JP3320835B2 - Distance control method and distance control device between optical probe and measured object, and electrical physical quantity measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for controlling the distance between an optical probe and an object to be measured and an apparatus for measuring an electric physical quantity applied to the measurement of an electric physical quantity (for example, the measurement of an internal node voltage) of an integrated circuit or the like. In this regard, the distance between the optical probe and the object to be measured is accurately measured, and the measured value is fed back to the position control means of the probe to control the distance between the probe and the object to be measured with high accuracy. The method and apparatus described above.

[0002]

2. Description of the Related Art In testing integrated circuits and the like, for example,
As disclosed in Japanese Patent Application Laid-Open No. 1-286431,
A non-contact type probe (hereinafter, referred to as an “EO probe”) using an electro-optic crystal (a crystal having an electro-optic effect) is brought close to a circuit to be measured, and a light pulse having a narrow pulse width is irradiated on the crystal. By detecting the change in the polarization state in the crystal, the voltage of the internal node of the circuit under test is brought into non-contact,
There is a non-invasive and ultra-fast test method.

In this method, the measurement sensitivity is usually E
It greatly depends on the separation distance between the O probe and the object to be measured,
The higher the control accuracy of the separation distance between the EO probe and the object to be measured, the more accurate the voltage measurement becomes. When the width of the wiring of the circuit to be measured is considered to be several μm, in order to obtain sufficient measurement sensitivity without disturbing the circuit,
The distance between the tip of the EO probe and the object to be measured is 1μ.
m.

As a specific method for bringing the EO probe close to the circuit to be measured, conventionally, (1) the EO probe is brought into contact with the circuit to be measured once and then separated from the circuit by a desired distance. Method for determining the separation distance of the circuit to be measured (Preliminary lectures of the 1992 IEICE Autumn Meeting C-309), (2) Japanese Patent Laid-Open No. 23838/1990
As described in Japanese Unexamined Patent Application Publication No. 2000-209, using light of two wavelengths and a lens having chromatic aberration on the optical axis for these two wavelengths, light of each wavelength is applied to the probe end face and the surface of the circuit to be measured. There is known a method of positioning a probe by focusing.

[0005] The method (1) involves an operation of bringing the probe into contact with the circuit to be measured.
O-probes and circuits to be measured may be mechanically destroyed.

Further, in this type of separation distance control, if there is no feedback system for measuring the separation distance and controlling the EO probe based on the measured value, the influence of external vibration is inevitable. However,
In the conventional method represented by (1), the separation distance cannot be measured or the separation distance cannot be measured with high accuracy, so that the above feedback system cannot be adopted. Therefore, it is considered that highly accurate separation distance control is difficult.

In the method (2), since the depth of focus itself is about 1 μm, the set value of the separation distance is several μm.
m is considered to be a limit, and it is considered that accurate measurement of the separation distance is difficult.

In particular, when measuring the absolute value of the voltage, it is necessary to calibrate the measured voltage value in accordance with the distance.
For this purpose, it is desired that the separation distance can be measured and that it can be set arbitrarily according to the situation. However, in the above method (2), the separation distance is determined at the time of designing the optical system, and therefore cannot be arbitrarily set when measuring the voltage.

[0009]

An object of the present invention is to provide a non-contact type optical probe (E)
O probe and magneto-optic crystal probe (MO probe)
The distance between an optical probe and an object to be measured applied to an apparatus for measuring a predetermined electrical physical quantity (for example, an internal node voltage of an integrated circuit, a current flowing through wiring of the integrated circuit) by bringing the object close to the object to be measured In the method and the distance control device, the distance between the optical probe and the circuit to be measured is accurately measured, and the measured value is fed back to the position control means of the probe to increase the distance between the optical probe and the object to be measured. The purpose is to control the accuracy.

[0010]

SUMMARY OF THE INVENTION A distance control method and a distance control device between an optical probe and a measured object according to the present invention are applied to an electric physical quantity measuring device for measuring an electric physical quantity of a surface of a measured object, and the distance control is performed. The method comprises: (1) reflecting distance measurement light having a predetermined wavelength band on an optical probe tip surface and a surface to be measured; and (2) reflecting light reflected on the optical probe tip surface and light reflected on the surface to be measured. Measuring the distance between the tip of the optical probe and the surface to be measured based on the phase difference of (3), and (3) feeding back the measured value to the position control means of the optical probe to control the distance. And

The distance control device includes: (1) a light source for generating distance measurement light having a wavelength band different from that of the electric physical quantity measurement light; (2) reflected light at the tip surface of the optical probe; Means for measuring the separation distance between the tip of the optical probe and the surface to be measured based on the phase difference from the reflected light on the surface; and (3) feeding back the measured value to the position control means of the optical probe, Means for controlling the separation distance.

The method and apparatus for controlling the distance between an optical probe and an object to be measured according to the present invention reflect light for measuring an electric physical quantity at a transparent tip surface of a non-contact type optical probe.
The present invention is also applied to an apparatus for measuring an electric physical quantity (an internal node voltage value, a current flowing through a wiring) on the surface to be measured by detecting a change in the polarization state of the reflected light in the optical probe. Note that a laser beam is usually used as the electric physical quantity measurement light.

In the present invention, light having a wavelength band different from that of the electric physical quantity measuring light is used as the distance measuring light. Further, the light source for generating the light for distance measurement usually includes a white light source having a short coherence length (for example, a halogen lamp, an LED or the like), a plurality of optical filters, and the like.

In the present invention, the distance measuring light having a wavelength band different from that of the electric physical quantity measuring light is incident on the optical path of the electric physical quantity measuring light. Normally, a dichroic mirror is used as a means for this incidence.
The above-mentioned incidence is realized by transmitting one of the distance measuring lights to the dichroic mirror and reflecting the other to the dichroic mirror.

Further, as means for measuring the separation distance between the tip of the optical probe and the surface of the object to be measured based on the phase difference between the reflected light on the surface of the optical probe and the light reflected on the surface of the object to be measured, Well-known optical means such as a Michelson interferometer (usually composed of a movable mirror, a light intensity detector and the like) are used.

Further, a piezo element is used to control the distance by feeding back the measured value of the distance to the position control means of the optical probe. In the present invention, by performing feedback control, the separation distance is maintained with high accuracy without being affected by external vibration. The separation distance is set to an arbitrary value as needed.

More specifically, according to the present invention, the distance measuring light has a predetermined bandwidth of a wavelength shorter than the wavelength band of the electric physical quantity measuring light, and the distance measuring light includes the optical probe and the optical path length. Shunt to a variable reflective mirror. Then, the reflected light from the reflecting mirror and the reflected light from the optical probe tip surface and the surface to be measured interfere with each other, and based on an interference output obtained by changing a phase difference between these reflected lights. Control the separation distance.

A beam splitter is used as a means for shunting the distance measuring light into two optical paths. Further, in order to change the optical path length of the distance measuring light reflected by the reflecting mirror, an optical path length increasing / decreasing means is provided.
As this optical path length increasing / decreasing means, a piezo element which is driven integrally with a reflection mirror is typically used.

The beam splitter is usually used as interference means for interfering the reflected light from the reflecting mirror with the reflected light from the tip surface of the optical probe and the surface to be measured. That is, as described above, the distance measuring light incident on the beam splitter is divided into two paths and output once, but these lights are reflected by the distal end surface of the optical probe and the surface to be measured. And is reflected by the reflection mirror and returns to the beam splitter again, where the two reflected lights interfere with each other. The interference output light from the interference means is received by the photodetector.

Then, the distance between the optical probe and the object to be measured is measured from the position of the interference peak obtained by the interference of the distance measuring light, and the measured value is fed back to the position control means of the optical probe while the measured value is fed back. When a halogen lamp is used as the light source, the optical probe can be brought close to the object to be measured while measuring the distance to 1 μm or less. At that time, it is considered that positioning accuracy of 0.1 μm or less can be realized by feedback control.

The light for measuring the distance is reflected on the distal end face of the optical probe and the surface to be measured, and the light for measuring the electric physical quantity is reflected on the distal end face of the optical probe and propagates along the same optical path. In order to measure the electric physical quantity, it is necessary to separate the light for measuring the electric physical quantity from the optical path. Since the electric physical quantity measuring light and the distance measuring light can be separated by a dichroic mirror or the like, the distance measuring light does not adversely affect the electric physical quantity measuring light.

Further, in the present invention, the distance measuring light has a predetermined bandwidth of a wavelength shorter than a wavelength band of the electric physical quantity measuring light, and the distance measuring light has a predetermined bandwidth on the tip surface of the optical probe and the surface of the object to be measured. Reflect light. Then, the reflected light is shunted to two optical paths, and reflective mirrors are provided on both optical paths, the optical path length of one of the reflective mirrors is changed, and the reflected lights from both reflective mirrors interfere with each other. The separation distance is controlled based on the interference output obtained by changing the phase difference.

In the specific example described above, the distance measuring light is first shunted to two optical paths, and these are shunted to the electro-optic crystal probe, the object to be measured, and the reflection mirror side. In this case, the light for distance measurement is sent to the electro-optic crystal probe and the object to be measured without shunting, and the light reflected by the tip surface of the electro-optic crystal probe and the surface to be measured is split into two optical paths by a beam splitter. Let it go.

Then, reflected light from a pair of reflecting mirrors provided on both optical paths (one of which is a reflecting mirror whose optical path length can be changed) is caused to interfere by interference means. Also in this case, a beam splitter is employed as a means for shunting the reflected light from the distal end surface of the optical probe and the surface to be measured into two optical paths. Further, the beam splitter can be used as an interference unit.

An optical fiber can be used as a means for guiding light to the optical probe. Further, the beam splitter and the interference unit may be constituted by an optical fiber coupler, and each optical path may be constituted by an optical fiber.

[0026]

【Example】

[First Embodiment] FIG. 1 is a view showing a first embodiment of the present invention, and shows an entire distance control system between an EO probe and an object to be measured.

In FIG. 1, white light emitted from a white light source 1 (here, a halogen lamp) passes through a collimating optical system composed of a condenser lens 3, a pinhole 4, and a collimating lens 5, and becomes parallel light. Is done. In the optical path of the white light, a heat ray absorption filter 2 and a color temperature conversion filter (indicated by an optical filter 6 in the figure) are provided, and the heat ray absorption filter 2 sets the wavelength band of the white light source 1 in a visible light region. And the optical filter 6 improves the resolution of the distance measurement. A light source for generating the light for distance measurement is constituted by the components indicated by the reference numerals 1 to 6 above.

The light from the light source is shunted by the beam splitter 7 into two optical paths. In one of these optical paths, a non-contact EO probe 31 is provided via a dichroic mirror 8, and an EO probe is provided.
The object to be measured (circuit under test 3)
2) is arranged. Also, of the above two optical paths,
The other optical path is provided with a reflection mirror 10 that moves in the optical axis direction via a chromatic dispersion compensating medium 24. The distance measuring light reflected on the distal end surface of the EO probe 31 and the surface of the circuit under test 32 and the distance measuring light reflected on the reflecting mirror 10 are combined by the beam splitter 7 and then condensed by the condensing lens 9. The light is received by the photodetector 33 and its intensity is measured.

In this embodiment, the reflection mirror 10 is scanned by the piezo element 44 with high accuracy along the optical axis. With this scanning, the optical path length between the beam splitter 7 and the reflecting mirror 10 changes continuously, and the photodetector 33 can measure the interference light intensity as a function of the position of the reflecting mirror 10.

Hereinafter, the principle of the separation distance measurement based on white light interference will be briefly described. Here, the EO probe 31
Since the purpose is to measure the separation distance between the circuit and the circuit 32 to be measured, the light for measuring the electric physical quantity is not considered.

In FIG. 1, a halogen lamp having a short coherence length is used as the white light source 1, and when the reflecting mirror 10 is moved along the optical axis, the mirror position becomes E.
A large interference output appears only when the position of the two reflection surfaces on the O probe 31 side (that is, the tip surface of the probe 31 and the surface of the circuit under test 32) coincides with the optical path length.

The end face of the EO probe 31 and the circuit under test 3 due to the interference output measured by the photodetector 33 in FIG.
An example of measuring the separation distance from the two surfaces will be described with reference to FIG. Of the two peaks shown in the figure, I0 represents the interference between the reflected light from the end face of the EO probe 31 and the reflected light from the reflecting mirror 10, and I1 represents the reflected light from the surface of the circuit 32 to be measured and the reflecting mirror. 10 shows the interference with the reflected light from 10. The difference between these two interference peaks (reflection mirror 1
The distance d between the end surface of the EO probe 31 and the surface of the circuit under test 32 can be measured from the moving distance of 0 (the moving direction is indicated by Z).

In this measurement, the distance resolution is determined by the half width of the envelope (shown by a broken line in FIG. 2) of one interference output. The interference output has a Fourier transform relationship with the spectrum of the light contributing to the interference. When the spectral distribution of light is assumed to be a Gaussian distribution, the half width is Δλ, and the distance resolution is Δ
ζ

[0034]

Δ１ = (2 · ln2 / π) · ｛(λ _c ² −Δλ)
^2/4) / ^Δλ}

The fringe of the interference appears at a period of の of the center wavelength λc. For example, λ _c
= 0.6 μm and Δλ = 0.3 μm, Δζ
= 0.5 μm. Therefore, in order to sharpen the peak of the interference output and increase the resolution of the separation distance, it is better that the spectral distribution of the light contributing to the interference be a high-bandwidth distribution and the central wavelength be short. Also, in order to separate and measure two interference peaks as in the present case, it is desired that one interference peak does not affect the other,
It is necessary to form an optical spectrum having a distribution such that side lobes do not appear due to Fourier transform. For that purpose, it is desirable that the light spectrum has a Gaussian distribution. Therefore, light having a spectral distribution in the visible light band as shown in FIG. 3 may be formed by the optical filter 6 described with reference to FIG. If light having such a spectral band is used, a separation distance resolution of 1 μm or less can be obtained.

In this way, as shown in FIG. 1, the separation distance d is measured by the signal processing circuit 43 from the output of the photodetector 33, and the measured value is fed back to the probe position control means 41 via the feedback circuit 42. Is done.
Then, the EO probe 31 is controlled such that the distance between the EO probe 31 and the circuit under measurement 32 becomes a desired value.

The light for measuring the electric physical quantity (here, the laser beam for measuring the voltage) is in the near infrared region, that is, 1.3.
By using light in the μm or 1.5 μm band, the electric physical quantity measurement light and the distance measurement light, which is white light in the visible light region, are sufficiently separated in the wavelength band (see FIG. 3). The voltage measuring optical system is indicated by reference numeral 45 in FIG.

In FIG. 1, a dichroic mirror 8
While the distance measuring light is incident on the optical path of the electric physical quantity measuring light, and both the measuring lights are guided to the EO probe 31.
The light reflected on the tip surface of the EO probe 31 and the surface of the circuit under test 32 is divided into light for measuring electric physical quantity and light for measuring distance. Note that the dichroic mirror 8 and the voltage measurement optical system 45 do not necessarily need to be arranged between the beam splitter 7 and the EO probe 31, and may be arranged on the light source side of the beam splitter 7.

By the way, in the two optical paths shunted by the beam splitter 7, if the chromatic dispersion characteristics are not equivalent, the envelope of the interference output is widened and the resolution of the distance measurement is reduced. Therefore, in FIG. 1, a chromatic dispersion compensating medium 24 such as quartz glass or an optical fiber is inserted into the optical path on the side of the reflection mirror 10 to correct the chromatic dispersion present on the optical path on the side of the EO probe 31.

[Second Embodiment] FIG. 4 is a diagram showing a second embodiment of the present invention, and shows the entire distance control system between the EO probe and the object to be measured.

The distance measuring light emitted from the white light source 1 passes through the heat ray absorbing filter 2 and the optical filter 6 as in the first embodiment, and is converted into parallel light by the above-described collimating optical system. 12. It is guided to the EO probe 31 and the circuit under measurement 32 via the dichroic mirror 8. The tip surface of the EO probe 31 and the circuit under test 3
The light reflected on the surface 2 is guided to the beam splitter 7 via the half mirror 12.

In the two optical paths shunted by the beam splitter 7, equivalent reflecting mirrors 10 and 11 are arranged, and the reflected light from each of the mirrors 10 and 11 interferes in the beam splitter 7. This interference light is condensed by the condensing lens 9 and further received by the photodetector 33 and detected as light intensity. Here, one reflection mirror 11 is fixed, while the other reflection mirror 10 is fixed.
Is configured to be able to scan with high accuracy in the optical axis direction by the piezo element 44. By this scanning, the optical path difference between the two optical paths changes continuously.

When the reflecting mirror 10 is moved along the optical axis, according to the principle of white light interference described in the first embodiment,
An interference output as shown in FIG. 5 is obtained. In the figure,
The interference output becomes maximum at the position of Z = 0 where the optical path lengths from the beam splitter 7 to the two reflection mirrors 10 and 11 coincide with each other, and the interference output appears at symmetric positions ± d before and after the position. Since the distance d corresponds to the distance between the EO probe 31 and the surface of the circuit under test 32, the distance d can be measured from the interference output. In FIG. 5, the envelope is indicated by a broken line.

The measured values are fed back to the probe position control means 41 via the signal processing circuit 43 and the feedback circuit 42, as in the first embodiment, and
The position of the EO probe 31 is controlled such that the distance d between the tip surface of the O-probe 31 and the surface of the circuit under test 32 becomes a desired value. Further, the laser beam for voltage measurement is emitted by the dichroic mirror 8 in the same manner as in the first embodiment.
It is led to the O probe 31.

In the second embodiment, the beam splitter 7
Since the chromatic dispersion characteristics are completely equivalent in the two optical paths shunted by, the distance resolution determined by the spectral distribution of white light can be obtained without a decrease in separation distance resolution due to chromatic dispersion.

[Third Embodiment] In the distance control system shown in FIG. 1, an EO probe 31 uses an optical fiber 15 provided with condensing lenses 13 and 14 at both ends, and a distance measuring light or an electric physical quantity is applied to the EO probe 31. Measurement light can be introduced (FIG. 6).
reference). In this case, since the EO probe 31 which is close to the circuit under measurement 32 and other optical systems are separated by the optical fiber 15, the EO probe 31 and the surface of the circuit under measurement 32 which are not affected by the vibration or noise generated by the device. , It is possible to perform highly accurate separation distance control. Also, the EO probe 31
Alignment when directing light to the light source is facilitated.

However, since the EO probe 31 is disposed on one of the two optical paths shunted by the beam splitter 7, when the optical fiber 15 guides the distance measuring light to the EO probe 31, Reflection mirror 10
By disposing an optical fiber having the same characteristics and the same length in the optical path on the side, it is necessary to compensate for the chromatic dispersion described above and avoid a decrease in resolution.

When an optical fiber is used in the optical path on the side of the reflection mirror 10, the piezo ring actuator 2 shown in FIG.
The optical path length on the reflection mirror side may be changed by a fiber phase modulator 23 (device driven by a piezo driving device 46 in which an optical fiber is wound around a piezo ring) constituted by 5. In this case, since there is no need to align the reflection mirror, stability when changing the optical path length is improved.

[Fourth Embodiment] In the distance control system shown in FIG. 2, similarly to the third embodiment, the light for distance measurement and the light for electric physical quantity measurement are introduced into the EO probe 31 using the optical fiber 15. (See FIG. 6). In this case, the third
Needless to say, the same effect as that described in the embodiment is expected.

In FIGS. 1 and 4, the beam splitter 7 is used.
Has been described, the respective optical paths may be configured by optical fiber couplers 22 as shown in FIG. 8 without using the beam splitter 7. In FIG. 4 (second embodiment), the beam splitter 7
Although the case where one of the two optical paths shunted by the optical path length is changed by the reflection mirror 10 has been described, the present invention is not limited to this, and the light extracted by the half mirror 12 in FIG. As long as it shunts and gives an optical path difference to these two lights, another means for changing the optical path length can be adopted.

For example, a polarization interferometer composed of two polarizers 18 and 20 and a Wollaston prism 19 as shown in FIG. 9A can be used. In this polarization interferometer, since the phase difference between two lights polarized at right angles changes in a one-dimensional direction perpendicular to the optical axis, the interference output is spatially reduced using an array-like photodetector such as a CCD. And this can be processed by the signal processing circuit 43.

Further, as shown in FIG. 9B, the same function can be configured by using the optical fiber coupler 21. In FIG. 7B, the light for distance measurement which is condensed on the end face of the optical fiber 17 a by the condenser lens 16 and shunted into two paths via the optical fiber coupler 21.
The CCD 34 is irradiated from the end faces of 7b and 17b. CC
Interference occurs at a point on the surface of D34 where the distances from the irradiation ports of both optical fibers 17b are different. Signal processing circuit 4
Numeral 3 processes the spatial interference output from the CCD 34 to perform the same measurement as in FIG.

As described above, when the interference output is obtained spatially, the influence of the vibration caused by the mechanical scanning of the reflection mirror 10 and the like is eliminated, and the interference output is obtained by the electrical scanning. Speed is greatly improved. Further, in the above embodiment, a halogen lamp is assumed as the white light source 1, but an appropriate white light source 1 is selected according to a required separation distance between the EO probe and the circuit to be measured. For example, if the separation distance is 10 μm
LED if it is of the order, and S if it is several tens of μm.
A low coherent light source such as an LD is employed.

Although the method of positioning the EO probe 31 for measuring the voltage value of the internal node of the circuit under test 32 has been described here, the present invention is not limited to the EO probe.
The method is not limited to only the method of positioning the probe 31. In other words, when it is necessary to keep the probe for measuring physical quantity using light at a distance of 1 μm to several tens of μm from the object to be measured, other than an EO probe whose probe material is transparent to the light of the light source The distance control according to the present invention can be performed also when the above-mentioned probe is used in place of the EO probe.

Fifth Embodiment For example, a non-contact current measuring device inside a circuit as shown in FIG. 10 can be considered. The device shown in the figure includes a circuit under test 52 formed on a substrate 53,
A magneto-optical probe (MO probe) 51 having a transparent tip is disposed close to the probe, and a current flowing through the circuit under measurement 52 is measured. In other words, this device converts a magnetic field formed by a current flowing through the circuit under measurement 52 inside the circuit (in the figure, lines of magnetic force are indicated by broken lines) by using a crystal having a magneto-optical effect to generate current (laser) light for current measurement. The measurement is performed in place of the rotation of the polarization plane, and the current value can be obtained by measuring the rotation angle of the polarization plane. When the probe control technique of the present invention is applied to this current measuring device, the control of the probe is significantly improved. The material of the MO probe used in place of the EO probe is YAG
(Yttrium Aluminum Garnet), YAG
(Yttrium, iron, garnet).

As is clear from the above-described embodiments of the EO probe and the MO probe, a member having an end face made of a transparent material is located at a predetermined distance from a measured portion, and thus other probes fixed to this member are used. Can also be used.

In the above embodiment, the positioning in the horizontal direction has not been described. However, since the positioning is performed in the same manner as in the related art, the description is omitted.

[0058]

As described above, according to the present invention, the following effects can be obtained. (1) Since the distance between the optical probe and the circuit to be measured is always measured while the distance between the optical probe and the circuit to be measured is kept close, the distance between the optical probe and the circuit to be measured does not need to be brought into contact with the circuit to be measured. Further, by feeding back the measured value of the separation distance to the probe position control means, positioning can be performed with high accuracy and high stability.

(2) The distance measuring light and the electric physical quantity measuring light can be separated in the wavelength band, so that the distance measuring light does not adversely affect the voltage measurement.

(3) It is not necessary to consider the influence of chromatic dispersion in the optical probe or the optical fiber, and the resolution of distance measurement determined by the spectral band of light contributing to interference can be obtained.

(4) The reliability of a non-contact type measuring device used for measuring an electric physical quantity is remarkably improved, and a highly accurate measurement of a voltage value of an internal node of a circuit under test becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an interference output obtained in the embodiment of FIG.

FIG. 3 is a diagram illustrating a spectrum distribution required for distance measuring light and a state of separation in an optical physical quantity measuring light in a wavelength band according to the present invention.

FIG. 4 is a diagram showing a second embodiment of the present invention.

FIG. 5 is a diagram illustrating an interference output obtained in the embodiment of FIG. 4;

FIG. 6 is a diagram illustrating an embodiment in which light is guided to an EO probe using an optical fiber in the distance control device of the present invention.

FIG. 7 is a diagram illustrating an example in which a change in optical path length is configured by a fiber phase modulator.

FIG. 8 is a diagram illustrating an example in which the beam splitter in FIGS. 1 and 4 is configured by an optical fiber coupler.

9A is a diagram showing one example of spatially obtaining an interference output by using a polarization interferometer and an array-like photodetector such as a CCD, and FIG. 9B is a diagram showing an optical fiber and an array such as a CCD; FIG. 7 is a diagram showing an example of spatially obtaining an interference output using a photodetector in a shape.

FIG. 10 is a view showing a fifth embodiment of the present invention, and is an explanatory view of a current measuring device using an MO probe.

[Explanation of symbols]

 1: White light source 2: Heat absorption filter 3, 9, 13, 16: Condensing lens 4: Pinhole 5: Collimating lens 6: Optical filter 7: Beam splitter 8: Dichroic mirror 10, 11: Reflection mirror 12: Half mirror 13, 14: condenser lens 15: optical fiber 16: condenser lens 18, 20: polarizer 19: wollaston prism 21, 22: optical fiber coupler 23: optical fiber phase modulator 24: chromatic dispersion compensating medium 31: EO probe 32: Circuit to be measured 33: Photodetector 34: CCD 41: Probe position control means 42: Feedback circuit 43: Signal processing circuit 44: Piezo element 45: Optical system for voltage measurement 46: Piezo drive 51: MO probe 52: Circuit to be measured 53: Substrate

──────────────────────────────────────────────────続 き Continued on the front page (73) Patent owner 399117121 395 Page Mill Road Palo Alto, California U.S.A. S. A. (56) References JP-A-4-236377 (JP, A) JP-A-61-76902 (JP, A) JP-B-4-23202 (JP, B2) (58) Fields investigated (Int. . ^7, DB name) G01R 31/28 - 31/302 G01B 11/00 - 11/06 H01L 21/66

Claims (7)

(57) [Claims] 1. A method for controlling a distance between an optical probe and an object to be measured applied to an electric physical quantity measuring device for measuring an electric physical quantity of a surface of the object to be measured, wherein a distance measuring light having a predetermined wavelength band is transmitted to the optical probe. The light is reflected on the transparent tip surface and the surface to be measured, and the reflected light on the distal surface of the optical probe and the phase difference between the reflected light on the surface to be measured and the optical probe tip and the object to be measured. the distance is measured, a method for controlling the distance by feeding back the measured value to the position control means of the optical probe, the distance measuring light wavelength band of the electrical physical quantity measuring light
A predetermined bandwidth of shorter wavelength, and the optical probe tip
For measuring the distance on the end face and the surface to be measured
Reflects light, shunts the reflected light into two optical paths,
A reflection mirror is provided in the optical path, and one of the reflection mirrors
By changing the optical path length, the reflected light from both reflecting mirrors interferes.
And the phase difference between these reflected light changes.
Controlling the separation distance based on the interference output to be measured. 2. A distance control device between an optical probe and an object to be measured applied to an electric physical quantity measurement device for measuring an electric physical quantity on a surface of an object to be measured, wherein the distance having a wavelength band different from that of the light for electric physical quantity measurement is provided. A light source for generating measurement light, the optical probe provided with position control means for adjusting a separation distance between the object to be measured, and reflected light on the tip surface of the optical probe, Means for measuring the distance between the tip of the optical probe and the object to be measured based on the phase difference with the reflected light, and the measured value is fed back to the position control means of the optical probe to control the distance. and means for, the distance measuring light wavelength band of the electrical physical quantity measuring light
Has a predetermined bandwidth of shorter wavelength and measures the separation distance
Means for moving the optical probe at the distal end face and the front face of the optical probe.
The reflected light reflected on the surface to be measured
A beam splitter for shunting to the optical path,
Pair of reflecting mirrors, one of which is the optical path length
Reflection mirror that can change the reflection and reflection from both reflection mirrors
Interfering means for interfering light, and
A photodetector that receives the interference output light and detects the intensity thereof;
Means for controlling the separation distance includes the signal
The output of No. processing circuit to the position control means of the optical probe
A feedback for controlling the distance by feedback.
A distance control device between an optical probe and an object to be measured , which comprises a lock circuit . 3. The optical probe according to claim 1, wherein the electric physical quantity is a voltage or a current, and the distance measuring light has a wavelength band different from that of the electric physical quantity measuring light. A method for controlling the distance between measurement targets. 4. The method according to claim 2, wherein the electric physical quantity is a voltage or a current, and the light source for the distance measuring light generates light having a wavelength band different from that of the electric physical quantity measuring light. The distance control device between the optical probe and the object to be measured as described in the above. 5. The distance measuring light has a predetermined bandwidth of a wavelength shorter than the wavelength band of the electric physical quantity measuring light, and the distance measuring light is shunted to the optical probe and a reflecting mirror having a variable optical path length. The reflected light from the reflecting mirror interferes with the reflected light from the optical probe tip surface and the surface to be measured, and the separation based on the interference output obtained by changing the phase difference between these reflected lights. 4. The distance control method according to claim 1, wherein the distance is controlled. 6. The distance measuring light has a predetermined bandwidth of a wavelength shorter than a wavelength band of the electric physical quantity measuring light, and the means for measuring the separation distance uses the distance measuring light with the optical probe. A beam splitter for shunting the light to a reflection mirror having a variable optical path length, an optical path length increasing / decreasing means for changing an optical path length of the reflection mirror, light reflected from the reflection mirror, a tip end surface of the optical probe and the object to be measured. Interfering means for interfering with reflected light from the target surface, a photodetector that receives the interference output light from the interfering means and detects the intensity thereof, and performs signal processing on the output of the photodetector, A signal processing circuit for measuring a separation distance between the tip of the optical probe and the object to be measured, wherein the means for controlling the separation distance controls the output of the signal processing circuit to control the position of the optical probe. A feedback circuit that controls the separation distance by feeding back to control means,
The optical probe according to claim 2, wherein:
A distance control device between objects to be measured. 7. The electrical physical quantity measuring device distance control device is provided according to claim 2, 4 or 6, detecting the polarization state change of the electric physical quantity measuring light in said optical probe Wherein the voltage or current of the wiring to be measured is obtained.