Semiconductor testing apparatus

Details Semiconductor testing apparatus Semiconductor testing apparatus

2001-07-24

2003-05-20

Cuneo, Kamand (Department: 2829)

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of individual circuit component or element

C356S369000

Reexamination Certificate

active

06566896

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to semiconductor testing apparatuses of the EOS (Electro-Optic Sampling) type for measuring voltages and/or electric fields by making use of the electro-optic effect, and more particularly to such a semiconductor testing apparatus which is capable of carrying out a measurement in terms of one-dimensional distribution and/or simultaneous measurements at a plurality of positions.
DESCRIPTION OF THE RELATED ART
Semiconductor testing apparatuses in the related art include, as an example, one described in an article “Handy-Type High-Impedance Probe Based on EOS” by Shinagawa et al., Fifteenth Meeting on Light-Wave Sensing Technology, pages 123 to 129, 1995.
FIG. 9
shows an improved version of the above-mentioned semiconductor testing apparatus which will be described hereunder. A light source
1
is driven by a light-source drive circuit
17
to emit a laser light. The laser light emitted from the light source
1
is converged by a collecting lens
2
and guided to a curved-surface mirror
3
. The laser light reflected by the curved-surface mirror
3
irradiates an electro-optic element
4
. The laser light is then reflected by a reflector
5
provided on the lower surface of the electro-optic element
4
, and is split by a polarizing beam splitter
8
into two after passing through a wavelength plate
7
. The split laser lights are converged by micro-lens arrays
9
-
1
and
9
-
2
and are then received by line sensors
10
-
1
and
10
-
2
, respectively. The path of the laser light is diagrammatically shown by numeral
18
in FIG.
9
.
The light source
1
, the collecting lens
2
and the curved-surface mirror
3
are arranged so that the laser light irradiates the boundary surface between the electro-optic element
4
and the reflector
5
in a substantially linear manner. More specifically, the arrangement of the light source
1
, the collecting lens
2
and the curved-surface mirror
3
is such that the cross section of the laser light beam on the boundary surface between the electro-optic element
4
and the reflector
5
(hereinafter referred to as “measurement plane”) is substantially a straight line (hereinafter referred to as a “measurement line”).
Each of the micro-lens arrays
9
-
1
and
9
-
2
is in the form of a compound lens constituted by a plurality of lenses which are arranged linearly so that the linear or oblong laser light beam can pass through the plurality of lenses.
A variation in voltage in a DUT (device under test)
6
, which the measured device, as brought about by an input to or an output from the DUT
6
, causes a change in the electric field in the electro-optic element
4
adjoining the DUT
6
. The polarization of the laser light passing through the electro-optic element
4
changes depending on the electric field therein. Since the laser light is linear or oblong as described above, the change in polarization caused by the electric field may be different at different positions in the linear or oblong cross-section of the laser light.
The wavelength plate
7
is chosen such that the laser light has an angle of polarization such that the polarizing beam splitter
8
splits the laser light into two substantially equal parts. The splitting ratio of the polarizing beam splitter
8
changes in accordance with the amount of polarization of the incident light, as a result of which the laser light whose polarization has been changed in the electro-optic element
4
is subject to a change in amplitude when passing through the polarizing beam splitter
8
.
As described above, a position-dependant change in the voltage in the DUT
6
results in a change in amplitude of the laser light which depends on the position in the cross-section of the beam. The laser light with a changed amplitude passes through the micro-lens arrays
9
-
1
and
9
-
2
and is received by the line sensors
10
-
1
and
10
-
2
, each of which then converts the change in amplitude of the laser light into a change in amplitude of an electric signal. Thus, electric signals which are proportional to the voltages or electric fields at the respective positions on the DUT
6
can be obtained from each of the line sensors
10
-
1
and
10
-
2
.
Since the changes in amplitude of the split outputs from the polarizing beam splitter
8
are opposite in phase, i.e., when one increases the other decreases, the signal component of the DUT
6
can be obtained more reliably by taking the difference between the output electric signals from the line sensors
10
-
1
and
10
-
2
.
For the above reason, as shown in
FIG. 9
, the output signals of the line sensors
10
-
1
and
10
-
2
are first amplified by amplifier circuits
11
-
1
and
11
-
2
, respectively, and then the difference between the two signals is taken by a differential circuit
26
. The differential signal thus obtained is sampled and held by a sample-and-hold circuit
12
. The output of the sample-and-hold circuit
12
is supplied through a selection circuit
13
to an A/D converter
14
, which converts the output into a digital signal which is fed to a calculation/display device
15
. The selection circuit
13
has the function of selecting one out of a plurality of signals. A plurality of amplifier circuits amplify the respectively outputs of the plurality of line sensors in a parallel fashion. Specifically, when the amplifier circuit
11
-
1
amplifies the output signal of the line sensor
10
-
1
, the amplifier circuit
11
-
2
amplifies the output signal of the line sensor
10
-
2
at the same time.
The plurality of output signals of the amplifier circuit
11
-
1
is supplied to a selection circuit
27
-
1
which in turn selects one of the plurality of output signals. Similarly, the plurality of output signals of the amplifier circuit
11
-
2
is supplied to the selection circuit
27
-
2
which selects the one of the plurality of output signals which has been obtained from the same measurement point as the output signal selected by the selection circuit
27
-
1
. The outputs from the selection circuits
27
-
1
and
27
-
2
are added together at the summing circuit
28
to obtain the laser-light intensity signal. The output of the summing circuit
28
is input to the selection circuit
13
. These circuits are provided not for the purpose of measuring the DUT
6
but for the purpose of obtaining the intensity of the laser light only, so that a sample-and-hold operation and other operations are not necessary.
If the light source
1
emits a pulsed light, the measurement signal obtained from a measuring zone on the DUT
6
, i.e., the output signals from the line sensors
10
-
1
and
10
-
2
, should be a repetitive signal which is synchronized with a trigger signal St. A timing generator
16
generates a pulse light-emission timing signal Sp, whose phase is delayed by &dgr;t each time the trigger signal St is received, to make the light source
1
to emit a pulsed light or a light pulse.
The measurement signals at respective measuring points on the DUT
6
, which are obtained by directing the light pulse through the collecting lens
2
, the curved-surface mirror
3
and the electro-optic element
4
towards the reflector
5
provided on the upper surface of the DUT
6
to irradiate it, are sampled and held at the same time by the sample-and-hold circuit
12
in synchronism with a sample-and-hold timing signal Ssh.
N signals output from the sample-and-hold circuit
12
are sequentially selected by the selection circuit
13
in accordance with a selection-circuit timing signal Ssel. The A/D converter
14
sequentially converts the analog signals selected by the selection circuit
13
into digital signals in synchronism with the A/D conversion timing signal Sad. Specifically, the N signals as obtained by a single sample-and-hold operation are sequentially A/D converted. By repeating the above operation, results of all the measurements of voltages or electric fields of the DUT
6
can be obtained.
The calculation/display device
15
converts the digital data obtained at the A/D convert

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