<s>
In	O
semiconductor	B-Architecture
manufacturing	I-Architecture
,	O
virtual	B-Algorithm
metrology	I-Algorithm
refers	O
to	O
methods	O
to	O
predict	O
the	O
properties	O
of	O
a	O
wafer	B-Architecture
based	O
on	O
machine	O
parameters	O
and	O
sensor	O
data	O
in	O
the	O
production	O
equipment	O
,	O
without	O
performing	O
the	O
(	O
costly	O
)	O
physical	O
measurement	O
of	O
the	O
wafer	B-Architecture
properties	O
.	O
</s>
<s>
Another	O
option	O
to	O
handle	O
missing	O
data	O
is	O
to	O
use	O
imputation	O
techniques	O
on	O
the	O
dataset	O
,	O
but	O
virtual	B-Algorithm
metrology	I-Algorithm
in	O
many	O
cases	O
,	O
can	O
be	O
a	O
more	O
accurate	O
method	O
.	O
</s>
<s>
Examples	O
of	O
virtual	B-Algorithm
metrology	I-Algorithm
include	O
:	O
</s>
<s>
the	O
prediction	O
of	O
the	O
silicon	O
nitride	O
(	O
)	O
layer	O
thickness	O
in	O
the	O
chemical	B-Algorithm
vapor	I-Algorithm
deposition	I-Algorithm
process	I-Algorithm
(	O
CVD	O
)	O
,	O
using	O
multivariate	O
regression	O
methods	O
;	O
</s>
<s>
the	O
prediction	O
of	O
critical	O
dimension	O
in	O
photolithography	B-Algorithm
,	O
using	O
multi-level	O
and	O
regularization	O
approaches	O
;	O
</s>
<s>
the	O
prediction	O
of	O
layer	O
width	O
in	O
etching	B-Algorithm
.	O
</s>
