<s>
Multiple	B-Algorithm
patterning	I-Algorithm
(	O
or	O
multi-patterning	B-Algorithm
)	O
is	O
a	O
class	O
of	O
technologies	O
for	O
manufacturing	O
integrated	O
circuits	O
(	O
ICs	O
)	O
,	O
developed	O
for	O
photolithography	B-Algorithm
to	O
enhance	O
the	O
feature	O
density	O
.	O
</s>
<s>
It	O
is	O
expected	O
to	O
be	O
necessary	O
for	O
the	O
10nm	O
and	O
7nm	B-Algorithm
node	O
semiconductor	O
processes	O
and	O
beyond	O
.	O
</s>
<s>
Even	O
for	O
electron-beam	B-Architecture
lithography	I-Architecture
,	O
single	O
exposure	O
appears	O
insufficient	O
at	O
~	O
10nm	O
half-pitch	O
,	O
hence	O
requiring	O
double	B-Algorithm
patterning	I-Algorithm
.	O
</s>
<s>
Double	B-Algorithm
patterning	I-Algorithm
lithography	O
was	O
first	O
demonstrated	O
in	O
1983	O
by	O
D.C.	O
Flanders	O
and	O
N.N.	O
</s>
<s>
Since	O
then	O
several	O
double	B-Algorithm
patterning	I-Algorithm
techniques	O
have	O
been	O
developed	O
such	O
as	O
self	O
alignment	O
double	B-Algorithm
patterning	I-Algorithm
(	O
SADP	O
)	O
and	O
a	O
litho-only	O
approach	O
to	O
double	B-Algorithm
patterning	I-Algorithm
.	O
</s>
<s>
Pitch	O
double-patterning	O
was	O
pioneered	O
by	O
Gurtej	O
Singh	O
Sandhu	O
of	O
Micron	O
Technology	O
during	O
the	O
2000s	O
,	O
leading	O
to	O
the	O
development	O
of	O
30-nm	B-Algorithm
class	O
NAND	O
flash	O
memory	O
.	O
</s>
<s>
Multi-patterning	B-Algorithm
has	O
since	O
been	O
widely	O
adopted	O
by	O
NAND	O
flash	O
and	O
random-access	B-Architecture
memory	I-Architecture
manufacturers	O
worldwide	O
.	O
</s>
<s>
There	O
are	O
a	O
number	O
of	O
situations	O
which	O
lead	O
to	O
multiple	B-Algorithm
patterning	I-Algorithm
being	O
required	O
.	O
</s>
<s>
The	O
most	O
obvious	O
case	O
requiring	O
multiple	B-Algorithm
patterning	I-Algorithm
is	O
when	O
the	O
feature	O
pitch	O
is	O
below	O
the	O
resolution	O
limit	O
of	O
the	O
optical	O
projection	O
system	O
.	O
</s>
<s>
The	O
resolution	O
limit	O
may	O
also	O
originate	O
from	O
stochastic	O
effects	O
,	O
as	O
in	O
the	O
case	O
of	O
EUV	B-Algorithm
.	O
</s>
<s>
Consequently	O
,	O
20	O
nm	O
linewidth	O
still	O
requires	O
EUV	B-Algorithm
double	B-Algorithm
patterning	I-Algorithm
,	O
due	O
to	O
larger	O
defectivity	O
at	O
larger	O
pitches	O
.	O
</s>
<s>
Hence	O
,	O
for	O
the	O
EUV-targeted	O
7nm	B-Algorithm
node	O
,	O
with	O
an	O
18	O
nm	O
metal	O
linewidth	O
(	O
k1	O
=	O
0.44	O
for	O
λ	O
=	O
13.5	O
nm	O
,	O
NA	O
=	O
0.33	O
)	O
,	O
the	O
line	O
tip	O
gap	O
of	O
less	O
than	O
25	O
nm	O
(	O
k1	O
=	O
0.61	O
)	O
entails	O
EUV	B-Algorithm
single	O
patterning	O
is	O
not	O
sufficient	O
;	O
a	O
second	O
cut	O
exposure	O
is	O
necessary	O
.	O
</s>
<s>
The	O
earliest	O
implementation	O
of	O
multiple	B-Algorithm
patterning	I-Algorithm
involved	O
line	O
cutting	O
.	O
</s>
<s>
EUV	B-Algorithm
stochastic	O
variability	O
causes	O
random	O
shaping	O
of	O
the	O
cuts	O
.	O
</s>
<s>
The	O
earliest	O
form	O
of	O
multiple	B-Algorithm
patterning	I-Algorithm
involved	O
simply	O
dividing	O
a	O
pattern	O
into	O
two	O
or	O
three	O
parts	O
,	O
each	O
of	O
which	O
may	O
be	O
processed	O
conventionally	O
,	O
with	O
the	O
entire	O
pattern	O
combined	O
at	O
the	O
end	O
in	O
the	O
final	O
layer	O
.	O
</s>
<s>
A	O
first	O
exposure	O
of	O
photoresist	O
is	O
transferred	O
to	O
an	O
underlying	O
hardmask	B-Algorithm
layer	O
.	O
</s>
<s>
After	O
the	O
photoresist	O
is	O
removed	O
following	O
the	O
hardmask	B-Algorithm
pattern	O
transfer	O
,	O
a	O
second	O
layer	O
of	O
photoresist	O
is	O
coated	O
onto	O
the	O
sample	O
and	O
this	O
layer	O
undergoes	O
a	O
second	O
exposure	O
,	O
imaging	O
features	O
in	O
between	O
the	O
features	O
patterned	O
in	O
the	O
hardmask	B-Algorithm
layer	O
.	O
</s>
<s>
A	O
variation	O
on	O
this	O
approach	O
which	O
eliminates	O
the	O
first	O
hardmask	B-Algorithm
etch	O
is	O
resist	O
freezing	O
,	O
which	O
allows	O
a	O
second	O
resist	O
coating	O
over	O
the	O
first	O
developed	O
resist	O
layer	O
.	O
</s>
<s>
JSR	O
has	O
demonstrated	O
32nm	B-Algorithm
lines	O
and	O
spaces	O
using	O
this	O
method	O
,	O
where	O
the	O
freezing	O
is	O
accomplished	O
by	O
surface	O
hardening	O
of	O
the	O
first	O
resist	O
layer	O
.	O
</s>
<s>
In	O
spacer	B-Algorithm
patterning	I-Algorithm
,	O
a	O
spacer	O
is	O
a	O
film	O
layer	O
formed	O
on	O
the	O
sidewall	O
of	O
a	O
pre-patterned	O
feature	O
.	O
</s>
<s>
This	O
is	O
commonly	O
referred	O
to	O
as	O
self-aligned	O
double	B-Algorithm
patterning	I-Algorithm
(	O
SADP	O
)	O
.	O
</s>
<s>
Many	O
approaches	O
for	O
spacer	B-Algorithm
patterning	I-Algorithm
have	O
been	O
published	O
(	O
some	O
listed	O
below	O
)	O
,	O
all	O
targeting	O
the	O
improved	O
management	O
(	O
and	O
reduction	O
)	O
of	O
the	O
cuts	O
.	O
</s>
<s>
As	O
spacer	O
materials	O
are	O
commonly	O
hardmask	B-Algorithm
materials	O
,	O
their	O
post-etch	O
pattern	O
quality	O
tends	O
to	O
be	O
superior	O
compared	O
to	O
photoresist	O
profiles	O
after	O
etch	O
,	O
which	O
are	O
generally	O
plagued	O
by	O
line	O
edge	O
roughness	O
.	O
</s>
<s>
With	O
76nm	O
being	O
the	O
expected	O
minimum	O
pitch	O
for	O
a	O
single	O
immersion	B-Algorithm
lithography	I-Algorithm
exposure	O
,	O
19nm	O
pitch	O
is	O
now	O
accessible	O
with	O
SAQP	O
.	O
</s>
<s>
It	O
makes	O
use	O
of	O
the	O
intersection	O
of	O
an	O
enlarged	O
feature	O
resist	O
mask	O
and	O
underlying	O
trenches	O
which	O
are	O
surrounded	O
by	O
a	O
pre-patterned	O
hardmask	B-Algorithm
layer	O
.	O
</s>
<s>
Since	O
32nm	B-Algorithm
node	O
,	O
Intel	O
has	O
applied	O
the	O
above-mentioned	O
self-aligned	O
via	O
approach	O
,	O
which	O
allows	O
two	O
vias	O
separated	O
by	O
a	O
small	O
enough	O
pitch	O
(	O
112.5nm	O
for	O
Intel	O
32nm	B-Algorithm
metal	O
)	O
to	O
be	O
patterned	O
with	O
one	O
resist	O
opening	O
instead	O
of	O
two	O
separate	O
ones	O
.	O
</s>
<s>
In	O
self-aligned	O
double	B-Algorithm
patterning	I-Algorithm
(	O
SADP	O
)	O
,	O
the	O
number	O
of	O
cut/block	O
masks	O
may	O
be	O
reduced	O
or	O
even	O
eliminated	O
in	O
dense	O
patches	O
when	O
the	O
spacer	O
is	O
used	O
to	O
directly	O
pattern	O
inter-metal	O
dielectric	O
instead	O
of	O
metal	O
features	O
.	O
</s>
<s>
Each	O
iteration	O
of	O
spacer	B-Algorithm
patterning	I-Algorithm
triples	O
the	O
density	O
,	O
effectively	O
reducing	O
2D	O
pitch	O
by	O
a	O
factor	O
of	O
sqrt(3 )	O
.	O
</s>
<s>
The	O
number	O
of	O
masks	O
used	O
for	O
sidewall	O
spacer	B-Algorithm
patterning	I-Algorithm
may	O
be	O
reduced	O
with	O
the	O
use	O
of	O
directed	O
self-assembly	O
(	O
DSA	O
)	O
due	O
to	O
the	O
provision	O
of	O
gridded	O
cuts	O
all	O
at	O
once	O
within	O
a	O
printed	O
area	O
,	O
which	O
can	O
then	O
be	O
selected	O
with	O
a	O
final	O
exposure	O
.	O
</s>
<s>
There	O
have	O
been	O
numerous	O
concerns	O
that	O
multiple	B-Algorithm
patterning	I-Algorithm
diminishes	O
or	O
even	O
reverses	O
the	O
node-to-node	O
cost	O
reduction	O
expected	O
with	O
Moore	O
's	O
Law	O
.	O
</s>
<s>
EUV	B-Algorithm
is	O
more	O
expensive	O
than	O
three	O
193i	O
exposures	O
(	O
i.e.	O
,	O
LELELE	O
)	O
,	O
considering	O
the	O
throughput	O
.	O
</s>
<s>
Moreover	O
,	O
EUV	B-Algorithm
is	O
more	O
liable	O
to	O
print	O
smaller	O
mask	O
defects	O
not	O
resolvable	O
by	O
193i	O
.	O
</s>
<s>
Some	O
aspects	O
of	O
other	O
considered	O
multi-patterning	B-Algorithm
techniques	O
are	O
discussed	O
below	O
.	O
</s>
<s>
Tilted	O
ion	O
implantation	O
was	O
proposed	O
in	O
2016	O
by	O
the	O
University	O
of	O
Berkeley	O
as	O
an	O
alternative	O
method	O
of	O
achieving	O
the	O
same	O
result	O
as	O
spacer	B-Algorithm
patterning	I-Algorithm
.	O
</s>
<s>
The	O
method	O
of	O
complementary	O
exposures	O
is	O
another	O
way	O
of	O
reducing	O
mask	O
exposures	O
for	O
multiple	B-Algorithm
patterning	I-Algorithm
.	O
</s>
<s>
This	O
approach	O
was	O
also	O
implemented	O
by	O
IMEC	O
as	O
two	O
"	O
keep	O
"	O
masks	O
for	O
the	O
M0A	O
layer	O
in	O
their	O
7nm	B-Algorithm
SRAM	O
cell	O
.	O
</s>
<s>
Cut-friendly	O
layouts	O
are	O
processed	O
with	O
the	O
same	O
minimum	O
number	O
of	O
masks	O
(	O
3	O
)	O
,	O
regardless	O
of	O
using	O
DUV	O
or	O
EUV	B-Algorithm
wavelength	O
.	O
</s>
<s>
Although	O
EUV	B-Algorithm
has	O
been	O
projected	O
to	O
be	O
the	O
next-generation	B-Algorithm
lithography	I-Algorithm
of	O
choice	O
,	O
it	O
could	O
still	O
require	O
more	O
than	O
one	O
lithographic	O
exposure	O
,	O
due	O
to	O
the	O
foreseen	O
need	O
to	O
first	O
print	O
a	O
series	O
of	O
lines	O
and	O
then	O
cut	O
them	O
;	O
a	O
single	O
EUV	B-Algorithm
exposure	O
pattern	O
has	O
difficulty	O
with	O
line	O
end-to-end	O
spacing	O
control	O
.	O
</s>
<s>
The	O
existing	O
0.33	O
NA	O
EUV	B-Algorithm
tools	I-Algorithm
are	O
challenged	O
below	O
16nm	O
half-pitch	O
resolution	O
.	O
</s>
<s>
Consequently	O
,	O
EUV	B-Algorithm
2D	O
patterning	O
is	O
limited	O
to	O
>32nm	O
pitch	O
.	O
</s>
<s>
Recent	O
studies	O
of	O
optimizing	O
the	O
EUV	B-Algorithm
mask	O
features	O
and	O
the	O
illumination	O
shape	O
simultaneously	O
have	O
indicated	O
that	O
different	O
patterns	O
in	O
the	O
same	O
metal	O
layer	O
could	O
require	O
different	O
illuminations	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
a	O
cross-pitch	O
source-mask	O
optimization	O
for	O
7nm	B-Algorithm
node	O
,	O
for	O
40-48nm	O
pitch	O
and	O
32nm	B-Algorithm
pitch	O
,	O
the	O
quality	O
as	O
determined	O
by	O
the	O
normalized	O
image	O
log	O
slope	O
was	O
insufficient	O
(	O
NILS	O
<	O
2	O
)	O
,	O
while	O
only	O
36nm	O
pitch	O
was	O
barely	O
satisfactory	O
for	O
bidirectional	O
single	O
exposure	O
.	O
</s>
<s>
The	O
underlying	O
situation	O
is	O
that	O
EUV	B-Algorithm
patterns	O
may	O
be	O
split	O
according	O
to	O
different	O
illuminations	O
for	O
different	O
pitches	O
,	O
or	O
different	O
pattern	O
types	O
(	O
e.g.	O
,	O
staggered	O
arrays	O
vs.	O
regular	O
arrays	O
)	O
.	O
</s>
<s>
It	O
is	O
also	O
likely	O
more	O
than	O
one	O
cut	O
would	O
be	O
needed	O
,	O
even	O
for	O
EUV	B-Algorithm
.	O
</s>
<s>
At	O
the	O
2016	O
EUVL	B-Algorithm
Workshop	O
,	O
ASML	O
reported	O
that	O
the	O
0.33	O
NA	O
NXE	O
EUV	B-Algorithm
tools	I-Algorithm
would	O
not	O
be	O
capable	O
of	O
standard	O
single	O
exposure	O
patterning	O
for	O
the	O
11-13nm	O
half-pitch	O
expected	O
at	O
the	O
5nm	O
node	O
.	O
</s>
<s>
A	O
higher	O
NA	O
of	O
0.55	O
would	O
allow	O
single	O
exposure	O
EUV	B-Algorithm
patterning	O
of	O
fields	O
which	O
are	O
half	O
the	O
26mm	O
x	O
33mm	O
standard	O
field	O
size	O
.	O
</s>
<s>
For	O
2x-nm	O
DRAM	O
and	O
flash	O
,	O
double	B-Algorithm
patterning	I-Algorithm
techniques	O
should	O
be	O
sufficient	O
.	O
</s>
<s>
Current	O
EUV	B-Algorithm
throughput	O
is	O
still	O
more	O
than	O
3x	O
slower	O
than	O
193nm	O
immersion	B-Algorithm
lithography	I-Algorithm
,	O
thus	O
allowing	O
the	O
latter	O
to	O
be	O
extended	O
by	O
multiple	B-Algorithm
patterning	I-Algorithm
.	O
</s>
<s>
Furthermore	O
,	O
the	O
lack	O
of	O
an	O
EUV	B-Algorithm
pellicle	O
is	O
also	O
prohibitive	O
.	O
</s>
<s>
TSMC	O
is	O
deploying	O
7nm	B-Algorithm
in	O
2017	O
with	O
multiple	B-Algorithm
patterning	I-Algorithm
;	O
specifically	O
,	O
pitch-splitting	O
,	O
down	O
to	O
40nm	O
pitch	O
.	O
</s>
<s>
Beyond	O
the	O
5nm	O
node	O
,	O
multiple	B-Algorithm
patterning	I-Algorithm
,	O
even	O
with	O
EUV	B-Algorithm
assistance	O
,	O
would	O
be	O
economically	O
challenging	O
,	O
since	O
the	O
departure	O
from	O
EUV	B-Algorithm
single	O
exposure	O
would	O
drive	O
up	O
the	O
cost	O
even	O
higher	O
.	O
</s>
<s>
However	O
,	O
at	O
least	O
down	O
to	O
12nm	O
half-pitch	O
,	O
LELE	O
followed	O
by	O
SADP	O
(	O
SID	O
)	O
appears	O
to	O
be	O
a	O
promising	O
approach	O
,	O
using	O
only	O
two	O
masks	O
,	O
and	O
also	O
using	O
the	O
most	O
mature	O
double	B-Algorithm
patterning	I-Algorithm
techniques	O
,	O
LELE	O
and	O
SADP	O
.	O
</s>
<s>
Compared	O
to	O
193i	O
SADP	O
,	O
EUV	B-Algorithm
SADP	O
cost	O
is	O
dominated	O
by	O
the	O
EUV	B-Algorithm
tool	O
exposure	O
,	O
while	O
the	O
193i	O
SAQP	O
cost	O
difference	O
is	O
from	O
the	O
added	O
depositions	O
and	O
etches	O
.	O
</s>
<s>
EUV	B-Algorithm
further	O
suffers	O
from	O
the	O
shot	O
noise	O
limit	O
,	O
which	O
forces	O
the	O
dose	O
to	O
increase	O
going	O
for	O
successive	O
nodes.F.	O
</s>
<s>
Even	O
with	O
the	O
introduction	O
of	O
EUV	B-Algorithm
technology	O
in	O
some	O
cases	O
,	O
multiple	B-Algorithm
patterning	I-Algorithm
has	O
continued	O
to	O
be	O
implemented	O
in	O
the	O
majority	O
of	O
layers	O
being	O
produced	O
.	O
</s>
<s>
For	O
example	O
,	O
quadruple	O
patterning	O
continues	O
to	O
be	O
used	O
for	O
7nm	B-Algorithm
by	O
Samsung	O
.	O
</s>
<s>
TSMC	O
's	O
7nm+	O
process	O
also	O
makes	O
use	O
of	O
EUV	B-Algorithm
in	O
a	O
multi-patterning	B-Algorithm
context.Mentor	O
extends	O
7nm	B-Algorithm
FinFET	O
Plus	O
support	O
Only	O
a	O
few	O
layers	O
are	O
affected	O
anyway	O
;	O
TSMC	O
2019	O
Q2	O
earnings	O
call	O
many	O
remain	O
conventional	O
multi-patterning	B-Algorithm
.	O
</s>
<s>
The	O
mask	O
cost	O
strongly	O
benefits	O
from	O
the	O
use	O
of	O
multiple	B-Algorithm
patterning	I-Algorithm
.	O
</s>
<s>
The	O
EUV	B-Algorithm
single	O
exposure	O
mask	O
has	O
smaller	O
features	O
which	O
take	O
much	O
longer	O
to	O
write	O
than	O
the	O
immersion	O
mask	O
.	O
</s>
<s>
Tool	O
EUV	B-Algorithm
EUV	B-Algorithm
Immersion	O
Immersion	O
WPH	O
(	O
wafers	O
per	O
hour	O
)	O
85	O
85	O
275	O
275#	O
tools	O
6	O
6	O
24Samsung	O
receives	O
24	O
immersion	O
tools	O
from	O
ASML	O
in	O
2010	O
24	O
uptime	O
70%	O
70%	O
90%	O
90%	O
#	O
passes	O
1	O
2	O
2	O
4	O
WPM	O
(	O
wafers	O
per	O
month	O
)	O
257,040	O
128,520	O
2,138,400	O
1,069,200	O
normalized	O
WPM	O
1	O
0.5	O
8	O
4Note	O
:	O
WPM	O
=	O
WPH	O
*	O
#	O
tools	O
*	O
uptime	O
/	O
#	O
passes	O
*	O
24	O
hrs/day	O
*	O
30	O
days/month	O
.	O
</s>
<s>
Multiple	B-Algorithm
patterning	I-Algorithm
with	O
immersion	O
scanners	O
can	O
be	O
expected	O
to	O
have	O
higher	O
wafer	O
productivity	O
than	O
EUV	B-Algorithm
,	O
even	O
with	O
as	O
many	O
as	O
4	O
passes	O
per	O
layer	O
,	O
due	O
to	O
faster	O
wafer	O
exposure	O
throughput	O
(	O
WPH	O
)	O
,	O
a	O
larger	O
number	O
of	O
tools	O
being	O
available	O
,	O
and	O
higher	O
uptime	O
.	O
</s>
<s>
Multiple	B-Algorithm
patterning	I-Algorithm
entails	O
the	O
use	O
of	O
many	O
processing	O
steps	O
to	O
form	O
a	O
patterned	O
layer	O
,	O
where	O
conventionally	O
only	O
one	O
lithographic	O
exposure	O
,	O
one	O
deposition	O
sequence	O
and	O
one	O
etch	O
sequence	O
would	O
be	O
sufficient	O
.	O
</s>
<s>
Consequently	O
,	O
there	O
are	O
more	O
sources	O
of	O
variations	O
and	O
possible	O
yield	O
loss	O
in	O
multiple	B-Algorithm
patterning	I-Algorithm
.	O
</s>
<s>
Multiple	B-Algorithm
patterning	I-Algorithm
is	O
evolving	O
toward	O
a	O
combination	O
of	O
multiple	O
exposures	O
,	O
spacer	B-Algorithm
patterning	I-Algorithm
,	O
and/or	O
EUV	B-Algorithm
.	O
</s>
<s>
Especially	O
with	O
tip-to-tip	O
scaling	O
being	O
difficult	O
in	O
a	O
single	O
exposure	O
on	O
current	O
EUV	B-Algorithm
tools	I-Algorithm
,	O
a	O
line-cutting	O
approach	O
may	O
be	O
necessary	O
.	O
</s>
<s>
IMEC	O
reported	O
that	O
double	B-Algorithm
patterning	I-Algorithm
is	O
becoming	O
a	O
requirement	O
for	O
EUV	B-Algorithm
.	O
</s>
<s>
For	O
line	O
patterning	O
,	O
SADP/SAQP	O
could	O
have	O
the	O
advantage	O
over	O
the	O
EUV	B-Algorithm
exposure	O
,	O
due	O
to	O
cost	O
and	O
maturity	O
of	O
the	O
former	O
approach	O
and	O
stochastic	O
missing	O
or	O
bridging	O
feature	O
issues	O
of	O
the	O
latter	O
.	O
</s>
<s>
For	O
grid	O
location	O
patterning	O
,	O
a	O
single	O
DUV	O
exposure	O
following	O
grid	O
formation	O
also	O
has	O
the	O
cost	O
and	O
maturity	O
advantages	O
(	O
e.g.	O
,	O
immersion	B-Algorithm
lithography	I-Algorithm
may	O
not	O
even	O
be	O
necessary	O
for	O
the	O
spacer	B-Algorithm
patterning	I-Algorithm
in	O
some	O
cases	O
)	O
and	O
no	O
stochastic	O
concerns	O
associated	O
with	O
EUV	B-Algorithm
.	O
</s>
<s>
Self-aligned	O
litho-etch-litho-etch	O
(	O
SALELE	O
)	O
is	O
a	O
hybrid	O
SADP/LELE	O
technique	O
whose	O
implementation	O
has	O
started	O
in	O
7nm	B-Algorithm
and	O
continued	O
use	O
in	O
5nm	O
.	O
</s>
<s>
The	O
evolution	O
of	O
multiple	B-Algorithm
patterning	I-Algorithm
is	O
being	O
considered	O
in	O
parallel	O
with	O
the	O
emergence	O
of	O
EUV	B-Algorithm
lithography	I-Algorithm
.	O
</s>
<s>
While	O
EUV	B-Algorithm
lithography	I-Algorithm
satisfies	O
10-20	O
nm	O
resolution	O
by	O
basic	O
optical	O
considerations	O
,	O
the	O
occurrence	O
of	O
stochastic	O
defects	O
as	O
well	O
as	O
other	O
infrastructure	O
gaps	O
and	O
throughput	O
considerations	O
prevent	O
its	O
adoption	O
currently	O
.	O
</s>
<s>
Consequently	O
,	O
7nm	B-Algorithm
tapeouts	O
have	O
largely	O
proceeded	O
without	O
EUV	B-Algorithm
.	O
</s>
<s>
In	O
other	O
words	O
,	O
the	O
multiple	B-Algorithm
patterning	I-Algorithm
is	O
not	O
prohibitive	O
,	O
but	O
more	O
like	O
a	O
nuisance	O
and	O
growing	O
expense	O
.	O
</s>
<s>
5nm	O
may	O
be	O
expected	O
in	O
2020	O
,	O
with	O
the	O
evolution	O
of	O
multiple	B-Algorithm
patterning	I-Algorithm
and	O
status	O
of	O
EUV	B-Algorithm
considered	O
at	O
that	O
time	O
.	O
</s>
<s>
Like	O
NAND	O
Flash	O
,	O
DRAM	O
has	O
also	O
made	O
regular	O
use	O
of	O
multiple	B-Algorithm
patterning	I-Algorithm
.	O
</s>
<s>
When	O
the	O
active	O
area	O
long	O
pitch	O
is	O
~	O
3.5	O
x	O
the	O
short	O
pitch	O
,	O
the	O
breaks	O
in	O
the	O
active	O
area	O
form	O
a	O
hexagonal	O
array	O
,	O
which	O
is	O
amenable	O
to	O
the	O
triangular	O
lattice	O
spacer	B-Algorithm
patterning	I-Algorithm
mentioned	O
above	O
.	O
</s>
<s>
While	O
it	O
does	O
not	O
scale	O
so	O
aggressively	O
laterally	O
,	O
the	O
use	O
of	O
string	O
stacking	O
in	O
3D	O
NAND	O
would	O
imply	O
the	O
use	O
of	O
multiple	B-Algorithm
patterning	I-Algorithm
(	O
litho-etch	O
style	O
)	O
to	O
pattern	O
the	O
vertical	O
channels	O
.	O
</s>
<s>
EUV	B-Algorithm
multiple	B-Algorithm
patterning	I-Algorithm
is	O
not	O
ruled	O
out	O
,	O
especially	O
for	O
5nm	O
node	O
.	O
</s>
<s>
When	O
minimum	O
pitch	O
is	O
reduced	O
to	O
32	B-Algorithm
nm	I-Algorithm
or	O
less	O
,	O
stochastic	O
defects	O
are	O
prevalent	O
enough	O
to	O
reconsider	O
double	B-Algorithm
patterning	I-Algorithm
at	O
larger	O
design	O
widths	O
.	O
</s>
<s>
At	O
pitches	O
of	O
~	O
30	O
nm	O
or	O
less	O
,	O
the	O
illumination	O
is	O
also	O
restricted	O
to	O
extremely	O
low	O
pupil	O
fills	O
below	O
20%	O
,	O
which	O
causes	O
a	O
significant	O
portion	O
of	O
the	O
EUV	B-Algorithm
source	O
power	O
to	O
be	O
unused	O
.	O
</s>
<s>
Hence	O
,	O
multiple	B-Algorithm
patterning	I-Algorithm
for	O
EUV	B-Algorithm
at	O
wider	O
design	O
rules	O
is	O
presently	O
a	O
practical	O
consideration	O
for	O
both	O
yield	O
and	O
throughput	O
reasons	O
.	O
</s>
