<s>
Immersion	B-Algorithm
lithography	I-Algorithm
is	O
a	O
photolithography	B-Algorithm
resolution	O
enhancement	O
technique	O
for	O
manufacturing	O
integrated	O
circuits	O
(	O
ICs	O
)	O
that	O
replaces	O
the	O
usual	O
air	O
gap	O
between	O
the	O
final	O
lens	O
and	O
the	O
wafer	B-Architecture
surface	O
with	O
a	O
liquid	O
medium	O
that	O
has	O
a	O
refractive	O
index	O
greater	O
than	O
one	O
.	O
</s>
<s>
Current	O
immersion	B-Algorithm
lithography	I-Algorithm
tools	O
use	O
highly	O
purified	O
water	O
for	O
this	O
liquid	O
,	O
achieving	O
feature	O
sizes	O
below	O
45	O
nanometers	O
.	O
</s>
<s>
The	O
idea	O
for	O
immersion	B-Algorithm
lithography	I-Algorithm
was	O
patented	O
in	O
1984	O
by	O
Takanashi	O
et	O
al	O
.	O
</s>
<s>
Immersion	B-Algorithm
lithography	I-Algorithm
is	O
now	O
being	O
extended	O
to	O
sub-20nm	O
nodes	O
through	O
the	O
use	O
of	O
multiple	B-Algorithm
patterning	I-Algorithm
.	O
</s>
<s>
The	O
ability	O
to	O
resolve	O
features	O
in	O
optical	B-Algorithm
lithography	I-Algorithm
is	O
directly	O
related	O
to	O
the	O
numerical	O
aperture	O
of	O
the	O
imaging	O
equipment	O
,	O
the	O
numerical	O
aperture	O
being	O
the	O
sine	O
of	O
the	O
maximum	O
refraction	O
angle	O
multiplied	O
by	O
the	O
refractive	O
index	O
of	O
the	O
medium	O
through	O
which	O
the	O
light	O
travels	O
.	O
</s>
<s>
The	O
lenses	O
in	O
the	O
highest	O
resolution	O
"	O
dry	O
"	O
photolithography	B-Algorithm
scanners	O
focus	O
light	O
in	O
a	O
cone	O
whose	O
boundary	O
is	O
nearly	O
parallel	O
to	O
the	O
wafer	B-Architecture
surface	O
.	O
</s>
<s>
As	O
it	O
is	O
impossible	O
to	O
increase	O
resolution	O
by	O
further	O
refraction	O
,	O
additional	O
resolution	O
is	O
obtained	O
by	O
inserting	O
an	O
immersion	O
medium	O
with	O
a	O
higher	O
index	O
of	O
refraction	O
between	O
the	O
lens	O
and	O
the	O
wafer	B-Architecture
.	I-Architecture
</s>
<s>
For	O
example	O
,	O
for	O
water	O
immersion	O
using	O
ultraviolet	B-Application
light	I-Application
at	O
193nm	O
wavelength	O
,	O
the	O
index	O
of	O
refraction	O
is	O
1.44	O
.	O
</s>
<s>
The	O
resolution	O
enhancement	O
from	O
immersion	B-Algorithm
lithography	I-Algorithm
is	O
about	O
30	O
–	O
40%	O
depending	O
on	O
materials	O
used	O
.	O
</s>
<s>
However	O
,	O
the	O
depth	O
of	O
focus	O
,	O
or	O
tolerance	O
in	O
wafer	B-Architecture
topography	O
flatness	O
,	O
is	O
improved	O
compared	O
to	O
the	O
corresponding	O
"	O
dry	O
"	O
tool	O
at	O
the	O
same	O
resolution	O
.	O
</s>
<s>
By	O
2008	O
,	O
defect	O
counts	O
on	O
wafers	B-Architecture
printed	O
by	O
immersion	B-Algorithm
lithography	I-Algorithm
had	O
reached	O
zero	O
level	O
capability	O
.	O
</s>
<s>
According	O
to	O
ASML	O
s	O
product	O
information	O
about	O
twinscan-nxt1980di	O
,	O
immersion	B-Algorithm
lithography	I-Algorithm
tools	O
currently	O
boasted	O
the	O
highest	O
throughputs	O
(	O
275	O
WPH	O
)	O
as	O
targeted	O
for	O
high	O
volume	O
manufacturing	O
.	O
</s>
<s>
Going	O
beyond	O
this	O
limit	O
to	O
sub-20nm	O
nodes	O
requires	O
multiple	B-Algorithm
patterning	I-Algorithm
.	O
</s>
<s>
At	O
the	O
20nm	O
foundry	O
and	O
memory	O
nodes	O
and	O
beyond	O
,	O
double	B-Algorithm
patterning	I-Algorithm
and	O
triple	O
patterning	O
are	O
already	O
being	O
used	O
with	O
immersion	B-Algorithm
lithography	I-Algorithm
for	O
the	O
densest	O
layers	O
.	O
</s>
