[mems-talk] Gold pad bonding problem

[Richard B. Keithley]

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.