U.S. patent application number 13/079732 was filed with the patent office on 2012-03-15 for nanomachining method and apparatus.
This patent application is currently assigned to General Nanotechnology LLC. Invention is credited to Victor B. Kley.
Application Number | 20120066801 13/079732 |
Document ID | / |
Family ID | 37886055 |
Filed Date | 2012-03-15 |
United States Patent
Application |
20120066801 |
Kind Code |
A1 |
Kley; Victor B. |
March 15, 2012 |
NANOMACHINING METHOD AND APPARATUS
Abstract
Methods and apparatus are disclosed for nanomachining
operations. Excitation energy settings are provided to minimize
machine induced scan cutting. Cut operations can be operated in a
feedback mode to provide controlled cutting operations. Measurement
and sweep techniques to facilitate nanomachining operations are
disclosed.
Inventors: |
Kley; Victor B.; (Berkeley,
CA) |
Assignee: |
General Nanotechnology LLC
Berkeley
CA
|
Family ID: |
37886055 |
Appl. No.: |
13/079732 |
Filed: |
April 4, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11728744 |
Mar 26, 2007 |
7947952 |
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13079732 |
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10093842 |
Mar 7, 2002 |
7196328 |
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11728744 |
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60287677 |
Apr 30, 2001 |
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60274501 |
Mar 8, 2001 |
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Current U.S.
Class: |
850/56 |
Current CPC
Class: |
G01Q 30/04 20130101;
B24B 37/11 20130101; G01Q 80/00 20130101 |
Class at
Publication: |
850/56 |
International
Class: |
G01Q 70/08 20100101
G01Q070/08 |
Claims
1. In a nanomachining system having an SPM scanning probe and a
translation apparatus coupled to provide translational motion of
the SPM scanning probe, a method for moving material disposed at a
first location of a workpiece comprising: (a) positioning the SPM
scanning probe to a start position proximate the first location;
(b) adjusting the SPM scanning probe along the Z-direction to a
Z-direction position; (c) translating the SPM scanning probe along
a first vector away from the first location to move at least a
portion of the material to a second location; and repeating steps
(a) through (c) using at least a second vector.
2. The method of claim 1 wherein the second vector effects movement
of another portion of the material to the second location.
3. The method of claim 1 wherein the first location is a region of
the workpiece being nanomachined and the material is debris
produced by a nanomachining operation.
4. The method of claim 1 wherein, in step (c), the scanning probe
moves away from the first location on a line of motion that is
substantially straight.
5. The method of claim 1 wherein, in step (c), the scanning probe
moves away from the first location on a line of motion having a
zig-zag pattern.
6. The method of claim 1 wherein steps (a) through (c) are
performed along the first vector for a first plurality of sweeps
and steps (a) through (c) are performed along the second vector for
a second plurality of sweeps, the first along the first vector
having a direction that is about 180.degree. relative to the along
the first vector.
7. The method of claim 6 wherein steps (a) through (c) are
performed along a third along the first vector for a third
plurality of sweeps and steps (a) through (c) are performed along a
fourth along the first vector for a fourth plurality of sweeps,
wherein each of the vectors is about 90.degree. or about
180.degree. relative to the other vectors.
8. The method of claim 1 wherein the Z-direction position is
located on the surface of the workpiece.
9. The method of claim 1 wherein the Z-direction position is
located above the surface of the workpiece.
10. In a nanomachining system having an SPM scanning probe and a
translation apparatus coupled to provide translational motion of
the SPM scanning probe, a method for moving material from a region
of a workpiece comprising: (a) positioning the SPM scanning probe
at a sweep-start position in the region, the sweep-start position
lying on a reference line, the reference line being one of one or
more reference lines passing through an origin location disposed in
the region; (b) adjusting the SPM scanning probe along the
Z-direction to a first Z-direction position; (c) translating the
SPM scanning probe in a direction substantially orthogonal to the
reference line on which the sweep-start position lies; and
repeating steps (a)-(c) using different sweep-start positions, each
sweep-start position lying along one of the one or more reference
lines.
11. The method of claim 10 wherein the region is a region being
nanomachined.
12. The method of claim 10 wherein, in step (c), the scanning probe
moves away from the sweep-start position along a substantially
straight line of motion.
13. The method of claim 10 wherein, in step (c), the scanning probe
moves away from the sweep-start position along a line of motion
having a zig-zag pattern.
14. In an SPM microscopy system having an SPM scanning probe and a
translation apparatus coupled to provide translational motion of
the SPM scanning probe, a method for manipulating material on a
surface of a workpiece comprising: positioning the SPM scanning
probe at a first position on the workpiece, the first position
having disposed thereat an amount of material; adjusting the SPM
scanning probe along the Z-axis to a first Z-position relative to
the amount of material; translating the SPM scanning probe in an
X-Y direction of movement to move at least a portion of material to
a second position; and applying an amount of energy to the material
to effect a physical change in the material.
15. The method of claim 14 wherein the amount of material to be
moved is obtained by performing a nanomachining operation on a
structure in the vicinity of the first position.
16. The method of claim 15 wherein the structure is an area of
surface in the vicinity of the first position.
17. The method of claim 14 wherein the material is one of chrome,
quartz, silicon, an oxide of silicon, silicon nitride, and
carbon.
18. The method of claim 14 wherein the energy is heat energy
sufficient to integrate the material with constituent material at
the second position.
19. A method for operating a nanomachining system having a scanning
probe, the method comprising: collecting first information
indicative of topological features of a surface of a workpiece;
performing one or more processing steps on the workpiece, the
processing steps subjecting the surface to changes in its topology
thereby producing one or more positive surface features;
translating the scanning probe over the surface using the first
information; and cutting the one or more positive surface features
from the surface of the workpiece, the positive surface features
being identified based on the first information.
20. The method of claim 19 wherein the translating includes
obtaining Z-direction measurements and comparing the Z-direction
measurements with a corresponding Z-direction data contained in the
first information, the positive surface features being identified
based on a result of the comparison.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] The present application is a Continuation Application of
U.S. application Ser. No. 11/728,744, filed Mar. 26, 2007, which is
a Continuation Application of U.S. application Ser. No. 10/093,842,
filed Mar. 7, 2002, which claims priority from U.S. Application No.
60/274,501, filed Mar. 8, 2001, and U.S. Application No.
60/287,677, filed Apr. 30, 2001, all of which are incorporated by
reference in their entirety for all purposes:
[0002] The following are incorporated by reference in its entirety
for all purposes: [0003] U.S. Pat. No. 6,752,008, issued Jun. 22,
2004; [0004] U.S. Pat. No. 7,196,328, issued Mar. 27, 2007; [0005]
U.S. Pat. No. 6,923,044, issued Aug. 2, 2005; [0006] U.S. patent
application Ser. No. 10/094,411, filed Mar. 7, 2002; [0007] U.S.
Pat. No. 6,802,646, filed Oct. 12, 2004; and [0008] U.S. Pat. No.
6,787,768, issued Sep. 7, 2004.
[0009] The following U.S. patents are incorporated by reference in
their entirety for all purposes: [0010] U.S. Pat. No. 6,144,028,
issued Nov. 7, 2000; [0011] U.S. Pat. No. 6,252,226, issued Jun.
26, 2001; [0012] U.S. Pat. No. 6,337,479, issued Jan. 8, 2002; and
[0013] U.S. Pat. No. 6,339,217, issued Jan. 15, 2002.
[0014] The disclosure of the following published PCT application is
incorporated by reference in its entirety for all purposes: [0015]
WO 01/03157 (International Publication Date: Jan. 11, 2001 based on
PCT Application No. PCT/US00/18041, filed Jun. 30, 2000 by Victor
B. Kley for "Object Inspection and/or Modification System and
Method."
BACKGROUND OF THE INVENTION
[0016] This invention is related generally to the field of Atomic
Force Microscopy (AFM), Scanning Tunneling Microscopy (STM), Near
field Scanning Optical Microscopy (NSOM), NanoSpectroPhotometry
(NSP), NanoPolarimetry (NP), Magnetic Field Microscopy (MFM) and
any other methods adaptable and suitable to guide the nanomachining
techniques described herein. Specifically, the invention is
directed to nanomachining techniques and apparatus, using AFM,
NSOM, NSP, NP, MFM and STM technologies. These technologies are
sometimes collectively referred to as Scanning probe Microscopy
(SPM). Generally, SPM technologies allow one to "see" atomic-scale
features on or in surfaces.
[0017] An AFM works by scanning a tip over a surface much the same
way as a phonograph needle scans a record. The tip is located at
the end of a cantilever beam and positioned over the surface to be
scanned. The combination of the cantilever beam and tip is
sometimes referred to collectively as a scanning probe or simply a
probe.
[0018] AFM techniques rely on the effects of the inter-atomic
interactions, such as van der Waals forces, that arise between the
atoms in the structure of the tip and the atoms at the surface
being imaged. As the tip is repelled by or attracted to the
surface, the cantilever beam is deflected. The magnitudes of the
deflections correspond to the topological features of the atomic
structure of the surface being scanned. The AFM can work with the
tip touching the sample (contact mode), or the tip can tap across
the surface (tapping mode), or made to not touch the surface at all
(non-contact mode--the preferred embodiment).
[0019] STM techniques rely on the fact that the electronprobability
cloud associated with the atoms at the surface extends a very small
distance above the surface as described by the quantum physical
model. When a tip is brought sufficiently close to such a surface,
there is an increadsingly stronger probability of an interaction
(current) between the electron cloud on the surface and that of the
tip atom. An electric tunneling current flows when a small voltage
is applied. The tunneling current is very sensitive to the distance
between the tip and the surface. These changes in the tunneling
current with distance as the tip is scanned over the surface are
used to produce an image of the surface.
[0020] AFM is being used to solve processing and materials problems
in a wide range of technologies affecting the electronics,
telecommunications, biological, chemical, automotive, aerospace,
and energy industries. The materials being investigated include
thin and thick film coatings, ceramics, composites, glasses,
synthetic and biological membranes, metals, polymers, and
semiconductors. The AFM is being applied to studies of phenomena
such as abrasion, adhesion, cleaning, corrosion, etching, friction,
lubrication, plating, and polishing.
[0021] The STM is widely used in both industrial and fundamental
research to obtain atomic-scale images of surfaces. It provides a
three-dimensional profile of the surface which is very useful for
characterizing surface roughness, observing surface defects, and
determining the size and conformation of molecules and aggregates
on the surface.
[0022] A common image scanning technique involves vibrating a probe
along the Z-axis as it is being translated in the X-Y plane about a
surface of interest (STM is another common scanning technique, but
is only suitable for conductive surfaces). The vibration is usually
sinusoidal and maintained at a particular frequency. Typically,
this frequency is the resonant frequency of the cantilever portion
of the probe. An excitation energy is applied to the probe to
create the vibratory motion, where the peak-to-peak deflection of
the tip is determined by the level of the excitation energy. There
are three common modes of operation: (1) the probe can work with
the tip touching the surface (contact mode), (2) non-contact mode
where the tip vibrates near the surface, and (3) the tip can tap
across the surface (tapping mode). As the tip is scanned across the
surface, the peak-to-peak deflection varies due to attractive
forces between the constituent atoms of the tip and the atomic
particles of the surface being scanned. An image of the surface is
produced from variations in the resonance required to maintain a
constant peak-to-peak deflection (e.g., using a feedback loop) by
applying known image processing methods as is well known in the
art.
[0023] Nanomachining involves removing material from a surface in a
controlled manner to attain specific surface features. Typically,
an appropriate scanning probe is manipulated so that its tip comes
into contact with a surface to be nanomachined. The scanning probe
is then translated along a pre-programmed vector, producing a
scraping action across the contacted surface and removing an amount
of material from the surface. An appropriate feed is applied to
control the amount of material removed. This is repeated until the
desired features are achieved. Any surface which is exposed to
contact by the scanning probe can be nanomachined. Thus, for
example the walls of a vertical structure can be nanomachined using
a scanning probe having an appropriately shaped tip applied to the
wall with an appropriate feed force. General techniques are more
fully discussed in the various above-identified commonly owned U.S.
patents and co-pending U.S. patent applications.
[0024] A commonly performed operation is the positioning of the
scanning probe to locate the probe prior to making a cut. The
process of locating involves scanning the surface to determine the
position, for example by any of the techniques available to SPM and
well known in the art. A side-effect of these scan methods is the
physical alteration of the surface being scanned due to the
contacting action of the probe tip upon the surface. This effect is
sometimes referred to as "scan cutting." Scan cutting can be
disastrous for nanomachining purposes. Nanomachining techniques
often involve making repeated motions along the same path.
Consequently, the cumulative effect of scan cutting that would
result during a nanomachining operation must be predictable and
controlled.
[0025] When performing a nanomachining operation, it may be
desirable to be able to verify or monitor the location of the
surface as it is being machined. For example, if a recess is being
formed into the surface of a workpiece, it might be desirable to
confirm the depth of the recess. It might be necessary to monitor
the progress of the nanomachining operation to detect when to stop
the process. For example, nanomachining a workpiece comprising a
multi-layered structure of different materials will likely progress
at different rates due to varying hardness from one layer to the
next. The ability to monitor the progression of the nanomachining
operation allows appropriate control of the feedforce of the tip
upon the surface to be nanomachined.
[0026] There is a need for techniques to improve nanomachining
practices.
BRIEF SUMMARY OF THE INVENTION
[0027] In accordance with the invention nanomachining methods and
apparatus include components for determining certain operating
parameters for nanomachining In one aspect of embodiments of the
invention one such parameter, namely excitation energy setting, is
determined with an iterative process. In another aspect of
embodiments of the invention, one or more cutting parameters are
adjusted in a feedback loop such as amount of feed, number of
cutting passes before a measure is made, number of strokes
comprising a pass, angle of the pass, tool tip used in a single or
multiple pass (e.g., roughing step and fine cutting step). In still
another aspect of the embodiments of the invention, various sweep
techniques are provided to facilitate the nanomachining operation.
In still yet another aspect of embodiments of the invention, sweep
techniques are provided to perform specialized cut operations.
[0028] A further understanding of the nature and advantages of the
present invention may be realized by reference to the remaining
portions of the specification and the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The teachings of the present invention can be readily
understood by considering the following detailed description in
conjunction with the accompanying drawings:
[0030] FIG. 1 is a high level block diagram illustrating a
nanomachining system in accordance with an embodiment of the
invention;
[0031] FIG. 2 is a schematic illustration of a typical scanning
probe suitable for use with the nanomachining methods and apparatus
of the invention;
[0032] FIG. 3 is a flowchart showing the general steps for
nanomachining operations in accordance with an embodiment of the
invention;
[0033] FIG. 4 is a flowchart showing the general steps for
determining the excitation energy in accordance with an embodiment
of the invention;
[0034] FIG. 5 is a gross scale top view representation of a surface
of a workpiece having various structures subject to
nanomachining;
[0035] FIGS. 6A-6C are side views of a portion of the workpiece of
FIG. 5, showing a recess forming sequence in accordance with an
embodiment of the invention;
[0036] FIGS. 7A-7D are side views of a portion of the workpiece of
FIG. 5, showing a recess forming sequence in accordance with
another embodiment of the invention;
[0037] FIGS. 8A and 8B are magnified views from FIG. 5 illustrating
a lateral positive surface feature subject to nanomachining;
[0038] FIGS. 9A and 9B are magnified views from FIG. 5 showing a
positive surface feature subject to nanomachining;
[0039] FIG. 10 is a flowchart illustrating a feedback loop for
cutting operations in accordance with an embodiment of the
invention;
[0040] FIGS. 11A and 11B illustrate some cutting parameters;
[0041] FIGS. 12A-12C illustrate measurement processing in
accordance with an embodiment of the invention;
[0042] FIG. 13 is a flowchart highlighting the steps for
measurement processing in accordance with an embodiment of the
invention;
[0043] FIGS. 14A-14C illustrate sweep patterns in accordance with
an embodiment of the invention;
[0044] FIGS. 15A-15D show a sweep sequence;
[0045] FIG. 16 shows a generalized sweep pattern;
[0046] FIG. 17 shows various sweep vectors;
[0047] FIG. 18 is a gross scale illustration of a sweep-cut
operation in accordance with an embodiment of the invention;
[0048] FIG. 19 is a gross scale illustration of a sweep-cut
operation in accordance with another embodiment of the invention;
and
[0049] FIG. 20 is a generalized flow chart for sweep-cut
processing.
DETAILED DESCRIPTION OF THE INVENTION
[0050] FIG. 1 shows an illustrative embodiment of the present
invention by way of a generalized block diagram, illustrating a
scanning probe microscopy system 100 that is adapted for
nanomachining A scanning probe 102 is the workhorse of the
nanomachining system. A typical probe comprises a cantilever and a
tip disposed at the free end of the cantilever. Various tip shapes
and configurations suitable for nanomachining are disclosed in the
various above-identified commonly owned issued patents and commonly
owned, co-pending patent applications.
[0051] FIG. 2 shows a typical scanning probe 102 suitable for use
with the present invention. A cantilever 230 is attached to a body
member 228 which provides structure for attachment to a probe
translation apparatus. Disposed at the free end of the cantilever
is an appropriately shaped probe tip 232. An enlarged portion of
the free end is shown in the side view. The particular dimensions
of the probe will vary depending on the particular application.
[0052] The probe 102 can be coupled to a first translation stage
104. The first translation stage can provide movement of the probe
in the X-Y plane. By convention, the X-Y plane is the plane
parallel to the major surface of a workpiece 132. Thus, the probe
can be positioned in the X-Y position relative to the workpiece by
the first translation stage. The first translation stage can also
provide movement of the probe in the Z-direction and thus position
the probe in three-dimensional space relative to the workpiece.
Such first translation stages are known and well understood
devices. Typically, they are piezoelectric devices.
[0053] Alternatively, a second translation stage 106 can be
provided. The workpiece 132 can be affixed to the second
translation stage to provide X-Y motion of the workpiece relative
to the probe 102. Furthermore, the second translation stage can
provide motion of the workpiece in the Z direction relative to the
probe. Such stages are typically linear motors, or precision ball
screw stages or combinations thereof with linear scale or
interferometric position feedback.
[0054] The relative motion between the probe 102 and the workpiece
132 can be achieved by any of a number of techniques. The probe can
be translated in three dimensions while maintaining the workpiece
in a stationary position. Conversely, the workpiece can move
relative to a stationary probe. Both the probe and the workpiece
can be moved in a coordinated fashion to achieve rapid positioning.
The first translation stage 104 might provide only X-Y motion,
while Z-axis positioning is provided by the second translation
stage 196; or vice-versa. These and still other combinations of
concerted motions of the probe and the workpiece can be performed
to effect relative motion between the probe and the workpiece.
[0055] In the principle embodiment using non-contact AFM an
excitation source 114 delivers an excitation energy to the probe
102 to make the probe vibrate in a resonant fashion. The excitation
energy can be any form of energy suitable to resonate the probe.
For example, a typical scanning probe used in atomic force
microscopy comprises a cantilever formed of silicon. A
piezoelectric bimorph or tube attached to the translation means has
the probe mounted on it and the piezoelectric element is then
electrically driven at a wavelength at which the cantilever
resonates. However, alternative probe architectures might use a
bi-metal construction that is driven by thermal energy. Surface
acoustic waves (SAW), linear or rotational MEMS structures and
piezoresistors can also be used to provide excitation energy for
resonating the probe.
[0056] A detection module 116 is coupled to detect atomic
interactions between the atoms which constitute the probe tip and
the constituent atoms of the surface being scanned. Many detection
techniques are known. For example, if the probe is operated in AFM
(atomic force microscopy) mode, the cantilever resonance point is
shifted by the interatomic forces acting between the tip and the
surface as the tip is scanned across the surface. Theresonance
change can be measured or the gross deflections can be measured
optically. A series of raster scans is then conventionally used to
form a surface map of the area scanned and may be capable of
producing data representative of the atomic scale topography of the
surface.
[0057] A generalized controller 112 can be configured to provide
various computer-based functions such as controlling the components
of the nanomachining system, performing data collection and
subsequent analysis, and so on. Typically, the controller is some
computer-based device; for example, common architectures are based
on a microcontroller, or a general purpose CPU, or even a custom
ASIC-based controller.
[0058] Appropriate control software is provided to operate the
computing components to perform the foregoing functions. For
example, control signals coordinate the components of the
nanomachining system to effect nanomachining operations disclosed
herein. It is understood that the generalized controller functions
can be allocated to other system components to meet particular
system requirements and constraints for a given implementation. For
example, data analysis functionality can easily be off-loaded to
another computer. The nanomachining system 100 can have a network
connection to a larger system. It is well within the capability of
persons of ordinary skill in the relevant arts to produce the
appropriate programming code needed to perform the control
sequencing and delivery of control signals to coordinate the
various components of the nanomachining system 100 to effect the
processing discussed below.
[0059] A user interface 122 is provided to allow a user to interact
with the system. The "user" can be a machine user. A machine
interface might be appropriate in an automated environment where
control decisions are provided by a machine.
[0060] A data store 152 contains various information to facilitate
nanomachining operations and for overall operation of the
nanomachining system. The data store contains the programming code
that executes on the controller 112, described in the flow charts
of FIGS. 3, 4, 10, 13, and 20. The data store can include a library
of one or more excitation energy preset levels. A preset level is
selected from the library via the user interface 122. The preset is
fed to the controller 112, which uses the information to control
the excitation energy level that is delivered to the scanning probe
102. Other kinds of information include cutting parameters for
setting up the nanomachining system to perform a nanomachining
operation. These pieces of information will be discussed below. The
data store shown in the figure can be any appropriate data storage
technology, ranging from a single disk drive unit to a distributed
data storage system.
[0061] Referring now to FIG. 3, a high level flowchart shows the
major processing steps for a nanomachining operation according to
an embodiment of the present invention. Nanomachining involves the
basic steps of: positioning the probe 102 to a location on the
workpiece 132; applying the tip of the probe to the surface to be
cut with an appropriate feed force; and translating the probe along
a translation vector. The foregoing sequence of actions is referred
to as a "cut pass."
[0062] A commonly performed operation is the positioning of the
probe at the beginning of a cut pass. This is accomplished by
scanning the probe across the surface of the workpiece. A probe is
scanned across the surface by applying an excitation energy to the
probe to set up a vibratory motion. As the probe tip is translated
across the surface, the position of the probe tip can be gauged by
the observable effect on the vibratory motion of the probe as the
tip is moved across the surface. However, as noted above, a
side-effect of the scanning is the physical alteration of the
surface being scanned due to the contacting action of the probe tip
upon the surface, an effect called "scan cutting."
[0063] A calibration procedure in accordance with the invention is
performed in a step 302, to determine an excitation energy level
that is appropriate for nanomachining An appropriate excitation
level is one where there is no appreciable scan cutting artifact
that results from the scanning that occurs during a nanomachining
operation. Once an appropriate excitation energy level is
determined, the scanning probe can be quickly set when performing
subsequent nanomachining operations without having to repeat the
calibration procedure. Or the tip calibration can be used to
estimate a proper setting for the excitation for every operation
when the measurement is sufficiently fast.
[0064] Next, a reference location is established in a step 304. As
the name implies, the location establishes a reference for gauging
the progress of the nanomachining operation. If a recess is being
formed into the surface of a workpiece, for example, it might be
desirable to determine the depth of the recess (a Z-direction
metric) in order to ascertain the stop point for the nanomachining
operation. This can be accomplished by making a Z-axis measurement
in the nanomachined area relative to the reference location.
[0065] The reference location can be a Z-axis location, or a
location in the X-Y plane. In the foregoing example of a
nanomachined recess, a Z-axis reference location is appropriate. On
the other hand, an unwanted feature protruding in the X-Y direction
from a structure would call for an X-Y reference location. If the
protrusion is to be shaved off by a lateral nanomachining
operation, it might be desirable to know when a sufficient portion
of the protrusion has been removed. This can be accomplished by
making X- and/or Y-axis distance measurements of the nanomachined
surface relative to an appropriately established reference location
in the X-Y plane. The measurement(s) provide information as to the
lateral distance traversed by the cut operation.
[0066] The term "distance" has a dual meaning, depending on its
usage. On the one hand, "distance" refers to vertical distance when
a recess is being nanomachined into existence, or when an unwanted
lump of material is to be shaved down toward the surface of the
workpiece. On the other hand, "distance" refers to a lateral metric
(X-Y plane) when nanomachining involves cutting (trimming) a
surface in a direction parallel to the X-Y plane. Distance is
generalized by
d= {square root over (x.sup.2+y.sup.2+z.sup.2)},
although pieced out, these measures can be used together to make
any arbitrary shape in three-dimensional space.
[0067] In a step 306, the cut operation is performed. As defined
above, one or more "cutting passes" might be performed during this
step. After making the one or more cutting sequences, a sweep
operation is performed in a step 308. The sweep operation in the
context of a cut operation serves to remove the debris from the
around the cut that is produced by the cut operation. As will be
explained, sweeping is itself a form of cut operation. Thus, while
the sweep operation used in conjunction with a cut operation is
performed for the purpose of removal of debris, additional uses of
the sweep operation will be discussed.
[0068] A measurement is made in a step 310 after the sweep
operation is completed. A distance measurement of the cut area is
made relative to the reference location determined in step 304. The
distance measurement provides an indication of the progress of the
cut operation. A stop condition for the cut operation, for example,
can arise once the desired distance (i.e., depth or lateral
distance) is reached. The stop condition can also simply be the
completion of a predetermined number of cut operations.
[0069] FIG. 4 is a high level flowchart showing a calibration
procedure according to an embodiment of the present invention. The
procedure determines a tolerable level of excitation energy that is
suitable for driving the scanning probe (102, FIG. 1) during the
scanning phases of a nanomachining operation.
[0070] In a step 402, a threshold level for the excitation energy
is determined. The threshold level is a sufficiently low level of
excitation energy that the peak-to-peak deflections of the tip are
not significantly detectable by the detection module 106. By
staying below the detection threshold of the detection module the
surface being scanned is not detectable. This threshold level
establishes a starting point for determining a tolerable level of
excitation energy for nanomachining purposes.
[0071] In one embodiment of the invention, the threshold level is
determined by setting the excitation energy to a level which can be
detected by the detection module. The scanning probe scans the
surface (the servo system of the primary embodiment maintains this
distance as is well known in the art). As the probe is scanned
across the surface, the excitation energy level is incrementally
decreased until the detection module no longer detects the surface.
The excitation energy level at that point is recorded as the
threshold level.
[0072] In another embodiment of the invention, the threshold level
is determined by setting the excitation lower after having first
found the surface and continuing to lower the excitation until the
signal is lost and then raising it a fixed amount above the
threshold. In non-contact mode (the preferred embodiment) no
scanning can take place without a signal for the servo system to
move the tip up and down (the z direction) while it is moved across
the surface in x and y (the scan). In contact mode (no excitation
is used in this mode) the tip is dragged over the surface and the
limp cantilever lets the tip fall or rise with the surface.
[0073] When the threshold level is determined, the process for
determining the tolerable excitation energy level can proceed. The
process is an iterative one. In step 404, an excitation energy
level is selected by incrementing the currently set excitation
energy level by a certain amount. The increment value can be a
fixed value. The increment value can vary from one iteration to the
next. In an embodiment of the invention, the increment value is a
fixed value. For the first iteration, the current excitation energy
level is set to the threshold level determined in step 402.
[0074] Next, in step a 406, a test surface on the surface of a
workpiece is selected. The workpiece can be a block of scrap
material that has the same material composition as the actual
workpiece to be nanomachined. Alternatively, the workpiece can be
the actual workpiece itself. Nanomachining typically involves areas
on the order of square nanometers of surface area. A macro-scale
workpiece typically has vast regions of available area. This
calibration procedure requires only a fraction of area to perform,
and thus can be performed on the actual workpiece in an area where
detrimental effects are not important.
[0075] The scanning probe is positioned at the selected test
surface and a scanning sequence is performed at a step 408 on the
test surface while driving the scanning probe at the selected
excitation energy level. The scanning sequence involves making a
certain number of passes on the test surface along a single scan
vector. A scan vector specifies the direction and distance of the
scan. A vector is chosen such that a clear image of a transition is
obtained (e.g., a rise or fall in the local topography) commonly
this transition structure is visible as an edge, optically. If
instead, a trench (rather than a degraded edge) is to be the scan
cut test result the vector can be anywhere that such a scan trench
would be easily discerned among the surrounding structure (like a
plane or flat, smooth area).
[0076] The number of scan passes (N) is based on the number of
expected scans for a particular nanomachining operation. The goal
of this calibration procedure is to determine a tolerable level of
excitation energy such that when the scanning probe is scanned at
the energy level during a nanomachining operation, the consequent
scan induced nanomachining is within a tolerable limit as
determined by the requirements of the workpiece being nanomachined.
The number of expected scans (M) during a nanomachining operation
typically is a priori knowledge, perhaps determined by a user
(human user or an automated design process) having knowledge of the
nanomachining operation to be performed.
[0077] The number of scan passes N can be set to the expected
number of scans M. The tolerable level determined in this manner,
in principle, should ensure that scan induced nanomachining will be
at acceptable levels. However, as with any engineering design
limit, a margin is usually factored in to provide a buffer zone for
variations in the process. Here, the value of N is determined by
S.times.M, where S is a scaling factor which provides a margin for
error. Typically, the scaling factor is set to 2, but can be set to
other values. The particular value will depend on factors not
relevant to the practice of the invention.
[0078] After the specified number of scan passes has been
performed, a determination of the degree of scan induced
nanomachining is made in a step 410. This determination can be made
by making a measurement of the depth of the trench formed in the
test surface that results from scan induced nanomachining One
measurement technique is discussed below. If the measured depth
does not exceed a tolerance limit set by the user, then the
procedure is repeated (step 411).
[0079] If the measured depth does exceed the tolerance limit, then
the process completes. The tolerance level can be set to the
current excitation energy level setting, which produces scan
induced nanomachining that just exceeds the user-specified
tolerance. Alternatively, the tolerance level can be set to the
previous setting. A factor to consider is that a higher excitation
energy increases the sensitivity of the scan. Since the scan pass N
already factors in a margin for error, it may be desirable to
select the higher excitation energy setting as the tolerable level
to obtain the benefit of the increased sensitivity.
[0080] The tolerable level of excitation energy determined by the
foregoing procedure is dependent on various factors including the
material of the surface, the constituent material of the scanning
tip, the mechanical properties of the cantilever, the number of
expected scans, and so on. Thus, it might be desirable to create a
library of tolerable excitation energy levels for various
combinations of materials expected to be encountered by the
particular nanomachining system. An appropriate tolerable level
setting can then be selected based on the specific materials and
conditions involved in a particular nanomachining operation.
[0081] FIGS. 5-9 are diagrammatic drawings illustrating highly
exaggerated features of micron- and submicron-scaled elements to
facilitate the discussion various cut operations that can be
performed for nanomachining in accordance with embodiments of the
present invention. FIG. 5 shows a highly simplified top view
representation of a surface 502 of a workpiece 500 to be
nanomachined. X- and Y-direction coordinates are referenced as
shown. The Z-direction coordinate is perpendicular to the drawing
sheet. A first region 512 shows a recess cutting operation. A
second region 514 illustrates a recess cutting operation using a
trim technique. A third region 516 shows a trim operation. A fourth
region 518 illustrates another trim operation. These cut and trim
operations will be discussed in more detail below.
[0082] Before proceeding, a few words about terminology would be
appropriate at this point. The terms such as "cut," "trim," and
their various grammatical forms all relate to the general notion of
nanomachining The only distinction among the terms used in this
application is the direction of the nanomachining operation. For
example, a "cut" is typically used when referring nanomachining
along the Z-axis. Similarly, a "trim" is a nanomachining operation
that proceeds laterally along the surface of the workpiece in the
X-Y plane. Though an attempt is made to use these terms
consistently, other terminology may slip in. For example, a trim
might be referred to as a lateral cut. To the extent that "cut" and
"trim" differ only with respect to the direction of the operation,
it is understood that these terms and others might be used
interchangeably and in combination to refer to nanomachining
operations in general. The orientation of the nanomachining
operation can be obtained from the context of the discussion.
Finally, the XYZ axis convention adopted in this application is for
the major surface of the workpiece to lie along the X-Y plane,
where the Z-axis lies perpendicular to the major surface. Further
it is understood that these methods may be combined to obtain any
arbitrary surface in three space.
[0083] Continuing then, a cut operation includes providing a
downfeed by appropriate movement of the translation stage (104,
FIG. 1) in the Z-direction. In the case of a lateral cut along a
direction in the X-Y plane, the lateral feed is applied by
appropriate movement of the translation stage in the X-Y
direction(s). The controller 112 provides the appropriate control
signals to coordinate these activities. It is understood that the
scanning probe 102 will be properly configured to perform scanning
operations and cutting operations as needed.
[0084] FIGS. 6A-6C is a sequence of cross-sectional views of region
512 taken along view lines 6-6 of FIG. 5. In one embodiment of the
invention, recess cutting involves taking multiple cut passes
across the exposed surface of the region to be nanomachined, in
this case region 512. FIG. 5 shows in region 512 multiple cut
passes 522 made in the region. Each cut pass is made by performing
a scan operation to properly position the scanning probe in the
region 512. A downfeed is applied to press the tip of the scanning
probe against the surface. The scanning probe is then translated
along an appropriate scan vector to effect a cut operation.
[0085] The cutting sequence is shown in FIGS. 6A-6C. FIG. 6A shows
in phantom the volume of material 612 to be removed from region
512. The cutting proceeds one layer at a time. In the particular
embodiment shown, all the cut passes 522 are performed to remove a
layer of material from the region 512 before performing cut passes
to remove the next layer. Thus, FIG. 6B illustrates that a first
layer of material 602 has been removed. FIG. 6C shows a second
layer of material 604 having been removed. This sequence is
repeated until the desired recess has been formed.
[0086] FIGS. 7A-7D is a sequence of cross-sectional views of region
514 taken along view lines 7-7 of FIG. 5. In one embodiment of the
invention, recess cutting using a trim (lateral cut) technique
involves producing an initial recess 532 at a beginning area of
region 514. This is followed by making multiple trim cut passes in
the exposed surface of the hole of the region to be nanomachined,
in this case region 514. FIG. 5 shows multiple trim cut passes 534
made in region 514. Each trim cut pass is performed by applying an
appropriate feed force to press the tip against the surface to be
trimmed.
[0087] The cutting sequence is shown in FIGS. 7A-7D. FIG. 7A shows
in phantom the volume of material 714 to be removed from region
514. The trim cut first creates the recess 532 formed into the
region, FIG. 7B. The recess can be created by cutting down and then
to the side. Subsequent trim cut passes proceed one layer at a
time. Thus, FIG. 7C illustrates that a first layer of material 702
has been removed. FIG. 7D shows a second layer of material 704
having been removed. This procedure is repeated until the recess
has been formed.
[0088] A structure which constitutes region 516 is shown in FIG. 5
to illustrate how a trim (lateral) cut can be performed on surface
structures. Here, as in the case of nanomachining the region 514,
the tip is pressed against a portion of the structure with an
appropriate feed force to produce a cutting action of the
structure. As the figure shows, a positive surface feature such as
the protruding portion 542 formed on the structure 516 represents
an unwanted feature to be removed by nanomachining (examples of a
negative surface feature include a detent or recess formed into the
surface). By applying an appropriate scan vector and an appropriate
feed, the scanning probe can remove the unwanted feature 542. A
lateral recess 542 can be formed into the structure 516 in very
much the same manner.
[0089] FIGS. 8A and 8B are top and side views, respectively, of the
structure 516 with its positive surface feature 542. FIG. 8A is an
enlargement of the top view of FIG. 5, showing a series of lateral
layers 821. In accordance with an embodiment of the invention, each
lateral layer 821 is cut before the next layer is cut. Thus,
referring to the cross-sectional side view shown in FIG. 8B, a
series of lateral cut passes 822 are performed for a given lateral
layer 821. When a lateral layer 821 is complete, the scanning probe
is incrementally fed in the Y-direction to cut the next lateral
layer. An additional note worth mentioning is that the lateral cut
passes 822 can be made in the vertical (Z-direction).
[0090] FIGS. 9A and 9B show top and side views, respectively, of a
positive surface feature 518 which can be removed using a cutting
sequence similar to the technique shown for nanomachining a recess
in region 512. Instead of forming a recess, material is removed
from a "bump" or other unwanted structure formed on the surface
502. FIG. 9A is an enlargement of the top view of FIG. 5, showing a
layer 922A cut by a series of cut passes 921. The layer 922A is the
topmost layer of the positive surface feature 518, as can be seen
from the cross-sectional side view shown in FIG. 9B. Successive
layers 922 are cut, one at a time until a desired portion of the
feature 518 is removed.
[0091] FIG. 10 is a generalized flowchart of cut processing in
accordance with an embodiment of the present invention will be
discussed. The process of initializing the distance reference in
step 304 shown in FIG. 10 has been discussed briefly in connection
with FIG. 3. Additional discussion is provided below in connection
with the handling of distance measurements.
[0092] A set of cutting parameters are obtained to set up the
nanomachining system for a cut operation (cutting sequence) in a
step 1002. These parameters include settings such as downfeed (or
lateral feed for side cuts), speed of cutting, tool angle relative
to the surface of the workpiece, direction of cut, and cut overlap.
The downfeed (or lateral feed) force can be adjusted by appropriate
translations of the translation stage 104. The feed setting affects
the amount of material to be removed. Speed of cutting is also
varied by proper control of the translation stage.
[0093] Refer for a moment to FIGS. 11A and 11B. FIG. 11A
diagrammatically illustrates that the tip (tool) 232 can be
adjusted to an angle .theta. relative to the surface 1102 of a
workpiece 1100. The figure also shows that the direction of travel
of the cutting tool (scanning probe) is a settable parameter. A cut
in one direction D.sub.1 will remove an amount of material
different than if the cut was made in different direction D.sub.2.
FIG. 11B shows that cut overlap can be varied.
[0094] FIG. 11B illustrates various cut overlap settings. A typical
cut operation will involve a series of cut passes; e.g., FIG. 5
shows a series of cut passes 522 in region 512 and a series of cut
passes 534 in region 514. Sequentially made cut passes can be made
to overlap or not overlap. Thus, in FIG. 11B, cuts C.sub.1 and
C.sub.2 are cuts made, one following the other, with an overlap
indicated by overlap region 1104. Similarly, cuts C.sub.2 and
C.sub.3 overlap. Alternatively, sequentially made cuts can lie
adjacent to each other. This situation is shown by cuts C.sub.3 and
C.sub.4, and by cuts C.sub.4 and C.sub.5. At the other extreme,
sequentially made cuts may have gap formed between them. Thus, cuts
C.sub.5 and C.sub.6 are made with a gap region G formed between
them. A later cut pass can be made that spans the gap region G.
Thus cut C.sub.7 is shown overlapping cuts C.sub.5 and C.sub.6 to
remove the material in the gap region G.
[0095] Returning to FIG. 10, initially the cutting parameters can
be obtained from predefined data sets stored in the data store 152
(FIG. 1). Some of the parameters can be set by the user (a human
user, or a machine user) before the cut operations begin. Typical
parameters include such factors as the angle, number of vectors (or
cutting tip width for downward cuts) and target depth of the cut,
the material to be cut, the direction, hold off and number of
vectors comprising the sweep.
[0096] Next, in a step 1004, a cutting sequence is performed.
Depending on the particular circumstances, this step may involve
multiple cutting sequences. The cutting sequences include the
sequences discussed above in connection with FIGS. 5-9B.
[0097] The next step shown in FIG. 10 is a sweep operation in a
step 308. This step has been discussed briefly in connection with
FIG. 3 and will be described with additional detail below. Briefly,
the region is swept clean of debris produced during the cut pass.
In an embodiment of the invention where recess cutting is being
performed, the debris is swept out of the recess. The surrounding
surface area about the recess can also be swept clear of
debris.
[0098] The step of taking measurement(s) (step 310) will be
discussed in more detail in connection with the handling of
distance measurements. The purpose of taking the measurements is
two-fold: First, the measurements determine the stop point for
terminating the nanomachining operation. Second, the measurement
can be used to adjust the cutting parameters prior to a subsequent
iteration of cutting sequences.
[0099] If the measurements made in step 310 indicate the need for
another iteration of cutting, then the cutting parameters can be
adjusted in a step 1006, in preparation for the next cutting
sequence. In accordance with embodiments of the invention, the
cutting parameters are adjusted based on various factors such as
the current cut parameter settings, measurements of the current cut
operation, type of material of the surface being nanomachined,
expected typed of material being nanomachined, shape of the tip,
constituent material of the tip, and so on. Measurements made of
the recently completed cut operation can provide information about
the removal rate of the material being nanomachined; for example,
by comparing against the previously determined measurements.
Information about the material being cut informs the system as to
the expected rate of material removal. Information about the
structure and material composition of the workpiece informs the
system what material it can expect to encounter after nanomachining
for a certain distance.
[0100] It can be appreciated that these and other factors can be
considered in various ways which can then be fed into
decision-making processes to adjust the cutting parameters before
making the next cutting sequence. For example, circumstances might
call for backing off the feed for the next cut, or perhaps
increasing the feed force. The number of cut passes may need to be
increased or decreased depending on the results of the recently
completed cut. The angle of the tool-tip may need to be adjusted.
The speed of the cut pass may need to be increased or decreased. It
can be seen that
[0101] FIGS. 12A-12C and 13 show the procedure for making distance
measurements in accordance with embodiments of the present
invention that are suitable for nanomachining operations. Distance
measurements are typically used to gauge the progression of the
nanomachining process. Measurements are used to verify the
structure being nanomachined and to indicate when the nanomachining
process is complete. Typically, there will be two categories of
measurements: Z-direction measurements are appropriate for vertical
measurements. XY-direction measurements are appropriate for lateral
measurements.
[0102] Generally, a reference position is selected against which
distance measurements about a region to be nanomachined are made.
For example, in forming a recess, it is important to be able to
measure the depth of the recess as the nanomachining operation
progresses, in order to determine when the recess has reached the
desired depth. In accordance with embodiments of the invention, a
reference position is selected. An initial distance metric is
determined, indicative of the distance between the reference
position and the region. A set of cut passes is performed on the
region, creating a modified region. A check is made by determining
an intermediate distance metric and comparing that against the
initial distance metric, and based on the outcome of the comparison
a decision is made whether to continue or to stop the nanomachining
operation.
[0103] FIGS. 12A-12C are diagrammatic figures showing highly
exaggerated features of micron- and submicron-scaled elements to
illustrate the processing of Z-direction measurements in accordance
with a particular embodiment of the invention. FIG. 12A shows a
region 1212 to be nanomachined. In a step 1302, one or more
reference positions 1232, 1234 are selected. The reference
positions are outside the bounds of the region 1212, located
somewhere on the workpiece. As can be seen in FIGS. 12A and 12B,
the reference position is not limited to a location directly on the
surface 1202 of the workpiece 1200. A reference position can be on
a structure 1242, so long as the location is sufficiently far from
the region to be nanomachined 1212 as to be free of debris. As will
become clear, the presence of debris at a reference position could
adversely affect that position for measurement purposes.
Consequently, the reference positions are sufficiently spaced apart
from the area of the region to be nanomachined so that debris
produced during the nanomachining operation will not change the
topography of the reference positions. Multiple reference positions
can be selected to increase the confidence of the height
determination, though in principle only one reference is
sufficient.
[0104] Next, in a step 1304 one or more checkpoint locations 1224
are selected. The checkpoint locations are used to compute the
Z-direction location of the surface of the region being
nanomachined. FIG. 12A shows the checkpoints 1224 to be within an
area bounded by the region to be nanomachined 1212. In accordance
with an embodiment of the invention, an imaginary maximal shape
1222 contained within the region 1212 is superimposed over the
region. The checkpoints are determined by imposing a 3.times.3 grid
within the shape 1222 where the cross-points of the grid constitute
the checkpoint locations. It is noted that shape 1222, of course,
is not limited to a rectilinear shape as shown in the figure. Other
geometric shapes might be more appropriate, depending on the object
of the nanomachining operation. Also, a grid pattern is not
necessary as a basis for selecting the checkpoint locations. The
idea is to select one or more checkpoints that would serve as an
accurate measurement of the location of the surface during a
nanomachining operation. In fact, any method for locating
checkpoints within the region to be nanomachined would be consonant
with the teachings of the present invention.
[0105] In step 306, an initial distance metric is determined. In
accordance with this particular embodiment of the invention, one
such metric is determined for each reference position. Thus for
each reference position 1232, 1234, the following is performed:
[0106] 1. A Z-direction distance (e.g., D.sub.0) is determined
between each checkpoint location 1224 and the reference position
(e.g., 1234). The distance is obtained by locating the scanning
probe at the reference position (e.g., 1234). This establishes a
Z-coordinate reference position for the scanning probe. The
scanning probe is then translated to the X-Y coordinate of a first
checkpoint 1224 and then lowered until the surface at that X-Y
coordinate is detected. The amount of lowering represents the
Z-direction distance between the reference position and that
checkpoint location. The scanning probe is then restored to the
Z-coordinate reference position and translated to the X-Y
coordinate of the second checkpoint location. The probe is again
lowered until the surface below that X-Y coordinate is detected.
This determines the Z-direction distance of the second checkpoint
location. The process is repeated for all of the checkpoint
locations. The result is a set of nine distance values. [0107] 2.
The nine distance values are then averaged to arrive at an initial
distance metric for the reference position. [0108] 3. This is
repeated for the other reference positions.
[0109] Each distance metric is a composite value representative of
the height of the surface of the region to be nanomachined 1212
relative to a reference position (1232, 1234) on the workpiece
1200.
[0110] Next, a cut operation (cutting sequence) is performed (step
306) which is followed by a sweep operation (step 308). A cut
operation comprises one or more cut passes. The cut operation
produces a "modified" region 1212 in that the region now has a new
surface that has been exposed by the cut. It may be desirable to
measure the distance of the surface in the modified region. In the
case of recess formation operation, the distance of interest is the
Z-direction distance. The sweep operation (step 308) clears debris
from the surface of the new region prior to making the measurement.
Sweep processing will be discussed in more detail below.
[0111] With reference to FIG. 12C, the cut operation produces a
modified region 1212', exposing a new surface 1202'. The height of
the newly exposed surface can be measured to ascertain the progress
of the nanomachining operation, and as discussed above can be used
to inform the feedback loop for changing the cutting parameters for
the next pass of cuts.
[0112] In step 1310, an intermediate distance metric is determined.
In this particular embodiment of the invention, one such metric is
determined relative to each of the reference positions (1232,
1234), in a manner as discussed above: [0113] 1. A Z-direction
distance (e.g., D.sub.1, D.sub.2) is determined between each
checkpoint location 1224 and the reference position (1232, 1234).
The distance is obtained by locating the scanning probe at the
reference position. This establishes a Z-coordinate reference
position for the scanning probe. The scanning probe is then
translated to the X-Y coordinate of a checkpoint 1224 and then
lowered until the newly exposed surface 1202' of the modified
region 1212' at that X-Y coordinate is detected. The amount of
lowering represents the Z-direction distance (e.g., D.sub.1)
between the reference position (e.g., 1232) and the level of the
newly exposed surface. The scanning probe is then restored to the
Z-coordinate reference position and translated to the X-Y
coordinate of the second checkpoint location. The probe is lowered
until the surface below that X-Y coordinate is detected, to
determine the Z-direction distance of the second checkpoint
location. The process is repeated for all of the checkpoint
locations. The result is a set of nine distance values. [0114] 2.
The nine distance values are then averaged to arrive at an
intermediate distance metric for the reference position. [0115] 3.
This is repeated for the other reference positions.
[0116] Based on the initial distance metrics and the intermediate
distance metrics, a decision (step 1313) can be made whether to
continue with a subsequent cutting sequence or not. For example,
the difference between the initial and intermediate metrics
represents the height of the nanomachined feature (in this case a
recess). Thus, a difference between the initial and intermediate
metrics for each reference position can be computed. A stop
condition can arise if both differences are within a predefined
tolerance of a target depth. It can be appreciated that other
algorithms for asserting a stop condition might be appropriate. For
example, one might simply specify that a certain number of cut
passes be performed in the subsequent cutting sequence.
[0117] Other information can be gleaned from the individual
distance values for each checkpoint location 1224 obtained above in
step (1), in addition to taking an average. The individual values
can be analyzed to ascertain the flatness of the cut operation,
such as the standard deviation, or standard deviation in four
directions from the center of the cut, etc. For example, variations
in the downfeed might produce a less than satisfactory cut where
the distance values along different parts of the region being
nanomachined vary beyond an acceptable tolerance. Knowledge of the
individual values can be used to set the cut parameters
appropriately for the next cutting sequence, perhaps making
additional cut passes at some areas of the region but not others.
This feedback can be used to produce flat surfaces and, in the
general case, surfaces having specific topological features.
[0118] It can be appreciated that the foregoing can be readily
extended to produce cuts in the X-direction and in the Y-direction.
More generally, arbitrary surface features can be produced by the
appropriate selection of checkpoint locations and reference
positions.
[0119] A discussion of so-called "sweep" operations will now be
made in connection with the illustrative examples shown in FIGS.
14A-19. Recall in FIG. 3 that a sweep operation (step 308) is
performed after each cutting sequence, during a nanomachining
procedure. FIGS. 14A-14 and 15A-15D show various patterns of sweep
that can be performed. A sweep operation includes positioning the
scanning probe at or relative to a starting location. An
appropriate downfeed is applied so that the tip is either touching
the surface to be swept or spaced apart from the surface by a small
distance. The probe is then translated in a direction away from the
start position, along a scan vector. Any material lying in the path
of the scan vector is "swept" along by the tip.
[0120] FIGS. 14A-14C illustrate some patterns. In FIG. 14A, a start
position 1402 for the sweep is identified. In this case, the start
position is identified by an X-Y coordinate pair. A scanning probe
(not shown) is positioned at the start position, adjusted with an
appropriate downfeed, and translated along a scan vector 1422. The
probe is then returned to the start position 1402, and translated
along a second scan vector. Since the probe is returned to the same
X-Y starting coordinates, the resulting sweep pattern is a radial
pattern as shown in FIG. 14A.
[0121] FIG. 14B shows a variation of the radial sweep pattern.
Rather than returning the scanning probe to X-Y starting coordinate
1402, the probe is probe is positioned to a location relative to
starting coordinate, more particularly, along a scan start line
1412 passing through the start position. Scan vectors 1424 can be
made in a direction that is orthogonal to the scan start line.
Alternatively, radially-directed scan vectors 1426 can be made,
each vector departing from the scan start line at angles other than
90.degree. relative to the line.
[0122] FIG. 14C shows another variation of the radial sweep
pattern. Here, the starting "position" comprises a set of locations
about the periphery of a region 1404 being nanomachined. The
scanning probe is positioned at a first location about the
periphery of the region 1404 and subsequently translated along a
scan vector 1428 directed away from the region.
[0123] FIGS. 15A-15D illustrate a sweep sequence according to an
embodiment of the present invention. Generally, the sweep pattern
is performed relative to an origin location 1502. In FIG. 15A, a
first series of sweep scans (indicated by the solid arrows) is
performed. The start position for each scan lies along a scan start
line 1506 passing through the location 1502. A scanning probe (not
shown) is positioned at a first position along the scan start line.
The sweep scan is performed along a scan vector that is
perpendicular to the line 1506. This is repeated for the first
series of sweeps.
[0124] Next, in FIG. 15B, a second series of sweep scans is shown.
The start positions lie along a scan start line 1504 passing
through the location 1502. The scanning probe is translated along
vectors perpendicular to the line 1504 shown by the solid arrows.
FIGS. 15C and 15D show third and fourth scans respectively,
performed in similar fashion. It can be appreciated that the vector
directions need not be perpendicular. In the most general case, the
vectors can be in any direction. However, "sweeping" of debris is
going to be effective with some patterns more than others.
[0125] FIG. 16 shows a generalization of the sweep pattern shown in
FIG. 15A-15D. Here, the sweep start positions lie along scan start
lines 1612, 1614, and 1616 which pass through an origin location
1602. As can be seen, any number of scan start lines can used.
Moreover, there is no requirement that the lines be orthogonal;
each line can be rotated by any angle relative to another line. The
specific number of start scan lines and their rotations will be
dependent on factors specific to the particular nanomachining
operation.
[0126] FIG. 17 shows various scan vectors that can be used with the
sweep operation. First, is a linear vector which proceeds from a
start position 1702 along a straight-line path. Second, is a
zig-zag vector having a sawtooth-style pattern. A third vector is a
curvilinear (arcuate) path. From these example vector shapes, it
can be appreciated that vectors other than straight line vectors
are possible and perhaps preferable given the right
circumstances.
[0127] It was mentioned above that sweep processing is just another
form of cut operation, albeit a somewhat specialized form of cut
operation. Referring now to FIGS. 18 through 20, additional kinds
of sweep-cut operations will now be described.
[0128] The sweep-cut operation shown in FIG. 18 involves an initial
data collection step. An initial scan is made to collect
information about the topology of the surface. The topological
information can include the X-Y coordinates of the translation
vectors that direct the scan, and information indicative of the
location of the various surface structures found during the scan of
the surface of the workpiece, typically X-Y coordinates, and
corresponding Z (height/depth) values. After the data collection
has been performed, the workpiece can then be subjected to various
processing steps. For example, some nanomachining operations may be
performed, or other processing. This subsequent processing may
produce surface artifacts which alter the topology of the
workpiece. The artifacts might be undesirable and if so should be
removed.
[0129] A subsequent sweep-scan is then performed. The scanning
probe is translated across the surface of the workpiece in the X-Y
direction according to the original translation vectors and in the
Z-direction. The X-Y translations and the Z translations of the
scanning probe are compared with the corresponding information
contained in the previously collected information. When an
unexpected positive feature, e.g., a protuberance from a surface, a
lump, a bump, etc., is encountered, the scanning probe can be
operated to perform a cut operation to remove the unexpected
feature.
[0130] FIG. 18 illustrates this scenario. During the data
collection step, topological information about the surface 1802 of
a workpiece 1800 is collected. The data contains information
indicative of the presence of surface feature 1812. Next, suppose
some process is performed on the workpiece which results in an
artifact that manifests itself as surface feature 1822. A
subsequent pass is performed wherein the tip is translated along a
set of vectors that correspond to the original surface, plus or
minus a certain offset amount in the Z direction (which may be 0).
During this pass, any debris or other element not originally on the
surface will be removed. This operation is not a scan operation in
the conventional sense where data is collected, since there is no
data collection taking place. In order to distinguish the foregoing
operation from a conventional data collecting scan, the phrases
"sweep-scan" and "sweep-cut" have been adopted.
[0131] Another sweep-cut operation, illustrated in FIG. 19, does
not rely on data collected by an initial surface scan. Here, the
surface scan is performed at the same time one or more cutting
operations are performed. A cut operation is made when the Z
translation exceeds a predetermined threshold value. Thus for
structures above this predetermined value, the tip begins
nanomachining and scanning (servoing up or down is turned off for a
short distance, which is a parameter to be set for this
modality).
[0132] FIG. 19 illustrates this so-called "threshold" sweep-cut
process. The process begins by establishing a baseline Z (height),
Z.sub.B. Typically this is the Z-value at a surface 1902 of the
workpiece 1900. Next, a scan is initiated along a scan path 1932.
As the scanning probe (not shown) is translated in the Z-direction
by the servo system as it detects various elements on the surface,
its change in the Z direction (.DELTA.Z) is determined and compared
against a threshold value .DELTA.Z.sub.T. If the threshold value is
not exceeded then the scanning progresses. This is the case with
the feature 1914, where the .DELTA.Z of the feature is less than
the threshold value. When a feature is encountered which drives the
scanning probe to a .DELTA.Z that exceeds .DELTA.Z.sub.T, then that
feature is cut. FIG. 19 shows this with feature 1912. Scanning
continues in this manner until completion.
[0133] FIG. 20 is a high level flowchart outlining the general
sequence of cut and sweep operations for manipulating surface
features at the micron and sub-micron level according to an
embodiment of the present invention. First, a location is selected
in step 2002 from which an amount of material is to be obtained.
The scanning probe is translated to the location. In step 2004, an
appropriate cut operation is selected to "scrape off" an amount of
material from the surface or from a structure. This creates a pile
of material in the area of the first location. Next, in step 2006,
the material is swept to a second location by any of the
aforementioned sweep techniques. An amount of energy, say heat, is
then applied (step 2008). This can initiate a physical change to
the amount of material just moved, causing it to coalesce with the
material in the area of the second location.
[0134] In an alternative embodiment of the invention, a workpiece
can be inspected to identify areas of defects. A suitable
subsequent processing operation can be employed to deposit or
otherwise form "lumps" of appropriate material proximate the areas
of defects. These lumps of material act as sources of material for
repairing certain types of defects. By applying the sequence
outlined in FIG. 20, the deposited material can be scraped off and
pushed around to the defect areas for repair.
[0135] In one example, a laser Mask repair device is used to
deposit an area of chrome on a chrome mask missing some features.
It can happen that the deposit is larger and less precise than the
desired feature. Processing in accordance with embodiments of the
present invention can be used to cut and trim the feature to size.
In another example, suppose chrome debris is produced by partially
nanomachining an area adjacent to the target area needing material
added. The debris from the machining can then be swept up into the
area needing material to a desired height and depth. Trim and
cutting may then be performed to refine the swept up shape and the
whole object baked at an elevated temperature either by exposure in
the nanomachining tool or in a separate heating arrangement such as
an external positionable laser spot source, or a conventional
furnace. This thermal processing integrates the chrome (or other
materials like quartz, silicon, an oxide of silicon (e.g., SiO,
SiO.sub.2), silicon nitride, carbon, and so on) debris into the
target structure.
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