JP5289989B2 - Phase difference measuring device - Google Patents

Description

  The present invention relates to a phase difference measuring apparatus that measures the axial direction and phase difference of a birefringent sample.

Conventionally, a phase difference measuring apparatus is known as an apparatus for measuring the axial direction and phase difference of a birefringent sample such as a lens glass material for an exposure device (see, for example, Patent Document 1). This phase difference measurement device modulates the polarization state of linearly polarized light from a light source at a predetermined frequency, irradiates the sample, measures the intensity of light transmitted through the sample, and calculates the axial orientation and phase difference based on the measurement data To do.
Generally, in a phase difference measuring apparatus, it is necessary to set the axis of the refractive index of a sample. Here, the axis of the refractive index indicates a fast axis and a slow axis when the sample causes birefringence, and the azimuth angle of these axes is referred to as an axial direction in the text. Further, the axis setting means that the sample is rotated around the optical axis and set to an orientation in which the absolute value of the signal derived from birefringence is maximized.

On the other hand, a near-field microscope based on a principle different from a general optical microscope or electron microscope has been developed and widely used (see, for example, Patent Document 2). The near-field microscope detects so-called near-field light. That is, when light is irradiated on the sample to be measured, a surface wave called near-field light is generated near the surface of the object to be measured. This surface wave is localized in a distance region within the wavelength of light. Therefore, a sharpened probe having a tip dimension less than the wavelength of light, a so-called near-field probe, is inserted into the near-field light field to scatter the near-field light, and the scattered light intensity is measured to measure the probe tip and the object to be covered. The distance to the surface of the measurement object can be defined.
For example, by scanning the probe so that the intensity of scattered light is constant, the probe tip position accurately reflects the unevenness of the surface of the object to be measured, and the probe tip exists in the near-field light field. Since the object to be measured is not in contact with the sample, it can be observed that the sample is non-contact, non-destructive and smaller than the wavelength of light.
At the tip of the near-field probe described in Patent Document 2, an elliptical or slit-shaped opening for obtaining linearly polarized light in a predetermined vibration direction is formed. Such a near-field probe is called a polarization probe, can collect linearly polarized light in a predetermined vibration direction from scattered light, and has good polarization in both the condensing mode and the irradiation mode. Shows selectivity.

  The inventors apply a technique for condensing the near field described in Patent Document 2 to the phase difference measurement apparatus of Patent Document 1 using a polarization probe, and detect light transmitted through the sample using a polarization probe. We have been diligently working on the development of a phase difference measuring device that can measure axial orientation and phase difference with higher accuracy.

JP 2004-184225 A JP 2002-162333 A

However, the sample must be rotated with respect to the polarizing probe in order to pivot the sample while the probe tip is close to the near field of the sample surface in nanometer units. In this case, the center of the sample has to be held with high accuracy so as not to damage the probe tip, which is difficult to achieve because it is restricted by the accuracy of the rotation mechanism.
On the other hand, as a method of measuring the phase difference without rotating the sample, the axial orientation of the analyzer provided at a stage after the sample is set to 0 ° and 45 °, and the detection light is set at each set position. Measure and extract a signal component having the same frequency as the polarization modulation frequency and a signal component having a frequency twice the polarization modulation frequency from the detection signal, and calculating the phase difference based on the signal component, or detection There is also a method in which the child is rotated 360 °, an intensity signal associated with the rotation angle is measured, and a phase difference is calculated from the amplitude and phase.
However, in any of these measurement methods, when a polarization probe is used, the polarization direction of the polarization probe must be rotated around the optical axis with the probe tip close to the sample surface. Due to the limitation on the accuracy of the rotating mechanism, it could not be implemented.

  The objective of this invention is providing the phase difference measuring apparatus which can measure an axial azimuth | direction and a phase difference with a high precision using a polarization probe.

The phase difference measuring apparatus of the present invention includes a polarizer that transmits light from an irradiation unit as linearly polarized light, and a modulator that is provided between the polarizer and the sample and modulates the polarization state of linearly polarized light from the polarizer. and tone, the variable polarization from tone is generated in the measurement surface of the sample by being irradiated out of the near-field light, the polarization probe having an aperture of elliptical or slit-shaped to transmit predetermined vibration direction of the linearly polarized light The polarizer and the modulator are rotated together so that the difference between the azimuth angle of the transmission axis of the polarizer and the azimuth angle of the modulation axis of the modulator is always 45 °, and the polarization a rotating mechanism the azimuth angle of the transmission axis of the polarizer the azimuth angle of the transmission axis of the probe as a reference to set the azimuth of the two types of 0 ° and 45 °, near-field light collected by the polarization probe Detects light intensity signal Calculation for calculating the phase difference between the polarization component of the fast axis direction and the polarization component of the slow axis direction and the axis direction of the sample generated by the polarized light irradiated to the sample based on the light intensity signal And the rotation mechanism sets the transmission axis of the polarizer to two azimuth angles of 0 ° and 45 °, and the detection unit detects near-field light at the set azimuth angle. Thus, the axial direction and phase difference of the sample are measured.

According to the present invention, a polarizing mechanism is provided by rotating a polarizer provided at the front stage of the sample, and rotating the transmission axis of the polarizer with respect to the transmission axis of the polarizing probe provided at the rear stage of the sample. Since the light intensity signal of the near-field light collected at is acquired, it is not necessary to rotate the sample with respect to the polarization probe or to rotate the polarization probe with respect to the sample.
In addition, by collecting near-field light using a polarization probe, the near-field light generated on the measurement surface of the sample can be measured by spatial resolution below the wavelength of the light.
Therefore, it is not necessary to rotate the sample or the polarization probe, and the axial direction and phase difference of the sample can be measured with high spatial resolution using the polarization probe.

  According to the present invention, the polarizer and the modulator are provided so as to be rotated together, and the azimuth angle of the transmission axis of the polarizer is set to two azimuth angles of 0 ° and 45 °, Since the light intensity signal corresponding to the azimuth angle is acquired, by analyzing the signals of these light intensity signals, it is possible to reliably calculate the phase difference and the axial direction, which are two unknowns related to the sample.

  In the phase difference measuring apparatus of the present invention, extraction is performed by extracting from the light intensity signal a signal having the same frequency as the modulation frequency when the modulator modulates the polarization state, and a signal having a frequency twice the modulation frequency. Preferably, the calculation unit calculates the axial direction and phase difference of the sample based on the magnitude of the signal extracted by the extraction unit.

  According to the present invention, the polarization state of linearly polarized light is periodically modulated by the modulator, so that the signal component (f signal) having the same frequency from the light intensity signal is referred to with reference to the modulation frequency (f), and 2 A signal component having a double frequency (2f signal) can be easily extracted, and the phase difference and axial orientation of the sample can be calculated in a short time.

In the phase difference measuring apparatus of the present invention, the signal extracted by the extraction unit has the same frequency as the modulation frequency f extracted from the light intensity signal when the azimuth angle of the transmission axis of the polarizer is 0 °. A signal component I ⁰ _f and a signal I ⁰ _2f having a frequency twice that of the modulation frequency extracted from the light intensity signal when the azimuth angle of the transmission axis of the polarizer is 45 °. signal is a component I ⁴⁵ _2f, the arithmetic unit is preferably calculated based on the axial orientation θ and the phase difference Δ of the sample of 1 or less.

According to the present invention, it is possible to quickly and easily calculate the phase difference and the axial direction of the sample based on Equation 1 simply by extracting the signal components I ⁰ _f , I ⁰ _2f and I ⁴⁵ _2f by the extraction unit. .

  In the phase difference measuring apparatus of the present invention, it is preferable that the rotation range of the transmission axis of the polarizer is −45 ° to 90 °.

  According to the present invention, even if the azimuth angle of the transmission axis of the polarization probe is unknown, the transmission axis of the polarizer can be changed by changing the azimuth angle of the transmission axis of the polarizer in the range of −45 ° to 90 °. It can coincide with the transmission axis of the polarization probe. Therefore, the setting operation of the transmission axis of the polarization probe can be omitted, and the efficiency of the measuring operation can be improved.

In the phase difference measuring apparatus according to the present invention, the rotation range of the transmission axis of the polarizer is 0 ° to 135 °, and the calculation unit is configured such that the azimuth angle of the transmission axis of the polarizer is 0 ° and 90 °. The sum of signal components I ⁰ _2f and I ⁹⁰ _{2f having} a frequency twice the modulation frequency of the modulator extracted from the light intensity signal and the azimuth of the transmission axis of the polarizer are 45 ° and 135 °. And the sum of the signal components I ⁴⁵ _2f and I ¹³⁵ _{2f having} a frequency twice the modulation frequency extracted from the light intensity signal in the case of It is preferable to correct the zero point.

According to the present invention, since the transmission axis of the polarizer can be rotated in the range of 0 ° to 135 °, the light when the azimuth angles of the transmission axis of the polarizer are 0 °, 45 °, 90 °, and 135 °. The signal components I ⁰ _2f , I ⁴⁵ _2f , I ⁹⁰ _2f and I ¹³⁵ _2f of the intensity signal can be acquired. Since the signal components I ⁰ _2f and I ⁹⁰ _2f are equivalent and opposite in sign, and the signal components I ⁴⁵ _2f and I ¹³⁵ _2f are also equivalent and opposite in sign, the sum of these signal components (I ⁰ _2f + I ⁹⁰ _2f , I ⁴⁵ _2f + I ¹³⁵ _2f ) can be used to correct the zero point of the axial orientation of the polarization probe.

  In the phase difference measuring apparatus of the present invention, it is preferable that the rotation range of the transmission axis of the polarizer is −45 ° to 180 °.

  According to the present invention, even if the azimuth angle of the transmission axis of the polarizing probe is unknown, the transmission axis of the polarizer is changed by changing the azimuth angle of the transmission axis of the polarizer in the range of −45 ° to 180 °. It can coincide with the transmission axis of the polarization probe. Therefore, the setting operation of the transmission axis of the polarization probe can be omitted, and the efficiency of the measuring operation can be improved.

The phase difference measuring apparatus of the present invention includes a polarizer that transmits light from an irradiation unit as linearly polarized light, and near-field light generated on a measurement surface of a sample by being irradiated with polarized light from the polarizer. In order to change the azimuth of the transmission axis of the polarizing probe with respect to the azimuth of the transmission axis of the polarizing probe, and a polarizing probe having an elliptical or slit-shaped opening that transmits linearly polarized light in a predetermined vibration direction A rotation mechanism that rotates the polarizer, a detection unit that detects a near-field light collected by the polarization probe and generates a light intensity signal, and a polarization that is applied to the sample based on the light intensity signal An arithmetic unit that calculates a phase difference between the polarization component of the fast axis direction and the polarization component of the slow axis direction and the axis direction of the sample. The rotation mechanism rotates the transmission axis of the polarizer, and at the same time, the detection unit detects near-field light collected by the polarization probe according to the azimuth angle of the transmission axis of the polarizer.

At this time, the calculation unit uses the cosine function cos2φ and sine function sin2φ of the azimuth angle twice the azimuth angle ^φ as the light intensity signal I ^φ corresponding to the azimuth angle φ of the transmission axis of the polarizer. Fitting is performed to obtain coefficients A and B represented by I ^φ = 1 + A cos 2φ + B sin 2φ, and the axial direction θ and the phase difference Δ of the sample are calculated based on the following formula 2.

According to the present invention, each phi azimuth of the transmission axis of the polarizer, so to obtain a light intensity signal I ^phi, and the light intensity signal I ^phi fitted by a cosine function cos2φ and sine functions sin2φ, I ^φ = 1 + Acos2φ The coefficients A and B indicated by + Bsin2φ can be easily calculated, and the phase difference and axial direction of the sample can be calculated in a short time.

  According to the present invention, it is possible to quickly and easily calculate the phase difference and the axial direction of the sample based on Equation 2 only by calculating the coefficients A and B by the calculation unit.

The figure which shows schematic structure of the phase difference measuring apparatus which concerns on 1st Embodiment of this invention. Explanatory drawing which shows the relationship of the axial direction of the polarization of each optical element of the said phase difference measuring apparatus. The figure which shows schematic structure of the phase difference measuring apparatus which concerns on 2nd Embodiment of this invention. Explanatory drawing which shows the relationship of the axial direction of the polarization of each optical element of the said phase difference measuring apparatus.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In the second and later embodiments described later, the same reference numerals are given to the same components and the same members as the components in the first embodiment described below, and the description will be simplified or omitted. .

[First Embodiment]
FIG. 1 is a diagram illustrating a schematic configuration of a phase difference measuring apparatus according to the present embodiment.
The phase difference measurement apparatus 1 is considered to be a limit in the conventional phase difference measurement apparatus using the polarization probe 2 having an elliptical or slit-shaped opening for obtaining linearly polarized light in a predetermined vibration direction from near-field light. High spatial resolution can be achieved.

  The phase difference measuring apparatus 1 includes, as an entire configuration, an irradiation unit 3 that generates light in a specific wavelength range, a modulation unit 4 that obtains linearly polarized light from the light from the irradiation unit 3 and periodically modulates the polarization state, A rotating mechanism 5 of the modulation unit 4, a polarization probe 2 that collects near-field light generated on the measurement surface of the sample S due to irradiation of polarized light from the modulation unit 4, and a detector that detects the collected near-field light 6, a control unit 7 that drives and controls each component, and a calculation unit 8 that calculates a phase difference and an axial direction of the sample S based on a detection signal from the detector 6.

The irradiation unit 3 includes a light source and a spectroscope 31 (not shown).
The modulation unit 4 is a polarizer 41 that transmits light from the irradiation unit 3 and linearly polarizes the light, a modulator composed of a photoelastic modulator (hereinafter referred to as PEM 42), and a PEM controller that drives and controls the PEM 42. 43.
The PEM 42 gives a phase difference δ to the linearly polarized light from the polarizer 41 and modulates the polarization direction with the frequency f. The PEM 42 is connected to the PEM controller 43, and an AC voltage having a frequency f is applied by the PEM controller 43. For example, the phase difference δ is sinusoidally modulated as δ = δ ₀ sin (2πft). Here, t represents time, and δ ₀ represents amplitude.

The polarization probe 2 is a near-field probe having good polarization selectivity, and is held close to the sample S so that the distance between the tip 21 and the measurement surface of the sample S is a size in nanometers. ing.
In the present embodiment, as shown in FIG. 1, the polarized light modulated by the PEM 42 is transmitted through the sample S, and the near-field light generated on the measurement surface of the sample S by the transmitted light is collected by the polarization probe 2. However, the present invention is not limited to this, and a configuration in which near-field light generated by reflected polarized light modulated by the PEM 42 is collected by the polarization probe 2 may be used.

Next, a rotation mechanism 5 that rotates the above-described modulation unit 4 around the optical axis will be described with reference to FIG.
FIG. 2 is an explanatory diagram showing the relationship of the polarization axis orientation of each optical element. In the figure, the optical axis is the Z axis, and the azimuth angle is 0 ° with reference to the axial direction that coincides with the X axis in the XY plane.
The rotation mechanism 5 rotates the polarizer 41 and the PEM 42 around the Z axis to change the azimuth angle of the transmission axis of the polarizer 41. The polarizer 41 and the PEM 42 are supported so that they can rotate as a unit. However, the difference between the azimuth angle of the transmission axis of the polarizer 41 and the azimuth angle of the modulation axis of the PEM 42 is always 45 °. ing.
On the other hand, the rotation mechanism 5 can set the azimuth angle of the transmission axis of the polarizer 41 to 0 ° and 45 °. In the figure, for example, the case where the azimuth angle of the transmission axis of the polarizer 41 is set to 0 ° is indicated by a solid line, and the case where the azimuth angle is set to 45 ° is indicated by a broken line. When the transmission axis is set to 45 °, the transmission axis coincides with a straight line of Y = X in the XY plane.

  On the other hand, the above-described polarization probe 2 has a transmission axis perpendicular to the major axis direction of the elliptical or slit-shaped opening, and selectively collects linearly polarized light that vibrates in the transmission axis direction. The azimuth angle of the transmission axis of the polarization probe 2 is fixed at 45 °. The detailed shape of the polarization probe 2 is as described in the above-mentioned Patent Document 2.

The detector 6 corresponds to a detection unit of the present invention, and detects the amount of detection light collected by the polarization probe 2 in a state where the azimuth angle of the polarizer 41 is set to 0 ° and 45 °, Output as a light intensity signal. As the detector 6, for example, a photomultiplier tube (PMT) can be adopted.
The control unit 7 includes an SPM (Scanning Probe Microscope) electric system control unit 71 and an ellipso electric system control unit 72. For example, the SPM electrical system control unit 71 connects the mounting table 9 of the sample S to the control unit 10 that performs mapping control and SF control, and mainly controls the scanning of the polarization probe 2. The ellipsoelectric system control unit 72 is connected to, for example, the spectroscope 31, the rotation mechanism 5, the detector 6, and the PEM controller 43, and controls devices related to detection of detection light collected by the polarization probe 2.

  The detection signal from the detector 6 is sent to a lock-in amplifier as an extraction unit (not shown) built in the ellipso electric system control unit 72. The lock-in amplifier refers to the frequency f applied to the PEM 42 and the doubled frequency 2f, and the signal component of the frequency f of the detection signal (referred to as f signal) and the signal component of the frequency 2f (referred to as 2f signal). To extract. The f signal and the 2f signal are sent to the calculation unit 8 such as a CPU. In the calculation unit 8, the axial orientation and phase difference of the sample S are calculated according to the stored calculation procedure based on the f signal and the 2f signal.

The principle of measuring the sample S using the above phase difference measuring apparatus 1 will be described.
First, when the axis direction which is the azimuth angle of the fast axis of the sample S which is a birefringent material is θ, the phase difference (retardation) is Δ, and the dichroism is Ψ, the Mueller matrix R _θ representing the sample S is It is shown in Equation 3. Here, the phase difference Δ indicates the phase difference at the time of sample emission between the polarization component of the fast axis direction and the polarization component of the slow axis direction.

Next, the Mueller matrix A ₄₅ representing the polarization probe 2 whose azimuth angle of the transmission axis is 45 ° is expressed by the following equation (4).

Here, the matrix A ₄₅ R _θ obtained by multiplying Equation 3 and Equation 4 and dividing factor ½ is Equation 5 below. Due to space constraints, the transpose matrix (A ₄₅ R _θ ) ^−t is shown.

The Stokes vector S ₀ indicating the irradiation light irradiated on the sample S will be described.
Stokes vector of irradiation light that is transmitted through a polarizer 41 having an azimuth angle of the transmission axis set to 0 °, and whose polarization state is modulated by the phase difference δ given by the PEM 42 in which the azimuth angle of the modulation axis is set to 45 ° S ₀ is represented by the following formula 6.

  Here, the reason why the azimuth angle difference between the polarizer 41 and the PEM 42 is always 45 ° is that the modulation efficiency is the best. Note that. You may set the difference of each azimuth angle of the polarizer 41 and PEM42 to arbitrary angles other than the optimal angle of 45 degrees.

Among the near-field light generated in the measurement surface of the sample S by the irradiated light, the Stokes vector of the detection light detected by a condensed by polarization probe 2 detector 6 When S ^0, the first component of the Stokes vector S ⁰ In other words, the expression representing the light intensity signal I ⁰ of the detection light is the first component of the result (A ₄₅ R _θ S ₀ ) obtained by multiplying Equation 6 by the matrix A ₄₅ R _θ , and is given by Equation 7 below.

Similarly, the Stokes vector S ₄₅ of the irradiation light transmitted through the polarizer 41 whose transmission axis azimuth is set to 45 ° and whose polarization state is modulated by the PEM 42 whose modulation axis azimuth is set to 90 ° is The following equation 8 is shown.

With this irradiation light, the Stokes vector of the detection light detected by a condensed by polarization probe 2 detector 6 and S ^45, the first component of the Stokes vector S ^45, that is the formula representing the light intensity signal I ⁴⁵ Is the first component of the result of multiplying the matrix 8 by the matrix A ₄₅ R _θ (A ₄₅ R _θ S ₄₅ ), and the following formula 9 is obtained.

In the equations of the light intensity signals I ⁰ and I ⁴⁵ , the coefficient of sin δ is the same frequency components I ⁰ _f and I ⁴⁵ _f as the modulation frequency f of the PEM 42, and depends on the f signal extracted from the detection signal of the detector 6. To be acquired. I ⁰ _f and I ⁴⁵ _f are expressed by the following formula 10, and have a relationship in which the sizes are equivalent and the signs are different from each other.

Further, in the expression of the light intensity signals I ⁰ and I ⁴⁵ , the coefficient of cos δ becomes signal components I ⁰ _2f and I ⁴⁵ _{2f having} a frequency twice the modulation frequency f of the PEM 42 and is extracted from the detection signal of the detector 6. 2f signal. I ⁰ _2f and I ⁴⁵ _2f are expressed by the following formula 11.

In the above equation for each signal component, Ψ = 45 °, that is, the dichroism of the sample S is zero.

Equation 12 relating to the 2f signal can be transformed as Equation 13 below.

Therefore, by using the following Expression 14 obtained from Expression 13, the axial azimuth θ is calculated based on the 2f signals (I ⁰ _2f , I ⁴⁵ _2f ) of 0 ° azimuth and 45 ° azimuth, and the axial azimuth θ, 0 The phase difference Δ can be calculated based on the f signal (I ⁰ _f ) and the 2f signal (I ⁰ _2f ) in the ° direction.

A measurement method based on the above measurement principle will be described.
In the measurement method of this embodiment, the modulator 4 is rotated by 45 °, the azimuth angle of the polarizer 41 is set in two ways, 0 ° and 45 °, and the light is collected by the polarization probe 2 at each set azimuth angle. This is a technique for detecting detected light.
In advance, with the sample S not installed, the modulator 4 is rotated with respect to the polarization probe 2, and the azimuth angle of the polarizer 41 is set to an azimuth in which the 2f signal (for example, 100 kHz signal) becomes zero. Alternatively, if the polarization probe 2 is provided so as to be rotatable with respect to the optical axis, the axis direction of the polarization probe 2 is rotated and the azimuth angle of the polarization probe 2 is set to an orientation where the 2f signal is zero. May be. With the above method, the azimuth angle of the polarization probe 2 can be set to 45 ° with respect to the azimuth angle of the polarizer 41. Subsequently, the sample S is rotated around the optical axis while the sample S is installed. Then, the azimuth angle of the sample S is set to the azimuth in which the absolute value of the f signal (for example, 50 kHz signal) is maximized. In this way, the sample S can be pivoted.
In the measurement method of the present embodiment, first, measurement is performed by setting the azimuth angle of the transmission axis of the polarizer 41 to 0 ° using the modulation unit 4, and the detection signal is acquired by the detector 6.
Next, measurement is performed by setting the azimuth angle of the polarizer 41 to 45 °, and a detection signal is acquired.
The control unit 7 extracts the f signal and the 2f signal from each detection signal.
Finally, the calculation unit 8 calculates the axial orientation θ and the phase difference Δ of the sample S by Equation 14 based on the f signal and the 2f signal.

In the present embodiment, the method of setting the transmission axis of the polarizer 41 in two ways after setting the orientation of the transmission axis of the polarization probe 2 to an azimuth angle of 45 ° in advance has been described. 5 may change the azimuth angle of the polarizer 41, that is, the rotation range of the polarizer 41 may be −45 ° to 90 °.
In this way, even if the azimuth angle of the transmission axis of the polarization probe 2 is unknown, the azimuth angle of the transmission axis of the polarizer 41 is changed in the range of −45 ° to 90 °, thereby The transmission axis can coincide with the transmission axis of the polarization probe 2. Therefore, the setting operation of the transmission axis of the polarization probe 2 can be omitted, and the efficiency of the measuring operation can be improved.

Alternatively, the rotation range of the polarizer 41 by the rotation mechanism 5 may be 0 ° to 135 °.
In this case, the azimuth angles of the transmission axis of the polarizer 41 are set to 0 °, 45 °, 90 °, and 135 °, and the signal components I ⁰ _2f , I ⁴⁵ _2f , I ⁹⁰ _2f, and I ¹³⁵ _2f can be acquired. Since the signal components I ⁰ _2f and I ⁹⁰ _2f are equivalent and opposite in sign, and the signal components I ⁴⁵ _2f and I ¹³⁵ _2f are also equivalent and opposite in sign, the sum of these signal components (I ⁰ _2f + I ⁹⁰ _2f , I ⁴⁵ _2f + I ¹³⁵ _2f ) is used to correct the zero point of the axial direction of the polarization probe 2, the measurement accuracy can be improved.

As described above, when the zero point is corrected, the rotation range of the polarizer 41 may be set to −45 ° to 180 °.
In this way, as described above, even if the azimuth angle of the transmission axis of the polarization probe 2 is unknown, the azimuth angle of the transmission axis of the polarizer 41 can be changed in the range of −45 ° to 180 °. The transmission axis of the polarizer 41 can be made to coincide with the transmission axis of the polarization probe 2, and the efficiency of measurement work can be improved.

According to this embodiment, the following effects can be achieved.
A rotation mechanism 5 that rotates the polarizer 41 at the front stage of the sample S integrally with the PEM 42 is provided, and the azimuth angle of the transmission axis of the polarizer 41 is changed with respect to the transmission axis of the polarization probe 2 provided at the rear stage of the sample S. Thus, since the light intensity signal of the near-field light collected by the polarization probe 2 is acquired, the sample S can be rotated with respect to the polarization probe 2 or the polarization probe 2 can be rotated with respect to the sample S. It becomes unnecessary.

  Furthermore, by collecting the near-field light using the polarization probe 2, the near-field light generated on the measurement surface of the sample S can be measured with spatial resolution below the wavelength of the light, exceeding the light diffraction limit. Thus, the axial orientation and phase difference of the sample S can be measured with high spatial resolution.

Further, since the azimuth angle of the transmission axis of the polarizer 41 is set to two azimuth angles of 0 ° and 45 °, the light intensity signals I ⁰ and I ⁴⁵ corresponding to the set azimuth angles are obtained. By analyzing the signals of these light intensity signals I ⁰ and I ⁴⁵ , the two unknowns regarding the sample S, the axial orientation θ and the phase difference Δ, can be calculated reliably.

Further, since the polarization state of the linearly polarized light is periodically modulated by the PEM 42, the signal components (f signal) having the same frequency from the light intensity signals I ⁰ and I ⁴⁵ and 2 are referred to with reference to the modulation frequency (f). A signal component having a double frequency (2f signal) can be easily extracted, and the axial orientation θ and the phase difference Δ of the sample S can be calculated in a short time.
At that time, based on the extracted signal components I ⁰ _f , I ⁰ _2f and I ⁴⁵ _2f , the axial orientation θ and the phase difference Δ of the sample S can be quickly and easily calculated using _Equation 14.

[Second Embodiment]
Next, a phase difference measuring apparatus according to a second embodiment of the present invention will be described with reference to FIGS.
FIG. 3 is a diagram showing a schematic configuration of the phase difference measuring apparatus 1A.
The phase difference measuring apparatus 1A is different from the measuring apparatus of the above-described embodiment in that a configuration including a rotating mechanism 5A that rotates the polarizer 41 instead of the rotating mechanism 5 of the modulation unit 4 is different. Other configurations are substantially the same as those of the above-described embodiment. That is, the phase difference measuring apparatus 1A can be used when calculating the phase difference and the axial direction of the sample S by the rotating polarizer method in which the polarizer 41 is rotated 360 ° to detect the detection light according to the rotation angle. It is. In addition, although this embodiment is a structure which is not provided with the above-mentioned PEM, you may provide PEM as a modulation | alteration part between the polarizer 41 and the sample S also in this embodiment.

The measurement principle will be described with reference to FIG. FIG. 4 is an explanatory diagram showing the relationship of the polarization axis orientation of each optical element.
When the azimuth angle of the transmission axis of the polarizer 41 is _{φ, the} Mueller matrix P _φ representing the polarizer 41 is expressed by the following formula 15.

Stokes vector S _phi of the irradiated light transmitted through the polarizer 41, with the exception of the 1/2 of the coefficient represented by the following Expression 16.

The Mueller matrix R _θ of the sample S having the axial azimuth θ and the phase difference Δ is expressed by the above-described formula 3. Here, the dichroism of the sample S is set to zero (Ψ = 45 °), and is expressed by the following formula 17. It is.

The Stokes vector S ^phi of light transmitted through the sample S, obtained by multiplying the right vector of numbers 16 to a matrix of Equation 17, indicated by the following Expression 18.

A Mueller matrix A ₄₅ representing the polarization probe 2 whose transmission axis has an azimuth angle of 45 ° is expressed by the above-described equation (4).
Of the near-field light generated on the measurement surface of the sample S by the illumination light, if the Stokes vector of the detection light collected by the polarization probe 2 and detected by the detector 6 is S ^φ ′, the Stokes vector S ^φ ′ An expression representing one component, that is, the light intensity signal ^Iφ of the detection light is a first component obtained by multiplying Equation 18 from Equation 4 from the right, and is represented by Equation 19 below.

In Equation 19, if the coefficients of cos2φ and sin2φ are A and B, respectively, the light intensity signal ^Iφ is expressed by the following Equation 20.

The coefficients A and B coincide with the 2f signal (Equation 12) of 0 ° azimuth and 45 ° azimuth in the method of rotating the polarizer 41 and the PEM 42 of the above-described embodiment by 45 ° integrally. Indicated.

That is, a detection signal having an azimuth angle twice as large as the azimuth angle φ of the polarizer 41 is applied to a function of sin 2φ and cos 2φ (data fitting), and the coefficients A and B are obtained. And the phase difference Δ can be calculated.

  Based on the above measurement principle, if the detector 41 rotates the polarizer 41 and the detection light collected by the polarization probe 2 according to the rotation angle φ is detected by the detector 6, the calculation unit 8 detects the detection signal. The coefficients A and B are acquired, and thereby the axial direction θ and the phase difference Δ of the sample are calculated.

According to this embodiment, the following effects can be achieved.
A rotation mechanism 5A for rotating the polarizer 41 in the front stage of the sample S is provided, and the polarization probe 2 is set in accordance with the azimuth angle φ of the transmission axis of the polarizer 41 with respect to the transmission axis of the polarization probe 2 provided in the rear stage of the sample S. in so it is the obtaining the light intensity signal I ^phi of the near-field light condensing, also rotate the sample S with respect to the polarization probe 2, it becomes unnecessary to rotate the polarization probe 2 with respect to the sample S.
Furthermore, by collecting the near-field light using the polarization probe 2, the near-field light generated on the measurement surface of the sample S can be measured with spatial resolution below the wavelength of the light, exceeding the light diffraction limit. Thus, the axial orientation and phase difference of the sample S can be measured with high spatial resolution.

Also, for each azimuth angle phi of the transmission axis of the polarizer 41, because to obtain the light intensity signal I ^phi, and the light intensity signal I ^phi fitted by a cosine function cos2φ and sine functions Sin2fai, with I ^φ = 1 + Acos2φ + Bsin2φ The coefficients A and B shown can be easily calculated, and the axial orientation θ and the phase difference Δ of the sample can be calculated in a short time based on the equation (22).

  It should be noted that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.

  The present invention can be used not only for a phase difference measuring apparatus that measures the axial direction and phase difference of a birefringent sample, but also widely used for an apparatus that measures other characteristics using the measured axial direction or phase difference. be able to.

1,1A Phase difference measuring device 2 Polarization probe (near field probe)
3 Irradiation unit 4 Modulation unit 5, 5A Rotation mechanism 6 Detector (detection unit)
8 Calculation unit
41 Polarizer 42 PEM (Modulator)
S sample

Claims (7)

A polarizer that transmits light from the irradiation unit into linearly polarized light, and
A modulator that is provided between the polarizer and the sample and modulates a polarization state of linearly polarized light from the polarizer;
Among the near-field light, wherein the polarized light from varying tone is generated in the measurement surface of the sample by being irradiated with polarized light probe having an aperture of elliptical or slit-shaped to transmit predetermined vibration direction of the linearly polarized light,
The polarizer and the modulator are rotated together so that the difference between the azimuth angle of the transmission axis of the polarizer and the azimuth angle of the modulation axis of the modulator is always 45 °, and the polarization probe a rotating mechanism to set the azimuth angle of the transmission axis of the polarizer azimuth of the transmission axis relative to the azimuth angle of the two types of 0 ° and 45 °,
A detector that detects near-field light collected by the polarization probe and generates a light intensity signal;
Based on the light intensity signal, the phase difference between the polarization component of the fast axis direction and the polarization component of the slow axis direction generated by the polarized light irradiated to the sample, and an arithmetic unit that calculates the axis direction of the sample;
The rotation mechanism sets the transmission axis of the polarizer to two azimuth angles of 0 ° and 45 °, and the detection unit detects near-field light at the set azimuth angle, A phase difference measuring apparatus for measuring an axial direction and a phase difference of a sample. The phase difference measuring apparatus according to claim 1 ,
An extraction unit for extracting from the light intensity signal a signal having the same frequency as the modulation frequency when the modulator modulates the polarization state, and a signal having a frequency twice the modulation frequency;
The phase difference measuring apparatus characterized in that the calculation unit calculates an axial direction and a phase difference of a sample based on a magnitude of a signal extracted by the extraction unit. The phase difference measuring apparatus according to claim 2 ,
The signal extracted by the extraction unit is:
A signal component I ⁰ _f having the same frequency as the modulation frequency f extracted from the light intensity signal when the azimuth angle of the transmission axis of the polarizer is 0 °, and a signal I ⁰ _2f having a double frequency,
A signal component I ⁴⁵ _2f having a frequency twice the modulation frequency extracted from the light intensity signal when the azimuth of the transmission axis of the polarizer is 45 °,
The arithmetic unit calculates the axial direction θ and the phase difference Δ of the sample based on the following Equation 1;

The phase difference measuring apparatus according to claim 1 ,
A phase difference measuring apparatus, wherein a rotation range of a transmission axis of the polarizer is −45 ° to 90 °. The phase difference measuring apparatus according to claim 1 ,
The rotation range of the transmission axis of the polarizer is 0 ° to 135 °,
The computing unit is
Of each signal component I ⁰ _2f , I ⁹⁰ _{2f having} a frequency twice the modulation frequency of the modulator extracted from the light intensity signal when the azimuth angle of the transmission axis of the polarizer is 0 ° and 90 ° Sum and
A sum of signal components I ⁴⁵ _2f and I ¹³⁵ _{2f having} a frequency twice the modulation frequency extracted from the light intensity signal when the azimuth of the transmission axis of the polarizer is 45 ° and 135 °;
The phase difference measuring device is calculated by correcting the zero point of the azimuth angle of the transmission axis of the polarizing probe. In the phase difference measuring apparatus according to claim 5 ,
A phase difference measuring apparatus, wherein a rotation range of a transmission axis of the polarizer is −45 ° to 180 °. A polarizer that transmits light from the irradiation unit into linearly polarized light, and
A polarizing probe having an elliptical or slit-shaped opening that transmits linearly polarized light in a predetermined vibration direction out of the near-field light generated on the measurement surface of the sample by being irradiated with polarized light from the polarizer;
A rotation mechanism for rotating the polarizer to change the azimuth angle of the transmission axis of the polarizer with respect to the azimuth angle of the transmission axis of the polarizing probe;
A detector that detects near-field light collected by the polarization probe and generates a light intensity signal;
Based on the light intensity signal, the phase difference between the polarization component of the fast axis direction and the polarization component of the slow axis direction generated by the polarized light irradiated to the sample, and an arithmetic unit that calculates the axis direction of the sample;
The equipped, at the same time when the rotation mechanism rotates the transmission axis of the polarizer, the detector is the polarization probe by detecting the near-field light that will be focused in accordance with the azimuth angle of the transmission axis of the polarizer,
The arithmetic unit fits the light intensity signal I ^φ corresponding to the azimuth angle φ of the transmission axis of the polarizer using a cosine function cos 2 φ and a sine function sin 2 ^φ having an azimuth angle twice the azimuth angle φ. , I ^φ = 1 + A cos 2φ + B sin 2φ, the coefficients A and B are obtained, and the axial orientation θ and the phase difference Δ of the sample are calculated based on the following equation (2) .

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