<s>
Computational	B-Algorithm
lithography	I-Algorithm
(	O
also	O
known	O
as	O
computational	B-Algorithm
scaling	I-Algorithm
)	O
is	O
the	O
set	O
of	O
mathematical	O
and	O
algorithmic	O
approaches	O
designed	O
to	O
improve	O
the	O
resolution	O
attainable	O
through	O
photolithography	B-Algorithm
.	O
</s>
<s>
Computational	B-Algorithm
lithography	I-Algorithm
has	O
come	O
to	O
the	O
forefront	O
of	O
photolithography	B-Algorithm
technologies	O
in	O
2008	O
when	O
semiconductor	O
industry	O
has	O
faced	O
the	O
challenges	O
associated	O
with	O
the	O
transition	O
to	O
22	B-Algorithm
nanometer	I-Algorithm
CMOS	B-Device
microfabrication	O
process	O
technology	O
and	O
beyond	O
.	O
</s>
<s>
Computational	B-Algorithm
lithography	I-Algorithm
means	O
the	O
use	O
of	O
computers	O
to	O
simulate	O
printing	O
of	O
micro-lithography	O
structures	O
.	O
</s>
<s>
Pioneering	O
work	O
was	O
done	O
by	O
Chris	O
Mack	O
at	O
NSA	O
in	O
developing	O
PROLITH	B-Algorithm
,	O
Rick	O
Dill	O
at	O
IBM	O
and	O
Andy	O
Neureuther	O
at	O
University	O
of	O
California	O
,	O
Berkeley	O
from	O
the	O
early	O
1980s	O
.	O
</s>
<s>
Commercial	O
full-chip	O
optical	B-Algorithm
proximity	I-Algorithm
correction	I-Algorithm
(	O
OPC	O
)	O
,	O
using	O
model	O
forms	O
,	O
was	O
first	O
implemented	O
by	O
TMA	O
(	O
now	O
a	O
subsidiary	O
of	O
Synopsys	O
)	O
and	O
Numerical	O
Technologies	O
(	O
also	O
part	O
of	O
Synopsys	O
)	O
around	O
1997	O
.	O
</s>
<s>
With	O
the	O
move	O
to	O
sub-wavelength	O
lithography	O
at	O
the	O
180nm	O
and	O
130nm	O
nodes	O
,	O
RET	O
techniques	O
such	O
as	O
Assist	O
features	O
,	O
phase	B-Algorithm
shift	I-Algorithm
masks	I-Algorithm
started	O
to	O
be	O
used	O
together	O
with	O
OPC	O
.	O
</s>
<s>
The	O
term	O
computational	B-Algorithm
lithography	I-Algorithm
was	O
first	O
used	O
by	O
Brion	O
Technology	O
(	O
now	O
a	O
subsidiary	O
of	O
ASML	O
)	O
in	O
2005	O
to	O
promote	O
their	O
hardware	O
accelerated	O
full	O
chip	O
lithography	O
simulation	O
platform	O
.	O
</s>
<s>
As	O
45nm	O
goes	O
into	O
full	O
production	O
and	O
EUV	B-Algorithm
lithography	I-Algorithm
introduction	O
is	O
delayed	O
,	O
32nm	B-Algorithm
and	O
22nm	B-Algorithm
are	O
expected	O
to	O
run	O
on	O
existing	O
193nm	O
scanners	O
technology	O
.	O
</s>
<s>
Now	O
,	O
not	O
only	O
are	O
throughput	O
and	O
capabilities	O
concerns	O
resurfacing	O
,	O
but	O
also	O
new	O
computational	B-Algorithm
lithography	I-Algorithm
techniques	O
such	O
as	O
Source	O
Mask	O
Optimization	O
(	O
SMO	O
)	O
is	O
seen	O
as	O
a	O
way	O
to	O
squeeze	O
better	O
resolution	O
specific	O
to	O
a	O
given	O
design	O
.	O
</s>
<s>
Today	O
,	O
all	O
the	O
major	O
mask	O
synthesis	O
vendors	O
have	O
settled	O
on	O
the	O
term	O
"	O
computational	B-Algorithm
lithography	I-Algorithm
"	O
to	O
describe	O
and	O
promote	O
the	O
set	O
of	O
mask	O
synthesis	O
technologies	O
required	O
for	O
22nm	B-Algorithm
.	O
</s>
<s>
Computational	B-Algorithm
lithography	I-Algorithm
makes	O
use	O
of	O
a	O
number	O
of	O
numerical	O
simulations	O
to	O
improve	O
the	O
performance	O
(	O
resolution	O
and	O
contrast	O
)	O
of	O
cutting-edge	O
photomasks	O
.	O
</s>
<s>
The	O
combined	O
techniques	O
include	O
Resolution	B-Algorithm
Enhancement	I-Algorithm
Technology	I-Algorithm
(	O
RET	O
)	O
,	O
Optical	B-Algorithm
Proximity	I-Algorithm
Correction	I-Algorithm
(	O
OPC	O
)	O
,	O
Source	O
Mask	O
Optimization	O
(	O
SMO	O
)	O
,	O
etc	O
.	O
</s>
<s>
Resolution	B-Algorithm
enhancement	I-Algorithm
technologies	I-Algorithm
,	O
first	O
used	O
in	O
the	O
90	O
nanometer	O
generation	O
,	O
using	O
the	O
mathematics	O
of	O
diffraction	O
optics	O
to	O
specify	O
multi-layer	O
phase-shift	B-Algorithm
photomasks	I-Algorithm
that	O
use	O
interference	O
patterns	O
in	O
the	O
photomask	O
that	O
enhance	O
resolution	O
on	O
the	O
printed	O
wafer	O
surface	O
.	O
</s>
<s>
Optical	B-Algorithm
proximity	I-Algorithm
correction	I-Algorithm
uses	O
computational	O
methods	O
to	O
counteract	O
the	O
effects	O
of	O
diffraction-related	O
blurring	O
and	O
under-exposure	O
by	O
modifying	O
on-mask	O
geometries	O
with	O
means	O
such	O
as	O
:	O
</s>
<s>
polarization	O
characteristics	O
of	O
the	O
lens	O
pupil	O
,	O
Jones	O
matrix	O
of	O
the	O
stepper	B-Algorithm
lens	O
,	O
optical	O
parameters	O
of	O
the	O
photoresist	O
stack	O
,	O
diffusion	O
through	O
the	O
photoresist	O
,	O
stepper	B-Algorithm
illumination	O
control	O
variables	O
.	O
</s>
<s>
This	O
does	O
not	O
include	O
modeling	O
the	O
3D	O
polarization	O
of	O
the	O
light	O
source	O
or	O
any	O
of	O
the	O
several	O
other	O
systems	O
that	O
need	O
to	O
be	O
modeled	O
in	O
production	O
computational	O
photolithographic	B-Algorithm
mask	O
making	O
flows	O
.	O
</s>
<s>
The	O
periodic	O
enhancement	O
in	O
the	O
resolution	O
achieved	O
through	O
photolithography	B-Algorithm
has	O
been	O
a	O
driving	O
force	O
behind	O
Moore	O
's	O
Law	O
.	O
</s>
<s>
The	O
minimum	O
feature	O
size	O
that	O
a	O
projection	O
system	O
typically	O
used	O
in	O
photolithography	B-Algorithm
can	O
print	O
is	O
given	O
approximately	O
by	O
:	O
</s>
<s>
Historically	O
,	O
resolution	O
enhancements	O
in	O
photolithography	B-Algorithm
have	O
been	O
achieved	O
through	O
the	O
progression	O
of	O
stepper	B-Algorithm
illumination	O
sources	O
to	O
smaller	O
and	O
smaller	O
wavelengths	O
from	O
"	O
g-line	O
"	O
(	O
436nm	O
)	O
and	O
"	O
i-line	O
"	O
(	O
365nm	O
)	O
sources	O
based	O
on	O
mercury	O
lamps	O
,	O
to	O
the	O
current	O
systems	O
based	O
on	O
deep	O
ultraviolet	O
excimer	O
lasers	O
sources	O
at	O
193nm	O
.	O
</s>
<s>
However	O
the	O
progression	O
to	O
yet	O
finer	O
wavelength	O
sources	O
has	O
been	O
stalled	O
by	O
the	O
intractable	O
problems	O
associated	O
with	O
extreme	B-Algorithm
ultraviolet	I-Algorithm
lithography	I-Algorithm
and	O
x-ray	B-Algorithm
lithography	I-Algorithm
,	O
forcing	O
semiconductor	O
manufacturers	O
to	O
extend	O
the	O
current	O
193nm	O
optical	B-Algorithm
lithography	I-Algorithm
systems	O
until	O
some	O
form	O
of	O
next-generation	B-Algorithm
lithography	I-Algorithm
proves	O
viable	O
(	O
although	O
157nm	O
steppers	B-Algorithm
have	O
also	O
been	O
marketed	O
,	O
they	O
have	O
proven	O
cost-prohibitive	O
at	O
$50M	O
each	O
)	O
.	O
</s>
<s>
Efforts	O
to	O
improve	O
resolution	O
by	O
increasing	O
the	O
numerical	O
aperture	O
have	O
led	O
to	O
the	O
use	O
of	O
immersion	B-Algorithm
lithography	I-Algorithm
.	O
</s>
<s>
The	O
k1	O
factor	O
can	O
be	O
reduced	O
through	O
process	O
improvements	O
,	O
such	O
as	O
phase-shift	B-Algorithm
photomasks	I-Algorithm
.	O
</s>
<s>
These	O
techniques	O
have	O
enabled	O
photolithography	B-Algorithm
at	O
the	O
32	B-Algorithm
nanometer	I-Algorithm
CMOS	B-Device
process	O
technology	O
node	O
using	O
a	O
wavelength	O
of	O
193nm	O
(	O
deep	O
ultraviolet	O
)	O
.	O
</s>
<s>
However	O
,	O
with	O
the	O
ITRS	O
roadmap	O
calling	O
for	O
the	O
22	B-Algorithm
nanometer	I-Algorithm
node	O
to	O
be	O
in	O
use	O
by	O
2011	O
,	O
photolithography	B-Algorithm
researchers	O
have	O
had	O
to	O
develop	O
an	O
additional	O
suite	O
of	O
improvements	O
to	O
make	O
22nm	B-Algorithm
technology	O
manufacturable	O
.	O
</s>
<s>
While	O
the	O
increase	O
in	O
mathematical	O
modeling	O
has	O
been	O
underway	O
for	O
some	O
time	O
,	O
the	O
degree	O
and	O
expense	O
of	O
those	O
calculations	O
has	O
justified	O
the	O
use	O
of	O
a	O
new	O
term	O
to	O
cover	O
the	O
changing	O
landscape	O
:	O
computational	B-Algorithm
lithography	I-Algorithm
.	O
</s>
