Hi Qing,
There is a good chance that hot Phosphoric acid will work
without attacking Silicon Oxide.  I have not tried it, but
Transene makes a chemical called "Transetch" with is
essentially concentrated Phosphoric acid--they claim it
etches Silicon Nitride at around 100 A/s (at 180 Deg. C) and
Silincon Dioxide < 5 A/sec.  I have the data sheet--if you
want to know the precise numbers, I can look it up for you.

-Bill

---- Original message ----
>Date: Thu, 1 Apr 2004 10:43:27 -0600
>From: "Qing Yao" 
>Subject: [mems-talk] how to remove Silicon Nitride
>To: "MEMS-talk" 
>
>Hi,
>
>
>I was wondering if H3PO4 (at between 160 to 180 degrees
centigrade) can
>remove Silicon Nitride without attacking Silicon Dioxide.
Are there any
>other methods I could use?
>
>
>Best Regards,
>
>
>Qing Yao
>___________________
>M&IE @ UIUC
>
>
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