Hi Kishore,

     The conditions would depend on your own criteria.  How thick is your
device layer, concentration and temperature of HF being used, stresses in
the structure, what is the purpose of the structure being released, amount
of time to consider incompatibilities, etc.  If you are just looking for
general information, I would recommend 2-5 um holes for a 50 um thick layer
because the etching will be limited by the thickness of the oxide layer and
not to the size of your hole. Have a symmetric arrangement of holes if you
want the structure to release uniformly.  Conduct an etch profile and hole
redesign to compensate for structural stress which can produce unwanted
silicon "divots".  Also use a microscope equipped with an IR camera to
determine the actual etch rates for your particular device and oxide
quality.  Good luck.

Phillipe Tabada

divots = created from high stressed structures during release as to rip out
silicon particles either from the device and/or substrate layer.



>From: Kishore Sundara-Rajan 
>Reply-To: kishore@u.washington.edu,General MEMS discussion
>
>To: mems-talk@memsnet.org
>Subject: [mems-talk] Oxide Release - Etch Holes
>Date: Tue, 24 Aug 2004 11:24:55 -0700
>
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>Hi All,
>       I have a rectangular structure of about 200 microns * 1200 microns.
>This structure has to be released using a 2000 A sacrificial oxide layer
>underneath it. I was wondering if someone could point me to resources
>that would give me a good idea as to how big and how many etch holes I
>need in the structure to release it using either HF or CO2 critical
>drying. Any input would be appreciated.
>Thanks,
>Kishore
>
>______________________________________________________________________________
>Kishore Sundara-Rajan                  Dept. of Electrical Engineering
>Graduate Research Assistant            University of Washington
>kishore@u.washington.edu               Campus Stop 352500
>Mobile : (206) 351-8101                        Seattle WA 98105
>Fax    : (206) 632-3080                        Office : (206) 221-6673
>http://students.washington.edu/kishore www.kishore-sr.com
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