JP4554385B2 - Surface shape measuring method and measuring apparatus - Google Patents

Surface shape measuring method and measuring apparatus Download PDF

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JP4554385B2
JP4554385B2 JP2005020159A JP2005020159A JP4554385B2 JP 4554385 B2 JP4554385 B2 JP 4554385B2 JP 2005020159 A JP2005020159 A JP 2005020159A JP 2005020159 A JP2005020159 A JP 2005020159A JP 4554385 B2 JP4554385 B2 JP 4554385B2
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徹 志水
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Hamamatsu Photonics KK
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Description

本発明は、計測対象面からの反射光と参照光とを干渉させて、得られる干渉光強度の変化から計測対象面の形状を計測する表面形状計測方法、及び表面形状計測装置に関するものである。   The present invention relates to a surface shape measuring method and a surface shape measuring apparatus for causing a reflected light from a measurement target surface to interfere with a reference light and measuring the shape of the measurement target surface from a change in interference light intensity obtained. .

垂直走査白色干渉法は、一定の波長幅を有する計測光（白色光）を用いて計測対象となる試料の表面を垂直方向に走査し、計測対象面からの反射光と参照光とを干渉させて、得られる干渉光強度の変化から計測対象面の形状を計測する方法である。   In the vertical scanning white light interferometry, the surface of the sample to be measured is scanned in the vertical direction using measurement light (white light) having a certain wavelength width, and the reflected light from the measurement target surface interferes with the reference light. Thus, the shape of the measurement target surface is measured from the change in the interference light intensity obtained.

このような計測方法では、計測光が波長幅に応じた短いコヒーレンス長を有するため、反射光と参照光との光路長が一致した付近でしか干渉が起こらず、その光路長が一致したときに干渉光強度の振幅（干渉強さ）が最大となる。したがって、反射光または参照光の光路長を変化させて計測対象面を垂直方向に走査し、得られる干渉強さのピーク位置を求めることで、計測位置における計測対象面の垂直方向の高さを導出することができる。さらに、このような計測を２次元で行えば、計測対象面の表面形状が計測できる（例えば、特許文献１、２参照）。
米国特許第５，１３３，６０１号公報 特開２００１−６６１２２号公報 In such a measurement method, since the measurement light has a short coherence length corresponding to the wavelength width, interference occurs only in the vicinity where the optical path lengths of the reflected light and the reference light match, and when the optical path lengths match. The amplitude of interference light intensity (interference strength) is maximized. Therefore, by changing the optical path length of the reflected light or the reference light, scanning the measurement target surface in the vertical direction, and obtaining the peak position of the obtained interference intensity, the vertical height of the measurement target surface at the measurement position is determined. Can be derived. Furthermore, if such measurement is performed in two dimensions, the surface shape of the measurement target surface can be measured (see, for example, Patent Documents 1 and 2).
US Pat. No. 5,133,601 JP 2001-66122 A

上記した干渉法によって表面形状計測を行う装置として、例えば特許文献１に記載された装置がある。この装置では、その基本的な構成は顕微鏡であるが、対物レンズとして、内部にビームスプリッタと参照ミラーとを有する干渉対物レンズを用いている。このような構成において、干渉対物レンズを計測光の照射方向である垂直方向に移動させることにより、計測対象面の垂直方向の走査による高さの計測を行うことができる。   As an apparatus for measuring the surface shape by the above-described interferometry, there is an apparatus described in Patent Document 1, for example. In this apparatus, the basic configuration is a microscope, but an interference objective lens having a beam splitter and a reference mirror inside is used as an objective lens. In such a configuration, by moving the interference objective lens in the vertical direction, which is the irradiation direction of the measurement light, the height can be measured by scanning the measurement target surface in the vertical direction.

具体的には、このような計測方法では、ある程度の計測間隔で計測対象面からの反射光と参照光との光路長差を変化させて、各計測点での干渉光強度を取得する。そして、得られた干渉光強度の光路長差についての変化に対し、オフセットを引いて絶対値変換した後にデータの平滑化等によって包絡線に相当する曲線を求め、そのピーク位置によって計測対象面の高さを導出する。   Specifically, in such a measurement method, the interference light intensity at each measurement point is acquired by changing the optical path length difference between the reflected light from the measurement target surface and the reference light at a certain measurement interval. Then, with respect to the change in the optical path length difference of the obtained interference light intensity, an absolute value conversion is performed by subtracting an offset, and then a curve corresponding to the envelope is obtained by data smoothing or the like. Deriving the height.

しかしながら、このような方法では、ある程度以上の細かい計測間隔、例えば１００ｎｍ程度の間隔で光路長差（上記構成では干渉対物レンズの位置）を変化させて、計測対象面の垂直方向の走査を行う必要がある。したがって、垂直方向で広範囲に計測を行う必要がある場合には、その計測時間が非常に長くなるという問題がある。   However, in such a method, it is necessary to scan the measurement target surface in the vertical direction by changing the optical path length difference (position of the interference objective lens in the above configuration) at a measurement interval of a certain degree or more, for example, about 100 nm. There is. Therefore, when it is necessary to perform measurement in a wide range in the vertical direction, there is a problem that the measurement time becomes very long.

本発明は、以上の問題点を解決するためになされたものであり、短い計測時間で計測対象面の形状を計測することが可能な表面形状計測方法及び計測装置を提供することを目的とする。   The present invention has been made to solve the above problems, and an object of the present invention is to provide a surface shape measurement method and a measurement apparatus capable of measuring the shape of a measurement target surface in a short measurement time. .

このような目的を達成するために、本発明による表面形状計測方法は、所定の波長幅を有する計測光を計測対象面に照射し、計測対象面からの反射光、及び反射光に対する光路長差が制御可能な参照光を干渉させて、得られる干渉光強度の光路長差についての変化から計測対象面の形状を計測する計測方法であって、（１）計測対象面における計測光の照射方向からみた計測位置に対して、反射光と参照光との光路長差について、計測光の波長に基づく微小計測間隔、及び微小計測間隔よりも大きい広域計測間隔を設定する設定ステップと、（２）計測位置に対して、光路長差として広域計測間隔でｎ個の光路長差（ｎは３以上の整数）を設定し、そのそれぞれの近傍において微小計測間隔で光路長差を変化させて干渉光強度の変化を計測する計測ステップと、（３）計測ステップで得られた干渉光強度の変化のｎ個の計測結果から求められるｎ個の光路長差のそれぞれでの干渉強さに基づいて、計測位置における計測対象面の照射方向の高さを導出する導出ステップとを備えることを特徴とする。   In order to achieve such an object, a surface shape measurement method according to the present invention irradiates a measurement target surface with measurement light having a predetermined wavelength width, and reflects the reflected light from the measurement target surface and the optical path length difference with respect to the reflected light. Is a measurement method for measuring the shape of the measurement target surface from the change in the optical path length difference of the interference light intensity obtained by interfering controllable reference light, and (1) the irradiation direction of the measurement light on the measurement target surface A setting step for setting a micro measurement interval based on the wavelength of the measurement light and a wide-area measurement interval larger than the micro measurement interval with respect to the optical path length difference between the reflected light and the reference light with respect to the measurement position viewed from the viewpoint (2) For the measurement position, n optical path length differences (n is an integer of 3 or more) are set as optical path length differences at wide-range measurement intervals, and interference light is changed by changing the optical path length difference at minute measurement intervals in the vicinity thereof. Measure changes in intensity The measurement target surface at the measurement position based on the measurement step and (3) the interference intensity at each of the n optical path length differences obtained from the n measurement results of the change in the interference light intensity obtained at the measurement step And a deriving step for deriving the height in the irradiation direction.

同様に、本発明による表面形状計測装置は、（ａ）所定の波長幅を有する計測光を供給する計測光供給手段と、（ｂ）計測光を計測対象面に照射するとともに、計測対象面からの反射光、及び反射光に対する光路長差が制御可能な参照光を干渉させる計測光学系と、（ｃ）計測光学系によって反射光及び参照光を干渉させて得られる干渉光強度を検出する検出手段と、（ｄ）反射光と参照光との光路長差を制御する光路長差制御手段と、（ｅ）検出手段によって検出された干渉光強度の光路長差についての変化から計測対象面の形状を導出する表面形状導出手段とを備え、（ｆ）光路長差制御手段は、計測対象面における計測光の照射方向からみた計測位置に対して、光路長差について、計測光の波長に基づく微小計測間隔、及び微小計測間隔よりも大きい広域計測間隔を設定するとともに、光路長差として広域計測間隔でｎ個の光路長差（ｎは３以上の整数）を設定し、そのそれぞれの近傍において微小計測間隔で光路長差を変化させて干渉光強度の変化を計測するｎ個の計測条件で光路長差を制御し、（ｇ）表面形状導出手段は、ｎ個の計測条件で得られた干渉光強度の変化のｎ個の計測結果から求められるｎ個の光路長差のそれぞれでの干渉強さに基づいて、計測位置における計測対象面の照射方向の高さを導出することを特徴とする。   Similarly, the surface shape measurement apparatus according to the present invention includes (a) measurement light supply means for supplying measurement light having a predetermined wavelength width, and (b) irradiating the measurement target surface with the measurement light, and from the measurement target surface. And a measurement optical system that interferes with the reflected light and a reference light whose optical path length difference with respect to the reflected light can be controlled, and (c) a detection that detects the interference light intensity obtained by causing the measurement optical system to interfere with the reflected light and the reference light. Means, (d) an optical path length difference control means for controlling the optical path length difference between the reflected light and the reference light, and (e) a change in the optical path length difference of the interference light intensity detected by the detecting means, A surface shape deriving unit for deriving the shape, and (f) the optical path length difference control unit is based on the wavelength of the measurement light with respect to the optical path length difference with respect to the measurement position viewed from the measurement light irradiation direction on the measurement target surface. Minute measurement interval and minute measurement interval A larger measurement interval is set, and n optical path length differences (n is an integer of 3 or more) are set as the optical path length difference, and the optical path length difference is set at a minute measurement interval in the vicinity thereof. The optical path length difference is controlled under n measurement conditions for measuring the change in interference light intensity by changing, and (g) the surface shape deriving means has n changes in the interference light intensity obtained under the n measurement conditions. The height in the irradiation direction of the measurement target surface at the measurement position is derived based on the interference intensity at each of the n optical path length differences obtained from the measurement results.

上記した表面形状計測方法及び計測装置においては、設定された光路長差の近傍において微小計測間隔で垂直方向の走査を行って、その光路長差での局所的な干渉強さを求めるとともに、このような局所的な計測を広域計測間隔でｎ個の光路長差について行うことにより、干渉強さのピーク位置の算出、及びそれによる計測対象面の垂直方向の高さの導出を行っている。このように、微小計測間隔及び広域計測間隔の２種類の計測間隔を設定して計測光による走査を行うことにより、短い計測時間で計測対象面の形状を計測することが可能となる。   In the above-described surface shape measuring method and measuring apparatus, scanning in the vertical direction is performed at a minute measurement interval in the vicinity of the set optical path length difference, and the local interference strength at the optical path length difference is obtained. By performing such local measurement for n optical path length differences at wide measurement intervals, the peak position of the interference intensity is calculated and the vertical height of the measurement target surface is thereby derived. In this way, by setting two types of measurement intervals, a minute measurement interval and a wide-range measurement interval, and performing scanning with measurement light, the shape of the measurement target surface can be measured in a short measurement time.

ここで、計測方法は、計測ステップにおいて、ｎ個の光路長差のそれぞれの近傍において、微小計測間隔で光路長差を３回以上変化させて干渉光強度の変化を計測することが好ましい。同様に、計測装置は、光路長差制御手段が、ｎ個の光路長差のそれぞれの近傍において、微小計測間隔で光路長差を３回以上変化させて干渉光強度の変化を計測する計測条件で光路長差を制御することが好ましい。これにより、ｎ個の光路長差のそれぞれでの干渉強さを好適に求めることができる。   Here, in the measurement method, it is preferable to measure the change in the interference light intensity by changing the optical path length difference at least three times at a minute measurement interval in the vicinity of each of the n optical path length differences. Similarly, the measurement apparatus is configured so that the optical path length difference control unit measures the change in the interference light intensity by changing the optical path length difference three times or more at a minute measurement interval in the vicinity of each of the n optical path length differences. It is preferable to control the optical path length difference. As a result, the interference intensity at each of the n optical path length differences can be suitably obtained.

干渉強さの具体的な求め方については、計測方法は、設定ステップにおいて、微小計測間隔をπ／２の位相差に対応する間隔に設定するとともに、計測ステップにおいて、ｎ個の光路長差のそれぞれの近傍において、微小計測間隔で光路長差を３回変化させて３個の干渉光強度Ｉ１、Ｉ２、Ｉ３を計測し、導出ステップにおいて、ｎ個の光路長差のそれぞれについて、式

Figure 0004554385
によって干渉強さを求める方法を用いることができる。 As for a specific method for obtaining the interference strength, the measurement method sets the minute measurement interval to an interval corresponding to a phase difference of π / 2 in the setting step, and the n optical path length differences in the measurement step. In each vicinity, three interference light intensities I 1 , I 2 , and I 3 are measured by changing the optical path length difference three times at a minute measurement interval, and in the derivation step, for each of the n optical path length differences, formula
Figure 0004554385
 A method for obtaining the interference strength can be used.

同様に、計測装置は、光路長差制御手段が、微小計測間隔をπ／２の位相差に対応する間隔に設定するとともに、ｎ個の光路長差のそれぞれの近傍において、微小計測間隔で光路長差を３回変化させて３個の干渉光強度Ｉ１、Ｉ２、Ｉ３を計測する計測条件で光路長差を制御し、表面形状導出手段が、ｎ個の光路長差のそれぞれについて、式

Figure 0004554385
によって干渉強さを求める構成を用いることができる。 Similarly, in the measurement apparatus, the optical path length difference control unit sets the minute measurement interval to an interval corresponding to the phase difference of π / 2, and the optical path at the minute measurement interval in the vicinity of each of the n optical path length differences. The optical path length difference is controlled under measurement conditions in which the length difference is changed three times and three interference light intensities I 1 , I 2 , and I 3 are measured, and the surface shape deriving means is configured for each of the n optical path length differences. ,formula
Figure 0004554385
 The structure which calculates | requires interference strength by can be used.

あるいは、計測方法は、導出ステップにおいて、ｎ個の光路長差のそれぞれについて、干渉光強度の変化の計測結果に対してフィッティング計算を行って干渉強さを求める方法を用いることができる。同様に、計測装置は、表面形状導出手段が、ｎ個の光路長差のそれぞれについて、干渉光強度の変化の計測結果に対してフィッティング計算を行って干渉強さを求める構成を用いることができる。   Alternatively, the measurement method can use a method of calculating the interference intensity by performing fitting calculation on the measurement result of the change in interference light intensity for each of the n optical path length differences in the derivation step. Similarly, the measurement apparatus can use a configuration in which the surface shape deriving unit obtains the interference intensity by performing fitting calculation on the measurement result of the change in interference light intensity for each of the n optical path length differences. .

あるいは、計測方法は、導出ステップにおいて、ｎ個の光路長差のそれぞれについて、干渉光強度の変化の計測結果でのばらつきによって干渉強さを求める方法を用いることができる。同様に、計測装置は、表面形状導出手段が、ｎ個の光路長差のそれぞれについて、干渉光強度の変化の計測結果でのばらつきによって干渉強さを求める構成を用いることができる。   Alternatively, as the measurement method, a method of obtaining the interference intensity by the variation in the measurement result of the change in the interference light intensity for each of the n optical path length differences in the derivation step can be used. Similarly, the measurement apparatus can use a configuration in which the surface shape deriving unit obtains the interference intensity based on the variation in the measurement result of the change in the interference light intensity for each of the n optical path length differences.

本発明によれば、設定された光路長差の近傍において微小計測間隔で垂直方向の走査を行って、その光路長差での局所的な干渉強さを求めるとともに、このような局所的な計測を広域計測間隔でｎ個の光路長差について行って計測対象面の垂直方向の高さを導出することにより、短い計測時間で計測対象面の形状を計測することが可能な表面形状計測方法及び計測装置が実現される。   According to the present invention, vertical scanning is performed at a minute measurement interval in the vicinity of the set optical path length difference to obtain local interference strength at the optical path length difference, and such local measurement is performed. A surface shape measurement method capable of measuring the shape of the measurement target surface in a short measurement time by deriving the vertical height of the measurement target surface by performing n optical path length differences at wide measurement intervals, and A measuring device is realized.

以下、図面とともに本発明による表面形状計測方法及び計測装置の好適な実施形態について詳細に説明する。なお、図面の説明においては同一要素には同一符号を付し、重複する説明を省略する。また、図面の寸法比率は、説明のものと必ずしも一致していない。   Hereinafter, preferred embodiments of a surface shape measuring method and a measuring apparatus according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the dimensional ratios in the drawings do not necessarily match those described.

図１は、本発明による表面形状計測装置の一実施形態の構成を示すブロック図である。この表面形状計測装置１Ａは、計測光供給部１０と、ＣＣＤカメラ１５と、計測光学系２０と、ＸＹステージ３０と、ピエゾ素子４０と、計測制御装置５０とを備えて構成されている。   FIG. 1 is a block diagram showing a configuration of an embodiment of a surface shape measuring apparatus according to the present invention. The surface shape measuring apparatus 1A includes a measuring light supply unit 10, a CCD camera 15, a measuring optical system 20, an XY stage 30, a piezo element 40, and a measurement control device 50.

本実施形態による表面形状計測装置１Ａは、所定の波長幅を有する計測光を試料Ｓの上面である計測対象面Ｓ１に照射し、計測対象面Ｓ１からの反射光、及び反射光に対する光路長差が制御可能な参照光を干渉させて、得られる干渉光強度の光路長差についての変化から計測対象面Ｓ１の形状を計測するように構成されている。ここで、本計測装置１Ａにおける計測光の照射方向となる垂直方向をＺ方向、Ｚ方向に直交する水平方向をＸ方向及びＹ方向とし、また、紙面をＸＺ平面とする。   The surface shape measuring apparatus 1A according to the present embodiment irradiates measurement light having a predetermined wavelength width onto the measurement target surface S1 that is the upper surface of the sample S, and the reflected light from the measurement target surface S1 and the optical path length difference with respect to the reflected light. Is configured to measure the shape of the measurement target surface S1 from the change in the optical path length difference of the obtained interference light intensity by causing the controllable reference light to interfere. Here, the vertical direction that is the measurement light irradiation direction in the measurement apparatus 1A is the Z direction, the horizontal directions orthogonal to the Z direction are the X direction and the Y direction, and the paper surface is the XZ plane.

計測対象面Ｓ１の形状計測に用いられる計測光は、計測光供給部１０によって供給される。本実施形態においては、計測光供給部１０は、白色光を供給する計測光源１１と、白色光を平行光とするレンズ１２と、波長フィルタであるバンドパスフィルタ１３とを有している。このような構成において、計測光源１１からの白色光が所定の透過特性を有するバンドパスフィルタ１３を透過することにより、所定の中心波長、及び波長幅を有する計測光が生成される。そして、生成された計測光は、図１に示すように、計測光供給部１０からＸ方向に沿って計測光学系２０へと供給される。   Measurement light used for measuring the shape of the measurement target surface S <b> 1 is supplied by the measurement light supply unit 10. In the present embodiment, the measurement light supply unit 10 includes a measurement light source 11 that supplies white light, a lens 12 that uses white light as parallel light, and a bandpass filter 13 that is a wavelength filter. In such a configuration, white light from the measurement light source 11 passes through the band-pass filter 13 having a predetermined transmission characteristic, thereby generating measurement light having a predetermined center wavelength and wavelength width. Then, as shown in FIG. 1, the generated measurement light is supplied from the measurement light supply unit 10 to the measurement optical system 20 along the X direction.

計測光学系２０は、Ｚ方向に沿った軸Ａｘを光軸とし、干渉対物レンズ２１と、ビームスプリッタ２６とを有して構成されている。ビームスプリッタ２６は、光軸Ａｘに対して４５°の角度で傾いて配置されており、ビームスプリッタ２６で反射された計測光供給部１０からの計測光が、下方に位置するＸＹステージ３０上の試料Ｓの計測対象面Ｓ１へと光軸Ａｘに沿って照射されるようになっている。   The measurement optical system 20 includes an interference objective lens 21 and a beam splitter 26 with an axis Ax along the Z direction as an optical axis. The beam splitter 26 is disposed at an angle of 45 ° with respect to the optical axis Ax, and the measurement light from the measurement light supply unit 10 reflected by the beam splitter 26 is on the XY stage 30 positioned below. The measurement target surface S1 of the sample S is irradiated along the optical axis Ax.

ビームスプリッタ２６とＸＹステージ３０との間には、干渉対物レンズ２１が設置されている。この干渉対物レンズ２１は、ビームスプリッタ２６からの計測光を計測対象面Ｓ１上の計測位置へと集束させるレンズ２２に加えて、干渉光学系を構成するためのビームスプリッタ２３と、参照ミラー２４とを有している。これらのレンズ２２、ビームスプリッタ２３、及び参照ミラー２４は、光軸Ａｘを中心とした筒状の保持部材２５によって、位置決めされた状態で一体に保持されている。また、この保持部材２５に対して、ピエゾ素子４０が設置されている。   An interference objective lens 21 is installed between the beam splitter 26 and the XY stage 30. The interference objective lens 21 includes a beam splitter 23 for forming an interference optical system, a reference mirror 24, in addition to a lens 22 that focuses measurement light from the beam splitter 26 to a measurement position on the measurement target surface S 1. have. The lens 22, the beam splitter 23, and the reference mirror 24 are integrally held in a positioned state by a cylindrical holding member 25 centered on the optical axis Ax. A piezo element 40 is installed on the holding member 25.

ビームスプリッタ２３は、レンズ２２からみてＸＹステージ３０側の所定位置に、光軸Ａｘに対して直交するように配置されている。また、レンズ２２とビームスプリッタ２３との間の光軸Ａｘ上の所定位置には、参照ミラー２４が配置されている。ビームスプリッタ２３は、レンズ２２からの計測光をＸＹステージ３０上の試料Ｓへと透過させるとともに、計測光の一部を反射して参照ミラー２４へと導く。   The beam splitter 23 is disposed at a predetermined position on the XY stage 30 side as viewed from the lens 22 so as to be orthogonal to the optical axis Ax. A reference mirror 24 is disposed at a predetermined position on the optical axis Ax between the lens 22 and the beam splitter 23. The beam splitter 23 transmits the measurement light from the lens 22 to the sample S on the XY stage 30 and reflects a part of the measurement light to guide it to the reference mirror 24.

このような干渉対物レンズ２１の構成において、レンズ２２からの計測光がビームスプリッタ２３を透過し、試料Ｓの計測対象面Ｓ１で反射された反射光が再びビームスプリッタ２３を透過してレンズ２２に到達する光路が、計測光路となっている。また、レンズ２２からの計測光がビームスプリッタ２３で反射されて参照光となり、参照ミラー２４で反射された参照光が再びビームスプリッタ２３で反射されてレンズ２２に到達する光路が、参照光路となっている。そして、計測光路を通った計測対象面Ｓ１からの反射光と、参照光路を通った参照ミラー２４からの参照光とが干渉し、得られた干渉光が光軸Ａｘに沿って干渉対物レンズ２１の上方へと出射される。   In such a configuration of the interference objective lens 21, the measurement light from the lens 22 passes through the beam splitter 23, and the reflected light reflected by the measurement target surface S 1 of the sample S passes through the beam splitter 23 again to the lens 22. The reaching optical path is a measurement optical path. Also, the measurement light from the lens 22 is reflected by the beam splitter 23 to become reference light, and the reference light reflected by the reference mirror 24 is reflected again by the beam splitter 23 and reaches the lens 22 becomes the reference light path. ing. Then, the reflected light from the measurement target surface S1 that has passed through the measurement optical path interferes with the reference light from the reference mirror 24 that has passed through the reference optical path, and the obtained interference light passes along the optical axis Ax to the interference objective lens 21. Is emitted upward.

ここで、計測光学系２０での上記した光路のうち、参照光路の光路長は一定であるが、計測光路の光路長については、干渉対物レンズ２１と計測対象面Ｓ１とのＺ方向の距離を変えることによって変化する。これにより、試料Ｓの計測対象面Ｓ１の形状計測に用いられる干渉光を生じさせる反射光と参照光との光路長差が制御可能となっている。   Here, among the optical paths described above in the measurement optical system 20, the optical path length of the reference optical path is constant, but the optical path length of the measurement optical path is the distance in the Z direction between the interference objective lens 21 and the measurement target surface S1. It changes by changing. Thereby, the optical path length difference between the reflected light and the reference light that generate the interference light used for the shape measurement of the measurement target surface S1 of the sample S can be controlled.

干渉対物レンズ２１及びビームスプリッタ２６に対して光軸Ａｘに沿って上方には、レンズ２７及びＣＣＤカメラ１５が設置されている。ＣＣＤカメラ１５は、計測光学系２０において反射光及び参照光が干渉した干渉光強度を検出する検出手段である。干渉対物レンズ２１から上方へと出射された干渉光は、レンズ２７によって集束されつつＣＣＤカメラ１５へと入射し、その干渉光強度がＣＣＤカメラ１５によって検出される。   A lens 27 and a CCD camera 15 are installed above the interference objective lens 21 and the beam splitter 26 along the optical axis Ax. The CCD camera 15 is a detection unit that detects interference light intensity at which the reflected light and the reference light interfere in the measurement optical system 20. The interference light emitted upward from the interference objective lens 21 is incident on the CCD camera 15 while being focused by the lens 27, and the interference light intensity is detected by the CCD camera 15.

計測光学系２０による試料Ｓの計測対象面Ｓ１の計測条件は、試料Ｓを載置するＸＹステージ３０、及び干渉対物レンズ２１に対して設置されたピエゾ素子４０によって設定または変更される。ＸＹステージ３０は、水平方向（Ｘ方向、Ｙ方向）に駆動可能なモータステージであり、試料Ｓの計測対象面Ｓ１における計測光の照射方向（垂直方向）からみた計測位置（ＸＹ平面上での位置）を設定するために用いられる。   The measurement conditions of the measurement target surface S1 of the sample S by the measurement optical system 20 are set or changed by the XY stage 30 on which the sample S is placed and the piezo element 40 installed with respect to the interference objective lens 21. The XY stage 30 is a motor stage that can be driven in the horizontal direction (X direction, Y direction), and is a measurement position (on the XY plane) as viewed from the measurement light irradiation direction (vertical direction) on the measurement target surface S1 of the sample S. Used to set the position).

ピエゾ素子４０は、干渉対物レンズ２１を垂直方向（Ｚ方向）に駆動させる駆動手段であり、干渉対物レンズ２１と計測対象面Ｓ１との距離を設定するために用いられる。本実施形態では、このピエゾ素子４０を駆動して干渉対物レンズ２１と計測対象面Ｓ１との距離を変化させることにより、反射光と参照光との光路長差が変化するようになっている。また、ＸＹステージ３０、及びピエゾ素子４０の駆動は、それぞれステージコントローラ６０、及びピエゾコントローラ７０によって制御されている。   The piezo element 40 is a driving unit that drives the interference objective lens 21 in the vertical direction (Z direction), and is used to set the distance between the interference objective lens 21 and the measurement target surface S1. In the present embodiment, the optical path length difference between the reflected light and the reference light is changed by driving this piezo element 40 to change the distance between the interference objective lens 21 and the measurement target surface S1. The driving of the XY stage 30 and the piezo element 40 is controlled by a stage controller 60 and a piezo controller 70, respectively.

これらの計測光供給部１０、計測光学系２０、ＣＣＤカメラ１５、ＸＹステージ３０、及びピエゾ素子４０に対し、コンピュータなどからなる計測制御装置５０が設けられている。この計測制御装置５０には、ＣＣＤカメラ１５、ステージコントローラ６０、及びピエゾコントローラ７０が接続されている。計測制御装置５０は、本計測装置１Ａの上記各部の動作を制御することにより、試料Ｓの計測対象面Ｓ１の形状計測を制御する。   For these measurement light supply unit 10, measurement optical system 20, CCD camera 15, XY stage 30, and piezo element 40, a measurement control device 50 including a computer or the like is provided. The measurement controller 50 is connected to the CCD camera 15, the stage controller 60, and the piezo controller 70. The measurement control device 50 controls the shape measurement of the measurement target surface S1 of the sample S by controlling the operations of the above-described units of the measurement device 1A.

計測制御装置５０は、光路長差制御部５１と、表面形状導出部５２とを有している。光路長差制御部５１は、試料Ｓの表面形状の計測において、計測光学系２０での反射光と参照光との光路長差などの計測条件を制御する。また、表面形状導出部５２は、ＣＣＤカメラ１５によって検出された反射光と参照光との干渉光強度の光路長差についての変化から計測対象面Ｓ１の形状を導出する。   The measurement control device 50 includes an optical path length difference control unit 51 and a surface shape deriving unit 52. The optical path length difference control unit 51 controls measurement conditions such as the optical path length difference between the reflected light and the reference light in the measurement optical system 20 in the measurement of the surface shape of the sample S. Further, the surface shape deriving unit 52 derives the shape of the measurement target surface S1 from the change in the optical path length difference of the interference light intensity between the reflected light detected by the CCD camera 15 and the reference light.

具体的には、光路長差制御部５１は、計測対象面Ｓ１におけるＸＹ平面上での計測位置に対して、計測光学系２０での反射光と参照光との光路長差について、計測光の波長に基づく微小計測間隔と、微小計測間隔よりも大きい広域計測間隔との２種類の計測間隔を設定する。そして、光路長差として広域計測間隔でｎ個の光路長差（ｎは３以上の整数）を設定し、そのそれぞれの近傍において微小計測間隔で光路長差を変化させて干渉光強度の変化を計測するｎ個の計測条件で光路長差を制御する。   Specifically, the optical path length difference control unit 51 determines the optical path length difference between the reflected light from the measurement optical system 20 and the reference light with respect to the measurement position on the XY plane in the measurement target surface S1. Two types of measurement intervals are set, a minute measurement interval based on the wavelength and a wide-range measurement interval larger than the minute measurement interval. Then, n optical path length differences (n is an integer of 3 or more) are set as the optical path length differences at wide-range measurement intervals, and the change of the interference light intensity is changed by changing the optical path length difference at the minute measurement intervals in the vicinity thereof. The optical path length difference is controlled with n measurement conditions to be measured.

また、表面形状導出部５２は、上記したｎ個の計測条件に対応して得られた干渉光強度の変化のｎ個の計測結果からｎ個の光路長差のそれぞれでの局所的な干渉強さを求める。そして、得られたｎ個の干渉強さに基づいて、計測位置における計測対象面Ｓ１の垂直方向の高さを導出する。また、このような計測対象面Ｓ１の高さを導出する計測を２次元で行えば、試料Ｓの計測対象面Ｓ１の形状（３次元形状）を計測することができる。なお、計測対象面Ｓ１の具体的な形状計測方法については後述する。   Further, the surface shape deriving unit 52 determines the local interference intensity at each of the n optical path length differences from the n measurement results of the change in the interference light intensity obtained corresponding to the n measurement conditions. I ask for it. Then, based on the obtained n interference strengths, the vertical height of the measurement target surface S1 at the measurement position is derived. Moreover, if the measurement for deriving the height of the measurement target surface S1 is performed in two dimensions, the shape (three-dimensional shape) of the measurement target surface S1 of the sample S can be measured. A specific method for measuring the shape of the measurement target surface S1 will be described later.

次に、図１に示した表面形状計測装置１Ａを用いた、本発明による表面形状計測方法について説明する。   Next, a surface shape measuring method according to the present invention using the surface shape measuring apparatus 1A shown in FIG. 1 will be described.

まず、所定の波長幅を有する計測光を用いた表面形状計測方法（垂直走査白色干渉法）について、図２を参照して説明する。図２は、計測対象面Ｓ１からの反射光と、参照ミラー２４からの参照光との干渉信号を示すグラフであり、横軸は光路長差に対応する干渉対物レンズ２１の位置を、縦軸は干渉光強度を示している。   First, a surface shape measurement method (vertical scanning white light interferometry) using measurement light having a predetermined wavelength width will be described with reference to FIG. FIG. 2 is a graph showing an interference signal between the reflected light from the measurement target surface S1 and the reference light from the reference mirror 24. The horizontal axis represents the position of the interference objective lens 21 corresponding to the optical path length difference, and the vertical axis. Indicates the interference light intensity.

このような計測光を用いた形状計測では、計測光が波長幅に応じた短いコヒーレント長を有する。このため、図２のグラフＦに示すように、得られる干渉信号は反射光と参照光との光路長が一致して光路長差＝０となる対物レンズの位置において干渉強さ（干渉信号の振幅）が最大となり、その付近の一定範囲で干渉が発生している信号となる。したがって、光路長差を変化させて干渉光強度の変化を計測し、その干渉強さが最大となる位置を求めることにより、そのときの反射光及び参照光の光路長から、計測位置での計測対象面Ｓ１の垂直方向（計測光の照射方向）の高さを導出することができる。   In shape measurement using such measurement light, the measurement light has a short coherent length corresponding to the wavelength width. For this reason, as shown in graph F of FIG. 2, the interference signal obtained has an interference strength (interference signal of the interference signal) at the position of the objective lens where the optical path lengths of the reflected light and the reference light match and the optical path length difference = 0. (Amplitude) becomes the maximum, and the signal has interference in a certain range in the vicinity thereof. Therefore, by measuring the change in the interference light intensity by changing the optical path length difference and obtaining the position where the interference intensity is maximized, the measurement at the measurement position is performed from the optical path length of the reflected light and the reference light at that time. The height in the vertical direction (irradiation direction of measurement light) of the target surface S1 can be derived.

また、図２のグラフＧは干渉信号Ｆの包絡線を示している。このような包絡線Ｇは光路長差に対する干渉強さの変化に対応しており、したがって、包絡線Ｇのピーク位置が計測対象面Ｓ１の垂直方向の高さに対応している。   A graph G in FIG. 2 shows an envelope of the interference signal F. Such an envelope G corresponds to a change in the interference intensity with respect to the optical path length difference, and therefore the peak position of the envelope G corresponds to the height in the vertical direction of the measurement target surface S1.

なお、以下においては、反射光と参照光とが干渉可能な対物レンズの位置（光路長差）の範囲を可干渉距離として、図２に示す通り定義することとする。この可干渉距離（コヒーレンス長）は、計測光の波長幅によって決まるものである。また、この光路長差の制御は、図１に示す計測装置１Ａにおいては干渉対物レンズ２１をＺ方向に駆動することによって行われるが、このときの光路長差の変化は、計測光学系２０における計測光路及び参照光路の構成により、干渉対物レンズ２１の移動距離の２倍となる。   In the following, the range of the objective lens position (optical path length difference) where the reflected light and the reference light can interfere is defined as a coherent distance as shown in FIG. This coherence distance (coherence length) is determined by the wavelength width of the measurement light. The optical path length difference is controlled by driving the interference objective lens 21 in the Z direction in the measurement apparatus 1A shown in FIG. 1, and the change in the optical path length difference at this time is caused by the measurement optical system 20. Depending on the configuration of the measurement optical path and the reference optical path, the distance of the interference objective lens 21 is doubled.

干渉光強度の光路長差についての変化における上記したピーク位置の決定、及びそれによる計測対象面Ｓ１の垂直方向の高さの導出は、図２に示した干渉信号Ｆの波形全体を一定の計測間隔で取得することによって実行することができる。この場合、干渉信号Ｆの計測間隔は、計測光の波長等を考慮してある程度以上の細かい間隔とする必要がある。   The above-described determination of the peak position in the change in the optical path length difference of the interference light intensity and the derivation of the height in the vertical direction of the measurement target surface S1 thereby result in a constant measurement of the entire waveform of the interference signal F shown in FIG. Can be performed by getting at intervals. In this case, the measurement interval of the interference signal F needs to be a fine interval of a certain degree or more in consideration of the wavelength of the measurement light and the like.

これに対して、本発明による表面形状計測方法では、図２のグラフ中に模式的に示すように、反射光と参照光との光路長差について、微小計測間隔、及び微小計測間隔よりも大きい広域計測間隔の２種類の計測間隔を設定して、干渉信号の計測を行う。これらの計測間隔のうち、微小計測間隔は、特定の光路長差の近傍における局所的な干渉強さを求めるための計測間隔であり、好ましくは、計測光の中心波長等に基づいて設定される。一方、広域計測間隔は、可干渉範囲における干渉強さの変化、及びそのピーク位置を求めるための計測間隔であり、好ましくは、計測光の波長幅（コヒーレンス長）等に基づいて設定される。   On the other hand, in the surface shape measurement method according to the present invention, as schematically shown in the graph of FIG. 2, the optical path length difference between the reflected light and the reference light is larger than the minute measurement interval and the minute measurement interval. Two types of measurement intervals, a wide-range measurement interval, are set, and interference signals are measured. Among these measurement intervals, the minute measurement interval is a measurement interval for obtaining local interference strength in the vicinity of a specific optical path length difference, and is preferably set based on the center wavelength of the measurement light or the like. . On the other hand, the wide-range measurement interval is a measurement interval for obtaining a change in the interference intensity in the coherent range and its peak position, and is preferably set based on the wavelength width (coherence length) of the measurement light.

本計測方法では、干渉強さの計測を行う光路長差として、広域計測間隔でｎ個の光路長差（ｎは３以上の整数、図２の例においてはｎ＝３）を設定する。そして、ｎ個の光路長差のそれぞれの近傍において微小計測間隔で光路長差を所定回数だけ変化（図２の例においては３回）させて局所的な干渉光強度の変化を計測し、その計測結果からｎ個の光路長差のそれぞれでの局所的な干渉強さを求める。このようにして得られたｎ個の干渉強さの光路長差に対する変化により、干渉強さのピーク位置が求まり、したがって、計測対象面Ｓ１の垂直方向の高さが導出される。   In this measurement method, n optical path length differences (n is an integer of 3 or more, n = 3 in the example of FIG. 2) are set as the optical path length difference for measuring the interference intensity at wide-range measurement intervals. Then, in the vicinity of each of the n optical path length differences, the optical path length difference is changed a predetermined number of times at a minute measurement interval (three times in the example of FIG. 2) to measure a local interference light intensity change, From the measurement results, the local interference strength at each of the n optical path length differences is obtained. The peak position of the interference intensity is obtained by the change of the n interference intensities obtained in this way with respect to the optical path length difference, and therefore the vertical height of the measurement target surface S1 is derived.

図３は、本発明による表面形状計測方法の一例を示すフローチャートである。この計測方法では、まず、計測制御装置５０の光路長差制御部５１において、計測対象となる試料Ｓの種類、計測光供給部１０から供給される計測光の中心波長及び波長幅等の諸条件を考慮して、反射光と参照光との光路長差についての上記した微小計測間隔、及び広域計測間隔を設定する（ステップＳ１０１、設定ステップ）。   FIG. 3 is a flowchart showing an example of the surface shape measuring method according to the present invention. In this measurement method, first, in the optical path length difference control unit 51 of the measurement control device 50, various conditions such as the type of the sample S to be measured, the center wavelength and the wavelength width of the measurement light supplied from the measurement light supply unit 10, and the like. In consideration of the above, the above-described minute measurement interval and wide-area measurement interval for the optical path length difference between the reflected light and the reference light are set (step S101, setting step).

また、微小計測間隔及び広域計測間隔を参照し、試料Ｓの計測対象面Ｓ１上で設定された計測位置に対する計測条件を設定する（Ｓ１０２）。ここで設定される計測条件としては、例えば、干渉強さの垂直方向での広域計測点数ｎ（ｎは３以上の整数）、計測点となる広域計測間隔でのｎ個の光路長差（対物レンズの位置）、ｎ個の光路長差のそれぞれの近傍における微小計測間隔での局所的な計測点数、などがある。   Further, the measurement conditions for the measurement position set on the measurement target surface S1 of the sample S are set with reference to the minute measurement interval and the wide area measurement interval (S102). The measurement conditions set here include, for example, the number n of wide-area measurement points (n is an integer of 3 or more) in the vertical direction of the interference intensity, and n optical path length differences (objectives) at the wide-area measurement intervals serving as measurement points. Lens position), the number of local measurement points at a minute measurement interval in the vicinity of each of the n optical path length differences, and the like.

なお、ステップＳ１０１及びＳ１０２において設定される計測間隔及び計測条件については、光路長差制御部５１において計測毎に設定しても良く、あるいはあらかじめ設定されたものを光路長差制御部５１に記憶させておいても良い。また、計測間隔及び計測条件の設定は、自動で、または操作者の入力等によって手動で行うことができる。   The measurement intervals and measurement conditions set in steps S101 and S102 may be set for each measurement by the optical path length difference control unit 51, or preset ones are stored in the optical path length difference control unit 51. You can keep it. The measurement interval and measurement conditions can be set automatically or manually by an operator's input.

計測条件の設定が終了したら、計測位置における計測対象面Ｓ１の垂直方向の高さの計測を実行する。このとき、光路長差制御部５１は設定された計測条件にしたがってピエゾ素子４０等を駆動し、これによって反射光と参照光との光路長差を制御する。まず、ピエゾ素子４０によって干渉対物レンズ２１をＺ方向に駆動し、計測光学系２０における反射光と参照光との光路長差を、最初の計測条件の第１の光路長差に設定する（Ｓ１０３）。続いて、設定された光路長差の近傍において微小計測間隔で光路長差を所定回数だけ変化させて、第１の光路長差での局所的な干渉光強度の変化を計測する（Ｓ１０４、計測ステップ）。さらに、得られた干渉光強度の変化の第１の計測結果から、第１の光路長差での干渉強さを算出する（Ｓ１０５）。   When the setting of the measurement conditions is completed, the vertical height of the measurement target surface S1 at the measurement position is measured. At this time, the optical path length difference control unit 51 drives the piezo element 40 and the like according to the set measurement conditions, thereby controlling the optical path length difference between the reflected light and the reference light. First, the interference objective lens 21 is driven in the Z direction by the piezo element 40, and the optical path length difference between the reflected light and the reference light in the measurement optical system 20 is set to the first optical path length difference of the first measurement condition (S103). ). Subsequently, the optical path length difference is changed by a predetermined number of times at a minute measurement interval in the vicinity of the set optical path length difference to measure a local change in interference light intensity at the first optical path length difference (S104, measurement). Step). Furthermore, the interference intensity at the first optical path length difference is calculated from the first measurement result of the obtained interference light intensity change (S105).

次に、所定の計測範囲（計測点数）での全計測が終了したかどうかを確認する（Ｓ１０６）。そして、計測が終了していなければ、反射光と参照光との光路長差を広域計測間隔だけ変化させて次の光路長差に設定し（Ｓ１０７）、ステップＳ１０４、Ｓ１０５を繰り返して実行する。例えば、現時点での光路長差が第１の光路長差であれば、その光路長差を広域計測間隔だけ変化させた第２の光路長差に変更して計測を行う。そして、得られた干渉光強度の変化の第２の計測結果から、第２の光路長差での干渉強さを算出する。   Next, it is confirmed whether or not all measurements within a predetermined measurement range (number of measurement points) have been completed (S106). If the measurement is not completed, the optical path length difference between the reflected light and the reference light is changed by the wide-range measurement interval and set to the next optical path length difference (S107), and steps S104 and S105 are repeated. For example, if the current optical path length difference is the first optical path length difference, the optical path length difference is changed to the second optical path length difference changed by the wide-area measurement interval, and measurement is performed. Then, the interference intensity at the second optical path length difference is calculated from the second measurement result of the obtained change in the interference light intensity.

所定の計測範囲での全計測が終了したら、ｎ個の光路長差のそれぞれに対応して求められたｎ個の干渉強さに基づき、その干渉強さの光路長差についての変化から、そのピーク位置を求める。これにより、計測対象面Ｓ１の垂直方向の高さが導出される（Ｓ１０８、導出ステップ）。また、計測対象面Ｓ１に対して複数の計測位置で垂直方向の高さを計測する必要がある場合には、計測位置を変えて繰り返して上記の計測を行う。以上により、計測対象面Ｓ１の表面形状が計測される。   When all the measurements in the predetermined measurement range are completed, based on the n interference intensities obtained corresponding to each of the n optical path length differences, the change of the interference intensity from the optical path length difference Find the peak position. Thereby, the vertical height of the measurement target surface S1 is derived (S108, derivation step). Further, when it is necessary to measure the height in the vertical direction at a plurality of measurement positions with respect to the measurement target surface S1, the above measurement is repeated by changing the measurement position. Thus, the surface shape of the measurement target surface S1 is measured.

本実施形態による表面形状計測方法及び計測装置の効果について説明する。   The effects of the surface shape measuring method and measuring apparatus according to the present embodiment will be described.

図１〜図３に示した表面形状計測方法及び計測装置１Ａにおいては、干渉対物レンズ２１を含む計測光学系２０において生成される計測対象面Ｓ１からの反射光と参照光との光路長差について、設定された光路長差の近傍において微小計測間隔で垂直方向の走査を行って、その光路長差での局所的な干渉強さを求める。そして、このような局所的な計測を広域計測間隔でｎ個の光路長差について行うことにより、干渉強さのピーク位置の算出、及びそれによる計測対象面Ｓ１の垂直方向の高さの導出を行っている。このように、微小計測間隔及び広域計測間隔の２種類の計測間隔を設定して計測光による走査を行うことにより、広域計測間隔をある程度広くとって全体としての計測点数を大幅に減らすことができる。したがって、短い計測時間で高速に計測対象面Ｓ１の形状を計測することが可能となる。   In the surface shape measuring method and the measuring apparatus 1A shown in FIGS. 1 to 3, the optical path length difference between the reflected light from the measurement target surface S1 generated in the measuring optical system 20 including the interference objective lens 21 and the reference light. In the vicinity of the set optical path length difference, scanning in the vertical direction is performed at minute measurement intervals, and the local interference strength at the optical path length difference is obtained. Then, by performing such local measurement for n optical path length differences at wide-area measurement intervals, the calculation of the peak position of the interference strength and the derivation of the vertical height of the measurement target surface S1 thereby are performed. Is going. As described above, by setting two kinds of measurement intervals, that is, a minute measurement interval and a wide measurement interval, and performing scanning with measurement light, the wide measurement interval can be widened to some extent, and the number of measurement points as a whole can be greatly reduced. . Therefore, it is possible to measure the shape of the measurement target surface S1 at high speed in a short measurement time.

ここで、干渉光強度の変化を局所的に計測する際の微小計測間隔については、上記したように計測光の波長に基づいて設定される。この微小計測間隔は、計測光の中心波長λに対してλ／２以下であることが好ましい。また、ｎ個の光路長差のそれぞれの近傍における微小計測間隔での計測回数については、微小計測間隔で光路長差を３回以上変化させて局所的な干渉光強度の変化を計測することが好ましい。これにより、ｎ個の光路長差のそれぞれでの干渉強さを好適に求めることができる。このような計測回数等は、局所的な干渉強さの具体的な算出方法等に応じて適宜設定すれば良い。   Here, as described above, the minute measurement interval when the change in the interference light intensity is locally measured is set based on the wavelength of the measurement light. This minute measurement interval is preferably λ / 2 or less with respect to the center wavelength λ of the measurement light. As for the number of times of measurement at a minute measurement interval in the vicinity of each of the n optical path length differences, it is possible to measure a local change in interference light intensity by changing the optical path length difference three times or more at the minute measurement interval. preferable. As a result, the interference intensity at each of the n optical path length differences can be suitably obtained. Such measurement times and the like may be set as appropriate in accordance with a specific method for calculating the local interference strength.

また、広域計測間隔については、計測光の波長幅を考慮して設定することが好ましい。すなわち、光路長差に対する干渉強さの変化、及びその可干渉距離（図２参照）は、計測光の波長幅によって決まるものである。したがって、可干渉範囲内で干渉強さの変化を計測するための広域計測間隔については、波長幅に応じた間隔に設定することが好ましい。   In addition, the wide-range measurement interval is preferably set in consideration of the wavelength width of the measurement light. That is, the change in interference intensity with respect to the optical path length difference and the coherence distance (see FIG. 2) are determined by the wavelength width of the measurement light. Therefore, it is preferable to set the wide-range measurement interval for measuring the change in the interference intensity within the coherent range to an interval according to the wavelength width.

実際には、例えば、計測対象面Ｓ１の予想される高さ範囲、必要とされる形状の計測精度等の具体的な条件を考慮し、可干渉距離、及びそれに対応する広域計測間隔を設定する。そして、設定された可干渉距離及び広域計測間隔が得られるように計測光の波長幅を設定し、それに対応した波長フィルタを選択して、計測光供給部１０のバンドパスフィルタ１３として設置する方法を用いることができる。また、計測光の中心波長λについては、計測光源１１に充分な強度があり、ＣＣＤカメラ１５などの検出手段に充分な感度がある波長範囲で選択すれば良い。   In practice, for example, the coherence distance and the corresponding wide-area measurement interval are set in consideration of specific conditions such as the expected height range of the measurement target surface S1 and the measurement accuracy of the required shape. . Then, the wavelength width of the measurement light is set so that the set coherence distance and wide-range measurement interval can be obtained, the wavelength filter corresponding to the measurement light is selected, and the bandpass filter 13 of the measurement light supply unit 10 is installed. Can be used. Further, the center wavelength λ of the measurement light may be selected in a wavelength range in which the measurement light source 11 has sufficient intensity and the detection means such as the CCD camera 15 has sufficient sensitivity.

また、干渉強さの変化におけるピーク位置（包絡線のピーク位置に対応）を、ある程度正確に求めるためには、ピークの半値幅の１／２程度の広域計測間隔が必要となる。ただし、ピークが存在する位置を大まかに求めるだけであれば、ピークの半値幅程度の計測間隔で良い。あるいは、最初にピークの半値幅程度の広域計測間隔で計測を行い、次にピークがあることが判明した高さ付近のみをピークの半値幅の１／２程度の間隔で計測して、ピーク位置を効率良くかつ正確に求めるなど、必要に応じて様々な方法を用いることが可能である。   Further, in order to obtain the peak position (corresponding to the peak position of the envelope) with a certain change in interference intensity to a certain degree of accuracy, a wide-area measurement interval of about ½ of the half-value width of the peak is required. However, if only the position where the peak exists is roughly determined, a measurement interval of about the half width of the peak may be used. Alternatively, measurement is first performed at a wide-range measurement interval of about half the peak width, and then only the vicinity of the height where the peak is found is measured at about half the peak half width, and the peak position It is possible to use various methods as needed, such as efficiently and accurately obtaining.

ここで、計測対象の例として、計測対象面Ｓ１に形成された高さ５０μｍのバンプ（図４参照）を考える。また、計測範囲をバンプ高さに対して上下１０μｍのマージンを加えて７０μｍとする。このような計測対象に対して、計測光供給部１０の計測光源１１としてハロゲンランプなどの白色光源を用い、バンドパスフィルタ１３として中心波長６００ｎｍ、波長幅１０ｎｍの波長フィルタを用いると、このときの可干渉距離は４０μｍ程度と推定される。また、干渉光の計測には、検出手段のＣＣＤカメラ１５としてフレームレートが３０ｆｐｓのＣＣＤカメラを用いることとする。   Here, as an example of the measurement target, a bump (see FIG. 4) having a height of 50 μm formed on the measurement target surface S1 is considered. Further, the measurement range is set to 70 μm by adding a margin of 10 μm above and below the bump height. For such a measurement target, when a white light source such as a halogen lamp is used as the measurement light source 11 of the measurement light supply unit 10 and a wavelength filter having a center wavelength of 600 nm and a wavelength width of 10 nm is used as the bandpass filter 13, The coherence distance is estimated to be about 40 μm. In the measurement of the interference light, a CCD camera having a frame rate of 30 fps is used as the CCD camera 15 of the detection means.

このような計測例に対し、微小走査の計測間隔及び計測点数は、計測光の中心波長と干渉強さの算出アルゴリズムによって決めることができる。ここでは、微小計測間隔をπ／２の位相差に対応する間隔に設定し、３点で計測を行って局所的な干渉強さを求めることとする。この場合、計測光の中心波長がλ＝６００ｎｍであるから、微小計測間隔は光路長差で１５０ｎｍ、対物レンズの位置で７５ｎｍとなる。   For such a measurement example, the measurement interval and the number of measurement points for micro scanning can be determined by a calculation algorithm for the center wavelength of the measurement light and the interference intensity. Here, the minute measurement interval is set to an interval corresponding to a phase difference of π / 2, and measurement is performed at three points to determine the local interference strength. In this case, since the center wavelength of the measurement light is λ = 600 nm, the minute measurement interval is 150 nm in terms of the optical path length difference and 75 nm in the position of the objective lens.

一方、広域走査については、干渉強さのピーク位置の決定に２次関数によるフィッティング計算を用いることとする。この場合、フィッティング計算には最低３点が必要となるため、広域計測間隔の最大値は可干渉距離の１／３となる。実際には、広域計測間隔は計測速度と最終的に必要とされる計測精度とに応じて決めることができるが、ここでは計測速度を優先して広域計測間隔を可干渉距離の１／３の１３．３μｍとする。   On the other hand, for wide-area scanning, fitting calculation using a quadratic function is used to determine the peak position of interference intensity. In this case, since the fitting calculation requires at least three points, the maximum value of the wide-area measurement interval is 1/3 of the coherence distance. Actually, the wide-area measurement interval can be determined according to the measurement speed and the finally required measurement accuracy, but here, the wide-area measurement interval is set to 1/3 of the coherent distance with priority on the measurement speed. 13.3 μm.

このような計測条件において、従来の計測方法では、７０μｍの計測範囲の全範囲を微小計測間隔７５ｎｍで走査する必要がある。このとき、３０ｆｐｓのカメラでは、計測速度は７５ｎｍ×３０フレーム／ｓｅｃ＝２．２５μｍ／ｓｅｃとなる。したがって、７０μｍの計測範囲を計測するために必要な計測時間は３１．１ｓｅｃとなる。   Under such measurement conditions, the conventional measurement method needs to scan the entire measurement range of 70 μm at a minute measurement interval of 75 nm. At this time, with a 30 fps camera, the measurement speed is 75 nm × 30 frames / sec = 2.25 μm / sec. Therefore, the measurement time required to measure the measurement range of 70 μm is 31.1 sec.

一方、上記した本発明による計測方法では、広域走査１点につき微小走査が３点必要であり、広域走査の見かけ上でのフレームレートが１０ｆｐｓとなることから、計測速度は１３．３μｍ×１０フレーム／ｓｅｃ＝１３３μｍ／ｓｅｃとなる。したがって、７０μｍの計測範囲を計測するために必要な計測時間は０．５３ｓｅｃとなる。これは、従来法による計測時間の約１／５９である。このように、本発明による計測方法によれば、従来の計測方法に比べて計測時間を大幅に短縮することができる。このように、本発明による表面形状計測方法及び計測装置は、段差が大きいバンプ計測や、最大で数ｍｍ程度となる半導体ウエハの反り計測など、広い計測範囲での表面形状計測に特に有効である。   On the other hand, in the measurement method according to the present invention, three fine scans are required for each wide-area scan, and the apparent frame rate of wide-area scan is 10 fps, so the measurement speed is 13.3 μm × 10 frames. / Sec = 133 μm / sec. Therefore, the measurement time required to measure the 70 μm measurement range is 0.53 sec. This is about 1/59 of the measurement time by the conventional method. As described above, according to the measurement method of the present invention, the measurement time can be significantly reduced as compared with the conventional measurement method. As described above, the surface shape measuring method and the measuring apparatus according to the present invention are particularly effective for surface shape measurement in a wide measurement range such as bump measurement with a large step and warpage measurement of a semiconductor wafer having a maximum of several millimeters. .

次に、ｎ個の光路長差のそれぞれの近傍における局所的な干渉強さの具体的な求め方について説明する。   Next, a specific method for obtaining the local interference strength in the vicinity of each of the n optical path length differences will be described.

干渉強さの具体的な求め方としては、微小計測間隔をπ／２の位相差に対応する間隔に設定するとともに、ｎ個の光路長差のそれぞれの近傍において、微小計測間隔で光路長差を３回変化させて３個の干渉光強度Ｉ１、Ｉ２、Ｉ３を計測し、式

Figure 0004554385
によって干渉強さを求める方法を用いることができる。 As a specific method for obtaining the interference intensity, the micro measurement interval is set to an interval corresponding to a phase difference of π / 2, and the optical path length difference is set at a micro measurement interval in the vicinity of each of the n optical path length differences. Is changed three times to measure three interference light intensities I 1 , I 2 , and I 3
Figure 0004554385
 A method for obtaining the interference strength can be used.

詳述すると、上記した計測方法で得られる干渉信号は、図２のグラフＦに示すように、正弦波に振幅変調を加えた波形の信号となる。したがって、１周期のみを取り出せば、干渉信号は局所的に正弦波信号で近似可能である。このとき、その正弦波信号は以下の式で表される。

Figure 0004554385
ここで、Ｉは干渉信号の強度、Ａは振幅、Ｂはオフセット、φは位相、φ０は初期位相である。 More specifically, the interference signal obtained by the above-described measurement method is a waveform signal obtained by adding amplitude modulation to a sine wave, as shown in the graph F of FIG. Therefore, if only one period is extracted, the interference signal can be locally approximated by a sine wave signal. At this time, the sine wave signal is expressed by the following equation.
Figure 0004554385
 Here, I is the intensity of the interference signal, A is the amplitude, B is the offset, φ is the phase, and φ 0 is the initial phase.

このとき、光路長差（対物レンズの位置）を微小に変化させて干渉光強度を計測することを考える。微小な変位量は位相の変位量としてφで表されるので、上記式において未知数は３個となる。よって、最低３点で計測を行えば、上記した干渉光強度Ｉの式は一意に定まり、したがって、干渉強さに相当する干渉信号の振幅が求められる。   At this time, it is considered to measure the interference light intensity by slightly changing the optical path length difference (position of the objective lens). Since the minute displacement amount is represented by φ as the phase displacement amount, there are three unknowns in the above equation. Therefore, if measurement is performed at a minimum of three points, the above-described equation of the interference light intensity I is uniquely determined, and therefore the amplitude of the interference signal corresponding to the interference intensity is obtained.

ここで、上記したように位相をπ／２ずつ変化させて３点で計測を行うと、計測結果として得られる３個の干渉光強度Ｉ１、Ｉ２、Ｉ３は、以下のように表される。

Figure 0004554385
また、これらの３式を変形すると、以下のようになる。
Figure 0004554385
 さらに、これらの３式より、以下の２式が求められる。
Figure 0004554385
 以上より、局所的な干渉強さに相当する干渉信号の振幅Ａは、次式によって求めることができる。
Figure 0004554385
 なお、この方法では、π／２ずつ位相を変えて計測を行っているが、π／２の位相差に相当する対物レンズの移動距離は、計測光の中心波長をλとして光路長差の１／２のλ／８である。 Here, when the phase is changed by π / 2 as described above and measurement is performed at three points, the three interference light intensities I 1 , I 2 , and I 3 obtained as measurement results are expressed as follows: Is done.
Figure 0004554385
 Further, when these three formulas are modified, the result is as follows.
Figure 0004554385
 Furthermore, the following two equations are obtained from these three equations.
Figure 0004554385
 As described above, the amplitude A of the interference signal corresponding to the local interference strength can be obtained by the following equation.
Figure 0004554385
 In this method, measurement is performed by changing the phase by π / 2, but the moving distance of the objective lens corresponding to the phase difference of π / 2 is 1 as the optical path length difference with the center wavelength of the measurement light as λ. Λ / 8 of / 2.

また、干渉強さの具体的な求め方としては、上記した方法以外にも、様々な方法を用いて良い。例えば、ｎ個の光路長差のそれぞれについて、干渉光強度の変化の計測結果に対してフィッティング計算を行って干渉強さを求める方法を用いることができる。具体的な例としては、微小計測間隔で光路長差を３回以上変化させて３点以上の計測を行い、正弦関数などの関数でフィッティングを行って、得られた振幅から局所的な干渉強さを求めることができる。なお、１周期のみを取り出せば、干渉信号は局所的に正弦波信号で近似可能であることは、上述した通りである。   In addition to the method described above, various methods may be used as a specific method for obtaining the interference strength. For example, for each of the n optical path length differences, a method of obtaining the interference intensity by performing fitting calculation on the measurement result of the change in the interference light intensity can be used. As a specific example, three or more points are measured by changing the optical path length difference at least three times at a minute measurement interval, and fitting is performed using a function such as a sine function. You can ask for it. As described above, if only one period is extracted, the interference signal can be locally approximated by a sine wave signal.

あるいは、ｎ個の光路長差のそれぞれについて、干渉光強度の変化の計測結果でのばらつきによって干渉強さを求める方法を用いることができる。このような方法としては、微小計測間隔で所定点数の計測を行い、それらの標準偏差を求める方法がある。具体的には例えば、π／２の位相差に対応する間隔で４点の計測を行い、その標準偏差を求めることによって局所的な干渉強さを求めることができる。   Alternatively, for each of the n optical path length differences, a method can be used in which the interference intensity is obtained by variation in the measurement result of the change in interference light intensity. As such a method, there is a method of measuring a predetermined number of points at a minute measurement interval and obtaining a standard deviation thereof. Specifically, for example, local interference strength can be obtained by measuring four points at intervals corresponding to a phase difference of π / 2 and obtaining the standard deviation.

また、このような方法では、標準偏差を求めるための計測を以下の条件で行う必要がある。すなわち、まず設定された光路長差の近傍における微小計測間隔については、正弦波の周期（中心波長の半分）の整数（４以上の整数）分の１とする。例えば、１／４周期、１／５周期、１／６周期、…等を微小計測間隔に設定する。また、計測点数については、１周期分またはその整数倍とする。例えば１周期分であれば、１／４周期間隔なら４点、１／５周期間隔なら５点、…等に計測点数を設定する。   Moreover, in such a method, it is necessary to perform measurement for obtaining the standard deviation under the following conditions. That is, the minute measurement interval in the vicinity of the set optical path length difference is set to 1 / integer (integer of 4 or more) of the sine wave period (half of the center wavelength). For example, a 1/4 cycle, 1/5 cycle, 1/6 cycle, etc. are set as the minute measurement interval. The number of measurement points is one cycle or an integer multiple thereof. For example, in the case of one cycle, the number of measurement points is set to 4 points for a 1/4 cycle interval, 5 points for a 1/5 cycle interval, and so on.

次に、試料Ｓの計測対象面Ｓ１に対する垂直方向の走査方法について、表面形状計測装置の他の実施形態とともに説明する。   Next, a scanning method in the direction perpendicular to the measurement target surface S1 of the sample S will be described together with other embodiments of the surface shape measuring apparatus.

本発明による表面形状計測方法では、上記したように微小計測間隔と広域計測間隔との２種類の計測間隔によって、計測対象面Ｓ１を垂直方向に走査する。ここで、微小計測間隔での走査については、干渉光強度の変化についての振幅情報を正確に取得するため、例えばｎｍオーダーなどの充分な精度で走査することが好ましい。一方、広域計測間隔での走査については、走査範囲や全体として必要な計測精度などに応じた精度とすれば良い。   In the surface shape measurement method according to the present invention, as described above, the measurement target surface S1 is scanned in the vertical direction by using two kinds of measurement intervals, that is, the minute measurement interval and the wide-area measurement interval. Here, for scanning at a minute measurement interval, it is preferable to scan with sufficient accuracy, for example, on the order of nm, in order to accurately acquire amplitude information about the change in interference light intensity. On the other hand, for scanning at a wide measurement interval, the accuracy may be in accordance with the scanning range and the necessary measurement accuracy as a whole.

また、計測対象面Ｓ１を垂直方向に走査するための装置構成については、図１に示す表面形状計測装置１Ａでは、微小計測間隔でのＺ方向の走査、及び広域計測間隔での走査の双方を、干渉対物レンズ２１に設けられたピエゾ素子４０によって行っている。このような構成については、これ以外にも様々な構成を用いることが可能である。   As for the apparatus configuration for scanning the measurement target surface S1 in the vertical direction, the surface shape measurement apparatus 1A shown in FIG. 1 performs both scanning in the Z direction at a minute measurement interval and scanning at a wide measurement interval. The piezo element 40 provided in the interference objective lens 21 is used. Various configurations other than this can be used for such a configuration.

図５は、表面形状計測装置の他の実施形態の構成を示すブロック図である。本実施形態による計測装置１Ｂが図１に示した計測装置１Ａと異なる点は、ＸＹステージ３０及びピエゾ素子４０に代えて、ステージコントローラ６２によって制御されたＸＹＺステージ３２と、ピエゾコントローラ７０によって制御されたピエゾ素子４０とを用いている点にある。このような構成では、例えば、微小計測間隔での走査をピエゾ素子４０で行うとともに、広域計測間隔での走査をＸＹＺステージ３２で行うことが可能である。   FIG. 5 is a block diagram showing a configuration of another embodiment of the surface shape measuring apparatus. The measurement apparatus 1B according to the present embodiment is different from the measurement apparatus 1A shown in FIG. 1 in that the XYZ stage 32 controlled by the stage controller 62 and the piezo controller 70 are controlled instead of the XY stage 30 and the piezo element 40. The piezoelectric element 40 is used. In such a configuration, for example, scanning at a minute measurement interval can be performed by the piezo element 40 and scanning at a wide measurement interval can be performed by the XYZ stage 32.

図６は、表面形状計測装置のさらに他の実施形態の構成を示すブロック図である。本実施形態による計測装置１Ｃが図１に示した計測装置１Ａと異なる点は、ＸＹステージ３０及びピエゾ素子４０に代えて、ステージコントローラ６４によって制御されたＸＹステージ３４及びＺステージ３５と、ピエゾコントローラ７０によって制御されたピエゾ素子４０とを用いている点にある。また、この構成では、Ｚステージ３５は、ピエゾ素子４０とともに干渉対物レンズ２１に対して設けられている。このような構成では、例えば、微小計測間隔での走査をピエゾ素子４０で行うとともに、広域計測間隔での走査をＺステージ３５で行うことが可能である。   FIG. 6 is a block diagram showing a configuration of still another embodiment of the surface shape measuring apparatus. The measurement apparatus 1C according to the present embodiment is different from the measurement apparatus 1A shown in FIG. 1 in that instead of the XY stage 30 and the piezo element 40, an XY stage 34 and a Z stage 35 controlled by a stage controller 64, and a piezo controller. The piezoelectric element 40 controlled by 70 is used. In this configuration, the Z stage 35 is provided for the interference objective lens 21 together with the piezoelectric element 40. In such a configuration, for example, it is possible to perform scanning at a minute measurement interval with the piezo element 40 and to perform scanning at a wide measurement interval with the Z stage 35.

このように、微小計測間隔での走査、及び広域計測間隔での走査については、必要とされる計測精度等に応じて、同じ走査機構またはそれぞれ別の走査機構を用いて実行することが可能である。例えば、高い計測精度が重視される場合には、図１に示す計測装置１Ａのように、微小走査及び広域走査をともに高精度のピエゾ素子で行う構成が可能である。一方、広い計測範囲が重視される場合には、図５に示す計測装置１Ｂ、及び図６に示す計測装置１Ｃのように、微小走査を高精度のピエゾ素子で行うとともに、広域走査をモータステージによるＺステージで行う構成が可能である。   As described above, scanning at a minute measurement interval and scanning at a wide measurement interval can be performed using the same scanning mechanism or different scanning mechanisms depending on the required measurement accuracy or the like. is there. For example, when high measurement accuracy is important, a configuration in which both fine scanning and wide-area scanning are performed with high-accuracy piezo elements as in the measurement apparatus 1A shown in FIG. 1 is possible. On the other hand, when a wide measurement range is emphasized, as in the measurement apparatus 1B shown in FIG. 5 and the measurement apparatus 1C shown in FIG. 6, a minute scan is performed with a high-precision piezo element, and a wide range scan is performed on the motor stage. It is possible to use a configuration that is performed on the Z stage.

なお、垂直方向の走査に用いられるピエゾ素子及びモータステージの一般的な性能としては、ピエゾ素子では、計測精度が１〜１０ｎｍ、計測範囲が１００〜５００μｍ程度である。また、モータステージでは、計測精度が０．１〜１０μｍ、計測範囲が１０〜２０ｍｍ程度である。   As general performance of the piezo element and the motor stage used for vertical scanning, the piezo element has a measurement accuracy of 1 to 10 nm and a measurement range of about 100 to 500 μm. In the motor stage, the measurement accuracy is about 0.1 to 10 μm, and the measurement range is about 10 to 20 mm.

本発明による表面形状計測方法及び計測装置は上記した実施形態に限られるものではなく、様々な変形が可能である。例えば、表面形状計測に用いる計測装置の具体的な構成については、図１の計測装置１Ａはその一例を示すものであり、この他にも様々な構成のものを用いることができる。例えば、計測対象面からの反射光と参照光とを干渉させる計測光学系については、図１に示した光学系以外にも、様々な構成を用いて良い。また、干渉光を検出する検出手段についても、図１に示したＣＣＤカメラ１５以外にも様々なものを用いて良い。   The surface shape measuring method and measuring apparatus according to the present invention are not limited to the above-described embodiments, and various modifications are possible. For example, as for the specific configuration of the measuring device used for surface shape measurement, the measuring device 1A in FIG. 1 shows an example thereof, and various other configurations can be used. For example, various configurations other than the optical system shown in FIG. 1 may be used for the measurement optical system that causes the reflected light from the measurement target surface to interfere with the reference light. Various detection means other than the CCD camera 15 shown in FIG. 1 may be used as detection means for detecting the interference light.

本発明は、短い計測時間で計測対象面の形状を計測することが可能な表面形状計測方法及び計測装置として利用可能である。   INDUSTRIAL APPLICABILITY The present invention can be used as a surface shape measurement method and a measurement apparatus that can measure the shape of a measurement target surface in a short measurement time.

表面形状計測装置の一実施形態の構成を示すブロック図である。It is a block diagram which shows the structure of one Embodiment of a surface shape measuring apparatus. 計測対象面からの反射光と参照光との干渉信号を示すグラフである。It is a graph which shows the interference signal of the reflected light from a measurement object surface, and reference light. 表面形状計測方法の一例を示すフローチャートである。It is a flowchart which shows an example of the surface shape measuring method. 計測対象面の一例としてバンプを有する計測対象面を示す図である。It is a figure which shows the measurement object surface which has a bump as an example of a measurement object surface. 表面形状計測装置の他の実施形態の構成を示すブロック図である。It is a block diagram which shows the structure of other embodiment of a surface shape measuring apparatus. 表面形状計測装置の他の実施形態の構成を示すブロック図である。It is a block diagram which shows the structure of other embodiment of a surface shape measuring apparatus.

符号の説明Explanation of symbols

１Ａ、１Ｂ、１Ｃ…表面形状計測装置、１０…計測光供給部、１１…計測光源、１２…レンズ、１３…バンドパスフィルタ、１５…ＣＣＤカメラ、２０…計測光学系、２１…干渉対物レンズ、２２…レンズ、２３…ビームスプリッタ、２４…参照ミラー、２５…保持部材、２６…ビームスプリッタ、２７…レンズ、３０…ＸＹステージ、３２…ＸＹＺステージ、３４…ＸＹステージ、３５…Ｚステージ、４０…ピエゾ素子、５０…計測制御装置、５１…光路長差制御部、５２…表面形状導出部、６０、６２、６４…ステージコントローラ、７０…ピエゾコントローラ。   DESCRIPTION OF SYMBOLS 1A, 1B, 1C ... Surface shape measuring device, 10 ... Measurement light supply part, 11 ... Measurement light source, 12 ... Lens, 13 ... Band pass filter, 15 ... CCD camera, 20 ... Measurement optical system, 21 ... Interference objective lens, 22 ... Lens, 23 ... Beam splitter, 24 ... Reference mirror, 25 ... Holding member, 26 ... Beam splitter, 27 ... Lens, 30 ... XY stage, 32 ... XYZ stage, 34 ... XY stage, 35 ... Z stage, 40 ... Piezo elements, 50 ... measurement control device, 51 ... optical path length difference control unit, 52 ... surface shape deriving unit, 60, 62, 64 ... stage controller, 70 ... piezo controller.

Claims (10)

所定の波長幅を有する計測光を計測対象面に照射し、前記計測対象面からの反射光、及び前記反射光に対する光路長差が制御可能な参照光を干渉させて、得られる干渉光強度の前記光路長差についての変化から前記計測対象面の形状を計測する計測方法であって、
前記計測対象面における前記計測光の照射方向からみた計測位置に対して、前記反射光と前記参照光との前記光路長差について、前記計測光の波長に基づく微小計測間隔、及び前記微小計測間隔よりも大きい広域計測間隔を設定する設定ステップと、
前記計測位置に対して、前記光路長差として前記広域計測間隔でｎ個の光路長差（ｎは３以上の整数）を設定し、そのそれぞれの近傍において前記微小計測間隔で光路長差を変化させて前記干渉光強度の変化を計測する計測ステップと、
前記計測ステップで得られた前記干渉光強度の変化のｎ個の計測結果から求められる前記ｎ個の光路長差のそれぞれでの干渉強さに基づいて、前記計測位置における前記計測対象面の前記照射方向の高さを導出する導出ステップと
を備えることを特徴とする表面形状計測方法。 The measurement light having a predetermined wavelength width is irradiated on the measurement target surface, the reflected light from the measurement target surface and the reference light whose optical path length difference with respect to the reflected light is controlled to interfere, and the interference light intensity obtained A measurement method for measuring the shape of the measurement target surface from a change in the optical path length difference,
With respect to the optical path length difference between the reflected light and the reference light with respect to the measurement position as viewed from the measurement light irradiation direction on the measurement target surface, the micro measurement interval based on the wavelength of the measurement light, and the micro measurement interval A setting step for setting a larger measurement interval than
For the measurement position, n optical path length differences (n is an integer of 3 or more) are set as the optical path length difference at the wide-area measurement interval, and the optical path length difference is changed at the minute measurement interval in the vicinity thereof. And measuring step of measuring the change of the interference light intensity,
Based on the interference intensity at each of the n optical path length differences obtained from the n measurement results of the change in the interference light intensity obtained in the measurement step, the measurement target surface at the measurement position is And a derivation step for deriving the height in the irradiation direction. 前記計測ステップにおいて、前記ｎ個の光路長差のそれぞれの近傍において、前記微小計測間隔で光路長差を３回以上変化させて前記干渉光強度の変化を計測することを特徴とする請求項１記載の表面形状計測方法。   2. The measuring step includes measuring the change in the interference light intensity by changing the optical path length difference at least three times at the minute measurement interval in the vicinity of each of the n optical path length differences. The surface shape measuring method as described. 前記設定ステップにおいて、前記微小計測間隔をπ／２の位相差に対応する間隔に設定するとともに、前記計測ステップにおいて、前記ｎ個の光路長差のそれぞれの近傍において、前記微小計測間隔で光路長差を３回変化させて３個の前記干渉光強度Ｉ１、Ｉ２、Ｉ３を計測し、
前記導出ステップにおいて、前記ｎ個の光路長差のそれぞれについて、式
Figure 0004554385
 によって前記干渉強さを求めることを特徴とする請求項１または２記載の表面形状計測方法。 In the setting step, the minute measurement interval is set to an interval corresponding to a phase difference of π / 2, and in the measurement step, an optical path length is set at the minute measurement interval in the vicinity of each of the n optical path length differences. Measuring the three interference light intensities I 1 , I 2 , I 3 by changing the difference three times;
In the derivation step, an equation for each of the n optical path length differences is given.
Figure 0004554385
 The surface shape measurement method according to claim 1, wherein the interference strength is obtained by: 前記導出ステップにおいて、前記ｎ個の光路長差のそれぞれについて、前記干渉光強度の変化の計測結果に対してフィッティング計算を行って前記干渉強さを求めることを特徴とする請求項１または２記載の表面形状計測方法。   3. The interference strength is obtained by performing fitting calculation on the measurement result of the change in interference light intensity for each of the n optical path length differences in the deriving step. Surface shape measurement method. 前記導出ステップにおいて、前記ｎ個の光路長差のそれぞれについて、前記干渉光強度の変化の計測結果でのばらつきによって前記干渉強さを求めることを特徴とする請求項１または２記載の表面形状計測方法。   3. The surface shape measurement according to claim 1, wherein, in the derivation step, the interference intensity is obtained for each of the n optical path length differences based on variations in measurement results of changes in the interference light intensity. Method. 所定の波長幅を有する計測光を供給する計測光供給手段と、
前記計測光を計測対象面に照射するとともに、前記計測対象面からの反射光、及び前記反射光に対する光路長差が制御可能な参照光を干渉させる計測光学系と、
前記計測光学系によって前記反射光及び前記参照光を干渉させて得られる干渉光強度を検出する検出手段と、
前記反射光と前記参照光との前記光路長差を制御する光路長差制御手段と、
前記検出手段によって検出された前記干渉光強度の前記光路長差についての変化から前記計測対象面の形状を導出する表面形状導出手段とを備え、
前記光路長差制御手段は、前記計測対象面における前記計測光の照射方向からみた計測位置に対して、前記光路長差について、前記計測光の波長に基づく微小計測間隔、及び前記微小計測間隔よりも大きい広域計測間隔を設定するとともに、前記光路長差として前記広域計測間隔でｎ個の光路長差（ｎは３以上の整数）を設定し、そのそれぞれの近傍において前記微小計測間隔で光路長差を変化させて前記干渉光強度の変化を計測するｎ個の計測条件で前記光路長差を制御し、
前記表面形状導出手段は、前記ｎ個の計測条件で得られた前記干渉光強度の変化のｎ個の計測結果から求められる前記ｎ個の光路長差のそれぞれでの干渉強さに基づいて、前記計測位置における前記計測対象面の前記照射方向の高さを導出する
ことを特徴とする表面形状計測装置。 Measurement light supply means for supplying measurement light having a predetermined wavelength width;
A measurement optical system that irradiates the measurement target surface with the measurement light and that interferes with reflected light from the measurement target surface and reference light whose optical path length difference with respect to the reflected light is controllable,
Detecting means for detecting an interference light intensity obtained by causing the reflected light and the reference light to interfere with each other by the measurement optical system;
Optical path length difference control means for controlling the optical path length difference between the reflected light and the reference light;
Surface shape deriving means for deriving the shape of the measurement target surface from a change in the optical path length difference of the interference light intensity detected by the detection means,
The optical path length difference control means, for the measurement position viewed from the measurement light irradiation direction on the measurement target surface, with respect to the optical path length difference, based on the micro measurement interval based on the wavelength of the measurement light, and the micro measurement interval Is set as the optical path length difference, and n optical path length differences (n is an integer of 3 or more) are set as the optical path length difference, and the optical path length is set at the minute measurement interval in the vicinity thereof. The optical path length difference is controlled under n measurement conditions for measuring the change in the interference light intensity by changing the difference,
The surface shape deriving means is based on the interference intensity at each of the n optical path length differences obtained from the n measurement results of the change in the interference light intensity obtained under the n measurement conditions. A surface shape measuring apparatus for deriving a height in the irradiation direction of the measurement target surface at the measurement position. 前記光路長差制御手段は、前記ｎ個の光路長差のそれぞれの近傍において、前記微小計測間隔で光路長差を３回以上変化させて前記干渉光強度の変化を計測する前記計測条件で前記光路長差を制御することを特徴とする請求項６記載の表面形状計測装置。   The optical path length difference control means measures the change in the interference light intensity by changing the optical path length difference at least three times at the minute measurement interval in the vicinity of each of the n optical path length differences. The surface shape measuring apparatus according to claim 6, wherein the optical path length difference is controlled. 前記光路長差制御手段は、前記微小計測間隔をπ／２の位相差に対応する間隔に設定するとともに、前記ｎ個の光路長差のそれぞれの近傍において、前記微小計測間隔で光路長差を３回変化させて３個の前記干渉光強度Ｉ１、Ｉ２、Ｉ３を計測する前記計測条件で前記光路長差を制御し、
前記表面形状導出手段は、前記ｎ個の光路長差のそれぞれについて、式
Figure 0004554385
 によって前記干渉強さを求めることを特徴とする請求項６または７記載の表面形状計測装置。 The optical path length difference control means sets the micro measurement interval to an interval corresponding to a phase difference of π / 2, and sets the optical path length difference at the micro measurement interval in the vicinity of each of the n optical path length differences. The optical path length difference is controlled under the measurement conditions for measuring the three interference light intensities I 1 , I 2 , and I 3 by changing three times,
The surface shape deriving means has an equation for each of the n optical path length differences.
Figure 0004554385
 The surface shape measuring apparatus according to claim 6, wherein the interference strength is obtained by: 前記表面形状導出手段は、前記ｎ個の光路長差のそれぞれについて、前記干渉光強度の変化の計測結果に対してフィッティング計算を行って前記干渉強さを求めることを特徴とする請求項６または７記載の表面形状計測装置。   The surface shape deriving means obtains the interference intensity by performing fitting calculation on the measurement result of the change in interference light intensity for each of the n optical path length differences. 7. The surface shape measuring apparatus according to 7. 前記表面形状導出手段は、前記ｎ個の光路長差のそれぞれについて、前記干渉光強度の変化の計測結果でのばらつきによって前記干渉強さを求めることを特徴とする請求項６または７記載の表面形状計測装置。   8. The surface according to claim 6, wherein the surface shape deriving unit obtains the interference intensity from each of the n optical path length differences based on variations in the measurement result of the change in the interference light intensity. Shape measuring device.
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