JP3714854B2

JP3714854B2 - Planar shape measuring method in phase shift interference fringe simultaneous imaging device

Info

Publication number: JP3714854B2
Application number: JP2000197484A
Authority: JP
Inventors: 川崎　　和彦; 宏配野
Original assignee: Mitutoyo Corp
Current assignee: Mitutoyo Corp
Priority date: 2000-06-30
Filing date: 2000-06-30
Publication date: 2005-11-09
Anticipated expiration: 2020-06-30
Also published as: JP2002013907A

Description

【０００１】
【発明の属する技術分野】
本発明は、被検面と参照面からの反射光が光学的に無干渉状態にある原光束を複数の分枝原光束に分割し、それぞれ分枝原光束に異なる固定的光学位相差を与えて干渉させ、複数の撮像装置で同時撮像を行う位相シフト干渉縞同時計測装置に関する。
【０００２】
【従来の技術】
従来、図１に示すような位相シフト干渉縞同時計測装置が本出願人による特願平１１−１３６８３１号出願で提案されている。
即ち、同位相シフト干渉縞同時計測装置においては、レーザ光源１からのレーザ光束はレンズ２よりビーム径を拡大され、ビームスプリッタ３を透過してコリメートレンズ４にて平行光束とされる。
そして、この平行光束は参照面５で反射された参照光と参照面５，１／４波長板６を透過し被検面７で反射された試料光を生成するが、この参照光と試料光は直交する直線偏光で光学的無干渉状態にある。
【０００３】
また、ビームスプリッタ３で反射された参照光と試料光は１／４波長板８でそれぞれ互いに回転方向の異なる円偏光状態となり三分光プリズム９で３つの分枝光束に分割される。それぞれの分枝光束の光路上には偏光板１０〜１２が配置され、光軸に対してほぼ直交する面内における偏光板の透過軸角度が設定され、固定的光学位相差を与えた分枝位相シフト干渉縞が発生し、これらの分枝位相シフト干渉縞が撮像装置１３〜１５により同時に撮像される。
【０００４】
【発明が解決しようとする課題】
つまり、この位相シフト干渉縞同時計測装置では、偏光板１０〜１２の透過軸の正確な角度の設定により、計測に必要な分枝位相シフト干渉縞が与えられるが、この装置において被検面起伏形状を高精度に計測するためには、３つの分枝位相シフト干渉縞間におけるバイアス、振幅が観測領域内の各点にて等しいことが前提となる。
ところが、三分光プリズム９における分割強度誤差や１／４波長板８の低速軸の設置誤差にともなう透過光の楕円偏光化などが原因となり、３つの分枝位相シフト干渉縞のバイアスと振幅は、実際にはそれぞれ異なるものとなる。このため従来は、分枝位相シフト干渉縞画像からバイアスと振幅の代表値を算出し相互の差を補正する対策がとられている。
しかし、分枝光路上に介在する光学素子を均一に作用させることは、現実にはむずかしく、分枝位相シフト干渉縞間のバイアスと振幅の値は観測領域内の各点にて異なるのが現実であり、代表値で一様に補正する方法では、一画面内においてバイアスと振幅のばらつきが補正後に残ってしまう問題がある。
【０００５】
本発明の目的は、前述したような位相シフト干渉縞同時撮像装置の問題に鑑み、３つの分枝位相シフト干渉縞の観測領域内の各点におけるバイアス、振幅が互いに異なっていても、高精度に解析できる位相シフト干渉縞画像を得ることができる平面形状計測方法を得るにある。
【０００６】
【課題を解決するための手段】
この目的を達成するため、本発明は、分枝位相シフト干渉縞のバイアスと振幅値と分枝ごとに観測される参照光を観測領域内の各点において予め計測し、計測によって得られたバイアスと振幅の値と参照光画像データを用いて、以後の被検面計測時に得られる分枝位相シフト干渉縞画像データに対し輝度変換を施してバイアス、振幅の整合を観測領域内の各点ごとに行なうことで、位相シフト干渉縞同時計測装置大幅な高精度化を図ることを提案するものである。
つまり、本発明においては、
レーザ光源からのコヒーレント光束を参照面と被検面に照射し、前記参照面及び前記被検面のそれぞれからの反射光である参照光と試料光の偏光面を偏光光学素子を介在させて互いに直交させることにより、光学的無干渉状態となした原光束を生成する観測光学系と、
前記原光束を複数に分光した分枝原光束に分け、前記分枝原光束のそれぞれに偏光光学素子を介して異なる固定的光学位相差を与えた複数の分枝位相シフト干渉縞を発生させ、前記被検面の観測範囲にある一つの位置がそれぞれの分枝観測座標系において同一位置になるよう位置の整合させ、分枝光束ごとに設けられた撮像装置でこれらの干渉縞に対応する画像データを取得し、前記被検面の観測範囲の平面起伏形状を位相シフト法を用いて数値データとして再現させる位相シフト干渉縞同時撮像装置において、
前記参照光と前記試料光との間に相対的な光学的位相差を別途与えたときに前記各撮像装置で得られる分枝ごとの位相シフト干渉縞画像データから算出した分枝原光束ごとのバイアスと振幅と、試料光がない状態で各分枝原光束ごとに得られる分枝参照光画像データとを用いて
平面起伏形状計測時の分枝ごとの位相シフト干渉縞画像データを輝度変換して、観測領域内の各点におけるバイアスと振幅を整合調整し、位相シフト法により干渉縞の各点ごとの位相算出を行う位相シフト干渉縞同時撮像装置における平面形状計測方法が提案される。
【０００７】
後述する本発明の好ましい実施例の説明においては、
1)前記参照光と前記試料光との間に相対的な光学的位相差を別途与える際、前記レーザ光源の波長をわずかづつ変化させることにより前記光学的位相差を発生させる方法、
2)前記参照光と前記試料光との間に相対的な光学的位相差を別途与える際、前記参照面あるいは前記被検面のどちらか一方を光軸に沿ってわずかづつ平行移動させることにより、前記光学的位相差を発生させる方法、
3)前記参照光と前記試料光との間に相対的な光学的位相差を別途与える際、前記参照面と前記被検面との間の光路に１より大きい屈折率をもつ無反射透過体であって、互いに厚みが異なる少なくとも１枚の平行板を挿入することにより前記光学位的相差を発生させる方法、
4)前記参照光と前記試料光との間に相対的な光学的位相差を別途与える際、前記参照面と前記被検面との間の光路に１より大きい屈折率を持つ無反射透過体であって、参照面及び被検面に向かい合う２面が平行でない光学楔を挿入し、光軸に対してほぼ略直交する面内において光学楔を楔方向に移動させ前記光学的位相差を発生させる方法、
5)前記参照光と前記試料光との間に相対的な光学的位相差を別途与える際、前記参照面を被検面との間に液晶を配置し、液晶の電気的な制御により屈折率を可変し、所定の光学的位相差を発生させる方法、
【０００８】
そして、本発明の実施例の説明においては、
1)各点ごとに求めた前記バイアスと振幅の他点との差異が、許容範囲である各点の集合ごとに整理された前記バイアスと振幅の値であるもの、
2)各点ごとに求めた前記バイアスと振幅の値から得た単純平均または中央値または２乗平均値が、バイアスと振幅の代表値として、各点の位置に関係なく全領域に用いられるもの、
3)前述した各平面形状計測方法を具体化するための、波長をわずかづつ変化できるレーザ光源、光軸に沿ってわずかづつ平行移動できる前記参照面あるいは前記被検面、前記参照面と前記被検面との間の光路に位置される１より大きい屈折率の無反射透過体平行板、前記参照面と前記被検面との間の光路に位置される１より大きい屈折率をもちかつ楔方向に移動できる光学楔、前記参照面と前記被検面との間の光路に位置されかつ電気的制御で屈折率を変化できる液晶を組み込まれた位相シフト干渉縞同時撮像装置
も説明される。
【０００９】
【発明の実施の形態】
本発明の平面形状計測方法は、図１に示した位相シフト干渉縞同時撮像装置において、分枝位相シフト干渉縞のバイアスと振幅値と分枝ごとに観測される参照光を観測領域内の各点において予め計測し、計測によって得られたバイアスと振幅の値と参照光画像データを用いて、以後の被検面計測時に得られる分枝位相シフト干渉縞画像データに対し輝度変換を施してバイアス、振幅の整合を観測領域内の各点ごとに行なうことを特徴とするものである。
【００１０】
本発明の平面形状計測方法を具体的に説明すると、位相シフト法を用いて３枚の干渉縞から被検面起伏形状を算出する場合、３枚の干渉縞を次式でそれぞれ表し、被検面起伏形状に相当するφ（ｘ，ｙ）を算出するのが一般的である。
【数１】

ここで、Ｉ₁ （ｘ，ｙ）、Ｉ₂ （ｘ，ｙ）、Ｉ₃ （ｘ，ｙ）はビデオカメラなどの撮像装置で計測される輝度情報を、Ｂ（ｘ，ｙ）、Ａ（ｘ，ｙ）はそれぞれの干渉縞のバイアス、振幅を、α（ｘ，ｙ）とβ（ｘ，ｙ）は干渉計にて計画的に付加される位相シフト量を表す。
【００１１】
図１に示した位相シフト干渉縞同時計測装置で被検面７を観測したときに撮像装置１３〜１５で得られる分枝位相シフト干渉縞も（１−１式）、（１−２式）、（１−３式）と同様に表されるのが理想である。
ところが、位相シフト干渉縞同時撮像装置においては位相シフト量α（ｘ，ｙ）、β（ｘ，ｙ）が計画値通り与えられていたとしても、円偏光生成に用いた１／４波長板６，８の低速軸設置誤差や３分割プリズムの光束分割誤差などが原因して、分枝位相シフト干渉縞間のバイアス、振幅はそれぞれ異なったものとなる。
さらには、干渉計構成部品の反射率や透過率の不均一性により、任意のｘ，ｙ座標上において３枚の干渉縞画像間で対応する点どおしのバイアスと振幅はｘ，ｙ各点にて異なるから、当然に、これらの問題に対して対策を施さなけれは、形状算出時に大きな誤差を生じることになる。
【００１２】
そこで、本発明では、３枚の干渉縞の輝度情報Ｉ₁ （ｘ，ｙ）、Ｉ₂ （ｘ，ｙ）、Ｉ₃ （ｘ，ｙ）に対して輝度変換を施し、分枝位相シフト干渉縞間のバイアス、振幅の整合調整をｘ，ｙ各点にて行なったものと計画的に与えられた位相シフト量α（ｘ，ｙ）、β（ｘ，ｙ）を用いて、φ（ｘ，ｙ）を算出するが、この具体的な方法を次に説明する。
【００１３】
前述したような問題を加味して、位相シフト干渉縞同時撮像装置の撮像装置１３〜１５で得られた干渉縞は次の（２−１式）〜（２−３式）でそれぞれ表される。
【００１４】
【数２】

【００１５】
また、参照光と試料光の間に光学的位相差δ_i を別途与えたときに、得られる分枝ごとの位相シフト干渉縞は次の（３−１式）〜（３−３式）で表わすことができる。
【数３】

【００１６】
δ_i を任意に変化させて分枝ごとに３枚以上の分枝位相シフト干渉縞を得ると、各分枝ごとのバイアスと振幅を算出することができる。ここで、一つの算出方法例を示すと、δ_i を干渉縞位相１周期２πを等しく分割する値
δ_i ＝ｉ２π／Ｎ；ｉ＝１，２，３，・・・Ｎ
とした場合には、以下の計算を行なうことにより各分枝ごとのバイアス及び振幅は次の（４−１式）〜（４−３式）及び（５−１式）〜（５−３式）で算出される。
【００１７】
【数４】

【００１８】
ここで得られたＢ₁ （ｘ，ｙ）、Ｂ₂ （ｘ，ｙ）、Ｂ₃ （ｘ，ｙ）、Ａ₁ （ｘ，ｙ）、Ａ₂ （ｘ，ｙ）、Ａ₃ （ｘ，ｙ）をバイアス及び振幅の整合調整用被検面Ｓを計測したときの値とし、また、参照光と試料光をそれぞれａ（ｘ，ｙ）、ｂ（ｘ，ｙ）とし、分枝ごとに配置した撮像装置１３〜１５に到達する参照光と試料光をａ₁ （ｘ，ｙ）、ａ₂ （ｘ，ｙ）、ａ₃ （ｘ，ｙ）とｂ₁ （ｘ，ｙ）、ｂ₂ （ｘ，ｙ）、ｂ₃ （ｘ，ｙ）とする（以後は、ｘ，ｙの次元を省き簡略化して示す）。
したがって、各分枝ごとのバイアスと振幅と参照光と試料光の関係は
【数５】

で表される。
【００１９】
次に、異なる被検面Ｔを計測する際に、先に算出したバイアス及び振幅値を用いて分枝位相シフト干渉縞画像に対して輝度変換を施し、バイアス及び振幅の整合調整を図り、被検面Ｔの起伏形状を算出する方法を説明する。
図２（ａ）はバイアス及び振幅整合調整用被検面Ｓを計測する場合の撮像装置に入力される反射光強度モデルを、図２（ｂ）は被検面Ｔの計測時に撮像装置に入力される反射光強度モデルをそれぞれ示す。
【００２０】
これらの図２（ａ），（ｂ）において、被検面Ｔ計測時の試料光ｂ’とｂがｂ’＝γｂの関係にあるとすると、３台の撮像装置１３〜１５に到達する試料光はそれぞれｂ’₁ ＝γｂ₁ 、ｂ’₂ ＝γｂ₂ 、ｂ’₃ ＝γｂ₃ のように同様の割合で影響を受けると考えることができる。
これらを考慮すると、被検面Ｔ計測時の分枝ごとのバイアスＢ₁ ’、Ｂ₂ ’、Ｂ₃ ’、振幅Ａ₁ ’、Ａ₂ ’、Ａ₃ ’と先に得られているバイアスＢ₁ 、Ｂ₂ 、Ｂ₃ と振幅Ａ₁ 、Ａ₂ 、Ａ₃ の関係は、次の（８−１式）〜（８−３式）及び（９−１式）〜（９−３式）で表される。
【数６】

【００２１】
よって、被検面Ｔの観測時に得られる３枚の分枝位相シフト干渉縞は、それぞれ
【数７】

で表されることになる。
【００２２】
（１０−１式）〜（１０−３式）中のａ₁ 、ａ₂ 、ａ₃ は、試料光を遮光したときに得られる参照光強度であり、被検面によらず時間的に一定の値である。
また、ｂ₁ 、ｂ₂ 、ｂ₃ はａ₁ 、ａ₂ 、ａ₃ とバイアス及び振幅の整合調整用被検面Ｓより得られた、Ｂ₁ 、Ｂ₂ 、Ｂ₃ の（６−１式）〜（７−３式）の関係から算出することができる。
【００２３】
式（１０−１）〜（１０−３）の３つの式を用いたφの算出を以下に説明すると、
（１０−１式）−ａ₁ から、
【数８】

（１０−２式）−ａ₂ から、
【数９】

（１０−３式）−ａ₃ から、
【数１０】

が得られる。
【００２４】
そして、（１１−１式）〜（１１−３式）から、
【数１１】

が得られる。
【００２５】
行列式は
【数１２】

になり、例えばα＝π／２、β＝πのときは、％１≠０でφについて解くことができる。
【００２６】
したがって、（１２式）は次式に書き換えられる。
【数１３】

となる。
【００２７】
よって、位相φは
【数１４】

より得られるが、これは、分枝位相シフト干渉縞間のバイアス及び振幅の差異が観測領域内のｘ，ｙ面内の各点にて解消された後に、算出されたφ（ｘ，ｙ）被検面起伏形状算出結果である。
【００２８】
次に、分枝位相シフト干渉縞のバイアスと振幅を計測するために、参照光と試料光に光学位相差を別途与える方法について説明する。
参照面５に対する被検面７の距離がｄ（ｘ，ｙ）の時に撮像装置１３より得られる干渉縞は前述した（１−１式）において、
【数１５】

であるから、次式で表される。
【数１６】

Ｉ（ｘ，ｙ）は干渉縞強度、Ｂ（ｘ，ｙ）、Ａ（ｘ，ｙ）はそれぞれバイアス、振幅、λはレーザ光源１の波長を表す。
【００２９】
ここで、波長λを微少量Δλ_i 変化させたときの干渉縞は、
【数１７】

ここで、
【数１８】

であるから、
【数１９】

で表される。
【００３０】
同様に、撮像装置１４、撮像装置１５によって得られる干渉縞は
【数２０】

【００３１】
で表される。
つまり、δ_i ＝Ｃ・Δλ_i に相当する量、及び／または、レーザ光源１の波長をΔλ_i だけ変化させることで、参照光と試料光に光学位相差を別途付加できる。そして、分枝ごとに得られる複数の位相シフト干渉縞画像から（４−１式）〜（４−３式）及び（５−１式）〜（５−３式）に示した演算を行なうことで、各分枝位相シフト干渉縞のバイアス及び振幅を、ｘ，ｙ各点ごとに算出することができる。
【００３２】
また、参照光と試料光に光学位相差を別途与える際に、図３や図４に示すように、参照面あるいは被検面を光軸方向にΔｄ_i 平行移動させても、各分枝位相シフト干渉縞のバイアス、振幅をｘ，ｙの各点ごとに算出することができる。その時の分枝位相シフト干渉縞は次式で表される。
【数２１】

【００３３】
つまり、（１８−１式）〜（１８−３式）から明らかなように、

に相当する変位量Δｄ_i を与えたときに、各分枝原光束ごとに得られる複数の位相シフト干渉縞から（４−１式）〜（４−２式）、（５−１式）〜（５−３式）に示した演算を行なうことで、各分枝位相シフト干渉縞のバイアス及び振幅を、ｘ，ｙの各点ごとに算出することができる。
【００３４】
また、参照光と試料光に光学位相差を別途与えるに当たっては、前記参照面５を被検面７との間の光路に１より大きい屈折率を持つ無反射透過体で厚みの異なる平行板を挿入しても、分枝位相シフト干渉縞間の固定的光学位相差を計測することができる。
【００３５】
例えば、図５に示すように屈折率ｎで厚みがｌ₁ 、ｌ₂ の平行板１６，１７を用い、
平行板１６，１７を挿入していない状態を δ₁
厚みｌ₁ の平行板１６の挿入時を δ₂
厚みｌ₂ の平行板１７の挿入時を δ₃
とする場合や、
図６に示すように、屈折率ｎ₁ 、ｎ₂ で厚みが同じｌの平行板１８，１９を用いて、
平行板１８，１９を挿入していない状態を δ₁
屈折率ｎ₁ の平行板１８の挿入時を δ₂
屈折率ｎ₂ の平行板１９の挿入時を δ₃
としても、参照光と試料光に光学的位相差を別途与えることが可能で、分枝位相シフト干渉縞のバイアス、振幅をｘ，ｙ各点ごとに算出することができる。
【００３６】
また、参照光と試料光に光学的位相差を別途与える際に、図７に示すように、前記参照面と被検面との間の光路に１より大きい屈折率を持つ無反射透過体であって、参照面と被検面と向かい合う２面が平行でない光学楔７を挿入し、光学楔７を光軸とほぼ直交する面内において楔方向に移動させ、各分枝位相シフト干渉縞のバイアス、振幅をｘ，ｙ各点ごとに算出することも可能である。
【００３７】
さらに、図８のように液晶２１を参照面と被検面の間に挿入し、制御装置２２による電圧などの電気的な制御により液晶２１の屈折率を可変させ、δ₁ 、δ₂ 、δ₃ に相当する光学的位相差を発生させても各分枝位相シフト干渉縞のバイアス、振幅をｘ，ｙ各点ごとに算出することも可能である。
【００３８】
勿論、前述した方法により得られる各分枝原光束の位相シフト干渉縞のバイアス及び振幅Ｂ₁ （ｘ，ｙ）、Ｂ₂ （ｘ，ｙ）、Ｂ₃ （ｘ，ｙ）、Ａ₁ （ｘ，ｙ）、Ａ₂ （ｘ，ｙ）、Ａ₃ （ｘ，ｙ）は、輝度変換による分枝位相シフト干渉縞のバイアス、振幅整合の調整にそのまま使用されてもよい。
【００３９】
データ処理をさらに容易にする方法について説明すると、図９はＢ₁ （ｘ，ｙ）のデータ中のあるｙ₁ に対する１次元のデータＢ₁ （ｘ，ｙ₁ ）を表しており、グラフはＢ₁ （ｘ，ｙ₁ ）が観測領域内の位置ｘに対して値が異なることを意味している。
図９において、本発明では、Ｂ₁ （Ｘ，ｙ₁ ）に対してある許容範囲ｔを設定し、その範囲内にある数値データ群を一まとめに整理して代表値で置き換え、Ｂ₁ ’（ｘ，ｙ₁ ）で図示したようなデータ列を作成する。この考えをｘ、ｙの２次元のデータ群に応用し、ある許容範囲ｔ内にある領域のデータ群を代表値で置き換える。
また、Ｂ₂ （ｘ，ｙ）、Ｂ₃ （ｘ，ｙ）、Ａ₁ （ｘ，ｙ）、Ａ₂ （ｘ，ｙ）、Ａ₃ （ｘ，ｙ）に対しても同様の処理を施し、Ｂ₂ ’（ｘ，ｙ）、Ｂ₃ ’（ｘ，ｙ）、Ａ₁ ’（ｘ，ｙ）、Ａ₂ ’（ｘ，ｙ）、Ａ₃ ’（ｘ，ｙ）を作成する。Ｂ₁ ’（ｘ，ｙ）、Ｂ₂ ’（ｘ，ｙ）、Ｂ₃ ’（ｘ，ｙ）、Ａ₁ ’（ｘ，ｙ）、Ａ₂ ’（ｘ，ｙ）、Ａ₃ ’（ｘ，ｙ）を使用して、計算機に内に保有するパラメータ数を減らすことでメモリ容量の節約が可能となる。
さらには、図１０に示すように、Ｂ₁ （ｘ，ｙ）、Ｂ₂ （ｘ，ｙ）、Ｂ₃ （ｘ，ｙ）、Ａ₁ （ｘ，ｙ）、Ａ₂ （ｘ，ｙ）、Ａ₃ （ｘ，ｙ）を単純平均や中央値Ｂ₁ ’、Ｂ₂ ’、Ｂ₃ ’、Ａ₁ ’、Ａ₂ ’、Ａ₃ ’で置き換えたり、あるいは、図１１に示すように、２乗平均より算出したＢ₁ ’（ｘ，ｙ）、Ｂ₂ ’（ｘ，ｙ）、Ｂ₃ ’（ｘ，ｙ）、Ａ₁ ’（ｘ，ｙ）、Ａ₂ ’（ｘ，ｙ）、Ａ₃ ’（ｘ，ｙ）にすれば、平面形状計測装置にて被検面起伏形状を算出する際に、さらに多くのメモリ容量の節約が可能となる。
【００４０】
【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、分枝ごとに、異なる分布状態から得られる分枝位相シフト干渉縞のバイアス、振幅を予め計測し、以後の被検面計測時に得られる分枝位相シフト干渉縞のバイアス、振幅を観測領域内のｘ，ｙ各点にて輝度変換を施して整合調整を行ない、被検起伏形状算出を行なうことで大幅な精度向上が実現できる。
【図面の簡単な説明】
【図１】本発明による位相シフト干渉縞同時撮像装置の光学系の概念図である。
【図２】（ａ），（ｂ）は被検面Ｓ，Ｔの計測時に撮像装置に入力される反射光強度の比較モデルである。
【図３】同位相シフト干渉縞同時撮像装置における第１の光学的位相差付与手段の説明図である。
【図４】同位相シフト干渉縞同時撮像装置における第２の光学的位相差付与手段の説明図である。
【図５】同位相シフト干渉縞同時撮像装置における第３の光学的位相差付与手段の説明図である。
【図６】同位相シフト干渉縞同時撮像装置における第４の光学的位相差付与手段の説明図である。
【図７】同位相シフト干渉縞同時撮像装置における第５の光学的位相差付与手段の説明図である。
【図８】同位相シフト干渉縞同時撮像装置における第６の光学的位相差付与手段の説明図である。
【図９】本発明による分枝ごとの干渉縞のバイアス、振幅の算出方法の説明図である。
【図１０】単純平均による分枝ごとの干渉縞のバイアス、振幅の算出方法の説明図である。
【図１１】２乗平均による分枝ごとの干渉縞のバイアス、振幅の算出方法の説明図である。
【符号の説明】
１レーザ光源
２レンズ
３ビームスプリッタ
４コリメータレンズ
５参照面
６１／４波長板
７被検面
８１／４波長板
９３分光プリズム
１０〜１２偏光板
１３〜１５撮像装置
１６〜１９平行板
２０光学楔
２１液晶
２２制御装置[0001]
BACKGROUND OF THE INVENTION
The present invention divides an original light beam in which reflected light from a test surface and a reference surface is in an optically non-interfering state into a plurality of branched original light beams, and gives each of the branched original light beams a different fixed optical phase difference. The present invention relates to a phase shift interference fringe simultaneous measurement apparatus that performs simultaneous imaging with a plurality of imaging apparatuses.
[0002]
[Prior art]
Conventionally, a phase shift interference fringe simultaneous measurement apparatus as shown in FIG. 1 has been proposed in Japanese Patent Application No. 11-136831 filed by the present applicant.
That is, in the same phase shift interference fringe simultaneous measurement apparatus, the laser beam from the laser light source 1 has a beam diameter larger than that of the lens 2, passes through the beam splitter 3, and is converted into a parallel beam by the collimator lens 4.
Then, the parallel light beam generates the reference light reflected by the reference surface 5 and the sample light that passes through the reference surface 5 and the quarter-wave plate 6 and is reflected by the surface 7 to be measured. Are orthogonally polarized light and in an optical non-interference state.
[0003]
Further, the reference light and the sample light reflected by the beam splitter 3 become circularly polarized states having different rotation directions from each other by the quarter wavelength plate 8 and are divided into three branched light beams by the three spectroscopic prism 9. The polarizing plates 10 to 12 are arranged on the optical path of each branched light beam, the transmission axis angle of the polarizing plate is set in a plane substantially orthogonal to the optical axis, and the branched optical phase difference is given. Phase shift interference fringes are generated, and these branched phase shift interference fringes are simultaneously imaged by the imaging devices 13-15.
[0004]
[Problems to be solved by the invention]
In other words, in this phase shift interference fringe simultaneous measurement apparatus, the branch phase shift interference fringes necessary for measurement are given by setting an accurate angle of the transmission axis of the polarizing plates 10 to 12, but in this apparatus, the test surface undulations In order to measure the shape with high accuracy, it is assumed that the bias and the amplitude between the three branch phase shift interference fringes are equal at each point in the observation region.
However, the bias and amplitude of the three branch phase shift interference fringes are caused by the split intensity error in the three-spectral prism 9 and the elliptical polarization of the transmitted light due to the installation error of the slow axis of the quarter wavelength plate 8. Actually, it will be different. For this reason, conventionally, countermeasures have been taken in which a representative value of bias and amplitude is calculated from a branched phase shift interference fringe image and the difference between them is corrected.
However, it is difficult in reality to make the optical elements intervening on the branch optical path work uniformly, and in reality the bias and amplitude values between the branch phase shift interference fringes are different at each point in the observation region. There is a problem that the method of uniformly correcting with the representative value has a problem that variations in bias and amplitude remain after correction within one screen.
[0005]
In view of the problem of the simultaneous phase shift interference fringe imaging device as described above, the object of the present invention is high accuracy even if the bias and amplitude at each point in the observation region of the three branched phase shift interference fringes are different from each other. The present invention provides a planar shape measuring method capable of obtaining a phase shift interference fringe image that can be analyzed easily.
[0006]
[Means for Solving the Problems]
In order to achieve this object, the present invention measures the bias of the branch phase shift interference fringe, the amplitude value, and the reference light observed for each branch in advance at each point in the observation region, and obtains the bias obtained by the measurement. Using the amplitude value and the reference light image data, brightness conversion is performed on the branched phase shift interference fringe image data obtained during the subsequent measurement of the test surface, and bias and amplitude matching is performed for each point in the observation area. By doing so, it is proposed that the phase shift interference fringe simultaneous measurement apparatus can be greatly improved in accuracy.
That is, in the present invention,
A reference surface and a test surface are irradiated with a coherent light beam from a laser light source, and the polarization planes of the reference light and the sample light that are reflected from each of the reference surface and the test surface are interposed with a polarization optical element. An observation optical system that generates an original light beam that is in an optically non-interfering state by being orthogonal to each other;
Dividing the original light beam into a plurality of branched original light beams, and generating a plurality of branched phase shift interference fringes each having a different fixed optical phase difference via a polarization optical element to each of the branched original light beams, Images corresponding to these interference fringes with an imaging device provided for each branched light beam, with the positions aligned so that one position in the observation range of the test surface is the same position in each branch observation coordinate system In the phase shift interference fringe simultaneous imaging device that acquires data and reproduces the planar undulation shape of the observation range of the test surface as numerical data using the phase shift method,
For each branch original light beam calculated from phase shift interference fringe image data for each branch obtained by each imaging device when a relative optical phase difference is separately given between the reference light and the sample light. Using the bias, amplitude, and branch reference light image data obtained for each branch original beam in the absence of sample light, the brightness of the phase-shifted interference fringe image data for each branch during planar undulation shape measurement is converted. Thus, a planar shape measuring method in the phase shift interference fringe simultaneous imaging apparatus is proposed in which the bias and amplitude at each point in the observation region are matched and adjusted, and the phase is calculated for each point of the interference fringe by the phase shift method.
[0007]
In the description of the preferred embodiments of the invention described below,
1) A method of generating the optical phase difference by slightly changing the wavelength of the laser light source when separately giving a relative optical phase difference between the reference light and the sample light,
2) When separately providing a relative optical phase difference between the reference light and the sample light, by moving one of the reference surface and the test surface slightly along the optical axis, , A method of generating the optical phase difference,
3) A non-reflective transmitter having a refractive index greater than 1 in the optical path between the reference surface and the test surface when a relative optical phase difference is separately provided between the reference light and the sample light. A method for generating the optical phase difference by inserting at least one parallel plate having different thicknesses,
4) A non-reflecting transparent body having a refractive index greater than 1 in the optical path between the reference surface and the test surface when a relative optical phase difference is separately provided between the reference light and the sample light. An optical wedge is inserted in which the two surfaces facing the reference surface and the test surface are not parallel, and the optical wedge is moved in the wedge direction in a plane substantially perpendicular to the optical axis to generate the optical phase difference. How to
5) When a relative optical phase difference is separately provided between the reference light and the sample light, a liquid crystal is disposed between the reference surface and the test surface, and the refractive index is controlled by electrical control of the liquid crystal. A method of generating a predetermined optical phase difference,
[0008]
And in the description of the embodiments of the present invention,
1) The difference between the bias obtained for each point and the other point of the amplitude is the value of the bias and the amplitude arranged for each set of points that is an allowable range,
2) The simple average, median, or mean square value obtained from the bias and amplitude values obtained for each point is used as the representative value of the bias and amplitude for the entire region regardless of the position of each point. ,
3) A laser light source capable of changing the wavelength slightly to embody each of the above-described planar shape measurement methods, the reference surface or the test surface that can be translated little by little along the optical axis, the reference surface and the object to be measured A non-reflective transparent parallel plate with a refractive index greater than 1 positioned in the optical path between the test surface and a wedge having a refractive index greater than 1 positioned in the optical path between the reference surface and the test surface A phase shift interference fringe simultaneous imaging device incorporating an optical wedge that can move in the direction and a liquid crystal that is positioned in the optical path between the reference surface and the test surface and that can change the refractive index by electrical control is also described.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The planar shape measuring method of the present invention is the same as the phase shift interference fringe simultaneous imaging apparatus shown in FIG. 1 except that the branch phase shift interference fringe bias, amplitude value, and reference light observed for each branch are measured in each observation region. Pre-measured at the point, using the bias and amplitude values obtained by the measurement and the reference light image data, and applying the brightness conversion to the branched phase shift interference fringe image data obtained during the subsequent measurement of the surface to be biased Amplitude matching is performed for each point in the observation region.
[0010]
The planar shape measurement method of the present invention will be described in detail. When calculating the surface undulation shape from three interference fringes using the phase shift method, the three interference fringes are respectively expressed by the following equations, Generally, φ (x, y) corresponding to the surface undulation shape is calculated.
[Expression 1]

Here, I ₁ (x, y), I ₂ (x, y), and I ₃ (x, y) are luminance information measured by an imaging device such as a video camera, and B (x, y), A ( x, y) represents the bias and amplitude of each interference fringe, and α (x, y) and β (x, y) represent the phase shift amount intentionally added by the interferometer.
[0011]
Branched phase shift interference fringes obtained by the imaging devices 13 to 15 when the test surface 7 is observed with the phase shift interference fringe simultaneous measurement apparatus shown in FIG. 1 are also represented by (1-1) and (1-2). , (1-3) is ideally expressed.
However, in the phase shift interference fringe simultaneous imaging apparatus, even if the phase shift amounts α (x, y) and β (x, y) are given as planned values, the quarter-wave plate 6 used for generating circularly polarized light. , 8 and the light splitting error of the three-divided prism, the biases and amplitudes between the branched phase shift interference fringes are different from each other.
Furthermore, due to the non-uniformity of the reflectivity and transmittance of the interferometer components, the corresponding bias and amplitude between three interference fringe images on an arbitrary x, y coordinate are x, y. Naturally, if these measures are not addressed, a large error will occur when calculating the shape.
[0012]
Therefore, in the present invention, the luminance information I ₁ (x, y), I ₂ (x, y), and I ₃ (x, y) of the _three interference fringes is subjected to luminance conversion, and branched phase shift interference. Using the phase shift amounts α (x, y) and β (x, y) that are intentionally given and the bias and amplitude matching adjustments between the fringes performed at the respective points x and y, φ (x , Y), this specific method will be described next.
[0013]
In consideration of the problems described above, the interference fringes obtained by the imaging devices 13 to 15 of the phase shift interference fringe simultaneous imaging device are represented by the following (2-1) to (2-3), respectively. .
[0014]
[Expression 2]

[0015]
In addition, when an optical phase difference δ _i is separately given between the reference light and the sample light, the obtained phase shift interference fringes for each branch are expressed by the following equations (3-1) to (3-3). Can be represented.
[Equation 3]

[0016]
If δ _i is arbitrarily changed and three or more branch phase shift interference fringes are obtained for each branch, the bias and amplitude for each branch can be calculated. Here, as an example of one calculation method, δ _i is a value obtained by equally dividing the interference fringe phase 1 period 2π δ _i = i2π / N; i = 1, 2, 3,... N
In this case, by performing the following calculation, the bias and amplitude for each branch are expressed by the following formulas (4-1) to (4-3) and formulas (5-1) to (5-3). ).
[0017]
[Expression 4]

[0018]
B ₁ (x, y), B ₂ (x, y), B ₃ (x, y), A ₁ (x, y), A ₂ (x, y), A ₃ (x, y) obtained here. y) is a value when the test surface S for adjusting the bias and amplitude is measured, and the reference light and the sample light are a (x, y) and b (x, y), respectively. The reference light and sample light reaching the arranged imaging devices 13 to 15 are a ₁ (x, y), a ₂ (x, y), a ₃ (x, y) and b ₁ (x, y), b _2. (X, y), b ₃ (x, y) (hereinafter, the dimensions of x and y are omitted for simplicity).
Therefore, the relationship between the bias, amplitude, reference light, and sample light for each branch is:

It is represented by
[0019]
Next, when measuring different test surfaces T, luminance conversion is performed on the branched phase shift interference fringe image using the previously calculated bias and amplitude values, and the bias and amplitude matching adjustment is performed. A method of calculating the undulating shape of the surface T will be described.
2A shows a reflected light intensity model input to the imaging apparatus when measuring the test surface S for adjusting bias and amplitude matching, and FIG. 2B shows the input to the imaging apparatus when measuring the test surface T. Each reflected light intensity model is shown.
[0020]
2A and 2B, if the sample lights b ′ and b at the time of measurement of the test surface T are in a relationship of b ′ = γb, the sample reaching the three imaging devices 13 to 15 It can be considered that the light is affected at the same rate as b ′ ₁ = γb ₁ , b ′ ₂ = γb ₂ , b ′ ₃ = γb ₃ , respectively.
Considering these, biases B ₁ ′, B ₂ ′, B ₃ ′ for each branch during measurement of the test surface T, amplitudes A ₁ ′, A ₂ ′, A ₃ ′, and the previously obtained bias B ₁ , B ₂ , B ₃ and the amplitudes A ₁ , A ₂ , A ₃ are represented by the following formulas (8-1) to (8-3) and (9-1) to (9-3). It is represented by
[Formula 6]

[0021]
Therefore, the three branched phase shift interference fringes obtained when observing the test surface T are expressed as follows:

It will be represented by
[0022]
A ₁ , a ₂ , and a ₃ in (10-1) to (10-3) are reference light intensities obtained when the sample light is shielded, and are constant in time regardless of the test surface. Is the value of
Further, b ₁ , b ₂ , and b ₃ are B ₁ , B ₂ , and B ₃ (formula 6-1) obtained from the test surface S for adjusting the bias and amplitude with a ₁ , a ₂ , and a _3. ) To (7-3 equation).
[0023]
The calculation of φ using the three equations (10-1) to (10-3) will be described below.
(10-1 type) from -a _1,
[Equation 8]

(10-2 type) from -a _2,
[Equation 9]

From (10-3 type) -a _3,
[Expression 10]

Is obtained.
[0024]
From (11-1) to (11-3),
[Expression 11]

Is obtained.
[0025]
The determinant is:

For example, when α = π / 2 and β = π, it is possible to solve for φ with% 1 ≠ 0.
[0026]
Therefore, (Equation 12) can be rewritten as
[Formula 13]

It becomes.
[0027]
Therefore, the phase φ is

This is obtained by calculating φ (x, y) after the difference in bias and amplitude between the branched phase shift interference fringes is resolved at each point in the x, y plane in the observation region. It is a calculation result of the undulation shape of the test surface.
[0028]
Next, a method for separately providing an optical phase difference between the reference light and the sample light in order to measure the bias and amplitude of the branched phase shift interference fringes will be described.
The interference fringes obtained from the imaging device 13 when the distance of the test surface 7 with respect to the reference surface 5 is d (x, y)
[Expression 15]

Therefore, it is expressed by the following formula.
[Expression 16]

I (x, y) represents the interference fringe intensity, B (x, y) and A (x, y) represent the bias and amplitude, respectively, and λ represents the wavelength of the laser light source 1.
[0029]
Here, the interference fringes when the wavelength λ is changed by a small amount Δλ _i is
[Expression 17]

here,
[Expression 18]

Because
[Equation 19]

It is represented by
[0030]
Similarly, the interference fringes obtained by the imaging device 14 and the imaging device 15 are:

[0031]
It is represented by
That is, an optical phase difference can be separately added to the reference light and the sample light by changing the amount corresponding to δ _i = C · Δλ _i and / or the wavelength of the laser light source 1 by Δλ _i . Then, the calculations shown in (4-1) to (4-3) and (5-1) to (5-3) are performed from a plurality of phase shift interference fringe images obtained for each branch. Thus, the bias and amplitude of each branch phase shift interference fringe can be calculated for each point of x and y.
[0032]
Further, in providing a reference beam and a sample beam optical phase difference separately 3 and 4, even when [Delta] d _i by translating the reference surface or the test surface in the optical axis direction, each branch phase The bias and amplitude of the shift interference fringe can be calculated for each point of x and y. The branched phase shift interference fringes at that time are expressed by the following equation.
[Expression 21]

[0033]
That is, as is clear from (18-1 formula) to (18-3 formula),

From the plurality of phase shift interference fringes obtained for each branched original light beam when a displacement amount Δd _i corresponding to is given, (Expression 4-1) to (4-2), (Expression 5-1) By performing the calculation shown in (Formula 5-3), the bias and amplitude of each branch phase shift interference fringe can be calculated for each point of x and y.
[0034]
In addition, when separately giving an optical phase difference to the reference light and the sample light, parallel plates with different thicknesses are formed with a non-reflective transparent body having a refractive index larger than 1 in the optical path between the reference surface 5 and the test surface 7. Even if it is inserted, the fixed optical phase difference between the branched phase shift interference fringes can be measured.
[0035]
For example, as shown in FIG. 5, using

parallel plates

16 and 17 having a refractive index n and thicknesses l ₁ and l ₂ ,
The state where the

parallel plates

16 and 17 are not inserted is δ ₁
When the parallel plate 16 having the thickness l ₁ is inserted, δ ₂
When inserting parallel plate 17 with thickness l ₂ δ ₃
Or
As shown in FIG. 6, using

parallel plates

18 and 19 having refractive indexes n ₁ and n ₂ and the same thickness l,
The state in which the

parallel plates

18 and 19 are not inserted is δ ₁
When the parallel plate 18 having a refractive index n ₁ is inserted, δ ₂
When the parallel plate 19 having a refractive index n ₂ is inserted, δ ₃
However, it is possible to separately provide an optical phase difference between the reference light and the sample light, and the bias and amplitude of the branched phase shift interference fringes can be calculated for each of the x and y points.
[0036]
Further, when an optical phase difference is separately given to the reference light and the sample light, as shown in FIG. 7, a non-reflective transmission body having a refractive index larger than 1 in the optical path between the reference surface and the test surface. Then, an optical wedge 7 whose two surfaces facing the reference surface and the test surface are not parallel is inserted, and the optical wedge 7 is moved in the wedge direction in a plane substantially orthogonal to the optical axis, so that each branch phase shift interference fringe It is also possible to calculate the bias and amplitude for each point of x and y.
[0037]
Further, as shown in FIG. 8, the liquid crystal 21 is inserted between the reference surface and the test surface, and the refractive index of the liquid crystal 21 is varied by electrical control such as voltage by the control device 22, so that δ ₁ , δ ₂ , δ _{Even if} an optical phase difference corresponding to ₃ is generated, it is possible to calculate the bias and amplitude of each branch phase shift interference fringe for each point of x and y.
[0038]
Of course, the phase shift interference fringe biases and amplitudes B ₁ (x, y), B ₂ (x, y), B ₃ (x, y), A ₁ (x , Y), A ₂ (x, y), and A ₃ (x, y) may be used as they are for adjusting the bias and amplitude matching of the branch phase shift interference fringes by luminance conversion.
[0039]
Referring to how to further facilitate data processing, Fig. 9 B ₁ (x, y) _{1-dimensional} data B ₁ (x, y ₁₎ for y ₁ with the data of which represent, graph B ₁ (x, y ₁ ) means that the value is different from the position x in the observation region.
In FIG. 9, in the present invention, a certain allowable range t is set for B ₁ (X, y ₁ ), numerical data groups within the range are arranged together and replaced with representative values, and B ₁ ′ A data string as illustrated in (x, y ₁ ) is created. This idea is applied to a two-dimensional data group of x and y, and a data group in a region within a certain allowable range t is replaced with a representative value.
The same processing is performed for B ₂ (x, y), B ₃ (x, y), A ₁ (x, y), A ₂ (x, y), and A ₃ (x, y). , B ₂ ′ (x, y), B ₃ ′ (x, y), A ₁ ′ (x, y), A ₂ ′ (x, y), A ₃ ′ (x, y) are created. B ₁ ′ (x, y), B ₂ ′ (x, y), B ₃ ′ (x, y), A ₁ ′ (x, y), A ₂ ′ (x, y), A ₃ ′ (x , Y), the memory capacity can be saved by reducing the number of parameters held in the computer.
Furthermore, as shown in FIG. 10, B ₁ (x, y), B ₂ (x, y), B ₃ (x, y), A ₁ (x, y), A ₂ (x, y), A ₃ (x, y) is replaced with a simple average or median B ₁ ′, B ₂ ′, B ₃ ′, A ₁ ′, A ₂ ′, A ₃ ′, or as shown in FIG. B ₁ ′ (x, y), B ₂ ′ (x, y), B ₃ ′ (x, y), A ₁ ′ (x, y), A ₂ ′ (x, y), calculated from the mean of multiplication, If A ₃ ′ (x, y) is set, it is possible to save much more memory capacity when calculating the undulated shape of the test surface with the planar shape measuring apparatus.
[0040]
【The invention's effect】
As is apparent from the above description, according to the present invention, the bias and amplitude of the branch phase shift interference fringes obtained from different distribution states are measured in advance for each branch, and are obtained during subsequent measurement of the test surface. The accuracy of the branch phase shift interference fringes can be greatly improved by performing brightness adjustment on the x and y points in the observation region, adjusting the alignment, and calculating the detected undulation shape.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of an optical system of a phase shift interference fringe simultaneous imaging apparatus according to the present invention.
FIGS. 2A and 2B are comparison models of reflected light intensity input to the imaging apparatus when measuring the test surfaces S and T. FIG.
FIG. 3 is an explanatory diagram of a first optical phase difference providing unit in the same phase shift interference fringe simultaneous imaging apparatus;
FIG. 4 is an explanatory diagram of second optical phase difference providing means in the same phase shift interference fringe simultaneous imaging apparatus;
FIG. 5 is an explanatory diagram of a third optical phase difference providing unit in the same phase shift interference fringe simultaneous imaging apparatus;
FIG. 6 is an explanatory diagram of a fourth optical phase difference providing unit in the same phase shift interference fringe simultaneous imaging apparatus;
FIG. 7 is an explanatory diagram of a fifth optical phase difference providing unit in the same phase shift interference fringe simultaneous imaging apparatus;
FIG. 8 is an explanatory diagram of a sixth optical phase difference providing unit in the same phase shift interference fringe simultaneous imaging apparatus;
FIG. 9 is an explanatory diagram of a method for calculating bias and amplitude of interference fringes for each branch according to the present invention;
FIG. 10 is an explanatory diagram of a method of calculating bias and amplitude of interference fringes for each branch by simple averaging.
FIG. 11 is an explanatory diagram of a method of calculating bias and amplitude of interference fringes for each branch by means of root mean square.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Laser light source 2 Lens 3 Beam splitter 4 Collimator lens 5 Reference surface 6 1/4 wavelength plate 7 Test surface 8 1/4 wavelength plate 9 3 Spectral prism 10-12 Polarizing plate 13-15 Imaging apparatus 16-19 Parallel plate 20 Optical wedge 21 Liquid crystal 22 Control device

Claims

A reference surface and a test surface are irradiated with a coherent light beam from a laser light source, and the polarization planes of the reference light and the sample light that are reflected from each of the reference surface and the test surface are interposed with a polarization optical element. An observation optical system that generates an original light beam that is in an optically non-interfering state by being orthogonal to each other;
Dividing the original light beam into a plurality of branched original light beams, and generating a plurality of branched phase shift interference fringes each having a different fixed optical phase difference via a polarization optical element to each of the branched original light beams, Images corresponding to these interference fringes with an imaging device provided for each branched light beam, with the positions aligned so that one position in the observation range of the test surface is the same position in each branch observation coordinate system In the phase shift interference fringe simultaneous imaging device that acquires data and reproduces the planar undulation shape of the observation range of the test surface as numerical data using the phase shift method,
A bias for each branch calculated from phase shift interference fringe image data for each branch obtained by each imaging device when a relative optical phase difference is separately given between the reference light and the sample light; Using the amplitude and branch reference light image data obtained for each branch in the absence of sample light, luminance conversion is performed on the phase shift interference fringe image data for each branch during planar undulation shape measurement, and the observation region A method for measuring a planar shape in a phase shift interference fringe simultaneous imaging apparatus, wherein the bias and amplitude at each point are matched and adjusted, and a phase calculation is performed for each point of the interference fringe by a phase shift method.

The optical phase difference is generated by changing a wavelength of the laser light source little by little when separately providing a relative optical phase difference between the reference light and the sample light. A planar shape measuring method in the phase shift interference fringe simultaneous imaging apparatus according to claim 1.

When separately providing a relative optical phase difference between the reference light and the sample light, by moving one of the reference surface and the test surface little by little along the optical axis, 2. The planar shape measuring method in the phase shift interference fringe simultaneous imaging apparatus according to claim 1, wherein an optical phase difference is generated.

When a relative optical phase difference is separately provided between the reference light and the sample light, the non-reflective transmission body has a refractive index greater than 1 in the optical path between the reference surface and the test surface. 2. The planar shape measuring method in the phase shift interference fringe simultaneous imaging apparatus according to claim 1, wherein the optical phase difference is generated by inserting at least one parallel plate having different thicknesses.

When a relative optical phase difference is separately provided between the reference light and the sample light, the non-reflective transmission member has a refractive index greater than 1 in the optical path between the reference surface and the test surface. Then, an optical wedge is inserted into which the two surfaces facing the reference surface and the test surface are not parallel, and the optical wedge is moved in the wedge direction within a plane substantially perpendicular to the optical axis to generate the optical phase difference. The planar shape measuring method in the interference fringe simultaneous imaging device according to claim 1.

When a relative optical phase difference is separately provided between the reference light and the sample light, a liquid crystal is disposed between the reference surface and the test surface, and the refractive index is variable by electrical control of the liquid crystal. 2. A method for measuring a planar shape in an interference fringe simultaneous imaging apparatus according to claim 1, wherein a predetermined optical phase difference is generated.

2. The interference fringe simultaneous imaging according to claim 1, wherein the bias and amplitude obtained for each point are the bias and amplitude values arranged for each set of points within an allowable range. Planar shape measuring method in apparatus.

A simple average, median value, or mean square value obtained from the bias and amplitude values obtained for each point is used as the representative value of the bias and amplitude for the entire region regardless of the position of each point. A planar shape measuring method in the interference fringe simultaneous imaging apparatus according to claim 7.

The laser light source according to claim 2, wherein the wavelength can be changed little by little, and the reference surface or the test surface according to claim 3, wherein the reference surface or the test surface can be moved slightly along the optical axis. 5. The nonreflective transparent parallel plate according to claim 4, having a refractive index greater than 1 positioned in the optical path, having a refractive index greater than 1 positioned in the optical path between the reference surface and the test surface and a wedge. The optical wedge according to claim 5, which is movable in a direction, and the liquid crystal according to claim 6, wherein the optical wedge is positioned in an optical path between the reference surface and the test surface and the refractive index can be changed electrically Phase shift interference fringe simultaneous imaging device.