Satish,

Cl2 at a very low pressure will work with selectivity's around 50 to 1.
You will need a turbo.

You do not have the gasses, but here are some that will work at the 20 to 60
mtorr pressure ranges:

H2 + CF4 around 4:1 gas ratio.  You can get excellent selectivity if you are
willing to sacrifice Oxide etch rates.

CHF3 + CF4 around 1:1.  You can get 5:1 oxide to Si selectivity's.

Ad Hall
StarCryoelectronics
ahall@starcryo.com

-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org]
On Behalf Of "
Sent: Thursday, April 10, 2008 1:16 PM
To: " General MEMS discussion" < mems-talk@memsnet.org>
Subject: [mems-talk] Best plasma chemistry for SiO2/Si selectivity

Hi all

I am wondering if someone can suggest me a good plasma chemistry to
get a very good selectivity between SiO2 and Si

I am using Trion's minilock phanthom III series ICP RIE etch system. I
have access to Ar, N2, O2, BCl3, Cl2, CF4 gases.

CF4 is etching both Si and SiO2, even Cl2/BCl3 combination is etching
both.