<s>
In	O
silicon	B-Architecture
wafer	I-Architecture
manufacturing	O
overlay	B-Algorithm
control	I-Algorithm
is	O
the	O
control	O
of	O
pattern-to-pattern	O
alignment	O
necessary	O
in	O
the	O
manufacture	O
of	O
silicon	B-Architecture
wafers	I-Architecture
.	O
</s>
<s>
Silicon	B-Architecture
wafers	I-Architecture
are	O
currently	O
manufactured	O
in	O
a	O
sequence	O
of	O
steps	O
,	O
each	O
stage	O
placing	O
a	O
pattern	O
of	O
material	O
on	O
the	O
wafer	B-Architecture
;	O
in	O
this	O
way	O
transistors	B-Application
,	O
contacts	O
,	O
etc.	O
,	O
all	O
made	O
of	O
different	O
materials	O
,	O
are	O
laid	O
down	O
.	O
</s>
<s>
In	O
order	O
for	O
the	O
final	O
device	O
to	O
function	O
correctly	O
,	O
these	O
separate	O
patterns	O
must	O
be	O
aligned	O
correctly	O
–	O
for	O
example	O
contacts	O
,	O
lines	O
and	O
transistors	B-Application
must	O
all	O
line	O
up	O
.	O
</s>
<s>
Overlay	B-Algorithm
control	I-Algorithm
has	O
always	O
played	O
an	O
important	O
role	O
in	O
semiconductor	B-Architecture
manufacturing	I-Architecture
,	O
helping	O
to	O
monitor	O
layer-to-layer	O
alignment	O
on	O
multi-layer	O
device	O
structures	O
.	O
</s>
<s>
Misalignment	O
of	O
any	O
kind	O
can	O
cause	O
short	O
circuits	O
and	O
connection	O
failures	O
,	O
which	O
in	O
turn	O
impact	O
fab	B-Algorithm
yield	O
and	O
profit	O
margins	O
.	O
</s>
<s>
Overlay	B-Algorithm
control	I-Algorithm
has	O
become	O
even	O
more	O
critical	O
now	O
because	O
the	O
combination	O
of	O
increasing	O
pattern	O
density	O
and	O
innovative	O
techniques	O
such	O
as	O
double	B-Algorithm
patterning	I-Algorithm
and	O
193nm	O
immersion	B-Algorithm
lithography	I-Algorithm
creates	O
a	O
novel	O
set	O
of	O
pattern-based	O
yield	O
challenges	O
at	O
the	O
45nm	O
technology	O
node	O
and	O
below	O
.	O
</s>
<s>
Higher	O
order	O
overlay	B-Algorithm
control	I-Algorithm
and	O
in-field	O
metrology	O
using	O
smaller	O
,	O
micro-grating	O
or	O
other	O
novel	O
targets	O
are	O
becoming	O
essential	O
for	O
successful	O
production	O
ramps	O
and	O
higher	O
yields	O
at	O
45nm	O
and	O
beyond	O
.	O
</s>
