JP2004226075A

JP2004226075A - Adjusting method of branched imaging mechanism in phase shift interference fringe simultaneous imaging device

Info

Publication number: JP2004226075A
Application number: JP2003010563A
Authority: JP
Inventors: Kazuhiko Kawasaki; 和彦川▲崎▼; Yasushi Uejima; 泰上島
Original assignee: Mitutoyo Corp; Mitsutoyo Kiko Co Ltd
Current assignee: Mitutoyo Corp; Mitsutoyo Kiko Co Ltd
Priority date: 2003-01-20
Filing date: 2003-01-20
Publication date: 2004-08-12
Anticipated expiration: 2023-01-20
Also published as: JP4145670B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adjusting method of a branched imaging mechanism which adjusts highly accurately positions of a plurality of branched phase shift interference fringes imaged by different imaging mechanisms. <P>SOLUTION: This method comprises a first adjusting means for imparting separately an optical phase difference to a sample light optical axis, and a second adjusting means for imparting separately an optical phase difference equivalent to the case where an inspection face capable of imaging an interference fringe is tilted to the sample light optical axis. A first fixed optical phase difference by the relative difference of numerical data at a positional temporary corresponding point is determined by the first adjusting means. The optical phase difference is imparted separately by the second adjusting means, and a second fixed optical phase difference by the relative difference of the numerical data at the temporary corresponding point is determined by the second adjusting means. The branched imaging mechanism is arranged and adjusted on the face approximately orthogonal to a branched original beam so that specific positions in an inspection face observation range are on the same position in each branched observation coordinate system by using the positional difference calculated from the relation between the first fixed optical phase difference and the second fixed optical phase difference. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は位相シフト干渉稿同時計測装置に関し、特に、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、複数の撮像機構で同時撮像し、被検面の形状を計測する位相シフト干渉計に関する。
【０００２】
【背景技術】
例えば、特願平１１−１３６８３１号出願に示すような図１の位相シフト干渉稿同時計測装置においては、レーザ光源１からのレーザー光束は、レンズ２に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にて平行光束にされる。そして、この平行光束から参照面５で反射された参照光と参照面５，λ／４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、試料光は再びλ／４板６を透過することで偏光面が参照光とは直交した光学的無干渉状態の原光束となる。
【０００３】
ビームスプリッタ３で反射された原光束に含まれる参照光と試料光はλ／４板８を透過することでそれぞれ互いに回転方向の異なる円偏光状態となり、三分割プリズム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、光軸に対して概略直交する面内において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稿が発生され、撮像機構１３〜１５により撮像が行われる。
【０００４】
この装置において、被検面形状を高精度に計測するためには、三分割プリズム９にて分割して発生させた分枝位相シフト干渉稿を異なる撮像機構にて撮像する際に、被検面の観測範囲にある任意の位置がそれぞれ分枝観測座標系において同一位置になるように位置の整合調整を施さなければならない。
しかし、実際には、一つの被検体を異なる撮像機構にて撮像しようとした場合、図２の例に示したように、個々の撮像機構の設置位置が設計値と異なることにより、出力画像中にて得られる被検体の位置は互いにずれたものとなる。
【０００５】
【発明が解決しようとする課題】
この課題を解決する方法としては、撮像機構１３〜１５にて撮像された基準図形の図芯の位置より、分枝観測座標系のずれ量を算出し、ソフトウェアによる座標変換により整合調整を施す方法が「画像計測システム及びその画像校正方法（特願平１１−２７６８）」にて提案されている。
ところが、基準図形を撮像して座標系のずれ量を算出する方法では、入力画像の強度情報が明らかでない場合には、撮像された基準図形の縁の決定の仕方などにより、算出される図芯の位置は異なってしまう。つまり、従来技術において、観測座標系の異なる複数の撮像機構の設置位置調整を高精度に行うためには、図芯を得るために使用される被検体から発せられる光強度が精度よく校正されており、しかもこの被検体を忠実に撮像する精度の高い観測光学系が必要である。
【０００６】
しかしながら、これら被検体および観測光学系が用いられたとしても、画素という有限サイズの離散的な輝度の集合から成る画像では、画素サイズ以下の精度で図芯を算出することは極めて困難である。
【０００７】
本発明の目的は、位相シフト干渉稿同時計測装置において、異なる撮像機構により撮像する複数の分枝位相シフト干渉稿の位置ずれの補正を高精度に行うことができる分枝撮像機構の調整方法を得るにある。
【０００８】
【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、レーザ光源より発する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、前記被検面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、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、
前記原光束を複数の分枝原光束に分け、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稿を発生させ、前記被検面の観測範囲にある任意の位置がそれぞれの分枝観測座標系にて同一位置になるよう位置の整合を施し、分枝ごとに設けられた分枝撮像機構によりこれら干渉稿に対応する画像データを取得し、位相シフト法にて前記被検面の観測範囲の平面起伏形状を数値データにより再現する平面形状計測装置において、
前記参照光と試料光の間に前記試料光光軸に対して直交する面内で相対的に一様な光学位相差を別途与える第１調整手段と、干渉稿が撮像可能な被検面を前記試料光光軸に対して傾斜させた時と等価な光学位相差を別途与える第２調整手段とからなり、
前記第１調整手段により、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それぞれの前記分枝撮像機構にて得られる複数の位相シフト干渉稿画像データから分枝ごとの平面起伏形状を位相シフト法により数値データとして算出し、位置的な仮対応点における前記数値データの相対的な差により第１の固定的光学位相差を求め、
次に、前記第２調整手段により前記試料光光軸に対して被検面を傾斜させた時と等価な光学的位相差を別途与え、前記第１調整手段により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それぞれの前記分枝撮像機構にて得られる複数の位相シフト干渉稿画像データから分枝ごとの平面起伏形状を位相シフト法により数値データとして算出し、前記仮対応点における前記数値データの相対的な差により第２の固定的光学位相差を求め、
第１の固定的光学位相差と第２の固定的光学位相差の関係から算出した前記位置的な仮対応点と実際に対応する点の差を用い、被検面観測範囲にある任意位置がそれぞれの前記分枝観測座標系において同一位置になるように前記分枝撮像機構を前記分枝原光束と概略直交する面内において配置調整するこ特徴とする位相シフト干渉稿同時撮像装置における分枝撮像機構の調整方法
を提案するものである。
【０００９】
後述する本発明の好ましい実施例の説明においては、
１）前記被検面観測範囲のある位置がそれぞれの前記分枝観測座標系において同一位置になるように前記分枝撮像機構を前記分枝原光束と概略直交する面内において調整する際、前記固定的光学位相と前記固定的光学位相の関係から算出した位置的な前記対応点と実際に対応する点の差を用い、配置調整を行うか、あるいは、ソフトウェアによる位置座標変換により調整する位相シフト干渉稿同時撮像装置における分枝撮像機構の調整方法、
２）前記参照光と前記試料光の間に前記試料光光軸に対して直交する面内で相対的に一様な光学位相差を別途与える前記第１調整手段は、前記参照光の光軸方向に平行移動できるステージを有し、前記試料光光軸に対して被検面を傾斜させた時と等価な光学位相差を別途与える前記第２調整手段は、前記試料光光軸に対して傾斜するステージを有することを特徴とする請求項１または請求項２記載の位相シフト干渉稿同時撮像機構における分枝撮像機構の調整方法、
３）前記参照光と前記試料光の間に前記試料光光軸に対して直交する面内で相対的に一様な光学位相差を別途与える前記第１調整手段は、前記レーザ光源の波長をわずかづつ変化させる方法であり、前記試料光光軸に対して被検面を傾斜させた時と等価な光学位相差を別途与える第２調整手段は、前記試料光光軸に対して傾斜するステージを有することを特徴とする請求項１または請求項２記載の位相シフト干渉稿同時撮像機構における分枝撮像機構の調整方法
が説明される。
【００１０】
【発明の実施の形態】
以下、図３から図６について本発明の好ましい実施例を説明する。
図３は本発明による一実施例に係る位相シフト干渉稿同時撮像装置における撮像機構の調整方法の装置構成を示す。
【００１１】
即ち、図３においては、位相シフト干渉稿同時撮像装置の開口部下に、参照光の光軸方向への平行移動と傾斜が可能なステージが設置され、このステージには干渉稿が撮像可能な被検面が配置される。
そして、被検面は参照面と平行に傾斜調整されるが、この時に撮像機構１３〜１５にて得られる分枝位相シフト干渉稿は、それぞれの分枝観測座標系上で同じ位置にあり、（ｘ，ｙ）座標上で仮に対応しているとみなせば、次式にて表される。

【００１２】
ここでは、Ｂ（ｘ，ｙ）及びＡ（ｘ，ｙ）は３枚の分枝位相シフト干渉稿のバイアス及び振幅をそれぞれ示し、φ（ｘ，ｙ）は参照面に対する被検面の相対起伏形状を表す干渉稿の位相を、そして、α（ｘ，ｙ）、β（ｘ，ｙ）は偏光板の透過軸角度などによって発生する第１の固定的光学位相差を表している。
【００１３】
次に、図３に示したステージにより被検面を光軸方向に平行移動させて参照光と試料光の間に光学的位相差δ_ｉを別途に与え、それぞれの撮像機構にて干渉稿を３枚以上ずつ撮像する。
この時に得られる分枝ごとの位相シフト干渉稿は次式で表される。

この時に得られた干渉稿から分枝ごとに独立に被検面起伏形状を算出するが、例えば、「δ_ｉ」を干渉稿位相１周期２πを等しく分割する値

に相当する量だけ被検面を平行移動させた場合には、各分枝ごとの被検面起伏形状は次式より得られる。

【００１４】
つまり、式（４−１），（４−２），（４−３）の左辺の関係から、お互いの差をとると、固定的光学位相差１であるα（ｘ，ｙ）とβ（ｘ，ｙ）が被検面観測領域内の各点にて算出できる。
【００１５】
次に、被検面を干渉稿が観測される範囲内で角度κだけ傾斜させて、同様に干渉稿を撮像する。
ここでは説明の簡略化のため、被検面をθ_ｙ軸回りに傾斜させた場合のｘ軸方向１ラインの参照面と被検面の相対関係にて示す。また、撮像機構１３の分枝観測座標系上の被検面位置を基準とし、撮像機構１４の分枝観測座標系上の被検面を同一位置に調整する場合を例に示す。
【００１６】
被検面を参照面に対して平行状態に設置した場合の光路差をｈ（ｘ）とし、ステージにより角度κだけ傾斜させた場合の様子を図５に示す。角度κは干渉稿が発生する範囲の微小な角度である。この時に撮像機構１３、１４にて得られる分枝位相シフト干渉稿は、図６に示す参照面に対する被検面の相対形状を表したものである。この時の干渉稿強度は、撮像機構１３と１４の間に生じる固定的光学位相差２をα’（ｘ）で表すと、次式にて表される。

【００１７】
この時に、撮像機構１３のｘ_１に対応する点が撮像機構１４上ではｘ_２であったとすると、被検面を傾斜させた時に算出されるα’（ｘ）には、α_{ｘ＿ｅｒｒｏｒ}が含まれる。
よって、図６に示す幾何的な関係から、観測座標系が異なることによるｘ方向の画像の横ずれ量Δｘ_２１とα_{ｘ＿ｅｒｒｏｒ}の間には次式の関係が得られる。

【００１８】
したがって、傾斜後前後に算出されたα（ｘ）とα’（ｘ）及び傾斜角度κが得られれば、撮像機構１３に対する撮像機構１４のｘ方向の位置ずれ量を算出することができる。撮像機構１５についても、先に示した方法で傾斜前後のβ（ｘ）とβ’（ｘ）を算出すれば、撮像機構１３に対する位置ずれ量Δｘ_３１を算出することができる。

【００１９】
また、撮像機構１４と撮像機構１５のｙ方向の位置ずれ量Δｙ_２１、Δｙ_３１も同様に、角度κ傾斜前後のα（ｙ）、α’（ｙ）とβ（ｙ）とβ’（ｙ）から算出できる。

このようにして得られる撮像機構間の位置ずれ量Δｘ_２１、Δｘ_３１、Δｙ_２１、Δｙ_３１の精度は、画素サイズに係わらず、傾斜角度κ、波長λ、およびα_{ｘ＿ｅｒｒｏｒ}の精度によって決定される。すなわち、必要精度に応じてこれらパラメータを設定すればよいと言える。角度κを与える傾斜装置やα_{ｘ＿ｅｒｒｏｒ}などを得るためにδ_ｉを付与する機構（ステージなど）は、既存の技術にて十分な精度が得られるため、画素サイズより細かく高精度に位置決めすることは容易である。
【００２０】
本発明においては、傾斜前では被検面を参照面に対して平行に設置することを示したが、平行でない場合でも傾斜前後の角度差κが既知であればよいことは自明である。
【００２１】
先の実施例にて撮像機構１４、１５を配置調整することを示したが、Δｘ_２１、Δｘ_３１、Δｙ_２１、Δｙ_３１を基に出力される分枝位相シフト干渉稿の画像を、ソフトウェアにて位置座標変換すれば、容易に位置の整合調整を行なえるのは改めて説明するまでもない（請求項２）。
【００２２】
また、参照光と試料光の間に光学的位相差δ_ｉを別途与える方法としては、被検面を光軸面を光軸方向に平行移動させるステージを使用する代わりに、レーザ光源の波長をわずかに変化させることでも、先に示した方法にて、Δｘ_２１、Δｘ_３１、Δｙ_２１、Δｙ_３１を算出し、位置の整合調整をすることができる（請求項４）。
【００２３】
【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、位相シフト干渉稿同時計測装置において、異なる撮像機構により得られる分枝シフト干渉稿間の位置の整合調整を行う際に、基準図形が不要で容易にかつ高精度に位置ずれ量を算出することができ、その結果、位相シフト干渉稿同時撮像装置の高精度化を実現できる。
【図面の簡単な説明】
【図１】位相シフト干渉縞同時撮像装置の原理説明図である。
【図２】分枝観測座標系での出力画像中での被検体の位置ずれの説明図である。
【図３】本発明による位相シフト干渉稿同時撮像装置における撮像機構の調整方法の装置構成の一例を表す。
【図４】傾斜ステージにおいてｙ軸を中心として傾斜させる場合の参照面と被検面との関係を示す。
【図５】ｘｚ面内において被検面を角度κ傾斜させた時の、参照面との相対的な関係を表したκ説明図である。
【図６】α_{ｘ＿ｅｒｒｏｒ}とｘ方向の位置ずれ量の関係を表した説明図である。
【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
６ λ／４板
７被検面
８ λ／４板
１０，１１，１２偏光板
１３，１４，１５撮像機構[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a phase shift interferometer simultaneous measurement apparatus, and in particular, 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, The present invention relates to a phase shift interferometer that gives a different fixed optical phase difference to a light beam to cause interference, and simultaneously captures images with a plurality of image capturing mechanisms to measure the shape of a surface to be inspected.
[0002]
[Background Art]
For example, in the phase shift interferometer simultaneous measurement apparatus shown in FIG. 1 as disclosed in Japanese Patent Application No. 11-136831, the beam diameter of a laser beam from a laser light source 1 is expanded by a lens 2 and transmitted through a beam splitter 3. Then, the light is converted into a parallel light beam by the collimator lens 4. Then, the reference light reflected by the reference surface 5 and the sample light transmitted through the reference surface 5 and the λ / 4 plate 6 and reflected by the test surface 7 are generated from the parallel light beam, and the sample light is again λ / 4. By transmitting through the plate 6, the original light beam in an optically non-interfering state whose polarization plane is orthogonal to the reference light is obtained.
[0003]
The reference light and the sample light included in the original light beam reflected by the beam splitter 3 pass through the λ / 4 plate 8 to be in a circularly polarized state having different rotation directions from each other. Divided. Polarizing plates 10 to 12 are arranged on the optical path of each of the branched light beams, the transmission axis angle of the polarizing plate is set in a plane substantially perpendicular to the optical axis, and a branch having a fixed optical phase difference is provided. A phase shift interference draft is generated, and imaging is performed by the imaging mechanisms 13 to 15.
[0004]
In this apparatus, in order to measure the shape of the surface to be measured with high accuracy, the surface of the surface to be inspected is imaged by a different imaging mechanism when the branched phase shift interference image generated by the division by the three-division prism 9 is imaged. Must be adjusted so that arbitrary positions in the observation range are the same in the branch observation coordinate system.
However, in practice, when trying to image one subject with different imaging mechanisms, as shown in the example of FIG. 2, the installation position of each imaging mechanism is different from the design value, so that Are shifted from each other.
[0005]
[Problems to be solved by the invention]
As a method for solving this problem, a method of calculating the amount of deviation of the branch observation coordinate system from the position of the center of the reference figure captured by the imaging mechanisms 13 to 15 and performing alignment adjustment by coordinate transformation by software. Has been proposed in "Image Measurement System and Image Calibration Method (Japanese Patent Application No. 11-2768)".
However, in the method of imaging the reference graphic and calculating the amount of displacement of the coordinate system, if the intensity information of the input image is not clear, the calculated center is determined by a method of determining the edge of the captured reference graphic. Will be different. That is, in the prior art, in order to adjust the installation position of a plurality of imaging mechanisms having different observation coordinate systems with high accuracy, the light intensity emitted from the subject used to obtain the centroid is calibrated with high accuracy. In addition, a high-precision observation optical system for faithfully imaging the subject is required.
[0006]
However, even if the subject and the observation optical system are used, it is extremely difficult to calculate the centroid with an accuracy equal to or less than the pixel size in an image composed of a set of finite-sized discrete luminances called pixels.
[0007]
An object of the present invention is to provide a method for adjusting a branch imaging mechanism capable of performing highly accurate correction of positional deviation of a plurality of branched phase shift interference drafts imaged by different imaging mechanisms in a phase shift interference draft simultaneous measurement apparatus. To get.
[0008]
[Means for Solving the Problems]
In order to achieve this object, the present invention irradiates a reference surface and a test surface with a coherent light beam emitted from a laser light source, and the reference surface and the reference light, which are reflected light from the test surface, and polarization of the sample light. An observation optical system that generates an original light beam that is orthogonal to each other with a polarizing optical element interposed therebetween, and that is in an optically non-interfering state;
Dividing the original light beam into a plurality of branched original light beams, generating a plurality of branched phase-shift interference images in which each of the branched original light beams is given a different fixed optical phase difference via a polarizing optical element, Position matching is performed so that any position within the observation range of the inspection surface is the same position in each branch observation coordinate system, and images corresponding to these interference drafts are provided by the branch imaging mechanism provided for each branch. In a plane shape measuring device that acquires data and reproduces a plane undulation shape of an observation range of the test surface by a phase shift method by numerical data,
First adjusting means for separately providing a relatively uniform optical phase difference in a plane orthogonal to the sample optical axis between the reference light and the sample light, and a test surface on which an interference draft can be imaged. A second adjusting means for separately providing an optical phase difference equivalent to when the sample is inclined with respect to the optical axis of the sample,
A plurality of phase shift interference image data obtained by each of the branch imaging mechanisms when a relative optical phase difference is separately provided between the reference light and the sample light by the first adjusting means; Calculate the planar undulation shape for each branch as numerical data by the phase shift method, and determine a first fixed optical phase difference from a relative difference between the numerical data at a positional temporary corresponding point,
Next, an optical phase difference equivalent to when the surface to be measured is inclined with respect to the optical axis of the sample is separately given by the second adjusting means, and the reference light and the sample light are compared by the first adjusting means. When a relative optical phase difference is separately provided between the plurality of phase-shift interference image data obtained by the respective branch imaging mechanisms, the plane undulation shape for each branch is converted into numerical data by the phase shift method. Calculating a second fixed optical phase difference based on the relative difference of the numerical data at the provisional corresponding point,
By using the difference between the positional temporary corresponding point and the actually corresponding point calculated from the relationship between the first fixed optical phase difference and the second fixed optical phase difference, an arbitrary position in the test surface observation range is determined. A branch imaging mechanism for adjusting the position of the branch imaging mechanism in a plane substantially perpendicular to the branch original light beam so that the branch imaging mechanism is located at the same position in each of the branch observation coordinate systems; An adjustment method of an imaging mechanism is proposed.
[0009]
In the description of the preferred embodiments of the invention described below,
1) When adjusting the branch imaging mechanism in a plane substantially orthogonal to the branch original light flux so that a certain position of the inspection surface observation range is the same position in each of the branch observation coordinate systems, Using the difference between the position corresponding to the fixed optical phase and the point corresponding to the position actually calculated from the relationship between the fixed optical phase and the position corresponding to the position, the arrangement is adjusted, or the phase shift is adjusted by position coordinate conversion by software. Adjustment method of branch imaging mechanism in interference draft simultaneous imaging apparatus,
2) the first adjusting means for separately providing a relatively uniform optical phase difference in a plane perpendicular to the optical axis of the sample between the reference light and the sample light, A stage that can be moved in parallel in the direction, and the second adjusting means for separately providing an optical phase difference equivalent to when the surface to be inspected is tilted with respect to the optical axis of the sample, 3. The method for adjusting a branch imaging mechanism in a phase shift interferogram simultaneous imaging mechanism according to claim 1 or 2, further comprising a stage that tilts.
3) The first adjusting means for separately providing a relatively uniform optical phase difference in a plane orthogonal to the optical axis of the sample between the reference light and the sample light, the wavelength of the laser light source being adjusted. A second adjusting means for separately giving an optical phase difference equivalent to that when the surface to be measured is inclined with respect to the optical axis of the sample, wherein the stage is inclined with respect to the optical axis of the sample. A method for adjusting a branch imaging mechanism in the phase shift interferometer simultaneous imaging mechanism according to claim 1 or 2, is described.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a preferred embodiment of the present invention will be described with reference to FIGS.
FIG. 3 shows an apparatus configuration of a method for adjusting an imaging mechanism in a phase shift interference image simultaneous imaging apparatus according to an embodiment of the present invention.
[0011]
That is, in FIG. 3, a stage capable of parallel movement and tilting of the reference light in the optical axis direction is installed below the opening of the phase shift interference draft simultaneous imaging apparatus. A test surface is placed.
Then, the test surface is tilted and adjusted in parallel with the reference surface. At this time, the branched phase shift interference images obtained by the imaging mechanisms 13 to 15 are at the same position on the respective branch observation coordinate systems, Assuming that they correspond on the (x, y) coordinates, they are expressed by the following equation.

[0012]
Here, B (x, y) and A (x, y) indicate the bias and amplitude of the three branched phase shift interference plots, respectively, and φ (x, y) is the relative undulation of the test surface with respect to the reference surface. Α (x, y) and β (x, y) represent the first fixed optical phase difference generated by the transmission axis angle of the polarizing plate and the like.
[0013]
Next, the test surface is moved in parallel in the optical axis direction by the stage shown in FIG. 3 to separately provide an optical phase difference δ _i between the reference light and the sample light. Image three or more images at a time.
The phase shift interference image for each branch obtained at this time is expressed by the following equation.

The undulating shape of the test surface is calculated independently for each branch from the interference draft obtained at this time. For example, “δ _i ” is a value that divides the interference draft phase 1 period 2π equally.

When the test surface is translated by an amount corresponding to the following expression, the undulation shape of the test surface for each branch is obtained by the following equation.

[0014]
That is, from the relations on the left sides of the equations (4-1), (4-2), and (4-3), when taking the difference therebetween, α (x, y) and β (x) which are fixed optical phase differences 1 x, y) can be calculated at each point in the inspection surface observation area.
[0015]
Next, the surface to be inspected is tilted by the angle κ within the range in which the interference draft is observed, and the interference draft is similarly imaged.
For simplicity of explanation here, indicated by the relative relationship between the x-axis direction one line of the reference surface and the test surface in the case of tilting the test surface to theta _y axis. In addition, an example will be described in which the test surface on the branch observation coordinate system of the imaging mechanism 14 is adjusted to the same position with reference to the position of the test surface on the branch observation coordinate system of the imaging mechanism 13.
[0016]
FIG. 5 shows a state where the optical path difference is h (x) when the test surface is set in a state parallel to the reference surface, and the stage is inclined by an angle κ by the stage. The angle κ is a minute angle in a range where an interference draft occurs. At this time, the branched phase shift interference images obtained by the

imaging mechanisms

13 and 14 represent the relative shape of the test surface with respect to the reference surface shown in FIG. The interference draft intensity at this time is expressed by the following equation, where α ′ (x) represents a fixed optical phase difference 2 generated between the

imaging mechanisms

13 and 14.

[0017]
At this time, when the point corresponding to x ₁ of the imaging mechanism 13 and is on the imaging mechanism 14 was x _2, the alpha is calculated when tilting the test surface '(x) include alpha _{X_error} .
Therefore, from the geometric relationships shown in FIG. 6, the following relationship is obtained between the amount of lateral deviation [Delta] x ₂₁ and alpha _{X_error} of the observation coordinate system of the x-direction due to the different images.

[0018]
Accordingly, if the α (x) and α ′ (x) calculated before and after the tilt and the tilt angle κ are obtained, it is possible to calculate the amount of displacement of the imaging mechanism 14 with respect to the imaging mechanism 13 in the x direction. For even imaging mechanism 15, can be calculated before and after the gradient by the method described above beta (x) and beta '(x), it calculates a position deviation amount [Delta] x ₃₁ relative to the imaging mechanism 13.

[0019]
Similarly, the displacement amounts Δy ₂₁ and Δy _{31 of} the imaging mechanism 14 and the imaging mechanism 15 in the y direction are also α (y), α ′ (y), β ′ (y) and β ′ (y before and after the angle κ inclination. ).

The accuracy of the positional deviation amounts Δx ₂₁ , Δx ₃₁ , Δy ₂₁ , Δy ₃₁ between the imaging mechanisms obtained in this manner is determined by the accuracy of the tilt angle κ, the wavelength λ, and α _{x_error irrespective} of the pixel size. . That is, it can be said that these parameters should be set according to the required accuracy. Mechanism that imparts [delta] _i in order to obtain such tilting device and alpha _{X_error} give angle kappa (such stage), because the sufficient accuracy can be obtained by the existing technology, be positioned finer precision than the pixel size Easy.
[0020]
In the present invention, the test surface is set to be parallel to the reference surface before tilting. However, it is obvious that the angle difference κ before and after tilting may be known even in the case of not being parallel.
[0021]
Although the arrangement of the imaging mechanisms 14 and 15 is adjusted in the previous embodiment, the image of the branched phase shift interference draft output based on Δx ₂₁ , Δx ₃₁ , Δy ₂₁ , and Δy ₃₁ is converted into software. It is needless to explain again that the position coordinate adjustment can be easily performed by the position coordinate conversion (claim 2).
[0022]
Further, as a separate method of providing an optical phase difference [delta] _i between the reference light and sample light, instead of using the stage for translating the test surface to the optical axis plane in the optical axis direction, the wavelength of the laser light source Even with a slight change, it is possible to calculate Δx ₂₁ , Δx ₃₁ , Δy ₂₁ , and Δy ₃₁ by the above-described method and adjust the position matching (claim 4).
[0023]
【The invention's effect】
As is clear from the above description, according to the present invention, in the phase shift interferogram simultaneous measurement apparatus, when performing position matching between branch shift interferograms obtained by different imaging mechanisms, a reference figure is not required. The position shift amount can be calculated easily and with high accuracy, and as a result, the high accuracy of the phase shift interferogram simultaneous imaging apparatus can be realized.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating the principle of a simultaneous phase shift interference fringe imaging apparatus.
FIG. 2 is an explanatory diagram of a displacement of a subject in an output image in a branch observation coordinate system.
FIG. 3 illustrates an example of a device configuration of a method of adjusting an imaging mechanism in a phase-shift interference simultaneous imaging device according to the present invention.
FIG. 4 shows a relationship between a reference surface and a test surface when the tilt stage is tilted about a y-axis.
FIG. 5 is a κ explanatory diagram showing a relative relationship with a reference surface when a test surface is inclined at an angle κ in an xz plane.
FIG. 6 is an explanatory diagram showing a relationship between α _{x_error} and a displacement amount in the x direction.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 laser light source 2 lens 3 beam splitter 4 collimator lens 5 reference surface 6 λ / 4 plate 7 test surface 8 λ / 4 plate 10, 11, 12

polarizing plate

13, 14, 15 imaging mechanism

Claims

A reference surface and a test surface are irradiated with a coherent light beam emitted from a laser light source, and the reference surface and the reference light, which are reflected light from the test surface, and the polarization surfaces of the sample light are orthogonal to each other with a polarization optical element interposed therebetween. An observation optical system that generates an original light beam in an optically non-interference state;
Dividing the original light beam into a plurality of branched original light beams, generating a plurality of branched phase-shift interference images in which each of the branched original light beams is given a different fixed optical phase difference via a polarizing optical element, Position matching is performed so that any position within the observation range of the inspection surface is the same position in each branch observation coordinate system, and images corresponding to these interference drafts are provided by the branch imaging mechanism provided for each branch. In a plane shape measuring device that acquires data and reproduces a plane undulation shape of an observation range of the test surface by a phase shift method by numerical data,
First adjusting means for separately providing a relatively uniform optical phase difference in a plane orthogonal to the sample optical axis between the reference light and the sample light, and a test surface on which an interference draft can be imaged. A second adjusting means for separately providing an optical phase difference equivalent to when the sample is inclined with respect to the optical axis of the sample,
A plurality of phase shift interference image data obtained by each of the branch imaging mechanisms when a relative optical phase difference is separately provided between the reference light and the sample light by the first adjusting means; The plane undulation shape for each branch is calculated as numerical data by the phase shift method, and a first fixed optical phase difference is obtained from a relative difference between the numerical data at a temporally tentative corresponding point,
Next, an optical phase difference equivalent to when the surface to be measured is inclined with respect to the optical axis of the sample is separately given by the second adjusting means, and the reference light and the sample light are compared by the first adjusting means. When a relative optical phase difference is separately provided between the plurality of phase-shift interference image data obtained by the respective branch imaging mechanisms, the plane undulation shape for each branch is converted into numerical data by the phase shift method. Calculating a second fixed optical phase difference based on the relative difference of the numerical data at the provisional corresponding point,
Using the difference between the positional temporary corresponding point and the actually corresponding point calculated from the relationship between the first fixed optical phase difference and the second fixed optical phase, arbitrary positions in the inspection surface observation range are respectively determined. Wherein the position of the branch imaging mechanism is adjusted in a plane substantially orthogonal to the branch original beam so as to be at the same position in the branch observation coordinate system. How to adjust the imaging mechanism.

When adjusting the branch imaging mechanism in a plane substantially orthogonal to the branch original light flux so that a certain position of the inspection surface observation range becomes the same position in each of the branch observation coordinate systems, the first Using a difference between the positional corresponding point and an actually corresponding point calculated from the relationship between the fixed optical phase and the second fixed optical phase, and performing position coordinate conversion by software. Item 2. An adjustment method of a branch image pickup mechanism in the phase shift interference image simultaneous image pickup device according to Item 1.

The first adjusting means for separately providing a relatively uniform optical phase difference between the reference light and the sample light in a plane orthogonal to the sample optical axis, in the optical axis direction of the reference light A second stage that has a stage that can be moved in parallel and additionally provides an optical phase difference equivalent to that when the surface to be measured is tilted with respect to the optical axis of the sample; 3. The method for adjusting a branch imaging mechanism in a phase shift interferogram simultaneous imaging mechanism according to claim 1, further comprising a stage.

The first adjusting means for separately giving a relatively uniform optical phase difference in a plane orthogonal to the sample optical axis between the reference light and the sample light, the wavelength of the laser light source is slightly reduced. A second adjusting means for separately providing an optical phase difference equivalent to when the surface to be measured is tilted with respect to the optical axis of the sample, the stage having a tilt with respect to the optical axis of the sample. 3. The method for adjusting a branch imaging mechanism in a phase shift interferogram simultaneous imaging mechanism according to claim 1 or claim 2.