Hi Alex.

I had a lot of problems with NR9 material as well.  I experimented a lot
with several two-step lift off materials, namely LOR from MicroChem and
ProLift from Brewer Science.  They both worked well, and the ProLift had
the added advantage of lifting in TMAH based developer solution which
saved a lot of solvent.  However, I ended up using AZ's nLOF 2000 series
because it seemed to lift easier after a relatively thick (>5000 A of
Pt/Ti/Au) deposition via e-beam evaporation.  It is also just a
single-step process so it saved me time as well.  Not sure of the cost
differences any longer, but I would definitely recommend trying it out.

Best Regards,
Dustin Warren

EV Group
invent * innovate * implement
Application Engineer - Direct: +1 (480) 305 2447, Main: +1 (480) 305
2400 Fax: +1 (480) 305 2401
Cell: +1 (480) 274 3894
E-Mail: D.Warren@EVGroup.com, Web: www.EVGroup.com


-----Original Message-----
From: Alex Mellnik [mailto:amellnik@physics.unc.edu]
Sent: Tuesday, April 07, 2009 6:05 PM
To: mems-talk@memsnet
Subject: [mems-talk] Problems with NR9-1500PY leaving residue behind
afterdevelopment

Hello,

I've used NR9 for a few years now and have had good results with it
since
developing a robust recipe for it.  However, in the past year I've
noticed
that NR9 seems to leave some sort of invisible residue behind on many
materials.  If the area of interest is Au for example, I can generally
get
ohmic contact with Ti/Au contacts patterned with NR9, but the second
layer
of metal often peels off during wirebonding.  When I try to make ohmic
contacts to highly doped p-type Ge with Ti/Au patterned with NR9 the
contacts are only ohmic for large areas, which is not the case when I
pattern the contacts with S1813.

Normally I would just ash for 1 min in oxygen plasma prior to
deposition,
but here I can't do this because it would either damage the surface of
the
Ge or an isolation layer in our device of hard-baked SU8 2000.5 .  I
spoke
with the Futurrex engineer about this, but all he could suggest was to
adjust the bake times, which didn't make any difference.  Does anyone
have
any other ideas I could try?

In the meantime we have been using S1813 to do the deposition, but it's
a
hassle to do liftoff since our contacts are usually 2kA or more thick.
I'm planning to buy a LOR resist to do two-step processing, and I was
thinking about LOR 3A since I use the metal-ion free developer MF 319.
However, I noticed that a lot of the people on this site use LOR B with
that same developer, even though MicroChem seems to not recommend it.
Is
there any particular reason to use one or the other?  Should I try the
trick with hardening the top layer with toluene first?

Thanks,

Alex