<s>
Phase-shift	B-Algorithm
masks	I-Algorithm
are	O
photomasks	B-Algorithm
that	O
take	O
advantage	O
of	O
the	O
interference	O
generated	O
by	O
phase	O
differences	O
to	O
improve	O
image	B-Algorithm
resolution	I-Algorithm
in	O
photolithography	B-Algorithm
.	O
</s>
<s>
There	O
exist	O
alternating	O
and	O
attenuated	O
phase	B-Algorithm
shift	I-Algorithm
masks	I-Algorithm
.	O
</s>
<s>
A	O
phase-shift	B-Algorithm
mask	I-Algorithm
relies	O
on	O
the	O
fact	O
that	O
light	O
passing	O
through	O
a	O
transparent	O
media	O
will	O
undergo	O
a	O
phase	O
change	O
as	O
a	O
function	O
of	O
its	O
optical	O
thickness	O
.	O
</s>
<s>
A	O
conventional	O
photomask	B-Algorithm
is	O
a	O
transparent	O
plate	O
with	O
the	O
same	O
thickness	O
everywhere	O
,	O
parts	O
of	O
which	O
are	O
covered	O
with	O
non-transmitting	O
material	O
in	O
order	O
to	O
create	O
a	O
pattern	O
on	O
the	O
semiconductor	B-Architecture
wafer	I-Architecture
when	O
illuminated	O
.	O
</s>
<s>
In	O
alternating	B-Algorithm
phase-shift	I-Algorithm
masks	I-Algorithm
,	O
certain	O
transmitting	O
regions	O
are	O
made	O
thinner	O
or	O
thicker	O
.	O
</s>
<s>
When	O
the	O
thickness	O
is	O
suitably	O
chosen	O
,	O
the	O
interference	O
of	O
the	O
phase-shifted	O
light	O
with	O
the	O
light	O
coming	O
from	O
unmodified	O
regions	O
of	O
the	O
mask	O
has	O
the	O
effect	O
of	O
improving	O
the	O
contrast	O
on	O
some	O
parts	O
of	O
the	O
wafer	B-Architecture
,	O
which	O
may	O
ultimately	O
increase	O
the	O
resolution	O
on	O
the	O
wafer	B-Architecture
.	O
</s>
<s>
Attenuated	B-Algorithm
phase-shift	I-Algorithm
masks	I-Algorithm
employ	O
a	O
different	O
approach	O
.	O
</s>
<s>
That	O
light	O
is	O
not	O
strong	O
enough	O
to	O
create	O
a	O
pattern	O
on	O
the	O
wafer	B-Architecture
,	O
but	O
it	O
can	O
interfere	O
with	O
the	O
light	O
coming	O
from	O
the	O
transparent	O
parts	O
of	O
the	O
mask	O
,	O
with	O
the	O
goal	O
again	O
of	O
improving	O
the	O
contrast	O
on	O
the	O
wafer	B-Architecture
.	O
</s>
<s>
Attenuated	B-Algorithm
phase-shift	I-Algorithm
masks	I-Algorithm
are	O
already	O
extensively	O
used	O
,	O
due	O
to	O
their	O
simpler	O
construction	O
and	O
operation	O
,	O
particularly	O
in	O
combination	O
with	O
optimized	O
illumination	O
for	O
memory	O
patterns	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
alternating	B-Algorithm
phase-shift	I-Algorithm
masks	I-Algorithm
are	O
more	O
difficult	O
to	O
manufacture	O
and	O
this	O
has	O
slowed	O
their	O
adoption	O
,	O
but	O
their	O
use	O
is	O
becoming	O
more	O
widespread	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
alternating	B-Algorithm
phase-shift	I-Algorithm
mask	I-Algorithm
technique	O
is	O
being	O
used	O
by	O
Intel	O
to	O
print	O
gates	O
for	O
their	O
65	B-Algorithm
nm	I-Algorithm
and	O
subsequent	O
node	O
transistors	O
.	O
</s>
<s>
While	O
alternating	B-Algorithm
phase-shift	I-Algorithm
masks	I-Algorithm
are	O
a	O
stronger	O
form	O
of	O
resolution	O
enhancement	O
than	O
attenuated	B-Algorithm
phase-shift	I-Algorithm
masks	I-Algorithm
,	O
their	O
use	O
has	O
more	O
complex	O
consequences	O
.	O
</s>
<s>
A	O
benefit	O
of	O
using	O
phase-shift	B-Algorithm
masks	I-Algorithm
in	O
lithography	O
is	O
the	O
reduced	O
sensitivity	O
to	O
variations	O
of	O
feature	O
sizes	O
on	O
the	O
mask	O
itself	O
.	O
</s>
<s>
This	O
is	O
most	O
commonly	O
used	O
in	O
alternating	B-Algorithm
phase-shift	I-Algorithm
masks	I-Algorithm
,	O
where	O
the	O
linewidth	O
becomes	O
less	O
and	O
less	O
sensitive	O
to	O
the	O
chrome	O
width	O
on	O
the	O
mask	O
,	O
as	O
the	O
chrome	O
width	O
decreases	O
.	O
</s>
<s>
Some	O
cases	O
of	O
attenuated	O
phase-shifting	B-Algorithm
masks	I-Algorithm
also	O
demonstrate	O
the	O
same	O
benefit	O
(	O
see	O
figure	O
)	O
.	O
</s>
<s>
Attenuated	B-Algorithm
phase-shift	I-Algorithm
masks	I-Algorithm
also	O
improve	O
the	O
image	O
log-slope	O
without	O
requiring	O
a	O
very	O
high	O
exposure	O
dose	O
with	O
a	O
widened	O
dark	O
feature	O
.	O
</s>
<s>
As	O
phase-shift	B-Algorithm
masks	I-Algorithm
are	O
applied	O
to	O
printing	O
smaller	O
and	O
smaller	O
features	O
,	O
it	O
becomes	O
more	O
and	O
more	O
important	O
to	O
model	O
them	O
accurately	O
using	O
rigorous	O
simulation	O
software	O
,	O
such	O
as	O
Panoramic	O
Technology	O
or	O
Sigma-C	O
.	O
</s>
<s>
The	O
performance	O
of	O
phase-shift	B-Algorithm
masks	I-Algorithm
can	O
also	O
be	O
previewed	O
with	O
the	O
use	O
of	O
aerial	O
image	O
microscopes	O
.	O
</s>
<s>
Defect	O
inspection	O
remains	O
a	O
critical	O
aspect	O
of	O
phase-shift	B-Algorithm
mask	I-Algorithm
technology	O
,	O
as	O
the	O
set	O
of	O
printable	O
mask	O
defects	O
has	O
expanded	O
to	O
include	O
those	O
with	O
phase	O
effects	O
in	O
addition	O
to	O
conventional	O
transmission	O
effects	O
.	O
</s>
<s>
Attenuated	O
phase	B-Algorithm
shift	I-Algorithm
masks	I-Algorithm
have	O
been	O
in	O
use	O
in	O
production	O
since	O
the	O
90nm	O
node	O
.	O
</s>
