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