We do lift-off with n-Lof 3070 and NMP, and what we discovered is that it is
critical to avoid all moisture in the glass you use to pour the NMP. We
usually flushed with DIW before pouring NMP, and the results were poor.
After skipping this flush, the lift-off of the metal proceeds in seconds at
room temperature (we have tested it with 100nm Al, with 70nm Ti and with
10nmPt/70nm Al, and everything was OK).

Good luck.

Enrique San Andrés. UCM.

-----Mensaje original-----
De: mikas remeika [mailto:remeika@physics.ucsd.edu]
Enviado el: miércoles, 17 de marzo de 2010 1:05
Para: General MEMS discussion
Asunto: Re: [mems-talk] Does ultrasonic damage metal film during lift-off?

In my experience, no more than 5 minutes of ultrasonic agitation are
required to liftoff most films, and in general no damage occurs even
to very high resolution patterns.  Also, I would start with the lowest
power of the ultrasonic that your bath will allow - its usually
unnecessary to go to high power for liftoff.

Also, generally I'm more concerned with thick films (rather than thin)
being damaged by ultrasonic agitation. This is because you need to be
concerned with the ratio of forces required to tear the film and the
force to peel the film. The force to peel the film in always the same,
but tearing the film requires more force when it is thick and hence
you're more likely to peel it off completely during liftoff.

Another trick regarding lift-off which might be useful - this is
especially useful when you're using SU-8: if after 15 minutes in the
ultrasonics bath no liftoff occurs, you can put the sample into an
oxygen plasma asher (not an RIE system, but an isotropic asher) for
some long time and repeat the liftoff. Usually plasma will etch resist
through any small holes that were formed in the material covering it
and after that liftoff will proceed very quickly.