I have a similar issue when I tried to place photoresist on top of
tungsten metal.  Adhesion was poor and the photoresist flaked more than
usual.  I used HF which removed the oxide layer and allowed for better
adhesion of my photoresist.  HF removed tungsten oxides, but does not
etch the W metal.  Here are some refs to that effect.

Hockett, L. A.; Creager, S. E. Review of Scientific Instruments 1993,
64, 263-264.
Paparazzo, E.; Moretto, L.; Selci, S.; Righini, M.; Farne, I. Vacuum
1999, 52, 421-426.

Also, we electrically deposited gold onto tungsten microwires.  The HF
helped the adhesion of the gold as well.  That reference is

Hermans, A.; Wightman, R. M.  Langmuir; 2006; 22(25); 10348-10353.

Just an idea.  Good Luck.

-Richard


Richard B. Keithley
UNC Analytical Chemistry Graduate Student &
National Defense Science and Engineering Graduate Fellow
Wightman Research Group
Chapel Hill, NC 27599
919-962-1108

Guillaume Bougrine wrote:
> Hello,
>
> I am currently facing a problem with gold pads deposited on a tungsten layer.
> My gold pads are deposited by sputtering and patterned by lift off.
> When a gold wire contacts the pad, the pad-wire bonding is stronger than the
tungsten-pad bonding and then the pad is removed.
>
> On one hand, I read papers where they assume this problem can come from the
creation of a thin tungsten oxide layer which avoid a stronger bonding. Then the
idea would be to etch tungsten a bit just before depositing gold. Do you think
it is right?
>
> On the other, friends of mine faced a similar problem but with Silicon instead
of Tungsten. They used a chrome layer in between Gold and Si (SiO2) and it
worked. I cannot find any information about this for the moment... So, do you
think it could work? (or do you know where I could find information?)
>
> Hope one of you will have an idea or at least will give me his/her opinion.