Travis, It could be, though I am not at all sure, that the reason the
aluminum etch rate went down with heating, which one would not expect, is
that when heated the rate of aluminum oxide formation went up forming a more
protective layer.  Hope this helps, could you tell by the appearance.  Gary

Gary Hillman
Service Support Specialties, Inc.
PO Box 365
9 Mars Court
Montville, NJ 07045
Telephone 973-263-0640 extension 35
Fax 973-263-8888

-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org]On Behalf Of Xiaoning Wang
Sent: Saturday, November 17, 2007 12:36 PM
To: mems-talk@memsnet.org
Subject: [mems-talk] Another question about silicon dioxide wet etching


Hello everyone!

I am a undergraduate student in Peking University, China.

I have been doing some experiments on silicon dioxide sacrificial layer
etching lately. And I used 4 parts NH4F (40%), 2 parts glycerin and 1 part
HF(40%) as the etchant. I noticed that the etching rate of silicon dioxide
was about 5000A/min at room temperature, far above those rates reported in
literatures even without heating. Can the fabrication method of SiO2 make
such a big difference in etching rate? Or is there any other possible
explanations for that?

Also, I found that Aluminum's etching rate was lower when the etchant
solution's temperature increased. Does that make any sense? Since normally
the etching rate should go up when heated, right? I tried to explain this
from a chemical kinetics' point of view, but was limited because of my major
(electrical engineering). So was that I screwed up my experiments? (though I
hope it's not likely) Or would anyone can tell me the reason, please?

Thank you for your time!

Best wishes!

btw, are there any differences between glycerin and glycerol? Their Chinese
meanings are exactly the same.