Peng,
     One way to get a negative angle is to use an image reversal technique.
My company manufacture a reversal unit which uses ammonia.  In principle you
do the first exposure which determines the C.D. then place in ammonia at 90
degrees centigrade for 45 minutes.  The ammonia neutralizes the acid in the
exposed areas.  Then flood expose which determines the angle of overhang.  I
have numerous technical papers on the subject as there are hundreds of units
in operation.  Typical C.D. would be 0.1 micron. typical overhang up to 22
degrees reverse angle.  Once the C.D. is established with the first exposure
the flood exposure controls the angle of the resist can be controlled from 22
degrees either side of vertical.  People looking for extreme resolution use
vertical side walls.  Bill Moffat

-----Original Message-----
From: Peng Yao [mailto:yaopeng@UDel.Edu]
Sent: Friday, March 08, 2002 11:44 AM
To: mems-talk@memsnet.org
Subject: [mems-talk] Lift-off of AZ5214


Hi,
The result of lift off is determined by the profile of your side wall of
PR structures after development. I usually use negative photoresist to get
the negtive angel I want. And for that, lift off is very easy.
According to the book "fundamentals of microfabrication", it was said if
you control the exposure and develop time, you can get both negative and
positive side wall, but I never succeeded in the former one. I am also
very interested in this topic. If anyone can make a negative side wall
using AZ5214?


Peng Yao
DOEs lab
Electrical Engineering Dept.
Univeristy of delaware
Newark D.E 19716
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