JP2006071458A - Double refraction phase difference measuring device and double refraction phase difference measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a measuring device and a measuring method capable of measuring a phase difference immediately only by setting a sample without a rotation mechanism. <P>SOLUTION: This double refraction phase difference measuring device is equipped with a light flux generation means 1 for generating a monochromatic light flux, a polarization irradiation means 2 by putting the light flux into a specific polarization state and irradiating a measuring object 3 therewith, a polarization state measuring means 4 for measuring the polarization state of the light flux transmitted through the measuring object 3 or reflected thereby by three or more kinds of analyzer angles and acquiring each analyzer output, and an operation means 6 for calculating the double refraction phase difference of the measuring object 3 from each analyzer output. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a birefringence phase difference measuring apparatus and a birefringence phase difference measuring method. Specifically, the present invention relates to a birefringence phase difference measuring apparatus and a birefringence phase difference measuring method for obtaining a birefringence phase difference of a measurement object from three or more analyzer outputs in a polarization state of a light beam transmitted or reflected by the measurement object.

  Conventionally, the birefringence phase difference measurement generally uses the Senarmon method or the rotation analyzer method. According to these methods, the phase difference of various samples can be measured with high accuracy. (For example, refer nonpatent literature 1).

  FIG. 9 shows an example of an ellipsometer as a conventional birefringence phase difference measuring apparatus. The ellipsometer includes a collimator arm 109 and a telescoping arm 110. The collimator arm is usually fixed, and the telescoping arm can rotate around the intersection of the optical axes in a plane including the optical axes of both arms. The angle of the two arms can be read to 0.01 ° using, for example, a rotary scale plate and a vernier. A sample stage is provided so that the measurement object (sample) 105 is placed at the center axis (intersection of both arms) of the apparatus. On the collimator arm 109 side, the monochromatic light beam is generated by passing the emitted light from the light source 101 through the monochromatic light filter 102, the monochromatic light beam is passed through the polarizer 103 to be in a polarized state, and a quarter wavelength plate (compensation plate) ) The measurement object 105 is irradiated after passing through 104. On the telescope arm 110 side, an analyzer angle is determined for the light beam reflected by the measurement object 105 using the analyzer 106, an analyzer output is detected by the photodetector 107, and a light output display arranged outside the arm. Displayed on the instrument 108. In order to measure the birefringence phase difference, two of the azimuth angle of the polarizer 103, the azimuth angle of the compensation plate 104, the azimuth angle of the analyzer 106, and the phase difference of the compensation plate 104 are fixed, and the two are changed. . Typically, the azimuth and phase difference of the compensation plate 104 are fixed, and the polarizer 103 and the analyzer 106 are rotated to obtain the azimuth of the polarizer 103 and the analyzer 106 at which the output is minimized. Ideally, the azimuth angles of the polarizer 103 and the analyzer 106 satisfying the extinction condition (output becomes 0) are obtained. Each of the polarizer 103 and the analyzer 106 can be rotated in a plane perpendicular to the optical axis, and can be read up to 0.005 ° using, for example, a rotary scale plate and a vernier. Polarization analysis parameters Δ and ψ on the sample surface are obtained from the azimuth angles of the polarizer 103 and the analyzer 106 that minimize the output, and the birefringence phase difference of the sample is obtained from the polarization analysis parameters Δ and ψ on the sample surface.

  The Senalmon method is a method in which the extinction condition is automatically detected by various servo mechanisms. The servo motor rotates the polarizer and the analyzer to obtain the azimuth angles of the polarizer 103 and the analyzer 106 that satisfy the extinction condition. These azimuth angles are divided into four zones depending on the combination of the polarizer and analyzer angles, and automatic detection is possible for all of these four zones.

  The rotation analyzer method is a method of detecting the polarization state of reflected (or transmitted) elliptically polarized light from a sample by rotating only the analyzer with a synchronous motor. The intensity of light incident on the detector is converted into, for example, 256 digital signals per rotation and processed by a computer to obtain ellipsometric parameters Δ and ψ on the sample surface.

Handbook of optical measurement Toshiharu Tada, Junpei Takiuchi, edited by Shigeo Minami Asakura Shoten, published in 1981 (Chapter 2, Hideyoko Yokota, Optical Measurements 2.4.2-2.4.4, pages 260-264, Fig. 2.4.4) (Fig. 2.4.9 etc.)

  However, these conventional apparatuses are accompanied by a driving mechanism for rotating the polarizing element, and it takes a time of several seconds to several tens of seconds for measurement. Moreover, high accuracy may not be required depending on the purpose of measurement.

An object of the present invention is to provide a measuring apparatus and a measuring method capable of measuring an absolute value of a phase difference immediately by setting a sample without a rotating mechanism.
Alternatively, it is an object to provide a measuring apparatus and a measuring method capable of measuring with a small number of angle points and shortening the measuring time.

In order to solve the above-described problem, a birefringence phase difference measuring apparatus according to claim 1 includes, as shown in FIG. 1, for example, a light beam generating unit 1 that generates a monochromatic light beam, and a light beam in a specific polarization state. A polarized light irradiating means 2 for irradiating the measuring object 3, and a polarization state measuring means 4 for measuring the polarization state of the light beam transmitted or reflected by the measuring object 3 at three or more analyzer angles and obtaining respective analyzer outputs; And calculating means 6 for calculating the birefringence phase difference of the measuring object 3 from each analyzer output.
If comprised in this way, the birefringence phase difference measuring apparatus which can measure a phase difference simply and in a short time can be provided.

Further, the invention according to claim 2 is the birefringence phase difference measuring apparatus according to claim 1, wherein, for example, as shown in FIG. 1, the polarization state measuring means 4 transmits three or more luminous fluxes transmitted or reflected. The beam splitting means 40 for splitting the beam, the analyzers 51A to 51C having different analyzer angles for transmitting the divided beams, and the light amounts transmitted through the analyzers 51A to 51C are detected to obtain respective analyzer outputs. Photo detectors 52A-52C.
Note that the light beam splitting means 40 and the analyzers 51A to 51C are not necessarily different from each other, and may be realized as one having both functions. With this configuration, the phase difference can be measured immediately by simply setting the sample without the rotation mechanism.

Further, in the invention according to claim 3, in the birefringence phase difference measuring apparatus according to claim 1 or 2, for example, as shown in FIG. 5, the polarization state measuring means 4 is configured to change the analyzer angle by rotation. There are three or more types of rotation analyzers 43 that can be changed, and a photodetector 52D that detects the amount of light transmitted through the rotation analyzer 43 and obtains the output of each analyzer.
With this configuration, the phase difference can be measured with a small number of angle points, and the measurement time can be shortened.

According to a fourth aspect of the present invention, in the birefringence phase difference measuring apparatus according to any one of the first to third aspects, the three or more types of analyzer angles include 0 degrees and 90 degrees. .
The angle includes values in the vicinity thereof, including variations in device manufacturing and optical device adjustment. If comprised in this way, the process of calculating a phase difference from an analyzer output will become simple, the load of a calculating means will be small, and processing time will be shortened.

According to a fifth aspect of the present invention, in the birefringence phase difference measuring device according to any one of the first to fourth aspects, the specific polarization state is circularly polarized light or linearly polarized light.
Note that circularly polarized light or linearly polarized light includes a state in the vicinity thereof, including variations in device manufacturing and variations in optical equipment adjustment. With this configuration, the calculation model can be simplified and the phase difference can be easily calculated.

Further, in the birefringence phase difference measuring method according to claim 6, as shown in FIG. 8, for example, as shown in FIG. 8, a light beam generation step (S 001) for generating a monochromatic light beam, And a polarization state measuring step (S002), and a polarization state measuring step of selectively measuring the polarization state of the light beam transmitted or reflected through the measuring object 3 at three or more analyzer angles to obtain each analyzer output ( S003) and a calculation step (S004) for calculating the birefringence phase difference of the measurement object 3 from each analyzer output.
If comprised in this way, the birefringence phase difference measuring method which can measure a phase difference simply and in a short time can be provided.

  According to the present invention, it is possible to provide a measuring apparatus and a measuring method capable of measuring the absolute value of the phase difference immediately by setting the sample without the rotation mechanism. Alternatively, it is possible to provide a measuring apparatus and a measuring method capable of measuring with a small number of angle points and shortening the measuring time.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a configuration example of a birefringence phase difference measuring apparatus according to the first embodiment. In the present embodiment, an example is shown in which the polarization state measuring unit 4 includes a beam splitting unit 40 that splits a transmitted beam into three or more beams.

  Reference numeral 1 denotes a light beam generating means for generating a monochromatic light beam, which is composed of a He-Ne laser 11A as a light source for emitting monochromatic light. Reference numeral 2 denotes polarized light irradiating means for irradiating the measurement object (sample) 3 with the monochromatic light beam generated by the light beam generating means 1 in a specific polarization state. The polarized light irradiation means 2 includes a polarizer 21 and a quarter wavelength plate 22. The polarizer 21 can polarize the light beam and adjust the polarization state. The quarter-wave plate 22 changes the polarization state (phase) of the light beam by 90 degrees (π / 2). In the present embodiment, the monochromatic light beam generated by the He—Ne laser 1 is converted into a linearly polarized light beam by the polarizer 21, converted into a circularly polarized light beam by the quarter wavelength plate 22, and is applied to the measurement object 3. Irradiated. The specific polarization state irradiated to the measuring object 3 is circularly polarized light.

  The light beam that has passed through the measurement object 3 enters the polarization state measuring means 4. The polarization state measuring means 4 selectively measures the polarization state of the light beam that has passed through the measurement object 3 at three or more analyzer angles to obtain each analyzer output. In this embodiment, the polarization state measurement means 4 transmits the light. A light beam splitting means 40 (including each analyzer 51A to 51C having a different detection angle for transmitting each divided light beam) and a light amount transmitted through each analyzer 51A to 51C are detected to split the light beam into three or more light beams. And photodetectors 52A to 52C for obtaining respective analyzer outputs.

  The beam splitting means 40 is composed of a first non-polarizing beam splitter 41A and first and second polarizing beam splitters 42A and 42B. The first non-polarizing beam splitter 41A divides the light beam that has passed through the measurement object 3 into two parts, one of the divided light beams into the first polarizing beam splitter 42A, and the other light beam into the second polarizing beam splitter 42B. Exit. The first polarizing beam splitter 42A divides the light beam incident from the non-polarizing beam splitter 41A into two parts according to the polarization state (P-polarized light and S-polarized light), and one of the divided light beams is supplied to the first photodetector 52A. The other is emitted to the second photodetector 52B. The second polarization beam splitter 42B emits the other light beam divided by the first non-polarization beam splitter 41A to the third photodetector 52C without being divided (whether it is all P-polarized light or S-polarized light). .

  In the present embodiment, the first polarization beam splitter 42A has the functions of the first analyzer 51A and the second analyzer 51B, and the second polarization beam splitter 42B has the function of the third analyzer 51C. Have Therefore, the analyzers 51A to 51C are included in the light beam splitting means 40. The polarization state of the light beam passing through the light beam splitting means 40 is set so as to obtain analyzer outputs at different predetermined analyzer angles. For example, the first analyzer angle is set to 0 degrees, the second analyzer angle is set to 90 degrees, and the third analyzer angle is set to the other analyzer angles. In the first non-polarizing beam splitter 41A, the polarization state of the transmitted light is unchanged. In the first polarization beam splitter 42A, the light is separated into P-polarized light and S-polarized light, but the analyzer angle is set so that the first analyzer angle is 0 degree for one of the divided light beams. A portion with an angle of 0 degree is emitted to the first photodetector 52A, and the analyzer angle is set to be the second analyzer angle of 90 degrees for the other light flux, and a portion with an analyzer angle of 90 degrees is the first part. The light is emitted to the second photodetector 52B. In the second polarization beam splitter 42B, one of P-polarized light and S-polarized light is emitted to the third photodetector 52C, and is set to have a third analyzer angle. When the analyzer angle is selected in this way, the calculation is facilitated as described later, which is preferable. Further, it is preferable to select 45 degrees and 135 degrees as the third (other) analyzer angle because the calculation becomes easy.

  The first to third photodetectors 52A to 52C detect the amount of light transmitted through the second or third polarization beam splitters 42A and 42B as the analyzers 51A to 51C, and obtain respective analyzer outputs. The analyzer outputs obtained by the first to third photodetectors 52 </ b> A to 52 </ b> C are amplified by the first to third optical amplifiers 53 </ b> A to 53 </ b> C, respectively, and transmitted to a personal computer as the computing means 6. The calculation means 6 acquires the outputs of the first to third optical amplifiers 53A to 53C with the analog input unit 62, and uses the built-in software (calculation program) 61 to measure the measurement object (sample) from each analyzer output. The birefringence phase difference of 3 is calculated. Thereby, as described later (see (Expression 11) to (Expression 13)), the phase difference can be calculated without being affected by the roll angle of the sample 3.

Next, how to calculate the birefringence phase difference (hereinafter simply referred to as phase difference for simplicity) will be described.
In the case of expressing the polarization state of light, in the three-dimensional xyz coordinate system, the x component of the elliptically polarized electric vector (may be a magnetic vector) traveling in the z direction is E _x , the y component is E _y , and the analyzer angle is 0 degree. If the parameter corresponding to the analyzer output is a _x , the parameter corresponding to the analyzer output at an analyzer angle of 90 degrees is a _y , and the phase difference is δ, (Equation 1) is established.

(E _x / a _x ) ² + (E _y / a _y ) ² − (2 E _x E _y / a _x a _x ) cos δ = sin ² δ (Equation 1)

If the parameter corresponding to the analyzer output at a detection angle of 135 ° (= 90 ° + 45 °) is a ₁₃₅ , the tangent to the ellipse (Equation 1) is expressed by (Equation 2).

y = x + k (Equation 2)

Here, k = (√2) a ₁₃₅ .

  FIG. 2 illustrates a change state of the polarization state due to the phase difference δ. Here, the high-speed axis direction is 0 °, the low-speed axis direction is 90 °, the azimuth angle is 45 °, and the phase difference is δ = 90 °, 90 ± 3 °, 90 ± 30 °, 90 ± 90 °. The state of elliptically polarized light in the case of measuring the quartz plate is shown. When the quartz plate is rotated, the azimuth angle of the ellipse is also rotated. From FIG. 2, when δ = 90 °, the linearly polarized light has an inclination of 45 °, and the roundness of the ellipse increases as δ moves away from 90 °, and when δ = 90 ± 90 °, the circularly polarized light appears. Recognize.

  The analyzer output is expressed by the distance from the origin of the tangent line that touches the coordinates (Ex, Ey) on the ellipse. For example, when the phase difference is 30 °, the analyzer angle of the first analyzer 51A is 0 °, the analyzer angle of the second analyzer 51B is 90 °, and the analyzer angle of the third analyzer 51C is 135 °. The outputs are 1.0, 1.0, and about 0.5 / √2, respectively.

For simplicity,
a = 1 / a _x , b = 1 / a _y , α = cos δ (formula 3)
x = E _x , y = E _y .. (Formula 4)
Is replaced by (Expression 5).

a ² x ² + b ² y ² -2abαxy = 1−α ² (Equation 5)

Substituting (Equation 2) into (Equation 5) yields (Equation 6).

a ² x ² + b ² (x + k) ² −2abαx (x + k) + α ² −1 = 0 (Equation 6)

By rearranging (Equation 6), a quadratic equation (Equation 7) is obtained.

(A ² + b ² −2abα) × ² +2 (b ² k−abαk) x + b ² k ² + α ² −1 = 0 (Equation 7)

Since the ellipse (Formula 1) and the straight line (Formula 2) are in contact, (Formula 7) has multiple roots.
Therefore, from the discriminant D = B ² −4AC = 0 of the quadratic equation Ax ² + Bx + C = 0, (Equation 8) is established.

D = 4k ² (b ² −abα) ² -4 (a ² + b ² −2abα) (b ² k ² + α ² −1) = 0 (Equation 8)

When this is arranged for α, (Equation 9) is obtained.

2abα ³ + (a ² b ² k ² −a ² −b ² ) α ² −2abα + a ² + b ² −a ² b ² k ² = 0 (Equation 9)

Here, since a, b, and k are constants and can be measured, it is possible to calculate α, that is, the phase difference δ from (Equation 9).

ｐ、ｑをａ，ｂ，ｋで表すと、（式１２）、（式１３）のようになる。

ｐ＝−（１＋（ａ^２ｂ^２ｋ^２−ａ^２−ｂ^２）^２／１２ａ^２ｂ^２）・・（式１２）

ｑ＝（ａ^２ｂ^２ｋ^２−ａ^２−ｂ^２）^３／１０８ａ^３ｂ^３−（ａ^２ｂ^２ｋ^２−ａ^２−ｂ^２）／６ａｂ＋（ａ^２＋ｂ^２−ａ^２ｂ^２ｋ^２）／２ａｂ・・（式１３）

これによりβを、すなわち、αを求めることができる。また、α＝ｃｏｓδ から位相差δを求めることができる。ただし、ｃｏｓ関数の特性により、δの符号はわからず、絶対値のみがわかる。
│δ│＝０〜１８０度である。 In general, when ex ³ + fx ² + gx + h = 0 is replaced with x = β−f / 3e and rearranged, (Expression 10) is obtained.

^{β 3 + (g / e-} f 2 / 3e 2) β + (2f 3 / 27e 3 -fg / 3e 2 + h / e) = 0 ·· ( Equation 10)

In general, the real number solution of β ³ + pβ + q = 0 is as shown in (Expression 11).

When p and q are represented by a, b, and k, they are as shown in (Expression 12) and (Expression 13).

p = − (1+ (a ² b ² k ² −a ² −b ² ) ² / 12a ² b ² ) (formula 12)

^{q = (a 2 b 2 k} 2 -a 2 -b 2) 3 / 108a 3 b 3 - (a 2 b 2 k 2 -a 2 -b 2) / 6ab + (a 2 + b 2 -a 2 b 2 k ² ) / 2ab (Equation 13)

Thereby, β, that is, α can be obtained. Further, the phase difference δ can be obtained from α = cos δ. However, due to the characteristic of the cos function, the sign of δ is not known and only the absolute value is known.
| Δ | = 0 to 180 degrees.

  FIG. 3 illustrates the polarization state in the case of an azimuth angle of 45 ° + 30 ° = 75 ° and a phase difference of ± 30 °. The state in which the azimuth angle is rotated 30 ° counterclockwise from the state of FIG. 2, that is, the crystal plate is rotated counterclockwise by 30 ° (the high speed axis and the low speed axis are rotated by 30 ° from the x axis and the y axis, respectively) ). Since the phase angle is 30 °, the polarization state is a state in which the elliptically polarized light having the phase angle of 30 ° in FIG. 2 is rotated counterclockwise by 30 °.

When obtaining the analyzer output at the detection angle 0 ° of the first analyzer 51A, the detection angle 90 ° of the second analyzer 51B, and the detection angle 135 ° of the third analyzer 51C, the equation of the tangent to the ellipse is , X = a ₀ , y = a ₉₀ , and y = x + (√2) a ₁₃₅ (respectively indicated by broken lines in the figure).
As described above, even when the azimuth angle changes, the analyzer output is determined correspondingly by the phase difference. Therefore, the phase difference can be obtained by measuring the three analyzer outputs.

  As described above, according to the present embodiment, the measurement object is irradiated with the monochromatic light beam, and the light beams transmitted or reflected by the measurement object are selectively measured for the three analyzer outputs having different analyzer angles. The absolute value of the phase difference can be obtained. According to this, it is possible to measure the phase difference immediately by simply setting the sample without the rotation mechanism.

In the case of this embodiment, even if non-polarized light is incident on the polarization state measuring means, the incident light quantity may be unbalanced between the first to third photodetectors 51A to 51C. Since the transmittance and reflectance of the splitter 41A and the polarization beam splitters 41B and 41C are known, correction is possible.
Further, it is possible to use a laser diode LD as a light source of the light beam generating means 1 instead of the laser.

  FIG. 4 shows a configuration example of a birefringence phase difference measuring apparatus according to the second embodiment. This embodiment is also an example in which the polarization state measuring unit 4 includes a beam splitting unit 40 that splits a transmitted beam into three or more beams. However, a light emitting diode LED is used instead of a laser as a light source, and an analyzer is used. The difference is that a Glan-Thompson prism is used instead of the polarizing beam splitter. The same parts as those in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted.

  Recently, since a high-power LED can be obtained, it can be used as a light source for the light flux generating means 1. However, since the light emitted from the LED 11B is not monochromatic light, the narrow band filter 12 is used to narrow the light beam to a predetermined wavelength. As the narrow band filter 12, for example, a filter having a half width of 5 nm is used. The first lens system 13A and the second lens system 13B are used for irradiating the measurement object 3 with a parallel light beam, condensing on the measurement object, or setting the light beam diameter to an appropriate value. The Here, the light beam generation means 1 is composed of an LED 11B, a narrow band filter 12, and a first lens system 13A. Further, since the light emitted from the LED 11B is non-polarized light, polarized light is created by the polarizer 21 (typically, linearly polarized light). The polarized light irradiation means 2 is the same as that of the first embodiment.

The light beam that has passed through the measurement object 3 passes through the second lens system 13B and then enters the polarization state measuring means 4. In the present embodiment, a light beam splitting unit that splits a transmitted light beam into three or more light beams, and analyzers having different analyzer angles that transmit the divided light beams are different from those in the first embodiment. The beam splitting means 40 is composed of second and third non-polarizing beam splitters 41B and 41C, and the first to third analyzers 51A to 51C are respectively connected to the first to third Glan-Thompson prisms 54A to 54C. Composed. The Glan-Thompson prism has a large extinction ratio and can be measured with high accuracy. The extinction ratio can be, for example, 10 ⁶ : 1 or more.

  The second non-polarizing beam splitter 41B divides the light beam transmitted through the measuring object 3 into two parts, and outputs one of the divided light beams to the third non-polarizing beam splitter 41C and the other to the third Glan-Thompson prism 54C. To do. The third non-polarizing beam splitter 41C divides one light beam divided by the second non-polarizing beam splitter 41B into two, the one divided light beam to the first Glan-Thompson prism 54A and the other to the second light beam. The light is emitted to the Glan Thompson prism 54B. The first Glan-Thompson prism 54A emits one light beam split by the third non-polarization beam splitter 41C to the first photodetector 52A, and the second Glan-Thompson prism 54B emits the third non-polarization beam. The other light beam split by the splitter 41C is emitted to the second photodetector 52B, and the third Glan-Thompson prism 54C converts the other light beam split by the second non-polarizing beam splitter 41B to the third light beam. The light is emitted to the photodetector 52C.

  Here, the beam splitting means 40 includes a second non-polarizing beam splitter 41B and a third non-polarizing beam splitter 41C. In the second and third non-polarizing beam splitters 41B and 41C, the polarization state of the transmitted light is unchanged. The light beam that has passed through the light beam splitting means 40 is incident on the first to third Glan-Thompson prisms 54A to 54C, and the first to third Glan-Thompson prisms 54A to 54C are the first to third analyzers 51A to 51C. It has the function of. The first to third Glan-Thompson prisms 54A to 54C are set so as to obtain analyzer outputs at different predetermined analyzer angles. For example, the first analyzer angle is set to 0 degrees, the second analyzer angle is set to 90 degrees, and the third analyzer angle is set to the other analyzer angles. In the first Glan-Thompson prism 54A, the analyzer angle is set to be the first analyzer angle 0 degree, and the analyzer angle of one light beam divided by the third non-polarizing beam splitter 41C is 0 degree. The portion is emitted to the first photodetector 52A. In the second Glan-Thompson prism 54B, the analyzer angle is set to be the second analyzer angle of 90 degrees, and the analyzer angle of the other light beam divided by the third non-polarizing beam splitter 41C is 90 degrees. The portion is emitted to the second photodetector 52B. In the third Glan-Thompson prism 54C, the analyzer angle is set to be the third analyzer angle, and the third analyzer angle (others) of the other light beam divided by the second non-polarizing beam splitter 41B is set. The analyzer angle) is emitted to the third photodetector 52C. It is preferable to select 45 degrees and 135 degrees as the third (other) analyzer angle.

Subsequent stages from the photodetectors 52A to 52C are the same as those in the first embodiment.
In addition to a Glan-Thompson prism using calcite as a polarizer and analyzer, a Gran Taylor prism using calcite and other thin polarizing elements can be used.

  FIG. 5 shows a configuration example of a birefringence phase difference measuring apparatus according to the third embodiment. In the present embodiment, the polarization state measuring unit 4 is an example in which the analyzer is rotated to selectively select three analyzer angles instead of having a beam splitting unit that splits the transmitted beam into three or more beams. Indicates. In the conventional rotating photon method, 0 to 360 degrees are continuously acquired. However, in this embodiment, only three points need be measured, and simplification is greatly achieved. Further, a white light source is used as the light source, and the wavelength is scanned. The same parts as those in FIGS. 1 and 2 are denoted by the same reference numerals, and redundant description is omitted.

  11C is a white light source such as a halogen lamp or a xenon lamp. The outgoing light from the white light source 11C is passed through a spectroscope (monochromator) 14 to obtain monochromatic light having a desired wavelength, which is used for phase difference measurement. Here, the light beam generation means 1 is composed of a white light source 11C and a spectroscope 14. Further, a third lens system 13C is used for condensing light on the incident side of the measurement object 3. The polarized light irradiation means 2 is the same as in the first and second embodiments.

  By measuring while changing the output wavelength of the spectroscope 14, the wavelength dependence of the phase difference can be grasped. A recent spectroscope can control the wavelength of the outgoing light by computer-controlling the angle of the reflection type rotary grating for spectroscopy, and can efficiently measure the wavelength dependence of the phase difference.

  In FIG. 5, reference numeral 43 denotes a rotating polarization beam splitter mechanism in which an analyzer is rotatably mounted and can selectively measure at three or more kinds of analyzer angles to obtain each analyzer output. For example, a rotating analyzer can be used as the rotating polarization beam splitter mechanism 43. For example, by selectively measuring the analyzer output at three types of analyzer angles, the absolute value of the phase difference of the measurement object 3 can be obtained by simple measurement as in the first and second embodiments. be able to.

  Reference numeral 44 denotes an angle encoder that outputs an analyzer angle (rotation angle) of an analyzer in the rotating polarization beam splitter mechanism 43 and transmits it to a personal computer as the computing means 6. The optical detector-optical amplifier may be a single system, and the fourth optical detector 52D and the fourth optical amplifier 53D are the first to third optical detectors 52A to 52C and the first to third optical amplifiers 53A. The thing similar to -53C can be used. The function of the personal computer 6 is almost the same as that of the first and second embodiments, but instead of acquiring the analyzer output at each analyzer angle from the three optical amplifiers, one optical amplifier 53D. To obtain analyzer outputs selectively measured at three analyzer angles. In addition to being connected to the spectrometer 14 to obtain the wavelength of the emitted light, it is connected to the angle encoder 44 to obtain the analyzer angle and not only to calculate the phase difference but also to calculate the wavelength dependence of the phase difference. Further, the influence of the phase difference due to the rotation angle of the analyzer of the rotating polarization beam splitter mechanism 43 can be grasped.

  FIG. 6 shows a configuration example of the birefringence phase difference measuring apparatus in the fourth embodiment. In the present embodiment, the SNR (signal-noise ratio) is improved based on the first embodiment. A drive circuit 15 is connected to a laser (for example, a semiconductor laser) 11D as a light source of the light beam generating means 1 and modulated at, for example, 100 kHz, while only signals near 100 kHz are applied to the first to third optical amplifiers 53A to 53C. Is inserted, and the laser 11D is driven by modulating the luminous flux. By narrowing the band to be measured, disturbance light (DC or low-frequency signal) can be cut and white noise of the circuit system (full band) can be cut, thereby increasing the SNR (signal-noise ratio). It is also possible to modulate by using a laser diode as the light source.

  FIG. 7 shows a configuration example of a birefringence phase difference measuring apparatus according to the fifth embodiment. In the present embodiment, the synchronizing signal source 7 is connected to the drive circuit 15 and the first to third optical amplifiers 53A to 53C of the fourth embodiment, and wavelength modulation and analyzer output are performed using the synchronizing signal. This is to synchronize detection. As a result, the SNR can be further increased. It is also possible to use a laser diode as a light source for modulated light emission and perform synchronous detection.

  FIG. 8 summarizes the processing flow of the birefringence phase difference measuring method in the first to fifth embodiments of the present invention. First, a monochromatic light beam is generated in a light beam generation step (step S001). A monochromatic light beam may be generated by using a monochromatic light source such as the laser 11A as in the first embodiment, and from the LED light source 11B and the white light source 11C as in the second and third embodiments. The monochromatic light beam may be generated through the narrow-band filter 12 and the spectroscope 14. Next, in the polarized light irradiation step (step S002), the measurement object 3 is irradiated with the light beam in a specific polarization state. A polarizer 21 and a quarter-wave plate 22 are used to bring the light beam into a specific polarization state. In the above embodiment, an example in which the specific polarization state is linearly polarized light has been shown. However, circularly polarized light or elliptically polarized light may be used. Next, in the polarization state measurement step (step S003), the polarization state of the light beam transmitted or reflected by the measurement object 3 is selectively measured at three or more analyzer angles to obtain each analyzer output. In order to obtain three or more kinds of analyzer angles, as in the first and second embodiments, the light beam dividing means 40 for dividing the transmitted light beam into three or more light beams is used. The light beams may be detected by the photodetectors 52A to 52C via the analyzers 51A to 51C having different analyzer angles, and transmitted to the computing means 6 via the optical amplifiers 53A to 53C. As in the third embodiment, each analyzer output is detected by the photodetector 52D at the three or more analyzer angles through the rotating analyzer 43 that can change the analyzer angle to three or more, and the optical amplifier 53D is detected. You may transmit to the calculating means 6 via. The light beam splitting means 40 may be a non-polarizing beam splitter or a polarizing beam splitter, and the analyzers 51A to 51C may be polarizing beamsplitters or Glan-Thompson prisms. Next, in the calculating step (step S004), the calculating means 6 calculates the birefringence phase difference of the measuring object 3 from each analyzer output. In the calculation, for example, the output parameters a, b. The birefringence phase difference δ is calculated from k.

  Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and it is obvious that modifications can be made as appropriate without departing from the spirit of the present invention.

  For example, in the above embodiment, the example in which the circularly polarized light is incident on the measurement object has been described, but linearly polarized light may be incident. In this case, for example, if the measurement object is a quarter wavelength plate, when linearly polarized light is incident, the emitted light becomes circularly polarized light. If the phase difference is 90 degrees, it becomes ideal circularly polarized light, but if the phase difference deviates from 90 degrees, it becomes elliptically polarized light. Therefore, the equation of elliptically polarized light can be obtained by the same method as in the above embodiment.

In the above embodiments, the case where the analyzer angles are 0 °, 90 °, and 135 ° has been described. However, the same calculation can be performed even if other angles are selected. In this case, the ternary cubic equation is solved, and the calculation becomes complicated.
Moreover, although the example using three types of analyzer angles was demonstrated in the above embodiment, you may use four or more types. In this case, since there are a plurality of sets of data that can be used for calculation, the reliability of the calculated phase difference is improved.

  Further, a lens or the like that does not substantially affect the polarization state may be inserted in order to enlarge / reduce the measurement range or obtain an appropriate light beam. Further, instead of arranging the optical elements in series, the optical elements may be connected using an optical fiber. In the above embodiment, an example in which a light beam is split using a beam splitter or a rotating analyzer has been described. However, three analyzers are arranged in parallel in the light beam, or mirrors having different reflection angles are provided in the light beam. The light beams may be divided and divided into three directions, or three optical fibers may be inserted into the light beam, and the light may be guided to three analyzers.

  It is used for birefringence phase difference measurement of optical parts.

It is a figure which shows the structural example of the birefringence phase difference measuring apparatus in 1st Embodiment. It is a figure which illustrates the mode of the change of the polarization state by a phase difference. It is a figure which illustrates the polarization state of phase difference +/- 30 degree and azimuth | direction angle 45 degrees +30 degrees. It is a figure which shows the structural example of the birefringence phase difference measuring apparatus in 2nd Embodiment. It is a figure which shows the structural example of the birefringence phase difference measuring apparatus in 3rd Embodiment. It is a figure which shows the structural example of the birefringence phase difference measuring apparatus in 4th Embodiment. It is a figure which shows the structural example of the birefringence phase difference measuring apparatus in 5th Embodiment. It is a figure which shows the processing flow of the birefringence phase difference measuring method in embodiment of this invention. It is a figure which shows the structural example of the conventional birefringence phase difference measuring apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light beam production | generation means 2 Polarization irradiation means 3 Measurement object (sample)
4 Polarization state measurement means 6 Calculation means 7 Synchronization signal source 11A He-Ne laser 11B Light emitting diode (LED)
11C White light source 12 Narrow band filters 13A to 13C First to third lens systems 14 Spectrometer 15 Driving circuit 21 Polarizer 22 1/4 wavelength plate 40 Light beam splitting means 41A to 41C First to third unpolarized beams Splitters 42A and 42B First and second polarizing beam splitters 43 Rotating polarizing beam splitter mechanism (rotating analyzer)
44 Angle encoders 51A to 51C First to third analyzers 52A to 52C First to third photodetectors 53A to 53C First to third optical amplifiers 54A to 54C First to third Glan-Thompson prisms 101 Light source 102 Monochromatic light filter 103 Polarizer 104 1/4 wavelength plate 105 Measurement object 106 Analyzer 107 Photo detector 108 Optical output display 109 Collimator arm 110 Telescope arm δ Phase difference

Claims (6)

Light flux generating means for generating a monochromatic light flux;
Polarized light irradiating means for irradiating the measurement object with the light beam in a specific polarization state;
Polarization state measuring means for selectively measuring the polarization state of a light beam transmitted or reflected by the measurement object at three or more analyzer angles to obtain each analyzer output;
Computing means for calculating a birefringence phase difference of the measurement object from each analyzer output;
Birefringence phase difference measuring device. The polarization state measuring means includes
Beam splitting means for splitting the transmitted or reflected beam into three or more beams;
Each analyzer at a different analyzer angle that transmits each split light beam;
A photodetector that detects the amount of light transmitted through each analyzer and obtains each analyzer output;
The birefringence phase difference measuring apparatus according to claim 1. The polarization state measuring means includes
A rotating analyzer capable of changing the analyzer angle to three or more by rotation;
A photodetector for detecting the amount of light transmitted through the rotating analyzer and obtaining the output of each analyzer;
The birefringence phase difference measuring apparatus according to claim 1. The three or more types of analyzer angles include 0 degrees and 90 degrees;
The birefringence phase difference measuring apparatus according to any one of claims 1 to 3. The specific polarization state is circularly polarized light or linearly polarized light;
The birefringence phase difference measuring apparatus according to any one of claims 1 to 4. A light flux generating step for generating a monochromatic light flux;
A polarized light irradiation step of irradiating the measurement object with the light beam in a specific polarization state;
A polarization state measurement step of selectively measuring the polarization state of the light beam transmitted or reflected by the measurement object at three or more analyzer angles to obtain each analyzer output;
A calculation step of calculating a birefringence phase difference of the measurement object from each analyzer output;
Birefringence phase difference measurement method.

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