Yaojian,
Using off the shelf positive resist and an ammonia gas reversal
process standard features less than 0.25 microns in size are commonplace. I
have seen 800 Angstrom lines and spaces. The process is simple. The resist
is exposed to a normal level of first exposure using a reverse density mask.
Then the wafer is placed in a temperature controlled ammonia atmosphere over
72 degrees and preferably below 95 degrees Celsius. At a pressure close to
atmosphere, we use 600 Torr. The ammonia gas diffuses through the resist and
the basic gas neutralizes the acid produced by exposure. If you stay at 90
Celsius the sensitizer in the remaining resist is not disturbed. Then you
flood expose at a figure between 2 and 3 times the first exposure. This
determines the angle of resist. Typical figures form 22 degrees through
vertical to 22 degrees overhang. All controlled by the amount of second
exposure. Then normal develop produces a perfect lift off profile. The added
good news is that reversed, i.e. exposed and neutralized, resist is very
temperature stable. I have friends who produce resist pillars and then flow
TEOS around the pillars with no resist flow. these pillars are 0.5 microns in
diameter and 1.2 microns high. I do not know how hot the sputtering will get
your resist, but again good news we ready and equipped to do the ammonia
reversal for free as a test. Let me know if we can help. Bill Mofat
-----Original Message-----
From: Lin, Yaojian [mailto:Ylin@sychip.com]
Sent: Wednesday, June 05, 2002 9:44 AM
To: 'mems-talk@memsnet.org'
Subject: [mems-talk] Photoresist for lift-off with fine patterns
Dear MEMS folks,
I am looking for the photoresist that can be used in the lift-off process
with fine patterns (<10um), and can stand under the relative high
temperature and sputtering /MOCVD. Could you please share any related
information with me?
With many thanks,
Yaojian
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