<s>
Nanoimprint	B-Algorithm
lithography	I-Algorithm
(	O
NIL	O
)	O
is	O
a	O
method	O
of	O
fabricating	O
nanometer	O
scale	O
patterns	O
.	O
</s>
<s>
It	O
is	O
a	O
simple	O
nanolithography	B-Algorithm
process	O
with	O
low	O
cost	O
,	O
high	O
throughput	O
and	O
high	O
resolution	O
.	O
</s>
<s>
The	O
imprint	O
resist	O
is	O
typically	O
a	O
monomer	O
or	O
polymer	B-Language
formulation	O
that	O
is	O
cured	O
by	O
heat	O
or	O
UV	O
light	O
during	O
the	O
imprinting	O
.	O
</s>
<s>
The	O
term	O
"	O
nanoimprint	B-Algorithm
lithography	I-Algorithm
"	O
was	O
coined	O
in	O
the	O
scientific	O
literature	O
in	O
1996	O
,	O
when	O
Prof	O
.	O
Stephen	O
Chou	O
and	O
his	O
students	O
published	O
a	O
report	O
in	O
Science	O
,	O
although	O
hot	O
embossing	O
(	O
now	O
taken	O
as	O
a	O
synonym	O
of	O
NIL	O
)	O
of	O
thermoplastics	O
had	O
been	O
appearing	O
in	O
the	O
patent	O
literature	O
for	O
a	O
few	O
years	O
already	O
.	O
</s>
<s>
At	O
this	O
point	O
,	O
nanoimprint	B-Algorithm
lithography	I-Algorithm
has	O
been	O
added	O
to	O
the	O
International	O
Technology	O
Roadmap	O
for	O
Semiconductors	O
(	O
ITRS	O
)	O
for	O
the	O
32	B-Algorithm
and	O
22	B-Algorithm
nm	I-Algorithm
nodes	O
.	O
</s>
<s>
resist-free	O
direct	O
thermal	O
nanoimprint	B-Algorithm
lithography	I-Algorithm
.	O
</s>
<s>
Thermoplastic	O
nanoimprint	B-Algorithm
lithography	I-Algorithm
(	O
T-NIL	O
)	O
is	O
the	O
earliest	O
nanoimprint	B-Algorithm
lithography	I-Algorithm
developed	O
by	O
Prof	O
.	O
Stephen	O
Chou	O
's	O
group	O
.	O
</s>
<s>
In	O
a	O
standard	O
T-NIL	O
process	O
,	O
a	O
thin	O
layer	O
of	O
imprint	O
resist	O
(	O
thermoplastic	O
polymer	B-Language
)	O
is	O
spin	O
coated	O
onto	O
the	O
sample	O
substrate	O
.	O
</s>
<s>
When	O
heated	O
up	O
above	O
the	O
glass	O
transition	O
temperature	O
of	O
the	O
polymer	B-Language
,	O
the	O
pattern	O
on	O
the	O
mold	O
is	O
pressed	O
into	O
the	O
softened	O
polymer	B-Language
film	O
.	O
</s>
<s>
A	O
pattern	O
transfer	O
process	O
(	O
reactive	B-Algorithm
ion	I-Algorithm
etching	I-Algorithm
,	O
normally	O
)	O
can	O
be	O
used	O
to	O
transfer	O
the	O
pattern	O
in	O
the	O
resist	O
to	O
the	O
underneath	O
substrate	O
.	O
</s>
<s>
In	O
photo	O
nanoimprint	B-Algorithm
lithography	I-Algorithm
(	O
P-NIL	O
)	O
,	O
a	O
photo	O
(	O
UV	O
)	O
curable	O
liquid	O
resist	O
is	O
applied	O
to	O
the	O
sample	O
substrate	O
and	O
the	O
mold	O
is	O
normally	O
made	O
of	O
transparent	O
material	O
like	O
fused	O
silica	O
or	O
PDMS	O
.	O
</s>
<s>
Different	O
from	O
the	O
above	O
mentioned	O
nanoimprint	B-Algorithm
methods	O
,	O
resist-free	O
direct	O
thermal	O
nanoimprint	B-Algorithm
does	O
not	O
require	O
an	O
extra	O
etching	O
step	O
to	O
transfer	O
patterns	O
from	O
imprint	O
resists	O
to	O
the	O
device	O
layer	O
.	O
</s>
<s>
Further	O
,	O
a	O
single-step	O
nanoimprint	B-Algorithm
directly	O
molds	O
thin	O
film	O
materials	O
into	O
desired	O
device	O
geometries	O
under	O
pressure	O
at	O
elevated	O
temperatures	O
.	O
</s>
<s>
In	O
thermal	O
nanoimprint	B-Algorithm
methods	O
the	O
trade	O
off	O
between	O
full	O
pattern	O
transfer	O
and	O
deforming	O
the	O
substrate	O
creates	O
limitations	O
in	O
quality	O
of	O
fabrication	O
.	O
</s>
<s>
In	O
a	O
full	O
wafer	O
nanoimprint	B-Algorithm
scheme	O
,	O
all	O
the	O
patterns	O
are	O
contained	O
in	O
a	O
single	O
nanoimprint	B-Algorithm
field	O
and	O
will	O
be	O
transferred	O
in	O
a	O
single	O
imprint	O
step	O
.	O
</s>
<s>
An	O
at	O
least	O
diameter	O
full-wafer	O
nanoimprint	B-Algorithm
with	O
high	O
fidelity	O
is	O
possible	O
.	O
</s>
<s>
To	O
ensure	O
the	O
pressure	O
and	O
pattern	O
uniformities	O
of	O
full	O
wafer	O
nanoimprint	B-Algorithm
processes	O
and	O
prolong	O
the	O
mold	O
lifetime	O
,	O
a	O
pressing	O
method	O
utilizing	O
isotropic	O
fluid	O
pressure	O
,	O
named	O
Air	O
Cushion	O
Press	O
(	O
ACP	O
)	O
by	O
its	O
inventors	O
,	O
is	O
developed	O
and	O
being	O
used	O
by	O
commercial	O
nanoimprint	B-Algorithm
systems	O
.	O
</s>
<s>
Nanoimprint	B-Algorithm
can	O
be	O
performed	O
in	O
a	O
way	O
similar	O
to	O
the	O
step	O
and	O
repeat	O
optical	O
lithography	O
.	O
</s>
<s>
The	O
imprint	O
field	O
(	O
die	O
)	O
is	O
typically	O
much	O
smaller	O
than	O
the	O
full	O
wafer	O
nanoimprint	B-Algorithm
field	O
.	O
</s>
<s>
This	O
scheme	O
is	O
good	O
for	O
nanoimprint	B-Algorithm
mold	O
creation	O
.	O
</s>
<s>
Nanoimprint	B-Algorithm
lithography	I-Algorithm
has	O
been	O
used	O
to	O
fabricate	O
devices	O
for	O
electrical	O
,	O
optical	O
,	O
photonic	O
and	O
biological	O
applications	O
.	O
</s>
<s>
For	O
electronics	O
devices	O
,	O
NIL	O
has	O
been	O
used	O
to	O
fabricate	O
MOSFET	B-Architecture
,	O
O-TFT	B-Algorithm
,	O
single	O
electron	O
memory	O
.	O
</s>
<s>
A	O
key	O
benefit	O
of	O
nanoimprint	B-Algorithm
lithography	I-Algorithm
is	O
its	O
sheer	O
simplicity	O
.	O
</s>
<s>
There	O
is	O
no	O
need	O
for	O
complex	O
optics	O
or	O
high-energy	O
radiation	O
sources	O
with	O
a	O
nanoimprint	B-Algorithm
tool	O
.	O
</s>
<s>
The	O
increased	O
material	O
variability	O
gives	O
chemists	O
the	O
freedom	O
to	O
design	O
new	O
functional	O
materials	O
rather	O
than	O
sacrificial	O
etch	O
resistant	O
polymers	B-Language
.	O
</s>
<s>
The	O
key	O
concerns	O
for	O
nanoimprint	B-Algorithm
lithography	I-Algorithm
are	O
overlay	O
,	O
defects	O
,	O
template	O
patterning	O
and	O
template	O
wear	O
.	O
</s>
<s>
The	O
current	O
overlay	O
3	O
sigma	B-General_Concept
capability	O
is	O
10	O
nm	O
.	O
</s>
<s>
As	O
with	O
immersion	B-Algorithm
lithography	I-Algorithm
,	O
defect	O
control	O
is	O
expected	O
to	O
improve	O
as	O
the	O
technology	O
matures	O
.	O
</s>
<s>
Other	O
defects	O
would	O
require	O
effective	O
template	O
cleaning	O
and/or	O
the	O
use	O
of	O
intermediate	O
polymer	B-Language
stamps	O
.	O
</s>
<s>
High	O
resolution	O
template	O
patterning	O
can	O
currently	O
be	O
performed	O
by	O
electron	B-Architecture
beam	I-Architecture
lithography	I-Architecture
or	O
focused	O
ion	O
beam	O
patterning	O
;	O
however	O
at	O
the	O
smallest	O
resolution	O
,	O
the	O
throughput	O
is	O
very	O
slow	O
.	O
</s>
<s>
whereby	O
robust	O
templates	O
were	O
rapidly	O
fabricated	O
by	O
optical	O
patterning	O
of	O
a	O
photoresist-coated	O
metal	O
substrate	O
through	O
a	O
photomask	B-Algorithm
.	O
</s>
<s>
If	O
homogeneous	O
patterns	O
on	O
large	O
areas	O
are	O
required	O
,	O
interference	B-Algorithm
lithography	I-Algorithm
is	O
a	O
very	O
attractive	O
patterning	O
technique	O
.	O
</s>
<s>
Other	O
patterning	O
techniques	O
(	O
including	O
even	O
double	B-Algorithm
patterning	I-Algorithm
)	O
may	O
also	O
be	O
used	O
.	O
</s>
<s>
Currently	O
,	O
state-of-the-art	O
nanoimprint	B-Algorithm
lithography	I-Algorithm
can	O
be	O
used	O
for	O
patterns	O
down	O
to	O
20nm	O
and	O
below	O
.	O
</s>
<s>
Future	O
applications	O
of	O
nanoimprint	B-Algorithm
lithography	I-Algorithm
may	O
involve	O
the	O
use	O
of	O
porous	O
low-κ	B-Algorithm
materials	O
.	O
</s>
<s>
A	O
key	O
characteristic	O
of	O
nanoimprint	B-Algorithm
lithography	I-Algorithm
(	O
except	O
for	O
electrochemical	O
nanoimprinting	O
)	O
is	O
the	O
residual	O
layer	O
following	O
the	O
imprint	O
process	O
.	O
</s>
<s>
However	O
,	O
this	O
renders	O
the	O
nanoimprint	B-Algorithm
lithography	I-Algorithm
step	O
less	O
critical	O
for	O
critical	O
dimension	O
(	O
CD	O
)	O
control	O
than	O
the	O
etch	O
step	O
used	O
to	O
remove	O
the	O
residual	O
layer	O
.	O
</s>
<s>
Hence	O
,	O
it	O
is	O
important	O
to	O
consider	O
the	O
residual	O
layer	O
removal	O
an	O
integrated	O
part	O
of	O
the	O
overall	O
nanoimprint	B-Algorithm
patterning	O
process	O
.	O
</s>
<s>
It	O
has	O
been	O
proposed	O
to	O
combine	O
photolithography	O
and	O
nanoimprint	B-Algorithm
lithography	I-Algorithm
techniques	O
in	O
one	O
step	O
in	O
order	O
to	O
eliminate	O
the	O
residual	O
layer	O
.	O
</s>
<s>
Nanoimprint	B-Algorithm
lithography	I-Algorithm
relies	O
on	O
displacing	O
polymer	B-Language
.	O
</s>
<s>
For	O
example	O
,	O
a	O
large	O
,	O
dense	O
array	O
of	O
protrusions	O
will	O
displace	O
significantly	O
more	O
polymer	B-Language
than	O
an	O
isolated	O
protrusion	O
.	O
</s>
<s>
Depending	O
on	O
the	O
distance	O
of	O
this	O
isolated	O
protrusion	O
from	O
the	O
array	O
,	O
the	O
isolated	O
feature	O
may	O
not	O
imprint	O
correctly	O
due	O
to	O
polymer	B-Language
displacement	O
and	O
thickening	O
.	O
</s>
<s>
Likewise	O
,	O
wider	O
depressions	O
in	O
the	O
template	O
do	O
not	O
fill	O
up	O
with	O
as	O
much	O
polymer	B-Language
as	O
narrower	O
depressions	O
,	O
resulting	O
in	O
misshapen	O
wide	O
lines	O
.	O
</s>
<s>
A	O
unique	O
benefit	O
of	O
nanoimprint	B-Algorithm
lithography	I-Algorithm
is	O
the	O
ability	O
to	O
pattern	O
3D	O
structures	O
,	O
such	O
as	O
damascene	O
interconnects	O
and	O
T-gates	O
,	O
in	O
fewer	O
steps	O
than	O
required	O
for	O
conventional	O
lithography	O
.	O
</s>
<s>
Similarly	O
,	O
nanoimprint	B-Algorithm
lithography	I-Algorithm
can	O
be	O
used	O
to	O
replicate	O
3D	O
structures	O
created	O
using	O
Focused	O
Ion	O
Beam	O
.	O
</s>
<s>
Using	O
UV-NIL	O
of	O
off-stoichiometric	O
thiol	O
–	O
ene-epoxy	O
polymer	B-Language
it	O
is	O
possible	O
to	O
fabricate	O
robust	O
,	O
large-area	O
,	O
and	O
high-aspect-ratio	O
nanostructures	O
as	O
well	O
as	O
complex	O
hierarchically	O
layered	O
structures	O
with	O
limited	O
collapse	O
and	O
defectivity	O
.	O
</s>
<s>
Ultrafast	O
Nanoimprint	B-Algorithm
Lithography	I-Algorithm
or	O
Pulsed-NIL	O
is	O
a	O
technique	O
based	O
on	O
the	O
use	O
of	O
stamps	O
with	O
an	O
heating	O
layer	O
integrated	O
beneath	O
the	O
nanopatterned	O
surface	O
.	O
</s>
<s>
Nanoimprint	B-Algorithm
lithography	I-Algorithm
is	O
a	O
simple	O
pattern	O
transfer	O
process	O
that	O
is	O
neither	O
limited	O
by	O
diffraction	O
nor	O
scattering	O
effects	O
nor	O
secondary	O
electrons	O
,	O
and	O
does	O
not	O
require	O
any	O
sophisticated	O
radiation	O
chemistry	O
.	O
</s>
<s>
It	O
is	O
also	O
possible	O
to	O
resolve	O
the	O
template	O
generation	O
issue	O
by	O
using	O
a	O
programmable	O
template	O
in	O
a	O
scheme	O
based	O
on	O
double	B-Algorithm
patterning	I-Algorithm
.	O
</s>
<s>
As	O
of	O
October	O
2007	O
,	O
Toshiba	O
is	O
the	O
only	O
company	O
to	O
have	O
validated	O
nanoimprint	B-Algorithm
lithography	I-Algorithm
for	O
22nm	B-Algorithm
and	O
beyond	O
.	O
</s>
<s>
What	O
is	O
more	O
significant	O
is	O
that	O
nanoimprint	B-Algorithm
lithography	I-Algorithm
was	O
the	O
first	O
sub-30nm	O
lithography	O
to	O
be	O
validated	O
by	O
an	O
industrial	O
user	O
.	O
</s>
