JPS61210920A - Automatic birefringence meter - Google Patents

Abstract

PURPOSE:To measure automatically the main vibration orientation and phase delay of a birefringence substance quickly at high accuracy by using a rotary polarizer and a rotary analyses. CONSTITUTION:A light beam with less polarization coming out of a single color light source composed of a light source 1 and a spectroscope or an interference filter 2, or laser is irradiated on the arbitrary part of the birefringence substance 5 made into a plate-like shape, which is fitted on a biaxial jogging device 6, through the rotary polarizer 4, and the polarized light component of the transmitted light is measured by a photodetector 9 through a rotary analyses 7. With the use of a microprocessor having display and arithmetic processing functions, a control, measurement, display and arithmetic processing part 10 adjusts the polarized light orientation of the rotary polarizer 4, that of the rotary analyses 7 and the biaxial jogging device 6 setting the irradiated part of the plate-like birefringence substance 5, and measures an electrical output signal from the photodetector 9. Thus, the birefringence and distribution can be automatically measured quickly at high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for configuring and measuring an automatic birefringence meter that can automatically measure the principal vibrational direction and phase delay of a birefringent substance at high speed and with high accuracy.

When a plane wave of light with a constant frequency is incident on a material that is optically anisotropic, or a material that has become optically anisotropic due to the addition of a force or an electromagnetic field, the light will split into two waves. The two plane waves are separated and travel in the same direction, but the direction of the linear deflection of the electric vector and the phase velocity are different, resulting in a difference in the refractive index of the material for the two plane waves. This difference in refractive index is called birefringence.Birefringence sensitively reflects the structure of materials and the influence of external fields applied to them, so it is a highly sensitive and useful method for studying the structure and properties of materials. give.

To measure birefringence, a monochromatic light source, a polarizer, a birefringent material to be measured, an analyzer, and a photodetector are generally used. After determining the principal vibration direction, the phase delay is determined. It is done by procedure.

However, if this is done manually, the adjustment operation requires considerable skill and the measurement takes a long time, so the development of an automatic birefringence meter that can automatically measure with high precision is strongly desired. ing. Furthermore, when performing multi-point measurements to measure birefringence in a dynamically changing system or to determine the distribution of birefringence, it is obvious that an automatic birefringence meter that can perform high-speed and automatic measurements is desirable. Furthermore, it is clear that it would be even more preferable to directly and automatically obtain information regarding the structure and properties of a substance from the measurement of birefringence, for example, the residual strain of a semiconductor wafer from the birefringence caused by the photoelastic effect.

The purpose of the present invention is to provide an automatic birefringence meter that can quickly and automatically measure the principal vibrational direction and phase delay of a birefringent substance with high precision, and to provide a configuration method and a measurement method for specifically realizing this. It's about giving.

First, the configuration of the automatic birefringence meter of the present invention will be explained with reference to FIG. 1. The transmitted light is irradiated onto the birefringent substance 5 to be measured, the transmitted light is collected by the lens 8, and the transmitted light can be detected as an electrical signal by the photodetector 9. In this case, in order to measure the distribution of birefringence, the birefringent substance 5 to be measured is moved by a two-wheel microstimulator 6 driven by a pulse motor or a servo motor.
The irradiation position can be set to any part using an external control signal. The monochromatic light source used here is
It is preferable that there is little bias, and if there is bias, it is necessary to reduce the bias using a depolarizer or the like. Further, instead of the monochromatic light source consisting of the light source 1 and the spectrometer or the interference filter 2, a laser may be used.

(W) The transmitted light measuring section includes a rotating polarizer 4 and a rotating analyzer, which are rotationally driven by a pulse generator or a servo motor, the polarization direction of which can be arbitrarily set using an external '5ifll signal, which are important components of the present invention. 7 at the front and back positions of the birefringent substance to be measured 5, light of any polarization direction can be irradiated to any part of the birefringent substance to be measured 5, and any polarization component of the transmitted light can be detected. This constitutes a polarized transmitted light measuring section.

(c) Two-wheel microstimulator 6, rotating polarizer 4, and rotating analyzer 7
A cap I measurement/display/arithmetic processing unit 10 is configured using a microprocessor having a display/arithmetic processing function capable of inputting/outputting control signals to and measuring electrical output signals from the photodetector 9. In this case, instead of the measurement/display/arithmetic processing unit 10 using a microprocessor, for example, an FI
A micro combinator for fi such as IJITStl FM-11 may be used by adding control and measurement functions.

Next, using an automatic birefringence meter consisting of a polarized transmitted light measurement section and a control/measurement/display/arithmetic processing section as described above,
We will explain a measurement method that automatically determines the principal vibrational direction and phase delay of a birefringent material made into a flat plate with high precision and at high speed.

In the automatic birefringence meter of the present invention, as shown in FIG.
One of the principal vibrational directions OD° and 0' of the birefringent material, which are orthogonal to each other with respect to the reference direction Ox, for example, 00'
is an angle ψ, and the polarization azimuth OP of the rotating polarizer 4 is an angle φ, and the polarization azimuth OA of the rotating analyzer 7 is an angle χ with respect to the polarization azimuth OP of the rotating polarizer 4. When light with an intensity of 1o is incident on the system, the intensity I of the transmitted light is determined by taking into account the reflection (reflectance: R) on the surface of the birefringent material, as described in the literature (M, 8orn and εJolf:
Pr1nciples of 0ptics 4th
ed, Pergamon Press, p. 6
95. '1970), 1-1o (1-R)''
(cos' x −5in2(φ−ψ)x 5in2
It is expressed as (φ−ψ+χ)sin”δ/2+ (1) where ψ and δ are the principal vibration direction and phase delay of the flat birefringent material to be measured, respectively.

Now consider the following two cases in this system.

(A) When the polarization direction of the rotating polarizer 4 and the polarization direction of the rotating analyzer 7 are parallel (χ-0), formula (1) is 1,, m1o(1-R) (1-sin 2(φ −φ)
, stnδ/21 (2).

(B) When the polarization direction of the rotating polarizer 4 and the polarization direction of the rotating analyzer 7 are perpendicular (χ-π/2), equation (1) is 1i=Io(1-R) Sln 2(φ-ψ) si
n”δ/2 (3).

From these two cases (A) and (B), that is, equations (2) and (3), the equation (4) that forms the basis of the new measurement method of the present invention is determined. This equation (4) is characterized in that it is not related to the incident light intensity ■0 and the reflectance R of the surface of the birefringent material. Therefore, we measure Ill and IJL as functions of φ,
All you have to do is determine ψ and δ that satisfy equation (4). At this time, φ that gives the minimum value on I/(Ih+1+) is the principal vibration direction ψ, and the maximum value of ■↓/(IA+II+) is si
Since n'δ/2 is obtained, the phase delay δ can be obtained from this. As a specific measurement method, for example, (a) First, the polarization directions of the rotating polarizer 4 and the rotating analyzer 7 are made parallel (χ-0), and the polarization direction is set at 10 degrees every 10 degrees from the reference direction OX.
Measure the intensity of the transmitted light during rotation (φ-0°, lOo, 20°...350°).

An example of the measurement results is shown in FIG. 3(a).

(b) Similarly, the polarization directions of the rotating polarizer 4 and the rotating analyzer 7 are set perpendicular (χ-π/2), and one rotation is made every 10 degrees from the reference direction OX (φ=0°, 10°, 20°...35
0") is measured. An example of the measurement results is shown in FIG. 3(b).

(C) Measured intensity of transmitted light I11 and ■One rotation every 10 degrees from machining! Engineering/CI +11. ).

An example of the calculation results is shown in FIG. 3(c).

(d) Calculation result of one rotation every 10 degrees [h/ (Ih+I
A least squares optimization method using the main vibration direction ψ and the phase delay δ as parameters is applied so that the 36 points of n) satisfy equation (4). At this time, the main vibration direction ψ is I/(L÷■11
), and the phase delay δ is equal to φ that gives the minimum value of
The maximum value of [L/(Ifu÷In), that is, sin”δ
/2. An example of the optimal calculation result is shown in Part 3 (c).
As shown in the figure.

As described above, the automatic birefringence meter of the present invention is composed of a polarized transmitted light measuring section and a cap I measurement/display/arithmetic processing section using a microprocessor. It has the ability to irradiate light with any polarization direction and quickly and automatically measure the component intensity of the transmitted light in any polarization direction. In addition, the measurement method is as follows: incident light intensity 1
o and the reflectance cost of the surface of a birefringent material (4
), the principal vibrational direction ψ and phase lag δ of the birefringent material
Since this method is used to determine by applying the least squares optimization method, birefringence can be determined with high accuracy. Therefore, the automatic birefringence meter of the present invention can measure birefringence and its distribution automatically with high precision and at high speed compared to conventional manual measurement methods, so it can be used as an evaluation or inspection tool in the manufacturing field. The use of birefringent needles becomes possible,
The use of birefringent needles as a research tool is greatly expanded.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an automatic birefringence meter according to the present invention. 1 is a light source, 2 is a spectrometer or an interference filter, 3 is a lens, 4 is a rotating polarizer, 5 is a birefringent material made into a flat plate, 6 is a biaxial fine shaker, 7 is a rotating analyzer, 8 is a lens, 9 1 is a photodetector, and 10 is a control/measurement/display/arithmetic processing unit using a microprocessor. ! ! Figure 2 shows the reference orientation OX, e in polarized transmitted light measurement.
11 is a diagram showing the relationship between the principal vibrational direction OD' of a refractive material and 000, the polarization direction OP of a polarizer, and the polarization direction 0^ of an analyzer. Figure f143 is a diagram showing an example of measurement and optimal calculation results obtained based on the measurement method of the present invention.

Claims (1)

[Claims] 1. An automatic system characterized by using a rotating polarizer (4) that can be set to any polarization direction using an external control signal and a rotating analyzer (7) that can detect polarization components in any direction. A birefringent meter comprising a light source (1) and a spectrometer or interference filter (2)
Light with little polarization emitted from a monochromatic light source or laser is passed through a rotating polarizer (4),
), which irradiates any part of the birefringent material (5) in the form of a flat plate, and measures the transmitted light with a photodetector (9) through a rotating analyzer (7); , controls the biaxial fine mover (6) that sets the polarization direction of the rotating polarizer (4) and the rotating analyzer (7) and the irradiation area of the flat birefringent material (5), and controls the photodetector (9). ) consists of a control/measurement/display/arithmetic processing unit (10) using a microprocessor equipped with display/arithmetic processing functions that can measure the electrical output signal from the controller (10) or a general-purpose microcomputer equipped with control/measurement functions. Automatic birefringence meter. 2. In the automatic birefringence meter according to claim 1, when the polarization directions of the rotating polarizer (4) and the rotating analyzer (7) are rotated parallel to each other, the polarization directions of the rotating polarizer (4) and the rotating analyzer (7) are rotated perpendicularly to (A). A least squares optimum is applied so that the transmitted light intensity measured as a function of the rotation angle in case (B) satisfies equation (4), which does not depend on the intensity of the light incident on the birefringent material (5) and its reflection at its surface. A measurement method that applies the method to determine the principal vibration direction and phase delay of a birefringent material (5).