Yahong,

We have shown that etching doped oxides with an HF vapor process releases MEMS
devices leaving a much cleaner interface.  I hold a patent on this process
titled "Method of HF Vapor Release of Micromachined Structures".  Is the residue
only present on a
doped poly surface or on the silicon nitride surface also?  LPCVD oxides
deposited over highly doped silicon surfaces form an "N+ skin"  that is not
etched by HF.

Bob Cole
Research Scientist
The Aerospace Corporation





                      "Yahong Yao"
                                           cc:
                      Sent by:                 Subject: [mems-talk] residue
after etching doped oxide
                      mems-talk-admin@
                      memsnet.org


                      09/17/02 07:41
                      PM
                      Please respond
                      to mems-talk






Hey Colleagues,

Recently, I observed residue after etching doped oxide by HF.  Two kinds of
films:

1. PSG deposited by LPCVD.  This film is used as the sacrificial layer.
After etching by HF (49%), a blanket-sheet-like residue stays on the sample
surface.  This can be removed by Piranha but Piranha is not good for my
device at this point.

2. Phosphorous doped LTO.  This film also leaves residue on the sample
surface after etched by HF.  This residue is not like a blanket.  There are
some spots sticking on pattern edges.

Did anybody come across the same problem?  Any help is highly appreciated.
Thanks.

Yahong

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