They are both resist strippers.  The first plasma unit for use in
semiconductors was copied from a unit that coroners used to ash portions
of bodies to do spectrographic analysis.  It was called an Asher because
it ashed pieces of bodies.  In the 1960's it was used to strip resist at
as fast a rate as possible.  The name carried over and it was called an
Asher.  Typical strip rate today would be 7,000 Angstroms per minute.
Then after resist exposure, development and hard bake.  There was a
small amount of resist left on the wafer surface which we called scum.
Now we want to remove this scum but not remove lots of the original
resist so we do a more controlled resist strip say 1,000 Angstroms a
minute that will remove the scum but not a lot of the protective resist.

Bill Moffat

-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of Evelyn B
Sent: Thursday, January 22, 2009 7:02 AM
To: General MEMS discussion; Evelyn Benabe
Subject: [mems-talk] Descum and Ashing Diff

Can you someone please tell me what is the difference between descum and
ashing?

EVELYN BENABE