WO2008010482A1

WO2008010482A1 - Optical elasticity measuring method and its device

Info

Publication number: WO2008010482A1
Application number: PCT/JP2007/064076
Authority: WO
Inventors: Takahisa Mitsui; Kazuyoshi Suzuki; Junichi Matsumura
Original assignee: Keio University; Toray Engineering Co., Ltd.
Priority date: 2006-07-19
Filing date: 2007-07-17
Publication date: 2008-01-24
Also published as: TW200813393A; JPWO2008010482A1; KR20090034870A

Abstract

A rectilinear polarized light changed into a rectilinear polarized light by a deflection plate (6) is separated by a second polarization beam splitter into a measurement light and a reference light which intersect orthogonally. Among measurement lights which have passed through a measurement object (W) and are reflected by a rear surface of a predetermined layer, a polarized component of the second direction orthogonally intersecting the first direction generated by a change of the polarized state and a rectilinear polarized light of the second direction reflected by a reference mirror are collected by the beam splitter so that they pass through the same optical path and generate interference and the interference light is outputted toward a polarimeter. The polarimeter removes a DC component so as to obtain an interference light intensity value. According to the light intensity value, it is possible to obtain birefringence change amount information, a main stress difference, and angle of respective layers of the measurement object (W) to which the stress is functioning.

Description

Photoelasticity measuring method and apparatus

Technical field

TECHNICAL FIELD [0001] The present invention relates to a photoelasticity measurement method and apparatus for measuring stress and strain acting on a measurement object having transparency such as a liquid crystal panel and a plasma display panel, and more particularly to a microscopic method. The present invention relates to a technique for accurately measuring stress acting on each of two bonded substrates arranged with a gap.

Background art

[0002] The following method is known as a method for obtaining a stress acting on a measurement object having transparency such as a glass substrate. The first method is to irradiate a measurement object held flat on a flat table, measure the reflected light that is reflected from the front and back surfaces of the measurement object, and change the reflected light. The difference and angle of the main stress acting on The second method is to determine the difference and angle of the principal stress that acts on the measurement object from the change in the transmitted light that has passed through the measurement object among the light irradiated to the measurement object. Yes.

[0003] Non-Patent Document 1: Latest Stress 'Strain Measurement' Evaluation Technology (Page 49, Page 66) Supervision: Kozo Kawada Publication: General Technology Center Co., Ltd.

Disclosure of the invention

Problems to be solved by the invention

[0004] However, the conventional method has the following problems.

[0005] Although both the first and second methods function effectively for a single substrate, which is a measurement object having transparency, a plurality of materials having different optical characteristics, particularly refractive indexes, are laminated. When measuring the difference and angle of the principal stress on a bonded substrate, especially two bonded substrates deployed with a small gap, the principal acting on either substrate or both substrates There is a problem that the difference and angle of stress cannot be obtained with high accuracy.

[0006] That is, when the first method is applied to the bonded substrate described above to measure the difference and angle of principal stress acting on either one of the two substrates or both substrates, All of the reflected light that is reflected back from the bonded substrates is synthesized from the front and back surfaces of each substrate. Therefore, even if it is desired to obtain only the reflected light from the back surface of each substrate necessary to know the difference and angle of the main stress, it cannot be easily separated individually. In addition, when the second method is applied, all the transmitted light transmitted through the bonded substrate is synthesized, and the transmitted light transmitted for each substrate cannot be separated individually.

The present invention has been made in view of such circumstances, and relates to a substrate in which a plurality of materials having different refractive indexes as optical characteristics are laminated, particularly a laminated substrate laminated with a minute gap. A photoelasticity measurement method and apparatus capable of accurately classifying a substrate on which stress is applied, and accurately determining the amount of change in birefringence caused by the stress acting on the substrate and the difference and angle of principal stress. The main purpose is to provide. Means for solving the problem

In order to achieve such an object, the present invention has the following configuration.

That is, according to the first aspect of the present invention, at least measurement is performed when irradiation light having a central wavelength force having a wavelength distribution in a predetermined range is irradiated to a measuring object having transparency and a reference surface. The object is irradiated with linearly polarized light in a predetermined first direction,

Of the reflected light that is reflected and returned from the measurement target surface of the predetermined layer of the measurement object, the polarized light component in the second direction orthogonal to the first direction and the reference surface force reflected light that is generated by the change in the polarization state. Together to cause interference in such a way that

Acquire light intensity of interference light by the same polarization components of the two reflected light beams and obtain information on the amount of change in polarization due to birefringence.

It is characterized by that.

[0010] According to the photoelasticity measurement method according to the first invention, the linearly polarized light in the first direction is irradiated toward the measurement object, and the other polarized light is irradiated on the reference surface. The linearly polarized light irradiated on the object to be measured is transmitted through a plurality of layers and reflected back from the front and back surfaces of each layer. At this time, when a stress is applied to the predetermined layer to be measured, the polarization state of the linearly polarized light in the first direction reflected and returned changes. The linearly polarized light in the second direction orthogonal to the linearly polarized light in the first direction in which the polarization state has changed is extracted from all reflected light reflected from the measurement object. The extracted linearly polarized light in the second direction and the reflected light reflected from the reference surface Are combined so as to pass through the same optical path, causing interference.

[0011] The light intensity of the interference light by the same polarization components is further obtained from the two reflected lights that are superimposed. The obtained light intensity change force polarization change information obtained by the birefringence in the object to be measured is obtained. At this time, the amount of change in birefringence = the difference in main stress, the difference in main stress, the thickness of the object to be measured, and the photoelastic coefficient are used. If the three parameters in this equation are known, the remaining unknown parameters can be found. In general, the thickness and photoelastic coefficient of the measurement object can be easily obtained by other means. Therefore, the difference in principal stress of a predetermined layer in a plurality of layers is obtained by obtaining the amount of birefringence as an unknown parameter. be able to.

At this time, the thickness of the measurement object can also be calculated simultaneously by acquiring the light intensity of the interference light while moving at least one of the measurement object or the reference surface back and forth in the light traveling direction. That is, if the optical distance between the layers of the measurement object and the reference surface light intensity substantially coincides with the optical distance between the layers of the measurement object, the light intensity varies due to interference. At this time, for example, if the horizontal axis is the moving distance of the object to be measured or the reference surface and the vertical axis is the light intensity, the change in the light intensity is plotted on a graph and the envelope of the absolute value of the light intensity is taken. The distance between the peaks coincides with the optical distance between the layers of the measurement object. Therefore, the distance force between the peaks and the thickness of the measurement object can be calculated simultaneously.

[0013] According to this method invention, the light intensity at which the light intensity of the interference light is maximized by moving the reference surface or the measurement target surface! /, Or back and forth with respect to the traveling direction of the irradiation light. It is preferred to obtain information U ヽ (claim 2).

[0014] In addition, the light intensity information power at this time can also obtain an accurate amount of change in birefringence, and thus, the difference in principal stress of the predetermined layer can be accurately obtained.

[0015] Further, according to this method invention, the phases of the both reflected light constituting the interference light are separated into approximately half so that the phases are shifted by half wavelength, and the difference between the two phases after separation is taken to obtain the interference light. It is preferable to remove the direct component of the light intensity (Claim 3).

In this case, both phases are inverted by 180 ° by shifting the phases of both reflected lights causing interference by a half wavelength. In other words, by taking the difference between both phases in this state, it is possible to remove the direct current component that does not change the polarization state that also reflects the reference surface force, and change the polarization state. It is possible to extract only the polarized components that have undergone conversion. That is, only the amount of change in polarization when birefringent at a predetermined layer on which stress is applied can be obtained with high accuracy.

[0017] Further, according to the method invention, a periodic relationship is obtained from the relationship between the amount of movement of the reference surface or the measurement target surface and the light intensity of the interference light, and the realization of this periodic relationship. It is preferable to compare the phase with a predetermined reference phase and, based on the result, determine whether the difference in principal stress acting on the predetermined layer of the object to be measured is a force compression force, which is a tension. (Claim 4).

In this case, experiments, theoretical calculations, simulations, etc. are performed using the same sample as the object to be measured, and the reference phase is determined by specifying the conditions of tension and compressive force acting as stress on this sample. Keep it. By comparing this reference phase with the actual phase when the predetermined layer of the measurement object is measured, it is determined whether the difference in the acting main stress is a force compression force, which is a tension.

In addition, according to this method invention, the linearly polarized light irradiated to the measurement target surface and the measurement target surface are rotated relative to each other around the optical axis of the linearly polarized light, and the polarization change due to birefringence is changed at each rotation angle. It is preferable to obtain information on the amount of change and obtain the difference and angle of the principal stress acting on the measurement object from both the information on the amount of change in polarization and the information on the rotation angle (claim 5). For example, the rotation angle is at least two angles, and it is preferable to obtain the angle of the principal stress difference by changing the direction of the linearly polarized light of the light irradiated from each angle (Claim 6).

[0020] In this case, the light intensity value of the interference light obtained at each rotation angle (for example, two angles) is subjected to a beta conversion, a vector of both rotation angles is synthesized, and the principal stress is calculated from the angle indicated by the vector synthesis. The difference angle can be specified.

[0021] Next, according to a seventh aspect of the present invention, at least irradiation light having a wavelength distribution in a predetermined range from the center wavelength is irradiated to a measurement target having a plurality of layers and a reference surface at least. The object to be measured is irradiated with substantially circularly polarized light in which a linearly polarized light in a predetermined first direction is shifted by 45 ° from a second direction component that is 45 ° different from the first direction.

The reflected light reflected from the measurement target surface of the predetermined layer of the measurement target is matched with the optical path length of the reflected light returning from the reference surface, and the reflected light from the measurement target surface is the second direction component. 1Z4 wavelength shifted back to almost linear polarization, and the polarization state changed The polarization component in the third direction orthogonal to the first direction caused by the above is extracted, and the polarization component in the third direction and the reflected light returning from the reference surface force are combined so as to cause interference in the same optical path. ,

It is characterized by that.

[0022] According to the photoelasticity measurement method according to the seventh aspect of the invention, the irradiation light is applied to both the measurement object and the reference surface. At this time, at least the surface to be measured is irradiated with the linearly polarized light in the first direction converted into substantially circularly polarized light. The substantially circularly polarized light applied to the object to be measured passes through a plurality of layers and is reflected on the front and back surfaces of each layer. At this time, when a stress is applied to the predetermined layer to be measured, the polarization state of the substantially circularly polarized light that is reflected back changes, that is, changes to elliptically polarized light. The polarization component in the original first direction is extracted with this polarization state. Then, the linearly polarized light in the third direction orthogonal to the linearly polarized light in the first direction is extracted from all the reflected light reflected by the measurement object. The linearly polarized light in the third direction and the reflected light reflected by the reference surface force are combined so as to pass through the same optical path, causing interference.

[0023] The light intensity of the interference light by the same polarization components is further obtained from the two reflected lights that are superimposed. The obtained light intensity change force polarization change information obtained by the birefringence in the object to be measured is obtained. As the polarization change information, an unknown parameter is obtained among the amount of change in birefringence caused by the stress applied to the predetermined layer to be measured, the thickness of the measurement object, and the photoelastic coefficient. For example, the amount of change in birefringence, which is an arithmetic expression for calculating the difference in principal stress = difference in principal stress X thickness of measurement object X photoelastic coefficient, and if at least two parameters are known, the remaining The unknown parameters can be easily obtained. Furthermore, if the parameters are aligned, the difference in principal stress acting on a given layer can be determined easily and accurately, and as a result, stress is applied to any of the multiple layers! You can also do additional IJ.

[0024] According to the method invention, the light intensity at which the light intensity of the interference light is maximized by moving back and forth of the reference surface or the measurement target surface relative to the traveling direction of the irradiation light. It is preferable to obtain information U ヽ (claim 8). [0025] In this case, by acquiring the light intensity information that maximizes the light intensity of the interference light, it is possible to easily discriminate that the stress is acting on the predetermined layer to be measured. In addition, the exact amount of change in birefringence can be obtained from the light intensity information at this time, and as a result, the difference in principal stress of the predetermined layer can be obtained with high accuracy.

[0026] Further, according to this method invention, the phases of the two reflected lights constituting the interference light are separated into approximately half so that they are shifted by a half wavelength, and the difference between the two phases after separation is taken to obtain the interference light. It is preferable to remove the direct component of the light intensity (claim 9).

[0027] In this case, both phases are inverted by 180 ° by shifting the reflected light by half a wavelength. In other words, by taking the difference between the two phases in this state, it is possible to remove the DC component that does not change in the polarization state reflected by the reference surface, and to extract only the polarization component that has changed in the polarization state. it can. Therefore, it is possible to accurately obtain only the amount of change in polarization when birefringence occurs in a predetermined layer on which stress is applied.

[0028] Further, according to this method invention, the circularly polarized light and the measurement object are relatively moved so that the measurement object surface orthogonal to the propagation direction of the irradiated circularly polarized light moves on the vertical plane. It is preferable to acquire information on the amount of change in polarization due to birefringence at a plurality of points in the process, and to estimate the direction of the stress acting on a predetermined layer of the measurement object from the distribution state (claim 10). In this case, it functions effectively to estimate the angle of principal stress when using substantially circular polarized light.

[0029] Next, an eleventh aspect of the invention is directed to irradiation means for outputting irradiation light having a central wavelength force and a wavelength distribution in a predetermined range;

The irradiation light from the irradiating means is separated into two linearly polarized lights, and the separated linearly polarized light in the first direction is output to a measuring object having a plurality of layers and the other second polarized light. Separating means for outputting linearly polarized light in the direction to the reference surface;

Extraction means for extracting a second direction component of reflected light from the measurement target surface of the predetermined layer;

A combination of the reflected light extracted through the extraction means reflected from the measurement target surface of the predetermined layer of the measurement object and the reflected light returning from the reference surface force so as to cause interference by collectively passing through the same optical path. Means, At least one of the measurement object and the reference surface is a straight line so that the optical path length of the reflected light returning from the measurement target surface of the predetermined layer to the coupling means and the reflected light returning from the reference surface to the coupling means match. Moving means for moving back and forth in the traveling direction of polarized light;

A detecting means for detecting a light intensity change of the same polarization component of the superimposed reflected light; a calculating means for obtaining polarization change amount information due to birefringence based on a detection result of the detecting means;

It is provided with.

[0030] According to the photoelasticity measurement apparatus according to the eleventh aspect of the present invention, the linearly polarized light in the first direction out of the irradiation light separated into two linearly polarized light by the separating means is applied to the measuring object composed of a plurality of layers. And the other linearly polarized light in the second direction is output toward the reference plane. Each linearly polarized light is reflected when it reaches the output destination. In particular, in a measurement object having transparency, the transmitted linearly polarized light is reflected on the front and back surfaces of each layer. The reflected light reflected from the plurality of surfaces changes its polarization state in the process of reciprocating through the layer when stress is applied to the predetermined layer. From this linearly polarized light whose polarization state has changed, only the polarization component in the second direction orthogonal to the first direction is extracted by the extraction means. Then, the coupling means causes the extracted polarized component and the reflected light from the reference surface to interfere together so as to pass through the same optical path.

[0031] By combining the reflected light into the coupling means, the moving means moves at least one of the measurement object or the reference surface back and forth in the direction of travel of the linearly polarized light, thereby returning to the coupling means. The optical path length to the reference surface force coupling means matches either one of the linearly polarized light in the second direction that is reflected back. In this case, when both optical path lengths coincide with each other, only the reflected light that reciprocates through the predetermined layer having the back surface can be extracted by the extraction means, and the extracted polarization component and the reflected light from the reference surface can be extracted. Of these, the light intensity change of the same polarization component is detected by the detection means. Then, based on the detection result, the calculation means obtains polarization change information due to birefringence at the measurement object. That is, the first method invention can be suitably realized.

[0032] According to the apparatus invention, the irradiation means, the reference surface, the separation means, the extraction means, and the coupling hand It is preferable to provide a rotation drive means for relatively rotating the optical system consisting of the stage and the detection means and the measurement object around the optical axis of the linearly polarized light output from the optical system to the measurement object ( Claim 12).

[0033] According to this configuration, it is possible to irradiate the measurement object with linearly polarized light at different angles.

That is, information on the amount of change in polarization due to birefringence can be obtained for each rotation angle. The angle of the principal stress can be specified by vector synthesis using both the value obtained by vector conversion of the interference light intensity, which is information on the amount of change in the plurality of polarizations, and the rotation angle information. That is, the fifth and sixth method inventions can be suitably realized.

[0034] Further, according to the invention of the apparatus, the moving amount when the moving means moves the reference surface or the sample of the same article as the object to be measured is shifted and the light intensity of the interference light The relationship force of the periodic relationship is also obtained experimentally, and the storage means stores the reference phase of the periodic relationship in advance, and the calculation means stores the real phase of the periodic relationship based on the actual measurement of the measurement object and the storage means. It is preferable to compare the read reference phase and determine whether the difference in the principal stress acting on the specified layer of the object to be measured is a force compressive force, which is a tension. Section 13).

[0035] According to this configuration, experiments, theoretical calculations, simulations, and the like are performed using the same sample as the object to be measured, and the conditions of tension and compressive force acting as stress on this sample are identified and the reference phase is determined. Is stored in the storage means. Then, by comparing this reference phase with the actual phase when a predetermined layer of the measurement object is measured, it is determined whether the difference in the acting main stress is a force compression force, which is a tension. Can do. That is, the fourth method invention can be suitably realized.

[0036] Next, the fourteenth invention comprises an irradiating means for outputting irradiation light having a central wavelength force and a wavelength distribution in a predetermined range;

First conversion means for converting linearly polarized light that is separated by the separating means and directed toward the measurement object into a substantially circularly polarized light by shifting a third direction component that is 45 ° different from the first direction by 1Z4 wavelength; Second conversion means for converting the reflected light reflected and returned from the measurement target surface of the predetermined layer into substantially linearly polarized light by shifting the third direction component by 1Z4 wavelength;

Extraction means for extracting a polarization component in a third direction orthogonal to the first direction, which is caused by a change in polarization state, of reflected light that has been substantially linearly polarized by the second conversion means; and A coupling means for causing interference in such a way that polarization components in three directions and reflected light returning from the reference surface pass along the same optical path;

At least one of the measurement object and the reference surface is a straight line so that the optical path length of the reflected light returning from the measurement target surface of the predetermined layer to the coupling means and the reflected light returning from the reference surface to the coupling means match. Moving means for moving back and forth in the traveling direction of polarized light;

It is provided with.

[0037] According to the photoelasticity measurement apparatus of the fourteenth aspect of the invention, the linearly polarized light in the first direction out of the irradiation light separated into two linearly polarized light by the separating means is applied to the measuring object composed of a plurality of layers. And the other linearly polarized light in the second direction is output toward the reference plane. The linearly polarized light in the first direction toward the measurement object is converted into substantially circularly polarized light by the first conversion means. Each linearly polarized light is reflected when it reaches the output destination. In particular, in a measurement object having transparency, the transmitted substantially circularly polarized light is reflected on the front and back surfaces of each layer. The reflected light reflected by these surfaces changes its polarization state in the process of reciprocating through the layer when stress is applied to the predetermined layer. That is, approximately circular polarization power changes to elliptical polarization. The elliptically polarized light is further returned to substantially linearly polarized light in the first direction by the second conversion means. Then, only the polarization component in the third direction orthogonal to the first direction is extracted by the extraction means. The extracted polarization component and the reflected light having the reference surface force are combined so as to pass through the same optical path by the coupling means, and interference occurs.

[0038] Before the two reflected lights are combined into the combining means, the moving means moves at least one of the measurement object or the reference surface back and forth in the traveling direction of the polarization, thereby combining means. The optical path length from the reference surface to the coupling means coincides with one of the substantially circularly polarized light in the first direction that is reflected back from the plurality of layers that return. In this case, if interference is caused in a state where the optical path lengths coincide with each other, the light intensity of the interference light of an arbitrary layer to be measured becomes maximum. When this light intensity reaches a maximum, a change in the light intensity of the same polarization component of the reflected light of the measurement target force and the reflected light of the reference surface force is detected by the detection means. Then, based on this detection result, the calculation means obtains polarization change information due to birefringence at the measurement object. That is, the seventh method invention can be suitably realized.

[0039] In the eleventh to fourteenth inventions, the moving means moves at least one of the measurement object and the reference surface back and forth in parallel with the traveling direction of the light, and the detecting means interferes with the movement process. The light intensity of the light is sequentially detected, and the calculation means obtains the maximum value of the light intensity of the interference light based on the detection result of the detection means, and obtains the information on the amount of change in polarization due to the resulting birefringence. Preferred (claim 15). That is, according to this configuration, the second and eighth method inventions can be suitably realized.

[0040] Further, in the eleventh to fifteenth inventions, an optical means is provided for separating the light into approximately half so that the phases of the both reflected light constituting the interference light caused by the coupling means are shifted by a half wavelength. The means preferably obtains information on the amount of change in polarization due to birefringence by removing the direct current component of the light intensity of the interference light based on the difference between both phases of the reflected light after separation (claim 16). That is, according to this configuration, the third and ninth inventions can be suitably realized.

The invention's effect

[0041] The photoelasticity measurement method and apparatus according to the present invention irradiates the measurement object and the reference surface with light, and extracts only the polarization component whose polarization state has changed from the reflected light of the measurement object force. By causing interference between the polarization component and the reflected light of the reference surface force, it is possible to extract the amount of change in birefringence caused by the effect of stress acting on an arbitrary layer. In addition, the amount of change in birefringence can be obtained with high accuracy the difference in principal stress acting on an arbitrary layer, and thus the layer on which the stress is applied can be separated.

Brief Description of Drawings

FIG. 1 is a diagram showing a schematic configuration of an apparatus for realizing a photoelasticity measurement method according to Embodiment 1. [2] FIG. 2 is a diagram showing a detection state of the light intensity of interference light.

[3] FIG. 3 is a diagram showing a detection state of the light intensity of interference light.

[4] FIG. 4 is a diagram showing a detection state of the light intensity of the interference light.

[5] FIG. 5 is a diagram illustrating a schematic configuration of an apparatus for realizing the photoelasticity measurement method according to the second embodiment. 6] FIG. 6 is a diagram showing a configuration of first and second polarimeters in the apparatus of the second embodiment. [7] FIG. 7 is a diagram showing a configuration of a modified device.

Explanation of symbols

1 ··· Optical unit

2 ··· Control unit

3 ··· Polarimeter

4,, Light source

5 ··· Collimating lens

6 ··· Polarizing plate

9 ··· 2nd polarization beam splitter

12 · '··· Polarizer

13 · '·. Reference mirror

14 · '.. Piezo element

19 · '' · Third beam splitter

22 · '' · First photodiode

23 '' 'Second photodiode

24 · '··· Calculator

Example 1

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, a case where linear polarization is used will be described as an example.

FIG. 1 is a diagram showing a schematic configuration of an apparatus using the photoelasticity measurement method of the present invention.

[0046] The apparatus of this example is a measurement object W in which two transparent glass substrates Wl and W2, such as a liquid crystal panel and a plasma display, are held on a flat mounting table 60 at a minute interval. The center frequency force is an optical system that emits light having a wavelength distribution within a predetermined range. Knit 1, control system unit 2 that controls optical system unit 1, and reflected light output from optical system unit 1 are used to reciprocate and transmit the measurement object, thereby reducing the stress acting on the predetermined layer. A polarization component whose polarization state has changed due to the influence is extracted, and a polarimeter 3 for detecting the light intensity of the interference light generated by using this polarization component. Further, the control system unit 2 includes an arithmetic processing unit 15 that obtains polarization change amount information based on the light intensity detected by the polarimeter 3. Hereinafter, each configuration will be described in detail.

The optical system unit 1 includes a collimating lens 5, a polarizing plate 6, a first polarizing beam splitter 7, an objective lens 8, and a second polarizing beam beam on an optical path irradiated from the light source 4 toward the measurement object W. They are deployed in the order of Plitter 9. In addition, a condensing lens 10 and a photodiode 11 are arranged on the optical path of light that is separated by the first polarization beam splitter 7 and travels in a direction different from the measurement target W. Furthermore, a polarizing plate 12 and a reference mirror 13 are arranged on the optical path of light that is separated by the second polarizing beam splitter 9 and travels in a direction different from the measurement target W. Each configuration will be specifically described below.

[0048] The light source 4 generates light having a relatively wide frequency band. For example, in this embodiment, a super luminescent diode having a band of 7 90 ± 20 nm is used. The light generated from the light source 4 is collimated by the collimating lens 5 and travels toward the polarizing plate 6. The light source 4 corresponds to the irradiation means of the present invention.

[0049] The polarizing plate 6 is arranged at 45 °. Among the random polarized light irradiated from the light source 4, the initial linearly polarized light having a polarization plane of 45 ° is extracted, and this linearly polarized light is extracted into the first polarizing beam splitter 7. Turn to.

[0050] The first polarization beam splitter 7 transmits linearly polarized light having a polarization plane of 45 °. That is, linearly polarized light having a polarization plane of 45 ° that has passed through the polarizing plate 6 passes as it is. Further, the first polarization beam splitter 7 directs the polarization component returned from the second polarization beam splitter 9 to the photodiode 11. In other words, of the linearly polarized light that is reflected by the front and back surfaces of the glass substrates Wl and W2 of the measurement object W and the reference mirror 13 and returns to the second polarizing beam splitter 9, the polarization plane does not rotate and the initial polarization The polarization component returning while maintaining the state is also returned to the first polarization beam splitter 7 by the second polarization beam splitter 9, and this first polarization beam splitter 7 directs the returned polarization component to the photodiode 11. [0051] The photodiode 11 detects the light of the polarization component returning from the second polarization beam splitter 9, and transmits a detection signal to the arithmetic processing unit 15 of the control system 2 described later.

The objective lens 8 is a lens that condenses the incident linearly polarized light toward the measurement target W and the reference mirror 13 on the downstream side. The linearly polarized light collected by the objective lens 8 reaches the second polarization beam splitter 9.

The second polarization beam splitter 9 separates the light collected by the condenser lens 8 into a set of orthogonal linearly polarized light. That is, the measurement light in the first direction directed to the measurement object W and the reference light in the second direction directed to the reference mirror 13 are separated. In addition, the second polarization beam splitter 9 recombines the reference light and the measurement light that are reflected by the measurement object W and the reference mirror 13 and return on the same optical path. At this time, only the polarization component of which the polarization state has changed is extracted from each of the measurement light and the reference light, this polarization component is directed to the polarimeter 3 side different from the initial optical path, and the polarization component which has no change in the polarization state is Return to the first polarized beam splitter 7 through the initial optical path. Note that the second polarizing beam splitter 9 functions as the separating means, extracting means, and combining means of the present invention.

[0054] The polarizing plate 12 is disposed on the optical path of the reference light from the second polarizing beam splitter 9 to the reference mirror 13, and transmits the linearly polarized light from the second polarizing beam splitter 9 to the polarizing surface. Is changed to linearly polarized light inclined at 45 °, and the reference light whose polarization state has changed is reflected by the reference mirror 13 and returned to the second polarizing beam splitter 9.

[0055] The reference mirror 13 is mounted perpendicular to the traveling direction of the reference light. The reference light reflected by the reference mirror 13 is returned to the second polarization beam splitter 9 through the same optical path. Further, the reference mirror 13 is configured to be able to move a minute distance back and forth with respect to the traveling direction of the reference light by the operation of the piezo element 14. The reference mirror 13 corresponds to the reference surface of the present invention, and the piezo element 14 corresponds to the moving means of the present invention.

The condensing lens 10 is a lens that condenses the linearly polarized light from the second polarizing beam splitter 9 toward the photodiode 11.

Next, the polarimeter 3 includes condensing lenses 20 and 21 for condensing the linearly polarized lights separated by the third polarizing beam splitter 19 and the third polarizing beam splitter 19, and condensing lenses 20, 21. 1st photodiode 22 and 2nd photodiode that receive linearly polarized light from It consists of 23 and. Hereinafter, each configuration will be specifically described.

The objective lens 18 is a lens that converts the linearly polarized light from the second polarization beam splitter 9 into parallel light toward the third polarization beam splitter 19.

[0059] The third polarization beam splitter 19 is disposed at 45 °, and is divided in half so that the phases of the measurement light and the reference light returning on the same optical path extracted by the second polarization beam splitter 9 are shifted by a half wavelength. The separated linearly polarized light is condensed by the condensing lenses 20 and 21 so as to reach the photodiodes 22 and 23. In other words, in the case of this example, the linearly polarized light composed of the measurement light and the reference light that are separated and aligned with each other at + 45 ° is directed to the first photodiode 22, and is measured with the 45 ° components aligned with each other. Linear polarization force that also includes light and reference light power. It is configured to face the second photodiode 23.

[0060] The first and second photodiodes 22 and 23 output the detected signal level of the light intensity of the linearly polarized light to the calculator 24, respectively. The first and second photodiodes 22 and 23 correspond to the detection means of the present invention. At this time, the signal of the light intensity detected by both photodiodes 22 and 23 becomes an interference waveform as shown in FIGS. 2 and 3, and each phase is inverted by 180 °.

The arithmetic unit 24 synthesizes so as to take a difference in signal level corresponding to the light intensity value detected by both photodiodes 22 and 23. In this case, as shown in FIGS. 2 and 3, since both phases of the interference waveform detected by both photodiodes 22 and 23 are inverted by 180 °, they are synthesized so as to take the difference between the two light intensity values. . As a result, as shown in FIG. 4, the DC component of the interference waveform is removed, and only the interference light due to the birefringence change component reflected from the measurement object W is extracted.

Next, the control unit 2 includes an arithmetic processing unit 15, a drive control unit 16, an operation unit 17, and the like. Each configuration will be specifically described below.

[0063] The arithmetic processing unit 15 performs focusing of the interference light as the first process, and as a second process, based on the difference in main stress acting on the predetermined glass substrate W1 or W2 of the measurement object W. An unknown parameter among the amount of change in birefringence generated, the photoelastic coefficient, and the thickness of the glass substrate, and the stress acting on the predetermined glass substrate are obtained. The arithmetic processing unit 15 corresponds to the arithmetic means of the present invention. [0064] As the first processing, for example, the photodiode 11 reflects the measurement object W and the reference mirror 13 from the reflected light that returns from the measurement object W and the reference mirror 13 without changing the polarization state. The interference light intensity at which the lights interfere with each other is detected. At this time, a command signal is transmitted to the drive control unit 16 to control the operation of the piezo element 14 while detecting the light intensity value sequentially detected by the photodiode 11 to thereby maximize the intensity of the interference light 13 Calculate the position of. That is, the position of the reference mirror 13 is also a position where the light intensity value of the interference light detected by the polarimeter 3 is maximum.

[0065] The light intensity incident on the photodiode 11 is greater than the light intensity incident on the polarimeter. Therefore, for example, when interference light is detected by the polarimeter 3, the birefringence variation force is too large, or the optical axis of the optical system is misaligned, especially because the measurement object W is not aligned properly. It can be determined that the light cannot be detected due to the deviation of the optical axis.

[0066] As the second processing, from the light intensity value of the interference light detected by the computing unit 24, information on the amount of change in birefringence changed at the measurement object W is acquired. In addition, the difference in principal stress applied to a predetermined measurement object can be obtained by the formula of change information of birefringence = difference in principal stress X thickness of measurement object X photoelastic coefficient. In other words, if information on the amount of change in birefringence is obtained, the difference in principal stress acting on the measurement object can be easily obtained from the known thickness and photoelastic coefficient of the measurement object. For example, when the object to be measured is a predetermined glass substrate, the difference in main stress acting on the predetermined glass substrate is the amount of change in birefringence information = the difference in main stress X the thickness of the glass substrate X the photoelastic coefficient. It is obtained by the formula. In other words, if information on the amount of change in birefringence is obtained, the difference in principal stress acting on the glass substrate can be easily obtained from the known thickness and photoelastic coefficient of the glass substrate.

The drive control unit 16 moves the optical system unit 1 by a predetermined distance before and after the linearly polarized light traveling from the light source 4 toward the measurement target W according to the conditions set by the operation unit 17. Make it. That is, by driving and controlling a moving means (not shown) such as a Norse motor, the distance L1 from the second polarizing beam splitter 9 to the back surface of the glass substrate W1 and the distance L2 from the second polarizing beam splitter 9 to the reference mirror 13 The distance L3 from the second polarizing beam splitter 9 to the back surface of the glass substrate W 2 and the distance L4 from the second polarizing beam splitter 9 to the reference mirror 13 The optical system unit 1 is moved so that the distances of the respective groups of the two groups substantially coincide with each other.

In addition, the drive control unit 16 controls the operation of the piezo element 14 so as to finely adjust the position of the reference mirror 13 so that the light intensity of the interference light is maximized according to the command signal from the arithmetic processing unit 15. I will do it.

[0069] The operation unit 17 is used to set and input various measurement conditions such as the thickness of the glass substrates W1 and W2, the photoelastic coefficient of each glass substrate, the material, the refractive index, and the distances L1 to L4 between the components. .

[0070] Next, a description will be given of a one-round operation for measuring the difference in principal stress acting on the measurement object W using the above-described embodiment apparatus. Note that a case where stress is applied to both of the glass substrates Wl and W2 constituting the measurement target W will be described as an example.

[0071] Measurement conditions are input from the operation unit 17, and measurement is started. First, the drive control is performed so that the distance L1 from the second polarizing beam splitter 9 to the back surface of the glass substrate 1 is the same as the distance L2 from the second polarizing beam splitter 9 to the reference mirror 13, that is, the optical path lengths are substantially the same. As described above, the drive control unit 16 controls the operation of a moving means such as a pulse motor (not shown) to move the optical system unit 1.

[0072] When the optical system unit 1 reaches a position where both optical path lengths substantially coincide with each other, light is emitted from the light source 4. The irradiated light is converted into parallel light by the collimating lens 5, and then the polarization plane is changed to 45 ° linearly polarized light by the polarizing plate 6, and the first polarizing beam splitter 7 arranged at 45 ° in the subsequent stage is changed. Pass through to the second polarizing beam splitter 9.

[0073] When the linearly polarized light collected by the objective lens 8 disposed in front of the second polarizing beam splitter 9 reaches the second polarizing beam splitter 9, it is separated into two orthogonal linearly polarized lights. The separated linearly polarized light (measurement light) in the first direction (horizontal direction) passes back and forth through the glass substrates Wl and W2 toward the measurement object W, and the surface of each glass substrate Wl and W2 and And return to the second polarizing beam splitter 9. The other linearly polarized light (reference light) in the second direction (vertical direction) is reflected by the reference mirror 13 and returned to the second polarizing beam splitter 9 to become linearly polarized light inclined by 45 ° by the polarizing plate 12. Return to 2 Polarizing Beam Splitter 9.

[0074] The second polarization beam splitter 9 is a polarization component of the second direction orthogonal to the first direction generated by the change in the polarization state of the measurement light reflected and returned from each surface of the measurement object W. so Only a certain measurement light is extracted and directed to the polarimeter 3. At this time, the extracted measurement light in the second direction and the reference light returning from the reference mirror 13 are combined again so as to pass through the same optical path, thereby causing interference.

It should be noted that the linearly polarized light is detected by the photodiode 11 via the upstream first polarization beam splitter 7 while the polarization state reflected and returned from the measurement object W changes.

[0076] When the position of the reference mirror 13 is determined, the linearly polarized light in the second direction from the second polarizing beam splitter 9 toward the polarimeter 3 is collected by the condenser lens 18, and then the third polarization constituting the polarimeter 3 is formed. A polarizing beam splitter 19 is reached.

[0077] The third polarization beam splitter 19 splits the linearly polarized light having the horizontal component force that has reached, into approximately half so that the phase is shifted by a half wavelength. At this time, the + 45 ° components and 45 ° components of the measurement light and the reference light are combined and aligned with linearly polarized light in the same direction. Of each set of linearly polarized light in which these directions are aligned, the linearly polarized light having a horizontal component force is condensed by the condensing lens 20 and detected by the first photodiode 22. The linearly polarized light composed of the vertical component is collected by the condenser lens 21 and detected by the second photodiode 23.

[0078] Both linearly polarized lights received by the respective photodiodes 22 and 23 are converted into respective light intensity values by the calculator 24 and subtracted. At this time, since the phases of both linearly polarized light are inverted by 180 °, the direct current component of the reference light reflected from the reference mirror 13 is removed, and only the interference component of the measurement light is obtained.

The light intensity value of the interference component is input to the arithmetic processing unit 15, and the arithmetic processing unit 15 obtains the difference between the birefringence change amount information and the principal stress.

This completes the processing for obtaining the difference between the birefringence change information and the principal stress of the glass substrate W1, and then the drive control unit 16 controls the moving means to move the optical system unit 1. The back surface force of the glass substrate W2 is also controlled by operating the piezo element 14 so that the optical distance between the distance L3 from the second polarizing beam splitter 9 and the optical distance L4 from the reference mirror 13 to the second polarizing beam splitter 9 is After adjusting so as to be approximately the same, the same processing as that for the glass substrate W1 is performed to obtain information on the amount of change in birefringence of the glass substrate W2 and the difference between principal stresses.

[0081] As described above, the optical system unit 1 is moved so that the distance from the second polarizing beam splitter 9 to the reference mirror 13 and the optical path length to the back surfaces of the glass substrates Wl and W2 are substantially matched. When the measurement light and reference light reflected back from the back surface of the substrates W1 and W2 and the reference mirror 13 are used, it is possible to accurately obtain the difference between the birefringence change information and the principal stress of any layer to be measured. . In other words, since the plane of polarization of the measurement light returning from the measurement object force on which the stress is acting changes, only the polarization component in the second direction orthogonal to the first direction is extracted by the second polarization beam splitter 9. This polarization component and the reference light returning from the reference mirror 13 can be combined so as to pass through the same optical path to cause interference, and this interference light can be reflected and output toward the polarimeter 3. The phase of the linearly polarized light in the second direction, which is the reference light and the measurement light power, is further separated by half a wavelength, and the polarization components are aligned with each other, so that they are compounded by the difference in principal stress acting on the glass substrate. Only the refracted polarization component can be detected as the light intensity of the interference light.

Therefore, by using the light intensity of the interference light, the amount of change in birefringence caused by the difference in principal stress acting on an arbitrary layer of a measurement target having a plurality of layers and having transparency is obtained. Thus, by using the amount of change in birefringence, the angle between the principal stress acting on the layer and the principal stress difference can be determined arbitrarily. In other words, the stress acting on each of the layers can be accurately classified by the vector component obtained from the angle of the main stress difference. In addition, the magnitude and direction of the stress acting on each of the plurality of layers can be accurately determined based on the angle of the main stress difference and the vector component obtained.

Example 2

In Example 1 above, the light emitted from the light source 4 is used after being converted into linearly polarized light. However, in this embodiment, circularly polarized light is used as the polarized light output toward the measurement object W. Will be described as an example. In the present embodiment, the same components as those in the above embodiment will be denoted by the same reference numerals, and different components will be specifically described.

FIG. 5 is a diagram showing a schematic configuration of a photoelasticity measurement apparatus using circularly polarized light according to the present invention.

The optical system unit 1, the control system unit 2, and the first polarimeter 3 of the apparatus of this embodiment are configured.

[0086] The optical system unit 1 also measures the superluminescent diode force that is the light source 30 as an object to be measured. On the optical path irradiated toward W, a collimating lens 31, a polarizing plate 32, a first polarizing beam splitter 33, and a quarter-wave plate 35 arranged at 45 ° are arranged in this order. In addition, a 1Z4 wavelength plate that is output from the first polarizing beam splitter 33 toward the measurement object W, reflected by the measurement object W, and reflected on the measurement light W toward the polarimeter 3 is reflected by a reflection mirror 36, −45 °. 37, reflecting mirror 38, polarizing plate 39, and second polarizing beam splitter 40 are arranged in this order. In addition, a reference mirror 41 is provided on the optical path of the light that is separated by the first polarization beam splitter 33 and travels in a direction different from that of the measurement object W, and is further reflected by the reference mirror 41 to the polarimeter 3. Reflecting mirrors 42 and 43, a polarizing plate 44, and a second polarizing beam splitter 40 are arranged in this order on the optical path of the reference light. Each configuration will be specifically described below.

The polarizing plate 32 is arranged at 45 °, and converts the parallel light from the collimating lens 31 into initial linearly polarized light having a polarization plane of 45 ° and directs this linearly polarized light to the first polarizing beam splitter 33. .

[0088] The first polarization beam splitter 33 is configured to measure linearly polarized light that has arrived from the polarizing plate 32, that is, measurement light in a first direction that is directed toward the measurement object W, and second light that is directed toward the reference mirror 13. Separated into reference light in direction. The first polarization beam splitter 33 corresponds to the separation means of the present invention.

The 1Z4 wavelength plate 35 arranged at 45 ° changes the linearly polarized light into substantially circularly polarized light by allowing the measurement light that is linearly polarized light in the third direction to pass therethrough. The 1Z4 wavelength plate 37 arranged at −45 ° corresponds to the first conversion means of the present invention.

[0090] Next, the reflection mirror 36 further reflects the reflected light reflected on each surface of the glass substrates Wl and W2 constituting the measurement object W, and the incident optical path is arranged on a different optical path at 45 °. Guide to the 1Z4 wave plate 37 of the arrangement.

[0091] The 1Z4 wavelength plate 37 arranged at 45 ° returns the reflected light reflected from each surface of the measurement target W to the inside thereof, thereby returning it to substantially linearly polarized light. In other words, when a stress is applied to the glass substrate W1 or W2 of the measuring object W, the polarization plane of the circularly polarized light rotates slightly and changes to elliptically polarized light. This elliptically polarized light is passed through and converted to linearly polarized light including the amount of change in birefringence. The 1Z4 wave plate 37 arranged at −45 ° corresponds to the second conversion means of the present invention. The

The reflection mirror 38 passes the measurement light, which has been converted into substantially linearly polarized light by the quarter-wave plate 37 arranged at 45 °, through the polarizing plate 39 and directs it to the second polarizing beam splitter 40.

The second polarization beam splitter 40 is arranged at a position where the measurement light reflected from the measurement object W and the reference light reflected from the reference mirror 41 intersect. Then, the second polarization beam splitter 40 again combines the reference light and the measurement light that are reflected by each measurement object W and the reference mirror 13 and return on the same optical path. At this time, only the polarization component whose polarization state has changed is extracted from the measurement light reflected and returned, and this polarization component is directed to the polarimeter 3 side, and the polarization component without change in the polarization state is the second stage. 2 Point to polarimeter 45. Note that the second polarization beam splitter 40 functions as the extracting means and the combining means of the present invention.

[0094] The reference mirror 41 reflects the reference light in a direction different from the reference light at the time of incidence. The reflected reference light is further directed to the subsequent polarizing plate 44 by two reflecting mirrors 42 and 43. Further, the reference mirror 41 is configured to be able to move back and forth with respect to the traveling direction of the reference light by the operation of the piezo element 14. The reference mirror 41 corresponds to the reference surface of the present invention.

The polarizing plate 44 is arranged at 45 °, and changes the reference light transmitted through the inside into 45 ° linearly polarized light. That is, the reference light is converted into linearly polarized light that differs by 90 ° by the action of the polarizing plate 32 and the polarizing plate 44 in the previous stage, and reaches the second polarizing beam splitter 40.

Next, as shown in FIG. 6, the first polarimeter 3 includes a third polarization beam splitter 46 and a first photodiode 22 that receives each linearly polarized light separated by the third polarization beam splitter 46. The second photodiode 23 and the arithmetic unit 24 are included. Hereinafter, each configuration will be described in detail.

[0097] The third polarization beam splitter 46 is arranged at 45 °, and is halved so that the phases of the measurement light and the reference light returning on the same optical path extracted by the second polarization beam splitter 40 are shifted by half a wavelength. The separated linearly polarized light is condensed by the condensing lenses 20 and 21 so as to reach the photodiodes 22 and 23. That is, in the case of the present embodiment, the measurement light and the linearly polarized light that also has the reference light power separated and aligned with the horizontal components are the first photo diode. The linearly polarized light composed of the measurement light and the reference light that are aligned with each other in the vertical direction is directed to the second photodiode 23.

[0098] The first and second photodiodes 22 and 23 output signals of detected light intensity values of polarized light to the calculator 24, respectively.

The arithmetic unit 24 synthesizes so as to take a difference in signal level corresponding to the light intensity value detected by both the photodiodes 22 and 23 shown in FIG. 2 and FIG. In this case, as shown in FIGS. 2 and 3, since both phases of the interference waveform detected by both photodiodes 22 and 23 are inverted by 180 °, they are combined so as to take the difference between the two light intensity values. As a result, as shown in FIG. 4, the DC component of the interference waveform is removed, and only the interference light due to the birefringence change component reflected from the measurement object W is extracted.

[0100] The second polarimeter 45 has the same configuration as the first polarimeter 3, and includes a third polarizing beam splitter 46 and first and second photodiodes 22 and 23. In other words, the second volatilizer 45 uses the polarized light separated by the third polarization beam splitter 40, and among the reflected light from the measurement object W and the reference mirror 41, the measurement object W and the reference mirror 41 The intensity of interference light in which reflected lights returning without changing the polarization state interfere with each other is detected. This signal is sent to the processing unit 15.

[0101] The control unit 2 has the same configuration as that of the first embodiment, and includes an arithmetic processing unit 15, a drive control unit 16, an operation unit 17, and the like.

[0102] Next, a round of operations for measuring the difference in principal stress acting on the measuring object W using the above-described embodiment apparatus will be described. Note that a case where stress is applied to both of the glass substrates Wl and W2 constituting the measurement target W will be described as an example.

[0103] Input measurement conditions from the operation unit 17 to start measurement. First, it is driven and controlled so that the distance from the first polarizing beam splitter 33 to the back surface of the glass substrate W1 is the same as the distance from the first polarizing beam splitter 33 to the reference mirror 41, that is, the optical path lengths coincide. Section 16 Force Moves the optical system unit 1 by controlling the operation of moving means such as a pulse motor, not shown.

When the optical system unit 1 reaches a position where the optical path lengths substantially coincide with each other, light is emitted from the light source 30. The irradiated light is collimated by a collimating lens 31 and then is polarized by a polarizing plate 32. Therefore, the polarization plane is changed to 45 ° linearly polarized light and reaches the first polarizing beam splitter 33.

The linearly polarized light is separated into two linearly polarized light orthogonal to each other by the first polarization beam splitter 33. The separated linearly polarized light in the first direction (horizontal direction) is directed to the measurement object W. The other linearly polarized light in the second direction (vertical direction) is directed to the reference mirror 41.

Here, the linearly polarized light directed toward the measurement object W is transmitted through the 1Z4 wavelength plate 35 arranged at 45 °.

At this time, the measurement light that is linearly polarized light is changed to measurement light that is substantially circularly polarized light.

[0107] This measurement light is reflected on the front and back surfaces of each measurement object Wl, W2 in the process of passing through the glass substrates Wl, W2 while facing the measurement object W. At this time, since stress acts on the glass substrate W1, the measurement light is converted into circularly polarized light and elliptically polarized light in the process of reciprocating transmission. The elliptically polarized measurement light is reflected obliquely and directed to the reflection mirror 42 because the measurement object W is arranged in an obliquely inclined posture. The measurement light reaching the reflection mirror 36 is directed to the 1Z4 wavelength plate 37 arranged at −45 °. The measurement light that has reached the quarter-wave plate 37 arranged at −45 ° is transmitted through the inside and returned to linearly polarized light including the amount of change in birefringence. The measurement light that has passed through the 1Z4 wavelength plate 37 disposed at 45 ° and returned to linearly polarized light is reflected by the reflecting mirror 38 and reaches the second polarizing beam splitter 40.

[0108] The reference light that is linearly polarized light in the second direction separated by the other first polarizing beam splitter 33 is reflected in an oblique direction different from the incident direction by the reference mirror 41 arranged in an obliquely inclined posture. . The reference light is reflected in the order of the reflection mirrors 42 and 43, passes through the polarizing plate 44, and reaches the second polarizing beam splitter 40.

[0109] The second polarization beam splitter 40 reflects the polarization component in the second direction caused by the change in the polarization state of the measurement light reflected and returned from each surface of the measurement object W and the reference mirror 41. The polarized light component in the first direction is extracted from the reference light that has passed through the polarizing plate 44 after being emitted, and is caused to interfere with the first polarimeter 3 so as to pass through the same optical path.

[0110] In addition, the second polarization beam splitter 40 includes a polarization component in the first direction, which is a component of the measurement light reflected and returned from each surface of the measurement object W and whose polarization state does not change. The polarized light component in the second direction is extracted from the reference light that has passed through the polarizing plate 44 after being reflected by the reference mirror 41, and causes the second polarimeter 45 to collectively interfere so as to pass through the same optical path. [0111] The third polarization beam splitter 46 of the first polarimeter 3 separates the linearly polarized light composed of the horizontal components of the measurement light and the reference light that have arrived into approximately half so that the phase is shifted by a half wavelength. At this time, the horizontal components and the vertical components of the measurement light and the reference light are combined and aligned with linearly polarized light in the same direction. Of each set of linearly polarized light in which these directions are aligned, linearly polarized light having a horizontal component force is condensed by the condenser lens 20 and detected by the first photodiode 22. The linearly polarized light, which is the vertical component, is collected by the condenser lens 21 and detected by the second photodiode 23.

[0112] The photodiodes 22 and 23 are combined so as to obtain a difference in signal level according to the light intensity value detected. In this case, as shown in Fig. 2 and Fig. 3, the phases of the interference waveforms detected by both photodiodes 22 and 23 are inverted by 180 °, so that they are combined so as to obtain the difference between the two light intensity values. The DC component of the interference waveform shown in Fig. 4 is removed.

[0114] The fourth polarization beam splitter 46 of the second polarimeter 45 separates the linearly polarized light composed of the horizontal components of the measurement light and the reference light that have arrived into approximately half so that the phase is shifted by a half wavelength. At this time, the horizontal components and the vertical components of the measurement light and the reference light are combined and aligned with linearly polarized light in the same direction. Of each set of linearly polarized light in which these directions are aligned, linearly polarized light having a horizontal component force is condensed by the condenser lens 20 and detected by the third photodiode 22. The linearly polarized light, which is the vertical component, is collected by the condenser lens 21 and detected by the fourth photodiode 23. As a result, the interference waveform corresponding to the linearly polarized light composed of the horizontal components of the measurement light and the reference light can be detected. The phase of this waveform can be used as a reference phase for determining whether the difference in main stress applied to a predetermined layer of the measurement object is a force or compressive force.

[0115] The reference phase is a relational force between the amount of movement when either the reference mirror 41 or the measurement target surface W is moved and the light intensity of the interference light. Relational force Indicates the phase to be obtained.

[0116] This completes the processing for obtaining the difference between the birefringence change information and the principal stress of the glass substrate W1, and then the drive control unit 16 controls the movement means (not shown) to control the optical system unit 1 The At the same time, the piezo element 14 is operated and controlled so that the back surface force of the glass substrate W2 is adjusted so that the distance from the first polarizing beam splitter 33 and the distance from the reference mirror 41 to the first polarizing beam splitter 33 are the same. After that, by performing the same processing as that for the glass substrate W1, information on the amount of change in birefringence of the glass substrate W2 and the difference between principal stresses are obtained.

[0117] According to the configuration described above, similarly to the case of using linearly polarized light, the light intensity of the interference light is used to act on an arbitrary layer of the measuring object having a plurality of layers of transparency. The amount of change in birefringence caused by the difference in principal stress can be obtained, and by using this amount of change in birefringence, the difference in principal stress acting on any layer can also be obtained. . That is, it is possible to accurately separate the stress acting on each of the plurality of layers.

[0118] Further, in this example, by using circularly polarized light, it is possible to reliably determine the presence or absence of stress by a single measurement regardless of the direction of stress.

[0119] The present invention is not limited to the above-described embodiments, and can be modified as follows.

(1) When the linearly polarized light of Example 1 is used, the following modifications may be made.

For example, as shown in FIG. 7, a half mirror is used instead of the first polarizing beam splitter 7 and the second polarizing beam splitter 9 in Example 1 on the optical path irradiated from the light source 4 and directed to the measurement object W. 50 and polarization beam splitter 51 are arranged in order, and return from measurement object W and reference mirror 13 Of the polarized light, the measurement light with its polarization plane reflected back from measurement object W and reflected from reference mirror 13 is reflected. Alternatively, the reference light guided through the plurality of reflecting mirrors 42 and 43 may be collectively output to the polarimeter 3. The half mirror 50 corresponds to the separation means of the present invention, and the polarization beam splitter 51 functions as the extraction means and the coupling means of the present invention.

(2) In each of the above embodiments, the object to be measured W and the optical system unit are rotated relative to each other around the optical axis, the difference and angle of principal stresses in a plurality of directions are obtained, and the direction at each rotation angle is determined. May be obtained by the arithmetic processing unit 15 to obtain the magnitude and direction of the stress acting on the measurement target W.

Here, when the magnitude and direction of the difference in principal stress are obtained using Example 1 and the deformation device, the optical system unit 1 itself may be rotated around the optical axis, or the measurement object W or turn the mounting table 60. [0124] (3) In each of the above embodiments, the force provided with the photodiode 11 and the second polarimeter 45 for obtaining the maximum value of the interference light. From each polarization beam splitter 9, 33 to the measurement object W. If the distance between the polarizing beam splitters 9 and 33 and the distance from the reference mirrors 13 and 41 can be accurately adjusted in advance, this configuration may not be provided.

(4) In each of the above-described embodiments, the measurement object W provided with the glass substrate is used. However, the measurement object W is not limited to this form, and has a plurality of transmittances. What laminated | stacked the target object may be sufficient. For example, there are combinations of objects to be measured having different refractive indexes, such as glass substrates and glass substrates and films. In particular, it has a low back surface reflectance and functions effectively for measuring combinations of objects to be measured.

(5) In each of the above embodiments, the optical path lengths of the reflected light reflected from the measurement object W and the reference mirror 13 are made to coincide with each other. For example, in a state where the reference mirrors 13 and 41 are fixed without operating the piezo element 14, both reflected light returning from the measurement object W and the reference mirror 13 are passed through the diffraction grating and orthogonal to the second direction. After changing to monochromatic light, the maximum interference intensity required when the piezo element 14 is operated may be obtained by calculation by detecting the interference intensity of each wavelength and performing Fourier transform.

(6) In each of the above embodiments, a super luminescent diode is used as the light source 4. However, the present invention is not limited to this, and any light source may be used as long as it generates light in a predetermined frequency band. For example, it may be configured such that light having a halogen lamp power is limited to a predetermined frequency band by a band pass filter.

(7) The apparatus of the present invention can be modified into a plurality of types of layouts by changing the type and number of mirrors of the optical element that is not limited to the above embodiment. Industrial applicability

[0129] As described above, the present invention is suitable for determining the difference between V and principal stress acting on each layer of a workpiece having a multi-layer force having permeability, and its direction.

Claims

The scope of the claims

[1] Central wavelength force When irradiating irradiation light having a wavelength distribution in a predetermined range to a measurement object having a plurality of layers and a reference surface, at least the measurement object has a predetermined first Irradiate linearly polarized light in the direction,

The photoelasticity measuring method characterized by the above-mentioned.

[2] In the photoelasticity measuring method according to claim 1,!

Either the reference surface or the measurement target surface is moved back and forth with respect to the traveling direction of the irradiation light to obtain light intensity information that maximizes the light intensity of the interference light.

The photoelasticity measuring method characterized by the above-mentioned.

[3] In the photoelasticity measurement method according to claim 1 or claim 2,

The phases of both reflected lights constituting the interference light are separated into approximately half so that the phases are shifted by a half wavelength, and the direct current component is removed from the light intensity of the interference light by taking the difference between the two phases after separation. A photoelasticity measuring method.

[4] In the photoelasticity measurement method according to claim 2 or claim 3,

The relationship force between the amount of movement of either the reference surface or the measurement target surface and the light intensity of the interference light is obtained as a periodic relationship, and the actual phase of this periodic relationship and a predetermined reference phase Compare

Based on the result, it is determined whether the difference in principal stress acting on the predetermined layer of the object to be measured is a force compression force that is a tension.

The photoelasticity measuring method characterized by the above-mentioned.

[5] The photoelasticity measurement method according to any one of claims 1 and 4 and

The linearly polarized light irradiated on the measurement target surface and the measurement target surface are rotated relative to each other around the optical axis of the linearly polarized light, and the amount of change in polarization due to birefringence is obtained for each rotation angle. Find the difference and angle of the principal stress acting on the measurement object from both the information on the amount of change in polarization and the information on the rotation angle.

The photoelasticity measuring method characterized by the above-mentioned.

[6] In the photoelasticity measurement method according to claim 5,

The rotation angle is at least two angles so that the direction of the linearly polarized light of the light irradiated from each angle is different.

The photoelasticity measuring method characterized by the above-mentioned.

[7] Central wavelength force When irradiating irradiation light having a wavelength distribution in a predetermined range to a measurement object having a plurality of layers and a reference surface, at least the measurement object has a predetermined first Irradiate a nearly circularly polarized light with a second direction component that is 45 ° different from the first direction by 1Z4 wavelength.

The reflected light reflected from the measurement target surface of the predetermined layer of the measurement target is matched with the optical path length of the reflected light returning from the reference surface, and the reflected light from the measurement target surface is the second direction component. Is shifted by 1Z4 wavelength to return to substantially linearly polarized light, and the polarization component in the third direction perpendicular to the first direction resulting from the change in the polarization state is extracted, and the polarization component in the third direction and the reference surface are extracted. Forces the reflected light back together to cause interference in the same optical path,

The photoelasticity measuring method characterized by the above-mentioned.

[8] In the photoelasticity measurement method according to claim 7,

The photoelasticity measuring method characterized by the above-mentioned.

[9] In the photoelasticity measurement method according to claim 7 or claim 8,

[10] According to the photoelasticity measurement method according to any one of claims 7 and 9, the measurement object plane perpendicular to the propagation direction of the irradiated circularly polarized light moves on a vertical plane. The circularly polarized light and the measurement object are moved relative to each other so that the information on the amount of change in polarization due to birefringence at multiple locations is acquired in the process, and the distribution state force is applied to a predetermined layer of the measurement object. Estimate stress difference and angle

The photoelasticity measuring method characterized by the above-mentioned.

[11] Central wavelength force: Irradiation means for outputting irradiation light having a wavelength distribution in a predetermined range; and irradiation light from the irradiation means is separated into two linearly polarized lights, and the separated first direction Separation means for outputting linearly polarized light to a measuring object having a plurality of layers and transmitting the other direction of linearly polarized light to a reference surface;

A combination of the reflected light extracted through the extraction means reflected from the measurement target surface of the predetermined layer of the measurement object and the reflected light returning from the reference surface force so as to cause interference by collectively passing through the same optical path. Means,

A photoelasticity measuring device comprising:

[12] In the photoelasticity measuring device according to claim 11,

The optical system composed of the irradiation means, the reference surface, the separation means, the extraction means, the coupling means, and the detection means and the measurement object are relative to each other around the optical axis of linearly polarized light output from the optical system to the measurement object. Provided with rotational drive means for rotating automatically

A photoelasticity measuring apparatus.

[13] In the photoelasticity measurement device according to claim 11 or claim 12,

Relationship between the amount of movement and the light intensity of the interference light when either the reference surface or the sample to be measured is moved by the moving means and the light intensity of the interference light. Comprising storage means for storing the reference phase of this periodic relationship in advance;

The arithmetic means compares the actual phase of the periodic relationship based on the actual measurement of the measurement object and the reference phase read from the storage means,

A photoelasticity measuring apparatus.

[14] Central wavelength force: Irradiation means for outputting irradiation light having a wavelength distribution in a predetermined range; and irradiation light from the irradiation means is separated into two linearly polarized lights, and the separated first direction Separation means for outputting linearly polarized light to a measuring object having a plurality of layers and transmitting the other direction of linearly polarized light to a reference surface;

First conversion means for converting linearly polarized light that is separated by the separating means and directed toward the measurement object into substantially circularly polarized light by shifting a third direction component that is 45 ° different from the first direction by 1Z4 wavelength; and A second conversion means for converting the reflected light that is reflected back from the measurement target surface into substantially linearly polarized light by shifting the third direction component by 1Z4 wavelength; and

A detecting means for detecting a light intensity change of the same polarization component of the superimposed reflected light; a calculating means for obtaining polarization change amount information due to birefringence based on a detection result of the detecting means; A photoelasticity measuring device comprising:

[15] In the photoelasticity measuring device according to any one of claims 11 and 14!

The moving means moves at least one of the measurement object or the reference surface back and forth in the light traveling direction,

The detection means sequentially detects the light intensity of the interference light in the movement process, and the calculation means obtains the maximum value of the light intensity of the interference light based on the detection result of the detection means, and obtains this. Resulting power Find information on the amount of change in polarization due to birefringence

A photoelasticity measuring apparatus.

[16] In the photoelasticity measuring device according to any one of claims 11 and 15!

Optical means for separating the reflected light constituting the interference light caused by the coupling means into substantially half so that the phases of both reflected lights are shifted by a half wavelength;

The calculation means obtains information on the amount of change in polarization due to birefringence by removing a direct current component from the light intensity of the interference light based on the difference between both phases of the reflected light after separation.

A photoelasticity measuring apparatus.