Hi Michael,

I had experienced the cracking too. There are several parameters can affect
the stress, like exposure time, and hard baking. What you can try is to let
the sample cool down with the hot plate after pre-bake and post-bake,
especially after post-bake, for it introduced a lot of stress in the film.
Also, I found that increase the exposure energy to fully crosslink the film
can largely reduce the cracking. If you need to hard bake the film, you can
also notice that after hard baking, the cracking become less and shallow.

Cheers,
Meifang

-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org]
On Behalf Of Haixin Zhu
Sent: Wednesday, 14 January 2009 5:18 AM
To: General MEMS discussion
Subject: [mems-talk] SU8 2050 stress issue

Dear fellow MEMS researchers,

I have been trying SU8 2050 to make contact holes, ranging from 20um to
250um in diameter, though I followed the vendor's recommended recipe,
there is always some stress induced film cracking after the PEB, is
there anyone having any suggestion to this issue,

Appreciate any input and help

Michael