U.S. patent application number 12/384219 was filed with the patent office on 2013-08-15 for large area nanopatterning method and apparatus.
This patent application is currently assigned to ROLITH, INC. The applicant listed for this patent is Boris Kobrin, Igor Landau, Boris Volf. Invention is credited to Boris Kobrin, Igor Landau, Boris Volf.
Application Number | 20130208251 12/384219 |
Document ID | / |
Family ID | 42171779 |
Filed Date | 2013-08-15 |
United States Patent
Application |
20130208251 |
Kind Code |
A9 |
Kobrin; Boris ; et
al. |
August 15, 2013 |
LARGE AREA NANOPATTERNING METHOD AND APPARATUS
Abstract
Embodiments of the invention relate to methods and apparatus
useful in the nanopatterning of large area substrates, where a
rotatable mask is used to image a radiation-sensitive material.
Typically the rotatable mask comprises a cylinder. The
nanopatterning technique makes use of Near-Field photolithography,
where the mask used to pattern the substrate is in contact or close
proximity 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.
Inventors: |
Kobrin; Boris; (Dublin,
CA) ; Volf; Boris; (Hillsborough, NJ) ;
Landau; Igor; (Palo Alto, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kobrin; Boris
Volf; Boris
Landau; Igor |
Dublin
Hillsborough
Palo Alto |
CA
NJ
CA |
US
US
US |
|
|
Assignee: |
ROLITH, INC
Pleasanton
CA
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20100123885 A1 |
May 20, 2010 |
|
|
Family ID: |
42171779 |
Appl. No.: |
12/384219 |
Filed: |
April 1, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/US2008/012901 |
Nov 18, 2008 |
|
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12384219 |
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61011861 |
Jan 22, 2008 |
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Current U.S.
Class: |
355/53 |
Current CPC
Class: |
G03F 7/70358 20130101;
G03F 7/7035 20130101; G03B 27/42 20130101; G03F 7/704 20130101;
G03F 7/70325 20130101; G03F 7/703 20130101 |
Class at
Publication: |
355/53 |
International
Class: |
G03B 27/42 20060101
G03B027/42 |
Claims
1. A method of near-field nanolithography comprising: a) providing
a substrate having a radiation-sensitive layer on said substrate
surface; b) providing a rotatable mask having a nanopattern on an
exterior surface of said rotatable mask; c) contacting said
nanopattern with said radiation-sensitive layer on said substrate
surface; d) distributing radiation through said nanopattern, while
rotating said rotatable mask over said radiation-sensitive layer,
whereby an image having a feature size ranging from less than 1
.mu.m down to about 1 nm is created in said radiation-sensitive
layer
2. A method in accordance with claim 1, wherein said feature size
ranges from about 100 nm down to 10 nm.
3. A method in accordance with claim 1, wherein said radiation has
a wavelength of 436 nm or less
4. A method in accordance with claim 1, wherein said nanopattern is
a conformable nanopattern, which conforms to said
radiation-sensitive layer on said substrate surface.
5. A method in accordance with claim 4, wherein said conformable
nanopattern is a shaped or nanostructured polymeric material.
6. A method in accordance with claim 3, wherein said rotatable mask
is a phase-shifting mask which causes radiation to form an
interference pattern in said radiation-sensitive
7. A method in accordance with claim 3, wherein said mask employs
surface plasmon behavior.
8. A method in accordance with claim 1, wherein said rotatable mask
is a cylinder.
9. A method in accordance with claim 8, wherein said cylinder has a
flexible wall, whereby said cylindrical shape may be deformed upon
contact with said substrate surface.
10. A method in accordance with claim 9, wherein an optically
transparent gas is used to fill said cylinder.
11. A method in accordance with claim 3, wherein said rotatable
mask is a transparent cylinder, whereby radiation may be
transmitted from a location interior of said cylinder.
11. (canceled)
12. A method in accordance with claim 11, wherein said mask is a
phase shifting mask which is present as a relief on a surface of
said transparent cylinder.
13. A method in accordance with claim 11, wherein said mask is a
phase shifting mask which is present on a layer applied over a
surface of said cylinder.
14. A method in accordance with claim 13, wherein at least one
nanopatterned film is applied to an exterior surface of said
cylinder, whereby imaged feature dimensions in said
radiation-sensitive layer more precisely represent prescribed
feature dimensions.
15. A method in accordance with claim 8, wherein said substrate is
moved in a direction toward or away from a contact surface of said
rotatable cylinder during distribution of radiation from said
contact surface of said cylinder.
16. A method in accordance with claim 8, wherein said cylinder is
rotated on said substrate while said substrate is static
17. A method in accordance with claim 1, wherein multiple rotating
masks are contacted with a radiation-sensitive layer.
18. A method in accordance with claim 1, wherein said rotatable
mask and said substrate surface are moved independently using a
stepper-motor and a motorized substrate translational mechanism,
and wherein movement of said rotatable mask and said substrate
surface are synchronized with each other, whereby a slip-free
contact exposure of said radiation-sensitive layer is achieved.
19. A method in accordance with claim 1, wherein a liquid is
supplied to an interface between said rotatable mask and said
substrate surface.
20. An apparatus to carry out near-field lithography, comprising:
a) a rotatable mask having a nanopattern on an exterior surface of
said mask; and b) a radiation source which supplies radiation of a
wavelength of 436 nm or less from said nanopattern, while said
nanopattern is in contact with a radiation-sensitive layer of
material.
21. An apparatus in accordance with claim 20, wherein said
rotatable mask is a cylinder.
22. An apparatus in accordance with claim 21, wherein said
rotatable mask is transparent.
23. An apparatus in accordance with claim 22, wherein said
rotatable mask is a phase-shifting mask.
24. An apparatus in accordance with claim 21, wherein said
rotatable mask employs radiation generated using surface plasmon
techniques.
25. An apparatus in accordance with claim 24, wherein a surface of
said mask comprises a metal layer including nanoholes.
25. (canceled)
26. An apparatus in accordance with claim 21, wherein said cylinder
is a flexible cylinder.
27. An apparatus in accordance with claim 26, wherein said flexible
cylinder is filled with an optically transparent gas.
28. An apparatus in accordance with claim 25, wherein multiple
cylinders are present in an arrangement so that said multiple
cylinders pass over a substrate in sequence.
29. An apparatus in accordance with claim 25, wherein multiple
cylinders are present, and wherein a cylinder is present on both
the top side and bottom side of a substrate which is imaged by said
apparatus.
30. An apparatus in accordance with claim 29, wherein at least one
cylinder which transmits imaging radiation is present on both the
top side and the bottom side of a substrate which is imaged by said
apparatus.
31. An apparatus in accordance with claim 20, wherein a rotatable
mask is suspended over said substrate by a tensioning device which
can be adjusted to control the amount of force applied to a surface
in contact with said rotatable mask.
Description
[0001] This application claims the benefit of U.S. provisional
Application No. 61/011,861, filed Jan. 22, 2008 and
PCT/US2008/012901 filed Nov. 18, 2008
FIELD
[0002] 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.
BACKGROUND
[0003] 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.
[0004] 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.
[0005] 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.
[0006] NanoImprint 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
NanoImprint Lithography (SFIL).
[0007] 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 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.
[0008] 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.
[0009] 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.
[0010] In the SFIL process, a UV curable liquid resist is applied
to the sample 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.
[0011] 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.
[0012] 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 (.mu.CP) with
self-assembled monolayers (SAMS). The basic process of .mu.CP
includes: 1. 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.
[0013] The best-established specific materials for forming SAMs on
gold or silver-coated surfaces are alkanethiolates. When the
substrate surface contains hydroxyl-terminated moieties such as
Si/SiO.sub.2, Al/Al.sub.2O.sub.3, glass, mica, and plasma-treated
polymers, alkylsiloxanes work well as the specific materials. With
respect to the alkanethiolates, .mu.CP of hexadecanethiol on
evaporated thin (10-200 nm thick) films of gold or silver appears
to be the most reproducible process. While these are the best-known
materials for carrying out the pattern formation, gold and silver
are not compatible with microelectronic devices based on silicon
technology, although gold or silver-containing electrodes or
conductive wires may used. Currently, .mu.CP for SAMS of siloxanes
on Si/SiO.sub.2 surfaces are not as tractable as the SAMS of
alkanethiolates on gold or silver. The SAMS of siloxanes on
Si/SiO.sub.2 often provide disordered SAMs, and in some cases
generate submonolayers or multilayers. Finally, the patterned molds
available for .mu.CP are flat "stamp" surfaces, and reproducible
and reliable printing on large areas not only requires very
accurate stitching of the printed pattern from the mold, but also
requires constant wetting of the stamp with the SAM-forming
specific material, which is quite problematic.
[0014] 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 .pi., a local null in the
intensity appears at the step edge of relief. When a positive
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.
[0015] 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 .mu.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 .mu.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.times.5 mm. 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.
[0016] 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 SiO.sub.2/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.
[0017] U.S. Pat. No. 6,753,131 to Rogers et al, issued Jun. 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.
[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 (.lamda.=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 .lamda./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
(.lamda.=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
.mu.m.times.5 .mu.m, with no scalability issues discussed in the
paper.
[0019] Joseph Martin has suggested a proximity masking device for
Near-filed lithography in U.S. Pat. No. 5,928,815, where
cylindrical block covered with metal film for light 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.
[0020] The only published idea about using rollers for optical
lithography can be found in the Japanese Unexamined Patent
Publication, No. 59200419A, published Nov. 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.
[0021] 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.).times.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
.mu.m.sup.2, which was apparently a square having a dimension of
about 22.2 .mu.m.times.22.2 .mu.m. 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-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.
SUMMARY
[0023] Embodiments of the invention pertain to methods and
apparatus useful in the nanopatterning of large area substrates
ranging from about 200 mm.sup.2 to about 1,000,000 mm.sup.2, by way
of example and not by way of limitation. In some instances the
substrate may be a film, which has a given width and an undefined
length, which is sold on a roll. The nanopatterning technique makes
use of Near-Field UV photolithography, where the mask used to
pattern the substrate is in contact or in very close proximity (in
the evanescent field, less than 100 nm) from the substrate. The
Near-Field photolithography may include a phase-shifting mask or
surface plasmon technology.
[0024] One embodiment the exposure apparatus which includes a
phase-shifting mask in the form of a UV-transparent rotatable mask
having specific phase shifting relief on it's outer surface. In
another embodiment of the phase-shifting mask technology, the
transparent rotatable mask, which is typically a cylinder, may have
a polymeric film which is the phase-shifting mask, and the mask is
attached to the cylinder's outer surface. When it is difficult to
obtain good and uniform contact with the substrate surface,
especially for large processing areas, it is advantageous to have
the polymeric film be a conformal, elastomeric polymeric film such
as PMDS, which makes excellent conformal contact with the substrate
through Van-der Waals forces. The polymeric film phase-shifting
mask may consist of multiple layers. Where the outer layer is
nanopatterned to more precisely represent prescribed feature
dimensions in a radiation-sensitive (photosensitive) layer.
[0025] Another embodiment of the exposure apparatus employs a soft
elastomeric photomask material, such as a PDMS film, having
non-transparent features fabricated on one of it's surfaces, which
is attached to the outer surface of the cylinder. Such feature may
be chrome features produced on the PDMS film using one of the
lithographic techniques known in the art.
[0026] In an embodiment of the exposure apparatus which includes
surface plasmon technology, a metal layer or film is laminated or
deposited onto the outer surface of the rotatable mask, which is
typically a transparent cylinder. The metal layer or film has a
specific series of through nanoholes. In another embodiment of the
surface plasmon technology, a layer of metal nanoparticles is
deposited on the transparent rotatable mask's outer surface, to
achieve the surface plasmons enhanced nanopatterning. A radiation
source is provided interior to the transparent cylinder. For
example, and not by way of limitation, a UV lamp may be installed
interior of the cylinder. In the alternative, the radiation source
may be placed outside the cylinder, with light from the radiation
source being piped to the interior of the cylinder through one or
both ends of the cylinder. The radiation may be directed from
outside the cylinder or within the cylinder toward particular areas
within the interior of the cylinder using an optical system
including mirrors, lenses, or combinations thereof, for example.
Radiation present within the cylinder may be directed toward the
mask substrate contact area using an optical grating. The radiation
may be directed toward the mask substrate area (coupled) through a
waveguide with a grating. The waveguide or grating is typically
placed inside the cylinder, to redirect radiation toward the
contact areas between the cylinder outer surface and the substrate
surface to be imaged.
[0027] In a specialized embodiment of a light source of radiation,
an OLED flexible display may be attached around the exterior of the
rotatable mask, to emit light from each of the pixels toward the
substrate. In this instance the rotatable mask does not need to be
transparent. In addition, the particular pattern to be transferred
to a radiation-sensitive material on the substrate surface may be
generated depending on the application, through control of the
light emitted from the OLED. The pattern to be transferred may be
changed "on the fly" without the need to shut down the
manufacturing line.
[0028] To provide high throughput of pattern transfer to a
radiation-sensitive material, and increase the quantity of
nanopatterned surface area, it is helpful to move the substrate or
the rotatable mask, such as a cylinder, against each other. The
cylinder is rotated on the substrate surface when the substrate is
static or the substrate is moved toward the cylinder while the
cylinder is static. For reasons discussed below, there are
advantages to moving the substrate toward the cylinder.
[0029] It is important to be able to control the amount of force
which occurs at the contact line between the cylinder and the
radiation-sensitive material on the surface of the substrate (for
example the contact line between an elastomeric nanopatterned film
present on the surface of the cylinder and a photoresist on the
substrate surface). To control this contact line, the cylinder may
be supported by a tensioning device, such as, for example, springs
which compensate for the cylinder's weight. The substrate or
cylinder (or both) are moved (upward and downward) toward each
other, so that a spacing between the surfaces is reduced, until
contact is made between the cylinder surface and the
radiation-sensitive material (the elastomeric nanopatterned film
and the photoresist on the substrate surface, for example). The
elastomeric nanopatterned film will create a bond with a
photoresist via Van-der Walls forces. The substrate position is
then moved back (downward) to a position at which the springs are
elongated, but the elastomeric nanopatterned film remains in
contact with the photoresist. The substrate may then be moved
toward the cylinder, forcing the cylinder to rotate, maintaining a
dynamic contact between the elastomeric nanopatterned film and the
photoresist on the substrate surface. alternatively, the cylinder
can be rotated and the substrate can be moved independently, but in
synchronous motion, which will assure slip-free contact during
dynamic exposure.
[0030] Multiple cylinders may be combined into one system and
arranged to expose the radiation-sensitive surface of the substrate
in a sequential mode, to provide double, triple, and multiple
patterning of the substrate surface. This exposure technique can be
used to provide higher resolution. The relative positions of the
cylinders may be controlled by interferometer and an appropriate
computerized control system.
[0031] In another embodiment, the exposure dose may affect the
lithography, so that an edge lithography (where narrow features can
be formed, which corresponds to a shift of phase in a PDMS mask,
for example) can be changed to a conventional lithography, and the
feature size in an imaged photoresist can be controlled by exposure
doze. Such control of the exposure dose is possible by controlling
the radiation source power or the rotational speed of the cylinder
(exposure time). The feature size produced in the photoresist may
also be controlled by changing the wavelength of the exposure
radiation, light source, for example.
[0032] The masks on the cylinders may be oriented by an angle to
the direction of substrate movement. This enables pattern formation
in different directions against the substrate. Two or more
cylinders can be placed in sequence to enable 2D patterns.
[0033] In another embodiment, the transparent cylindrical chamber
need not be rigid, but may be formed from a flexible material which
may be pressurized with an optically transparent gas. The mask may
be the cylinder wall or may be a conformal material present on the
surface of the cylinder wall. This permits the cylinder to be
rolled upon a substrate which is not flat, while making conformal
contact with the substrate surface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] 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.
[0035] FIG. 1A shows a cross-sectional view of one embodiment of an
apparatus 100 useful in patterning of large areas of substrate
material, where a radiation transparent cylinder 106 has a hollow
interior 104 in which a radiation source 102 resides. In this
embodiment, the exterior surface 111 of the cylinder 106 is
patterned with a specific surface relief 112. The cylinder 106
rolls over a radiation sensitive material 108 which overlies a
substrate 110.
[0036] FIG. 1B shows a top view of the apparatus and substrate
illustrated in FIG. 1A, where the radiation sensitive material 108
has been imaged 109 by radiation (not shown) passing through
surface relief 112.
[0037] FIG. 2 shows a cross-sectional view of another embodiment of
an apparatus 200 useful in patterning of large areas of substrate
material. In FIG. 2, the substrate is a film 208 upon which a
pattern is imaged by radiation which passes through surface relief
212 on a first (transparent) cylinder 206 while film 208 travels
from roll 211 to roll 213. A second cylinder 215 is provided on the
backside 209 of film 208 to control the contact between the film
208 and the first cylinder 206.
[0038] FIG. 3 shows a cross-sectional view of another embodiment of
an apparatus 300 useful in patterning large areas of substrate
material. In FIG. 3, the substrate is a film 308 which travels from
roll 311 to roll 313. A first transparent cylinder 306 with surface
relief 312 is used to pattern the topside 310 of film 308, while a
second transparent cylinder 326 with surface relief 332 is used to
pattern the bottom side 309 of film 308.
[0039] FIG. 4A shows a cross-sectional view of an embodiment 400 of
a transparent cylinder 406 which includes a hollow center area 404
with an internal source of radiation 402. The surface relief area
412 is a conformal structure which includes polymer film 415 with a
patterned surface 413 which is particularly useful for near-field
lithography.
[0040] FIG. 4B shows an enlargement of surface 413, which is a
surface relief polymer structure 413 on top of polymeric base
material 415. In FIG. 4B, the polymer base material 415 may be
either the same polymeric material or may be a different polymeric
material from the patterned surface material 413.
[0041] FIG. 5A shows a cross sectional view of an alternative
embodiment 500 of surface relief 512 which is present on a hollow
transparent cylinder 506.
[0042] FIG. 5B shows an enlargement of the surface relief 512,
which is a thin metal layer 514 which is patterned with a series of
nanoholes 513, where the metal layer is applied over the exterior
surface 511 of hollow transparent cylinder 506.
[0043] FIG. 5C shows an alternative surface relief 522 which may be
used on the surface of transparent cylinder 506. Surface relief 522
is formed by metal particles 526 which may be applied directly upon
the exterior surface 511 of hollow transparent cylinder 506 or may
be applied on a transparent film 524 which is attached to the
exterior surface 511 of hollow transparent cylinder 506.
[0044] FIG. 6A is a schematic three dimensional illustration 600 of
a transparent cylinder 604 having a patterned surface 608, where
the cylinder 604 is suspended above a substrate 610 using a
tensioning device 602 illustrated as springs.
[0045] FIG. 6B is a schematic of an embodiment 620 where the
radiation used to accomplish imaging is supplied from a radiation
source 612 exterior to cylinder 604, with the radiation distributed
internally 615 and 616 within the hollow portion of the cylinder
604.
[0046] FIG. 6C is a schematic of an embodiment 630 where the
radiation used to accomplish imaging is supplied from the exterior
radiation source 612 is focused 617 into a waveguide 618 and
distributed from the waveguide 618 to an optical grating 621
present on the interior surface 601 of the cylinder 604.
[0047] FIG. 6D is a schematic of an embodiment 640 where the
radiation used to accomplish imaging is supplied from two exterior
radiation sources 612A and 612B, and is focused 621 and 619,
respectively upon an optical grating 621 present on the interior
surface 601 of cylinder 604.
[0048] FIG. 7A is a schematic showing the use of multiple
cylinders, such as two cylinders 702 and 704, for example, in
series to provide multiple patterning, which may be used to obtain
higher resolution, for example.
[0049] FIG. 7B is a cross-sectional schematic showing a pattern 706
created by a first cylinder 702 after imaging and development of a
radiation-sensitive material 710. The altered pattern 708 is after
imaging and development of the radiation-sensitive material 710
where the altered pattern 708 is created by use of the first
cylinder 702 in combination with a second cylinder 704.
[0050] FIG. 8 shows a cross-sectional schematic of a deformable
cylinder 800, the interior 804 of which is pressurized using an
apparatus 813 which supplies an optically transparent gas. The
outer surface 811 of deformable cylinder 800 may be a
nanopatterned/nanostructured film 802 of a conformable material,
which can be rolled upon a non-flat substrate 805 so that radiation
from radiation source 902 can be precisely applied over a surface
816 of substrate 805.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0051] 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.
[0052] When the word "about" is used herein, this is intended to
mean that the nominal value presented is precise within
.+-.10%.
[0053] Embodiments of the invention relate to methods and apparatus
useful in the nanopatterning of large area substrates, where a
rotatable mask is used to image a radiation-sensitive material.
Typically the rotatable mask comprises a cylinder. 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 nanoparticles on the surface of a
transparent rotating cylinder, or may employ surface plasmon
technology, where a metal layer on the rotating cylinder surface
comprises nano holes. 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.
[0054] Although the rotating mask used to generate a nanopattern
within a layer of radiation-sensitive material may be of any
configuration which is beneficial, and a number of these are
described below, a hollow cylinder is particularly advantageous in
terms of imaged substrate manufacturability at minimal maintenance
costs. FIG. 1A shows a cross-sectional view of one embodiment of an
apparatus 100 useful in patterning of large areas of substrate
material, where a radiation transparent cylinder 106 has a hollow
interior 104 in which a radiation source 102 resides. In this
embodiment, the exterior surface 111 of the cylinder 106 is
patterned with a specific surface relief 112. The cylinder 106
rolls over a radiation sensitive material 108 which overlies a
substrate 110. FIG. 1B shows a top view of the apparatus and
substrate illustrated in FIG. 1A, where the radiation sensitive
material 108 has been imaged 109 by radiation (not shown) passing
through surface relief 112. The cylinder is rotating in the
direction shown by arrow 118, and radiation from a radiation source
102 passes through the nanopattern 112 present on the exterior
surface 103 of rotating cylinder 106 to image the
radiation-sensitive layer (not shown) on substrate 108, providing
an imaged pattern 109 within the radiation-sensitive layer. The
radiation-sensitive layer is subsequently developed to provide a
nanostructure on the surface of substrate 108. In FIG. 1B, the
rotatable cylinder 106 and the substrate 120 are shown to be
independently driven relative to each other. In another embodiment,
the substrate 120 may be kept in dynamic contact with a rotatable
cylinder 106 and moved in a direction toward or away from a contact
surface of the rotatable cylinder 106 to provide motion to an
otherwise static rotatable cylinder 106. In yet another embodiment,
the rotatable cylinder 106 may be rotated on a substrate 120 while
the substrate is static.
[0055] The specific surface relief 112 may be etched into the
exterior surface of the transparent rotating cylinder 106. In the
alternative, the specific surface relief 112 may be present on a
film of polymeric material which is adhered to the exterior surface
of rotating cylinder 106. The film of polymeric material may be
produced by deposition of a polymeric material onto a mold
(master). The master, created on a silicon substrate, for example,
is typically generated using an e-beam direct writing of a pattern
into a photoresist present on the silicon substrate. Subsequently
the pattern is etched into the silicon substrate. The pattern on
the silicon master mold is then replicated into the polymeric
material deposited on the surface of the mold. The polymeric
material is preferably a conformal material, which exhibits
sufficient rigidity to wear well when used as a contact mask
against a substrate, but which also can make excellent contact with
the radiation-sensitive material on the substrate surface. One
example of the conformal materials generally used as a transfer
masking material is PDMS, which can be cast upon the master mold
surface, cured with UV radiation, and peeled from the mold to
produce excellent replication of the mold surface.
[0056] FIG. 2 shows a cross-sectional view 200 of another
embodiment of an apparatus 200 useful in patterning of large areas
of substrate material. In FIG. 2, the substrate is a film 208 upon
which a pattern is imaged by radiation which passes through surface
relief 212 on a first (transparent) cylinder 206 while film 208
travels from roll 211 to roll 213. A second cylinder 215 is
provided on the backside 209 of film 208 to control the contact
between the film 208 and the first cylinder 206. The radiation
source 202 which is present in the hollow space 204 within
transparent cylinder 206 may be a mercury vapor lamp or another
radiation source which provides a radiation wavelength of 365 nm or
less. The surface relief 212 may be a phase-shift mask, for
example, where the mask includes a diffracting surface having a
plurality of indentations and protrusions, as discussed above in
the Background Art. The protrusions are brought into contact with a
surface of a positive photoresist (a radiation-sensitive material),
and the surface is exposed to 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. An
elastomeric phase mask conforms well to the surface of the
photoresist, and following development of the photoresist, features
smaller than 100 nm can be obtained
[0057] FIG. 3 shows a cross-sectional view 300 of another
embodiment of an apparatus 300 useful in patterning large areas of
substrate material. The substrate is a film 308 which travels from
roll 311 to roll 313. There is a layer of radiation-sensitive
material (not shown) on both the topside 310 of film 308 and the
bottom side 309 of film 308. There is a first transparent cylinder
306, with a hollow center 304, which includes a radiation source
302, having surface relief 312, which is used to pattern the top
side 310 of film 308. There is a second transparent cylinder 326,
with a hollow center 324, which includes a radiation source 322,
having surface relief 332, which is used to pattern the bottom side
209 of film 308.
[0058] FIG. 4A shows a cross-sectional view 400 of an embodiment of
a transparent cylinder 406 which includes a hollow center area 404
with an internal source of radiation 402. The surface relief 412 is
a conformal structure which includes polymer film 415 with a
patterned surface 413 which is particularly useful for near-field
lithography. The polymeric material of patterned surface 413 needs
to be sufficiently rigid that the pattern will contact a substrate
surface to be imaged in the proper location. At the same time, the
polymeric material must conform to the surface of a
radiation-sensitive material (not shown) which is to be imaged.
[0059] FIG. 4B shows an enlargement of surface 413, which is a
surface relief polymer structure 413 on top of polymeric base
material 415. In FIG. 4B, the polymer base material 415 may be
either the same polymeric material or may be a different polymeric
material from the patterned surface material 413. A transparent
conformal material such as a silicone or PDMS, for example, may be
used as polymer film 415, in combination with a more rigid
transparent overlying layer of material, such as PDMS with a
different ratio of mixing components, or polymethyl methacrylate
PMMA, for example. This provides a patterned surface 413, which
helps avoid distortion of features upon contact with a location on
the radiation-sensitive surface of a substrate (not shown), while
the polymeric base material simultaneously provides conformance
with the substrate surface in general.
[0060] FIG. 5A shows a cross sectional view 500 of a transparent
cylinder 506, with hollow central area 504 including a radiation
source 502, where the surface 511 presents an alternative
embodiment of surface relief 512. FIG. 5B shows an enlargement of
the surface relief 512, which is a thin metal layer 514 which is
patterned with a series of nanoholes 513, where the metal layer is
present on the exterior surface 511 of hollow transparent cylinder
506. The metal layer may be a patterned layer adhered to the
exterior surface of transparent cylinder 506. In the alternative, a
metal layer may be deposited on the surface of the transparent
cylinder by evaporation or sputtering or another technique known in
the art and then may subsequently etched or ablated with a laser to
provide a patterned metal exterior surface 511. FIG. 5C shows an
alternative surface relief 522 which may be used on the surface of
transparent cylinder 506. Surface relief 522 is formed by metal
particles 526 which are applied on an exterior surface 511 of
hollow transparent cylinder 506, or on a transparent film 524 which
is attached to the exterior surface 511 of hollow transparent
cylinder 506.
[0061] FIG. 6A is a schematic three dimensional illustration 600 of
a transparent cylinder 604 having a patterned surface 608. A
radiation source (not shown) is present within the interior of
transparent cylinder 604. The transparent cylinder 604 is suspended
above a substrate 610 using a tensioning device 602, which is shown
as springs in illustration 600. One of skill in the art of
mechanical engineering will be familiar with a number of tensioning
devices which may be used to obtain the proper amount of contact
between the outer surface 608 of transparent cylinder 604 and the
surface of substrate 610. In one embodiment method of using the
apparatus shown in FIG. 6A, the apparatus is used to image a
radiation-sensitive material (not shown) on a substrate 610, where
substrate 610 is a polymeric film, which may be supplied and
retrieved on a roll to roll system of the kind shown in FIG. 2. The
transparent cylinder 604 is lowered toward the polymeric film
substrate (or the polymeric film substrate is raised), until
contact is made with the radiation-sensitive material. The
polymeric film, which is typically elastomeric will create a
Van-der-Walls force bond with the radiation-sensitive material. The
transparent cylinder 604 may then be raised (or the polymeric film
substrate lowered) to a position where contact remains between the
surface 608 of transparent cylinder 604 and the surface of the
radiation-sensitive material, but the tension between the two
surfaces is such that the force placed on the surface 608 is
minimal. This enables the use of very fine nanopatterned features
on the surface 608 of transparent cylinder 604. When the substrate
610 begins to move, the transparent cylinder 604 will also move,
forcing transparent cylinder 604 to rotate, maintaining the dynamic
contact between the radiation-sensitive material and the underlying
polymeric film substrate 610. At any moment of the dynamic
exposure, the contact between the cylinder and a photosensitive
layer is limited to one narrow line. Due to strong Van-der Walls
forces between an elastomeric film, for example, on the cylinder
exterior surface and the radiation sensitive (photo sensitive)
layer on the substrate, contact is maintained uniform throughout
the entire process, and along the entire width of the mask (length)
on the cylinder surface. In instances where an elastomeric material
is not present on the cylinder surface which contacts the
substrate, an actuating (rotating) cylinder using a stepper-motor
synchronized with the translational movement of the substrate may
be used. This provides a slip-free exposure process for polymeric
or other cylinder surface material which does not provide strong
adhesion forces relative to the substrate.
[0062] FIG. 6B is a schematic of an embodiment 620 where the
radiation used to accomplish imaging is supplied from a radiation
source 612 exterior to cylinder 604, with the radiation distributed
internally 615 and 616 within the hollow portion of the cylinder
604. The radiation may be directed through the transparent cylinder
604 through the patterned mask surface 608 toward the
radiation-sensitive surface (not shown) of substrate 608 using
various lenses, mirrors, and combinations thereof.
[0063] FIG. 6C is a schematic of an embodiment 630 where the
radiation used to accomplish imaging of the radiation-sensitive
material is supplied from a location which is exterior to the
transparent cylinder 604. The exterior radiation source 612 is
focused 617 into a waveguide 618 and distributed from the waveguide
618 to an optical grating 620 present on the interior surface 601
of the cylinder 604.
[0064] FIG. 6D is a schematic of an embodiment 640 where the
radiation used to accomplish imaging is supplied from two exterior
radiation sources 612A and 612B, and is focused 621 and 619,
respectively, upon an optical grating 620 present on the interior
surface 601 of cylinder 604.
[0065] FIG. 7A is a schematic 700 showing the use of multiple
cylinders, such as two cylinders 702 and 704, for example, in
series to provide multiple patterning, which may be used to obtain
higher resolution, for example. The relative positions of the
cylinders 702 and 704, for example may be controlled using data
from an interferometer (not shown) in combination with a
computerized control system (not shown).
[0066] FIG. 7B is a cross-sectional schematic 720 showing a pattern
706 created by a first cylinder 702 after imaging and development
of a radiation-sensitive material 710. The altered pattern 708 is
after imaging and development of the radiation-sensitive material
710 where the altered pattern 708 is created by use of the first
cylinder 702 in combination with a second cylinder 704.
[0067] FIG. 8 shows a cross-sectional schematic of a deformable
cylinder 800, the interior 804 of which is pressurized using an
apparatus 813 which supplies an optically transparent gas, such as
nitrogen, for example. The outer surface 811 of deformable cylinder
800 may be a nanopatterned/nanostructured film 812 of a conformable
material, which can be rolled upon a non-flat substrate 805 so that
radiation from radiation source 802 can be precisely applied over a
surface 816 of substrate 805.
[0068] In another embodiment, a liquid having a refractive index of
greater than one may be used between the cylinder surface and a
radiation sensitive (photo sensitive, for example) material present
on the substrate surface. Water may be used, for example. This
enhances the pattern feature's contrast in the photosensitive
layer.
[0069] While the invention has been described in detail for a
variety of embodiments above, various modifications within the
scope and spirit of the invention will be apparent to those of
working skill in this technological field. Accordingly, the scope
of the invention should be measured by the appended claim
* * * * *