U.S. patent application number 12/475837 was filed with the patent office on 2009-10-15 for thermal control of deposition in dip pen nanolithography.
Invention is credited to William P. King, Paul E. Sheehan, Lloyd J. Whitman.
Application Number | 20090255465 12/475837 |
Document ID | / |
Family ID | 35909933 |
Filed Date | 2009-10-15 |
United States Patent
Application |
20090255465 |
Kind Code |
A1 |
Sheehan; Paul E. ; et
al. |
October 15, 2009 |
THERMAL CONTROL OF DEPOSITION IN DIP PEN NANOLITHOGRAPHY
Abstract
The present invention describes an apparatus for nanolithography
and a process for thermally controlling the deposition of a solid
organic "ink" from the tip of an atomic force microscope to a
substrate. The invention may be used to turn deposition of the ink
to the substrate on or off by either raising its temperature above
or lowing its temperature below the ink's melting temperature. This
process may be useful as it allows ink deposition to be turned on
and off and the deposition rate to change without the tip breaking
contact with the substrate. The same tip can then be used for
imaging purposes without fear of contamination. This invention can
allow ink to be deposited in a vacuum enclosure, and can also allow
for greater spatial resolution as the inks used have lower surface
mobilities once cooled than those used in other nanolithography
methods.
Inventors: |
Sheehan; Paul E.;
(Springfield, VA) ; Whitman; Lloyd J.;
(Alexandria, VA) ; King; William P.; (Atlanta,
GA) |
Correspondence
Address: |
NAVAL RESEARCH LABORATORY;ASSOCIATE COUNSEL (PATENTS)
CODE 1008.2, 4555 OVERLOOK AVENUE, S.W.
WASHINGTON
DC
20375-5320
US
|
Family ID: |
35909933 |
Appl. No.: |
12/475837 |
Filed: |
June 1, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10956596 |
Sep 29, 2004 |
7541062 |
|
|
12475837 |
|
|
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|
60603508 |
Aug 20, 2004 |
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Current U.S.
Class: |
118/667 |
Current CPC
Class: |
G01Q 80/00 20130101;
Y10S 977/857 20130101; B82Y 40/00 20130101; Y10S 977/849 20130101;
B82Y 10/00 20130101; G03F 7/0002 20130101; Y10S 977/855 20130101;
Y10S 977/851 20130101 |
Class at
Publication: |
118/667 |
International
Class: |
B05C 11/00 20060101
B05C011/00 |
Claims
1. A thermal control apparatus comprising: a scanning probe
microscope tip capable of being coated with at least one patterning
compound; and a temperature control device, operatively connected
to the tip, wherein the temperature control device alters the
temperature of the patterning compound more than the average
temperature of the environment of the tip.
2. The apparatus of claim 1, wherein the temperature control device
causes the patterning compound to transition between immobile and
mobile
3. The apparatus of claim 1, wherein the tip is in a gas-filled
chamber; and wherein the temperature control device alters the
temperature of the patterning compound more than the average
temperature of the gas in the chamber.
4. The apparatus of claim 1, wherein the tip is exposed to the
ambient atmosphere; and wherein the temperature control device
alters the temperature of the patterning compound more than the
average temperature of the ambient atmosphere.
5. The apparatus of claim 1, wherein the temperature control device
alters the temperature of the patterning compound more than the
temperature of a substrate onto which the patterning compound may
be deposited.
6. The apparatus of claim 1, wherein the temperature control device
alters the temperature of a substrate in contact with the
patterning compound.
7. The apparatus of claim 1, wherein the patterning compound is
octadecylphosphonic acid.
8. The apparatus of claim 1, wherein the patterning compound is
10-undecenyl tricholorosilane.
9. The apparatus of claim 1, wherein the tip is formed on a distal
end of a cantilever and the temperature control device is a
piezoresistive element integrated into the cantilever.
10. The apparatus of claim 1, wherein the tip is formed on a distal
end of a cantilever and the temperature control device is a
resistive element integrated into the cantilever.
11. The apparatus of claim 1, wherein the temperature control
device is a remote electromagnetic energy source.
12. The apparatus of claim 11, wherein the remote electromagnetic
energy source is attuned to an absorption band of the patterning
compound.
13. The apparatus of claim 11, wherein the remote electromagnetic
energy source is attuned to the absorption band of the tip.
14. The apparatus of claim 11, wherein the remote electromagnetic
energy source is attuned to the absorption band of an absorber that
is operatively connected to the tip.
15. The apparatus of claim 1, wherein the tip is formed on a distal
end of a cantilever and the temperature control device is a cooling
element built into the cantilever.
16. The apparatus of claim 15, wherein the cooling element utilizes
the Peltier effect.
17. The apparatus of claim 15 wherein the cooling element is a
thermionic cooler.
Description
[0001] This application is a divisional application of U.S. Pat.
No. 7,541,026, which claims the benefit of U.S. Provisional
Application No. 60/603,508, filed on Aug. 18, 2004.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to an apparatus and method for
thermally controlling deposition in Dip-Pen Nanolithography, or DPN
(Dip-Pen Nanolithography, and DPN are registered trademarks of
Nanoink).
[0004] 2. Description of the Prior Art
[0005] The ability to create ever smaller structures and patterns
is the key to producing smaller and faster electronics. Some of the
newest technologies allow the creation of structures on the
nanometer, or 10.sup.-9 meter, scale. One of these technologies is
DPN, which is described in U.S. Pat. No. 6,635,311 and is
incorporated herein by reference (all patent and publication
references included in this specification hereinafter are also
incorporated by reference). DPN is a method for depositing
molecules onto a surface with the tip of an atomic force microscope
(AFM). The method is very much like dipping a pen into an inkwell
and then using it to write except DPN is on a much smaller scale.
In DPN, the AFM tip, or "pen," is dipped or coated with the desired
molecule or "ink" and then brought into contact with the surface,
onto which the molecules diffuse. Lines or patterns can be created
by moving the tip over the surface in much the same way one would
move a pen over paper.
[0006] With this technology, however come some limitations. When
writing with a pen on paper one must lift the pen to stop writing.
The same is true for DPN; to stop deposition the AFM tip must break
contact with the surface. Unfortunately, this can often lead to a
loss of registry between the tip and the surface. Another drawback
to DPN is that a coated tip cannot be used for imaging purposes
while in contact mode without causing contamination--deposition of
unwanted ink. Therefore, a need exists for a device that can turn
deposition on or off while the tip maintains contact with the
surface.
[0007] DPN is further limited in that besides changing the ink, the
tip, or the tip's speed, there is little control over the
deposition rate once a molecule has been coated onto the tip. The
typical ink molecules utilized in DPN have to be sufficiently
mobile to transfer from the AFM tip to the surface under ambient
conditions. This ambient temperature mobility requirement limits
the types of inks that may be used in DPN and results in "bleeding"
or spreading out of the ink once it is deposited onto a surface,
which in turn limits the precision of structures that can be
created with DPN. Because of this necessary volatility of the inks
used in DPN, the process cannot be performed in a vacuum; the ink
would evaporate too quickly and contaminate the system. The need
exists for a better method that may be performed in a vacuum and
that allows for the use of a greater variety of inks. A better
method is also needed to control the rate of deposition and to
limit the excess diffusion of molecules over the surface after
deposition.
[0008] Information relevant to attempts to address these problems
can be found in U.S. Pat. Nos. 6,737,646 and 6,642,129. However,
each one of these references suffers from one or more of the
following disadvantages: inability to image in contact mode without
contaminating, inability to turn deposition on or off, and
inability to control excess diffusion of ink once deposited. For
the foregoing reasons, there is a need for a process of turning ink
deposition on and off in DPN without breaking contact between the
tip and the surface. Likewise, there is a need for an apparatus
that can control the ink deposition rate and limit the amount of
excess ink diffusion or contamination over the surface.
SUMMARY OF THE INVENTION
[0009] This invention is directed to a thermal control apparatus, a
deposition control method, and a multiple patterning compounds
deposition method. A thermal control apparatus that has features of
this invention comprises a temperature control device that is
operatively connected to a scanning probe microscope tip. The tip
is capable of being coated with at least one patterning compound,
or ink, and the temperature control device alters the temperature
of the patterning compound more than the average temperature of the
environment of the tip.
[0010] Another aspect of this invention provides a deposition
control method comprising providing a surface or substrate and a
scanning probe microscope tip coated with at least one patterning
compound. When the patterning compound is in contact with the
substrate, the temperature of the patterning compound is altered so
that it becomes mobile or immobile. In its mobile phase, the
compound can be deposited to the substrate in a desired pattern.
The temperature of the patterning compound is altered more than the
average temperature of the environment of the tip.
[0011] Another aspect of the present invention provides a method
for depositing multiple patterning compounds. The method comprises
providing a substrate and a scanning probe microscope tip coated
with at least two patterning compounds in order of their different
melting temperatures, e.g. coating the tip with the compound with
the highest melting temperature first. The temperature of the
patterning compounds may be altered to allow only those patterning
compounds whose immobile-to-mobile temperatures have been reached
or exceeded to be deposited onto a substrate in contact with the
patterning compound.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] A more complete appreciation of the invention will be
readily obtained by reference to the following Description of the
Example Embodiments and the accompanying drawings.
[0013] FIG. 1 schematically illustrates an apparatus of the
invention.
[0014] FIG. 2 shows ellipsometry data regarding the deposition of
OPA onto an AFM tip.
[0015] FIG. 3 shows a micrograph of OPA written onto mica using
tDPN at different temperatures.
[0016] FIG. 4 shows a friction image of the sample shown in FIG.
3.
[0017] FIG. 5 shows three lines written by tDPN, two of which were
made after the heating was turned off.
[0018] FIG. 6 shows a micrograph of a line of PDDT written by
tDPN.
[0019] FIG. 7 shows a micrograph of lines of indium written by
tDPN
DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS
[0020] Although it has been widely assumed that DPN requires a
water meniscus to transfer ink from an AFM tip to a surface, it has
been shown that transfer can occur under xeric conditions, a method
called "dry deposition." Recent studies of dry deposition have led
to a number of insights into how DPN can be extended beyond "wet"
inks. For example, deposition should be possible at high
temperatures (i.e., above the boiling point of water) and, thus,
temperature could be used to control deposition.
[0021] Thermal DPN (tDPN) enhances traditional DPN in many ways.
First, it can allow exquisite control over writing. Deposition may
be turned on or off and the deposition rate changed without
breaking contact with the surface. Secondly, the inks used have can
have lower surface mobilities once cooled and so are able to
achieve higher spatial resolution. Thirdly, imaging with a cool tip
may not contaminate the surface. This allows in situ confirmation
of the deposited pattern without fear of contamination. Finally,
tDPN expands the range of useable inks.
[0022] This method may utilize patterning compounds with high
melting temperatures. Patterning compounds with high melting
temperatures generally have low vapor pressures and diffuse more
slowly than compounds with low melting temperatures. This
characteristic helps limit the amount of bleeding and makes it
possible to perform the method in a vacuum enclosure.
[0023] The present invention is primarily directed to thermally
controlling the deposition onto a substrate of a patterning
compound, coated onto a scanning probe microscope tip. Thermal
control allows for deposition independent of time and for
deposition to be stopped. This invention may utilize scanning probe
microscope tips used in atomic scale imaging such as atomic force
microscope (AFM) tips, near field scanning optical microscope tips,
scanning tunneling microscope tips, and any other similar devices
with a tip that is capable of being coated with a patterning
compound and is controllable in three dimensions with respect to a
substrate. The invention also has a means for altering the
temperature of the patterning compound on the tip sufficiently to
allow the patterning compound to transition from immobile to
mobile. Once mobile, the patterning compound is free to transfer
from the tip to the contact area with the substrate. In its
immobile phase, no compound is deposited. The exact order of the
steps taken in this method is not critical, as long as they result
in a deposit of patterning compound on the substrate. For example,
the patterning compound may be contacted to the substrate before or
after altering its temperature. A desired pattern may be created by
moving the substrate with respect to the tip. A single tip may be
used in tDPN or a plurality of parallel tips, each coated with a
desired patterning compound may be used. If multiple tips are used,
one or more tips may be coated with different patterning
compounds.
[0024] The temperature of the patterning compound is altered more
than the temperature of the environment. This can create sharp
patterns or features on the nanometer scale. The "environment" of
the tip refers to the greater volume of gases or liquid around the
tip, but not merely the immediately adjacent gases or liquid. For
example, if the tip is in a closed, gas-filled chamber, the
environment refers to the entire bulk of the gas in the chamber. If
the tip is exposed to the atmosphere, the environment refers to the
ambient air. When the tip is in a vacuum, there is considered to be
no change to the average temperature of the environment. The
temperature of the patterning compound is altered more than that of
the environment to allow for fast cooling of the patterning
compound to stop the writing.
[0025] By changing the temperature of the ink on the tip this
version of the present invention can be used to start or stop ink
deposition without the tip having to break contact with the
surface. One example embodiment of tDPN utilizes patterning
compounds with high melting temperatures, above 25.degree. C.,
which generally diffuse more slowly than compounds with low melting
temperatures, equal to or less than 25.degree. C. Low surface
diffusivity limits the spread or "bleeding" over the substrate. The
lower the diffusivity, the tighter the pattern created with tDPN.
In basic Dip-Pen Nanolithography, without thermal control, low
surface diffusivity is undesirable since it also means lower
diffusivity on the tip as well, preventing the patterning compound
from flowing. In tDPN, diffusivity on the tip is controlled by
heating the patterning compound, such that good flow is obtained
with no bleeding. If the bulk of the air were heated to heat the
patterning compound on the tip, the air would also heat the
substrate, which may cause the patterning compound to bleed over
the substrate. Thus the temperature of the patterning compound may
be altered more than that of the substrate. Heating the bulk of the
air may also cause slower cooling of the ink on the tip, resulting
in slow turn-off of writing.
[0026] However, if greater surface mobility of the patterning
compound over the substrate is desired, the following example
allows for that. This example of an embodiment of tDPN provides for
heating or cooling the substrate as a means of controlling the
temperature, and therefore, the deposition of the patterning
compound when the tip is in contact with the substrate.
[0027] Scanning probe microscope tips are commonly formed on a
distal end of a cantilever. The patterning compound may be heated
when it is on the cantilever tip, the cantilever beam or both. When
the patterning compound is heated to or above its melting
temperature (T.sub.m), the melted patterning compound is free to
flow onto the substrate. This method not only allows the deposition
of molecules that are not mobile at room temperature, or about
25.degree. C., but also allows control of the rate at which they
are deposited. The greater the temperature above T.sub.m, the
greater is the deposition rate. When the patterning compound is not
heated or heated to a temperature less than T.sub.m, no deposition
may occur.
[0028] One embodiment of tDPN is the use of AFM cantilevers with
integrated resistive heaters to deposit an ink that is solid at
25.degree. C. The cantilever may be made of many materials such as
plastic, metal, ceramic, or a combination of the above. If the
resistive heating occurs away from the tip, that cantilever may be
designed to provide that enough heat flows into the patterning
compound on the tip to allow for deposition. The cantilever tip may
be heated at a constant heating power, or at a time-varying heating
power, or in short pulses of heating power. Desired changes in the
heating and cooling constants of the cantilever tip may be altered
by changing the design of the cantilever. One version of the tDPN
apparatus utilizes a silicon AFM cantilever produced for
thermomechanical data storage by the IBM Zurich Research Lab. This
cantilever was fabricated with a standard silicon-on-oxide
cantilever fabrication process, and has a tip on its distal end
with a radius of curvature of about 100 nanometers. The cantilever
has a heating time of about 1 to 20 microseconds and a cooling time
in the range of 1 to 50 microseconds. The cantilever can approach
700.degree. C. in short pulses and, because the resistive heating
element is also a temperature sensor, calibration of the cantilever
temperature response is possible to 1.degree. C.
[0029] FIG. 1 schematically illustrates the apparatus of the
invention. Tip 10 contains a coating 20, and is placed in contact
with a substrate 30. In this embodiment, the tip 10 is formed on a
cantilever 40. The drawing is not to scale, and the tip is actually
much smaller relative to the cantilever than depicted. A heating
element 50 is attached to the cantilever 40 for heating the tip 10,
by way of a resistive element 60. The arrows indicate current
passing through the cantilever 40 and tip 10, heating the tip 10,
and causing deposition 70 of patterning compound on the
substrate.
[0030] The cantilever can be coated with octadecylphosphonic acid
(OPA), which is a versatile molecule that self-assembles into
monolayers on mica, metals such as stainless steel and aluminum,
and metal oxides such as TiO.sub.2 and Al.sub.2O.sub.3. OPA's
T.sub.m of about 99.degree. C. is well suited for tDPN as its
T.sub.m is well above 25.degree. C. and within the thermal range of
the integrated resistive heater. One way to coat OPA to the tip is
by evaporation. This may be accomplished by first heating a
scintillation vial containing about 60 mg of OPA on a hot plate set
at 110.degree. C. The cap of the scintillation vial may then be
replaced for about 30 minutes with a tip holder maintained at about
35.degree. C. From the ellipsometry data shown in FIG. 2, it is
known that this procedure deposits the mass equivalent of two
complete monolayers of OPA onto the tip.
[0031] Another suitable patterning compound is indium, which could
be used for nanoscale soldering. The method could also pattern
functional organic molecules, allowing for direct write
manufacturing. The deposited compound can form a template to direct
or nucleate the growth of nanostructures.
[0032] Many different patterning compounds that melt before
degrading such as polymers, inorganic polymers, low T.sub.m metal
eutectics, or organic molecules may be used in tDPN. Although the
dependence on T.sub.m has been noted above, any molecule that
undergoes a transition from immobile to mobile as a function of
temperature may be used. For instance, a transition from a solid to
a liquid or liquid crystal may be sufficient for deposition, or
from highly viscous liquid or glass to less viscous liquid. The
substrate may be of any size, shape, or material that may be
modified by a patterning compound to provide a stable surface
structure. One example embodiment of tDPN utilizes freshly-cleaved
mica as a substrate.
[0033] Besides integrated resistive heaters, any means that can
sufficiently alter the temperature of the patterning compound on
the tip to allow the compound to transition from immobile to mobile
may be used for tDPN. One example is commercially available or
custom fabricated piezoresistive cantilevers, which have an
internal electrically resistive element that will heat if biased at
a sufficiently high voltage. Another example would be a remote
electromagnetic energy source that could be attuned to an
absorption band of the patterning compound, the tip onto which the
compound is coated, or an absorber, which could transfer the
electromagnetic energy it receives into the patterning compound on
the tip. An absorber in the example above could be a
micro-fabricated antenna on the cantilever, or any an absorbent
material integrated into the tip or cantilever. Also, used in
conjunction with patterning compounds with melting temperatures
equal to or below 25.degree. C., cooling elements may be used to
alter the temperature of the patterning compound. The cooling
element would keep the patterning compound frozen or immobile until
deposition onto the substrate is desired. Such cooling elements
could be a thermionic cooler or utilize the Peltier effect. These
cooling elements may be integrated directly into the cantilever to
provide for deposition of patterning compounds that would be too
volatile to deposit with basic DPN. Using a cooling element, a
volatile patterning compound may be immobilized on the tip until
deposition is desired. Once the temperature of the patterning
compound reaches or exceeds its T.sub.m, deposition occurs and
reaction with the substrate prevents subsequent evaporation of the
patterning compound.
[0034] An example embodiment of tDPN may be utilized to create
three-dimensional structures. Because tDPN allows a patterning
compound's fluidity to be enhanced mostly on the cantilever and
tip, a patterning compound may be used that solidifies upon contact
with the substrate. Thus, structures could be built up slowly to a
desired thickness either by scanning and depositing several times
over the same area or by holding the tip stationary in the plane of
the sample and slowly raising it as patterning compound is
deposited.
[0035] Another example embodiment of tDPN provides for depositing a
patterning compound in a vacuum enclosure. Because of the necessary
volatility of the patterning compounds used in basic DPN, it is not
possible to place the coated cantilever in ultra-high vacuum (UHV).
The patterning compound would evaporate too quickly and would
contaminate the system. An embodiment of tDPN obviates this problem
by allowing the use of high T.sub.m patterning compounds, which
consequently have low vapor pressures. The lower vapor pressure
means that the patterning compound will remain on the tip long
enough to be patterned onto the surface. The temperature ramping of
the patterning compound to control deposition may therefore be used
in a vacuum enclosure. Additionally, due to the broad range of
patterning compounds that may be used in tDPN, it is also possible
to perform tDPN in a liquid-filled or gas-filled enclosure.
[0036] Another example embodiment of tDPN allows for the deposition
of multiple patterning compounds from the same tip. For instance,
if three patterning compounds (A, B, & C) were coated onto the
tip in order of their melting temperatures with C forming the first
coat on the tip and T.sub.m(A)<T.sub.m(B)<T.sub.m(C), then
just A may be deposited by keeping the working temperature below
T.sub.m(B). Similarly, just patterning compounds A and B may be
deposited at working temperatures less that T.sub.m(C). All three
may be deposited at temperatures above T.sub.m(C). The patterning
compounds must be chosen carefully to avoid solvation effects that
could lower their melting temperatures and facilitate
co-deposition. This same embodiment could be used with an array of
tips, where one or more of the tips in the array could be coated
with several different patterning compounds.
[0037] The development of tDPN opens several opportunities for
DPN-based nanofabrication. Large arrays of heater cantilevers may
be fabricated that can write more than 10.sup.6 pixels/s, and thus
reasonable write times could be achieved over wafer-scale areas.
Thermal control should allow deposition of a wide variety of solid
inks that were previously inaccessible to DPN. For instance, metals
of appropriate melting temperatures could be patterned with this
technique, creating a nanometer scale "soldering iron." Finally
because the molecules in tDPN can be solid at 25.degree. C., it
should be possible to build up multilayer multi-component patterns
to create true three-dimensional nanostructures.
[0038] Having described the invention, the following examples are
given to illustrate specific applications of the invention. These
specific examples are not intended to limit the scope of the
invention described in this application.
EXAMPLE 1
[0039] Deposition of OPA--An AFM tip, coated with OPA in the manner
described above, was rastered over four, 500 nanometer square
regions on a mica substrate at 2 Hz and 128 lines per scan, or for
a total scan time of 256 s. For each square, the temperature of the
cantilever was increased, finally exceeding OPA's melting
temperature. When the temperature of the tip was held below OPA's
T.sub.m, either at 25.degree. C. or at 57.degree. C., no patterned
squares were observed. Raising the tip temperature to 98.degree.
C., near OPA's T.sub.m, resulted in light deposition. The average
height of this area was 1.1 nm, which is slightly less than
one-half the height of a full monolayer. Robust deposition was
finally seen when the cantilever temperature was raised to
122.degree. C., creating a square pattern with a height of 2.5 nm,
indicative of a full monolayer, as shown in FIG. 3. The
corresponding friction image, shown in FIG. 4, confirms OPA
deposition. The binding of OPA to mica exposes a methyl terminal
group, which would reduce friction relative to the bare mica
surface. No change in friction was observed for the lower
cantilever temperatures. The light deposition at 98.degree. C.
reduced friction slightly, as expected, and the full monolayer
deposited at 122.degree. C. reduced friction much further.
[0040] Although deposition started instantaneously upon heating,
deposition continued for a time after the heating current was
stopped. FIG. 5 shows three lines written via tDPN where the tip
sequentially traced three vertical lines for 1 min apiece. The
cantilever was heated only for the first, upper left, line. Thus,
deposition continued for roughly 2 minutes after the cantilever
heating was stopped. Modification of ultra-thin polymer layers on a
silicon surface for data storage applications has been shown to be
highly localized near the tip and fully complete in the range of
1-10 microseconds. (King et al., Design of Atomic Force Microscope
Cantilevers for Combined Thermomechanical Writing and Thermal
Reading in Array Operation, Journal of Microelectromechanical
Systems, Vol. 11, No. 6, 2002) The present system differs from the
system presented in King et al. in that the tip is coated with the
patterning compound and in that the mica substrate has a much lower
thermal conductivity than Si. The present experiments do not
indicate whether the ink remains hot on the tip or whether the
substrate is significantly heated by the tip; although, a simple
scaling of the cooling time constants yields .about.10 microseconds
for the cantilever, .about.100 nanoseconds for the tip, .about.10
nanoseconds for the ink, and .about.10 nanoseconds for the heated
region of the substrate. Thus, it is likely that residual heat in
the substrate prolonged the writing and that deposition would cease
quickly on substrates with greater thermal conductivity, such as Si
or a metal. Careful selection of the substrate material and
engineering of the write speeds could reduce the tDPN write time
into the 100 kHz range demonstrated in the data storage
application.
[0041] Two features of FIG. 5 reveal the potential for
significantly improving this lithography method. First, the
line-width (full width at half maximum of cross section) in this
non-optimized system is only 98 nanometers across, which is
comparable to the radius of curvature of the tip used, .about.100
nanometers (from a SEM). Heated cantilevers with tips sharper than
20 nanometers may be fabricated, which can make marks in a polymer
as small as 23 nm. Advances in tip construction should therefore
allow a decrease in line-width by an order of magnitude. Second,
although the ink is presumably cooler with each subsequent line,
there is no appreciable change in line-width. The independence of
line-width on temperature suggests that the width is mainly
determined by the sharpness of the tip, not diffusion of the OPA
molecules following deposition. This aspect of tDPN is in contrast
to conventional DPN, where increasing the global temperature
increases both the deposition rate and the subsequent spreading of
the pattern caused by surface diffusion. Global heating thereby
leads to larger patterns presumably having larger halos of
contamination. Thus, local control over heating will allow fast
deposition rates and sharp features. Careful engineering of the
cantilever, tip, and substrate should allow tDPN to write features
as small as 10 nanometers. In the present invention, none of the
hallmarks of contamination were observed, such as halos around
deposited features or "fill-in" patterns following repeated imaging
with coated tips.
EXAMPLE 2
[0042] Deposition of PDDT--tDPN was used to deposit conducting
polymer between electrodes. The polymer was
poly(3-dodecylthiophene) (PDDT), a semiconducting polymer useful
for organic FETs. The tip was heated to .about.200.degree. C. under
nitrogen (to avoid oxidation). The tip was then scanned from one
electrode to the other for 2 minutes. The deposited line was 20 nm
thick and 150 nm wide and spaned an 800 nm wide gap.
EXAMPLE 3
[0043] Deposition of Indium--For the repair of nanoscale circuits
or of the photomasks used to make modem circuitry, it is important
to be able to write small, conducting wires. tDPN was used to
pattern indium, a low melting point metal and a common solder. FIG.
7 shows a series of 3 .mu.m lines written at a tip speed of 3
.mu.m/s. Each line was traversed 64 times (i.e., 32 trace/retraces)
by the depositing tip. The top two lines written at 95.degree. C.
and 135.degree. C. do not show, the faint line at bottom left was
written at 156.degree. C. which is close to the melting temperature
of the indium, 156.6.degree. C. The line at bottom right was
written at 196.degree. C., which is well above the melting
temperature of indium, and demonstrates robust deposition at this
temperature.
[0044] Obviously, many modifications and variations of the present
invention are possible in light of the above teachings. It is
therefore to be understood that the claimed invention may be
practiced otherwise than as specifically described.
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