Matteo,
       It is impossible to get vertical side walls, without image reversal.
Your light source is not 100% collimated.  The exposure light is then refracted
at the resist interface so you will always get a slight angle with normal
exposure.  If you reverse mask expose, then neutralize in an image reversal
unit.  It is then possible to control the flood exposure to get any angle, from
a positive 22 degrees, through vertical to a negative 22 degrees.  Perfect
vertical side walls or perfect lift off profile.  Any Thickness I have used 40
microns thick and with 1 micron thick resist have seen 0.08 micron geometry.
Contact me for multiple technical papers.  Bill Moffat


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