JP4536873B2 - Three-dimensional shape measuring method and apparatus - Google Patents

Three-dimensional shape measuring method and apparatus Download PDF

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JP4536873B2
JP4536873B2 JP2000168195A JP2000168195A JP4536873B2 JP 4536873 B2 JP4536873 B2 JP 4536873B2 JP 2000168195 A JP2000168195 A JP 2000168195A JP 2000168195 A JP2000168195 A JP 2000168195A JP 4536873 B2 JP4536873 B2 JP 4536873B2
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仁 飯島
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Canon Inc
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Description

【０００１】
【発明の属する技術分野】
本発明は三次元形状計測方法及び装置に関し特に光ヘテロダイン法を用いた高精度な三次元形状計測方法及び装置に良好に適用できる。
【０００２】
【従来の技術】
被測定物体の三次元的な形状を非接触かつ高精度に測定する三次元形状測定に関しては、例えば図6の特公平2-11084号公報で提案されている光ヘテロダインを用いた装置が知られている。図中、光源301はゼーマンレーザでわずかに異なる周波数f1、f2で互いに直交する偏光方向を持つ2つの直線偏光を同時発振する。光源301から発振したレーザの内の一部の光はビームスプリッタ302により光検出器303に入射し、参照ビート信号として光電検出される。
【０００３】
ビームスプリッタ302を通過したレーザ光のうち周波数f2のレーザ光は偏光ビームスプリッタ304で上方へ反射されてレンズで集光され固定鏡305で反射された後、光検出器306に達する。一方、偏光ビームスプリッタ304を透過した周波数f1のレーザ光はハーフミラー307を通過し、対物レンズ308により被測定試料309に入射する。被測定試料309で反射したレーザ光は偏光ビームスプリッタ304まで元の光路を戻り、そこで反射されて光検出器306に達して周波数f2の光と干渉し、測定ビート信号が光電検出される。ここで参照ビート信号と測定ビート信号の周波数差Δfを積分すると、被測定試料の変位あるいは形状が測定できる。
【０００４】
本測定法では測定光が被測定試料309面上にフォーカスしていなければならないため、被測定試料309からの反射光の一部はハーフミラー307により分岐され、光検出器310、311によりフォーカスサーボ用の信号が検出される。該フォーカスサーボ信号より対物レンズ308を光軸方向、及び光軸と直交する方向に移動させて、レーザ光が常に被測定試料309面上にフォーカスし、かつ被測定試料309の法線方向から入射するように制御している。この状態で、被測定試料309を駆動装置312により回転対称軸回りに回転(θ)させるとともに、半径方向に移動させることで被測定試料309全体が測定される。
【０００５】
【発明が解決しようとする課題】
しかしながら、上記従来の方法では測定光を被測定面上にフォーカスさせ、かつ被測定面の法線方向から測定光を入射させるために形状測定用の光学系とは別にフォーカス検出用の光学系が必要となり、装置が複雑になるという問題がある。又、フォーカス検出をより高い精度で行える装置が求められてきた。
【０００６】
本発明では高精度に被測定物を非接触測定できる三次元形状測定方法及び装置を提供することを目的としている。本発明は更にこれを簡易な構成で実現できる方法及び装置の提供を他の目的としている。
【０００７】
【課題を解決するための手段】
請求項１の発明の三次元形状計測装置は、光ヘッドを用いて測定光を被測定試料上にフォーカスさせ、該被測定試料の三次元形状を測定する三次元形状測定装置において、
光源からの光により得られる光ヘテロダインの参照ビート信号と、
該被測定試料からの光により得られる光ヘテロダインの測定ビート信号を、ローパスフィルタとハイパスフィルタに通して直流成分と交流成分とを検出し、検出した直流成分の強度に対する交流成分の強度の比が最大になる位置における該測定ビート信号との位相差を記憶して初期位相差とし、
前記参照ビート信号と前記測定ビート信号との位相差が、記憶された前記初期位相差からの変化を打ち消すように該光ヘッドの光軸方向のフォーカスサーボを行いながら、該被測定試料の形状を測定することを特徴としている。
【０００８】
請求項２の発明の三次元形状計測装置は、光ヘッドを用いて測定光を被測定試料上にフォーカスさせ、該被測定試料の三次元形状を測定する三次元形状測定装置において、
該被測定試料からの光により得られる光ヘテロダインの測定ビート信号を、ローパスフィルタとハイパスフィルタに通して直流成分と交流成分とを検出し、検出した直流成分の強度に対する交流成分の強度の比が最大になるように該光ヘッドの光軸方向にフォーカスサーボを行いながら、該被測定試料の三次元形状を測定することを特徴としている。
【０００９】
請求項３の発明は請求項１の発明において、該フォーカスサーボを該光ヘッドを光軸方向に移動させて行うとともに、該被測定試料を載置したステージを光軸と直交する方向に走査し、走査時の該ステージの座標と該光ヘッドの光軸方向の座標値をモニタすることにより該被測定試料の三次元形状を測定することを特徴としている。
【００１０】
請求項４の発明は請求項１の発明において、該フォーカスサーボを該被測定試料を載置したステージを光軸方向に移動させて行うとともに、該ステージを光軸と直交する方向に走査し、走査時の該ステージの光軸方向、及び光軸と直交方向の座標値をモニタすることにより該被測定試料の三次元形状を測定することを特徴としている。
【００１１】
請求項５の発明は請求項１の発明において、該フォーカスサーボを該被測定試料に対し該光ヘッドを光軸方向と光軸と直交方向に走査し、走査時の該光ヘッドの座標値をモニタすることにより該被測定試料の三次元形状を測定することを特徴としている。
【００１２】
請求項６の発明の三次元形状計測方法は、光ヘッドを用いて測定光を被測定試料上にフォーカスさせ、該被測定試料の三次元形状を測定する三次元形状測定方法において、
光源からの光により得られる光ヘテロダインの参照ビート信号と、
該被測定試料からの光により得られる光ヘテロダインの測定ビート信号を、ローパスフィルタとハイパスフィルタに通して直流成分と交流成分とを検出し、検出した直流成分の強度に対する交流成分の強度の比が最大になる位置における該測定ビート信号と、
の位相差を記憶して初期位相差とし、
前記参照ビート信号と前記測定ビート信号との位相差が、記憶された前記初期位相差からの変化を打ち消すように該光ヘッドの光軸方向にフォーカスサーボを行いながら、該被測定試料の形状を測定することを特徴としている。
【００１３】
請求項７の発明の三次元形状計測方法は、光ヘッドを用いて測定光を被測定試料上にフォーカスさせ、該被測定試料の三次元形状を測定する三次元形状測定方法において、
該被測定試料からの光により得られる光ヘテロダインの測定ビート信号を、ローパスフィルタとハイパスフィルタに通して直流成分と交流成分とを検出し、検出した直流成分の強度に対する交流成分の強度の比が最大になるように該光ヘッドの光軸方向にフォーカスサーボを行いながら、該被測定試料の三次元形状を測定することを特徴としている。
【００２０】
【発明の実施の形態】
図１は本発明の実施形態1を示すものである。図中、101は可干渉性の単一周波数の光を放射するレーザ光源である。レーザ光源から発振されたレーザ光はミラーM1で反射し、ビームスプリッタ102により反射光と透過光に分割される。反射光はM2で反射され、音響光学素子104aで周波数シフトを受けて周波数f1のレーザ光となる。透過光は音響光学素子104bで周波数シフトを受け周波数f2のレーザ光となり、ミラーM3で反射された後、半波長板105により偏光方位が90°回転する。音響光学素子104a、104bは音響光学素子ドライバ104cで駆動されている。周波数f1、f2のレーザ光は偏光ビームスプリッタ103で合成されて互いに直交する直線偏光となる。上記、直線偏光の生成にはゼーマン効果を利用したゼーマンレーザを使用することも可能である。
【００２１】
レーザ光はビームスプリッタ106で透過光と反射光に分割される。反射した周波数f1、f2の光は直線偏光素子107aを通過後に干渉し、光検出器108で参照ビート信号として光電検出される。該参照信号は音響光学素子ドライバ104cの駆動電圧からミキサ回路を用いて作ることも可能である。
【００２２】
透過した光は偏光面保存光ファイバ109に入射し、偏光面を保存されたまま光ヘッドへ導かれる。光ヘッド内で偏光面保存光ファイバから出射したレーザ光はビームエキスパンダ110でビーム径を拡大され、偏光ビームスプリッタ111へ入射する。偏光ビームスプリッタ111に入射したレーザ光は偏光成分により二つに分割される。周波数f1の偏光成分は四分の一波長板112aを通過し、対物レンズ113により被測定試料114の面上に焦点を結び、反射される。被測定試料114の面に面傾斜がある場合でも、面傾斜角が対物レンズ113の半開角以下であれば反射光の一部は対物レンズ113を通り、同じ光路を戻る。
【００２３】
被測定試料114は光軸と直交する面内方向の二軸(XY軸)を持つ試料ステージ115上に設置されている。試料ステージ115にはX軸レーザ測長器116とX軸測長用ミラー117、及び図には記入されていないがY軸レーザ測長器とY軸測長用ミラーが設置され、試料ステージ115の位置が精密に測定される。
【００２４】
一方、周波数f2の偏光成分は四分の一波長板112bを通過し、参照平面鏡118で反射される。両方の光路中にある四分の一波長板112a、112bは入射偏光に対して出射偏光方位を90°回転させることで、光源へ反射光を戻さない役割をしている。
周波数f1、f2の反射光は再び偏光ビームスプリッタ111で一つに合成される。合成されたレーザ光は直線偏光素子107bを通過後に干渉し、集光レンズ119により光検出器120上に集光され光電検出されて測定ビート信号を生成する。
【００２５】
光ヘッド121には光軸であるZ方向に測長用ミラー122が固定され、Z軸方向の位置をZ軸レーザ測長器123で精密測定する。光検出器120で光電検出された測定ビート信号は参照ビート信号とロックインアンプ124で同期検出され、測定ビート信号の強度、参照ビート信号と測定ビート信号の位相差（初期位相差）が検出される。測定ビート信号の強度、位相差及びZ軸測長器からの信号はA/D変換器125を介して、コンピュータ126に取り込まれ、該コンピュータ126からの信号はサーボドライバ127を介して駆動信号に変換されて、試料ステージ115または光ヘッド121を駆動する。実際の測定の流れを示したのが図2である。最初はフォーカス検出で、光ヘッド121を被測定試料114にZ軸方向から接近させながら光検出器120で測定ビート信号を検出し、該測定ビート信号の強度が最大になる位置で光ヘッド121を止める。測定ビート信号の強度が最大になった状態で測定光は被測定試料114面上にフォーカスしているので、この位置における参照ビート信号と測定ビート信号の位相差を測定する。測定された位相差により、参照鏡118と被測定試料114の光路長差が求められる。従って、位相差が一定になるように光ヘッド121のZ軸方向にサーボをかけながら試料ステージ115をXY軸に走査し、光ヘッド121のZ軸方向の移動をZ軸レーザ測長器123で検出すると、光ヘッド121のZ軸方向の動きは試料の表面をなぞることになる。従って、測定ビート信号からサーボ系のエラーを求め、Z測長器123からのデータを補正することにより被測定試料114の三次元形状を精密に補正することができる。
【００２６】
上記実施例では光ヘッドZを軸、試料ステージをXY方向に移動させたが、光ヘッドと試料ステージがXYZ座標で相対的に任意に移動できれば、光ヘッド、試料ステージのどちらを移動させてもよい。例えばXYZ軸移動の全ての機能を光ヘッドに持たせて各軸をレーザ測長器でモニタする構成も、同様に試料ステージ側で行う構成も可能である。
【００２７】
測定光のフォーカスの検出を詳しく説明したのが図3である。図示したように対物レンズによる測定光が被測定面上にフォーカスしている場合に光検出器120で検出されるビート信号の強度が最大になる。測定光が被測定面上にフォーカスしていない場合は、光検出器120上に干渉縞が生じるため、検出されるビート信号の強度が小さくなる。従って、光検出器120で検出されるビート信号が最大になるように光ヘッド121または試料ステージ115を光軸(Z)方向に移動することで、測定光を常に被測定面上にフォーカスさせることができる。また、被測定試料114が面傾斜を有する場合、反射光は図4のようにずれて戻ってくるが、この場合も干渉縞の影響で被測定試料114面上に測定光がフォーカスされた時に検出されるビート信号の強度が最大になるため、同様の方法で測定光を被測定試料114面上にフォーカスさせることができる。ビート信号の強度の検出について上記実施例ではロックインアンプを用いた構成を示したが、検出信号をハイパスフィルタに通して直流成分をカットした後、ピークディテクタにより交流成分の強度を検出する方法、あるいは検出信号を二つに分け、一方をローパスフィルタに通して直流成分、他方をハイパスフィルタに通して交流成分を検出し、交流成分と直流成分の比(ビジビリティ)をビート信号強度として検出する方法、また検出信号をローパスフィルタに通過させて直流成分を検出し、該直流成分の強度からビート信号強度を求める方法を用いることもできる。ビート信号の位相についても本実施形態ではロックインアンプを用いて検出したが、位相計を用いても検出が可能である。
【００２８】
本発明の実施形態2も装置構成は図1と同様である。本実施形態における実際の測定の流れを説明したのが図5である。先ず最初に光ヘッド121を被測定試料114にZ軸方向から接近させながら光検出器120で測定ビート信号を検出し、該信号の強度が最大になる位置で光ヘッド121を止める。測定ビート信号強度が最大となった状態で測定光は被測定試料114面上にフォーカスしているので、測定ビート信号の強度が常に最大になるように光ヘッド121をZ軸方向にサーボをかけながら試料ステージ115をXY軸に走査する。走査に伴い光ヘッド121のZ軸方向の移動がZ軸レーザ測長器123で検出される。Z軸レーザ測長器123からの測定値と測定ビート信号から参照鏡118と被測定試料114の光路長差が求められるため、被測定試料114の三次元形状を精密に測定することができる。
【００２９】
本実施形態では光ヘッド121をZ軸、試料ステージ115をXY方向に移動させたが、実施形態1の説明で述べたように、光ヘッド121と試料ステージ115がXYZ座標で相対的に任意に移動できれば、光ヘッド121、試料ステージ115のどちらを移動させてもよい。
【００３０】
【発明の効果】
以上説明したように、本発明の三次元形状計測方法及び装置では、対物レンズを用いて測定光を被測定面上にフォーカスさせつつ、三次元形状を計測する際、へテロダインの測定ビート信号の例えば強度あるいは位相を測定光のフォーカス状態の検出に利用することを特徴としている。これにより精度良くフォーカス検出ができ、測定精度が向上する。本発明では例えば光ヘテロダイン法を用いて三次元形状を計測する際には測定光を被測定試料面上にフォーカスするためのフォーカス状態検出用光学系を特別に用意する必要がないため、装置構成が簡単になるとともに、測定信号自体を用いてフォーカスの検出を行うため、高い測定精度で被測定試料の三次元形状を非接触測定することができる。
【図面の簡単な説明】
【図１】 本発明の実施形態１の構成図、
【図２】 実施形態1の測定フローチャート、
【図３】 測定光のフォーカスの説明図、
【図４】 面傾斜がある場合の測定光のフォーカスの説明図、
【図５】 実施形態2のフローチャート、
【図６】 従来の三次元形状測定装置を示す図
【符号の説明】
101 レーザ光源
103、111 偏光ビームスプリッタ
104a、104b 音響光学素子
104c 音響光学素子ドライバ
105 半波長板
102、 106 ビームスプリッタ
107a、107b 直線偏光子
108 光検出器
109 偏光面保存光ファイバ
110 ビームエキスパンダ
111 偏光ビームスプリッタ
112a、112b 四分の一波長板
113 対物レンズ
114 被測定試料
115 試料ステージ
116 X軸レーザ測長器
117 X軸測長用ミラー
118 参照平面鏡
119 集光レンズ
120 光検出器
121 光ヘッド
122 Z軸測長用ミラー
123 Z軸測長器
124 ロックインアンプ
125 A/D変換器
126 コンピュータ
127 サーボドライバ
301 ゼーマンレーザ
302 ビームスプリッタ
303、306、310、311 光検出器
304 偏光ビームスプリッタ
305 固定鏡
307 ハーフミラー
308 対物レンズ
309 被測定試料
312 駆動装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for measuring a three-dimensional shape, and is particularly applicable to a method and apparatus for measuring a three-dimensional shape with high accuracy using an optical heterodyne method.
[0002]
[Prior art]
Regarding the three-dimensional shape measurement for measuring the three-dimensional shape of an object to be measured in a non-contact and high-precision manner, for example, an apparatus using an optical heterodyne proposed in Japanese Patent Publication No. 2-1084 in FIG. 6 is known. ing. In the figure, a light source 301 is a Zeeman laser that simultaneously oscillates two linearly polarized lights having polarization directions orthogonal to each other at slightly different frequencies f1 and f2. A part of the laser light oscillated from the light source 301 is incident on the photodetector 303 by the beam splitter 302 and is photoelectrically detected as a reference beat signal.
[0003]
Of the laser light that has passed through the beam splitter 302, the laser light having the frequency f2 is reflected upward by the polarization beam splitter 304, condensed by the lens, reflected by the fixed mirror 305, and then reaches the photodetector 306. On the other hand, the laser beam having the frequency f 1 that has passed through the polarizing beam splitter 304 passes through the half mirror 307 and is incident on the sample 309 to be measured by the objective lens 308. The laser beam reflected by the sample 309 to be measured returns to the original optical path to the polarization beam splitter 304, is reflected there, reaches the photodetector 306, interferes with the light of frequency f2, and the measurement beat signal is photoelectrically detected. Here, by integrating the frequency difference Δf between the reference beat signal and the measurement beat signal, the displacement or shape of the sample to be measured can be measured.
[0004]
In this measurement method, since the measurement light must be focused on the surface of the sample 309 to be measured, a part of the reflected light from the sample 309 to be measured is branched by the half mirror 307 and is focused by the photodetectors 310 and 311. A signal is detected. By moving the objective lens 308 in the direction of the optical axis and in the direction perpendicular to the optical axis from the focus servo signal, the laser beam is always focused on the surface of the sample 309 to be measured and is incident from the normal direction of the sample 309 to be measured. You are in control. In this state, the measured sample 309 is rotated (θ) about the rotational symmetry axis by the driving device 312 and moved in the radial direction, whereby the measured sample 309 as a whole is measured.
[0005]
[Problems to be solved by the invention]
However, in the conventional method, a focus detection optical system is provided separately from the shape measurement optical system in order to focus the measurement light on the surface to be measured and to make the measurement light incident from the normal direction of the surface to be measured. There is a problem that it becomes necessary and the apparatus becomes complicated. There has also been a demand for an apparatus that can perform focus detection with higher accuracy.
[0006]
An object of the present invention is to provide a three-dimensional shape measuring method and apparatus capable of non-contact measurement of an object to be measured with high accuracy. Another object of the present invention is to provide a method and apparatus capable of realizing this with a simple configuration.
[0007]
[Means for Solving the Problems]
The three-dimensional shape measuring apparatus according to the first aspect of the present invention is the three-dimensional shape measuring apparatus for focusing the measurement light on the sample to be measured using an optical head and measuring the three-dimensional shape of the sample to be measured.
An optical heterodyne reference beat signal obtained by light from the light source;
The measurement beat signal of the optical heterodyne obtained by the light from the sample to be measured is passed through a low-pass filter and a high-pass filter to detect a DC component and an AC component, and the ratio of the intensity of the AC component to the detected DC component intensity is Store the phase difference with the measured beat signal at the maximum position to obtain the initial phase difference,
While performing focus servo in the optical axis direction of the optical head so that the phase difference between the reference beat signal and the measurement beat signal cancels the change from the stored initial phase difference , the shape of the sample to be measured is changed. It is characterized by measuring.
[0008]
A three-dimensional shape measuring apparatus according to a second aspect of the present invention is the three-dimensional shape measuring apparatus for focusing the measurement light on the sample to be measured using an optical head and measuring the three-dimensional shape of the sample to be measured.
The measurement beat signal of the optical heterodyne obtained by the light from the sample to be measured is passed through a low-pass filter and a high-pass filter to detect a DC component and an AC component, and the ratio of the intensity of the AC component to the detected DC component intensity is The three-dimensional shape of the sample to be measured is measured while performing focus servo in the optical axis direction of the optical head so as to be maximized.
[0009]
According to a third aspect of the present invention, in the first aspect of the invention, the focus servo is performed by moving the optical head in the optical axis direction, and the stage on which the sample to be measured is placed is scanned in a direction perpendicular to the optical axis. The three-dimensional shape of the sample to be measured is measured by monitoring the coordinates of the stage during scanning and the coordinate value of the optical head in the optical axis direction.
[0010]
The invention of claim 4 is the invention of claim 1, wherein the focus servo is performed by moving a stage on which the sample to be measured is placed in the optical axis direction, and scanning the stage in a direction perpendicular to the optical axis, The three-dimensional shape of the sample to be measured is measured by monitoring the optical axis direction of the stage during scanning and the coordinate value in the direction orthogonal to the optical axis.
[0011]
According to a fifth aspect of the invention, in the first aspect of the invention, the focus servo scans the optical head with respect to the sample to be measured in an optical axis direction and a direction orthogonal to the optical axis, and the coordinate value of the optical head during scanning is obtained. The three-dimensional shape of the sample to be measured is measured by monitoring.
[0012]
The three-dimensional shape measuring method of the invention of claim 6 is a three-dimensional shape measuring method for measuring the three-dimensional shape of the sample to be measured by focusing the measurement light on the sample to be measured using an optical head.
An optical heterodyne reference beat signal obtained by light from the light source;
The measurement beat signal of the optical heterodyne obtained by the light from the sample to be measured is passed through a low-pass filter and a high-pass filter to detect a DC component and an AC component, and the ratio of the intensity of the AC component to the detected DC component intensity is The measured beat signal at the maximum position;
The phase difference is memorized as the initial phase difference,
While performing focus servo in the optical axis direction of the optical head so that the phase difference between the reference beat signal and the measurement beat signal cancels the change from the stored initial phase difference , the shape of the sample to be measured is changed. It is characterized by measuring.
[0013]
A three-dimensional shape measuring method according to a seventh aspect of the invention is the three-dimensional shape measuring method for measuring the three-dimensional shape of the sample to be measured by focusing the measurement light on the sample to be measured using an optical head.
The measurement beat signal of the optical heterodyne obtained by the light from the sample to be measured is passed through a low-pass filter and a high-pass filter to detect a DC component and an AC component, and the ratio of the intensity of the AC component to the detected DC component intensity is The three-dimensional shape of the sample to be measured is measured while performing focus servo in the optical axis direction of the optical head so as to be maximized.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows Embodiment 1 of the present invention. In the figure, reference numeral 101 denotes a laser light source that emits coherent single-frequency light. The laser light oscillated from the laser light source is reflected by the mirror M1, and is split into reflected light and transmitted light by the beam splitter 102. The reflected light is reflected by M2, undergoes frequency shift by the acoustooptic device 104a, and becomes laser light of frequency f1. The transmitted light is frequency-shifted by the acoustooptic device 104b to become laser light of frequency f2, reflected by the mirror M3, and then rotated by 90 ° by the half-wave plate 105. The acoustooptic elements 104a and 104b are driven by an acoustooptic element driver 104c. The laser beams having the frequencies f1 and f2 are combined by the polarization beam splitter 103 and become linearly polarized light orthogonal to each other. It is also possible to use a Zeeman laser utilizing the Zeeman effect for the generation of the linearly polarized light.
[0021]
The laser light is split into transmitted light and reflected light by the beam splitter 106. The reflected light with the frequencies f1 and f2 interferes after passing through the linearly polarizing element 107a, and is detected by the photodetector 108 as a reference beat signal. The reference signal can be generated from the driving voltage of the acoustooptic device driver 104c using a mixer circuit.
[0022]
The transmitted light enters the polarization plane preserving optical fiber 109 and is guided to the optical head while maintaining the polarization plane. The laser beam emitted from the polarization plane preserving optical fiber in the optical head is expanded in beam diameter by the beam expander 110 and enters the polarization beam splitter 111. The laser beam incident on the polarization beam splitter 111 is divided into two by the polarization component. The polarization component of the frequency f1 passes through the quarter-wave plate 112a, is focused on the surface of the sample 114 to be measured by the objective lens 113, and is reflected. Even when the surface of the sample 114 to be measured has a surface inclination, if the surface inclination angle is equal to or smaller than the half-open angle of the objective lens 113, a part of the reflected light passes through the objective lens 113 and returns to the same optical path.
[0023]
The sample 114 to be measured is placed on a sample stage 115 having two axes (XY axes) in the in-plane direction orthogonal to the optical axis. The sample stage 115 is provided with an X-axis laser length measuring instrument 116 and an X-axis length measuring mirror 117, and a Y-axis laser length measuring instrument and a Y-axis length measuring mirror (not shown in the figure). Is accurately measured.
[0024]
On the other hand, the polarization component of the frequency f2 passes through the quarter-wave plate 112b and is reflected by the reference plane mirror 118. The quarter-wave plates 112a and 112b in both optical paths serve to prevent the reflected light from returning to the light source by rotating the outgoing polarization direction by 90 ° with respect to the incident polarized light.
The reflected lights of the frequencies f1 and f2 are again combined into one by the polarization beam splitter 111. The synthesized laser beam interferes after passing through the linearly polarizing element 107b, is condensed on the photodetector 120 by the condenser lens 119, and is photoelectrically detected to generate a measurement beat signal.
[0025]
A length measuring mirror 122 is fixed to the optical head 121 in the Z direction, which is the optical axis, and the position in the Z axis direction is precisely measured by the Z axis laser length measuring device 123. The measurement beat signal photoelectrically detected by the photodetector 120 is synchronously detected by the reference beat signal and the lock-in amplifier 124, and the intensity of the measurement beat signal and the phase difference (initial phase difference) between the reference beat signal and the measurement beat signal are detected. The The intensity of the measurement beat signal, the phase difference, and the signal from the Z-axis length measuring device are taken into the computer 126 via the A / D converter 125, and the signal from the computer 126 is converted into a drive signal via the servo driver 127. The sample stage 115 or the optical head 121 is driven after the conversion. Fig. 2 shows the actual measurement flow. First, focus detection is performed, and the optical beat 121 is detected by the photodetector 120 while the optical head 121 is approaching the sample 114 to be measured from the Z-axis direction, and the optical head 121 is placed at a position where the intensity of the measurement beat signal is maximum. stop. Since the measurement light is focused on the surface of the sample 114 to be measured in a state where the intensity of the measurement beat signal is maximized, the phase difference between the reference beat signal and the measurement beat signal at this position is measured. Based on the measured phase difference, the optical path length difference between the reference mirror 118 and the sample 114 to be measured is obtained. Therefore, the sample stage 115 is scanned in the XY axis while applying a servo in the Z-axis direction of the optical head 121 so that the phase difference is constant, and the Z-axis laser length measuring device 123 moves the optical head 121 in the Z-axis direction. When detected, the movement of the optical head 121 in the Z-axis direction follows the surface of the sample. Therefore, the three-dimensional shape of the sample 114 to be measured can be accurately corrected by obtaining a servo system error from the measurement beat signal and correcting the data from the Z length measuring device 123.
[0026]
In the above embodiment, the optical head Z is moved along the axis and the sample stage is moved in the XY direction. However, if the optical head and the sample stage can be moved relatively arbitrarily in the XYZ coordinates, either the optical head or the sample stage can be moved. Good. For example, a configuration in which the optical head is provided with all the functions of moving the XYZ axes and each axis is monitored by a laser length measuring device, or a configuration in which the same is performed on the sample stage side is also possible.
[0027]
FIG. 3 illustrates the detection of the focus of the measurement light in detail. As shown in the figure, the intensity of the beat signal detected by the photodetector 120 is maximized when the measurement light from the objective lens is focused on the surface to be measured. When the measurement light is not focused on the surface to be measured, interference fringes are generated on the photodetector 120, so that the intensity of the detected beat signal is reduced. Therefore, the measurement light is always focused on the surface to be measured by moving the optical head 121 or the sample stage 115 in the direction of the optical axis (Z) so that the beat signal detected by the photodetector 120 is maximized. Can do. In addition, when the sample 114 to be measured has a surface inclination, the reflected light deviates and returns as shown in FIG. 4, but in this case as well, when the measurement light is focused on the surface of the sample 114 to be measured due to interference fringes, Since the intensity of the detected beat signal is maximized, the measurement light can be focused on the surface of the sample 114 to be measured by the same method. About the detection of the intensity of the beat signal In the above embodiment, the configuration using the lock-in amplifier is shown, but after the detection signal is passed through the high-pass filter to cut the DC component, the method of detecting the intensity of the AC component by the peak detector, Alternatively, the detection signal is divided into two, one is passed through a low-pass filter and the other is passed through a high-pass filter to detect the AC component, and the ratio of the AC component to the DC component (visibility) is detected as the beat signal intensity. Alternatively, a method can be used in which a detection signal is passed through a low-pass filter to detect a DC component and a beat signal intensity is obtained from the intensity of the DC component. Although the phase of the beat signal is also detected using the lock-in amplifier in this embodiment, it can also be detected using a phase meter.
[0028]
The configuration of the second embodiment of the present invention is the same as that shown in FIG. FIG. 5 illustrates an actual measurement flow in the present embodiment. First, a measurement beat signal is detected by the photodetector 120 while the optical head 121 is approaching the sample 114 to be measured from the Z-axis direction, and the optical head 121 is stopped at a position where the intensity of the signal is maximized. Since the measurement light is focused on the surface of the sample 114 to be measured with the measurement beat signal intensity maximized, the optical head 121 is servoed in the Z-axis direction so that the measurement beat signal intensity is always maximized. The sample stage 115 is scanned along the XY axes. Along with scanning, the movement of the optical head 121 in the Z-axis direction is detected by the Z-axis laser length measuring device 123. Since the optical path length difference between the reference mirror 118 and the sample 114 to be measured is obtained from the measurement value from the Z-axis laser length measuring device 123 and the measurement beat signal, the three-dimensional shape of the sample 114 to be measured can be accurately measured.
[0029]
In this embodiment, the optical head 121 is moved in the Z axis and the sample stage 115 is moved in the XY direction. However, as described in the description of the first embodiment, the optical head 121 and the sample stage 115 can be relatively arbitrarily set in the XYZ coordinates. If it can be moved, either the optical head 121 or the sample stage 115 may be moved.
[0030]
【The invention's effect】
As described above, in the three-dimensional shape measurement method and apparatus of the present invention, when measuring a three-dimensional shape while focusing the measurement light on the surface to be measured using the objective lens, the measurement beat signal of the heterodyne is measured. For example, the intensity or phase is used for detecting the focus state of the measurement light. Thereby, focus detection can be performed with high accuracy, and measurement accuracy is improved. There is no need to specially prepare the focus state detection optical system for focusing the measuring beam onto the sample surface when measuring the three-dimensional shape using the optical heterodyne method if example embodiment in the present invention, Since the apparatus configuration is simplified and the focus is detected using the measurement signal itself, the three-dimensional shape of the sample to be measured can be measured in a non-contact manner with high measurement accuracy.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of Embodiment 1 of the present invention;
FIG. 2 is a measurement flowchart of Embodiment 1.
FIG. 3 is an explanatory diagram of the focus of measurement light;
FIG. 4 is an explanatory diagram of the focus of measurement light when there is a surface inclination;
FIG. 5 is a flowchart of Embodiment 2.
FIG. 6 is a diagram showing a conventional three-dimensional shape measuring apparatus.
101 Laser light source
103, 111 Polarizing beam splitter
104a, 104b Acoustooptic device
104c Acousto-optic device driver
105 half-wave plate
102, 106 Beam splitter
107a, 107b linear polarizer
108 photodetector
109 Polarization-preserving optical fiber
110 beam expander
111 Polarizing beam splitter
112a, 112b quarter wave plate
113 Objective lens
114 Sample to be measured
115 Sample stage
116 X-axis laser length measuring instrument
117 X-axis measuring mirror
118 Reference plane mirror
119 Condensing lens
120 photodetectors
121 optical head
122 Z-axis measuring mirror
123 Z-axis measuring instrument
124 Lock-in amplifier
125 A / D converter
126 computers
127 Servo driver
301 Zeeman laser
302 Beam splitter
303, 306, 310, 311 photodetector
304 Polarizing beam splitter
305 fixed mirror
307 half mirror
308 Objective lens
309 Sample to be measured
312 Drive unit

Claims (7)

光ヘッドを用いて測定光を被測定試料上にフォーカスさせ、該被測定試料の三次元形状を測定する三次元形状測定装置において、
光源からの光により得られる光ヘテロダインの参照ビート信号と、
該被測定試料からの光により得られる光ヘテロダインの測定ビート信号を、ローパスフィルタとハイパスフィルタに通して直流成分と交流成分とを検出し、検出した直流成分の強度に対する交流成分の強度の比が最大になる位置における該測定ビート信号との位相差を記憶して初期位相差とし、
前記参照ビート信号と前記測定ビート信号との位相差が、記憶された前記初期位相差からの変化を打ち消すように該光ヘッドの光軸方向のフォーカスサーボを行いながら、該被測定試料の形状を測定することを特徴とする三次元形状計測装置。In the three-dimensional shape measuring apparatus that focuses the measurement light on the sample to be measured using an optical head and measures the three-dimensional shape of the sample to be measured.
An optical heterodyne reference beat signal obtained by light from the light source;
The measurement beat signal of the optical heterodyne obtained by the light from the sample to be measured is passed through a low-pass filter and a high-pass filter to detect a DC component and an AC component, and the ratio of the intensity of the AC component to the detected DC component intensity is Store the phase difference with the measured beat signal at the maximum position to obtain the initial phase difference,
While performing focus servo in the optical axis direction of the optical head so that the phase difference between the reference beat signal and the measurement beat signal cancels the change from the stored initial phase difference , the shape of the sample to be measured is changed. A three-dimensional shape measuring apparatus characterized by measuring. 光ヘッドを用いて測定光を被測定試料上にフォーカスさせ、該被測定試料の三次元形状を測定する三次元形状測定装置において、
該被測定試料からの光により得られる光ヘテロダインの測定ビート信号を、ローパスフィルタとハイパスフィルタに通して直流成分と交流成分とを検出し、検出した直流成分の強度に対する交流成分の強度の比が最大になるように該光ヘッドの光軸方向にフォーカスサーボを行いながら、該被測定試料の三次元形状を測定することを特徴とする三次元形状計測装置。 In the three-dimensional shape measuring apparatus that focuses the measurement light on the sample to be measured using an optical head and measures the three-dimensional shape of the sample to be measured.
The measurement beat signal of the optical heterodyne obtained by the light from the sample to be measured is passed through a low-pass filter and a high-pass filter to detect a DC component and an AC component, and the ratio of the intensity of the AC component to the detected DC component intensity is A three-dimensional shape measuring apparatus for measuring the three-dimensional shape of the sample to be measured while performing focus servo in the optical axis direction of the optical head so as to be maximized. 該フォーカスサーボを該光ヘッドを光軸方向に移動させて行うとともに、該被測定試料を載置したステージを光軸と直交する方向に走査し、走査時の該ステージの座標と該光ヘッドの光軸方向の座標値をモニタすることにより該被測定試料の三次元形状を測定することを特徴とする請求項１記載の三次元形状計測装置。The focus servo is performed by moving the optical head in the direction of the optical axis, and the stage on which the sample to be measured is placed is scanned in a direction orthogonal to the optical axis, and the coordinates of the stage during scanning and the optical head The three-dimensional shape measuring apparatus according to claim 1, wherein the three-dimensional shape of the sample to be measured is measured by monitoring coordinate values in the optical axis direction. 該フォーカスサーボを該被測定試料を載置したステージを光軸方向に移動させて行うとともに、該ステージを光軸と直交する方向に走査し、走査時の該ステージの光軸方向、及び光軸と直交方向の座標値をモニタすることにより該被測定試料の三次元形状を測定することを特徴とする請求項１記載の三次元形状計測装置。The focus servo is performed by moving the stage on which the sample to be measured is moved in the optical axis direction, scanning the stage in a direction orthogonal to the optical axis, and the optical axis direction of the stage at the time of scanning, and the optical axis. 2. The three-dimensional shape measuring apparatus according to claim 1, wherein the three-dimensional shape of the sample to be measured is measured by monitoring coordinate values in a direction orthogonal to the measurement target. 該フォーカスサーボを該被測定試料に対し該光ヘッドを光軸方向と光軸と直交方向に走査し、走査時の該光ヘッドの座標値をモニタすることにより該被測定試料の三次元形状を測定することを特徴とする請求項１記載の三次元形状計測装置。The focus servo scans the sample to be measured with the optical head in the direction of the optical axis and the direction orthogonal to the optical axis, and monitors the coordinate value of the optical head during scanning to obtain the three-dimensional shape of the sample to be measured. The three-dimensional shape measurement apparatus according to claim 1, wherein measurement is performed. 光ヘッドを用いて測定光を被測定試料上にフォーカスさせ、該被測定試料の三次元形状を測定する三次元形状測定方法において、
光源からの光により得られる光ヘテロダインの参照ビート信号と、
該被測定試料からの光により得られる光ヘテロダインの測定ビート信号を、ローパスフィルタとハイパスフィルタに通して直流成分と交流成分とを検出し、検出した直流成分の強度に対する交流成分の強度の比が最大になる位置における該測定ビート信号と、
の位相差を記憶して初期位相差とし、
前記参照ビート信号と前記測定ビート信号との位相差が、記憶された前記初期位相差からの変化を打ち消すように該光ヘッドの光軸方向にフォーカスサーボを行いながら、該被測定試料の形状を測定することを特徴とする三次元形状計測方法。In a three-dimensional shape measurement method for focusing measurement light on a sample to be measured using an optical head and measuring the three-dimensional shape of the sample to be measured.
An optical heterodyne reference beat signal obtained by light from the light source;
The measurement beat signal of the optical heterodyne obtained by the light from the sample to be measured is passed through a low-pass filter and a high-pass filter to detect a DC component and an AC component, and the ratio of the intensity of the AC component to the detected DC component intensity is The measured beat signal at the maximum position;
The phase difference is memorized as the initial phase difference,
While performing focus servo in the optical axis direction of the optical head so that the phase difference between the reference beat signal and the measurement beat signal cancels the change from the stored initial phase difference , the shape of the sample to be measured is changed. A three-dimensional shape measuring method characterized by measuring. 光ヘッドを用いて測定光を被測定試料上にフォーカスさせ、該被測定試料の三次元形状を測定する三次元形状測定方法において、
該被測定試料からの光により得られる光ヘテロダインの測定ビート信号を、ローパスフィルタとハイパスフィルタに通して直流成分と交流成分とを検出し、検出した直流成分の強度に対する交流成分の強度の比が最大になるように該光ヘッドの光軸方向にフォーカスサーボを行いながら、該被測定試料の三次元形状を測定することを特徴とする三次元形状計測方法。 In a three-dimensional shape measurement method for focusing measurement light on a sample to be measured using an optical head and measuring the three-dimensional shape of the sample to be measured.
The measurement beat signal of the optical heterodyne obtained by the light from the sample to be measured is passed through a low-pass filter and a high-pass filter to detect a DC component and an AC component, and the ratio of the intensity of the AC component to the detected DC component intensity is A three-dimensional shape measuring method, comprising: measuring a three-dimensional shape of the sample to be measured while performing focus servo in an optical axis direction of the optical head so as to be maximized.
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