The major problem of cracks is stress.
This can be divided into two:
1. Internal stresses due to the deposition - one solution is to use PECVD.
2. Internal stress due to thermal expansion coef. mismatch between the
polyimide and the SiO2- the solution is to deposit the polyimide at the
higher temperature that you can plus slow ramping of the temperature during
cure. You didn't mentioned the thickness of the polyimide, but you may
reduce its thickness (if you can).

Thank you in advance,
Doron Schlumm
Director of Technology
Flixel LTD.
Tel : 972-3-5629505
Fax : 972-3-5621639
Cell : 972-52-446 6704

-----Original Message-----
From: Aamer Mahmood [mailto:amahmood@engr.smu.edu]
Sent: Tuesday, August 31, 2004 4:50 PM
To: mems-talk@memsnet.org
Subject: [mems-talk] Deposition of thick SiO2 layer

Hello all,
I have deposited ~ 2-3um of SiO2 on a polyimide (PI2610). Subsequent
process steps require curing @ ~ 265 C. I notice big cracks in the Oxide
and also large chunks of it just peel off.
Before resorting to sputtering, I have also tried spin-on-glass but faced
similar problems.
Any suggestions on the cause and/or remedy would be greatly appreciated.
Thanks.

Aamer Mahmood
Grad Res Assist
Microsensors lab
UT Arlington