To etch SiO2 you should use CHF3 for better stoichiometry. The sidewall
slopes will be more influenced by the amount of directional reactive ion
etch component versus chemical etching. Also, the buildup of polymers in
sidewalls, but that is more for poly etching I think.

So switch to CHF3 or even compounds with a higher ration of
Carbon/Hydrogen to Flourine and have a high bias on your wafer.

Ed

-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of liuxf
Sent: Monday, September 22, 2008 11:29 AM
To: mems-talk@memsnet.org
Subject: [mems-talk] CF4 RIE etch of SiO2

Hi all,

My SiO2 film thickness is about 200nm, and I want to open a hole with
diameter 3um so that to pass through my electrode. I wonder when I etch
it with CF4 plasma, will this have a bad aspect ratio? I mean probably
only the center of the hole is opened but the other area still has some
SiO2 left?

BTW: how about CHF3 compared with CF4?

thank you in advance
shane