U.S. patent application number 11/827480 was filed with the patent office on 2007-11-08 for increasing adhesion in an imprinting procedure.
Invention is credited to Sivapackia Ganapathlappan, Gun Young Jung, Zhiyong Li, Richard Stanley Williams.
Application Number | 20070259189 11/827480 |
Document ID | / |
Family ID | 35595839 |
Filed Date | 2007-11-08 |
United States Patent
Application |
20070259189 |
Kind Code |
A1 |
Jung; Gun Young ; et
al. |
November 8, 2007 |
Increasing adhesion in an imprinting procedure
Abstract
A method for increasing adhesion between a substrate and a
polymeric imprintable material during an imprinting procedure. The
method includes chemically bonding a plurality of molecules to a
surface of a substrate to form a self-assembled monolayer thereon.
A monomer is copolymerized with the self-assembled monolayer to
form a polymeric imprintable material that is chemically bonded to
the self-assembled monolayer. Adhesion between the polymeric
imprintable material and the substrate is substantially increased
by the self-assembled monolayer.
Inventors: |
Jung; Gun Young; (Mountain
View, CA) ; Li; Zhiyong; (Palo Alto, CA) ;
Williams; Richard Stanley; (Portola Valley, CA) ;
Ganapathlappan; Sivapackia; (Los Altos, CA) |
Correspondence
Address: |
HEWLETT PACKARD COMPANY
P O BOX 272400, 3404 E. HARMONY ROAD
INTELLECTUAL PROPERTY ADMINISTRATION
FORT COLLINS
CO
80527-2400
US
|
Family ID: |
35595839 |
Appl. No.: |
11/827480 |
Filed: |
July 11, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10929810 |
Aug 30, 2004 |
7252862 |
|
|
11827480 |
Jul 11, 2007 |
|
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Current U.S.
Class: |
428/429 |
Current CPC
Class: |
B82Y 30/00 20130101;
Y10T 428/31935 20150401; B82Y 40/00 20130101; Y10T 428/31855
20150401; Y10T 428/31692 20150401; G03F 7/0002 20130101; B05D 1/185
20130101; B82Y 10/00 20130101; Y10T 428/31612 20150401; Y10T
428/31938 20150401 |
Class at
Publication: |
428/429 |
International
Class: |
B32B 17/06 20060101
B32B017/06 |
Claims
1-22. (canceled)
23. A substrate for use in an imprinting process, the substrate
comprising: a self-assembled monolayer formed on a surface of the
substrate; and a polymeric imprintable material chemically bonded
to the self-assembled monolayer; wherein the self-assembled
monolayer substantially increases adhesion between the substrate
and the polymeric imprintable material.
24. The substrate as defined in claim 23 wherein the substrate
comprises silicon, silicon dioxide, glass, quartz, alumina,
germanium, germanium oxide, tin, tin oxide, and mixtures
thereof.
25. The substrate as defined in claim 23 wherein the self-assembled
monolayer comprises a plurality of molecules, each of the plurality
of molecules having a self-assembling connecting group at one end
and a linking group at an opposed end.
26. The substrate as defined in claim 25 wherein the self-assembled
monolayer is formed by chemically bonding the surface of the
substrate to the self-assembling connecting groups of the plurality
of molecules.
27. The substrate as defined in claim 25 wherein the
self-assembling connecting group comprises at least one of hydroxyl
groups, chlorine groups, acetoxy groups, amino groups, thiol
groups, and mixtures thereof; and wherein the linking group
comprises at least one of acryloxy groups, methacryloxy groups,
vinyl groups, and mixtures thereof.
28. The substrate as defined in claim 25, further comprising at
least one of hydroxyl groups, chlorine groups, amino groups, thiol
groups, and acetoxy groups attached to the surface of the
substrate, the at least one of the hydroxyl groups, chlorine
groups, amino groups, thiol groups, and acetoxy groups adapted to
chemically bond to at least one of the plurality of molecules via
the self-assembling connecting groups, wherein the polymeric
imprintable material is adapted to chemically bond to the
self-assembled monolayer.
29. The substrate as defined in claim 25 wherein the plurality of
molecules comprises at least one molecular species selected from
methacryloxy propyltrichlorosilane,
(methacryloyloxypropyl)trimethoxysilane,
3-methacryloxypropylbis(trimethylsiloxy)methylsilane,
3-methacryloxypropyldimethylchlorosilane,
3-methacryloxypropylmethyldichlorosilane,
3-methacryloxypropylmethyldimethoxysilane,
3-acryloxypropylmethyldichlorosilane,
acryloxypropylmethyldimethoxysilane,
3-acryloxypropyltrichlorosilane, acryloxypropyltrimethoxysilane,
vinyltriacetoxysilane, vinylmethyldiethoxysilane,
vinyltrichlorosilane, vinyltrimethoxysilane,
vinylmethyidiacetoxysilane, hydroxyethyl methacrylate, hydroxyethyl
acrylate, and mixtures thereof.
30. The substrate as defined in claim 23, further comprising at
least one of hydroxyl groups, chlorine groups, amino groups, thiol
groups, and acetoxy groups chemically bonding the surface of the
substrate to the self-assembled monolayer.
31. The substrate as defined in claim 23 wherein the polymeric
imprintable material is formed by copolymerizing a monomer with the
self-assembled monolayer.
32. The substrate as defined in claim 31 wherein copolymerization
is initiated by at least one of ultraviolet irradiation and thermal
treatment.
33. The substrate as defined in claim 31 wherein the monomer
comprises at least one of benzyl methacrylate, styrene, methyl
methacrylate, hexyl acrylate, hexyl methacrylate, butyl
methacrylate, butyl acrylate, lauryl methacrylate, lauryl acrylate,
isodecyl acrylate, isodecyl methacrylate, octadecyl acrylate,
octadecyl methacrylate, ethylene glycol dimethacrylate,
divinylbenzene, vinylbenzyl chloride, hydroxyethyl methacrylate,
hydroxyethyl acrylate, and mixtures thereof.
34. The substrate as defined in claim 23 wherein the polymeric
imprintable material comprises a resist polymer.
35. A method for increasing adhesion between a substrate and a
polymeric imprintable material during an imprinting procedure, the
method comprising: attaching a plurality of monomers of an
imprintable material to a plurality of molecules, the plurality of
molecules adapted to form a self-assembled monolayer; chemically
bonding the plurality of molecules to a surface of the substrate to
form a self-assembled monolayer having the plurality of monomers
attached thereto; and copolymerizing the plurality of monomers with
the self-assembled monolayer to form the polymeric imprintable
material chemically bonded to the self-assembled monolayer; wherein
the self-assembled monolayer substantially increase adhesion
between the polymeric imprintable material and the substrate.
36. The method as defined in claim 35 wherein each of the plurality
of molecules comprises a self-assembling connecting group at one
end and a linking group at an opposed end.
37. The method as defined in claim 36 wherein the self-assembled
monolayer is chemically bonded to the polymeric imprintable
material via the linking group.
38. The method as defined in claim 36 wherein the self-assembled
monolayer is chemically bonded to the surface of the substrate via
the self-assembling connecting group.
39. The method as defined in claim 36 wherein the self-assembling
connecting group comprises at least one of hydroxyl groups,
chlorine groups, acetoxy groups, amino groups, thiol groups, and
mixtures thereof; and wherein the linking group comprises at least
one of acryloxy groups, methacryloxy groups, vinyl groups, and
mixtures thereof.
40. The method as defined in claim 36, further comprising forming
at least one of hydroxyl groups, chlorine groups, amino groups,
thiol groups, and acetoxy groups on the surface of the substrate
prior to chemically bonding the plurality of molecules, and wherein
the at least one of the hydroxyl groups, chlorine groups, amino
groups, thiol groups, and acetoxy groups is adapted to chemically
bond to at least one of the self-assembling connecting groups.
41. The method as defined in claim 35, further comprising forming
at least one of hydroxyl groups, chlorine groups, amino groups,
thiol groups, and acetoxy groups on the surface of the substrate
prior to chemically bonding the plurality of molecules, and wherein
the at least one of the hydroxyl groups, chlorine groups, amino
groups, thiol groups, and acetoxy groups is adapted to chemically
bond to the plurality of molecules.
42. The method as defined in claim 35 wherein chemically bonding is
accomplished via ionic bonding, covalent bonding, and coordination
bonding.
43. The method as defined in claim 35 wherein copolymerization is
initiated by at least one of ultraviolet irradiation and thermal
treatment.
44. The method as defined in claim 35 wherein the plurality of
monomers comprises at least one of benzyl methacrylate, styrene,
methyl methacrylate, hexyl acrylate, hexyl methacrylate, butyl
methacrylate, butyl acrylate, lauryl methacrylate, lauryl acrylate,
isodecyl acrylate, isodecyl methacrylate, octadecyl acrylate,
octadecyl methacrylate, ethylene glycol dimethacrylate,
divinylbenzene, vinylbenzyl chloride, hydroxyethyl methacrylate,
hydroxyethyl acrylate, and mixtures thereof.
45. The method as defined in claim 35 wherein the plurality of
molecules comprises at least one molecular species selected from
methacryloxy propyltrichlorosilane,
(methacryloyloxypropyl)trimethoxysilane,
3-methacryloxypropylbis(trimethylsiloxy)methylsilane,
3-methacryloxypropyldimethylchlorosilane,
3-methacryloxypropylmethyidichlorosilane,
3-methacryloxypropylmethyldimethoxysilane,
3-acryloxypropylmethyldichlorosilane,
acryloxypropylmethyldimethoxysilane,
3-acryloxypropyltrichlorosilane, acryloxypropyltrimethoxysilane,
vinyltriacetoxysilane, vinylmethyldiethoxysilane,
vinyltrichlorosilane, vinyltrimethoxysilane,
vinylmethyidiacetoxysilane, hydroxyethyl methacrylate, hydroxyethyl
acrylate, and mixtures thereof.
46. The method as defined in claim 35 wherein the substrate
comprises silicon, silicon dioxide, glass, quartz, alumina,
germanium, germanium oxide, tin, tin oxide, and mixtures
thereof.
47. The method as defined in claim 35 wherein the polymeric
imprintable material comprises a resist polymer.
48. The method as defined in claim 35 wherein attaching the
plurality of monomers to the plurality of molecules is accomplished
by chemical bonding.
49. A method for aiding release of a polymeric imprintable material
from a mold having features thereon during an imprinting procedure,
the method comprising forming the polymeric imprintable material
such that it is chemically bonded to a self-assembled monolayer
that is chemically bonded to a surface of a substrate, wherein the
polymeric imprintable material is adapted to contact the mold
during the imprinting procedure, and wherein the self-assembled
monolayer substantially increases adhesion between the polymeric
imprintable material and the substrate, thereby aiding in release
of the polymeric imprintable material from the mold.
50. The method as defined in claim 49 wherein the mold comprises a
release layer disposed thereon.
51. The method as defined in claim 49 wherein the self-assembled
monolayer comprises a plurality of molecules, each of the plurality
of molecules having a self-assembling connecting group at one end
and a linking group at an opposed end, and wherein the plurality of
molecules chemically bonds to the substrate surface via the
self-assembling connecting groups.
52. The method as defined in claim 51 wherein a plurality of
monomers is attached to the linking groups of the plurality of
molecules prior to chemically bonding the self-assembling
connecting groups to the surface of the substrate to form the
self-assembled monolayer.
53. The method as defined in claim 52 wherein the polymeric
imprintable material is formed by the copolymerization of the
plurality of monomers with the linking groups.
54. The method as defined in claim 53 wherein copolymerization is
initiated by at least one of ultraviolet irradiation and thermal
treatment.
55. The method as defined in claim 51 wherein the polymeric
imprintable material is formed by copolymerizing a plurality of
monomers with the linking groups after the self-assembling
connecting groups are bonded to the substrate surface.
56. The method as defined in claim 55 wherein copolymerization is
initiated by at least one of ultraviolet irradiation and thermal
treatment.
57. A molecule for increasing adhesion between a substrate and a
polymeric imprintable material, the molecule comprising: a
self-assembling connecting group at one end of the molecule, the
self-assembling connecting group adapted to connect the molecule to
the substrate, thereby forming a self-assembled monolayer; and a
linking group at an opposed end of the molecule, the linking group
adapted to connect the self-assembled monolayer to the polymeric
imprintable material; wherein adhesion between the polymeric
imprintable material and the substrate is substantially increased
by the self-assembled monolayer.
58. The molecule as defined in claim 57 wherein the self-assembling
connecting group comprises at least one of hydroxyl groups,
chlorine groups, acetoxy groups, amino groups, thiol groups, and
mixtures thereof; and wherein the linking group comprises at least
one of acryloxy groups, methacryloxy groups, vinyl groups, and
mixtures thereof.
59. The molecule as defined in claim 57, further comprising at
least one of hydroxyl groups, chlorine groups, amino groups, thiol
groups, and acetoxy groups attached to a surface of the substrate,
the at least one of the hydroxyl groups, chlorine groups, amino
groups, thiol groups, and acetoxy groups adapted to chemically bond
to the molecule via the self-assembling connecting group, wherein
the polymeric imprintable material is adapted to chemically bond to
the self-assembled monolayer.
60. The molecule as defined in claim 57 wherein the molecule
comprises at least one molecular species selected from methacryloxy
propyltrichlorosilane, (methacryloyloxypropyl)trimethoxysilane,
3-methacryloxypropylbis(trimethylsiloxy)methylsilane,
3-methacryloxypropyldimethylchlorosilane,
3-methacryloxypropylmethyldichlorosilane,
3-methacryloxypropylmethyldimethoxysilane,
3-acryloxypropylmethyldichlorosilane,
acryloxypropylmethyldimethoxysilane,
3-acryloxypropyltrichlorosilane, acryloxypropyltrimethoxysilane,
vinyltriacetoxysilane, vinylmethyldiethoxysilane,
vinyltrichlorosilane, vinyltrimethoxysilane,
vinylmethyldiacetoxysilane, hydroxyethyl methacrylate, hydroxyethyl
acrylate, and mixtures thereof.
Description
BACKGROUND
[0001] The present disclosure relates generally to imprinting
procedures and more particularly to increasing adhesion between
elements used in imprinting procedures.
[0002] Nano-imprint lithography was initiated as an alternate
process to achieve nanoscale features (about 100 nm or smaller)
with high throughput and relatively low cost. During the imprinting
process, the nanoscale structures are transferred from a mold to a
polymer layer. The mold may be used for the thermal imprint
process, as well as for the UV-based imprint process.
[0003] In the thermal imprint process, to deform the shape of the
polymer, the temperature of the film and mold is generally higher
than the glass transition temperature of the polymer, so that the
polymer flows more easily to conform to the shape of the mold.
Hydrostatic pressure may be used to press the mold into the polymer
film, thus forming a replica of the mold in the polymer layer. The
press is then cooled below the glass transition temperature to
"freeze" the polymer and form a more rigid copy of the features in
the mold. The mold is then removed from the substrate.
[0004] In the alternate UV imprint process, a UV-curable monomer
solution is used instead of a thermoplastic polymer. The monomer
layer is formed between the mold and the substrate. When exposed to
a UV light, the monomer layer is polymerized to form a film with
the desired patterns thereon. The UV-based nanoimprint process may
generate patterns at room temperature with low pressure.
[0005] A potential problem with these techniques is the possible
adhesion of the polymer to the mold. If the polymer sticks to the
mold, then the imprinted pattern and/or the mold itself may be
damaged when pulling the mold off the substrate. This may damage
and/or ruin the imprinted patterns and/or deleteriously affect the
mold (which may be very expensive and time-consuming to
produce).
[0006] To reduce the adhesion of the polymer to the mold, high
quality releasing self-assembled monolayers (SAMs) have been
attached to the surface of the mold by immersing the mold in a
solution of the release agent at a concentration of, for example,
1.times.10.sup.-4 M. The improved release properties allowed for
the enhancement of pattern resolution in the polymer film. "Release
property," as referred to herein means how well the mold detaches
from the polymer layer after imprinting without the polymer
sticking to the mold.
[0007] However, where the gap between features on the mold is
reduced, the problem regarding adhesion of the polymer to the mold
may, in some instances, arise even when a releasing layer is
disposed on the mold. In those instances, the polymer may stick to
the mold gap and detach from the substrate surface. The substrate
surface area may not be large enough to hold the resist because the
mold surface area facing the resist may be larger.
[0008] Thus, there is a need to provide increased adhesion between
the polymer and the substrate so as to substantially avoid the
foregoing drawbacks.
SUMMARY
[0009] Embodiments of the method increase adhesion between a
substrate and a polymeric imprintable material during an imprinting
procedure. The method includes chemically bonding a plurality of
molecules to a substrate surface to form a self-assembled monolayer
thereon. A monomer is copolymerized with the self-assembled
monolayer to form the polymeric imprintable material chemically
bonded to the self-assembled monolayer. The self-assembled
monolayer substantially increases adhesion between the polymeric
imprintable material and the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Objects, features and advantages of embodiments of the
present disclosure will become apparent by reference to the
following detailed description and drawings, in which like
reference numerals correspond to similar, though not necessarily
identical components. For the sake of brevity, reference numerals
having a previously described function may not necessarily be
described in connection with subsequent drawings in which they
appear.
[0011] FIG. 1 is a schematic flow diagram depicting an embodiment
of a method for increasing adhesion between a substrate and a
polymeric imprintable material;
[0012] FIG. 2 is a schematic flow diagram depicting an alternate
embodiment of the method;
[0013] FIG. 3 is similar to FIG. 1, but depicts an alternate
embodiment of a method;
[0014] FIG. 4A is a schematic view of a mold in contact with an
embodiment of the polymeric imprintable material chemically bonded
to a substrate via a self-assembled monolayer;
[0015] FIG. 4B is a schematic view of the mold detached from an
embodiment of the polymeric imprintable material chemically bonded
to the substrate via the self-assembled monolayer;
[0016] FIG. 5 is a graph comparing the RAIR spectra of the
monolayer on a silicon substrate to the bulk spectra of the
molecules; and
[0017] FIG. 6 is a SEM image of an embodiment of the polymeric
imprintable material imprinted with a pattern of 37 nanowires.
DETAILED DESCRIPTION
[0018] Embodiments of the present invention advantageously use a
novel concept of providing a self-assembled monolayer (SAM) to
substantially improve adhesion during imprinting procedures. It is
to be understood that embodiment(s) of the present disclosure may
be used for thermal imprint processes, as well as for UV-based
imprint processes. In an embodiment, the SAM acts as a linker
between a substrate and a polymeric imprintable material (a
non-limitative example of which is a resist material) so that the
polymeric imprintable material chemically bonds to the substrate.
Without being bound to any theory, it is believed that this
chemical bond may also aid in the release of the polymeric
imprintable material from a mold having features thereon that is
used to imprint the polymeric material during, for example, a
nano-imprinting procedure.
[0019] As used herein, the term "nano-imprint" in connection with a
mold refers to molds having features thereon/therein (e.g.,
protrusions that are adapted to define nanoscale features in a
polymer layer, the features being separated by a spacing on the
order of between about 30 nanometers (nm) and about 100 nanometers
(nm) or smaller). Embodiments of the present disclosure may also
advantageously be used in connection with molds having features
thereon/therein being separated by a spacing less than 30 nm.
Embodiment(s) of the present method may be applied to any processes
that may benefit from increased adhesion as disclosed herein for
their application.
[0020] The nano-imprinting process itself is provided in greater
detail in, for example, U.S. Pat. No. 6,294,450, entitled
"Nanoscale Patterning for the Formation of Extensive Wires" and
issued on Sep. 25, 2001, to Yong Chen et al; U.S. Pat. No.
6,407,443, entitled "Nanoscale Patterning for the Formation of
Extensive Wires" and issued on Jun. 18, 2002, to Yong Chen et al;
U.S. Pat. No. 6,432,740, entitled "Fabrication of Molecular
Electronic Circuit by Imprinting" and issued on Aug. 13, 2002, to
Yong Chen; and U.S. Pat. No. 6,579,742, entitled "Fabrication of
Molecular Electronic Circuit by Imprinting" and issued on Jun. 17,
2003, to Yong Chen. The contents of the foregoing references are
incorporated herein by reference.
[0021] Generally, embodiment(s) of the method include forming a
polymeric imprintable material such that it is chemically bonded to
a self-assembled monolayer that is chemically bonded to a surface
of a substrate. These embodiment(s) will be discussed in further
detail in reference to the Figures and the Examples.
[0022] Referring now to FIG. 1, embodiments of a method for
substantially increasing adhesion between a substrate 10 and a
polymeric imprintable material 12 during an imprinting process
generally includes bonding a self-assembled monolayer (SAM) 14 to
the substrate 10. It is to be understood that the substrate 10 may
be any suitable material. In an embodiment, the substrate 10 is
silicon, silicon dioxide, glass, quartz, alumina, germanium,
germanium oxide, tin, tin oxide, and mixtures thereof. Further, the
substrate 10 may be formed from one or more layers of suitable
materials. In a non-limitative example, the substrate 10 is silicon
having a layer of silicon dioxide thereon.
[0023] The substrate 10 may be treated such that one or more
attaching/terminal groups (R) 16 are formed on its surface 18. In
an embodiment, the substrate 10 is treated with a piranha solution
(e.g., 1 part by volume of 30% H.sub.2O.sub.2 to 3 parts by volume
of concentrated H.sub.2SO.sub.4) to form the attaching group(s) (R)
16. It is to be understood that the attaching group(s) (R) 16 may
be any suitable group that is capable of chemically bonding to the
molecules 20 that will form the SAM 14. In an embodiment, the
attaching groups (R) 16 are hydroxyl groups (--OH), chlorine groups
(--Cl), amino groups (--NH.sub.2), thiol groups (--SH), acetoxy
groups (--OCOR' where R' is an alkyl or a substituted alkyl),
and/or mixtures thereof. It is to be understood that the formation
of the attaching groups (R) 16 may be accomplished in solution or
by a vapor phase treatment.
[0024] "Chemically bonding," "chemical bonds," "chemically bonded,"
and the like as referred to herein may include ionic bonding,
covalent bonding, and coordination bonding.
[0025] The method further includes chemically bonding a plurality
of molecules 20 to the surface 18 of the substrate 10 (for example,
via the attaching groups (R) 16) via a SAM process, thus forming
the self-assembled monolayer 14. Non-limitative examples of
suitable molecule(s) 20 include methacryloxy propyltrichlorosilane,
(methacryloyloxypropyl)trimethoxysilane,
3-methacryloxypropylbis(trimethylsiloxy)methylsilane,
3-methacryloxypropyldimethylchlorosilane,
3-methacryloxypropylmethyldichlorosilane,
3-methacryloxypropylmethyidimethoxysilane,
3-acryloxypropylmethyldichlorosilane,
acryloxypropylmethyidimethoxysilane,
3-acryloxypropyltrichlorosilane, acryloxypropyltrimethoxysilane,
vinyltriacetoxysilane, vinylmethyldiethoxysilane,
vinyltrichlorosilane, vinyltrimethoxysilane,
vinylmethyldiacetoxysilane, hydroxyethyl methacrylate, hydroxyethyl
acrylate, and/or mixtures thereof.
[0026] It is to be understood that each molecule 20 has a
self-assembling connecting group (SACG) 22 at one end and a linking
group (LG) 24 at an opposed end. In an embodiment, the
self-assembling connecting group (SACG) 22 is adapted to chemically
bond the surface 18 of the substrate 10 (e.g. via the attaching
group(s) (R) 16) to the SAM 14. Examples of suitable
self-assembling connecting groups (SACG) 22 include, but are not
limited to hydroxyl groups, chlorine groups, acetoxy groups, amino
groups, thiol groups, and mixtures thereof.
[0027] The linking group (LG) 24 of SAM 14 is adapted to
copolymerize with a monomer 26 to form the polymeric imprintable
material 12. Examples of suitable linking groups (LG) 24 include,
but are not limited to acryloxy groups, methacryloxy groups, vinyl
groups, and mixtures thereof.
[0028] The method further includes copolymerizing the monomer 26
with the linking group (LG) 24 of SAM 14. Any suitable monomer that
is capable of copolymerizing with the self-assembled monolayer 14
may be used. In an embodiment, the monomer 26 includes, but is not
limited to vinyl monomers, acrylic moieties, styrene moieties,
and/or mixtures thereof. Some non-limitative examples of monomer 26
include benzyl methacrylate, styrene, methyl methacrylate, hexyl
acrylate, hexyl methacrylate, butyl methacrylate, butyl acrylate,
lauryl methacrylate, lauryl acrylate, isodecyl acrylate, isodecyl
methacrylate, octadecyl acrylate, octadecyl methacrylate, ethylene
glycol dimethacrylate, divinylbenzene, vinylbenzyl chloride,
hydroxyethyl methacrylate, hydroxyethyl acrylate, and/or mixtures
thereof.
[0029] Copolymerization may be initiated by ultraviolet (UV)
irradiation and/or thermal treatment. In an embodiment, the
ultraviolet light used to copolymerize the monomer 26 with the
monolayer 14 may also be the UV light that accomplishes the curing
step of a nano-imprinting procedure. It is to be understood that
these methods may be performed simultaneously.
[0030] As depicted in FIG. 1, the copolymerization of the monomer
26 with the linking group (LG) of SAM 14 forms a polymeric
imprintable material 12 chemically bonded to the self-assembled
monolayer 14. It is to be understood that the polymeric imprintable
material 12 may be a copolymer of any suitable combination of the
monomers of linking group (LG) 24 and the monomer 26. In an
embodiment, polymeric imprintable material 12 is a negative and/or
positive resist polymer. Suitable non-limitative examples of
polymeric imprintable material 12 include poly(benzyl
methacrylate), poly(styrene), poly(methyl methacrylate), poly(hexyl
acrylate), poly(hexyl methacrylate), poly(butyl methacrylate),
poly(butyl acrylate), poly(lauryl methacrylate), poly(lauryl
acrylate), poly(isodecyl acrylate), poly(isodecyl methacrylate),
poly(octadecyl acrylate), poly(octadecyl methacrylate),
poly(ethylene glycol dimethacrylate), poly(divinylbenzene),
poly(vinylbenzyl chloride), poly(hydroxyethyl methacrylate),
poly(hydroxyethyl acrylate), and/or mixtures thereof. In a further
embodiment, polymeric imprintable material 12 is
poly(benzylmethacrylate). It is to be understood that the polymeric
imprintable material 12 is capable of being imprinted with features
from, for example, a mold (depicted as 28 in FIGS. 4A and 4B)
during an imprinting procedure (e.g. nano-imprinting).
[0031] Referring now to FIG. 2, an alternate embodiment of the
method is depicted. It is to be understood that the materials
described in reference to FIG. 1 may also be used in this
embodiment. The method includes first attaching monomers 26 (i.e. a
plurality of monomers 26) to the linking groups (LG) 24 of the
molecules 20 (i.e. plurality of molecules 20). It is to be
understood that attaching the molecules 20 to the monomers 26 may
be accomplished by any suitable method that will form a chemical
bond between the two.
[0032] In this embodiment, the molecules 20 having the monomers 26
attached thereto are chemically bonded via a SAM process to the
surface 18 of substrate 10 to form a SAM 14 having the monomers 26
attached thereto. As previously described, the substrate. 10 may
have attaching groups (R) 16 that are capable of chemically bonding
to the molecule(s) 20 to form the SAM 14.
[0033] The plurality of monomers 26 may then be copolymerized with
linking groups (LG) 24 of the SAM 14 to form the polymeric
imprintable material 12 chemically bonded to the SAM 14. The
copolymerization may be initiated via UV light and/or thermal
treatment.
[0034] Without being bound to any theory, it is believed that the
incorporation of the SAM 14 between the substrate 10 and the
polymeric imprintable material 12 via embodiments of the method
disclosed herein advantageously substantially increases the
adhesion between the substrate 10 and the polymeric imprintable
material 12. It is believed that the self-assembled monolayer 14
acts as a linker between the substrate 10 and the polymeric
imprintable material 12 so that the polymeric imprintable material
12 chemically bonds to the substrate 10. The chemical bond and
increase in adhesion may advantageously decrease the undesirable
detachment of the polymeric imprintable material 12 from the
substrate 10 during an imprinting process. Further, in embodiments
of the method in which a mold is used to imprint the material, the
polymeric imprintable material 12 is adapted to contact the mold.
It is believed that the increased adhesion between the polymeric
imprintable material 12 and the substrate aids in releasing the
polymeric imprintable material 12 from the mold.
[0035] Non-limitative embodiments of the method and the substrate
10 are shown in FIG. 3. In this embodiment, the surface 18 of the
substrate 10 is treated with the piranha solution described above
to form --OH attaching groups (R) 16 thereon. The molecules 20 that
are adapted to form the SAM 14 are methacryloxy
propyltrichlorosilane molecules where the trichlorosilane end is
the self-assembling connecting group (SACG) 22 and the methacryloxy
end is the linking group (LG) 24. The molecules 20 are covalently
bonded via the connecting group(s) (SACG) 22 to the --OH groups on
the substrate 10. It is to be understood that once the SAM 14 is
formed, the substrate 10 may be cleaned and dried prior to
copolymerization.
[0036] The SAM 14 is then copolymerized in ultraviolet irradiation
with a solution of benzyl methacrylate. The methacrylate chemically
bonds to the methacryloxy end of the molecule 20.
[0037] FIG. 4A depicts a non-limitative embodiment wherein a mold
28 is in contact with the polymeric imprintable material 12. The
polymeric imprintable material 12 is attached to a substrate 10 via
a self-assembled monolayer 14 formed by an embodiment of the method
disclosed herein. As shown in FIG. 4A, the mold 28 has features 30
defined therein to which the polymeric imprintable material 12 may
conform during an imprinting process. One challenge that may arise
during imprinting is that the polymeric imprintable material 12
may, in some instances, adhere to the mold 28 rather than to the
substrate 10 when the substrate 10 is separated from the mold 28.
Without being bound to any theory, it is believed that this may be
due, at least in part, to surface and interfacial energies. The
total free energies of the surfaces and interfaces of the initial
system before mold 28--substrate 10 separation may be expressed by
the following equation:
G.sub.i=A.sub.r-s.gamma..sub.r-s+A.sub.r-m.gamma..sub.r-m. (1)
After separation, there are two possible outcomes--the polymeric
imprintable material 12 may adhere to the mold 28 or to the
substrate 10. If the polymeric imprintable material 12 detaches
from the mold 28, the total free energy of the final system is:
G.sub.f=A.sub.r-s.gamma..sub.r-s+A.sub.r-m(.gamma..sub.r+.gamma..sub.m).
(2) However, if the polymeric imprintable material 12 detaches from
the substrate 10, the total free energy of the final system is:
G.sub.f=A.sub.r-m.gamma..sub.r-m+A.sub.r-s(.gamma..sub.r+.gamma..sub.s)
(3) In the above equations, .gamma..sub.r, .gamma..sub.s, and
.gamma..sub.m are the surface free energies per area of the
polymeric imprintable material 12, of the substrate 10, and of the
mold 28, respectively; .gamma..sub.r-m and .gamma..sub.r-s are
interface free energies per area of the polymeric imprintable
material 12--mold 28 interface and of the polymeric imprintable
material 12--substrate 10 interface, respectively; A.sub.r-s and
A.sub.r-m are the interface areas between the polymeric imprintable
material 12 and the substrate 10 and between the polymeric
imprintable material 12 and the mold 28, respectively. For the
polymeric imprintable material 12 to detach from the mold 28 and to
adhere to the substrate 10, the following applies:
.DELTA.G.sub.Detachment from mold<.DELTA.G.sub.Detachment from
substrate (4)
A.sub.r-m(.gamma..sub.r+.gamma..sub.m-.gamma..sub.r-m)<A.sub.r-s(.gamm-
a..sub.r+.gamma..sub.s-.gamma..sub.r-s) (5)
[0038] Without subscribing to any particular theory, it is believed
that in single layer processing, the height of the polymeric
imprintable material 12 may remain consistent in order to preserve
process latitude in subsequent steps even though the lateral
feature 30 size of the mold 28 may be shrinking as the pitch sizes
decrease. This may cause the contact area between the mold 28 and
the polymeric imprintable material 12, A.sub.r-m, to increase. At
certain pitch sizes, the left hand term in equation (5) will become
larger than the right hand term, and the polymeric imprintable
material 12 may adhere to the mold 28 and detach from the substrate
10.
[0039] Referring now to FIG. 4B, the presence of the SAM 14 assists
in increasing the adhesion between the substrate 10 and the
polymeric imprintable material 12. As depicted, upon releasing the
mold 28 from the substrate 10, the polymeric imprintable material
12 remains adhered to the substrate 10. Without subscribing to any
particular theory, it is believed that the SAM 14 assists in
decreasing the free energy of the polymeric imprintable material
12--substrate 10 interface .gamma..sub.r-s, thus increasing
adhesion between the polymeric imprintable material 12 and the
substrate 10.
[0040] To further illustrate embodiment(s) as disclosed herein,
reference is made to the following examples. The following examples
are for illustrative purposes and are not intended to limit the
scope of the present disclosure.
EXAMPLES
[0041] Doped silicon substrates (As>10.sup.20 cm.sup.-3) and
BOROFLOAT.RTM. brand (commercially available from SCHOTT North
America, Inc. in Elmsford, N.Y.) borosilicate float glass
substrates were used. The borosilicate float glass substrates had a
thickness of about 0.7 mm and were polished to a low surface
roughness of about 0.4 nm rms in 1 .mu.m.sup.2 Hydroxyl
terminations on the silicon substrate surface and the glass
substrate surface were generated by dipping the substrates in the
piranha solution for about 15 minutes and then subjecting the
substrates to a water vapor plasma treatment for about 10 minutes
at a power of about 10 W and a pressure of about 0.7 torr.
[0042] The silicon and glass substrates with hydroxyl groups
attached thereon were dipped into a toluene solution containing
about 0.2 wt % of methacryloxy propyltrichlorosilane molecules for
about 1 hour to form the self-assembled monolayer (SAM). The
substrates were cleaned with a toluene solvent in an ultrasonic
bath and dried by a nitrogen blow.
[0043] The monolayer formed on the silicon substrate was
investigated by ellipsometry thickness measurements and Reflection
Absorption Infrared Spectroscopy (RAIRS). The ellipsometry
measurements taken included both the thicknesses of the surface
layer for a bare silicon substrate having a native oxide layer
thereon (0.91.+-.0.15 nm), and of the silicon substrate with the
monolayer (2.13.+-.0.19 nm). The difference between the two
measurements is about 1.2 nm, which is consistent with the length
of the molecules used to form the monolayer.
[0044] The RAIR spectra of the monolayer on the silicon substrate
is compared to the bulk spectra of the surface promoter (e.g. the
methacryloxy propyl-trichlorosilane molecules) as shown in FIG. 5.
As depicted, the majority of the peaks from the bulk sample spectra
are also present in the monolayer spectra. In particular, the peak
located at 1726 cm.sup.-1, which is a characteristic vibration mode
of carbonyl groups in the methacryloxy molecules, is observed with
strong intensity in the monolayer. Further, peaks at 1635 cm.sup.-1
(C.dbd.C stretch), 1300 cm.sup.-1 (C--O--C stretch) and 1173
cm.sup.-1 (C--O stretch) were found in the monolayer. These peaks
indicate the formation of a methacryloxy propyltrichlorosilane
monolayer on the silicon substrate surface.
[0045] The formulation of the UV-curable monomer solution was
composed of three ingredients. IRGACURE 184 (absorption peak: 280
nm and 320 nm, available commercially from Ciba located in Basel,
Switzerland) was used as the UV-sensitive free radical generator
and was dissolved into a benzyl methacrylate monomer solution
(commercially available from Aldrich located in St. Louis, Mo.). In
addition, 2-hydroxyethyl methacrylate (commercially available from
Aldrich) was added to lower the surface energy for easy mold
release from the resist (i.e. the polymeric imprintable material
12). The composition of the solution was 77 wt. % of monomer, 20
wt. % of releasing promoter, and 3 wt. % of free radical generator.
The solution was filtrated through syringe filters with a 0.2 .mu.m
pore size to remove residual particles.
[0046] The SAM layer on both the silicon substrates and the glass
substrates was copolymerized with the UV-curable monomer solution.
Copolymerization was initiated with ultraviolet irradiation. A
mercury lamp (280 nm.about.320 nm) was used as the UV light source
with an intensity of about 7 W/cm.sup.2. Molds having a releasing
agent of organosilane were used to nano-imprint the resists under
the UV light.
[0047] FIG. 6 depicts a SEM image of a pattern of 37 nanowires
imprinted in the polymer resist attached to the glass substrate.
The molecules that formed the monolayer substantially improved the
resist adhesion to the glass substrate surface through the chemical
bond, resulting in the 37 isolated nanowire patterns. It is
believed that the bond substantially advantageously prevented the
resist from peeling off of the glass substrate while the mold was
detached from the resist by hand. 4
[0048] Embodiment(s) of the method disclosed herein offer many
advantages, non-limitative embodiments of which include the
following. In an embodiment, the formation of a monolayer on a
substrate surface substantially increases the adhesion between the
substrate and the formed polymeric imprintable material in an
imprinting process. This may advantageously allow the polymeric
imprintable material to adhere to the substrate rather than to a
mold upon releasing the material from the mold.
[0049] While several embodiments have been described in detail, it
will be apparent to those skilled in the art that the disclosed
embodiments may be modified. Therefore, the foregoing description
is to be considered exemplary rather than limiting.
* * * * *