<s>
Deep	B-Algorithm
reactive-ion	I-Algorithm
etching	I-Algorithm
(	O
DRIE	B-Algorithm
)	O
is	O
a	O
highly	O
anisotropic	O
etch	B-Algorithm
process	O
used	O
to	O
create	O
deep	O
penetration	O
,	O
steep-sided	O
holes	O
and	O
trenches	O
in	O
wafers/substrates	O
,	O
typically	O
with	O
high	O
aspect	B-Device
ratios	I-Device
.	O
</s>
<s>
It	O
was	O
developed	O
for	O
microelectromechanical	B-Architecture
systems	I-Architecture
(	O
MEMS	B-Architecture
)	O
,	O
which	O
require	O
these	O
features	O
,	O
but	O
is	O
also	O
used	O
to	O
excavate	O
trenches	O
for	O
high-density	O
capacitors	O
for	O
DRAM	O
and	O
more	O
recently	O
for	O
creating	O
through	B-Algorithm
silicon	I-Algorithm
vias	I-Algorithm
(	O
TSVs	B-Algorithm
)	O
in	O
advanced	O
3D	O
wafer	B-Architecture
level	O
packaging	O
technology	O
.	O
</s>
<s>
In	O
DRIE	B-Algorithm
,	O
the	O
substrate	B-Architecture
is	O
placed	O
inside	O
a	O
reactor	O
,	O
and	O
several	O
gases	O
are	O
introduced	O
.	O
</s>
<s>
This	O
is	O
known	O
as	O
the	O
chemical	O
part	O
of	O
the	O
reactive	B-Algorithm
ion	I-Algorithm
etching	I-Algorithm
.	O
</s>
<s>
DRIE	B-Algorithm
is	O
a	O
special	O
subclass	O
of	O
RIE	O
.	O
</s>
<s>
There	O
are	O
two	O
main	O
technologies	O
for	O
high-rate	O
DRIE	B-Algorithm
:	O
cryogenic	O
and	O
Bosch	O
,	O
although	O
the	O
Bosch	O
process	O
is	O
the	O
only	O
recognised	O
production	O
technique	O
.	O
</s>
<s>
Another	O
mechanism	O
is	O
sidewall	O
passivation	B-Application
:	O
SiOxFy	O
functional	O
groups	O
(	O
which	O
originate	O
from	O
sulphur	O
hexafluoride	O
and	O
oxygen	O
etch	B-Algorithm
gases	O
)	O
condense	O
on	O
the	O
sidewalls	O
,	O
and	O
protect	O
them	O
from	O
lateral	O
etching	B-Algorithm
.	O
</s>
<s>
In	O
cryogenic-DRIE	O
,	O
the	O
wafer	B-Architecture
is	O
chilled	O
to	O
−110°C	O
(	O
163	O
K	B-Operating_System
)	O
.	O
</s>
<s>
The	O
low	O
temperature	O
slows	O
down	O
the	O
chemical	O
reaction	O
that	O
produces	O
isotropic	O
etching	B-Algorithm
.	O
</s>
<s>
However	O
,	O
ions	O
continue	O
to	O
bombard	O
upward-facing	O
surfaces	O
and	O
etch	B-Algorithm
them	O
away	O
.	O
</s>
<s>
The	O
primary	O
issues	O
with	O
cryo-DRIE	O
is	O
that	O
the	O
standard	O
masks	O
on	O
substrates	B-Architecture
crack	O
under	O
the	O
extreme	O
cold	O
,	O
plus	O
etch	B-Algorithm
by-products	O
have	O
a	O
tendency	O
of	O
depositing	O
on	O
the	O
nearest	O
cold	O
surface	O
,	O
i.e.	O
</s>
<s>
the	O
substrate	B-Architecture
or	O
electrode	O
.	O
</s>
<s>
The	O
Bosch	O
process	O
,	O
named	O
after	O
the	O
German	O
company	O
Robert	O
Bosch	O
GmbH	O
which	O
patented	O
the	O
process	O
,	O
also	O
known	O
as	O
pulsed	O
or	O
time-multiplexed	O
etching	B-Algorithm
,	O
alternates	O
repeatedly	O
between	O
two	O
modes	O
to	O
achieve	O
nearly	O
vertical	O
structures	O
:	O
</s>
<s>
A	O
standard	O
,	O
nearly	O
isotropic	O
plasma	B-Algorithm
etch	I-Algorithm
.	O
</s>
<s>
The	O
plasma	O
contains	O
some	O
ions	O
,	O
which	O
attack	O
the	O
wafer	B-Architecture
from	O
a	O
nearly	O
vertical	O
direction	O
.	O
</s>
<s>
Deposition	O
of	O
a	O
chemically	O
inert	O
passivation	B-Application
layer	I-Application
.	O
</s>
<s>
The	O
passivation	B-Application
layer	I-Application
protects	O
the	O
entire	O
substrate	B-Architecture
from	O
further	O
chemical	O
attack	O
and	O
prevents	O
further	O
etching	B-Algorithm
.	O
</s>
<s>
However	O
,	O
during	O
the	O
etching	B-Algorithm
phase	O
,	O
the	O
directional	O
ions	O
that	O
bombard	O
the	O
substrate	B-Architecture
attack	O
the	O
passivation	B-Application
layer	I-Application
at	O
the	O
bottom	O
of	O
the	O
trench	O
(	O
but	O
not	O
along	O
the	O
sides	O
)	O
.	O
</s>
<s>
They	O
collide	O
with	O
it	O
and	O
sputter	O
it	O
off	O
,	O
exposing	O
the	O
substrate	B-Architecture
to	O
the	O
chemical	O
etchant	O
.	O
</s>
<s>
These	O
etch/deposit	O
steps	O
are	O
repeated	O
many	O
times	O
over	O
resulting	O
in	O
a	O
large	O
number	O
of	O
very	O
small	O
isotropic	O
etch	B-Algorithm
steps	O
taking	O
place	O
only	O
at	O
the	O
bottom	O
of	O
the	O
etched	O
pits	O
.	O
</s>
<s>
To	O
etch	B-Algorithm
through	O
a	O
0.5mm	O
silicon	B-Architecture
wafer	I-Architecture
,	O
for	O
example	O
,	O
100	O
–	O
1000	O
etch/deposit	O
steps	O
are	O
needed	O
.	O
</s>
<s>
The	O
cycle	O
time	O
can	O
be	O
adjusted	O
:	O
short	O
cycles	O
yield	O
smoother	O
walls	O
,	O
and	O
long	O
cycles	O
yield	O
a	O
higher	O
etch	B-Algorithm
rate	O
.	O
</s>
<s>
in	O
MEMS	B-Architecture
,	O
DRIE	B-Algorithm
is	O
used	O
for	O
anything	O
from	O
a	O
few	O
micrometers	O
to	O
0.5mm	O
.	O
</s>
<s>
in	O
irregular	O
chip	O
dicing	O
,	O
DRIE	B-Algorithm
is	O
used	O
with	O
a	O
novel	O
hybrid	O
soft/hard	O
mask	O
to	O
achieve	O
sub-millimeter	O
etching	B-Algorithm
to	O
dice	O
silicon	O
dies	O
into	O
lego-like	O
pieces	O
with	O
irregular	O
shapes	O
.	O
</s>
<s>
in	O
flexible	O
electronics	O
,	O
DRIE	B-Algorithm
is	O
used	O
to	O
make	O
traditional	O
monolithic	O
CMOS	O
devices	O
flexible	O
by	O
reducing	O
the	O
thickness	O
of	O
silicon	O
substrates	B-Architecture
to	O
few	O
to	O
tens	O
of	O
micrometers	O
.	O
</s>
<s>
What	O
distinguishes	O
DRIE	B-Algorithm
from	O
RIE	O
is	O
etch	B-Algorithm
depth	O
:	O
Practical	O
etch	B-Algorithm
depths	O
for	O
RIE	O
(	O
as	O
used	O
in	O
IC	O
manufacturing	O
)	O
would	O
be	O
limited	O
to	O
around	O
10µm	O
at	O
a	O
rate	O
up	O
to	O
1µm/min	O
,	O
while	O
DRIE	B-Algorithm
can	O
etch	B-Algorithm
features	O
much	O
greater	O
,	O
up	O
to	O
600µm	O
or	O
more	O
with	O
rates	O
up	O
to	O
20µm/min	O
or	O
more	O
in	O
some	O
applications	O
.	O
</s>
<s>
DRIE	B-Algorithm
of	O
glass	O
requires	O
high	O
plasma	O
power	O
,	O
which	O
makes	O
it	O
difficult	O
to	O
find	O
suitable	O
mask	O
materials	O
for	O
truly	O
deep	O
etching	B-Algorithm
.	O
</s>
<s>
In	O
DRIE	B-Algorithm
of	O
polymers	O
,	O
Bosch	O
process	O
with	O
alternating	O
steps	O
of	O
SF6	O
etching	B-Algorithm
and	O
C4F8	O
passivation	B-Application
take	O
place	O
.	O
</s>
<s>
Metal	O
masks	O
are	O
not	O
necessary	O
however	O
on	O
various	O
substrates	B-Architecture
(	O
Si	O
[	O
up	O
to	O
800µm ]	O
,	O
InP	O
[	O
up	O
to	O
40µm ]	O
or	O
glass	O
[	O
up	O
to	O
12µm ]	O
)	O
if	O
using	O
chemically	O
amplified	O
negative	O
resists	O
.	O
</s>
<s>
Gallium	O
ion	O
implantion	O
can	O
be	O
used	O
as	O
etch	B-Algorithm
mask	O
in	O
cryo-DRIE	O
.	O
</s>
<s>
Combined	O
nanofabrication	O
process	O
of	O
focused	O
ion	O
beam	O
and	O
cryo-DRIE	O
was	O
first	O
reported	O
by	O
N	O
Chekurov	O
et	O
al	O
in	O
their	O
article	O
"	O
The	O
fabrication	O
of	O
silicon	O
nanostructures	O
by	O
local	O
gallium	O
implantation	O
and	O
cryogenic	O
deep	B-Algorithm
reactive	I-Algorithm
ion	I-Algorithm
etching	I-Algorithm
"	O
.	O
</s>
<s>
DRIE	B-Algorithm
has	O
enabled	O
the	O
use	O
of	O
silicon	O
mechanical	O
components	O
in	O
high-end	O
wristwatches	O
.	O
</s>
<s>
According	O
to	O
an	O
engineer	O
at	O
Cartier	O
,	O
“	O
There	O
is	O
no	O
limit	O
to	O
geometric	O
shapes	O
with	O
DRIE	B-Algorithm
,	O
”	O
.	O
</s>
<s>
With	O
DRIE	B-Algorithm
it	O
is	O
possible	O
to	O
obtain	O
an	O
aspect	B-Device
ratio	I-Device
of	O
30	O
or	O
more	O
,	O
meaning	O
that	O
a	O
surface	O
can	O
be	O
etched	O
with	O
a	O
vertical-walled	O
trench	O
30	O
times	O
deeper	O
than	O
its	O
width	O
.	O
</s>
