Hi,

First of all you need at least 5000A of Au to wire bond successfully,
1um is even better. You would have better luck with Cr/Au but you cannot
break vacuum if you want good film adhesion. Ti grows oxides very
quickly and the Au will not adhere to a Ti surface exposed to air and
processed.

So try to evap fresh Ti then at least 5000A of Au, when you wire bond
keep the heat up 120C to 150c and use low power.

Rick


-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of mikas remeika
Sent: Friday, June 19, 2009 4:19 PM
To: General MEMS discussion
Subject: [mems-talk] Gold adhesion to Ti oxide

Hello,

does anybody have experience dealing with this kind of issue:

I'm trying to deposit a film of gold on top of a thin film of titanium
(e-beam evaporated), the titanium is exposed to air (and oxygen plasma)
during previous processing, so its inevitable that there is a thin layer
of
oxide on the surface of the titanium.

A Gold film is e-beam evaporated onto the surface of the Ti (TiO2).
Resulting film adheres well enough to perform lift-off, however,
mechanical
stress such as wireboding results in large sections of the gold film
peeling
off.  I have tried evaporating a fresh layer of Ti under the gold (in
the
same vacuum), that did not give any improvement in adhesion.  I also
have
access to sputtering machines, however in previous experience evaporated
gold adhered more reliably to different surfaces.

So my question - is there are way to treat the titanium/TiO2 surface to
create good adhesion to the gold layer? I have acceess to a range of
materials for sputtering and evaporation, if there is a specific
material
that adheres well to both gold and TiO2 I would really like to know what
it
is.

Some notes: The sample in this case cannot be heated to more than 100C
and
cannot be exposed to RIE type plasma.  Also, it is necessary to have
electrical contact between the gold and titanium (the naturally formed
oxide
in this case does not create electrical insulation).