<s>
Plasma-activated	B-Algorithm
bonding	I-Algorithm
is	O
a	O
derivative	O
,	O
directed	O
to	O
lower	O
processing	O
temperatures	O
for	O
direct	B-Algorithm
bonding	I-Algorithm
with	O
hydrophilic	O
surfaces	O
.	O
</s>
<s>
The	O
main	O
requirements	O
for	O
lowering	O
temperatures	O
of	O
direct	B-Algorithm
bonding	I-Algorithm
are	O
the	O
use	O
of	O
materials	O
melting	O
at	O
low	O
temperatures	O
and	O
with	O
different	O
coefficients	O
of	O
thermal	O
expansion	O
(	O
CTE	O
)	O
.	O
</s>
<s>
The	O
decrease	O
of	O
temperature	O
is	O
based	O
on	O
the	O
increase	O
of	O
bonding	O
strength	O
using	O
plasma	O
activation	O
on	O
clean	O
wafer	B-Architecture
surfaces	O
.	O
</s>
<s>
Further	O
,	O
the	O
increase	O
is	O
caused	O
by	O
elevation	O
in	O
amount	O
of	O
Si-OH	O
groups	O
,	O
removal	O
of	O
contaminants	O
on	O
the	O
wafer	B-Architecture
surface	O
,	O
the	O
enhancement	O
of	O
viscous	O
flow	O
of	O
the	O
surface	O
layer	O
and	O
the	O
enhanced	O
diffusivity	O
of	O
water	O
and	O
gas	O
trapped	O
at	O
the	O
interface	O
.	O
</s>
<s>
Based	O
on	O
ambient	O
pressure	O
,	O
two	O
main	O
surface	O
activation	O
fields	O
using	O
plasma	O
treatment	O
are	O
established	O
for	O
wafer	B-Architecture
preprocessing	O
to	O
lower	O
the	O
temperatures	O
during	O
annealing	O
.	O
</s>
<s>
Plasma	B-Algorithm
activated	I-Algorithm
bonding	I-Algorithm
is	O
based	O
on	O
process	O
pressure	O
divided	O
into	O
:	O
</s>
<s>
This	O
method	O
is	O
to	O
ignite	O
plasma	O
without	O
using	O
a	O
low	O
pressure	O
environment	O
,	O
so	O
no	O
expensive	O
equipment	O
for	O
vacuum	B-General_Concept
generation	O
is	O
needed	O
.	O
</s>
<s>
Atmospheric	O
Pressure-Plasma	O
Activated	O
Bonding	O
enables	O
the	O
possibility	O
to	O
ignite	O
plasma	O
at	O
specific	O
local	O
areas	O
or	O
the	O
whole	O
surface	O
of	O
the	O
substrate	B-Architecture
.	O
</s>
<s>
The	O
wafer	B-Architecture
pairs	O
pass	O
the	O
following	O
process	O
flow	O
:	O
</s>
<s>
If	O
using	O
glass	O
,	O
based	O
on	O
the	O
high	O
surface	O
roughness	O
,	O
a	O
chemical-mechanical	B-Algorithm
planarization	I-Algorithm
(	O
CMP	O
)	O
step	O
after	O
rinsing	O
is	O
necessary	O
to	O
improve	O
the	O
bonding	O
quality	O
.	O
</s>
<s>
The	O
bond	O
strength	O
is	O
characterized	O
by	O
fracture	O
toughness	O
determined	O
by	O
micro	B-Algorithm
chevron	I-Algorithm
tests	I-Algorithm
.	O
</s>
<s>
Plasma	O
activated	O
wafer	B-Architecture
bonds	O
can	O
achieve	O
fracture	O
toughnesses	O
that	O
are	O
comparable	O
to	O
bulk	O
material	O
.	O
</s>
<s>
The	O
shape	O
of	O
the	O
electrode	O
is	O
similar	O
to	O
the	O
substrate	B-Architecture
geometry	O
used	O
to	O
cover	O
the	O
entire	O
surface	O
.	O
</s>
<s>
The	O
activation	O
equipment	O
consists	O
of	O
the	O
grounded	O
chuck	O
acting	O
as	O
wafer	B-Architecture
carrier	O
and	O
an	O
indium	O
tin	O
oxide	O
(	O
ITO	O
)	O
coated	O
glass	O
electrode	O
.	O
</s>
<s>
Further	O
,	O
the	O
glass	O
substrate	B-Architecture
is	O
used	O
as	O
dielectric	O
barrier	O
and	O
the	O
discharge	O
is	O
powered	O
by	O
a	O
corona	O
generator	O
.	O
</s>
<s>
The	O
Low	O
Pressure-Plasma	O
Activated	O
Bonding	O
operates	O
in	O
fine	O
vacuum	B-General_Concept
(	O
0.1	O
–	O
100Pa	O
)	O
with	O
a	O
continuous	O
gas	O
flow	O
.	O
</s>
<s>
Due	O
to	O
its	O
positive	O
orientation	O
the	O
massive	O
ions	O
,	O
that	O
are	O
not	O
able	O
to	O
follow	O
the	O
HF	O
field	O
,	O
move	O
to	O
the	O
negatively	O
charged	O
electrode	O
,	O
where	O
the	O
wafer	B-Architecture
is	O
placed	O
.	O
</s>
<s>
Within	O
those	O
environment	O
the	O
surface	O
activation	O
is	O
based	O
on	O
the	O
striking	O
ions	O
and	O
radicals	O
interacting	O
with	O
the	O
surface	O
of	O
the	O
wafer	B-Architecture
(	O
compare	O
to	O
figure	O
"	O
Scheme	O
of	O
a	O
plasma	O
reactor	O
for	O
low	O
pressure	O
plasma	B-Algorithm
activated	I-Algorithm
bonding	I-Algorithm
"	O
)	O
.	O
</s>
<s>
The	O
electrode	O
attached	O
to	O
the	O
HF-Generator	O
is	O
used	O
as	O
carrier	O
of	O
the	O
wafer	B-Architecture
.	O
</s>
<s>
Following	O
,	O
the	O
surfaces	O
of	O
the	O
wafers	B-Architecture
charge	O
up	O
negatively	O
caused	O
by	O
the	O
electrons	O
and	O
attract	O
the	O
positive	O
ions	O
of	O
the	O
plasma	O
.	O
</s>
<s>
The	O
plasma	O
ignites	O
in	O
the	O
RIE-reactor	O
(	O
shown	O
in	O
figure	O
"	O
Scheme	O
of	O
a	O
plasma	O
reactor	O
for	O
low	O
pressure	O
plasma	B-Algorithm
activated	I-Algorithm
bonding	I-Algorithm
"	O
)	O
.	O
</s>
<s>
The	O
maximal	O
bond	O
strength	O
is	O
achieved	O
with	O
nitrogen	O
and	O
oxygen	O
as	O
process	O
gases	O
and	O
is	O
sufficiently	O
high	O
with	O
a	O
homogeneous	O
dispersion	O
over	O
the	O
wafers	B-Architecture
after	O
annealing	O
at	O
250°C	O
.	O
</s>
<s>
The	O
bond	O
energy	O
is	O
characterized	O
>200	O
%	O
of	O
non-activated	O
reference	O
wafer	B-Architecture
annealed	O
at	O
the	O
same	O
temperature	O
.	O
</s>
<s>
The	O
surface	O
activated	O
wafer	B-Architecture
pair	O
has	O
15%	O
less	O
bond	O
energy	O
compared	O
to	O
a	O
high	O
temperature	O
bonded	O
wafer	B-Architecture
pair	O
.	O
</s>
<s>
The	O
wafers	B-Architecture
are	O
activated	O
with	O
short	O
RIE	O
plasma	O
followed	O
by	O
a	O
radical	O
treatment	O
in	O
one	O
reactor	O
chamber	O
.	O
</s>
