Hi Andrew,

I was trying to say 'the 4 um (unexposed) features could not be fully developed
and I did not get a good structure'. The resist layer looked ok after
development, I mean, there was no sign the entire SU-8 layer was washed away.

When you say 'I have to make sure the exposure gap is minimized', did you mean I
should expose the wafer after soft bake as soon as possible?

By the way, I did not mention in my previous email that I found lots of micro-
cracks near the edge of the features. I guess these cracks must be related to
the soft and hard bake processes. I was aware of the stress and cracks in SU-8,
so I use two steps to bake and cool down. I put the wafer on the 65 C hotplate
for 1 min, then 95 C hotplate for 3 mins, then put it back to the 65 C hotplate
for half minute, then a piece of tissue. Do you have any comment on this?

Thanks a lot!

Yingtao

________________________________________
From: [email protected] [mems-talk-
[email protected]] On Behalf Of Andrew Sarangan
[[email protected]]
Sent: 11 January 2012 14:31
To: General MEMS discussion
Subject: Re: [mems-talk] SU-8 process development

When you say you "could not get the features cleared" do you mean that
you could not fully dissolve the unexposed areas, or did you meant
that all the SU8 washed away with nothing remaining? You need to
clarify more what you meant by "I did not get anything useful."

Also, 4um features on a 5um thick resist will require some care. You
have to make sure the exposure gap is minimized and the edge bead is
not large.