<s>
Extreme	B-Algorithm
ultraviolet	I-Algorithm
lithography	I-Algorithm
(	O
also	O
known	O
as	O
EUV	O
or	O
EUVL	B-Algorithm
)	O
is	O
an	O
optical	B-Algorithm
lithography	I-Algorithm
technology	O
used	O
in	O
semiconductor	B-Architecture
device	I-Architecture
fabrication	I-Architecture
to	O
make	O
integrated	O
circuits	O
(	O
ICs	O
)	O
.	O
</s>
<s>
It	O
uses	O
extreme	O
ultraviolet	O
(	O
EUV	O
)	O
wavelengths	O
near	O
13.5	O
nm	O
,	O
using	O
a	O
laser-pulsed	O
tin	B-Protocol
(	O
Sn	O
)	O
droplet	O
plasma	O
,	O
to	O
produce	O
a	O
pattern	O
by	O
using	O
a	O
reflective	O
photomask	B-Algorithm
to	O
expose	O
a	O
substrate	B-Architecture
covered	O
by	O
photoresist	O
.	O
</s>
<s>
It	O
is	O
currently	O
applied	O
only	O
in	O
the	O
most	O
advanced	O
semiconductor	B-Architecture
device	I-Architecture
fabrication	I-Architecture
.	O
</s>
<s>
The	O
then	O
leading	O
producers	O
of	O
steppers	O
,	O
Japanese	O
companies	O
Canon	O
and	O
Nikon	B-Algorithm
gave	O
up	O
trying	O
.	O
</s>
<s>
Intel	O
,	O
Canon	O
and	O
Nikon	B-Algorithm
(	O
leaders	O
in	O
the	O
field	O
at	O
the	O
time	O
)	O
,	O
as	O
well	O
as	O
ASML	O
and	O
Silicon	O
Valley	O
Group	O
(	O
SVG	O
)	O
all	O
sought	O
licensing	O
,	O
however	O
Congress	O
denied	O
Japanese	O
companies	O
the	O
necessary	O
permission	O
as	O
they	O
were	O
perceived	O
as	O
strong	O
technical	O
competitors	O
at	O
the	O
time	O
,	O
and	O
should	O
not	O
benefit	O
from	O
taxpayer-funded	O
research	O
at	O
the	O
expense	O
of	O
American	O
companies	O
.	O
</s>
<s>
By	O
2018	O
Dutch	O
company	O
ASML	O
succeeded	O
in	O
deploying	O
the	O
EUV-LLC	O
IP	O
after	O
several	O
decades	O
of	O
developmental	O
research	O
,	O
with	O
incorporation	O
of	O
European-funded	O
EUCLIDES	O
(	O
Extreme	O
UV	O
Concept	O
Lithography	B-Algorithm
Development	O
System	O
)	O
and	O
long-standing	O
partner	O
German	O
optics	O
manufacturer	O
ZEISS	O
and	O
synchrotron	O
light	O
source	O
supplier	O
Oxford	O
Instruments	O
.	O
</s>
<s>
The	O
first	O
prototype	O
in	O
2006	O
produced	O
one	O
wafer	B-Architecture
in	O
23	O
hours	O
.	O
</s>
<s>
As	O
of	O
2022	O
,	O
a	O
scanner	O
produces	O
up	O
to	O
200	O
wafers	B-Architecture
per	O
hour	O
.	O
</s>
<s>
This	O
made	O
the	O
once	O
small	O
company	O
ASML	O
the	O
world	O
leader	O
in	O
the	O
production	O
of	O
scanners	O
and	O
monopolist	O
in	O
this	O
cutting	O
edge	O
technology	O
and	O
resulted	O
in	O
a	O
record	O
turnover	O
of	O
18.6	O
billion	O
€	O
in	O
2021	O
,	O
dwarfing	O
their	O
competitors	O
Canon	O
and	O
Nikon	B-Algorithm
who	O
were	O
denied	O
IP	O
access	O
.	O
</s>
<s>
EUV	O
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>
This	O
is	O
in	O
contrast	O
to	O
conventional	O
photomasks	B-Algorithm
which	O
work	O
by	O
blocking	O
light	O
using	O
a	O
single	O
chromium	O
layer	O
on	O
a	O
quartz	O
substrate	B-Architecture
.	O
</s>
<s>
Blank	O
photomasks	B-Algorithm
are	O
mainly	O
made	O
by	O
two	O
companies	O
:	O
AGC	O
Inc	O
.	O
and	O
Hoya	O
Corporation	O
.	O
</s>
<s>
A	O
blank	O
photomask	B-Algorithm
is	O
covered	O
with	O
photoresist	O
,	O
which	O
is	O
then	O
baked	O
(	O
solidified	O
)	O
in	O
an	O
oven	O
,	O
and	O
later	O
exposed	O
to	O
laser	O
light	O
,	O
using	O
maskless	B-Algorithm
lithography	I-Algorithm
.	O
</s>
<s>
Etching	O
must	O
be	O
done	O
to	O
a	O
very	O
specific	O
depth	O
thus	O
making	O
etching	O
difficult	O
when	O
compared	O
with	O
conventional	O
photomask	B-Algorithm
manufacturing	O
.	O
</s>
<s>
The	O
tool	O
consists	O
of	O
a	O
laser-driven	O
tin	B-Protocol
(	O
Sn	O
)	O
plasma	O
light	O
source	O
,	O
reflective	O
optics	O
comprising	O
multilayer	O
mirrors	O
,	O
contained	O
within	O
a	O
hydrogen	O
gas	O
ambient	O
.	O
</s>
<s>
EUVL	B-Algorithm
is	O
a	O
significant	O
departure	O
from	O
the	O
deep	O
ultraviolet	O
lithography	B-Algorithm
standard	O
.	O
</s>
<s>
Hence	O
,	O
EUV	B-Algorithm
lithography	I-Algorithm
requires	O
a	O
vacuum	O
.	O
</s>
<s>
All	O
optical	O
elements	O
,	O
including	O
the	O
photomask	B-Algorithm
,	O
must	O
use	O
defect-free	O
molybdenum/silicon	O
(	O
Mo/Si	O
)	O
multilayers	O
(	O
consisting	O
of	O
40	O
Mo/Si	O
bilayers	O
)	O
that	O
act	O
to	O
reflect	O
light	O
by	O
means	O
of	O
interlayer	O
interference	O
;	O
any	O
one	O
of	O
these	O
mirrors	O
absorb	O
around	O
30%	O
of	O
the	O
incident	O
light	O
.	O
</s>
<s>
Current	O
EUVL	B-Algorithm
systems	O
contain	O
at	O
least	O
two	O
condenser	O
multilayer	O
mirrors	O
,	O
six	O
projection	O
multilayer	O
mirrors	O
and	O
a	O
multilayer	O
object	O
(	O
mask	O
)	O
.	O
</s>
<s>
The	O
mirror	O
responsible	O
for	O
collecting	O
the	O
light	O
is	O
directly	O
exposed	O
to	O
the	O
plasma	O
and	O
is	O
vulnerable	O
to	O
damage	O
from	O
high-energy	O
ions	O
and	O
other	O
debris	O
such	O
as	O
tin	B-Protocol
droplets	O
,	O
which	O
require	O
the	O
costly	O
collector	O
mirror	O
to	O
be	O
replaced	O
every	O
year	O
.	O
</s>
<s>
Hynix	O
reported	O
at	O
the	O
2009	O
EUV	O
Symposium	O
that	O
the	O
wall	O
plug	O
efficiency	O
was	O
~	O
0.02	O
%	O
for	O
EUV	O
,	O
i.e.	O
,	O
to	O
get	O
200-watts	O
at	O
intermediate	O
focus	O
for	O
100wafers-per-hour	O
,	O
one	O
would	O
require	O
1-megawatt	O
of	O
input	O
power	O
,	O
compared	O
to	O
165-kilowatts	O
for	O
an	O
ArF	B-Algorithm
immersion	I-Algorithm
scanner	O
,	O
and	O
that	O
even	O
at	O
the	O
same	O
throughput	O
,	O
the	O
footprint	O
of	O
the	O
EUV	O
scanner	O
was	O
~	O
3x	O
the	O
footprint	O
of	O
an	O
ArF	B-Algorithm
immersion	I-Algorithm
scanner	O
,	O
resulting	O
in	O
productivity	O
loss	O
.	O
</s>
<s>
DUV	O
vs.	O
EUV	O
Tool	O
Energy	O
Consumption	O
(	O
measured	O
2020	O
)	O
:	O
EUV	B-Algorithm
tools	I-Algorithm
consume	O
at	O
least	O
10x	O
more	O
energy	O
than	O
immersion	O
tools	O
.	O
</s>
<s>
The	O
following	O
table	O
summarizes	O
key	O
differences	O
between	O
EUV	O
systems	O
in	O
development	O
and	O
ArF	B-Algorithm
immersion	I-Algorithm
systems	O
which	O
are	O
widely	O
used	O
in	O
production	O
today	O
:	O
</s>
<s>
EUV	O
ArF	B-Algorithm
immersion	I-Algorithm
Wavelength	O
2%	O
FWHM	O
bandwidth	O
about	O
13.5	O
nm	O
193	O
nm	O
Photon	O
energy	O
91	O
...	O
93	O
eV	O
6.4	O
eV	O
Light	O
source	O
CO2	O
laser	O
+	O
Sn	O
plasma	O
ArF	O
excimer	O
laser	O
Wavelength	O
bandwidth	O
5.9	O
%	O
<	O
0.16	O
%	O
Secondary	O
electrons	O
produced	O
by	O
absorption	O
Yes	O
No	O
Optics	O
Reflective	O
multilayers	O
(	O
~	O
40%	O
absorbing	O
per	O
mirror	O
)	O
Transmissive	O
lenses	O
Numerical	O
aperture	O
(	O
NA	O
)	O
0.25	O
:	O
NXE:3100	O
0.33	O
:	O
NXE:33x0	O
and	O
NXE:3400B	O
High	O
NA	O
(	O
0.55	O
)	O
:	O
in	O
development	O
1.20	O
,	O
1.35	O
Resolution	O
spec	O
NXE:3100	O
:	O
27	O
nm	O
(	O
k1	O
=	O
0.50	O
)	O
NXE:3300B	O
:	O
22	O
nm	O
(	O
k1	O
=	O
0.54	O
)	O
,	O
18	O
nm	O
(	O
k1	O
=	O
0.44	O
)	O
with	O
off-axis	O
illuminationNXE:3350B	O
:	O
16	O
nm	O
(	O
k1	O
=	O
0.39	O
)	O
NXE:3400B/C	O
,	O
NXE:3600D	O
:	O
13	O
nm	O
(	O
k1	O
=	O
0.32	O
)	O
38	O
nm	O
(	O
k1	O
=	O
0.27	O
)	O
Flare	O
4%	O
<	O
1%	O
Illumination	O
Central	O
angle	O
6°	O
off	O
axis	O
onto	O
reticle	O
On	O
axis	O
Field	O
size	O
0.25	O
and	O
0.33	O
NA	O
:	O
26	O
mm	O
×	O
33	O
mm	O
High	O
NA	O
:	O
26	O
mm	O
×	O
16.5	O
mm	O
26	O
mm	O
×	O
33	O
mm	O
Magnification	O
0.25	O
and	O
0.33	O
NA	O
:	O
4X	O
isomorphic	O
High	O
NA	O
:	O
4X/8X	O
anamorphic	O
4X	O
Ambient	O
Vacuum	O
hydrogen	O
Air	O
(	O
exposed	O
wafer	B-Architecture
area	O
underwater	O
)	O
Aberration	O
control	O
(	O
including	O
thermal	O
)	O
None	O
Yes	O
,	O
e.g.	O
,	O
FlexWaveY	O
.	O
</s>
<s>
As	O
of	O
2016	O
,	O
the	O
established	O
EUV	O
light	O
source	O
is	O
a	O
laser-pulsed	O
tin	B-Protocol
plasma	O
.	O
</s>
<s>
The	O
ions	O
absorb	O
the	O
EUV	O
light	O
they	O
emit	O
,	O
and	O
are	O
easily	O
neutralized	O
by	O
electrons	O
in	O
the	O
plasma	O
to	O
lower	O
charge	O
states	O
which	O
produce	O
light	O
mainly	O
at	O
other	O
,	O
unusable	O
wavelengths	O
,	O
which	O
results	O
in	O
a	O
much	O
reduced	O
efficiency	O
of	O
light	O
generation	O
for	O
lithography	B-Algorithm
at	O
higher	O
plasma	O
power	O
density	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
conventional	O
immersion	B-Algorithm
lithography	I-Algorithm
tools	O
for	O
double-patterning	O
provide	O
consistent	O
output	O
for	O
up	O
to	O
a	O
year	O
.	O
</s>
<s>
Due	O
to	O
the	O
use	O
of	O
EUV	O
mirrors	O
which	O
also	O
absorb	O
EUV	O
light	O
,	O
only	O
a	O
small	O
fraction	O
of	O
the	O
source	O
light	O
is	O
finally	O
available	O
at	O
the	O
wafer	B-Architecture
.	O
</s>
<s>
With	O
11	O
reflections	O
,	O
only	O
~	O
2%	O
of	O
the	O
EUV	O
source	O
light	O
is	O
available	O
at	O
the	O
wafer	B-Architecture
.	O
</s>
<s>
EUV	O
(	O
10	O
–	O
121nm	O
)	O
is	O
the	O
band	O
longer	O
than	O
X-rays	B-Library
(	O
0.1	O
–	O
10nm	O
)	O
and	O
shorter	O
than	O
the	O
hydrogen	O
Lyman-alpha	O
line	O
.	O
</s>
<s>
A	O
state-of-the-art	O
ArF	B-Algorithm
immersion	I-Algorithm
lithography	B-Algorithm
120	O
W	O
light	O
source	O
requires	O
no	O
more	O
than	O
40kW	O
while	O
EUV	O
sources	O
are	O
targeted	O
to	O
exceed	O
40kW	O
.	O
</s>
<s>
The	O
power	O
target	O
for	O
EUV	B-Algorithm
lithography	I-Algorithm
is	O
at	O
least	O
250	O
W	O
,	O
while	O
for	O
other	O
conventional	O
lithography	B-Algorithm
sources	O
,	O
it	O
is	O
much	O
less	O
.	O
</s>
<s>
For	O
example	O
,	O
immersion	B-Algorithm
lithography	I-Algorithm
light	O
sources	O
target	O
90	O
W	O
,	O
dry	O
ArF	O
sources	O
45	O
W	O
,	O
and	O
KrF	O
sources	O
40	O
W	O
.	O
High-NA	O
EUV	O
sources	O
are	O
expected	O
to	O
require	O
at	O
least	O
500	O
W	O
.	O
</s>
<s>
A	O
fundamental	O
aspect	O
of	O
EUVL	B-Algorithm
tools	O
,	O
resulting	O
from	O
the	O
use	O
of	O
reflective	O
optics	O
,	O
is	O
the	O
off-axis	B-Algorithm
illumination	I-Algorithm
(	O
at	O
an	O
angle	O
of	O
6	O
degrees	O
,	O
in	O
different	O
direction	O
at	O
different	O
positions	O
within	O
the	O
illumination	O
slit	O
)	O
on	O
a	O
multilayer	O
mask	O
.	O
</s>
<s>
Most	O
conspicuously	O
,	O
identically	O
sized	O
horizontal	O
and	O
vertical	O
lines	O
on	O
the	O
EUV	O
mask	O
are	O
printed	O
at	O
different	O
sizes	O
on	O
the	O
wafer	B-Architecture
.	O
</s>
<s>
One	O
of	O
EUVL	B-Algorithm
's	O
key	O
issues	O
is	O
the	O
asymmetry	O
between	O
the	O
top	O
and	O
bottom	O
line	O
of	O
a	O
pair	O
of	O
horizontal	O
lines	O
(	O
the	O
so-called	O
"	O
two-bar	O
"	O
)	O
.	O
</s>
<s>
The	O
use	O
of	O
reflection	O
causes	O
wafer	B-Architecture
exposure	O
position	O
to	O
be	O
extremely	O
sensitive	O
to	O
the	O
reticle	O
flatness	O
and	O
the	O
reticle	O
clamp	O
.	O
</s>
<s>
Small	O
(	O
mrad-scale	O
)	O
deviations	O
in	O
mask	O
flatness	O
in	O
the	O
local	O
slope	O
,	O
coupled	O
with	O
wafer	B-Architecture
defocus	O
.	O
</s>
<s>
The	O
off-axis	B-Algorithm
illumination	I-Algorithm
of	O
the	O
reticle	O
is	O
also	O
the	O
cause	O
of	O
non-telecentricity	O
in	O
wafer	B-Architecture
defocus	O
,	O
which	O
consumes	O
most	O
of	O
the	O
1.4nm	O
overlay	O
budget	O
of	O
the	O
NXE:3400	O
EUV	O
scanner	O
even	O
for	O
design	O
rules	O
as	O
loose	O
as	O
100nm	O
pitch	O
.	O
</s>
<s>
The	O
worst	O
uncorrectable	O
pattern	O
placement	O
error	O
for	O
a	O
24nm	O
line	O
was	O
about	O
1.1nm	O
,	O
relative	O
to	O
an	O
adjacent	O
72nm	O
power	O
line	O
,	O
per	O
80nm	O
wafer	B-Architecture
focus	O
position	O
shift	O
at	O
a	O
single	O
slit	O
position	O
;	O
when	O
across-slit	O
performance	O
is	O
included	O
,	O
the	O
worst	O
error	O
is	O
over	O
1.5nm	O
in	O
the	O
wafer	B-Architecture
defocus	O
window	O
In	O
2017	O
,	O
an	O
actinic	O
microscope	O
mimicking	O
a	O
0.33	O
NA	O
EUV	B-Algorithm
lithography	I-Algorithm
system	O
with	O
0.2/0.9	O
quasar	O
45	O
illumination	O
showed	O
that	O
an	O
80nm	O
pitch	O
contact	O
array	O
shifted	O
-0.6	O
to	O
1.0nm	O
while	O
a	O
56nm	O
pitch	O
contact	O
array	O
shifted	O
-1.7	O
to	O
1.0nm	O
relative	O
to	O
a	O
horizontal	O
reference	O
line	O
,	O
within	O
a	O
+	O
/	O
-	O
50nm	O
defocus	O
window	O
.	O
</s>
<s>
Wafer	B-Architecture
defocus	O
also	O
leads	O
to	O
image	O
placement	O
errors	O
due	O
to	O
deviations	O
from	O
local	O
mask	O
flatness	O
.	O
</s>
<s>
Simulations	O
as	O
well	O
as	O
experiments	O
have	O
shown	O
that	O
pupil	O
imbalances	O
in	O
EUV	B-Algorithm
lithography	I-Algorithm
can	O
result	O
in	O
pitch-dependent	O
pattern	O
placement	O
errors	O
.	O
</s>
<s>
The	O
rotating	O
plane	O
of	O
incidence	O
(	O
azimuthal	O
range	O
within	O
-25	O
°	O
to	O
25°	O
)	O
is	O
confirmed	O
in	O
the	O
SHARP	O
actinic	O
review	O
microscope	O
at	O
CXRO	O
which	O
mimics	O
the	O
optics	O
for	O
EUV	O
projection	O
lithography	B-Algorithm
systems	O
.	O
</s>
<s>
Unlike	O
DUV	O
lithography	B-Algorithm
sources	O
,	O
based	O
on	O
excimer	O
lasers	O
,	O
EUV	O
plasma	O
sources	O
produce	O
light	O
across	O
a	O
broad	O
range	O
of	O
wavelengths	O
roughly	O
spanning	O
a	O
2%	O
FWHM	O
bandwidth	O
near	O
13.5	O
nm	O
(	O
13.36nm	O
–	O
13.65nm	O
at	O
50%	O
power	O
)	O
.	O
</s>
<s>
EUV	O
(	O
10	O
–	O
121nm	O
)	O
is	O
the	O
band	O
longer	O
than	O
X-Rays	B-Library
(	O
0.1	O
–	O
10nm	O
)	O
and	O
shorter	O
than	O
the	O
hydrogen	O
Lyman-alpha	O
line	O
.	O
</s>
<s>
This	O
is	O
in	O
part	O
due	O
to	O
lower	O
image	O
contrast	O
for	O
the	O
binary	O
masks	O
used	O
in	O
EUV	B-Algorithm
lithography	I-Algorithm
,	O
which	O
is	O
not	O
encountered	O
with	O
the	O
use	O
of	O
phase	B-Algorithm
shift	I-Algorithm
masks	I-Algorithm
in	O
immersion	B-Algorithm
lithography	I-Algorithm
.	O
</s>
<s>
The	O
use	O
of	O
phase-shift	B-Algorithm
masks	I-Algorithm
in	O
EUV	B-Algorithm
lithography	I-Algorithm
has	O
been	O
studied	O
but	O
encounters	O
difficulties	O
from	O
phase	O
control	O
in	O
thin	O
layers	O
as	O
well	O
as	O
the	O
bandwidth	O
of	O
the	O
EUV	O
light	O
itself	O
.	O
</s>
<s>
More	O
conventionally	O
,	O
optical	B-Algorithm
proximity	I-Algorithm
correction	I-Algorithm
(	O
OPC	O
)	O
is	O
used	O
to	O
address	O
the	O
corner	O
rounding	O
and	O
line-end	O
shortening	O
.	O
</s>
<s>
For	O
the	O
40nm	O
pitch	O
vertical	O
lines	O
,	O
an	O
18nm	O
nominal	O
tip-to-tip	O
drawn	O
gap	O
resulted	O
in	O
an	O
actual	O
tip-to-tip	O
distance	O
of	O
29nm	O
with	O
OPC	O
(	O
optical	B-Algorithm
proximity	I-Algorithm
correction	I-Algorithm
)	O
,	O
while	O
for	O
32nm	O
pitch	O
horizontal	O
lines	O
,	O
the	O
tip-to-tip	O
distance	O
with	O
a	O
14nm	O
nominal	O
gap	O
went	O
to	O
31nm	O
with	O
OPC	O
.	O
</s>
<s>
For	O
this	O
situation	O
,	O
double	O
exposure	O
lithography	B-Algorithm
would	O
be	O
required	O
for	O
2D	O
patterns	O
,	O
due	O
to	O
the	O
presence	O
of	O
both	O
X	O
-	O
and	O
Y-oriented	O
patterns	O
,	O
each	O
requiring	O
its	O
own	O
1D	O
pattern	O
mask	O
and	O
dipole	O
orientation	O
.	O
</s>
<s>
At	O
each	O
slit	O
position	O
,	O
although	O
optical	B-Algorithm
proximity	I-Algorithm
correction	I-Algorithm
(	O
OPC	O
)	O
,	O
including	O
the	O
assist	O
features	O
mentioned	O
above	O
,	O
may	O
also	O
be	O
applied	O
to	O
address	O
the	O
aberrations	O
,	O
they	O
also	O
feedback	O
into	O
the	O
illumination	O
specification	O
,	O
since	O
the	O
benefits	O
differ	O
for	O
different	O
illumination	O
conditions	O
.	O
</s>
<s>
A	O
commonly	O
touted	O
advantage	O
of	O
EUV	O
has	O
been	O
the	O
relative	O
ease	O
of	O
lithography	B-Algorithm
,	O
as	O
indicated	O
by	O
the	O
ratio	O
of	O
feature	O
size	O
to	O
the	O
wavelength	O
multiplied	O
by	O
the	O
numerical	O
aperture	O
,	O
also	O
known	O
as	O
the	O
k1	O
ratio	O
.	O
</s>
<s>
For	O
the	O
k1	O
approaching	O
0.5	O
,	O
some	O
weak	O
resolution	O
enhancement	O
including	O
attenuated	B-Algorithm
phase	I-Algorithm
shift	I-Algorithm
masks	I-Algorithm
has	O
been	O
used	O
as	O
essential	O
to	O
production	O
with	O
the	O
ArF	O
laser	O
wavelength	O
(	O
193nm	O
)	O
,	O
whereas	O
this	O
resolution	O
enhancement	O
is	O
not	O
available	O
for	O
EUV	O
.	O
</s>
<s>
A	O
study	O
by	O
the	O
College	O
of	O
Nanoscale	O
Science	O
and	O
Engineering	O
(	O
CNSE	O
)	O
presented	O
at	O
the	O
2013	O
EUVL	B-Algorithm
Workshop	O
indicated	O
that	O
,	O
as	O
a	O
measure	O
of	O
EUV	O
photoelectron	O
and	O
secondary	O
electron	O
blur	O
,	O
50	O
–	O
100	O
eV	O
electrons	O
easily	O
penetrated	O
beyond	O
15nm	O
of	O
resist	O
thickness	O
(	O
PMMA	O
or	O
commercial	O
resist	O
)	O
,	O
indicating	O
more	O
than	O
30nm	O
range	O
of	O
resist	O
affected	O
centered	O
on	O
the	O
EUV	O
point	O
of	O
absorption	O
,	O
for	O
doses	O
exceeding	O
200	O
–	O
300	O
uC/cm2	O
.	O
</s>
<s>
The	O
dose-dependent	O
spread	O
of	O
secondary	O
electrons	O
was	O
also	O
known	O
before	O
from	O
electron	O
beam	O
lithography	B-Algorithm
.	O
</s>
<s>
Atomic	O
hydrogen	O
in	O
the	O
tool	O
chambers	O
is	O
used	O
to	O
clean	O
tin	B-Protocol
and	O
carbon	O
which	O
deposit	O
on	O
the	O
EUV	O
optical	O
surfaces	O
.	O
</s>
<s>
The	O
reaction	O
with	O
tin	B-Protocol
in	O
the	O
light	O
source	O
or	O
resist	O
or	O
on	O
an	O
optical	O
surface	O
to	O
form	O
volatile	O
SnH4	O
proceeds	O
via	O
the	O
reaction	O
:	O
</s>
<s>
However	O
,	O
overall	O
,	O
the	O
tin	B-Protocol
cleaning	O
efficiency	O
is	O
less	O
than	O
0.01	O
%	O
,	O
due	O
to	O
both	O
redeposition	O
and	O
hydrogen	O
desorption	O
,	O
leading	O
to	O
formation	O
of	O
hydrogen	O
molecules	O
at	O
the	O
expense	O
of	O
atomic	O
hydrogen	O
.	O
</s>
<s>
To	O
help	O
mitigate	O
the	O
above	O
effects	O
,	O
the	O
latest	O
EUV	O
tool	O
introduced	O
in	O
2017	O
,	O
the	O
NXE:3400B	O
,	O
features	O
a	O
membrane	O
that	O
separates	O
the	O
wafer	B-Architecture
from	O
the	O
projection	O
optics	O
of	O
the	O
tool	O
,	O
protecting	O
the	O
latter	O
from	O
outgassing	O
from	O
the	O
resist	O
on	O
the	O
wafer	B-Architecture
.	O
</s>
<s>
There	O
is	O
of	O
course	O
,	O
accumulated	O
contamination	O
from	O
wafer	B-Architecture
outgassing	O
as	O
well	O
as	O
particles	O
in	O
general	O
(	O
although	O
the	O
latter	O
are	O
out	O
of	O
focus	O
,	O
they	O
may	O
still	O
obstruct	O
light	O
)	O
.	O
</s>
<s>
Reducing	O
defects	O
on	O
extreme	O
ultraviolet	O
(	O
EUV	O
)	O
masks	O
is	O
currently	O
one	O
of	O
the	O
most	O
critical	O
issues	O
to	O
be	O
addressed	O
for	O
commercialization	O
of	O
EUV	B-Algorithm
lithography	I-Algorithm
.	O
</s>
<s>
IBM	O
and	O
Toppan	O
reported	O
at	O
Photomask	B-Algorithm
Japan	O
2015	O
that	O
smaller	O
defects	O
,	O
e.g.	O
,	O
50nm	O
size	O
,	O
can	O
have	O
10%	O
CD	O
impact	O
even	O
with	O
0.6nm	O
height	O
,	O
yet	O
remain	O
undetectable	O
.	O
</s>
<s>
Production	O
EUV	B-Algorithm
tools	I-Algorithm
need	O
a	O
pellicle	B-Algorithm
to	O
protect	O
the	O
mask	O
from	O
contamination	O
.	O
</s>
<s>
Without	O
pellicles	O
,	O
particle	O
adders	O
would	O
reduce	O
yield	O
,	O
which	O
has	O
not	O
been	O
an	O
issue	O
for	O
conventional	O
optical	B-Algorithm
lithography	I-Algorithm
with	O
193nm	O
light	O
and	O
pellicles	O
.	O
</s>
<s>
However	O
,	O
for	O
EUV	O
,	O
the	O
feasibility	O
of	O
pellicle	B-Algorithm
use	O
is	O
severely	O
challenged	O
,	O
due	O
to	O
the	O
required	O
thinness	O
of	O
the	O
shielding	O
films	O
to	O
prevent	O
excessive	O
EUV	O
absorption	O
.	O
</s>
<s>
Heating	O
of	O
the	O
EUV	O
mask	O
pellicle	B-Algorithm
(	O
film	O
temperature	O
up	O
to	O
750	O
K	O
for	O
80	O
W	O
incident	O
power	O
)	O
is	O
a	O
significant	O
concern	O
,	O
due	O
to	O
the	O
resulting	O
deformation	O
and	O
transmission	O
decrease	O
.	O
</s>
<s>
ASML	O
developed	O
a	O
70nm	O
thick	O
polysilicon	O
pellicle	B-Algorithm
membrane	O
,	O
which	O
allows	O
EUV	O
transmission	O
of	O
82%	O
;	O
however	O
,	O
less	O
than	O
half	O
of	O
the	O
membranes	O
survived	O
expected	O
EUV	O
power	O
levels	O
.	O
</s>
<s>
SiNx	O
pellicle	B-Algorithm
membranes	O
also	O
failed	O
at	O
82	O
W	O
equivalent	O
EUV	O
source	O
power	O
levels	O
.	O
</s>
<s>
At	O
target	O
250	O
W	O
levels	O
,	O
the	O
pellicle	B-Algorithm
is	O
expected	O
to	O
reach	O
686	O
degrees	O
Celsius	O
,	O
well	O
over	O
the	O
melting	O
point	O
of	O
aluminum	O
.	O
</s>
<s>
In	O
the	O
absence	O
of	O
pellicles	O
,	O
EUV	O
mask	O
cleanliness	O
would	O
have	O
to	O
be	O
checked	O
before	O
actual	O
product	O
wafers	B-Architecture
are	O
exposed	O
,	O
using	O
wafers	B-Architecture
specially	O
prepared	O
for	O
defect	O
inspection	O
.	O
</s>
<s>
These	O
wafers	B-Architecture
are	O
inspected	O
after	O
printing	O
for	O
repeating	O
defects	O
indicating	O
a	O
dirty	O
mask	O
;	O
if	O
any	O
are	O
found	O
,	O
the	O
mask	O
must	O
be	O
cleaned	O
and	O
another	O
set	O
of	O
inspection	O
wafers	B-Architecture
are	O
exposed	O
,	O
repeating	O
the	O
flow	O
until	O
the	O
mask	O
is	O
clean	O
.	O
</s>
<s>
Any	O
affected	O
product	O
wafers	B-Architecture
must	O
be	O
reworked	O
.	O
</s>
<s>
TSMC	O
reported	O
starting	O
limited	O
use	O
of	O
its	O
own	O
pellicle	B-Algorithm
in	O
2019	O
and	O
continuing	O
to	O
expand	O
afterwards	O
,	O
and	O
Samsung	O
is	O
planning	O
pellicle	B-Algorithm
introduction	O
in	O
2022	O
.	O
</s>
<s>
EUV	B-Algorithm
lithography	I-Algorithm
is	O
particularly	O
sensitive	O
to	O
stochastic	O
effects	O
.	O
</s>
<s>
The	O
resolution	O
of	O
EUV	B-Algorithm
lithography	I-Algorithm
for	O
the	O
future	O
faces	O
challenges	O
in	O
maintaining	O
throughput	O
,	O
i.e.	O
,	O
how	O
many	O
wafers	B-Architecture
are	O
processed	O
by	O
an	O
EUV	O
tool	O
per	O
day	O
.	O
</s>
<s>
Due	O
to	O
stochastic	O
considerations	O
,	O
the	O
IRDS	O
2022	O
lithography	B-Algorithm
roadmap	O
now	O
acknowledges	O
increasing	O
doses	O
for	O
smaller	O
feature	O
sizes	O
.	O
</s>
<s>
In	O
H2	O
2018	O
,	O
TSMC	O
confirmed	O
that	O
its	O
5nm	O
EUV	O
scheme	O
still	O
used	O
multi-patterning	B-Algorithm
,	O
also	O
indicating	O
that	O
mask	O
count	O
did	O
not	O
decrease	O
from	O
its	O
7nm	O
node	O
,	O
which	O
used	O
extensive	O
DUV	O
multi-patterning	B-Algorithm
,	O
to	O
its	O
5nm	O
node	O
,	O
which	O
used	O
extensive	O
EUV	O
.	O
</s>
<s>
EDA	O
vendors	O
also	O
indicated	O
the	O
continued	O
use	O
of	O
multi-patterning	B-Algorithm
flows	O
.	O
</s>
<s>
In	O
Intel	O
's	O
complementary	O
lithography	B-Algorithm
scheme	O
at	O
20nm	O
half-pitch	O
,	O
EUV	O
would	O
be	O
used	O
only	O
in	O
a	O
second	O
line-cutting	O
exposure	O
after	O
a	O
first	O
193nm	O
line-printing	O
exposure	O
.	O
</s>
<s>
However	O
,	O
the	O
0.55	O
NA	O
has	O
a	O
much	O
smaller	O
depth	O
of	O
focus	O
than	O
immersion	B-Algorithm
lithography	I-Algorithm
.	O
</s>
<s>
Also	O
,	O
an	O
anamorphic	O
0.52	O
NA	O
tool	O
has	O
been	O
found	O
to	O
exhibit	O
too	O
much	O
CD	O
and	O
placement	O
variability	O
for	O
5nm	O
node	O
single	O
exposure	O
and	O
multi-patterning	B-Algorithm
cutting	O
.	O
</s>
<s>
Depth	O
of	O
focus	O
being	O
reduced	O
by	O
increasing	O
NA	O
is	O
also	O
a	O
concern	O
,	O
especially	O
in	O
comparison	O
with	O
multi-patterning	B-Algorithm
exposures	O
using	O
193nm	O
immersion	B-Algorithm
lithography	I-Algorithm
:	O
</s>
<s>
High-NA	O
EUV	B-Algorithm
tools	I-Algorithm
also	O
suffer	O
from	O
obscuration	O
,	O
which	O
can	O
cause	O
errors	O
in	O
the	O
imaging	O
of	O
certain	O
patterns	O
.	O
</s>
