Dear Lando,

Make sure that your step 2 doesn't remove too much of the PMMA. Maybe you
can measure the thickness of the PMMA with a surface profiler. If the
remaining layer of PMMA gets thinner, the lift-off gets more difficult.
I guess you already do the Ti deposition by e-beam evaporation. Sputtering
would also cover the PMMA sidewalls.
For me, I always need ultrasonic agitation (5 min in Acetone + 5 min in IPA)
to do the lift-off. Only soaking in acetone will not lift-off the metal.

Regards,

--Christoph

-----Original Message-----
From: landobasa [mailto:landobasa@yahoo.com]
Sent: Tuesday, June 01, 2010 11:09 PM
To: mems-talk@memsnet.org
Subject: [mems-talk] PMMA cracking during e beam evaporation

Dear Researcher,

I am still a beginner in fabrication, and I have these following problems in
the lift-off process. In order to provide the context, let me briefly write
the process steps:

1) PMMA film (200nm thickness) is patterned using Electron  Beam Lithography
(developed for 60s and IPA for 30s).
2) Patterned PMMA film was subjected to UV Ozone Stripper (SAMCO UV-1) for
60s.
3) The sample was deposited by Ti with 20nm thickness (with the rate of
0.06nm/s)
4) The sample was soaked in Acetone.

Problems:
1) There are cracks everywhere in PMMA film after E-Beam Evaporation.
2) The PMMA cannot be removed by acetone.

Any help would be very much appreciated.

Best Regards,

Lando