Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2000-01-26
2001-10-02
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
Reexamination Certificate
active
06297651
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electro-optic sampling probe (or prober) in which an electric field generated due to a target signal to be measured is applied to an electro-optic crystal, and an optical pulse signal generated based on a timing signal is incident onto the electro-optic crystal, and the waveform of the target signal is observed according to the polarization state of the incident optical pulse signal. In particular, the present invention relates to an electro-optic sampling probe whose optical system is revised and improved.
This application is based on Patent Application No. Hei 11-19138 filed in Japan, the contents of which are incorporated herein by reference.
2. Description of the Related Art
In a conventional technique, the waveform of a target signal (to be measured) can be observed by applying an electric field generated due to the target signal to an electro-optic crystal, inputting a laser beam to the electro-optic crystal, and observing the waveform of the target signal according to the polarization state of the laser beam. If a laser beam transformed into a pulse form is used for sampling the target signal, the measurement can be performed with a very high temporal resolution. The electro-optic sampling probe (abbreviated to “EOS probe”, hereinbelow) employs an electro-optic probe having the above function.
In comparison with the conventional probes employing known electric probes, the above EOS probe has the following characteristics and thus has received widespread notice:
(1) A ground line is unnecessary for measuring the signal.
(2) The tip of the electro-optic probe is insulated from the circuit; thus, a high input impedance can be obtained and (the state of) the point to be measured is not significantly disturbed.
(3) An optical pulse signal is used; thus, wide-band measurement of a GHz order can be performed.
(4) An electro-optic crystal can be made to contact a wafer of an IC (or the like), and a laser beam is converged on the wiring printed on the IC wafer, thereby enabling the measurement of thin wiring which a metallic pin cannot physically contact.
The structure of a conventional EOS probe will be explained with reference to FIG.
3
. In
FIG. 3
, reference numeral
1
indicates an IC wafer connected to an external device via a power supply line and a signal line. Reference numeral
2
indicates an electro-optic element using an electro-optic crysal. Reference numeral
31
indicates an objective used for converging the beam incident on the electro-optic element
2
. Reference numeral
41
indicates the (main) body of the probe, comprising a dichroic mirror
41
a
and a half mirror
41
b
. Reference numeral
6
a
indicates an EOS optical system module (called “EOS optical system”, hereinbelow) comprising a photodiode, a polarized beam splitter, a wave plate, and so on. Reference numeral
69
indicates a fiber collimator attached to one end of the EOS optical system.
Reference numeral
7
indicates a halogen lamp for irradiating IC wafer
1
to be measured. Reference numeral
8
indicates an infrared camera (abbreviated to “IR camera”, hereinbelow) for confirming the positioning for converging a beam onto a target wiring provided on the IC wafer
1
. Reference numeral
9
indicates a suction stage for fixing the IC wafer
1
, which can be finely moved in the x, y, and z directions. Reference numeral
10
indicates a surface plate (only a portion shown here) to which the suction stage
9
is attached. Reference numeral
11
indicates an optical fiber for transmitting a laser beam emitted from an external device.
Below, with reference to
FIG. 3
, the optical path of the laser beam from an external device will be explained. In the figure, the optical path of the laser beam inside the probe body
41
is indicated by reference symbol A.
The laser beam incident via optical fiber
11
on EOS optical system
6
a
is collimated by fiber collimator
69
, and linearly progresses in the EOS optical system
6
a
and is input into probe body
41
. The input beam further progresses straight inside the probe body
41
, and is then deflected by 90 degrees by dichroic mirror
41
a
and then converged by objective
31
onto the electro-optic element
2
disposed on the wiring on the IC wafer
1
. Here, the beam is converged onto the face (of the electro-optic element
2
) which faces the IC wafer
1
.
The wavelength of the laser beam incident via optical fiber
11
on the EOS optical system is 1550 nm. On the other hand, the dichroic mirror
41
a
has the characteristic of transmitting 5% (and reflecting 95%) of the beam having a wavelength of 1550 nm. Therefore, 95% of the beam emitted from the laser source is reflected and deflected by 90 degrees.
A dielectric mirror is deposited on the face of the electro-optic element
2
, which faces the IC wafer
1
. The laser beam reflected by this face is again collimated by objective
31
and returns to the EOS optical system
6
a
through the same path, and is incident on a photodiode in the EOS optical system
6
a
. The structure of the EOS optical system
6
a
will be explained later in detail.
Hereinbelow, the operation of positioning the IC wafer
1
by using the halogen lamp
7
and IR camera
8
will be explained. Here, the optical path of the beam emitted from the halogen lamp
7
and the positioning operation will be explained. In
FIG. 3
, the optical path of the beam emitted from the halogen lamp
7
is indicated by reference symbol B.
The halogen lamp
7
used here emits a light beam having a wavelength range from 400 nm to 1650 nm. The light beam emitted from the halogen lamp
7
is deflected by 90 degrees by half mirror
41
b
and progresses straight through the dichroic mirror
41
a
, so that the IC wafer
1
is irradiated by the light beam. In the half mirror
41
b
used here, the light intensities of the reflected and transmitted beams are the same.
The image of a portion of the IC wafer
1
irradiated by the halogen lamp
7
, observed in the field of view of the objective
31
, is picked up by the IR camera
8
. This IR image is then displayed in monitor
8
a
. The operator finely moves and adjusts the suction stage
9
while observing the image displayed in monitor
8
a
, so as to position a target wiring portion (on the IC wafer
1
, to be measured) inside the field of view.
The laser beam incident via optical fiber
11
on the EOS optical system
6
a
is reflected at the face of the electro-optic element
2
positioned on the wiring of IC wafer
1
, and is further transmitted through the dichroic mirror
41
a
. This transmitted beam is confirmed by the operator by observing the image of IR camera
8
, and thereby adjusting the suction stage
9
or probe body
41
so as to converge the laser beam at a point on the face of the electro-optic element
2
positioned on the target wiring portion to be measured. Here, the dichroic mirror
41
a
has a characteristic of transmitting 5% of (the wavelength range of) the laser beam; thus, this laser beam can be confirmed using the IR camera
8
.
Below, the operation of measuring a target signal (to be measured) using the EOS probe (shown in
FIG. 3
) will be explained.
When a voltage is applied to the target wiring on the IC wafer
1
, the corresponding electric field is applied to the electro-optic element
2
, and the refractive index thereof is then changed due to the Pockels effect. As explained above, the laser beam is incident on the electro-optic element
2
, and is reflected by the face which faces the IC wafer
1
and returned through the same optical path. According to the above effect, the polarization state of the beam output from the electro-optic element
2
is changed. This laser beam having a changed polarization state is again incident on the EOS optical system
6
a.
In the EOS optical system
6
a
, the change of the polarization state of this incident laser beam is converted into a change of light intensity, which is detected by a photodiode and further converted into an electric si
Akikuni Fumio
Nagatsuma Tadao
Ohta Katsushi
Shinagawa Mitsuru
Yamada Junzo
Ando Electric Co. Ltd.
Darby & Darby
LeRoux E.
Metjahic Safet
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