Radiant energy – Inspection of solids or liquids by charged particles – Analyte supports
Reexamination Certificate
1999-03-09
2002-08-20
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Analyte supports
C250S306000
Reexamination Certificate
active
06437343
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a scanning probe microscope capable of measuring specimen surface information with atomic-order resolution, and more particularly, to a scanner system and a piezoelectric micro-inching mechanism used in a scanning probe microscope.
Scanning tunneling microscopes (STMs) and atomic force microscopes (AFMs) are typical examples of scanning probe microscopes (SPMs).
In the scanning tunneling microscopes, which are the original version of scanning probe microscopes, the surface shape of a specimen is measured with atomic-order resolution by utilizing a tunneling current flowing between a metallic probe and an electrically conductive specimen which are located close to each other. Utilizing the tunneling current, the scanning tunneling microscopes is used to observe electrically conductive specimens only.
The atomic force microscopes have been developed by utilizing the servo technique and other STM techniques. In these microscopes, the surface shape of a specimen is measured with atomic-order resolution by utilizing an atomic force which acts between atoms in the apex of a probe and the surface of a specimen. Accordingly, the atomic force microscopes is used to observe electrically insulating specimens as well as conductive ones.
In order to enjoy high resolution, the scanning probe microscopes require a scanning mechanism that can control the relative positions of the probe and the specimen with high accuracy. In general, these microscopes use a piezoelectric micro-inching mechanism, especially a cylindrical piezoelectric scanner or so-called tube scanner.
First Prior Art
FIGS. 11A
,
11
B and
11
C show an arrangement of one such tube scanner.
FIG. 11A
is a perspective view of the tube scanner,
FIG. 11B
is a development showing outside electrodes of the scanner, and
FIG. 11C
is a development showing an inside electrode.
A tube scanner
1040
comprises a piezoelectric ceramic
1041
in the form of a hollow cylinder, Z-axis driving electrode
1044
, X-axis driving electrodes
1042
a
and
1042
b
, Y-axis driving electrodes
1043
a
and
1043
b
, and common electrode
1045
. The electrodes
1044
,
1042
a
,
1042
b
,
1043
a
and
1043
b
are arranged outside the ceramic
1041
, and the electrode
1045
inside. The X-axis driving electrodes
1042
a
and
1042
b
are located in positions at an angular distance of 90° from the Y-axis driving electrodes
1043
a
and
1043
b
, respectively. The Z-axis driving electrode
1044
, X-axis driving electrodes
1042
a
and
1042
b
, and Y-axis. driving electrodes
1043
a
and
1043
b
face the common electrode
1045
across the piezoelectric ceramic
1045
.
The tube scanner
1040
is displaced in the X-axis direction as opposite-polarity voltages are applied to the X-axis driving electrodes
1042
a
and
1042
b
, individually, with the common electrode
1045
grounded, and is displaced in the Y-axis direction as opposite-polarity voltages are applied to the Y-axis driving electrodes
1043
a
and
1043
b
, individually. The piezoelectric ceramic
1041
extends or contracts to be displaced in the Z-axis direction, depending on the polarity of a voltage applied to the Z-axis driving electrode
1044
.
In order to obtain a substantial displacement in the Z-axis direction in the tube scanner shown in
FIGS. 11A
to
11
C, the height of the Z-axis driving electrode
1044
or the voltage applied thereto must be increased.
If the height of the Z-axis driving electrode
1044
is increased, however, the tube scanner
104
is lengthened inevitably, resulting in lowered resonance frequency and hence poorer responsivity.
An expensive power source and a driver circuit are needed to apply a high voltage to the Z-axis driving electrode
1044
to drive it.
Second Prior Art
An example of a scanning probe microscope which uses a tube scanner is described in Jpn. Pat. Appln. KOKAI Publication No. 5-312564.
FIG. 12
shows a configuration of this microscope.
As shown in
FIG. 12
, a specimen
1103
is fixed to a free end of a cylindrical piezoelectric element (tube scanner)
1102
. The piezoelectric element
1102
is moved for scanning in the X- and Y-directions in response to X- and Y-scan signals which are generated from an X-scan signal generator
1111
and a Y-scan signal generator
1112
, respectively. Thus, the specimen
1103
on the piezoelectric element
1102
is scanned in the X- and Y-directions. The cantilever
1104
, which is located close to the specimen
1103
, is deflected in the Z-direction, depending on the surface irregularity of the specimen
1103
.
Light emitted from a laser diode
1105
is reflected by a mirror
1106
, to be incident upon the surface of the cantilever
1104
, and the reflected light is projected on a photodiode
1107
. The deflection of the cantilever
1104
is detected by monitoring the position of a beam spot on the photodiode
1107
by means of a differential amplifier
1108
. The cylindrical piezoelectric element
1102
is feedback-controlled in the Z-direction by means of a servo circuit
1109
to keep the deflection constant.
If a computer
1110
directly fetches as height information or surface irregularity information a voltage applied to the piezoelectric element to drive it in the Z-direction, an obtained image is subject to distortion attributable to hysteresis, creeping, etc., which are peculiar to the piezoelectric element.
Accordingly, an optical fiber
1114
is located inside the cylindrical piezoelectric element
1102
, and the Z-direction displacement of a mirror
1116
is detected through the fiber
1114
by means of optical interferometer
1115
. The computer
1110
fetches the resulting displacement signal as height information or surface irregularity information, thereby forming a surface irregularity image.
Referring now to
FIG. 13
, there will be described a drawback of the system shown in FIG.
12
. If the cylindrical piezoelectric element
1102
is displaced in the X-direction, as shown in
FIG. 13
, the mirror
1116
located on the undersurface of a specimen stage
1120
which is fixed to the free end of the element
1102
, is displaced at an angle to the end face of the optical fiber
1114
in the X-direction.
Accordingly, an object of measurement by means of the optical interferometer
1115
shifts its position from a point a on the mirror
1116
to another point b. Therefore, a Z-displacement measured by the interferometer
1115
involves the influence of change of the inclination of the mirror
1116
or surface conditions. Thus, the shifts of the inclination of the object of measurement and the measuring position, which are caused as the tube scanner is displaced in the X-direction, are primary factors that lower the accuracy of the Z-displacement measurement.
Third Prior Art
A scanning probe microscope in which an optical microscope is incorporated in an atomic force microscope is described in Jpn. Pat. Appln. KOKAI Publication No. 8-285865. As shown in
FIG. 14
, for example, this microscope comprises a quadruple scanner
1206
having a quadruple electrode, a cantilever displacement sensor
1208
in the form of an optical lever, and an objective lens
1210
for optical microscope. The scanner
1206
moves a cantilever
1202
with respect to a specimen
1204
. The sensor
1208
optically detects the deflective displacement of a free end of the cantilever
1202
, which is based on the interaction, e.g., atomic force or frictional force or adsorptive force or contact force, between the apex of a probe
1212
and the specimen
1204
. The objective lens
1210
is inserted in the scanner
1206
so that a scanning region for the cantilever
1202
, i.e., the surface of the specimen
1204
, can be optically observed through the lens
1210
.
After the probe
1212
on the cantilever
1202
is situated in the scanning region with use of the objective lens
1210
, the scanner is
1206
is feedback-controlled in the Z-direction in response to a Z-displacement signal from the displacement sensor
1208
. At the same time, the distance between th
Fujimoto Hirohisa
Ito Shuichi
Okazaki Kenya
Frishauf Holtz Goodman & Chick P.C.
Olympus Optical Co,. Ltd.
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