Hi Kamlesh, Most likely the reason is one of the following: 1. Your PR was not able to withstand BHF for 8 mins and got stripped off exposing the underlying SiO2. You will know that once you look under the microscope. 2. You used PECVD/LPCVD oxide instead of thermal oxide. In this case the oxide etch rate is very high if you use BHF and it laterally etched through your 6 micron channel width in 8 mins stripping the PR on top and eventually leaving nothing behind. If this is the case I suggest you use 1:10 DHF (dilute HF). Hope it helps. Regards, Mantavya -----Original Message----- From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org] On Behalf Of kamlesh_engg@iitb.ac.in Sent: Tuesday, September 16, 2008 3:47 PM To: mems-talk@memsnet.org Subject: [mems-talk] problem in BHF etching hi i am doing BHF etch on silicon dioxide deposited on silicon wafer. i am using 5:1 BHF etchant etch rate 120 nm/min i want to etch 1 micron deeep channel with 200 micron width. there are multiple channels in parallel each seprated by 6 micron. so i diped my sample in BHF for 8.33 min but after the etch no channels was formed and everything is etched away. can anyone tell me what could be the problem ??? -- Kamlesh Pawar M.Tech (Biomedical Engg) Mob :+919870062960 IIT-Bombay