Hello Sumant,

Depending on your applications, other than PSG, thin photoresist or the self
assembled organic thin film (e.g. organosilicon derivatives) could be used.

Regarding to the observed bubbles, may be you can try to dehydrate your wafer
that has been deposited with PSG/Au/Ti in vacuum oven prior to coating and
processing of polyimide .

regards

Han Chong

>Date:          4 Mar 2004 16:59:45 -0000
>From:          "Sumant Sood"  >[add to address book]
[protect or block sender]
>Subject:       [mems-talk] multi stack films problem
>To:    [email protected]
>Reply To:      Sumant Sood ,General MEMS discussion


>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









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