Are you controlling the temperature of your wafer in any way?  If your
wafer gets too warm during deposition, the resist will start to flow and
it will distort your pattern.  The fine features will be the first to
have problems.

Dan

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of James Paul Grant
Sent: Friday, January 16, 2009 2:04 AM
To: General MEMS discussion
Subject: Re: [mems-talk] Lifting-Off 1um metal

Thank you to all who have replied so far to my questions

I shall state a few other relevant points:

1. The Al is e-beam evaporated at a base pressure of ~ 1x10-7 mbar.
Sputtering deposition tools are also available.
2. Deposition rate is 0.3 nm/s
3. The bi-layer resist thickness is 1.3 um while the metal thickness is
1um. Now I know one should always have a resist thickness at least two
time greater than the metal thickness however I can add the caveat that
one of the groups here at Glasgow Uni have successfully lifted off 1.2
microns Au using the same resist thickness (1.3 microns) - and they say
their process is very repeatable! The problem my colleague has is he is
already using the thickest e-beam resist he has available. He could
probably sneak another 200 nm from spinning the resist at lower rpm
which may of course aid lift-off.
4. I told him to try sonication which he has done for around 10 minutes.

No joy.
5. All processing was completed within 2 days (i.e. substrate clean,
resist spinning, bake, exposure, development, ashing, HF dip, Al
evaporation)
6. He has not attempted to deposit thin Al

I had a look at his sample for him and the metal in large areas has
lifted off however in the fine feature areas (~1 um feature size) the
metal has not even begun to lift-off.

His next step will be to deposit 500 nm instead of 1um. I hope lift-off
is more successful this time.

Thanks for all your helpful comments,

James