Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2003-11-19
2004-09-07
Raevis, Robert (Department: 2856)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
Reexamination Certificate
active
06788086
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. 24
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. 25
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. 25
, 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. 25
, 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.
At this moment, there is no other SPM technology available which allows the manufacture of scanning probes on wafer scale that can be used to measure structures with high and super-high topography. An important issue in such processing is often to measure the roughness on the bottom of deep structures, and also the top-bottom step height of the structures. Conventional probe
50
cannot do such measurements for two reasons. First, tip
55
is only 5-15 &mgr;m high, which determines the deepest structure that can be measured. Second, cantilever
51
is perfectly straight and in-plane with holder chip
52
, which means that the probe would bump against the substrate surface if tip
55
enters a structure deeper than the height of tip
55
. Step height measurements are commonly done by profilometers that use special probes (i.e., sharpness as small as 10 nm) that can measure large step heights (e.g., 30 to 50 &mgr;m). However, these profilometer probes cost up to ten times as much as SPM probes.
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 spring probe assemblies for scanning probe systems (e.g., scanning probe microscopes (SPM) and profilometer systems) that are formed using stress-engineered spring material films. Each spring probe includes a fixed end (anchor portion) attached to a transparent (e.g., glass or quartz) substrate, and a cantilever (central) section bending away from the substrate. Curvature of the cantilever section is selectively controlled to form a long free end terminating in a tip that is located in the range of 15 to 500 &mgr;m from the substrate. The probe assembly, which includes the substrate and the spring probe, is then mounted in scanning probe system such that the probe tip is scanned over the surface of a sample. A conventional measurement device (e.g., a laser beam and photosensor array) is utilized to detect tip movement while scanning.
Spring probes of the present invention are formed by forming (e.g., sputtering, chemical vapor deposition, or electroplating) a spring material (e.g., metal, silicon, nitride, or oxide) onto a substrate while varying the process parameters (e.g., pressure, temperature, and applied bias) such that a stress-engineered spring material film is formed with an internal stress gradient in the growth direction (i.e., normal to the substrate). The spring material film is then etched to form an elongated island of spring material, and an anchor portion (fixed end) of the spring material island is then masked. The unmasked portion of the spring material island is then “released” by removing (etching) a sacrificial material located under the unmasked portion. In one embodiment, the sacrificial material removed during the release process is a separate “release” material layer (e.g., Si, SiNx, SiOx, or Ti) that is formed between
Chow Eugene M.
Fork David K.
Hantschel Thomas
Bever Patrick T.
Bever Hoffman & Harms LLP
Raevis Robert
Xerox Corporation
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