U.S. patent application number 10/763885 was filed with the patent office on 2005-07-28 for materials and methods for imprint lithography.
This patent application is currently assigned to MOLECULAR IMPRINTS, INC.. Invention is credited to Lad, Pankaj B., McMackin, Ian M., Xu, Frank Y..
Application Number | 20050160934 10/763885 |
Document ID | / |
Family ID | 34795158 |
Filed Date | 2005-07-28 |
United States Patent
Application |
20050160934 |
Kind Code |
A1 |
Xu, Frank Y. ; et
al. |
July 28, 2005 |
Materials and methods for imprint lithography
Abstract
One embodiment of the present invention relates to an imprinting
material for imprint lithography that includes the surfactant
3M.TM. Novec.TM. Fluorosurfactant FC-4432, and another embodiment
of the present invention relates to a method for imprint
lithography that uses the imprinting material.
Inventors: |
Xu, Frank Y.; (Austin,
TX) ; Lad, Pankaj B.; (Austin, TX) ; McMackin,
Ian M.; (Austin, TX) |
Correspondence
Address: |
MOLECULAR IMPRINTS, INC.
KENNETH C. BROOKS
PO BOX 81536
AUSTIN
TX
78708-1536
US
|
Assignee: |
MOLECULAR IMPRINTS, INC.
Austin
TX
78758
|
Family ID: |
34795158 |
Appl. No.: |
10/763885 |
Filed: |
January 23, 2004 |
Current U.S.
Class: |
101/454 |
Current CPC
Class: |
B82Y 30/00 20130101;
B41C 1/10 20130101; B82Y 10/00 20130101; B82Y 40/00 20130101; Y10S
977/887 20130101; B41M 7/0072 20130101; B41M 7/0081 20130101; G03F
7/0002 20130101 |
Class at
Publication: |
101/454 |
International
Class: |
B41N 001/00 |
Claims
What is claimed:
1. A method of imprint lithography that comprises: depositing an
imprinting material on a substrate; varying release properties
associated with an imprint template by contacting a solution
including imprinting materials and a polymeric fluorinated
surfactant; and energizing the imprinting materials to cause a
solid material to be produced therefrom.
2. The method as recited in claim 1 wherein said varying further
include providing said solution with a mixture of said imprinting
materials and 3M.TM. Novec.TM. Fluorosurfactant FC-4432.
3. The method of claim 1 which includes pre-treating the surface of
the imprint template to be hydrophilic.
4. The method of claim 2 which includes further pre-treating the
surface of the imprint template by applying a composition that
includes the surfactant.
5. The method of claim 4 wherein the composition is a mixture of
isopropyl alcohol and the surfactant.
6. A method of imprint lithography that comprises: depositing an
imprinting material on a substrate; moving an imprint template
towards the substrate so that the imprinting materials coats a
surface of the imprint template and a surface of the substrate; and
energizing the imprinting material to cause a solid material to be
produced therefrom; and wherein the imprinting material includes a
surfactant having a composition that includes 87% polymeric
fluorochemical actives, 7% non-fluorochemical actives, 5%
1-methyl-2-pyrudiinone, and <1% toluene.
7. The method of claim 1 wherein the imprinting material includes
acryloxymethylpentamethyldisiloxane, isobornyl acrylate, ethylene
glycol diacrylate, and
2-hydrozy-2-methyl-1-phenyl-propan-1-one.
8. The method of claim 6 wherein the imprinting material includes
acryloxymethylpentamethyldisiloxane, isobornyl acrylate, ethylene
glycol diacrylate, and
2-hydrozy-2-methyl-1-phenyl-propan-1-one.
9. The method of claim 7 wherein the surfactant is <1% of the
imprinting material.
10. The method of claim 8 wherein the surfactant is <1% of the
imprinting material.
11. The method of claim 6 wherein depositing includes depositing a
plurality of droplets upon the substrate.
12. The method of claim 6 wherein depositing includes
spin-coating.
13. The method of claim 6 which includes pre-treating the surface
of the imprint template to be hydrophilic.
14. The method of claim 13 wherein pre-treating includes
hydrolyzing.
15. The method of claim 14 wherein hydrolyzing includes forming
--OH bonds at the surface of the imprint template.
16. A method of imprint lithography that comprises: pre-treating a
surface of an imprint template to cause it to be hydrophilic;
pre-treating the surface of the imprint template by applying a
composition that includes 3M.TM. Novec.TM. Fluorosurfactant
FC-4432; depositing an imprinting material on a substrate; moving
an imprint template towards the substrate so that the imprinting
materials coats the surface of the imprint template and a surface
of the substrate; and energizing the imprinting material to cause a
solid material to be produced therefrom.
17. An imprinting material for use in imprint lithography that
comprises a polymeric fluorinated surfactant.
18. The imprinting material of claim 17 wherein said polymeric
fluorinated surfactant consists of 3M.TM. Novec.TM.
Fluorosurfactant FC-4432.
19. The imprinting material of claim 17 which further includes a UV
photoinitiator.
20. The imprinting material of claim 19 which further includes
acryloxymethylpentamethyldisiloxane, isobornyl acrylate, ethylene
glycol diacrylate, and
2-hydrozy-2-methyl-1-phenyl-propan-1-one.
21. The imprinting material of claim 18 wherein 3M.TM. Novec.TM.
Fluorosurfactant FC-4432 comprises <1% of the material.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] One or more embodiments of the present invention relate
generally to imprint lithography. In particular, one or more
embodiments of the present invention relate to materials and
methods for imprint lithography.
BACKGROUND OF THE INVENTION
[0002] Micro-fabrication involves the fabrication of very small
structures, for example, and without limitation, structures having
features on the order of micro-meters or smaller. One area in which
micro-fabrication has had a sizeable impact is in processing of
integrated circuits. As the semiconductor processing industry
continues to strive for larger production yields while increasing
the circuits per unit area formed on a substrate, micro-fabrication
becomes increasingly important since micro-fabrication provides
greater process control while allowing a reduction in the minimum
feature dimension of the structures formed. Other areas of
development in which micro-fabrication have been employed include
biotechnology, optical technology, mechanical systems and the
like.
[0003] An exemplary micro-fabrication technique is disclosed in
U.S. Pat. No. 6,334,960 to Willson et al. In particular, the
Willson et al. patent discloses a method of imprint lithography to
form a relief pattern in a structure. The method includes providing
a substrate having a transfer layer (typically spin-coated), and
covering the transfer layer, in turn, with a low viscosity,
polymerizable (typically UV curable) fluid composition (typically
in the form of droplets). The method further includes mechanically
contacting an imprint template or mold having a relief structure
with the polymerizable fluid composition wherein the polymerizable
fluid composition fills a gap between the imprint template and the
substrate and fills the relief structure of the imprint template.
Next, the method includes subjecting the polymerizable fluid
composition to conditions to solidify and to polymerize the same
(typically, exposing the polymerizable fluid composition to UV to
crosslink it), thereby forming a solidified polymeric material on
the transfer layer that contains a relief structure complimentary
to that of the imprint template. Next, the method includes
separating the imprint template from the substrate to leave solid
polymeric material on the substrate, which solid polymeric material
includes a relief pattern in the form of the complimentary relief
structure. Next, the solidified polymeric material and the transfer
layer are subjected to an environment to selectively etch the
transfer layer relative to the solidified polymeric material to
form a relief image in the transfer layer.
[0004] The following issues that relate to selective adhesion of
the solidified polymeric material to different surfaces are
typically considered when one develops a method and/or a material
useful in forming fine-feature relief patterns in the solidified
polymeric material. First, the solidified polymeric material ought
to adhere well to the transfer layer on the substrate, and second,
it ought to be easily released from the surface of the imprint
template. These issues are typically referred to as release
characteristics and selective/preferential adhesion, and if they
are satisfied, the relief pattern recorded in the solidified
polymeric material will not be distorted during separation of the
imprint template from the substrate. To improve release
characteristics, Willson et al. teaches forming a release layer on
the surface of the imprint template, which release layer is
typically hydrophobic and/or has low surface energy. Such a release
layer will provide a weak boundary layer between the imprint
template and the solidified polymeric material. This type of
release layer is referred to, for purposes of the present
discussion, as an a priori release layer, i.e., a release layer
that is solidified to the surface of the imprint template.
[0005] Another prior art approach to improving the release
characteristics is described by Bender et al. in "Multiple
Imprinting in UV-based Nanoimprint Lithography: Related Material
Issues," Microeletronic Engineering 61-62 (2002), pp. 407-413.
Specifically, Bender et al. utilizes an imprint template having an
a priori release layer in conjunction with a fluorine-containing UV
curable material. To that end, a UV curable layer is applied to a
substrate by spin-coating a 200 cps UV curable fluid to form a UV
curable layer. The UV curable layer is enriched with fluorine
groups to improve its release characteristics.
[0006] A priori release layers, however, typically have a limited
operational life. As a result, a single imprint template needs to
be coated multiple times with an a priori release layer during
imprint processing. This can result in several hours of down-time
for a given imprint template, thereby reducing throughput.
Additionally, the molecular structure of the a priori release layer
may limit the minimization of the minimum feature dimension that is
printed.
[0007] One measure of imprint lithography quality relates to
feature filling. As is well known, sufficient wetting, along with
other factors, ensures feature filling, and thereby prevents voids.
To test one imprint lithography method and imprint material, we
made imprints utilizing a 25 mm.times.25 mm imprint template having
reasonably well scattered features (i.e., the features were
scattered widely enough to avoid repeated high density
patterns--less than 10% of the template surface was covered by
features) with feature heights of about 100 nm to provide imprints
wherein a typical residual layer thickness was about 50-100 nm (as
is well known, solidified polymeric material disposed between
features is typically referred to as a residual layer). In
particular, we were able to provide void free imprints utilizing
the following method steps: (a) pre-cleaning the surface of the
imprint template by dipping its surface in a 2.5:1 solution of
H.sub.2SO.sub.4 and H.sub.2O.sub.2; (b) further pre-treating the
surface of the imprint template with a spray of diluted surfactant
solution consisting of 0.1% FSO-100 in isopropyl alcohol ("IPA")
where FSO-100 is a surfactant that is available under the
designation ZONYL.RTM. FSO-100 from DUPONT.TM. (FSO-100 has a
general structure of R.sub.1R.sub.2 where
R.sub.1=F(CF.sub.2CF.sub.2).sub.Y, with Y being in a range of 1 to
7, inclusive, and R.sub.2=CH.sub.2CH.sub.2O(CH-
.sub.2CH.sub.2O).sub.XH, where X is in a range of 0 to 15,
inclusive); (c) purging a gap between the imprint template and the
substrate using an .about.5 psi Helium purge; (d) depositing a
pattern of substantially equidistant droplets of the following
imprinting fluid on the surface of the substrate (where each
component is listed by weight): (i)
acryloxymethylpentamethyldisiloxane (37 gm) which is available
under the designation XG-1064 from Gelest, Inc. of Morrisville,
Pa., (ii) isobornyl acrylate ("IBOA") (42 gm) which is available
under the designation SR 506 from Aldrich Chemical Company of
Milwaukee, Wis., (iii) ethylene glycol diacrylate (18 gm) which is
available under the designation EGDA from Aldrich Chemical Company
of Milwaukee, Wis., (iv) a UV photoinitiator, i.e.,
2-hydrozy-2-methyl-1-phenyl-propan-1-one (3 gm) which is available
under the designation Darocur 1173 from CIBA.RTM. of Tarrytown,
N.Y.), and (v) FSO-100 (0.5 gm); and (e) performing imprint
lithography steps as described above. In this example, the
substrate was covered with a transfer layer of a cross-linked BARC
material (as is well known, BARC or "bottom antireflective coating"
is an organic antireflective coating that is typically produced by
a spin-on process). The BARC layer was used to prevent intermixing
between the imprinting material and the transfer layer, which
intermixing may be particularly problematic when using an
imprinting material comprised of low viscosity acrylate components
because such components have solvency toward many polymers. Such
intermixing may cause problems, such as, for example, and without
limitation, distortion of features when the imprint template is
separated from the substrate after exposure to polymerizing
radiation. In particular, this can be problematic when feature
thicknesses are as small as 50 nm to 100 nm.
[0008] Despite the above-described successful imprinting, material
voids were observed when we imprinted a high feature density
imprint template using the above-described imprinting method. Two
important differences between the high feature density imprint
template and the above-described imprint template were that the
feature density was much higher (for example, and without
limitation, about 30% to about 40% of the surface of the template
was covered by features in the high feature density imprint
template) and the feature height of the high feature density
imprint template was much higher, i.e., a height of 200 nm as
compared to a height of 100 nm.
[0009] In light of the above, there is a need for imprinting
methods and materials for use in imprint lithography that overcome
one or more of the above-identified problems.
SUMMARY OF THE INVENTION
[0010] One or more embodiments of the present invention satisfy one
or more of the above-identified needs in the art. In particular,
one embodiment of the present invention is a method of imprint
lithography that comprises depositing an imprinting material on a
substrate; varying release properties associated with an imprint
template by contacting a solution including imprinting materials
and a polymeric fluorinated surfactant; and energizing the
imprinting materials to cause a solid material to be produced
therefrom. Specifically, it was recognized that employing a
polymeric surfactant containing solution to a surface of an imprint
template substantially reduced, if not prevented, formation of
voids during imprinting. To that end, an exemplary polymeric
fluorinated surfactant is 3M.TM. Novec.TM. Fluorosurfactant
FC-4432. Specifically, it was found that by including in the
polymeric fluorinated surfactant in a solution containing
imprinting material, the desired release and wetting properties of
the imprint template may be established. In this manner, the
imprint template may be efficiently wetted with the imprint
material, while provided with the desired release properties to
reduce, if not prevent, distortions in the pattern recorded in the
solidified imprint layer upon separation of the imprint template
therefrom. Further, by including the polymeric fluorinated
surfactant in the imprinting material is was found the surface
energy associated with the imprint template may be regenerated
during imprint to maintain the desired release and wetting
properties. In accordance with another embodiment, a pre-treatment
of the imprint template may be undertaken to coat the imprint
template with a polymeric fluorinate surfactant before contacting
the imprint material containing solution. In yet another embodiment
of the present invention is an imprinting material that includes a
polymeric fluorinated surfactant, such as 3M.TM. Novec.TM.
Fluorosurfactant FC-4432.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a perspective view of a lithographic system useful
in carrying out one or more embodiments of the present
invention;
[0012] FIG. 2 is a simplified elevation view of a lithographic
system shown in FIG. 1;
[0013] FIG. 3 is a simplified representation of material from which
an imprinting layer, shown in FIG. 2, is comprised before being
polymerized and cross-linked;
[0014] FIG. 4 is a simplified representation of cross-linked
polymer material into which the material shown in FIG. 3 is
transformed after being subjected to radiation;
[0015] FIG. 5 is a simplified elevation view of a mold spaced-apart
from the imprinting layer, shown in FIG. 1, after patterning of the
imprinting layer; and
[0016] FIG. 6 is a simplified elevation view of imprint material
disposed on a substrate in accordance with the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0017] FIG. 1 shows lithographic system 10 that may be used to
carry out imprint lithography in accordance with one or more
embodiments of the present invention and utilizing imprinting
materials fabricated in accordance with one or more embodiments of
the present invention. As shown in FIG. 1, system 10 includes a
pair of spaced-apart bridge supports 12 having bridge 14 and stage
support 16 extending therebetween. As further shown in FIG. 1,
bridge 14 and stage support 16 are spaced-apart. Imprint head 18 is
coupled to bridge 14, and extends from bridge 14 toward stage
support 16. Motion stage 20 is disposed upon stage support 16 to
face imprint head, and motion stage 20 is configured to move with
respect to stage support 16 along X- and Y-axes. Radiation source
22 is coupled to system 10 to impinge actinic radiation upon motion
stage 20. As further shown in FIG. 1, radiation source 22 is
coupled to bridge 14, and includes power generator 23 connected to
radiation source 22.
[0018] Referring to FIGS. 1 and 2, connected to imprint head 18 is
imprint template 26 having mold 28 thereon. Mold 28 includes a
plurality of features defined by a plurality of spaced-apart
recessions 28a and protrusions 28b. The plurality of features
defines an original pattern that is to be transferred into
substrate 31 positioned on motion stage 20. Substrate 31 may
comprise a bare wafer or a wafer with one or more layers disposed
thereon. To that end, imprint head 18 is adapted to move along the
Z-axis and vary a distance "d" between mold 28 and substrate 31. In
this manner, features on mold 28 may be imprinted into a
conformable region of substrate 31, discussed more fully below.
Radiation source 22 is located so that mold 28 is positioned
between radiation source 22 and substrate 31. As a result, mold 28
is fabricated from material that allows it to be substantially
transparent to the radiation produced by radiation source 22.
[0019] Referring to FIGS. 2 and 3, a conformable region, such as
imprinting layer 34, is disposed on a portion of surface 32 that
presents a substantially planar profile. It should be understood
that the conformable region may be formed using any known technique
to produce conformable material on surface 32, such as a hot
embossing process disclosed in U.S. Pat. No. 5,772,905 to Chou,
which is incorporated by reference in its entirety herein, or a
laser assisted direct imprinting (LADI) process of the type
described by Chou et al. in Ultrafast and Direct Imprint of
Nanostructures in Silicon, Nature, Col. 417, pp. 835-837, June
2002. In accordance with one embodiment of the present invention,
the conformable region consists of imprinting layer 34 being
deposited as a plurality of spaced-apart discrete droplets 36 of
material 36a on substrate 31, discussed more fully below.
Imprinting layer 34 is formed from a material 36a that may be
selectively polymerized and cross-linked to record the original
pattern therein, defining a recorded pattern. Material 36a is shown
in FIG. 4 as being cross-linked at points 36b, forming cross-linked
polymer material 36c.
[0020] Referring to FIGS. 2, 3 and 5, the pattern recorded in
imprinting layer 34 is produced, in part, by mechanical contact
with mold 28. To that end, imprint head 18 reduces the distance "d"
to allow imprinting layer 34 to come into mechanical contact with
mold 28, spreading droplets 36 so as to form imprinting layer 34
with a contiguous formation of material 36a over surface 32. In one
embodiment, distance "d" is reduced to allow sub-portions 34a of
imprinting layer 34 to ingress into and fill recessions 28a.
[0021] To facilitate filling of recessions 28a, material 36a is
provided with the requisite properties to completely fill
recessions 28a while covering surface 32 with a contiguous
formation of material 36a. In accordance with one embodiment of the
present invention, sub-portions 34b of imprinting layer 34 in
superimposition with protrusions 28b remain after the desired,
usually minimum distance "d", has been reached, leaving
sub-portions 34a with a thickness t.sub.1, and sub-portions 34b
with a thickness t.sub.2. Thicknesses "t.sub.1" and "t.sub.2" may
be any thickness desired, dependent upon the application.
[0022] Referring to FIGS. 2, 3 and 4, after a desired distance "d"
has been reached, radiation source 22 produces actinic radiation
that polymerizes and cross-links material 36a, forming polymer
material 36c in which a substantial portion thereof is
cross-linked. As a result, material 36a transforms to polymer
material 36c, which is a solid, forming imprinting layer 134, shown
in FIG. 5. Specifically, polymer material 36c is solidified to
provide side 34c of imprinting layer 134 with a shape conforming to
a shape of a surface 28c of mold 28, with imprinting layer 134
having recesses 30 (the bottom of the recesses may be referred to
as a residual layer). After imprinting layer 134 is transformed to
consist of polymer material 36c, shown in FIG. 4, imprint head 18,
shown in FIG. 2, is moved to increase distance "d" so that mold 28
and imprinting layer 134 are spaced-apart.
[0023] Referring to FIG. 5, additional processing may be employed
to complete the patterning of substrate 31. For example, substrate
31 and imprinting layer 134 may be etched to transfer the pattern
of imprinting layer 134 into substrate 31, providing a patterned
surface (not shown). To facilitate etching, the material from which
imprinting layer 134 is formed may be varied to define a relative
etch rate with respect to substrate 31, as desired.
[0024] To that end, etching may be performed in a two-step process.
S. C. Johnson, T. C. Bailey, M. D. Dickey, B. J. Smith, E. K. Kim,
A. T. Jamieson, N. A. Stacey, J. G. Ekerdt, and C. G. Willson
describe suitable etch processes in an article entitled "Advances
in Step and Flash Imprint Lithography" SPIE Microlithography
Conference, February 2003, which article is available on the
Internet at www.molecularimprints.com, and which article is
incorporated by reference herein. As set forth in the article, the
first etch step, referred to as a "break-through etch,"
anisotropically removes residual cross-linked material 134 to break
through to an underlying transfer later (in this respect, better
etch selectivity is enabled by keeping the residual layer thin).
The second etch step, referred to as a "transfer etch," uses the
remaining pattern in cross-linked material 134 as an etch mask to
transfer the pattern into the underlying transfer layer. In one
embodiment, silicon in cross-link material 134, and lack of silicon
in the transfer layer, provides etch selectivity therebetween. In
such an embodiment, the etching may be done in a LAM Research
9400SE obtained from Lam Research, Inc. of Fremont, Calif. For
example, and without limitation, a halogen "breakthrough etch" may
be utilized which comprises an anisotropic halogen reactive ion
etch ("RIE") rich in fluorine, i.e., wherein at least one of the
precursors was a fluorine-containing material (for example, and
without limitation, a combination of CHF.sub.3 and O.sub.2, where
the organosilicon nature of cross-linked material 134 may call for
the use of a halogen gas). Other suitable halogen compounds
include, for example, and without limitation, CF.sub.4. This etch
is similar to a standard SiO.sub.2 etch performed in modern
integrated circuit processing. Next, an anisotropic oxygen reactive
ion etch may be used to transfer the features to underlying
substrate 31 wherein the remaining silicon containing features
serve as an etch mask to transfer the pattern to underlying
substrate 31. The "transfer etch" may be achieved, for example, and
without limitation, with a standard, anisotropic, oxygen RIE
processing tool. However, in general, any suitable etch process may
be employed dependent upon the etch rate desired and the underlying
constituents that form substrate 31 and imprinting layer 134.
Exemplary etch processes may include plasma etching, reactive ion
etching, chemical wet etching and the like.
[0025] Referring to both FIGS. 1 and 2, exemplary radiation source
22 may produce ultraviolet radiation; however, any known radiation
source may be employed. The selection of radiation employed to
initiate the polymerization of the material in imprinting layer 34
is known to one skilled in the art and typically depends on the
specific application which is desired. Furthermore, the plurality
of features on mold 28 are shown as recessions 28a extending along
a direction parallel to protrusions 28b that provide a
cross-section of mold 28 with a shape of a battlement. However,
recessions 28a and protrusions 28b may correspond to virtually any
feature required to create an integrated circuit and may be as
small as a few tenths of nanometers.
[0026] Referring to FIGS. 1, 2 and 5, the pattern produced by the
present patterning technique may be transferred into substrate 31
to provide features having aspect ratios as great as 30:1. To that
end, one embodiment of mold 28 has recessions 28a defining an
aspect ratio in a range of 1:1 to 10:1. Specifically, protrusions
28b have a width W.sub.1 in a range of about 10 nm to about 5000
.mu.m, and recessions 28a have a width W.sub.2 in a range of 10 nm
to about 5000 .mu.m. As a result, mold 28 and/or template 26, may
be formed from various conventional materials, such as, but not
limited to, fused-silica, quartz, silicon, organic polymers,
siloxane polymers, borosilicate glass, fluorocarbon polymers,
metal, hardened sapphire and the like.
[0027] Referring to FIGS. 1, 2 and 3, the characteristics of
material 36a are important to efficiently pattern substrate 31 in
light of the deposition process employed. As mentioned above,
material 36a is deposited on substrate 31 as a plurality of
discrete and spaced-apart droplets 36. The combined volume of
droplets 36 is such that the material 36a is distributed
appropriately over an area of surface 32 where imprinting layer 34
is to be formed. As a result, imprinting layer 34 is spread and
patterned concurrently, with the pattern being subsequently set
into imprinting layer 34 by exposure to radiation, such as
ultraviolet radiation. As a result of the deposition process, it is
desired that material 36a have certain characteristics to
facilitate rapid and even spreading of material 36a in droplets 36
over surface 32 so that all thicknesses t.sub.1 are substantially
uniform and all thicknesses t.sub.2 are substantially uniform. The
desirable characteristics include having a low viscosity, for
example, and without limitation, in a range of about 0.5 to about
10 centepoise (cps), as well as the ability to wet surface of
substrate 31 and mold 28 and to avoid subsequent pit or hole
formation after polymerization. Preferably, the viscosity is in a
range of 0.5 to 5 cps. With these characteristics satisfied,
imprinting layer 34 may be made sufficiently thin while avoiding
formation of pits or holes in the thinner regions, such as
sub-portions 34b, shown in FIG. 5.
[0028] The constituent components that form material 36a to provide
the aforementioned characteristics may differ. This results from
substrate 31 being formed from a number of different materials. As
a result, the chemical composition of surface 32 varies dependent
upon the material from which substrate 31 is formed. For example,
substrate 31 may be formed from silicon, plastics, gallium
arsenide, mercury telluride, and composites thereof. Additionally,
substrate 31 may include one or more layers in sub-portion 34b, for
example, dielectric layer, metal-layer, semiconductor layer,
planarization layer and the like.
[0029] Referring to FIGS. 2, 3 and 4, it is desired, however, that
material 36a include components to provide mold 28 with surface
characteristics such that mold 28 may satisfy two--seemingly
contradictory--surface energy requirements. Specifically, once
material 36a is solidified into material 36c, mold 28 should have
the requisite surface energy to release from solidified material
36c so as to minimize distortions in the pattern recorded in
solidified material 36c. Additionally, to ensure efficient filling
of features of mold 28, it is desired that the surface of mold 28
have a sufficiently high surface energy to facilitate wetting of
mold 28 with imprinting material 36a.
[0030] As was discussed in the Background of the Invention, in
accordance with one particular method of imprinting, one manner in
which the two aforementioned requirements for mold surface were
balanced involved pre-treating the surface of mold 28 and including
a surfactant in imprinting material. To that end, a pre-treatment
solution including isopropyl alcohol ("IPA") and a surfactant
consisting of 0.1% FSO-100 was employed. The imprinting material
also included the surfactant FSO-100. FSO-100 is available under
the designation ZONYL.RTM. FSO-100 from DUPONT.TM. and has a
general structure of R.sub.1R.sub.2 where
R.sub.1=F(CF.sub.2CF.sub.2).sub.Y, with Y being in a range of 1 to
7, inclusive, and
R.sub.2=CH.sub.2CH.sub.2O(CH.sub.2CH.sub.2O).sub.XH, where X is in
a range of 0 to 15, inclusive. FSO-100 is a fluorinated surfactant
having a molecular weight of about 600, and it aligns efficiently
at the surface of the imprint template with hydrophobic --CF.sub.3
groups projecting towards the surface of the imprint template. Such
alignment is promoted by pre-cleaning the surface (prior to
pre-treatment utilizing a surfactant solution consisting of 0.1%
FSO-100 in IPA) to create silanol functional groups on the surface.
However, the present invention provides an improved method and
material that substantially reduces, if not prevents, void
formation when imprinting high density features having a height of
about 200 nm.
[0031] This is achieved, in part, by employing a polymeric
fluorinated surfactant. An exemplary polymeric fluorinated
surfactant is available under the designation 3M.TM. Novec.TM.
Fluorosurfactant FC-4432 (hereafter referred to as FC-4432) from 3M
Company of St. Paul, Minn. in the manner described in detail below
to provide an imprinting material and methods for imprint
lithography. FC-4432 is a non-ionic polymeric fluorochemical
surfactant belonging to a class of coating additives which provide
low surface tensions in organic coating systems. The composition of
FC-4432 is 87% polymeric fluorochemical actives, 7%
non-fluorochemical actives, 5% 1-methyl-2-pyrudiinone, and <1%
toluene. FC-4432 is a wetting, leveling and flow control agent for
radiation curable polymer coating systems, and continues to be
active throughout the curing process. FC-4432 is the first in a new
line of fluorochemical surfactants from the 3M Company based on
perfluorosulfate (PFBS), where PFBS refers collectively to
perfluorobutane sulfonyl compounds including perfluorobutance
sulfonates. In addition, such PFBS-based surfactants with only four
perfluorinated carbon atoms offer improved environmental
properties. The molecular weight of FC-4432 is about 4000, and
because of its higher molecular weight than that of FSO-100, the
fluorinated groups of FC-4432 align differently at the surface of
an imprint template than those in FSO-100. In particular, besides
--CF.sub.3 groups of FSO-100, FC-4432 has a higher percentage of
--CF.sub.2 groups situated at the surface when compared to FSO-100.
Because a --CF.sub.2 group provides a higher surface energy than a
--CF.sub.3 group, the presence of a higher percentage of --CF.sub.2
groups in FC-4432 at template surface provides a material having
better wetting than FS-100. However, despite its higher surface
energy, a --CF2-- group is hydrophobic enough so that its use
produces a material having a good release property. In addition, it
is believed that the higher molecular weight of FC-4432 (when
compared to that of FSO-100) causes FC-4432 to act like a loosely
packed coil structure that results in more porous molecular packing
of surfactant molecules at the surface of the imprint template. It
is further believed that this coil structure helps enhance wetting
over that provided by FSO-100, and in addition to that provided by
the presence of a higher percentage of surface --CF.sub.2 groups in
FC-4432 when compared to FSO-100.
[0032] An exemplary composition for material 36a that utilizes the
surfactant FC-4432 is produced by mixing (with exemplary
proportions being given in weight): (i)
acryloxymethylpentamethyldisiloxane (for example, and without
limitation, about 37 gm) which is available under the designation
XG-1064 from Gelest, Inc. of Morrisville, Pa., (ii) isobornyl
acrylate ("IBOA") (for example, and without limitation, about 42
gm) which is available under the designation SR 506 from Aldrich
Chemical Company of Milwaukee, Wis., (iii) ethylene glycol
diacrylate (for example, and without limitation, about 18 gm) which
is available under the designation EGDA from Aldrich Chemical
Company of Milwaukee, Wis., (iv) a UV photoinitiator, for example,
and without limitation, 2-hydrozy-2-methyl-1-phenyl-propan-1-one
(for example, and without limitation, about 3 gm) which is
available under the designation Darocur 1173 from CIBA.RTM. of
Tarrytown, N.Y.), and (v) FC-4432 (for example, and without
limitation, about 0.5 gm). The above-identified composition may
also include stabilizers that are well known in the chemical art to
increase the operational life of the composition. In a typical such
embodiment, the surfactant comprises less than 1% of the imprinting
material. However, the percentage of the surfactant may be greater
than 1%.
[0033] An advantage provided by the above-described imprinting
material is that it abrogates the need for an a priori release
layer, i.e., a separate hydrophobic and/or low surface energy
release layer disposed on imprint template 28 (as described in the
Background of the Invention). Specifically, the imprinting material
provides desirable release properties to mold 28 and imprinting
layer 34 so that material 36c, shown in FIG. 4, does not adhere to
mold 28 with sufficient force to distort the pattern recorded
therein.
[0034] Referring to FIG. 6, it is believed that surfactant
molecules in droplets 36 of the imprinting material preferentially
move toward the gas-liquid interface in less than about 1 sec. As
such, it is believed that droplets 36 have a higher concentration
of the surfactant in region 136 when compared with region 137 in
which the polymerizable components are concentrated. It is believed
that this is the result of an energy minimization process wherein
the surfactant tends to move to the gas-liquid interface so that
its hydrophobic end aligns towards the gas. For example, it is
believed that the fluorinated, hydrophobic end of the FC-4432 (for
example, comprised of --CF.sub.3 and --CF.sub.2 groups) is aligned
to project out of the liquid and into the gas, and the hydrophilic
end (i.e., --OH and polar ethylene oxide groups) is aligned to
project into the liquid. However, when the imprinting material
contacts the surface of the imprint template, it is believed that
exposed silanol bonds on the surface of the imprint template cause
the hydrophilic end of the surfactant molecule to flip and to
contact the exposed silanol bonds so that --CF3 groups and
--CF.sub.2 groups face downward (i.e., outward from the surface of
the imprint template) to enable adhesion reduction. It is further
believed that surfactant lamella may also be formed at the surface
of the imprint template, which lamella may comprise, for example,
two (2) layers of surfactant molecules.
[0035] Referring to FIG. 2, an additional advantage provided by the
above-described imprinting material is that the time required to
wet mold 28 and, therefore, to spread droplets 36 may be reduced.
Specifically, by abrogating the need to have an a priori release
layer on mold 28, the surface of mold 28 may be provided with
increased surface energy. Of course, the above-described imprinting
material may be employed with an a priori release layer, such as
those known in the prior art.
[0036] Another manner by which to improve the release properties of
mold 28 includes conditioning the pattern of mold 28 by exposing
the same to a conditioning mixture including an additive that will
remain on mold 28 to reduce the surface energy of the mold surface.
An exemplary additive is a surfactant.
[0037] The above-described imprinting material is useful in
providing substantially void free imprint lithography utilizing
high feature density and relatively tall feature height (for
example, and without limitation, feature heights of about 200 nm)
with residual layer thicknesses of 50-100 nm (note that providing
thin residual layers requires low viscosity and small drops of
imprinting material, i.e., viscosity below about 10 cps, and
preferably below 5 cps, and drops at or below about 80
pico-liters).
[0038] The following describes a method for imprint lithography
that utilizes one or more embodiments of the above-described
imprinting material. As a first step, the surface of a quartz
imprint template is pre-treated to create hydrophilic bonds at the
surface, for example, and without limitation silanol (Si--OH)
bonds. In accordance with one or more embodiments of the present
invention, the surface of the imprint template is dipped in a 2.5:1
solution of H.sub.2SO.sub.4 and H.sub.2O.sub.2 to hydrolyze the
surface, i.e., to create silanol bonds at the surface. As a next
step, the surface is further pre-treated by spraying the surface of
the imprint template with a diluted FC-4432 solution (for example,
and without limitation, 0.1% FC-4432 in IPA). Exposure of the
surface of the imprint template may be achieved by virtually any
method known in the art, including dipping the surface into a
volume of pre-treatment solution, wiping the surface with a cloth
saturated with pre-treatment solution, and spraying a stream of
pre-treatment solution onto the surface. The IPA in the
pre-treatment solution may be allowed to evaporate before using the
mold 28. In this manner, the IPA facilitates removing undesired
contaminants from the surface while leaving the surfactant. Because
the surfactant includes a hydrophobic, fluorine-rich end, and a
hydrophilic end, the silanol groups promote alignment of the
surfactant so that the hydrophilic end "adsorbs" to the --OH end of
the silanol groups, and the hydrophobic, fluorine-rich end points
away from the surface. In a next step, a gap between the imprint
template and the substrate may be purged of air (mainly O.sub.2 and
N.sub.2) using, for example, and without limitation, an .about.5
psi Helium purge. In a next step, the imprinting material
containing the FC-4432 surfactant is applied to the substrate, for
example, and without limitation, by placing a pattern of
substantially equidistant droplets of imprinting material on the
substrate, by spin-coating, or by any other method known to those
of ordinary skill in the art. In this example, the substrate was
covered with a transfer layer whose top layer was a cross-linked
BARC material (BARC or "bottom antireflective coating" is an
organic antireflective coating that is typically produced by a
spin-on process). The BARC layer was used to prevent intermixing
between an imprinting material and the transfer layer, which
intermixing may be particularly problematic when using an
imprinting material comprised of low viscosity acrylate components
because such components have solvency toward many polymers.
Intermixing may cause problems such as, for example, and without
limitation, distortion of features when an imprint template is
separated from a substrate after exposure to polymerizing
radiation. This can be particularly problematic when feature
thicknesses are as small as 50 to 100 nm. Next, the familiar steps
of imprint lithography are carried out, i.e., exposure to actinic
radiation to polymerize the imprinting material; separation of the
imprint template and the substrate; and selective etching to
transfer the feature pattern to the substrate.
[0039] It is believed that the use of surface pre-treatments
described above utilizing FC-4432 may be useful by itself in
helping to provide substantially void free imprint lithography. For
example, we have run experiments where the surface was pre-treated
as described directly above, and wherein the imprinting material
included FSO-100 as a surfactant rather than FC-4432. In this case
a few void free imprints were made, but it is believed that as soon
as the FC-4432 supplied to the surface of the imprint template by
pre-treatment was abraded away, imprints having voids soon
appeared.
[0040] It is believed that even when pre-treating the surface of
the imprint template as described above utilizing FC-4432, FC-4432
adhered to the silanol groups on the surface of the imprint
template ultimately is abraded away. However, as was described
above, the FC-4432 contained in the imprinting material itself
rapidly comes to the gas-liquid surface of the droplets, and the
surface of the imprint template is re-coated with FC-4432 as a
normal consequence of imprinting. As such, in accordance with one
or more embodiments of the present invention, the pre-treatment
step of applying the surfactant solution to the surface of the
imprint template may be eliminated. In fact, in accordance with one
or more further embodiments of the present invention, the imprint
template may be contacted a few times with the imprinting material
as a replacement for the pre-treatment step of applying the
surfactant solution to the surface. In this manner, the use of the
polymeric fluorinated surfactant, as discussed above, enables
varying the surface characteristics of mold 28, and therefore
template 26, to satisfying the two aforementioned contradictory
surface energy requirements.
[0041] The embodiments of the present invention described above are
exemplary. Many changes and modifications may be made to the
disclosure recited above, while remaining within the scope of the
invention. The scope of the invention should, therefore, be
determined not with reference to the above description, but instead
should be determined with reference to the appended claims along
with their full scope of equivalents.
* * * * *
References