Andrea,
If you used nitride other than LPCVD nitride - it will be etched by hot KOH.
Also, even LPCVD nitride etches slowly in hot KOH. One reason for higher
etch rates in KOH is fluoride leftovers in the solution from HF or BOE
cleans prior to KOH

shay

-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org]
On Behalf Of Andrea Mazzolari
Sent: Monday, May 21, 2007 11:01 PM
To: General MEMS discussion
Subject: [mems-talk] silicon nitride etch by koh?!

Hi all,
i deposited about 20nm of silicon nitride on a silicon wafer.
After patterning silicon nitride, i etched silicon in KOH (20%) at 100°C.
After about 2 hours etch, silicon nitride was completely removed!
I always knew silicon nitride perfecly mask against KOH etch!
What could be happened ?