Anshu,
The crystals you are describing are more than likely dendrites, which
could be coming from the aluminum contact pads.
I have encountered similar situations when working with nitric acid as
an etchant. During those etches there was no glycerol present, so I do
not think the dendrite growth you are experiencing is necessarily caused
by glycerol residues. To resolve the dendrite issues, our chemist tried
various rinsing techniques, which involved different solvents and the
orders-of-operation. In the end it appeared some solvents were the
catalyzing agent in the dendrite growth, and we found that an acetone
rinse, followed by a D.I. water rinse, and then N2 dry worked the best.
For your situation, you may want to characterize your rinse process by
changing the rinsing agents and the orders-or-operation until you can
determine which step is causing the dendrite growth. If you have a DOE
established, this can be accomplished in a short period of time.
Hope this helps!
Best Regards,
Tim Watson
Microfabrication Technician
MicroMD laboratory
1381 Kinnear Road, Suite 100
Columbus, OH 43212
Tel: 614-688-8474
Fax: 614-688-3379
www.micromd.org
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
anshu mehta
Sent: Monday, December 01, 2003 4:13 AM
To: [email protected]
Subject: [mems-talk] Wet etching Buffered HF/Glycerol
Hi
We use wet etching for sacrificial etching of oxide
followed by supercritical CO2 drying.
For the wet etch, we use a solution of 2 Buffered HF:1
glycerol because of exposed Al contact pads. Following
the etch, we rinse the sample in glycerol, DI water
and then IPA. However, we observed during the methanol
rinse, some form of crystals are formed on the surface
of the sample, which stay even after drying.
Sometimes, a little longer etch helps to get rid of
some of it, but not all.
I wanted to ask if anyone else has observed the same
and has some solution for it.
Also, we think it is because of glycerol residues
which is difficult to rinse away. Has anyone worked
with a lower glycerol concentration, and does it
shield the Al pads well?
Also, we were consdiering removing these crystals by a
O2 plasma etch. Is that recommended? Please suggest.
Thanks,
Anshu Mehta.
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