The HF etch of silicon nitride depends strongly on what type of silicon nitride is exposed. LPCVD silicon nitride, both stoichiometric and silicon-rich, etches slowly. PEVCD silicon nitride is really SixNyHz, containing a lot of hydrogen, and can etch rapidly. --Kirt Williams -----Original Message----- From: mems-talk-bounces+kirt_williams=sbcglobal.net@memsnet.org [mailto:mems-talk-bounces+kirt_williams=sbcglobal.net@memsnet.org] On Behalf Of Morrison, Richard H., Jr. Sent: Wednesday, June 08, 2011 3:24 AM To: General MEMS discussion Subject: Re: [mems-talk] Ti wet etch with selectivity to Si3N4 You should be able to etch Ti on Nitride, the HF etch rate of Nitride in 10% HF should be very low and 1000A of Ti will etch in 40 seconds. The mixture of NH4OH:H2O2:H2O (1:1:5) will etch Ti very fast and it will not etch Nitride at all. However, resist will not stand up to the mixture. Rick Morrison Senior Member Technical Staff Acting Group Leader Mems Fabrication Draper Laboratory 555 Technology Square Cambridge, MA 02139