<s>
A	O
diffusion	B-Algorithm
barrier	I-Algorithm
is	O
a	O
thin	O
layer	O
(	O
usually	O
micrometres	O
thick	O
)	O
of	O
metal	O
usually	O
placed	O
between	O
two	O
other	O
metals	O
.	O
</s>
<s>
The	O
role	O
of	O
a	O
diffusion	B-Algorithm
barrier	I-Algorithm
is	O
to	O
prevent	O
or	O
to	O
retard	O
the	O
inter-diffusion	O
of	O
the	O
two	O
superposed	O
metals	O
.	O
</s>
<s>
Therefore	O
,	O
to	O
be	O
effective	O
,	O
a	O
good	O
diffusion	B-Algorithm
barrier	I-Algorithm
requires	O
inertness	O
with	O
respect	O
to	O
adjacent	O
materials	O
.	O
</s>
<s>
To	O
obtain	O
good	O
adhesion	O
and	O
a	O
diffusion	B-Algorithm
barrier	I-Algorithm
simultaneously	O
,	O
the	O
bonding	O
between	O
layers	O
needs	O
to	O
come	O
from	O
a	O
chemical	O
reaction	O
of	O
limited	O
range	O
at	O
both	O
boundaries	O
.	O
</s>
<s>
Materials	O
providing	O
good	O
adhesion	O
are	O
not	O
necessarily	O
good	O
diffusion	B-Algorithm
barriers	I-Algorithm
and	O
vice	O
versa	O
.	O
</s>
<s>
While	O
the	O
choice	O
of	O
diffusion	B-Algorithm
barrier	I-Algorithm
depends	O
on	O
the	O
final	O
function	O
,	O
anticipated	O
operating	O
temperature	O
,	O
and	O
service	O
life	O
,	O
are	O
critical	O
parameters	O
to	O
select	O
diffusion	B-Algorithm
barrier	I-Algorithm
materials	O
.	O
</s>
<s>
Many	O
thin	O
film	O
metal	O
combinations	O
have	O
been	O
evaluated	O
for	O
their	O
adhesion	O
and	O
diffusion	B-Algorithm
barrier	I-Algorithm
properties	O
.	O
</s>
<s>
Aluminum	O
provides	O
good	O
electrical	O
and	O
thermal	O
conductivity	O
,	O
adhesion	O
and	O
reliability	O
because	O
of	O
its	O
oxygen	O
reactivity	O
and	O
the	O
self-passivation	O
properties	O
of	O
its	O
oxide	O
.	O
</s>
<s>
Chromium	B-Language
has	O
excellent	O
adhesion	O
to	O
many	O
materials	O
because	O
of	O
its	O
reactivity	O
.	O
</s>
<s>
Its	O
affinity	O
for	O
oxygen	O
forms	O
a	O
thin	O
stable	O
oxide	O
coat	O
on	O
the	O
outer	O
surface	O
,	O
creating	O
a	O
passivation	B-Application
layer	I-Application
which	O
prevents	O
further	O
oxidation	O
of	O
the	O
chromium	B-Language
,	O
and	O
of	O
the	O
underlying	O
metal	O
(	O
if	O
any	O
)	O
,	O
even	O
in	O
corrosive	O
environments	O
.	O
</s>
<s>
Chromium	B-Language
plating	O
on	O
steel	O
for	O
automotive	O
use	O
involves	O
three	O
diffusion	B-Algorithm
barrier	I-Algorithm
layers	O
—	O
copper	O
,	O
nickel	O
,	O
then	O
chromium	B-Language
—	O
to	O
provide	O
long	O
term	O
durability	O
where	O
there	O
will	O
be	O
many	O
large	O
temperature	O
changes	O
.	O
</s>
<s>
If	O
chromium	B-Language
is	O
plated	O
directly	O
onto	O
the	O
steel	O
,	O
then	O
their	O
different	O
thermal	O
expansion	O
coefficients	O
will	O
cause	O
the	O
chrome	O
plating	O
to	O
peel	O
off	O
the	O
steel	O
.	O
</s>
<s>
Nickel	O
,	O
Nichrome	O
,	O
tantalum	O
,	O
hafnium	O
,	O
niobium	O
,	O
zirconium	O
,	O
vanadium	O
,	O
and	O
tungsten	B-Application
are	O
a	O
few	O
of	O
the	O
metal	O
combinations	O
used	O
to	O
form	O
diffusion	B-Algorithm
barriers	I-Algorithm
for	O
specific	O
applications	O
.	O
</s>
<s>
Conductive	O
ceramics	O
can	O
be	O
also	O
used	O
,	O
such	O
as	O
tantalum	O
nitride	O
,	O
indium	O
oxide	O
,	O
copper	O
silicide	O
,	O
tungsten	B-Application
nitride	O
,	O
and	O
titanium	O
nitride	O
.	O
</s>
<s>
A	O
barrier	B-Algorithm
metal	I-Algorithm
is	O
a	O
material	O
used	O
in	O
integrated	O
circuits	O
to	O
chemically	O
isolate	O
semiconductors	O
from	O
soft	O
metal	O
interconnects	O
,	O
while	O
maintaining	O
an	O
electrical	O
connection	O
between	O
them	O
.	O
</s>
<s>
For	O
instance	O
,	O
a	O
layer	O
of	O
barrier	B-Algorithm
metal	I-Algorithm
must	O
surround	O
every	O
copper	O
interconnect	O
in	O
modern	O
integrated	O
circuits	O
,	O
to	O
prevent	O
diffusion	O
of	O
copper	O
into	O
surrounding	O
materials	O
.	O
</s>
<s>
As	O
the	O
name	O
implies	O
,	O
a	O
barrier	B-Algorithm
metal	I-Algorithm
must	O
have	O
high	O
electrical	O
conductivity	O
in	O
order	O
to	O
maintain	O
a	O
good	O
electronic	O
contact	O
,	O
while	O
maintaining	O
a	O
low	O
enough	O
copper	O
diffusivity	O
to	O
sufficiently	O
chemically	O
isolate	O
these	O
copper	O
conductor	O
films	O
from	O
underlying	O
device	O
silicon	O
.	O
</s>
<s>
The	O
thickness	O
of	O
the	O
barrier	O
films	O
is	O
also	O
quite	O
important	O
;	O
with	O
too	O
thin	O
a	O
barrier	B-Algorithm
layer	I-Algorithm
,	O
the	O
inner	O
copper	O
may	O
contact	O
and	O
poison	O
the	O
very	O
devices	O
that	O
they	O
supply	O
with	O
energy	O
and	O
information	O
;	O
with	O
barrier	B-Algorithm
layers	I-Algorithm
too	O
thick	O
,	O
these	O
wrapped	O
stacks	O
of	O
two	O
barrier	B-Algorithm
metal	I-Algorithm
films	O
and	O
an	O
inner	O
copper	O
conductor	O
can	O
have	O
a	O
greater	O
total	O
resistance	O
than	O
the	O
traditional	O
aluminum	O
interconnections	O
would	O
have	O
,	O
eliminating	O
any	O
benefit	O
derived	O
from	O
the	O
new	O
metallization	O
technology	O
.	O
</s>
<s>
Some	O
materials	O
that	O
have	O
been	O
used	O
as	O
barrier	B-Algorithm
metals	I-Algorithm
include	O
cobalt	B-Algorithm
,	O
ruthenium	O
,	O
tantalum	O
,	O
tantalum	O
nitride	O
,	O
indium	O
oxide	O
,	O
tungsten	B-Application
nitride	O
,	O
and	O
titanium	O
nitride	O
(	O
the	O
last	O
four	O
being	O
conductive	O
ceramics	O
,	O
but	O
"	O
metals	O
"	O
in	O
this	O
context	O
)	O
.	O
</s>
