<s>
Reactive-ion	B-Algorithm
etching	I-Algorithm
(	O
RIE	O
)	O
is	O
an	O
etching	B-Algorithm
technology	O
used	O
in	O
microfabrication	O
.	O
</s>
<s>
RIE	O
is	O
a	O
type	O
of	O
dry	B-Algorithm
etching	I-Algorithm
which	O
has	O
different	O
characteristics	O
than	O
wet	O
etching	B-Algorithm
.	O
</s>
<s>
RIE	O
uses	O
chemically	O
reactive	O
plasma	O
to	O
remove	O
material	O
deposited	O
on	O
wafers	B-Architecture
.	O
</s>
<s>
The	O
plasma	O
is	O
generated	O
under	O
low	O
pressure	O
(	O
vacuum	B-General_Concept
)	O
by	O
an	O
electromagnetic	O
field	O
.	O
</s>
<s>
High-energy	O
ions	O
from	O
the	O
plasma	O
attack	O
the	O
wafer	B-Architecture
surface	O
and	O
react	O
with	O
it	O
.	O
</s>
<s>
A	O
typical	O
(	O
parallel	O
plate	O
)	O
RIE	O
system	O
consists	O
of	O
a	O
cylindrical	O
vacuum	B-General_Concept
chamber	O
,	O
with	O
a	O
wafer	B-Architecture
platter	O
situated	O
in	O
the	O
bottom	O
portion	O
of	O
the	O
chamber	O
.	O
</s>
<s>
The	O
wafer	B-Architecture
platter	O
is	O
electrically	O
isolated	O
from	O
the	O
rest	O
of	O
the	O
chamber	O
.	O
</s>
<s>
Gas	O
enters	O
through	O
small	O
inlets	O
in	O
the	O
top	O
of	O
the	O
chamber	O
,	O
and	O
exits	O
to	O
the	O
vacuum	B-General_Concept
pump	O
system	O
through	O
the	O
bottom	O
.	O
</s>
<s>
The	O
types	O
and	O
amount	O
of	O
gas	O
used	O
vary	O
depending	O
upon	O
the	O
etch	O
process	O
;	O
for	O
instance	O
,	O
sulfur	O
hexafluoride	O
is	O
commonly	O
used	O
for	O
etching	B-Algorithm
silicon	O
.	O
</s>
<s>
In	O
this	O
system	O
,	O
the	O
ICP	O
is	O
employed	O
as	O
a	O
high	O
density	O
source	O
of	O
ions	O
which	O
increases	O
the	O
etch	O
rate	O
,	O
whereas	O
a	O
separate	O
RF	O
bias	O
is	O
applied	O
to	O
the	O
substrate	B-Architecture
(	O
silicon	B-Architecture
wafer	I-Architecture
)	O
to	O
create	O
directional	O
electric	O
fields	O
near	O
the	O
substrate	B-Architecture
to	O
achieve	O
more	O
anisotropic	O
etch	O
profiles	O
.	O
</s>
<s>
Plasma	O
is	O
initiated	O
in	O
the	O
system	O
by	O
applying	O
a	O
strong	O
RF	O
(	O
radio	O
frequency	O
)	O
electromagnetic	O
field	O
to	O
the	O
wafer	B-Architecture
platter	O
.	O
</s>
<s>
The	O
field	O
is	O
typically	O
set	O
to	O
a	O
frequency	O
of	O
13.56	B-Algorithm
Megahertz	O
,	O
applied	O
at	O
a	O
few	O
hundred	O
watts	O
.	O
</s>
<s>
In	O
each	O
cycle	O
of	O
the	O
field	O
,	O
the	O
electrons	O
are	O
electrically	O
accelerated	O
up	O
and	O
down	O
in	O
the	O
chamber	O
,	O
sometimes	O
striking	O
both	O
the	O
upper	O
wall	O
of	O
the	O
chamber	O
and	O
the	O
wafer	B-Architecture
platter	O
.	O
</s>
<s>
However	O
,	O
electrons	O
deposited	O
on	O
the	O
wafer	B-Architecture
platter	O
cause	O
the	O
platter	O
to	O
build	O
up	O
charge	O
due	O
to	O
its	O
DC	O
isolation	O
.	O
</s>
<s>
Because	O
of	O
the	O
large	O
voltage	O
difference	O
,	O
the	O
positive	O
ions	O
tend	O
to	O
drift	O
toward	O
the	O
wafer	B-Architecture
platter	O
,	O
where	O
they	O
collide	O
with	O
the	O
samples	O
to	O
be	O
etched	O
.	O
</s>
<s>
Due	O
to	O
the	O
mostly	O
vertical	O
delivery	O
of	O
reactive	O
ions	O
,	O
reactive-ion	B-Algorithm
etching	I-Algorithm
can	O
produce	O
very	O
anisotropic	O
etch	O
profiles	O
,	O
which	O
contrast	O
with	O
the	O
typically	O
isotropic	O
profiles	O
of	O
wet	O
chemical	O
etching	B-Algorithm
.	O
</s>
<s>
A	O
modified	O
version	O
of	O
RIE	O
is	O
deep	B-Algorithm
reactive-ion	I-Algorithm
etching	I-Algorithm
,	O
used	O
to	O
excavate	O
deep	O
features	O
.	O
</s>
