Other factors can be if using a hot plate or fast soft bake you tend to
overheat the bottom of the resist.  A perfect soft bake is long time 30
minutes 90 C.  Or even better 30 minutes 90 C vacuum to pull out
solvent.  To get close to this with a fast soft bake you use more heat
110 or above and the resist at the wafer resist interface is more
difficult to develop.  Other common problem is not having an overlap
long enough of the developing solvent and the rinse.  In production I
used 5 seconds to 10 seconds overlap then about 20 seconds of rinse.
Bill Moffat

________________________________

From: [email protected] on behalf of Paul Nguyen
Sent: Fri 1/15/2010 10:47 PM
To: [email protected]
Subject: [mems-talk] Factors in scumming in case of thick negative resist?

Hi,

I have tried to figure out the main factors that cause scumming for small
trenches (i.e 10um) in my negative thick resist (up to 45um).  They are resist
(temperature,RH), exposure, developer (temperature, RH, time), Soft Bake
(time/temp), PEB (time/temp).*  I'm going to run DOE but need help from
your expertise, so it may save my time and energy.  In the same token, which
of those are main factors for 10um ring lifting, perhaps *surface
cleanliness* should be included.

Thanks in advance,
Paul