Note: Descriptions are shown in the official language in which they were submitted.
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[0001] NANOPATTERNING METHOD AND APPARATUS
[0002] Field
Embodiments of the invention relate to nanopatterning methods which can be
used to
pattern large substrates or substrates such as films which may be sold as
rolled goods.
Other embodiments of the invention pertain to apparatus which may be used to
pattern
substrates, and which may be used to carry out method embodiments, including
the kind
described.
[0003] Background
[0004] This section describes background subject matter related to the
disclosed
embodiments of the present invention. There is no intention, either express or
implied,
that the background art discussed in this section legally constitutes prior
art.
[0005] Nanostructuring is necessary for many present applications and
industries and
for new technologies which are under development. Improvements in efficiency
can be
achieved for current applications in areas such as solar cells and LEDs, and
in next
generation data storage devices, for example and not by way of limitation.
[0006] Nanostructured substrates may be fabricated using techniques such as e-
beam
direct writing, Deep UV lithography, nanosphere lithography, nanoimprint
lithography,
near-filed phase shift lithography, and plasmonic lithography, for example.
[0007] Nanolmprint Lithography (NIL) creates patterns by mechanical
deformation
of an imprint resist, followed by subsequent processing. The imprint resist is
typically a
monomeric or polymeric formulation that is cured by heat or by UV light during
the
imprinting. There are a number of variations of NIL. However, two of the
processes
appear to be the most important. These are Thermoplastic NanoImprint
Lithography
(TNIL) and Step and Flash Nanolmprint Lithography (SFIL).
[0008] TNIL is the earliest and most mature nanoimprint lithography. In a
standard
TNIL process, a thin layer of imprint resist (a thermoplastic polymer) is spin
coated onto
a sample substrate. Then a mold, which has predefined topological patterns, is
brought
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into contact with the sample, and pressed against the sample under a given
pressure.
When heated above the glass transition temperature of the thermoplastic
polymer, the
pattern on the mold is pressed into a thermoplastic polymer film melt. After
the sample,
with impressed mold is cooled down, the mold is separated from the sample and
the
imprint resist is left on the sample substrate surface. The pattern does not
pass through
the imprint resist; there is a residual thickness of unchanged thermoplastic
polymer film
remaining on the sample substrate surface. A pattern transfer process, such as
reactive
ion etching, can be used to transfer the pattern in the resist to the
underlying substrate.
The variation in the residual thickness of unaltered thermoplastic polymer
film presents a
problem with respect to uniformity and optimization of the etch process used
to transfer
the pattern to the substrate.
100091 Tapio Makela et al. of VTT, a technical research center in Finland,
have
published information about a custom built laboratory scale roll-to-roll
imprinting tool
dedicated to manufacturing of submicron structures with high throughput.
Hitachi and
others have developed a sheet or roll-to-roll prototype NIL machine, and have
demonstrated capability to process 15 meter long sheets. The goal has been to
create a
continuous imprint process using belt molding (nickel plated molds) to imprint
polystyrene sheets for large geometry applications such as membranes for fuel
cells,
batteries and possibly displays.
[00101 Hua Tan et al of Princeton University have published 2 implementations
of roller Nanoimprint lithography: rolling cylinder mold on flat, solid
substrate, and
putting a flat mold directly on a substrate and rolling a smooth roller on top
of the mold.
Both methods are based on TNIL approach, where roller temperature is set above
the
glass transition temperature, Tg, of the resist (PMMA), while the platform is
set to
temperature below Tg. Currently the prototype tools do not offer a desirable
throughput.
In addition, there is a need to improve reliability and repeatability with
respect to the
imprinted surface.
[00111 In the SFIL process, a UV curable liquid resist is applied to the
sample
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substrate and the mold is made of a transparent substrate, such as fused
silica. After the
mold and the sample substrate are pressed together, the resist is cured using
UV light, and
becomes solid. After separation of the mold from the cured resist material, a
similar
pattern to that used in TNIL may be used to transfer the pattern to the
underlying sample
substrate. Dae-Geun Choi from Korea Institute of Machinery suggested using
fluorinated
organic-inorganic hybrid mold as a stamp for Nanoimprint lithography, which
does not
require anti-stiction layer for demolding it from the substrate materials.
[0012] Since Nanoimprint lithography is based on mechanical deformation of
resist, there are a number of challenges with both the SFIL and TNIL
processes, in static,
step-and-repeat, or roll-to-roll implementations,. Those challenges include
template
lifetime, throughput rate, imprint layer tolerances, and critical dimension
control during
transfer of the pattern to the underlying substrate. The residual, non-
imprinted layer
which remains after the imprinting process requires an additional etch step
prior to the
main pattern transfer etch. Defects can be produced by incomplete filling of
negative
patterns and the shrinkage phenomenon which often occurs with respect to
polymeric
materials. Difference in thermal expansion coefficients between the mold and
the
substrate cause lateral strain, and the strain is concentrated at the corner
of the pattern.
The strain induces defects and causes fracture defects at the base part of the
pattern mold
releasing step.
[0013] Soft lithography is an alternative to Nanoimprint lithography method of
micro and nano fabrication. This technology relates to replica molding of self
assembling
monolayers. In soft lithography, an elastomeric stamp with patterned relief
structures on
its surface is used to generate patterns and structures with feature sizes
ranging from 30
nm to 100 nm. The most promising soft lithography technique is microcontact
printing
( CP) with self-assembled monolayers (SAMS). The basic process of CP
includes: 1.
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A polydimethylsiloxane (PDMS) mold is dipped into a solution of a specific
material,
where the specific material is capable of forming a self-assembled monolayer
(SAM).
Such specific materials may be referred to as an ink. The specific material
sticks to a
protruding pattern on the PDMS master surface. 2. The PDMS mold, with the
material-
coated surface facing downward, is contacted with a surface of a metal-coated
substrate
such as gold or silver, so that only the pattern on the PDMS mold surface
contacts the
metal-coated substrate. 3. The specific material forms a chemical bond with
the metal,
so that only the specific material which is on the protruding pattern surface
sill remain on
the metal-coated surface after removal of the PDMS mold. The specific material
forms a
SAM on the metal-coated substrate which extends above the metal-coated surface
approximately one to two nanometers (just like ink on a piece of paper). 4.
The PDMS
mold is removed from the metal-coated surface of the substrate, leaving the
patterned
SAM on the metal-coated surface.
[00141 Optical Lithography does not use mechanical deformation or phase change
of resist materials, like Nanoimprint lithography, and does not have materials
management problems like Soft Lithography, thus providing better feature
replication
accuracy and more Manufacturable processing. Though regular optical
lithography is
limited in resolution by diffraction effects some new optical lithography
techniques based
on near field evanescent effects have already demonstrated advantages in
printing sub-
100 nm structures, though on small areas only. Near-field phase shift
lithography NFPSL
involves exposure of a photoresist layer to ultraviolet (UV) light that passes
through an
elastomeric phase mask while the mask is in conformal contact with a
photoresist.
Bringing an elastomeric phase mask into contact with a thin layer of
photoresist causes
the photoresist to "wet" the surface of the contact surface of the mask.
Passing UV light
through the mask while it is in contact with the photoresist exposes the
photoresist to the
distribution of light intensity that develops at the surface of the mask. In
the case of a
mask with a depth of relief that is designed to modulate the phase of the
transmitted light
by ir, a local null in the intensity appears at the step edge of relief. When
a positive
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photoresist is used, exposure through such a mask, followed by development,
yields a
line of photoresist with a width equal to the characteristic width of the null
in intensity.
For 365 nm (Near UV) light in combination with a conventional photoresist, the
width o
the null in intensity is approximately 100 nm. A PDMS mask can be used to form
a
conformal, atomic scale contact with a flat, solid layer of photoresist. This
contact is
established spontaneously upon contact, without applied pressure. Generalized
adhesion
forces guide this process and provide a simple and convenient method of
aligning the
mask in angle and position in the direction normal to the photoresist surface,
to establish
perfect contact. There is no physical gap with respect to the photoresist.
PDMS is
transparent to UV light with wavelengths greater than 300 nm. Passing light
from a
mercury lamp (where the main spectral lines are at 355 - 365 nm) through the
PDMS
while it is in conformal contact with a layer of photoresist exposes the
photoresist to the
intensity distribution that forms at the mask.
[00151 Yasuhisa Inao, in a presentation entitled "Near-Field Lithography as a
prototype nano-fabrication tool", at the 32nd International Conference on
Micro and
Nano Engineering in 2006, described a step-and-repeat near-field
nanolithography
developed by Canon, Inc. Near-field lithography (NFL) is used, where the
distance
between a mask and the photoresist to which a pattern is to be transferred are
as close as
possible. The initial distance between the mask and a wafer substrate was set
at about 50
m. The patterning technique was described as a "tri-layer resist process",
using a very
thin photoresist. A pattern transfer mask was attached to the bottom of a
pressure vessel
and pressurized to accomplish a "perfect physical contact" between the mask
and a wafer
surface. The mask was "deformed to fit to the wafer". The initial 50 m
distance
between the mask and the wafer is said to allows movement of the mask to
another
position for exposure and patterning of areas more than 5 mm x 5mm. The
patterning
system made use of i-line (365 nm) radiation from a mercury lamp as a light
source. A
successful patterning of a 4 inch silicon wafer with structures smaller than
50 nm was
accomplished by such a step-and-repeat method.
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[00161 In an article entitled "Large-area patterning of 50 nm structures on
flexible
substrates using near-field 193 nm radiation", JVST B 21 (2002), at pages 78 -
81, Kunz
et al. applied near-field phase shift mask lithography to the nanopatterning
of flexible
sheets (Polyimide films) using rigid fused silica masks and deep UV wavelength
exposure. In a subsequent article entitled "Experimental and computational
studies of
phase shift lithography with binary elastomeric masks", JVST B 24(2) (2006) at
pages
828 - 835, Maria et al. present experimental and computational studies of a
phase
shifting photolithographic technique that uses binary elastomeric phase masks
in
conformal contact with layers of photoresist. The work incorporates optimized
masks
formed by casting and curing prepolymers to the elastomer
poly(dimethylsiloxane)
against anisotropically etched structures of single crystal silicon on
Si02/Si. The authors
report on the capability of using the PDMS phase mask to form resist features
in the
overall geometry of the relief on the mask.
[00171 U.S. Patent No. 6,753,131 to Rogers et al, issued June 22, 2004, titled
"Transparent Elastomeric, Contact-Mode Photolithography Mask, Sensor, and
Wavefront
Engineering Element", describes a contact-mode photolithography phase mask
which
includes a diffracting surface having a plurality of indentations and
protrusions. The
protrusions are brought into contact with a surface of a positive photoresist,
and the
surface is exposed o electromagnetic radiation through the phase mask. The
phase shift
due to radiation passing through indentations as opposed to the protrusions is
essentially
complete. Minima in intensity of electromagnetic radiation are thereby
produced at
boundaries between the indentations and protrusions. The elastomeric mask
conforms
well to the surface of the photoresist, and following development of the
photoresist,
features smaller than 100 nm can be obtained.(Abstract) In one embodiment,
reflective
plates are used exterior to the substrate and the contact mask, so radiation
will be
bounced to a desired location at a shifted phase. In another embodiment, the
substrate
may be shaped in a manner which causes a deformation of the phase shifting
mask,
affecting the behavior of the phase shifting mask during exposure.
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[0018] Near Field Surface Plasmon Lithography (NFSPL) makes use of near-field
excitation to induce photochemical or photophysical changes to produce
nanostructures.
The main near-field technique is based on the local field enhancement around
metal
nanostructures when illuminated at the surface plasmon resonance frequency.
Plasmon
printing consists of the use of plasmon guided evanescent waves through
metallic
nanostructures to produce photochemical and photophysical changes in a layer
below the
metallic structure. In particular, visible exposure (?, = 410 nm) of silver
nanoparticles in
close proximity to a thin film of a g-line photoresist (AZ- 1813 available
from AZ-
Electronic Materials, MicroChemicals GmbH, Ulm, Germany) can produce
selectively
exposed areas with a diameter smaller than x./20. W. Srituravanich et al. in
an article
entitled "Plasmonic Nanolithography", Nanoletters V4, N6 (2004), pp. 1085 -
1088,
describes the use of near UV light ( X = 230 nm - 350 nm) to excite SPs on a
metal
substrate, to enhance the transmission through subwavelength periodic
apertures with
effectively shorter wavelengths compared to the excitation light wavelength. A
plasmonic mask designed for lithography in the UV range is composed of an
aluminum
layer perforated with 2 dimensional periodic hole arrays and two surrounding
dielectric
layers, one on each side. Aluminum is chosen since it can excite the SPs in
the UV
range. Quartz is employed as the mask support substrate, with a poly(methyl
methacrylate) spacer layer which acts as adhesive for the aluminum foil and as
a
dielectric between the aluminum and the quartz. Poly(methyl methacrylate is
used in
combination with quartz, because their transparency to UV light at the
exposure
wavelength (i-line at 365 nm) and comparable dielectric constants (2.18 and
2.30, quartz
and PMMA, respectively). A sub-100 nm dot array pattern on a 170 nm period has
been
successfully generated using an exposure radiation of 365 nm wavelength.
Apparently
the total area of patterning was about 5 pm x 5 m, with no scalability issues
discussed in
the paper.
[0019] Joseph Martin has suggested a proximity masking device for Near-filed
lithography in US 5,928,815, where cylindrical block covered with metal film
for light
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internal reflection is used for directing light to the one end of the cylinder
(base of the
cylinder), which contains a surface relief pattern used for Near-field
exposure. This block
is kept in some proximity distance ("very small, but not zero") from the
photoresist on
the sample. Cylinder is translated in horizontal direction using some precise
mechanism,
which is used to pattern photoresist area.
100201 The only published idea about using rollers for optical lithography can
be
found in the Japanese Unexamined Patent Publication, No. 59200419A, published
November 13, 1984, titled "Large Area Exposure Apparatus". Toshio Aoki et al.
described the use of a transparent cylindrical drum which can rotate and
translate with an
internal light source and a film of patterned photomask material attached on
the outside
of the cylindrical drum. A film of a transparent heat reflective material is
present on the
inside of the drum. A substrate with an aluminum film on its surface and a
photoresist
overlying the aluminum film is contacted with the patterned photomask on the
drum
surface and imaging light is passed through the photomask to image the
photoresist on
the surface of the aluminum film. The photoresist is subsequently developed,
to provide
a patterned photoresist. The patterned photoresist is then used as an etch
mask for an
aluminum film present on the substrate.
[00211 There is no description regarding the kinds of materials which were
used as
a photomask film or as a photoresist on the surface of the aluminum film. A
high
pressure mercury lamp light source (500 W) was used to image the photoresist
overlying
the aluminum film. Glass substrates about 210 mm (8.3 in.) x 150 mm (5.9 in.)
and
about 0.2 mm (0.008.in.) thick were produced using the cylindrical drum
pattern transfer
apparatus. The feature size of the pattern transferred using the technique was
about 500
m2, which was apparently a square having a dimension of about 22.2 m x 22.2
gm.
This feature size was based on the approximate pixel size of an LCD display at
the time
the patent application was filed in 1984. The photomask film on the outside of
the
cylindrical drum was said to last for approximately 140,000 pattern transfers.
The
contact lithography scheme used by Toshio Aoki et al. is not capable of
producing sub-
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micron features.
[0022] It does not appear that an nanoimprinting methods (thermal or UV-cured)
or
soft lithography using printing with SAM materials are highly manufacturable
processes.
In general, the imprinting method creates deformation of the substrate
material due to the
thermal treatment (thermal NIL, for example) or shrinkage of pattern features
upon
polymer curing (UV-cured polymeric features). Moreover, due to the application
of
pressure (hard contact) between a stamp and a substrate, defects are
essentially
unavoidable, and a stamp has a very limited lifetime. Soft lithography does
have an
advantage in that it is thermal and stress-free printing technology. However,
the use of a
SAM as an "ink" for a sub-100 nm pattern is very problematic due to the
drifting of
molecules over the surface, and application over large areas has not been
proved
experimentally.
[0023] Earlier authors have suggested a method of nanopatterning large areas
of
rigid and flexible substrate materials based on near-field optical lithography
described in
Patent applications W02009094009 and US20090297989, where a rotatable
cylindrical
or cone-shaped mask is used to image a radiation-sensitive material. The
nanopatterning
technique makes use of Near-Field photolithography, where the mask used to
pattern the
substrate is in contact with the substrate. The Near-Field photolithography
may make use
of an elastomeric phase-shifting mask, or may employ surface plasmon
technology,
where a rotating cylinder surface comprises metal nano holes or nanoparticles.
[0024] SUMMARY
[0025] Embodiments of the invention pertain to methods and apparatus useful in
the
nanopatterning of large area substrates, rigid flat or curved objects or
flexible films. The
nanopatterning technique makes use of Near-Field UV photolithography, where
the mask
used to pattern the substrate is in contact with the substrate. The Near-Field
photolithography may include a phase-shifting mask or surface plasmon
technology.
The Near-field mask is fabricated from a flexible film, which is
nanostructured in
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accordance with the desired pattern. In phase-shift method, one can use
nanostructuctured
elastomeric film, for example, Polydimethylsiloxane (PDMS) film.
Nanostructuring can
be done using laser treatment, selective etching or other available
techniques, or it can be
done by replication (molding, casting) from the nanostructured "masters",
which are
fabricated using known nanofabrication methods (like, e-beam writing,
holographic
lithography, direct laser writing or Nanoimprint step-and-repeat or roll-to-
roll
lithography). This film can be supported by another transparent flexible film
(carrier). In
plasmonic method one can use a film with metal layer having nanohole
structure, created
using one of the abovementioned methods or by depositing metal nanoparticles,
for
example, deposited from a colloid solution. In order to provide uniform
contact area for
near-field lithography we rely on Van-der-Vaals forces of stiction between
elastomeric
film and photoresist layer on the substrate. Alternatively, a transparent
cylinder is used to
provide controllable contact between nanostructured film and a substrate. Such
cylinder
may have flexible walls and can be pressurized by a gas to provide
controllable pressure
between a nanostructured film and a substrate.
[0026] BRIEF DESCRIPTION OF THE DRAWINGS
[0027] So that the manner in which the exemplary embodiments of the present
invention are attained is clear and can be understood in detail, with
reference to the
particular description provided above, and with reference to the detailed
description of
exemplary embodiments, applicants have provided illustrating drawings. It is
to be
appreciated that drawings are provided only when necessary to understand
exemplary
embodiments of the invention and that certain well known processes and
apparatus are
not illustrated herein in order not to obscure the inventive nature of the
subject matter of
the disclosure.
[0028] Figure 1 A shows a cross-sectional view of an embodiment of a flexible
nanostructured film 1, having a phase-shift mask properties. Surface relief
nanostructure
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3 is fabricated on one of the surfaces of the film 2.
[00291 Figure 1 B shows a cross-sectional view of an embodiment of a flexible
nanostructured film 1, having a plasmonic mask properties. Array of nanoholes
are
created in the film or array of nanoparticles are deposited on it's surface.
[00301 Figure 2 shows a suggested nanopatterning system prior to starting the
process. A nanostructured film 1 is wrapped around support drums 4 and 5.
Substrate 6
has a photoresist layer 7 deposited on it's surface.
[00311 Figure 3 shows another embodiment where nanostructured film 1 can be
rolled from one roll 4 to another roll 5.
[00321 Figure 4 shows a starting point of the process, when a film 1 is
brought to
contact with a photoresist 7 using movable arm 8.
[00331 Figure 5 shows the patterning process, when the arm 8 is removed from
the film-substrate contact, substrate 6 is translating in one direction, and
UV light source
7 is illuminating the contact zone between a film and a substrate.
[00341 Figure 6 shows another embodiment, where nanopatterned film is in
contact with the substrate in quite wide surface area.
[00351 Figure 7 shows the embodiment, where the transparent cylinder 11 is
used
to bring nanostructured film 1 in contact with photoresist 7 on the substrate
6.
[00361 Figure 8 shows the embodiment, where the substrate is a flexible film
12,
which can be translated from one roll 14 to another 13.
[00371 Figure 9 shows the embodiment, where the substrate is nanopatterned
from the both sides
[00381 DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[00391 As a preface to the detailed description, it should be noted that, as
used in this
specification and the appended claims, the singular forms "a", "an", and "the"
include
plural referents, unless the context clearly dictates otherwise.
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100401 When the word "about" is used herein, this is intended to mean that the
nominal value presented is precise within 10 %.
[00411 Embodiments of the invention relate to methods and apparatus useful in
the
nanopatterning of large area substrates, where a flexible nanostructured film
is used to
image a radiation-sensitive material. The nanopatterning technique makes use
of near-
field photolithography, where the wavelength of radiation used to image a
radiation-
sensitive layer on a substrate is 650 nm or less, and where the mask used to
pattern the
substrate is in contact with the substrate. The near-field photolithography
may make use
of a phase-shifting mask, or may employ surface plasmon technology, where a
metal
layer on movable flexible film's surface comprises nano holes, or metal
nanoparticles are
dispersed on the surface of such flexible film. The detailed description
provided below
is just a sampling of the possibilities which will be recognized by one
skilled in the art
upon reading the disclosure herein.
[00421 One of the embodiments suggests a phase-shift mask approach and is
implemented by flexible nanostructured film. The problem of providing a
uniform and
permanent contact between such flexible nanostructured film and a substrate is
solved by
manufacturing this film from a material capable of creating strong but
temporary bond to
photoresist layer. One example of such material is an elastomer, for example
Polydimethylsiloxane (PDMS). A PDMS film can be used to form a conformal,
atomic
scale contact with a flat, solid layer of photoresist. This contact is
established
spontaneously upon contact, without applied pressure. Schematic of such film
is shown
on Fig. 1 A, where film 2 has a nanostructure 3 in the form of transparent
surface relief.
[00431 Film 2 can be made from one material (for example, PDMS) or be a
composite or multi-layer comprised of more than one material, for example,
nanostructured PDMS can be laminated or deposited on a transparent and
flexible support
film. Such support film can be made of polycarbonate (PC),
polymethylmethacrylate
(PMMA), Polyethylene terephthalate (PET), amorphous fluoric-polymer, for
example
CYTOP, and other materials. Deposition of PDMS on transparent flexible support
film
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can be done using one of available techniques, for example, dipping, spraying
or casting.
Support film can be treated using oxygen plasma, UV ozone, corona discharge or
adhesion promoters, like silanes to promote better adhesion between
elastomeric film and
a polymer film support.
[00441 Another embodiment of "sticky" material, which can be used instead of
elastomer, to create a dynamic contact with photoresist is cross-linked silane
material.
Such material can be deposited from a silane precursor (usually used to
deposit self-
assembled monolayers, SAMs) with abundance of water/moisture. For example,
DDMS
(dichlorodimethylsilane) creates very sticky surface if deposited with
abundance of
moisture. In this embodiment, the carrier layer is nanostructured using one of
known
nanostructuring techniques (preferably, Roll-to-Roll Nanoimprint lithography)
and then
coated with silane material to provide "stickyness".
[00451 A surface relief for phase-shift lithography can be created in the
elastomeric or silane film using any of the following methods: First,
nanostructured
"master" can be obtained using one of the available nanofabrication techniques
(deep-UV
stepper, e-beam, ion-beam, holography, laser treatment, embossing,
Nanoimprint, and
others). Second, a replica of desired nanostructure can be obtained from such
master on
the surface of elastomeric film using, for example, casting or molding, in
roll-to-roll or
step-and-repeat mode.
[00461 Another embodiment suggests that the carrier layer is nanostructured
using one of known nanostructuring techniques (preferably, Roll-to-Roll
Nanoimprint
lithography) and then coated with elastomer material (like PDMS) or silane
material (like
DDMS) to provide "stickyness".
[00471 Nanostructure of such mask can be designed to act as phase shifter, and
in
this case the height of the features should be proportional ton. For example,
PDMS
material having refractive index 1.43 for wavelength of exposure 365 rim
should have a
features with depth about 400 nm to cause a phase shift effect. In this case a
local minima
of light intensity will happen at the step edges of the mask. For example,
lines from 20
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nm to 150 nm can be obtained in photoresist corresponding to the positions of
surface
relief edges in the phase-shift mask. Thus this lithography has image
reduction properties,
and nanostructures can be achieved using much larger features on the mask.
[0048] Another embodiment is using nanostructure on flexible mask to act as
1:1
replication mask. As it was demonstrated in previous publications, for
example, Tae-Woo
Lee, at al in Advanced Functional Materials, 2005, 15,1435., depending on
specific
parameters of photoresist exposure and development, one can achieve 1:1
replication of
the features from mask to photoresist or feature size reduction using phase-
shift on the
surface relief edges on the same elastomeric mask. Specifically, underexposure
or
underdevelopment against the normal exposure doze and development time, would
cause
a significant differential between an effective exposure doze in non-contact
and contact
regions of the mask. This can be used to create al :1 replication from mask to
photoresist
in positive or negative tone (depending on photoresist type).
[0049] Another embodiment suggests a plasmonic mask approach. Such
plasmonic film could be a flexible metal film, shown on Fig 1B, which has
arrays of
nanoholes according to the desired pattern. Alternatively, metal layer is
deposited on
flexible transparent film. Metal layer patterning can be done using one of
available
nanopatterning techniques (deep-UV stepper, e-beam, ion-beam, holography,
laser
treatment, embossing, Nanoimprint, and others), followed by metal layer
etching.
[0050] Alternatively, nanopattern can be fabricated using abovementioned
methods on a transparent film, and then metal material can be deposited over
nanopatterned resist, followed by metal layer lift-off.
[0051] And yet another embodiment uses metal nanoparticles dispensed in
controllable way over the surface of the flexible transparent film to create a
plasmonic
mask. For example, metal nanoparticles can be mixed with PDMS material in a
liquid
phase prior to depositing it onto the flexible transparent support film.
Alternatively, metal
nanoparticles can be deposited onto nanotemplate fabricated in elastomeric
layer.
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100521 Nanostructured film can be wrapped around support drums 4 and 5, and
kept at a controllable tension, as shown on Fig. 2 .
[00531 Alternatively, nanostructured films can be rolled from one roll 4 to
another
roll 5, as shown on Fig. 3.
[00541 The process starts by bringing a nanostructured film 1 in contact with
the
photoresist 7 deposited on the substrate 6, using a movable arm 8, as shown on
Fig. 4.
Such contact will engage Van-der-Vaals forces and make film temporary stick to
the
photoresist. Then, as it is shown on Fig. 5, movable arm 8 is removed from the
film-
substrate contact, light source, which may include optical focusing,
collimating or
filtering system, 9 is turned on, providing exposure to the area of film-
substrate contact,
and substrate 6 is translated in one direction using constant or variable
speed. Such
translation will make film to move as well in the direction of the
translation, exposing
different parts of the substrate to the same or different pattern, depending
on the
nanostructure fabricated on the film.
[00551 Another embodiment, presented on Fig. 6 shows nanostructured film in
contact with the photoresist across a wider area. This area of contact starts
to move as
soon as substrate begins translation in one direction. The width of contact
area between a
nanostructured film and a substrate can be changed by changing a relative
position
between the substrate 6 and drums 4 and 5, and also by changing tackiness of
the
nanostructured film material. This configuration also allows to increase area
of
nanostructured film exposure to light, which helps to improve a throughput of
the method
due to increase in dynamic exposure dosage.
[00561 When nanostructured film surface contact is not tacky enough (like, for
example, in case of plasmonic mask approach) the movable arm is not retracted,
keeping
controllable and uniform pressure between the nanostructured film and a
substrate. For
example, the movable arm can be fabricated in the form of transparent cylinder
11, as
shown on Fig. 7. This cylinder is actuated by the mechanical system providing
controllable and uniform contact between nanostructured film and a substrate.
In that
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case, source of illumination 9 could be located inside such cylinder.
[00571 Such cylinder can be made from transparent flexible material and
pressurized by a gas. In such case the area of contact and pressure between a
mask and a
substrate can be controlled by gas pressure.
[00591 The gas can be flown through flexible-wall cylinder constantly such as
to
create necessary controllable pressure and at the same time cool down the
light source
positioned inside this cylinder.
[00601 Disclosed nanopatterning methods can be used to pattern flexible films
12,
as shown on Fig. 8, which can be translated from one roll 14 to another roll
13 during
exposure.
[00611 Disclosed nanopatterning methods can be used to pattern rigid or
flexible
materials from the both sides, as shown on Fig. 9
100621 Disclosed nanopatterning methods can be used to pattern non-flat or
curved substrates, as shown on Fig. 10. Fig. 10a shows how cylinder on a
movable arm is
following the curvature of the substrate, and Fig. 1 Ob shows how flexible-
wall gas
pressurized cylinder is following the curvature of the substrate. In latter
case, instead of
moving arm in vertical direction, one can adjust pressure inside cylinder to
accommodate
substrate height deviation caused by curvature.
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