JP5140789B2 - Spectroscopic polarimeter - Google Patents

Description

  The present invention relates to an apparatus and method for performing measurement of spectral polarization characteristics of a measurement object using a channeled spectrum with high accuracy.

  Light has the property of “transverse wave”. On the premise of three axes (x, y, z) orthogonal to each other, assuming that the traveling direction of light is the z-axis direction, the vibration direction of light is a direction along the xy plane. There is a bias in the vibration direction of light in the xy plane. This polarization of light is called “polarized light”. In this specification, the method of polarization of light is hereinafter referred to as “polarization state”. This polarization state generally varies depending on the wavelength (color) of light.

  When light in a certain polarization state is incident on the measurement object and outgoing light such as transmitted light or reflected light is obtained, if the measurement object has anisotropy with respect to the light, it is between the incident light and the outgoing light. A change in the polarization state is observed. Obtaining information on the anisotropy of the measurement object from the change in the polarization state is referred to as “polarization measurement”. Examples of such anisotropy include molecular structure anisotropy, the presence of stress (pressure), the presence of a local electric field and a magnetic field, and the like.

  The change in the polarization state between the incident light and the outgoing light is obtained for each wavelength, and obtaining information on the anisotropy of the measurement object from them is particularly called “spectral polarization measurement”. According to this spectroscopic polarimetry, there is an advantage that much more information can be acquired compared to the case of measurement using a single wavelength (monochrome). In this spectroscopic polarimetry, a device that acquires information about a change in polarization state between incident light and outgoing light, that is, a polarization spectroscopic device is a key device.

  As application fields of spectroscopic polarimetry, the spectroscopic ellipsometry field, the medical field, and the like are known. For example, in the spectroscopic ellipsometry field, the film thickness and complex refractive index of a thin film can be measured non-destructively and in a non-contact manner, so that it has been applied to optoelectronic equipment, semiconductor inspection, research, and the like. In the medical field, since some types of cells have polarization characteristics, attempts have been made to early detect glaucoma and cancer cells.

As a typical representative spectropolarimetry method, a rotational phase shifter method and a polarization modulation method are known.
In these methods, a measurement light is modulated using a mechanical or electrical polarization control element, and a polarization state, such as a Stokes parameter, is obtained from a change in spectrum accompanying the modulation.

  However, these measurement methods require [1] a mechanical or electrical drive device, [2] have to repeatedly measure multiple spectra while changing the conditions of the polarization control device, etc. The problem was pointed out.

  In order to solve these problems, a channeled spectroscopic polarimetry has been devised (see Non-Patent Document 1).

  In Non-Patent Document 1, two phase shifters are installed between the sample and the spectroscope. However, in Patent Document 1 and Non-Patent Document 2, two phase shifters are provided between the sample and the light source. The measurement by the composition which installs is proposed. As a result, even when the direction of the light beam varies depending on the sample, it is possible to perform measurement with a small measurement error.

  FIG. 1 shows the configuration of the polarization spectrometer disclosed in Patent Document 1. Except for the thickness ratio of the phase shifter which is not shown, the configuration shown in FIG. 1 is also a configuration common to the present invention. The optical system shown in FIG. 1 includes a light source 7, a polarizer P, phase shifters R 1 and R 2, an analyzer A, and a spectrometer 8. The light emitted from the light source 7 passes through the polarizer P, the phase shifter R1, and the phase shifter R2 in order, reflects or transmits the sample D, passes through the analyzer A, and enters the spectroscope 8. Thereafter, the spectrum of the incident light is acquired by the spectroscope 8, and the spectral polarization parameter and the like of the sample are calculated by the procedure described later.

  The directions of the fast axes of the phase shifter R1 and the phase shifter R2 are inclined by 45 °, and the direction of the transmission axis of the polarizer P coincides with the direction of the fast axis of the phase shifter R2. In the figure, the fast axis of the phase shifter is represented as “fast” and the slow axis is represented as “slow”. Further, θ is the azimuth angle of the transmission axis of the analyzer with respect to the fast axis of the phase shifter R2.

  In each of the two phase shifters R1 and R2, the phase difference generated between the orthogonal polarization components depends on the frequency. For this reason, a channeled spectrum including three carrier components is obtained from the spectroscope functioning as an optical spectrum analyzer. The amplitude and phase of each carrier component are modulated by the spectral polarization parameter of the sample. Therefore, each spectral polarization parameter can be obtained by performing signal processing using Fourier transform on a computer.

  An example of the result of the experiment is shown in FIG. 2 (cited from Non-Patent Document 2). This is the measurement of the ellipsometric parameter Ψ, which is the spectral polarization parameter of the thin film sample, and the characteristics Ψ (λ), Δ (λ) with respect to the wavelength λ, by measuring the reflected light of the thin film sample. . The two solid lines in FIG. 2 indicate the ellipsometric parameters Ψ (λ) and Δ (λ), respectively. It will be appreciated that the spectral polarization parameter of the sample varies with frequency.

  Further, by fitting the measured ellipsometric parameters ψ (λ) and Δ (λ) with theoretical values, a result with a film thickness of 52.6 nm is obtained (theoretical values are dotted lines in FIG. 2). In this film thickness calculation, the film thickness value was used as a fitting parameter, and the film thickness value with the smallest square error between the measured value and the theoretical value was obtained. The measurement result is relatively close to the value of 49.3 nm measured by the conventional rotary phase shifter method.

  As described above, according to the channeled spectroscopic polarimetry, the spectral polarization parameter of the sample can be obtained by frequency analysis (or wave number analysis) of the characteristic of the spectral light quantity. However, prior to frequency analysis, it is necessary to obtain retardation in advance for each of the two phase shifters R1 and R2. Here, the retardation is a phase difference generated between the fast axis component and the slow axis component.

According to the above-mentioned channeled spectroscopic polarimetry, [1] a mechanical movable element such as a rotary phase shifter is unnecessary, and [2] an active element such as an electro-optic modulator is unnecessary. In addition, [3] four Stokes parameters can be obtained from one spectrum at a time, so-called snapshot measurement can be performed, and [4] the configuration is simple and suitable for miniaturization. Further, the retardations of R1 and R2 do not change even when the inclination of the sample is changed, thereby enabling measurement with a small measurement error.
JP 2006-308550 A Takayuki Kato, Kazuhiko Oka, Satoshi Tanaka, Yoshihiro Otsuka, "Spectral distribution measurement of polarized light based on frequency domain interferometry," Proceedings of the 34th Annual Meeting of the Japan Society of Applied Physics Hokkaido (Sapporo, 1998, Japan Society of Applied Physics, Sapporo, 1998) ), P.41 H. Okabe, K. Matoba, M. Hayakawa, A. Taniguchi, K. Oka, H. Naito, N. Nakatsuka, "New configuration of channeled spectropolarimeter for snapshot polarimetric measurement of materials", Proceedings of SPIE, Vol.5878, August 31, 2005, p. 58780H

  However, in the channeled spectroscopic polarimetry shown in Patent Document 1 and Non-Patent Document 2, the theory about the cause of the measurement error has not been sufficiently studied, and is therefore optimal for measuring with high accuracy. The thickness ratio of the two phase shifters is unknown.

  As shown in Non-Patent Document 2, when the thickness ratio of the two phase shifters is set to 2: 1, the retardation δ (σ) of the birefringent sample is measured and compared with the true value. Measurement accuracy was evaluated. Here, σ is the reciprocal of the wavelength λ, and hereinafter referred to as the wave number. Note that the method for obtaining the retardation δ (σ) of the birefringent sample by using the channeled spectroscopic ellipsometry is specified in paragraph 0226 and subsequent paragraphs of Patent Document 1, and is omitted here.

  FIG. 3 shows the result of δ (λ) obtained by converting the horizontal axis of the measured value δ (σ) into the wavelength axis. Channeled spectroscopic polarimetry by comparing the measurement results under the same conditions with the two methods of the channeled spectroscopic ellipsometry (dotted line) and the rotation compensator method (solid line), which is one of the general measuring methods. The measurement accuracy of was confirmed. As can be seen from the results of FIG. 3, when measuring the retardation of a birefringent sample, a large measurement error occurs compared to the conventional method. This error is reproducible and is considered to be a systematic error caused by the measurement principle.

Also, in the experimental result of calculating the film thickness of Non-Patent Document 2 shown in FIG. 2, there is a slight difference from the experimental result of 52.6 nm with respect to the value of 49.3 nm measured by the conventional rotary phase shifter method. It can be estimated that the system spectroscopic polarimetry includes a systematic error due to the measurement principle.
Thus, there existed errors that could not be explained by conventional theories.

  The present invention has been made paying attention to the above-mentioned problems, and the object of the present invention is to reduce errors that appear when a conventional channeled spectroscopic polarimeter is used, and to achieve higher accuracy. An object of the present invention is to provide an apparatus and a method that enable spectroscopic polarimetry.

  Still other objects and operational effects of the present invention will be easily understood by those skilled in the art by referring to the following description.

The polarization spectrometer according to the present invention includes a light source, a polarizer, a first phase shifter, and a second phase shifter, wherein light emitted from the light source is a polarizer, a first phase shifter, and a second phase shifter. The first phase shifter is arranged so that its main axis direction is different from the direction of the transmission axis of the polarizer. The second phase shifter is made of the same material as the first phase shifter, and is fixedly arranged such that its main axis direction is different from the main axis direction of the first phase shifter. An optical optical system; an analyzer that transmits light emitted from the light projecting optical system and reflected or transmitted in the measurement target region; and a means for obtaining a spectral light amount of the light transmitted through the analyzer. D ₁ the thickness of the retarder, the first retarder and the thickness is taken as D _2, the ratio of D ₁ and D _{2 are, 17/7 ≦ D 1 /} D 2 ≦ 7,9 / 7 ≦ any of _{D 1 / D 2 ≦ 5/} 3 It is intended to meet the.

  Here, the “analyzer” is an optical element that exhibits different transmittances with respect to polarization components that are orthogonal to each other, and is not limited to a plate-like or film-like one. For example, a polarizing beam splitter can be used as an “analyzer”. As the “means for obtaining the spectral light amount”, a spectroscope may be used, or a light source whose wavelength is scanned may be used. The light receiver in the case where a light source whose wavelength is scanned is used as long as it can detect the amount of received light, and the detection timing of the received light amount is associated with the wavelength of light.

  If such a polarization spectrometer is used, the measurement result of the spectral polarization parameter resulting from the measurement principle is obtained by setting the ratio of the thickness of the first phase shifter and the thickness of the second phase shifter to at least the above range. It is possible to reduce the systematic error included in.

For reasons described herein, the ratio of the D ₁ and D ₂ are substantially most preferable if it meets the D ₁ / D ₂ = 3.

  Combining the polarized light spectroscopic device with an arithmetic device for obtaining at least one of the spectral polarization parameters of the measurement object arranged in the measurement target region using the spectral light amount obtained by the polarization spectroscopic device, Can be obtained.

  Here, the “arithmetic apparatus” may be an apparatus integrated with the polarization spectrometer, or may be installed at a location different from the polarization spectrometer via a network or the like.

  The “measurement object” includes a sample whose spectral polarization characteristic is unknown and that is to be subjected to spectral polarization measurement, and a polarizing element whose spectral polarization characteristic is known, such as a phase compensator, is placed on the optical path. In some cases, such a polarizing element is also included in the “measurement object”.

  An optical device including a light projecting optical system and an analyzer of the polarization spectroscopic device or a light projecting device including a light projecting optical system of the polarization spectroscopic device realizes a characteristic thickness ratio of the phase shifter. The unit can solve the problem by measuring the spectral polarization parameter using these units.

  The spectral polarization measurement method of the present invention includes a step of preparing a measurement object, a step of preparing the polarization spectroscopy device, and a step of obtaining a spectral light amount of the measurement object using the polarization spectroscopy device. It is.

  In order to actually obtain the measurement result, in addition to the spectral polarization measurement method, a step of obtaining at least one of the spectral polarization parameters of the measurement object may be executed using the obtained spectral light quantity. This step may be executed at a place different from the step until the spectral light amount is obtained or at a time interval.

In the step of determining at least one of the spectral polarization parameters of the measurement object, the fast axis transmission and the slow axis transmission of the second phase shifter are used according to the theory disclosed in section 2 of this specification. Or, more specifically, using the arc tangent (γ ₂ (σ)) of the ratio of the fast axis transmission to the slow axis transmission of the second phase shifter. You may make it do. In this case, a case in which a mathematically equivalent operation is performed although the expression is different from the theoretical formula disclosed in the present specification is also included.

In the step of obtaining at least one of the spectral polarization parameters of the measurement object, a correction operation for removing the influence of the γ ₂ error term may be performed. The “γ ₂ error term” is described in section 3.2 of this specification. In this way, the systematic error due to the measurement principle can be further reduced for the reason detailed in Section 3.2.

  By using a spectroscopic polarization measurement device in which the thickness ratio of the two phase shifters is appropriately designed, systematic errors included in the measurement result of the spectroscopic polarization parameter due to the measurement principle can be reduced.

  First, in Section 1, the method of Patent Document 1 is generalized and described. Although the explanation in this section is mathematically equivalent to Patent Document 1, in order to develop the theory that leads to the present invention, Patent Document 1 is generalized and the theoretical formula is reconstructed. Next, in Section 2, a theoretical formula that considers error factors that were not considered in the conventional theoretical formula will be described. Section 3 describes the configuration of the invention derived from the new theoretical formula, and finally Section 4 describes experimental verification of the error reduction effect.

1 Theory for calculating the spectral polarization parameter of a sample: conventional theory FIG. 1 shows the configuration of a polarization spectrometer shown in Patent Document 1. Except for the thickness ratio of the phase shifter which is not shown, the configuration shown in FIG. 1 is also a configuration common to the present invention. The optical system shown in FIG. 1 includes a light source 7, a polarizer P, phase shifters R 1 and R 2, an analyzer A, and a spectrometer 8. The light emitted from the light source 7 passes through the polarizer P, the phase shifter R1, and the phase shifter R2 in order, reflects or transmits the sample D, passes through the analyzer A, and enters the spectroscope 8. Thereafter, the spectrum of the incident light is acquired by the spectroscope 8, and the spectral polarization parameter and the like of the sample are calculated by the procedure described later.

  The directions of the fast axes of the phase shifter R1 and the phase shifter R2 are inclined by 45 °, and the direction of the transmission axis of the polarizer P coincides with the direction of the fast axis of the phase shifter R2. In the figure, the fast axis of the phase shifter is represented as “fast” and the slow axis is represented as “slow”. Further, θ is the azimuth angle of the transmission axis of the analyzer with respect to the fast axis of the phase shifter R2.

  Here, the phase shifter is an element having a property of changing a phase difference between linearly polarized light components orthogonal to each other before and after transmission through the element. This amount of change in phase difference is called retardation. The coordinate axes taken along the two linearly polarized directions are called main axes, and the axis along the linearly polarized light whose phase advances relatively fast is called the fast axis and the other axis is called the slow axis.

  Here, the “spectral polarization parameter” is used in the present specification to mean a parameter representing the spectral polarization characteristic of the measurement object. This is a general term for parameters used to quantitatively represent a change in polarization caused by reflection or transmission of an object to be measured. Ellipsometric parameters Ψ (σ), Δ (σ) and retardation δ (σ) of the birefringent medium are examples of spectral polarization parameters. In general, the spectral polarization characteristic of the measurement object is completely expressed by 16 elements of a 4 × 4 Mueller matrix, but there are few cases where these 16 elements are all independent variables. Often, all these factors are determined from only a few parameters at most. Practically, these independent parameters may be obtained as the spectroscopic polarization parameters. Furthermore, there are applications in which it is sufficient to obtain only a part of the spectral polarization parameter regardless of whether it is independent or non-independent.

と記述する。 At this time, the Mueller matrix of the sample

Is described.

A Stokes parameter is used as a parameter for more efficiently expressing the degree of polarization of light, ellipticity angle, azimuth angle, and the like. This Stokes parameter is composed of four parameters having the following definitions.
S ₀ : Total strength
S ₁ : Difference in azimuth 0 °, 90 ° linear polarization component intensity
S ₂ : Azimuth ± 45 ° Difference in linearly polarized light component intensity
S ₃ : Difference in intensity of left and right circularly polarized light components

Assuming a sphere with a radius S ₀ centered at the origin in a three-dimensional space in which three axes orthogonal to each other are S ₁ , S ₂ , and S ₃ , the polarization state of any light is one point in this three-dimensional space. And the degree of polarization is expressed by the following equation.
Polarization degree = (distance from the origin to the point _{(S 1, S 2, S} 3)) / S 0
= (S ² ₁ + S ² ₂ + S ² ₃ ) ^1/2 / S ₀

  Here, the Mueller matrix will be described with reference to FIG. The Mueller matrix is a matrix representing the interaction of light such as reflection or transmission to a sample or a polarizing element to be measured. As an example, light whose polarization state is represented by the Stokes parameter S (σ) as the polarization state 1 (State of Polarization 1) enters the sample, is affected by the measurement object such as a polarizing element or sample, and the polarization state Is emitted as a polarization state 2 (State of Polarization 2) represented by S ′ (σ) (see FIG. 4A). At this time, the Mueller matrix to be measured is expressed as a 4 × 4 matrix by the relational expression shown in FIG.

The theory of Patent Document 1 is to obtain the Mueller matrix to be measured from one spectrum.
1. Role of the light projecting department 2. Relationship between spectrum obtained by spectroscope and spectral polarization parameter of sample 3. Demodulation procedure of each signal component 4. Wavenumber resolution of spectral pseudo-Stokes parameters A description will be given in the order of examples of measurement samples.

1.1 Role of the projector-Channeled spectrum polarization state generator (CSPSG)
In this section, the role of the light projecting unit (light source 7, polarizer P, phase shifters R1 and R2) of the optical system is considered. This can be defined as a “polarization state generator” that emits light whose polarization state is modulated. This is specifically named “Channeled Spectroscopic Polarization State Generator (hereinafter referred to as CSPSG)”. This optical meaning will be described.

となる。ここで、φ_j(σ)（j=1,2）は移相子Ｒ_ｊ（j=1,2）のリタデーション、P₀(σ)は光源のスペクトルである。 FIG. 5 shows the configuration of the channeled spectrum polarization state generator CCSPG. This optical system is configured to transmit light emitted from the light source 7 through the polarizer P and the phase shifters R1 and R2, and has the same configuration as the components from the light source in FIG. Also, the azimuth angle of the element is the same as in FIG. In FIG. 5, the polarizer P, the phase shifter R1, and the phase shifter R2 are shown in close contact with each other, but actually, an air or adhesive layer is provided between the elements. Exists. At this time, the light emitted from the CSPSG is light whose polarization state is modulated along the wavenumber axis. The Stokes vector S _PSG (σ) emitted from the CSPSG is calculated by using the Mueller matrix of the polarizer P, the phase shifter R1, and the phase shifter R2.

It becomes. Here, φ _j (σ) (j = 1, 2) is the retardation of the phase shifter R _j (j = 1, 2), and P ₀ (σ) is the spectrum of the light source.

となる。ここで、D_j はＲ_jの厚さであり、Ｂ(σ)はその複屈折である。また、σ₀は被測定光の中心波数を示す。以下、移相子のリタデーションφ_j(σ)を基準位相関数とよぶ。 φ _j (σ) (j = 1, 2) can be decomposed into a term that changes linearly with a proportional coefficient 2πL _j with respect to the wave number σ and a term Φ _j (σ) that changes nonlinearly as in the following equation.

φ _j (σ) = 2πB (σ) D _j σ = 2πL _j σ + Φ _j (σ), (3)

However,

It becomes. Here, D _j is the thickness of R _j , and B (σ) is its birefringence. Further, σ ₀ indicates the center wave number of the light to be measured. Hereinafter, the retardation φ _j (σ) of the phase shifter is referred to as a reference phase function.

ただし、

となる。式（６）より、ＣＳＰＳＧから出射される光は、次の３つの特徴をもつ、波数軸に沿って変調された光であることがわかる。（ａ） S₁(σ) は周期１／Ｌ_１で擬似正弦的に変調されている。（ｂ）S₂(σ) とS₃(σ) は、両者とも、周期１／Ｌ₋と１／Ｌ_＋の、２つの擬似正弦的に変調された成分からなっている。（ｃ） S₂(σ) とS₃(σ) において、同じ周期の擬似正弦成分は、初期位相が互いに９０度異なっている。よって、ＣＳＰＳＧから出射された光は、４つストークスパラメータそれぞれが独立に異なる周期又は位相で変調された光と考えることができる。これより、このＣＳＰＳＧは完備な偏光状態発生器と言える。従来の構成は、この完備な偏光状態発生器であるＣＳＰＳＧと光源と検光子と分光器とを組み合わせ、測定対象物の分光偏光パラメータを求める構成であると定義することができる。 Now, if the dispersion of B (σ) (rate of change with respect to wave number) is not so large, Φ _j (σ) becomes small, and as can be seen from equation (3), φ _j (σ) is almost equal to wave number σ. It will increase linearly. Substituting equation (3) into equation (2),

However,

It becomes. From the equation (6), it can be seen that the light emitted from the CSPSG is light modulated along the wavenumber axis having the following three characteristics. (A) S ₁ (σ) is modulated in a pseudo-sinusoidal manner with a period 1 / L ₁ . (B) S ₂ (σ) and S ₃ (σ) both consist of two pseudo-sinusoidally modulated components with periods 1 / L ₋ and 1 / L ₊ . (C) In S ₂ (σ) and S ₃ (σ), the initial phases of pseudo-sine components having the same period differ from each other by 90 degrees. Therefore, the light emitted from the CSPSG can be considered as light in which each of the four Stokes parameters is independently modulated with a different period or phase. Thus, it can be said that this CSPSG is a complete polarization state generator. The conventional configuration can be defined as a configuration in which the complete polarization state generator, CSPSG, a light source, an analyzer, and a spectrometer are combined to obtain a spectral polarization parameter of a measurement object.

1.2 Relationship between spectrum obtained by spectroscope and spectral polarization parameter of sample In this section, a spectrum obtained by a spectroscope will be described with reference to FIG. The light emitted from the CSPSG is incident on a block composed of a sample to be measured and a polarization state analyzer (PSA), hereinafter referred to as PSA, and the light transmitted through (or reflected by) the block is spectrally separated. Is incident on the vessel. Here, the polarization state measuring instrument (PSA) is the name of the optical system installed between the sample to be measured and the photoelectric element in order to measure the polarization state (refer to “Polarized Light Second Edition”). (2nd edition) ”Dennis Goldstein (P.533-534). Hereinafter, a block obtained by combining the sample and the PSA is referred to as an S-PSA (sample and PSA) block. A polarizing element having a known spectral polarization parameter may be installed in front of or behind the sample. Here, it is assumed that the change of the spectral polarization parameter of the S-PSA block on the wavenumber axis is sufficiently smaller than the fluctuation of the polarization state of the outgoing light from the CSPSG, and the spectral polarization parameter of the S-PSA block is obtained. Let M ^a (σ) be the Mueller matrix of the entire S-PSA block multiplied by the Mueller row example of each element of the S-PSA block. At this time, the spectrum obtained by the spectroscope is expressed by the following equation.

ここで

となる。n₀(σ)、n_-(σ)、n₁(σ)、n₊(σ)は分光器が細かい振動成分に十分ついていけないことによる減衰振幅率を示し、以下では基準振幅関数と呼ぶ。式（１２）からわかるように、分光器から得られるスペクトルP(σ)には、４つの成分が含まれている。このうちの１つは波数σに対して緩やかに変動する成分であり、m^a ₀₀(σ)に関する情報が含まれている。残りの３つは、波数σに対して振動する擬似正弦的な成分となっており、m^a ₀₁(σ)又はm^a ₂₃(σ)に関する情報をもっている。これらを模式的に示したのが図７である。よって、信号P(σ)の各成分の振幅と位相を復調すれば、受光したスペクトルP(σ)よりM^a(σ)の１行目の４要素m^a _0k (k = 0,1,2, 3)を求められることがわかる。なお、これら４要素m^a _0k (k = 0,1,2, 3)を特許文献１では試料の分光擬ストークスパラメータと命名していた。以下、本明細書でも便宜上、分光擬ストークスパラメータと命名する。この４つの分光擬ストークスパラメータの復調の手順を次節で説明する。 This indicates that the obtained spectrum P (σ) depends on the four elements in the first row of M ^a (σ). In the above equation, it is assumed that the spectroscope can measure the amplitude of the fine vibration component without attenuation. Substituting equation (2) into equation (11) and taking into account the attenuation of the amplitude of the vibration component during measurement with the spectrometer,

here

It becomes. n ₀ (σ), n ₋ (σ), n ₁ (σ), and n ₊ (σ) indicate the attenuation amplitude rate due to the spectroscope not being sufficiently attached to the fine vibration component, and hereinafter referred to as a reference amplitude function. As can be seen from the equation (12), the spectrum P (σ) obtained from the spectroscope includes four components. One of these is a component that fluctuates gently with respect to the wave number σ, and includes information about m ^a ₀₀ (σ). The remaining three are pseudo-sinusoidal components that vibrate with respect to the wave number σ, and have information on m ^a ₀₁ (σ) or m ^a ₂₃ (σ). These are schematically shown in FIG. Therefore, if the amplitude and phase of each component of the signal P (σ) are demodulated, the four elements m ^a _0k (k = 0,1,2) in the first row of M ^a (σ) from the received spectrum P (σ). , 3) is required. Note that these four elements m ^a _0k (k = 0, 1, 2, 3) are named as spectral pseudo-Stokes parameters of the sample in Patent Document 1. Hereinafter, for the sake of convenience, this specification will also be referred to as a spectral pseudo-Stokes parameter. The procedure for demodulating these four spectral pseudo-Stokes parameters will be described in the next section.

1.3 Demodulation procedure for each signal component As one procedure for signal processing for demodulation of the four spectral pseudo-Stokes parameters m ^a _0k (k = 0, 1, 2, 3), the “Fourier transform method” is used. This will be described with reference to FIG.

ただし、

である。ここで、hは光路差である。この相関関数C(h)は、図８の右上部に示されるように、各振動成分の周期の逆数０，±Ｌ₋，±Ｌ_１，±Ｌ_＋を中心とする７つの成分を含むこととなる。 In this method, the spectrum P (σ) measured by the spectroscope in the channeled spectropolarimeter is first subjected to inverse Fourier transform. The result is a correlation function of the incident light from the spectrometer.

However,

It is. Here, h is an optical path difference. This correlation function C (h) includes seven components centered on reciprocals 0, ± L ₋ , ± L ₁ , ± L ₊ of the period of each vibration component, as shown in the upper right part of FIG. It becomes.

となる。よって、偏光計自体の特性のみで決まるパラメータである、

を測定前に較正しておけば、４つの分光擬ストークスパラメータm^a _0k (k = 0,1,2,3)が、上式より求められることがわかる。 Here, if the reciprocals 0, ± L ₋ , ± L ₁ , ± L ₊ of these periods are appropriately designed, the components included in C (h) can be separated from each other on the h axis. Note that the reciprocal of the period is determined by the birefringence and thickness of the phase shifter from Equation (4). Of these, four components centered on h = 0, L ₋ , L ₁ , L ₊ are extracted and each is Fourier transformed.

It becomes. Therefore, it is a parameter determined only by the characteristics of the polarimeter itself.

Is calibrated before measurement, it can be seen that four spectral pseudo-Stokes parameters m ^a _0k (k = 0, 1, 2, 3) can be obtained from the above equation.

  Note that the procedure for calibrating the reference amplitude function and the reference phase function before the measurement is described in Patent Document 1, and is therefore omitted here.

1.4 Wavenumber Resolution of Spectral Pseudo-Stokes Parameter The wavenumber resolution of the obtained parameter is an important index in the performance of the spectroscopic polarimeter. However, in the channeled spectroscopic polarimetry apparatus, the spectrum pseudo-Stokes parameter is obtained after processing of inverse Fourier transform and Fourier transform, as shown in FIG. The frequency characteristic is the parameter characteristic to be obtained. The frequency characteristic of this spectral pseudo-Stokes parameter is equivalent to the wave number resolution in other types of spectropolarimeters, and there is no difference from the wave number resolution from the user's standpoint. This is called the wave number resolution of the Stokes parameter. Note that in the channeled spectroscopic polarimeter, the wave number resolution of the spectroscope and the wave number resolution of the spectral pseudo-Stokes parameter are different values.

  In this section, the factors that determine the wave number resolution of the obtained spectral pseudo-Stokes parameter will be described with reference to FIG. 8 used in the previous section. In addition, when considering the wave number resolution of the spectroscope, the optimum thickness ratio of the phase shifter that can apply the wave number resolution of the spectral pseudo-Stokes parameter to the highest frequency will be described.

First, what is determined by the wave number resolution of the spectral pseudo-Stokes parameter will be described. As described in the previous section, the spectral pseudo-Stokes parameter is obtained by Fourier transform of the extracted components as shown in the lower right part of FIG. Here, in the process of extracting each component from the upper right part to the lower right part in FIG. 8, the function C (h) is obtained by integrating a window function having a constant width and the center of which coincides with the center of the component. Examples of the window function include a rectangular window, a Hanning window, and a Hamming window that are generally used in Fourier transform. The characteristics of this window function are not described here because they are described in a special book on Fourier transform. What is important here is that the wave number resolution of the obtained spectral pseudo-Stokes parameter is determined by the width of the window function due to the characteristics of the Fourier transform. The wider the window function, the higher the wave number resolution of the spectral pseudo-Stokes parameter obtained after Fourier transformation. Conversely, in order to increase the wave number resolution, it is necessary to widen the width of the window function used when extracting each component. However, if the window function is too wide, other components will be mixed, resulting in measurement errors. Therefore, the width of the window function is limited by the interval of each component on the h-axis, as is apparent from the upper right part of FIG. Therefore, the wave number resolution of the spectral pseudo-Stokes parameter is determined by the interval where the interval between the components on the h-axis is the narrowest. As described above, the center positions L ₋ , L ₁ and L ₊ of each component are determined by the thickness of the phase shifter from the equations (4), (7), and (8). The thickness design is important.

Next, the thickness ratio of the phase shifter that provides the highest wave number resolution will be described. If the interval between each component is made as wide as possible, the wave number resolution becomes high, but there is a limitation on the resolution of the spectrometer at that time. Therefore, an allowable design upper limit value of L ₊ having the highest vibration period among the components is limited by the resolution of the spectrometer. At this time, since the wave number resolution is determined by the narrowest part among the intervals of the respective components, the design in which the intervals of the respective components are equally spaced is the optimum design. In order to make the interval of each component equal, it can be found from the equations (4), (7), and (8) that the thickness ratio of the two phase shifters is 2: 1.

となる。この方程式を解くと、試料のエリプソメトリックパラメータΨ(σ)，Δ(σ)は

となり、m^a _0k (k = 0,1,2,3)より求められることが理解できる。この実験結果が先に説明した非特許文献２に明記されている図２の計測結果となる。 1.5 Example of measurement sample As an example in Non-Patent Document 2, a thin film sample is used as the sample, an analyzer is used as the PSA, and the light reflected from the sample is received by the spectroscope through the PSA. An optical system for measuring Ψ (σ) and Δ (σ) is shown (FIG. 9). When the azimuth angle of the analyzer is 45 °, the four spectral pseudo-Stokes parameters multiplied by the Mueller matrix of each element of the S-PSA block are

It becomes. Solving this equation, the ellipsometric parameters Ψ (σ) and Δ (σ) of the sample are

Thus, it can be understood that it is obtained from m ^a _0k (k = 0, 1, 2, 3). This experimental result becomes the measurement result of FIG. 2 specified in the nonpatent literature 2 demonstrated previously.

となる。この方程式を解くと試料の方位角αとリタデーションδ(σ)は、

となり、m^a _0k (k =0,1,2,3)より求められることが理解できる。 As another example, consider an optical system that measures the transmitted light of a sample having birefringence and measures the azimuth angle α and retardation δ (σ) of the birefringent sample (FIG. 10). As in the previous example, when the azimuth angle of the analyzer is 45 °, the four spectral pseudo-Stokes parameters are

It becomes. Solving this equation, the azimuth α and retardation δ (σ) of the sample are

Thus, it can be understood that it is obtained from m ^a _0k (k = 0, 1, 2, 3).

2 Theoretical Formula Considering Error Factors The inventors of the present invention have found an error factor that has not been derived by the conventional method and a theoretical formula including the factor.

In the conventional theory, the theoretical formula is derived on the assumption that the transmittance of the two phase shifters is the same. However, in practice, since the transmittance at the interface of the phase shifter is determined by the refractive index, the transmittance of the fast axis and the slow axis are naturally different. For example, when the phase shifter is calcite, the fast axis transmittance T _f (σ) and the slow axis transmittance T _s (σ) are 1.54 cm ⁻¹ (wavelength 650 nm), and T _f ( σ) = 0.92, T _s (σ) = 0.88. This difference in transmittance between the fast axis and the slow axis is an error factor that has not been derived by the conventional method. The transmittance here was calculated as the product of the transmittances of the front and rear interfaces of the phase shifter, assuming that the interface of each phase shifter is in contact with air.

と定義すると、式（１２）で求めていた分光器から得られるスペクトルP(σ)は次式の形に変わる。

In order to explain this error factor, a theoretical formula that takes into account the difference in transmittance between the fast axis and the slow axis is derived below. The inverse tangent of the ratio of the transmittance of the fast axis and the slow axis of the two phase shifters R1, R2 is γ ₁ and γ ₂

Is defined, the spectrum P (σ) obtained from the spectroscope determined by the equation (12) changes into the following equation.

In the above formula, the amplitude of each vibration _{component, sin2γ 1 sin2γ 2, sin2γ 1} , or Sin2ganma ₂ is the coefficient of Cos2ganma ₁ are accumulated, they reference amplitude function and _{n - (σ), n 1} (σ) , N ₊ (σ), or n ₂ (σ) are collectively calibrated and may be considered to be included in the reference amplitude function. Therefore, Expression (36) takes the form of the following expression.

Here, the value of γ ₂ is a parameter determined only by the characteristics of the polarimeter itself. For example, the refractive index of the phase shifters R1 and R2 and the refractive index of the medium (air or adhesive) existing before and after R1 and R2. It can be calculated more theoretically. Therefore, it is possible to obtain γ ₂ in advance and substitute it into the expression (37). From the expression (37), the first line of M ^a (σ) can be calculated in the same way as the expression (12). It seems that four elements are required. However, it can be explained from Equation (37) that there is an unavoidable error component depending on the thickness ratio of the two phase shifters. Hereinafter, this error component and a method for avoiding this error will be described.

FIG. 11 shows a schematic diagram of a power spectrum and a formulation of a channeled spectrum (Equations (37) and (12)) when the dependency on transmittance is taken into consideration and when not taken into consideration. Five terms of equation (37), in order from paragraph, DC component, L _- component, _{L 1} component, _{L +} components, is _{L 2} component. Considering the crystal axis dependence of the transmittance of the phase shifter, the existence of a vibration component (carrier frequency L ₂ : cos (φ ₂ −Arg (m ₂₃ ))) that should not exist if not considered becomes clear. Hereinafter, this vibration component is referred to as a “fifth vibration component”. Since the carrier frequency is proportional to the thickness of the phase shifter as shown in Equation (4), depending on the thickness of the phase shifter, this “fifth vibration component” (L ₂ ) is a vibration component ( _{L -, L 1, L +} ) and overlap (Figure 12). If the thickness of the phase shifters R1 and R2 is D ₁ and D ₂ , respectively, when the thickness of the phase shifter is D ₂ : D ₁ = 1: 2, L ₂ = L ₋ and the vibration components overlap, An error occurs in the polarization measurement. The error seen in the "Previous Issues" is due to this overlap.

3 Invention Configuration 3.1 Optimization of Thickness Ratio of Phase Shifter To cope with newly found error factors, vibration components (L ₋ , L ₁ , L ₊ ) used for polarization measurement and not used for polarization measurement ” The phase shifter thickness ratios D ₁ and D ₂ are set to appropriate values so that the fifth vibration component “(L ₂ ) does not overlap (FIG. 13). In other words, the phase shifter thickness ratios D ₁ and D ₂ are set to appropriate values so that the five terms represented by the equation (37) can be decomposed independently of each other by the Fourier transform method. Thus, the error by the difference in the transmittance | permeability can be avoided by making the thickness of a phase shifter suitable.

The optimum thickness ratio is when the wavenumber resolution is highest as discussed in section 1.4. Based on the same concept as in Section 1.4, the optimal thickness ratio is when the intervals of the five components including the DC component are equal. Therefore, D ₁ / D ₂ = 3 (D ₁ : D ₂ = 3: 1) (FIG. 14) in which the five components are equally spaced is the optimum thickness ratio. This is different from the optimum thickness ratio D ₁ / D ₂ = 2 when the difference in transmittance is not considered, that is, when the fifth vibration component (L ₂ ) is ignored.

Polarization measurement is possible even if the thickness ratio is not optimal. In order to set a phase shifter thickness ratio suitable for measurement, an interval between five components including a DC component is important. The idea of obtaining the appropriate thickness ratio range of the phase shifter will be described according to the following two concepts.
Concept 1: When considering the vibration frequency of the highest frequency component L ₊ out of the vibration components Concept 2: When considering the smallest interval among the components of the vibration component However, the results of the two ideas are the same.

[Concept 1]
Assuming that the L ₊ value that determines the resolution of the spectroscope required for the spectroscopic polarimeter is constant, the vertical axis indicates the thickness ratio D ₁ / D ₂ when D ₁ / D ₂ ≧ 1, and the horizontal axis indicates each vibration component _{L 1, L 2, L -} , was plotted _{L +.} In addition, on the right side of the graph, the narrowest width ΔL _min is plotted at the intervals of the peaks of each vibration component. The optimum thickness ratio is the ratio at which ΔL _min is the largest compared to the concept shown in Section 1.4. From the figure, it can be seen that D ₁ / D ₂ = 3 (D ₁ : D ₂ = 3: 1) where ΔL _min is the largest is optimal as described above.

Next, with respect to the wave number resolution obtained at the optimum thickness ratio D ₁ / D ₂ = 3, an appropriate thickness ratio will be shown based on the criterion that the thickness ratio that achieves a wave number resolution of 1/2 is inappropriate. This is because the degradation of the wave number resolution of about 1/2 is considered not to have a large difference in the practical value of the spectropolarimeter. In FIG. 15, the thickness ratio at which ΔL _min is 1/2 or less of the optimum value is indicated by hatching. As a list of mathematical expressions, ΔL _{min in} the case of D ₁ / D ₂ ≧ 1 is shown in FIG. 16 using L ₊ and the thickness ratio D ₁ / D ₂ . When ΔL _min = 1 / 4L ₊ at D1 / D2 = 3, the area where ΔL _min is 1 / 8L ₊ , which is 1/2, is obtained.

17/7 ≦ D ₁ / D ₂ ≦ 7 (38)

9/7 ≦ D ₁ / D ₂ ≦ 5/3 (39)

It is . The upper than the thickness ratio of D ₁ and D ₂ are formula (38), is satisfied or (39), while maintaining a certain wavenumber resolution, the difference in the transmittance of the fast axis and slow axis It is possible to remove the error caused by it.

[Concept 2]
Assuming that the specific application to which the invention is applied is determined, the wave number resolution of the parameter that needs to be obtained by the spectropolarimeter is given. FIG. 17 plots L ₁ , L ₂ , L ₋ , and L ₊ at various thickness ratios with a thickness ratio D ₁ / D ₂ ≧ 1, assuming that ΔL _min that determines the wave number resolution of the required parameters is constant. The resolution required for the spectroscope is determined by the vibration frequency of L _{+ which is} the highest frequency. The spectrometer resolution may be lowest when L ₊ is smallest. From FIG. 17, L ₊ is the smallest when D ₁ / D ₂ = 3 (D ₁ : D ₂ = 3: 1), and it can be considered that this thickness ratio is optimal.

It can also be seen that a high-resolution spectrometer is required in the vicinity of the thickness ratio D ₁ / D ₂ = 1, 2 or when the thickness ratio is large.

Therefore, an appropriate thickness ratio region should be indicated based on the criterion that the thickness ratio that requires a spectrometer with a resolution of at least twice the required resolution at the optimal thickness ratio D ₁ / D ₂ = 3 is inappropriate. To. This is because, in order to obtain a resolution of 2 times or more, it is necessary to increase the size of the spectrometer, so that it is necessary to increase the cost and the size of the apparatus. In FIG. 17, the thickness ratio at which L ₊ is twice or more the minimum value is indicated by hatching. As a list, L _{+ in} the case of D ₁ / D ₂ ≧ 1 is shown in FIG. 18 using ΔL _min and the thickness ratio D ₁ / D ₂ . When the region where L ₊ is doubled to 8ΔL _min with respect to L ₊ = 4ΔL _min at D ₁ / D ₂ = 3 is determined, the appropriate thickness of the phase shifter is

17/7 ≦ D ₁ / D ₂ ≦ 7 (42)

9/7 ≦ D ₁ / D ₂ ≦ 5/3 (43)

It is . The upper than the thickness ratio of D ₁ and D ₂ are formula (42), is satisfied or (43), keeping the wave number resolution, without significant increase in cost of the spectrometer, fast axis and slow It is possible to remove an error caused by a difference in the transmittance of the shaft.

3.2 Computation using the transmissivity of the fast axis and slow axis of the phase shifter When the overlap problem is solved, there still remains an error factor in equation (37). The error factor can be solved by incorporating the transmissivity of the fast axis and slow axis of the phase shifter into an arithmetic expression for calculating the spectral pseudo-Stokes parameter. This section describes the error factors and calculation methods to solve them.

と異なっている。よって、従来の計算手法だと、求めた擬ストークスパラメータm ^a ₀₀ (σ)及びm ^a ₀₁ (σ)にcos 2γ₂ m ^a ₀₁ (σ)及びcos 2γ₂ m ^a ₀₀ (σ)がそれぞれ誤差として加算される。この２つの付加項を「γ₂誤差項」とよぶ。補正については、事前にγ₂を求めておくことで、m ^a ₀₀ (σ)及びm ^a ₀₁ (σ)を変数とした連立方程式を解くと、誤差要因を除去したm ^a ₀₀ (σ)及びm ^a ₀₁ (σ)が求まる。連立方程式の解については容易であるため、割愛する。 When comparing Equation (12) and Equation (37), the parameters obtained from the components of the first and third terms are

Is different. Therefore, when it conventional calculation method, the obtained quasi-Stokes parameter m ^a ₀₀ (σ) and m ^a ₀₁ (σ) in _{^{cos 2γ 2 m a 01 (σ}} ) and _{^{cos 2γ 2 m a 00 (σ}} ) error, respectively Is added as These two additional terms are called “γ ₂ error terms”. For correction, by obtaining γ ₂ in advance, solving the simultaneous equations with m ^a ₀₀ (σ) and m ^a ₀₁ (σ) as variables, m ^a ₀₀ (σ) and m ^a ₀₁ (σ) is obtained. Since it is easy to solve the simultaneous equations, it is omitted.

Note that the transmittance of the fast axis and the slow axis of the phase shifter can be obtained mainly by using one of the following three methods.
(1) It is calculated theoretically using the refractive index of the phase shifter available from literature and the refractive index of the medium existing before and after the phase shifter.
(2) Measurement is performed in a state where the spectral pseudo-Stokes parameter is known, and γ ₂ is obtained from the coefficient (or the first term) of cos φ ₁ (σ) in the third term obtained by the equation (37). If the spectral pseudo-Stokes parameter is known, there are two unknowns (γ ₂ and n ₁ (σ)) in the coefficient of cosφ ₁ (σ), so by measuring two or more states, I want.
(3) When the medium before and after the phase shifter is air, the transmittance is directly measured using a device capable of measuring the transmittance.

4. Experimental Demonstration of Error Reduction Effect FIG. 19 shows the result of measuring retardation of a birefringent sample with the thickness of the phase shifter set to D ₁ / D ₂ = 3. Compared to the case of D ₁ / D ₂ = 2 shown in FIG. 3, the error with the rotation compensator method (RCE) could be greatly improved.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. A configuration diagram of an embodiment of the spectroscopic polarimeter is shown in FIG. As shown in the figure, this apparatus includes a light projecting side unit 200 and a light receiving side unit 300. In addition, 400 is a sample.

  The light emitting side unit 200 includes a power source 201, a light source 202 that is lit by being supplied with power from the power source 201, a pinhole plate 203 disposed on the front side in the emission direction of the light source 202, and light passing through the pinhole of the pinhole plate 203 A collimating lens 204 for collimating light, a shutter 205 on the front side of the collimating lens 204 for opening and closing the passing light, a polarizer 206 on which the light passing through the shutter is incident, and a first light through which the transmitted light from the polarizer is transmitted. The phase shifter 207 and the second phase shifter 208 are included.

  The light after passing through the second phase shifter 208 is emitted from the light projecting unit 200 and emitted toward the measurement target region, that is, the region where the sample is scheduled to be installed. When the sample 400 is installed in the measurement target region, the light transmitted through the sample 400 or reflected by the sample 400 is incident on the light receiving side unit 300.

  On the incident light path in the light receiving side unit 300, an analyzer 301 and a spectroscope 302 are installed in this order. Here, the relative angle between the direction of the fast axis of the second phase shifter 208 and the direction of the transmission axis of the analyzer 301 is set to be a known angle.

  In the spectroscope 302, a diffraction grating 302a that splits incident light, a CCD 302b on which light dispersed by the diffraction grating 302a is incident on a light receiving surface, and an A / D that converts a light reception output of the CCD 302b into a digital signal. Converter 302c. A digital light reception output signal obtained from the A / D converter 302c is taken out from the spectroscope 302 and processed by a computer 303 such as a personal computer (PC).

  As is well known, the computer 303 includes an arithmetic processing unit 303a configured by a microprocessor, a memory unit 303b configured by ROM, RAM, HDD, and the like, a display, a printer, various data output devices, a communication device, and the like. Measurement result output unit 303c.

  Next, FIG. 21 shows a more specific configuration diagram regarding the sensor head portion of the spectroscopic polarimeter. The sensor head unit 100 includes a light projecting unit 110 that emits light, a light receiving unit 120 that receives light reflected or transmitted from the sample, and a housing 130 that protects the light projecting unit 110 and the light receiving unit 120. Reference numeral 50 denotes a sample.

  The light projecting unit 110 converts the light emitted from a light source (not shown) through the optical fiber cable 111, the cable head 112 through which the light transmitted from the optical fiber cable 111 passes, and the light passing through the cable head 112 is converted into parallel light. A collimating lens (projecting lens) 115, a polarizer 116 on the front side of the collimating lens 115 that transmits incident light, a first phase shifter 117 and a second phase shifter 117 that sequentially transmit light emitted from the polarizer. , And an optical system holding member 113 and a mounting member 114 for mounting these optical systems on the housing 130. A solid line 119 is a light projection axis of light passing through the light projecting unit 110.

  The light receiving unit 120 includes an analyzer 122 that transmits light reflected or transmitted to the sample 50, a light receiving lens 123 that collects light transmitted from the analyzer 122, and a cable head 126 that passes light that has passed through the light receiving lens 123. And an optical fiber cable 127 connected to a spectroscope (not shown), an attachment member 124 for mounting these optical systems on the housing 130, and an optical system holding member 125. A solid line 121 is a light receiving axis of light reflected or transmitted by the sample 50.

Two pre-calibrations are performed before entering the measurement. A flowchart of the first pre-calibration procedure 1 is shown in FIG. First, in step 2001, γ ₂ is calculated from equation (35) using the transmittance of the phase shifter 118.

Next, in step 2002, the calculated γ ₂ is stored in the memory unit 303b, whereby pre-calibration 1 is completed.

  Next, a flowchart of the pre-calibration procedure 2 is shown in FIG. As shown in the figure, as a pre-calibration procedure, first, in step 2101, light is incident on the apparatus. However, in this apparatus, the relative angle between the direction of the fast axis of the second phase shifter 208 and the direction of the transmission axis of the analyzer 301 is a known angle, and the second phase shifter 208 and the analyzer It is assumed that no element that changes the polarization state of light is disposed between the element 301 and the element 301.

  Next, in Step 2102, the spectral light amount in the transmitted light from the analyzer 301 is measured with a spectroscope. At this time, the shutter 205 can be used to reduce the influence of unnecessary light such as stray light. Specifically, if the difference between the spectra measured in the shutter open and closed states is taken, the spectrum of unnecessary light is canceled.

  Next, in step 2103, the spectral light amount of the received light is transferred from the spectroscope to the computer 303 for use in computation in the arithmetic processing unit 303a.

Next, in step 2104, in the computer 303, the arithmetic processing unit 303a acquires γ ₂ from the memory unit 303b.

Next, in step 2105, by the arithmetic processing section 303a, from the spectral intensity and gamma ₂ of the received light, the reference phase functions and reference amplitude functions are calculated.

  Next, in step 2106, the calculated reference phase function and reference amplitude function are stored in the memory unit 303b, whereby the pre-calibration procedure 2 is completed.

  Next, a flowchart of the measurement procedure is shown in FIG. As shown in the figure, as a measurement procedure, first, in step 2201, light is incident on the apparatus.

  Next, in step 2202, the spectroscopic light quantity of the transmitted light that has passed through the analyzer 301 after being reflected or transmitted by the spectroscope 302 is measured. At this time, the shutter 205 can be used to reduce the influence of unnecessary light, for example, stray light. Specifically, if the difference between the spectra measured in the shutter open and closed states is taken, the spectrum of unnecessary light is canceled.

  Next, in step 2203, the spectral light quantity of the transmitted light is transferred from the spectroscope 302 to the computer 303 and used for processing in the arithmetic processing unit 303a.

Next, in step 2204, the computer 303, the arithmetic processing unit 303a acquires reference phase functions and reference amplitude functions and the gamma ₂ from the memory unit 303b.

Next, in step 2205, in the computer 303, the arithmetic processing unit 303 a calculates the change amount (Δφ ₂ and Δφ ₁ ) of the reference phase function using the measured spectral light amount and the reference phase function / reference amplitude function. Note that the theory and method for obtaining the amount of change in the reference phase function are omitted in this specification, but the same method as in Patent Document 1 can be applied, and is specified in paragraphs 0174 to 0216 of Patent Document 1.

Next, in step 2206, in the computer 303, the arithmetic processing unit 303 a calculates a spectral pseudo-Stokes parameter using the measured spectral light amount, the amount of change in the reference phase function / reference amplitude function, and γ ₂ .

  Next, in step 2207, in the computer 303, the arithmetic processing unit 303a outputs the spectral polarization parameter of the sample 400. At this time, examples of the measurement result output unit 303c include a memory, a hard disk, and other processing units (film thickness, complex refractive index calculation unit, etc.).

  As described above, in the spectroscopic polarimeter of this embodiment, the pre-calibration procedure shown in FIGS. 22 and 23 and the measurement procedure shown in FIG. 24 are performed in the system configuration shown in FIGS. Thus, the spectral polarization parameter of the sample is calculated.

It is a figure which shows the structure of a polarization spectrometer. It is a figure which shows the experimental result by the conventional apparatus. It is a figure which shows the measurement result of the retardation of the birefringent sample by the conventional apparatus. It is explanatory drawing regarding spectral polarization measurement. It is a block diagram of a channeled spectrum polarization state generator CCSPG. It is a figure explaining the spectroscopic polarimetry using CSPSG. It is explanatory drawing which shows the relationship between the channeled spectrum obtained from a spectrometer and its four components. It is explanatory drawing of a Fourier-transform method. It is a figure which shows the optical system which calculates | requires the ellipsometric parameter of a thin film sample. It is explanatory drawing regarding the measurement of the azimuth and retardation of a birefringent sample. It is a figure explaining the 5th vibration component produced by the crystal axis dependence of the transmittance | permeability of a phase shifter. It is a figure explaining that a vibration component overlaps with the thickness ratio of a phase shifter. It is a figure explaining the state where a vibration component does not overlap. It is a figure which shows the vibration component in case the thickness ratio of a phase shifter is 3: 1. It is a figure explaining the influence of the thickness ratio of a phase shifter when the vibration frequency L ₊ of the highest frequency vibration component is fixed. Is a diagram showing an equation for [Delta] L _min depending on the range of the thickness ratio of the retarder. Is a diagram illustrating the effect of retarders thickness ratio for fixed smallest spacing [Delta] L _min vibration components. It is a figure which shows the type | formula which calculates | requires L ₊ according to the range of the thickness ratio of a phase shifter. It is a figure which shows the result of having measured the retardation of the birefringent sample by applying this invention. It is a block diagram (the 1) of one Example of a spectroscopic polarimeter. It is a block diagram (the 2) of one Example of a spectroscopic polarimeter. 3 is a flowchart showing a pre-calibration procedure 1. 10 is a flowchart showing a pre-calibration procedure 2. It is a flowchart which shows a measurement procedure.

Explanation of symbols

7 Light source 8 Spectrometer 50 Sample 100 Sensor head 110 Projection unit 111 Optical fiber cable 112 Cable head 113 Optical system holding member 114 Mounting member 115 Collimator lens 116 Polarizer 117 First phase shifter 118 Second phase shifter 119 Light Emitting Shaft 120 Light Receiving Section 121 Light Receiving Shaft 122 Analyzer 123 Light Receiving Lens 124 Mounting Member 125 Optical System Holding Member 126 Cable Head 127 Optical Fiber Cable 130 Housing 200 Light Emitting Side Unit 201 Power Supply 202 Light Source 203 Pinhole Plate 204 Collimating Lens 205 Shutter 206 Polarizer 207 First phase shifter 208 Second phase shifter 300 Light receiving side unit 301 Analyzer 302 Spectroscope 303 Computer 302a Diffraction grating 302b CCD
302c A / D converter 303a Arithmetic processing unit 303b Memory unit 303c Measurement result output unit 400 Sample A analyzer D Sample that reflects or transmits light P Polarizer R1 Phase shifter R2 Phase shifter

Claims (14)

Light emitted from the light source passes through the light source, the polarizer, the first phase shifter, and the second phase shifter in the order of the polarizer, the first phase shifter, and the second phase shifter. The first phase shifter is fixedly arranged such that the principal axis direction thereof is different from the direction of the transmission axis of the polarizer, and the second phase shifter is arranged to be emitted toward the measurement target region. The phase shifter is made of the same material as the first phase shifter, and is fixedly arranged so that the principal axis direction thereof is different from the principal axis direction of the first phase shifter;
An analyzer that transmits light emitted from the light projecting optical system and reflected or transmitted in the measurement target region;
Means for obtaining a spectral light amount of light transmitted through the analyzer,
A first retarder and the thickness D _1, the second retarder and the thickness is taken as D _2, the ratio of D ₁ and D _2, and the
17/7 ≦ D ₁ / D ₂ ≦ 7,
9/7 ≦ D ₁ / D ₂ ≦ 5/3
A polarization spectrometer that satisfies any of the above. The ratio of the D ₁ and D ₂ are substantially satisfy D ₁ / D ₂ = 3, the polarimetric spectroscope according to claim 1. Light emitted from the light source passes through the light source, the polarizer, the first phase shifter, and the second phase shifter in the order of the polarizer, the first phase shifter, and the second phase shifter. The first phase shifter is fixedly arranged such that the principal axis direction thereof is different from the direction of the transmission axis of the polarizer, and the second phase shifter is arranged to be emitted toward the measurement target region. The phase shifter is made of the same material as the first phase shifter, and is fixedly arranged so that the principal axis direction thereof is different from the principal axis direction of the first phase shifter;
An analyzer that transmits light emitted from the light projecting optical system and reflected or transmitted in the measurement target region;
A polarization spectrometer comprising: means for obtaining a spectral light amount of light transmitted through the analyzer;
An arithmetic unit that obtains at least one of the spectral polarization parameters of the measurement object disposed in the measurement target region using the spectral light amount;
A first retarder and the thickness D _1, the second retarder and the thickness is taken as D _2, the ratio of D ₁ and D _2, and the
17/7 ≦ D ₁ / D ₂ ≦ 7,
9/7 ≦ D ₁ / D ₂ ≦ 5/3
A spectroscopic polarimeter that satisfies any one of the above. The ratio of the D ₁ and D ₂ are substantially satisfy D ₁ / D ₂ = 3, the spectroscopic polarimeter of claim 3. Light emitted from the light source passes through the light source, the polarizer, the first phase shifter, and the second phase shifter in the order of the polarizer, the first phase shifter, and the second phase shifter. The first phase shifter is fixedly arranged such that the principal axis direction thereof is different from the direction of the transmission axis of the polarizer, and the second phase shifter is arranged to be emitted toward the measurement target region. The phase shifter is made of the same material as the first phase shifter, and is fixedly arranged so that the principal axis direction thereof is different from the principal axis direction of the first phase shifter;
An analyzer that transmits light emitted from the light projecting optical system and reflected or transmitted in the measurement target region;
A first retarder and the thickness D _1, the second retarder and the thickness is taken as D _2, the ratio of D ₁ and D _2, and the
17/7 ≦ D ₁ / D ₂ ≦ 7,
9/7 ≦ D ₁ / D ₂ ≦ 5/3
An optical device that satisfies any of the following. The ratio between D ₁ and D ₂ are substantially satisfy D ₁ / D ₂ = 3, the optical device according to claim 5. Light emitted from the light source passes through the light source, the polarizer, the first phase shifter, and the second phase shifter in the order of the polarizer, the first phase shifter, and the second phase shifter. The first phase shifter is fixedly arranged such that the principal axis direction thereof is different from the direction of the transmission axis of the polarizer, and the second phase shifter is arranged to be emitted toward the measurement target region. The phase shifter is made of the same material as the first phase shifter, and is fixedly disposed such that the principal axis direction thereof is different from the principal axis direction of the first phase shifter.
A first retarder and the thickness D _1, the second retarder and the thickness is taken as D _2, the ratio of D ₁ and D _2, and the
17/7 ≦ D ₁ / D ₂ ≦ 7,
9/7 ≦ D ₁ / D ₂ ≦ 5/3
A floodlighting device that meets any of these requirements. The ratio of the D ₁ and D ₂ are substantially satisfy D ₁ / D ₂ = 3, the light projecting device of claim 7. Preparing a measurement object;
Light emitted from the light source passes through the light source, the polarizer, the first phase shifter, and the second phase shifter in the order of the polarizer, the first phase shifter, and the second phase shifter. The first phase shifter is fixedly arranged such that the principal axis direction thereof is different from the direction of the transmission axis of the polarizer, and the second phase shifter is arranged to be emitted toward the measurement target region. The phase shifter is made of the same material as the first phase shifter, and is fixedly arranged so that the principal axis direction thereof is different from the principal axis direction of the first phase shifter;
An analyzer that transmits light emitted from the light projecting optical system and reflected or transmitted in the measurement target region;
Means for obtaining a spectral light amount of light transmitted through the analyzer,
A first retarder and the thickness D _1, the second retarder and the thickness is taken as D _2, the ratio of D ₁ and D _2, and the
17/7 ≦ D ₁ / D ₂ ≦ 7,
9/7 ≦ D ₁ / D ₂ ≦ 5/3
Satisfy one of the steps of providing a polarimetric spectroscope,
Obtaining a spectral light amount for a measurement object using the polarization spectrometer;
A spectroscopic polarimetry method comprising: The ratio of the D ₁ and D ₂ are substantially satisfies D ₁ / D ₂ = 3, spectroscopic polarimetry according to claim 9.   The spectral polarization measurement method according to claim 9, further comprising a step of obtaining at least one of the spectral polarization parameters of the measurement object using the obtained spectral light amount.   The spectroscopic method according to claim 11, wherein in the step of obtaining at least one of the spectral polarization parameters of the measurement object, calculation is performed using the fast axis transmittance and the slow axis transmittance of the second phase shifter. Polarization measurement method. In the step of obtaining at least one of the spectral polarization parameters of the measurement object, the arc tangent (γ ₂ (σ)) of the ratio between the fast axis transmittance and the slow axis transmittance of the second phase shifter is used. The spectroscopic polarimetry method according to claim 11, wherein the calculation is performed. The spectral polarization measurement method according to claim 11, wherein in the step of obtaining at least one of the spectral polarization parameters of the measurement object, correction calculation is performed to remove the influence of the γ ₂ error term.

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