I would descum before the hardbake prior to wet etch. Any type of bake
will make your resist more resistant to descum.

Also, in positive resist imageing over a substrate with topology, you
also have a risk of "stringers." These are very thin strips of resist at
the bottom edge of a step or in crevices which will not be exposed out.
They tend to be thicker than the residue from develop. Descum will
remove them. A hard bake might harden them such that your O2 plasma
won't remove them.

You often can't eliminate stringers by increased exposure since it
results in the general pattern being blown out. This is especially true
on metallized substrates with topology. Photons have finite dimensions
and don't fit into crevices and edges easily.

They can be difficult to see until after the etch and you then see your
product is ruined or at the end of the process when you find your device
is electrically shorted and ruined.

One of the reasons plasma etch caught on so readily in semiconductor
processing is not just the closer packing feasible with anisotropic
etching, but it also eliminated stringers as a worry.

Edward H. Sebesta

-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of Evelyn B
Sent: Sunday, March 22, 2009 7:25 PM
To: General MEMS discussion; Evelyn Benabe
Subject: [mems-talk] Post-development bake


Is the post-development bake done after development supposed to be done
after or before descum.  I am doing a descum of 1813 resist before BST
etching in BOE solution.  I am planning on doing a post-development bake
to make the resist more resistant to the BOE but I am not sure if I
should do it right before the actual etch or before the descum.  Right
now m process is as follows

1. Resist coating
2. Soft-bake and exposure
3. Development
4. Post-development bake
5. Descum
6. BST etch