Qingwei,
        Lift off will work well on thick metal.  One of our customers is using
image reversal and 3 micron thick resist to pattern 1 micron thick gold.  The
reversal process is more repeatable because you are not trying to swell resist
to produce the overhang profile.  For image control that is more precise than
you need.  There are good technical papers showing control to 80 Angstroms in
10,000 Angstrom thick resist.  One other approach using reversal could be
plate up.  With reversal you can achieve any angle of resist profile easily.
One of our customers is using 30 micron thick resist to plate up 20 micron
copper connections.  Let me know if you need any more technical help.  Bill
Moffat

-----Original Message-----
From: Qingwei Mo [mailto:[email protected]]
Sent: Wednesday, April 17, 2002 5:31 PM
To: [email protected]
Subject: [mems-talk] pattern thick silver layer?


    I am trying to pattern a thick silver layer on GaAs. The thickness could
be 5000A to 1um . The pattern I try to make is a 30X20um rectanglular
openning. I once tried the silver etchant from Transene. It gave me huge
undercut and ugly etch front. Anyone has the similar problem before? I
deposit silver in CHA E-beam deposition system at about 3~5A/sec.
   Is it OK to lift off this pattern in suck a thick layer? As I know, it is
normally more difficult to lift off a small openning than a mesa or ridge.
   Anther question is, I am using AZ5214, and AZ4330 now. will the image
reversal give these PR a better profile for lift off? Will the Chlorobenzene
process or toluene work to them too?

  Thanks a lot for your help
   Qingwei

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