U.S. patent application number 09/574155 was filed with the patent office on 2002-10-03 for probe for electro-optic sampling oscilloscope.
Invention is credited to Nagatsuma, Tadao, Toriyama, Noriyuki, Yagi, Toshiyuki.
Application Number | 20020140416 09/574155 |
Document ID | / |
Family ID | 15643280 |
Filed Date | 2002-10-03 |
United States Patent
Application |
20020140416 |
Kind Code |
A1 |
Toriyama, Noriyuki ; et
al. |
October 3, 2002 |
PROBE FOR ELECTRO-OPTIC SAMPLING OSCILLOSCOPE
Abstract
An electro-optic sampling probe is provided, capable of
irradiating a plurality of excitation light beams on a plurality of
light receiving portions mounted on an IC wafer which is an object
for measurement. The electro-optic sampling probe comprises a
plurality of excitation optical system modules which commonly uses
an objective lens for condensing the excitation light beams on the
IC wafer and a detachable portion for attaching and detaching the
excitation optical system module, a second probe body for covering
the optical path of a light beam emitted from the excitation
optical system module is provided at the rear side of the IC wafer,
and at least one of the plurality of excitation optical system
modules have an optical axis which differs from those of other
modules; thereby at least two excitation light beams can be
irradiated on the light receiving portions on the IC wafer
surface.
Inventors: |
Toriyama, Noriyuki; (Tokyo,
JP) ; Yagi, Toshiyuki; (Tokyo, JP) ;
Nagatsuma, Tadao; (Sagamihara-shi, JP) |
Correspondence
Address: |
Darby & Darby PC
805 Third Avenue
New York
NY
10022
US
|
Family ID: |
15643280 |
Appl. No.: |
09/574155 |
Filed: |
May 18, 2000 |
Current U.S.
Class: |
324/97 |
Current CPC
Class: |
G01R 1/071 20130101;
G01R 31/2831 20130101; G01R 31/311 20130101 |
Class at
Publication: |
324/97 |
International
Class: |
G01R 013/38; G01R
013/40 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 3, 1999 |
JP |
11-157150 |
Claims
What is claimed is:
1. An electro-optical sampling probe comprising: an electro-optic
element, optical properties of which change due to an electric
field applied through a wiring, when the wiring on a surface of an
IC wafer is in contact therewith; an electro-optic sampling optical
system module, which comprises therein a polarization beam
splitter, a half wave plate, and a photodiode, for converting a
laser beam into an electric signal, separated after the laser beam
externally generated has been propagated through said electro-optic
element and reflected at a surface of said electro-optic element
facing said wiring; and a first detachable portion for attaching
and detaching said electro-optic sampling optical system module; a
first probe body for covering a light path output from said
electro-optic sampling optical system module; an excitation optical
system module for irradiating a light in a condensed state for
excitation of said IC wafer; and a second detachable portion for
attaching and detaching said excitation optical system module; and
a second probe body for covering a light path output from said
excitation optical system module; wherein the electro-optic
sampling probe further comprises a plurality of excitation optical
system modules which commonly uses an objective lens for condensing
said plurality of excitation light beams on said IC wafer, and at
least one of said plurality of excitation optical system modules
has a light axis which differs from that of the other excitation
optical system modules, so that the excitation light beams are
irradiated on at least two different light receiving portions
disposed on said IC wafer.
2. An electro-optic sampling probe according to claim 2, wherein
the electro-optic sampling probe further comprises a light axis
adjusting portion at the output side of said excitation optical
system module, capable of adjusting the light axis of light beams
emitted by said excitation optical system module.
3. An electro-optic sampling probe according to claim 1, wherein
said light axis adjusting portion comprises a gonio-stage which
moves on a circumference around the input portion into said
objective lens.
4. An electro-optic sampling probe according to claim 2, wherein
said light axis adjusting portion comprises: an XY stage finely
movable in two directions crossing at a right angle; a first lens
for condensing a light beam output from said excitation optical
system module; a second lens for collimating the light beam
condensed by said first lens into a parallel beam.
5. An electro-optic sampling probe according to claim 1, wherein
said excitation optical system module is constituted including a
half-wave plate.
6. An electro-optic sampling probe according to claim 1, wherein
said detachable portion installed in said first probe body and
detachable portion installed in said second probe body have an
identical form.
7. An electro-optic sampling probe according to claim 1, wherein
said electro-optic sampling probe uses a light beam emitted from
said electro-optic sampling optical system module as the excitation
light source.
8. A method of measurement using the electro-optic sampling probe
according to claim 1, wherein the method comprises the steps of:
irradiating excitation light beams originating from a plurality of
excitation optical system modules on a plurality of light receiving
portions mounted on one surface of the IC wafer; and carrying out a
measurement of electric signals on another surface of the IC wafer
using the electro-optic sampling optical system module.
9. A method of measurement according to claim 8, wherein said
method of measurement comprises the step of carrying out the
measurement of electric signals by irradiating a plurality of light
beams originated from a plurality of excitation optical system
modules by changing irradiation timing.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an electro-optic sampling
probe, which is used for observing the waveforms of a test signal
based on a change in the polarization state of a light pulse caused
when the light pulse generated by a timing signal is input into an
electro-optic crystal which is coupled with an electric field
generated by the test measuring signal, and particulaly relates to
the electro-optic sampling probe provided with an improved optical
system of the probe.
[0003] 2. Background Art
[0004] An electro-optic probe is capable of observing waveforms of
a test signal based on a change in the polarization state of a
laser light caused when the light pulse generated by a timing
signal is input into an electro-optic crystal which is coupled with
an electric field generated by the test measuring signal. When the
laser light is emitted in a pulsed mode, and when the test signal
is used after sampling, the measurement can be executed that has a
very high time resolution. An electro-optic sampling probe is
developed by the use of the electro-optic probe utilizing the above
phenomenon.
[0005] The electro-optic sampling probe (hereinafter, called EOS
probe) has following advantages over the conventional probe using
an electric probe, and thus such a probe is attracting
attention.
[0006] (1) Measurement is easy, because a ground line is not
necessary during measurement.
[0007] (2) Since the top end of the present electro-optic probe is
insulated from the measuring circuit, a high input impedance is
provided, which results in eliminating factors that disturb the
conditions of the test point.
[0008] (3) The use of the light pulse allows carrying out wideband
measurement reaching to the GHz order.
[0009] (4) Measurement can be executed for wiring that is too fine
to be measured by direct contact with a metal pin by placing an
electro-optic crystal in contact with an IC (Integrated Circuit)
and by collimating the laser beam on the IC wafer.
[0010] The structure of the conventional electro-optic probe will
be described with reference to FIG. 6. In FIG. 6, the numeral 1
denotes an IC wafer, which is connected with the outside through an
electric source line and a signal line. The numeral 2 denotes an
electro-optic element formed by an electro-optic crystal. The
numeral 31 is an objective lens used for condensing a light
incident to the electro-optic element. The numeral 41 is a probe
body provided with a dichromic mirror 41a and a half-mirror 41b.
The numeral 6a denotes an EOS optical module (hereinafter called an
EOS optical system), and a fiber collimator 69 is mounted on one
end of the EOS optical system.
[0011] The numeral 7 denotes a halogen lamp for illuminating the IC
wafer for measurement. The numeral 8 denotes an infrared camera
(hereinafter, called IR camera) used for confirming the positioning
of the light condensed on the wiring of the IC wafer 1. The numeral
9 denotes an absorption stage for absorbing and fixing the IC wafer
1, and the absorption stage is capable of fine movement in the
three directions of the x-axis, the y-axis, and the z-axis, which
crosses each other at right angles. The numeral 10 denotes a
standard table (partly omitted) to which the absorption stage 9 is
fixed. The numeral 11 denotes an optical fiber for propagating the
laser light that enters from the outside.
[0012] A light path of the laser light that enters from the outside
is described with reference to FIG. 6. The light path of the laser
light in the probe body 41 is shown by a reference symbol A.
[0013] The laser light incident to the EOS optical system 6a
through the optical fiber is collimated into a parallel light beam
by a fiber collimator 69, propagates through the EOS optical system
6a, and enters into probe body 41. Furthermore, the laser light
propagates into the probe body 41, turned by 90 degrees by a
dichromic mirror 41a, and condensed by an objective lens to the
electro-optic element 2 at its surface that faces the IC wafer
1.
[0014] Here, a wavelength of the laser light entering into the EOS
optical system though the optical fiber 11 is 1550 nm. In contrast,
the optical properties of the above-mentioned dichromic color 41a
allow transmission of 5% and reflectance of 95% of the light with a
wavelength of 1550 nm. Therefore, 95% of the light emitted from the
laser source is reflected and turned by 90 degrees.
[0015] A dielectric mirror is deposited on the surface of the
electro-optic element that faces the IC wafer 1, and the laser
light reflected at that surface is again collimated into parallel
beams by the objective lens 31, returns to the EOS system 6a
passing along the same optical path, and entered into a photodiode
(not shown) in the EOS optical system 6a.
[0016] Next, a description is given on the light path of a light
emitted by the halogen lamp 7 and a positioning operation of the IC
wafer 1, when the positioning operation of the IC wafer 1 is
carried out by use of the halogen lamp 7 and the IR camera 8. In
FIG. 6, the symbol B denotes the light path of the halogen lamp
7.
[0017] The halogen lamp 7 used in this positioning operation emits
light having wavelengths ranging from 400 nm to 1650 nm.
[0018] The light emitted from the halogen lamp 7 is turned by 90
degrees by the half mirror 41b, passes through the dichromic mirror
41a, and illuminates the IC wafer 1. The half mirror 41b used in
this positioning operation yields reflected light with the same
intensity as that of the transmitted light.
[0019] The IR camera 8 picks up an image of a part of the IC wafer
1 in the field of the objective lens illuminated by the halogen
lamp 7, and the IR image is displayed on a monitor 8a. An operator
executes fine movement of the absorption stage such that a
measuring object, that is, the wiring on the IC wafer enters to a
field of view.
[0020] Furthermore, the operator adjusts the position of the
absorption stage 9 or the probe body 41 such that the laser light
is condensed precisely on the surface of the electro-optic element
2 placed on the wiring of the IC wafer by confirming the laser
light from the image of the IR camera 8 enters into the EOS
ooptical system through the optical fiber 11, is reflected by the
surface of the electro-optic element 2 placed on the wiring of the
IC wafer 1, and passes through the dichromic mirrors 41a.
[0021] In this operation, the laser light passing through the
dichromic mirror 41a can be recognized by the IR camera 8, since
the dichromic mirror can transmit about 5% of light in the
wavelength range of the laser light.
[0022] Here, a measuring operation of test signals by use of the
EOS probe shown in FIG. 6 is described.
[0023] When a voltage is applied on the wiring of the IC wafer, the
electric field is applied to the electro-optic element 2, causing a
change in its refractive index due to the Pockels effect. Thereby,
when the laser light enters into the electro-optic element,
reflected at the surface of the electro-optic element placed facing
the IC wafer, returns the same light path, and exits from the
electro-optic element, the polarizing state of the laser light
changes. After being subjected to the change of the polarizing
state, the laser light enters again on the EOS optical system
6a.
[0024] Since the polarized state of the electro-optic element in
the EOS optical system has been changed, the intensity of the light
incident to the EOS optical system is changed in accordance with
the change of polarized state, the change of the light intensity is
converted into an electric signal after being received by a
photodiode, and the electric signals applied to the IC wafer 1 can
be measured by processing the signals from the photodiode.
[0025] There are some ICs such as light switches which are operated
by irradiation of excitation light, that is, light for excitation
on the front surface or the rear surface of the IC wafer. However,
the problem arises in the conventional electro-optic sampling probe
that the measurement of the electric signals can not be
simultaneously carried out while the excitation light is irradiated
on the front or the rear surfaces.
[0026] In order to solve the above problem, Japanese Unexamined
Patent Application, First Publication No. Hei 10-340824, discloses
an electro-optic sampling probe, capable of irradiating the
excitation light from both surfaces of the IC wafer without
displacing the IC wafer and capable of measuring electric signals
while irradiating sampling light from surfaces of the IC wafer.
[0027] However, the problem still arises in the above electro-optic
sampling probe that the excitation light can not simultaneously
enters on a plurality of light receiving portions provided on the
IC wafer 1. If the spot size of the excitation light is enlarged so
as to simultaneously irradiate the plurality of light receiving
portions, the excitation light irradiates the surface area outside
of the light receiving portion, which leads to an inaccurate
measurement. In addition, the problem still remains that the
enlarged spot irradiation does not allow sequential time
measurement.
SUMMARY OF THE INVENTION
[0028] It is therefore an object of the present invention to
provide an electrooptic sampling probe capable of entering the
excitation light simultaneously on a plurality of light receivers
provided on the IC wafer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a diagram showing a structure of one embodiment of
the present invention.
[0030] FIG. 2 is a diagram showing a structure of an EOS optical
system 6a shown in FIG. 1
[0031] FIG. 3 is a diagram showing a structure of an excitation
optical system 6b shown in FIG. 1.
[0032] FIG. 4 is a diagram for explaining a structure of a light
axis adjusting portion 5d shown in FIG. 1 and a light path of the
excitation light.
[0033] FIG. 5 is a diagram for explaining a structure of a light
axis adjusting portion 5d shown in FIG. 1 and a light path of the
excitation light.
[0034] FIG. 6 is a diagram showing a structure of a conventional
electro-optic sampling probe.
DETAILED DESCRIPTION OF THE INVENTION
[0035] An electro-optic sampling probe according to one embodiment
of the present invention will be described with reference to
attached drawings.
[0036] FIG. 1 is a diagram showing a structure of one embodiment of
the present invention. In FIG. 1, the same components as those of
the conventional probe shown in FIG. 6 are denoted by the same
reference numerals and explanations for these components are
omitted. The differences between the electro-optic probe shown in
FIG. 1 and the conventional probe are the provision of two
excitation optical systems for outputting the excitation light 6b
and 6b' (hereinafter, called excitation optical system) under the
standard table 10, provision of a probe body 42, and fixation of
these two excitation optical systems 6b and 6b' to the probe body
42 by means of detachable portions 5b and 5c.
[0037] Here, the above two excitation optical systems 6b and 6b'
have the same structure.
[0038] Furthermore, the excitation optical systems 6b and 6b' are
fixed through respective light axis adjusting portions 5d provided
between the probe body 42 and the light axis adjusting portions
5b.
[0039] FIG. 2 is a diagram showing a structure of an EOS optical
system 6a shown in FIG. 1 In FIG. 2, the numerals 61, 64, and 70
denote half-wave plates, and 62 denotes a quarter-wave plate. The
numerals 63 and 66 denote polarized beam splitters, and 65 denotes
a Faraday element. An optical system constituted by half-wave
plates 61, 64, and 70, the quarterwave plate 62, polarized beam
splitters 63 and 66, and the Faraday element 65 is an optical
isolator. The numerals 67 and 68 denote photodiodes.
[0040] FIG. 3 is a diagram showing a structure of an excitation
optical system 6b shown in FIG. 1. This excitation optical system
6b has the same structure as that of the EOS optical system 6a, and
the excitation optical system 6b is constituted only by the one
optical component of the half-wave plate 64.
[0041] FIG. 4 and 5 are diagrams for explaining a structure of a
light axis adjusting portion 5d shown in FIG. 1 and a light path of
the excitation light.
[0042] Here, an operation is described to measure the electric
signals on the front surface of the IC wafer 1, when the excitation
light is irradiated on the rear surface.
[0043] First, an operation is described to irradiate the rear
surface with the excitation light.
[0044] Laser light is supplied from the outside to the excitation
optical system 6b through an optical fiber 11. This laser light is
collimated into a parallel beam by the fiber collimator 69.
[0045] The collimated laser beam is then turned by 90 degrees by a
half mirror 42a and is condensed to the rear surface of the IC
wafer 1 by an objective lens 32. Thereby, the IC wafer, that is,
the object for measurement can be operated by irradiating the
excitation light on the rear surface.
[0046] It is to be noted that, when two polarization optical
systems are provided, efficient condensation of the polarization
light by two optical systems can be realized without loss of light
by inserting a polarization controller for each excitation light
system and by replacing each half mirror 42a with a polarized beam
splitter (PBS), respectively.
[0047] Next, an operation is described for making excitation light
incident on respective light receiving portions when two light
receiving portions are provided on the IC wafer 1.
[0048] First, an explanation is given of an example of the light
axis adjusting portion which is constituted by a goniometer. The
excitation optical system 6b' shown in FIG. 4 is fixed to the probe
body 42, and the parallel light emitted from this excitation
optical system 6b' goes straight into the probe body 42, propagates
through the half mirror 42a, and is condensed on the light
receiving portion of the IC wafer 1 by the objective lens 32. Since
the objective lens 32 is disposed separated from the IC wafer as
far as a focal distance ft of the objective lens 32, the parallel
light is condensed into a point on the IC wafer 1.
[0049] Next, when the light must be condensed into two different
points by adjusting the light axis adjusting portion, this can be
achieved by rotating the goniometer. The distance between the two
different points can be determined by the rotating angle of the
goniometer. That is, when it is assumed that the distance between
two points is A, the focal distance of the objective lens 32 is ft,
the rotating angle of the light axis adjusting portion 5d is
.theta. a, the light condensation distance A is obtained by the
following equation; A=ft x tan .theta. a. The change of the light
axis at an angle of .theta. a is shown in FIG. 4 by a one-dot chain
line.
[0050] As shown above, even when there are two light receiving
portions on the IC wafer, it is possible to enter light exclusively
on light receiving portions by condensing light accurately into two
points, and using two excitation optical system 6b and 6b' and the
objective lens commonly.
[0051] Next, an example is described in which the light axis
adjusting portion is constituted by a telecentric optical system
with reference to FIG. 5. In the example shown in FIG. 5, the light
axis adjusting portion 5d comprises a condenser lens 5e, an XY
stage 5f, which can be moved finely in two directions crossing each
other at an right angle, and a collimation lens 5g for
re-converting the condensed light into parallel light.
[0052] The excitation optical system 6b', the half mirrors 42a, and
the objective lens 32 are the same as those shown in FIG. 4, so
that explanations of these components are omitted.
[0053] The excitation optical system 6b, the detachable portion 5b,
and the condenser lens 5e are finely aligned by precisely sliding
the XY stage 5f having sliding surfaces 5f, shown in FIG. 5. The
condenser lens 32 and the collimation lens 5g are arranged such
that the light path length between the light entering surface of
the condenser lens 32 and the collimation lens 5g is identical with
the rear side focal length fb of the collimation lens 5g. In
addition, the collimation lens 5e may be distanced from the
excitation optical system as far as the focal length. Thus, the
light beam spread at the point C becomes collimated into a parallel
beam. The thus collimated parallel beam is turned by the
half-mirror 32, enters into the objective lens, and is condensed on
a point on the IC wafer 1 by the objective lens 32.
[0054] The XY stage 5f is arranged so as to condense the parallel
beam generated by the excitation optical system 6b on a position C'
initially. In this arrangement, since the light axis of the
parallel beam output from the collimation lens 5g crosses the light
axis of light originated from the excitation optical system 6b' at
an right angle, these two parallel beams are condensed on a
position on the IC wafer 1. When the polarization optical system 6b
is displaced from this initial arrangement to a position at a
distance of F by sliding the XY stage 5f, parallel beams condensed
on one position on the IC wafer 1 are separated into two positions
by a distance of F'. Since the distances of F and F' are identical,
two condensed light beams can be separated by a distance in
proportion to the sliding distance of the XY stage 5f. In addition,
since the XY stage 5f can be displaced into two directions, the
light beam can be positioned at any position around the position of
the initial position of light originating from the excitation
optical system 6b'.
[0055] As shown above, provision of the telecentric optical system
allows two light beams condensed exclusively only in two light
receiving portions located at two different positions by finely
displacing the excitation optical system 6b.
[0056] It is noted that, since these two excitation optical systems
6b and 6b' uses independent light sources, respectively, any one of
the light beams emitted from those light sources can be made
incident on the IC wafer by changing the timing of emission, which
allows a particular measurement in the case of changing the
entering timing to a plurality of respective light receiving
portions.
[0057] Next, a measurement operation of the electric signal in the
wiring on the IC wafer 1 by the EOS optical system 6a is
described.
[0058] A laser beam is supplied to the EOS optical system 6a from
the outside using an optical fiber 11. The laser beam is converted
into a parallel beam by a fiber collimator 69.
[0059] Next, this parallel light is turned by 90 degrees by the
dichromic mirror 41a in the probe body 41 and is condensed by the
objective lens 31. The thus condensed laser light arrives at the
surface of the electro-optic element facing the wiring on the IC
wafer 1, after propagating through the electro-optic element.
[0060] At this time, the refractive index of the electro-optic
element 2 changes by the Pockels effect due to the electric field
applied to the electro-optic element 2 caused by the applied
voltage to the wiring. Thereby, the polarization state of the laser
light changes after entering and during propagating through the
electro-optic element. After being subjected to the change of the
polarization state, the laser light is reflected by the mirror
formed on the electro-optic element placed on the wiring of the IC
wafer, and enters into the EOS optical system after propagating in
the opposite direction of the same light path that starts from
entering into the electro-optic element. This laser light is
isolated by the light isolator 60, is made incident on the
photodiode, and is converted into an electric signal.
[0061] The fluctuation of the voltage applied to the wiring of the
IC wafer causes a change of the polarization state of the
electro-optic element, which produces an output difference between
the outputs from the first and second photodiodes 67 and 68. The
electric signal transmitting in the wiring of the IC wafer 1 can be
measured by detecting this output difference.
[0062] As shown above, the preset apparatus is designed such that
the electric signal propagating through the wiring of the IC wafer
1 can be detected, while irradiating the excitation light from the
rear surface of the IC wafer 1, the measurement can be carried out
for the rear surface irradiation-type IC. In addition, provision of
two excitation optical systems 6b and 6b' which commonly use an
objective lens makes it possible to project two condensed light
beams exclusively on two different light receiving portions.
[0063] Projection of the excitation light can be made not only by
the excitation optical system 6b, but also by the EOS optical
system 6a. When the EOS optical system is used as the light source,
the EOS system may be used for emitting light to project the
condensed light on the rear surface, as when measuring the electric
signal. In this case, the outputs of two photodiodes 67 and 68
cannot be used for further processing.
[0064] Addition of necessary numbers of excitation optical systems
6b and half mirrors allows projecting condensed light beams on more
than three light receiving portions. Furthermore, installation of
the EOS optical system instead of the excitation optical system
makes it possible to carry out measurement even for an IC wafer, in
which the light receiving portion is present on the same surface
for measurement.
[0065] When the IC wafer comprises a substrate made of an
electro-optic crystal such as GaAsInP, fitting of an EOS optical
system 6a to the probe body 42 installed on the rear surface of the
IC wafer makes it possible to measure by condensing the laser light
directly projecting on the rear surface of the IC wafer1. By
adopting such a method, it is possible to carry out the measurement
of the electric signal not only for the wiring on one side but also
for both surfaces, if wiring exists on both surfaces.
[0066] As explained above, the EOS sampling probe of the present
invention provides the excitation optical system for projecting an
excitation light beam on the rear surface of the IC wafer, the
present invention has the effect that the EOS sampling probe may
carry out an signal measurement for the particular IC wafer which
is excited from the rear surface.
[0067] According to this invention, since the present EOS optical
system provides a detachable portion, to which the EOS optical
system and the excitation optical system are commonly attachable,
and since the excitation optical system can be attached at the
front surface of the IC wafer and the EOS optical system can be
attached at the rear surface, the effect is obtained that
measurement can be made by selecting either the front or rear
surfaces in accordance with the specification of the IC wafer.
Since it is also possible to substitute one element for both
objective lens and half mirror of the excitation optical system,
the EOS probe of the present invention can be constituted by a
simple structure using a reduced number of elements.
[0068] The present invention exhibits the effect that the
measurement of the electric signals can be made for both surfaces
of the IC wafer simultaneously when the IC wafer has wiring on both
surfaces, by replacing the excitation optical system with the EOS
optical system.
[0069] Furthermore, the present invention exhibits the further
effect that it is possible to project condensed light beams onto a
plurality of light receiving portion, because a light axis
adjusting means is provided between the excitation optical system
and the probe body.
* * * * *