As noted, the dominant process for etching Silicon Nitride is Hot Phosphoric
Acid. Typically this is done in a heated quartz tank with condensing collar
and lid to retain water vapor.

It is typically done in the 155 to 180°C range with higher etch rates being
achieved at higher temps. Common control methods for this process inject
water based on the temperature. Since the solution should be always boiling,
water injection is used to maintain acid concentration and thereby also
controlling the temperature. Good controls will provide very good uniformity
and safe operation.

Mark West
Imtec Acculine, Inc.

-----Original Message-----
From: antwi nimo [mailto:nimoantwi1980@yahoo.com]
Sent: Thursday, May 27, 2010 4:33 AM
To: mems-talk@memsnet.org
Subject: [mems-talk] SiliconNitride etch with selectivity to Oxide

Hi everyone,

I was wondering what is the best way to etch both stoichiometric(Si3N4) and
high concentration silicon Nitride with selectivity to oxide(thermal oxide).
I have been reading the LOCOS process and have come accross Phosphorus
solution and so on but would like to ask some practical experience in
etching Nitride with selectivity to oxide as i have no experience. May be
the methods used and the etch rate between Si3N4 and oxide if any.

Thanks in advance for any help.
Nimo