How are you rinsing the BOE? Are you sure that you have displaced the BOE
completely with DI and then Methanol? Seems like you are pretty careful
with rinsing but that would be my first suspection.

Another guess is that the flushing of Methanol with CO2 is not complete. At
UCLA we used to flush the chamber about 10-15 times (Roughly 20 minutes)
continuously. You are only flushing for a total of 6 minutes.

What grade of CO2 are you using? Some grades come with a bit of oil. They
will cause stiction as well. Try spectroscopy grade CO2.

The haze in the chamber is not that big of a deal assuming that there is
only CO2 present. They might just be localized inhomogeniety. We used to
seem them in our Polarion chamber.

Good luck.

Henry Yang
IBM Almaden Research Center
408-927-2319

"Sang Park" @memsnet.org on 04/11/2002 10:27:56 AM

Please respond to mems-talk@memsnet.org

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Subject:    [mems-talk] Critical point drying.



Hi, all.
I am using the SPI critical point drying apparatus form PSI supplies
(division
of Structure Probe, Inc.) to release comb-finger structures (0.5um wide,
0.5
um thick, and 10um long) on 1 um thick SiO2 on a Si substrate. I usually
use
Buffered Oxide Etchant to remove SiO2 under comb-finger structures to be
released without any atiction problem. After I put my sample in the ample
boat
with methanol, I load the boat into the critical point drying apparatus.
Then
I flush with CO2 for about 3 minutes and wait for 30 minutes for methanol
and
CO2 to be mixed well. And I do flusing agian for 3 minutes and the
apparatus
is heated up above 35C with the pressure of more than 1300 psi. After I
wait
for 10 minutes or so, I vent the CO2 gas.
But there is the point I have a problem. While I'm venting the CO2, I
notice a
little haze generated and that can be seen by my own eyes.
After finishing the venting and taking out the sample, I noticed some parts
are o.k., but some parts, especially the end of suspended structurs, are
stuck
to the substrate.
Please send me any processing tips to solve this problem.
Thanks.

=================================
Sang Won Park
Graduate Research Assistant
Electrical Engineering
The University of Texas at Dallas
Phone) 972 - 883 - 2893
Fax) 972 - 883 - 6839
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