They are essentially the same, except that descum is the term used when
you are just removing possible residues from an open area in
photomasking by an oxygen plasma, and ashing refers to removing a layer
of resist or some other organic layer.

Ashing more generally means taking an organic sample, putting it in a
platinum crubile, and heating it until there was just ash. Though I
don't know if this laboratory usage resulted in the general
semiconductor usage.

Descum is generally easy since you just need enough oxygen species to
oxidize a molecular layer or two. Also, descum will modify the surfaces
of an organic making them more wettable. So if you had a contact photo
process a descum would both clear the contact of organics at the bottom
and render the surface of the photoresist more wettable. Though I would
still use a super wet BOE and perhaps a pre-dip.

Edward H. Sebesta
Independent Semiconductor and MEMS Engineer

-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of Evelyn B
Sent: Thursday, January 22, 2009 9:02 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