JP6592796B2

JP6592796B2 - Object shape measuring method, object shape measuring apparatus, optical phase measuring method, and optical phase measuring apparatus

Info

Publication number: JP6592796B2
Application number: JP2015208139A
Authority: JP
Inventors: 淳岡本; 仁野澤; 昌孝戸田; 靖幸久野; 幸男市川
Original assignee: Aisin Seiki Co Ltd; Hokkaido University NUC; Aisin Corp
Current assignee: Hokkaido University NUC; Aisin Corp
Priority date: 2015-10-22
Filing date: 2015-10-22
Publication date: 2019-10-23
Anticipated expiration: 2035-10-22
Also published as: JP2017083177A

Description

本発明は、物体形状測定方法、物体形状測定装置、光位相測定方法および光位相測定装置に関する。 The present invention relates to an object shape measuring method, an object shape measuring apparatus, an optical phase measuring method, and an optical phase measuring apparatus.

現在、光の位相分布を測定できる技術は、光学分野においてきわめて重要な役割を担っている。この光位相測定において高解像度に位相分布を測定できる有力な技術として、位相シフトデジタルホログラフィが提案されている（非特許文献１参照）。この手法では、物体光（信号光）と参照光との干渉縞を複数生成し、これらの強度分布から光の位相分布を算出する。このような位相測定技術を用いて得られる位相情報は、被測定物体の深さ方向（奥行きｚ）の情報を有しているため、物体の３次元情報の測定に極めて有用である（非特許文献２参照）。しかし、位相の最大値は２πであるため、深さ方向の測定可能域は制限される。たとえば、波長５３２ｎｍの光を用いて物体からの透過光によって物体の厚さを測定する場合、厚さ方向の測定可能域は波長と等しい５３２ｎｍに制限される。また、波長５３２ｎｍの光を用いて物体からの反射光によって物体表面の凹部の深さを測定する場合、深さ方向の測定可能域は波長の半分の２６６ｎｍに制限される。 Currently, a technique capable of measuring the phase distribution of light plays a very important role in the optical field. Phase shift digital holography has been proposed as a promising technique capable of measuring the phase distribution with high resolution in this optical phase measurement (see Non-Patent Document 1). In this method, a plurality of interference fringes between object light (signal light) and reference light are generated, and the light phase distribution is calculated from these intensity distributions. The phase information obtained by using such a phase measurement technique has information on the depth direction (depth z) of the object to be measured, and is thus extremely useful for measuring three-dimensional information of an object (non-patent). Reference 2). However, since the maximum value of the phase is 2π, the measurable range in the depth direction is limited. For example, when measuring the thickness of an object using light having a wavelength of 532 nm by light transmitted from the object, the measurable range in the thickness direction is limited to 532 nm, which is equal to the wavelength. Further, when the depth of the concave portion on the surface of the object is measured by reflected light from the object using light having a wavelength of 532 nm, the measurable range in the depth direction is limited to 266 nm, which is half the wavelength.

このため、従来技術においては、物体の面方向（ｘ，ｙ）の複数の位置の位相情報から２πを超える位相差を推定する「位相接続」と呼ばれる方法により、使用する光の波長を超える深さ分布を取得している（非特許文献３参照）。位相接続では、測定された位相分布の不連続点を検出し、その不連続点を繋ぎ合わせることで物体の位相分布を深さ分布へと変換する。このことから、位相分布の不連続点を正確に検出するために、被測定物体の測定面の変化が一定であること、および測定された位相分布のノイズが十分に抑制されていることが求められる。このため、従来技術には、被測定物体の形状がある程度緩やかに変化するものに限定されたり、実際の測定可能域が波長の数倍程度までに制限されたりするなどの課題がある。 For this reason, in the prior art, a depth exceeding the wavelength of light to be used is determined by a method called “phase connection” that estimates phase differences exceeding 2π from phase information at a plurality of positions in the surface direction (x, y) of the object. The depth distribution is acquired (see Non-Patent Document 3). In the phase connection, a discontinuous point of the measured phase distribution is detected, and the phase distribution of the object is converted into a depth distribution by connecting the discontinuous points. From this, in order to accurately detect discontinuities in the phase distribution, it is required that the change in the measurement surface of the measured object is constant and that the noise in the measured phase distribution is sufficiently suppressed. It is done. For this reason, the prior art has problems such as being limited to those in which the shape of the object to be measured changes moderately to some extent, or limiting the actual measurable range to several times the wavelength.

Ichirou Yamaguchi and Tong Zhang, "Phase-shifting digital holography", Optics Letters, Vol. 22, No. 16, pp. 1268-1270.Ichirou Yamaguchi and Tong Zhang, "Phase-shifting digital holography", Optics Letters, Vol. 22, No. 16, pp. 1268-1270. Bahram Javidi and Daesuk Kim, “Three-dimensional-object recognition by use of single-exposure on-axis digital holography”, Optics Letters, Vol. 30, No. 3 , pp. 236-238.Bahram Javidi and Daesuk Kim, “Three-dimensional-object recognition by use of single-exposure on-axis digital holography”, Optics Letters, Vol. 30, No. 3, pp. 236-238. Pietro Ferraro, Sergio De Nicola, Andrea Finizio, Giuseppe Coppola, Simonetta Grilli, Carlo Magro, and Giobanni Peerattini, “Compensation of the inherent wave front curvature in digital holographic coherent microscopy for quantitative phase-contrast imaging”, Applied Optics, Vol. 42, No. 11, pp. 1938-1946.Pietro Ferraro, Sergio De Nicola, Andrea Finizio, Giuseppe Coppola, Simonetta Grilli, Carlo Magro, and Giobanni Peerattini, “Compensation of the inherent wave front curvature in digital holographic coherent microscopy for quantitative phase-contrast imaging”, Applied Optics, Vol. 42 , No. 11, pp. 1938-1946.

上述のように、位相接続を用いた従来の物体形状測定方法では、被測定物体の測定面の変化が一定であること、および測定された位相分布のノイズが十分に抑制されていることが求められる。したがって、従来の測定方法では、平面鏡やレンズなどの単純な形状を有する物体の形状を測定することはできるが、複雑な構造を有する物体の形状を測定することは難しい。また、フィルタリング処理などのノイズ除去を行うと、ノイズと共に位相分布の不連続点も同時に除去してしまう可能性があるため、ノイズ除去および位相接続の両方を行うことは難しい。すなわち、位相接続を用いた従来の物体形状測定方法には、形状が予測できる物体しか形状を測定することができない点、およびノイズ除去により位相接続の精度が低下する点の２つの欠点がある。このため、従来の測定方法は、その適用範囲が著しく狭かった。 As described above, in the conventional object shape measuring method using phase connection, it is required that the change in the measurement surface of the object to be measured is constant and that the noise of the measured phase distribution is sufficiently suppressed. It is done. Therefore, the conventional measurement method can measure the shape of an object having a simple shape such as a plane mirror or a lens, but it is difficult to measure the shape of an object having a complicated structure. Further, when noise removal such as filtering processing is performed, discontinuous points in the phase distribution may be removed at the same time as noise, so it is difficult to perform both noise removal and phase connection. That is, the conventional object shape measurement method using phase connection has two drawbacks: only the object whose shape can be predicted can be measured, and the accuracy of phase connection is reduced by noise removal. For this reason, the application range of the conventional measurement method is extremely narrow.

そこで、本発明は、位相接続をすることなく、使用する光の波長を超える高低差を含みうる物体の表面形状を測定できる物体形状測定方法および物体形状測定装置を提供することを目的とする。また、本発明は、２枚の干渉縞を用いて、物体光と参照光の強度比に依存せずに位相分布を測定することができる光位相測定方法および光位相測定装置を提供することも目的とする。 Accordingly, an object of the present invention is to provide an object shape measuring method and an object shape measuring apparatus capable of measuring the surface shape of an object that may include a height difference exceeding the wavelength of light to be used without phase connection. The present invention also provides an optical phase measurement method and an optical phase measurement device that can measure a phase distribution using two interference fringes without depending on the intensity ratio of object light and reference light. Objective.

本発明は、以下の物体形状測定方法および物体形状測定装置に関する。
［１］使用する光の波長を超える高低差を含みうる、物体の表面形状を測定する物体形状測定方法であって、物体の表面形状に由来する第１位相分布を含む第１波長の第１物体光と、前記第１波長の第１参照光とから、互いに位相差が異なる第１干渉縞および第２干渉縞を生成し、前記第１干渉縞の強度分布および前記第２干渉縞の強度分布を検出する工程と、前記第１物体光と前記第１参照光とから生成されうる、前記第１干渉縞および前記第２干渉縞のいずれとも位相差が異なり、かつ互いに位相差が異なる第３干渉縞および第４干渉縞を仮想的に生成し、前記第３干渉縞の強度分布および前記第４干渉縞の強度分布を算出する工程と、前記第１干渉縞の強度分布、前記第２干渉縞の強度分布、前記第３干渉縞の強度分布および前記第４干渉縞の強度分布から、前記第１物体光に含まれる前記第１位相分布を算出する工程と、前記物体の表面形状に由来する第２位相分布を含む、前記第１波長とは異なる第２波長の第２物体光と、前記第２波長の参照光とから、互いに位相差が異なる第５干渉縞および第６干渉縞を生成し、前記第５干渉縞の強度分布および前記第６干渉縞の強度分布を検出する工程と、前記第２物体光と前記第２参照光とから生成されうる、前記第５干渉縞および前記第６干渉縞のいずれとも位相差が異なり、かつ互いに位相差が異なる第７干渉縞および第８干渉縞を仮想的に生成し、前記第７干渉縞の強度分布および前記第８干渉縞の強度分布を算出する工程と、前記第５干渉縞の強度分布、前記第６干渉縞の強度分布、前記第７干渉縞の強度分布および前記第８干渉縞の強度分布から、前記第２物体光に含まれる前記第２位相分布を算出する工程と、算出された前記第１位相分布および前記第２位相分布から、前記第１波長および前記第２波長を超える高低差を含みうる、前記物体の表面形状を表す深さ分布を算出する工程と、を含み、前記第３干渉縞の強度分布および前記第４干渉縞の強度分布は、前記第１干渉縞の強度分布と、前記第２干渉縞の強度分布と、前記第１干渉縞の生成に用いられた前記第１物体光の強度と、前記第１干渉縞の生成に用いられた前記第１参照光の強度分布と、前記第１干渉縞の生成に用いられた前記第１物体光の強度に対する前記第２干渉縞の生成に用いられた前記第１物体光の強度の比の分布と、前記第１干渉縞の生成に用いられた前記第１参照光の強度に対する前記第２干渉縞の生成に用いられた前記第１参照光の強度の比の分布とから算出され、前記第７干渉縞の強度分布および前記第８干渉縞の強度分布は、前記第５干渉縞の強度分布と、前記第６干渉縞の強度分布と、前記第５干渉縞の生成に用いられた前記第２物体光の強度分布と、前記第５干渉縞の生成に用いられた前記第２参照光の強度分布と、前記第５干渉縞の生成に用いられた前記第２物体光の強度に対する前記第６干渉縞の生成に用いられた前記第２物体光の強度の比の分布と、前記第５干渉縞の生成に用いられた前記第２参照光の強度に対する前記第６干渉縞の生成に用いられた前記第２参照光の強度の比の分布とから算出される、
物体形状測定方法。
［２］前記第３干渉縞の強度分布、前記第４干渉縞の強度分布、前記第７干渉縞の強度分布および前記第８干渉縞の強度分布は、それぞれ以下の式（１）、式（２）、式（３）および式（４）により算出される、［１］に記載の物体形状測定方法。
（式（１）および式（２）において、Ｈ_１は前記第１干渉縞の強度分布であり、Ｈ_２は前記第２干渉縞の強度分布であり、Ｈ_３は前記第３干渉縞の強度分布であり、Ｈ_４は前記第４干渉縞の強度分布であり、Ａ_ｏ ^２は前記第１干渉縞の生成に用いられた前記第１物体光の強度分布であり、Ａ_ｒ ^２は前記第１干渉縞の生成に用いられた前記第１参照光の強度分布であり、αは前記第１干渉縞の生成に用いられた前記第１物体光の強度に対する前記第２干渉縞の生成に用いられた前記第１物体光の強度の比の分布であり、βは前記第１干渉縞の生成に用いられた前記第１参照光の強度に対する前記第２干渉縞の生成に用いられた前記第１参照光の強度の比の分布である。）
（式（３）および式（４）において、Ｈ_５は前記第５干渉縞の強度分布であり、Ｈ_６は前記第６干渉縞の強度分布であり、Ｈ_７は前記第７干渉縞の強度分布であり、Ｈ_８は前記第８干渉縞の強度分布であり、Ａ_ｏ’^２は前記第５干渉縞の生成に用いられた前記第２物体光の強度分布であり、Ａ_ｒ’^２は前記第５干渉縞の生成に用いられた前記第２参照光の強度分布であり、α’は前記第５干渉縞の生成に用いられた前記第２物体光の強度に対する前記第６干渉縞の生成に用いられた前記第２物体光の強度の比の分布であり、β’は前記第５干渉縞の生成に用いられた前記第２参照光の強度に対する前記第６干渉縞の生成に用いられた前記第２参照光の強度の比の分布である。）
［３］前記第１位相分布および前記第２位相分布は、それぞれ以下の式（５）および式（６）により算出される複素振幅の分布である、［２］に記載の物体形状測定方法。
（式（５）において、Ａ_ｏｅｘｐ（ｉφ）は前記第１位相分布であり、Ｈ_１は前記第１干渉縞の強度分布であり、Ｈ_２は前記第２干渉縞の強度分布であり、Ｈ_３は前記第３干渉縞の強度分布であり、Ｈ_４は前記第４干渉縞の強度分布であり、Ａ_ｒは前記第１干渉縞の生成に用いられた前記第１参照光の強度の平方根の分布であり、αは前記第１干渉縞の生成に用いられた前記第１物体光の強度に対する前記第２干渉縞の生成に用いられた前記第１物体光の強度の比の分布であり、βは前記第１干渉縞の生成に用いられた前記第１参照光の強度に対する前記第２干渉縞の生成に用いられた前記第１参照光の強度の比の分布であり、γは前記第１干渉縞と前記第２干渉縞との位相差である。）
（式（６）において、Ａ_ｏ’ｅｘｐ（ｉφ）は前記第２位相分布であり、Ｈ_５は前記第５干渉縞の強度分布であり、Ｈ_６は前記第６干渉縞の強度分布であり、Ｈ_７は前記第７干渉縞の強度分布であり、Ｈ_８は前記第８干渉縞の強度分布であり、Ａ_ｒ’は前記第５干渉縞の生成に用いられた前記第２参照光の強度の平方根の分布であり、α’は前記第５干渉縞の生成に用いられた前記第２物体光の強度に対する前記第６干渉縞の生成に用いられた前記第２物体光の強度の比の分布であり、β’は前記第５干渉縞の生成に用いられた前記第２参照光の強度に対する前記第６干渉縞の生成に用いられた前記第２参照光の強度の比の分布であり、γ’は前記第５干渉縞と前記第６干渉縞との位相差である。）
［４］前記深さ分布は、以下の式（７）および式（８）を用いてＬ_１＝Ｌ_２となるときのｍおよびｎの値を算出し、算出されたｍおよびｎの値を代入した式（７）および式（８）により算出される、［１］〜［３］のいずれか一項に記載の物体形状測定方法。
（式（７）において、Ｌ_１は前記物体の表面の任意の点における深さであり、φ_１は前記物体の表面の任意の点に対応する前記第１位相分布の点における位相の算出値（−π≦φ_１≦π）であり、λ_１は第１波長であり、ｍは正の整数である。）
（式（８）において、Ｌ_２は前記物体の表面の任意の点における深さであり、φ_２は前記物体の表面の任意の点に対応する前記第２位相分布の点における位相の算出値（−π≦φ_２≦π）であり、λ_２は第２波長であり、ｎは正の整数である。）
［５］使用する光の波長を超える高低差を含みうる、物体の表面形状を測定する物体形状測定装置であって、第１波長のレーザー光と、前記第１波長とは異なる第２波長のレーザー光とを同一光軸上に出射する光源部と、前記光源部から出射されたレーザー光を、物体光および参照光に分離する光分離部と、物体に対して透過または反射させた、前記物体の表面形状に由来する位相分布を含む前記物体光と、前記参照光とを合波して干渉波を生成する干渉波生成部と、前記干渉波から互いに位相差が異なる２つの干渉縞を生成し、前記２つの干渉縞の強度分布を検出する検出部と、前記光源部が前記第１波長のレーザー光を出射したときに前記検出部が検出した２つの干渉縞の強度分布と、前記光源部が前記第２波長のレーザー光を出射したときに前記検出部が検出した２つの干渉縞の強度分布とから、前記第１波長および前記第２波長を超える高低差を含みうる、前記物体の表面形状を表す深さ分布を算出する処理部と、を有する、物体形状測定装置。 The present invention relates to the following object shape measuring method and object shape measuring apparatus.
[1] An object shape measuring method for measuring a surface shape of an object, which may include a height difference exceeding the wavelength of light to be used, and includes a first wavelength having a first phase distribution derived from the surface shape of the object. A first interference fringe and a second interference fringe having different phase differences from each other are generated from the object light and the first reference light of the first wavelength, and the intensity distribution of the first interference fringe and the intensity of the second interference fringe A step of detecting a distribution, a phase difference that is different from each of the first interference fringe and the second interference fringe, and can be generated from the first object light and the first reference light; Virtually generating three interference fringes and a fourth interference fringe, calculating an intensity distribution of the third interference fringes and an intensity distribution of the fourth interference fringes, an intensity distribution of the first interference fringes, and the second Interference fringe intensity distribution, third interference fringe intensity distribution, and fourth A second phase different from the first wavelength includes a step of calculating the first phase distribution included in the first object light from an intensity distribution of interference fringes, and a second phase distribution derived from the surface shape of the object. A fifth interference fringe and a sixth interference fringe having different phase differences from each other are generated from the second object light of the wavelength and the reference light of the second wavelength, and the intensity distribution of the fifth interference fringe and the sixth interference fringe The phase difference is different from each of the fifth interference fringe and the sixth interference fringe that can be generated from the second object light and the second reference light, and the phase difference is mutually different. Virtually generating different seventh interference fringes and eighth interference fringes, calculating the intensity distribution of the seventh interference fringes and the intensity distribution of the eighth interference fringes, the intensity distribution of the fifth interference fringes, Intensity distribution of the sixth interference fringe, intensity distribution of the seventh interference fringe and front Calculating the second phase distribution contained in the second object light from the intensity distribution of the eighth interference fringes, and calculating the first wavelength and the second phase distribution from the calculated first phase distribution and the second phase distribution. Calculating a depth distribution representing the surface shape of the object, which may include a height difference exceeding a second wavelength, wherein the intensity distribution of the third interference fringes and the intensity distribution of the fourth interference fringes are The intensity distribution of the first interference fringes, the intensity distribution of the second interference fringes, the intensity of the first object light used to generate the first interference fringes, and the generation of the first interference fringes The intensity distribution of the first reference light and the ratio of the intensity of the first object light used to generate the second interference fringe to the intensity of the first object light used to generate the first interference fringe. The distribution and the intensity of the first reference light used to generate the first interference fringes. And the intensity distribution of the seventh interference fringe and the intensity distribution of the eighth interference fringe are calculated from the intensity ratio distribution of the first reference light used for generating the second interference fringes. The intensity distribution of the interference fringes, the intensity distribution of the sixth interference fringes, the intensity distribution of the second object light used for generating the fifth interference fringes, and the intensity used for generating the fifth interference fringes Distribution of the intensity distribution of the second reference light and the ratio of the intensity of the second object light used to generate the sixth interference fringe to the intensity of the second object light used to generate the fifth interference fringe And the distribution of the ratio of the intensity of the second reference light used to generate the sixth interference fringe to the intensity of the second reference light used to generate the fifth interference fringe.
Object shape measurement method.
[2] The intensity distribution of the third interference fringe, the intensity distribution of the fourth interference fringe, the intensity distribution of the seventh interference fringe, and the intensity distribution of the eighth interference fringe are respectively expressed by the following equations (1) and ( 2) The object shape measuring method according to [1], which is calculated by the equations (3) and (4).
(In Equations (1) and (2), H ₁ is the intensity distribution of the first interference fringes, H ₂ is the intensity distribution of the second interference fringes, and H ₃ is the intensity of the third interference fringes. H ₄ is the intensity distribution of the fourth interference fringes, A _o ² is the intensity distribution of the first object light used for generating the first interference fringes, and A _r ² is the first distribution of the first interference fringes. 1 is an intensity distribution of the first reference light used to generate one interference fringe, and α is used to generate the second interference fringe with respect to the intensity of the first object light used to generate the first interference fringe. Is the distribution of the ratio of the intensity of the first object light, and β is the first interference fringe used for generating the second interference fringe with respect to the intensity of the first reference light used for generating the first interference fringe. 1 is the distribution of the intensity ratio of the reference light.)
(In Expressions (3) and (4), H ₅ is the intensity distribution of the fifth interference fringe, H ₆ is the intensity distribution of the sixth interference fringe, and H ₇ is the intensity of the seventh interference fringe. H ₈ is the intensity distribution of the eighth interference fringe, A _o ′ ² is the intensity distribution of the second object light used to generate the fifth interference fringe, and A _r ′ ² is An intensity distribution of the second reference light used to generate the fifth interference fringe, and α ′ represents the intensity of the second interference light with respect to the intensity of the second object light used to generate the fifth interference fringe. The intensity distribution of the second object light used for generation is β ′, which is used for generation of the sixth interference fringe with respect to the intensity of the second reference light used for generation of the fifth interference fringe. The distribution of the intensity ratio of the second reference light.
[3] The object shape measuring method according to [2], wherein the first phase distribution and the second phase distribution are distributions of complex amplitudes calculated by the following equations (5) and (6), respectively.
(In Expression (5), A _o exp (iφ) is the first phase distribution, H ₁ is the intensity distribution of the first interference fringes, and H ₂ is the intensity distribution of the second interference fringes, H ₃ is the intensity distribution of the third interference fringe, H ₄ is the intensity distribution of the fourth interference fringe, and _Ar is the intensity of the first reference light used to generate the first interference fringe. Is a square root distribution, and α is a distribution of a ratio of the intensity of the first object light used to generate the second interference fringe to the intensity of the first object light used to generate the first interference fringe. And β is a distribution of the ratio of the intensity of the first reference light used to generate the second interference fringe to the intensity of the first reference light used to generate the first interference fringe, and γ is (It is a phase difference between the first interference fringe and the second interference fringe.)
(In Expression (6), A _o 'exp (iφ) is the second phase distribution, H ₅ is the intensity distribution of the fifth interference fringe, and H ₆ is the intensity distribution of the sixth interference fringe. , H ₇ is the intensity distribution of the seventh interference fringe, H ₈ is the intensity distribution of the eighth interference fringe, and A _r ′ is the second reference light used to generate the fifth interference fringe. Is the distribution of the square root of intensity, and α ′ is the ratio of the intensity of the second object light used to generate the sixth interference fringe to the intensity of the second object light used to generate the fifth interference fringe. Β ′ is a distribution of the ratio of the intensity of the second reference light used to generate the sixth interference fringe to the intensity of the second reference light used to generate the fifth interference fringe. And γ ′ is a phase difference between the fifth interference fringe and the sixth interference fringe.)
[4] the depth distribution, the following equation (7) and calculates the value of m and n when the L _{1 =} L ₂ using the equation (8), the value of the calculated m and n The object shape measuring method according to any one of [1] to [3], which is calculated by the substituted formula (7) and formula (8).
(In Expression (7), L ₁ is a depth at an arbitrary point on the surface of the object, and φ ₁ is a calculated value of a phase at a point of the first phase distribution corresponding to an arbitrary point on the surface of the object. (−π ≦ φ ₁ ≦ π), λ ₁ is the first wavelength, and m is a positive integer.)
(In Expression (8), L ₂ is a depth at an arbitrary point on the surface of the object, and φ ₂ is a calculated value of a phase at a point of the second phase distribution corresponding to an arbitrary point on the surface of the object. (−π ≦ φ ₂ ≦ π), λ ₂ is the second wavelength, and n is a positive integer.)
[5] An object shape measuring apparatus for measuring a surface shape of an object, which may include a height difference exceeding the wavelength of light to be used, wherein the first wavelength laser light and a second wavelength different from the first wavelength are used. A light source unit that emits laser light on the same optical axis, a light separation unit that separates laser light emitted from the light source unit into object light and reference light, and is transmitted or reflected on the object, An interference wave generation unit that generates an interference wave by combining the object light including the phase distribution derived from the surface shape of the object and the reference light; and two interference fringes having different phase differences from the interference wave. A detection unit that generates and detects the intensity distribution of the two interference fringes, the intensity distribution of the two interference fringes detected by the detection unit when the light source unit emits the laser light of the first wavelength, and The light source unit emitted the second wavelength laser beam. A processing unit that calculates a depth distribution representing the surface shape of the object, which may include a height difference exceeding the first wavelength and the second wavelength, from intensity distributions of two interference fringes detected by the detection unit And an object shape measuring apparatus.

また、本発明は、以下の光位相測定方法および光位相測定装置に関する。
［６］位相分布を含む物体光と、前記物体光と同一波長の参照光とから、互いに位相差が異なる第１干渉縞および第２干渉縞を生成し、前記第１干渉縞の強度分布および前記第２干渉縞の強度分布を検出する工程と、前記物体光と前記参照光とから生成されうる、前記第１干渉縞および前記第２干渉縞のいずれとも位相差が異なり、かつ互いに位相差が異なる第３干渉縞および第４干渉縞を仮想的に生成し、前記第３干渉縞の強度分布および前記第４干渉縞の強度分布を算出する工程と、前記第１干渉縞の強度分布、前記第２干渉縞の強度分布、前記第３干渉縞の強度分布および前記第４干渉縞の強度分布から、前記物体光に含まれる前記位相分布を算出する工程と、を含み、前記第３干渉縞の強度分布および前記第４干渉縞の強度分布は、前記第１干渉縞の強度分布と、前記第２干渉縞の強度分布と、前記第１干渉縞の生成に用いられた前記物体光の強度分布と、前記第１干渉縞の生成に用いられた前記参照光の強度分布と、前記第１干渉縞の生成に用いられた前記物体光の強度に対する前記第２干渉縞の生成に用いられた前記物体光の強度の比の分布と、前記第１干渉縞の生成に用いられた前記参照光の強度に対する前記第２干渉縞の生成に用いられた前記参照光の強度の比の分布とから算出される、光位相測定方法。
［７］前記第３干渉縞の強度分布および前記第４干渉縞の強度分布は、それぞれ以下の式（１）および式（２）により算出される、［６］に記載の光位相測定方法。
（式（１）および式（２）において、Ｈ_１は前記第１干渉縞の強度分布であり、Ｈ_２は前記第２干渉縞の強度分布であり、Ｈ_３は前記第３干渉縞の強度分布であり、Ｈ_４は前記第４干渉縞の強度分布であり、Ａ_ｏ ^２は前記第１干渉縞の生成に用いられた前記物体光の強度分布であり、Ａ_ｒ ^２は前記第１干渉縞の生成に用いられた前記参照光の強度分布であり、αは前記第１干渉縞の生成に用いられた前記物体光の強度に対する前記第２干渉縞の生成に用いられた前記物体光の強度の比の分布であり、βは前記第１干渉縞の生成に用いられた前記参照光の強度に対する前記第２干渉縞の生成に用いられた前記参照光の強度の比の分布である。）
［８］前記位相分布は、以下の式（５）により算出される複素振幅の分布である、［７］に記載の光位相測定方法。
（式（５）において、Ａ_ｏｅｘｐ（ｉφ）は前記位相分布であり、Ｈ_１は前記第１干渉縞の強度分布であり、Ｈ_２は前記第２干渉縞の強度分布であり、Ｈ_３は前記第３干渉縞の強度分布であり、Ｈ_４は前記第４干渉縞の強度分布であり、Ａ_ｒは前記第１干渉縞の生成に用いられた前記参照光の強度の平方根の分布であり、αは前記第１干渉縞の生成に用いられた前記物体光の強度に対する前記第２干渉縞の生成に用いられた前記物体光の強度の比の分布であり、βは前記第１干渉縞の生成に用いられた前記参照光の強度に対する前記第２干渉縞の生成に用いられた前記参照光の強度の比の分布であり、γは前記第１干渉縞と前記第２干渉縞との位相差である。）
［９］位相分布を含む物体光と、参照光とを合波して干渉波を生成する干渉波生成部と、前記干渉波から互いに位相差が異なる第１の干渉縞および第２の干渉縞を生成し、前記第１の干渉縞の強度分布および前記第２の干渉縞の強度分布を検出する検出部と、前記第１の干渉縞の強度分布および前記第２の干渉縞の強度分布から前記位相分布を算出する処理部と、を有し、前記処理部は、前記第１の干渉縞の強度分布および前記第２の干渉縞の強度分布から、前記第１干渉縞および前記第２干渉縞のいずれとも位相差が異なり、かつ互いに位相差が異なる第３干渉縞および第４干渉縞を仮想的に生成し、前記第３干渉縞の強度分布および前記第４干渉縞の強度分布を算出し、前記第１干渉縞の強度分布、前記第２干渉縞の強度分布、前記第３干渉縞の強度分布および前記第４干渉縞の強度分布から、前記位相分布を算出する、光位相測定装置。 The present invention also relates to the following optical phase measurement method and optical phase measurement apparatus.
[6] A first interference fringe and a second interference fringe having different phase differences are generated from the object light including the phase distribution and the reference light having the same wavelength as the object light, and the intensity distribution of the first interference fringe and The step of detecting the intensity distribution of the second interference fringe, and the phase difference of the first interference fringe and the second interference fringe that can be generated from the object light and the reference light are different from each other. Virtually generating a third interference fringe and a fourth interference fringe different from each other, calculating an intensity distribution of the third interference fringe and an intensity distribution of the fourth interference fringe, and an intensity distribution of the first interference fringe, Calculating the phase distribution included in the object light from the intensity distribution of the second interference fringe, the intensity distribution of the third interference fringe, and the intensity distribution of the fourth interference fringe, and the third interference The intensity distribution of the fringes and the intensity distribution of the fourth interference fringes are: The intensity distribution of the first interference fringes, the intensity distribution of the second interference fringes, the intensity distribution of the object light used to generate the first interference fringes, and the generation of the first interference fringes An intensity distribution of the reference light, a distribution of a ratio of the intensity of the object light used to generate the second interference fringe to the intensity of the object light used to generate the first interference fringe, and the first An optical phase measurement method calculated from the distribution of the ratio of the intensity of the reference light used for generating the second interference fringe to the intensity of the reference light used for generating the interference fringe.
[7] The optical phase measurement method according to [6], wherein the intensity distribution of the third interference fringes and the intensity distribution of the fourth interference fringes are calculated by the following expressions (1) and (2), respectively.
(In Equations (1) and (2), H ₁ is the intensity distribution of the first interference fringes, H ₂ is the intensity distribution of the second interference fringes, and H ₃ is the intensity of the third interference fringes. H ₄ is an intensity distribution of the fourth interference fringes, A _o ² is an intensity distribution of the object light used for generating the first interference fringes, and A _r ² is the first interference. Is an intensity distribution of the reference light used for generating the fringes, and α is the intensity of the object light used for generating the second interference fringes with respect to the intensity of the object light used for generating the first interference fringes. Β is a distribution of the ratio of the intensity of the reference light used for generating the second interference fringe to the intensity of the reference light used for generating the first interference fringe. )
[8] The optical phase measurement method according to [7], wherein the phase distribution is a distribution of complex amplitudes calculated by the following equation (5).
(In Expression (5), A _o exp (iφ) is the phase distribution, H ₁ is the intensity distribution of the first interference fringe, H ₂ is the intensity distribution of the second interference fringe, and H ₃ Is the intensity distribution of the third interference fringes, H ₄ is the intensity distribution of the fourth interference fringes, and _Ar is the distribution of the square root of the intensity of the reference light used to generate the first interference fringes. A is the distribution of the ratio of the intensity of the object light used to generate the second interference fringe to the intensity of the object light used to generate the first interference fringe, and β is the first interference A distribution of a ratio of the intensity of the reference light used for generating the second interference fringe to the intensity of the reference light used for generating the fringe, and γ is the first interference fringe and the second interference fringe The phase difference of
[9] An interference wave generator that generates an interference wave by combining the object light including the phase distribution and the reference light, and the first interference fringe and the second interference fringe having a phase difference different from each other from the interference wave And detecting the intensity distribution of the first interference fringes and the intensity distribution of the second interference fringes, and the intensity distribution of the first interference fringes and the intensity distribution of the second interference fringes A processing unit that calculates the phase distribution, and the processing unit calculates the first interference fringe and the second interference from the intensity distribution of the first interference fringe and the intensity distribution of the second interference fringe. A third interference fringe and a fourth interference fringe having a phase difference different from any of the fringes and having a phase difference different from each other are virtually generated, and the intensity distribution of the third interference fringe and the intensity distribution of the fourth interference fringe are calculated. The intensity distribution of the first interference fringes, the intensity distribution of the second interference fringes, the third From the intensity distribution and the intensity distribution of the fourth interference fringes Watarushima, calculates the phase distribution, the optical phase measurement device.

本発明に係る物体形状測定方法および物体形状測定装置によれば、位相接続をすることなく、使用する光の波長を超える高低差を含みうる物体の表面形状を測定することができる。したがって、本発明に係る物体形状測定方法および物体形状測定装置によれば、複雑な形状の物体表面の形状を測定ノイズを除去しなくても高精度に測定することができる。また、本発明に係る光位相測定方法および光位相測定装置によれば、２枚の干渉縞を用いて、物体光と参照光の強度の比の分布に依存せずに位相分布を測定することができる。 According to the object shape measuring method and the object shape measuring apparatus according to the present invention, it is possible to measure the surface shape of an object that may include a height difference exceeding the wavelength of light to be used without phase connection. Therefore, according to the object shape measuring method and the object shape measuring apparatus according to the present invention, the shape of the object surface having a complicated shape can be measured with high accuracy without removing the measurement noise. In addition, according to the optical phase measurement method and the optical phase measurement device according to the present invention, the phase distribution can be measured using two interference fringes without depending on the distribution of the intensity ratio between the object light and the reference light. Can do.

図１は、本発明の一実施の形態に係る物体形状測定装置の構成を示す模式図である。FIG. 1 is a schematic diagram showing a configuration of an object shape measuring apparatus according to an embodiment of the present invention. 図２は、２枚の干渉縞から別の２枚の干渉縞を仮想的に生成する方法を説明するための概念図である。FIG. 2 is a conceptual diagram for explaining a method of virtually generating two interference fringes from two interference fringes. 図３は、４枚の干渉縞の強度分布を用いて、物体光に含まれる位相情報を算出する方法を説明するための概念図である。FIG. 3 is a conceptual diagram for explaining a method of calculating phase information included in object light using the intensity distribution of four interference fringes. 図４は、位相の測定値をそのまま深さに変換した値と、物体表面の実際の深さとの関係を示すグラフである。FIG. 4 is a graph showing the relationship between the value obtained by directly converting the phase measurement value into the depth and the actual depth of the object surface. 図５は、ｍおよびｎを決定する手順の一例を示すフローチャートであるFIG. 5 is a flowchart showing an example of a procedure for determining m and n. 図６は、物体形状測定装置の変形例の構成を示す模式図である。FIG. 6 is a schematic diagram illustrating a configuration of a modified example of the object shape measuring apparatus. 図７Ａ〜Ｄは、本発明に係る物体形状測定方法のシミュレーション結果である。7A to 7D are simulation results of the object shape measuring method according to the present invention. 図８は、本発明に係る方法および従来の方法における、位相の算出値の誤差を示すグラフである。FIG. 8 is a graph showing an error in the calculated value of the phase in the method according to the present invention and the conventional method. 図９Ａ〜Ｃは、本発明に係る方法と従来の方法とを用いて位相変調信号を測定した結果を示す図である。9A to 9C are diagrams showing the results of measuring the phase modulation signal using the method according to the present invention and the conventional method.

１．物体形状測定方法および物体形状測定装置
［物体形状測定方法］
本発明に係る物体形状測定方法は、使用する光の波長を超える高低差を含んでいても位相接続をすることなく物体の表面形状を測定することができる方法である。以下、本発明に係る物体形状測定方法の内容について説明する。 1. Object shape measuring method and object shape measuring apparatus [Object shape measuring method]
The object shape measuring method according to the present invention is a method capable of measuring the surface shape of an object without phase connection even if the height difference exceeds the wavelength of light to be used. The contents of the object shape measuring method according to the present invention will be described below.

本発明に係る物体形状測定方法では、第１工程として、測定対象の物体に対して第１波長の光を反射または透過して得られる第１波長の第１物体光と、第１波長の第１参照光とを干渉させて得られる、２枚の干渉縞の強度分布を測定する。そして、これらの２枚の干渉縞の強度分布を用いて、第１物体光に含まれる第１位相分布を算出する。この第１位相分布は、第１波長λ_１で測定されたときの位相φ_１（−π≦φ_１≦π）という形態で物体の表面形状の情報を含む。 In the object shape measuring method according to the present invention, as the first step, the first object light of the first wavelength obtained by reflecting or transmitting the light of the first wavelength with respect to the object to be measured, and the first object of the first wavelength. The intensity distribution of two interference fringes obtained by causing interference with one reference beam is measured. Then, the first phase distribution included in the first object light is calculated using the intensity distribution of these two interference fringes. This first phase distribution includes information on the surface shape of the object in the form of phase φ ₁ (−π ≦ φ ₁ ≦ π) measured at the first wavelength λ ₁ .

また、第２工程として、測定対象の物体に対して第１波長とは異なる第２波長の光を反射または透過して得られる第２波長の第２物体光と、第２波長の第２参照光とを干渉させて得られる、２枚の干渉縞の強度分布を測定する。そして、これらの２枚の干渉縞の強度分布を用いて、第２物体光に含まれる第２位相分布を算出する。この第２位相分布は、第２波長λ_２で測定されたときの位相φ_２（−π≦φ_２≦π）という形態で物体の表面形状の情報を含む。第１位相分布と第２位相分布とでは、物体の同一箇所の表面形状の情報を含むという点では共通しているが、波長が異なるため位相の測定値は互いに異なっている（偶然一致している場合もある）。 Further, as the second step, the second object light having the second wavelength obtained by reflecting or transmitting the light having the second wavelength different from the first wavelength with respect to the object to be measured, and the second reference of the second wavelength. The intensity distribution of two interference fringes obtained by interference with light is measured. Then, the second phase distribution included in the second object light is calculated using the intensity distribution of these two interference fringes. This second phase distribution includes information on the surface shape of the object in the form of phase φ ₂ (−π ≦ φ ₂ ≦ π) as measured at the second wavelength λ ₂ . The first phase distribution and the second phase distribution are common in that they include information on the surface shape of the same part of the object, but the measured values of the phases are different from each other due to different wavelengths (coincidentally coincident with each other). In some cases).

なお、第１工程および第２工程は、いずれもこの次に説明する第３工程より前に行われるが、第１工程および第２工程の順番は特に限定されない。たとえば、第１工程を第２工程より先に行ってもよいし、第２工程を第１工程より先に行ってもよい。また、第１工程および第２工程を並行して行ってもよい。 In addition, although a 1st process and a 2nd process are both performed before the 3rd process demonstrated next, the order of a 1st process and a 2nd process is not specifically limited. For example, the first step may be performed before the second step, or the second step may be performed before the first step. Moreover, you may perform a 1st process and a 2nd process in parallel.

次いで、第３工程として、第１工程で算出された第１位相分布と、第２工程で算出された第２位相分布とから、物体の表面形状を表す深さ分布を位相接続をすることなく算出する。この第３工程で算出される深さ分布は、第１波長および第２波長を超える高低差を含むことができる。 Next, as a third step, the depth distribution representing the surface shape of the object is not phase-connected from the first phase distribution calculated in the first step and the second phase distribution calculated in the second step. calculate. The depth distribution calculated in the third step can include a height difference exceeding the first wavelength and the second wavelength.

以下、第１工程、第２工程および第３工程の各工程について説明する。 Hereinafter, each process of a 1st process, a 2nd process, and a 3rd process is demonstrated.

（第１工程）
第１工程は、より詳細には、（１）第１波長の第１物体光と第１参照光とから生成される第１干渉縞および第２干渉縞の強度分布を検出する工程と、（２）第１物体光と第１参照光とから仮想的に生成される第３干渉縞および第４干渉縞の強度分布を算出する工程と、（３）第１干渉縞の強度分布、第２干渉縞の強度分布、第３干渉縞の強度分布および第４干渉縞の強度分布を用いて、第１物体光に含まれる第１位相分布を算出する工程と、を含む。 (First step)
More specifically, the first step is (1) detecting the intensity distribution of the first interference fringe and the second interference fringe generated from the first object light of the first wavelength and the first reference light; 2) calculating the intensity distribution of the third interference fringe and the fourth interference fringe virtually generated from the first object light and the first reference light, and (3) the intensity distribution of the first interference fringe, the second Calculating a first phase distribution included in the first object light using the intensity distribution of the interference fringes, the intensity distribution of the third interference fringes, and the intensity distribution of the fourth interference fringes.

まず、第１波長の第１物体光と第１参照光とから、互いに位相差が異なる第１干渉縞および第２干渉縞を生成し、第１干渉縞の強度分布および第２干渉縞の強度分布を検出する（上記（１）の工程）。第１物体光は、測定対象の物体に対して第１波長の光を反射または透過して得られる光であり、物体の表面形状に由来する第１位相分布を含む。第１参照光は、第１物体光と干渉可能な第１波長の光である。 First, a first interference fringe and a second interference fringe having different phase differences from each other are generated from the first object light of the first wavelength and the first reference light, and the intensity distribution of the first interference fringe and the intensity of the second interference fringe Distribution is detected (step (1) above). The first object light is light obtained by reflecting or transmitting light of the first wavelength with respect to the object to be measured, and includes a first phase distribution derived from the surface shape of the object. The first reference light is light having a first wavelength that can interfere with the first object light.

図１に示される光学系（後述の物体形状測定装置の項で詳細に説明する）を用いて説明する。ここでは、第１レーザー光源（Laser 1）から出射された波長５３２ｎｍのレーザー光を分岐して第１物体光（Object beam）および第１参照光（Reference beam）を生成している。第１物体光は、測定対象の物体（Object）の表面で反射している。直線偏光の第１物体光は第２半波長板（ＨＷＰ２）によりその偏向角が４５°回転させられる。したがって、第１物体光は、第３ビームスプリッター（ＢＳ３）の位置において、互いに同位相の水平偏光成分と垂直偏光成分とを半分ずつ有している。一方、直線偏光の第１参照光は、１／４波長板（ＱＷＰ）によってその偏光状態を円偏光に変換される。円偏光とは、水平偏光成分と垂直偏光成分の位相差がπ／２である偏光状態を意味する。したがって、第１参照光は、第３ビームスプリッター（ＢＳ３）の位置において、互いの位相差がπ／２である水平偏光成分と垂直偏光成分とを半分ずつ有している。 A description will be given using the optical system shown in FIG. 1 (which will be described in detail in the section of an object shape measuring apparatus described later). Here, the laser beam with a wavelength of 532 nm emitted from the first laser light source (Laser 1) is branched to generate the first object beam (Object beam) and the first reference beam (Reference beam). The first object light is reflected on the surface of the object to be measured (Object). The deflection angle of the linearly polarized first object light is rotated by 45 ° by the second half-wave plate (HWP2). Therefore, the first object light has a horizontal polarization component and a vertical polarization component in half at the same phase at the position of the third beam splitter (BS3). On the other hand, the linearly polarized first reference light is converted into circularly polarized light by a quarter wave plate (QWP). Circularly polarized light means a polarization state in which the phase difference between the horizontal polarization component and the vertical polarization component is π / 2. Accordingly, the first reference light has a horizontal polarization component and a vertical polarization component each having a half phase difference of π / 2 at the position of the third beam splitter (BS3).

このようにして得られた４５°直線偏光の第１物体光と円偏光の第１参照光とは、第３ビームスプリッター（ＢＳ３）において合波され、第２偏光ビームスプリッター（ＰＢＳ２）に向かう。第１物体光の水平偏光成分および第１参照光の水平偏光成分は、第２偏光ビームスプリッター（ＰＢＳ２）を透過（直進）し、第１検出部（ＣＣＤ１）の検出面上に第１干渉縞を生成する。第１検出部（ＣＣＤ１）は、この第１干渉縞の強度分布を検出する。一方、第１物体光の垂直偏光成分および第１参照光の垂直偏光成分は、第２偏光ビームスプリッター（ＰＢＳ２）で反射し、第２検出部（ＣＣＤ２）の検出面上に第２干渉縞を生成する。このとき、円偏光の第１参照光では、水平偏光成分と垂直偏光成分との位相差がπ／２であるため、第１干渉縞を生成する干渉波と、第２干渉縞を生成する干渉波との間には、π／２の位相差が発生する。第２検出部（ＣＣＤ２）は、この第１干渉縞の強度分布を検出する。 The 45 ° linearly polarized first object light and the circularly polarized first reference light obtained in this way are combined in the third beam splitter (BS3) and travel toward the second polarizing beam splitter (PBS2). The horizontal polarization component of the first object light and the horizontal polarization component of the first reference light are transmitted (straight forward) through the second polarization beam splitter (PBS2), and the first interference fringes are formed on the detection surface of the first detection unit (CCD1). Is generated. The first detector (CCD 1) detects the intensity distribution of the first interference fringes. On the other hand, the vertical polarization component of the first object light and the vertical polarization component of the first reference light are reflected by the second polarization beam splitter (PBS2), and the second interference fringes are formed on the detection surface of the second detection unit (CCD2). Generate. At this time, since the phase difference between the horizontal polarization component and the vertical polarization component is π / 2 in the circularly polarized first reference light, the interference wave that generates the first interference fringe and the interference that generates the second interference fringe. A phase difference of π / 2 occurs between the waves. The second detector (CCD2) detects the intensity distribution of the first interference fringes.

上記のとおり、円偏光の第１参照光では水平偏光成分と垂直偏光成分との位相差がπ／２であるため、第１干渉縞と第２干渉縞との位相差はπ／２となるはずである。しかしながら、半波長板および１／４波長板には対応波長があるため、第１干渉縞と第２干渉縞との実際の位相差はπ／２から外れることがある。波長板の対応波長をλ_ｅ、波長板に入射する光の波長をλとすると、半波長板が与える位相差δ_１および１／４波長板が与える位相差δ_２は、以下の式（９）および式（１０）のように記述されうる。
As described above, since the phase difference between the horizontal polarization component and the vertical polarization component is π / 2 in the circularly polarized first reference light, the phase difference between the first interference fringe and the second interference fringe is π / 2. It should be. However, since the half-wave plate and the quarter-wave plate have corresponding wavelengths, the actual phase difference between the first interference fringe and the second interference fringe may deviate from π / 2. When the corresponding wavelength of the wave plate is λ _e and the wavelength of light incident on the wave plate is λ, the phase difference δ ₁ given by the half-wave plate and the phase difference δ ₂ given by the quarter-wave plate are expressed by ) And equation (10).

これら２つの位相差の差分が干渉縞に与えられる位相差となるので、第１干渉縞と第２干渉縞との位相差δは、以下の式（１１）のように導出される。このことからわかるように、第１干渉縞と第２干渉縞との位相差は、厳密にはπ／２とはならないことがある。この後説明するように、本発明に係る物体形状測定方法では、第１干渉縞と第２干渉縞との位相差がπ／２でなくても特に問題無く、物体の表面形状を測定することができる。
Since the difference between these two phase differences is the phase difference given to the interference fringes, the phase difference δ between the first interference fringes and the second interference fringes is derived as in the following equation (11). As can be seen from this, the phase difference between the first interference fringes and the second interference fringes may not be strictly π / 2. As will be described later, in the object shape measuring method according to the present invention, the surface shape of the object is measured without any problem even if the phase difference between the first interference fringe and the second interference fringe is not π / 2. Can do.

次いで、第１干渉縞の強度分布および第２干渉縞の強度分布の測定結果を用いて、第１物体光と第１参照光とから第３干渉縞および第４干渉縞を仮想的に生成し、第３干渉縞の強度分布および第４干渉縞の強度分布を算出する（上記（２）の工程）。第３干渉縞は、第１物体光と第１参照光とから生成されうる干渉縞であって、第１干渉縞および第２干渉縞のいずれとも位相差が異なる干渉縞である。また、第４干渉縞は、第１物体光と第１参照光とから生成されうる干渉縞であって、第１干渉縞、第２干渉縞および第３干渉光のいずれとも位相差が異なる干渉縞である。 Next, using the measurement results of the intensity distribution of the first interference fringe and the intensity distribution of the second interference fringe, a third interference fringe and a fourth interference fringe are virtually generated from the first object light and the first reference light. The intensity distribution of the third interference fringes and the intensity distribution of the fourth interference fringes are calculated (step (2) above). The third interference fringes are interference fringes that can be generated from the first object light and the first reference light and are different in phase difference from both the first interference fringes and the second interference fringes. The fourth interference fringe is an interference fringe that can be generated from the first object light and the first reference light, and has a phase difference different from any of the first interference fringe, the second interference fringe, and the third interference light. It is a stripe.

図２は、第３干渉縞および第４干渉縞を仮想的に生成する方法を説明するための概念図である。Ｈ_１は実際に生成された第１干渉縞の強度分布であり、Ｈ_２は実際に生成された第２干渉縞の強度分布である。Ｈ_３は仮想的に生成された第３干渉縞の強度分布であり、Ｈ_４は仮想的に生成された第４干渉縞の強度分布である。Ｓ_１は第１干渉縞の生成に用いられた第１物体光の強度分布であり、Ｒ_１は第１干渉縞の生成に用いられた第１参照光の強度分布である。Ｓ_２は第２干渉縞の生成に用いられた第１物体光の強度分布であり、Ｒ_２は第２干渉縞の生成に用いられた第１参照光の強度分布である。この図に示されるように、第３干渉縞の強度分布Ｈ_３および第４干渉縞の強度分布Ｈ_３は、第１干渉縞の強度分布Ｈ_１と、第２干渉縞の強度分布Ｈ_２と、第１干渉縞の生成に用いられた第１物体光の強度分布Ｓ_１と、第１干渉縞の生成に用いられた第１参照光の強度分布Ｒ_１と、第２干渉縞の生成に用いられた第１物体光の強度分布Ｓ_２と、第２干渉縞の生成に用いられた第１参照光の強度分布Ｒ_２とから計算機上において仮想的に生成されうる。以下、第３干渉縞および第４干渉縞が仮想的に生成されうることについて説明する。 FIG. 2 is a conceptual diagram for explaining a method of virtually generating the third interference fringe and the fourth interference fringe. H ₁ is the intensity distribution of the actually generated first interference fringe, and H ₂ is the intensity distribution of the actually generated second interference fringe. H ₃ is the intensity distribution of the virtually generated third interference fringe, and H ₄ is the intensity distribution of the virtually generated fourth interference fringe. S ₁ is the intensity distribution of the first object light used for generating the first interference fringes, and R ₁ is the intensity distribution of the first reference light used for generating the first interference fringes. S ₂ is the intensity distribution of the first object light used for generating the second interference fringes, and R ₂ is the intensity distribution of the first reference light used for generating the second interference fringes. As shown in this figure, the intensity distribution H ₃ of the intensity distribution H ₃ and fourth interference fringe of the third interference fringes, the intensity distribution H ₁ of the first interference fringe, the intensity distribution of H ₂ second interference fringe The first object light intensity distribution S ₁ used for generating the first interference fringes, the first reference light intensity distribution R ₁ used for generating the first interference fringes, and the second interference fringe generation. the intensity distribution S ₂ of the first object light used may be virtually generated on a computer from the first reference light intensity distribution R ₂ Metropolitan used to generate the second interference fringes. Hereinafter, the fact that the third interference fringe and the fourth interference fringe can be virtually generated will be described.

まず、第１干渉縞の生成に用いられた第１物体光の強度分布をＡ_Ｏ ^２（図２ではＳ_１と表記）とし、第１干渉縞の生成に用いられた第１参照光の強度分布をＡ_ｒ ^２（図２ではＲ_１と表記）とすると、第１干渉縞の強度分布Ｈ_１および第２干渉縞の強度分布Ｈ_２は、それぞれ以下の式（１２）および式（１３）のように記述されうる。ここで、αは第１干渉縞の生成に用いられた第１物体光の強度Ａ_Ｏ ^２（図２ではＳ_１と表記）に対する第２干渉縞の生成に用いられた第１物体光の強度（図２ではＳ_２と表記）の比の分布であり、βは第１干渉縞の生成に用いられた第１参照光の強度Ａ_ｒ ^２（図２ではＲ_１と表記）に対する第２干渉縞の生成に用いられた第１参照光の強度（図２ではＲ_２と表記）の比の分布である。また、φは第１物体光と第１参照光との位相差の分布であり、γは第１干渉縞と第２干渉縞との位相差である。
First, the intensity distribution of the first object light used to generate the first interference fringe is A _O ² (denoted as S _{1 in} FIG. 2), and the intensity of the first reference light used to generate the first interference fringe. Assuming that the distribution is A _r ² (indicated as R _{1 in} FIG. 2), the intensity distribution H ₁ of the first interference fringes and the intensity distribution H ₂ of the second interference fringes are expressed by the following equations (12) and (13), respectively. It can be described as follows. Here, α is the intensity of the first object light used for generating the second interference fringe with respect to the intensity A _O ² (denoted as S _{1 in} FIG. 2) of the first object light used for generating the first interference fringe. a distribution ratio (denoted in FIG. 2 S _2), beta second interference to intensity a _{r 2} of the first reference beam used for generating the first interference fringe ⁽ⁱⁿ FIG. 2 denoted as R ₁₎ the distribution of the ratio is the intensity of the first reference beam used for generating the fringe (denoted in FIG. 2 R _2). Φ is the phase difference distribution between the first object beam and the first reference beam, and γ is the phase difference between the first interference fringe and the second interference fringe.

第１参照光が理想的な平面波である、すなわち第１参照光の位相が０であると仮定した場合、φは第１物体光の位相差の分布となる。よって、φを導出することが物体表面の形状を測定する上での目的となる。このとき、式（１２）および式（１３）中の三角関数は、それぞれ以下の式（１４）および式（１５）のように展開されうる。
When it is assumed that the first reference light is an ideal plane wave, that is, the phase of the first reference light is 0, φ is a distribution of the phase difference of the first object light. Therefore, deriving φ is the purpose in measuring the shape of the object surface. At this time, the trigonometric functions in the equations (12) and (13) can be developed as the following equations (14) and (15), respectively.

これらのことから、第１の干渉縞から位相差がπずれた第３の干渉縞の強度分布Ｈ_３は、以下の式（１６）により与えられる。同様に、第２の干渉縞から位相差がπずれた第４の干渉縞の強度分布Ｈ_４は、以下の式（１７）により与えられる。
From these facts, the intensity distribution H ₃ of the third interference fringe having a phase difference of π from the first interference fringe is given by the following equation (16). Similarly, the intensity distribution H ₄ of the fourth interference fringe having a phase difference of π from the second interference fringe is given by the following equation (17).

式（１６）および式（１７）により、第３の干渉縞の強度分布Ｈ_３および第４の干渉縞の強度分布Ｈ_４は、第１物体光の強度比の分布α、第１参照光の強度比の分布β、第１物体光の強度分布Ａ_Ｏ ^２、第１参照光の強度分布Ａ_ｒ ^２、第１の干渉縞の強度分布Ｈ_１および第２の干渉縞の強度分布Ｈ_２の関数として記述されうることがわかる。これら６つの変数は、すべて検出部（図１の例では第１検出部（ＣＣＤ１）および第２検出部（ＣＣＤ２））において直接取得されうる。したがって、実際に取得した第１の干渉縞の強度分布Ｈ_１および第２の干渉縞の強度分布Ｈ_２から、それぞれ位相がπずれた第３の干渉縞の強度分布Ｈ_３および第４の干渉縞の強度分布Ｈ_４を計算機上で仮想的に生成することができる。 The equation (16) and (17), the intensity distribution H ₄ of the third interference fringe intensity distribution H ₃ and fourth interference fringe is the first object light distribution intensity ratio alpha, the first reference beam Of the intensity ratio distribution β, the first object light intensity distribution A _O ² , the first reference light intensity distribution A _r ² , the first interference fringe intensity distribution H _1, and the second interference fringe intensity distribution H ₂ . It can be seen that it can be described as a function. All of these six variables can be directly acquired by the detection unit (the first detection unit (CCD1) and the second detection unit (CCD2) in the example of FIG. 1). Therefore, the intensity distribution H ₃ and the fourth interference of the third interference fringes whose phases are shifted by π from the intensity distribution H ₁ of the first interference fringes and the intensity distribution H ₂ of the second interference fringes actually acquired, respectively. it can be virtually generated an intensity distribution H ₄ stripes on a computer.

次いで、第１干渉縞の強度分布、第２干渉縞の強度分布、第３干渉縞の強度分布および第４干渉縞の強度分布を用いて、第１物体光に含まれる第１位相分布を算出する（上記（３）の工程）。このように互いに位相差が異なる４枚の干渉縞の強度分布を用いることで、物体光と参照光との強度比に依存することなく位相分布を算出することができる。 Next, the first phase distribution included in the first object light is calculated using the intensity distribution of the first interference fringe, the intensity distribution of the second interference fringe, the intensity distribution of the third interference fringe, and the intensity distribution of the fourth interference fringe. (Step (3) above). As described above, by using the intensity distribution of the four interference fringes having different phase differences, the phase distribution can be calculated without depending on the intensity ratio between the object light and the reference light.

図３は、第１干渉縞の強度分布、第２干渉縞の強度分布、第３干渉縞の強度分布および第４干渉縞の強度分布を用いて、第１物体光に含まれる第１位相分布を算出する方法を説明するための概念図である。Ｈ_１は実際に生成された第１干渉縞の強度分布であり、Ｈ_２は実際に生成された第２干渉縞の強度分布である。Ｈ_３は仮想的に生成された第３干渉縞の強度分布であり、Ｈ_４は仮想的に生成された第４干渉縞の強度分布である。αは第１干渉縞の生成に用いられた第１物体光の強度（図３ではＳ_１と表記）に対する第２干渉縞の生成に用いられた第１物体光の強度（図３ではＳ_２と表記）の比の分布であり、βは第１干渉縞の生成に用いられた第１参照光の強度（図３ではＲ_１と表記）に対する第２干渉縞の生成に用いられた第１参照光の強度（図３ではＲ_２と表記）の比の分布である。γは第１干渉縞と第２干渉縞との位相差である。この図に示されるように、第１物体光に含まれる第１位相分布は、第１干渉縞の強度分布Ｈ_１と、第２干渉縞の強度分布Ｈ_２と、第３干渉縞の強度分布Ｈ_３と、第４干渉縞の強度分布Ｈ_４と、第１物体光の強度比の分布αと、第１参照光の強度比の分布βと、第１干渉縞と第２干渉縞との位相差γとから算出されうる。以下、第１物体光に含まれる第１位相分布がこれらの値から算出されうることについて説明する。 FIG. 3 shows the first phase distribution included in the first object light by using the intensity distribution of the first interference fringe, the intensity distribution of the second interference fringe, the intensity distribution of the third interference fringe, and the intensity distribution of the fourth interference fringe. It is a conceptual diagram for demonstrating the method to calculate. H ₁ is the intensity distribution of the actually generated first interference fringe, and H ₂ is the intensity distribution of the actually generated second interference fringe. H ₃ is the intensity distribution of the virtually generated third interference fringe, and H ₄ is the intensity distribution of the virtually generated fourth interference fringe. α is the intensity of the first object light used to generate the second interference fringe (S _{2 in} FIG. 3) with respect to the intensity of the first object light used to generate the first interference fringe (denoted as S _{1 in} FIG. 3). ), And β is the first interference fringe used for generating the second interference fringes with respect to the intensity of the first reference light (denoted as R _{1 in} FIG. 3) used for generating the first interference fringes. It is a distribution of the ratio of the intensity of the reference light (indicated as R _{2 in} FIG. 3). γ is a phase difference between the first interference fringes and the second interference fringes. As shown in this figure, the first phase distribution included in the first object beam, the intensity distribution H ₁ of the first interference fringe, the intensity distribution of H ₂ second interference fringe intensity distribution of the third interference fringe H ₃ , intensity distribution H ₄ of the fourth interference fringe, intensity ratio distribution α of the first object light, intensity ratio distribution β of the first reference light, and the first interference fringe and the second interference fringe It can be calculated from the phase difference γ. Hereinafter, it will be described that the first phase distribution included in the first object light can be calculated from these values.

第１物体光に含まれる第１位相分布、すなわち第１物体光の複素振幅の分布は、上記（１）および（２）の工程で得られた第１干渉縞の強度分布Ｈ_１、第２干渉縞の強度分布Ｈ_２、第３干渉縞の強度分布Ｈ_３および第４干渉縞の強度分布Ｈ_４を用いて式（１８）のように導出される。
The first phase distribution included in the first object light, that is, the distribution of the complex amplitude of the first object light, is the first interference fringe intensity distribution H ₁ , second obtained in the steps (1) and (2). The interference fringe intensity distribution H ₂ , the third interference fringe intensity distribution H _3, and the fourth interference fringe intensity distribution H ₄ are derived as shown in Expression (18).

このことから、２つの第１物体光の強度分布Ａ_ｏ ^２（Ｓ_１），αＡ_ｏ ^２（Ｓ_２）、２つの第１参照光の強度分布Ａ_ｒ ^２（Ｒ_１），βＡ_ｒ ^２（Ｒ_２）および任意の位相差を持つ２つの干渉縞の強度分布Ｈ_１，Ｈ_２を取得することで、第１物体光に含まれる第１位相分布を正確に測定できることがわかる。 From this, the intensity distributions A _o ² (S ₁ ), αA _o ² (S ₂ ) of the two first object lights, the intensity distributions A _r ² (R ₁ ), βA _r ² ( It can be seen that the first phase distribution included in the first object beam can be accurately measured by acquiring R ₂ ) and the intensity distributions H ₁ and H ₂ of two interference fringes having an arbitrary phase difference.

（第２工程）
第２工程は、より詳細には、（４）第２波長の第２物体光と第２参照光とから生成される第５干渉縞および第６干渉縞の強度分布を検出する工程と、（５）第２物体光と第２参照光とから仮想的に生成される第７干渉縞および第８干渉縞の強度分布を算出する工程と、（６）第５干渉縞の強度分布、第６干渉縞の強度分布、第７干渉縞の強度分布および第８干渉縞の強度分布から、第２物体光に含まれる第２位相分布を算出する工程と、を含む。 (Second step)
More specifically, the second step (4) detecting the intensity distribution of the fifth interference fringe and the sixth interference fringe generated from the second object light of the second wavelength and the second reference light; 5) calculating the intensity distribution of the seventh interference pattern and the eighth interference pattern virtually generated from the second object light and the second reference light; (6) the intensity distribution of the fifth interference pattern; Calculating a second phase distribution included in the second object light from the intensity distribution of the interference fringes, the intensity distribution of the seventh interference fringes, and the intensity distribution of the eighth interference fringes.

第１工程では、第１波長の第１物体光および第１波長の第１参照光を使用するのに対し、第２工程では、第２波長の第２物体光および第２波長の第２参照光を使用する。すなわち、第１工程と第２工程とでは、使用する光の波長が異なる。第１波長の値および第２波長の値は、互いに異なっていれば特に限定されず、任意に設定されうる。たとえば、図１に示される光学系では、第２レーザー光源（Laser 2）から出射された波長５９３ｎｍのレーザー光を分岐して第２物体光（Object beam）および第２参照光（Reference beam）を生成している。第２物体光および第２参照光は、それぞれ第１物体光および第１参照光と同じ光路を進み、第１検出部（ＣＣＤ１）の検出面上に第５干渉縞を生成し、第２検出部（ＣＣＤ２）の検出面上に第６干渉縞を生成する。第１干渉縞および第２干渉縞と同様に、第５干渉縞と第６干渉縞との位相差は、おおよそπ／２である。 In the first step, the first object light having the first wavelength and the first reference light having the first wavelength are used, whereas in the second step, the second object light having the second wavelength and the second reference having the second wavelength are used. Use light. That is, the wavelength of light to be used is different between the first step and the second step. The value of the first wavelength and the value of the second wavelength are not particularly limited as long as they are different from each other, and can be set arbitrarily. For example, in the optical system shown in FIG. 1, a laser beam having a wavelength of 593 nm emitted from a second laser light source (Laser 2) is branched to generate a second object beam (Object beam) and a second reference beam (Reference beam). Is generated. The second object light and the second reference light travel on the same optical path as the first object light and the first reference light, respectively, generate a fifth interference fringe on the detection surface of the first detection unit (CCD1), and perform the second detection. A sixth interference fringe is generated on the detection surface of the unit (CCD2). Similar to the first interference fringes and the second interference fringes, the phase difference between the fifth interference fringes and the sixth interference fringes is approximately π / 2.

第２工程における上記（４）〜（６）の工程は、波長が異なる点を除いては、それぞれ第１工程における（１）〜（３）の工程と同じである。したがって、上記（４）〜（６）の工程については、詳細な説明を省略し、簡単に説明する。 The steps (4) to (6) in the second step are the same as the steps (1) to (3) in the first step, respectively, except that the wavelengths are different. Therefore, detailed description of the steps (4) to (6) will be omitted, and a simple description will be given.

まず、第２波長の第２物体光と第２参照光とから、互いに位相差が異なる第５干渉縞および第６干渉縞を生成し、第５干渉縞の強度分布および第６干渉縞の強度分布を検出する（上記（４）の工程）。第２物体光は、測定対象の物体に対して第２波長の光を反射または透過して得られる光であり、物体の表面形状に由来する第２位相分布を含む。第２参照光は、第２物体光と干渉可能な第２波長の光である。第１工程での説明と同様の理由により、第５干渉縞と第６干渉縞との位相差は、厳密にはπ／２とはならないことがある。 First, a fifth interference fringe and a sixth interference fringe having different phase differences are generated from the second object light having the second wavelength and the second reference light, and the intensity distribution of the fifth interference fringe and the intensity of the sixth interference fringe are generated. Distribution is detected (step (4) above). The second object light is light obtained by reflecting or transmitting light of the second wavelength with respect to the object to be measured, and includes a second phase distribution derived from the surface shape of the object. The second reference light is light having a second wavelength that can interfere with the second object light. For the same reason as described in the first step, the phase difference between the fifth interference fringe and the sixth interference fringe may not be strictly π / 2.

次いで、第５干渉縞の強度分布および第６干渉縞の強度分布の測定結果を用いて、第２物体光と第２参照光とから第７干渉縞および第８干渉縞を仮想的に生成し、第７干渉縞の強度分布および第８干渉縞の強度分布を算出する（上記（５）の工程、図２参照）。第７干渉縞は、第２物体光と第２参照光とから生成されうる干渉縞であって、第５干渉縞および第６干渉縞のいずれとも位相差が異なる干渉縞である。また、第８干渉縞は、第２物体光と第２参照光とから生成されうる干渉縞であって、第５干渉縞、第６干渉縞および第７干渉光のいずれとも位相差が異なる干渉縞である。 Next, using the measurement result of the intensity distribution of the fifth interference fringe and the intensity distribution of the sixth interference fringe, the seventh interference fringe and the eighth interference fringe are virtually generated from the second object light and the second reference light. Then, the intensity distribution of the seventh interference fringe and the intensity distribution of the eighth interference fringe are calculated (step (5) above, see FIG. 2). The seventh interference fringes are interference fringes that can be generated from the second object light and the second reference light, and are different in phase difference from both the fifth interference fringe and the sixth interference fringe. In addition, the eighth interference fringe is an interference fringe that can be generated from the second object light and the second reference light, and is an interference having a phase difference different from any of the fifth interference fringe, the sixth interference fringe, and the seventh interference light. It is a stripe.

第１干渉縞の強度分布Ｈ_１および第２干渉縞の強度分布Ｈ_２と同様に、第５干渉縞の強度分布Ｈ_５および第６干渉縞の強度分布Ｈ_６は、それぞれ以下の式（１９）および式（２０）のように記述されうる。ここで、Ａ_Ｏ’^２は第５干渉縞の生成に用いられた第２物体光の強度分布であり、Ａ_ｒ’^２は第５干渉縞の生成に用いられた第２参照光の強度分布である。α’は第５干渉縞の生成に用いられた第２物体光の強度に対する第６干渉縞の生成に用いられた第２物体光の強度の比の分布であり、β’は第５干渉縞の生成に用いられた第２参照光の強度に対する第６干渉縞の生成に用いられた第２参照光の強度の比の分布である。また、φ’は第２物体光と第２参照光との位相差の分布であり、γ’は第５干渉縞と第６干渉縞との位相差である。
Similar to the intensity distribution H ₁ and the intensity distribution of H ₂ second interference pattern of the first interference fringe intensity distribution H ₆ of the intensity distribution H ₅ and sixth interference fringes fifth interference fringes, each of the following formula (19 ) And equation (20). Here, A _O ′ ² is the intensity distribution of the second object light used for generating the fifth interference fringe, and A _r ′ ² is the intensity distribution of the second reference light used for generating the fifth interference fringe. It is. α ′ is a distribution of the ratio of the intensity of the second object light used to generate the sixth interference fringe to the intensity of the second object light used to generate the fifth interference fringe, and β ′ is the fifth interference fringe. Is a distribution of the ratio of the intensity of the second reference light used to generate the sixth interference fringes to the intensity of the second reference light used to generate the second reference light. Φ ′ is a phase difference distribution between the second object light and the second reference light, and γ ′ is a phase difference between the fifth interference fringe and the sixth interference fringe.

そして、第５の干渉縞から位相差がπずれた第７の干渉縞の強度分布Ｈ_７は、以下の式（２１）により与えられる。同様に、第６の干渉縞から位相差がπずれた第８の干渉縞の強度分布Ｈ_８は、以下の式（２２）により与えられる。
Then, the intensity distribution H ₇ of the seventh interference fringe whose phase difference is shifted by π from the fifth interference fringe is given by the following equation (21). Similarly, the eighth intensity distribution H ₈ of the interference fringes of the phase difference from the interference fringes of the first 6 is shifted π is given by the following equation (22).

次いで、第５干渉縞の強度分布、第６干渉縞の強度分布、第７干渉縞の強度分布および第８干渉縞の強度分布を用いて、第２物体光に含まれる第２位相分布を算出する（上記（６）の工程、図３参照）。 Next, the second phase distribution included in the second object light is calculated using the intensity distribution of the fifth interference fringe, the intensity distribution of the sixth interference fringe, the intensity distribution of the seventh interference fringe, and the intensity distribution of the eighth interference fringe. (See step (6) above, see FIG. 3).

第２物体光に含まれる第２位相分布、すなわち第２物体光の複素振幅の分布は、上記（４）および（５）の工程で得られた第５干渉縞の強度分布Ｈ_５、第６干渉縞の強度分布Ｈ_６、第７干渉縞の強度分布Ｈ_７および第８干渉縞の強度分布Ｈ_８を用いて式（２３）のように導出される。
The second phase distribution included in the second object light, that is, the distribution of the complex amplitude of the second object light, is the fifth interference fringe intensity distribution H ₅ , sixth obtained in the steps (4) and (5). The interference fringe intensity distribution H ₆ , the seventh interference fringe intensity distribution H _7, and the eighth interference fringe intensity distribution H ₈ are derived as shown in Expression (23).

このことから、２つの第２物体光の強度分布Ａ_ｏ’^２，α’Ａ_ｏ’^２、２つの第２参照光の強度分布Ａ_ｒ’^２，β’Ａ_ｒ’^２および任意の位相差を持つ２つの干渉縞の強度分布Ｈ_５，Ｈ_６を取得することで、第２物体光に含まれる第２位相分布を正確に測定できることがわかる。 From this, the intensity distributions A _o ' ² and α'A _o ' ² of the two second object beams, the intensity distributions A _r ' ² and β'A _r ' ² of the two second reference beams, and an arbitrary phase difference It can be seen that the second phase distribution contained in the second object light can be accurately measured by acquiring the intensity distributions H ₅ and H ₆ of the two interference fringes having the following.

（第３工程）
第３工程では、第１工程で算出された第１位相分布と、第２工程で算出された第２位相分布とから、物体の表面形状を表す深さ分布を算出する。前述のとおり、第３工程で算出される深さ分布は、第１波長および第２波長を超える高低差を含むことができる。 (Third step)
In the third step, a depth distribution representing the surface shape of the object is calculated from the first phase distribution calculated in the first step and the second phase distribution calculated in the second step. As described above, the depth distribution calculated in the third step can include a height difference exceeding the first wavelength and the second wavelength.

図４は、第１位相分布および第２位相分布に含まれる位相の測定値をそのまま深さに変換した値と、物体表面の実際の深さとの関係を示すグラフである。横軸は物体表面の位置（ｘ座標またはｙ座標の変化）を示し、縦軸は物体表面の深さ（ｚ座標）を示している。細い実線は、第１波長（例えば５３２ｎｍ）の光を用いて得られた位相の測定値（第１位相分布）をそのまま深さに変換した値を示し、細い破線は、第２波長（例えば５９３ｎｍ）の光を用いて得られた位相の測定値（第２位相分布）をそのまま深さに変換した値を示している。太い実線は、物体表面の実際の深さを示している。 FIG. 4 is a graph showing a relationship between a value obtained by directly converting a measured value of a phase included in the first phase distribution and the second phase distribution into a depth and an actual depth of the object surface. The horizontal axis indicates the position of the object surface (change in x coordinate or y coordinate), and the vertical axis indicates the depth (z coordinate) of the object surface. A thin solid line indicates a value obtained by directly converting a measured value (first phase distribution) of a phase obtained using light of a first wavelength (for example, 532 nm) into a depth, and a thin broken line indicates a second wavelength (for example, 593 nm). ) Shows a value obtained by converting the measured phase value (second phase distribution) obtained by using the light to the depth as it is. The thick solid line indicates the actual depth of the object surface.

このグラフにおいて細い実線および細い破線で示されるように、波長λ_１および波長λ_２よりも長い高低差を有する物体表面を波長λ_１の光および波長λ_２の光を使用して測定した場合には、位相の折り返し点が発生するため、最大でも波長の長さまでしか測定することができない。しかしながら、ある点での位相の測定値について位相の折り返し点の数がわかれば、その折り返し点の数に波長を掛けた値を位相の測定値に足し合わせることで、位相の測定値を物体の深さに変換することができる。 In this graph, as shown by a thin solid line and a thin broken line, when an object surface having a height difference longer than the wavelength λ ₁ and the wavelength λ ₂ is measured using the light of the wavelength λ _{1 and} the light of the wavelength λ ₂ Since a phase turning point occurs, measurement is possible only up to the length of the wavelength at the maximum. However, if the number of phase folding points is known for the phase measurement value at a certain point, the phase measurement value is calculated by adding the value obtained by multiplying the number of folding points by the wavelength to the phase measurement value. Can be converted to depth.

具体的には、まず、波長λ_１の光および波長λ_２の光を使用して測定した位相の測定値を深さに変換するために、以下の式（２４）および式（２５）のように深さを定義する（図４参照）。
Specifically, first, in order to convert the measured value of the phase measured using the light with the wavelength λ _{1 and} the light with the wavelength λ ₂ into the depth, the following equations (24) and (25) The depth is defined as (see FIG. 4).

Ｌ_１およびＬ_２は物体の表面の任意の点における深さである。φ_１は波長λ_１の光で測定された前記任意の点の位相の測定値であり、φ_２は波長λ_２で測定された前記任意の点の位相の測定値である。ｍはφ_１についての位相の折り返し回数であり、ｎはφ_２についての位相の折り返し回数である。ｍおよびｎはいずれも正の整数である（図４ではｍ＝２、ｎ＝２）。φ_１およびφ_２は測定値であるため、ｍおよびｎの値を決定できれば、位相の測定値を物体の深さに変換することができる。しかしながら、式（２４）または式（２５）単独ではｍおよびｎの値を決定できない。ここで、同じ物体を波長λ_１の光および波長λ_２の光で測定した場合に、位相測定が理想的に行われたと仮定したとき、Ｌ_１＝Ｌ_２となるｍおよびｎの組み合わせが必ず存在するはずである。そして、そのときのＬ_１およびＬ_２は物体の深さに対応する。たとえば、λ_１を５３２ｎｍとし、λ_２を５９３ｎｍとして厚さ１μｍの物体を測定した場合、φ_１は約１.７６πであり、φ_２は約１.３７πである。このとき、Ｌ_１＝Ｌ_２となるためのｍおよびｎは、両方とも１である。 L ₁ and L ₂ are depths at arbitrary points on the surface of the object. φ ₁ is a measured value of the phase of the arbitrary point measured with light of wavelength λ ₁ , and φ ₂ is a measured value of the phase of the arbitrary point measured with wavelength λ ₂ . m is the number of phase folds for φ ₁ , and n is the number of phase folds for φ ₂ . m and n are both positive integers (in FIG. 4, m = 2, n = 2). Since φ ₁ and φ ₂ are measured values, if the values of m and n can be determined, the measured values of the phase can be converted into the depth of the object. However, the values of m and n cannot be determined by the formula (24) or the formula (25) alone. Here, when the same object is measured with light of wavelength λ ₁ and light of wavelength λ ₂ , when it is assumed that phase measurement is ideally performed, a combination of m and n such that L ₁ = L ₂ is always obtained. Should exist. Then, L ₁ and L _{2 at} that time correspond to the depth of the object. For example, when an object having a thickness of 1 μm is measured with λ ₁ of 532 nm and λ ₂ of 593 nm, φ ₁ is about 1.76π and φ ₂ is about 1.37π. At this time, m and n for L ₁ = L ₂ are both 1.

したがって、物体の表面形状を表す深さ分布は、上記の式（２４）および式（２５）を用いてＬ_１＝Ｌ_２となるときのｍおよびｎの値を算出し、算出されたｍおよびｎの値を代入した式（２４）および式（２５）を用いることで算出されうることがわかる。 Accordingly, the depth distribution representing the surface shape of the object is calculated by calculating the values of m and n when L ₁ = L ₂ using the above formulas (24) and (25), It can be seen that the calculation can be performed by using the equations (24) and (25) in which the value of n is substituted.

図５は、ｍおよびｎを決定する手順の一例を示すフローチャートである。まず、上記の式（２４）および式（２５）で定義されたＬ_１およびＬ_２のｍおよびｎにそれぞれ０を代入し（工程Ｓ１０）、Ｌ_１−Ｌ_２の絶対値が十分に小さいか否かを評価する（工程Ｓ２０）。このとき、Ｌ_１−Ｌ_２の絶対値が十分に小さければ（｜Ｌ_１−Ｌ_２｜≒０）、ｍおよびｎが０であると決定する（工程Ｓ３０）。一方、Ｌ_１−Ｌ_２の絶対値が大きければ、Ｌ_１＞Ｌ_２であるか否かを評価する（工程Ｓ４０）。そして、Ｌ_１＞Ｌ_２であればｎの値を１大きくし（工程Ｓ５０）、Ｌ_１＜Ｌ_２であればｍの値を１大きくして（工程Ｓ６０）、改めてＬ_１−Ｌ_２の絶対値が十分に小さいか否かを評価する（工程Ｓ２０）。これらの工程を繰り返して、Ｌ_１−Ｌ_２の絶対値が十分に小さい（｜Ｌ_１−Ｌ_２｜≒０）ときにｍおよびｎに代入されている数値を、ｍおよびｎとして決定する（工程Ｓ３０）。なお、工程Ｓ２０においてＬ_１−Ｌ_２の絶対値が十分に小さいか否かの評価基準は、任意に設定されうる。たとえば、第１波長が５３２ｎｍおよび第２波長が５９３ｎｍである場合に、｜Ｌ_１−Ｌ_２｜が小さい方の波長の３％（約１６ｎｍ＝５３２ｎｍ×０.０３）以下であれば、Ｌ_１−Ｌ_２の絶対値が十分に小さいと評価するようにしてもよい。 FIG. 5 is a flowchart showing an example of a procedure for determining m and n. First, 0 is substituted for m and n of L ₁ and L ₂ defined in the above formulas (24) and (25) (step S10), and the absolute value of L ₁ -L ₂ is sufficiently small. Whether or not is evaluated (step S20). At this time, if the absolute value of L ₁ -L ₂ is sufficiently small (| L ₁ -L ₂ | ≈0), it is determined that m and n are 0 (step S30). On the other hand, if the absolute value of L ₁ -L ₂ is large, it is evaluated whether or not L ₁ > L ₂ (step S40). _Then, L 1> if _{L 2} and the value of n 1 greater (step _S50), L 1 <to 1 increasing the value of m if _{L 2} (step S60), the newly _L 1 -L ₂ It is evaluated whether or not the absolute value is sufficiently small (step S20). By repeating these steps, the numerical values assigned to m and n when the absolute value of L ₁ -L ₂ is sufficiently small (| L ₁ -L ₂ | ≈0) are determined as m and n ( Step S30). In addition, the evaluation criteria as to whether or not the absolute value of L ₁ -L ₂ is sufficiently small in step S20 can be arbitrarily set. For example, when the first wavelength is 532 nm and the second wavelength is 593 nm, if L ₁ −L ₂ | is 3% or less of the smaller wavelength (about 16 nm = 532 nm × 0.03), L ₁ the absolute value of -L ₂ may be evaluated as sufficiently small.

以上の手順により、２種類の波長の光を用いて位相測定を行うことで、位相接続することなく波長を超える物体の表面形状の測定をすることができる。 By performing phase measurement using light of two types of wavelengths by the above procedure, the surface shape of an object exceeding the wavelength can be measured without phase connection.

本発明に係る物体形状測定方法を行うための装置および光学系の構成は、特に限定されない。たとえば、次に説明する本発明に係る物体形状測定装置を用いることで、本発明に係る物体形状測定方法を行うことができる。 The configuration of the apparatus and the optical system for performing the object shape measuring method according to the present invention is not particularly limited. For example, the object shape measuring method according to the present invention can be performed by using the object shape measuring apparatus according to the present invention described below.

［物体形状測定装置］
本発明に係る物体形状測定装置は、本発明に係る物体形状測定方法を行うための装置である。本発明に係る物体形状測定装置は、少なくとも、光源部、光分離部、干渉波生成部、検出部および処理部を有する。 [Object shape measuring device]
The object shape measuring apparatus according to the present invention is an apparatus for performing the object shape measuring method according to the present invention. The object shape measurement apparatus according to the present invention includes at least a light source unit, a light separation unit, an interference wave generation unit, a detection unit, and a processing unit.

光源部は、第１波長のレーザー光と、前記第１波長とは異なる第２波長のレーザー光とを同一光軸上に出射する。光源部は、互いに波長が異なる２つのレーザー光源を有していてもよいし、２波長のレーザー光を出力可能なレーザー光源を１つ有していてもよい。光源部が２つのレーザー光源を有している場合、ビームスプリッターなどを用いて一方のレーザー光源の光軸と他方のレーザー光源の光軸が重ね合わされる。 The light source unit emits laser light having a first wavelength and laser light having a second wavelength different from the first wavelength on the same optical axis. The light source unit may include two laser light sources having different wavelengths from each other, or may include one laser light source capable of outputting laser light having two wavelengths. When the light source section has two laser light sources, the optical axis of one laser light source and the optical axis of the other laser light source are overlapped using a beam splitter or the like.

光分離部は、前記光源部から出射されたレーザー光を、物体光および参照光に分離する。第１波長のレーザー光からは第１物体光および第１参照光が生成され、第２波長のレーザー光からは第２物体光および第２参照光が生成される。たとえば、光分離部は、偏光ビームスプリッターである。分離された物体光（第１物体光または第２物体光）は、測定対象の物体に向かって進行し、この物体に対して透過または反射させられる。これにより、物体光（第１物体光または第２物体光）は、物体の表面形状に由来する位相分布（第１位相分布または第２位相分布）を含む光となる。 The light separation unit separates the laser light emitted from the light source unit into object light and reference light. The first object light and the first reference light are generated from the first wavelength laser light, and the second object light and the second reference light are generated from the second wavelength laser light. For example, the light separation unit is a polarization beam splitter. The separated object light (first object light or second object light) travels toward the object to be measured, and is transmitted or reflected on the object. Thereby, the object light (first object light or second object light) becomes light including a phase distribution (first phase distribution or second phase distribution) derived from the surface shape of the object.

干渉波生成部は、物体に対して透過または反射させた、物体の表面形状に由来する位相分布を含む物体光（第１物体光または第２物体光）と、参照光（第１参照光または第２参照光）とを合波して干渉波を生成する。たとえば、干渉波生成部は、ビームスプリッターである。 The interference wave generation unit transmits or reflects the object light including the phase distribution derived from the surface shape of the object (first object light or second object light) and reference light (first reference light or And the second reference light) to generate an interference wave. For example, the interference wave generation unit is a beam splitter.

検出部は、干渉波生成部により生成された干渉波から互いに位相差が異なる２つの干渉縞（第１干渉縞および第２干渉縞、または第５干渉縞および第６干渉縞）を生成し、これら２つの干渉縞（第１干渉縞および第２干渉縞、または第５干渉縞および第６干渉縞）の強度分布を検出する。 The detection unit generates two interference fringes (first interference fringe and second interference fringe, or fifth interference fringe and sixth interference fringe) having different phase differences from the interference wave generated by the interference wave generation unit, The intensity distribution of these two interference fringes (first interference fringe and second interference fringe, or fifth interference fringe and sixth interference fringe) is detected.

処理部は、光源部が第１波長のレーザー光を出射したときに検出部が検出した２つの干渉縞（第１干渉縞および第２干渉縞）の強度分布と、光源部が第２波長のレーザー光を出射したときに検出部が検出した２つの干渉縞（第５干渉縞および第６干渉縞）の強度分布とから、第１波長および第２波長を超える高低差を含みうる、物体の表面形状を表す深さ分布を算出する。より具体的には、処理部は、第１の干渉縞の強度分布および第２の干渉縞の強度分布から仮想的に生成される第３干渉縞の強度分布および第４干渉縞の強度分布を算出し、第１干渉縞の強度分布、第２干渉縞の強度分布、第３干渉縞の強度分布および第４干渉縞の強度分布から、第１物体光に含まれる第１位相分布を算出する（本発明に係る物体形状測定方法の第１工程）。また、処理部は、第５の干渉縞の強度分布および第６の干渉縞の強度分布から仮想的に生成される第７干渉縞の強度分布および前記第８干渉縞の強度分布を算出し、第５干渉縞の強度分布、第６干渉縞の強度分布、第７干渉縞の強度分布および第８干渉縞の強度分布から、第２物体光に含まれる第２位相分布を算出する（本発明に係る物体形状測定方法の第２工程）。そして、処理部は、第１位相分布および第２位相分布から、物体の表面形状を表す深さ分布を算出する（本発明に係る物体形状測定方法の第３工程）。 The processing unit includes an intensity distribution of two interference fringes (first interference fringe and second interference fringe) detected by the detection unit when the light source unit emits laser light having the first wavelength, and the light source unit has the second wavelength. From the intensity distribution of the two interference fringes (the fifth interference fringe and the sixth interference fringe) detected by the detection unit when the laser beam is emitted, the object may include a height difference exceeding the first wavelength and the second wavelength. A depth distribution representing the surface shape is calculated. More specifically, the processing unit calculates the intensity distribution of the third interference fringe and the intensity distribution of the fourth interference fringe virtually generated from the intensity distribution of the first interference fringe and the intensity distribution of the second interference fringe. The first phase distribution included in the first object light is calculated from the intensity distribution of the first interference fringe, the intensity distribution of the second interference fringe, the intensity distribution of the third interference fringe, and the intensity distribution of the fourth interference fringe. (First step of the object shape measuring method according to the present invention). The processing unit calculates the intensity distribution of the seventh interference fringe and the intensity distribution of the eighth interference fringe virtually generated from the intensity distribution of the fifth interference fringe and the intensity distribution of the sixth interference fringe, The second phase distribution included in the second object light is calculated from the intensity distribution of the fifth interference fringe, the intensity distribution of the sixth interference fringe, the intensity distribution of the seventh interference fringe, and the intensity distribution of the eighth interference fringe (the present invention). The second step of the object shape measuring method according to FIG. Then, the processing unit calculates a depth distribution representing the surface shape of the object from the first phase distribution and the second phase distribution (third step of the object shape measuring method according to the present invention).

図１は、本発明の一実施の形態に係る物体形状測定装置の構成を示す模式図である。図１に示される物体形状測定装置では、第１レーザー光源（Laser 1）、第２レーザー光源（Laser 2）、２つのアイソレーター（Isolator）、２つのＮＤフィルター（ND filter）、４つのレンズ（Lens 1-4）、２つのミラー（Mirror）および第１ビームスプリッター（ＢＳ１）が光源部を構成する。また、第１半波長板（ＨＷＰ１）および第１偏光ビームスプリッター（ＰＢＳ１）が、物体光（Object beam）および参照光（Reference beam）を生成する光分離部を構成する。また、物体光の光路上に配置されている第１半波長板（ＨＷＰ１）、参照光の光路上に配置されている１／４波長板（ＱＷＰ）および第２ビームスプリッター（ＢＳ２）が、干渉波生成部を構成する。また、第２偏光ビームスプリッター（ＰＢＳ２）、第１検出部（ＣＣＤ１）および第２検出部（ＣＣＤ２）が、検出部を構成する。また、コンピューター（ＰＣ）が、処理部を構成する。 FIG. 1 is a schematic diagram showing a configuration of an object shape measuring apparatus according to an embodiment of the present invention. In the object shape measuring apparatus shown in FIG. 1, a first laser light source (Laser 1), a second laser light source (Laser 2), two isolators (Isolator), two ND filters (ND filter), four lenses (Lens) 1-4) The two mirrors (Mirror) and the first beam splitter (BS1) constitute a light source unit. In addition, the first half-wave plate (HWP1) and the first polarization beam splitter (PBS1) constitute a light separation unit that generates object beam and reference beam. Further, the first half-wave plate (HWP1) disposed on the optical path of the object light, the quarter-wave plate (QWP) disposed on the optical path of the reference light, and the second beam splitter (BS2) interfere with each other. A wave generation unit is configured. The second polarizing beam splitter (PBS2), the first detection unit (CCD1), and the second detection unit (CCD2) constitute a detection unit. A computer (PC) constitutes a processing unit.

図１に示される物体形状測定装置では、第１レーザー光源（Laser 1）から出射された第１波長（例えば５３２ｎｍ）のレーザー光は、第１半波長板（ＨＷＰ１）および第１偏光ビームスプリッター（ＰＢＳ１）によって、直線偏光の第１物体光（Object beam）および直線偏光の第１参照光（Reference beam）に分離される。第１物体光は、測定対象の物体（Object）の表面で反射した後、第２半波長板（ＨＷＰ２）によりその偏向角が４５°回転させられる。また、第１参照光は、１／４波長板（ＱＷＰ）によってその偏光状態を円偏光に変換される。このようにして得られた４５°直線偏光の第１物体光と円偏光の第１参照光とは、第３ビームスプリッター（ＢＳ３）において合波され、第２偏光ビームスプリッター（ＰＢＳ２）に向かう。第１物体光の水平偏光成分および第１参照光の水平偏光成分は、第２偏光ビームスプリッター（ＰＢＳ２）を透過（直進）し、第１検出部（ＣＣＤ１）の検出面上に第１干渉縞を生成する。第１検出部（ＣＣＤ１）は、この第１干渉縞の強度分布を検出する。一方、第１物体光の垂直偏光成分および第１参照光の垂直偏光成分は、第２偏光ビームスプリッター（ＰＢＳ２）で反射し、第２検出部（ＣＣＤ２）の検出面上に第２干渉縞を生成する。このとき、円偏光の第１参照光では、水平偏光成分と垂直偏光成分との位相差がπ／２であるため、第１干渉縞を生成する干渉波と、第２干渉縞を生成する干渉波との間には、π／２の位相差が発生する。第２検出部（ＣＣＤ２）は、この第１干渉縞の強度分布を検出する。 In the object shape measuring apparatus shown in FIG. 1, laser light having a first wavelength (for example, 532 nm) emitted from a first laser light source (Laser 1) is emitted from a first half-wave plate (HWP1) and a first polarization beam splitter ( The PBS 1) separates the first object beam (linearly polarized object beam) and the first reference beam (linearly polarized light). The first object light is reflected by the surface of the object to be measured (Object), and then the deflection angle thereof is rotated by 45 ° by the second half-wave plate (HWP2). Further, the polarization state of the first reference light is converted into circularly polarized light by a quarter wave plate (QWP). The 45 ° linearly polarized first object light and the circularly polarized first reference light obtained in this way are combined in the third beam splitter (BS3) and travel toward the second polarizing beam splitter (PBS2). The horizontal polarization component of the first object light and the horizontal polarization component of the first reference light are transmitted (straight forward) through the second polarization beam splitter (PBS2), and the first interference fringes are formed on the detection surface of the first detection unit (CCD1). Is generated. The first detector (CCD 1) detects the intensity distribution of the first interference fringes. On the other hand, the vertical polarization component of the first object light and the vertical polarization component of the first reference light are reflected by the second polarization beam splitter (PBS2), and the second interference fringes are formed on the detection surface of the second detection unit (CCD2). Generate. At this time, since the phase difference between the horizontal polarization component and the vertical polarization component is π / 2 in the circularly polarized first reference light, the interference wave that generates the first interference fringe and the interference that generates the second interference fringe. A phase difference of π / 2 occurs between the waves. The second detector (CCD2) detects the intensity distribution of the first interference fringes.

同様に、第２レーザー光源（Laser 1）から出射された第２波長（例えば５９３ｎｍ）のレーザー光は、第１半波長板（ＨＷＰ１）および第１偏光ビームスプリッター（ＰＢＳ１）によって、直線偏光の第２物体光（Object beam）および直線偏光の第２参照光（Reference beam）に分離される。第２物体光は、測定対象の物体（Object）の表面で反射した後、第２半波長板（ＨＷＰ２）によりその偏向角が４５°回転させられる。また、第２参照光は、１／４波長板（ＱＷＰ）によってその偏光状態を円偏光に変換される。このようにして得られた４５°直線偏光の第２物体光と円偏光の第２参照光とは、第３ビームスプリッター（ＢＳ３）において合波され、第２偏光ビームスプリッター（ＰＢＳ２）に向かう。第２物体光の水平偏光成分および第２参照光の水平偏光成分は、第２偏光ビームスプリッター（ＰＢＳ２）を透過（直進）し、第１検出部（ＣＣＤ１）の検出面上に第５干渉縞を生成する。第１検出部（ＣＣＤ１）は、この第５干渉縞の強度分布を検出する。一方、第２物体光の垂直偏光成分および第２参照光の垂直偏光成分は、第２偏光ビームスプリッター（ＰＢＳ２）で反射し、第２検出部（ＣＣＤ２）の検出面上に第６干渉縞を生成する。このとき、円偏光の第２参照光では、水平偏光成分と垂直偏光成分との位相差がπ／２であるため、第５干渉縞を生成する干渉波と、第６干渉縞を生成する干渉波との間には、π／２の位相差が発生する。第２検出部（ＣＣＤ２）は、この第６干渉縞の強度分布を検出する。 Similarly, the second wavelength (for example, 593 nm) laser light emitted from the second laser light source (Laser 1) is linearly polarized by the first half-wave plate (HWP1) and the first polarization beam splitter (PBS1). It is separated into two object beams (Object beam) and linearly polarized second reference beam (Reference beam). After the second object light is reflected by the surface of the object to be measured (Object), the deflection angle thereof is rotated by 45 ° by the second half-wave plate (HWP2). Further, the polarization state of the second reference light is converted into circularly polarized light by a quarter wavelength plate (QWP). The 45 ° linearly polarized second object light and the circularly polarized second reference light obtained in this way are combined in the third beam splitter (BS3) and travel toward the second polarizing beam splitter (PBS2). The horizontal polarization component of the second object light and the horizontal polarization component of the second reference light are transmitted (straight forward) through the second polarization beam splitter (PBS2), and the fifth interference fringes are formed on the detection surface of the first detection unit (CCD1). Is generated. The first detection unit (CCD1) detects the intensity distribution of the fifth interference fringes. On the other hand, the vertical polarization component of the second object light and the vertical polarization component of the second reference light are reflected by the second polarization beam splitter (PBS2), and the sixth interference fringes are formed on the detection surface of the second detection unit (CCD2). Generate. At this time, in the circularly polarized second reference light, since the phase difference between the horizontal polarization component and the vertical polarization component is π / 2, the interference wave that generates the fifth interference fringe and the interference that generates the sixth interference fringe. A phase difference of π / 2 occurs between the waves. The second detector (CCD2) detects the intensity distribution of the sixth interference fringes.

その後、コンピューター（ＰＣ）は、第１検出部（ＣＣＤ１）および第２検出部（ＣＣＤ２）が検出した第１の干渉縞の強度分布および第２の干渉縞の強度分布から、第３干渉縞および第４干渉縞を仮想的に生成し、第３干渉縞の強度分布および第４干渉縞の強度分布を算出する。そして、コンピューター（ＰＣ）は、第１干渉縞の強度分布、第２干渉縞の強度分布、第３干渉縞の強度分布および第４干渉縞の強度分布から、第１物体光に含まれる第１位相分布を算出する（本発明に係る物体形状測定方法の第１工程）。 Thereafter, the computer (PC) calculates the third interference fringes and the intensity distributions of the first interference fringes and the second interference fringes detected by the first detection unit (CCD1) and the second detection unit (CCD2). A fourth interference fringe is virtually generated, and the intensity distribution of the third interference fringe and the intensity distribution of the fourth interference fringe are calculated. The computer (PC) then includes the first interference light from the intensity distribution of the first interference fringe, the intensity distribution of the second interference fringe, the intensity distribution of the third interference fringe, and the intensity distribution of the fourth interference fringe. The phase distribution is calculated (first step of the object shape measuring method according to the present invention).

同様に、コンピューター（ＰＣ）は、第１検出部（ＣＣＤ１）および第２検出部（ＣＣＤ２）が検出した第５の干渉縞の強度分布および第６の干渉縞の強度分布から、第７干渉縞および第８干渉縞を仮想的に生成し、第７干渉縞の強度分布および第８干渉縞の強度分布を算出する。そして、コンピューター（ＰＣ）は、第５干渉縞の強度分布、第６干渉縞の強度分布、第７干渉縞の強度分布および第８干渉縞の強度分布から、第２物体光に含まれる第２位相分布を算出する（本発明に係る物体形状測定方法の第２工程）。 Similarly, the computer (PC) calculates the seventh interference fringe from the intensity distribution of the fifth interference fringe and the intensity distribution of the sixth interference fringe detected by the first detection unit (CCD1) and the second detection unit (CCD2). Then, the eighth interference fringe is virtually generated, and the intensity distribution of the seventh interference fringe and the intensity distribution of the eighth interference fringe are calculated. Then, the computer (PC) calculates the second object light included in the second object light from the intensity distribution of the fifth interference fringe, the intensity distribution of the sixth interference fringe, the intensity distribution of the seventh interference fringe, and the intensity distribution of the eighth interference fringe. The phase distribution is calculated (second step of the object shape measuring method according to the present invention).

そして、コンピューター（ＰＣ）は、算出した第１位相分布および第２位相分布から、物体の表面形状を表す深さ分布を算出する（本発明に係る物体形状測定方法の第３工程）。 Then, the computer (PC) calculates a depth distribution representing the surface shape of the object from the calculated first phase distribution and second phase distribution (third step of the object shape measuring method according to the present invention).

なお、本発明に係る物体形状測定装置は、図１に示される構成に限定されるものではない。たとえば、図６に示されるように、第１干渉縞および第２干渉縞を生成する光学系と、第５干渉縞および第６干渉縞を生成する光学系とが別であってもよい。図６に示される例では、第２波長の光を遮断する第１波長フィルタ（Filter 1）と、第１波長の光を遮断する第２波長フィルタ（Filter 2）とが所定の位置に配置されているため、第１干渉縞の強度分布は、第１検出部（ＣＣＤ１）で検出され、第２干渉縞の強度分布は、第２検出部（ＣＣＤ２）で検出され、第５干渉縞の強度分布は、第３検出部（ＣＣＤ３）で検出され、第６干渉縞の強度分布は、第４検出部（ＣＣＤ４）で検出される。 The object shape measuring apparatus according to the present invention is not limited to the configuration shown in FIG. For example, as shown in FIG. 6, the optical system that generates the first interference fringe and the second interference fringe may be different from the optical system that generates the fifth interference fringe and the sixth interference fringe. In the example shown in FIG. 6, a first wavelength filter (Filter 1) that blocks light of the second wavelength and a second wavelength filter (Filter 2) that blocks light of the first wavelength are arranged at predetermined positions. Therefore, the intensity distribution of the first interference fringe is detected by the first detection unit (CCD1), the intensity distribution of the second interference fringe is detected by the second detection unit (CCD2), and the intensity of the fifth interference fringe is detected. The distribution is detected by the third detector (CCD3), and the intensity distribution of the sixth interference fringe is detected by the fourth detector (CCD4).

また、図１および図６に示される例では、複数の検出部（ＣＣＤ）がそれぞれ１枚の干渉縞の強度分布を同時に検出しているが、光路長を変更させながら１つの検出部（ＣＣＤ）が互いに位相差が異なる２枚の干渉縞の強度分布を検出してもよい。 In the example shown in FIGS. 1 and 6, each of the plurality of detection units (CCD) simultaneously detects the intensity distribution of one interference fringe, but one detection unit (CCD) while changing the optical path length. ) May detect the intensity distribution of two interference fringes having different phase differences from each other.

［効果］
以上のように、本発明に係る物体形状測定方法および物体形状測定装置では、異なる波長の光を用いて位相測定を行うことにより、位相接続を行うことなく、また物体の表面形状によらず、使用する光の波長の半波長を大幅に超える高低差を有する物体の表面形状の測定を可能にする。たとえば、波長５３２ｎｍの光と波長５９３ｎｍの光を用いて物体の表面形状の測定を行う場合、本発明に係る物体形状測定方法および物体形状測定装置は、波長の約６００倍の３００μｍ程度までの高低差の測定が可能である。また、本発明に係る物体形状測定方法および物体形状測定装置は、位相の不連続点の検出を行うのではなく、測定した位相分布を基に１画素レベルで深さを測定できるため、これまで位相接続が不可能であった複雑な表面形状の被測定物体の測定にも対応できる。 [effect]
As described above, the object shape measuring method and the object shape measuring apparatus according to the present invention perform phase measurement using light of different wavelengths, without performing phase connection, and regardless of the surface shape of the object, This makes it possible to measure the surface shape of an object having a height difference that greatly exceeds half the wavelength of the light used. For example, when measuring the surface shape of an object using light having a wavelength of 532 nm and light having a wavelength of 593 nm, the object shape measuring method and the object shape measuring apparatus according to the present invention are high and low up to about 300 μm, which is about 600 times the wavelength. Differences can be measured. In addition, since the object shape measuring method and the object shape measuring apparatus according to the present invention can measure the depth at the level of one pixel based on the measured phase distribution instead of detecting the phase discontinuity, It can cope with the measurement of a measured object having a complicated surface shape that could not be phase-connected.

また、従来の位相シフトデジタルホログラフィでは、位相測定を実現するために３枚または４枚の互いに位相の異なる干渉縞を必要とした。これに対して、２枚の干渉縞から位相を測定する方法が提案されている（国際公開第２０１４／０５０１４１号、X. F. Meng et al., “Two-step phase-shifting interferometry and its application in image encryption”, Optics Letters, Vol. 31, pp. 1414-1416.）。この方法は、必要な干渉縞の数が少ないという大きなメリットがあるが、２枚の干渉縞の位相差を正確にπ／２に設定する必要があった。本発明に係る物体形状測定方法は、この方法と同様に２枚の干渉縞による位相測定を行うものであるが、２枚の干渉縞の位相差がπ／２でない場合にも正確な位相測定を行うことができる。具体的には、本発明に係る物体形状測定方法は、位相差がπ／２でない２枚の干渉縞から、位相差の異なる４枚の干渉縞を生成し、位相測定を行う（図２参照）。本発明に係る物体形状測定方法では、互いに異なる２種類の波長の光を用いるため、単一の干渉光学系を用いて、両方の波長の光について光路長を変えることなく２枚の干渉縞の位相差をπ／２に設定することは、光学素子の特性上困難である。たとえば、第１波長の光に対して互いの位相差がπ／２である２枚の干渉縞が同時に得られるように設定した干渉光学系に、第１波長とは異なる第２波長の光を入射した場合に得られる２枚の干渉縞の位相差はπ／２＋δとなり、π／２とは異なる値となる。このため、上記非特許文献（X. F. Meng et al.）の方法では、位相測定を行うことができないが、本発明に係る物体形状測定方法では、位相差がπ／２＋δであっても位相測定を行うことができる。したがって、本発明に係る物体形状測定方法では、単一の干渉光学系を用いて互いに異なる２種類の波長による位相測定が可能である。 Further, in the conventional phase shift digital holography, three or four interference fringes having different phases are required to realize phase measurement. In contrast, a method for measuring the phase from two interference fringes has been proposed (International Publication No. 2014/050141, XF Meng et al., “Two-step phase-shifting interferometry and its application in image encryption”. ", Optics Letters, Vol. 31, pp. 1414-1416.). This method has a great merit that the number of necessary interference fringes is small, but it is necessary to set the phase difference between the two interference fringes accurately to π / 2. The object shape measuring method according to the present invention performs phase measurement using two interference fringes in the same manner as this method. However, accurate phase measurement is possible even when the phase difference between the two interference fringes is not π / 2. It can be performed. Specifically, in the object shape measuring method according to the present invention, four interference fringes having different phase differences are generated from two interference fringes having a phase difference other than π / 2, and phase measurement is performed (see FIG. 2). ). Since the object shape measuring method according to the present invention uses light of two different wavelengths, a single interference optical system can be used to detect two interference fringes without changing the optical path length for light of both wavelengths. Setting the phase difference to π / 2 is difficult due to the characteristics of the optical element. For example, a second wavelength light different from the first wavelength is applied to an interference optical system that is set so that two interference fringes having a phase difference of π / 2 with respect to the first wavelength light can be obtained simultaneously. The phase difference between the two interference fringes obtained upon incidence is π / 2 + δ, which is a value different from π / 2. For this reason, the method of the non-patent document (XF Meng et al.) Cannot perform phase measurement, but the object shape measurement method according to the present invention does not perform phase measurement even when the phase difference is π / 2 + δ. It can be carried out. Therefore, in the object shape measuring method according to the present invention, it is possible to perform phase measurement using two different wavelengths using a single interference optical system.

また、本発明に係る物体形状測定方法は、位相差がπ／２でない場合にも正確な位相測定を行うことができるため、物体光と参照光の強度比を自由に設定できる。このため、本発明に係る物体形状測定方法は、測定条件を限定されない正確な位相測定の実現にも大きく貢献する。 In addition, since the object shape measuring method according to the present invention can perform accurate phase measurement even when the phase difference is not π / 2, the intensity ratio between the object light and the reference light can be freely set. For this reason, the object shape measurement method according to the present invention greatly contributes to the realization of accurate phase measurement without limiting the measurement conditions.

本発明の原理は、異なる波長で測定した位相分布から２つの長さＬ_１とＬ_２を定義し、その２つの長さが等しくなるｍおよびｎの組み合わせを探すことにある。このことから、条件を満たすｍおよびｎの組み合わせがただ１つであるときにのみ本手法は適用できる。つまり、本手法で測定できる深さ方向の測定可能域は使用する２つの波長の整数の最小公倍数で定義される。たとえば、５３２ｎｍと５９３ｎｍの２つの光を用いて本手法を行う場合、その測定可能域は５３２×５９３ｎｍということになり、１つの波長を使用する場合と比べて約６００倍に拡張される。 The principle of the present invention is to define _two lengths L ₁ and L ₂ from phase distributions measured at different wavelengths, and to find a combination of m and n where the two lengths are equal. From this, this technique can be applied only when there is only one combination of m and n that satisfies the condition. That is, the measurable range in the depth direction that can be measured by this method is defined by the least common multiple of integers of two wavelengths to be used. For example, when this method is performed using two lights of 532 nm and 593 nm, the measurable range is 532 × 593 nm, which is expanded about 600 times compared to the case of using one wavelength.

また、本発明に係る物体形状測定方法は、位相差がπ／２でない場合にも正確な位相測定を行うことができるため、物体光と参照光の強度比を自由に設定できる。従来の位相測定では、計算の成立のために参照光強度を物体光強度の数十倍から百倍程度に大きくする必要があったため、撮像素子のダイナミックレンジの飽和をもたらし、測定精度を下げる要因となっていた。これに対し、本発明に係る物体形状測定方法は、測定した２枚の干渉縞を用いて４枚の干渉縞を生成することで、４枚の干渉縞を用いる位相計算方法（Daniel Malacara（編集）、成相恭二、清原順子、辻内順平（翻訳）、「光学実験・測定法II」、アドコム・メディア株式会社、２０１０年６月２９日、ｐ．１１６〜１１９）を利用することが可能である。このため、強度に対する制約が一切なく、測定精度の低下を防止する効果も有する。したがって、本発明に係る物体形状測定方法は、互いに異なる２種類の波長の光を用いた物体の形状測定だけでなく、単一波長による位相測定においても、測定条件を限定されない正確な位相測定を実現することができる（この後説明する光位相測定方法）。 In addition, since the object shape measuring method according to the present invention can perform accurate phase measurement even when the phase difference is not π / 2, the intensity ratio between the object light and the reference light can be freely set. In the conventional phase measurement, it was necessary to increase the reference light intensity to several tens to one hundred times the object light intensity for the establishment of the calculation, which caused the saturation of the dynamic range of the image sensor and reduced the measurement accuracy. It was. On the other hand, the object shape measuring method according to the present invention generates four interference fringes using the two measured interference fringes, thereby generating a phase calculation method using four interference fringes (Daniel Malacara (editing). ), Junji Sei phase, Junko Kiyohara, Junpei Takiuchi (translation), “Optical Experiment and Measurement Method II”, Adcom Media Co., Ltd., June 29, 2010, p. 116-119) can be used. is there. For this reason, there is no restriction | limiting with respect to intensity | strength and it also has the effect which prevents the fall of a measurement precision. Therefore, the object shape measurement method according to the present invention provides accurate phase measurement that does not limit the measurement conditions not only in object shape measurement using light of two different wavelengths but also in phase measurement using a single wavelength. This can be realized (an optical phase measurement method described later).

２．光位相測定方法および光位相測定装置
［光位相測定方法］
本発明に係る光位相測定方法は、２枚の干渉縞を用いて、物体光（信号光）と参照光の強度比に依存せずに位相分布を測定することができる方法である。前述のとおり、本発明に係る物体形状測定方法の第１工程および第２工程では、互いに位相差が異なる２枚の干渉縞（例えば第１干渉縞および第２干渉縞）の強度分布を用いて２枚の干渉縞（例えば第３干渉縞および第４干渉縞）を仮想的に生成し、これら２枚の干渉縞の強度分布を算出する。そして、これら４枚の干渉縞の強度分布を用いることで、物体光（信号光）と参照光の強度比に依存せずに、物体光（信号光）に含まれる位相分布を高精度に測定することを可能としている。本発明に係る光位相測定方法は、このように上記の第１工程（または第２工程）のみを行うことで、２枚の干渉縞を用いて、物体光（信号光）と参照光の強度比に依存せずに位相分布を測定する。 2. Optical phase measurement method and optical phase measurement device [Optical phase measurement method]
The optical phase measurement method according to the present invention is a method that can measure a phase distribution using two interference fringes without depending on the intensity ratio of object light (signal light) and reference light. As described above, in the first step and the second step of the object shape measuring method according to the present invention, the intensity distribution of two interference fringes (for example, the first interference fringe and the second interference fringe) having different phase differences from each other is used. Two interference fringes (for example, the third interference fringe and the fourth interference fringe) are virtually generated, and the intensity distribution of these two interference fringes is calculated. By using the intensity distribution of these four interference fringes, the phase distribution contained in the object light (signal light) can be measured with high accuracy without depending on the intensity ratio between the object light (signal light) and the reference light. It is possible to do. In the optical phase measurement method according to the present invention, the intensity of object light (signal light) and reference light is obtained using only two interference fringes by performing only the first step (or second step). The phase distribution is measured without depending on the ratio.

具体的には、本発明に係る光位相測定方法は、（７）物体光（信号光）と参照光とから生成される第１干渉縞および第２干渉縞の強度分布を検出する工程と、（８）物体光と参照光とから仮想的に生成される第３干渉縞および第４干渉縞の強度分布を算出する工程と、（９）第１干渉縞の強度分布、第２干渉縞の強度分布、第３干渉縞の強度分布および第４干渉縞の強度分布から、物体光に含まれる位相分布を算出する工程と、を含む。 Specifically, the optical phase measurement method according to the present invention includes (7) detecting the intensity distribution of the first interference fringe and the second interference fringe generated from the object light (signal light) and the reference light; (8) calculating the intensity distribution of the third interference fringe and the fourth interference fringe virtually generated from the object light and the reference light; and (9) the intensity distribution of the first interference fringe and the second interference fringe. Calculating a phase distribution included in the object light from the intensity distribution, the intensity distribution of the third interference fringes, and the intensity distribution of the fourth interference fringes.

本発明に係る光位相測定方法における上記（７）〜（９）の工程は、それぞれ本発明に係る物体形状測定方法における（１）〜（３）の工程と同じである。したがって、上記（７）〜（９）の工程については、詳細な説明を省略し、簡単に説明する。 The steps (7) to (9) in the optical phase measurement method according to the present invention are the same as the steps (1) to (3) in the object shape measurement method according to the present invention, respectively. Therefore, detailed description of the steps (7) to (9) is omitted, and a simple description will be given.

まず、測定対象の位相分布を含む物体光と参照光とから、互いに位相差が異なる第１干渉縞および第２干渉縞を生成し、第１干渉縞の強度分布および第２干渉縞の強度分布を検出する（上記（７）の工程）。物体光は、測定対象の位相分布を含む光であり、例えば物体からの反射光または透過光である。ここで物体が空間光位相変調器（ＳＬＭ）である場合は、物体光は位相変調信号を含む光（信号光）となる。参照光は、物体光と干渉可能な同一波長の光である。前述のとおり、第１干渉縞と第２干渉縞との位相差は、厳密にはπ／２とはならないことがある。 First, a first interference fringe and a second interference fringe having different phase differences are generated from the object light including the phase distribution to be measured and the reference light, and the intensity distribution of the first interference fringe and the intensity distribution of the second interference fringe are generated. Is detected (step (7) above). The object light is light including the phase distribution to be measured, for example, reflected light or transmitted light from the object. Here, when the object is a spatial light phase modulator (SLM), the object light becomes light including a phase modulation signal (signal light). The reference light is light having the same wavelength that can interfere with the object light. As described above, the phase difference between the first interference fringes and the second interference fringes may not be strictly π / 2.

次いで、第１干渉縞の強度分布および第２干渉縞の強度分布の測定結果を用いて、物体光と参照光とから第３干渉縞および第４干渉縞を仮想的に生成し、第３干渉縞の強度分布および第４干渉縞の強度分布を算出する（上記（８）の工程、図２参照）。第３干渉縞は、物体光と参照光とから生成されうる干渉縞であって、第１干渉縞および第２干渉縞のいずれとも位相差が異なる干渉縞である。また、第４干渉縞は、物体光と参照光とから生成されうる干渉縞であって、第１干渉縞、第２干渉縞および第３干渉光のいずれとも位相差が異なる干渉縞である。 Next, using the measurement result of the intensity distribution of the first interference fringe and the intensity distribution of the second interference fringe, the third interference fringe and the fourth interference fringe are virtually generated from the object light and the reference light, and the third interference The intensity distribution of the fringes and the intensity distribution of the fourth interference fringes are calculated (step (8) above, see FIG. 2). The third interference fringes are interference fringes that can be generated from the object light and the reference light, and have different phase differences from both the first interference fringes and the second interference fringes. Further, the fourth interference fringes are interference fringes that can be generated from the object light and the reference light, and are different in phase difference from any of the first interference fringes, the second interference fringes, and the third interference lights.

第１干渉縞の強度分布Ｈ_１および第２干渉縞の強度分布Ｈ_２は、それぞれ以下の式（１２）および式（１３）のように記述されうる。ここで、Ａ_Ｏ ^２は第１干渉縞の生成に用いられた物体光の強度分布であり、Ａ_ｒ ^２は第１干渉縞の生成に用いられた参照光の強度分布である。αは第１干渉縞の生成に用いられた物体光の強度に対する第２干渉縞の生成に用いられた物体光の強度の比の分布であり、βは第１干渉縞の生成に用いられた参照光の強度に対する第２干渉縞の生成に用いられた参照光の強度の比の分布である。また、φは物体光と参照光との位相差の分布であり、γは第１干渉縞と第２干渉縞との位相差である。
Intensity distribution H ₁ and the intensity distribution of H ₂ second interference fringes of the first interference fringe may respectively be written as the following equation (12) and (13). Here, A _O ² is the intensity distribution of the object light used for generating the first interference fringes, and A _r ² is the intensity distribution of the reference light used for generating the first interference fringes. α is a distribution of the ratio of the intensity of the object light used for generating the second interference fringe to the intensity of the object light used for generating the first interference fringe, and β is used for generating the first interference fringe. It is distribution of ratio of the intensity | strength of the reference light used for the production | generation of the 2nd interference fringe with respect to the intensity | strength of reference light. Φ is the phase difference distribution between the object beam and the reference beam, and γ is the phase difference between the first interference fringe and the second interference fringe.

そして、第１の干渉縞から位相差がπずれた第３の干渉縞の強度分布Ｈ_３は、以下の式（１６）により与えられる。同様に、第２の干渉縞から位相差がπずれた第４の干渉縞の強度分布Ｈ_４は、以下の式（１７）により与えられる。
Then, the intensity distribution H ₃ of the third interference fringe having a phase difference of π from the first interference fringe is given by the following equation (16). Similarly, the intensity distribution H ₄ of the fourth interference fringe having a phase difference of π from the second interference fringe is given by the following equation (17).

次いで、第１干渉縞の強度分布、第２干渉縞の強度分布、第３干渉縞の強度分布および第４干渉縞の強度分布を用いて、物体光に含まれる位相分布を算出する（上記（９）の工程、図３参照）。 Next, using the intensity distribution of the first interference fringe, the intensity distribution of the second interference fringe, the intensity distribution of the third interference fringe, and the intensity distribution of the fourth interference fringe, a phase distribution included in the object light is calculated ((( 9), see FIG.

物体光に含まれる位相分布、すなわち物体光の複素振幅の分布は、上記（７）および（８）の工程で得られた第１干渉縞の強度分布Ｈ_１、第２干渉縞の強度分布Ｈ_２、第３干渉縞の強度分布Ｈ_３および第４干渉縞の強度分布Ｈ_４を用いて式（１８）のように導出される。
The phase distribution included in the object light, that is, the distribution of the complex amplitude of the object light, is the first interference fringe intensity distribution H ₁ and the second interference fringe intensity distribution H obtained in the steps (7) and (8). _2, is derived as equation (18) using the intensity distribution H ₄ of the intensity distribution H ₃ and fourth interference fringe of the third interference fringe.

このことから、２つの物体光の強度分布Ａ_ｏ ^２，αＡ_ｏ ^２、２つの参照光の強度分布Ａ_ｒ ^２，βＡ_ｒ ^２および任意の位相差を持つ２つの干渉縞の強度分布Ｈ_１，Ｈ_２を取得することで、物体光に含まれる位相分布を正確に測定できることがわかる。 From this, the intensity distributions A _o ² and αA _o ^{2 of} the two object lights, the intensity distributions A _r ² and βA _r ^{2 of the} ^two reference lights, and the intensity distributions H ₁ of two interference fringes having an arbitrary phase difference, by acquiring the H _2, it can be seen that accurate measurement of the phase distribution contained in the object light.

以上の手順により、物体光（信号光）と参照光の強度比に依存せずに、物体光（信号光）に含まれる位相分布を高精度に測定することができる。 By the above procedure, the phase distribution included in the object light (signal light) can be measured with high accuracy without depending on the intensity ratio between the object light (signal light) and the reference light.

本発明に係る光位相測定方法を行うための装置および光学系の構成は、特に限定されない。たとえば、次に説明する本発明に係る光位相測定装置を用いることで、本発明に係る光位相測定方法を行うことができる。 The configuration of the apparatus and the optical system for performing the optical phase measurement method according to the present invention is not particularly limited. For example, the optical phase measurement method according to the present invention can be performed by using the optical phase measurement device according to the present invention described below.

［光位相測定装置］
本発明に係る光位相測定装置は、本発明に係る光位相測定方法を行うための装置である。本発明に係る光位相測定装置は、少なくとも、干渉波生成部、検出部および処理部を有する。 [Optical phase measurement device]
The optical phase measurement apparatus according to the present invention is an apparatus for performing the optical phase measurement method according to the present invention. The optical phase measurement device according to the present invention includes at least an interference wave generation unit, a detection unit, and a processing unit.

干渉波生成部は、位相分布を含む物体光と、参照光とを合波して干渉波を生成する。たとえば、干渉波生成部は、ビームスプリッターである。 The interference wave generating unit generates an interference wave by combining the object light including the phase distribution and the reference light. For example, the interference wave generation unit is a beam splitter.

検出部は、干渉波生成部により生成された干渉波から互いに位相差が異なる２つの干渉縞（第１干渉縞および第２干渉縞）を生成し、これら２つの干渉縞（第１干渉縞および第２干渉縞）の強度分布を検出する。 The detection unit generates two interference fringes (first interference fringe and second interference fringe) having different phase differences from the interference wave generated by the interference wave generation unit, and these two interference fringes (first interference fringe and The intensity distribution of the second interference fringes) is detected.

処理部は、第１の干渉縞の強度分布および第２の干渉縞の強度分布から仮想的に生成される第３干渉縞の強度分布および第４干渉縞の強度分布を算出し、第１干渉縞の強度分布、第２干渉縞の強度分布、第３干渉縞の強度分布および第４干渉縞の強度分布から、物体光に含まれる位相分布を算出する。 The processing unit calculates the intensity distribution of the third interference fringe and the intensity distribution of the fourth interference fringe virtually generated from the intensity distribution of the first interference fringe and the intensity distribution of the second interference fringe, and the first interference fringe A phase distribution included in the object light is calculated from the intensity distribution of the fringes, the intensity distribution of the second interference fringes, the intensity distribution of the third interference fringes, and the intensity distribution of the fourth interference fringes.

本発明に係る光位相測定装置としては、例えば図１に示される物体形状測定装置や図６に示される物体形状測定装置を用いることができる。これらの図に示される物体形状測定装置を光位相測定装置として用いる場合、位相分布を含む物体光および参照光を生成することもできる。前述のとおり、物体が空間光位相変調器（ＳＬＭ）である場合は、物体光は位相変調信号を含む光（信号光）となる。一方、外部で生成された物体光（信号光）の位相分布を外部で生成された参照光を用いて測定する場合は、これらの図に示される光源部（２つのレーザー光源）および光分離部（半波長板および偏光ビームスプリッター）は不要である。 As the optical phase measuring device according to the present invention, for example, the object shape measuring device shown in FIG. 1 or the object shape measuring device shown in FIG. 6 can be used. When the object shape measuring apparatus shown in these figures is used as an optical phase measuring apparatus, object light and reference light including a phase distribution can be generated. As described above, when the object is a spatial light phase modulator (SLM), the object light is light including a phase modulation signal (signal light). On the other hand, when measuring the phase distribution of the object light (signal light) generated outside using the reference light generated outside, the light source unit (two laser light sources) and the light separation unit shown in these drawings (Half-wave plate and polarizing beam splitter) are unnecessary.

［効果］
以上のように、本発明に係る光位相測定方法は、位相差がπ／２でない場合にも正確な位相測定を行うことができるため、物体光と参照光の強度比を自由に設定できる。このため、本発明に係る物体形状測定方法は、測定条件を限定されない正確な位相測定の実現にも大きく貢献する。 [effect]
As described above, since the optical phase measurement method according to the present invention can perform accurate phase measurement even when the phase difference is not π / 2, the intensity ratio between the object beam and the reference beam can be freely set. For this reason, the object shape measurement method according to the present invention greatly contributes to the realization of accurate phase measurement without limiting the measurement conditions.

以下、本発明について実施例を参照して詳細に説明するが、本発明はこれらの実施例により限定されない。 EXAMPLES Hereinafter, although this invention is demonstrated in detail with reference to an Example, this invention is not limited by these Examples.

［実施例１］
本実施例では、本発明に係る物体形状測定方法により、波長を超える高低差を有する物体の表面形状の測定を行った場合についてシミュレーションを行った。 [Example 1]
In this example, a simulation was performed for the case where the surface shape of an object having a height difference exceeding the wavelength was measured by the object shape measuring method according to the present invention.

図７Ａ〜Ｄは、本発明に係る物体形状測定方法により、波長を超える高低差を有する物体の表面形状の測定を行った場合のシミュレーション結果である。図７Ａは、測定対象の物体の表面における深さ分布を示す図である。この図では、黒に近いほど表面の位置が高く、白に近いほど表面の位置が低いことを示している。この図に示されるように、測定対象の物体の表面には高低差１０μｍの傾斜が設けられている。図７Ｂは、第１波長（５３２ｎｍ）の光を用いて位相測定した結果（第１位相分布）を示す図であり、図７Ｃは、第２波長（５９３ｎｍ）の光を用いて位相測定した結果（第２位相分布）を示す図である。これらの図では、黒に近いほど位相が小さく、白に近いほど位相が大きいことを示している。波長より長い高低差を測定しているため、いずれの図においても位相の不連続点が生じ、縞が発生している。このような場合は、一般的には位相接続を行うことが必要である。図７Ｄは、上記第３工程で説明した手順により第１位相分布および第２位相分布から算出された深さ分布を示す図である。この図でも、図７Ａと同様に、黒に近いほど表面の位置が高く、白に近いほど表面の位置が低いことを示している。図７Ａに示される深さ分布と図７Ｄに示される深さ分布とが完全に同一であることから、本発明に係る物体形状測定方法により、位相接続をすることなく波長の２０倍程度の深さをもつ物体の表面形状を測定できることがわかる。 7A to 7D are simulation results when the surface shape of an object having a height difference exceeding the wavelength is measured by the object shape measuring method according to the present invention. FIG. 7A is a diagram showing the depth distribution on the surface of the object to be measured. In this figure, the closer to black, the higher the surface position, and the closer to white, the lower the surface position. As shown in this figure, the surface of the object to be measured is provided with an inclination with a height difference of 10 μm. FIG. 7B is a diagram showing a result of phase measurement (first phase distribution) using light of the first wavelength (532 nm), and FIG. 7C is a result of phase measurement using light of the second wavelength (593 nm). It is a figure which shows (2nd phase distribution). In these figures, the closer to black, the smaller the phase, and the closer to white, the larger the phase. Since the height difference longer than the wavelength is measured, phase discontinuities occur in all the figures, and fringes are generated. In such a case, it is generally necessary to perform phase connection. FIG. 7D is a diagram illustrating a depth distribution calculated from the first phase distribution and the second phase distribution by the procedure described in the third step. This figure also shows that, as in FIG. 7A, the closer to black, the higher the surface position, and the closer to white, the lower the surface position. Since the depth distribution shown in FIG. 7A and the depth distribution shown in FIG. 7D are completely the same, the object shape measurement method according to the present invention enables a depth of about 20 times the wavelength without phase connection. It can be seen that the surface shape of an object having a thickness can be measured.

［実施例２］
本実施例では、本発明に係る方法により、任意の位相差を有する２枚の干渉縞から位相分布を算出するシミュレーションを行った。 [Example 2]
In this example, a simulation for calculating a phase distribution from two interference fringes having an arbitrary phase difference was performed by the method according to the present invention.

図８は、本発明に係る方法および従来の方法における、位相の算出値の誤差を示すグラフである。このグラフでは、２枚の干渉縞間の位相差を変化させた場合における、位相の算出値の誤差の変化を示している。横軸は２枚の干渉縞間の位相差であり、縦軸は相関係数（ＲＭＳＥ）と呼ばれる誤差指標である。この指標が１のとき、誤差が０となる。本発明に係る方法の結果を黒塗りの三角で示し、従来の方法の結果を白塗りの四角で示す。このグラフより、本発明に係る方法は０、πおよび−πを除いたすべての位相差において誤差が０であることがわかる。なお、これらの３点は、位相差を与えてないのと同義であるため、除外すべきものである。この結果から、本発明の方法により、任意の位相差を持つ２枚の干渉縞から位相分布を正確に算出できることがわかる。 FIG. 8 is a graph showing an error in the calculated value of the phase in the method according to the present invention and the conventional method. This graph shows a change in the error of the calculated value of the phase when the phase difference between the two interference fringes is changed. The horizontal axis is the phase difference between the two interference fringes, and the vertical axis is an error index called correlation coefficient (RMSE). When this index is 1, the error is 0. The results of the method according to the present invention are indicated by black triangles, and the results of the conventional method are indicated by white squares. From this graph, it can be seen that the method according to the present invention has zero error in all phase differences except 0, π, and −π. Note that these three points should be excluded because they are synonymous with no phase difference. From this result, it can be seen that the phase distribution can be accurately calculated from two interference fringes having an arbitrary phase difference by the method of the present invention.

［実施例３］
本実施例では、本発明に係る方法により位相変調信号を実際に測定した。 [Example 3]
In this example, the phase modulation signal was actually measured by the method according to the present invention.

図９Ａ〜Ｃは、参照光の強度を信号光（物体光）の強度より低くした条件で、本発明に係る方法と従来の方法とを用いて位相変調信号を測定した結果を示す図である。図９Ａは、測定対象となる２値の位相変調信号を示す図である。図９Ｂは、従来の方法で測定された位相分布を示す図であり、図９Ｂは、本発明に係る方法により測定された位相分布を示す図である。図９Ｂにおいて破線で囲んだ領域に示されるように、従来の方法では測定誤差である黒点がおよそ５万個発生していた。これに対し、本発明に係る方法ではまったく測定誤差が発生しなかった。これらのことから、本発明に係る方法は、信号光（物体光）と参照光の強度比に依存することなく、正確に位相分布を測定できることがわかる。 9A to 9C are diagrams showing the results of measuring the phase modulation signal using the method according to the present invention and the conventional method under the condition that the intensity of the reference light is lower than the intensity of the signal light (object light). . FIG. 9A is a diagram illustrating a binary phase modulation signal to be measured. FIG. 9B is a diagram showing the phase distribution measured by the conventional method, and FIG. 9B is a diagram showing the phase distribution measured by the method according to the present invention. As shown in the area surrounded by the broken line in FIG. 9B, about 50,000 black spots, which are measurement errors, were generated in the conventional method. On the other hand, no measurement error occurred in the method according to the present invention. From these, it can be seen that the method according to the present invention can accurately measure the phase distribution without depending on the intensity ratio of the signal light (object light) and the reference light.

本発明に係る物体形状測定方法および物体形状測定装置は、使用する光の波長を超える高低差を含みうる物体の表面形状を高精度に測定できるため、様々な分野において利用されうる。 The object shape measuring method and the object shape measuring apparatus according to the present invention can be used in various fields because the surface shape of an object that can include a height difference exceeding the wavelength of light to be used can be measured with high accuracy.

Claims

An object shape measuring method for measuring a surface shape of an object, which may include a height difference exceeding the wavelength of light to be used,
A first interference fringe and a second interference fringe having different phase differences from the first object light having the first wavelength including the first phase distribution derived from the surface shape of the object and the first reference light having the first wavelength. Generating and detecting an intensity distribution of the first interference fringes and an intensity distribution of the second interference fringes;
A third interference fringe and a fourth interference, which can be generated from the first object light and the first reference light, have a phase difference different from both the first interference fringe and the second interference fringe and have a phase difference different from each other. Virtually generating fringes and calculating an intensity distribution of the third interference fringes and an intensity distribution of the fourth interference fringes;
The first phase distribution included in the first object light from the intensity distribution of the first interference fringe, the intensity distribution of the second interference fringe, the intensity distribution of the third interference fringe, and the intensity distribution of the fourth interference fringe. Calculating
A fifth interference having a second phase distribution derived from the surface shape of the object and having a phase difference between the second object light having a second wavelength different from the first wavelength and the reference light having the second wavelength. Generating a fringe and a sixth interference fringe and detecting an intensity distribution of the fifth interference fringe and an intensity distribution of the sixth interference fringe;
A seventh interference fringe and an eighth interference, which can be generated from the second object light and the second reference light, have a phase difference different from both the fifth interference fringe and the sixth interference fringe, and have a phase difference different from each other. Virtually generating fringes and calculating the intensity distribution of the seventh interference fringes and the intensity distribution of the eighth interference fringes;
From the intensity distribution of the fifth interference fringe, the intensity distribution of the sixth interference fringe, the intensity distribution of the seventh interference fringe, and the intensity distribution of the eighth interference fringe, the second phase distribution included in the second object light Calculating
Calculating a depth distribution representing a surface shape of the object, which may include a height difference exceeding the first wavelength and the second wavelength, from the calculated first phase distribution and the second phase distribution;
Including
The intensity distribution of the third interference fringe and the intensity distribution of the fourth interference fringe were used to generate the intensity distribution of the first interference fringe, the intensity distribution of the second interference fringe, and the generation of the first interference fringe. The intensity distribution of the first object light, the intensity distribution of the first reference light used for generating the first interference fringe, and the intensity of the first object light used for generating the first interference fringe Distribution of the ratio of the intensity of the first object light used for generating the second interference fringe and generation of the second interference fringe with respect to the intensity of the first reference light used for generating the first interference fringe Calculated from the distribution of the intensity ratio of the first reference light used in
The intensity distribution of the seventh interference fringe and the intensity distribution of the eighth interference fringe were used to generate the intensity distribution of the fifth interference fringe, the intensity distribution of the sixth interference fringe, and the generation of the fifth interference fringe. The intensity distribution of the second object light, the intensity distribution of the second reference light used to generate the fifth interference fringe, and the intensity of the second object light used to generate the fifth interference fringe Distribution of intensity ratio of the second object light used for generation of the sixth interference fringe and generation of the sixth interference fringe with respect to intensity of the second reference light used for generation of the fifth interference fringe Calculated from the intensity ratio distribution of the second reference light used in
Object shape measurement method.

The intensity distribution of the third interference fringe, the intensity distribution of the fourth interference fringe, the intensity distribution of the seventh interference fringe, and the intensity distribution of the eighth interference fringe are represented by the following equations (1), (2), The object shape measuring method according to claim 1, wherein the object shape measuring method is calculated by the equations (3) and (4).
(In Equations (1) and (2), H ₁ is the intensity distribution of the first interference fringes, H ₂ is the intensity distribution of the second interference fringes, and H ₃ is the intensity of the third interference fringes. H ₄ is the intensity distribution of the fourth interference fringes, A _o ² is the intensity distribution of the first object light used for generating the first interference fringes, and A _r ² is the first distribution of the first interference fringes. 1 is an intensity distribution of the first reference light used to generate one interference fringe, and α is used to generate the second interference fringe with respect to the intensity of the first object light used to generate the first interference fringe. Is the distribution of the ratio of the intensity of the first object light, and β is the first interference fringe used for generating the second interference fringe with respect to the intensity of the first reference light used for generating the first interference fringe. 1 is the distribution of the intensity ratio of the reference light.)
(In Expressions (3) and (4), H ₅ is the intensity distribution of the fifth interference fringe, H ₆ is the intensity distribution of the sixth interference fringe, and H ₇ is the intensity of the seventh interference fringe. H ₈ is the intensity distribution of the eighth interference fringe, A _o ′ ² is the intensity distribution of the second object light used to generate the fifth interference fringe, and A _r ′ ² is An intensity distribution of the second reference light used to generate the fifth interference fringe, and α ′ represents the intensity of the second interference light with respect to the intensity of the second object light used to generate the fifth interference fringe. The intensity distribution of the second object light used for generation is β ′, which is used for generation of the sixth interference fringe with respect to the intensity of the second reference light used for generation of the fifth interference fringe. The distribution of the intensity ratio of the second reference light.

The object shape measurement method according to claim 2, wherein the first phase distribution and the second phase distribution are distributions of complex amplitudes calculated by the following expressions (5) and (6), respectively.
(In Expression (5), A _o exp (iφ) is the first phase distribution, H ₁ is the intensity distribution of the first interference fringes, and H ₂ is the intensity distribution of the second interference fringes, H ₃ is the intensity distribution of the third interference fringe, H ₄ is the intensity distribution of the fourth interference fringe, and _Ar is the intensity of the first reference light used to generate the first interference fringe. Is a square root distribution, and α is a distribution of a ratio of the intensity of the first object light used to generate the second interference fringe to the intensity of the first object light used to generate the first interference fringe. And β is a distribution of the ratio of the intensity of the first reference light used to generate the second interference fringe to the intensity of the first reference light used to generate the first interference fringe, and γ is (It is a phase difference between the first interference fringe and the second interference fringe.)
(In Expression (6), A _o 'exp (iφ) is the second phase distribution, H ₅ is the intensity distribution of the fifth interference fringe, and H ₆ is the intensity distribution of the sixth interference fringe. , H ₇ is the intensity distribution of the seventh interference fringe, H ₈ is the intensity distribution of the eighth interference fringe, and A _r ′ is the second reference light used to generate the fifth interference fringe. Is the distribution of the square root of intensity, and α ′ is the ratio of the intensity of the second object light used to generate the sixth interference fringe to the intensity of the second object light used to generate the fifth interference fringe. Β ′ is a distribution of the ratio of the intensity of the second reference light used to generate the sixth interference fringe to the intensity of the second reference light used to generate the fifth interference fringe. And γ ′ is a phase difference between the fifth interference fringe and the sixth interference fringe.)

The depth distribution is calculated by substituting the calculated values of m and n for the values of m and n when L ₁ = L ₂ using the following formulas (7) and (8). The object shape measuring method according to any one of claims 1 to 3, which is calculated by (7) and formula (8).
(In Expression (7), L ₁ is a depth at an arbitrary point on the surface of the object, and φ ₁ is a calculated value of a phase at a point of the first phase distribution corresponding to an arbitrary point on the surface of the object. (−π ≦ φ ₁ ≦ π), λ ₁ is the first wavelength, and m is a positive integer.)
(In Expression (8), L ₂ is a depth at an arbitrary point on the surface of the object, and φ ₂ is a calculated value of a phase at a point of the second phase distribution corresponding to an arbitrary point on the surface of the object. (−π ≦ φ ₂ ≦ π), λ ₂ is the second wavelength, and n is a positive integer.)

An object shape measuring apparatus for measuring a surface shape of an object, which may include a height difference exceeding the wavelength of light to be used,
A light source unit that emits laser light of a first wavelength and laser light of a second wavelength different from the first wavelength on the same optical axis;
A light separating unit that separates laser light emitted from the light source unit into object light and reference light;
An interference wave generation unit configured to generate an interference wave by combining the object light including the phase distribution derived from the surface shape of the object, which is transmitted or reflected with respect to the object, and the reference light;
A detector that generates two interference fringes having different phase differences from the interference wave, and detects an intensity distribution of the two interference fringes;
The intensity distribution of the two interference fringes detected by the detection unit when the light source unit emits the first wavelength laser beam, and the detection unit when the light source unit emits the second wavelength laser beam. A processing unit for calculating a depth distribution representing the surface shape of the object, which may include a height difference exceeding the first wavelength and the second wavelength, from the intensity distribution of the two interference fringes detected by
I have a,
The detection unit includes the first object light as the object light derived from the laser light of the first wavelength and the first reference light as the reference light derived from the laser light of the first wavelength. Generating a first interference fringe and a second interference fringe as two interference fringes, detecting an intensity distribution of the first interference fringe and an intensity distribution of the second interference fringe;
The processing unit includes an intensity distribution of the first interference fringes, an intensity distribution of the second interference fringes, an intensity distribution of the first object light used for generating the first interference fringes, and the first interference. The first reference light used for generating the second interference fringes with respect to the intensity distribution of the first reference light used for generating the fringes and the intensity of the first object light used for generating the first interference fringes. The distribution of the ratio of the intensity of the object light and the ratio of the intensity of the first reference light used to generate the second interference fringe to the intensity of the first reference light used to generate the first interference fringe From the distribution, a third interference fringe and a fourth interference fringe having a phase difference different from both the first interference fringe and the second interference fringe and having a phase difference from each other are virtually generated, and the third interference fringe And an intensity distribution of the fourth interference fringes,
The detection unit includes the second object light as the object light derived from the laser light of the second wavelength and the second reference light as the reference light derived from the laser light of the second wavelength. Generating a fifth interference fringe and a sixth interference fringe as two interference fringes, detecting an intensity distribution of the fifth interference fringe and an intensity distribution of the sixth interference fringe;
The processing unit includes an intensity distribution of the fifth interference fringe, an intensity distribution of the sixth interference fringe, an intensity distribution of the second object light used for generating the fifth interference fringe, and the fifth interference. The second reference light used for generation of the sixth interference fringes with respect to the intensity distribution of the second reference light used for generation of fringes and the intensity of the second object light used for generation of the fifth interference fringes. The distribution of the ratio of the intensity of the object light and the ratio of the intensity of the second reference light used to generate the sixth interference fringe to the intensity of the second reference light used to generate the fifth interference fringe From the distribution, a seventh interference fringe and an eighth interference fringe having a phase difference different from both of the fifth interference fringe and the sixth interference fringe and different in phase from each other are virtually generated, and the seventh interference fringe And an intensity distribution of the eighth interference fringe,
The processing unit includes an intensity distribution of the first interference fringe, an intensity distribution of the second interference fringe, an intensity distribution of the third interference fringe, an intensity distribution of the fourth interference fringe, an intensity distribution of the fifth interference fringe, The shape of the surface of the object that may include a height difference exceeding the first wavelength and the second wavelength from the intensity distribution of the sixth interference fringe, the intensity distribution of the seventh interference fringe, and the intensity distribution of the eighth interference fringe. A depth distribution representing
Object shape measuring device.

A first interference fringe and a second interference fringe having different phase differences are generated from the object light including the phase distribution and the reference light having the same wavelength as the object light, and the intensity distribution of the first interference fringe and the second Detecting the intensity distribution of interference fringes;
The third interference fringe and the fourth interference fringe, which can be generated from the object light and the reference light, have a phase difference different from both the first interference fringe and the second interference fringe and have a phase difference different from each other. And calculating the intensity distribution of the third interference fringes and the intensity distribution of the fourth interference fringes,
Calculating the phase distribution included in the object light from the intensity distribution of the first interference fringes, the intensity distribution of the second interference fringes, the intensity distribution of the third interference fringes, and the intensity distribution of the fourth interference fringes; When,
Including
The intensity distribution of the third interference fringe and the intensity distribution of the fourth interference fringe were used to generate the intensity distribution of the first interference fringe, the intensity distribution of the second interference fringe, and the generation of the first interference fringe. The intensity distribution of the object light, the intensity distribution of the reference light used to generate the first interference fringe, and the second interference fringe with respect to the intensity of the object light used to generate the first interference fringe. The distribution of the ratio of the intensity of the object light used for generation and the intensity of the reference light used for generation of the second interference fringe with respect to the intensity of the reference light used for generation of the first interference fringe. Calculated from the ratio distribution,
Optical phase measurement method.

The optical phase measurement method according to claim 6, wherein the intensity distribution of the third interference fringes and the intensity distribution of the fourth interference fringes are calculated by the following expressions (1) and (2), respectively.
(In Equations (1) and (2), H ₁ is the intensity distribution of the first interference fringes, H ₂ is the intensity distribution of the second interference fringes, and H ₃ is the intensity of the third interference fringes. H ₄ is an intensity distribution of the fourth interference fringes, A _o ² is an intensity distribution of the object light used for generating the first interference fringes, and A _r ² is the first interference. Is an intensity distribution of the reference light used for generating the fringes, and α is the intensity of the object light used for generating the second interference fringes with respect to the intensity of the object light used for generating the first interference fringes. Β is a distribution of the ratio of the intensity of the reference light used for generating the second interference fringe to the intensity of the reference light used for generating the first interference fringe. )

The optical phase measurement method according to claim 7, wherein the phase distribution is a distribution of complex amplitudes calculated by the following equation (5).
(In Expression (5), A _o exp (iφ) is the phase distribution, H ₁ is the intensity distribution of the first interference fringe, H ₂ is the intensity distribution of the second interference fringe, and H ₃ Is the intensity distribution of the third interference fringes, H ₄ is the intensity distribution of the fourth interference fringes, and _Ar is the distribution of the square root of the intensity of the reference light used to generate the first interference fringes. A is the distribution of the ratio of the intensity of the object light used to generate the second interference fringe to the intensity of the object light used to generate the first interference fringe, and β is the first interference A distribution of a ratio of the intensity of the reference light used for generating the second interference fringe to the intensity of the reference light used for generating the fringe, and γ is the first interference fringe and the second interference fringe The phase difference of

An interference wave generating unit that generates an interference wave by combining the object light including the phase distribution and the reference light having the same wavelength as the object light ;
A detector that generates a first interference fringe and a second interference fringe having different phase differences from the interference wave, and detects an intensity distribution of the first interference fringe and an intensity distribution of the second interference fringe;
A processing unit that calculates the phase distribution from the intensity distribution of the first interference fringes and the intensity distribution of the second interference fringes;
Have
The processing unit includes an intensity distribution of the first interference fringes, an intensity distribution of the second interference fringes, an intensity distribution of the object light used for generating the first interference fringes, and the first interference. The intensity distribution of the reference light used for generating fringes and the ratio of the intensity of the object light used for generating the second interference fringes to the intensity of the object light used for generating the first interference fringes And the distribution of the ratio of the intensity of the reference light used to generate the second interference fringe to the intensity of the reference light used to generate the first interference fringe, A third interference fringe and a fourth interference fringe having a phase difference different from any of the second interference fringes and having a phase difference from each other are virtually generated, and the intensity distribution of the third interference fringes and the fourth interference fringes An intensity distribution is calculated, the intensity distribution of the first interference fringes, the intensity of the second interference fringes Cloth, from the intensity distribution and the intensity distribution of the fourth interference fringe of the third interference fringe, to calculate the phase distribution,
Optical phase measurement device.