<s>
A	O
photomask	B-Algorithm
is	O
an	O
opaque	O
plate	O
with	O
transparent	O
areas	O
that	O
allow	O
light	O
to	O
shine	O
through	O
in	O
a	O
defined	O
pattern	O
.	O
</s>
<s>
Photomasks	B-Algorithm
are	O
commonly	O
used	O
in	O
photolithography	B-Algorithm
for	O
the	O
production	O
of	O
integrated	O
circuits	O
(	O
ICs	O
or	O
"	O
chips	O
"	O
)	O
to	O
produce	O
a	O
pattern	O
on	O
a	O
thin	O
wafer	B-Architecture
of	O
material	O
(	O
usually	O
silicon	O
)	O
.	O
</s>
<s>
Several	O
masks	O
are	O
used	O
in	O
turn	O
,	O
each	O
one	O
reproducing	O
a	O
layer	O
of	O
the	O
completed	O
design	O
,	O
and	O
together	O
known	O
as	O
a	O
mask	B-Algorithm
set	I-Algorithm
.	O
</s>
<s>
The	O
design	O
of	O
one	O
layer	O
was	O
cut	O
into	O
the	O
rubylith	O
,	O
initially	O
by	O
hand	O
on	O
an	O
illuminated	O
drafting	O
table	O
(	O
later	O
by	O
machine	O
(	O
plotter	B-Operating_System
)	O
)	O
and	O
the	O
unwanted	O
rubylith	O
was	O
peeled	O
off	O
by	O
hand	O
,	O
forming	O
the	O
master	O
image	O
of	O
that	O
layer	O
of	O
the	O
chip	O
.	O
</s>
<s>
The	O
reticle	O
was	O
by	O
step-and-repeater	O
photolithography	B-Algorithm
and	O
etching	O
used	O
to	O
produce	O
a	O
photomask	B-Algorithm
with	O
image-size	O
the	O
same	O
as	O
the	O
final	O
chip	O
.	O
</s>
<s>
The	O
photomask	B-Algorithm
might	O
be	O
used	O
directly	O
in	O
the	O
fab	O
or	O
be	O
used	O
as	O
master-photomask	O
to	O
produce	O
the	O
final	O
actual	O
working	O
photomasks	B-Algorithm
.	O
</s>
<s>
As	O
feature	O
size	O
shrank	O
the	O
only	O
way	O
to	O
properly	O
focus	O
the	O
image	O
was	O
to	O
place	O
it	O
in	O
direct	O
contact	O
with	O
the	O
wafer	B-Architecture
.	O
</s>
<s>
These	O
contact	O
aligners	O
often	O
lifted	O
some	O
of	O
the	O
photoresist	O
off	O
the	O
wafer	B-Architecture
and	O
onto	O
the	O
photomask	B-Algorithm
and	O
it	O
had	O
to	O
be	O
cleaned	O
or	O
discarded	O
.	O
</s>
<s>
This	O
drove	O
the	O
adoption	O
of	O
reverse	O
master	O
photomasks	B-Algorithm
(	O
see	O
above	O
)	O
,	O
which	O
were	O
used	O
to	O
produce	O
(	O
with	O
contact	O
photolithography	B-Algorithm
and	O
etching	O
)	O
the	O
needed	O
many	O
actual	O
working	O
photomasks	B-Algorithm
.	O
</s>
<s>
Later	O
,	O
projection	O
photo-lithography	B-Algorithm
meant	O
photomask	B-Algorithm
lifetime	O
was	O
indefinite	O
.	O
</s>
<s>
Still	O
later	O
direct-step-on-wafer	O
stepper	B-Algorithm
photo-lithography	B-Algorithm
used	O
reticles	O
directly	O
and	O
ended	O
the	O
use	O
of	O
photomasks	B-Algorithm
.	O
</s>
<s>
Photomask	B-Algorithm
materials	O
changed	O
over	O
time	O
.	O
</s>
<s>
Later	O
borosilicate	O
and	O
then	O
fused	O
silica	O
to	O
control	O
expansion	O
,	O
and	O
chromium	B-Language
which	O
has	O
better	O
opacity	O
to	O
ultraviolet	O
light	O
were	O
introduced	O
.	O
</s>
<s>
The	O
original	O
pattern	O
generators	O
have	O
since	O
been	O
replaced	O
by	O
electron	B-Architecture
beam	I-Architecture
lithography	I-Architecture
and	O
laser-driven	O
systems	O
which	O
generate	O
reticles	O
directly	O
from	O
the	O
original	O
computerized	O
design	O
.	O
</s>
<s>
Lithographic	O
photomasks	B-Algorithm
are	O
typically	O
transparent	O
fused	O
silica	O
plates	O
covered	O
with	O
a	O
pattern	O
defined	O
with	O
a	O
chromium	B-Language
(	O
Cr	O
)	O
or	O
Fe2O3	O
metal	O
absorbing	O
film	O
.	O
</s>
<s>
Photomasks	B-Algorithm
are	O
used	O
at	O
wavelengths	O
of	O
365	O
nm	O
,	O
248nm	O
,	O
and	O
193nm	O
.	O
</s>
<s>
Photomasks	B-Algorithm
have	O
also	O
been	O
developed	O
for	O
other	O
forms	O
of	O
radiation	O
such	O
as	O
157nm	O
,	O
13.5nm	O
(	O
EUV	B-Algorithm
)	O
,	O
X-ray	B-Library
,	O
electrons	O
,	O
and	O
ions	O
;	O
but	O
these	O
require	O
entirely	O
new	O
materials	O
for	O
the	O
substrate	B-Architecture
and	O
the	O
pattern	O
film	O
.	O
</s>
<s>
A	O
set	B-Algorithm
of	I-Algorithm
photomasks	I-Algorithm
,	O
each	O
defining	O
a	O
pattern	O
layer	O
in	O
integrated	B-Architecture
circuit	I-Architecture
fabrication	I-Architecture
,	O
is	O
fed	O
into	O
a	O
photolithography	B-Algorithm
stepper	B-Algorithm
or	O
scanner	O
,	O
and	O
individually	O
selected	O
for	O
exposure	O
.	O
</s>
<s>
In	O
multi-patterning	B-Algorithm
techniques	O
,	O
a	O
photomask	B-Algorithm
would	O
correspond	O
to	O
a	O
subset	O
of	O
the	O
layer	O
pattern	O
.	O
</s>
<s>
In	O
photolithography	B-Algorithm
for	O
the	O
mass	O
production	O
of	O
integrated	O
circuit	O
devices	O
,	O
the	O
more	O
correct	O
term	O
is	O
usually	O
photoreticle	B-Algorithm
or	O
simply	O
reticle	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
a	O
photomask	B-Algorithm
,	O
there	O
is	O
a	O
one-to-one	O
correspondence	O
between	O
the	O
mask	O
pattern	O
and	O
the	O
wafer	B-Architecture
pattern	O
.	O
</s>
<s>
This	O
was	O
the	O
standard	O
for	O
the	O
1:1	O
mask	O
aligners	O
that	O
were	O
succeeded	O
by	O
steppers	B-Algorithm
and	O
scanners	O
with	O
reduction	O
optics	O
.	O
</s>
<s>
As	O
used	O
in	O
steppers	B-Algorithm
and	O
scanners	O
,	O
the	O
reticle	O
commonly	O
contains	O
only	O
one	O
layer	O
of	O
the	O
designed	O
VLSI	O
circuit	O
.	O
</s>
<s>
(	O
However	O
,	O
some	O
photolithography	B-Algorithm
fabrications	B-Architecture
utilize	O
reticles	O
with	O
more	O
than	O
one	O
layer	O
placed	O
side	O
by	O
side	O
onto	O
the	O
same	O
mask	O
)	O
.	O
</s>
<s>
The	O
pattern	O
is	O
projected	O
and	O
shrunk	O
by	O
four	O
or	O
five	O
times	O
onto	O
the	O
wafer	B-Architecture
surface	O
.	O
</s>
<s>
To	O
achieve	O
complete	O
wafer	B-Architecture
coverage	O
,	O
the	O
wafer	B-Architecture
is	O
repeatedly	O
"	O
stepped	B-Algorithm
"	O
from	O
position	O
to	O
position	O
under	O
the	O
optical	O
column	O
until	O
full	O
exposure	O
is	O
achieved	O
.	O
</s>
<s>
Features	O
150nm	O
or	O
below	O
in	O
size	O
generally	O
require	O
phase-shifting	B-Algorithm
to	O
enhance	O
the	O
image	O
quality	O
to	O
acceptable	O
values	O
.	O
</s>
<s>
The	O
two	O
most	O
common	O
methods	O
are	O
to	O
use	O
an	O
attenuated	O
phase-shifting	B-Algorithm
background	O
film	O
on	O
the	O
mask	O
to	O
increase	O
the	O
contrast	O
of	O
small	O
intensity	O
peaks	O
,	O
or	O
to	O
etch	O
the	O
exposed	O
quartz	B-General_Concept
so	O
that	O
the	O
edge	O
between	O
the	O
etched	O
and	O
unetched	O
areas	O
can	O
be	O
used	O
to	O
image	O
nearly	O
zero	O
intensity	O
.	O
</s>
<s>
The	O
former	O
method	O
is	O
attenuated	O
phase-shifting	B-Algorithm
,	O
and	O
is	O
often	O
considered	O
a	O
weak	O
enhancement	O
,	O
requiring	O
special	O
illumination	O
for	O
the	O
most	O
enhancement	O
,	O
while	O
the	O
latter	O
method	O
is	O
known	O
as	O
alternating-aperture	O
phase-shifting	B-Algorithm
,	O
and	O
is	O
the	O
most	O
popular	O
strong	O
enhancement	O
technique	O
.	O
</s>
<s>
As	O
leading-edge	O
semiconductor	O
features	O
shrink	O
,	O
photomask	B-Algorithm
features	O
that	O
are	O
4×	O
larger	O
must	O
inevitably	O
shrink	O
as	O
well	O
.	O
</s>
<s>
A	O
2005	O
study	O
by	O
IMEC	O
found	O
that	O
thinner	O
absorbers	O
degrade	O
image	O
contrast	O
and	O
therefore	O
contribute	O
to	O
line-edge	O
roughness	O
,	O
using	O
state-of-the-art	O
photolithography	B-Algorithm
tools	O
.	O
</s>
<s>
One	O
possibility	O
is	O
to	O
eliminate	O
absorbers	O
altogether	O
and	O
use	O
"	O
chromeless	O
"	O
masks	O
,	O
relying	O
solely	O
on	O
phase-shifting	B-Algorithm
for	O
imaging	O
.	O
</s>
<s>
The	O
emergence	O
of	O
immersion	B-Algorithm
lithography	I-Algorithm
has	O
a	O
strong	O
impact	O
on	O
photomask	B-Algorithm
requirements	O
.	O
</s>
<s>
The	O
commonly	O
used	O
attenuated	O
phase-shifting	B-Algorithm
mask	I-Algorithm
is	O
more	O
sensitive	O
to	O
the	O
higher	O
incidence	O
angles	O
applied	O
in	O
"	O
hyper-NA	O
"	O
lithography	O
,	O
due	O
to	O
the	O
longer	O
optical	O
path	O
through	O
the	O
patterned	O
film	O
.	O
</s>
<s>
EUV	B-Algorithm
photomasks	B-Algorithm
work	O
by	O
reflecting	O
light	O
,	O
which	O
is	O
achieved	O
by	O
using	O
multiple	O
alternating	O
layers	O
of	O
molybdenum	O
and	O
silicon	O
.	O
</s>
<s>
Leading-edge	O
photomasks	B-Algorithm
(	O
pre-corrected	O
)	O
images	O
of	O
the	O
final	O
chip	O
patterns	O
are	O
magnified	O
by	O
four	O
times	O
.	O
</s>
<s>
However	O
,	O
as	O
features	O
continue	O
to	O
shrink	O
,	O
two	O
trends	O
come	O
into	O
play	O
:	O
the	O
first	O
is	O
that	O
the	O
mask	O
error	O
factor	O
begins	O
to	O
exceed	O
one	O
,	O
i.e.	O
,	O
the	O
dimension	O
error	O
on	O
the	O
wafer	B-Architecture
may	O
be	O
more	O
than	O
1/4	O
the	O
dimension	O
error	O
on	O
the	O
mask	O
,	O
and	O
the	O
second	O
is	O
that	O
the	O
mask	O
feature	O
is	O
becoming	O
smaller	O
,	O
and	O
the	O
dimension	O
tolerance	O
is	O
approaching	O
a	O
few	O
nanometers	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
25nm	O
wafer	B-Architecture
pattern	O
should	O
correspond	O
to	O
a	O
100nm	O
mask	O
pattern	O
,	O
but	O
the	O
wafer	B-Architecture
tolerance	O
could	O
be	O
1.25nm	O
(	O
5%	O
spec	O
)	O
,	O
which	O
translates	O
into	O
5nm	O
on	O
the	O
photomask	B-Algorithm
.	O
</s>
<s>
The	O
variation	O
of	O
electron	O
beam	O
scattering	O
in	O
directly	O
writing	O
the	O
photomask	B-Algorithm
pattern	O
can	O
easily	O
well	O
exceed	O
this	O
.	O
</s>
<s>
at	O
IBM	O
patented	O
a	O
process	O
to	O
use	O
the	O
"	O
pellicle	O
"	O
as	O
a	O
dust	O
cover	O
to	O
protect	O
a	O
photomask	B-Algorithm
or	O
reticle	O
.	O
</s>
<s>
In	O
the	O
context	O
of	O
this	O
entry	O
,	O
"	O
pellicle	O
"	O
means	O
"	O
thin	O
film	O
dust	O
cover	O
to	O
protect	O
a	O
photomask	B-Algorithm
"	O
.	O
</s>
<s>
Particle	O
contamination	O
can	O
be	O
a	O
significant	O
problem	O
in	O
semiconductor	B-Architecture
manufacturing	I-Architecture
.	O
</s>
<s>
A	O
photomask	B-Algorithm
is	O
protected	O
from	O
particles	O
by	O
a	O
pelliclea	O
thin	O
transparent	O
film	O
stretched	O
over	O
a	O
frame	O
that	O
is	O
glued	O
over	O
one	O
side	O
of	O
the	O
photomask	B-Algorithm
.	O
</s>
<s>
The	O
SPIE	O
Annual	O
Conference	O
,	O
Photomask	B-Algorithm
Technology	O
reports	O
the	O
SEMATECH	O
Mask	O
Industry	O
Assessment	O
which	O
includes	O
current	O
industry	O
analysis	O
and	O
the	O
results	O
of	O
their	O
annual	O
photomask	B-Algorithm
manufacturers	O
survey	O
.	O
</s>
<s>
Major	O
chipmakers	O
such	O
as	O
Intel	O
,	O
Globalfoundries	O
,	O
IBM	O
,	O
NEC	O
,	O
TSMC	O
,	O
UMC	O
,	O
Samsung	B-Application
,	O
and	O
Micron	O
Technology	O
,	O
have	O
their	O
own	O
large	O
maskmaking	O
facilities	O
or	O
joint	O
ventures	O
with	O
the	O
abovementioned	O
companies	O
.	O
</s>
<s>
The	O
worldwide	O
photomask	B-Algorithm
market	O
was	O
estimated	O
as	O
$3.2	O
billion	O
in	O
2012	O
and	O
$3.1	O
billion	O
in	O
2013	O
.	O
</s>
<s>
The	O
purchase	O
price	O
of	O
a	O
photomask	B-Algorithm
,	O
in	O
2006	O
,	O
could	O
range	O
from	O
$250	O
to	O
$	O
100,000	O
for	O
a	O
single	O
high-end	O
phase-shift	B-Algorithm
mask	I-Algorithm
.	O
</s>
<s>
As	O
many	O
as	O
30	O
masks	O
(	O
of	O
varying	O
price	O
)	O
may	O
be	O
required	O
to	O
form	O
a	O
complete	O
mask	B-Algorithm
set	I-Algorithm
.	O
</s>
