限される周波数帯域を特定周波数帯域として、その特定周波数帯域を予め把握しておき、その帯域制限された周波数帯域を本発明における特定周波数帯域とすることもできる。
【０１１０】
（４）上記各実施例では、撮像手段としてＣＣＤカメラ１９を用いたが、例えば、特定箇所の干渉光の強度値のみを撮像（検出）することに鑑みれば、一列または平面状に構成された受光素子などで撮像手段を構成することもできる。
【０１１１】
（５）上記各実施例では、白色光源１０から白色光をコリメートレンズ１１で平行光にした後に、バンドパスフィルタ１２を設けて特定周波数帯域の白色光を通過させるように構成していたが、バンドパスフィルタ１２を備えない構成のものであってもよい。
【０１１２】
（６）上記各実施例において、特性関数および補正量を規定するためのパラメータを予め求めて設定しおくことが好ましい。このパラメータとしては、例えば、反射率が既知の測定対象物３０の試料を用いて求めた装置パラメータや、膜厚が既知の測定対象物３０の試料を用いて求めた装置パラメータなどが挙げられる。これら各種パラメータを予め設定することによって、透明膜の膜厚、測定対象面Ａの高さ、および透明膜の表面高さをより一層精度よく求めることができる。
【０１１３】
【発明の効果】
以上の説明から明らかなように、本発明によれば、白色光を透明膜で覆われた測定対象面と参照面との距離を変動させながら照射し、取得した特定箇所における干渉光の強度値群を取得する。この強度値群から干渉光の強度値の変化の実測値による平均値を求める。つまり、測定対象物と同じ対象物の干渉光の強度値の平均値と透明膜の膜厚の関係について予め求めた相関関係に基づいて、この実測値による強度値の平均値から透明膜の膜厚を求めることができる。また、干渉光の強度値群から包絡線または２乗包絡線に相当する特性値を求めて特性関数を作成し、この特性関数から測定対象面と参照面との距離に関連するピーク位置情報が得られ、このピーク維持情報に基づいて測定対象面の表面高さを求めることができる。さらに、求まった透明膜の膜厚と測定対象面の表面高さから透明膜の表面高さを求めることができる。
【０１１４】
したがって、予め求めた干渉光の強度値の平均値と透明膜の膜厚との関係による相関関係を利用することによって、実測によって求めた干渉光の強度値の平均値から透明膜の膜厚を容易、かつ精度よく求めることができ、ひいては、測定対象面の表面高さおよび透明膜の表面高さも精度よく求めることができる。
【図面の簡単な説明】
【図１】本実施例に係る表面形状測定装置の概略構成を示す図である。
【図２】第１および第２実施例の表面形状測定装置における処理を示すフローチャートである。
【図３】強度値の平均値と膜厚との関係を示した図である。
【図４】図３の拡大図である。
【図５】特定関数のピーク位置を求める処理を説明するための説明図である。
【図６】特定関数のピーク位置を求める処理を説明するための説明図である。
【図７】バンドパスフィルタを通過した白色光のスペクトル分布を示した図である。
【図８】透明膜の表面高さの補正量を求めるシミュレーションを示した図である。
【図９】透明膜の表面高さの補正量を求めるシミュレーションを示した図である。
【図１０】透明膜の表面高さの補正量を求めるシミュレーションを示した図である。
【符号の説明】
１ … 光学系ユニット
２ … 制御系ユニット
１０ … 白色光源
１１ … コリメートレンズ
１３ … ハーフミラー
１４ … 対物レンズ
１５ … 参照面
１６ … ミラー
１７ … ビームスプリッタ
１８ … 結像レンズ
１９ … ＣＣＤカメラ
２０ … ＣＰＵ
２１ … メモリ
２２ … 入力部
２３ … モニタ
２４ … 駆動部
３０ … 測定対象物
３０Ａ… 測定対象面（測定対象物）
３１ … 透明膜
３１Ａ… 測定対象面（透明膜）
Ｄ … 膜厚（透明膜）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface shape and / or film thickness measurement method and apparatus for measuring the uneven shape and thickness of a measurement target surface covered with a transparent film, and more particularly to a measurement target surface shape in a non-contact manner using white light. And / or a technique for measuring a film thickness.
[0002]
[Prior art]
As a conventional device of this type, a surface shape measuring device using a method for measuring the uneven shape of a precision processed product such as a semiconductor wafer or a glass substrate for a liquid crystal display using interference of white light is widely known.
[0003]
That is, the optical path difference of reflected light that reflects the measurement target surface and the reference surface by changing the distance of the measurement target surface while irradiating the measurement target surface and the reference surface of the measurement target object with white light from the white light source And the intensity value of the interference light at this time is sampled at a predetermined interval. A characteristic value group of interference fringe waveform peaks is obtained based on the intensity value group obtained by this sampling, and each peak position information is obtained from an envelope obtained by smoothing the characteristic value by a low-pass filter. The surface height of the measurement object is obtained from the obtained peak position information. (See Patent Document 1)
[0004]
[Patent Document 1]
US Patent Publication USP 5,133,601
[0005]
[Problems to be solved by the invention]
However, in the case of these conventional examples, there is a problem that the surface height of the measurement object cannot be obtained with high accuracy.
[0006]
That is, when the surface of the object is covered with the transparent film, the white light is reflected by the surface of the transparent film and the surface of the measurement object that is transmitted through the transparent film and joined to the back surface of the transparent film. Two reflected lights are generated. When the intensity value of a given pixel in multiple images acquired with this reflected light superimposed is represented by an intensity waveform, it is as simple as when measuring an object whose surface is not covered with a transparent film. Two peaks corresponding to the surface of the transparent film and the surface of the object to be measured are generated.
[0007]
For example, when the transparent film is thin, the waveform of the reflected light from the surface of the transparent film and the surface of the measurement object is substantially superimposed, and each peak appears on the waveform. In such a case, in the conventional method for obtaining the position information of one peak, the peak position information is obtained by performing smoothing processing by simply considering the two peaks as one peak by a low-pass filter. become.
[0008]
Therefore, there is a problem that it is impossible to obtain accurate peak position information of the surface height of the measurement object, and it is impossible to accurately obtain peak position information of the surface height of the measurement object under the transparent film. is there.
[0009]
Further, there is a problem that the film thickness of the transparent film cannot be accurately obtained unless the peak position information is accurately obtained and the surface height of the measurement object and the surface height of the transparent film are obtained.
[0010]
The present invention has been made in view of such circumstances, and the surface height of the transparent film at the specific location of the measurement object covered by the transparent film, the surface height of the measurement object, and the transparent film The main object is to provide a surface shape and / or film thickness measuring method and apparatus capable of accurately determining the film thickness.
[0011]
[Means for Solving the Problems]
  In order to achieve such an object, the present invention has the following configuration.
  That is, the invention according to claim 1 varies the distance between the measurement target surface and the reference surface while irradiating the measurement target surface and the reference surface covered with a transparent film with white light from a white light source. Causes the interference fringe to change due to the reflected light reflected from the measurement target surface and the reference surface and returning from the same optical path, and the surface height of the transparent film at a specific location on the measurement target surface is determined based on the intensity value of the interference light at this time. In the method for measuring the surface shape and / or film thickness of the measurement object surface for obtaining at least one of the surface height of the measurement object surface and the film thickness of the transparent film,
  A first step of changing a distance between the measurement target surface irradiated with white light of the specific frequency band and a reference surface;
  A second process of continuously acquiring images of the measurement target surface at predetermined intervals in the process of changing the distance between the measurement target surface and the reference surface;
  A third step of obtaining a change in the intensity value group of the interference light in each pixel of the plurality of images continuously acquired at the predetermined interval;
  A fourth step of calculating an average value of the obtained intensity value group;
  Correlation between the average value of the interference light intensity value obtained in advance for the same object as the measurement object and the film thickness of the transparent filmFormula

, Where C ( D ) Is the average intensity value, k _u Is the upper limit of the wave number of the irradiated light, k ₁ Is the lower limit value of the wave number of the irradiated light, R and S are parameters determined by the physical properties of the apparatus and the measurement object, α is the refractive index of air, and k is the angular wave number, n _s Is the film refractive index, D is the film thickness of the transparent filmA fifth step of obtaining the thickness of the transparent film from the average value of the intensity values obtained by actual measurement in the fourth step based on
  From the obtained intensity value groupThe direct current component is removed to obtain only the alternating current component, and the alternating current component is squared and emphasized on the plus side.A sixth process of acquiring characteristic value groups;
  The characteristic value groupBecomes an envelope fromA seventh step of obtaining a characteristic function, and obtaining peak position information related to a distance between the measurement target surface and the reference surface based on the characteristic function;
  An eighth step of obtaining the surface height of the measurement target surface based on the obtained peak position information;
  A ninth process for determining the surface height of the transparent film from the film thickness of the transparent film determined in the fifth process and the surface height of the measurement target surface determined in the eighth process;
  It is characterized by comprising.
[0012]
(Operation / Effect) According to the first aspect of the present invention, the white light generated from the white light source is applied to the measurement target surface and the reference surface. Interference fringes that interfere with each other according to the optical path difference of the white light reflected by the surface to be measured and the reference surface, which are the surfaces of the object bonded to the surface of the transparent film and the surface side, are generated. Here, by varying the distance between the measurement target surface and the reference surface, each of the optical path difference is changed to obtain an image of a plurality of measurement target surfaces continuously at predetermined intervals while changing the interference fringes, A change in the intensity value group of the interference light in each pixel for each image is obtained. An average value is obtained from the change of the intensity value group. Next, based on the correlation between the average value of the interference light intensity values obtained in advance for the same object as the measurement object and the transparent film, the film thickness of the transparent film is obtained from the average value of the intensity value group obtained by actual measurement. . A characteristic value group corresponding to the envelope is acquired from the intensity value group acquired at the same time, and a characteristic function is obtained from the waveform data indicated by the characteristic value group. From this characteristic function, peak position information related to the distance between the measurement target surface and the reference surface is obtained, and the surface height of the measurement target surface is obtained based on the peak position information. The obtained surface height of the measurement target surface and the film thickness of the transparent film obtained by actual measurement are used. That is, the surface height of the transparent film is obtained by adding the respective values. That is, by using the average value of the intensity value group of the interference light, the film thickness of the transparent film can be obtained accurately, and by using the film thickness of this transparent film, the surface height of the transparent film can be more accurately determined. I can stop.
[0013]
Further, the invention according to claim 2 is the surface shape and / or film thickness measuring method according to claim 1, wherein the surface height (h) of the transparent film obtained in the ninth step is a film of the transparent film. The film thickness f (n, D) including the correction amount of the film thickness of the transparent film obtained in advance from the relationship between the thickness (D) and the refractive index (n) of the transparent film is the surface of the measurement object obtained in the eighth step. It is a value obtained by adding to the surface height (ha).
[0014]
Further, the invention according to claim 3 is the surface shape and / or film thickness measuring method according to claim 2, wherein the film thickness f (n, D) of the transparent film including the correction amount of the transparent film is f It is represented by the relational expression of (n, D) = n × D.
[0015]
(Function / Effect) According to the inventions of claim 2 and claim 3, the surface height (h) of the transparent film is determined from the film thickness (D) of the transparent film and the refractive index (n) of the transparent film. The film thickness f (n, D) of the transparent film including the correction amount of the obtained film thickness is added to the surface height (h) of the surface to be measured. The film thickness f (n, D) of the transparent film including the correction amount at this time can be expressed by a relational expression f (n, D) = n × D. Therefore, the surface height of the transparent film can be determined with higher accuracy.
[0016]
According to a fourth aspect of the present invention, in the surface shape and / or film thickness measuring method according to any of the first to third aspects, the characteristic function obtained in the seventh step is an envelope or 2 It is a characteristic envelope.
[0017]
(Function / Effect) According to the invention described in claim 4, an envelope or a square envelope is used as the characteristic function. Therefore, the peak position information can be obtained in a state where the noise component of the interference fringe waveform is removed. Therefore, the surface height of the measurement target surface can be obtained with high accuracy, and consequently the surface height of the transparent film can also be obtained with high accuracy.
[0018]
The invention according to claim 5 is the surface shape and / or film thickness measuring method according to any one of claims 1 to 4, wherein the characteristic function is obtained based on a band-pass sampling theorem. It is characterized by this.
[0019]
(Operation / Effect) According to the invention described in claim 5, by using the band-pass sampling theorem, the characteristic function can be easily restored from the characteristic value group acquired at the sampling interval of the sub-Nyquist. it can.
[0020]
The invention according to claim 6 is the surface shape and / or film thickness measurement method according to any one of claims 2 to 5, wherein the parameter is for defining a correction amount of the film thickness of the transparent film. As described above, the apparatus parameters are obtained in advance using a sample of a measurement object whose reflectance is known.
[0021]
The invention according to claim 7 is a parameter for defining a correction amount of the film thickness of the transparent film in the surface shape and / or film thickness measurement method according to any one of claims 2 to 6. As described above, the apparatus parameters are obtained in advance using a sample of a measurement object having a known film thickness.
[0022]
(Operation / Effect) According to the inventions of claims 6 and 7, since the surface of the measurement object is covered with the transparent film, the reflection is required to define the correction amount of the film thickness of the transparent film. By using the respective samples of the transparent film having a known rate and the object to be measured (Claim 6), or using the sample of the transparent film having a known film thickness (Claim 7), the apparatus parameters are obtained in advance. The film thickness of the transparent film, the height of the surface to be measured, and the surface height of the transparent film can be determined with higher accuracy.
[0023]
Further, the invention according to claim 8 is the surface shape and / or film thickness measuring method according to any one of claims 1 to 7, further comprising the white light source before the first step. The white light frequency band is limited to a specific frequency band.
[0024]
The invention according to claim 9 is characterized in that in the surface shape and / or film thickness measuring method according to claim 8, a plurality of different specific frequency bands are used.
[0025]
(Operation / Effect) According to the inventions of claims 8 and 9, it is possible to detect reflected light from the surface to be measured more accurately by limiting the frequency band of white light to a specific frequency band. it can. Note that it is preferable to use a plurality of different specific frequency bands. That is, in the fifth process for obtaining the film thickness of the transparent film from the average value of intensity values, there are generally a plurality of film thickness candidate values. If it is known that the target film thickness value is within a sufficiently narrow range, the film thickness of the transparent film can be uniquely specified, but if that is not possible, a plurality of specific frequency bands can be specified. The candidate for the film thickness of the transparent film is obtained, and the film thickness candidate common to all the bands is selected, whereby the film thickness of the transparent film can be specified with high accuracy.
[0026]
  According to a tenth aspect of the present invention, there is provided a white light source that generates white light to be irradiated on the measurement target surface and the reference surface covered with a transparent film, and a variation that varies a distance between the measurement target surface and the reference surface. The interference fringes are changed by reflected light that reflects from the measurement target surface and the reference surface and returns on the same optical path as the distance between the measurement target surface irradiated with the white light and the reference surface varies. An imaging unit that images the measurement target surface, a sampling unit that captures intensity values of interference light at a plurality of specific locations on the imaged measurement target surface, and a plurality of each specific location captured by the sampling unit Storage means for storing each interference light intensity value group that is an intensity value, and the surface height of the transparent film at the specific location and the surface height of the measurement target surface based on each interference light intensity value group stored in the storage means And transparent In the surface shape and / or thickness measuring device and a computing means for determining at least one of the thickness of the film,
  A frequency band limiting means for limiting a frequency band of white light generated from the white light source to a specific frequency band;
  The sampling unit responds to a change in interference fringes caused by reflected light that is reflected from the measurement target surface and the reference surface and returns on the same optical path as the distance between the measurement target surface and the reference surface is changed by the changing unit. Sequentially fetching the intensity value of the interference light at a specific location at a sampling interval according to the bandwidth of the specific frequency band
  The storage means stores an interference light intensity value group that is a plurality of intensity values captured at the sampling interval,
  The calculation means obtains at least one of the surface height of the transparent film at a specific location on the measurement target surface, the surface height of the measurement target surface, and / or the film thickness of the transparent film according to the following process.
(1) Obtain a change in the interference light intensity value group from the interference light in each pixel stored in the storage means,
(2) Obtain an average value of changes in the intensity value group of the obtained interference light,
(3) Correlation between the average value of the interference light intensity values obtained in advance for the same object as the measurement object and the film thickness of the transparent filmFormula

, Where C ( D ) Is the average intensity value, k _u Is the upper limit of the wave number of the irradiated light, k ₁ Is the lower limit value of the wave number of the irradiated light, R and S are parameters determined by the physical properties of the apparatus and the measurement object, α is the refractive index of air, and k is the angular wave number, n _s Is the film refractive index, D is the film thickness of the transparent filmBased onRealObtain the film thickness of the transparent film from the average of the intensity values obtained by measurement,
(4)The DC component is removed from the intensity value group to obtain only the AC component, the AC component is squared to obtain a characteristic value group emphasized on the plus side, and an envelope is obtained from the characteristic value.Find characteristic function
(5) BeforeSpecial mentionThe peak position information related to the distance between the measurement target surface and the reference surface is obtained based on the sex function,
(6) Based on the obtained peak position information, the surface height of the measurement target surface is obtained,
(7) The surface height of the transparent film is obtained from the obtained film thickness of the transparent film and the surface height of the measurement target surface.
[0027]
(Operation / Effect) The white light source irradiates the measurement target surface and the reference surface covered with the transparent film with white light. The changing means changes the distance between the measurement target surface and the reference surface. The imaging means images the measurement target surface together with a change in interference fringes that occurs with a change in the relative distance between the measurement target surface irradiated with white light and the reference surface. The sampling means captures the intensity values of the interference light at a plurality of specific locations on the measured measurement target surface. The storage means stores each interference light intensity value group, which is a plurality of intensity values for each specific location captured by the sampling means. The calculation means obtains a change in the interference light intensity value from the actually measured interference light intensity value group in each pixel stored in the storage means, and obtains an average value of the intensity value group. Next, the film of the transparent film is obtained from the average value of the intensity value group obtained by actual measurement based on the correlation between the average value of the intensity value group of the interference light previously obtained from the same object as the measurement object and the film thickness of the transparent film. Find the thickness. Simultaneously, a characteristic value group corresponding to the envelope is obtained from the intensity value group, a characteristic function is created, and peak position information related to the distance between the measurement target surface and the reference surface is obtained based on the specific function. The surface height of the measurement target surface is obtained based on the peak position information. The obtained film thickness of the transparent film and the surface height of the measurement target surface are used. That is, the surface height of the transparent film can be obtained by adding the respective values. That is, the method according to claim 1 can be suitably realized.
[0028]
The invention according to claim 11 is the surface shape and / or film thickness measuring device according to claim 10, wherein the computing means is further transparent based on the film thickness of the transparent film and the refractive index of the transparent film. A correction calculation process is performed on the surface height of the film.
[0029]
(Operation / Effect) According to the invention described in claim 11, the arithmetic processing means further corrects and calculates the surface height of the transparent film based on the film thickness of the transparent film and the refractive index of the transparent film. The surface height of the film can be determined more accurately. That is, the method according to claim 2 and claim 3 can be suitably realized.
[0030]
The invention according to claim 12 is the surface shape and / or film thickness measuring device according to claim 10 or 11, wherein the frequency band limiting means is provided in an optical path from the white light source to the imaging means. It is a band-pass filter that allows only white light in a specific frequency band to be attached.
[0031]
(Operation / Effect) According to the invention described in claim 12, the band-pass filter attached to the optical path from the white light source to the imaging means allows only white light in a specific frequency band to pass. Thereby, in the imaging means, the interference fringes and the measurement target surface by the white light in the specific frequency band are imaged. Therefore, the device configuration can be simplified, and the specific frequency band can be changed to an arbitrary frequency band by using a bandpass filter that passes an arbitrary frequency band.
[0032]
The invention according to claim 13 is the surface shape and / or film thickness measuring device according to claim 10 or 11, wherein the frequency band limiting means is a frequency of white light emitted from the white light source. It is an optical system from the white light source to the imaging means that narrows the band to a specific frequency band.
[0033]
(Operation / Effect) According to the invention described in claim 13, the optical system from the white light source to the imaging means has a frequency band of white light before the white light generated from the white light source reaches the imaging means. To a specific frequency band. Thereby, in the imaging means, the interference fringes and the measurement target surface by the white light in the specific frequency band are imaged. Therefore, the apparatus configuration can be further simplified.
[0034]
The invention according to claim 14 is the surface shape and / or film thickness measuring device according to claim 10 or 11, wherein the frequency band limiting means senses the white light in a specific frequency band. It is the frequency sensitivity of the means.
[0035]
(Operation / Effect) According to the invention described in claim 14, the imaging means images the interference fringes and the measurement target surface by the white light in the specific frequency band based on the frequency characteristics. Therefore, the apparatus configuration can be further simplified.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of a surface shape measuring apparatus according to an embodiment of the present invention.
[0037]
This surface shape measuring apparatus includes a transparent film 31 that covers the surface of the measurement object 30 such as a semiconductor wafer, a glass substrate, or a metal substrate, and a fine object formed on the measurement object 30 that is bonded to the back surface side of the transparent film 31. An optical system unit 1 that irradiates white light in a specific frequency band in a simple pattern and a control system unit 2 that controls the optical system unit 1 are configured.
[0038]
The optical system unit 1 includes a white light source 10 that generates white light to be irradiated on the measurement target surfaces 30A and 31A and the reference surface 15, a collimator lens 11 that converts the white light from the white light source 10 into parallel light, and white in a specific frequency band. A band-pass filter 12 that allows only light to pass through, and a half mirror 13 that reflects white light that has passed through the band-pass filter 12 in the direction of the measurement object 30 while allowing white light from the direction of the measurement object 30 to pass. The objective lens 14 that collects the white light reflected by the half mirror 13, the white light that has passed through the objective lens 14 is passed through the reference surface 15 and the measurement target surfaces 30 </ b> A and 31 </ b> A. In addition to the measurement light, the reference light reflected by the reference surface 15 and the measurement light reflected by the measurement target surfaces 30A and 31A are combined again and dried. A beam splitter 17 that generates fringes, a mirror 16 provided to reflect the reference light on the reference surface 15, an imaging lens 18 that forms white light in which the reference light and the measurement light are combined, and interference A CCD camera 19 that images the measurement target surface 30A together with the stripes is provided.
[0039]
The white light source 10 is a white light lamp, for example, and generates white light in a relatively wide frequency band. The white light generated from the white light source 10 is collimated by the collimating lens 11 and enters the bandpass filter 12.
[0040]
The band pass filter 12 is a filter for allowing only white light in a specific frequency band to pass, and is attached to the optical path from the white light source 10 to the CCD camera 19. Preferably, the white light from the white light source 10 is attached to an optical path between the reference light to the reference surface 15 and the measurement light on the measurement target surface 30A. In this embodiment, for example, it is attached to the optical path between the collimating lens 11 and the half mirror 13. As the band-pass filter 12, for example, a band-pass optical interference filter having a center wavelength of 600 nm is used. The white light that has passed through the band-pass filter 12 has its frequency band narrowed, and only white light in a specific frequency band passes through the band-pass filter 12.
[0041]
The half mirror 13 reflects white light in a specific frequency band that has passed through the bandpass filter 12 toward the direction of the measurement target 30, while allowing white light returned from the direction of the measurement target 30 to pass therethrough. is there. White light in a specific frequency band reflected by the half mirror 13 enters the objective lens 14.
[0042]
The objective lens 14 is a lens that focuses incident white light toward the focal point P. The white light condensed by the objective lens 14 passes through the reference surface 15 and reaches the beam splitter 17.
[0043]
The beam splitter 17 reflects the white light collected by the objective lens 14 on the reference surface 15 and, for example, the reference light reflected on the upper surface of the beam splitter 17 and the measurement target surfaces 30A and 31A. In addition to dividing the measurement light to pass through the beam splitter 17, the reference light and the measurement light are combined again to generate interference fringes. The white light reaching the beam splitter 17 is divided into reference light reflected by the upper surface of the beam splitter 17 and measurement light passing through the beam splitter 17, and the reference light reaches the reference surface 15. It reaches the measurement target surface 30A, which is the surface of the measurement target 30 covered with the transparent film 31 and the surface of the measurement target 30 joined to the back surface of the transparent film.
[0044]
A mirror 16 for reflecting the reference light in the direction of the beam splitter 17 is attached to the reference surface 15. The reference light reflected by the mirror 16 reaches the beam splitter 17, and the reference light is Reflected by the beam splitter 17.
[0045]
The measurement light that has passed through the beam splitter 17 is condensed toward the focal points P and P ′, and reflected on the measurement target surfaces 30A and 31A. The reflected two measurement lights reach the beam splitter 17 and pass through the beam splitter 17.
[0046]
The beam splitter 17 combines the reference light and the measurement light again. At this time, an optical path difference is caused by a difference in distance between the distance L1 between the reference surface 15 and the beam splitter 17 and the distance L2 between the beam splitter 17 and the measurement target surfaces 30A and 31A. According to this optical path difference, the reference light and the measurement light interfere with each other, thereby generating interference fringes. The white light in the state where the interference fringes are generated passes through the half mirror 13, is imaged by the imaging lens 18, and enters the CCD camera 19.
[0047]
The CCD camera 19 captures an image in the vicinity of the focal points P and P ′ of the measurement target surfaces 30A and 31A projected by the measurement light, together with the white light in a state where the interference fringes are generated. The captured image data is collected by the control system unit 2. Further, as will be apparent later, for example, the optical system unit 1 is vertically and horizontally changed by the drive unit 24 of the control system unit 2 corresponding to the changing means of the present invention. In particular, the distance between the distance L1 and the distance L2 is changed by driving the optical system unit 1 in the vertical direction. As a result, the interference fringes gradually change according to the difference in distance between the distance L1 and the distance L2. The CCD camera 19 captures images of the measurement target surfaces 30 </ b> A and 31 </ b> A with changes in interference fringes at predetermined sampling intervals described later, and the image data is collected by the control system unit 2. The CCD camera 19 corresponds to the image pickup means in the present invention.
[0048]
The control system unit 2 performs overall control of the entire surface shape measuring apparatus and CPU 20 for performing predetermined calculation processing, and various data such as image data sequentially collected by the CPU 20 and calculation results by the CPU 20. A memory 21 to be stored, an input unit 22 such as a mouse or a keyboard for inputting a sampling interval and other setting information, a monitor 23 for displaying an image of the measurement target surface 30A, and the optical system unit 1 in accordance with an instruction from the CPU 20 For example, a three-axis drive type servo motor. The CPU 20 corresponds to sampling means and arithmetic means in the present invention, the memory 21 corresponds to storage means in the present invention, and the drive unit 25 corresponds to fluctuation means in the present invention.
[0049]
The CPU 20 is a so-called central processing unit that controls the CCD camera 19, the memory 21, and the drive unit 24, and based on the image data of the measurement target surface 30 </ b> A including the interference fringes imaged by the CCD camera 19. The calculation processing which calculates | requires the surface height of the transparent film 31 of 30 specific places, the surface height of the measuring object 30, and the film thickness D of the transparent film 31 is performed. This process will be described later in detail. Further, a monitor 23 and an input unit 22 such as a keyboard and a mouse are connected to the CPU 20, and the operator can observe various operation information displayed on the monitor 23 from the input unit 22. Input. Further, after the measurement of the measurement target surface 30A, the surface height of the measurement target surfaces 30A and 31A, the film thickness D of the transparent film 31, the uneven shape of the measurement target surface, and the like are displayed on the monitor 23 as numerical values and images. The
[0050]
The drive unit 24 has a difference in distance between a fixed distance L1 between the reference surface 15 in the optical system unit 1 and the beam splitter 17 and a variable distance L2 between the beam splitter 17 and the measurement target surface 30A. Is a device that varies the optical system unit 1 in three orthogonal axes, and drives the optical system unit 1 in the X, Y, and Z directions according to instructions from the CPU 20, for example, a three-axis drive type servo motor It is comprised with the drive mechanism provided with. The drive unit 24 corresponds to the changing means in the present invention, and the relative distance in the present invention indicates the distance from the reference surface 15 to the measurement target surface 30A, that is, the distance L1 and the distance L2. In this embodiment, the optical system unit 1 is operated. For example, a table (not shown) on which the measurement object 30 is placed may be varied in the three orthogonal axes.
[0051]
Hereinafter, processing performed by the entire surface shape measuring apparatus, which is a characteristic part of the present embodiment, will be described in detail with reference to the flowchart of FIG.
[0052]
[First embodiment]
In this embodiment, a bandpass filter 12 having a center frequency of 600 nm is inserted, and an oxide film (SiO2) of about 0.45 μm is formed as a transparent film 31 on the surface of the Si substrate that is the measurement object 30.₂A case where measurement is performed using a material formed with a) will be described as an example. FIG. 7 is a diagram showing the distribution of the wavelength spectrum of white light that has passed through the band-pass filter 12.
[0053]
<Step S1> Condition setting
Various conditions such as a scanning speed and a scanning range for moving the optical system unit in the z-axis direction, an average value of the intensity values of interference light using a sample of the same object as the measurement object, and the film of the transparent film 31 Thickness correlation is obtained in advance, and its relational expression and the like are input and set.
[0054]
In the case of the present embodiment, as various conditions, for example, the center frequency of white light whose specific frequency band is limited by the band pass filter 12 is set to 600 nm.
[0055]
A relational expression based on the correlation between the average value of the intensity values of the interference light and the film thickness of the transparent film 31 is obtained as follows.
[0056]
White light transmitted through the transparent film and white light (reflected light) reflected by the measurement target surface 30A are reflected in multiple in the transparent film. However, in this embodiment, since the intensity of the interference light due to the multiple reflection is sufficiently small, it is ignored and it is assumed that the light is reflected once by the measurement target surface 30A. The observed luminance g (intensity value) at this time is expressed by the following equation.
[0057]
[Expression 1]

[0058]
Here, zp is the surface height of the measurement target surface 30A, D is the film thickness of the transparent film 31, α = 2k (assuming that the refractive index of air = 1), k is the angular wave number, ns is the film refractive index, kl Is the lower limit value of the wave number of the irradiated light, ku is the upper limit value of the wave number of the irradiated light, and P, Q, R, and S are parameters determined by the apparatus and physical properties of the target film.
[0059]
When the alternating current component (AC component) of the intensity value g obtained from the above equation (1) is f and the direct current component (DC component) is C, each component can be expressed by the following equation.
[0060]
[Expression 2]

[0061]
[Equation 3]

[0062]
That is, in the equation (3), the right side does not include the peak height zp, and is an unknown parameter of the film thickness D of the transparent film. Therefore, it is understood that the film thickness D is obtained when the actually measured value C (D) of the intensity value is given.
[0063]
Further, given the conditions of the apparatus and the film thickness of the transparent film, the relationship between the average value C of the intensity values and the film thickness D can be obtained as shown in FIG. 3 and FIG. 4 (range enlarged view of FIG. 3). it can. The relationship between the obtained average value C of the intensity values and the film thickness D of the transparent film is linearly approximated as shown in FIGS. 3 and 4, and is set and stored in advance in the memory 21 of the control system unit 2 or the like.
[0064]
3 and 4, the intensity average curve has a period of (λ / 2) / n where the wavelength of illumination light is λ and the refractive index of the transparent film is n. In this embodiment, the cycle is approximately 200 nm.
[0065]
<Step S2> Acquisition of measurement data
The optical system unit 1 irradiates the measurement target surfaces 30 </ b> A and 31 </ b> A and the reference surface 15 with white light generated by white light generated from the white light source 10 limited to a specific frequency band by the bandpass filter 12. The process until the frequency is limited to a specific frequency by the band-pass filter 12 or an optical system that is divided into measurement light and reference light described later corresponds to the process before the first process according to claim 8 of the present invention.
[0066]
Further, the CPU 20 gives the drive unit 24 a change start instruction for starting movement of the optical system unit 1 that has been moved to a predetermined measurement location in the z-axis direction. The drive unit 24 drives a drive system such as a stepping motor (not shown) to move the optical system unit 1 by a predetermined distance in the z-axis direction. Thereby, the distance between the reference surface 15 and the measurement target surface 30A is changed. This process corresponds to the first process in the present invention.
[0067]
Each time the optical system unit 1 moves by the sampling interval, the CPU 20 collects image data of the measurement target surface 30 </ b> A including the interference fringes imaged by the CCD 19 and sequentially stores it in the memory 21. As the optical system unit 1 moves by a predetermined distance, the memory 21 stores a plurality of pieces of image data determined by the moving distance of the optical system unit 1 and the sampling interval. This process corresponds to the second process in the present invention.
[0068]
<Step S3> Acquire a group of interference light intensity values at a specific location
For example, while observing the measurement target surface 30 </ b> A displayed on the monitor 23, the operator inputs a plurality of specific locations for which the heights of the measurement target surfaces 30 </ b> A and 31 </ b> A are to be measured from the input unit 22. The CPU 20 grasps a plurality of input specific locations, and outputs a plurality of density values of pixels corresponding to the plurality of specific locations on an image obtained by imaging the measurement target surface 30A, that is, interference light intensity values at the specific locations. Each from the image data. Thereby, a plurality of intensity values (interference light intensity value group) at each specific location are obtained. This process corresponds to the third process in the present invention.
[0069]
<Step S4> Obtain an average value from the intensity value group
As shown in FIG. 5, the CPU 20 obtains the intensity value of the interference light based on the interference light intensity value group at the specific location obtained discretely. This process corresponds to the fourth process in the present invention.
[0070]
<Step S5> Obtaining the thickness of the transparent film
The film thickness D of the transparent film 31 is obtained by using the linear approximation expression of Expression (3) in which the average value of the intensity values obtained in Step S4 is set and inputted in advance.
[0071]
In this example, since the average value of the intensity value is 71.5, it is assumed from the average value of the intensity value that the film thickness D is between 0.4 and 0.5 μm using the relationship of FIG. The film thickness D is determined to be 0.46 μm.
[0072]
This process corresponds to the fifth process of the present invention.
[0073]
<Step S6> A characteristic value is obtained from an average value of intensity values.
The CPU 20 uses the average value of the interference light intensity values obtained based on the interference light intensity value group in step S4, and subtracts the average value from each intensity value of the interference light intensity value group (adjustment value group). Ask for. That is, as shown in FIG. 6, the direct current component is removed from the interference fringe waveform, leaving only the alternating current component.
[0074]
The adjustment value is further squared to obtain a characteristic value with the intensity value emphasized on the plus side. Step S6 corresponds to the sixth process in the present invention.
[0075]
<Step S7> Acquisition of peak position
The CPU 20 uses the characteristic value group obtained in step S6 and creates a characteristic function that is a square envelope or an envelope. As this creation, for example, the waveform may be restored by a band-pass sampling theorem, or the characteristic value may be leveled by a band-pass filter. From this created characteristic function, a point where the characteristic value reaches a peak is read. That is, the number (numerical value) of the acquired image is read as the peak position of the measurement target surface 30A.
[0076]
<Step S8a> Measurement of surface shape
The CPU 20 obtains the surface height of the measurement target surface 30A by taking a product of a known sample point interval set in advance to the value (numerical value) of the number of images obtained by capturing the obtained peak position. The steps up to step S8 correspond to the eighth process of the present invention.
[0077]
Next, the surface height of the transparent film 31 is obtained by adding the film thickness D of the transparent film 31 obtained in step S5 to the surface height of the measurement target surface 30A. Step S8 corresponds to the ninth process in the present invention.
[0078]
<Step S9> Are all specific locations finished?
CPU20 repeats the process of step S3-S8 until all the specific places are complete | finished, and calculates | requires the height of all the specific places.
[0079]
<Step S10> Display
The CPU 20 displays information on the surface height of the transparent film 31 at the specific location of the transparent film 31, the surface height of the measurement target surface 30 </ b> A, and the film thickness D on the monitor 23, or based on the information on the height of each specific location. 3D or 2D images are displayed. The operator can grasp the uneven shape of the measurement target surface 30A of the measurement target 30 and the surface 31A of the transparent film 31 by observing these displays.
[0080]
3 and 4, C (D) has a white light (illumination light) wavelength λ and a refractive index n of the transparent film 31 having a period of (λ / 2) / n. In this embodiment, the period is about 200 nm.
[0081]
Therefore, when the average value C of the intensity values is given, generally there are candidates for the film thickness D of the plurality of transparent films 31. When it is known that the value of the target film thickness D exists in a sufficiently narrow range, the film thickness D can be uniquely determined.
[0082]
When it is difficult to uniquely determine the film thickness as described above, the same measurement is performed at a plurality of different specific frequency band wavelengths, and a common film thickness D candidate is selected from a plurality of measurement results. The film thickness D of the transparent film 31 can be uniquely determined.
[0083]
According to the above-described embodiment, Equation (3) based on the correlation between the average value of the interference light intensity of the same object as the measurement object 30 covered with the transparent film 31 and the film thickness D of the transparent film 31 is obtained in advance. The film thickness D of the transparent film 31 can be obtained with high accuracy by substituting the calculated intensity value obtained by actual measurement and substituting the calculated intensity value into the equation (3). Further, a characteristic value group corresponding to the envelope is obtained from the intensity value group of the interference light, and a square envelope as a characteristic function is obtained from the waveform data indicated by the characteristic value group. The peak position information of the square envelope is obtained, and the surface height of a specific portion of the measurement target surface 30A is obtained based on the peak position information. The surface height of the transparent film 31 can be obtained from the addition of the surface height of the measurement target surface 30A and the film thickness D of the transparent film 31. That is, the uneven shape of the transparent film 31 can be measured from the film thickness D of the transparent film 31 and the surface height of the measurement target surface 30A.
[0084]
[Second Embodiment]
In the present embodiment, a case will be described in which the amount of deviation of the peak position caused by the influence of reflected light on the transparent film surface is strictly corrected and the surface height of the transparent film 31 is obtained correctly.
[0085]
Hereinafter, the principle will be described.
[0086]
Expression (2) in which the alternating current component of the intensity value g in the above expression (2) is expressed as f is transformed as a product of the cos function and the amplitude component.
[0087]
f (z; zp, D) = m (z; zp, D) cos {β (z−zp) + A (z)} (4)
[0088]
The square of the envelope function r is defined by the following equation (5).
r (z; zp, D) = [m (z; zp, D)]²    (5)
[0089]
The peak position zp obtained from the equation (5) is not an accurate value but a peak position zp ′ including a shift amount due to the influence of the transparent film.
[0090]
According to Formula (2), the peak position information zp appears only in the relationship of z-zp. Therefore, when the value of zp changes, the function f itself is not deformed, and the peak position translates in the z-axis direction. As a result, the square envelope function itself has the same characteristics.
[0091]
Therefore, the peak position zp ′ (0) of the square envelope function r when zp = 0 is a deviation amount from the true peak position zp = 0, and is the same as the deviation amount when zp is other than zero. is there. That is, the relationship is zp−zp ′ = 0−zp ′ (0). Therefore, the true peak position not including the deviation amount is expressed by the following equation (6).
[0092]
zp = zp′−zp ′ (0) (6)
[0093]
From this, the second term on the right side in the above formula (6) can be obtained in advance as a correction term when the film thickness D of the transparent film 31 is known. That is, if f is defined as f0 and z is defined as r0 when zp = 0, the above equations (4) and (5) can be expressed as the following equations (7) and (8). (8) is an arithmetic expression for obtaining a peak position with corrected deviation.
[0094]
[Expression 4]

[0095]
r0 (z; D) = [m (z; 0, D)]²    (8)
[0096]
In the above equation, when the film thickness D is known, r0 is a function of only z, and therefore the peak position zp ′ (0) can be obtained.
[0097]
It can be seen that the amount of deviation of the surface height of the transparent film 31 depends on the relationship between the film thickness D of the transparent film 31 and the refractive index n of the transparent film. Accordingly, the surface height h of the true transparent film 31 to be obtained can be expressed by the relationship h = ha + f (n, D). Here, ha is the surface height of the measurement target surface 30A obtained by actual measurement, and f (n, D) is the film thickness of the transparent film including the film thickness correction amount (hereinafter referred to as “correction amount” as appropriate). .
[0098]
Further, the correction amount f (n, D) can also be approximately obtained by integration of n × D. This has been confirmed by the inventors' experiment simulation as follows.
In addition, the experiment simulation was performed about three types shown in the following Table 1 in the some combination of a transparent film and a measurement object surface.
[0099]
[Table 1]

[0100]
The relationship between the film thickness D of the transparent film 31 and the correction amount in FIGS. 8 to 10 showing the results of the experimental simulation performed under the conditions of Table 1 above is that the reflected light from the surface 30A of the measurement target surface 30A is from Experimental Example 1. It was found that as the experimental example 3 became stronger, the correction amount f (n, D) = n × D was approximated.
[0101]
Next, processing performed by the entire surface shape measuring apparatus of the present embodiment will be specifically described with reference to the flowchart of FIG. In this embodiment, the description of the processes (steps S1 to S6) common to the first embodiment is omitted.
[0102]
<Step S7> Acquisition of peak position
The CPU 20 uses the characteristic value group obtained in step S6 to create a characteristic function that is an envelope or a square envelope. As this creation, for example, the waveform may be restored by a band-pass sampling theorem, or the characteristic value may be leveled by a band-pass filter. From this created characteristic function, a point where the characteristic value reaches a peak is read. That is, the number (numerical value) of the acquired image is read as the peak position of the measurement target surface 30A.
[0103]
<Step S8b> Measurement of surface shape
CPU20 calculates | requires the surface height of 30 A of measurement object surfaces using the peak position calculated | required by actual measurement. The surface height of the measurement target surface 30A is obtained, for example, by an integration process of the numerical value of the number of images taken at the peak position and the sampling point interval.
[0104]
Next, the amount of deviation of the surface height of the transparent film 31 that is affected by the amount of deviation of the peak position with respect to the surface height of the measurement target surface 30A obtained by actual measurement is corrected. That is, the surface height of the true transparent film 31 is obtained by adding the correction amount f (n, D) obtained in advance to the surface height of the measurement target surface 30A. Step S8b corresponds to the ninth process of the present invention and the method described in claim 2.
[0105]
Hereinafter, step S9 and step S10 are the same processing as step S9 and step S10 of the first embodiment, and a specific description thereof will be omitted here.
[0106]
As described above, an accurate surface height of the transparent film 31 can be obtained by correcting the shift amount of the peak position due to the influence of the transparent film 31 covering the measurement target surface 30A.
[0107]
The present invention is not limited to the embodiment described above, and can be modified as follows.
(1) In each of the above embodiments, the configuration is such that the intensity value of the interference light at the specific location is acquired after the image data of the measurement target surface 30A is captured. However, the present invention is not limited to this. For example, an intensity value in a pixel corresponding to a specific location on the captured image can be acquired in real time, and the intensity values of the interference light can be sequentially stored in the memory 21.
[0108]
(2) In each of the above embodiments, the frequency band of the white light emitted from the white light source is band-limited to the specific frequency band by the band pass filter 11, but the present invention is not limited to this, and the white light source The frequency band of the white light from the white light source is band-limited by the optical system (including the light source, the lens, and each mirror) from the white light to the CCD camera 19 that is the imaging means. Can be grasped in advance, and the frequency band whose band is limited can be set as the specific frequency band in the present invention.
[0109]
(3) In each of the above embodiments, a specific frequency band is defined as a frequency band limited by the frequency characteristics of the CCD camera 19 serving as an imaging unit, and the specific frequency band is determined in advance. The specific frequency band in the present invention can also be used.
[0110]
(4) In each of the above-described embodiments, the CCD camera 19 is used as the imaging means. However, in view of imaging (detecting) only the intensity value of the interference light at a specific location, the CCD camera 19 is configured in a line or a plane. The imaging means can also be configured by a light receiving element or the like.
[0111]
(5) In each of the above embodiments, the white light from the white light source 10 is converted into parallel light by the collimator lens 11 and then the band pass filter 12 is provided to pass the white light in the specific frequency band. A configuration without the bandpass filter 12 may also be used.
[0112]
(6) In each of the above embodiments, it is preferable that parameters for defining the characteristic function and the correction amount are obtained and set in advance. Examples of this parameter include an apparatus parameter obtained using a sample of the measurement object 30 with a known reflectance, an apparatus parameter obtained using a sample of the measurement object 30 with a known film thickness, and the like. By setting these various parameters in advance, the film thickness of the transparent film, the height of the measurement target surface A, and the surface height of the transparent film can be determined with higher accuracy.
[0113]
【The invention's effect】
As is clear from the above description, according to the present invention, white light is irradiated while varying the distance between the measurement target surface covered with the transparent film and the reference surface, and the intensity value of the interference light at the acquired specific location is obtained. Get a group. From this intensity value group, an average value based on actually measured values of changes in the intensity value of the interference light is obtained. That is, based on the correlation obtained in advance with respect to the relationship between the average value of the interference light intensity value of the same object as the measurement object and the film thickness of the transparent film, the film of the transparent film Thickness can be determined. In addition, a characteristic function corresponding to an envelope or a square envelope is obtained from the intensity value group of the interference light, and a characteristic function is created. From this characteristic function, peak position information related to the distance between the measurement target surface and the reference surface is obtained. The surface height of the measurement target surface can be obtained based on the obtained peak maintenance information. Furthermore, the surface height of the transparent film can be obtained from the obtained film thickness of the transparent film and the surface height of the measurement target surface.
[0114]
Therefore, by using the correlation based on the relationship between the average value of the interference light intensity value obtained in advance and the film thickness of the transparent film, the film thickness of the transparent film is calculated from the average value of the interference light intensity value obtained by actual measurement. The surface height of the surface to be measured and the surface height of the transparent film can be determined with high accuracy.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a surface shape measuring apparatus according to an embodiment.
FIG. 2 is a flowchart showing processing in the surface shape measuring apparatus according to the first and second embodiments.
FIG. 3 is a diagram showing a relationship between an average value of intensity values and a film thickness.
FIG. 4 is an enlarged view of FIG. 3;
FIG. 5 is an explanatory diagram for explaining processing for obtaining a peak position of a specific function;
FIG. 6 is an explanatory diagram for explaining processing for obtaining a peak position of a specific function.
FIG. 7 is a diagram showing a spectral distribution of white light that has passed through a band-pass filter.
FIG. 8 is a diagram showing a simulation for obtaining a correction amount of the surface height of the transparent film.
FIG. 9 is a diagram showing a simulation for obtaining a correction amount of the surface height of the transparent film.
FIG. 10 is a diagram showing a simulation for obtaining a correction amount of the surface height of the transparent film.
[Explanation of symbols]
1 ... Optical system unit
2… Control system unit
10 ... White light source
11 ... Collimating lens
13… Half mirror
14 ... Objective lens
15 ... Reference plane
16 ... Mirror
17 ... Beam splitter
18… Imaging lens
19 ... CCD camera
20 ... CPU
21 ... Memory
22 ... Input section
23… Monitor
24 ... Drive unit
30 ... Measurement object
30A ... Measurement target surface (measurement object)
31 ... Transparent film
31A ... Measuring surface (transparent film)
D ... Film thickness (transparent film)

Claims (14)

While irradiating the measurement target surface and the reference surface covered with a transparent film with white light from a white light source, the distance between the measurement target surface and the reference surface is varied to reflect from the measurement target surface and the reference surface. The interference light is caused to change by the reflected light returning from the same optical path, and based on the intensity value of the interference light at this time, the surface height of the transparent film at the specific location of the measurement target surface, the surface height of the measurement target surface, and In the surface shape and / or film thickness measurement method of the measurement target surface for obtaining at least one of the film thicknesses of the transparent film,
A first step of changing a distance between the measurement target surface irradiated with white light of the specific frequency band and a reference surface;
A second process of continuously acquiring images of the measurement target surface at predetermined intervals in the process of changing the distance between the measurement target surface and the reference surface;
A third step of obtaining a change in the intensity value group of the interference light in each pixel of the plurality of images continuously acquired at the predetermined interval;
A fourth step of calculating an average value of the obtained intensity value group;
Mean values and by membrane correlation thickness of the transparent film wherein the intensity values of pre-determined interference light for the same object as the measurement object

Where C ( D ) is the average value of intensity values, k _u is the upper limit value of the wave number of the irradiated light, k ₁ is the lower limit value of the wave number of the irradiated light, and R and S are the physical properties of the apparatus and the object to be measured. , Α is the refractive index of air, k is the angular wave number, n _s is the refractive index of the film, and D is the average value of the intensity values actually measured in the fourth step based on the film thickness of the transparent film A fifth process for determining the film thickness of the transparent film from
A sixth step of obtaining only the AC component by removing the DC component from the obtained intensity value group, obtaining the characteristic value group emphasized on the positive side by squaring the AC component ;
Obtaining a characteristic function that becomes an envelope from the characteristic value group, and obtaining a peak position information related to a distance between the measurement target surface and a reference surface based on the characteristic function;
An eighth step of obtaining the surface height of the measurement target surface based on the obtained peak position information;
And a ninth process for determining the surface height of the transparent film from the film thickness of the transparent film determined in the fifth process and the surface height of the measurement target surface determined in the eighth process. A surface shape and / or film thickness measuring method. In the surface shape and / or film thickness measuring method according to claim 1,
The surface height (h) of the transparent film obtained in the ninth process is the correction amount of the film thickness of the transparent film obtained in advance from the relationship between the film thickness (D) of the transparent film and the refractive index (n) of the transparent film. Surface shape and / or film characterized in that it is a value obtained by adding the film thickness f (n, D) of the transparent film to be added to the surface height (ha) of the surface to be measured obtained in the eighth step Thickness measurement method. In the surface shape and / or film thickness measuring method according to claim 2,
The film thickness f (n, D) of the transparent film including the correction amount of the transparent film is represented by the relational expression f (n, D) = n × D. Measuring method. In the surface shape and / or film thickness measuring method according to any one of claims 1 to 3,
The surface shape and / or film thickness measuring method, wherein the characteristic function obtained in the seventh step is an envelope or a square envelope. In the surface shape and / or film thickness measuring method according to any one of claims 1 to 4,
The surface shape and / or film thickness measurement method, wherein the characteristic function is obtained based on a band-pass sampling theorem. In the surface shape and / or film thickness measuring method according to any one of claims 2 to 5,
Surface shape and / or film thickness measurement characterized in that apparatus parameters are obtained in advance using a sample of a measurement object with a known reflectance as a parameter for defining the correction amount of the film thickness of the transparent film. Method. In the surface shape and / or film thickness measuring method according to any one of claims 2 to 6,
Surface shape and / or film thickness measurement characterized in that apparatus parameters are obtained in advance using a sample of a measuring object whose film thickness is known as a parameter for defining the correction amount of the film thickness of the transparent film. Method. In the surface shape and / or film thickness measuring method according to any one of claims 1 to 7,
The surface shape and / or film thickness measuring method further comprising a step of limiting a frequency band of white light from the white light source to a specific frequency band before the first step. In the surface shape and / or film thickness measuring method according to claim 8,
A surface shape and / or film thickness measuring method, wherein a plurality of different specific frequency bands are used. A white light source that generates white light to be irradiated on the measurement target surface and the reference surface covered with a transparent film, a fluctuating unit that varies a distance between the measurement target surface and the reference surface, and a measurement in which the white light is irradiated An imaging means for causing an interference fringe change by reflected light reflected from the measurement target surface and the reference surface and returning from the same optical path as the distance between the target surface and the reference surface varies, and for imaging the measurement target surface; Sampling means for capturing the intensity values of interference light at a plurality of specific locations on the imaged measurement target surface, and each interference light intensity value group that is a plurality of intensity values for each specific location captured by the sampling means. Storage means for storing, and at least one of the surface height of the transparent film at the specific location, the surface height of the measurement target surface, and the film thickness of the transparent film based on each interference light intensity value group stored in the storage means one In the surface shape and / or thickness measuring device and a calculation means for calculating a
A frequency band limiting means for limiting a frequency band of white light generated from the white light source to a specific frequency band;
The sampling unit responds to a change in interference fringes caused by reflected light that is reflected from the measurement target surface and the reference surface and returns on the same optical path as the distance between the measurement target surface and the reference surface is changed by the changing unit. Sequentially fetching the intensity value of the interference light at a specific location at a sampling interval according to the bandwidth of the specific frequency band,
The storage means stores an interference light intensity value group that is a plurality of intensity values captured at the sampling interval,
The calculation means obtains at least one of the surface height of the transparent film at the specific location on the surface to be measured, the surface height of the surface to be measured, and / or the film thickness of the transparent film according to the following process (1). ) Obtain a change in the interference light intensity value group from the interference light in each pixel stored in the storage means,
(2) Obtain an average value of changes in the intensity value group of the obtained interference light,
(3) According to the film correlation between the thickness of the average value and the transparent film of the intensity values of pre-determined interference light for the same object as the measurement object formula

Where C ( D ) is the average value of intensity values, k _u is the upper limit value of the wave number of the irradiated light, k ₁ is the lower limit value of the wave number of the irradiated light, and R and S are the physical properties of the apparatus and the object to be measured. the film thickness of the determined parameters, alpha is the refractive index of air, and, k is the angular wavenumber, n _s is the film refractive index, D is a transparent film from the average value of the intensity values obtained by actual measurement on the basis of the thickness of the transparent film by Seeking
(4) The DC component is removed from the intensity value group to obtain only the AC component, the AC component is squared to obtain a characteristic value group emphasized on the plus side, and a characteristic function that becomes an envelope from the characteristic value is obtained. calculated (5) obtains the relevant peak position information on the distance between the object surface and the reference surface based on prior Kitoku property function,
(6) Based on the obtained peak position information, the surface height of the measurement target surface is obtained,
(7) A surface shape and / or film thickness measuring apparatus, wherein the surface height of the transparent film is determined from the determined film thickness of the transparent film and the surface height of the surface to be measured. In the surface shape and / or film thickness measuring device according to claim 10,
The surface shape and / or film thickness measuring apparatus, wherein the calculation means further performs a correction calculation process on the surface height of the transparent film based on the film thickness of the transparent film and the refractive index of the transparent film. In the surface shape and / or film thickness measuring device according to claim 10 or 11,
The surface shape and / or film thickness measuring device, wherein the frequency band limiting means is a bandpass filter that is attached to an optical path from the white light source to the imaging means and passes only white light in a specific frequency band . In the surface shape and / or film thickness measuring device according to claim 10 or 11,
The frequency band limiting means is an optical system from the white light source to the imaging means that narrows the frequency band of white light emitted from the white light source to a specific frequency band, and / or Film thickness measuring device. In the surface shape and / or film thickness measuring device according to claim 10 or 11,
The surface shape and / or film thickness measuring apparatus, wherein the frequency band limiting means is frequency sensitivity of the imaging means for sensing white light in a specific frequency band.

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