You are having problems with the lift-off because you have no
overhanging resist.  You should use a PMMA bilayer, such as 950k PMMA on
top of either low molecular weight PMMA (such as 50k) or co-polymer
PMMA/PMAA.  Bottom layer must be 1.5 - 2x as thick as the metal to be
deposited (say 250 or 300 nm) while the top layer (950k PMMA) can be
thinner (200 nm or so is probably fine).  The 950k layer (top layer)
will define the patterns, while the bottom layer will develop a little
bit faster and undercut under the 950k.  This will result in the
required overhang for lift-off.
Bill Lanford-Crick
Micro and Nanotechnology Laboratory and
Department of Electrical and Computer Engineering
University of Illinois at Urbana-Champaign

-----Original Message-----
From: Zhiwei Zou
Subject: [mems-talk] Problems about the Lift-off

I met a problem when I doing the lift-off after the E-ebeam lithography.