<s>
Stencil	B-Algorithm
lithography	I-Algorithm
is	O
a	O
novel	O
method	O
of	O
fabricating	O
nanometer	O
scale	O
patterns	O
using	O
nanostencils	B-Algorithm
,	O
stencils	B-Algorithm
(	O
shadow	O
mask	O
)	O
with	O
nanometer	O
size	O
apertures	B-General_Concept
.	O
</s>
<s>
It	O
is	O
a	O
resist-less	O
,	O
simple	O
,	O
parallel	O
nanolithography	B-Algorithm
process	O
,	O
and	O
it	O
does	O
not	O
involve	O
any	O
heat	O
or	O
chemical	O
treatment	O
of	O
the	O
substrates	O
(	O
unlike	O
resist-based	O
techniques	O
)	O
.	O
</s>
<s>
Stencil	B-Algorithm
lithography	I-Algorithm
was	O
first	O
reported	O
in	O
a	O
scientific	O
journal	O
as	O
a	O
micro-structuring	O
technique	O
by	O
S	O
.	O
Gray	O
and	O
P	O
.	O
K	O
.	O
Weimer	O
in	O
1959	O
.	O
</s>
<s>
Today	O
the	O
stencil	B-Algorithm
apertures	B-General_Concept
can	O
be	O
scaled	O
down	O
to	O
sub-micrometer	O
size	O
at	O
full	O
4	O
"	O
wafer	O
scale	O
.	O
</s>
<s>
This	O
is	O
called	O
a	O
nanostencil	B-Algorithm
.	O
</s>
<s>
Nano-scale	O
stencil	B-Algorithm
apertures	B-General_Concept
have	O
been	O
fabricated	O
using	O
laser	O
interference	B-Algorithm
lithography	I-Algorithm
(	O
LIL	O
)	O
,	O
electron	B-Architecture
beam	I-Architecture
lithography	I-Architecture
,	O
and	O
focused	O
ion	O
beam	O
lithography	O
.	O
</s>
<s>
Several	O
process	O
are	O
available	O
using	O
stencil	B-Algorithm
lithography	I-Algorithm
:	O
material	O
deposition	O
and	O
etching	O
,	O
as	O
well	O
as	O
implantation	O
of	O
ions	O
.	O
</s>
<s>
Different	O
stencil	B-Algorithm
requirements	O
are	O
necessary	O
for	O
the	O
various	O
processes	O
,	O
e	O
.	O
g	O
.	O
an	O
extra	O
etch-resistant	O
layer	O
on	O
the	O
backside	O
of	O
the	O
stencil	B-Algorithm
for	O
etching	O
(	O
if	O
the	O
membrane	O
material	O
is	O
sensitive	O
to	O
the	O
etching	O
process	O
)	O
or	O
a	O
conductive	O
layer	O
on	O
the	O
backside	O
of	O
the	O
stencil	B-Algorithm
for	O
ion	O
implantation	O
.	O
</s>
<s>
The	O
main	O
deposition	O
method	O
used	O
with	O
stencil	B-Algorithm
lithography	I-Algorithm
is	O
physical	O
vapor	O
deposition	O
.	O
</s>
<s>
This	O
includes	O
thermal	O
and	O
electron	O
beam	O
physical	O
vapor	O
deposition	O
,	O
molecular	B-Algorithm
beam	I-Algorithm
epitaxy	I-Algorithm
,	O
sputtering	O
,	O
and	O
pulsed	O
laser	O
deposition	O
.	O
</s>
<s>
The	O
more	O
directional	O
the	O
material	O
flux	O
is	O
,	O
the	O
more	O
accurate	O
the	O
pattern	O
is	O
transferred	O
from	O
the	O
stencil	B-Algorithm
to	O
the	O
substrate	O
.	O
</s>
<s>
The	O
stencil	B-Algorithm
in	O
this	O
case	O
is	O
used	O
as	O
a	O
hard	O
mask	O
,	O
protecting	O
the	O
covered	O
regions	O
of	O
the	O
substrate	O
,	O
while	O
allowing	O
the	O
substrate	O
under	O
the	O
stencil	B-Algorithm
apertures	B-General_Concept
to	O
be	O
etched	O
.	O
</s>
<s>
The	O
ions	O
will	O
then	O
implant	O
only	O
under	O
the	O
stencil	B-Algorithm
apertures	B-General_Concept
,	O
into	O
the	O
substrate	O
.	O
</s>
<s>
There	O
are	O
three	O
main	O
modes	O
of	O
operation	O
of	O
stencil	B-Algorithm
lithography	I-Algorithm
:	O
static	O
,	O
quasi-dynamic	O
and	O
dynamic	O
.	O
</s>
<s>
While	O
all	O
the	O
above	O
described	O
processes	O
have	O
been	O
proven	O
using	O
the	O
static	O
mode	O
(	O
stencil	B-Algorithm
does	O
n't	O
move	O
relative	O
to	O
substate	O
during	O
material	O
or	O
ion	O
processing	O
)	O
,	O
only	O
ion	O
implantation	O
has	O
been	O
shown	O
for	O
the	O
non-static	O
modes	O
(	O
quasi-dynamic	O
)	O
.	O
</s>
<s>
In	O
the	O
static	O
mode	O
,	O
the	O
stencil	B-Algorithm
is	O
aligned	O
(	O
if	O
necessary	O
)	O
and	O
fixed	O
to	O
a	O
substrate	O
.	O
</s>
<s>
The	O
stencil-substrate	O
pair	O
is	O
placed	O
in	O
the	O
evaporation/etching/ion	O
implantation	O
machine	O
,	O
and	O
after	O
the	O
processing	O
is	O
done	O
,	O
the	O
stencil	B-Algorithm
is	O
simply	O
removed	O
from	O
the	O
now	O
patterned	O
substrate	O
.	O
</s>
<s>
In	O
the	O
quasi-dynamic	O
mode	O
(	O
or	O
step-and-repeat	O
)	O
,	O
the	O
stencil	B-Algorithm
moves	O
relative	O
to	O
the	O
substrate	O
in	O
between	O
depositions	O
,	O
without	O
breaking	O
the	O
vacuum	O
.	O
</s>
<s>
In	O
the	O
dynamic	O
mode	O
,	O
the	O
stencil	B-Algorithm
moves	O
relative	O
to	O
the	O
substrate	O
during	O
deposition	O
,	O
allowing	O
the	O
fabrication	O
of	O
patterns	O
with	O
variable	O
height	O
profiles	O
by	O
changing	O
the	O
stencil	B-Algorithm
speed	O
during	O
a	O
constant	O
material	O
deposition	O
rate	O
.	O
</s>
<s>
Despite	O
it	O
being	O
a	O
versatile	O
technique	O
,	O
there	O
are	O
still	O
several	O
challenges	O
to	O
be	O
addressed	O
by	O
stencil	B-Algorithm
lithography	I-Algorithm
.	O
</s>
<s>
During	O
deposition	O
through	O
the	O
stencil	B-Algorithm
,	O
material	O
is	O
deposited	O
not	O
only	O
on	O
the	O
substrate	O
through	O
the	O
apertures	B-General_Concept
but	O
also	O
on	O
the	O
stencil	B-Algorithm
backside	O
,	O
including	O
around	O
and	O
inside	O
the	O
apertures	B-General_Concept
.	O
</s>
<s>
This	O
reduces	O
the	O
effective	O
aperture	B-General_Concept
size	O
by	O
an	O
amount	O
proportional	O
to	O
the	O
deposited	O
material	O
,	O
leading	O
ultimately	O
to	O
aperture	B-General_Concept
clogging	O
.	O
</s>
<s>
The	O
accuracy	O
of	O
the	O
pattern	O
transfer	O
from	O
the	O
stencil	B-Algorithm
to	O
the	O
substrate	O
depends	O
on	O
many	O
parameters	O
.	O
</s>
