U.S. patent application number 15/989622 was filed with the patent office on 2018-09-27 for substrate pretreatment and etch uniformity in nanoimprint lithography.
The applicant listed for this patent is Canon Kabushiki Kaisha. Invention is credited to Gary Doyle, Niyaz Khusnatdinov, Weijun Liu, Timothy Stachowiak, Fen Wan.
Application Number | 20180275511 15/989622 |
Document ID | / |
Family ID | 58190412 |
Filed Date | 2018-09-27 |
United States Patent
Application |
20180275511 |
Kind Code |
A1 |
Stachowiak; Timothy ; et
al. |
September 27, 2018 |
SUBSTRATE PRETREATMENT AND ETCH UNIFORMITY IN NANOIMPRINT
LITHOGRAPHY
Abstract
A nanoimprint lithography method includes contacting a composite
polymerizable coating formed from a pretreatment composition and an
imprint resist with a nanoimprint lithography template defining
recesses. The composite polymerizable coating is polymerized to
yield a composite polymeric layer defining a pre-etch plurality of
protrusions corresponding to the recesses of the nanoimprint
lithography template. The nanoimprint lithography template is
separated from the composite polymeric layer. At least one of the
pre-etch plurality of protrusions corresponds to a boundary between
two of the discrete portions of the imprint resist, and the
pre-etch plurality of protrusions have a variation in pre-etch
height of .+-.10% of a pre-etch average height. The pre-etch
plurality of protrusions is etched to yield a post-etch plurality
of protrusions having a variation in post-etch height of .+-.10% of
a post-etch average height, and the pre-etch average height exceeds
the post-etch average height.
Inventors: |
Stachowiak; Timothy;
(Austin, TX) ; Liu; Weijun; (Cedar Park, TX)
; Wan; Fen; (Austin, TX) ; Doyle; Gary;
(Round Rock, TX) ; Khusnatdinov; Niyaz; (Round
Rock, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Canon Kabushiki Kaisha |
TOKYO |
|
JP |
|
|
Family ID: |
58190412 |
Appl. No.: |
15/989622 |
Filed: |
May 25, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15260073 |
Sep 8, 2016 |
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15989622 |
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15195789 |
Jun 28, 2016 |
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15260073 |
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15004679 |
Jan 22, 2016 |
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15195789 |
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62355814 |
Jun 28, 2016 |
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62215316 |
Sep 8, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C 2059/023 20130101;
B29C 59/026 20130101; B29C 59/02 20130101; G03F 7/0002 20130101;
C09K 13/00 20130101 |
International
Class: |
G03F 7/00 20060101
G03F007/00 |
Claims
1-17. (canceled)
18. A nanoimprint lithography stack comprising: a nanoimprint
lithography substrate; and a composite polymeric layer on the
nanoimprint lithography substrate, wherein the composite polymeric
layer is formed from discrete portions of an imprint resist on a
pretreatment coating and defines a pre-etch plurality of
protrusions, at least one of the protrusions corresponding to a
boundary between two of the discrete portions of the imprint
resist, the pre-etch plurality of protrusions have a variation in
pre-etch height of .+-.10% of a pre-etch average height, wherein
after etching of the pre-etch plurality of protrusions to yield a
post-etch plurality of protrusions, the post-etch plurality of
protrusions has a variation in post-etch height of .+-.10% of a
post-etch average height, and the pre-etch average height exceeds
the post-etch average height.
19. The nanoimprint lithography stack of claim 18, wherein the
boundary between the two of the discrete portions of the imprint
resist is formed from an inhomogeneous mixture of the pretreatment
composition and the imprint resist.
20. The nanoimprint lithography stack of claim 18, wherein the
variation in post-etch average height is .+-.5% of the post-etch
average height.
21. A component formed by a method comprising: disposing a
pretreatment composition on a nanoimprint lithography substrate to
yield a liquid pretreatment coating on the nanoimprint lithography
substrate, wherein the pretreatment composition comprises a
polymerizable component; disposing discrete portions of an imprint
resist on the pretreatment coating, wherein the imprint resist is a
polymerizable composition; forming a composite polymerizable
coating on the nanoimprint lithography substrate as each discrete
portion of the imprint resist spreads on the liquid pretreatment
coating; contacting the composite polymerizable coating with a
nanoimprint lithography template defining recesses; polymerizing
the composite polymerizable coating to yield a composite polymeric
layer defining a pre-etch plurality of protrusions corresponding to
the recesses of the nanoimprint lithography template, wherein at
least one of the pre-etch plurality of protrusions corresponds to a
boundary between two of the discrete portions of the imprint
resist, and the pre-etch plurality of protrusions have a variation
in pre-etch height of .+-.10% of a pre-etch average height;
separating the nanoimprint lithography template from the composite
polymeric layer; and etching the pre-etch plurality of protrusions
to yield a post-etch plurality of protrusions, wherein the
post-etch plurality of protrusions have a variation in post-etch
height of .+-.10% of a post-etch average height, and the pre-etch
average height exceeds the post-etch average height.
22. The component of claim 21, wherein the component is an imprint
lithography stack.
23. The component of claim 21, wherein the component is a
device.
24. A nanoimprint lithography stack formed by a method comprising:
disposing a pretreatment composition on a nanoimprint lithography
substrate to form a pretreatment coating on the nanoimprint
lithography substrate, wherein the pretreatment composition
comprises a polymerizable component; disposing discrete portions of
imprint resist on the pretreatment coating, each discrete portion
of the imprint resist covering a target area of the nanoimprint
lithography substrate, wherein the imprint resist is a
polymerizable composition; forming a composite polymerizable
coating on the nanoimprint lithography substrate as each discrete
portion of the imprint resist spreads beyond its target area,
wherein the composite polymerizable coating comprises a mixture of
the pretreatment composition and the imprint resist; contacting the
composite polymerizable coating with a nanoimprint lithography
template; and polymerizing the composite polymerizable coating to
yield a composite polymeric layer on the nanoimprint lithography
substrate, wherein the interfacial surface energy between the
pretreatment composition-and air exceeds the interfacial surface
energy between the imprint resist and air.
25. A nanoimprint lithography stack comprising: a nanoimprint
lithography substrate; and a composite polymeric layer formed on a
surface of the nanoimprint lithography substrate, wherein the
chemical composition of the composite polymeric layer is
non-uniform, and comprises a plurality of center regions separated
by boundaries, wherein the chemical composition of the composite
polymeric layer at the boundaries differs from the chemical
composition of the composite polymeric layer at the interior of the
center regions.
26. The nanoimprint lithography stack of claim 25, wherein the
nanoimprint lithography substrate comprises an adhesion layer, and
the composite polymeric layer is formed on a surface of the
adhesion layer.
27. The nanoimprint lithography stack of claim 25, wherein the
center regions and the boundaries of the polymeric layer are formed
from an inhomogeneous mixture of a pretreatment composition and an
imprint resist, wherein a polymerizable component of the imprint
resist and a polymerizable component of the pretreatment
composition react to form a covalent bond during formation of the
composite polymeric layer.
28. The nanoimprint lithography stack of claim 27, wherein the
polymerizable component of the imprint resist and the polymerizable
component of the pretreatment composition have a common functional
group.
29. The nanoimprint lithography stack of claim 28, wherein the
common functional group is an acrylate group.
30. A component formed by a method comprising: disposing a
pretreatment composition on a substrate to form a pretreatment
coating on the substrate, wherein the pretreatment composition
comprises a polymerizable component; disposing discrete portions of
imprint resist on the pretreatment coating, each discrete portion
of the imprint resist covering a target area of the substrate,
wherein the imprint resist is a polymerizable composition; forming
a composite polymerizable coating on the substrate as each discrete
portion of the imprint resist spreads beyond its target area,
wherein the composite polymerizable coating comprises a mixture of
the pretreatment composition and the imprint resist; contacting the
composite polymerizable coating with a nanoimprint lithography
template; polymerizing the composite polymerizable coating to yield
a composite polymeric layer on the substrate; and separating the
nanoimprint lithography template from the composite polymeric layer
to yield the component, wherein: the interfacial surface energy
between the pretreatment composition and air exceeds the
interfacial surface energy between the imprint resist and air, the
difference between the interfacial surface energy between the
pretreatment composition and air and between the imprint resist and
air is in a range of 0.5 mN/m to 25 mN/m, the interfacial surface
energy between the imprint resist and air is in a range of 20 mN/m
to 60 mN/m, and the interfacial surface energy between the
pretreatment composition and air is in a range of 30 mN/m to 45
mN/m.
31. The component of claim 30, wherein the component is a processed
substrate.
32. The component of claim 30, wherein the component is an optical
component.
33. The component of claim 30, wherein the component is a quartz
mold replica.
Description
CROSS-REERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 15/260,073 entitled "SUBSTRATE PRETREATMENT AND ETCH UNIFORMITY
IN NANOIMPRINT LITHOGRAPHY" filed on Sep. 8, 2016, which claims
priority to U.S. application Ser. No. 62/355,814 entitled
"SUBSTRATE PRETREATMENT AND ETCH UNIFORMITY IN NANOIMPRINT
LITHOGRAPHY" filed on Jun. 28, 2016, and is a continuation-in-part
of U.S. application Ser. No. 15/195,789 entitled "SUBSTRATE
PRETREATMENT FOR REDUCING FILL TIME IN NANOIMPRINT LITHOGRAPHY"
filed on Jun. 28, 2016, which is a continuation-in-part of U.S.
application Ser. No. 15/004,679 entitled "SUBSTRATE PRETREATMENT
FOR REDUCING FILL TIME IN NANOIMPRINT LITHOGRAPHY" filed on Jan.
22, 2016, which claims priority to U.S. Application Ser. No.
62/215,316 entitled "SUBSTRATE PRETREATMENT FOR REDUCING FILL TIME
IN NANOIMPRINT LITHOGRAPHY" filed on Sep. 8, 2015, all of which are
herein incorporated by reference in their entirety.
TECHNICAL FIELD
[0002] This invention relates to facilitating throughput in
nanoimprint lithography processes by treating a nanoimprint
lithography substrate with a pretreatment composition to promote
spreading of an imprint resist on the nanoimprint lithography
substrate, and matching the etch rate of the pretreatment
composition and the imprint resist to achieve uniform etching
across the imprinted field.
BACKGROUND
[0003] As the semiconductor processing industry strives for larger
production yields while increasing the number of circuits per unit
area, attention has been focused on the continued development of
reliable high-resolution patterning techniques. One such technique
in use today is commonly referred to as imprint lithography.
Imprint lithography processes are described in detail in numerous
publications, such as U.S. Patent Application Publication No.
2004/0065252, and U.S. Pat. No.6,936,194 and U.S. Pat. No.
8,349,241, all of which are incorporated by reference herein. Other
areas of development in which imprint lithography has been employed
include biotechnology, optical technology, and mechanical
systems.
[0004] An imprint lithography technique disclosed in each of the
aforementioned patent documents includes formation of a relief
pattern in an imprint resist and transferring a pattern
corresponding to the relief pattern into an underlying substrate.
The patterning process uses a template spaced apart from the
substrate and a polymerizable composition (an "imprint resist")
disposed between the template and the substrate. In some cases, the
imprint resist is disposed on the substrate in the form of
discrete, spaced-apart drops. The drops are allowed to spread
before the imprint resist is contacted with the template. After the
imprint resist is contacted with the template, the resist is
allowed to uniformly fill the space between the substrate and the
template, then the imprint resist is solidified to form a layer
that has a pattern conforming to a shape of the surface of the
template. After solidification, the template is separated from the
patterned layer such that the template and the substrate are spaced
apart.
[0005] Throughput in an imprint lithography process generally
depends on a variety of factors. When the imprint resist is
disposed on the substrate in the form of discrete, spaced-apart
drops, throughput depends at least in part on the efficiency and
uniformity of spreading of the drops on the substrate. Spreading of
the imprint resist may be inhibited by factors such as gas voids
between the drops and incomplete wetting of the substrate and/or
the template by the drops. Spreading of the imprint resist may be
facilitated by pretreating the substrate with a composition having
a higher surface tension than that of the imprint resist. However,
the difference in composition of the pretreatment composition and
the imprint resist, together with a non-uniform distribution of the
pretreatment composition and the imprint resist may cause
non-uniform etching across the field, resulting in poor critical
dimension uniformity or incomplete etching.
SUMMARY
[0006] In a first general aspect, a nanoimprint lithography method
includes disposing a pretreatment composition on a nanoimprint
lithography substrate to yield a liquid pretreatment coating on the
nanoimprint lithography substrate, disposing discrete portions of
an imprint resist on the pretreatment coating, and forming a
composite polymerizable coating on the nanoimprint lithography
substrate as each discrete portion of the imprint resist spreads on
the liquid pretreatment coating. The pretreatment composition
includes a polymerizable component, and the imprint resist is a
polymerizable composition. The composite polymerizable coating is
contacted with a nanoimprint lithography template defining
recesses, and the composite polymerizable coating is polymerized to
yield a composite polymeric layer defining a pre-etch plurality of
protrusions corresponding to the recesses of the nanoimprint
lithography template. At least one of the pre-etch plurality of
protrusions corresponds to a boundary between two of the discrete
portions of the imprint resist, and the pre-etch plurality of
protrusions has a variation in pre-etch height of .+-.10% of a
pre-etch average height. The nanoimprint lithography template is
separated from the composite polymeric layer, and the pre-etch
plurality of protrusions is etched to yield a post-etch plurality
of protrusions. The post-etch plurality of protrusions has a
variation in post-etch height of .+-.10% of a post-etch average
height, and the pre-etch average height exceeds the post-etch
average height.
[0007] Implementations of the first general aspect may include one
or more of the following features.
[0008] The pre-etch average height may be up to 1 .mu.m, up to 500
nm, or up to 200 nm. The variation in post-etch height may be
.+-.5% or .+-.2% of the post-etch average height. At least two of
the pre-etch plurality of protrusions correspond to boundaries
between two of the discrete portions of the imprint resist. In some
cases, each protrusion in the pre-etch plurality of protrusions has
a width in a range of 5 nm to 100 .mu.m along a dimension of the
nanoimprint lithography substrate. In certain cases, the pre-etch
plurality of protrusions corresponds to a linear dimension of up to
50 mm along a dimension of the nanoimprint lithography substrate.
The boundary between the two of the discrete portions of the
imprint resist may be formed from an inhomogeneous mixture of the
imprint resist and the pretreatment composition. The pre-etch
average height typically exceeds the post-etch average height by at
least 1 nm. The pre-etch height and the post-etch height are
assessed at intervals in a range of 1 .mu.m to 50 .mu.m along a
dimension of the nanoimprint lithography substrate.
[0009] Etching the pre-etch plurality of protrusions may include
exposing the plurality of protrusions to an oxygen- or
halogen-containing plasma. The pre-etch height and the post-etch
height may be assessed by atomic force microscopy, reflectometry,
ellipsometry, or profilometry.
[0010] In some cases, the interfacial surface energy between the
pretreatment composition and air exceeds the interfacial surface
energy between the imprint resist and air or between at least a
component of the imprint resist and air. The difference between the
interfacial surface energy between the pretreatment composition and
air and the interfacial surface energy between the imprint resist
and air may be in a range of 0.5 mN/m to 25 mN/m, 0.5 mN/m to 15
mN/m, or 0.5 mN/m to 7 mN/m; the interfacial surface energy between
the imprint resist and air may be in a range of 20 mN/m to 60 mN/m,
28 mN/m to 40 mN/m, or 32 mN/m to 35 mN/m; and the interfacial
surface energy between the pretreatment composition and air may be
in a range of 30 mN/m to 45 mN/m. The viscosity of the pretreatment
composition may be in a range of 1 cP to 200 cP, 1 cP to 100 cP, or
1 cP to 50 cP at 23.degree. C. The viscosity of the imprint resist
may be in a range of 1 cP to 50 cP, 1 cP to 25 cP, or 5 cP to 15 cP
at 23.degree. C.
[0011] The pretreatment composition may include or consist
essentially of a single monomer. In some cases, the pretreatment
composition is a single monomer. In some cases, the pretreatment
composition includes two or more monomers. The pretreatment
composition may include a monofunctional, difunctional, or
multifunctional acrylate monomer. In certain cases, the
pretreatment composition includes at least one of
tricyclodecanedimethanol diacrylate, 1,3-adamantanediol diacrylate,
m-xylylene diacrylate, p-xylylene diacrylate,
2-phenyl-1,3-propanediol diacrylate, phenylethyleneglycol
diacrylate, 1,9-nonanediol diacrylate, 1,12-dodecanediol
diacrylate, and trimethylolpropane triacrylate. The imprint resist
may include at least one of benzyl acrylate, m-xylylene diacrylate,
p-xylylene diacrylate, 2-phenyl-1,3-propanediol diacrylate, and
phenylethyleneglycol diacrylate.
[0012] The imprint resist may include 0 wt % to 80 wt %, 20 wt % to
80 wt %, or 40 wt % to 80 wt % of one or more monofunctional
acrylates; 20 wt % to 98 wt % of one or more difunctional or
multifunctional acrylates; 1 wt % to 10 wt % of one or more
photoinitiators; and 1 wt % to 10 wt % of one or more surfactants.
The imprint resist may include 90 wt % to 98 wt % of one or more
difunctional or multifunctional acrylates and may be essentially
free of monofunctional acrylates. The imprint resist may include
one or more monofunctional acrylates and 20 wt % to 75 wt % of one
or more difunctional or multifunctional acrylates.
[0013] In some cases, the polymerizable component of the
pretreatment composition and a polymerizable component of the
imprint resist react to form a covalent bond during the
polymerizing of the composite polymerizable coating.
[0014] Disposing the pretreatment composition on the nanoimprint
lithography substrate may include spin coating the pretreatment
composition on the nanoimprint lithography substrate. Disposing
discrete portions of the imprint resist on the pretreatment coating
may include dispensing drops of the imprint resist on the
pretreatment coating.
[0015] A second general aspect includes a nanoimprint lithography
stack formed by the first general aspect.
[0016] A third general aspect includes a method for manufacturing a
device, the method including the nanoimprint lithography method of
the first general aspect.
[0017] A fourth general aspect includes the device formed by the
method of the third general aspect.
[0018] In a fifth general aspect, a nanoimprint lithography stack
includes a nanoimprint lithography substrate and a composite
polymeric layer on the nanoimprint lithography substrate. The
composite polymeric layer is formed from discrete portions of an
imprint resist on a pretreatment coating and defines a pre-etch
plurality of protrusions. At least one of the protrusions
corresponds to a boundary between two of the discrete portions of
the imprint resist, and the pre-etch plurality of protrusions has a
variation in pre-etch height of .+-.10% of a pre-etch average
height. After etching of the pre-etch plurality of protrusions to
yield a post-etch plurality of protrusions, the post-etch plurality
of protrusions has a variation in post-etch height of .+-.10% of a
post-etch average height, and the pre-etch average height exceeds
the post-etch average height.
[0019] Implementations of the fifth general aspect may include one
or more of the following features.
[0020] In some cases, the boundary between the two of the discrete
portions of the imprint resist is formed from an inhomogeneous
mixture of the pretreatment composition and the imprint resist. In
certain cases, the variation in post-etch average height is .+-.5%
of the post-etch average height.
[0021] The details of one or more implementations of the subject
matter described in this specification are set forth in the
accompanying drawings and the description below. Other features,
aspects, and advantages of the subject matter will become apparent
from the description, the drawings, and the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 depicts a simplified side view of a lithographic
system.
[0023] FIG. 2 depicts a simplified side view of the substrate shown
in FIG. 1, with a patterned layer formed on the substrate.
[0024] FIGS. 3A-3D depict spreading interactions between a drop of
a second liquid on a layer of a first liquid.
[0025] FIG. 4 is a flowchart depicting a process for facilitating
nanoimprint lithography throughput.
[0026] FIG. 5A depicts a nanoimprint lithography substrate. FIG. 5B
depicts a pretreatment coating disposed on a nanoimprint
lithography substrate.
[0027] FIGS. 6A-6D depict formation of a composite coating from
drops of imprint resist disposed on a substrate having a
pretreatment coating.
[0028] FIGS. 7A-7D depict cross-sectional views along lines w-w,
x-x, y-y, and z-z of FIGS. 6A-6D, respectively.
[0029] FIGS. 8A and 8B depict cross-sectional views of a
pretreatment coating displaced by drops on a nanoimprint
lithography substrate.
[0030] FIGS. 9A-9C depict cross-sectional views of a template in
contact with a homogeneous composite coating and the resulting
nanoimprint lithography stack.
[0031] FIGS. 10A-10C depict cross-sectional views of a template in
contact with an inhomogeneous composite coating and the resulting
nanoimprint lithography stack.
[0032] FIG. 11 is an image of drops of an imprint resist after
spreading on an adhesion layer of a substrate without a
pretreatment coating, corresponding to Comparative Example 1.
[0033] FIG. 12 is an image of drops of an imprint resist after
spreading on a pretreatment coating as described in Example 1.
[0034] FIG. 13 is an image of drops of an imprint resist after
spreading on a pretreatment coating as described in Example 2.
[0035] FIG. 14 is an image of drops of an imprint resist after
spreading on a pretreatment coating as described in Example 3.
[0036] FIG. 15 shows defect density as a function of prespreading
time for the imprint resist and pretreatment of Example 2.
[0037] FIG. 16 shows drop diameter versus time for spreading
pretreatment compositions.
[0038] FIG. 17A shows viscosity as a function of fractional
composition of one component in a two-component pretreatment
composition. FIG. 17B shows drop diameter versus time for various
ratios of components in a two-component pretreatment composition.
FIG. 17C shows surface tension of a two-component pretreatment
composition versus fraction of one component in the two-component
pretreatment composition.
[0039] FIG. 18 shows etch rates of pretreatment compositions
relative to the etch rate of an imprint resist.
[0040] FIGS. 19A and 19B show imprint feature height of imprint
patterns before and after etching.
DETAILED DESCRIPTION
[0041] FIG. 1 depicts an imprint lithographic system 100 of the
sort used to form a relief pattern on substrate 102. Substrate 102
may include a base and an adhesion layer adhered to the base.
Substrate 102 may be coupled to substrate chuck 104. As
illustrated, substrate chuck 104 is a vacuum chuck. Substrate chuck
104, however, may be any chuck including, but not limited to,
vacuum, pin-type, groove-type, electromagnetic, and/or the like.
Exemplary chucks are described in U.S. Pat. No. 6,873,087, which is
incorporated by reference herein. Substrate 102 and substrate chuck
104 may be further supported by stage 106. Stage 106 may provide
motion about the x-, y-, and z-axes. Stage 106, substrate 102, and
substrate chuck 104 may also be positioned on a base.
[0042] Spaced apart from substrate 102 is a template 108. Template
108 generally includes a rectangular or square mesa 110 some
distance from the surface of the template towards substrate 102. A
surface of mesa 110 may be patterned. In some cases, mesa 110 is
referred to as mold 110 or mask 110. Template 108, mold 110, or
both may be formed from such materials including, but not limited
to, fused silica, quartz, silicon, silicon nitride, organic
polymers, siloxane polymers, borosilicate glass, fluorocarbon
polymers, metal (e.g., chrome, tantalum), hardened sapphire, or the
like, or a combination thereof. As illustrated, patterning of
surface 112 includes features defined by a plurality of
spaced-apart recesses 114 and protrusions 116, though embodiments
are not limited to such configurations. Patterning of surface 112
may define any original pattern that forms the basis of a pattern
to be formed on substrate 102.
[0043] Template 108 is coupled to chuck 118. Chuck 118 is typically
configured as, but not limited to, vacuum, pin-type, groove-type,
electromagnetic, or other similar chuck types. Exemplary chucks are
further described in U.S. Pat. No. 6,873,087, which is incorporated
by reference herein. Further, chuck 118 may be coupled to imprint
head 120 such that chuck 118 and/or imprint head 120 may be
configured to facilitate movement of template 108.
[0044] System 100 may further include a fluid dispense system 122.
Fluid dispense system 122 may be used to deposit imprint resist 124
on substrate 102. Imprint resist 124 may be dispensed upon
substrate 102 using techniques such as drop dispense, spin-coating,
dip coating, chemical vapor deposition (CVD), physical vapor
deposition (PVD), thin film deposition, thick film deposition, or
the like. In a drop dispense method, imprint resist 124 is disposed
on substrate 102 in the form of discrete, spaced-apart drops, as
depicted in FIG. 1.
[0045] System 100 may further include an energy source 126 coupled
to direct energy along path 128. Imprint head 120 and stage 106 may
be configured to position template 108 and substrate 102 in
superimposition with path 128. System 100 may be regulated by a
processor 130 in communication with stage 106, imprint head 120,
fluid dispense system 122, and/or source 126, and may operate on a
computer readable program stored in memory 132.
[0046] Imprint head 120 may apply a force to template 108 such that
mold 110 contacts imprint resist 124. After the desired volume is
filled with imprint resist 124, source 126 produces energy (e.g.,
electromagnetic radiation or thermal energy), causing imprint
resist 124 to solidify (e.g., polymerize and/or crosslink),
conforming to the shape of surface 134 of substrate 102 and
patterning surface 112. After solidification of imprint resist 124
to yield a polymeric layer on substrate 102, mold 110 is separated
from the polymeric layer.
[0047] FIG. 2 depicts nanoimprint lithography stack 200 formed by
solidifying imprint resist 124 to yield patterned polymeric layer
202 on substrate 102. Patterned layer 202 may include a residual
layer 204 and a plurality of features shown as protrusions 206 and
recesses 208, with protrusions 206 having a thickness t.sub.1 and
residual layer 204 having a thickness t.sub.2. In nanoimprint
lithography, a length of one or more protrusions 206, recessions
208, or both parallel to substrate 102 is less than 100 nm, less
than 50 nm, or less than 25 nm. In some cases, a length of one or
more protrusions 206, recessions 208, or both is between 1 nm and
25 nm or between 1 nm and 10 nm.
[0048] The above-described system and process may be further
implemented in imprint lithography processes and systems such as
those referred to in U.S. Pat. Nos. 6,932,934; 7,077,992;
7,197,396; and U.S. Pat. No. 7,396,475, all of which are
incorporated by reference herein.
[0049] For a drop-on-demand or drop dispense nanoimprint
lithography process, in which imprint resist 124 is disposed on
substrate 102 as discrete portions ("drops"), as depicted in FIG.
1, the drops of the imprint resist typically spread on the
substrate 102 before and after mold 110 contacts the imprint
resist. If the spreading of the drops of imprint resist 124 is
insufficient to cover substrate 102 or fill recesses 114 of mold
110, polymeric layer 202 may be formed with defects in the form of
voids. Thus, a drop-on-demand nanoimprint lithography process
typically includes a delay between initiation of dispensation of
the drops of imprint resist 124 and initiation of movement of the
mold 110 toward the imprint resist on the substrate 102 and
subsequent filling of the space between the substrate and the
template. Thus, throughput of an automated nanoimprint lithography
process is generally limited by the rate of spreading of the
imprint resist on the substrate and filling of the template.
Accordingly, throughput of a drop-on-demand or drop dispense
nanoimprint lithography process may be improved by reducing "fill
time" (i.e., the time required to completely fill the space between
the template and substrate without voids). One way to decrease fill
time is to increase the rate of spreading of the drops of the
imprint resist and coverage of the substrate with the imprint
resist before movement of the mold toward the substrate is
initiated. The rate of spreading of an imprint resist and the
uniformity of coverage of the substrate may be improved by
pretreating the substrate with a liquid that promotes rapid and
even spreading of the discrete portions of the imprint resist and
polymerizes with the imprint resist during formation of the
patterned layer.
[0050] Spreading of discrete portions of a second liquid on a first
liquid may be understood with reference to FIGS. 3A-3D. FIGS. 3A-3D
depict first liquid 300 and second liquid 302 on substrate 304 and
in contact with gas 306 (e.g., air, an inert gas such as helium or
nitrogen, or a combination of inert gases). First liquid 300 is
present on substrate 304 in the form of coating or layer, used here
interchangeably. In some cases, first liquid 300 is present as a
layer having a thickness of a few nanometers (e.g., between 1 nm
and 15 nm, or between 5 nm and 10 nm). Second liquid 302 is present
in the form of a discrete portion ("drop"). The properties of first
liquid 300 and second liquid 302 may vary with respect to each
other. For instance, in some cases, first liquid 300 may be more
viscous and dense than second liquid 302.
[0051] The interfacial surface energy, or surface tension, between
second liquid 302 and first liquid 300 is denoted as
.gamma..sub.L1L2. The interfacial surface energy between first
liquid 300 and gas 306 is denoted as .gamma..sub.L1G. The
interfacial surface energy between second liquid 302 and gas 306 is
denoted as .gamma..sub.L2G. The interfacial surface energy between
first liquid 300 and substrate 304 is denoted as .gamma..sub.SL1.
The interfacial surface energy between second liquid 302 and
substrate 304 is denoted as .gamma..sub.SL2.
[0052] FIG. 3A depicts second liquid 302 as a drop disposed on
first liquid 300. Second liquid 302 does not deform first liquid
300 and does not touch substrate 304. As depicted, first liquid 300
and second liquid 302 do not intermix, and the interface between
the first liquid and the second liquid is depicted as flat. At
equilibrium, the contact angle of second liquid 302 on first liquid
300 is .theta., which is related to the interfacial surface
energies .gamma..sub.L1G, .gamma..sub.L2G, and .gamma..sub.L1L2 by
Young's equation:
.gamma..sub.L1G=.gamma..sub.L1L2+.gamma..sub.L2Gcos(.theta.)
(1)
If
.gamma..sub.L1G.gtoreq..gamma..sub.L1L2+.gamma..sub.L2G (2)
then .theta.=0.degree., and second liquid 302 spreads completely on
first liquid 300. If the liquids are intermixable, then after some
elapsed time,
.gamma..sub.L1L2=0 (3)
In this case, the condition for complete spreading of second liquid
302 on first liquid 300 is
.gamma..sub.L1G.gtoreq..gamma..sub.L2G (4)
For thin films of first liquid 300 and small drops of second liquid
302, intermixing may be limited by diffusion processes. Thus, for
second liquid 302 to spread on first liquid 300, the inequality (2)
is more applicable in the initial stages of spreading, when second
liquid 302 is disposed on first liquid 300 in the form of a
drop.
[0053] FIG. 3B depicts contact angle formation for a drop of second
liquid 302 when the underlying layer of first liquid 300 is thick.
In this case, the drop does not touch the substrate 304. Drop of
second liquid 302 and layer of first liquid 300 intersect at angles
.alpha., .beta., and .theta., with
.alpha.+.beta.+0=2.pi. (5)
There are three conditions for the force balance along each
interface:
.gamma..sub.L2G+.gamma..sub.L1L2cos(.theta.)+.gamma..sub.L1Gcos(.alpha.)-
=0 (6)
.gamma..sub.L2Gcos(.theta.)+.gamma..sub.L1L2+.gamma..sub.L1Gcos(.beta.)=-
0 (7)
.gamma..sub.L2Gcos(.alpha.)+.gamma..sub.L1L2cos(.beta.)+.gamma..sub.L1G=-
0 (8)
If first liquid 300 and second liquid 302 are intermixable,
then
.gamma..sub.L1L2=0 (9)
and equations (6)-(8) become:
.gamma..sub.L2G+.gamma..sub.L1Gcos(.alpha.)=0 (10)
.gamma..sub.L2Gcos(.theta.)+.gamma..sub.L1Gcos(.beta.)=0 (11)
.gamma..sub.L2Gcos(.alpha.)+.gamma..sub.L1G=0 (12)
[0054] Equations (10) and (12) give
cos .sup.2(.alpha.)=1 (13)
and
.alpha.=0, .pi. (14)
When second liquid 302 wets first liquid 300,
.alpha.=.pi. (15)
.gamma..sub.L2G=.gamma..sub.L1G (16)
and equation (11) gives
cos(.theta.)+cos(.beta.)=0 (17)
Combining this result with equations (5) and (15) gives:
.theta.=0 (18)
.beta.=.pi. (19)
Thus, equations equations (15), (18), and (19) give solutions for
angles .alpha., .beta., and .theta.. When
.gamma..sub.L1G.gtoreq..gamma..sub.L2G (20)
there is no equilibrium between the interfaces. Equation (12)
becomes an inequality even for .alpha.=.pi., and second liquid 302
spreads continuously on first liquid 300.
[0055] FIG. 3C depicts a more complex geometry for a drop of second
liquid 302 touching substrate 304 while also having an interface
with first liquid 300. Interfacial regions between first liquid
300, second liquid 302, and gas 306 (defined by angles .alpha.,
.beta., and .theta..sub.1) and first liquid 300, second liquid 302,
and substrate 304 (defined by angle .theta..sub.2) must be
considered to determine spreading behavior of the second liquid on
the first liquid.
[0056] The interfacial region between first liquid 300, second
liquid 302, and gas 306 is governed by equations (6)-(8). Since
first liquid 300 and second liquid 302 are intermixable,
.gamma..sub.L1L2=0 (21)
The solutions for angle .alpha. are given by equation (14). In this
case, let
.alpha.=0 (22)
and
.theta..sub.1=.pi. (23)
.beta.=.pi. (24)
When
.gamma..sub.L1G.gtoreq..gamma..sub.L2G (25)
there is no equilibrium between the drop of second liquid 302 and
first liquid 300, and the drop spreads continuously along the
interface between the second liquid and the gas until limited by
other physical limitations (e.g., conservation of volume and
intermixing).
[0057] For the interfacial region between first liquid 300, second
liquid 302, and substrate 304, an equation similar to equation (1)
should be considered:
.gamma..sub.SL1=.gamma..sub.SL2+.gamma..sub.L1L2cos (.theta..sub.2)
(26)
If
.gamma..sub.SL1.gtoreq..gamma..sub.SL2+.gamma..sub.L1L2 (27)
the drop spreads completely, and .theta..sub.2=0. Again, as for the
intermixable liquids, the second term .gamma..sub.L1L2=0, and the
inequality (27) simplifies to
.gamma..sub.SL1.gtoreq..gamma.SL2 (28)
The combined condition for the drop spreading is expressed as
.gamma..sub.L1G+.gamma..sub.SL1.gtoreq..gamma..sub.L2G+.gamma..sub.SL2
(29)
when energies before and after the spreading are considered. There
should be an energetically favorable transition (i.e., the
transition that minimizes the energy of the system).
[0058] Different relationships between the four terms in the
inequality (29) will determine the drop spreading character. The
drop of second liquid 302 can initially spread along the surface of
the first liquid 300 if the inequality (25) is valid but the
inequality (28) is not. Or the drop can start spreading along
liquid-solid interface provided the inequality (28) holds up and
the inequality (25) does not. Eventually first liquid 300 and
second liquid 302 will intermix, thus introducing more
complexity.
[0059] FIG. 3D depicts a geometry for a drop of second liquid 302
touching substrate 304 while having an interface with first liquid
300. As indicated in FIG. 3D, there are two interfacial regions of
interest on each side of the drop of second liquid 302. The first
interfacial region is where first liquid 300, second liquid 302,
and gas 306 meet, indicated by angles .alpha., .beta., and
.theta..sub.1. The second interfacial region of interest is where
first liquid 300, second liquid 302, and substrate 304 meet,
indicated by angle .theta..sub.2. Here, .theta..sub.1 approaches
0.degree. and .theta..sub.2 approaches 180.degree. as the drop
spreads when the surface tension of the interface between second
liquid 302 and substrate 304 exceeds the surface tension of the
interface between first liquid 300 and the substrate
(.gamma..sub.SL2.gtoreq..gamma..sub.SL1). That is, drop of second
liquid 302 spreads along the interface between first liquid 300 and
the second liquid and does not spread along the interface between
the second liquid and substrate 304.
[0060] For the interface between first liquid 300, second liquid
302, and gas 306, equations (6)-(8) are applicable. First liquid
300 and second liquid 302 are intermixable, so
.gamma..sub.L1L2=0 (30)
The solutions for angle a are given by equation (14). For
.alpha.=.pi. (31)
Equation (11) gives
cos(.theta..sub.1)+cos(.beta.)=0 (32)
and
.theta..sub.1=0 (33)
.beta.=.pi. (34)
When
.gamma..sub.L1G.gtoreq..gamma..sub.L2G (35)
there is no equilibrium between the drop of second liquid 302 and
liquid 300, and the drop spreads continuously along the interface
between the second liquid and the gas until limited by other
physical limitations (e.g., conservation of volume and
intermixing).
[0061] For the interfacial region between second liquid 302 and
substrate 304,
.gamma. SL 1 = .gamma. SL 2 + .gamma. L 1 L 2 cos ( .theta. 2 ) (
36 ) cos ( .theta. 2 ) = .gamma. SL 1 - .gamma. SL 2 .gamma. L 1 L
2 ( 37 ) If .gamma. SL 1 .ltoreq. .gamma. SL 2 ( 38 )
##EQU00001##
and the liquids are intermixable, i.e.,
.gamma..sub.L1L2.fwdarw.0 (39)
-.infin..ltoreq.cos(.theta..sub.2).ltoreq.-1 (40)
the angle .theta..sub.2 approaches 180.degree. and then becomes
undefined. That is, second liquid 302 has a tendency to contract
along the substrate interface and spread along the interface
between first liquid 300 and gas 306.
[0062] Spreading of second liquid 302 on first liquid 300 can be
summarized for three different cases, along with the surface energy
relationship for complete spreading. In the first case, drop of
second liquid 302 is disposed on layer of first liquid 300, and the
drop of the second liquid does not contact substrate 304. Layer of
first liquid 300 can be thick or thin, and the first liquid 300 and
second liquid 302 are intermixable. Under ideal conditions, when
the surface energy of first liquid 300 in the gas 306 is greater
than or equal to the surface energy of the second liquid 302 in the
gas (.gamma..sub.L1G.gtoreq..gamma..sub.L2G), complete spreading of
the drop of second liquid 302 occurs on layer of first liquid 300.
In the second case, drop of second liquid 302 is disposed on layer
of first liquid 300 while touching and spreading at the same time
on substrate 304. The first liquid and second liquid 302 are
intermixable. Under ideal conditions, complete spreading occurs
when: (i) the surface energy of first liquid 300 in the gas is
greater than or equal to the surface energy of second liquid 302 in
the gas (.gamma..sub.L1G.gtoreq..gamma..sub.L2G); and (ii) the
surface energy of the interface between the first liquid and
substrate 304 exceeds the surface energy of the interface between
the second liquid and the substrate
(.gamma..sub.SL1.gtoreq..gamma..sub.SL2). In the third case, drop
of second liquid 302 is disposed on layer of the first liquid 300
while touching substrate 304. Spreading may occur along the
interface between second liquid 302 and first liquid 300 or the
interface between the second liquid and substrate 304. The first
liquid and second liquid 302 are intermixable. Under ideal
conditions, complete spreading occurs when the sum of the surface
energy of first liquid 300 in the gas and the surface energy of the
interface between the first liquid and substrate 304 is greater
than or equal to the sum of the surface energy of second liquid 302
in the gas and the surface energy of the interface between the
second liquid and the substrate
(.gamma..sub.L1G+.gamma..sub.SL1.gtoreq..gamma..sub.L2G+.gamma..sub.SL2)
while the surface energy of first liquid 300 in the gas is greater
than or equal to the surface energy of second liquid 302 in the gas
(.gamma..sub.L1G.gtoreq..gamma..sub.L2G) or (ii) the surface energy
of the interface between the first liquid and substrate 304 exceeds
the surface energy of the interface between the second liquid and
the substrate (.gamma..sub.SL1.gtoreq..gamma..sub.SL2).
[0063] By pretreating a nanoimprint lithography substrate with a
liquid selected to have a surface energy greater than that of the
imprint resist in the ambient atmosphere (e.g., air or an inert
gas), the rate at which an imprint resist spreads on the substrate
in a drop-on-demand nanoimprint lithography process may be
increased and a more uniform thickness of the imprint resist on the
substrate may be established before the imprint resist is contacted
with the template, thereby facilitating throughput in the
nanoimprint lithography process. If the pretreatment composition
includes polymerizable components capable of intermixing with the
imprint resist, then this can advantageously contribute to
formation of the resulting polymeric layer without the addition of
undesired components, and may result in more uniform curing,
thereby providing more uniform mechanical and etch properties.
[0064] FIG. 4 is a flowchart showing a process 400 for facilitating
throughput in drop-on-demand nanoimprint lithography. Process 400
includes operations 402-410. In operation 402, a pretreatment
composition is disposed on a nanoimprint lithography substrate to
form a pretreatment coating on the substrate. In operation 404,
discrete portions ("drops") of an imprint resist are disposed on
the pretreatment coating, with each drop covering a target area of
the substrate. The pretreatment composition and the imprint resist
are selected such that the interfacial surface energy between the
pretreatment composition and the air exceeds the interfacial
surface energy between the imprint resist and the air.
[0065] In operation 406, a composite polymerizable coating
("composite coating") is formed on the substrate as each drop of
the imprint resist spreads beyond its target area. The composite
coating includes a homogeneous or inhomogeneous mixture of the
pretreatment composition and the imprint resist. In operation 408,
the composite coating is contacted with a nanoimprint lithography
template ("template"), and allowed to spread and fill all the
volume between the template and substrate, and in operation 410,
the composite coating is polymerized to yield a polymeric layer on
the substrate. After polymerization of the composite coating, the
template is separated from the polymeric layer, leaving a
nanoimprint lithography stack. As used herein, "nanoimprint
lithography stack" generally refers to the substrate and the
polymeric layer adhered to the substrate, each or both of which may
include one or more additional (e.g., intervening) layers. In one
example, the substrate includes a base and an adhesion layer
adhered to the base.
[0066] In process 400, the pretreatment composition and the imprint
resist may include a mixture of components as described, for
example, in U.S. Pat. No. 7,157,036 and U.S. Pat. No. 8,076,386, as
well as Chou et al. 1995, Imprint of sub-25 nm vias and trenches in
polymers. Applied Physics Letters 67(21):3114-3116; Chou et al.
1996, Nanoimprint lithography. Journal of Vacuum Science Technology
B 14(6): 4129-4133; and Long et al. 2007, Materials for step and
flash imprint lithography (S-FIL.RTM.. Journal of Materials
Chemistry 17:3575-3580, all of which are incorporated by reference
herein. Suitable compositions include polymerizable monomers
("monomers"), crosslinkers, resins, photoinitiators, surfactants,
or any combination thereof. Classes of monomers include acrylates,
methacrylates, vinyl ethers, and epoxides, as well as
polyfunctional derivatives thereof. In some cases, the pretreatment
composition, the imprint resist, or both are substantially free of
silicon. In other cases, the pretreatment composition, the imprint
resist, or both are silicon-containing. Silicon-containing monomers
include, for example, siloxanes and disiloxanes. Resins can be
silicon-containing (e.g., silsesquioxanes) and
non-silicon-containing (e.g., novolak resins). The pretreatment
composition, the imprint resist, or both may also include one or
more polymerization initiators or free radical generators. Classes
of polymerization initiators include, for example, photoinitiators
(e.g., acyloins, xanthones, and phenones), photoacid generators
(e.g., sulfonates and onium salts), and photobase generators (e.g.,
ortho-nitrobenzyl carbamates, oxime urethanes, and O-acyl
oximes).
[0067] Suitable monomers include monofunctional, difunctional, or
multifunctional acrylates, methacrylates, vinyl ethers, and
epoxides, in which mono-, di-, and multi- refer to one, two, and
three or more of the indicated functional groups, respectively.
Some or all of the monomers may be fluorinated (e.g.,
perfluorinated). In the case of acrylates, for example, the
pretreatment, the imprint resist, or both may include one or more
monofunctional acrylates, one or more difunctional acrylates, one
or more multifunctional acrylates, or a combination thereof.
[0068] Examples of suitable monofunctional acrylates include
isobornyl acrylate, 3,3,5-trimethylcyclohexyl acrylate,
dicyclopentenyl acrylate, benzyl acrylate, 1-naphthyl acrylate,
4-cyanobenzyl acrylate, pentafluorobenzyl acrylate, 2-phenylethyl
acrylate, phenyl acrylate,
(2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl acrylate, n-hexyl
acrylate, 4-tert-butylcyclohexyl acrylate, methoxy polyethylene
glycol (350) monoacrylate, and methoxy polyethylene glycol (550)
monoacrylate.
[0069] Examples of suitable diacrylates include ethylene glycol
diacrylate, diethylene glycol diacrylate, triethylene glycol
diacrylate, tetraethylene glycol diacrylate, polyethylene glycol
diacrylate (e.g., Mn, avg=575), 1,2-propanediol diacrylate,
dipropylene glycol diacrylate, tripropylene glycol diacrylate,
polypropylene glycol diacrylate, 1,3-propanediol diacrylate,
1,4-butanediol diacrylate, 2-butene-1,4-diacrylate, 1,3-butylene
glycol diacrylate, 3-methyl-1,3-butanediol diacrylate,
1,5-pentanediol diacrylate, 1,6-hexanediol diacrylate,
1H,1H,6H,6H-perfluoro-1,6-hexanediol diacrylate, 1,9-nonanediol
diacrylate, 1,10-decanediol diacrylate, 1,12-dodecanediol
diacrylate, neopentyl glycol diacrylate, cyclohexane dimethanol
diacrylate, tricyclodecane dimethanol diacrylate, bisphenol A
diacrylate, ethoxylated bisphenol A diacrylate, m-xylylene
diacrylate, ethoxylated (3) bisphenol A diacrylate, ethoxylated (4)
bisphenol A diacrylate, ethoxylated (10) bisphenol A diacrylate,
tricyclodecane dimethanol diacrylate, 1,2-adamantanediol
diacrylate, 2,4-diethylpentane-1,5-diol diacrylate, poly(ethylene
glycol) (400) diacrylate, poly(ethylene glycol) (300) diacrylate,
1,6-hexanediol (EO).sub.2 diacrylate, 1,6-hexanediol (EO).sub.5
diacrylate, and alkoxylated aliphatic diacrylate ester.
[0070] Examples of suitable multifunctional acrylates include
trimethylolpropane triacrylate, propoxylated trimethylolpropane
triacrylate (e.g., propoxylated (3) trimethylolpropane triacrylate,
propoxylated (6) trimethylolpropane triacrylate),
trimethylolpropane ethoxylate triacrylate (e.g., n.about.1.3, 3,
5), di(trimethylolpropane) tetraacrylate, propoxylated glyceryl
triacrylate (e.g., propoxylated (3) glyceryl triacrylate), tris
(2-hydroxy ethyl) isocyanurate triacrylate, pentaerythritol
triacrylate, pentaerythritol tetracrylate, ethoxylated
pentaerythritol tetracrylate, dipentaerythritol pentaacrylate,
tripentaerythritol octaacrylate.
[0071] Examples of suitable crosslinkers include difunctional
acrylates and multifunctional acrylates, such as those described
herein.
[0072] Examples of suitable photoinitiators include IRGACURE 907,
IRGACURE 4265, 651, 1173, 819, TPO, and TPO-L.
[0073] A surfactant can be applied to a patterned surface of an
imprint lithography template, added to an imprint lithography
resist, or both, to reduce the separation force between the
solidified resist and the template, thereby reducing separation
defects in imprinted patterns formed in an imprint lithography
process and to increase the number of successive imprints that can
be made with an imprint lithography template. Factors in selecting
a release agent for an imprint resist include, for example,
affinity with the surface and desired surface properties of the
treated surface.
[0074] Examples of suitable surfactants include fluorinated and
non-fluorinated surfactants. The fluorinated and non-fluorinated
surfactants may be ionic or non-ionic surfactants. Suitable
non-ionic fluorinated surfactants include fluoro-aliphatic
polymeric esters, perfluoroether surfactants, fluorosurfactants of
polyoxyethylene, fluorosurfactants of polyalkyl ethers, fluoroalkyl
polyethers, and the like. Suitable non-ionic non-fluorinated
surfactants include ethoxylated alcohols, ethoxylated alkylphenols,
and polyethyleneoxide-polypropyleneoxide block copolymers.
[0075] Exemplary commercially available surfactant components
include, but are not limited to, ZONYL.RTM. FSO and ZONYL.RTM.
FS-300, manufactured by E.I. du Pont de Nemours and Company having
an office located in Wilmington, Del.; FC-4432 and FC-4430,
manufactured by 3M having an office located in Maplewood, Minn.;
MASURF.RTM. FS-1700, FS-2000, and FS-2800 manufactured by Pilot
Chemical Company having an office located in Cincinnati, Ohio.;
S-107B, manufactured by Chemguard having an office located in
Mansfield, Tex.; FTERGENT 222F, FTERGENT 250, FTERGENT 251,
manufactured by NEOS Chemical Chuo-ku, Kobe-shi, Japan; PolyFox
PF-656, manufactured by OMNOVA Solutions Inc. having an office
located in Akron, Ohio; Pluronic L35, L42, L43, L44, L63, L64, etc.
manufactured by BASF having an office located in Florham Park,
N.J.; Brij 35, 58, 78, etc. manufactured by Croda Inc. having an
office located in Edison, N.J.
[0076] In some examples, an imprint resist includes 0 wt % to 80 wt
% (e.g., 20 wt % to 80 wt % or 40 wt % to 80 wt %) of one or more
monofunctional acrylates; 90 wt % to 98 wt % of one or more
difunctional or multifunctional acrylates (e.g., the imprint resist
may be substantially free of monofunctional acrylates) or 20 wt %
to 75 wt % of one or more difunctional or multifunctional acrylates
(e.g., when one or more monofunctional acrylates is present); 1 wt
% to 10 wt % of one or more photoinitiators; and 1 wt % to 10 wt %
of one or more surfactants. In one example, an imprint resist
includes about 40 wt % to about 50 wt % of one or more
monofunctional acrylates, about 45 wt % to about 55 wt % of one or
more difunctional acrylates, about 4 wt % to about 6 wt % of one or
more photoinitiators, and about 3 wt % surfactant. In another
example, an imprint resist includes about 44 wt % of one or more
monofunctional acrylates, about 48 wt % of one or more difunctional
acrylates, about 5 wt % of one or more photoinitiators, and about 3
wt % surfactant. In yet another example, an imprint resist includes
about 10 wt % of a first monofunctional acrylate (e.g., isobornyl
acrylate), about 34 wt % of a second monofunctional acrylate (e.g.,
benzyl acrylate) about 48 wt % of a difunctional acrylate (e.g.,
neopentyl glycol diacrylate), about 2 wt % of a first
photoinitiator (e.g., IRGACURE TPO), about 3 wt % of a second
photoinitiator (e.g., DAROCUR 4265), and about 3 wt % surfactant.
Examples of suitable surfactants include
X--R--(OCH.sub.2CH.sub.2).sub.nOH, where R=alkyl, aryl, or
poly(propylene glycol), X.dbd.H or --(OCH.sub.2CH.sub.2).sub.nOH,
and n is an integer (e.g., 2 to 20, 5 to 15, or 10 to 12) (e.g.,
X.dbd.--(OCH.sub.2CH.sub.2).sub.nOH, R=poly(propylene glycol), and
n=10 to 12); Y--R--(OCH.sub.2CH.sub.2).sub.nOH, where R=alkyl,
aryl, or poly(propylene glycol), Y=a fluorinated chain
(perfluorinated alkyl or perfluorinated ether) or poly(ethylene
glycol) capped with a fluorinated chain, and n is an integer (e.g.,
2 to 20, 5 to 15, or 10 to 12) (e.g., Y=poly(ethylene glycol)
capped with a perfluorinated alkyl group, R=poly(propylene glycol),
and n=10 to 12); and a combination thereof. The viscosity of the
imprint resist is typically between 0.1 cP and 25 cP, or between 5
cP and 15 cP at 23.degree. C. The interfacial surface energy
between the imprint resist and air is typically between 20 mN/m and
36 mN/m.
[0077] In one example, a pretreatment composition includes 0 wt %
to 80 wt % (e.g., 20 wt % to 80 wt % or 40 wt % to 80 wt %) of one
or more monofunctional acrylates; 90 wt % to 100 wt % of one or
more difunctional or multifunctional acrylates (e.g., the
pretreatment composition is substantially free of monofunctional
acrylates) or 20 wt % to 75 wt % of one or more difunctional or
multifunctional acrylates (e.g., when one or more monofunctional
acrylates is present); 0 wt % to 10 wt % of one or more
photoinitiators; and 0 wt % to 10 wt % of one or more
surfactants.
[0078] The pretreatment composition is typically miscible with the
imprint resist. The pretreatment composition typically has a low
vapor pressure, such that it remains present as a thin film on the
substrate until the composite coating is polymerized. In one
example, the vapor pressure of a pretreatment composition is less
than 1.times.10.sup.-4 mmHg at 25.degree. C. The pretreatment
composition also typically has a low viscosity to facilitate rapid
spreading of the pretreatment composition on the substrate. In one
example, the viscosity of a pretreatment composition is less than
90 cP at 23.degree. C. The interfacial surface energy between the
pretreatment composition and air is typically between 30 mN/m and
45 mN/m. The pretreatment composition is typically selected to be
chemically stable, such that decomposition does not occur during
use.
[0079] A pretreatment composition may be a single polymerizable
component (e.g., a monomer such as a monofunctional acrylate, a
difunctional acrylate, or a multifunctional acrylate), a mixture of
two or more polymerizable components (e.g., a mixture of two or
more monomers), or a mixture of one or more polymerizable
components and one or more other components (e.g., a mixture of
monomers; a mixture of two or more monomers and a surfactant, a
photoinitiator, or both; and the like). In some examples, a
pretreatment composition includes trimethylolpropane triacrylate,
trimethylolpropane ethoxylate triacrylate, 1,12-dodecanediol
diacrylate, poly(ethylene glycol) diacrylate, tetraethylene glycol
diacrylate, 1,3-adamantanediol diacrylate, nonanediol diacrylate,
m-xylylene diacrylate, tricyclodecane dimethanol diacrylate, or any
combination thereof.
[0080] Mixtures of polymerizable components may result in
synergistic effects, yielding pretreatment compositions having a
more advantageous combination of properties (e.g., low viscosity,
good etch resistance and film stability) than a pretreatment
composition with a single polymerizable component. In one example,
the pretreatment composition is a mixture of 1,12-dodecanediol
diacrylate and tricyclodecane dimethanol diacrylate. In another
example, the pretreatment composition is a mixture of
tricyclodecane dimethanol diacrylate and tetraethylene glycol
diacrylate. The pretreatment composition is generally selected such
that one or more components of the pretreatment composition
polymerizes (e.g., covalently bonds) with one or more components of
the imprint resist during polymerization of the composite
polymerizable coating. In some cases, the pretreatment composition
includes a polymerizable component that is also in the imprint
resist, or a polymerizable component that has a functional group in
common with one or more polymerizable components in the imprint
resist (e.g., an acrylate group). Suitable examples of pretreatment
compositions include multifunctional acrylates such as those
described herein, including propoxylated (3) trimethylolpropane
triacrylate, trimethylolpropane triacrylate, and dipentaerythritol
pentaacrylate.
[0081] A pretreatment composition is typically selected such that
the interfacial surface energy at an interface between the
pretreatment and air exceeds that of the imprint resist used in
conjunction with the pretreatment composition, thereby promoting
rapid spreading of the liquid imprint resist on the liquid
pretreatment composition to form a uniform composite coating on the
substrate before the composite coating is contacted with the
template. The interfacial surface energy between the pretreatment
composition and air typically exceeds that between the imprint
resist and air or between at least a component of the imprint
resist and air by at least 0.5 mN/m or at least 1 mN/m up to 25
mN/m (e.g., 0.5 mN/m to 25 mN/m, 0.5 mN/m to 15 mN/m, 0.5 mN/m to 7
mN/m,1 mN/m to 25 mN/m, 1 mN/m to 15 mN/m, or 1 mN/m to 7 mN/m,
although these ranges may vary based on chemical and physical
properties of the pretreatment composition and the imprint resist
and the resulting interaction between these two liquids. When the
difference between surface energies is too low, limited spreading
of the imprint resist results, and the drops maintain a spherical
cap-like shape and remain separated by the pretreatment
composition. When the difference between surface energies is too
high, excessive spreading of the imprint resist results, with most
of the imprint resist moving toward the adjacent drops, emptying
the drop centers, such that the composite coating has convex
regions above the drop centers. Thus, when the difference between
surface energies is too low or too high, the resulting composite
coating is nonuniform, with significant concave or convex regions.
When the difference in surface energies is appropriately selected,
the imprint resist spreads quickly to yield a substantially uniform
composite coating. Advantageous selection of the pretreatment
composition and the imprint resist allows fill time to be reduced
by 50-90%, such that filling can be achieved in as little as 1 sec,
or in some cases even as little as 0.1 sec.
[0082] To achieve these advantages related to improved throughput
associated with the surface tension gradient between the
pretreatment composition and the imprint resist, the pretreatment
composition and the imprint resist differ in surface energy, and
therefore composition. Complete mixing of the pretreatment
composition and the imprint resist is difficult to achieve given
the short spreading time of the imprint resist needed for high
throughput processing. As such, the distribution of the
pretreatment composition and the imprint resist across the imprint
field is typically non-uniform (i.e., the pretreatment composition
is typically pushed to the drop boundary areas due to the nature of
the spreading mechanism). There can be non-uniform distributions of
the types of monomers, the relative amounts of monofunctional and
multifunctional monomers, and the concentration of photoinitiators
and/or other additives (e.g., sensitizers or surfactants). These
non-uniformities can affect the composition and also the extent of
curing, both of which impact the resulting etch rate of the
composite coating.
[0083] After polymerization of the composite coating, a non-uniform
composition or extent of curing may cause non-uniform etching
across the field, thereby resulting in poor critical dimension
uniformity or incomplete etching. As described herein, etch
uniformity may be promoted by minimizing the variation in etch rate
across a composite polymeric layer formed from a pretreatment
composition and an imprint resist (e.g., by "matching the etch
rate"). As used herein, "etch rate" generally refers to the
thickness of material etched divided by the etching time (typically
with units, nm/s). A measure of matching etch rates includes
comparing the variation in pre-etch height and post-etch height in
a composite polymeric layer formed by a nanoimprint process. In one
example, a variation in post-etch height across a composite
polymeric layer is less than or equal to a variation in pre-etch
height across a composite polymeric layer. In some cases, the
variation in pre-etch height is .+-.20% or .+-.10% of the pre-etch
average height of a composite polymeric layer, and a variation in
post-etch height is .+-.10% of the post-etch average height of the
composite polymeric layer. In certain cases, the variation in
pre-etch height is .+-.5% of the pre-etch average height of a
composite polymeric layer, and a variation in post-etch height is
.+-.5% of the post-etch average height of the composite polymeric
layer.
[0084] As described herein, etching may be achieved by any of a
number of processes known in the art, including oxygen- or
halogen-containing plasma chemistries using reactive ion etching or
high density etching (e.g., inductively coupled plasma reactive ion
etching, magnetically enhanced reactive ion etching, transmission
coupled plasma etching, or the like). To achieve etch uniformity,
the composition of the pretreatment composition and the imprint
resist may be selected to minimize the difference between the etch
rate of the pretreatment composition and the etch rate of the
imprint resist. While the pretreatment composition and the imprint
resist may have some desired properties in common (e.g., low
viscosity, rapid curing, mechanical strength), different
constraints for the pretreatment composition and the imprint resist
make it challenging to match etch rate. In particular, a desirable
pretreatment composition has low volatility and a higher surface
tension than the imprint resist. Low volatility of the pretreatment
composition typically imparts stability over a relatively long
period of time on the substrate prior to imprinting. In contrast,
the imprint resist is typically dispensed and then imprinted in
less than one second, so the requirement for low volatility is
typically relaxed for the imprint resist relative to the
pretreatment composition.
[0085] Monomers having at least one of higher molecular mass and
higher intermolecular forces typically demonstrate low volatility.
Thus, pretreatment compositions generally include higher molecular
mass multifunctional monomers (e.g., multifunctional acrylates) and
are typically free of the more volatile monofunctional acrylates
found in imprint resists. As used herein, "higher molecular mass"
typically refers to a molecular mass of at least 250 Da or at least
300 Da. A high percentage of multifunctional monomers in a
pretreatment composition may result in more extensive crosslinking
than found in typical imprint resists, and more extensive
crosslinking may impart higher etch resistance, and thus a lower
etch rate.
[0086] Monomers with relatively strong intermolecular forces are
also associated with low volatility. Monomers with larger polarity
and, especially those capable of hydrogen bonding, generally have
higher intermolecular forces and, therefore demonstrate lower
volatility. Monomers with greater polarity may also advantageously
promote higher surface tension. In some cases, greater polarity is
due, at least in part, to the presence of more oxygen atoms in the
molecule (e.g., in the form of ethylene glycol units, hydroxyl
groups, carboxyl groups, and the like). While often contributing to
strong intermolecular forces and higher surface tension, the
presence of oxygen atoms also tends to reduce etch resistance and
thus increase etch rate. Thus, a pretreatment composition typically
includes monomers having lower etch resistance and a higher etch
rate than monomers in an imprint resist.
[0087] With respect to viscosity, an imprint resist is generally
more constrained than a pretreatment composition, since the imprint
resist is typically dispensed via inkjet. This method of
application may set an upper limit on viscosity of the imprint
resist. To achieve low viscosity, the imprint resist will typically
include a greater amount of small, low molecular weight monomers
(e.g., monofunctional acrylates) than the pretreatment composition.
While it may be advantageous for a pretreatment composition to have
a low viscosity, other constraints (e.g., low volatility) typically
result in higher viscosity for a pretreatment composition than an
imprint resist. As with surface tension and volatility, viscosity
is also closely related to intermolecular forces, and greater
intermolecular forces contribute to higher viscosity. On the other
hand, a pretreatment composition can be applied by spin coating,
which relaxes the upper limit on viscosity relative to the imprint
resist. As a result, the viscosity of a pretreatment composition
can be at least 1.5 times, 2 times, 10 times, or 50 times higher
than that of an imprint resist.
[0088] Thus, constraints related to volatility, surface tension,
and viscosity of a pretreatment composition and an imprint resist
typically result in an imprint resist having a lower etch rate than
a pretreatment composition in terms of chemical composition.
However, the difference in etch rate between a pretreatment
composition and an imprint resist may be reduced by a higher
percentage of multifunctional monomers (crosslinkers) in a
pretreatment composition (i.e., a lower etch rate of the
pretreatment composition). To minimize the difference between the
etch rate of a pretreatment composition and an imprint resist, the
pretreatment composition may be selected to include one or more
high etch resistance monomers, a high percentage of multifunctional
monomers, or a combination thereof.
[0089] Examples of higher etch resistance monomers include
tricyclodecanedimethanol diacrylate, 1,3-adamantanediol diacrylate,
m-xylylene diacrylate, p-xylylene diacrylate,
2-phenyl-1,3-propanediol diacrylate, phenylethyleneglycol
diacrylate, 1,9-nonanediol diacrylate, 1,12-dodecanediol
diacrylate, and trimethylolpropane triacrylate. Estimates of the
etch resistance or etch rate of each material can be made using
composition- or structure-based parameters, such as the Ohnishi
number or the ring parameter. The Ohnishi number is equal to the
total number of atoms in a polymer repeat unit divided by the
difference between the number of carbon atoms and the number of
oxygen atoms: Ohnishi
number=N.sub.total/(N.sub.carbon-N.sub.oxygen). The ring parameter
is equal to the mass of the resist existing as carbon atoms in a
ring structure, M.sub.CR, divided by the total resist mass,
M.sub.TOT: ring parameter r=M.sub.CR/M.sub.TOT.
[0090] The ratios of the Ohnishi numbers calculated for different
pretreatment compositions are listed in Table 2. However, these
parameters are empirical and have limited accuracy; more accurate
values for etch rate are typically obtained experimentally.
Experimentally determined etch rate for a pretreatment composition
is typically lower than that predicted based on the Ohnishi number.
Thus, it may be advantageous to increase the etch resistance or
lower the etch rate of an imprint resist to match that of a
pretreatment composition. Due to the low viscosity constraints of
the imprint resist, small aromatic monomers may be suitable for
increasing etch resistance or lowering etch rate while maintaining
low viscosity. Exemplary low viscosity, high etch resistance
monomers include benzyl acrylate, m-xylylene diacrylate, p-xylylene
diacrylate, 2-phenyl-1,3-propanediol diacrylate, and
phenylethyleneglycol diacrylate.
[0091] Referring to operation 402 of process 400, FIG. 5A depicts
substrate 102 including base 500 and adhesion layer 502. Base 500
is typically a silicon wafer. Other suitable materials for base 500
include fused silica, quartz, silicon germanium, gallium arsenide,
and indium phosphide. Adhesion layer 502 serves to increase
adhesion of the polymeric layer to base 500, thereby reducing
formation of defects in the polymeric layer during separation of
the template from the polymeric layer after polymerization of the
composite coating. A thickness of adhesion layer 502 is typically
between 1 nm and 10 nm. Examples of suitable materials for adhesion
layer 502 include those disclosed in U.S. Pat. Nos. 7,759,407;
8,361,546; 8,557,351; 8,808,808; and U.S. Pat. No. 8,846,195, all
of which are incorporated by reference herein. In one example, an
adhesion layer is formed from a composition including ISORAD 501,
CYMEL 303ULF, CYCAT 4040 or TAG 2678 (a quaternary ammonium blocked
trifluoromethanesulfonic acid), and PM Acetate (a solvent
consisting of 2-(1-methoxy)propyl acetate available from Eastman
Chemical Company of Kingsport, Tenn.). In some cases, substrate 102
includes one or more additional layers between base 500 and
adhesion layer 502. In certain cases, substrate 102 includes one or
more additional layers on adhesion layer 502. For simplicity,
substrate 102 is depicted as including only base 500 and adhesion
layer 502.
[0092] FIG. 5B depicts pretreatment composition 504 after the
pretreatment composition has been disposed on substrate 102 to form
pretreatment coating 506. As depicted in FIG. 5B, pretreatment
coating 506 is formed directly on adhesion layer 502 of substrate
102. In some cases, pretreatment coating 506 is formed on another
surface of substrate 102 (e.g., directly on base 500). Pretreatment
coating 506 is formed on substrate 102 using techniques such as
spin-coating, dip coating, chemical vapor deposition (CVD),
physical vapor deposition (PVD). In the case of, for example,
spin-coating or dip coating and the like, the pretreatment
composition can be dissolved in one or more solvents (e.g.,
propylene glycol methyl ether acetate (PGMEA), propylene glycol
monomethyl ether (PGME), and the like) for application to the
substrate, with the solvent then evaporated away to leave the
pretreatment coating. A thickness t.sub.p of pretreatment coating
506 is typically between 1 nm and 100 nm (e.g., between 1 nm and 50
nm, between 1 nm and 25 nm, or between 1 nm and 10 nm).
[0093] Referring again to FIG. 4, operation 404 of process 400
includes disposing drops of imprint resist on the pretreatment
coating, such that each drop of the imprint resist covers a target
area of the substrate. A volume of the imprint resist drops is
typically between 0.6 pL and 30 pL, and a distance between drop
centers is typically between 35 .mu.m and 350 .mu.m. In some cases,
the volume ratio of the imprint resist to the pretreatment is
between 1:1 and 15:1. In operation 406, a composite coating is
formed on the substrate as each drop of the imprint resist spreads
beyond its target area, forming a composite coating. As used
herein, "prespreading" refers to the spontaneous spreading of the
drops of imprint resist that occurs between the time when the drops
initially contact the pretreatment coating and spread beyond the
target areas, and the time when the template contacts the composite
coating.
[0094] FIGS. 6A-6D depict top-down views of drops of imprint resist
on pretreatment coating at the time of disposal of the drops on
target areas, and of the composite coating before, during, and at
the end of drop spreading. Although the drops are depicted in a
square grid, the drop pattern is not limited to square or geometric
patterns.
[0095] FIG. 6A depicts a top-down view of drops 600 on pretreatment
coating 506 at the time when the drops are initially disposed on
the pretreatment coating, such that the drops cover but do not
extend beyond target areas 602. After drops 600 are disposed on
pretreatment coating 506, the drops spread spontaneously to cover a
surface area of the substrate larger than that of the target areas,
thereby forming a composite coating on the substrate. FIG. 6B
depicts a top-down view of composite coating 604 during
prespreading (after some spreading of drops 600 beyond the target
areas 602), and typically after some intermixing of the imprint
resist and the pretreatment. As depicted, composite coating 604 is
a mixture of the liquid pretreatment composition and the liquid
imprint resist, with regions 606 containing a majority of imprint
resist ("enriched" with imprint resist), and regions 608 containing
a majority of pretreatment ("enriched" with pretreatment). As
prespreading progresses, composite coating 604 may form a more
homogeneous mixture of the pretreatment composition and the imprint
resist.
[0096] Spreading may progress until one or more of regions 606
contacts one or more adjacent regions 606. FIGS. 6C and 6D depict
composite coating 604 at the end of spreading. As depicted in FIG.
6C, each of regions 606 has spread to contact each adjacent region
606 at boundaries 610, with regions 608 reduced to discrete
(non-continuous) portions between regions 606. In other cases, as
depicted in FIG. 6D, regions 606 spread to form a continuous layer,
such that regions 608 are not distinguishable. In FIG. 6D,
composite coating 604 may be a homogenous mixture of the
pretreatment composition and the imprint resist.
[0097] FIGS. 7A-7D are cross-sectional views along lines w-w, x-x,
y-y, and z-z of FIGS. 6A-D, respectively. FIG. 7A is a
cross-sectional view along line w-w of FIG. 6A, depicting drops of
imprint resist 600 covering a surface area of substrate 102
corresponding to target areas 602. Each target area (and each drop
as initially disposed) has a center as indicated by line c-c, and
line b-b indicates a location equidistant between the centers of
two target areas 602. For simplicity, drops 600 are depicted as
contacting adhesion layer 502 of substrate 102, and no intermixing
of the imprint resist and the pretreatment composition is depicted.
FIG. 7B is a cross-sectional view along line x-x of FIG. 6B,
depicting composite coating 604 with regions 608 exposed between
regions 606, after regions 606 have spread beyond target areas 602.
FIG. 7C is a cross-sectional view along line y-y of FIG. 6C at the
end of prespreading, depicting composite coating 604 as a
homogeneous mixture of the pretreatment composition and imprint
resist. As depicted, regions 606 have spread to cover a greater
surface of the substrate than in FIG. 7B, and regions 608 are
correspondingly reduced. Regions 606 originating from drops 600 are
depicted as convex, however, composite coating 604 may be
substantially planar or include concave regions. In certain cases,
prespreading may continue beyond that depicted in FIG. 7C, with the
imprint resist forming a continuous layer over the pretreatment
(with no intermixing or with full or partial intermixing). FIG. 7D
is a cross-sectional view along line z-z of FIG. 6D, depicting
composite coating 604 as a homogenous mixture of the pretreatment
composition and the imprint resist at the end of spreading, with
concave regions of the composite coating about drop centers cc
meeting at boundaries 610, such that the thickness of the
polymerizable coating at the drop boundaries exceeds the thickness
of the composite coating of the drop centers. As depicted in FIGS.
7C and 7D, a thickness of composite coating 604 at a location
equidistant between the centers of two target areas may differ from
a thickness of the composite coating at the center of one of the
two target areas when the composite coating is contacted with the
nanoimprint lithography template.
[0098] Referring again to FIG. 4, operations 408 and 410 of process
400 include contacting the composite coating with a template, and
polymerizing the composite coating to yield a nanoimprint
lithography stack having a composite polymeric layer on the
nanoimprint lithography substrate, respectively.
[0099] In some cases, as depicted in FIGS. 7C and 7D, composite
coating 604 is a homogeneous mixture or substantially homogenous
mixture (e.g., at the air-composite coating interface) at the end
of prespreading (i.e., just before the composite coating is
contacted with the template). As such, the template contacts a
homogenous mixture, with a majority of the mixture typically
derived from the imprint resist. Thus, the release properties of
the imprint resist would generally govern the interaction of the
composite coating with the template, as well as the separation of
the polymeric layer from the template, including defect formation
(or absence thereof) due to separation forces between the template
and the polymeric layer.
[0100] As depicted in FIGS. 8A and 8B, however, composite coating
604 may include regions 608 and 606 that are enriched with the
pretreatment composition and enriched with the imprint resist,
respectively, such that template 110 contacts regions of composite
coating 604 having different physical and chemical properties. For
simplicity, the imprint resist in regions 606 is depicted as having
displaced the pretreatment coating, such that regions 606 are in
direct contact with the substrate, and no intermixing is shown.
Thus, the pretreatment composition in regions 608 is non-uniform in
thickness. In FIG. 8A, the maximum height p of regions 606 exceeds
the maximum height i of the pretreatment composition, such that
template 110 primarily contacts regions 606. In FIG. 8B maximum
height i of regions 608 exceeds the maximum height p of the imprint
resist, such that template 110 primarily contacts regions 608.
Thus, separation of template 110 from the resulting composite
polymeric layer and the defect density associated therewith is
nonuniform and based on the different interactions between the
template and the imprint resist and between the template and the
pretreatment composition. Thus, for certain pretreatment
compositions (e.g., pretreatment compositions that include a single
monomer or a mixture of two or more monomers, but no surfactant),
it may be advantageous for the composite coating to form a
homogenous mixture, or at least a substantially homogenous mixture
at the gas-liquid interface at which the template contacts the
composite coating.
[0101] FIGS. 9A-9C and 10A-10C are cross-sectional views depicting
template 110 and composite coating 604 on substrate 102 having base
500 and adhesion layer 502 before and during contact of the
composite coating with the template, and after separation of the
template from the composite polymeric layer to yield a nanoimprint
lithography stack. In FIGS. 9A-9C, composite coating 604 is
depicted as a homogeneous mixture of the pretreatment composition
and the imprint resist. In FIGS. 10A-10C, composite coating 604 is
depicted as an inhomogeneous mixture of the pretreatment
composition and the imprint resist.
[0102] FIG. 9A depicts a cross-sectional view of initial contact of
template 110 with homogeneous composite coating 900 on substrate
102. In FIG. 9B, template 110 has been advanced toward substrate
102 such that composite coating 900 fills recesses of template 110.
After polymerization of composite coating 900 to yield a
homogeneous polymeric layer on substrate 102, template 110 is
separated from the polymeric layer. FIG. 9C depicts a
cross-sectional view of nanoimprint lithography stack 902 having
homogeneous composite polymeric layer 904.
[0103] FIG. 10A depicts a cross-sectional view of initial contact
of template 110 with composite coating 604 on substrate 102.
Inhomogeneous composite coating 1000 includes regions 606 and 608.
As depicted, little or no intermixing has occurred between the
imprint resist in region 606 and the pretreatment composition in
region 608. In FIG. 10B, template 110 has been advanced toward
substrate 102 such that composite coating 1000 fills recesses of
template 110. After polymerization of composite coating 1000 to
yield an inhomogeneous polymeric layer on substrate 102, template
110 is separated from the polymeric layer. FIG. 10C depicts a
cross-sectional view of nanoimprint lithography stack 1002 having
inhomogeneous polymeric layer 1004 with regions 1006 and 1008
corresponding to regions 606 and 608 of inhomogeneous composite
coating 1000. Thus, the chemical composition of composite polymeric
layer 1002 is inhomogeneous or non-uniform, and includes regions
1006 having a composition derived from a mixture enriched with the
imprint resist and regions 1008 having a composition derived from a
mixture enriched with the pretreatment composition. The relative
size (e.g., exposed surface area, surface area of template covered,
or volume) of regions 1006 and 1008 may vary based at least in part
on the extent of prespreading before contact of the composite
coating with the template or spreading due to contact with the
template. In some cases, regions 1006 may be separated or bounded
by regions 1008, such that composite polymeric layer includes a
plurality of center regions separated by boundaries, with the
chemical composition of the composite polymeric layer 1004 at the
boundaries differing from the chemical composition of the composite
polymeric layer at the interior of the center regions.
EXAMPLES
[0104] In the Examples below, the reported interfacial surface
energy at the interface between the imprint resist and air was
measured by the maximum bubble pressure method. The measurements
were made using a BP2 bubble pressure tensiometer manufactured by
Kruss GmbH of Hamburg, Germany. In the maximum bubble pressure
method, the maximum internal pressure of a gas bubble which is
formed in a liquid by means of a capillary is measured. With a
capillary of known diameter, the surface tension can be calculated
from the Young-Laplace equation. For the some of the pretreatment
compositions, the manufacturer's reported values for the
interfacial surface energy at the interface between the
pretreatment composition and air are provided.
[0105] The viscosities were measured using a Brookfield DV-II+ Pro
with a small sample adapter using a temperature-controlled bath set
at 23.degree. C. Reported viscosity values are the average of five
measurements.
[0106] Adhesion layers were prepared on substrates formed by curing
an adhesive composition made by combining about 77 g ISORAD 501,
about 22 g CYMEL 303ULF, and about 1 g TAG 2678, introducing this
mixture into approximately 1900 grams of PM Acetate. The adhesive
composition was spun onto a substrate (e.g., a silicon wafer) at a
rotational velocity between 500 and 4,000 revolutions per minute so
as to provide a substantially smooth, if not planar layer with
uniform thickness. The spun-on composition was exposed to thermal
actinic energy of 160.degree. C. for approximately two minutes. The
resulting adhesion layers were about 3 nm to about 4 nm thick.
[0107] In Comparative Example 1 and Examples 1-3, an imprint resist
with a surface tension of 33 mN/m at an air/imprint resist
interface was used to demonstrate spreading of the imprint resist
on various surfaces. The imprint resist was a polymerizable
composition including about 45 wt % monofunctional acrylate (e.g.,
isobornyl acrylate and benzyl acrylate), about 48 wt % difunctional
acrylate (e.g., neopentyl glycol diacrylate), about 5 wt %
photoinitiator (e.g., TPO and 4265), and about 3 wt % surfactant
(e.g., a mixture of X--R--(OCH.sub.2CH.sub.2).sub.nOH, where
R=alkyl, aryl, or poly(propylene glycol), X.dbd.H or
--(OCH.sub.2CH.sub.2).sub.nOH, and n is an integer (e.g., 2 to 20,
5 to 15, or 10-12) (e.g., X.dbd.--(OCH.sub.2CH.sub.2).sub.nOH,
R=poly(propylene glycol), and n=10-12) and a fluorosurfactant,
where X=perfluorinated alkyl.
[0108] In Comparative Example 1, the imprint resist was disposed
directly on the adhesion layer of a nanoimprint lithography
substrate. FIG. 11 is an image of drops 1100 of the imprint resist
on the adhesion layer 1102 of a substrate 1.7 sec after
dispensation of the drops in a lattice pattern was initiated. As
seen in the image, drops 1100 have spread outward from the target
areas on the substrate. However, spreading beyond the target area
was limited, and the area of the exposed adhesion layer 1102
exceeded that of drops 1100. Rings visible in this and other
images, such as ring 1104, are Newton interference rings, which
indicate a difference in thickness in various regions of the drop.
Resist drop size was approximately 2.5 pL. FIG. 11 has a 2.times.7
(pitch).sup.2 interleaved lattice of drops (e.g., 2 units in the
horizontal direction, with 3.5 units between the lines). Each
following line shifted 1 unit in the horizontal direction.
[0109] In Examples 1-3, pretreatment compositions A-C,
respectively, were disposed on a nanoimprint lithography substrate
to form a pretreatment coating. Drops of the imprint resist were
disposed on the pretreatment coatings. FIGS. 12-14 show images of
the composite coating after dispensation of drops of the imprint
resist was initiated. Although intermixing occurs between the
pretreatment composition and imprint resist in these examples, for
simplicity, the drops of imprint resist and pretreatment coating
are described below without reference to intermixing. The
pretreatment composition was disposed on a wafer substrate via
spin-on coating. More particularly, the pretreatment composition
was dissolved in PGMEA (0.3 wt % pretreatment composition/99.7 wt %
PGMEA) and spun onto the wafer substrate. Upon evaporation of the
solvent, the typical thickness of the resultant pretreatment
coating on the substrate was in the range from 5 nm to 10 nm (e.g.,
8 nm). Resist drop size was approximately 2.5 pL in FIGS. 12-14.
FIGS. 12 and 14 have a 2.times.7 (pitch).sup.2 interleaved lattice
of drops (e.g., 2 units in the horizontal direction, with 3.5 units
between the lines). Each following line shifted 1 unit in the
horizontal direction. FIG. 13 shows a 2.times.6 (pitch).sup.2
interleaved lattice of drops. The pitch value was 84.5 .mu.m. The
ratios of the volumes of resist to the pretreatment layer were in
the range of 1 to 15 (e.g., 6-7).
[0110] Table 1 lists the surface tension (air/liquid interface) for
the pretreatment compositions A-C and the imprint resist used in
Examples 1-3.
TABLE-US-00001 TABLE 1 Surface Tension for Pretreatment
Compositions Imprint Difference Pretreatment resist in surface
surface surface Pretreatment tension tension tension Example
composition (mN/m) (mN/m) (mN/m) 1 A (Sartomer 492) 34 33 1 2 B
(Sartomer 351HP) 36.4 33 3.1 3 C (Sartomer 399LV) 39.9 33 6.9
[0111] In Example 1, drops of the imprint resist were disposed on a
substrate having a coating of pretreatment composition A (Sartomer
492 or "SR492"). SR492, available from Sartomer, Inc. (Pa., U.S.),
is propoxylated (3) trimethylolpropane triacrylate (a
multifunctional acrylate). FIG. 12 shows an image of drops 1200 of
the imprint resist on pretreatment coating 1202 and the resulting
composite coating 1204 1.7 seconds after dispensation of the
discrete portions in an interleaved lattice pattern was initiated.
In this example, the drop retains its spherical cap-like shape and
the spreading of the imprint resist is limited. As seen in FIG. 12,
while spreading of the drops 1200 exceeds that of the imprint
resist on the adhesion layer in Comparative Example 1, the drops
remain separated by pretreatment coating 1202, which forms
boundaries 1206 around the drops. Certain components of the imprint
resist spread beyond the drop centers, forming regions 1208
surrounding drops 1200. Regions 1208 are separated by pretreatment
coating 1202. The limited spreading is attributed at least in part
to the small difference in surface tension (1 mN/m) between
pretreatment composition A and the imprint resist, such that there
is no significant energy advantage for spreading of the drops.
Other factors, such as friction, are also understood to influence
the extent of spreading.
[0112] In Example 2, drops of the imprint resist were disposed on a
substrate having a coating of pretreatment composition B (Sartomer
351HP or "SR351HP"). SR351HP, available from Sartomer, Inc. (Pa.,
U.S.), is trimethylolpropane triacrylate (a multifunctional
acrylate). FIG. 13 shows images of drops 1300 of the imprint resist
on pretreatment coating 1302 and the resulting composite coating
1304 1.7 sec after dispensation of the drops in a square lattice
pattern was initiated. After 1.7 sec, drops 1300 cover the majority
of the surface area of the substrate, and are separated by
pretreatment coating 1302, which forms boundaries 1306 around the
drops. Drops 1300 are more uniform than drops 1200 of Example 1,
and thus significant improvement is observed over the spreading in
Example 1. The greater extent of spreading is attributed at least
in part to the greater difference in surface tension (3.1 mN/m)
between pretreatment composition B and the imprint resist than
pretreatment A and the imprint resist of Example 1.
[0113] In Example 3, drops of the imprint resist were disposed on a
substrate having a coating of pretreatment composition C (Sartomer
399LV or "SR399LV"). SR399LV, available from Sartomer, Inc. (Pa.,
U.S.), is dipentaerythritol pentaacrylate (a multifunctional
acrylate). FIG. 14 shows an image of drops 1400 of the imprint
resist on pretreatment coating 1402 and the resulting composite
coating 1404 1.7 sec after dispensation of the drops in a
triangular lattice pattern was initiated. As seen in FIG. 14, drops
1400 are separated at boundaries 1406 by pretreatment coating 1402.
However, most of the imprint resist is accumulated at the drop
boundaries, such that most of the polymerizable material is at the
drop boundaries, and the drop centers are substantially empty. The
extent of spreading is attributed at least in part to the large
difference in surface tension (6.9 mN/m) between pretreatment
composition C and the imprint resist.
[0114] Defect density was measured as a function of prespreading
time for the imprint resist of Examples 1-3 and pretreatment
composition B of Example 2. FIG. 15 shows defect density (voids)
due to non-filling of the template. Plot 1500 shows defect density
(number of defects per cm.sup.2) as a function of spread time (sec)
for 28 nm line/space pattern regions, with the defect density
approaching 0.1/cm.sup.2 at 0.9 sec. Plot 1502 shows defect density
(number of defects per cm.sup.2) as a function of spread time (sec)
over the whole field having a range of feature sizes with the
defect density approaching 0.1/cm.sup.2 at 1 sec. By way of
comparison, with no pretreatment, a defect density approaching
0.1/cm.sup.2 is typically achieved for the whole field at a spread
time between 2.5 sec and 3.0 sec.
[0115] Properties of pretreatment compositions PC1-PC9 are shown in
Table 2. A key for PC1-PC9 is shown below. Viscosities were
measured as described herein at a temperature of 23.degree. C. To
calculate the diameter ratio (Diam. Ratio) at 500 ms as shown in
Table 2, drops of imprint resist (drop size .about.25 pL) were
allowed to spread on a substrate coated with a pretreatment
composition (thickness of about 8 nm to 10 nm) on top of an
adhesion layer, and the drop diameter was recorded at an elapsed
time of 500 ms. The drop diameter with each pretreatment
composition was divided by the drop diameter of the imprint resist
on an adhesion layer with no pretreatment composition at 500 ms. As
shown in Table 2, the drop diameter of the imprint resist on PC1 at
500 ms was 60% more than the drop diameter of imprint resist on an
adhesion layer with no pretreatment coating. FIG. 16 shows drop
diameter (.mu.m) as a function of time (ms) for pretreatment
compositions PC1-PC9. Relative etch resistance is the Ohnishi
parameter of each pretreatment composition divided by the Ohnishi
parameter of the imprint resist. Relative etch resistance of
PC1-PC9 (the ratio of etch resistance of the pretreatment
composition to the etch resistance of the imprint resist) is shown
in Table 2.
TABLE-US-00002 TABLE 2 Properties of Pretreatment Compositions
PC1-PC9 Surface Viscosity Diam. Rel. Etch Pretreatment Tension (cP)
Ratio Resistance Composition (mN/m) at 23.degree. C. at 500 ms
(Ohnishi Ratio) PC1 36.4 .+-. 0.1 111 .+-. 1 1.59 1.3 PC2 37.7 .+-.
0.1 66.6 .+-. 0.3 1.86 1.5 PC3 33.9 .+-. 0.1 15.5 .+-. 0.1 2.46 1.1
PC4 41.8 .+-. 0.1 64.9 .+-. 0.3 1.92 1.9 PC5 38.5 .+-. 0.3 18.4
.+-. 0.1 2.73 1.7 PC6 NA NA 1.75 0.9 PC7 35.5 .+-. 0.3 8.7 .+-. 0.1
2.36 1.1 PC8 39.3 .+-. 0.1 10.0 .+-. 0.1 2.69 0.9 PC9 38.6 .+-. 0.1
143 .+-. 1 1.95 0.9 Imprint 33 1.00 1.0 Resist PC1:
trimethylolpropane triacrylate (Sartomer) PC2: trimethylolpropane
ethoxylate triacrylate, n ~1.3 (Osaka Organic) PC3:
1,12-dodecanediol diacrylate PC4: poly(ethylene glycol) diacrylate,
Mn, avg = 575 (Sigma-Aldrich) PC5: tetraethylene glycol diacrylate
(Sartomer) PC6: 1,3-adamantanediol diacrylate PC7: nonanediol
diacrylate PC8: m-xylylene diacrylate PC9: tricyclodecane
dimethanol diacrylate (Sartomer)
[0116] Pretreatment compositions PC3 and PC9 were combined in
various weight ratios to yield pretreatment compositions PC10-PC13
having the weight ratios shown in Table 3. Comparison of properties
of PC3 and PC9 with mixtures formed therefrom revealed synergistic
effects. For example, PC3 has relatively low viscosity and allows
for relatively fast template filling, but has relatively poor etch
resistance. In contrast, PC9 has relatively good etch resistance
and film stability (low evaporative loss), but is relatively
viscous and demonstrates relatively slow template filling.
Combinations of PC3 and PC9, however, resulted in pretreatment
compositions with a combination of advantageous properties,
including relatively low viscosity, relatively fast template
filling, and relatively good etch resistance. For example, a
pretreatment composition having 30 wt % PC3 and 70 wt % PC9 was
found to have a surface tension of 37.2 mN/m, a diameter ratio of
1.61, and an Ohnishi parameter of 3.5.
TABLE-US-00003 TABLE 3 Composition of Pretreatment Compositions
PC10-PC13 Pretreatment PC3 PC9 Composition (wt %) (wt %) PC10 25 75
PC11 35 65 PC12 50 50 PC13 75 25
[0117] FIG. 17A shows a plot of viscosity for pretreatment
compositions including various ratios of PC3 and PC9 (i.e., from
100 wt % PC3 to 100 wt % PC9). FIG. 17B shows drop diameter
(measured as described with respect to Table 2) for PC3, PC13,
PC12, PC11, PC10, and PC9. FIG. 17C shows surface tension (mN/m)
versus fraction of PC3 and PC9.
[0118] FIG. 18 shows ratios of the etch rate of pretreatment
composition to the etch rate of the imprint resist for PC3, PC9,
mixtures of PC3 and PC9, and the imprint resist referenced in Table
2. Thin cured films of the pretreatment compositions PC9 (1800); 25
wt % PC3+75 wt % PC9 (1802); 30 wt % PC3+70 wt % PC9 (1804); PC12
(1806); PC3 (1808)) were prepared on silicon substrates. Thin cured
films of the same thickness of the imprint resist were also
prepared. The samples were etched in a plasma etcher with
fluorocarbon etch chemistry. The etch processes were performed
using a reactive ion etch tool from Trion Technology with 75 W RIE
power and 150 W ICP power, 5 sccm CF.sub.4 and 30 sccm argon at 120
mTorr, and a process time of 90 s. The thickness of each thin film
sample before and after etching was measured by reflectometry.
[0119] PC3 (1,12-dodecanediol diacrylate) and PC9 (tricyclodecane
dimethanol diacrylate) are both difunctional acrylates. PC9 has a
cyclic hydrocarbon backbone which was expected to provide
relatively high etch resistance. Based on the Ohnishi number, PC9
was expected to have a higher etch resistance (lower etch rate)
than the imprint resist, and PC3 was expected to have a lower etch
resistance (higher etch rate) than the imprint resist. The results
shown in FIG. 18 indicate that PC3 actually has a similar, though
slightly higher, etch resistance (lower etch rate) than the imprint
resist. PC9 has an even higher etch resistance (lower etch rate)
than the imprint resist, with an etch rate of about 70% that of the
imprint resist. The higher etch resistance of PC3 and PC9 than
predicted based on the Ohnishi numbers may be related, at least in
part, to the greater degree of crosslinking in PC3 and PC9 relative
to the imprint resist.
[0120] In another example, PC1 was used in a standard imprint
process with the imprint resist referenced in Table 2. The spread
time was short enough to ensure that PC1 and the imprint resist did
not have time to completely mix, so there was a non-uniform
distribution of PC1 and the imprint resist across the imprint
field, with PC1 concentrated at drop boundary regions. Atomic force
microscope (AFM) measurements were made of imprint feature heights
before and after etching with oxygen etch chemistry to determine if
any difference in etch rate between drop center and drop boundary
regions could be detected. The oxygen etches were performed using a
reactive ion etch tool from Trion Technology at 70 W with 5 sccm
oxygen and 20 sccm argon at 15 mTorr and a process time of 20 s.
Plot 1900 in FIG. 19A shows imprint feature height (nm) measured at
5 .mu.m intervals along a 160 .mu.m horizontal distance on the
imprint field. It can be difficult to determine the location of
drop centers and drop boundaries visually, so measurements were
made across a distance equal to the drop pitch so that at least one
drop boundary would be included in the set of measurements. The
drop pitch in these samples was .about.158 .mu.m in the horizontal
direction. Plot 1900 shows a pre-etch average feature height of
about 58.1 nm with a range of about .+-.1.5 nm. Plot 1910 in FIG.
19B shows post-etch imprint feature height measured at 5 .mu.m
intervals along a 320 .mu.m horizontal distance on the imprint
field. The post-etch average feature height was about 46.4 nm with
a range of about .+-.1.5 nm. Therefore, no significant difference
in etch rate was observed along this scan length, which would cover
at least two drop boundary regions, indicating a close match of
etch rate between the two materials under typical imprint
conditions. Based on the Ohnishi number, PC1 is expected to have an
etch rate approximately 30% greater than that of the resist.
However, since PC1 (trimethylolpropane triacrylate) is a
trifunctional acrylate, the higher degree of crosslinking relative
to the resist may have contributed to an increase of the etch
resistance, such that the etch rates of PC1 and the imprint resist
were found to be similar for the two materials.
[0121] A number of embodiments have been described. Nevertheless,
it will be understood that various modifications may be made
without departing from the spirit and scope of the disclosure.
Accordingly, other embodiments are within the scope of the
following claims.
* * * * *