U.S. patent application number 10/776881 was filed with the patent office on 2004-10-14 for apparatus for fabricating nanoscale patterns in light curable compositions using an electric field.
This patent application is currently assigned to The Board of Regents, The University of Texas System. Invention is credited to Bonnecaze, Roger T., Sreenivasan, Sidlgata V., Willson, Carlton Grant.
Application Number | 20040200411 10/776881 |
Document ID | / |
Family ID | 33132244 |
Filed Date | 2004-10-14 |
United States Patent
Application |
20040200411 |
Kind Code |
A1 |
Willson, Carlton Grant ; et
al. |
October 14, 2004 |
Apparatus for fabricating nanoscale patterns in light curable
compositions using an electric field
Abstract
The present invention is directed to an apparatus for patterning
a liquid on a substrate, with the apparatus including, a template
having a pair of spaced-apart recessions with a protrusion disposed
therebetween, with the protrusion being spaced-apart from the
substrate a first distance and each of the pair of spaced-apart
recessions being spaced-apart from the substrate a second distance,
with the second distance being greater than the first distance; and
a source of voltage in electrical communication with the template
to produce an electric field between the template and the
substrate, with a strength of the electrical field being inversely
proportional to the first and second distances.
Inventors: |
Willson, Carlton Grant;
(Austin, TX) ; Sreenivasan, Sidlgata V.; (Austin,
TX) ; Bonnecaze, Roger T.; (Austin, TX) |
Correspondence
Address: |
Kenneth C. Brooks
Molecular Imprints, Inc.
Legal Department
P.O. BOX 81536
Austin
TX
78708-1536
US
|
Assignee: |
The Board of Regents, The
University of Texas System
Austin
TX
|
Family ID: |
33132244 |
Appl. No.: |
10/776881 |
Filed: |
February 11, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10776881 |
Feb 11, 2004 |
|
|
|
09905718 |
May 16, 2001 |
|
|
|
Current U.S.
Class: |
118/500 ;
118/503 |
Current CPC
Class: |
B05D 3/067 20130101;
G03F 7/0002 20130101; B82Y 10/00 20130101; B81C 1/0046 20130101;
B05D 1/40 20130101; B29C 2043/3211 20130101; B05D 3/145 20130101;
B82Y 40/00 20130101; B29C 2043/025 20130101; B29C 43/003
20130101 |
Class at
Publication: |
118/500 ;
118/503 |
International
Class: |
B05D 001/04 |
Claims
What is claimed is:
1. An apparatus for patterning a liquid on a substrate, said
apparatus comprising: a template having a pair of spaced-apart
recessions with a protrusion disposed therebetween, with said
protrusion being spaced-apart from said substrate a first distance
and each of said pair of spaced-apart recessions being spaced-apart
from said substrate a second distance, with said second distance
being greater than said first distance; and a source of voltage in
electrical communication with said template to produce an electric
field between said template and said substrate, with a strength of
said electrical field being inversely proportional to said first
and second distances.
2. The apparatus as recited in claim 1 wherein a difference between
said first distance and said second distance defines an electric
field gradient, with a portion of said electric field present
between said protrusion and said substrate being greater than a
subsection of said electric field present between each of said pair
of spaced-apart recessions and said substrate, with said portion
having sufficient magnitude to create a contiguous region of said
liquid on said an area of said substrate in superimposition with
said protrusion.
3. The apparatus as recited in claim 1 wherein said protrusion
consists of Indium Tin Oxide (ITO).
4. The apparatus as recited in claim 1 wherein said template
further includes a layer of Indium Tin Oxide (ITO) and said pair of
spaced-apart recessions and said protrusion are formed in said
layer of ITO.
5. The apparatus as recited in claim 1 wherein said template
further includes a layer of fused silica and a layer of Indium Tin
Oxide (ITO).
6. The apparatus as recited in claim 1 wherein said template
further includes a layer of fused silica and a layer of Indium Tin
Oxide (ITO), with said source of voltage being in electrical
communication with said layer of ITO.
7. The apparatus as recited in claim 1 wherein said template is
substantially transparent to ultraviolet light.
8. The apparatus as recited in claim 1 wherein said template
further includes a fluorine containing monolayer.
9. The apparatus as recited in claim 1 wherein template further
includes a layer of Indium Tin Oxide (ITO) and said pair of
spaced-apart recessions and said protrusion are formed in said
layer of ITO and further including a fluorine containing monolayer
positioned adjacent to said layer of ITO, with said fluorine
containing monolayer being positioned between said substrate and
said layer of ITO.
10. An apparatus for patterning a liquid on a substrate, said
apparatus comprising: a template having a plurality of protrusions,
each of which is spaced-apart from said substrate a first distance,
and a plurality of recessions, each of which is spaced-apart from
said substrate a second distance; and a source of voltage in
electrical communication with said template to produce an electric
field between said template and said substrate, with a difference
between said first distance and said second distance defining a
plurality of electric field gradients, with a portion of said
electric field present between said plurality of protrusions and
said substrate being greater than a subsection of said electric
field present between said plurality of recessions and said
substrate.
11. The apparatus as recited in claim 10 wherein said plurality of
protrusion consist of Indium Tin Oxide (ITO).
12. The apparatus as recited in claim 10 wherein said template
further includes a layer of Indium Tin Oxide (ITO), with said
plurality of protrusions and said plurality of recessions being
present in said layer of ITO.
13. The apparatus as recited in claim 10 wherein said template
further includes a layer of fused silica and a layer of Indium Tin
Oxide (ITO).
14. The apparatus as recited in claim 10 wherein said template
further includes a layer of fused silica and a layer of Indium Tin
Oxide (ITO), with said source of voltage being in electrical
communication with said layer of ITO.
15. The apparatus as recited in claim 10 wherein said template is
substantially transparent to ultraviolet light.
16. The apparatus as recited in claim 10 wherein said template
further includes a fluorine containing monolayer.
17. The apparatus as recited in claim 10 wherein said template
further includes a layer of Indium Tin Oxide (ITO), with said
plurality of recessions and said plurality of protrusions are
formed in said layer of ITO and further including a fluorine
containing monolayer positioned adjacent to said layer of ITO, with
said fluorine containing monolayer being positioned between said
substrate and said layer of ITO.
18. The apparatus as recited in claim 10 wherein said portion of
said electric field has sufficient magnitude to create a contiguous
region of said liquid on an area of said substrate in
superimposition with said plurality of protrusions.
19. An apparatus for patterning a liquid on a substrate, said
apparatus comprising: a template having a plurality of protrusions
and recessions, spaced apart from said substrate, with said liquid
being disposed therebetween; a source of voltage in electrical
communication with said template to produce an electric field
between said template and said substrate, with a subportion of said
electric field present between each of said plurality of
protrusions being greater than a subpart of said electric field
present between each of said plurality of recessions, with adjacent
subportions and subparts defining an electric field gradient, with
said subportions having sufficient magnitude to move said liquid to
form a continuous region of said liquid between each of said
plurality of protrusions and said substrate, and said electric
field gradient preventing said liquid from forming a continuous
area of said liquid in regions of said substrate in superimposition
with each of said plurality of recessions.
20. The apparatus as recited in claim 19 wherein said template
further includes a layer of Indium Tin Oxide (ITO), with said
plurality of protrusions and recessions being present in said layer
of ITO.
21. The apparatus as recited in claim 19 wherein said template
further includes a layer fused silica and a layer of Indium Tin
Oxide (ITO).
22. The apparatus as recited in claim 19 wherein said template
further includes a layer of fused silica and a layer of Indium Tin
Oxide (ITO), with said source
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a divisional of U.S. patent
application Ser. No. 09/905,718 filed on May 16, 2001 entitled
"Method and System for Fabricating Nanoscale Patterns in Light
Curable Compositions using an Electric Field," which is
incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention generally relates to the area of low cost,
high-resolution, high-throughput lithography with the potential to
make structures that are below 100 nm in size.
[0004] 2. Description of the Relevant Art
[0005] Optical lithography techniques are currently used to make
microelectronic devices. However, these methods are reaching their
limits in resolution. Sub-micron scale lithography has been a
critical process in the microelectronics industry. The use of
sub-micron scale lithography allows manufacturers to meet the
increased demand for smaller and more densely packed electronic
components on chips. The finest structures producible in the
microelectronics industry are currently on the order of about 0.13
.mu.m. It is expected that in the coming years, the
microelectronics industry will pursue structures that are smaller
than 0.05 .mu.m (50 nm). Further, there are emerging applications
of nanometer scale lithography in the areas of opto-electronics and
magnetic storage. For example, photonic crystals and high-density
patterned magnetic memory of the order of terabytes per square inch
require nanometer scale lithography.
[0006] For making sub-50 nm structures, optical lithography
techniques may require the use of very short wavelengths of light
(for instance 13.2 nm). At these short wavelengths, few, if any,
materials are optically transparent and therefore imaging systems
typically have to be constructed using complicated reflective
optics [1]. Furthermore, obtaining a light source that has
sufficient output intensity at these wavelengths of light is
difficult. Such systems lead to extremely complicated equipment and
processes that appear to be prohibitively expensive.
High-resolution e-beam lithography techniques, though very precise,
typically are too slow for high-volume commercial applications.
[0007] One of the main challenges with current imprint lithography
technologies is the need to establish direct contact between the
template (master) and the substrate. This may lead to defects, low
process yields, and low template life. Additionally, the template
in imprint lithography typically is the same size as the eventual
structures on the substrate (1.times.), as compared to 4.times.
masks typically used in optical lithography. The cost of preparing
the template and the life of the template are issues that may make
imprint lithography impractical. Hence there exists a need for
improved lithography techniques that address the challenges
associated with optical lithography, e-beam lithography and imprint
lithography for creating very high-resolution features.
SUMMARY OF THE INVENTION
[0008] The present invention is directed to an apparatus for
patterning a liquid on a substrate, with the apparatus including, a
template having a pair of spaced-apart recessions with a protrusion
disposed therebetween, with the protrusion being spaced-apart from
the substrate a first distance and each of the pair of spaced-apart
recessions being spaced-apart from the substrate a second distance,
with the second distance being greater than the first distance; and
a source of voltage in electrical communication with the template
to produce an electric field between the template and the
substrate, with a strength of the electrical field being inversely
proportional to the first and second distances. These and other
embodiments are discussed below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIGS. 1A-1E illustrate a version of the imprint lithography
process according to the invention;
[0010] FIG. 2 is a process flow diagram showing the sequence of
steps of the imprint lithography process of FIGS. 1A-1E;
[0011] FIG. 3 is a side view of a template positioned over a
substrate for electric field based lithography;
[0012] FIG. 4 is a side view of a process for forming nanoscale
structures using direct contact with a template;
[0013] FIG. 5 is a side view of a process for forming nanoscale
structures using non-direct contact with a template;
[0014] FIG. 6 is a side view of a substrate holder configured to
alter the planarity of the substrate; and
[0015] FIG. 7 is a side view of an apparatus for positioning a
template over a substrate.
DETAILED DESCRIPTION OF THE INVENTION
[0016] FIGS. 1A through 1E illustrate an imprint lithography
process according to the invention, denoted generally as 10. In
FIG. 1A, a template 12 is orientated in spaced relation to a
substrate 14 so that a gap 16 is formed in the space separating
template 12 and substrate 14. A surface 18 of template 12 is
treated with a thin layer 20 that lowers the template surface
energy and assists in separation of template 12 from substrate 14.
The manner of orientation including devices for controlling of gap
16 between template 12 and substrate 14 are discussed below. Next,
in FIG. 1B, gap 16 is filled with a substance 22 that conforms to
the shape of surface 18. Preferably, substance 22 is a liquid so
that it fills the space of gap 16 rather easily without the use of
high temperatures and gap 16 can be closed without requiring high
pressures.
[0017] A curing agent 24, shown in FIG. 1C, is applied to template
12 causing substance 22 to harden and to assume the shape of the
space defined by gap 16 between template 12 and substrate 14. In
this way, desired features 26, shown in FIG. 1D, from template 12
are transferred to the upper surface of substrate 14. A transfer
layer 28 is provided directly on the upper surface of substrate 14
which facilitates the amplification of features transferred from
template 12 onto substrate 14 to generate high aspect ratio
features.
[0018] In FIG. 1D, template 12 is removed from substrate 14 leaving
the desired features 26 thereon. The separation of template 12 from
substrate 14 must be done so that desired features 26 remain intact
without shearing or tearing from the surface of substrate 14.
[0019] Finally, in FIG. 1E, features 26 transferred from template
12, shown in FIG. 1D, to substrate 14 are amplified in vertical
size by the action of transfer layer 28, as is known in the use of
bi-layer resist processes. The resulting structure can be further
processed to complete the manufacturing process using well-known
techniques. FIG. 2 summarizes the imprint lithography process,
denoted generally as 30, of the present invention in flow chart
form. Initially, at step 32, course orientation of a template and a
substrate is performed so that a rough alignment of the template
and the substrate is achieved. The advantage of course orientation
at step 32 is that it allows pre-calibration in a manufacturing
environment where numerous devices are to be manufactured with
efficiency and with high production yields. For example, where the
substrate comprises one of many die on a semiconductor wafer,
course alignment (step 32) can be performed once on the first die
and applied to all other dies during a single production run. In
this way, production cycle times are reduced and yields are
increased.
[0020] Next, at step 34, the spacing between the template and the
substrate is controlled so that a relatively uniform gap is created
between the two layers permitting the type of precise orientation
required for successful imprinting. The present invention provides
a device and a system for achieving the type of orientation (both
course and fine) required at step 34. At step 36, a liquid is
dispensed into the gap between the template and the substrate.
Preferably, the liquid is a UV curable organosilicon solution or
other organic liquids that become a solid when exposed to UV light.
The fact that a liquid is used eliminates the need for high
temperatures and high pressures associated with prior art
lithography techniques.
[0021] At step 38, the gap is closed with fine orientation of the
template about the substrate and the liquid is cured resulting in a
hardening of the liquid into a form having the features of the
template. Next, the template is separated from the substrate, step
40, resulting in features from the template being imprinted or
transferred onto the substrate. Finally, the structure is etched,
step 42, using a preliminary etch to remove residual material and a
well-known oxygen etching technique to etch the transfer layer.
[0022] As mentioned above, recent imprint lithography techniques
with UV curable liquids [2, 3, 4, 5] and polymers [6] have been
described for preparing nanoscale structures. These techniques may
potentially be significantly lower cost than optical lithography
techniques for sub-50 nm resolution. Recent research [7, 8] has
also investigated the possibility of applying electric fields and
van der Waals attractions between a template that possesses a
topography and a substrate that contains a polymeric material to
form nanoscale structures. This research has been for systems of
polymeric material that may be heated to temperatures that are
slightly above their glass transition temperature. These viscous
polymeric materials tend to react very slowly to the electric
fields (order of several minutes) making them less desirable for
commercial applications.
[0023] The embodiments described herein may potentially create
lithographic patterned structures quickly (in a time of less than
about 1 second). The structures may have sizes of tens of
nanometers. The structures may be created by curing a polymerizable
composition (e.g., a spin-coated UV curable liquid) in the presence
of electric fields. Curing the polymerizable composition then sets
the pattern of structures on the substrate. The pattern may be
created by placing a template with a specific nanometer-scale
topography at a carefully controlled nanoscale distance from the
surface of a thin layer of the liquid on a substrate. If all or a
portion of the desired structures are regularly repeating patterns
(such as an array of dots), the pattern on the template may be
considerably larger than the size of the desired repeating
structures. The template may be formed using direct write e-beam
lithography. The template may be used repeatedly in a
high-throughput process to replicate nanostructures onto
substrates. In one embodiment, the template may be fabricated from
a conducting material such as Indium Tin Oxide that is also
transparent to UV light. The template fabrication process is
similar to that of phase shift photomasks for optical lithography;
phase shift masks require an etch step that creates a topography on
the template.
[0024] The replication of the pattern on the template may be
achieved by applying an electric field between the template and the
substrate. Because the liquid and air (or vacuum) have different
dielectric constants and the electric field varies locally due to
the presence of the topography of the template, an electrostatic
force may be generated that attracts regions of the liquid toward
the template. At high electric field strengths, the polymerizable
composition may be made to attach to the template and dewet from
the substrate at certain points. This polymerizable composition may
be hardened in place by polymerization of the composition. The
template may be treated with a low energy self-assembled monolayer
film (e.g., a fluorinated surfactant) to aid in detachment of the
template the polymerized composition.
[0025] It may be possible to control the electric field, the design
of the topography of the template and the proximity of the template
to the liquid surface so as to create a pattern in the
polymerizable composition that does not come into contact with the
surface of the template. This technique may eliminate the need for
mechanical separation of the template from the polymerized
composition. This technique may also eliminate a potential source
of defects in the pattern. In the absence of contact, however, the
liquid may not form sharp, high-resolution structures that are as
well defined as in the case of contact. This may be addressed by
first creating structures in the polymerizable composition that are
partially defined at a given electric field. Subsequently, the gap
may be increased between the template and substrate while
simultaneously increasing the magnitude of the electric field to
"draw-out" the liquid to form clearly defined structures without
requiring contact.
[0026] The polymerizable composition may be deposited on top of a
hard-baked resist material to lead to a bi-layer process. Such a
bi-layer process allows for the formation of low aspect ratio,
high-resolution structures using the electrical fields followed by
an anisotropic etch that results in high-aspect ratio,
high-resolution structures. Such a bi-layer process may also be
used to perform a "metal lift-off process" to deposit a metal on
the substrate such that the metal is left behind after lift-off in
the trench areas of the originally created structures.
[0027] By using a low viscosity polymerizable composition, the
pattern formation due to the electric field may be fast (e.g., less
than about 1 sec.), and the structure may be rapidly cured.
Avoiding temperature variations in the substrate and the
polymerizable composition may also avoid undesirable pattern
distortion that makes nano-resolution layer-to-layer alignment
impractical. In addition, as mentioned above, it is possible to
quickly form a pattern without contact with the template, thus
eliminating defects associated with imprint methods that require
direct contact.
[0028] FIG. 3 depicts an embodiment of the template and the
substrate designs. Template 12 may be formed from a material that
is transparent to activating light produced by curing agent 24 to
allow curing of substance 22, with substance 22 being a
polymerizable composition, by exposure to activating light. Forming
template 12 from a transparent material may also allow the use of
established optical techniques to measure gap 16 between template
12 and substrate 14 and to measure overlay marks to perform overlay
alignment and magnification correction during formation of the
structures. Template 12 may also be thermally and mechanically
stable to provide nano-resolution patterning capability. Template
12 may also include an electrically conducting material to allow
electric fields to be generated at the template-substrate
interface.
[0029] In one embodiment, depicted in FIG. 3, a thick blank of
fused silica has been chosen as the base material for template 12.
Indium Tin Oxide (ITO) may be deposited onto the fused Silica. ITO
is transparent to visible and UV light and is a conducting
material. ITO may be patterned using high-resolution e-beam
lithography. Thin layer 20 (for example, a fluorine containing
self-assembly monolayer) may be coated onto template 12 to improve
the release characteristics between template 12 and substance 22.
Substrate 14 may include standard wafer materials, such as Si,
GaAs, SiGeC and InP. A UV curable liquid may be used as substance
22. Substance 22 may be spin coated onto substrate 14. An optional
transfer layer 28 may be placed between substrate 14 and substance
22. Transfer layer 28 may be used for bi-layer process. Transfer
layer 28 material properties and thickness may be chosen to allow
for the creation of high-aspect ratio structures from low-aspect
ratio structures created in substance 22. An electric field may be
generated between template 12 and substrate 14 by connecting the
ITO to a voltage source.
[0030] In FIGS. 4 and 5, two variants of the above-described
process are presented. In each variant, it is assumed that a
desired uniform gap 16 may be maintained between template 12 and
substrate 14. An electric field of the desired magnitude may be
applied resulting in the attraction of substance 22 towards the
raised portions of template 12. In FIG. 4, gap 16 and the field
magnitudes are such that substance 22 makes direct contact and
adheres to template-12. A UV curing process may be used to harden
substance 22 in that configuration. Once the structures have been
formed, template 12 is separated from substrate 14 by either
increasing gap 16 till the separation is achieved, or by initiating
a peel and pull motion wherein template 12 is peeled away from
substrate 14 starting at one edge of template 12. Prior to its use,
template 12 is assumed to be treated with thin layer 20 that
assists in the separation step.
[0031] In FIG. 5, gap 16 and the field magnitudes are chosen such
that substance 22 achieves a topography that is essentially the
same as that of template 12. This topography may be achieved
without making direct contact with template 12. A UV curing process
may be used to harden substance 22 in that configuration. In both
the processes of FIGS. 4 and 5, a subsequent etch process may be
used to eliminate the residual layer of the UV cured material. A
further etch may also be used if transfer layer 28 is present
between substance 22 and substrate 14, as shown in FIGS. 4 and 5.
As mentioned earlier, transfer layer 28 may be used to obtain a
high-aspect ratio structure from a low aspect ratio structure
created in substance 22.
[0032] FIG. 6 illustrates mechanical devices that may increase the
planarity of the substrate. The template may be formed from
high-quality optical flats of fused-silica with Indium Tin Oxide
deposited on the fused silica. Therefore, the template typically
possess extremely high planarity. The substrates typically have low
planarity. Sources of variations in the planarity of the substrate
include poor finishing of the back side of the wafer, the presence
of particular contaminants trapped between the wafer and the wafer
chuck, and wafer distortions caused by thermal processing of the
wafer. In one embodiment, the substrate may be mounted on a chuck
whose top surface shape may be altered by a large array of
piezoelectric actuators. The chuck thickness may be such that
accurate corrections in surface topography of up to a few microns
may be achieved. The substrate may be mounted to the chuck such
that it substantially conforms to the shape of the chuck. Once the
substrate is loaded on to the chuck, a sensing system (e.g., an
optical surface topography measurement system) may be used to map
the top surface of the substrate accurately. Once the surface
topology is known, the array of piezoelectric actuators may be
actuated to rectify the topography variations such that the upper
surface of the substrate exhibits a planarity of less than about
lam. Since the template is assumed to be made from an optically
flat material, this leads to template and substrate that are high
quality planar surfaces.
[0033] The mechanical device in FIG. 7 may be used to perform a
high-resolution gap control at the template-substrate interface.
This device may control two tilting degrees of freedom (about
orthogonal axes that lie on the surface of the template) and the
vertical translation degree of freedom of the template. The
magnitude of the gap between the template and the substrate may be
measured in real-time. These real-time measurements may be used to
identify the corrective template motions required about the tilting
degrees of freedom and the vertical displacement degree of freedom.
The three gap measurements may be obtained by using a broadband
optical interferometric approach that is similar to the one used
for measuring thicknesses of thin films and thin film stacks. This
approach of capacitive sensing may also be used for measuring these
three gaps.
[0034] Further modifications and alternative embodiments of various
aspects of the invention will be apparent to those skilled in the
art in view of this description. Accordingly, this description is
to be construed as illustrative only and is for the purpose of
teaching those skilled in the art the general manner of carrying
out the invention. It is to be understood that the forms of the
invention shown and described herein are to be taken as the
presently preferred embodiments. Elements and materials may be
substituted for those illustrated and described herein, parts and
processes may be reversed, and certain features of the invention
may be utilized independently, all as would be apparent to one
skilled in the art after having the benefit of this description of
the invention. Changes may be made in the elements described herein
without departing from the spirit and scope of the invention as
described in the following claims.
References
[0035] The following references are specifically incorporated
herein by reference:
[0036] 1. "Getting More from Moore's," Gary Stix, Scientific
American, April 2001.
[0037] 2. "Step and Flash Imprint Lithography: An alternative
approach to high resolution patterning," M. Colburn, S. Johnson, M.
Stewart, S. Damle, B. J. Choi, T. Bailey, M. Wedlake, T.
Michaelson, S. V. Sreenivasan, J. Ekerdt, C. G. Willson, Proc. SPIE
Vol.3676, 379-389, 1999.
[0038] 3. "Design of Orientation Stages for Step and Flash Imprint
Lithography," B. J. Choi, S. Johnson, M. Colburn, S. V.
Sreenivasan, C. G. Willson, To appear in J. of Precision
Engineering.
[0039] 4. U.S. patent application Ser. No. 09/266,663 entitled
"Step and Flash Imprint Lithography" to Grant Willson and Matt
Colburn.
[0040] 5. U.S. patent application Ser. No. 09/698,317 entitled
"High Precision Orientation Alignment and Gap Control Stages for
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Steve Johnson.
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B 17 (6), 3197-3202, 1999
[0043] 8. "Large Area Domain Alignment in Block Copolymer Thin
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Pitsikalis, T. Morkved, H. Jaeger and T. Russell, Macromolecules
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