R Zhang,
        My company manufactures plasma equipment, some of our units have
been running for the last 15 years doing 100% SF6 Plasma etching.  The
trick is to avoid atmosphere to soon after the plasma.  If you create
SF6 plasma you naturally get 6 Fluorine molecules/ions to do the
etching.  You also get 1 sulphur molecule/ion that you do not need.  If
there is any floating sulphur molecules when you go back to atmosphere
you get S+O+H2O(Moisture in the air.  This gives you H2SO3 or sulphurous
acid which will eat any metalics.  The chamber on my normal units is
aluminum.  After 15 years there are pits in the aluminum where Sulphur
was left on the chamber wall at the end of the process allowing
Sulphurous acid.  Apart from the unattractive pits, the aluminum
chamber, electrodes and shelves survives well, that is 15 years later.
Be aware that you can have a problem with the vacuum pump seeing
Sulphurous acid also.  We use oil filtration units on oil pumps that are
used with SF6 plasma.


Bill Moffat, CEO
Yield Engineering Systems, Inc.
2185 Oakland Rd., San Jose, CA  95131
(408) 954-8353