<s>
A	O
stepper	B-Algorithm
is	O
a	O
device	O
used	O
in	O
the	O
manufacture	O
of	O
integrated	O
circuits	O
(	O
ICs	O
)	O
that	O
is	O
similar	O
in	O
operation	O
to	O
a	O
slide	B-Device
projector	I-Device
or	O
a	O
photographic	O
enlarger	O
.	O
</s>
<s>
Stepper	B-Algorithm
is	O
short	O
for	O
step-and-repeat	O
camera	O
.	O
</s>
<s>
Steppers	B-Algorithm
are	O
an	O
essential	O
part	O
of	O
the	O
complex	O
process	O
,	O
called	O
photolithography	B-Algorithm
,	O
which	O
creates	O
millions	O
of	O
microscopic	O
circuit	O
elements	O
on	O
the	O
surface	O
of	O
silicon	B-Architecture
wafers	I-Architecture
out	O
of	O
which	O
chips	O
are	O
made	O
.	O
</s>
<s>
The	O
stepper	B-Algorithm
emerged	O
in	O
the	O
late	O
1970s	O
but	O
did	O
not	O
become	O
widespread	O
until	O
the	O
1980s	O
.	O
</s>
<s>
This	O
was	O
because	O
it	O
was	O
replacing	O
an	O
earlier	O
technology	O
,	O
the	O
mask	O
aligner	B-Algorithm
.	O
</s>
<s>
Aligners	B-Algorithm
imaged	O
the	O
entire	O
surface	O
of	O
a	O
wafer	B-Architecture
at	O
the	O
same	O
time	O
,	O
producing	O
many	O
chips	O
in	O
a	O
single	O
operation	O
.	O
</s>
<s>
In	O
contrast	O
,	O
the	O
stepper	B-Algorithm
imaged	O
only	O
one	O
chip	O
at	O
a	O
time	O
,	O
and	O
was	O
thus	O
much	O
slower	O
to	O
operate	O
.	O
</s>
<s>
The	O
stepper	B-Algorithm
eventually	O
displaced	O
the	O
aligner	B-Algorithm
when	O
the	O
relentless	O
forces	O
of	O
Moore	O
's	O
Law	O
demanded	O
that	O
smaller	O
feature	O
sizes	O
be	O
used	O
.	O
</s>
<s>
Because	O
the	O
stepper	B-Algorithm
imaged	O
only	O
one	O
chip	O
at	O
a	O
time	O
it	O
offered	O
higher	O
resolution	O
and	O
was	O
the	O
first	O
technology	O
to	O
exceed	O
the	O
1	O
micron	O
limit	O
.	O
</s>
<s>
The	O
addition	O
of	O
auto-alignment	O
systems	O
reduced	O
the	O
setup	O
time	O
needed	O
to	O
image	O
multiple	O
ICs	O
,	O
and	O
by	O
the	O
late	O
1980s	O
,	O
the	O
stepper	B-Algorithm
had	O
almost	O
entirely	O
replaced	O
the	O
aligner	B-Algorithm
in	O
the	O
high-end	O
market	O
.	O
</s>
<s>
The	O
stepper	B-Algorithm
was	O
itself	O
replaced	O
by	O
the	O
step-and-scan	O
systems	O
(	O
scanners	O
)	O
which	O
offered	O
an	O
additional	O
order	O
of	O
magnitude	O
resolution	O
advance	O
,	O
and	O
work	O
by	O
scanning	O
only	O
a	O
small	O
portion	O
of	O
the	O
mask	O
for	O
an	O
individual	O
IC	O
,	O
and	O
thus	O
require	O
much	O
longer	O
operation	O
times	O
than	O
the	O
original	O
steppers	B-Algorithm
.	O
</s>
<s>
Today	O
,	O
step-and-scan	O
systems	O
are	O
so	O
widespread	O
that	O
they	O
are	O
often	O
simply	O
referred	O
to	O
as	O
steppers	B-Algorithm
.	O
</s>
<s>
1957	O
:	O
Attempts	O
to	O
miniaturize	O
electronic	O
circuits	O
started	O
back	O
in	O
1957	O
when	O
Jay	O
Lathrop	O
and	O
James	O
Nall	O
of	O
the	O
U.S.	O
Army	O
's	O
Diamond	O
Ordnance	O
Fuse	O
Laboratories	O
were	O
granted	O
a	O
US2890395A	O
patent	O
for	O
a	O
photolithographic	B-Algorithm
technique	O
that	O
could	O
be	O
used	O
to	O
deposit	O
thin-film	O
metal	O
strips	O
that	O
in	O
turn	O
used	O
to	O
connect	O
discrete	O
transistors	O
on	O
a	O
ceramic	O
plate	O
.	O
</s>
<s>
1958	O
:	O
Based	O
on	O
their	O
works	O
,	O
Jay	O
Last	O
and	O
Robert	O
Noyce	O
at	O
Fairchild	O
Semiconductor	O
built	O
one	O
of	O
the	O
first	O
«	O
step-and-repeat	O
»	O
cameras	O
that	O
repeated	O
identical	O
patterns	O
of	O
the	O
transistors	O
on	O
a	O
single	O
wafer	B-Architecture
using	O
photolithography	B-Algorithm
.	O
</s>
<s>
1959	O
:	O
(	O
Or	O
no	O
later	O
1961	O
)	O
;	O
The	O
David	O
W	O
.	O
Mann	O
division	O
of	O
GCA	O
Corporation	O
became	O
the	O
first	O
company	O
to	O
make	O
commercial	O
step	O
and	O
repeat	O
mask	O
reduction	O
devices	O
called	O
photo-repeaters	O
,	O
which	O
were	O
the	O
predcessors	O
of	O
modern	O
day	O
photolithography	B-Algorithm
steppers	B-Algorithm
.	O
</s>
<s>
The	O
company	O
made	O
what	O
would	O
later	O
be	O
called	O
wafer	B-Architecture
steppers	B-Algorithm
or	O
lithography	O
machines	O
,	O
at	O
the	O
time	O
referred	O
as	O
mask	B-Algorithm
aligners	I-Algorithm
.	O
</s>
<s>
The	O
throughput	O
of	O
this	O
machine	O
was	O
one	O
2-Inches	O
wide	O
wafer	B-Architecture
at	O
a	O
time	O
.	O
</s>
<s>
1973	O
:	O
Perkin-Elmer	O
had	O
introduced	O
Micralign	B-Algorithm
projection	O
aligner	B-Algorithm
.	O
</s>
<s>
Integrated	O
circuits	O
(	O
ICs	O
)	O
are	O
produced	O
in	O
a	O
process	O
known	O
as	O
photolithography	B-Algorithm
.	O
</s>
<s>
The	O
process	O
starts	O
with	O
a	O
large	O
highly	O
purified	O
cylindrical	O
crystal	O
of	O
the	O
semiconductor	O
material	O
known	O
as	O
a	O
boule	B-Algorithm
.	O
</s>
<s>
Thin	O
slices	B-Architecture
are	O
cut	O
off	O
the	O
boule	B-Algorithm
to	O
form	O
disks	O
,	O
and	O
then	O
undergo	O
initial	O
processing	O
and	O
treatment	O
to	O
create	O
a	O
silicon	B-Architecture
wafer	I-Architecture
.	O
</s>
<s>
Elements	O
of	O
the	O
circuit	O
to	O
be	O
created	O
on	O
the	O
IC	O
are	O
reproduced	O
in	O
a	O
pattern	O
of	O
transparent	O
and	O
opaque	O
areas	O
on	O
the	O
surface	O
of	O
a	O
glass	O
or	O
plastic	O
plate	O
called	O
a	O
photomask	B-Algorithm
or	O
reticle	O
.	O
</s>
<s>
The	O
wafer	B-Architecture
is	O
coated	O
with	O
a	O
photosensitive	O
material	O
called	O
photoresist	O
.	O
</s>
<s>
The	O
mask	O
is	O
positioned	O
over	O
the	O
wafer	B-Architecture
and	O
bright	O
light	O
,	O
normally	O
ultraviolet	B-Application
,	O
is	O
shone	O
through	O
the	O
mask	O
.	O
</s>
<s>
After	O
exposure	O
,	O
the	O
wafer	B-Architecture
is	O
developed	O
like	O
photographic	O
film	O
,	O
causing	O
the	O
photoresist	O
to	O
dissolve	O
in	O
certain	O
areas	O
according	O
to	O
the	O
amount	O
of	O
light	O
the	O
areas	O
received	O
during	O
exposure	O
.	O
</s>
<s>
The	O
developed	O
wafer	B-Architecture
is	O
then	O
exposed	O
to	O
solvents	O
.	O
</s>
<s>
The	O
solvent	O
etches	O
away	O
the	O
silicon	O
in	O
the	O
parts	O
of	O
the	O
wafer	B-Architecture
that	O
are	O
no	O
longer	O
protected	O
by	O
the	O
photoresist	O
coating	O
.	O
</s>
<s>
The	O
wafer	B-Architecture
is	O
then	O
cleaned	O
,	O
recoated	O
with	O
photoresist	O
,	O
then	O
passed	O
through	O
the	O
process	O
again	O
in	O
a	O
process	O
that	O
creates	O
the	O
circuit	O
on	O
the	O
silicon	O
,	O
layer	O
by	O
layer	O
.	O
</s>
<s>
Once	O
the	O
entire	O
process	O
is	O
complete	O
,	O
the	O
wafer	B-Architecture
is	O
sawn	O
apart	O
into	O
individual	O
chips	O
,	O
tested	O
,	O
and	O
packaged	O
for	O
sale	O
.	O
</s>
<s>
Before	O
steppers	B-Algorithm
,	O
wafers	B-Architecture
were	O
exposed	O
using	O
mask	B-Algorithm
aligners	I-Algorithm
,	O
which	O
pattern	O
the	O
entire	O
wafer	B-Architecture
at	O
once	O
.	O
</s>
<s>
Between	O
each	O
step	O
,	O
the	O
operator	O
would	O
use	O
a	O
microscope	O
to	O
align	O
the	O
wafer	B-Architecture
with	O
the	O
next	O
mask	O
to	O
be	O
applied	O
.	O
</s>
<s>
During	O
the	O
1970s	O
,	O
aligners	B-Algorithm
generally	O
worked	O
at	O
a	O
one-to-one	O
magnification	O
,	O
which	O
limited	O
the	O
amount	O
of	O
detail	O
on	O
the	O
wafer	B-Architecture
to	O
about	O
whatever	O
could	O
be	O
produced	O
on	O
the	O
mask	O
.	O
</s>
<s>
GCA	O
continued	O
development	O
of	O
the	O
hardware	O
as	O
a	O
direct-to-wafer	O
system	O
,	O
eliminating	O
the	O
need	O
to	O
produce	O
a	O
mask	O
from	O
the	O
reticle	O
and	O
instead	O
using	O
the	O
reticle	O
to	O
expose	O
the	O
wafer	B-Architecture
directly	O
.	O
</s>
<s>
To	O
pattern	O
the	O
entire	O
wafer	B-Architecture
,	O
the	O
mask	O
is	O
repeatedly	O
moved	O
,	O
or	O
stepped	O
,	O
across	O
the	O
surface	O
of	O
the	O
wafer	B-Architecture
.	O
</s>
<s>
This	O
requires	O
the	O
stepping	B-General_Concept
mechanism	O
to	O
be	O
incredibly	O
accurate	O
,	O
demanding	O
precise	O
alignment	O
.	O
</s>
<s>
As	O
each	O
exposure	O
takes	O
as	O
long	O
as	O
the	O
entire	O
mask	O
in	O
an	O
aligner	B-Algorithm
,	O
steppers	B-Algorithm
are	O
inherently	O
slower	O
to	O
use	O
than	O
aligners	B-Algorithm
,	O
so	O
aligners	B-Algorithm
remain	O
in	O
use	O
for	O
roles	O
where	O
higher	O
resolutions	O
are	O
not	O
required	O
.	O
</s>
<s>
Steppers	B-Algorithm
increased	O
the	O
possible	O
resolution	O
many	O
times	O
over	O
that	O
of	O
the	O
aligners	B-Algorithm
and	O
were	O
the	O
first	O
systems	O
to	O
allow	O
features	O
smaller	O
than	O
1	O
micron	O
.	O
</s>
<s>
This	O
led	O
to	O
the	O
1990	O
introduction	O
of	O
the	O
step-and-scan	O
systems	O
,	O
which	O
combine	O
a	O
stepper	B-Algorithm
system	O
with	O
a	O
scanner	O
that	O
images	O
only	O
a	O
portion	O
of	O
the	O
mask	O
at	O
a	O
time	O
.	O
</s>
<s>
As	O
of	O
2008	O
,	O
step-and-scan	O
systems	O
are	O
the	O
most	O
widely	O
used	O
systems	O
for	O
high-end	O
semiconductor	B-Architecture
device	I-Architecture
fabrication	I-Architecture
.	O
</s>
<s>
A	O
typical	O
stepper	B-Algorithm
has	O
the	O
following	O
subassemblies	O
:	O
wafer	B-Architecture
loader	O
,	O
wafer	B-Architecture
stage	O
,	O
wafer	B-Architecture
alignment	O
system	O
,	O
reticle	O
loader	O
,	O
reticle	O
stage	O
,	O
reticle	O
alignment	O
system	O
,	O
reduction	O
lens	O
,	O
and	O
illumination	O
system	O
.	O
</s>
<s>
Process	O
programs	O
for	O
each	O
layer	O
printed	O
on	O
the	O
wafer	B-Architecture
are	O
executed	O
by	O
a	O
control	O
system	O
centering	O
on	O
a	O
computer	O
that	O
stores	O
the	O
process	O
program	O
,	O
reads	O
it	O
,	O
and	O
communicates	O
with	O
the	O
various	O
subassemblies	O
of	O
the	O
stepper	B-Algorithm
in	O
carrying	O
out	O
the	O
program	O
's	O
instructions	O
.	O
</s>
<s>
The	O
components	O
of	O
the	O
stepper	B-Algorithm
are	O
contained	O
in	O
a	O
sealed	O
chamber	O
that	O
is	O
maintained	O
at	O
a	O
precise	O
temperature	O
to	O
prevent	O
distortions	O
in	O
the	O
printed	O
patterns	O
that	O
might	O
be	O
caused	O
by	O
expansion	O
or	O
contraction	O
of	O
the	O
wafer	B-Architecture
due	O
to	O
temperature	O
variations	O
.	O
</s>
<s>
The	O
silicon	B-Architecture
wafers	I-Architecture
are	O
coated	O
with	O
photoresist	O
,	O
and	O
placed	O
in	O
a	O
cassette	O
or	O
"	O
boat	O
"	O
that	O
holds	O
a	O
number	O
of	O
wafers	B-Architecture
.	O
</s>
<s>
This	O
is	O
then	O
placed	O
in	O
a	O
part	O
of	O
the	O
stepper	B-Algorithm
called	O
the	O
wafer	B-Architecture
loader	O
,	O
usually	O
located	O
at	O
the	O
lower	O
front	O
of	O
the	O
stepper	B-Algorithm
.	O
</s>
<s>
A	O
robot	B-Algorithm
in	O
the	O
wafer	B-Architecture
loader	O
picks	O
up	O
one	O
of	O
the	O
wafers	B-Architecture
from	O
the	O
cassette	O
and	O
loads	O
it	O
onto	O
the	O
wafer	B-Architecture
stage	O
where	O
it	O
is	O
aligned	O
to	O
enable	O
another	O
,	O
finer	O
alignment	O
process	O
that	O
will	O
occur	O
later	O
on	O
.	O
</s>
<s>
The	O
pattern	O
of	O
the	O
circuitry	O
for	O
each	O
chip	O
is	O
contained	O
in	O
a	O
pattern	O
etched	O
in	O
chrome	O
on	O
the	O
reticle	O
,	O
which	O
is	O
a	O
plate	O
of	O
transparent	O
quartz	B-General_Concept
.	O
</s>
<s>
A	O
typical	O
reticle	O
used	O
in	O
steppers	B-Algorithm
is	O
6	O
inches	O
square	O
and	O
has	O
a	O
usable	O
area	O
of	O
104mm	O
by	O
132mm	O
.	O
</s>
<s>
A	O
variety	O
of	O
reticles	O
,	O
each	O
appropriate	O
for	O
one	O
stage	O
in	O
the	O
process	O
,	O
are	O
contained	O
in	O
a	O
rack	O
in	O
the	O
reticle	O
loader	O
,	O
usually	O
located	O
at	O
the	O
upper	O
front	O
of	O
the	O
stepper	B-Algorithm
.	O
</s>
<s>
Before	O
the	O
wafer	B-Architecture
is	O
exposed	O
a	O
reticle	O
is	O
loaded	O
onto	O
the	O
reticle	O
stage	O
by	O
a	O
robot	B-Algorithm
,	O
where	O
it	O
is	O
also	O
very	O
precisely	O
aligned	O
.	O
</s>
<s>
Since	O
the	O
same	O
reticle	O
can	O
be	O
used	O
to	O
expose	O
many	O
wafers	B-Architecture
,	O
it	O
is	O
loaded	O
once	O
before	O
a	O
series	O
of	O
wafers	B-Architecture
is	O
exposed	O
,	O
and	O
is	O
realigned	O
periodically	O
.	O
</s>
<s>
Once	O
the	O
wafer	B-Architecture
and	O
reticle	O
are	O
in	O
place	O
and	O
aligned	O
,	O
the	O
wafer	B-Architecture
stage	O
,	O
which	O
is	O
moved	O
very	O
precisely	O
in	O
the	O
X	O
and	O
Y	O
directions	O
(	O
front	O
to	O
back	O
and	O
left	O
to	O
right	O
)	O
by	O
worm	O
screws	O
or	O
linear	O
motors	O
,	O
carries	O
the	O
wafer	B-Architecture
so	O
that	O
the	O
first	O
of	O
the	O
many	O
patterns	O
(	O
or	O
"	O
shots	O
"	O
)	O
to	O
be	O
exposed	O
on	O
it	O
is	O
located	O
below	O
the	O
lens	O
,	O
directly	O
under	O
the	O
reticle	O
.	O
</s>
<s>
Although	O
the	O
wafer	B-Architecture
is	O
aligned	O
after	O
it	O
is	O
placed	O
on	O
the	O
wafer	B-Architecture
stage	O
,	O
this	O
alignment	O
is	O
not	O
sufficient	O
to	O
ensure	O
that	O
the	O
layer	O
of	O
circuitry	O
to	O
be	O
printed	O
onto	O
the	O
wafer	B-Architecture
exactly	O
overlays	O
previous	O
layers	O
already	O
there	O
.	O
</s>
<s>
Once	O
this	O
fine	O
alignment	O
is	O
completed	O
,	O
the	O
shot	O
is	O
exposed	O
by	O
light	O
from	O
the	O
stepper	B-Algorithm
's	O
illumination	O
system	O
that	O
passes	O
through	O
the	O
reticle	O
,	O
through	O
a	O
reduction	O
lens	O
,	O
and	O
on	O
to	O
the	O
surface	O
of	O
the	O
wafer	B-Architecture
.	O
</s>
<s>
Each	O
shot	O
located	O
in	O
a	O
grid	O
pattern	O
on	O
the	O
wafer	B-Architecture
and	O
is	O
exposed	O
in	O
turn	O
as	O
the	O
wafer	B-Architecture
is	O
stepped	O
back	O
and	O
forth	O
under	O
the	O
lens	O
.	O
</s>
<s>
When	O
all	O
shots	O
on	O
the	O
wafer	B-Architecture
are	O
exposed	O
,	O
the	O
wafer	B-Architecture
is	O
unloaded	O
by	O
the	O
wafer	B-Architecture
loader	O
robot	B-Algorithm
,	O
and	O
another	O
wafer	B-Architecture
takes	O
its	O
place	O
on	O
the	O
stage	O
.	O
</s>
<s>
The	O
exposed	O
wafer	B-Architecture
is	O
eventually	O
moved	O
to	O
a	O
developer	O
where	O
the	O
photoresist	O
on	O
its	O
surface	O
is	O
exposed	O
to	O
developing	O
chemicals	O
that	O
wash	O
away	O
areas	O
of	O
the	O
photoresist	O
,	O
based	O
on	O
whether	O
or	O
not	O
they	O
were	O
exposed	O
to	O
the	O
light	O
passing	O
through	O
the	O
reticle	O
.	O
</s>
<s>
The	O
developed	O
surface	O
is	O
then	O
subjected	O
to	O
other	O
processes	O
of	O
photolithography	B-Algorithm
.	O
</s>
<s>
The	O
greatest	O
limitation	O
on	O
the	O
ability	O
to	O
produce	O
increasingly	O
finer	O
lines	O
on	O
the	O
surface	O
of	O
the	O
wafer	B-Architecture
has	O
been	O
the	O
wavelength	O
of	O
the	O
light	O
used	O
in	O
the	O
exposure	O
system	O
.	O
</s>
<s>
As	O
the	O
required	O
lines	O
have	O
become	O
narrower	O
and	O
narrower	O
,	O
illumination	O
sources	O
producing	O
light	O
with	O
progressively	O
shorter	O
wavelengths	O
have	O
been	O
put	O
into	O
service	O
in	O
steppers	B-Algorithm
and	O
scanners	O
.	O
</s>
<s>
An	O
alternative	O
to	O
conventional	O
light	O
based	O
lithography	O
is	O
nanoimprint	B-Algorithm
lithography	I-Algorithm
.	O
</s>
<s>
The	O
ability	O
of	O
an	O
exposure	O
system	O
,	O
such	O
as	O
a	O
stepper	B-Algorithm
,	O
to	O
resolve	O
narrow	O
lines	O
is	O
limited	O
by	O
the	O
wavelength	O
of	O
the	O
light	O
used	O
for	O
illumination	O
,	O
the	O
ability	O
of	O
the	O
lens	O
to	O
capture	O
light	O
(	O
or	O
actually	O
orders	O
of	O
diffraction	O
)	O
coming	O
at	O
increasingly	O
wider	O
angles	O
(	O
called	O
numerical	O
aperture	O
or	O
N.A.	O
</s>
<s>
Decreasing	O
the	O
wavelength	O
of	O
the	O
light	O
in	O
the	O
illumination	O
system	O
increases	O
the	O
resolving	O
power	O
of	O
the	O
stepper	B-Algorithm
.	O
</s>
<s>
Twenty	O
years	O
ago	O
,	O
the	O
"	O
g-line	O
"	O
(	O
436nm	O
)	O
of	O
the	O
mercury	O
spectrum	O
was	O
used	O
to	O
create	O
lines	O
in	O
the	O
750nm	O
range	O
in	O
steppers	B-Algorithm
that	O
employed	O
mercury	O
lamps	O
as	O
their	O
illumination	O
source	O
.	O
</s>
<s>
Several	O
years	O
later	O
systems	O
employing	O
the	O
ultraviolet	B-Application
"	O
i-line	O
"	O
(	O
365nm	O
)	O
from	O
mercury	O
lamps	O
were	O
introduced	O
to	O
create	O
lines	O
as	O
low	O
as	O
350nm	O
.	O
</s>
<s>
Eventually	O
however	O
,	O
the	O
desired	O
line	O
widths	O
became	O
narrower	O
than	O
what	O
was	O
possible	O
using	O
mercury	O
lamps	O
,	O
and	O
near	O
the	O
middle	O
of	O
the	O
2000s	O
,	O
the	O
semiconductor	O
industry	O
moved	O
towards	O
steppers	B-Algorithm
that	O
employed	O
krypton-fluoride	O
(	O
KrF	O
)	O
excimer	O
lasers	O
producing	O
248nm	O
light	O
.	O
</s>
<s>
Lines	O
as	O
low	O
as	O
32nm	O
are	O
being	O
resolved	O
by	O
production-capable	O
steppers	B-Algorithm
using	O
argon-fluoride	O
(	O
ArF	O
)	O
excimer	O
lasers	O
that	O
emit	O
light	O
with	O
a	O
wavelength	O
of	O
193nm	O
.	O
</s>
<s>
Although	O
fluoride	O
(	O
F2	O
)	O
lasers	O
are	O
available	O
that	O
produce	O
157nm	O
light	O
,	O
they	O
are	O
not	O
practical	O
because	O
of	O
their	O
low	O
power	O
and	O
because	O
they	O
quickly	O
degrade	O
photoresist	O
and	O
other	O
materials	O
used	O
in	O
the	O
stepper	B-Algorithm
.	O
</s>
<s>
This	O
is	O
done	O
by	O
further	O
improving	O
techniques	O
for	O
manipulating	O
the	O
light	O
as	O
it	O
passes	O
through	O
the	O
illumination	O
system	O
and	O
the	O
reticle	O
,	O
as	O
well	O
as	O
improving	O
techniques	O
for	O
processing	O
the	O
wafer	B-Architecture
before	O
and	O
after	O
exposure	O
.	O
</s>
<s>
Ultimately	O
,	O
other	O
sources	O
of	O
illumination	O
will	O
have	O
to	O
be	O
put	O
to	O
use	O
,	O
such	O
as	O
electron	O
beams	O
,	O
x-rays	B-Library
or	O
similar	O
sources	O
of	O
electromagnetic	O
energy	O
with	O
wavelengths	O
much	B-Algorithm
shorter	I-Algorithm
than	I-Algorithm
visible	I-Algorithm
light	I-Algorithm
.	O
</s>
<s>
This	O
method	O
,	O
called	O
immersion	B-Algorithm
lithography	I-Algorithm
,	O
is	O
the	O
current	O
cutting	O
edge	O
of	O
practical	O
production	O
technology	O
.	O
</s>
<s>
Modern	O
scanners	O
are	O
steppers	B-Algorithm
that	O
increase	O
the	O
length	O
of	O
the	O
area	O
exposed	O
in	O
each	O
shot	O
(	O
the	O
exposure	O
field	O
)	O
by	O
moving	O
the	O
reticle	O
stage	O
and	O
wafer	B-Architecture
stage	O
in	O
opposite	O
directions	O
to	O
each	O
other	O
during	O
the	O
exposure	O
.	O
</s>
<s>
The	O
field	O
can	O
be	O
exposed	O
with	O
a	O
lesser	O
reduction	O
of	O
size	O
from	O
the	O
reticle	O
to	O
the	O
wafer	B-Architecture
(	O
such	O
as	O
4x	O
reduction	O
on	O
a	O
scanner	O
,	O
compared	O
with	O
5x	O
reduction	O
on	O
a	O
stepper	B-Algorithm
)	O
,	O
while	O
allowing	O
a	O
field	O
size	O
much	O
larger	O
than	O
that	O
which	O
can	O
be	O
exposed	O
with	O
a	O
typical	O
stepper	B-Algorithm
.	O
</s>
<s>
Also	O
the	O
optical	O
properties	O
of	O
the	O
projection	O
lens	O
can	O
be	O
optimized	O
in	O
the	O
area	O
through	O
which	O
the	O
image	O
of	O
the	O
projection	O
slit	O
passes	O
,	O
while	O
optical	O
aberrations	O
can	O
be	O
ignored	O
outside	O
of	O
this	O
area	O
,	O
because	O
they	O
will	O
not	O
affect	O
the	O
exposed	O
area	O
on	O
the	O
wafer	B-Architecture
.	O
</s>
<s>
Successful	O
scanning	O
requires	O
extremely	O
precise	O
synchronization	O
between	O
the	O
moving	O
reticle	O
and	O
wafer	B-Architecture
stages	O
during	O
the	O
exposure	O
.	O
</s>
