Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2000-04-03
2002-09-03
Karlsen, Ernest (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S750010, C324S754120
Reexamination Certificate
active
06445198
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electro-optic sampling probe which combines an electric field produced by a signal, which is a target of measurement, with an electro-optic crystal, emits laser light through this electro-optic crystal, and observes waveforms of the measurement target signal, based on the polarization state of the laser light, and in particular, to an electro-optic sampling probe which improves an optical system of the probe.
This application is based on Japanese Patent Application No. Hei 11-99381, the contents of which are incorporated herein by reference.
2. Description of the Related Art
By combining an electric field produced by a signal, which is a target of measurement, with an electro-optic crystal, and by emitting laser light through this electro-optic crystal, waveforms of the measurement target signal can be observed, based on the polarization state of the laser light. When the measurement target signal is sampled by pulses of the laser light, the time resolution can be remarkably increased. An electro-optic probe, which utilizes this phenomenon, is utilized by an electro-optic sampling probe.
As compared with a conventional probe using an electric probe, the electro-optic sampling probe (hereinafter, referred to as an “EOS probe”) has the following advantages:
1) because a ground line is not required to measure the signal, the measurement is facilitated,
2) because the end of the electro-optic probe is insulated from a circuit system, a high input impedance can be obtained, and, as the result, the condition of the measurement target point is not disturbed.
3) the light pluses enables a wide range measurement on the order of GHz, and
4) by contacting the electro-optic crystal with a wafer such as an IC and collecting laser light on the wiring on the IC wafer, even thin wiring which a metal pin cannot contact physically can be measured.
These features have gained attention.
The EOS probe of the background technique will be explained with reference to FIG.
4
.
In
FIG. 4
, reference numeral
1
denotes an IC wafer, which is connected through power source lines, and signal lines to the outside. Reference numeral
2
denotes an electro-optic element made of an electro-optic crystal. Reference numeral
3
denotes an objective lens for collecting light entering the electro-optic element
2
. Reference numeral
4
denotes a probe having a dichroic mirror
4
a,
and a half mirror
4
b.
Reference numeral
6
a
denotes an EOS optical system module (hereinafter referred to as an “EOS optical system”), which comprises a photo diode, a polarized beam splitter, a wavelength plate, etc. Reference numeral
69
denotes a fiber collimator attached to one end of the EOS optical system.
Reference numeral
7
denotes a halogen lamp for illuminating the IC wafer
1
to be measured. Reference numeral
8
denotes an infrared camera (hereinafter referred to as an IR camera) for attaining a condensed light point on the wiring on the IC. Reference numeral
9
denotes an absorbing stage for absorbing and fixing the IC wafer
1
, which is precisely movable in the directions of X-, Y-, and Z-axes which are perpendicular to each other. Reference numeral
10
denotes a level block (a part thereof is omitted) on which the absorbing stage
9
is mounted. Reference numeral
11
denotes an optical fiber for transmitting laser light from the outside, which is fixed to the fiber collimator
69
by means of the optical fiber end
11
a.
This optical fiber end
11
a
is detachable so that a different optical fiber
11
can be used.
Referring to
FIG. 4
, an optical path for the laser light from the outside will be explained. In
FIG. 4
, reference character A denotes the optical path of the laser light within the probe
4
.
The laser light, which enters the EOS optical system
6
a
from the optical fiber
11
, is converted into collimated light by the fiber collimator
69
, proceeds through the EOS optical system
6
a,
and enters the probe
4
. The light proceeds through the probe
4
, and is deflected by the dichroic mirror
4
a
by 90 degrees, and condensed by the objective lens
3
onto the surface, which faces the IC wafer
1
, of the electro-optic element
2
placed on the wiring on the IC wafer
1
.
The wavelength of the laser light entering the EOS optical system
6
a
through the optical fiber
11
is 1550 nm. The dichroic mirror
4
a
has characteristics to allow 5% of light at the wavelength of 1550 nm to transmit and to reflect 95% of the light. That is, 95% of the light emitted from the laser light source is reflected and deflected by 90 degrees.
On the surface facing the IC wafer
1
of the electro-optic element
2
, a dielectric mirror is disposed. The laser light reflected on the mirror is converted into collimated light by the objective lens
3
, returns to the EOS optical system
6
a
through the same path, and enters the photo diode of the EOS optical system
6
a.
The construction of the EOS optical system
6
a
will be described later.
Next, the operation for positioning the IC wafer
1
with respect to the path of the light from the halogen lamp
9
using the halogen lamp
7
and the IR camera
8
will be explained. In
FIG. 4
, reference character B denotes the light path of the light from the halogen lamp
7
.
The halogen lamp
7
emits light having wavelengths between 400 nm and 1650 nm.
The light emitted from the halogen lamp
7
is deflected by 90 degrees at the half mirror
4
b,
proceeds straight through the dichroic mirror
4
a,
and illuminates the IC wafer
1
. The half mirror
4
b
equalizes the reflected light and the transmitted light.
The IR camera
8
receives an image of a part of the IC wafer
1
which is within the field of view of the objective lens
3
and is illuminated by the halogen lamp
7
, and displays the infrared image on a monitor
8
a.
An operator precisely adjusts the absorbing stage
9
while watching the image displayed on the monitor
8
a,
so that the wiring which is the measurement target on the IC wafer
1
enters the field of view.
Further, the operator adjusts the absorbing stage
9
or the probe
4
while confirming from the image from the IR camera
8
that the laser light, which enters the EOS optical system
6
a
through the optical fiber
11
, is reflected from the surface of the electro-optic element
2
placed on the wiring on the IC wafer
1
, and passes through the dichroic mirror
4
a,
so that this laser light condenses at one point on the surface of the electro-optic element
2
on the wiring which is the measurement target. Because the dichroic mirror
4
a
has characteristics to allow 5% of the wavelengths of the laser light to be transmitted, this laser light can be confirmed by the IR camera
8
.
Next, the operation for measuring the measurement target signal by the EOS probe shown in
FIG. 4
will be explained.
When a voltage is applied on the wiring on the IC wafer
1
, an electric field is applied to the electro-optic element
2
, in which the refractive index then changes because of Pockels effect. Thus, while the laser light enters the electro-optic element
2
, is reflected from the surface facing the IC wafer
1
, returns through the same path, and goes out of the electro-optic element
2
, the polarization of the light varies. The light whose polarization vanes enters the EOS optical system
6
a
again.
The EOS optical system
6
a
converts the change in polarization into a change in light intensity, which is then converted by the photo diode into an electric signal. This signal is processed by a signal processor (not shown). Thus, the electric signal applied to the wiring on the IC wafer
1
can be measured.
Next, the construction of the EOS optical system
6
a
shown in
FIG. 4
will be explained.
FIG. 5
shows the construction of the EOS optical system
6
a
in detail. In
FIG. 5
, reference numerals
61
and
64
denote half wave plates, and reference numeral
62
denotes a quarter wave plate. Reference numerals
63
and
66
denote polarizat
Akikuni Fumio
Nagatsuma Tadao
Ohta Katsushi
Shinagawa Mitsuru
Yamada Junzo
Ando Electric Co. Ltd.
Darby & Darby
Karlsen Ernest
Tang Minh
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