Dear Yu,

did you ever consider using HF vapor instead of BOE?  We have been using this
method just recently to make nanobeam cavities and used HF vapor to remove the
sacrificial oxide. The devices were fabricated on a  SOI substrate (SOITEC Inc.)
with a device layer of 220nm and an insulator layer of 2um. In this case you
have almost no problems with the selectivity between the oxide and nitrite +
the amount of HF used is minimal. Commercial systems are available for
comparatively little cost (check ammt.com)

Good luck,
Chris.


----- Original Message ----
From: Yu Wang 
To: General MEMS discussion 
Sent: Thursday, May 14, 2009 7:15:15 PM
Subject: [mems-talk] Selectivity of etching LTO over sputtered silicon nitride
using BHF/BOE

Hi,  I want to release my sacrificial LTO (deposited by LPCVD) layer uisng
BHF/BOE, and would like to know wether the selectivity over silicon nitride
(sputterred at room temperature and a rate of ~1.5nm/min) varies with the
NH4F:HF ration in BOE? Does the selectivity increases or decreases with the
ratio?  Any answer will be appreciated.  Thanks,  Yu Wang