Radiant energy – Inspection of solids or liquids by charged particles
Reexamination Certificate
2002-04-30
2004-05-11
Wells, Nikita (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
C250S307000, C073S105000
Reexamination Certificate
active
06734425
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to scanning probe systems, such as scanning probe microscopes and profilometers, and more particularly to the probe assemblies used in these scanning probe systems.
BACKGROUND OF THE INVENTION
Scanning probe microscopy (SPM; also known as atomic force microscopy (AFM)) is considered a spin-off of scanning tunneling microscopy (STM). An SPM system measures the topography of a sample by scanning (sliding) a probe having a small tip over the sample's surface and monitoring the tip position in the z-direction at each point along the scan path. Alternatively the SPM probe can be used as a nano-Spreading Resistance Probe (nano-SRP), used for the determination of the resistance and carrier profile of a semiconductor element, or for nano-potentiometry measurements of the electrical potential distribution on a semiconductor element.
FIG. 30
is a perspective view showing a conventional SPM system
40
. SPM system
40
includes a movable XY stage
42
for supporting a sample
45
, a probe
50
mounted to a suitable structure (holder plate)
60
, a probe measurement device
70
, and a computer/workstation
80
that serves as both a system controller and a measurement data processor. Holder plate
60
is movable in the z-axis direction by a suitable motor (e.g., a piezoelectric device) to selectively position probe
50
relative to sample
45
. Similar motors (not shown) drive XY stage
42
in the xy-plane, thereby causing probe
50
to scan along the upper surface of sample
45
, when the probe is in the lowered position. Computer
80
generates control signals that are utilized to control the movements of holder plate
60
and XY stage
42
. In most conventional SPM systems, the up-and-down motion of probe
50
is detected by measurement device
70
using the so-called “optical lever” method, wherein a laser beam LB generated by a laser
72
shines onto a cantilever surface of probe
50
, and the reflected beam hits a two- or four-segment photodiode
75
. Measurement data generated by photodiode
75
is passed to computer
80
, which processes the measurement data, and typically generates a magnified view of the scanned sample.
FIG. 31
shows probe
50
in additional detail. Probe
50
includes a holder chip (mounting block)
51
, a straight cantilever section (stylus)
52
extending from holder chip
51
, and an “out-of-plane” tip
55
that extends perpendicular to cantilever section
52
. Probe
50
is supported by holder block
60
at an angle to facilitate contact between tip
55
and an upper surface of sample
45
. The choice of the materials from which holder chip
51
, cantilever section
52
, and tip
55
are composed depends on the type of measurement the probe is intended for. For topography measurement, a dielectric or a semi-conductive tip can be used, whereas for resistance determination and nano potentiometry require a highly conductive tip, preferably with high hardness and low wear.
One problem associated with conventional probes is that they are expensive and difficult to produce. Conventional probes are typically formed by bulk micromachining high quality, and therefore expensive, monocrystalline silicon (Si) wafers. As indicated in
FIG. 31
, the relatively large size of each probe
50
is due to the integrated holder chip
51
, which is mounted to holder plate
60
, and cantilever
52
, which must extend from under holder plate
60
to facilitate the “optical-lever” measurement method. Further, the probes are separated from the Si substrates by etching away the wafer material beneath the probe, which is a time-consuming and costly process. Because of their relatively large size, and because much of the Si substrate is etched or otherwise destroyed during the production process, relatively few probes
50
are formed from each expensive Si wafer, thereby making the cost of each conventional probe
50
relatively high.
Another problem associated with conventional probes is that out-of-plane tips
55
must be fabricated during a separate process from that used to form holder chip
51
and cantilever section
52
, and probe
50
must be mounted onto holder plate
60
at an angle relative to an underlying sample
45
. Conventional methods needed to form out-of-plane tips, such as tip
55
shown in
FIG. 31
, add time and expense to the probe manufacturing process. Most conventional out-of-plane probe tips are either etched out of a material (e.g. Si) or they are molded (a pyramidal mold is formed by anisotropic Si etching, the mold is filled up with a material such as a metal or diamond, the mold material is removed). Further, the tip height is limited to only about 15 &mgr;m, so probe
50
must be mounted onto holder plate
60
at an angle relative to an underlying sample
45
to facilitate contact between tip
55
and sample
45
. To facilitate this angled probe orientation, conventional holder plate
60
is provided with an angled portion
65
to which holder chip
51
is mounted. This mounting process also takes time, and is required for each probe mounted in an SPM system.
Yet another problem associated with conventional spring probes is that, when the tip wears out, a significant amount of system downtime is required to remove and replace the worn-out probe.
What is needed is a probe structure for scanning probe systems that avoids the problems associated with conventional probes that are described above.
SUMMARY OF THE INVENTION
The present invention directed to scanning probe systems (e.g., scanning probe microscopes (SPMs)) that utilize spring probes formed from stress-engineered spring material films, and include an actuation circuit for electronically controlling the spring probe, a sensor circuit for electronically detecting the position of the spring probe, or both an actuation circuit and a sensor circuit. Each spring probe includes a fixed end (anchor portion) attached to a substrate, and a cantilever (central) section bending away from the substrate. Curvature of the cantilever section is selectively controlled during fabrication to form a long free end terminating in a tip that is located away from the substrate in an un-actuated (i.e., unbiased) state. The probe assembly, which includes the substrate, the spring probe, and optional actuation/position sensing circuits, is then mounted in a scanning probe system such that the probe tip is positioned over the surface of a sample. When the position sensing circuit is not used, a conventional measurement device (e.g., a laser beam and photosensor array) is utilized to detect tip movement while scanning.
According to a first aspect of the present invention, the actuating circuit is utilized to control the bent position of the spring probe relative to the substrate. In one series of embodiments, this actuation circuit involves electrostatic actuation utilizing an actuation electrode that is capacitively coupled to an associated spring probe. The spring probe is subsequently moved relative to the substrate by applying a differential actuation voltage to the spring probe and the actuation electrode. In one embodiment, tapered offset actuation electrodes are utilized to produce constant force, constant height, and tapping mode operations over large topographies (10s of microns), which takes advantages of the tall tip structures that can be formed by the spring probes. In other embodiments, actuation of the spring probe is performed using magnetic, acoustic and piezoelectric arrangements.
According to another aspect of the present invention, the position sensing circuit is utilized to determine the deflected position of a spring probe relative to the substrate. In one series of embodiments, this actuation circuit involves forming a resistive electrode under the spring probe, and determining the spring probe positioned by measuring the amount of current passed through the resistive element. Alternative methods, such as utilizing a piezoresistive element mounted on the spring probe, are also disclosed.
According to yet another aspect of the present inventi
Chow Eugene M.
De Bruyker Dirk
Fork David K.
Hantschel Thomas
Rosa Michel A.
Bever Patrick T.
Bever Hoffman & Harms LLP
Wells Nikita
Xerox Corporation
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