JP4100663B2 - Absolute thickness measuring device - Google Patents

Description

【００１１】
また、前記波長可変光源を波長可変レーザ光源とし、前記第１および第２の干渉計をフィゾー型干渉計とすることが可能である。
【００１２】
また、本発明の第２の絶対厚み測定装置は、光源からの出射光束を２分割し、一方の光束を被検面に入射させてその反射光を物体光とするとともに他方の光束を基準面に入射させてその反射光を参照光とし、これら物体光および参照光の光干渉により生じる干渉縞に基づいて前記被検面を測定するように構成された１対の第１および第２の干渉計と、被検体となる不透明の平行平面板を保持する被検体保持部材とを備え、
前記平行平面板の両面の一面側に第１の等光路長型干渉計を、他面側に第２の等光路長型干渉計を各々の出射光束が対向するように配置した状態で該平行平面板の両面を被検面として干渉測定を行うように構成された測定装置において、
前記光源を低可干渉光出力光源とするとともに、前記平行平面板の両面に各々離間対向して、基準位置決定面を有する透明な基準位置決定板を各々設け、
前記第１および第２の等光路長型干渉計の前記第１および第２基準面を各々光軸方向に移動可能とするとともに、前記第１および第２基準面各々の現在位置を読取可能な検出手段を設け、
前記第１の等光路長型干渉計の前記第１基準面を移動することにより、前記平行平面板の該第１の等光路長型干渉計側に配設された第１基準位置決定面、前記平行平面板の前記第２の等光路長型干渉計側に配設された第２基準位置決定面、および前記平行平面板の前記第１の等光路長型干渉計側の面の各々について、干渉縞が得られた際の、前記第１の等光路長型干渉計の前記第１基準面の各現在位置情報に基づき、前記第１基準位置決定面から前記平行平面板の前記第１の等光路長型干渉計側の面までの距離Ｄ_Ａと、前記第１基準位置決定面から前記第２基準位置決定面までの距離Ｄ_Ｃを得、
前記第２の等光路長型干渉計の前記第２基準面を移動することにより、前記第２基準位置決定面、および前記平行平面板の前記第２の等光路長型干渉計側の面の各々について、干渉縞が得られた際の前記第２の等光路長型干渉計の前記第２基準面の各現在位置情報に基づき、前記第２基準位置決定面から前記平行平面板の前記第２の等光路長型干渉計側の面までの距離Ｄ_Ｂを得、
前記距離Ｄ_Ａと前記距離Ｄ_Ｂとを、前記距離Ｄ_Ｃから減算処理して前記平行平面板の絶対厚みを算出するように構成されてなることを特徴とするものである。
【００１３】
また、前記被検体保持部材が、前記平行平面板を１対の前記干渉計の光束に対して挿脱自在とし得るように構成することが好ましい。
【００１４】
あるいは、前記被検体保持部材が、１対の前記干渉計の一方から出射された光束の一部を１対の前記干渉計の他方の前記基準面まで到達せしめる開口部を備えることが好ましい。
【００１５】
これらの場合において、１対の前記干渉計のうち前記干渉縞を観察する際に前記測定には関与しない干渉計から出射される光束が、前記測定に関与する干渉計に入射することを防止する遮光部材を設けることが好ましい。
【００１６】
なお、上述した「等光路長型干渉計」とは、物体光の光路長と参照光の光路長が略等しくなるように構成された干渉計のことをいうものとする。
また、上記「低可干渉光」とは、上述した如く、この低可干渉光によって形成された干渉縞が現れた際の、第１および第２基準面位置の読取精度に大きな影響を与えない程度の小さい可干渉距離（例えば数μｍ以下）を有する光をいうものとし、白色光が代表的な例であるが、必ずしも可視光域全域に亘って強度を有する必要はない。
【００１７】
【発明の実施の形態】
以下、図面を用いて、本発明の実施の形態について説明する。
【００１８】
＜第１の実施形態＞
まず、本発明に係る第１の実施形態について説明する。
図２は、波長可変レーザ光源を用いた第１の実施形態に係る絶対厚み測定装置１０を示す全体構成図である。
【００１９】
図示のように、この絶対厚み測定装置１０は、１対の干渉計１２Ａ、１２Ｂと、被検体となる不透明の平行平面板（例えば、セラミック板、金属板、ブロックゲージ等）２を保持する被検体保持部材１４と、コンピュータ１６と、モニタ１８とを備えてなり、平行平面板２の両側に１対の干渉計１２Ａ、１２Ｂを対向配置した状態で平行平面板２の両面２ａ、２ｂを被検面として干渉縞測定を行うことにより、平行平面板２の絶対厚みおよび厚みムラを測定するように構成されている。
【００２０】
各干渉計１２Ａ、１２Ｂは、フィゾー型の干渉計であって、その干渉計本体２０Ａ、２０Ｂにより、図示しない波長可変レーザ光源からの可干渉光を基準板２２Ａ、２２Ｂの基準面２２Ａａ、２２Ｂａに入射させ、該基準面２２Ａａ、２２Ｂａにおいて透過光線束と反射光線束とに２分割し、透過光線束を被検面２ａ、２ｂに入射させてその反射光を物体光とするとともに基準面２２Ａａ、２２Ｂａにおける反射光を参照光とし、これら物体光および参照光の光干渉により生じる干渉縞を図示しないＣＣＤカメラに取り込んで干渉縞を測定するようになっている。
【００２１】
ところで、本実施形態装置においては、上述したように測定用光源として、波長可変レーザ光源を用いている。これは、波長可変レーザ光源からの光の波長を走査し、所定の波長走査毎に取り込んだ干渉縞に対して所定の周波数解析を施すことによって光路長差を求めることができる、という論理に基づいている。このように、本実施形態装置においては、測定用光源として光路長差を求めることのできる波長可変レーザ光源を用いることにより、被検体となる平行平面板の絶対厚みおよび厚みムラを測定することができるようになっている。
【００２２】
上述した周波数解析による光路長差の測定は、具体的には以下のような手順で行われる。
すなわち、波長可変レーザにより、波数をｋ_１からｋ_２に走査し、Δｋ毎に画像を取り込んだ場合には、干渉縞強度変化Ｉ(ｘ、ｙ、ｋ)は、下式（１）で表される。
【００２３】
【数１】

【００２４】
ここで、Ｌ（ｘ、ｙ）は光路長差、Ｉ_０（ｘ、ｙ）は強度分布、γは干渉縞モジュレーションをそれぞれ示す。このときの所定画素における干渉縞変化がｎ回であったとすると、下式（２）で表される。
【００２５】
【数２】

ここで、ｋ=２π／λであるから、下式（３）が求められる。
【００２６】
【数３】

【００２７】
すなわち、波長を走査した際の周波数ｎを求めることにより、光路長差を測定することが可能となる。
なお、上記周波数ｎを決定するためには、本出願人が既に開示している特開2001−272214号公報に記載されているようにフーリエ変換を用いることが可能である。
【００２８】
また、本実施形態においては、より詳しい縞解析が可能な位相シフト波長走査干渉法を用いている。位相シフト波長走査干渉法とは、波長可変レーザ光源を用いた干渉計において、高精度な測定を実現するために、波長を走査し、所定の波長走査毎に、PZT等により参照面を光軸方向に移動させ、位相シフトさせて位相を求め、これにより各波長毎の位相を順次測定して光路長差Ｌ（ｘ、ｙ）を求める手法である。位相シフト波長走査干渉法についての詳細な説明については上述した特開2001−272214号公報に記載されているので、ここでは数式的な解法についての説明は省略し、それを可能とするための機構についての構成のみについて言及する。
【００２９】
すなわち、各干渉計１２Ａ、１２Ｂの基準板２２Ａ、２２Ｂは、ＰＺＴ駆動回路２４Ａ、２４Ｂに接続された複数のピエゾ素子２６Ａ、２６Ｂを介して基準板支持部材２８Ａ、２８Ｂに支持されている。そして、各干渉計１２Ａ、１２Ｂにおいては、波長可変レーザ光源による所定の波長走査毎にピエゾ素子２６Ａ、２６Ｂに所定電圧を印加して該ピエゾ素子２６Ａ、２６Ｂを駆動することにより基準板２２Ａ、２２Ｂを光軸Ａｘ方向に移動させるとともに、この移動により変化する干渉縞の画像データをコンピュータ１６に出力するようになっている。
【００３０】
コンピュータ１６は、各干渉計１２Ａ、１２Ｂから入力された干渉縞の画像データに基づいてフリンジスキャニング法を用いて干渉縞の自動解析を行い、被検面２ａ、２ｂの形状測定（凹凸判定および立体形状測定）を行うとともに、干渉縞あるいは立体形状の画像データをモニタ１８に表示するようになっている。なお、ここでいうフリンジスキャニング法とは、基準面２２Ａａ、２２Ｂａと被検面２ａ、２ｂとの相対距離を変化させながら所定のフリンジスキャンステップ毎の干渉縞画像データから被検面２ａ、２ｂの各点における干渉縞強度を測定し、その測定結果を用いて、その波長における、各点の位相計算等の干渉縞解析を行う手法である。
【００３１】
本実施形態に係る絶対厚み測定装置１０は、上述したように平行平面板２の両面２ａ、２ｂの表面形状の測定を行うとともに、両干渉計１２Ａ、１２Ｂの干渉縞測定結果を用いて平行平面板２の絶対厚みおよび厚みムラを解析的に測定するように構成されている。
【００３２】
なお、本実施形態装置においては、干渉計本体２０Ａ、２０Ｂは、図１に示す如く構成されている。すなわち、各々の干渉計本体２０Ａ、２０Ｂにおいて、波長可変レーザ光源３１Ａ、３１Ｂから出力されたレーザ光はレンズ３２Ａ、３２Ｂによって発散され、ハーフプリズム３３Ａ，３３Ｂを介し、コリメータレンズ３４Ａ、３４Ｂによって平行光束として外部に出力されるように構成されている。
【００３３】
一方、基準板２２Ａ，２２Ｂ方向から入射した干渉光はハーフプリズム３３Ａ、３３Ｂにより反射されて、結像レンズ３８Ａ、３８Ｂを介してＣＣＤカメラ等からなる撮像装置３９Ａ、３９Ｂ内に入射するように構成されている。
【００３４】
本実施形態に係る絶対厚み測定装置１０においては、以下に示す手順〈1〉〜〈9〉に従い、上述した平行平面板２の両面２ａ，２ｂの表面形状の測定を行うとともに、両干渉計１２Ａ，１２Ｂの干渉縞測定結果を用いて平行平面板２の絶対厚みおよび厚みムラを解析的に測定するようになっている。以下、図１〜５を参照しつつ説明する。
【００３５】
〈1〉平行平面板２を図３に示す如く光路上から退出させる。また、後述する遮光部材３０（図３参照）を光路上に挿入する。
【００３６】
〈2〉干渉計１２Ａにおいて波長可変レーザ光源３１Ａからレーザ光を出射するとともに、該レーザ光の波数をｋ_１からｋ_２まで走査し、Δｋ毎に、上述したフリンジスキャニング法を用いて干渉縞画像を取り込み、取込んだ干渉縞画像を解析し、上述した式（３）を用いて干渉計１２Ａの基準面２２Ａａと干渉計１２Ｂの基準面２２Ｂａとの間隔Ｄ_Ｃを求め、これをコンピュータ１６のメモリ内に記憶する。
【００３７】
〈3〉平行平面板２を図２に示す如く干渉計１２Ａの基準板２２Ａと干渉計１２Ｂの基準板２２Ｂとの間の光路上に挿入する。また、後述する遮光部材３０（図２参照）を光路上から退出させる。
【００３８】
〈4〉波長可変レーザ光源３１Ａからレーザ光を出射するとともに、該レーザ光の波数をｋ_１からｋ_２まで走査し、Δｋ毎に、上述したフリンジスキャニング法を用いて干渉縞画像を取り込み、取込んだ干渉縞画像を解析し、上述した式（３）を用いて干渉計１２Ａの基準面２２Ａａと平行平面板２のＡ側面２ａ上の所定点Ｐａ（図示せず）との間隔Ｄ_Ａを求めるとともに、平行平面板２のＡ側表面２ａの全体形状分布を求め、これをコンピュータ１６のメモリ内に記憶する。
【００３９】
〈5〉波長可変レーザ光源３１Ｂからレーザ光を出射するとともに、該レーザ光の波数をｋ_１からｋ_２まで走査し、Δｋ毎に、上述したフリンジスキャニング法を用いて干渉縞画像を取り込み、取込んだ干渉縞画像を解析し、上述した式（３）を用いて干渉計１２Ｂの基準面２２Ｂａと、平行平面板２のＢ側面２ｂ上の上記図示しない所定点Ｐａと表裏の位置関係にある所定点Ｐｂ（図示せず）との間隔Ｄ_Ｂを求めるとともに、平行平面板２のＢ側表面２ｂの全体形状分布を求め、これをコンピュータ１６のメモリ内に記憶する。
【００４０】
〈6〉上記手順〈2〉において求めた干渉計１２Ａの基準面２２Ａａと干渉計１２Ｂの基準面２２Ｂａとの間隔Ｄ_Ｃから、上記手順〈4〉において求めた干渉計１２Ａの基準面２２Ａａと平行平面板２のＡ側表面２ａ上の所定点Ｐａとの間隔Ｄ_Ａ、および上記手順〈5〉において求めた干渉計１２Ｂの基準面２２Ｂａと平行平面板２のＢ側表面２ｂ上の所定点Ｐｂとの間隔Ｄ_Ｂを差し引くことで、平行平面板２の点Ｐａ，Ｐｂ間における絶対厚みｄを求める。図４は、この手法を模式的に示すものである。
【００４１】
〈7〉図４に示すように上記手順〈6〉において求めた平行平面板２の点Ｐａ，Ｐｂ間における絶対厚みｄと、上記手順〈4〉において求めた平行平面板２のＡ側表面２ａの形状と、上記手順〈5〉において求めた平行平面板２のＢ側表面２ｂの形状とから、平行平面板２全体の絶対厚みと厚みムラの分布とを求める。
【００４２】
また、上述した厚みムラ測定は、図５に示すように、平行平面板２の各面２ａ、２ｂにおける各点の光軸直交平面からの変位量Δａ、Δｂのデータを用い、その差Δａ−Δｂを算出することにより行われる。
【００４３】
その際、両干渉計１２Ａ、１２Ｂの基準面２２Ａａ、２２Ｂａが完全に平行であれば、上記Δａ−Δｂの値がそのまま平行平面板２の厚みムラを表わすこととなるが、一般には基準面２２Ａａ、２２Ｂａが完全に平行ということはあり得ないので、基準面２２Ａａ、２２Ｂａ相互の平行度を加味して厚みムラの測定が行われるようにすることが好ましい。具体的には、上記手順〈2〉において、フリンジスキャニング法を用いて得られた、複数枚干渉縞画像に基づいて両干渉計１２Ａ、１２Ｂの基準面２２Ａａ、２２Ｂａ相互の平行度を測定し、そのずれを補正すればよい。
【００４４】
このようにして求められた、平行平面板２全体の厚みムラの分布を上述した点Ｐａ，Ｐｂ間における絶対厚みｄに加味することにより、平行平面板２全体の絶対厚みを求めることができる。
【００４５】
本実施形態においては、被検面２ａ、２ｂおよび基準面２２Ａａ、２２Ｂａ間の干渉縞測定とともに基準面２２Ａａ、２２Ｂａ相互間の干渉縞測定を行い得るようにするため、以下のような構成が採用されている。
【００４６】
図２は、被検面２ａ、２ｂおよび基準面２２Ａａ、２２Ｂａ間の干渉縞測定の様子を示すものであり、図３は、基準面２２Ａａ、２２Ｂａ相互間の干渉縞測定の様子を示すものである。
【００４７】
被検体保持部材１４は、図２および図３において矢印で示すように、両基準板２２Ａ、２２Ｂの中間において両干渉計１２Ａ、１２Ｂの光路内の被検体測定位置（図２に示す位置）と光路外の退避位置（図３に示す位置）とを採り得るよう光軸直交方向に移動可能に設けられている。そして、この被検体保持部材１４は、被検面２ａ、２ｂおよび基準面２２Ａａ、２２Ｂａ間に形成される干渉縞を測定する際には、被検体測定位置に移動せしめられ、これにより各干渉計１２Ａ、１２Ｂによる被検面２ａ、２ｂの形状測定を可能ならしめるようになっている。一方、基準面２２Ａａ、２２Ｂａ相互間の干渉縞を測定する際には、退避位置に移動せしめられるようになっている。
【００４８】
また、１対の干渉計１２Ａ、１２Ｂのうち一方の干渉計１２Ｂには、その光源からの可干渉光を遮蔽し得る遮光部材３０が設けられている。この遮光部材３０は、図２および図３において矢印で示すように、干渉計本体２０Ｂと基準面２２Ｂａとの間において光路内の遮蔽位置（図３に示す位置）と光路外の退避位置（図２に示す位置）とを採り得るよう光軸直交方向に移動可能に設けられている。そして、この遮光部材３０は、被検面２ａ、２ｂおよび基準面２２Ａａ、２２Ｂａ間に形成される干渉縞を測定する際には、退避位置に移動せしめられた状態にあるが、基準面２２Ａａ、２２Ｂａ相互間に形成される干渉縞を測定する際には、遮蔽位置に移動せしめられ、これにより干渉計１２Ｂの光源からの可干渉光を遮蔽した状態で、他方の干渉計１２Ａによる基準面２２Ａａ、２２Ｂａ相互間の干渉縞測定を可能ならしめるようになっている。
【００４９】
以上詳述したように、本実施形態に係る絶対厚み測定装置１０は、各干渉計１２Ａ、１２Ｂにより被検体保持部材１４に保持された平行平面板２の各面２ａ、２ｂを被検面として干渉縞測定を行うようになっているが、被検体保持部材１４は１対の干渉計１２Ａ、１２Ｂの光路外へ退避可能に設けられるとともに、一方の干渉計１２Ｂにはその光源からの可干渉光を遮断し得る遮光部材３０が設けられているので、上記干渉縞測定の前または後に、被検体保持部材３０を光路外に退避させるとともに遮光部材３０により干渉計１２Ｂの光源からの可干渉光を遮断することにより、この状態で干渉計１２Ａによる基準面２２Ａａ、２２Ｂａ相互間の干渉縞測定を行うことができる。
【００５０】
そしてこれにより、平行平面板２の両面２ａ、２ｂの表面形状の測定およびその厚みムラの測定を行う際、基準面２２Ａａ、２２Ｂａ相互間の干渉縞測定結果を用いてその平行度のずれを補正することができる。
【００５１】
したがって、本実施形態によれば、両干渉計１２Ａ、１２Ｂの基準面２２Ａａ、２２Ｂａ相互の平行度が十分に得られないまま干渉縞測定が行われた場合においても、平行平面板２の両面２ａ、２ｂの表面形状、その絶対厚みおよび厚みムラを正確に測定することができる。
【００５２】
＜第２の実施形態＞
次に、本発明に係る第２の実施形態について説明する。
【００５３】
図６は、本実施形態に係る絶対厚み測定装置１１０を示す全体構成図である。図示のように、この絶対厚み測定装置１１０は、基本的構成は図２に示す絶対厚み測定装置１０と同様であるが、被検体保持部材１４および遮光部材３０の構成が異なっている。
【００５４】
すなわち、本実施形態における被検体保持部材１１４は両干渉計１２Ａ、１２Ｂの光路内に固定配置されており、該被検体保持部材１１４には、各干渉計１２Ａ、１２Ｂの可干渉光の一部を他方の干渉計の基準面まで到達させるための開口部１１４ａが形成されている。また、本実施形態における遮光部材１３０は、干渉計１２Ｂの波長可変レーザ光源３１Ａ、３１Ｂからの可干渉光のうち開口部１１４ａに入射する可干渉光を遮断するようにして固定配置されている。
【００５５】
本実施形態においては、遮光部材１３０が設けられていない干渉計１２Ａにより開口部１１４ａを通して基準面２２Ａａ、２２Ｂａ相互間の干渉縞測定を行うことができる。しかも、この基準面２２Ａａ、２２Ｂａ相互間の干渉縞測定と同時に、各干渉計１２Ａ、１２Ｂにより平行平面板２の各面２ａ、２ｂを被検面とする干渉縞測定を同時に行うことができる。そして、平行平面板２の両面２ａ、２ｂの表面形状の測定、その絶対厚みおよび厚みムラの測定を行う際、基準面２２Ａａ、２２Ｂａ相互間の干渉縞測定結果を用いてその平行度のずれを補正することができる。
【００５６】
したがって、本実施形態によれば、両干渉計１２Ａ、１２Ｂの基準面２２Ａａ、２２Ｂａ相互の平行度が十分に得られないまま干渉縞測定が行われた場合においても、平行平面板２の両面２ａ、２ｂの表面形状、その絶対厚みおよび厚みムラを正確に測定することができる。しかも、本実施形態においては、被検体保持部材１４を光路外に退避させる必要がないので、短時間で干渉縞測定を行うことができる。
【００５７】
＜第３の実施形態＞
次に、本発明に係る第３の実施形態について説明する。
【００５８】
図７は、本実施形態に係る絶対厚み測定装置２１０を示す全体構成図である。
図示のように、この絶対厚み測定装置２１０も、基本的構成は図２に示す絶対厚み測定装置１０と同様であるが、被検体保持部材１４および遮光部材３０の構成が異なっている。
【００５９】
すなわち、本実施形態においては、図６に示す被検体保持部材１１４と同様、被検体保持部材２１４が両干渉計１２Ａ、１２Ｂの光路内に固定配置されており、該被検体保持部材２１４には、各干渉計１２Ａ、１２Ｂの可干渉光の一部を他方の干渉計の基準面まで到達させるための開口部２１４ａが形成されている。
【００６０】
また、本実施形態においては、１対の遮光部材２３０Ａ、２３０Ｂが用いられている。これら遮光部材２３０Ａ、２３０Ｂは、図２に示す遮光部材３０と同様、干渉計本体２０Ａ、２０Ｂと基準面２２Ａａ、２２Ｂａとの間において光路内の遮蔽位置と光路外の退避位置とを採り得るよう光軸直交方向に移動可能に設けられている。ただし、これら遮光部材２３０Ａ、２３０Ｂは、一方が遮蔽位置にあるとき、他方は退避位置にあるように移動制御されるようになっている。
【００６１】
本実施形態においては、遮光部材２３０Ｂにより干渉計１２Ｂの波長可変レーザ光源３１Ｂからの可干渉光を遮断した状態で、干渉計１２Ａにより基準面２２Ａａ、２２Ｂａ相互間の干渉縞測定および平行平面板２の干渉計１２Ａ側の面２ａを被検面とする干渉縞測定を同時に行うことができ、また、遮光部材２３０Ａにより干渉計１２Ａの波長可変レーザ光源３１Ｂからの可干渉光を遮断した状態で、干渉計１２Ｂにより基準面２２Ａａ、２２Ｂａ相互間の干渉縞測定および平行平面板２の干渉計１２Ｂ側の面２ｂを被検面とする干渉縞測定を同時に行うことができる。
【００６２】
そして、平行平面板２の両面２ａ、２ｂの表面形状の測定およびその厚みムラの測定を行う際、基準面２２Ａａ、２２Ｂａ相互間の干渉縞測定結果を用いてその平行度のずれを補正することができる。
【００６３】
したがって、本実施形態によれば、両干渉計１２Ａ、１２Ｂの基準面２２Ａａ、２２Ｂａ相互の平行度が十分に得られないまま干渉縞測定が行われた場合においても、平行平面板２の両面２ａ、２ｂの表面形状、その絶対厚みおよび厚みムラを正確に測定することができる。
【００６４】
その際、基準面２２Ａａ、２２Ｂａ相互間の干渉縞測定結果は、いずれか一方の干渉計のものを用いれば足りるが、両干渉計１２Ａ、１２Ｂの干渉縞測定結果を用いて開口部２１４ａの光軸直交方向の位置ズレ（例えば開口部２１４ａの中心位置の位置ズレ）を比較するようにすれば、両干渉計１２Ａ、１２Ｂの光軸ズレをも測定することができる。したがって、この測定結果を用いて、平行平面板２の両面２ａ、２ｂの表面形状の測定、その絶対厚みおよび厚みムラの測定を行う際に光軸ズレの補正を行うようにすれば、平行平面板２の両面２ａ、２ｂの表面形状およびその厚みムラをより正確に測定することができる。
【００６５】
なお、上記各実施形態においては、各干渉計１２Ａ、１２Ｂとしてフィゾー型の干渉計を用いたものについて説明しているが、他の不等光路長型干渉計やマイケルソン型等の等光路長型干渉計を用いた場合等においても、上記各実施形態と同様の構成を採用することにより上記各実施形態と同様の作用効果を得ることができる。
【００６６】
また、上記説明においては、干渉計としていわゆる縦型のものを用いているが、これに代え、光軸を水平方向に配したいわゆる横型の干渉計を用いることも可能である。
【００６７】
上述した第１〜３の実施形態では、光源として波長可変レーザ光源を用いているが、本発明の絶対厚み測定装置においては下記第４の実施形態に説明するように、光源として白色光源を用いることも可能である。ただし、光源として白色光源を用いた場合には、干渉計をマイケルソン型等の等光路長型のものによって構成することが必要である。
【００６８】
＜第４の実施形態＞
図８は、本実施形態に係る絶対厚み測定装置５００を示す全体構成図である。
図示のように、この絶対厚み測定装置５００は、１対の干渉計５１０Ａ，５１０Ｂと、被検体となる平行平面板６００を２軸調整可能に保持する被検体保持部材５０４と、図示せぬコンピュータおよびモニタとを備えてなり、平行平面板６００の両側に１対の干渉計５１０Ａ，５１０Ｂを対向配置した状態で平行平面板６００の両面６００ａ，６００ｂを被検面として干渉縞測定を行うことにより、該両面６００ａ，６００ｂの表面形状、平行平面板６００の絶対厚みおよび厚みムラを測定するように構成されている。
【００６９】
各干渉計５１０Ａ、５１０Ｂは、マイケルソン型（トワイマングリーン型）の干渉計であって、ハロゲンランプ等の白色光源５１１Ａ，５１１Ｂ、コリメータレンズ５１２Ａ，５１２Ｂ、ハーフミラーからなるビームスプリッタ５１３Ａ，５１３Ｂ、該ビームスプリッタ５１３Ａ，５１３Ｂによる光路長差を補正する補正板５１４Ａ，５１４Ｂ、反射型の基準板５１５Ａ，５１５Ｂ、透明な基準位置ガラス５１６Ａ，５１６Ｂ、集光レンズ５１７Ａ，５１７Ｂ、結像レンズ５１８Ａ，５１８Ｂ、およびＣＣＤカメラ等の撮像装置５１９Ａ，５１９Ｂを備えてなる。そして、各干渉計５１０Ａ、５１０Ｂにおいては、白色光源５１１Ａ，５１１Ｂから出力されたコヒーレントレングスの短い白色光を、ビームスプリッタ５１３Ａ，５１３Ｂの光束分割面５１３Ａａ、５１３Ｂａに入射させ、該光束分割面５１３Ａａ、５１３Ｂａにおいて透過光線束と反射光線束とに２分割する。そして、透過光線束を基準位置ガラス５１６Ａ，５１６Ｂを介して平行平面板６００の被検面６００ａ、６００ｂに入射させてその反射光を物体光とするとともに、反射光線束を基準板５１５Ａ，５１５Ｂの基準面５１５Ａａ，５１５Ｂａに入射させてその反射光を参照光とし、これら物体光および参照光の光干渉により生じる干渉縞を撮像装置５１９Ａ，５１９Ｂにより取り込んで干渉縞を測定するようになっている。
【００７０】
また、これら各干渉計５１０Ａ，５１０Ｂは、フリンジスキャン解析機能を備えている。すなわち、各干渉計５１０Ａ，５１０Ｂの基準板５１５Ａ，５１５Ｂは、図示せぬＰＺＴ駆動回路に接続された複数のピエゾ素子（不図示）を介してＰＺＴステージ５２１Ａ，５２１Ｂに支持されている。そして、各干渉計５１０Ａ，５１０Ｂにおいては、所定のタイミングでピエゾ素子に所定電圧を印加して該ピエゾ素子を駆動することにより基準板５１５Ａ，５１５Ｂを光軸方向に移動させるとともに、この移動により変化する干渉縞の画像データをコンピュータに出力するようになっている。また、各干渉計５１０Ａ，５１０Ｂにおいては、ＰＺＴステージ５２１Ａ，５２１Ｂは、図示せぬパルスモータ駆動回路に接続された図示せぬパルスモータを備えてなるパルスモータステージ５２２Ａ，５２２Ｂに支持されており、該パルスモータを駆動することによりＰＺＴステージ５２１Ａ，５２１Ｂを基準板５１５Ａ，５１５Ｂと共に光軸方向に移動できるようになっている。
【００７１】
本実施形態に係る絶対厚み測定装置５００においては、以下に示す手順〈1〉〜〈13〉に従い、上述した平行平面板６００の両面６００ａ，６００ｂの表面形状の測定を行うとともに、両干渉計５１０Ａ，５１０Ｂの干渉縞測定結果を用いて平行平面板６００の絶対厚みおよび厚みムラを解析的に測定するようになっている。
【００７２】
〈1〉平行平面板６００を光路上から退出させた状態で、干渉計５１０Ａにおいて白色光源５１１Ａから白色光を照射すると共に、設計値に基づき、該基準面５１５Ａａと、干渉計５１０Ｂの基準位置ガラス５１６Ｂの基準位置決定面５１６Ｂａとの、光源５１１Ａからの光路長が等しくなる前記基準面５１５Ａａの位置を特定し、この位置よりもわずかに前または後にずれた位置に、パルスモータステージ５２２Ａにより該基準板５１５Ａを移動させる。
【００７３】
〈2〉設計値に基づいて、該基準面５１５Ａａと、干渉計５１０Ｂの基準位置ガラス５１６Ｂの基準位置決定面５１６Ｂａとの、光源５１１Ａからの光路長が等しくなる方向に、干渉計５１０Ａの基準板５１５Ａをパルスモータステージ５２２Ａにより、例えば１μｍずつ動かしながら干渉縞画像を取り込み、干渉縞のコントラストがピークとなる時の基準板５１５Ａの位置を求め、その位置をＡＢ０位置としてコンピュータのメモリ内に記憶する。
【００７４】
〈3〉設計値に基づき、該基準面５１５Ａａと、干渉計５１０Ａの基準位置ガラス５１６Ａの基準位置決定面５１６Ａａとの、光源５１１Ａからの光路長が等しくなる前記基準面５１５Ａａの位置を特定し、パルスモータステージ５２２Ａにより、この位置よりもわずかに前または後にずれた位置に該基準板５１５Ａを移動させる。
【００７５】
〈4〉設計値に基づいて、手順〈2〉と同様に、該基準面５１５Ａａと、干渉計５１０Ａの基準位置ガラス５１６Ａの基準位置決定面５１６Ａａとの光路長が等しくなる方向に、干渉計５１０Ａの基準板５１５Ａを動かしながら干渉縞画像を取り込み、干渉縞のコントラストがピークとなる時の基準板５１５Ａの位置を求め、その位置をＡＡ０位置としてコンピュータ１６のメモリ内に記憶する。このＡＡ０位置と上記手順〈2〉において記憶したＡＢ０位置との差Ｄ_Ｃにより、干渉計５１０Ａの基準位置決定面５１６Ａａと干渉計５１０Ｂの基準位置決定面５１６Ｂａとの間隔を求めてコンピュータのメモリ内に記憶する。
【００７６】
〈5〉平行平面板６００を干渉計５１０Ａの基準位置ガラス５１６Ａと干渉計５１０Ｂの基準位置ガラス５１６Ｂとの間の光路上に挿入する。
【００７７】
〈6〉干渉計５１０Ａの基準板５１５Ａを、平行平面板６００の設計厚み値に基づいて、平行平面板６００のＡ側面６００ａとの、光源５１１Ａからの光路長が等しくなると思われる位置よりもわずかに前または後にずれた位置に移動させる。
【００７８】
〈7〉手順〈2〉と同様に、該基準面５１５Ａａと、平行平面板６００のＡ側表面６００ａとの、光源５１１Ａからの光路長が等しくなる方向に、干渉計５１０Ａの基準板５１５Ａを動かしながら干渉縞の発生を観察し、画像の一部に干渉縞が観察されたら画像の全面に干渉縞が現れるように平行平面板６００を２軸調整する。
【００７９】
〈8〉その後、基準板５１５Ａの移動を継続しながら干渉縞画像を取り込み、平行平面板６００のＡ側表面６００ａ上の所定点Ｐａ（図示せず）において干渉縞のコントラストがピークとなる時の基準板５１５Ａの位置を求め、その位置をＡａ０位置として記憶する。このＡａ０位置と上記手順〈4〉において記憶したＡＡ０位置との差により、干渉計５１０Ａの基準位置決定面５１６Ａａと平行平面板６００のＡ側表面６００ａ上の所定点Ｐａとの間隔Ｄ_Ａを求めてコンピュータのメモリ内に記憶する。
【００８０】
〈9〉ＰＺＴステージ５２１Ａのピエゾ素子の駆動により基準板５１５Ａをシフトさせてフリンジスキャン測定を行ない、平行平面板６００のＡ側表面６００ａの形状を求める。
【００８１】
〈10〉干渉計５１０Ａに対して行った上記手順〈2〉，〈3〉を干渉計５１０Ｂに対して行ない、干渉計５１０Ｂの基準板５１５Ｂと干渉計５１０Ｂの基準位置決定面５１６Ｂａとの位置関係を求める。
【００８２】
〈11〉干渉計５１０Ａに対して行った上記手順〈6〉，〈8〉，〈9〉を干渉計５１０Ｂに対して行ない、干渉計５１０Ｂの基準位置決定面５１６Ｂａと平行平面板６００のＢ側表面６００ｂ上における上記所定点Ｐａに対応する点Ｐｂ（図示せず）との間隔Ｄ_Ｂと、平行平面板６００のＢ側表面６００ｂの形状とを求める。
【００８３】
〈12〉上記手順〈4〉において求めた干渉計５１０Ａの基準位置決定面５１６Ａａと干渉計５１０Ｂの基準位置決定面５１６Ｂａとの間隔Ｄ_Ｃから、上記手順〈8〉において求めた干渉計５１０Ａの基準位置決定面５１６Ａａと平行平面板６００のＡ側表面６００ａ上の所定点Ｐａとの間隔Ｄ_Ａ、および上記手順〈11〉において求めた干渉計５１０Ｂの基準位置決定面５１６Ｂａと平行平面板６００のＢ側表面６００ｂ上の所定点Ｐｂとの間隔Ｄ_Ｂを差し引くことで、平行平面板６００の点Ｐａ，Ｐｂ間における絶対厚みｄを求める。
【００８４】
〈13〉上記手順〈12〉において求めた平行平面板６００の点Ｐａ，Ｐｂ間における絶対厚みｄと、上記手順〈9〉において求めた平行平面板６００のＡ側表面６００ａの形状と、上記手順〈11〉において求めた平行平面板６００のＢ側表面６００ｂの形状とから、平行平面板６００全体の絶対厚みと厚みムラの分布を求める。
【００８５】
なお、上記手順〈9〉のフリンジスキャン測定におけるフリンジスキャニング法および上記手順〈13〉の厚みムラ分布の測定手法としては、それぞれ、上述した第１の実施形態において用いられるフリンジスキャニング法および厚みムラ分布の測定手法と同様の手法を用いることが可能である。
【００８６】
また、上記第４の実施形態装置において、干渉計５１０Ａの基準位置決定面５１６Ａａと干渉計５１０Ｂの基準位置決定面５１６Ｂａとの間隔を測定する際に、一方の干渉計の光源５１１Ａ、５１１Ｂからの白色光が他の干渉計に入射するのを防止し得るように、第１の実施形態装置における遮光部材を採用することが可能である。また、基準位置決定面５１６Ａａ、５１６Ｂａの相互間の距離Ｄ_Ｃを測定する際に、平行平面板６００を光路外へ退出させるのではなく、上述した第２および第３の実施形態に示されるように、被検体保持部材５０４の一部に開口部を形成し、その開口部を通して白色光の一部を他方の干渉計の基準位置決定面に到達させるようにしてもよい。この場合においても、遮光部材を、上記第２および第３の実施形態に示されるように構成して用いることが可能である。
【００８７】
また、上記第４の実施形態のものにおいては、構成要素としての１対の干渉計として、物体光光路および参照光光路の長さが互いに等しくなるトワイマングリーン型干渉計が用いられているが、これ以外のマイケルソン型やマッハツェンダ型等の種々の等光路長型干渉計を適用することが可能である。
【００８８】
なお、本発明の絶対厚み測定装置においては、上述した実施形態のものに限られるものではなく、種々の態様の変更が可能であり、例えば、上記第１〜第３の実施形態においては、位相シフト波長走査干渉法を用いており、位相シフト手段として、ピエゾ素子を用いて基準板を光軸に沿って移動させるようにしているが、これに替え、ピエゾ素子を用いて被検体を光軸に沿って移動させるようにしてもよいし、位相シフトを波長走査により行なうようにしてもよい。
【００８９】
なお、本発明の延長線上の構成として、上記１対の干渉計のうち一方を上記第１の実施形態において説明した波長可変レーザ光源を搭載したものとし、他方を上記第４の実施形態において説明した白色光出力光源を搭載したものとすることが可能である。
【００９０】
【発明の効果】
本発明に係る第１の絶対厚み測定装置は、被検体として平行平面板を挟んで１対の第１および第２の干渉計を向かい合わせ、各干渉計に搭載された波長可変光源からの可干渉光を用いて干渉縞を測定するようにしており、波長可変光源からの光の波長を走査することで、２つの面の間隔を測定可能とし、第１の干渉計により、第１の干渉計の基準面と平行平面板の第１の干渉計側の面との距離Ｄ_Ａおよび２つの干渉計の基準面の距離Ｄ_Ｃとを測定するとともに、第２の干渉計により第２の干渉計の基準面と平行平面板の第２の干渉計側の面との距離Ｄ_Ｂとを測定しているので、これらの３つの距離Ｄ_Ａ、Ｄ_Ｂ、Ｄ_Ｃに基づいて平行平面板の厚みを容易に得ることができる。
【００９１】
本発明に係る第２の絶対厚み測定装置は、被検体としての平行平面板を挟んで１対の第１および第２の等光路長型干渉計を向かい合わせ、各干渉計に搭載された、コヒーレンス長の短い低可干渉光出力光源からの可干渉光を用いて物体光と参照光が等しくなったときにのみ干渉縞が測定されるようにしており、さらに平行平面板の両面に各々離間対向して、基準位置決定面を有する透明な基準位置決定板を各々設け、かつ１対の前記干渉計の基準面を各々その光軸方向に移動可能とするとともに、該各々の基準面の現在位置を読取可能な検出手段を設けるようにしているため、
前記第１の干渉計により、該第１の干渉計側の前記基準位置決定面である第１基準位置決定面、前記第２の干渉計側の前記基準位置決定面である第２基準位置決定面、および前記平行平面板の第１の干渉計側の面の各々について干渉縞が得られた際の前記第１の干渉計の基準面の各現在位置である、前記検出手段の読取値は、第１基準位置決定面、第２基準位置決定面、および前記平行平面板の第１の干渉計側の面の相対位置を示すこととなっており、
さらに、前記第２の干渉計により、前記第２基準位置決定面、および前記平行平面板の第２の干渉計側の面の各々について干渉縞が得られた際の前記他方の干渉計の基準面の各現在位置である、前記検出手段の読取値は、第２基準位置決定面と前記平行平面板の第２の干渉計側の面の相対位置を示すこととなっている。
【００９２】
これにより、第１の干渉計の基準面と平行平面板の第１の干渉計側の面との距離Ｄ_Ａおよびこれら２つの干渉計の基準面の距離Ｄ_Ｃとを測定することができるとともに、第２の干渉計により第２の干渉計の基準面と平行平面板の第２の干渉計側の面との距離Ｄ_Ｂとを測定することができるので、これらの３つの距離Ｄ_Ａ、Ｄ_Ｂ、Ｄ_Ｃに基づいて平行平面板の厚みを容易に得ることができる。
【図面の簡単な説明】
【図１】本発明の第１の実施形態に係る絶対厚み測定装置の作用を説明するための概念図
【図２】本発明の第１の実施形態に係る絶対厚み測定装置を示す全体構成図
【図３】図１の実施形態装置において基準面相互間の干渉縞測定の様子を示す図
【図４】図１の実施形態装置において干渉縞測定結果を用いて平行平面板の絶対厚みを解析的に測定する原理を示す図
【図５】図１の実施形態装置において干渉縞測定結果を用いて平行平面板の厚みムラを解析的に測定する手順を示す図
【図６】本発明の第２の実施形態に係る絶対厚み測定装置を示す全体構成図
【図７】本発明の第３の実施形態に係る絶対厚み測定装置を示す全体構成図
【図８】本発明の第４の実施形態に係る絶対厚み測定装置の作用を説明するための概念図
【符号の説明】
２、６００ 平行平面板
２ａ、２ｂ、６００ａ、６００ｂ 両面（被検面）
１０、１１０、２１０、５００ 絶対厚み測定装置
１２Ａ、１２Ｂ、５１０Ａ、５１０Ｂ 干渉計
１４、１１４、２１４、５０４ 被検体保持部材
１６ コンピュータ
１８ モニタ
２０Ａ、２０Ｂ 干渉計本体
２２Ａ、２２Ｂ、５１５Ａ、５１５Ｂ 基準板
２２Ａａ、２２Ｂａ、５１５Ａａ、５１５Ｂａ 基準面
２４Ａ、２４Ｂ ＰＺＴ駆動回路
２６Ａ、２６Ｂ ピエゾ素子
２８Ａ、２８Ｂ 基準板支持部材
３０、１３０、２３０Ａ、２３０Ｂ 遮光部材
３１Ａ、３１Ｂ 波長可変レーザ光源
３９Ａａ、３９Ｂａ、５１９Ａ、５１９Ｂ 撮像装置
５１６Ａ、５１６Ｂ 基準位置決定板
５１６Ａａ、５１６Ｂｂ 基準位置決定面
５２１Ａ、５２１Ｂ ＰＺＴステージ
５２１Ａ、５２１Ｂ パルスモータステージ
Ａｘ 光軸[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an absolute thickness measuring apparatus configured to measure an absolute thickness of a parallel plane plate, which is a subject, with high accuracy. Specifically, each interferometer is opposed to each side of a parallel plane plate, and each interference The present invention relates to an absolute thickness measuring apparatus configured to obtain interference fringe information about a plane of a plane parallel plate corresponding to the interferometer.
[0002]
[Prior art]
Conventionally, as a means for measuring the surface shape of an object such as an optical member, coherent light from a light source is divided into two, and one reflected light beam is incident on the surface to be measured, and the reflected light is used as object light. There is known an interferometer device for measuring the surface shape of an object based on interference fringes caused by the interference of the object light and the reference light by making the other light beam incident on a reference surface and using the reflected light as reference light. . Also known is an apparatus for measuring both-side shape and thickness unevenness of a plane-parallel plate using such an interferometer.
[0003]
In this double-sided shape and thickness unevenness measuring apparatus, an opaque parallel flat plate as a subject is held by a subject holding member, and a pair of interferometers are arranged oppositely on both sides of the both sides of the parallel flat plate. By measuring the interference fringe on the surface to be measured, the surface shape of both sides of the parallel plane plate is measured, and the thickness unevenness of the parallel plane plate is analytically measured using the interference fringe measurement results of both interferometers. It is configured.
[0004]
In this type of double-sided shape and thickness unevenness measuring device, interference fringe measurement is performed on the assumption that the parallelism between the reference surfaces of both interferometers is sufficiently secured, but the parallelism is sufficiently obtained. When the interference fringe measurement is performed without the interference fringes, there is a problem that the surface shape of both surfaces of the parallel flat plate and the measurement result of the thickness unevenness become inaccurate.
[0005]
Therefore, the present inventor accurately determines the surface shape and thickness unevenness of both surfaces of the parallel flat plate even when interference fringe measurement is performed without sufficient parallelism between the reference surfaces of both interferometers. A double-sided shape and thickness unevenness measuring apparatus capable of measuring is disclosed (Japanese Patent Laid-Open No. 2000-275022). In this apparatus, a pair of interferometers are arranged opposite to each other on both sides of an opaque parallel plane plate (for example, a ceramic plate, a metal plate, a block gauge, etc.) to be an object, and the planes on which the parallel plane plate is opposed by each interferometer. Is used to measure the interference fringes, and before and after this, the interference fringes between the reference planes are measured.
[0006]
As a result, when measuring the surface shape of both surfaces of the parallel flat plate and measuring the thickness unevenness, the deviation of the parallelism between the reference surfaces of both interferometers is corrected using the interference fringe measurement result between the reference surfaces. be able to.
[0007]
[Problems to be solved by the invention]
However, in the above-described measuring apparatus, even when interference fringe measurement is performed without sufficient parallelism between the reference surfaces of both interferometers, the surface shape and thickness unevenness of both surfaces of the parallel plane plate are reduced. Although it can be measured accurately, it is difficult to measure the absolute thickness of the plane parallel plate.
[0008]
In recent years, in various fields such as optics and material technology, there is a strong demand for measuring the absolute thickness of an opaque parallel flat plate in a non-contact manner with high accuracy, and a simple measuring device has been desired.
[0009]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a simple absolute thickness measuring apparatus capable of measuring the absolute thickness of an opaque parallel flat plate in a non-contact and high accuracy. .
[0010]
[Means for Solving the Problems]
The first absolute thickness measuring apparatus according to the present invention divides a light beam emitted from a light source into two parts, causes one light beam to enter a test surface, and uses the reflected light as object light, and the other light beam enters a reference surface. A pair of first and second interferometers configured to measure the surface to be measured based on interference fringes generated by optical interference between the object light and the reference light. An object holding member for holding an opaque parallel flat plate to be the object,
The first plane interferometer is placed on one side of both sides of the plane parallel plate, and the second interferometer is placed on the other side of the plane parallel plate so that the emitted light beams face each other. In a measuring device configured to perform interference measurement as a surface inspection,
While changing the wavelength of the light emitted from the light source for each of the first and second interferometers while changing the light source as a wavelength variable light source, an interference fringe image is obtained each time it is changed by a predetermined wavelength, Based on these obtained interference fringe images, the following arithmetic expressions (1) to (3) are used to measure the distance between the test surface and the reference surface,
A distance D measured by the first interferometer between a first reference plane which is a reference plane of the first interferometer and the plane of the parallel plane plate facing the first reference plane. _A And a distance D measured by the second interferometer between the second reference surface, which is the reference surface of the second interferometer, and the plane of the parallel plane plate facing the second reference surface _B Is a distance D from the first reference plane to the second reference plane, measured by the first or second interferometer. _C The absolute thickness d of the parallel flat plate is calculated by subtracting from the parallel plane plate.
[Expression 2]

[0011]
The wavelength tunable light source may be a wavelength tunable laser light source, and the first and second interferometers may be Fizeau interferometers.
[0012]
Further, the second absolute thickness measuring apparatus of the present invention divides the light beam emitted from the light source into two parts, makes one light beam incident on the surface to be measured and uses the reflected light as object light, and the other light beam as the reference surface. A pair of first and second interferences configured to measure the surface to be measured based on interference fringes caused by optical interference between the object light and the reference light. And a subject holding member that holds an opaque parallel flat plate to be the subject,
In a state where the first equal optical path length type interferometer is arranged on one side of both surfaces of the parallel flat plate and the second equal optical path length type interferometer is arranged on the other side so that the respective emitted light beams face each other. In a measuring apparatus configured to perform interference measurement using both surfaces of a flat plate as test surfaces,
The light source is a low coherence light output light source, and a transparent reference position determination plate having a reference position determination surface is provided respectively on both sides of the plane-parallel plate so as to face each other.
The first and second reference planes of the first and second equal optical path length type interferometers can be moved in the optical axis direction, and the current positions of the first and second reference planes can be read. Providing detection means;
A first reference position determination plane disposed on the first equal optical path length type interferometer side of the parallel plane plate by moving the first reference plane of the first equal optical path length type interferometer; Each of the second reference position determination surface disposed on the second equal optical path length type interferometer side of the parallel plane plate and the first equal optical path length type interferometer side surface of the parallel plane plate Based on the current position information of the first reference plane of the first equal optical path length type interferometer when the interference fringes are obtained, the first of the parallel plane plates from the first reference position determination plane Distance D to the surface of the equal optical path length type interferometer _A And a distance D from the first reference position determination plane to the second reference position determination plane _C And
By moving the second reference plane of the second equal optical path length type interferometer, the second reference position determining plane and the plane of the parallel plane plate on the second equal optical path length type interferometer side For each, based on each current position information of the second reference plane of the second equal optical path length type interferometer when an interference fringe is obtained, the second of the parallel plane plate from the second reference position determination plane Distance D to the surface of the 2 equal optical path length type interferometer side _B And
The distance D _A And the distance D _B And the distance D _C The absolute thickness of the plane parallel plate is calculated by subtracting from the parallel plane plate.
[0013]
Further, it is preferable that the subject holding member is configured such that the parallel flat plate can be inserted into and removed from the light beam of the pair of interferometers.
[0014]
Alternatively, it is preferable that the subject holding member includes an opening that allows a part of a light beam emitted from one of the pair of interferometers to reach the other reference plane of the pair of interferometers.
[0015]
In these cases, when observing the interference fringes of the pair of interferometers, light beams emitted from the interferometers not involved in the measurement are prevented from entering the interferometers involved in the measurement. It is preferable to provide a light shielding member.
[0016]
The above-mentioned “equal optical path length interferometer” refers to an interferometer configured such that the optical path length of the object light and the optical path length of the reference light are substantially equal.
The “low coherence light” does not greatly affect the reading accuracy of the first and second reference plane positions when the interference fringes formed by the low coherence light appear as described above. Light having a small coherence distance (for example, several μm or less) is a typical example, and white light is a typical example, but it is not always necessary to have intensity over the entire visible light range.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0018]
<First Embodiment>
First, a first embodiment according to the present invention will be described.
FIG. 2 is an overall configuration diagram showing the absolute thickness measuring apparatus 10 according to the first embodiment using a wavelength tunable laser light source.
[0019]
As shown in the figure, the absolute thickness measuring apparatus 10 includes a pair of interferometers 12A and 12B and an object that holds an opaque parallel flat plate (for example, a ceramic plate, a metal plate, a block gauge, etc.) 2 as a subject. A specimen holding member 14, a computer 16, and a monitor 18 are provided, and both surfaces 2a and 2b of the parallel flat plate 2 are covered with a pair of interferometers 12A and 12B facing each other on both sides of the parallel flat plate 2. By performing interference fringe measurement as the inspection surface, the absolute thickness and thickness unevenness of the parallel flat plate 2 are measured.
[0020]
Each of the interferometers 12A and 12B is a Fizeau interferometer. The interferometer bodies 20A and 20B allow coherent light from a wavelength variable laser light source (not shown) to be applied to the reference surfaces 22Aa and 22Ba of the reference plates 22A and 22B. The incident light is split into two, a transmitted light beam and a reflected light beam at the reference surfaces 22Aa and 22Ba, the transmitted light beam is incident on the test surfaces 2a and 2b, and the reflected light is used as object light. The reflected light at 22Ba is used as reference light, and interference fringes generated by optical interference of these object light and reference light are taken into a CCD camera (not shown) to measure the interference fringes.
[0021]
By the way, in the apparatus of this embodiment, as described above, the wavelength tunable laser light source is used as the measurement light source. This is based on the logic that the optical path length difference can be obtained by scanning the wavelength of the light from the tunable laser light source and performing a predetermined frequency analysis on the interference fringes captured every predetermined wavelength scanning. ing. As described above, in the apparatus according to the present embodiment, by using the wavelength tunable laser light source capable of obtaining the optical path length difference as the measurement light source, it is possible to measure the absolute thickness and thickness unevenness of the parallel flat plate serving as the subject. It can be done.
[0022]
The measurement of the optical path length difference by the frequency analysis described above is specifically performed by the following procedure.
That is, the wave number is set to k by a wavelength tunable laser. ₁ To k ₂ When the image is captured every Δk, the interference fringe intensity change I (x, y, k) is expressed by the following equation (1).
[0023]
[Expression 1]

[0024]
Here, L (x, y) is the optical path length difference, I ₀ (X, y) represents intensity distribution, and γ represents interference fringe modulation. If the interference fringe change in the predetermined pixel at this time is n times, it is expressed by the following equation (2).
[0025]
[Expression 2]

Here, since k = 2π / λ, the following expression (3) is obtained.
[0026]
[Equation 3]

[0027]
That is, the optical path length difference can be measured by obtaining the frequency n when the wavelength is scanned.
In order to determine the frequency n, it is possible to use a Fourier transform as described in Japanese Patent Laid-Open No. 2001-272214, which has already been disclosed by the present applicant.
[0028]
In this embodiment, the phase shift wavelength scanning interferometry capable of more detailed fringe analysis is used. Phase shift wavelength scanning interferometry is an interferometer that uses a wavelength tunable laser light source, and in order to achieve high-accuracy measurement, the wavelength is scanned, and the reference surface is aligned with the optical axis by PZT or the like for each predetermined wavelength scan This is a method of obtaining the optical path length difference L (x, y) by sequentially measuring the phase for each wavelength by moving in the direction and shifting the phase and thereby measuring the phase for each wavelength. The detailed description of the phase shift wavelength scanning interferometry is described in the above-mentioned Japanese Patent Application Laid-Open No. 2001-272214. Therefore, the description of the mathematical solution is omitted here, and a mechanism for enabling it. Only the configuration of is mentioned.
[0029]
That is, the reference plates 22A and 22B of the interferometers 12A and 12B are supported by the reference plate support members 28A and 28B via the plurality of piezoelectric elements 26A and 26B connected to the PZT drive circuits 24A and 24B. In each of the interferometers 12A and 12B, the reference plates 22A and 22B are driven by applying a predetermined voltage to the piezo elements 26A and 26B and driving the piezo elements 26A and 26B for every predetermined wavelength scanning by the wavelength tunable laser light source. Is moved in the direction of the optical axis Ax, and image data of interference fringes that change due to this movement is output to the computer 16.
[0030]
The computer 16 automatically analyzes the interference fringes using the fringe scanning method based on the image data of the interference fringes input from the interferometers 12A and 12B, and measures the shape of the test surfaces 2a and 2b (determination of unevenness and three-dimensionality). Shape measurement) and image data of interference fringes or a three-dimensional shape is displayed on the monitor 18. Note that the fringe scanning method here refers to the detection surface 2a, 2b from the interference fringe image data for each predetermined fringe scanning step while changing the relative distance between the reference surfaces 22Aa, 22Ba and the inspection surfaces 2a, 2b. This is a technique of measuring interference fringe intensity at each point and performing interference fringe analysis such as phase calculation of each point at the wavelength using the measurement result.
[0031]
The absolute thickness measuring apparatus 10 according to the present embodiment measures the surface shape of both surfaces 2a and 2b of the plane parallel plate 2 as described above, and uses the interference fringe measurement results of both interferometers 12A and 12B. The absolute thickness and thickness unevenness of the face plate 2 are analytically measured.
[0032]
In this embodiment, the interferometer bodies 20A and 20B are configured as shown in FIG. That is, in each of the interferometer bodies 20A and 20B, the laser beams output from the wavelength tunable laser light sources 31A and 31B are diverged by the lenses 32A and 32B, and are collimated by the collimator lenses 34A and 34B via the half prisms 33A and 33B. Is output to the outside.
[0033]
On the other hand, the interference light incident from the directions of the reference plates 22A and 22B is reflected by the half prisms 33A and 33B, and enters the imaging devices 39A and 39B including a CCD camera or the like via the imaging lenses 38A and 38B. Has been.
[0034]
In the absolute thickness measuring apparatus 10 according to the present embodiment, the surface shapes of both surfaces 2a and 2b of the plane-parallel plate 2 described above are measured according to the following procedures <1> to <9>, and both interferometers 12A are used. , 12B are used to analytically measure the absolute thickness and thickness unevenness of the plane-parallel plate 2 using the interference fringe measurement results. Hereinafter, a description will be given with reference to FIGS.
[0035]
<1> The parallel flat plate 2 is moved out of the optical path as shown in FIG. Further, a light shielding member 30 (see FIG. 3) described later is inserted on the optical path.
[0036]
<2> In the interferometer 12A, laser light is emitted from the wavelength tunable laser light source 31A, and the wave number of the laser light is set to k. ₁ To k ₂ For each Δk, the interference fringe image is captured using the fringe scanning method described above, the captured interference fringe image is analyzed, and interference with the reference surface 22Aa of the interferometer 12A is performed using the above-described equation (3). The distance D from the reference surface 22Ba of the total 12B _C Is stored in the memory of the computer 16.
[0037]
<3> The parallel plane plate 2 is inserted on the optical path between the reference plate 22A of the interferometer 12A and the reference plate 22B of the interferometer 12B as shown in FIG. Further, a light shielding member 30 (see FIG. 2) described later is withdrawn from the optical path.
[0038]
<4> The laser beam is emitted from the wavelength tunable laser light source 31A, and the wave number of the laser beam is set to k. ₁ To k ₂ Until every Δk, an interference fringe image is captured using the fringe scanning method described above, the captured interference fringe image is analyzed, and parallel to the reference plane 22Aa of the interferometer 12A using the above equation (3). Distance D with a predetermined point Pa (not shown) on the A side surface 2a of the flat plate 2 _A And the overall shape distribution of the A-side surface 2a of the plane parallel plate 2 is obtained and stored in the memory of the computer 16.
[0039]
<5> A laser beam is emitted from the wavelength tunable laser light source 31B, and the wave number of the laser beam is set to k. ₁ To k ₂ Until every Δk, the fringe scanning method is used to capture an interference fringe image, the captured interference fringe image is analyzed, and the reference plane 22Ba of the interferometer 12B using the above-described equation (3); A distance D between a predetermined point Pa (not shown) on the B-side surface 2b of the plane parallel plate 2 and a predetermined point Pb (not shown) in a front-back positional relationship. _B And the overall shape distribution of the B-side surface 2b of the plane parallel plate 2 is obtained and stored in the memory of the computer 16.
[0040]
<6> Distance D between the reference surface 22Aa of the interferometer 12A and the reference surface 22Ba of the interferometer 12B obtained in the above procedure <2> _C From the distance D between the reference surface 22Aa of the interferometer 12A obtained in the above procedure <4> and the predetermined point Pa on the A-side surface 2a of the parallel flat plate 2 _A , And the distance D between the reference surface 22Ba of the interferometer 12B determined in the above procedure <5> and the predetermined point Pb on the B-side surface 2b of the parallel flat plate 2 _B Is obtained, the absolute thickness d between the points Pa and Pb of the plane parallel plate 2 is obtained. FIG. 4 schematically shows this technique.
[0041]
<7> As shown in FIG. 4, the absolute thickness d between the points Pa and Pb of the plane parallel plate 2 obtained in the above step <6> and the A-side surface 2a of the plane parallel plate 2 obtained in the above step <4>. And the shape of the B-side surface 2b of the parallel flat plate 2 obtained in the above procedure <5>, the absolute thickness of the entire parallel flat plate 2 and the distribution of thickness unevenness are obtained.
[0042]
Further, the thickness unevenness measurement described above is performed using data of displacement amounts Δa and Δb of the respective points 2a and 2b of the plane-parallel plate 2 from the plane orthogonal to the optical axis as shown in FIG. This is done by calculating Δb.
[0043]
At this time, if the reference surfaces 22Aa and 22Ba of both interferometers 12A and 12B are completely parallel, the value of Δa−Δb directly represents the thickness unevenness of the parallel flat plate 2, but generally the reference surface 22Aa. , 22Ba cannot be completely parallel, and it is preferable to measure the thickness unevenness in consideration of the parallelism between the reference surfaces 22Aa and 22Ba. Specifically, in the above procedure <2>, the parallelism between the reference planes 22Aa and 22Ba of both interferometers 12A and 12B is measured based on a plurality of interference fringe images obtained using the fringe scanning method, The deviation may be corrected.
[0044]
The absolute thickness of the entire parallel flat plate 2 can be obtained by adding the distribution of thickness unevenness of the entire parallel flat plate 2 thus obtained to the absolute thickness d between the points Pa and Pb described above.
[0045]
In the present embodiment, in order to be able to perform interference fringe measurement between the reference surfaces 22Aa and 22Ba as well as interference fringe measurement between the test surfaces 2a and 2b and the reference surfaces 22Aa and 22Ba, the following configuration is adopted. Has been.
[0046]
FIG. 2 shows a state of interference fringe measurement between the test surfaces 2a and 2b and the reference surfaces 22Aa and 22Ba, and FIG. 3 shows a state of interference fringe measurement between the reference surfaces 22Aa and 22Ba. is there.
[0047]
As shown by arrows in FIGS. 2 and 3, the subject holding member 14 is positioned between the reference plates 22A and 22B and the subject measurement position (position shown in FIG. 2) in the optical path of both interferometers 12A and 12B. It is provided so as to be movable in the direction perpendicular to the optical axis so as to be able to adopt a retracted position (position shown in FIG. 3) outside the optical path. The subject holding member 14 is moved to the subject measurement position when measuring the interference fringes formed between the test surfaces 2a and 2b and the reference surfaces 22Aa and 22Ba. The shape of the test surfaces 2a and 2b can be measured by 12A and 12B. On the other hand, when measuring the interference fringes between the reference surfaces 22Aa and 22Ba, they are moved to the retracted position.
[0048]
Further, one interferometer 12B of the pair of interferometers 12A and 12B is provided with a light shielding member 30 that can block coherent light from the light source. 2 and 3, the light shielding member 30 has a shielding position (position shown in FIG. 3) in the optical path between the interferometer body 20B and the reference surface 22Ba and a retracted position outside the optical path (see FIG. 3). 2) is provided so as to be movable in the direction perpendicular to the optical axis. The light shielding member 30 is moved to the retracted position when measuring the interference fringes formed between the test surfaces 2a and 2b and the reference surfaces 22Aa and 22Ba. When measuring the interference fringes formed between 22Ba, the reference plane 22Aa by the other interferometer 12A is moved to the shielding position, thereby blocking the coherent light from the light source of the interferometer 12B. , 22Ba makes it possible to measure interference fringes.
[0049]
As described above in detail, the absolute thickness measuring apparatus 10 according to the present embodiment uses the surfaces 2a and 2b of the plane parallel plate 2 held by the subject holding member 14 by the interferometers 12A and 12B as test surfaces. Although the interference fringe measurement is performed, the subject holding member 14 is provided so as to be retractable out of the optical path of the pair of interferometers 12A and 12B, and one interferometer 12B has coherence from the light source. Since the light blocking member 30 capable of blocking light is provided, the object holding member 30 is retracted out of the optical path before or after the interference fringe measurement, and the coherent light from the light source of the interferometer 12B is blocked by the light blocking member 30. In this state, the interference fringes between the reference surfaces 22Aa and 22Ba can be measured in this state.
[0050]
And thereby, when measuring the surface shape of both surfaces 2a and 2b of the parallel flat plate 2 and measuring the thickness unevenness, the deviation of the parallelism is corrected using the interference fringe measurement result between the reference surfaces 22Aa and 22Ba. can do.
[0051]
Therefore, according to the present embodiment, both surfaces 2a of the plane parallel plate 2 can be obtained even when interference fringe measurement is performed without sufficiently obtaining the parallelism between the reference planes 22Aa and 22Ba of the interferometers 12A and 12B. It is possible to accurately measure the surface shape of 2b, its absolute thickness and thickness unevenness.
[0052]
<Second Embodiment>
Next, a second embodiment according to the present invention will be described.
[0053]
FIG. 6 is an overall configuration diagram showing the absolute thickness measuring apparatus 110 according to the present embodiment. As shown in the figure, the absolute thickness measuring apparatus 110 has the same basic configuration as the absolute thickness measuring apparatus 10 shown in FIG. 2, but the configurations of the subject holding member 14 and the light shielding member 30 are different.
[0054]
That is, the subject holding member 114 in the present embodiment is fixedly disposed in the optical path of both the interferometers 12A and 12B, and the subject holding member 114 has a part of the coherent light of each interferometer 12A and 12B. Is formed so as to reach the reference plane of the other interferometer. Further, the light shielding member 130 in the present embodiment is fixedly arranged so as to block the coherent light incident on the opening 114a among coherent light from the wavelength variable laser light sources 31A and 31B of the interferometer 12B.
[0055]
In the present embodiment, the interference fringe measurement between the reference surfaces 22Aa and 22Ba can be performed through the opening 114a by the interferometer 12A in which the light shielding member 130 is not provided. Moreover, simultaneously with the measurement of the interference fringes between the reference surfaces 22Aa and 22Ba, the interference fringes can be simultaneously measured using the respective surfaces 2a and 2b of the parallel flat plate 2 by the interferometers 12A and 12B. And when measuring the surface shape of both surfaces 2a and 2b of the plane parallel plate 2, and measuring the absolute thickness and thickness unevenness, the deviation of the parallelism is calculated using the interference fringe measurement results between the reference surfaces 22Aa and 22Ba. It can be corrected.
[0056]
Therefore, according to the present embodiment, both surfaces 2a of the plane parallel plate 2 can be obtained even when interference fringe measurement is performed without sufficiently obtaining the parallelism between the reference planes 22Aa and 22Ba of the interferometers 12A and 12B. It is possible to accurately measure the surface shape of 2b, its absolute thickness and thickness unevenness. In addition, in the present embodiment, it is not necessary to retract the subject holding member 14 out of the optical path, so that interference fringe measurement can be performed in a short time.
[0057]
<Third Embodiment>
Next, a third embodiment according to the present invention will be described.
[0058]
FIG. 7 is an overall configuration diagram showing the absolute thickness measuring apparatus 210 according to the present embodiment.
As shown in the figure, the absolute thickness measuring apparatus 210 has the same basic configuration as the absolute thickness measuring apparatus 10 shown in FIG. 2, but the configurations of the subject holding member 14 and the light shielding member 30 are different.
[0059]
That is, in the present embodiment, similarly to the subject holding member 114 shown in FIG. 6, the subject holding member 214 is fixedly disposed in the optical path of both interferometers 12A and 12B. In addition, an opening 214a for allowing a part of coherent light of each interferometer 12A, 12B to reach the reference plane of the other interferometer is formed.
[0060]
In the present embodiment, a pair of light shielding members 230A and 230B is used. These light shielding members 230A and 230B can adopt a shielding position in the optical path and a retracted position outside the optical path between the interferometer bodies 20A and 20B and the reference surfaces 22Aa and 22Ba, similarly to the light shielding member 30 shown in FIG. It is provided so as to be movable in the direction perpendicular to the optical axis. However, these light shielding members 230A and 230B are controlled to move so that when one is in the shielding position, the other is in the retracted position.
[0061]
In the present embodiment, in the state where the coherent light from the wavelength tunable laser light source 31B of the interferometer 12B is blocked by the light blocking member 230B, the interferometer 12A performs interference fringe measurement between the reference surfaces 22Aa and 22Ba and the parallel flat plate 2 Interference fringe measurement using the surface 2a on the interferometer 12A side as a test surface can be performed at the same time, and the coherent light from the wavelength variable laser light source 31B of the interferometer 12A is blocked by the light shielding member 230A. The interferometer 12B can simultaneously perform interference fringe measurement between the reference surfaces 22Aa and 22Ba and interference fringe measurement using the surface 2b of the parallel plane plate 2 on the interferometer 12B side as a test surface.
[0062]
And when measuring the surface shape of both surfaces 2a and 2b of the parallel flat plate 2 and measuring the thickness unevenness thereof, the deviation of the parallelism is corrected using the interference fringe measurement result between the reference surfaces 22Aa and 22Ba. Can do.
[0063]
Therefore, according to the present embodiment, both surfaces 2a of the plane parallel plate 2 can be obtained even when interference fringe measurement is performed without sufficiently obtaining the parallelism between the reference planes 22Aa and 22Ba of the interferometers 12A and 12B. It is possible to accurately measure the surface shape of 2b, its absolute thickness and thickness unevenness.
[0064]
At that time, the interference fringe measurement result between the reference planes 22Aa and 22Ba may be that of one of the interferometers, but the interference fringe measurement result of both the interferometers 12A and 12B is used. If the positional deviation in the direction perpendicular to the axis (for example, the positional deviation of the center position of the opening 214a) is compared, the optical axis deviation of both the interferometers 12A and 12B can also be measured. Therefore, if the measurement result is used to correct the optical axis deviation when measuring the surface shape of both surfaces 2a and 2b of the parallel flat plate 2 and measuring the absolute thickness and thickness unevenness, the parallel flat plate 2 is corrected. The surface shape and thickness unevenness of both surfaces 2a, 2b of the face plate 2 can be measured more accurately.
[0065]
In each of the above embodiments, the interferometers 12A and 12B have been described as using Fizeau interferometers. However, other optical path length interferometers such as other unequal optical path length interferometers and Michelson types are used. Even when a type interferometer is used, the same effects as those of the above embodiments can be obtained by adopting the same configuration as that of the above embodiments.
[0066]
In the above description, a so-called vertical interferometer is used, but a so-called horizontal interferometer having an optical axis arranged in the horizontal direction can be used instead.
[0067]
In the first to third embodiments described above, a wavelength tunable laser light source is used as the light source. However, in the absolute thickness measuring apparatus of the present invention, a white light source is used as the light source as described in the fourth embodiment below. It is also possible. However, when a white light source is used as the light source, it is necessary to configure the interferometer with an equal optical path length type such as a Michelson type.
[0068]
<Fourth Embodiment>
FIG. 8 is an overall configuration diagram showing an absolute thickness measuring apparatus 500 according to the present embodiment.
As shown in the figure, the absolute thickness measuring apparatus 500 includes a pair of interferometers 510A and 510B, a subject holding member 504 that holds a parallel flat plate 600 serving as a subject so that two axes can be adjusted, and a computer (not shown). And a monitor, and interference fringe measurement is performed using both surfaces 600a and 600b of the parallel plane plate 600 as test surfaces in a state where a pair of interferometers 510A and 510B are disposed opposite to each other on both sides of the parallel plane plate 600. The surface shape of the both surfaces 600a and 600b, the absolute thickness and the thickness unevenness of the parallel flat plate 600 are measured.
[0069]
Each of the interferometers 510A and 510B is a Michelson type (Twiman Green type) interferometer, and includes white light sources 511A and 511B such as halogen lamps, collimator lenses 512A and 512B, and beam splitters 513A and 513B including half mirrors. Correction plates 514A and 514B for correcting the optical path length difference by the beam splitters 513A and 513B, reflection-type reference plates 515A and 515B, transparent reference position glasses 516A and 516B, condensing lenses 517A and 517B, and imaging lenses 518A and 518B And imaging devices 519A and 519B such as a CCD camera. In each interferometer 510A, 510B, white light having a short coherent length output from the white light sources 511A, 511B is incident on the beam splitting surfaces 513Aa, 513Ba of the beam splitters 513A, 513B, and the beam splitting surfaces 513Aa, At 513Ba, the transmitted light beam and the reflected light beam are divided into two. The transmitted light beam is incident on the test surfaces 600a and 600b of the parallel flat plate 600 through the reference position glasses 516A and 516B, and the reflected light is used as object light, and the reflected light beam is used as the reference plates 515A and 515B. The reflected light is incident on the reference surfaces 515Aa and 515Ba and the reflected light is used as reference light, and interference fringes caused by optical interference between the object light and the reference light are captured by the imaging devices 519A and 519B, and the interference fringes are measured.
[0070]
Each of these interferometers 510A and 510B has a fringe scan analysis function. That is, the reference plates 515A and 515B of the interferometers 510A and 510B are supported by the PZT stages 521A and 521B via a plurality of piezo elements (not shown) connected to a PZT drive circuit (not shown). In each of the interferometers 510A and 510B, the reference plates 515A and 515B are moved in the optical axis direction by applying a predetermined voltage to the piezo elements at a predetermined timing to drive the piezo elements. The image data of interference fringes is output to a computer. In each of the interferometers 510A and 510B, the PZT stages 521A and 521B are supported by pulse motor stages 522A and 522B each having a pulse motor (not shown) connected to a pulse motor drive circuit (not shown). By driving the pulse motor, the PZT stages 521A and 521B can be moved in the optical axis direction together with the reference plates 515A and 515B.
[0071]
In the absolute thickness measuring apparatus 500 according to the present embodiment, the surface shapes of both surfaces 600a and 600b of the plane parallel plate 600 described above are measured according to the following procedures <1> to <13>, and both interferometers 510A are used. , 510B, the absolute thickness and the thickness unevenness of the plane-parallel plate 600 are analytically measured using the interference fringe measurement result.
[0072]
<1> While the parallel plane plate 600 is retracted from the optical path, the interferometer 510A emits white light from the white light source 511A, and based on the design value, the reference surface 515Aa and the reference position glass of the interferometer 510B The position of the reference surface 515Aa with which the optical path length from the light source 511A is equal to the reference position determination surface 516Ba of 516B is specified, and the reference is determined by the pulse motor stage 522A at a position slightly shifted before or after this position. The plate 515A is moved.
[0073]
<2> Based on the design value, the reference plate of the interferometer 510A is arranged so that the optical path lengths from the light source 511A are equal between the reference surface 515Aa and the reference position determination surface 516Ba of the reference position glass 516B of the interferometer 510B. Interference fringe images are captured while the pulse motor stage 522A is moved, for example, by 1 μm by the pulse motor stage 522A, the position of the reference plate 515A when the contrast of the interference fringes reaches a peak is obtained, and the position is stored as AB0 in the memory of the computer. .
[0074]
<3> Based on the design value, specify the position of the reference surface 515Aa where the optical path length from the light source 511A is equal between the reference surface 515Aa and the reference position determination surface 516Aa of the reference position glass 516A of the interferometer 510A, The reference plate 515A is moved to a position slightly shifted from this position by the pulse motor stage 522A.
[0075]
<4> Based on the design value, similarly to the procedure <2>, the interferometer 510A is arranged in the direction in which the optical path lengths of the reference surface 515Aa and the reference position determination surface 516Aa of the reference position glass 516A of the interferometer 510A are equal. The interference fringe image is captured while moving the reference plate 515A, the position of the reference plate 515A when the contrast of the interference fringe reaches a peak is obtained, and the position is stored in the memory of the computer 16 as the AA0 position. Difference D between this AA0 position and the AB0 position stored in the above procedure <2> _C Thus, the interval between the reference position determination surface 516Aa of the interferometer 510A and the reference position determination surface 516Ba of the interferometer 510B is obtained and stored in the memory of the computer.
[0076]
<5> The parallel plane plate 600 is inserted into the optical path between the reference position glass 516A of the interferometer 510A and the reference position glass 516B of the interferometer 510B.
[0077]
<6> The reference plate 515A of the interferometer 510A is slightly smaller than the position where the optical path length from the light source 511A is supposed to be equal to the A side surface 600a of the parallel flat plate 600 based on the design thickness value of the parallel flat plate 600. To a position shifted forward or backward.
[0078]
<7> Similarly to the procedure <2>, the reference plate 515A of the interferometer 510A is moved in the direction in which the optical path length from the light source 511A is equal between the reference surface 515Aa and the A-side surface 600a of the parallel flat plate 600. While observing the occurrence of interference fringes, the parallel plane plate 600 is adjusted in two axes so that the interference fringes appear on the entire surface of the image.
[0079]
<8> After that, the interference fringe image is captured while continuing the movement of the reference plate 515A, and when the contrast of the interference fringe reaches a peak at a predetermined point Pa (not shown) on the A-side surface 600a of the parallel flat plate 600. The position of the reference plate 515A is obtained, and the position is stored as the Aa0 position. The distance D between the reference position determination surface 516Aa of the interferometer 510A and the predetermined point Pa on the A-side surface 600a of the parallel flat plate 600 due to the difference between this Aa0 position and the AA0 position stored in the above procedure <4>. _A Is stored in the memory of the computer.
[0080]
<9> The fringe scan measurement is performed by shifting the reference plate 515A by driving the piezoelectric element of the PZT stage 521A, and the shape of the A-side surface 600a of the parallel flat plate 600 is obtained.
[0081]
<10> The above steps <2> and <3> performed on the interferometer 510A are performed on the interferometer 510B, and the positional relationship between the reference plate 515B of the interferometer 510B and the reference position determination surface 516Ba of the interferometer 510B. Ask for.
[0082]
<11> The steps <6>, <8>, and <9> performed on the interferometer 510A are performed on the interferometer 510B, and the reference position determination surface 516Ba of the interferometer 510B and the B side of the parallel flat plate 600 A distance D from a point Pb (not shown) corresponding to the predetermined point Pa on the surface 600b. _B And the shape of the B-side surface 600b of the plane parallel plate 600.
[0083]
<12> Distance D between the reference position determination surface 516Aa of the interferometer 510A and the reference position determination surface 516Ba of the interferometer 510B obtained in the above procedure <4> _C Thus, the distance D between the reference position determining surface 516Aa of the interferometer 510A obtained in the procedure <8> and the predetermined point Pa on the A-side surface 600a of the parallel flat plate 600. _A , And the distance D between the reference position determination surface 516Ba of the interferometer 510B obtained in the procedure <11> and the predetermined point Pb on the B-side surface 600b of the parallel flat plate 600 _B Is obtained, the absolute thickness d between the points Pa and Pb of the plane parallel plate 600 is obtained.
[0084]
<13> The absolute thickness d between the points Pa and Pb of the plane parallel plate 600 determined in the above step <12>, the shape of the A-side surface 600a of the plane parallel plate 600 determined in the above step <9>, and the above procedure From the shape of the B-side surface 600b of the parallel flat plate 600 obtained in <11>, the absolute thickness and thickness unevenness distribution of the entire parallel flat plate 600 are obtained.
[0085]
The fringe scanning method in the fringe scan measurement of the procedure <9> and the thickness unevenness distribution measurement method of the procedure <13> are the fringe scanning method and the thickness unevenness distribution used in the first embodiment described above, respectively. It is possible to use a method similar to the measurement method.
[0086]
In the apparatus of the fourth embodiment, when measuring the distance between the reference position determination surface 516Aa of the interferometer 510A and the reference position determination surface 516Ba of the interferometer 510B, the light from the light sources 511A and 511B of one interferometer The light shielding member in the first embodiment apparatus can be employed so that white light can be prevented from entering other interferometers. Further, a distance D between the reference position determination surfaces 516Aa and 516Ba. _C , The parallel plane plate 600 is not moved out of the optical path, but an opening is formed in a part of the subject holding member 504 as shown in the second and third embodiments described above. A part of the white light may reach the reference position determination surface of the other interferometer through the opening. Even in this case, the light shielding member can be configured and used as shown in the second and third embodiments.
[0087]
In the fourth embodiment, as a pair of interferometers as components, a Twiman Green interferometer in which the lengths of the object light optical path and the reference light optical path are equal to each other is used. Various other equal optical path length type interferometers such as Michelson type and Mach-Zehnder type can be applied.
[0088]
The absolute thickness measuring apparatus of the present invention is not limited to the above-described embodiment, and various modifications can be made. For example, in the first to third embodiments, the phase is changed. Shift wavelength scanning interferometry is used, and the reference plate is moved along the optical axis using a piezo element as a phase shift means. Instead, the subject is moved to the optical axis using the piezo element. The phase shift may be performed by wavelength scanning.
[0089]
As a configuration on the extension line of the present invention, one of the pair of interferometers is mounted with the wavelength variable laser light source described in the first embodiment, and the other is described in the fourth embodiment. It is possible to mount a white light output light source.
[0090]
【The invention's effect】
A first absolute thickness measuring apparatus according to the present invention is configured to allow a pair of first and second interferometers to face each other with a plane parallel plate as an object, and to allow a variable wavelength light source mounted on each interferometer. The interference fringes are measured using the interference light, and the distance between the two surfaces can be measured by scanning the wavelength of the light from the wavelength tunable light source. The first interferometer allows the first interference to be measured. Distance D between the reference plane of the meter and the surface of the parallel plane plate on the first interferometer side _A And the distance D between the reference planes of the two interferometers _C And a distance D between the reference plane of the second interferometer and the surface on the second interferometer side of the parallel plane plate by the second interferometer _B And these three distances D _A , D _B , D _C Therefore, the thickness of the parallel flat plate can be easily obtained.
[0091]
The second absolute thickness measurement device according to the present invention is mounted on each interferometer, with a pair of first and second equal optical path length type interferometers facing each other across a parallel plane plate as a subject. The interference fringes are measured only when the object light and the reference light are equal using the coherent light from the low coherence light output source with a short coherence length. Oppositely, a transparent reference position determination plate having a reference position determination surface is provided, and the reference surfaces of the pair of interferometers can be moved in the direction of the optical axis of each of the interferometers. Since the detection means capable of reading the position is provided,
The first interferometer determines a first reference position determination plane that is the reference position determination plane on the first interferometer side, and a second reference position determination that is the reference position determination plane on the second interferometer side. The reading value of the detection means is the current position of the reference plane of the first interferometer when interference fringes are obtained for each of the plane and the plane on the first interferometer side of the plane parallel plate , The first reference position determination plane, the second reference position determination plane, and the relative position of the plane on the first interferometer side of the parallel plane plate,
Furthermore, the reference of the other interferometer when interference fringes are obtained by the second interferometer for each of the second reference position determination plane and the second interferometer side surface of the parallel plane plate. The reading value of the detection means, which is the current position of the surface, indicates the relative position between the second reference position determination surface and the surface of the parallel plane plate on the second interferometer side.
[0092]
Thereby, the distance D between the reference surface of the first interferometer and the surface on the first interferometer side of the parallel plane plate. _A And the distance D between the reference planes of these two interferometers _C And a distance D between the reference surface of the second interferometer and the surface on the second interferometer side of the parallel plane plate by the second interferometer. _B And these three distances D _A , D _B , D _C Therefore, the thickness of the parallel flat plate can be easily obtained.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram for explaining the operation of an absolute thickness measuring apparatus according to a first embodiment of the present invention.
FIG. 2 is an overall configuration diagram showing an absolute thickness measuring apparatus according to the first embodiment of the present invention.
FIG. 3 is a diagram showing a state of measuring interference fringes between reference planes in the embodiment apparatus of FIG. 1;
4 is a diagram showing the principle of analytically measuring the absolute thickness of a plane parallel plate using interference fringe measurement results in the embodiment apparatus of FIG. 1;
5 is a diagram showing a procedure for analytically measuring thickness unevenness of a plane parallel plate using interference fringe measurement results in the embodiment apparatus of FIG. 1;
FIG. 6 is an overall configuration diagram showing an absolute thickness measuring apparatus according to a second embodiment of the present invention.
FIG. 7 is an overall configuration diagram showing an absolute thickness measuring apparatus according to a third embodiment of the present invention.
FIG. 8 is a conceptual diagram for explaining the operation of an absolute thickness measuring apparatus according to a fourth embodiment of the present invention.
[Explanation of symbols]
2,600 parallel plane plate
2a, 2b, 600a, 600b Both sides (test surface)
10, 110, 210, 500 Absolute thickness measuring device
12A, 12B, 510A, 510B Interferometer
14, 114, 214, 504 Subject holding member
16 computers
18 Monitor
20A, 20B Interferometer body
22A, 22B, 515A, 515B Reference plate
22Aa, 22Ba, 515Aa, 515Ba Reference plane
24A, 24B PZT drive circuit
26A, 26B Piezo element
28A, 28B Reference plate support member
30, 130, 230A, 230B Light shielding member
31A, 31B Tunable laser light source
39Aa, 39Ba, 519A, 519B Imaging device
516A, 516B Reference position determination plate
516Aa, 516Bb Reference position determination plane
521A, 521B PZT stage
521A, 521B Pulse motor stage
Ax optical axis

Claims (7)

The light beam emitted from the light source is divided into two, and one of the light beams is incident on the surface to be tested to make the reflected light the object light, and the other light beam is incident on the reference surface to make the reflected light the reference light. A pair of first and second interferometers configured to measure the test surface based on interference fringes generated by light interference of light and reference light, and an opaque parallel flat plate serving as a test object are held A subject holding member that
The first plane interferometer is placed on one side of both sides of the plane parallel plate, and the second interferometer is placed on the other side of the plane parallel plate so that the emitted light beams face each other. In a measuring device configured to perform interference measurement as a surface inspection,
While changing the wavelength of the light emitted from the light source for each of the first and second interferometers while changing the light source as a wavelength variable light source, an interference fringe image is obtained each time it is changed by a predetermined wavelength, Based on these obtained interference fringe images, the following arithmetic expressions (1) to (3) are used to measure the distance between the test surface and the reference surface,
_A distance D _A measured by the first interferometer between a first reference plane which is a reference plane of the first interferometer and the plane of the parallel plane plate facing the first reference plane; and the second interferometer It measured by, and a distance D _B to the surface of the parallel flat plate and the second reference surface opposed thereto which is the reference surface of the second interferometer, the measurement by the first or second interferometer It has been an absolute thickness measurement apparatus characterized by comprising configured to calculate the absolute thickness d of the parallel flat plate from the distance D _C subtraction process to up to the second reference plane from the first reference plane .

  2. The absolute thickness measuring apparatus according to claim 1, wherein the wavelength tunable light source is a wavelength tunable laser light source, and the first and second interferometers are Fizeau interferometers. The light beam emitted from the light source is divided into two, and one of the light beams is incident on the surface to be tested to make the reflected light the object light, and the other light beam is incident on the reference surface to make the reflected light the reference light. A pair of first and second interferometers configured to measure the test surface based on interference fringes generated by light interference of light and reference light, and an opaque parallel flat plate serving as a test object are held A subject holding member that
In a state where the first equal optical path length type interferometer is arranged on one side of both surfaces of the parallel flat plate and the second equal optical path length type interferometer is arranged on the other side so that the respective emitted light beams face each other. In a measuring apparatus configured to perform interference measurement using both surfaces of a flat plate as test surfaces,
The light source is a low coherence light output light source, and a transparent reference position determination plate having a reference position determination surface is provided respectively on both sides of the plane-parallel plate so as to face each other.
The first and second reference planes of the first and second equal optical path length type interferometers can be moved in the optical axis direction, and the current positions of the first and second reference planes can be read. Providing detection means;
A first reference position determination plane disposed on the first equal optical path length type interferometer side of the parallel plane plate by moving the first reference plane of the first equal optical path length type interferometer; Each of the second reference position determination surface disposed on the second equal optical path length type interferometer side of the parallel plane plate and the first equal optical path length type interferometer side surface of the parallel plane plate Based on the current position information of the first reference plane of the first equal optical path length type interferometer when the interference fringes are obtained, the first of the parallel plane plates from the first reference position determination plane the resulting distance D _a to the surface of the equal optical path length interferometer side, the distance D _C from the first reference position determination plane to the second reference position determination surfaces of
By moving the second reference plane of the second equal optical path length type interferometer, the second reference position determining plane and the plane of the parallel plane plate on the second equal optical path length type interferometer side For each, based on each current position information of the second reference plane of the second equal optical path length type interferometer when an interference fringe is obtained, the second of the parallel plane plate from the second reference position determination plane to a surface of equal optical path length interferometer side of 2 to obtain a distance D _B of
An absolute thickness measuring apparatus configured to calculate the absolute thickness of the plane-parallel plate by subtracting the distance D _A and the distance D _B from the distance D _C.   The said object holding member is comprised so that the said parallel plane plate can be inserted or removed with respect to the light beam of a pair of said interferometer, The any one of Claims 1-3 characterized by the above-mentioned. The absolute thickness measuring apparatus described.   The object holding member includes an opening that allows a part of a light beam emitted from one of the pair of interferometers to reach the other reference plane of the pair of interferometers. The absolute thickness measuring device according to any one of Items 1 to 3. A light-shielding member is provided to prevent a light beam emitted from an interferometer not involved in the measurement from entering the interferometer involved in the measurement when observing the interference fringes of the pair of interferometers. The absolute thickness measuring apparatus according to claim 4 or 5, wherein   The interferometer analyzes the interference fringes by finely moving the reference surface of the interferometer in the optical axis direction of the reference surface to change the relative distance between the reference surface and the test surface. It is comprised, The absolute thickness measuring apparatus of any one of Claims 1-6 characterized by the above-mentioned.

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