I see some problems with this.

1. CF4 will have difficulty in etching SiO2. The stoichiometry is unbalanced.

2. The anistropic or isotropic nature of a plasma etch is driven by the
substrate to plasma bias and not the chemistry.

3. When SiO2 is etched with CHF3 or something with a lower F:C ratio, it needs
an Reactive Ion Etch where there is a carbon residue and bombarment of this
residue by use of a bias to drive a Carbon oxygen reaction to facilitate the
etching of SiO2. This is inherently anisotropic.

4. If you need to etch isotropically 5 microns, I would use a wet etch solution
which is inherently isotropic.

Ed

-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org] On
Behalf Of Sebastian Sosin
Sent: Monday, October 06, 2008 4:00 AM
To: mems-talk@memsnet.org
Subject: [mems-talk] SiO2 isotropic plasma etch


I need to etch 5 microns of sacrificial PECVD SiO2 using isotropic plasma etch.
Does anyone have any experience with this? I have seen that in literature CF4 is
mentioned to be isotropic plasma but not too many details.
Any extra info will is welcome.

Sincerely yours,

Sebastian Sosin