JPH0830721B2 - Voltage detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage detecting device for detecting a voltage of a predetermined portion of an object to be measured, for example, an integrated circuit or the like, and in particular, to a voltage of a predetermined portion of the device to be measured. The present invention relates to a voltage detecting device of a type that detects a voltage by utilizing the fact that the polarization state of a light beam changes due to the change.

[Conventional technology]

Conventionally, various voltage detection devices have been used to detect the voltage of a predetermined portion of an object to be measured such as an integrated circuit.

Among this type of voltage detecting device, a type of voltage detecting device has been recently developed which detects the voltage of the DUT by utilizing the fact that the polarization state of the light beam changes depending on the voltage of a predetermined portion of the DUT. There is.

For example, in the voltage detection device described in the patent application filed on May 30, 1987 by the applicant of the present application under the name of “voltage detection device”, an electro-optic material whose refractive index changes depending on the voltage of a measured object is used. Stored in an optical probe with a minute cross-section,
By injecting a light beam having a predetermined polarization component into the electro-optical material of this optical probe and detecting the amount of change in the polarization state of the light beam due to the change in the refractive index of the electro-optical material, It is designed to detect the voltage at one measurement position.

[Problems to be solved by the invention]

By the way, there are cases where the user desires to simultaneously measure the voltage at each two-dimensional position of an object to be measured such as an integrated circuit. However, the voltage detection device as described above has a problem that it is not possible to simultaneously detect the voltages at two-dimensional positions of the object to be measured.

An object of the present invention is to provide a voltage detection device capable of simultaneously detecting voltages at two-dimensional positions of a measured object.

[Means for solving problems]

The present invention is to improve a type of voltage detecting device using an electro-optical material whose refractive index changes when a voltage is applied. In the first invention, the electro-optical material is positioned so as to cover a plurality of two-dimensional positions of an object to be measured whose voltage is to be detected, and the electro-optical material corresponds to the plurality of two-dimensional positions of the object to be measured. A light beam from a light source is made into parallel light and uniformly enters each two-dimensional portion of the electro-optical material, and changes in polarization state of light emitted from the plurality of two-dimensional portions of the electro-optical material. Is detected by a detector.

In the second invention, an observation light source that outputs a light beam having a wavelength different from that of the light source (pulse light source) for observing the wiring shape of the DUT, a light beam from the observation light source, and the pulse Switching means for switching the light beam from the light source to be incident on the electro-optical material, and when observing the wiring shape of the DUT, the phase of the emitted light is in a phase different from that when detecting the change in the polarization state. And a phase compensation means for adjusting the voltage of the two-dimensional position of the DUT observed based on the change of the polarization state of the emitted light is superimposed on the wiring shape of the DUT observed by the detector. Display means for displaying, and variable delay means for shifting the incident timing of the light beam from the pulsed light source to the electro-optical material in order to sample and measure the voltage change at the two-dimensional position of the object to be measured. Special It is an.

[Action]

In the present invention, the electro-optical material is positioned so as to cover a plurality of two-dimensional positions of the measured object whose voltage is to be detected,
A light beam from a light source is made to uniformly enter each two-dimensional portion of the electro-optical material corresponding to a plurality of two-dimensional positions of the measured object. Since the refractive index of each two-dimensional portion of the electro-optical material changes depending on the voltage of each two-dimensional position of the measured object corresponding to each two-dimensional portion, The polarization state of the incident light beam changes in accordance with the change in the refractive index of each two-dimensional portion of the electro-optical material and is output from the electro-optical material as emitted light, so that a detector such as a two-dimensional photodetector array or It is incident on the streak camera. As a result, the detector can simultaneously detect the voltage at the two-dimensional position of the measured object.

Further, in the second invention, the voltage distribution at the two-dimensional position of the measured object is displayed by being superimposed on the wiring shape of the measured object. First, in order to observe the wiring shape of the DUT, the switching means switches the light beam from the observation light source to enter the electro-optic material, and the phase compensation means adjusts the phase of the emitted light for observation. To do. Upon such switching and adjustment, the light beam from the observation light source enters the electro-optical material as parallel light, passes through the electro-optical material, and enters the surface of the object to be measured. It is assumed that the bottom surface of the electro-optical material is provided with a dielectric multilayer mirror that transmits the light beam from the observation light source but reflects the light beam from the voltage detection light source. A part of the light beam from the observation light source that has entered the surface of the object to be measured is reflected by the wiring shape on the surface of the object to be measured and is output from the electro-optic material as emitted light. The emitted light output from the electro-optical material is applied to the two-dimensional detector via the phase compensating means, and is detected by the detector as visible image data of the wiring shape of the measured object. After detecting the visible image data of the wiring shape in this way, in order to detect the voltage at the two-dimensional position of the object to be measured, the switching means switches the light beam from the pulse light source to enter the electro-optical material. The phase of the outgoing light is adjusted by the phase compensating means for voltage detection. At this time, the operation of the DUT needs to be synchronized with the pulsed light. When such switching and adjustment are performed, the voltage at the two-dimensional position of the measured object at one sampling timing is detected by the detector in the same manner as in the first aspect of the invention. Then, the display unit displays the visible image data of the wiring shape of the measured object adjusted by the detector on a display or the like and superimposes it on the display to display the voltage distribution of the measured object at one sampling timing. Then, the light beam from the pulse light source is delayed a little by the variable delay means, and the voltage at the two-dimensional position of the object to be measured is detected at a timing slightly deviated from the previous sampling timing and displayed by the display means. As a result, on the display screen, it is possible to visually observe the temporal change of the voltage distribution at the two-dimensional position of the object to be measured by superimposing it on the wiring shape of the object to be measured.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram of a first embodiment of a voltage detecting device according to the present invention.

In the voltage detecting device 1 shown in FIG. 1, the electro-optical material 2 is fixed by approaching the device under test 3 such as an integrated circuit or by contacting the device 3 under test. This electro-optic material 2
Has a cross section cut into a size that covers a plurality of two-dimensional positions of the DUT 3. A reflecting mirror 8 made of a metal or a dielectric multilayer film is formed on the bottom surface of the electro-optical material 2.

Further, the voltage detection device 1 includes a pulse light source 4 that outputs a light beam having a very short pulse width, a variable delay unit 5 that variably delays the light beam from the pulse light source 4, and a variable delay unit 5 that delays the light beam. And a magnifying optical system 6 that magnifies the expanded light beam into a two-dimensional spread into parallel light.
The polarizer 7 that extracts a predetermined polarization component from the light beam that has been made into parallel light by the parallel light, and the parallel light having the predetermined polarization component that is extracted by the polarizer 7, that is, the light beam, is electro-optical material 2.
A beam splitter that makes the light emitted from the electro-optic material 2 reflected by a reflecting mirror 8 formed on the bottom surface of the electro-optic material 2 and directed toward the imaging optical system 9 while being incident on the imaging optical system 2. 10, a phase compensator 11 that adjusts the phase of light emitted from the imaging optical system 9, and an analyzer that passes only a light beam of a predetermined polarization component of the light emitted from the light whose phase is adjusted by the phase compensator 11. 12 and a detector 13 on which the emitted light that has passed through the analyzer 12 is incident.

The collimated light incident on the electro-optical material 2 has a two-dimensional spread by the magnifying optical system 6, and is uniformly incident on the electro-optic material 2 with a predetermined spread. Further, the parallel light that is uniformly incident on the electro-optical material 2 is cut out in a size that the cross section of the electro-optical material 2 covers a plurality of two-dimensional positions of the DUT 3, so that the The polarization state is changed by the change in the refractive index of the two-dimensional portion of the electro-optical material 2 corresponding to these two-dimensional positions due to the voltage at the plurality of two-dimensional positions, so that the electro-optical material 2 is output as emitted light. Has become. That is, the electro-optical material 2
The emitted light output from the light source has the same spread as the parallel light, and the change in the polarization state of each part reflects the voltage at each two-dimensional position of the DUT 3.

The phase compensator 11 adjusts the phase of the emitted light and sets the polarization component of the emitted light extracted by the analyzer 12 to a predetermined angle with the polarization component of the parallel light extracted by the polarizer 7, The polarization component of the emitted light extracted by the analyzer 12 can be the same as or orthogonal to the polarization component of the parallel light extracted by the polarizer 7.

The detector 13 is a CCD camera, a photodiode array,
A two-dimensional detector such as a vidicon camera,
Is detected and the voltage at the two-dimensional position of the DUT 3 is simultaneously detected from the change in the refractive index of the electro-optical material 2.

When the pulse light source 4 and the two-dimensional detector 13 are used in combination, the voltage at each two-dimensional position of the DUT 3 must change periodically in synchronization with the light pulse. That is, the light beam from the pulse light source 4 is divided into two by the beam splitter 17, one of which is made incident on the variable delay means 5 for sampling measurement, and the other is made incident on the detector 18 and photoelectrically converted. The photoelectrically converted signal is the trigger circuit 19
A drive circuit 29 is reached via the switch to periodically operate the DUT 3 in synchronization with the optical pulse. The voltage that repeatedly changes in this manner is detected by sampling. This sampling is performed by gradually delaying the light beam from the pulse light source 4 by the variable delay means 5, and such control of the variable delay means 5 is performed by a computer.
Made by 14. That is, after detecting the voltage of each two-dimensional position of the DUT 3 by the detector 13 at a certain timing, the computer 14 processes the voltage of each two-dimensional position at this time and stores it in a memory (not shown). The driving circuit 15 is controlled and the variable delay means 5 is driven by the driving circuit 15 to delay the light beam from the pulse light source 4 to slightly shift the sampling timing. As a result, it is possible to detect a temporal change in the voltage at each two-dimensional position of the DUT 3.

In the voltage detection device 1 having such a configuration, the phase compensator 11 is first adjusted so that the polarization component of the outgoing light extracted by the analyzer 12 is orthogonal to the polarization component of the parallel light extracted by the polarizer 7. . Thus, when the polarization state of the emitted light from the electro-optical material 2 is the same as the parallel light incident on the electro-optical material 2 (when no voltage is applied to the electro-optical material 2), the emitted light causes the analyzer 12 to pass through. Do not pass. After setting the phase compensator 11 in this way, the voltage measurement at the two-dimensional position of the DUT 3 is started.

The cross section of the electro-optical material 2 is cut to a size that covers each two-dimensional position of the DUT 3, so that the DUT 3 is
The voltage at each of the two-dimensional positions changes the refractive index of the local portion of the electro-optical material 2 corresponding to these two-dimensional positions. Therefore, the parallel light uniformly incident on the electro-optical material 2 changes its polarization state due to the change in the refractive index of the two-dimensional portion of the electro-optical material 2 corresponding to each two-dimensional position of the DUT 3, and the electro-optical material is changed. The material 2 outputs the emitted light. These emitted lights are further applied to the phase compensating means 11 via the beam splitter 10 and the imaging optical system 9, and the phases are adjusted by the phase compensator 11 to be incident on the analyzer 12. Phase compensator 11
Is adjusted so that the analyzer 12 passes only the light beam of the polarization component orthogonal to the polarization component of the polarizer 7,
The intensity of each outgoing light incident on the analyzer 12 is determined by the analyzer 12.
It becomes proportional to sin ² [(π / 2) ・ V _ij / V ₀ ]
Will be joining 13. Here, V _ij is the voltage at each two-dimensional position (i, j) of the DUT 3, and V ₀ is the half-wave voltage.

In this way, each emitted light changes due to the change in the refractive index of the local portion of the electro-optical material 2 accompanying the change in the voltage at each two-dimensional position of the DUT 3, and accordingly, the integrated circuit in the detector 13 is based on this. It is possible to simultaneously detect the voltage at the two-dimensional position of the measured object such as.

When the detector 13 detects the voltage at the two-dimensional position of the DUT 3 at a certain timing, the result is stored in the memory of the computer 14, and the computer 14 further detects the voltage at the next timing. The drive circuit 15 is controlled to drive the variable delay means 5, the light beam from the pulse light source 4 is delayed by a predetermined amount, the sampling timing is slightly shifted, and similar voltage detection processing is repeated. In this way, the voltage at the two-dimensional position of the DUT 3 is measured by sampling the change over time. Since the results of the sampling measurement are stored in the memory of the computer 14, the computer 14 displays these voltage detection results on the display 16 at the time when the sampling measurement within a predetermined time is finished, and the whole process is finished. .

In the voltage detection device 1 of FIG. 1, the pulse light source 4 and the CCD
In combination with a two-dimensional detector 13 such as a camera, a photodiode array, or a vidicon camera, the voltage which cyclically and repeatedly changes at the two-dimensional position of the DUT 3 is detected by sampling. If the voltage change at the two-dimensional position of the object is not periodic, the voltage detection device 1 of FIG. 1 cannot be used.

FIG. 2 is a partial schematic configuration diagram of a voltage detection device for detecting a voltage at a two-dimensional position of an object to be measured using a streak camera.

In the voltage detection device 20 of FIG. 2, instead of the two-dimensional detector 13 of FIG. 1, a phase compensator 11, a bundle of optical fibers 21 for guiding the emitted light that has passed through the analyzer 12, and an optical fiber bundle 21 Bunch 21
Streak camera into which outgoing light guided by
22 and are provided. At this time, the pulse light source 4 or the DC light source may be used as the light source.

As can be seen from FIG. 2, the bundle of optical fibers converts the two-dimensional array of emitted light into a one-dimensional array and makes it enter the slit 23 of the streak camera 22.

In the voltage detection device 20 having such a configuration, the phase compensator 11 is adjusted in the same manner as the voltage detection device 1 of FIG. 1, and then collimated light is made incident on the electro-optical material 2 from the pulse light source 4 or the DC light source. Phase compensator output from electro-optic material 2
11, the emitted light that has passed through the analyzer 12 is made incident on the bundle 21 of optical fibers in a two-dimensional array. Since the bundle 21 of optical fibers is one-dimensionally arranged at the slit 23 of the streak camera 22, the voltage information of the two-dimensional position of the DUT 3 is converted into one-dimensional information and is transmitted to the streak camera 22. The light enters and is detected by the streak camera 22 with high time resolution. When the streak camera is used, the variable delay means 5 is not necessary, and the voltage change of the DUT 3 can be measured even if it is a single-shot phenomenon.

In the above-described embodiment, only the voltage at the two-dimensional position of the DUT 3 is detected and displayed on the display 16. However, for the user, the wiring shape of the DUT 3 such as an integrated circuit can be further determined. It may be desired to observe at the same time and superimpose on the observed wiring shape to display the voltage at each two-dimensional position.

FIG. 3 is a configuration diagram of a voltage detection device that can display a voltage at a two-dimensional position by superimposing it on the wiring shape of the object to be measured. In FIG. 3, the same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

In the voltage detection device 30 of FIG. 3, an observation light source 31 that outputs pulsed light or DC light for observing the wiring shape of the DUT 3 is provided separately from the pulsed light source 4. The wavelength of the light beam output from the observation light source 31 is different from the wavelength of the light beam output from the pulse light source 4, and the light beam from the pulse light source 4 is a dielectric formed on the bottom surface of the electro-optical material 2. Although reflected by the multilayer mirror 32, the light beam from the light source 31 is transmitted through the dielectric multilayer mirror and is incident on the surface of the DUT 3.

The light beam from the observation light source 31 and the light beam from the pulse light source 4 are switched by the switching means 33 under the control of the computer 14, and the switching means 33 is
When observing the wiring shape of the DUT 3, the observation light source 31
The light beam from the pulse light source 4 is selected when the voltage at the two-dimensional position of the DUT 3 is detected while the light beam from the B is selected to be incident on the DUT 3 through the electro-optic material 2. It is adapted to be selected and made incident on the electro-optical material 2.

The phase compensator 11 is adapted to be adjusted by the computer 14, and when observing the wiring shape of the DUT 3, the analyzer 12 passes the emitted light of the same polarization component as the polarization component of the polarizer 7. 3 to be measured.
When the voltage at the two-dimensional position is detected, the analyzer 12 is adjusted so as to pass the emitted light of the polarization component orthogonal to the polarization component of the polarizer 7.

In the voltage detection device 30 having such a configuration, the computer 14 controls the switching means 33 in order to observe the wiring shape of the DUT 3 in advance so that the light beam from the observation light source 31 is emitted to the DUT 3. The light is incident on the surface as parallel light and the analyzer
The phase compensator 11 is adjusted so that 12 passes the emitted light of the same polarization component as the polarization component of the polarizer 7.

As a result, the light beam from the observation light source 31 enters the electro-optical material 2 as parallel light through the variable delay means 5, the expanding optical system 6, the polarizer 7 and the beam splitter 10, and further the dielectric multilayer film mirror 32. And is incident on the surface of the DUT 3. The parallel light incident on the surface of the DUT 3 is partially reflected by the wiring shape and material of the surface of the DUT 3, and the dielectric multilayer mirror
32, the electro-optic material 2 is returned, and is incident on the analyzer 12 as outgoing light through the beam splitter 10, the imaging optical system 9, and the phase compensator 11. By the way, in the phase compensator 11, the analyzer 12 has the polarizer 7
Since it is adjusted so as to pass the emitted light of the same polarized component as the polarized component of, the emitted light incident on the analyzer 12 passes through the analyzer 12 as it is and is added to the two-dimensional detector 13 such as a CCD camera. . The emitted light applied to the detector 13 has visible image information of the wiring shape of the DUT 3, so that the detector 13
Then, this can be photoelectrically converted to obtain visible image data of the wiring shape. This visible image data is stored in the computer 14
And is stored in the memory (not shown) of the computer 14.

After obtaining the visible image data of the wiring shape of the DUT 3 in this manner, the computer 14 initializes the variable delay means 5 and controls the switching means 33 so that the light beam from the pulse light source 4 is electrically turned on. The parallel light is made incident on the optical material 2,
Further, the phase compensator 11 is adjusted so that the analyzer 12 allows the outgoing light of the polarization component orthogonal to the polarization component of the polarizer 7 to pass, and the voltage at the two-dimensional position of the DUT 3 is simultaneously detected. At this time, the light beam from the pulse light source 4 is incident on the electro-optical material 2 as parallel light, and then is reflected by the dielectric multilayer film mirror 32, and the polarization state changes as the refractive index of the electro-optical material 2 changes. The emitted light enters the phase compensator 11 and the analyzer 12. The analyzer 12 passes only the emitted light of a predetermined polarization component and makes it incident on the two-dimensional detector 13. Detector 13
Then, the voltage at the two-dimensional position of the DUT 3 at the timing set by the variable delay means 5 is sampled and simultaneously detected. The voltage detection result at one timing is sent to the computer 14 and stored in the memory. Thereafter, the voltage detection result of the two-dimensional position of the DUT 3 sampled at one timing by superimposing it on the visible image data of the wiring shape of the DUT 3 previously stored in the memory is displayed on the display 16. indicate.

FIG. 4A shows the voltage detection result of the two-dimensional position of the DUT 3 at one sampling timing displayed on the display 16 so as to be superimposed on the wiring shape of the DUT 3. In FIG. 4A, the wiring shape of the DUT 3
The voltage distributions G1, G2, and G3 at two-dimensional positions are displayed so as to be superimposed on WF.

After the voltage detection result at one sampling timing is superimposed and displayed on the wiring shape in this way, the computer 14 controls the drive circuit 15 to drive the variable delay means 5 to output the light beam from the pulse light source 4. By changing the delay of
The sampling timing is slightly shifted, the same voltage detection processing is performed, and the same display is performed on the display 16.

FIG. 4B shows a state in which the voltage at the two-dimensional position of the DUT 3 detected by slightly shifting the sampling timing is superimposed and displayed on the wiring shape of the DUT 3. In FIG. 4 (b), the voltage distributions G1 ', G2', G3 'are
Voltage distribution G in Fig. 4 (a) on the wiring shape WF of DUT 3.
1, G2, G3 are time-varying.

As can be seen from FIGS. 4 (a) and 4 (b), in the voltage detection device 30 of FIG. 3, it is easy to visually check the time variation of the voltage distribution on the wiring shape WF of the DUT 3 on the display 16. It can be grasped and the voltage detection result can be easily understood.

〔The invention's effect〕

As described above, in the first aspect of the invention, the light beam from the light source becomes uniform light in each two-dimensional portion of the electro-optical material corresponding to the plurality of two-dimensional positions of the measured object. Since the detector detects changes in the polarization state of the light emitted from each two-dimensional portion of the electro-optical material, it is possible to detect the voltage at the two-dimensional position of the DUT at the same time. it can.

Further, in the second invention, since the voltage distribution of the two-dimensional position of the measured object is displayed by being superimposed on the wiring shape of the measured object, it is possible to easily understand the voltage detection result of the two-dimensional position. You can

[Brief description of drawings]

FIG. 1 is a configuration diagram of a voltage detection device of the present invention using a pulse light source and a two-dimensional detector, FIG. 2 is a partial configuration diagram of the voltage detection device of the present invention using a streak camera, and FIG. The configuration diagram of the voltage detection device capable of displaying the voltage distribution by superimposing it on the wiring shape of the DUT, FIGS. 4A and 4B show different sampling timings displayed in the voltage detection device of FIG. 3, respectively. It is a figure which shows the example of a display of. 1,20,30 ... Voltage detector, 2 ... electro-optical material, 3 ... measurement object, 4 ... pulse light source, 5 ... variable delay means, 6 ... magnifying optical system, 7 ... polarizer , 11 …… phase compensator, 12 …… analyzer, 13 …… detector, 14 …… computer, 16 …… display, 21 …… bundle of optical fibers, 22 …… streak camera, 31 …… observation light source , 32 ... Dielectric multilayer mirror, 33 ... Switching means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01L 21/66 C 7735-4M

Claims (8)

[Claims] 1. A voltage detecting device of a type using an electro-optical material, the refractive index of which changes when a voltage is applied,
The electro-optical material is a single electro-optical material and has a size such that it covers a plurality of two-dimensional positions of the measured object whose voltage is to be detected, and the measured object whose voltage is to be detected. Each of the two-dimensional portions of the electro-optical material corresponding to the plurality of two-dimensional positions of the object to be measured have a two-dimensional spread from the light source. A voltage detection device, wherein a light beam is incident and a change in polarization state of light emitted from the plurality of two-dimensional portions of the electro-optical material is detected by a detector. 2. The light source is a pulsed light source that outputs a light beam having a short pulse width, the detector is a two-dimensional photoelectric conversion detector, and the two-dimensional photoelectric conversion detector is
The voltage detecting apparatus according to claim 1, wherein the voltage change at a two-dimensional position of the object to be measured is sampled and measured. 3. The light source is a DC light source or a pulsed light source, the detector is a fast response detector, and the emitted light is a bundle of optical fibers for converting a two-dimensional array into a one-dimensional array. The voltage detection device according to claim 1, wherein the voltage detection device is guided to the high-speed response detector. 4. The voltage detection device according to claim 3, wherein the fast response detector is a streak camera. 5. The voltage detecting device according to claim 1, wherein a reflecting mirror made of a metal or dielectric multilayer film is formed on the bottom surface of the electro-optical material. 6. A voltage detecting device of a type using an electro-optical material, the refractive index of which changes when a voltage is applied,
The electro-optical material is positioned so as to cover a plurality of two-dimensional positions of the measured object whose voltage is to be detected, and each of the two electro-optical materials corresponding to the plurality of two-dimensional positions of the measured object. A short pulse width light beam from a pulse light source is incident on the two-dimensional portion in parallel, and a change in the polarization state of the emitted light from the plurality of two-dimensional portions of the electro-optical material is detected by a detector. The observation light source that outputs a light beam having a wavelength different from that of the pulse light source for observing the wiring shape of the DUT, and the light beam from the observation light source and the pulse light source. Switching means for switching the light beam to be incident on the electro-optical material, and a phase for adjusting the phase of the emitted light at a phase different from that at the time of detecting the change in the polarization state when observing the wiring shape of the DUT. Compensation means and before Display means for displaying the voltage of the two-dimensional position of the measured object measured based on the change of the polarization state of the emitted light by superimposing it on the wiring shape of the measured object observed by the detector. A voltage detection device characterized by the above. 7. A dielectric multi-layered film mirror is formed on the bottom surface of the electro-optical material, and the dielectric multi-layered film mirror transmits the light beam from the observation light source while transmitting light from the pulse light source. The voltage detection device according to claim 6, wherein the voltage detection device is configured to reflect a beam. 8. The phase compensating means adjusts the phase of the emitted light so that the emitted light from the electro-optical material is applied to the detector as it is when observing the wiring shape of an object to be measured. On the other hand, when detecting the voltage at the two-dimensional position of the DUT, only the change in the polarization state is extracted from the emitted light from the electro-optical material and the emitted light is added to the detector. 7. The voltage detecting device according to claim 6, wherein the voltage is adjusted.