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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an E-O (Electro-Optic) probe and
electro-optic voltage detector which can measure a voltage or voltage
waveforms on electrical conductors.
2. Related Background Art
With an increase in fineness of semiconductor integrated circuits,
potential measuring apparatus (electro-optic voltage detector) using the
E-O probe utilizing the electrooptic effect are in the limelight as
apparatus for accurately measuring voltage signal waveforms of elements in
such integrated circuits.
The potential measuring apparatus using the E-O probe are apparatus in
which an electrooptic crystal is opposed to a measured object, the
electrooptic crystal is irradiated with a light beam of linear
polarization or circular polarization from the side opposite to the
measured object, and the light beam reflected by the opposed end face (to
the measured object) of the electrooptic crystal is led through an
analyzer to enter a photodetector, whereby the beam is detected.
The technology related to such E-O probe is described, for example, in
Japanese Laid-open patent Application No. 4-29344.
SUMMARY OF THE INVENTION
E-O probes may be so arranged that conductive members fixed to a
electrooptic crystal on the measured sample surface side are made in the
needle shape. In this technology using this needle shape conductive
member, electric fields induced by potentials of wires or electrodes
formed on a semiconductor substrate are guided with high spatial
resolution through the needle shape conductive member to the electrooptic
crystal. When a multitude of conductive members are made over the entire
surface of electrooptic crystal, in case of a plurality of portions being
measured, the total measurement time is reduced.
However, if the plurality of conductive members are brought close to the
measured object to measure a potential distribution in a fine region in
the measured object with scan of laser light beam on the plural conductive
members, the spatial resolution is very poor, because reflected light from
a certain conductive member is measured simultaneously with reflected
light from neighboring conductive members, using the laser beam with large
beam size.
Thus, high resolution measurement is impossible if the spaces between the
wires or needlelike conductive members are narrower than the beam size.
Further, high resolution measurement is impossible if a high resolution is
desired for the potential distribution in the fine region in the wiring.
Of course, thinning of the beam size can reduce interference from
neighboring conductive members, but the potential distribution cannot be
measured for devices of submicron order, because the beam size cannot be a
size smaller than the submicron order. That is, the convergence limit of
beam size is determined by the numerical number of a lens for converging
the beam and the wavelength of the beam.
The present invention has been accomplished in view of such problems, and
an object of the present invention is to provide an E-O probe and
electro-optic voltage detector (this is an apparatus comprising the E-O
probe) which can measure potentials at plural points in a fine region
while enlarging them.
To solve the above problems, the present invention is directed to an E-O
probe which comprises an electrooptic member changing a refractive index
thereof in accordance with an electric field applied thereto, and a
plurality of needlelike, conductive members bases of which are fixed to a
surface of the electrooptic member, wherein each space on a side of the
bases between the plurality of needlelike, conductive members is greater
than each space on a side of the tips between the needlelike, conductive
members.
According to such an arrangement, electric fields corresponding to
potentials in the fine region in the measured object are induced as
enlarged in a wide region in the electrooptic member through the
needlelike, conductive members. Since the electrooptic member changes its
refractive index depending upon the potential, the incident light into the
electrooptic member is changed in polarization state upon reflection in
accordance with the potentials in the fine region in the measured object.
In addition, the potentials induced by the fine region in the measured
object are enlarged to be transmitted to the electrooptic member, and,
therefore, detecting the light changed in polarization state by the
electrooptic member, the potential distribution can be measured for a
smaller region in the measured object than the convergence limit of the
incidence laser light beam into the E-O probe. The space between the bases
of the needlelike conductive members is greater than the incident laser
beam size.
Also, since the tip of the plurality of needlelike, conductive members are
located on a substantially same plane, the needlelike, conductive members
can be brought uniformly close to the fine region in the measured object.
Then, if the needlelike, conductive members are buried in a retaining
portion made of an insulator member, the needlelike, conductive members
can not only be reinforced, but also electrically insulated from each
other.
Especially, when the tip of the plurality of needlelike, conductive members
are located on a substantially same plane, and a surface of the insulator
member facing to the sample is parallel to the sample surface or has a
plane, the needlelike, conductive members can be brought uniformly close
to the fine region in the measured object only by making contact the tip
with the sample surface.
Further, if a light reflection film is interposed in portions where the
bases of the plural needlelike, conductive members are fixed to the
electrooptic member and a light shield film is formed on exposed surfaces
around fixed surfaces of the bases, the intensity of reflection can be
enhanced for reflected light from the portions of the electrooptic member
where the needlelike, conductive members are fixed, and at the same time
the interference can be prevented with reflected light from the
neighboring needlelike, conductive members.
The present invention will become more fully understood from the detailed
description given hereinbelow and the accompanying drawings which are
given by way of illustration only, and thus are not to be considered as
limiting the present invention.
Further scope of applicability of the present invention will become
apparent from the detailed description given hereinafter. However, it
should be understood that the detailed description and specific examples,
while indicating preferred embodiments of the invention, are given by way
of illustration only, since various changes and modifications within the
spirit and scope of the invention will become apparent to those skilled in
the art from this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an E-O probe of the first embodiment of the
present invention.
FIG. 2 is a diagrammatic drawing of a potential measuring apparatus using
the E-O probe of the first embodiment of the present invention.
FIG. 3 is a diagrammatic drawing of a potential measuring apparatus using
the E-O probe of the first embodiment of the present invention.
FIG. 4 is a perspective view of an E-O probe of the second embodiment of
the present invention.
FIG. 5 is a perspective view of an E-O probe of the third embodiment of the
present invention.
FIG. 6 is a perspective view of an E-O probe of the fourth embodiment of
the present invention.
FIGS. 7A-7D are explanatory drawings to illustrate a process for producing
the E-O probe of the first embodiment of the present invention.
FIG. 8 is a cross sectional view of an E-O probe the fifth embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be described in detail as to preferred
embodiments of Electro-Optical voltage detector having E-O probe with
reference to the accompanying drawings. In the description same elements
will be denoted by same reference numerals or symbols, and redundant
description will be omitted.
First Embodiment
FIG. 1 is a perspective view to show the structure of an E-O probe of the
first embodiment of the present invention.
This E-O probe comprises a transparent support member 1, grounded
transparent electrode 2, electrooptic member 3, reflection film 4, and
first through fifth needlelike, conductive members 5a-5e as shown in FIG.
1.
The support member 1 is made of a transparent material such as glass. The
quarts glass support 1 is in the size of 300.times.300.times.200 .mu.m.
The transparent electrode 2 is made of Indium-Tin-Oxide (ITO), and fixed
to the support member 1. The electrooptic member 3 is made of a material
such as ZnTe, the electrooptic member 3 is fixed to the transparent
electrode 2, and the thickness of the electrooptic member 3 is some ten
.mu.m. The reflection film 4 is a dielectric multilayer film, and fixed to
the electrooptic member 3. Below the reflection film 4, a plurality of
(five in the drawing) conical, conductive members (electric needles) 5a-5e
are fixed to the lower surface of the reflection film 4 on base surfaces
of the members 5a-5e so that the lower ends thereof project downward.
Needle spaces between the plurality of conical, electric needles 5a-5e
decrease toward a measured device (measured device 112 shown in FIG. 2)
located below the needles, whereby they can guide potentials in a fine
region in the measured device to the electrooptic member 3 while enlarging
them.
Further, the lower end portions (second end portion) of the electric
needles 5a-5e are formed in a substantially same plane, so that they can
accurately measure an in-plane distribution of the potentials in the fine
region measured.
Other materials for the electrooptic member 3, than above ZnTe, may be
LiNbO.sub.3, BSO, GaAs, CdTe, LiTaO.sub.3, etc.
When the electric needles 5a-5e in the E-O probe as so arranged are brought
close to the measured device (measured device 112 shown in FIG. 2),
electric fields induced by potentials in the measured device are
transmitted through the electric needles 5 to the electrooptic member 3 to
change the refractive index of the electrooptic member 3 by the Pockels
effect.
On this occasion, letting laser light of linear polarization, circular
polarization, or elliptical polarization enter the electrooptic member 3
from above the support member 1, the polarization state of the laser light
is changed by the change of refractive index according to the potentials
in the measured device. Then the laser light is reflected by the
reflection film 4 attached to the lower surface of the electrooptic member
3 to be outgoing upward the support 1. In this connection, the electric
needles 5 may be set in contact with the measured object in measurement.
Here, let us consider a case that potentials of electrodes in an integrated
circuit are measured using the E-O probe provided with such electric
needles 5a-5b. The minimum width W of electrodes (not shown) of the
integrated circuit is 0.5 .mu.m, for example. Thus, letting "b" be the
spaces at the lower end points (second end portions) between the electric
needle 5c (first needlelike member) and needle 5d (second needlelike
member) shown in FIG. 1, it is necessary that "b" be set to about
W.about.0.5 .mu.m. Further, assuming that the numerical aperture NA of an
objective lens (objective lens 110 shown in FIG. 2) set above the
electrooptic member 3 is 0.4, the diameter a.sub.0 of a focused beam is
given by the following formula from the diffraction limit of light.
a.sub.0 =2 .lambda./(.pi..multidot.NA) (where .pi. is the circular
constant)
Supposing laser light of wavelength .lambda.=1 .mu.m is focused by the
objective lens then to enter the electrooptic member 3, the diameter
a.sub.0 of the focused beam becomes 1.6 .mu.m from the above formula.
Namely, the convergence limit of the light is thus not less than 1.6
.mu.m.
Accordingly, in order to remove the effect of signals from neighboring
electric needles 5a-5e, it is necessary that a=2 .mu.m or more where "a"
is the spaces on the bottom surface between the electric needle 5c and 5d
shown in FIG. 1. That is, the spaces "a" on the bottom surface between the
electric needle 5c and needle 5d need to be set to about four or more
times larger than the spaces "b" at the lower end points, more precisely
to 2.lambda./(.pi..multidot.NA.multidot.W) or more times.
FIG. 2 shows the structure of an apparatus of an E-O probing system
(electro-optic voltage detector) which detects the laser light first
incident into the E-O probe in FIG. 1 and then outgoing upward from the
support member 1 to measure potentials in the measured device 112. Next
described is the structure of the apparatus shown in FIG. 2 together with
the operation thereof.
The apparatus electro-optic voltage detector comprises a main body 117, a
device-to-be-measured support table 113, a movable stage (118, 119, 120),
an optical unit 126 and a microscope unit 123.
The device-to-be measured support table 113 is attached to the main body
117, and the support table 113 faces to the first and second needlelike
members 5c, 5d show in FIG. 1.
The movable stage (118) is attached to the main body 117 for moving the
first and second needlelike members (5a-5e) shown in FIG. 1 related to the
support table 113.
The optical unit 126 is attached to the main body 117. The optical unit 126
has a laser light source 100, a wave plate 105, a photodetector 127 and a
polarization beam splitter 104. The laser light source 100, wave plate 105
and polarization beam splitter 104 are so arranged that an incident laser
beam from the laser light source 100 is made incident through the
polarization beam splitter 104 and said wave plate 105 in a first
direction. Further, the wave plate 105, photodetector 127 and polarization
beam splitter 104 are so arranged that a reflection laser beam from the
wave plate 105, travelling in a second direction is reflected by the
polarization beam splitter 104 and is made incident on the photodetector
127.
The microscope unit 123 is attached to the main body 117. The microscope
unit 123 has an objective lens 110. The objective lens 110 is so arranged
that the incident laser beam is made incident through the objective lens
110 and is made incident on the reflection film 4 shown in FIG. 1.
Further, the objective lens 110 is so arranged that the reflection laser
beam reflected by the reflection film 4 is made incident thorough the
objective lens 110 and is made incident thorough the wave plate 105 in the
second direction. Next, the structure of the apparatus shown in FIG. 2 is
explained more precisely.
This E-O probing system is an apparatus for measuring potentials in a
measured device 112 on the support table 113 set on an upper surface of
the stationary portion 117 of the main body in such a manner that laser
light emitted from an optical unit 126 is made to fall on the above E-O
probe 111 set above and near the measured device and that reflected laser
light from the E-O probe 111 is detected by the photodetector 127 in the
optical unit 126.
There are the laser light source 100, a lens 101, an optical isolator 103,
the polarization beam splitter 104, the wave plate 105, a deflecting
element 102, and a mirror 106 sequentially arranged in the optical unit
126. The optical unit 126 has a light shielding case LS1, and these
elements 100, 101, 103, 104, 105, 106 are arranged in the light shielding
case LS1. First, the laser light emitted from the laser light source 100
is made incident through the lens 101 and the optical isolator 103 which
allows the light to pass only in one direction, into the polarization beam
splitter 104.
Then the light incident into the polarization beam splitter 104 is made
incident through the 1/8 wave plate 105 into the deflecting element 102.
The deflecting element 102 is an element for temporally changing the
direction in which the laser light is projected. Applicable elements as
the deflecting element 102 are, for example, a mechanical element
including a combination of two rotary polygon mirrors which effects
two-dimensional scan of beam by rotating the mirrors, an element utilizing
the electrooptic effect, such as a Pockels modulator, etc. The laser light
thus changed in the direction of projection is made to fall on the mirror
106, whereby the optical path thereof is changed.
The laser light thus changed in the optical path by the mirror 106 is then
made incident into the microscope unit 123 disposed below the optical unit
126. The laser light incident into the microscope unit 123 is then made
incident via a dichroic mirror 107, a mirror 108, and a dichroic mirror
109 set on the optical path and in the microscope unit 123, into an
objective lens 110.
The laser light converged by the objective lens 110 is made incident into
the E-O probe 111 (the E-O probe 111 is precisely shown in FIGS. 1, 4, 5,
8), where the polarization state thereof is changed in accordance with
potentials in the measured device 112 and then the laser light is
reflected upward the E-O probe 111. The outgoing laser light travels in
the reverse direction to the incident path to pass through the 1/8 wave
plate 105, which provides the light with a bias-like phase difference.
Then the light travels via the polarization beam splitter 104, where the
change in polarization state is converted into a change in intensity. Then
the light enters a photodetector 127 (for example, a PIN photodiode).
Here, the 1/8 wave plate 105 provides the light with a phase difference of
a quarter of the wavelength during the double passage of go and return.
The laser light detected by the photodetector 127 is converted into an
electric signal, and the electric signal is amplified by an amplifier 128
to be put into a digital oscilloscope 130.
The electric signal (photo intensity signal) put into the digital
oscilloscope 130 is displayed on the digital oscilloscope 130 and also put
into a computer (signal convertor) 131 to be converted into potentials
(voltages) in the measured device 112. As described, the potentials in the
measured device 112 are thus measured.
A drive voltage is supplied from a manipulator 115 on a control table 116
through an electric needle 114 to the measured device 112. Images of the
measured device 112 and E-O probe 111 are observed on a monitor 129
connected with a CCD 125 in such a manner that light from an illumination
light source 132 in the microscope unit 123 is guided via the dichroic
mirror 107, the mirror 108, and the dichroic mirror 109 and through the
objective lens 110 to fall on the surface of the measured device 112 and
that reflected light is let to pass through the dichroic mirror 109 to
impinge on the CCD 125 located on the transmission path, so that the
images are picked up thereby.
The CCD 125 is a visible light camera (TV camera) in case of the E-O probe
111 being a crystal transparent to part of the visible region, such as
ZnTe, or an infrared camera in case of the E-O probe 111 being a crystal
transparent to the infrared region, such as GaAs.
Also, the monitor 129 includes a built-in image memory, so that it can
store the input images as still images or display them on a display of the
computer 131 connected with the monitor 129. These images can be observed
by the bare eyes through eyepieces 124 located on the optical path of the
transmitted light through the dichroic mirror 109.
Observing such images, the E-O probe 111 can be moved to the measured
region in the measured device 112 by the following moving mechanism.
The E-O probe 111 is fixed to the probe stage 119 through a support needle
134 connected with the grounded, transparent electrode in the E-O probe
111. The probe stage 119 is arranged as vertically slidable, so that it
can move the E-O probe 111 in the vertical directions (directions along
the Z-axis) in the drawing. The probe stage 119 is fixed to the microscope
unit 123, and the microscope unit 123 is also arranged as slidable in the
directions along the Z-axis by the Z-axis stage 120 supporting it.
The Z-axis stage 120 is fixed to the XY axis stage 118 through a movable
portion 121 of the main body, so that it can horizontally move the E-O
probe 111 in the XY plane (plane perpendicular to the Z-axis). By the
above arrangement, the E-O probe 111 can be moved in a three-dimensional
space, and the focal length of the microscope unit 123 can be adjusted
independently of it.
Connected with the Z-axis stage 120 is an automatic focusing mechanism for
automatically focusing the microscope unit 123 by analyzing the contrast
of the image displayed on the computer 131. When the operator gives the
computer 131 an input through a keyboard 133, the XY axis stage 118 and
probe stage 119 are made to slide under an instruction from the computer
131 so as to move the E-O probe 111 in the directions along the XY axes
and in the directions along the Z-axis, whereby the E-O probe 111 can be
horizontally moved to above the measured region and be then brought close
thereto at a desired proximity distance.
FIG. 3 shows another arrangement obtained by modifying the E-O probing
system of FIG. 2 in such a manner that in place of the deflecting element
102 a lens 202 is disposed between the lens 101 and the light isolator 103
and that photodetectors 227 two-dimensionally arranged replace the
photodetector 127 (for example a photodiode array or CCD image sensor).
This arrangement makes the laser light emitted from the laser light source
100 enlarged and collimated. Guiding the enlarged and collimated light
into the E-O probe 111, the information on the electric field induced in
the electric needles 5a-5e of FIG. 1 can be put in parallel into the
photodetectors 227 two-dimensionally arranged.
The reflected light including the information on the electric field from
each electric needle 5a-5e is processed in the same manner as in the
apparatus of FIG. 2, whereby the potentials in the measured device 112 can
be measured. As described, the apparatus of FIG. 3 can measure a
distribution of electric field in the measured device 112 in parallel.
Since the electric needles 5a-5e of FIG. 1 radially spread from the
measured device 115 toward the electrooptic member 3 and are connected to
the broad region of the electrooptic member, the potential information
from the electric needles 5a-5e, included in the reflected light, can be
readily separated from each other to be put into the photodetectors 227
two-dimensionally arranged.
According to the first embodiment as described above, the spaces between
the electric needles 5a-5e are made narrower toward the lower ends
thereof, so that the potentials in the measured device can be measured as
enlarged. Also, since the lower ends of the electric needles 5a-5e are
formed on the same plane, the in-plane distribution of potentials in the
measured device can be accurately measured.
Second Embodiment
FIG. 4 is a perspective view to show the structure of an E-O probe of the
second embodiment of the present invention.
The present embodiment is a modification in the shape of the electric
needles 5a-5e shown in FIG. 1. This E-O probe comprises a transparent
support member 11, a transparent electrode 12 fixed to the support member
11, an electrooptic member 13 fixed to the transparent electrode 12, a
reflection film 14 fixed to the electrooptic member 13, and needlelike,
conductive members 15a-15e fixed to the reflection film 14 at their ends
(first end portions) as shown in the FIG. 4.
The lower end portions of the electric needles 15a-15e in the E-O probe
are thinner than the upper end portions thereof and the distance between
the electric needles 15 becomes shorter toward the lower ends. Further,
the longitudinal direction of the lower end portions of the electric
needles 15a-15e is made approximately perpendicular to the surface of the
measured device. In other words, the longitudinal direction of the lower
end portions (second end portions) of the electric needles 15a-15e is
approximately perpendicular to reflection film 14.
Such an arrangement that the longitudinal direction of the lower end
portions of the electric needles 15a-15e is made approximately
perpendicular to the surface of the measured device (integrated circuit
chip 112 shown in FIG. 2 or 3) can prevent interference with an electric
field induced by neighboring elements (not shown) in the measured device
(integrated circuit 112 shown in FIG. 2 or 3) and can permit the electric
field induced at the lower end portions of the electric needles 15a-15e to
be accurately detected with high spatial resolution.
Since the lower ends of the electric needles 15a-15e are also formed in an
approximately same plane, similarly as the electric needles 5a-5e in FIG.
1, the in-plane distribution of potentials in a fine region in the
measured object can be accurately measured.
According to the second embodiment as described above, the longitudinal
direction of the lower end portions of the electric needles 15 is made
approximately perpendicular to the surface of the measured device, whereby
the interference can be prevented with the electric field induced by the
potentials in the neighboring elements in the measured device and the
potentials in the measured device can be detected with high spatial
resolution.
Even if the E-O probe is brought into contact with the measured device
under a strong force because of an operational error or the like during
measurement of potentials in the measured device, a transverse stress
exerted on the interface between the electric needles 15a-15e and a
reflection film 14 to which the electric needles 15a-15e are fixed can be
reduced as compared with the E-O probe of the first embodiment, whereby
the electric needles 15a-15e can be prevented from breaking because of
such an operational error or the like.
Third Embodiment
FIG. 5 is a perspective view, partly in vertical section, to show the
structure of an E-O probe of the third embodiment of the present
invention.
The present embodiment is a modification in the shape of the electric
needles 5a-5e shown in FIG. 1. This E-O probe comprises a transparent
support member 21, a transparent electrode 22 fixed to the support member
21, an electrooptic member 23 fixed to the transparent electrode 22, a
light shield film 41 fixed to the electrooptic member 23, a reflection
film 42 fixed to the electrooptic member 23, and needlelike, conductive
members 25a-25i fixed to the reflection film 42 at their ends (first end
portions) as shown in the FIG. 5.
The present embodiment is so arranged that the electric needles 5a-5e in
FIG. 1 are replaced by electric needles 25a-25i in which a conductive
material is mixed in core portions in a taper fiber plate shaped in a
frustum of circular cone. The core portions to become the electric needles
25a-25i are buried in a clad portion 26 in the taper fiber plate. The
light shield film 41 and reflection film 42 are formed on the lower
surface of the electrooptic member 23 in place of the reflection film 4 in
FIG. 1. Further, the bottom surface of the taper fiber plate is fixed to
lower surfaces of the light shield film 41 and the reflection film 42.
The upper end face and lower end face of the taper fiber plate are
polished, whereby the lower end faces of the electric needles 25a-25i are
on a substantially same plane, which is such an arrangement that all the
lower end faces of the electric needles 25a-25i can be located in the
vicinity of or in contact with a measured surface of the measured device
in parallel therewith.
In more details, if the lower end faces of the electric needles 25a-25i are
located above the lower end surface of the clad portion 26, the lower end
surface of the clad portion 26 is made in contact with the surface of the
measured device whereby the electric needles 25a-25i can be located in the
vicinity of the surface of the measured device with a clearance of a
difference between the lower end surface of the clad portion 26 and the
lower end faces of the electric needles 25a-25i. Accordingly, as shown in
FIG. 8, this figure shows a special structure E-O probe illustrated in
FIG. 5, the clearance described above is defined by a gap "d" between the
lower end faces (reference level) of the electric needles 250a-250c and
lower end surface of the clad portion 260, or between the lower end faces
of the electric needles 250a-250c and a surface of an electrode EL of a
measured device SM.
Further, in FIG. 5, if the lower end faces of the electric needles 25a-25i
are located below the lower end surface of the clad portion 26, all the
lower end faces of the electric needles 25a-25i can be located in contact
with or in the vicinity of the surface of the measured device in parallel
therewith.
It is of course that if the lower end surface of the clad portion 26 is
coincident in height with the lower end faces of the electric needles 25,
the electric needles 25 can be readily made uniformly in contact with the
measured device by bringing the clad portion 26 into contact with the
surface of the measured device. This type of E-O probe can be fabricated
by a process comprising a step of forming an E-O probe including the
needles 25a-25i buried in the clad portion 26, said needles 25a-25i having
a first end portions and second end portions, wherein said first end
portions are fixed to the reflection film 42; and a step of polishing a
surfaces of the clad portion 26 and second end porions of the needles
25a-25i simultaneously.
Not only does the clad portion 26 mechanically reinforce the electric
needles 25 of thin wires, but it also separates the electric needles 25
from each other without mutual contact. Further, similarly as in FIG. 1,
the reflection film 42 is fixed to the upper end faces of the electric
needles 25, while the light shield film 41 is fixed to the lower end
surface of the electrooptic member 23 except for the surfaces where the
reflection film 42 is fixed.
This arrangement can prevent the detection of light including information
on potentials from the neighboring electric needles 25a-25i, when the
laser light is made incident from above the support 21 to extract the
information on the electric field induced in the electric needles 25a-25i,
as light.
Although the present embodiment employed the taper fiber plate, the same
effect can be enjoyed by any modification in which the conductive needles
25 are buried in an insulating medium or member (the clad portion 26 in
FIG. 5). An example of such a modification is shown in FIG. 6. In this
example, electric needles 25a-25i shown in FIG. 5 are so constructed that
a conductive metal is deposited inside through holes 51 shown in FIG. 6 in
a taper multichannel plate base (taper capillary plate base) 50 shaped in
a frustum of circular cone made of an insulating material such as glass
and having a plurality of vertical through holes 51.
In more detail, it may be formed in such a manner that the taper
multichannel plate base 50 is set in a vacuum vessel (not shown), glass
materials such as GeO.sub.2 and P.sub.2 O.sub.5 in the vapor phase are
made to vertically flow while heating the base with an oxyhydrogen burner
(not shown), and at the same time, a conductive metal Pb or Au is heated
to be made to flow in the vapor phase, whereby conductive glass is
deposited over inner walls of the through holes 51. The conductive
electric needles can also be formed in the through holes 51 in the above
manner.
Also, a value of resistance of the electric needles of the conductive glass
or the like thus deposited can be changed by changing a mixture ratio of
the glass materials for the multichannel plate base 50. Further, the
deposition may be effected not only in the vapor phase but also in the
liquid phase, and the glass materials are not always limited to GeO.sub.2
and P.sub.2 O.sub.5 as long as they can form the electric needles 25a-25i
having conductivity.
According to the third embodiment as described above, the lower end surface
of the taper fiber plate is polished, so that the lower ends of the
electric needles 25 can be readily formed on the substantially same plane.
In addition, since the electric needles 25a-25i are buried in the clad
portion 26, the mechanical strength of the electric needles 25a-25i can be
improved and the electric needles 25a-25i can be separated from each other
without mutual contact. Further, the light shield film 41 is fixed to the
lower end surface of the electrooptic member 23 except for the surfaces
where the reflection film 42 is fixed, which can prevent the light
including the information on potentials from the neighboring electric
needles 25 from being detected.
It is noted that the light shield film 41 can also be applied to the E-O
probes in the first and second embodiments.
Next described is a process for producing the electric needles 5a-5e in the
E-O probe shown in FIG. 1.
FIGS. 7A-7D show production steps for the E-O probe electric needles 5a-5c
in the first embodiment of the present invention to be formed on the lower
surface of the reflection film 4 fixed to the electrooptic member 3.
First, as shown in FIG. 7A, the bottom surfaces of the electric needles
5a-5c preliminarily pin-pointed at the lower end portions are fixed to the
lower surface of the reflection film 4. (first step)
Next, the lower end portions of the electric needles 5a-5c are bundled into
one as shown in FIG. 7B. (second step) Then, as shown in FIG. 7C, the
bundled lower end portions of the electric needles 5a-5c are dipped in an
etching solution to chemically remove the tip portions and to align the
lower end positions of the electric needles 5a-5c. (third step)
Thus, the E-O probe base is obtained with the electric needles 5a-5c
converging toward the lower ends thereof and formed on the lower surface
of the electrooptic member through the reflection film 4, as shown in FIG.
7D. The E-O probe shown in FIG. 1 is obtained by fixing this base to the
support 1 through the transparent electrode 2.
Although the electric needles 5a-5c preliminarily pin-pointed toward the
tip were employed in the above first step, this step may be replaced by
such a step that small balls of a conductive material such as the metal
solder are fixed on the lower surface of the reflection film 4 and
thereafter, heating the conductive material, the balls are pulled downward
to form the electric needles 5a-5c of fine wires. Also, the first step may
be arranged in such a manner that a conductive adhesive with high
viscosity is bonded to the lower surface of the reflection film 4 and
thereafter part thereof is pulled downward to form the electric needles
5a-5c of fine wires.
The shape of the E-O probe electric needles 15 in the second embodiment can
be achieved by mechanically processing the electric needles 5a-5c in the
thus produced E-O probe base by means of cutting pliers or the like.
According to the present invention, as detailed above, the electric field
corresponding to potentials in a fine region in the measured object is
induced as enlarged in a broad region in the electrooptic member through
the needlelike, conductive members (5a-5e, 15a-15e, 25a-25i), whereby a
distribution of potentials in the fine region in the measured object (112,
EL) can be measured, which was conventionally impossible because of the
diffraction limit of light.
In addition, since the lower ends of the needlelike, conductive members
(5a-5e, 15a-15e, 25a-25i) are formed on the substantially same plane, the
needlelike, conductive members (5a-5e, 15a-15e, 25a-25i) can be set
uniformly close to the fine region in the measured object, whereby the
in-plane distribution of potentials in the fine region in the measured
object can be accurately measured.
Further, since the needlelike, conductive members (25a-25i) are buried in
the insulator (26, 260), the needlelike, con | | |
