Hello,
I am trying to fabricate a this stack on a silicon wafer:

Silicon/Sacrificial layer/Gold/Ti/Polyimide/Ti/Au

After the whole stack is completed, I want to etch off the
sacrificial layer off the silicon substrate somehow to get the
kapton like film coated with gold on both sides. The Ti thickness
is 200A and is being used as a seed layeer for adhesion of Gold to
the polyimide.
Right now, I am using P20B PSG from filmtronics as the sacrificial
layer.
I have no problems until the polymide. During the soft bake of
polyimide, I see, round bubbles forming beneath the polyimide film
and I am not sure why is it happening. I have tried a very small
ramp rate too to decerese the stress in the polymide films but it
does not seem to work.My polyimide process uses a 150 C softbake
for 4 minutes and 350C hardbake for 1 hour in N2.



  At this point, I have two queries:

Can i use any other sacrificial layer instead of PSG ( spin on
glass) that would be easy to etch off without affecting the metals
and polymide.

Secondly for the above process, can i chage any of my polyimide
processing steps to remove those bubbles and get a uniform
polymide film.

Thanks in advance
Sumant Sood

Advanced Materials Processing and Analysis Center




Sumant Sood
http://pegasus.cc.ucf.edu/~ssood