JP5116346B2 - Phase difference measuring device using a spectroscope - Google Patents

Description

  The present invention relates to a phase difference measuring device, and more particularly to a phase difference measuring device capable of determining a small phase difference with high accuracy.

The phase difference measuring apparatus has been used for phase difference film evaluation for a liquid crystal display (LCD), quality control of optical elements such as optical discs and plastics. Conventional phase difference measurement equipment mainly uses monochromatic light, but in recent years, characteristics over the entire visible light area, such as LCDs, have become important. The need for measurement is increasing.
The phase difference can be accurately measured by measuring using ellipsometry ellipsometry. However, ellipsometry is a mechanism for rotating a polarizer and a compensator at high speed, or a method for modulating polarization or phase such as a photoelastic modulator (PEM) or a left and right circularly polarized heterodyne interferometry, and for processing the acquired data at high speed This is a complicated and expensive method in principle. Furthermore, since this method is based on measurement data at a single wavelength, there is a problem that when wavelength dispersion measurement of a phase difference is necessary, wavelength scanning is performed with a monochromator or the like, so that high-speed measurement cannot be performed.

As an inexpensive phase difference measurement apparatus, for example, as disclosed in Non-Patent Document 1 and Patent Documents 1 and 2, a method of determining a phase difference using a spectrum obtained by a spectrophotometer or the like is known. . By this method, the phase difference can be measured in the required wavelength range, and the wavelength dispersion of the phase difference can be easily determined. However, in principle, this method, in which peaks and valleys of the spectrum are required to be observed in the measurement wavelength range due to phase difference interference, is not suitable for measuring a small phase difference of about several tens of nanometers or less. . In addition, since a normal spectrophotometer scans a wavelength with a monochromator, the measurement time is long.
West et al., Journal of Optical Society of America, vol. 39, p. 791-794 (1949). Japanese Patent No. 3777659 Japanese Patent Publication No.5-18370

  An object of the present invention is to provide a phase difference measuring apparatus that can easily and accurately measure a small phase difference.

That is, the present invention provides the following [1] to [7].
[1] A phase difference measuring apparatus including an optical system in which a light source, a polarizer, a sample stage, an analyzer, and a spectrometer are arranged in this order, and a calculation means,
A wave plate is disposed between the polarizer and the analyzer, and the retardation value of the wave plate is divided by an integer of 0.5 or more or a half integer at each of two or more wavelengths within the measurement wavelength range. A phase difference measuring device whose value matches the wavelength.
[2] The phase difference measuring apparatus according to [1], wherein the resolution F defined by the FWHM of the spectroscope and the maximum value n1 that the integer or half integer can take satisfy the following condition (B).
(B) F × n1 ≦ 50 nm

[3] The retardation measuring device according to [1] or [2], wherein the retardation value of the wave plate is 3 × λ min or more at a lower limit wavelength λ min of the measurement wavelength region.
[4] The phase difference measuring apparatus according to any one of [1] to [3], wherein the wavelength plate includes means for inserting and retracting with respect to an optical axis.
[5] The phase difference measuring apparatus according to any one of [1] to [4], wherein the spectrometer is a multichannel spectrometer including a diffraction grating and a one-dimensional light receiving array.

[6] A method for determining a phase difference of a sample from a spectrum measured by an optical system in which a light source, a polarizer, a sample, an analyzer, and a spectrometer are arranged in this order,
Select the wave plate product lambda ^x n ^x is the wavelength lambda ^x showing a retardation value of the wavelength plate with 0.5 or more integer or half-integer n ^x there are two or more in the measurement wavelength range Ramudamin～ramudamax,
Placing the waveplate between a polarizer and an analyzer.
[7] The method according to [6], wherein the wavelength plate and the optical axis of the sample are made coincident or orthogonal at the time of spectral measurement.

  According to the present invention, there is provided a phase difference measuring apparatus capable of easily and accurately measuring a small phase difference.

Hereinafter, the present invention will be described in detail.
In the present specification, “to” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value.
In the present specification, when an angle is described, an error from a strict angle may be within a range of ± 1 degree, and more preferably within a range of ± 0.1 degree.
0 degree represents a state in which the angles formed by the two axes are substantially parallel, and 90 degrees represents a state in which the angles formed by the two axes are substantially orthogonal.

Paranicol means that the angle formed by the transmission axis of the polarizer and the analyzer is 0 degree, and crossed Nicol means that the angle made by the transmission axis of the polarizer and the analyzer is 90 degrees. In the optical system used in the measuring apparatus of the present invention, the position where the incident light transmittance is the smallest and the position where the greatest incident light is crossed are respectively crossed with respect to the arrangement of the polarizer and the analyzer without the sample. In some cases, the positions are Nicol and Paranicol.
In this specification, “spectral spectrum” means “absorption spectrum”, “scattering spectrum”, “transmission spectrum”, and the like, and is preferably “transmission spectrum”.

[Principle of phase difference measurement]
The principle of determining the phase difference of the sample from the spectroscopic spectrum will be described below.
Optical characteristics such as the polarization state and the transmittance based on the polarization state can be described by a Jones matrix or a Mueller matrix. In the following, a description will be given using a Mueller matrix that can take into account the degree of depolarization. According to the Mueller matrix, the polarization state is described by a Stokes parameter, and the change of the polarization state by each element when passing through a retardation film, a polarizer, an analyzer or the like is described by a 4 × 4 Mueller matrix.
First, the light transmittance of the retardation film in which the polarizer and the analyzer are crossed Nicols and the optical axis is inclined by 45 degrees with respect to the transmission axis of the polarizer will be described.

If the transmission axis of the polarizer is the reference direction (0 degree),
The Mueller matrix Mp of the polarizer is described as in equation (1).

Similarly, the Mueller matrix Ma of the analyzer is described as shown in Equation (2).

The Mueller matrix Mr of the retardation film whose optical axis is inclined by 45 degrees with respect to the transmission axis of the polarizer is described as in Expression (3).

Here, Γ is a value represented by Expression (4).

In the formula, Re is a retardation of the retardation film, and λ is a measurement wavelength.
When the incident light is polarized light passing through the polarizer 100%, in other words, when the light passing through the polarizer is 100%, the Stokes parameter passing through the polarizer → retardation film → analyzer It becomes like 5).

  The first component of the above formula Sout is the light transmittance. That is, the light transmittance T (λ) is expressed by the following equation (6).

From equation (6), the polarizer T and the analyzer are crossed Nicols, and the light transmittance T (λ) of the film having a phase difference Re whose optical axis is inclined 45 degrees with respect to the transmission axis of the polarizer It can be seen that when Re / λ is an integer, 0 (transmittance 0%), and when Re / λ is a half integer, 1 (transmittance 100%). FIG. 1 shows an example of the spectral transmission spectrum of a sample (film) with Re = 2000 nm.
Similarly, the light transmittance of the retardation film in which the polarizer and the analyzer are paranicol and the optical axis is inclined by 45 degrees with respect to the transmission axis of the polarizer is expressed by the following formula (7).

From equation (7), it can be seen that, theoretically, Re / λ is 0 (transmittance 0%) when Re / λ is an integer, and 1 (transmittance 100%) when Re / λ is a half integer.
Therefore, when the polarizer, the sample, and the analyzer have any of the above arrangements, the wavelength at the valley position (transmittance 0%) and the wavelength at the peak position (transmittance 100%) in the spectral spectrum It can be seen that the value of the phase difference Re can be obtained by reading.

[Chromatic dispersion of phase difference]
When there is chromatic dispersion in the phase difference of the sample, the wavelength at the peak of the peak and valley in the spectrum is shifted from the wavelength explained in the above theory. For example, in the example of FIG. 1, when the phase difference is 2000 nm at 500 nm, the transmittance is 0% as shown in FIG. 1. However, if the phase difference at 400 nm is 2200 nm in terms of chromatic dispersion, the transmittance is 100 because it is a half integer multiple. %, Which is different from FIG. This 2200 nm is 5.5 times 400 nm, but one-fifth of 2000 nm is about 363 nm. Therefore, the peak of the mountain seen at 400 nm of the sample having this wavelength dispersion is outside the graph in FIG. The peak of the peak that should exist at 363 nm is shifted to the long wave side due to the increase in phase difference. Since the wavelength dispersion of the phase difference can be described by the Cauchy dispersion formula, it is preferable to use the Cauchy dispersion formula to obtain the phase difference by fitting from the transmission spectrum.

The Cauchy's dispersion formula is generally used to express the wavelength dependence (wavelength dispersion) of the refractive index, and is described as the formula (8).

Retardation is birefringence, that is, the difference between two different refractive indexes multiplied by the thickness d of the sample. Therefore, the Cauchy's dispersion formula can be applied as in the formula (*), as with the refractive index.

  Cauchy's dispersion formula often uses up to the 4th order of the wavelength, but in order to make fitting more simple and fast, it may be up to the 2nd order. It may be used. From the balance of accuracy and speed, it is preferable to use up to the fourth order. In addition to Cauchy's dispersion formula, the chromatic dispersion of the phase difference can be found in Handbook of optics (2nd ed.), Vol. 1 (McGraw-Hill) p. Any formula described in 33.61-33.84 or any sum of two or more can be used.

[Use of wave plate]
FIG. 2 shows an example of a spectrum of a sample (film) with Re = 100 nm. When the phase difference is reduced in this way, neither half-integer multiple nor integer multiple is observed in the measurement wavelength range, so that no peak is seen in the spectrum. Theoretically, the phase difference can be obtained using a spectrum where no peak is observed, but in reality, the absolute value of the spectrum changes due to the influence of measurement system noise, sample absorption, scattering, depolarization, etc. Therefore, the accuracy of the calculated phase difference is affected.

In the apparatus of the present invention, a wavelength plate is used in order to obtain a state in which a peak is observed in the spectrum of the measurement wavelength range. For example, it is possible to insert a known wave plate whose optical axis coincides with the optical axis of the sample.
The Mueller matrix Mwp of the wave plate whose optical axis is inclined by 45 degrees with respect to the transmission axis of the polarizer is as shown in Expression (10).

An optical system having a sample in which the polarizer and the analyzer are crossed Nicols, the optical axis is inclined by 45 degrees with respect to the transmission axis of the polarizer, and the wave plate whose optical axis is inclined by 45 degrees with respect to the transmission axis of the polarizer. The Stokes parameter is expressed by Equation (11).

であり、Re_wpは波長板の位相差を表す。

Re _wp represents the phase difference of the wave plate.

That is, the light transmittance T (λ) is expressed by the following equation (12).

As can be seen from equation (12), in the apparatus of the present invention, the phase difference is raised by the wave plate. The phase difference of the sample may be calculated by detecting a peak in the spectrum in the measurement wavelength range, determining the measured phase difference, and subtracting the phase difference of the wave plate.

[Phase difference measuring device]
Next, the outline of the phase difference measuring apparatus of the present invention will be described. The phase difference measuring apparatus of the present invention includes a light source, a polarizer, a sample stage, an analyzer, and a spectrometer, and these are preferably arranged in the order shown in FIG. Further, the phase difference measuring apparatus includes the above-described wave plate, and further includes an optical signal analyzing apparatus and the like as calculation means for performing the above correction, fitting and the like. As a calculation means, a method of analyzing as software on a computer, a method of analyzing with a dedicated board equipped with a memory and an arithmetic processor, or picking up several points that can be manually calculated for characteristic points such as peaks, etc. There is a means for determining the phase difference by itself so that the values match.

[light source]
The light source is preferably a white light source. The white light source is not particularly limited as long as it has an output in the measurement wavelength range rather than a narrow wavelength range such as a laser or LED. If the measurement wavelength range is a part of the visible range, it is not always visible. It does not have to be white. Examples of such a light source include a halogen lamp and a xenon lamp. Further, a plurality of color light sources may be mixed and used. Since the output of the light source changes depending on the input power supply and the environmental temperature, it is preferable that the change in luminance is 5% / hour or less after leaving the power supply for about 20 minutes to 1 hour. A stabilizing device is preferably used.

[Polarizer, Analyzer]
The polarizer does not require a rotation mechanism, but a rotation mechanism about the optical axis is preferable because it allows omnidirectional measurement. It is preferable that the analyzer has a rotation mechanism around the optical axis because the transmission axis of the analyzer needs to be paranicol or crossed Nicol with the transmission axis of the polarizer.
As a polarizer and an analyzer, it is desirable to have a high degree of polarization in a wide wavelength region because a spectroscope is used. Since the phase difference measuring apparatus of the present invention is less affected by the absolute value of the transmittance than the conventional apparatus, the degree of polarization may be 95% or more. The wavelength region having this degree of polarization is particularly preferably 390 to 800 nm. As long as it has this degree of polarization, the polarizer may be an absorptive polarizer or a reflective polarizer, but the analyzer is preferably an absorptive polarizer. Specifically, an iodine-based polarizer having a relatively high degree of polarization in a wide wavelength range, a dichroic dye polarizer using a dichroic dye, a Glan-Thompson polarizer as a prism polarizer, and a Grand Taylor polarization Examples of the polarizer and other polarizers include a wire grid polarizer and a dielectric polarizer, and iodine-type polarizers and prism-type polarizers having a wide wavelength range are preferable, and have a wider wavelength range and a required degree of polarization. An iodine polarizer is particularly preferred.

[Sample stand]
A sample stage is arranged between the polarizer and the analyzer, but the sample stage preferably has a rotation mechanism centered on the optical axis, and in order to measure the phase difference at oblique incidence, the entire sample stage is There is preferably a rotating mechanism.

[Wave plate]
The wave plate may be disposed on the polarizer side of the sample stage (FIG. 4) or on the analyzer side. It is preferable that the wave plate has a rotation mechanism around the optical axis and a uniaxial stage for retracting the wave plate from the optical axis. With the wave plate, it is possible to measure a sample having a small phase difference as described above. In addition, light sources and spectrometers have a slight polarization dependence that can affect spectral measurements, so between the light source and the polarizer and between the analyzer and the spectrometer in the measurement wavelength range. It is also possible to insert a depolarizer having as little absorption as possible.
The wave plate, the wave plate, measurement wavelength range λmin~ wavelength λx the product lambda ^x n ^x and n ^x is 0.5 or more integer or half-integer indicates the retardation value of the wavelength plate Two or more at λmax. That is, as the wave plate, a wave plate having at least one peak and one valley in the spectrum of the measurement wavelength region is selected.

Per above conditions are satisfied wavelength plate, a retardation wave plate (which may be a value without consideration of wavelength dispersion) and the measurement wavelength range, the maximum value n1 and the minimum value n2 which n ^x can take the following Can be decided. Values obtained by dividing the retardation of the wave plate by the respective wavelengths at λmax and λmin are defined as nmax and nmin. n1 is an integer or a half integer that is smaller than and smaller than nmin. n2 is an integer or half integer that is greater than nmax and is closest. This coincides with the order of peaks (n ^x ) of peaks or valleys existing on both sides of the spectral spectrum of the wavelength plate alone, that is, when the air is measured with the phase difference measuring device of the present invention. .

N2 of the wave plate is 0.5 or more, preferably 1.0 or more, and more preferably 5 or more.
Usually, the retardation of the wave plate is preferably λmin or more, more preferably λmin × 3 or more, and further preferably λmin × 5 or more. That is, when the measurement wavelength region is 400 nm or more, it is preferably about 400 nm or more, more preferably about 1200 nm or more, and further preferably about 2000 nm or more.

  On the contrary, if the retardation of the wave plate is too large, a problem arises. In the crossed Nicols measurement, a valley peak is given when Γ is an even multiple of π. For example, when Γ = 2nπ, Re = nλpeak. That is, the peak position λpeak is expressed by Equation (13).

この分光スペクトルで見られるピーク位置λpeakは、波長による位相差の変化によってシフトするが、そのシフト量は式（１４）のように記述される。

The peak position λpeak seen in this spectroscopic spectrum is shifted by the change of the phase difference depending on the wavelength, and the shift amount is described as in the equation (14).

  From equation (14), it can be seen that the peak shift due to the change in phase difference decreases as n increases. From this, it can be seen that when a wave plate having a large phase difference is used, the shift amount of the spectrum is reduced and the measurement accuracy is lowered.

The measurement accuracy also depends on the wavelength resolution of the spectrometer. A spectroscope with high wavelength resolution can detect even a slight peak shift with sufficient accuracy. The wavelength resolution of the spectroscope is usually expressed by FWHM (Full Width Half Maximum), and the peak position detection accuracy can be detected by about 1 / 100th depending on the intensity resolution of the detector used in the spectroscope. Therefore, when using a spectroscope whose FWHM is F and the wave plate has a phase difference n times the specific measurement wavelength, if the measurement phase difference accuracy is ± A nm at the measurement wavelength, the optical system specifications are (15) may be satisfied.
F × n ≦ A × 200 nm (15)
For example, if the measurement phase difference accuracy is ± 0.25 nm, F × n ≦ 50 nm
Should be satisfied.

Furthermore, F × n is more preferably 30 nm or less, and most preferably 20 nm or less.
As an apparatus, it is preferable that n1 is selected as n and the above equation (15) is determined.
In consideration of the above two points and the FWHM of a commercially available spectroscope, a wave plate with n1 of 33 or less is preferable, and a wave plate with 15 or less is more preferable. However, considering the thickness of a commercially available wave plate, the retardation of the wave plate is usually preferably about 10,000 nm or less, more preferably about 8000 nm or less, and further preferably about 6000 nm or less.
The material of the wave plate generally includes stretched polymer film, inorganic crystals such as quartz and calcite, but the wave plate directly affects the measured retardation value, so it changes depending on the environment such as temperature and humidity. Difficult things are desirable. Preferable examples of such a wave plate include quartz, calcite, and a polymer stretched film sandwiched with glass.

[Spectrometer]
The spectroscope is not particularly limited as long as it can perform spectroscopy in a necessary wavelength range and has sufficient resolution of light intensity. A spectroscope that scans with a monochromator or a multi-channel type spectroscope that measures light dispersed by a diffraction grating with a one-dimensional photodetector array may be used, but a multi-channel type with a short measurement time is preferable. The resolution of the intensity of the spectroscope is preferably 8 bits or more and particularly preferably 12 bits or more if it is digital. Further, since the wavelength resolution F corresponds to the measurement accuracy of the phase difference, the FWHM is preferably 10 nm or less, and particularly preferably 5 nm or less.

[Measurement procedure]
An example of the measurement procedure will be described.
The incident polarizer fixes the transmission axis at 45 degrees with respect to the rotation axis direction of the entire sample stage. Next, the analyzer is rotated 360 degrees with no wave plate and sample on the optical axis, and the transmission spectrum is observed with a spectroscope while the position with the smallest transmittance and the position with the largest transmittance are crossed Nicols, Detect as paranicol position. The optical system is calibrated by setting the spectrums at that time to 0% and 100%, respectively, so that the transmittance can be measured, and then the analyzer is placed in crossed Nicol or para Nicol. Hereinafter, cross-Nicol will be described. Next, the phase difference of the standard wave plate is measured. The wave plate is rotated 360 degrees by rotating the optical axis, and the angle at which the transmittance of the sample is minimized is detected. Next, when the spectroscopic spectrum is measured by rotating 45 degrees from the minimum angle (bright light level under crossed Nicols), a spectrum as shown in FIG. 1 is obtained. The phase difference can be obtained by fitting the spectrum using the first element of Expression (7). Since a known wave plate may be used, the slow axis of the wave plate (the axis having the higher refractive index, which is parallel or orthogonal to the optical axis) is known in advance. The spectroscopic spectrum may be measured in a state tilted by a predetermined degree.

  Next, the wave plate is retracted from the optical axis, and the sample is rotated 360 degrees by rotating the optical axis, and the angle at which the transmittance of the sample is minimized is detected. Next, the wavelength plate is inserted with the slow axis set at 45 degrees, and the sample is set at ± 45 degrees from the angle at which the transmittance is minimized, and two spectrums are measured. When this spectral spectrum is fitted in the same manner as in the case of the wave plate, the wave plate + sample, or wave plate-sample (the polarizer and the analyzer are crossed Nicols according to the equation (11), and the transmission axis of the polarizer is used. The Stokes parameter of an optical system having a sample whose slow axis is tilted by −45 degrees and a wave plate whose slow axis is tilted by 45 degrees with respect to the transmission axis of the polarizer is obtained in the same manner as in equation (11). A phase difference can be obtained. Of the two arrangements of ± 45 degrees, the arrangement of obtaining the waveplate and the sample has the same slow axis of the waveplate and the sample, so that the slow axis of the sample can be identified. As described above, the wavelength dispersion of the phase difference and the direction of the slow axis can be obtained.

  In the case of a sample having absorption or scattering, after the wave plate measurement, the wave plate is retracted, and the sample is rotated 360 degrees by rotating the optical axis to detect the angle at which the transmittance of the sample is minimized, and the spectrum is kept in this arrangement. May be obtained to obtain a spectrum (absorption / scattering spectrum) that is not affected by the phase difference. The spectral spectrum at ± 45 degrees of the sample is obtained in the same manner as described above with the wave plate inserted, but by dividing this spectral spectrum by the spectral spectrum that is not affected by the phase difference before fitting, Transmission loss can be corrected. Thereby, even for a sample having absorption or scattering, the phase difference can be accurately measured.

[Correction and fitting means]
In practice, it is preferable to use Cauchy's equation as the wavelength dispersion of the phase difference, and to perform fitting using Equation (16), taking into account the change in transmittance due to noise in the optical system.

  Tmax (λ) and Tmin (λ) are for correcting the transmittance, and may be constants having no wavelength dependency, linear expressions (17), quadratic expressions (18), or exponential functions (19). In terms of accuracy, a linear expression is sufficient, which is preferable.

  As a fitting method, for example, a non-linear optimization method as described in “Introduction to data processing for scientific measurement”, supervised by Shigeo Minami, edited by Kei Kawada, a genetic algorithm, or the like can be used. In these methods, the initial value at the time of fitting is important. However, in order to perform fitting with high accuracy, the initial fitting is performed using C = 0, Tmax = 1, and Tmin = 0 in Equation (16) as initial values. It is preferable to fit the parameters. In fitting, it is most popular and preferable to minimize the square error. Alternatively, the peak position of the valley is important for the square error of each wavelength. For example, a method of multiplying the square of (50-T (λ)) as a weight function or a portion with high transmittance of the absorption / scattering spectrum is important. Therefore, it is preferable to use a method such as a method of multiplying absorption / scattering spectra, or a combination thereof.

  The phase difference measuring apparatus of the present invention is not limited to the above method as long as necessary measurement data can be obtained even if it is not in the above order. Further, the rotation of the sample and the wave plate on the optical axis can be performed at 180 degrees instead of 360 degrees. Furthermore, the measurement can be performed even if the polarizer is arranged at a position other than 45 degrees, and the measurement can be performed even if the polarizer and the analyzer are not crossed Nicols but paranicols.

  The present invention will be described more specifically with reference to the following examples. The following embodiments can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the following specific examples.

(Configuration of phase difference measuring device)
A phase difference measuring apparatus having the configuration shown in FIG. 4 was used. The polarizer was fixed at 45 degrees, and three quartz plates having the phase difference shown in FIG. 5 were used as wavelength plates. The light source is a halogen lamp (EDI100DH, manufactured by Mitsubishi Rayon), the polarizer and analyzer are iodine-based polarizers (HC2-8118, manufactured by Sanlitz), and the spectrometer is a fiber-type multichannel spectrometer (USB2000, Ocean Optics). A / D resolution 12 bits, wavelength resolution (FWHM) 1.5 nm). The measurement wavelength range was 400 to 700 nm.

(Example 1, Comparative Examples 1 and 2)
A sample having a phase difference of approximately λ / 4 at 550 nm was measured at n = 10. Example 1 using a wave plate having a retardation of about 10λ at 550 nm Example 1 using a wave plate having a retardation of about 2λ at 550 nm Example 2 Using a wave plate having a retardation of about 2λ at 550 nm What used the wave plate which it has was made into the comparative example 1. According to the above procedure, the measurement was performed with the polarizer and analyzer arranged in crossed Nicols and the slow axis of the wave plate and sample set to 45 degrees with respect to the transmission axis of the polarizer. For fitting, equations (16) and (17) were used, and the solution giving the least square error was used as the solution. The phase difference was obtained by calculating on the computer using the Levenberg-Marquardt algorithm, which is known to be fast and highly accurate as one of nonlinear optimization. N1, n2 and F × n1 of Examples 1 and 2 and Comparative Example 1 are shown in Table 1, and average values of phase differences measured at 450, 550 and 650 nm measured in Examples 1, 2 and Comparative Example 1 are shown in Table 2. Standard deviations are shown in Table 3.

  From Table 2, the phase differences in Examples 1 and 2 were correct values, whereas the phase difference in Comparative Example 1 was clearly deviated from the actual sample values. Moreover, as can be seen from Table 3, Comparative Example 3 had a result that varied greatly for each measurement. In Examples 1 and 2, the repetition accuracy was about the same in the vicinity of 550 nm, but in the vicinity of 450 and 650 nm, the repetition accuracy of Example 1 was superior. This is due to the fact that Example 1 has an overwhelmingly larger number of measured spectral peaks. From the above results, it can be seen that the phase difference can be accurately measured in the phase difference sample having absorption or scattering by the phase difference device of the present invention.

It is a fundamental figure of the spectrum in the phase difference measurement of this invention. It is a fundamental figure of the spectral spectrum with respect to the sample of a small phase difference in the phase difference measurement of this invention. It is the schematic which shows the preferable arrangement | positioning of the light source in the phase difference measuring apparatus of this invention, a polarizer, a sample stand, an analyzer, and a spectrometer. It is the schematic of the phase difference measuring apparatus of this invention. It is wavelength dispersion of the phase difference of the waveplate used for the Example of this invention.

Claims (7)

A phase difference measuring device including an optical system in which a light source, a polarizer, a sample stage, an analyzer, and a spectrometer are arranged in this order, and a calculation means,
A wave plate is disposed between the polarizer and the analyzer,
In each of two or more wavelengths in the measurement wavelength range, the value obtained by dividing the retardation value of the wave plate by an integer of 0.5 or more or a half integer matches the wavelength ,
The retardation value of the wave plate is 3 × λ min or more at the lower limit wavelength λ min of the measurement wavelength range, and
A phase difference measuring apparatus in which the resolution F defined by the FWHM of the spectroscope and the maximum value n1 that the integer or half integer can take satisfy the following condition (B):
(B) F × n1 ≦ 50 nm. The phase difference measurement apparatus according to claim 1, wherein the measurement wavelength region includes 400 nm to 700 nm, and the retardation value of the wave plate is 1200 nm or more and 10,000 nm or less. The phase difference measuring apparatus according to claim 1, wherein the wavelength plate includes means for inserting and retracting the optical plate with respect to the optical axis. The phase difference measuring apparatus according to any one of claims 1 to 3, wherein the spectroscope is a multi-channel spectroscope including a diffraction grating and a one-dimensional light receiving array. A method for determining a phase difference of a sample from a spectrum measured by an optical system in which a light source, a polarizer, a sample, an analyzer, and a spectrometer are arranged in this order,
Select the wave plate product lambda ^x n ^x is the wavelength lambda ^x showing a retardation value of the wavelength plate with 0.5 or more integer or half-integer n ^x there are two or more in the measurement wavelength range Ramudamin～ramudamax,
It looks including placing a wavelength plate between the polarizer and the analyzer,
The retardation value of the wave plate is 3 × λ min or more at the lower limit wavelength λ min of the measurement wavelength range,
How the maximum value n1 resolution F and n ^x being defined by the spectrometer FWHM can take satisfy the following condition (B):
(B) F × n1 ≦ 50 nm. The method according to claim 5, wherein the measurement wavelength region includes 400 nm to 700 nm, and the retardation value of the wave plate is 1200 nm or more and 10,000 nm or less. The method according to claim 5 or 6, wherein the wavelength plate and the optical axis of the sample are made coincident or perpendicular to each other at the time of spectral measurement.

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