[mems-talk] Cr-Au layer detached after baking

[Jie Zou]

Hey everyone,

Using a Photoresist S1813 - LOR3A bilayer, I evaporated about 3nm Cr (as
adhesion) 120nm gold and 130nm Cr (from bottom to top). Then I lifted it
off. So far so good. I need to do a e-beam lithography after that. Thus I
spinned PMMA A4 and baked it @ 180 C (30mins in oven). After I lift-off or
just washed away the PMMA, I found parts of the metal layer detached and it
coiled itself. I ran a test that without the PMMA, I directly baked the
sample with the metal layer on the hot-plate, and the detachment happened
again. I also tried a sample with only 120nm gold or only Cr layer (and the
3nm Cr adhesion layer) baking under the same condition. It is fine.

I think this detachment and coiling is due to the stress difference between
the Cr and Au, since I don't have any problem with only gold or only Cr.
When I heated my sample, the two metals extended and release its stress in
different ways.

Sometimes the first evaporation also failed. I think it was also due to the
high temperature in the evaporation chamber.

Anyone had the same experience and any suggestion? Is there some annealing
process I could try?

Thanks a lot.

Jay