Andrea,
          Totally vertical side walls are difficult.  First you need
total collimation which is not possible without a true point source of
light.  Next if you get any out of collimation you get refraction as the
light enters the resist which causes a slight increase in the angle of
the light.  All of this causes a true vertical to be difficult.  The
pictures  on the S1813 show close to vertical.  Brad has some good
suggestions.  If totally vertical is essential image reversal is one
technique to achieve totally vertical lines.  With the right resist.
exposure source and developer
+22 degrees to -22 degrees and any angle in between is achievable.
Bill Moffat.

________________________________

From: [email protected] on behalf of Andrea Mazzolari
Sent: Sun 1/17/2010 5:20 AM
To: General MEMS discussion
Subject: [mems-talk] S1813 vertical sidewalls

Hi All,

i need to pattern S1813 with vertical sidewalls, but at the present time i
get an angle of about 54 deg. Awful...
My maskaligner is an old karl suss.

Here is my procedure:
-spinning of S1813
-soft bake 3 min at 115 deg
-photolitography in contact mode (150mJ)
-development in MF319 (about 45 seconds)
-hard bake 15 min at 115.

Any suggestion to improve the sidewall angle ?

Best regards,
Andrea