JP5199141B2

JP5199141B2 - Shape measuring device

Info

Publication number: JP5199141B2
Application number: JP2009021290A
Authority: JP
Inventors: 将人甘中; 英二高橋; 昌和梶田
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 2009-02-02
Filing date: 2009-02-02
Publication date: 2013-05-15
Anticipated expiration: 2029-02-02
Also published as: JP2010175499A

Description

本発明は，半導体ウェハ等の被測定物の厚みを光干渉法により非接触で測定する形状測定装置に関するものである。 The present invention relates to a shape measuring apparatus that measures the thickness of an object to be measured such as a semiconductor wafer in a non-contact manner by an optical interference method.

薄板状の半導体ウェハ（被測定物の一例，以下，ウェハという）の形状測定において，干渉計を用いた非接触型の形状測定装置が普及している。これは，２つに分岐された一方の光線を被測定物の表面に反射させた反射光である測定光と，もう一方の光線を所定の参照面に反射させた反射光である参照光とを含む干渉光を受光し，その干渉光により形成される干渉画像から被測定物の表面形状（表面高さの分布）を求めるものである。これにより，非接触でウェハの表面形状を測定できるので，触針式の形状計で測定する場合のように，ウェハ表面に傷等を生じさせることなくその表面形状を測定できる。ウェハの形状測定では，その表面全体に渡る形状を測定する必要があるため，一般に，ウェハ周辺のエッジ部を支持（通常は３点支持）した状態で測定がなされる。 In the shape measurement of a thin semiconductor wafer (an example of an object to be measured, hereinafter referred to as a wafer), a non-contact type shape measuring apparatus using an interferometer has become widespread. This is because measurement light that is reflected light that reflects one of the light beams branched into two on the surface of the object to be measured, and reference light that is reflected light that reflects the other light beam on a predetermined reference surface, and The surface shape (surface height distribution) of the object to be measured is obtained from the interference image formed by the interference light. As a result, the surface shape of the wafer can be measured in a non-contact manner, so that the surface shape can be measured without causing scratches or the like on the wafer surface as in the case of measuring with a stylus type shape meter. In the measurement of the shape of the wafer, it is necessary to measure the shape over the entire surface thereof, and therefore generally the measurement is performed with the edge portion around the wafer supported (usually, three points are supported).

ところで，ウェハのような薄板状（例えば，厚みが１ｍｍ未満）の被測定物をそのエッジ部のみで支持した場合，わずかな風圧や他の機械の振動等によってウェハが振動する。この振動は，非常に高い測定精度（例えば，誤差２０ｎｍ以下）が要求されるウェハの形状測定においては，無視できない振幅の振動となる。このようなウェハの振動を防止するため，特許文献１には，透明な剛体をウェハに近接して配置することにより，ウェハの振動を抑制する方法が示されている。しかし，この方法では，透明な剛体を光路に挿入することによって干渉光に乱れが生じるおそれがあるという問題点があった。
また，特許文献２には，周波数がわずかに異なる２種類の測定光を２分岐させて被測定物の表裏各面のヘテロダイン干渉計へ導き，表裏のヘテロダイン干渉計において物体光と参照光との関係を反対にして被測定物の厚みを測定する形状測定装置が示されている。
特許文献２に示される技術によれば，表裏のヘテロダイン干渉計の検出信号の差分をとることにより，振動によって生じる被測定物の変位の影響が除去され，被測定物の振動の影響を受けずに高精度な厚み測定が可能となる。
さらに，特許文献２には，表裏のヘテロダイン干渉計へ入射する直前の２種類の測定光の分岐光を干渉させ，その干渉光の強度信号を前記ヘテロダイン干渉計の検出信号に対する参照信号として用いることについて示されている。これにより，光源から２つのヘテロダイン干渉計へ至る光路において生じる２種類の測定光の位相の揺らぎに起因する測定誤差を解消することができる。 By the way, when a thin plate-like object to be measured such as a wafer (for example, a thickness of less than 1 mm) is supported only by its edge portion, the wafer vibrates due to slight wind pressure, vibration of other machines, or the like. This vibration is a vibration having a non-negligible amplitude in wafer shape measurement that requires very high measurement accuracy (for example, an error of 20 nm or less). In order to prevent such wafer vibration, Patent Document 1 discloses a method of suppressing wafer vibration by disposing a transparent rigid body close to the wafer. However, this method has a problem that interference light may be disturbed by inserting a transparent rigid body into the optical path.
In Patent Document 2, two types of measurement light having slightly different frequencies are branched into two and guided to the heterodyne interferometers on the front and back surfaces of the object to be measured. A shape measuring device for measuring the thickness of an object to be measured by reversing the relationship is shown.
According to the technique disclosed in Patent Document 2, by taking the difference between the detection signals of the front and back heterodyne interferometers, the influence of the displacement of the object to be measured caused by vibration is eliminated, and the influence of the vibration of the object to be measured is not affected. Highly accurate thickness measurement is possible.
Further, in Patent Document 2, two kinds of branched light beams of measurement light immediately before entering the front and back heterodyne interferometers are caused to interfere, and the intensity signal of the interference light is used as a reference signal for the detection signal of the heterodyne interferometer. Is shown about. As a result, it is possible to eliminate measurement errors caused by phase fluctuations of the two types of measurement light that occur in the optical path from the light source to the two heterodyne interferometers.

特開２００２−５６４０号公報JP 2002-5640 A 特開２００８−１８０７０８号公報JP 2008-180708 A

しかしながら，特許文献２に示される技術によっても，光源から２つのヘテロダイン干渉計へ至る光路で生じる２種類の測定光の位相の揺らぎが高速である場合には，位相検波の回路がその変化の速さに十分に追従できない。例えば，２種類の測定光が，光源から２つのヘテロダイン干渉計まで光ファイバにより伝送された場合，周囲の環境によって光ファイバが高速に振動し，２種類の測定光の位相が高速で揺らぐ場合がある。そうすると，特許文献２に示される技術において，前記参照信号を用いて２種類の測定光の位相の揺らぎを解消する処理が十分に機能しない。このように，特許文献２に示される技術によっても，２種類の測定光の位相の揺らぎに起因する測定誤差が十分に解消されない状況が生じ得るという問題点があった。
従って，本発明は上記事情に鑑みてなされたものであり，その目的とするところは，被測定物の振動及び光源から干渉計に至る測定光の伝送媒体の振動の影響を受けずに，被測定物の厚みを簡易に高精度で測定できる形状測定装置を提供することにある。 However, even with the technique disclosed in Patent Document 2, when the phase fluctuations of the two types of measurement light generated in the optical path from the light source to the two heterodyne interferometers are high-speed, the phase detection circuit changes the speed of the change. I can't follow it enough. For example, when two types of measurement light are transmitted from the light source to two heterodyne interferometers using an optical fiber, the optical fiber may vibrate at high speed depending on the surrounding environment, and the phase of the two types of measurement light may fluctuate at high speed. is there. Then, in the technique disclosed in Patent Document 2, the processing for eliminating the phase fluctuation of the two types of measurement light using the reference signal does not function sufficiently. As described above, even the technique disclosed in Patent Document 2 has a problem in that a measurement error caused by phase fluctuations of two types of measurement light may not be sufficiently eliminated.
Therefore, the present invention has been made in view of the above circumstances, and the object of the present invention is not to be affected by the vibration of the object to be measured and the vibration of the transmission medium of the measurement light from the light source to the interferometer. An object of the present invention is to provide a shape measuring apparatus that can easily and accurately measure the thickness of a measurement object.

上記目的を達成するために本発明に係る形状測定装置は，被測定物の表裏各面を走査してその被測定物の厚み分布を非接触で測定するために用いられる測定装置であり，次の（１）〜（１１）に示される各構成要素を備える。
（１）所定の光源から出射される基幹光を二分岐させる第１の光分岐手段。
（２）前記第１の光分岐手段による分岐光それぞれを前記被測定物の表裏各面の表裏相対する測定部位それぞれの方向へ導く導光手段。
（３）前記被測定物の表裏それぞれにおける前記測定部位の方向へ導かれた前記基幹光の分岐光それぞれをさらに二分岐させる第２の光分岐手段。
（４）前記被測定物の表裏それぞれにおける前記第２の光分岐手段による分岐光の一方又は両方に周波数変調を施してそれぞれ周波数の異なる２つの測定光を生成する光変調手段。
（５）前記被測定物の表裏それぞれにおいて，一方の前記測定光を前記測定部位に照射させ，その測定部位で反射した一方の前記測定光である物体光と他方の前記測定光である参照光とを干渉させる２つのヘテロダイン干渉計。
（６）前記被測定物の表裏それぞれにおいて，２つの前記測定光それぞれを前記ヘテロダイン干渉計に入力される主光とそれ以外の副光とに二分岐させる第３の光分岐手段。
（７）前記被測定物の表裏それぞれにおいて，前記第３の光分岐手段により分岐された２つの前記副光を干渉させる副光干渉手段。
（８）前記被測定物の表裏それぞれにおいて，前記第２の光分岐手段，前記光変調手段，前記ヘテロダイン干渉計，前記第３の光分岐手段及び前記副光干渉手段を含む測定光学系を一体に保持する測定光学系保持手段。
（９）２つの前記ヘテロダイン干渉計により得られる干渉光それぞれを受光してその強度信号を出力する測定用光強度検出手段。
（１０）前記被測定物の表裏それぞれにおいて，前記副光干渉手段により得られる干渉光を受光してその強度信号を出力する参照用光強度検出手段。
（１１）前記被測定物の表裏それぞれにおける前記測定用光強度検出手段の出力信号及び前記参照用光強度検出手段の出力信号からなる２つのビート信号の位相検波によりそれら２つのビート信号の位相差を検出する位相情報検出手段。 In order to achieve the above object, a shape measuring apparatus according to the present invention is a measuring apparatus used for scanning the front and back surfaces of a measured object and measuring the thickness distribution of the measured object in a non-contact manner. The components shown in (1) to (11) are provided.
(1) First light branching means for bifurcating basic light emitted from a predetermined light source.
(2) A light guiding means for guiding each of the branched lights by the first light branching means in the respective directions of the measurement parts facing each other on the front and back surfaces of the object to be measured.
(3) Second light branching means for further branching each branched light of the basic light guided in the direction of the measurement site on each of the front and back sides of the object to be measured.
(4) Light modulation means for performing frequency modulation on one or both of the branched lights by the second light branching means on the front and back of the object to be measured to generate two measurement lights having different frequencies.
(5) On each of the front and back sides of the object to be measured, one of the measurement light beams is irradiated onto the measurement site, and the object beam that is the one measurement beam reflected by the measurement site and the reference beam that is the other measurement beam Two heterodyne interferometers that interfere with each other.
(6) Third optical branching means for bifurcating each of the two measurement lights into main light input to the heterodyne interferometer and other auxiliary light on each of the front and back sides of the object to be measured.
(7) Sub-light interference means for causing the two sub-lights branched by the third light branch means to interfere with each other on the front and back sides of the object to be measured.
(8) The measurement optical system including the second optical branching unit, the optical modulation unit, the heterodyne interferometer, the third optical branching unit, and the auxiliary optical interference unit is integrated on each side of the object to be measured. Measuring optical system holding means for holding.
(9) Measuring light intensity detecting means for receiving each interference light obtained by the two heterodyne interferometers and outputting an intensity signal thereof.
(10) Reference light intensity detection means for receiving the interference light obtained by the auxiliary light interference means and outputting the intensity signal on each of the front and back sides of the object to be measured.
(11) The phase difference between the two beat signals by phase detection of the two beat signals composed of the output signal of the measurement light intensity detection means and the output signal of the reference light intensity detection means on the front and back sides of the object to be measured. Means for detecting phase information.

本発明に係る形状測定装置においては，周知のヘテロダイン干渉計の原理により，表裏の前記ヘテロダイン干渉計各々に対応する前記測定用光強度検出手段の検出信号（ビート信号）の位相は，前記被測定物の表裏相対する前記測定部位の高さに応じて定まる。
また，前記被測定物の表裏の前記測定部位各々について前記位相情報検出手段により検出される前記２つのビート信号の位相差は，前記ヘテロダイン干渉計から前記測定部位までの距離，即ち，前記測定部位の高さを表す。従って，前記被測定物の表裏各々についての前記位相情報検出手段の検出結果の差分から，前記被測定物の厚みの測定値を得ることができる。
さらに，本発明に係る形状測定装置においては，前記光源から出射される１つの前記基幹光に基づく分岐光が，前記被測定物の表裏各面の測定部位の近傍へ導かれた後に，前記光変調手段によって前記ヘテロダイン干渉計に入力される２種類の測定光へ変換される。そのため，前記光源から表裏の前記ヘテロダイン干渉計に至る前記分岐光の光路において，２種類の測定光の位相の揺らぎは発生し得ない。
また，前記光変調手段により生成される２種類の測定光を伝送する前記測定光学系が，前記被測定物の表裏において一体に保持される。そのため，前記測定光学系において生じ得る２種類の測定光の位相の揺らぎは，ごく小さく抑制される。
また，以上のようにして得られる前記被測定物の厚みの測定値は，前記被測定物の振動による変位量の成分が前記被測定物の表裏両側について相殺された測定値となる。従って，本発明に係る形状測定装置は，前記被測定物の振動の影響を受けずに前記被測定物の厚みを測定できる。
また，前記測定光学系において，２種類の前記測定光に多少の位相の揺らぎが生じた場合でも，その位相の揺らぎは，前記２つのビート信号各々においてほぼ同等に生じる。そのため，２種類の前記測定光に多少の位相の揺らぎが生じた場合でも，その位相の揺らぎは前記２つのビート信号の位相差にはほとんど反映されない。
従って，本発明に係る形状測定装置は，非常に高精度での形状測定が可能となる。 In the shape measuring apparatus according to the present invention, the phase of the detection signal (beat signal) of the measurement light intensity detecting means corresponding to each of the front and back heterodyne interferometers is determined according to the principle of a known heterodyne interferometer. It is determined according to the height of the measurement part opposite to the front and back of the object.
The phase difference between the two beat signals detected by the phase information detection means for each of the measurement sites on the front and back sides of the object to be measured is the distance from the heterodyne interferometer to the measurement site, that is, the measurement site. Represents the height of. Therefore, the measured value of the thickness of the object to be measured can be obtained from the difference between the detection results of the phase information detecting means for the front and back of the object to be measured.
Further, in the shape measuring apparatus according to the present invention, after the branched light based on the one basic light emitted from the light source is guided to the vicinity of the measurement site on each of the front and back surfaces of the object to be measured, the light The light is converted into two types of measurement light input to the heterodyne interferometer by the modulation means. Therefore, in the optical path of the branched light from the light source to the heterodyne interferometers on the front and back, two types of phase fluctuations of the measurement light cannot occur.
Further, the measurement optical system for transmitting two kinds of measurement light generated by the light modulation means is integrally held on the front and back of the object to be measured. Therefore, the phase fluctuation of the two types of measurement light that can occur in the measurement optical system is suppressed to a very small level.
Further, the measured value of the thickness of the measurement object obtained as described above is a measurement value in which the displacement component due to the vibration of the measurement object is canceled on both the front and back sides of the measurement object. Therefore, the shape measuring apparatus according to the present invention can measure the thickness of the measurement object without being affected by the vibration of the measurement object.
In the measurement optical system, even if some phase fluctuations occur in the two types of measurement light, the phase fluctuations occur approximately equally in each of the two beat signals. For this reason, even if some phase fluctuation occurs in the two types of measurement light, the phase fluctuation is hardly reflected in the phase difference between the two beat signals.
Therefore, the shape measuring apparatus according to the present invention can measure the shape with very high accuracy.

また，本発明に係る形状測定装置において，前記測定光学系保持手段が，表裏各々において前記測定光学系を分担して保持する板状の保持部を有する剛体であり，前記板状の保持部に前記測定光学系を伝播する光を通過させる貫通孔が形成されたものであれば好適である。この場合，前記測定光学系保持手段は，前記測定光学系を，前記板状の保持部の両側に渡って三次元的に保持する。
これにより，前記測定光学系を保持する前記板状の保持部を小さくでき，その小さな板状の保持部は，比較的薄い軽量な部材が採用されても，十分な剛性を確保できる。そのため，小型でごく簡易な構造の前記測定光学系保持手段により，前記板状の保持部の変形（撓み）に起因する２種類の前記測定光の位相のずれの発生を防止できる。例えば，前記板状の保持部は，その縁部が他の部材に固定されることによって補強された部材であることが考えられる。
ところで，装置をコンパクト化するために前記測定用光強度検出手段から前記位相検波手段に至るまでの信号伝送経路と，前記参照用光強度検出手段から前記位相検波手段に至るまでの信号伝送経路とを近接させると，一方のビート信号の伝送経路から発生する電磁波の不要輻射が他方のビート信号に対するノイズとなり，測定精度を悪化させる。
そこで，本発明に係る形状測定装置が，さらに次の（１２）に示される構成要素を備えればより一層好適である。
（１２）前記測定用光強度検出手段から前記位相情報検出手段に至るまでの信号伝送経路と前記参照用光強度検出手段から前記位相情報検出手段に至るまでの信号伝送経路との間に配置された金属製のシールド板。
これにより，前記不要輻射による測定精度の悪化を防止できる。 Further, in the shape measuring apparatus according to the present invention, the measurement optical system holding means is a rigid body having a plate-like holding portion that shares and holds the measurement optical system on each of the front and back sides, and the plate-like holding portion includes It is suitable if a through-hole through which light propagating through the measurement optical system passes is formed. In this case, the measurement optical system holding means holds the measurement optical system in a three-dimensional manner across both sides of the plate-like holding unit.
Thereby, the plate-like holding portion for holding the measurement optical system can be made small, and the small plate-like holding portion can ensure sufficient rigidity even when a relatively thin and lightweight member is employed. Therefore, the measurement optical system holding means having a small and very simple structure can prevent the occurrence of a phase shift of the two types of measurement light due to deformation (deflection) of the plate-like holding part. For example, the plate-like holding portion may be a member reinforced by fixing its edge to another member.
By the way, in order to make the apparatus compact, a signal transmission path from the measurement light intensity detection means to the phase detection means, a signal transmission path from the reference light intensity detection means to the phase detection means, If they are placed close to each other, unnecessary radiation of electromagnetic waves generated from the transmission path of one beat signal becomes noise with respect to the other beat signal, thereby degrading measurement accuracy.
Therefore, it is more preferable that the shape measuring apparatus according to the present invention further includes the constituent element shown in the following (12).
(12) Arranged between a signal transmission path from the measurement light intensity detection means to the phase information detection means and a signal transmission path from the reference light intensity detection means to the phase information detection means. Metal shield plate.
Thereby, the deterioration of the measurement accuracy due to the unnecessary radiation can be prevented.

本発明に係る形状測定装置によれば，被測定物の振動及び光源から干渉計に至る測定光の伝送媒体の振動の影響を受けずに，被測定物の厚みを簡易に高精度で測定できる。 According to the shape measuring apparatus according to the present invention, the thickness of the object to be measured can be easily and accurately measured without being affected by the vibration of the object to be measured and the vibration of the transmission medium of the measurement light from the light source to the interferometer. .

本発明の実施形態に係る形状測定装置Ｘの構成図。The block diagram of the shape measuring apparatus X which concerns on embodiment of this invention. 形状測定装置Ｘが備える測定光学ユニットＺの一例の概略構成図。The schematic block diagram of an example of the measurement optical unit Z with which the shape measuring apparatus X is provided. 形状測定装置Ｘを用いた被測定物の厚み分布測定方法の一例を表す模式図。The schematic diagram showing an example of the thickness distribution measuring method of the to-be-measured object using the shape measuring apparatus X. FIG. 形状測定装置Ｘを用いて被測定物の厚み分布測定を行う場合の測定部位の軌跡の一例を表す模式図。The schematic diagram showing an example of the locus | trajectory of the measurement site | part in the case of measuring the thickness distribution of a to-be-measured object using the shape measuring apparatus X. FIG. 従来の形状測定装置の測定値の時系列変化の一例を表すグラフ。The graph showing an example of the time-sequential change of the measured value of the conventional shape measuring apparatus. 形状測定装置Ｘの測定値の時系列変化の一例を表すグラフ。The graph showing an example of the time-sequential change of the measured value of the shape measuring apparatus X.

以下添付図面を参照しながら，本発明の実施の形態について説明し，本発明の理解に供する。尚，以下の実施の形態は，本発明を具体化した一例であって，本発明の技術的範囲を限定する性格のものではない。 Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.

以下，図１に示される構成図を参照しながら，本発明の実施形態に係る形状測定装置Ｘについて説明する。
形状測定装置Ｘは，例えば半導体ウェハなどの薄板状の被測定物１の厚みを非接触で測定するために用いられる測定装置である。
図１に示されるように，形状測定装置Ｘは，光源ユニットＹと，被測定物１の表裏各面に対向配置される２つの測定光学ユニットＺと，その測定光学ユニットＺごとに設けられる２つの位相検波回路Ｗと，計算機６とを備えている。
以下，便宜上，被測定物１の一方の面（図１における上側の面）をＡ面，これと表裏の関係にある他方の面をＢ面という。また，被測定物１の厚みの測定位置におけるＡ面側の表面部分をＡ面測定部位１ａ，そのＡ面測定部位１ａと表裏相対するＢ面の表面部分をＢ面測定部位１ｂという。また，前記Ａ面に対向配置された前記測定光学ユニットＺをＡ面側測定光学ユニットａＺ，前記Ｂ面に対向配置された前記測定光学ユニットＺをＢ面側測定光学ユニットｂＺと称する。また，Ａ面側測定光学ユニットａＺに対して設けられた前記位相検波回路ＷをＡ面側位相検波回路ａＷ，Ｂ面側測定光学ユニットｂＺに対して設けられた前記位相検波回路ＷをＢ面側位相検波回路ｂＷと称する。
なお，図１には示されていないが，形状測定装置Ｘは，被測定物１の周辺のエッジ部を支持（例えば３点支持）する支持部と，その支持部を２次元方向（被測定物１の両測定面に平行な２次元方向）に移動させることにより被測定物１を２次元方向に移動させる移動機構とを備えている。そして，形状測定装置Ｘは，その移動機構により被測定物１を移動させることにより，被測定物１における前記Ａ面測定部位１ａ及び前記Ｂ面測定部位１ｂの位置を変更しつつ測定値を得る。 Hereinafter, the shape measuring apparatus X according to the embodiment of the present invention will be described with reference to the configuration diagram shown in FIG.
The shape measuring device X is a measuring device used to measure the thickness of a thin plate-like object 1 such as a semiconductor wafer without contact.
As shown in FIG. 1, the shape measuring device X includes a light source unit Y, two measuring optical units Z disposed opposite to the front and back surfaces of the DUT 1, and 2 provided for each measuring optical unit Z. Two phase detection circuits W and a computer 6 are provided.
Hereinafter, for the sake of convenience, one surface (the upper surface in FIG. 1) of the DUT 1 is referred to as the A surface, and the other surface having the front and back relationship is referred to as the B surface. Further, the surface portion on the A surface side at the measurement position of the thickness of the DUT 1 is referred to as an A surface measurement site 1a, and the surface portion of the B surface facing the A surface measurement region 1a is referred to as a B surface measurement region 1b. Further, the measurement optical unit Z disposed to face the A surface is referred to as an A surface side measurement optical unit aZ, and the measurement optical unit Z disposed to face the B surface is referred to as a B surface side measurement optical unit bZ. Further, the phase detection circuit W provided for the A-plane side measurement optical unit aZ is used as the A-plane-side phase detection circuit aW, and the phase detection circuit W provided for the B-plane measurement optical unit bZ is used as the B-plane. This is referred to as a side phase detection circuit bW.
Although not shown in FIG. 1, the shape measuring apparatus X supports a peripheral portion of the object to be measured 1 (for example, three-point support), and the support portion in a two-dimensional direction (measured object). A moving mechanism for moving the object to be measured 1 in a two-dimensional direction by moving the object 1 in a two-dimensional direction parallel to both measurement surfaces of the object 1. Then, the shape measuring apparatus X obtains measurement values while changing the positions of the A-surface measurement site 1a and the B-surface measurement site 1b in the measurement object 1 by moving the device 1 by the moving mechanism. .

前記光源ユニットＹは，所定の可干渉光であるビーム光Ｐ０を出射する単波長レーザ光源２と，アイソレータ２ｘと，無偏光のビームスプリッタ３と，２つの波長板２ｙと，２つの光ファイバ接続端子１１とを備えている。
前記単波長レーザ光源２は，周波数ω0の単波長レーザ光を出力するレーザ光源である。例えば，前記短波長レーザ光源２として，波長６３３ｎｍのレーザ光を出力するヘリウムネオンレーザ等を採用することが考えられる。以下，便宜上，前記短波長レーザ光源２の出射光を基幹光Ｐ０と称する。
前記ビームスプリッタ３は，前記単波長レーザ光源２から出射される前記基幹光Ｐ０を二分岐させる前記第１の光分岐手段の一例である。 The light source unit Y includes a single-wavelength laser light source 2 that emits beam light P0 that is predetermined coherent light, an isolator 2x, a non-polarized beam splitter 3, two wavelength plates 2y, and two optical fiber connections. And a terminal 11.
The single wavelength laser light source 2 is a laser light source that outputs a single wavelength laser beam having a frequency ω0. For example, as the short-wavelength laser light source 2, a helium neon laser that outputs laser light having a wavelength of 633 nm may be employed. Hereinafter, for the sake of convenience, the light emitted from the short-wavelength laser light source 2 is referred to as basic light P0.
The beam splitter 3 is an example of the first light branching unit that splits the basic light P0 emitted from the single wavelength laser light source 2 into two.

また，前記形状測定装置Ｘは，前記ビームスプリッタ３による分岐光それぞれを前記被測定物１における前記Ａ面側測定部位１ａ及び前記Ｂ面側測定部位１ｂそれぞれの方向へ導く入力側の光ファイバａ１０，ｂ１０を備えている。より具体的には，一方の前記光ファイバａ１０は，前記分岐光の一方を前記被測定物１のＡ面に対向配置された前記Ａ面側測定光学ユニットａＺまで導光する。また，他方の前記光ファイバｂ１０は，前記分岐光の他方を前記被測定物１のＢ面に対向配置された前記Ｂ面側測定光学ユニットｂＺまで導光する。
前記光ファイバａ１０，ｂ１０はシングルモードの光ファイバである。これにより，前記光ファイバａ１０，ｂ１０により伝送される前記分岐光の偏波面が，途中で乱れないよう一定に維持される。
なお，前記光ファイバａ１０，ｂ１０に代えて，ミラー等の導光手段が設けられることも考えられる。但し，その場合，前記基幹光Ｐ０の分岐光の光路調整に手間を要する。 Further, the shape measuring apparatus X has an input-side optical fiber a10 that guides each of the branched lights from the beam splitter 3 in the directions of the A-side measurement site 1a and the B-side measurement site 1b of the DUT 1, respectively. , B10. More specifically, one of the optical fibers a10 guides one of the branched lights to the A-side measurement optical unit aZ that is disposed to face the A-side of the DUT 1. The other optical fiber b10 guides the other of the branched lights to the B-side measurement optical unit bZ arranged to face the B-side of the DUT 1.
The optical fibers a10 and b10 are single mode optical fibers. Thereby, the polarization plane of the branched light transmitted through the optical fibers a10 and b10 is kept constant so as not to be disturbed in the middle.
Note that light guiding means such as a mirror may be provided instead of the optical fibers a10 and b10. However, in this case, it takes time to adjust the optical path of the branched light of the basic light P0.

前記光ファイバ接続端子１１は，前記光ファイバａ１０，ｂ１０それぞれの一端が接続される端子である。
また，前記波長板２ｙは，前記ビームスプリッタ３と前記光ファイバａ１０，ｂ１０の光の導入口との間に配置され，前記光ファイバａ１０，ｂ１０に入力される前記分岐光の偏波面（偏波方向）を調整する光学素子である。
また，前記アイソレータ２ｘは，前記単波長レーザ光源２と前記ビームスプリッタ３との間に配置され，前記ビームスプリッタ３や前記光ファイバａ１０，ｂ１０の入口等からの反射光が前記単波長レーザ光源２に戻ることを防止する光学素子である。前記アイソレータ２ｘにより，前記単波長レーザ光源２に前記反射光が戻って前記単波長レーザ光源２の出射光が不安定になることを防止できる。 The optical fiber connection terminal 11 is a terminal to which one end of each of the optical fibers a10 and b10 is connected.
The wave plate 2y is disposed between the beam splitter 3 and the light inlets of the optical fibers a10 and b10, and the polarization plane (polarized wave) of the branched light input to the optical fibers a10 and b10. Direction).
The isolator 2x is disposed between the single-wavelength laser light source 2 and the beam splitter 3, and reflected light from the beam splitter 3, entrances of the optical fibers a10 and b10, and the like. It is an optical element which prevents returning to (1). The isolator 2x can prevent the reflected light from returning to the single wavelength laser light source 2 and the light emitted from the single wavelength laser light source 2 from becoming unstable.

また，図１に示されるように，前記測定光学ユニットＺは，入力側の光ファイバ接続端子１２と，一次側の無偏光のビームスプリッタ１３と，２つの音響光学素子１５，１６と，ヘテロダイン干渉計２０と，参照用干渉計３０と，出力側の２つの光ファイバ接続端子２６，３６とを備えている。
前記光ファイバ接続端子１２は，前記光源ユニットＹと接続される前記光ファイバａ１０，ｂ１０の一端が接続される端子である。前記光ファイバ接続端子１２を通じて，前記光源ユニットＹにおける前記基幹光Ｐ０の分岐光が前記測定光学ユニットＺに導入される。 As shown in FIG. 1, the measurement optical unit Z includes an optical fiber connection terminal 12 on the input side, a non-polarized beam splitter 13 on the primary side, two acoustooptic elements 15 and 16, and heterodyne interference. A total of 20, a reference interferometer 30, and two optical fiber connection terminals 26 and 36 on the output side are provided.
The optical fiber connection terminal 12 is a terminal to which one end of the optical fibers a10 and b10 connected to the light source unit Y is connected. The branched light of the basic light P0 in the light source unit Y is introduced into the measurement optical unit Z through the optical fiber connection terminal 12.

前記ビームスプリッタ１３は，前記光ファイバａ１０，ｂ１０によって前記被測定物１の表裏それぞれにおける前記測定部位１ａ，１ｂの方向へ導かれた前記基幹光Ｐ０の分岐光それぞれをさらに二分岐させる前記第２の光分岐手段の一例である。
また，前記音響光学素子１５，１６は，前記被測定物１の表裏それぞれにおける前記ビームスプリッタ１３による分岐光の各々に周波数変調を施してそれぞれ周波数の異なる２つの測定光Ｐ１，Ｐ２を生成する光変調手段の一例である。
例えば，２つの前記音響光学素子１５，１６の一方の変調周波数が８０ＭＨｚ，他方の変調周波数が８１ＭＨｚ程度であることが考えられる。
２種類の前記測定光Ｐ１，Ｐ２は，それぞれ単波長のビーム光である。前記測定光Ｐ１，Ｐ２それぞれの周波数（ω，ω＋Δω）は，特に限定されるものではないが，例えば，両ビーム光の周波数の差Δωは数十ｋＨｚ乃至数メガＨｚ程度である。 The beam splitter 13 further splits the branched light of the basic light P0 guided in the direction of the measurement sites 1a and 1b on the front and back surfaces of the device under test 1 by the optical fibers a10 and b10, respectively. It is an example of the optical branching means.
The acousto-optic elements 15 and 16 are light that generates two measurement lights P1 and P2 having different frequencies by frequency-modulating each of the branched lights by the beam splitter 13 on the front and back sides of the device under test 1, respectively. It is an example of a modulation | alteration means.
For example, it is conceivable that one of the two acoustooptic elements 15 and 16 has a modulation frequency of 80 MHz and the other modulation frequency is about 81 MHz.
The two types of measurement lights P1 and P2 are single wavelength beam lights, respectively. The frequencies (ω, ω + Δω) of the measurement lights P1 and P2 are not particularly limited. For example, the frequency difference Δω between the two light beams is about several tens of kHz to several megaHz.

また，前記ヘテロダイン干渉計２０は，前記被測定物１の表裏それぞれにおいて，一方の前記測定光Ｐ１を前記測定部位１ａ又は１ｂに照射させ，その測定部位で反射した前記測定光Ｐ１である物体光と，他方の前記測定光Ｐ２である参照光とを干渉させる干渉計である。前記ヘテロダイン干渉計２０は，２つの前記測定光学ユニットＺそれぞれに１つずつ設けられている。
前記ヘテロダイン干渉計２０は，図１に示されるように，偏光ビームスプリッタ２１と，四分の一波長板２２と，無偏光のビームスプリッタ２４と，偏光板２５とを備えている。
前記偏光ビームスプリッタ２１は，一方の前記測定光Ｐ１を前記測定部位１ａ又は１ｂの方向へ通過させるとともに，前記測定部位１ａ又は１ｂで反射した前記測定光Ｐ１である物体光を所定の方向へ反射する。
前記四分の一波長板２２は，前記偏光ビームスプリッタ２１と前記測定部位１ａ又は１ｂとの間に配置されている。この四分の一波長板２２の存在により，前記偏光ビームスプリッタ２１から前記測定部位１ａ又は１ｂへ向かう前記測定光Ｐ１の偏光の状態（Ｐ偏光かＳ偏光か）と，前記測定部位１ａ又は１ｂに反射して前記偏光ビームスプリッタ２１に入射する前記測定光Ｐ１である物体光の偏光の状態とが入れ替わる。
また，前記測定光学ユニットＺは，前記被測定物１の表面に対向配置された集光レンズ２３も備えている。この集光レンズ２３は，前記測定光Ｐ１を前記測定部位１ａ又は１ｂに集光させるとともに，前記測定部位１ａ又は１ｂで反射した物体光を往路の光軸に沿って前記偏光ビームスプリッタ２１へ入射させる。
前記ビームスプリッタ２４は，一方の前記測定光Ｐ１の前記測定部位１ａ又は１ｂでの反射光である物体光と，他方の前記測定光Ｐ２である参照光との光軸を一致させて同一方向へ導く光学素子である。
また，前記偏光板２５は，前記ビームスプリッタ２４により光軸が一致した前記物体光及び前記参照光を入力し，それらの同一方向の偏光成分を抽出することによって前記物体光及び前記参照光の干渉光Ｐｓを出力する光学素子である。
以下，前記ヘテロダイン干渉計２０により得られる前記物体光及び前記参照光の干渉光Ｐｓのことを測定干渉光Ｐｓと称する。
なお，前記ヘテロダイン干渉計２０には，必要に応じて，２つの前記測定光Ｐ１，Ｐ２の一方又は両方の光路を変向させるミラー等の変向素子も設けられる。 Further, the heterodyne interferometer 20 irradiates the measurement site 1a or 1b with one measurement beam P1 on each of the front and back sides of the object 1 to be measured, and the object beam that is the measurement beam P1 reflected at the measurement site. And an interferometer that interferes with the reference light that is the other measurement light P2. One heterodyne interferometer 20 is provided for each of the two measurement optical units Z.
As shown in FIG. 1, the heterodyne interferometer 20 includes a polarizing beam splitter 21, a quarter-wave plate 22, a non-polarizing beam splitter 24, and a polarizing plate 25.
The polarization beam splitter 21 passes one measurement light P1 in the direction of the measurement site 1a or 1b and reflects the object light that is the measurement light P1 reflected by the measurement site 1a or 1b in a predetermined direction. To do.
The quarter-wave plate 22 is disposed between the polarization beam splitter 21 and the measurement site 1a or 1b. Due to the presence of the quarter-wave plate 22, the polarization state of the measurement light P1 (P-polarized light or S-polarized light) from the polarization beam splitter 21 toward the measurement site 1a or 1b, and the measurement site 1a or 1b The state of polarization of the object light, which is the measurement light P <b> 1 that is reflected by and reflected on the polarization beam splitter 21, is switched.
The measurement optical unit Z also includes a condensing lens 23 that is disposed opposite to the surface of the device under test 1. The condensing lens 23 condenses the measurement light P1 on the measurement site 1a or 1b and makes the object light reflected by the measurement site 1a or 1b enter the polarization beam splitter 21 along the optical axis of the forward path. Let
The beam splitter 24 aligns the optical axes of the object light that is the reflected light of the one measurement light P1 at the measurement site 1a or 1b and the reference light that is the other measurement light P2 in the same direction. The optical element to guide.
Further, the polarizing plate 25 receives the object light and the reference light whose optical axes coincide with each other by the beam splitter 24, and extracts the polarization components in the same direction, thereby interference between the object light and the reference light. It is an optical element that outputs light Ps.
Hereinafter, the interference light Ps of the object light and the reference light obtained by the heterodyne interferometer 20 is referred to as measurement interference light Ps.
The heterodyne interferometer 20 is also provided with a deflecting element such as a mirror for redirecting one or both of the two measurement beams P1 and P2 as necessary.

また，前記参照用干渉計３０は，前記被測定物１の表裏それぞれにおいて，２つの前記測定光Ｐ１，Ｐ２それぞれを前記ヘテロダイン干渉計２０に入力される主光とそれ以外の副光とに二分岐させるとともに，それら２つの前記副光を干渉させる干渉計である。
前記参照用干渉計３０は，図１に示されるように，３つの無偏光のビームスプリッタ３１，３２，３４と，偏光板３５とを備えている。
前記ビームスプリッタ３１，３２は，前記被測定物の表裏それぞれにおいて，２つの前記測定光Ｐ１，Ｐ２それぞれを前記ヘテロダイン干渉計２０に入力される主光とそれ以外の副光とに二分岐させる第３の光分岐手段の一例である。
また，前記ビームスプリッタ３４は，前記ビームスプリッタ３１，３２による２つの前記測定光Ｐ１，Ｐ２の分岐光である２つの前記副光の光軸を一致させて同一方向へ導く光学素子である。
前記偏光板３５は，前記ビームスプリッタ３４により光軸が一致した２つの前記副光を入力し，それらの同一方向の偏光成分を抽出することによって２つの前記副光の干渉光Ｐｒを出力する光学素子である。
前記ビームスプリッタ３４及び前記偏光板３５が，前記被測定物１の表裏それぞれにおいて２つの前記副光を干渉させる副光干渉手段の一例である。
以下，前記参照用干渉計３０により得られる２つの前記副光の干渉光Ｐｒのことを参照干渉光Ｐｒと称する。
なお，前記参照用干渉計３０には，必要に応じて，２つの前記副光の一方又は両方の光路を変向させるミラー等の光学素子も設けられている。図１に示される前記参照用干渉計３０は，前記測定光Ｐ２の分岐光を変向させるミラー３３を備えている。 In addition, the reference interferometer 30 converts the two measurement lights P1 and P2 into the main light input to the heterodyne interferometer 20 and the other auxiliary light on the front and back sides of the device under test 1, respectively. It is an interferometer that causes the two auxiliary lights to interfere while branching.
As shown in FIG. 1, the reference interferometer 30 includes three non-polarized beam splitters 31, 32, and 34 and a polarizing plate 35.
The beam splitters 31 and 32 split the two measurement lights P1 and P2 into the main light input to the heterodyne interferometer 20 and the other auxiliary light on the front and back sides of the object to be measured, respectively. 3 is an example of a third optical branching unit.
The beam splitter 34 is an optical element that matches the optical axes of the two sub-lights that are branched lights of the two measurement lights P1 and P2 by the beam splitters 31 and 32 and guides them in the same direction.
The polarizing plate 35 receives the two sub-lights whose optical axes coincide with each other by the beam splitter 34, and outputs the interference light Pr of the two sub-lights by extracting the polarization components in the same direction. It is an element.
The beam splitter 34 and the polarizing plate 35 are an example of a secondary light interference unit that causes the secondary light to interfere with each other on the front and back of the DUT 1.
Hereinafter, the two interference lights Pr of the secondary light obtained by the reference interferometer 30 will be referred to as reference interference lights Pr.
Note that the reference interferometer 30 is also provided with an optical element such as a mirror for changing the optical path of one or both of the two sub-lights as necessary. The reference interferometer 30 shown in FIG. 1 includes a mirror 33 that redirects the branched light of the measurement light P2.

出力側の一方の前記光ファイバ接続端子２６は，前記測定干渉光Ｐｓを後述する測定用光検出器ｂ２８へ伝送するための光ファイバａ２７又はｂ２７の一端が接続される端子である。なお，一方の前記光ファイバａ２７は，前記被測定物１のＡ面側における前記測定干渉光Ｐｓを伝送するものであり，他方の前記光ファイバｂ２７は，前記被測定物１のＢ面側における前記測定干渉光Ｐｓを伝送するものである。
また，出力側の他方の前記光ファイバ接続端子３６は，前記参照干渉光Ｐｒを後述する参照用光検出器ｂ３８へ伝送するための光ファイバａ３７又はｂ３７の一端が接続される端子である。なお，一方の前記光ファイバａ３７は，前記被測定物１のＡ面側における前記参照干渉光Ｐｒを伝送するものであり，他方の前記光ファイバｂ３７は，前記被測定物１のＢ面側における前記参照干渉光Ｐｒを伝送するものである。
前記測定干渉光Ｐｓ及び前記参照干渉光Ｐｒは，その伝送経路において特に波面の保持の必要がないため，出力側の前記光ファイバａ２７，ａ３７，ｂ２７，ｂ３７は，一般的なマルチモードの光ファイバが採用される。ここで，前記光ファイバａ２７，ａ３７，ｂ２７，ｂ３７としてシングルモードの光ファイバが採用されてもよい。
一般に，マルチモードの光ファイバは，シングルモードの光ファイバよりもファイバのコア径が大きく，伝播光の光軸調整が容易であるとともに，より大きな光量の光を伝播できる。そのため，光軸調整及び伝播光の光量の優位性の面から，出力側の前記光ファイバａ２７，ａ３７，ｂ２７，ｂ３７としてマルチモードの光ファイバを用いることが好適である。 One optical fiber connection terminal 26 on the output side is a terminal to which one end of an optical fiber a27 or b27 for transmitting the measurement interference light Ps to a measurement photodetector b28 described later is connected. One optical fiber a27 transmits the measurement interference light Ps on the A surface side of the DUT 1, and the other optical fiber b27 is on the B surface side of the DUT 1. The measurement interference light Ps is transmitted.
The other optical fiber connection terminal 36 on the output side is a terminal to which one end of an optical fiber a37 or b37 for transmitting the reference interference light Pr to a reference photodetector b38 to be described later is connected. One optical fiber a37 transmits the reference interference light Pr on the A surface side of the DUT 1, and the other optical fiber b37 is provided on the B surface side of the DUT 1. The reference interference light Pr is transmitted.
Since the measurement interference light Ps and the reference interference light Pr do not need to hold a wavefront in the transmission path, the optical fibers a27, a37, b27, and b37 on the output side are general multimode optical fibers. Is adopted. Here, single-mode optical fibers may be employed as the optical fibers a27, a37, b27, and b37.
In general, a multi-mode optical fiber has a fiber core diameter larger than that of a single-mode optical fiber, can easily adjust the optical axis of propagating light, and can propagate a larger amount of light. Therefore, it is preferable to use a multimode optical fiber as the optical fibers a27, a37, b27, and b37 on the output side from the viewpoint of optical axis adjustment and the superiority of the amount of propagating light.

また，前記位相検波回路Ｗは，図１に示されるように，測定用光検出器２８，参照用光検出器３８，測定系及び参照系それぞれの信号増幅用のアンプ２９，３９，位相検波器４及びシールド板８を備えている。
前記測定用光検出器２８は，前記ヘテロダイン干渉計２０により得られる前記測定干渉光Ｐｓを受光してその強度信号Ｓｉｇ１又はＳｉｇ２を出力する光電変換素子である。なお，前記強度信号Ｓｉｇ１は，前記被測定物１のＡ面側において得られた信号，前記強度信号Ｓｉｇ２は，前記被測定物１のＢ面側において得られた信号である。
以下，前記強度信号Ｓｉｇ１，Ｓｉｇ２のことを，測定ビート信号Ｓｉｇ１，Ｓｉｇ２と称する。
また，前記参照用光検出器３８は，前記参照用干渉計３０により得られる前記参照干渉光Ｐｒを受光してその強度信号Ｒｅｆ１又はＲｅｆ２を出力する光電変換素子である。なお，前記強度信号Ｒｅｆ１は，前記被測定物１のＡ面側において得られた信号，前記強度信号Ｒｅｆ２は，前記被測定物１のＢ面側において得られた信号である。
以下，前記強度信号Ｒｅｆ１，Ｒｅｆ２のことを，参照ビート信号Ｒｅｆ１，Ｒｅｆ２と称する。 As shown in FIG. 1, the phase detection circuit W includes a measurement photodetector 28, a reference photodetector 38, amplifiers 29 and 39 for signal amplification of the measurement system and the reference system, and a phase detector. 4 and a shield plate 8.
The measurement photodetector 28 is a photoelectric conversion element that receives the measurement interference light Ps obtained by the heterodyne interferometer 20 and outputs the intensity signal Sig1 or Sig2. The intensity signal Sig1 is a signal obtained on the A plane side of the device under test 1, and the intensity signal Sig2 is a signal obtained on the B surface side of the device under test 1.
Hereinafter, the intensity signals Sig1 and Sig2 are referred to as measurement beat signals Sig1 and Sig2.
The reference photodetector 38 is a photoelectric conversion element that receives the reference interference light Pr obtained by the reference interferometer 30 and outputs the intensity signal Ref1 or Ref2. The intensity signal Ref1 is a signal obtained on the A surface side of the device under test 1, and the intensity signal Ref2 is a signal obtained on the B surface side of the device under test 1.
Hereinafter, the intensity signals Ref1 and Ref2 are referred to as reference beat signals Ref1 and Ref2.

前記位相検波器４は，前記測定用光検出器２８の出力信号である前記測定ビート信号Ｓｉｇ１又はＳｉｇ２と，前記参照用光検出器３８の出力信号である前記参照ビート信号Ｒｅｆ１又はＲｅｆ２とからなる２つのビート信号の位相検波を行うことにより，その２つのビート信号の位相差ΔΦ１又はΔΦ２を検出する電子部品である。即ち，前記Ａ面側位相検波回路ａＷにおける前記位相検波器４は，前記測定ビート信号Ｓｉｇ１と前記参照ビート信号Ｒｅｆ１との間の位相差ΔΦ１を検出する。また，前記Ｂ面側位相検波回路ｂＷにおける前記位相検波器４は，前記測定ビート信号Ｓｉｇ２と前記参照ビート信号Ｒｅｆ２との間の位相差ΔΦ２を検出する。
前記被測定物１の表裏それぞれについて得られた前記２つのビート信号の位相差の差分（ΔΦ１−ΔΦ２）は，前記被測定物１の厚みを表す測定値となる。
また，Ａ面側及びＢ面側の２つの前記位相検波器４は，前記計算機６から出力される同期信号に同期して２つのビート信号の位相検波を同時に行う。これにより，前記２つのビート信号の位相差の差分（ΔΦ１−ΔΦ２）は，前記被測定物１の振動の影響を受けることなく，前記被測定物１の厚みを表す。
前記位相検波器４は，例えば，ロックインアンプ等を採用できる。
なお，前記位相検波器４が，前記位相情報検出手段の一例である。 The phase detector 4 includes the measurement beat signal Sig1 or Sig2 that is an output signal of the measurement photodetector 28 and the reference beat signal Ref1 or Ref2 that is an output signal of the reference photodetector 38. The electronic component detects the phase difference ΔΦ1 or ΔΦ2 between the two beat signals by performing phase detection of the two beat signals. That is, the phase detector 4 in the phase A side phase detection circuit aW detects a phase difference ΔΦ1 between the measurement beat signal Sig1 and the reference beat signal Ref1. In addition, the phase detector 4 in the B-side phase detection circuit bW detects a phase difference ΔΦ2 between the measurement beat signal Sig2 and the reference beat signal Ref2.
The difference (ΔΦ1−ΔΦ2) of the phase difference between the two beat signals obtained for each of the front and back surfaces of the device under test 1 is a measurement value representing the thickness of the device under test 1.
The two phase detectors 4 on the A plane side and the B plane side simultaneously perform phase detection of the two beat signals in synchronization with the synchronization signal output from the computer 6. Thereby, the difference (ΔΦ1−ΔΦ2) of the phase difference between the two beat signals represents the thickness of the device under test 1 without being affected by the vibration of the device under test 1.
For example, a lock-in amplifier or the like can be used as the phase detector 4.
The phase detector 4 is an example of the phase information detecting means.

前記シールド板８は，前記測定用光検出器２８から前記位相検波器４に至るまでの信号伝送経路と，前記参照用光検出器３８から前記位相検波器４に至るまでの信号伝送経路との間に配置された金属製の板である。
装置をコンパクト化するために前記測定用光検出器２８，前記参照用光検出器３８及び前記位相検波器４を近接して配置すると，一方のビート信号の伝送経路から発生する電磁波の不要輻射が他方のビート信号に対するノイズとして干渉し，測定精度を悪化させる。サブナノメートルオーダーの形状測定の精度を実現するためには，前記不要輻射による相互干渉のノイズ成分を信号成分の０．５％未満に抑える必要がある。
前記シールド板８の存在により，前記不要輻射に起因する測定精度の悪化を防止できる。
また，前記不要輻射による相互干渉の抑制のために，２つの前記ビート信号の伝送経路の間隔が２０ｍｍ程度以上であることが望ましい。 The shield plate 8 includes a signal transmission path from the measurement photodetector 28 to the phase detector 4 and a signal transmission path from the reference photodetector 38 to the phase detector 4. It is a metal plate arranged between them.
If the measurement photodetector 28, the reference photodetector 38, and the phase detector 4 are arranged close to each other in order to make the apparatus compact, unnecessary radiation of electromagnetic waves generated from one beat signal transmission path is generated. The other beat signal interferes with noise and degrades measurement accuracy. In order to realize sub-nanometer order shape measurement accuracy, it is necessary to suppress the noise component of mutual interference due to unnecessary radiation to less than 0.5% of the signal component.
Due to the presence of the shield plate 8, it is possible to prevent the measurement accuracy from deteriorating due to the unnecessary radiation.
Further, in order to suppress mutual interference due to the unnecessary radiation, it is desirable that the interval between the transmission paths of the two beat signals is about 20 mm or more.

また，前記計算機６は，前記被測定物１の表裏それぞれについて得られた前記２つのビート信号の位相差の差分（ΔΦ１−ΔΦ２）に応じた前記被測定物１の厚みの測定値を算出する厚み算出処理を実行する。
具体的には，前記計算機６は，前記２つのビート信号の位相差ΔΦ１，ΔΦ２を次の（ｄ１）式に代入することにより，前記被測定物１の厚みの測定値Ｄsを算出する。
Ｄs ＝ (ΔΦ１−ΔΦ２)×(λ／２)／(２π) …（ｄ１）
なお，（ｄ１）式において，λは前記測定光Ｐ１の波長である。また，（ｄ１）式は，前記測定光Ｐ２の波長が前記測定光Ｐ１の波長と等しいとの近似に基づく式である。さらに，（ｄ１）式は，Ａ面側及びＢ面側の前記測定光学ユニットＺにおいて，２つの前記測定光Ｐ１，Ｐ２のいずれを物体光又は参照光とするかの関係が同じ場合，即ち，Ａ面側及びＢ面側で物体光の周波数と参照光の周波数との関係が同じ場合の式である。
一方，Ａ面側及びＢ面側の前記測定光学ユニットＺにおいて，２つの前記測定光Ｐ１，Ｐ２のいずれを物体光又は参照光とするかの条件が逆である場合，即ち，Ａ面側及びＢ面側で物体光の周波数と参照光の周波数との関係が逆である場合の前記被測定物１の厚みの測定値Ｄsの算出式は，次の（ｄ２）式となる。
Ｄs ＝ (ΔΦ１＋ΔΦ２)×(λ／２)／(２π) …（ｄ２） Further, the calculator 6 calculates a measured value of the thickness of the DUT 1 according to the difference (ΔΦ1−ΔΦ2) of the phase difference between the two beat signals obtained for the front and back sides of the DUT 1. A thickness calculation process is executed.
Specifically, the calculator 6 calculates the measured value Ds of the thickness of the DUT 1 by substituting the phase differences ΔΦ1 and ΔΦ2 of the two beat signals into the following equation (d1).
Ds = (ΔΦ1-ΔΦ2) × (λ / 2) / (2π) (d1)
In the equation (d1), λ is the wavelength of the measurement light P1. The equation (d1) is an equation based on an approximation that the wavelength of the measurement light P2 is equal to the wavelength of the measurement light P1. Further, the equation (d1) is obtained when the relationship between which one of the two measurement beams P1 and P2 is the object beam or the reference beam is the same in the measurement optical unit Z on the A side and the B side, that is, This is an expression in the case where the relationship between the frequency of the object light and the frequency of the reference light is the same on the A plane side and the B plane side.
On the other hand, in the measurement optical unit Z on the A surface side and the B surface side, when the conditions regarding which of the two measurement beams P1 and P2 are the object beam or the reference beam are reversed, that is, on the A plane side and The equation for calculating the measured value Ds of the thickness of the DUT 1 when the relationship between the frequency of the object light and the frequency of the reference light is opposite on the B side is the following equation (d2).
Ds = (ΔΦ1 + ΔΦ2) × (λ / 2) / (2π) (d2)

次に，図２を参照しつつ，前記測定光学ユニットＺの構造の具体例について説明する。図２は，前記測定光学ユニットＺの一例の概略構成図である。図２には，前記測定光学ユニットＺの側面図（ａ）が示されている。なお，図２において，図１に示される各構成要素と同じ構成要素については同じ符号が付されている。
前記測定光学ユニットに含まれる各種光学素子は，前記被測定物１の表裏それぞれにおいて，所定の光学系保持具７０により一体に保持されている。
図２（ｂ）は，側面図（ａ）の視野方向に対して９０°異なる方向から見た前記光学系保持具７０の側面図である。
以下，前記測定光学ユニットに含まれる機器，即ち，前記光ファイバ接続端子１２，２６，３６，前記ビームスプリッタ１３，前記音響光学素子１５，１６，前記ヘテロダイン干渉計２０と前記参照用干渉計３０とを構成する機器，及び前記集光レンズ２３を測定光学系と総称する。
前記光学系保持具７０は，表裏各々において前記測定光学系の一部又は全部を分担して保持する板状の保持部７１を有する剛体である。前記板状の保持部７１には，前記測定光学系を伝播するビーム光を通過させる貫通孔７１ｈが形成されている。例えば，前記板状の保持部７１には，前記測定光学系のうち前記集光レンズ２３を除く残りの光学素子が保持される。
図２に示されるように，前記光学系保持具７０は，前記測定光学系を，前記板状の保持部７１の両側に渡って三次元的に保持する。これにより，前記測定光学系を保持する前記板状の保持部７１を小さくでき，その小さな板状の保持部７１は，比較的薄い軽量な部材が採用されても，十分な剛性を確保できる。そのため，小型でごく簡易な構造の前記光学系保持具７０により，前記板状の保持部７１の変形（撓み）に起因する２種類の前記測定光Ｐ１，Ｐ２の位相のずれの発生を防止できる。
例えば，前記光学系保持具７０は，１５０ｍｍ×９０ｍｍ×１００ｍｍ程度の大きさで，前記測定光学系を一体に保持できる。
なお，図２（ａ）において，前記測定光学系を前記板状の保持部７１に対して固定する支持部材の記載は省略されている。 Next, a specific example of the structure of the measurement optical unit Z will be described with reference to FIG. FIG. 2 is a schematic configuration diagram of an example of the measurement optical unit Z. FIG. 2 shows a side view (a) of the measurement optical unit Z. In FIG. 2, the same components as those shown in FIG. 1 are denoted by the same reference numerals.
Various optical elements included in the measurement optical unit are integrally held by a predetermined optical system holder 70 on each of the front and back sides of the DUT 1.
FIG. 2B is a side view of the optical system holder 70 viewed from a direction different from 90 ° with respect to the viewing direction of the side view of FIG.
Hereinafter, the devices included in the measurement optical unit, that is, the optical fiber connection terminals 12, 26, 36, the beam splitter 13, the acoustooptic elements 15, 16, the heterodyne interferometer 20, and the reference interferometer 30, And the condenser lens 23 are collectively referred to as a measurement optical system.
The optical system holder 70 is a rigid body having a plate-like holding part 71 that shares and holds part or all of the measurement optical system on each of the front and back sides. The plate-like holding portion 71 is formed with a through hole 71h through which the light beam propagating through the measurement optical system passes. For example, the plate-shaped holding unit 71 holds the remaining optical elements other than the condenser lens 23 in the measurement optical system.
As shown in FIG. 2, the optical system holder 70 holds the measurement optical system three-dimensionally on both sides of the plate-like holding portion 71. Thereby, the plate-like holding portion 71 holding the measurement optical system can be made small, and the small plate-like holding portion 71 can ensure sufficient rigidity even if a relatively thin and lightweight member is adopted. Therefore, the optical system holder 70 having a small and very simple structure can prevent occurrence of a phase shift between the two types of the measurement light beams P1 and P2 due to the deformation (deflection) of the plate-like holding portion 71. .
For example, the optical system holder 70 has a size of about 150 mm × 90 mm × 100 mm and can integrally hold the measurement optical system.
In FIG. 2A, the description of the support member that fixes the measurement optical system to the plate-like holding portion 71 is omitted.

また，前記板状の保持部７１は，その縁部が他の部材に固定されることによって補強された部材である。
図２に示される例では，前記板状の保持部７１は矩形状の板材であり，その三辺の縁部が屈曲状に連結された３つの補強板７２〜７４に固定されることによって補強されている。
また，図２に示される例では，１つの前記補強板７４にも，前記被測定物１の方向へ通ずる貫通穴７４ｈが形成されており，その貫通孔７４ｈが前記測定光Ｐ１の光路となっている。また，前記補強板７４には，前記集光レンズ２３が保持されている。
前記光学系保持具７０は，例えば，ステンレスや鉄，アルミニウム等の金属製の部材により構成される。 Further, the plate-like holding portion 71 is a member reinforced by fixing its edge to another member.
In the example shown in FIG. 2, the plate-like holding portion 71 is a rectangular plate material, and the three side edges thereof are fixed to three reinforcing plates 72 to 74 that are connected in a bent shape, thereby reinforcing the plate-like holding portion 71. Has been.
Further, in the example shown in FIG. 2, a through hole 74 h that passes in the direction of the DUT 1 is also formed in one of the reinforcing plates 74, and the through hole 74 h is an optical path of the measurement light P <b> 1. ing. The condensing lens 23 is held on the reinforcing plate 74.
The optical system holder 70 is made of a metal member such as stainless steel, iron, or aluminum.

次に，図３を参照しつつ，前記形状測定装置Ｘにより前記被測定物１の表面を走査する機構について説明する。
図３に示されるように，前記形状測定装置Ｘは，前記被測定物１を移動可能に支持する可動支持装置４０を備えている。
前記形状測定装置Ｘは，前記被測定物１の振動の影響を受けることなく，前記被測定物１の特定の部位の厚みを高精度かつ高速で測定できる。
そして，前記形状測定装置Ｘは，前記被測定物１をその中央部や端部等で支持し，前記被測定物１をその厚み方向に直交する平面内（被測定物１の表裏各面に平行な面内）で移動させつつ前記被測定物１に対する物体光の走査を行う可動支持装置４０を備えている。 Next, a mechanism for scanning the surface of the DUT 1 with the shape measuring device X will be described with reference to FIG.
As shown in FIG. 3, the shape measuring apparatus X includes a movable support device 40 that movably supports the device under test 1.
The shape measuring apparatus X can measure the thickness of a specific part of the device under test 1 with high accuracy and high speed without being affected by the vibration of the device under test 1.
Then, the shape measuring apparatus X supports the device under test 1 at its center, end, or the like, and places the device under test 1 in a plane perpendicular to its thickness direction (on the front and back surfaces of the device under test 1). A movable support device 40 is provided which scans the object to be measured 1 while moving in a parallel plane.

図３に示される前記可動支持装置４０は，半導体ウェハ等の円盤状の前記被測定物１を，その縁部（エッジ部）において，円周上の三箇所に配置された支持部４４により３点支持する。これら３つの支持部４４は，前記円周の中心に向かって伸びる回転軸４１に連結されている。
さらに，その支持軸４１は，サーボモータ等の回転駆動部４２によって回転駆動される。これにより，前記被測定物１は，その中央部を回転中心として回転される。
また，前記支持軸４１及び前記回転駆動部４２は，直線移動機構４３により，前記被測定物１の表裏各面に平行な方向（厚み方向に直交する方向）に所定の移動範囲内で直線移動される。即ち，前記直線移動機構４３は，前記被測定物１をその半径方向に沿って移動させる。
また，前記支持軸４１，前記回転駆動部４２及び前記直線移動機構４３を備えた前記可撓支持装置４０は，前記Ａ面側の前記ヘテロダイン干渉計２０による前記測定光Ｐ１の照射位置と前記Ｂ面側の前記ヘテロダイン干渉計２０による前記測定光Ｐ１の照射位置との間に前記被測定物１を支持する。 The movable support device 40 shown in FIG. 3 is configured so that the disk-shaped object 1 such as a semiconductor wafer 3 is supported by support portions 44 arranged at three locations on the circumference at the edge (edge portion). Point support. These three support portions 44 are connected to a rotation shaft 41 extending toward the center of the circumference.
Further, the support shaft 41 is rotationally driven by a rotational drive unit 42 such as a servo motor. As a result, the DUT 1 is rotated with its center portion as the center of rotation.
Further, the support shaft 41 and the rotation drive unit 42 are linearly moved within a predetermined movement range in a direction parallel to the front and back surfaces of the DUT 1 (direction perpendicular to the thickness direction) by the linear movement mechanism 43. Is done. That is, the linear movement mechanism 43 moves the device under test 1 along its radial direction.
Further, the flexible support device 40 including the support shaft 41, the rotation drive unit 42, and the linear movement mechanism 43 includes the irradiation position of the measurement light P1 by the heterodyne interferometer 20 on the A plane side and the B The object to be measured 1 is supported between the irradiation position of the measurement light P1 by the heterodyne interferometer 20 on the surface side.

そして，前記回転駆動部４２による前記被測定物１の回転と，前記直線移動機構４３による前記被測定物１の直線方向の移動とを併用することにより，前記被測定物１における前記測定部位１ａ，１ｂの位置を順次変更しつつ前記形状測定装置Ｘによる厚み測定を実行する。
例えば，前記被測定物１を一定速度で連続的に回転及び直線移動させつつ，一定周期で，或いは測定点１ａ，１ｂの位置が予め定められた位置となるごとに，前記計算機６が，前記Ａ面側及び前記Ｂ面側の前記位相差ΔΦ１，ΔΦ２のデータを前記位相検波器４から取得する。さらに，前記計算機６が，それら２つの位相差ΔΦ１，ΔΦ２を前記（ｃ１）式に代入することにより，前記被測定物１の厚みＤsを算出する。
図４は，前記被測定物１における前記測定部位１ａ，１ｂの分布の一例を表す模式図である。
前記被測定物１を回転及び直線移動させつつ干渉光の位相検出を順次行った場合，図４に示されるように，前記測定部位１ａ，１ｂの位置は，前記被測定物１の表面における渦巻き状の線（波線）に沿って順次変化する。
そして，前記可動支持装置４０により前記被測定物１の保持位置を二次元方向に移動させつつ厚み測定を順次行い，その測定データを所定の記憶部に記憶させれば，前記被測定物１の厚み分布データが得られる。
ここで，円盤状の前記被測定物１の厚みが薄い場合，その被測定物１は，図３に示されるように一部で支持されると，わずかな風圧や床の振動によって厚み方向に振動する。しかしながら，前記形状測定装置Ｘは，前記被測定物１がそのように振動しても，その振動の影響を受けずに高精度で前記被測定物１の厚み分布を測定できる。
なお，前記被測定物１をその表面に平行な面内で位置決めする機構は，図３に示される機構の他，いわゆるＸ−Ｙプロッタのように，前記被測定物１の支持部を交差する２直線それぞれに沿って移動させる機構であってもよい。 Then, by using both the rotation of the device under test 1 by the rotation drive unit 42 and the movement of the device under test 1 in the linear direction by the linear movement mechanism 43, the measurement site 1a of the device under test 1 is measured. , 1b, the thickness is measured by the shape measuring device X while the position is sequentially changed.
For example, while continuously rotating and linearly moving the object to be measured 1 at a constant speed, the computer 6 is configured so that the measurement point 1a, 1b becomes a predetermined position every time the measurement point 1a, 1b becomes a predetermined position. Data of the phase differences ΔΦ1 and ΔΦ2 on the A plane side and the B plane side are acquired from the phase detector 4. Further, the calculator 6 calculates the thickness Ds of the DUT 1 by substituting these two phase differences ΔΦ1 and ΔΦ2 into the equation (c1).
FIG. 4 is a schematic diagram showing an example of the distribution of the measurement sites 1a and 1b in the DUT 1.
When the phase of the interference light is sequentially detected while rotating and linearly moving the device under test 1, the positions of the measurement sites 1 a and 1 b are spirals on the surface of the device under test 1 as shown in FIG. 4. It changes sequentially along a line (wave line).
Then, if the thickness measurement is sequentially performed by moving the holding position of the DUT 1 in the two-dimensional direction by the movable support device 40 and the measurement data is stored in a predetermined storage unit, the DUT 1 Thickness distribution data is obtained.
Here, when the disk-shaped object to be measured 1 is thin, if the object to be measured 1 is supported in part as shown in FIG. Vibrate. However, even if the device under test 1 vibrates in this way, the shape measuring apparatus X can measure the thickness distribution of the device under test 1 with high accuracy without being affected by the vibration.
In addition, the mechanism for positioning the device under test 1 in a plane parallel to the surface thereof crosses the support portion of the device under test 1 such as a so-called XY plotter in addition to the mechanism shown in FIG. It may be a mechanism that moves along two straight lines.

図５は，従来の形状測定装置の測定値の時系列変化の一例を表すグラフ，図６は，前記形状測定装置Ｘの測定値の時系列変化の一例を表すグラフである。ここで，従来の形状測定装置は，周波数がわずかに異なる２つの前記測定光Ｐ１，Ｐ２を光源の位置から光ファイバを用いて前記Ａ面側及び前記Ｂ面側それぞれの前記参照用干渉計３０及び前記ヘテロダイン干渉計２０の位置まで伝送することによって前記被測定物１の厚み測定を行う装置である。なお，前記従来の形状測定装置及び前記形状測定装置Ｘにおいて，２つの前記測定光Ｐ１，Ｐ２又は前記基幹光Ｐ０の分岐光を光源の位置から前記被測定物１の両面へ伝送する光ファイバに対し，特に振動防止用の措置は施されていない。
図５に示されるように，前記従来の形状測定装置は，２つの前記測定光Ｐ１，Ｐ２の伝送経路の振動等のノイズに起因して，厚みの測定値が大きく変動する。
一方，前記形状測定装置Ｘは，前記光ファイバａ１０，ｂ１０に対して特に信号防止対策が取られていないにもかかわらず，安定した厚みの測定値が得られる。
従って，前記形状測定装置Ｘによれば，前記被測定物１の振動及び前記単波長レーザ光源２から前記測定光学ユニットＺに至る前記基幹光Ｐ０の分岐光の伝送媒体の振動の影響を受けずに，前記被測定物１の厚みを簡易に高精度で測定できる。 FIG. 5 is a graph showing an example of the time series change of the measurement value of the conventional shape measuring apparatus, and FIG. 6 is a graph showing an example of the time series change of the measurement value of the shape measuring apparatus X. Here, in the conventional shape measuring apparatus, the reference interferometers 30 on the A-side and B-side are respectively sent from the position of the light source to the two measuring beams P1, P2 having slightly different frequencies by using an optical fiber. And a device for measuring the thickness of the DUT 1 by transmitting to the position of the heterodyne interferometer 20. In the conventional shape measuring apparatus and the shape measuring apparatus X, the two optical beams P1 and P2 or the branched light of the basic light P0 are transmitted from the position of the light source to both surfaces of the object 1 to be measured. On the other hand, no measures are taken to prevent vibration.
As shown in FIG. 5, in the conventional shape measuring apparatus, the measured value of the thickness largely fluctuates due to noise such as vibration of the transmission path of the two measuring beams P1 and P2.
On the other hand, the shape measuring apparatus X can obtain a stable thickness measurement value even though no signal prevention measures are taken for the optical fibers a10 and b10.
Therefore, according to the shape measuring apparatus X, it is not affected by the vibration of the device under test 1 and the vibration of the transmission medium of the branched light of the basic light P0 from the single wavelength laser light source 2 to the measurement optical unit Z. In addition, the thickness of the DUT 1 can be easily measured with high accuracy.

本発明は，半導体ウェハ等の被測定物についての形状測定装置に利用可能である。 The present invention is applicable to a shape measuring apparatus for an object to be measured such as a semiconductor wafer.

Ｘ：本発明の実施形態に係る形状測定装置
Ｙ：光源ユニット
Ｚ：測定光学ユニット
Ｗ：位相検波回路
１：被測定物
１ａ，１ｂ：測定部位
２：単波長レーザ光源
３：ビームスプリッタ
４：位相検波器
６：計算機
１１，１２，２６，３６：光ファイバ接続端子
１５，１６：音響光学素子
２０：ヘテロダイン干渉計
３０：参照用干渉計
４０：可動支持装置
ａ１０，ｂ１０：入力側の光ファイバ
ａ２７，ｂ２７，ａ３７，ｂ３７：出力側の光ファイバ
Ｐ０：基幹光
Ｐ１，Ｐ２：測定光 X: shape measuring apparatus Y according to an embodiment of the present invention Y: light source unit Z: measurement optical unit W: phase detection circuit 1: measured object 1a, 1b: measurement site 2: single wavelength laser light source 3: beam splitter 4: phase Detector 6: Computers 11, 12, 26, 36: Optical fiber connection terminals 15, 16: Acousto-optic element 20: Heterodyne interferometer 30: Interferometer for reference 40: Movable support devices a10, b10: Optical fiber a27 on the input side , B27, a37, b37: output side optical fiber P0: backbone light P1, P2: measurement light

Claims

被測定物の表裏各面を走査して該被測定物の厚み分布を非接触で測定するために用いられる形状測定装置であって，
所定の光源から出射される基幹光を二分岐させる第１の光分岐手段と，
前記第１の光分岐手段による分岐光それぞれを前記被測定物の表裏各面の表裏相対する測定部位それぞれの方向へ導く導光手段と，
前記被測定物の表裏それぞれにおける前記測定部位の方向へ導かれた前記基幹光の分岐光それぞれをさらに二分岐させる第２の光分岐手段と，
前記被測定物の表裏それぞれにおける前記第２の光分岐手段による分岐光の一方又は両方に周波数変調を施してそれぞれ周波数の異なる２つの測定光を生成する光変調手段と，
前記被測定物の表裏それぞれにおいて，一方の前記測定光を前記測定部位に照射させ，該測定部位で反射した一方の前記測定光である物体光と他方の前記測定光である参照光とを干渉させる２つのヘテロダイン干渉計と，
前記被測定物の表裏それぞれにおいて，２つの前記測定光それぞれを前記ヘテロダイン干渉計に入力される主光とそれ以外の副光とに二分岐させる第３の光分岐手段と，
前記被測定物の表裏それぞれにおいて，前記第３の光分岐手段により分岐された２つの前記副光を干渉させる副光干渉手段と，
前記被測定物の表裏それぞれにおいて，前記第２の光分岐手段，前記光変調手段，前記ヘテロダイン干渉計，前記第３の光分岐手段及び前記副光干渉手段を含む測定光学系を一体に保持する測定光学系保持手段と，
２つの前記ヘテロダイン干渉計により得られる干渉光それぞれを受光してその強度信号を出力する測定用光強度検出手段と，
前記被測定物の表裏それぞれにおいて，前記副光干渉手段により得られる干渉光を受光してその強度信号を出力する参照用光強度検出手段と，
前記被測定物の表裏それぞれにおける前記測定用光強度検出手段の出力信号及び前記参照用光強度検出手段の出力信号からなる２つのビート信号の位相検波により該２つのビート信号の位相差を検出する位相情報検出手段と，
を具備してなることを特徴とする形状測定装置。 A shape measuring device used for scanning the front and back surfaces of a measured object to measure the thickness distribution of the measured object in a non-contact manner,
First light branching means for branching the basic light emitted from a predetermined light source;
A light guiding means for guiding each of the branched lights by the first light branching means in the respective directions of the measurement parts opposite to the front and back surfaces of the object to be measured;
Second light branching means for further branching the branched light of the basic light guided in the direction of the measurement site on each of the front and back sides of the object to be measured;
Light modulating means for performing frequency modulation on one or both of the branched lights by the second light branching means on each of the front and back sides of the object to be measured to generate two measurement lights having different frequencies,
In each of the front and back sides of the object to be measured, one measurement light is irradiated onto the measurement site, and the object light that is one measurement light reflected from the measurement site interferes with the reference light that is the other measurement light. Two heterodyne interferometers to be
Third optical branching means for bifurcating each of the two measurement lights into main light input to the heterodyne interferometer and other auxiliary light on each of the front and back sides of the object to be measured;
Sub-light interference means for causing the two sub-lights branched by the third light branch means to interfere with each other on the front and back sides of the object to be measured;
Measurement optical systems including the second optical branching unit, the optical modulation unit, the heterodyne interferometer, the third optical branching unit, and the auxiliary optical interference unit are integrally held on the front and back sides of the object to be measured. Measuring optical system holding means;
A measuring light intensity detecting means for receiving interference light obtained by the two heterodyne interferometers and outputting an intensity signal thereof;
A reference light intensity detecting means for receiving interference light obtained by the auxiliary light interference means and outputting an intensity signal on each of the front and back sides of the object to be measured;
The phase difference between the two beat signals is detected by phase detection of two beat signals composed of the output signal of the measurement light intensity detection means and the output signal of the reference light intensity detection means on the front and back sides of the object to be measured. Phase information detection means;
A shape measuring apparatus comprising:

前記測定光学系保持手段が，表裏各々において前記測定光学系を分担して保持する板状の保持部を有する剛体であり，前記板状の保持部に前記測定光学系を伝播する光を通過させる貫通孔が形成されてなる請求項１に記載の形状測定装置。 The measurement optical system holding means is a rigid body having a plate-like holding portion that shares and holds the measurement optical system on each of the front and back sides, and allows light propagating through the measurement optical system to pass through the plate-like holding portion. The shape measuring apparatus according to claim 1, wherein a through hole is formed.

前記測定用光強度検出手段から前記位相情報検出手段に至るまでの信号伝送経路と前記参照用光強度検出手段から前記位相情報検出手段に至るまでの信号伝送経路との間に配置された金属製のシールド板を具備してなる請求項１又は２のいずれかに記載の形状測定装置。 Metal made between a signal transmission path from the measurement light intensity detection means to the phase information detection means and a signal transmission path from the reference light intensity detection means to the phase information detection means The shape measuring apparatus according to claim 1, comprising a shield plate.