Leonardo,

I run a process with similar chemistry in a Trion ICP-RIE at 15 mTorr with
350 W ICP and 70 W RIE, CHF3/O2 125/9 and achieve very good results with
anisotropic oxide etching (however, I don't use ZEP as an etch mask). If you
can't use an ICP-RIE system, your best bet is to use as low a pressure as
possible.

Good luck,
Evan Lunt

---------- Forwarded message ----------
From: Leonardo Lesser-Rojas 
To: mems-talk@memsnet.org
Date: Fri, 4 Dec 2009 15:05:56 +0800
Subject: [mems-talk] How to improve an RIE process
I am using a CHF3/02 RIE process in an Oxford 80Plus etching reactor that
uses ZEP520 e-beam resist as a mask to etch  shallow features on SiO2
(40-50nm deep) and that achieves almost anisotropic profiles (a bit barrel
like but ok).  However the slight undercut (10/15 nm) will make the very
thin features on the mask (6-15 nm or so resist stripes  between exposed
areas ) to be removed away during the etching process, I guess the undercuts
though small, overlap under the stripe.  What can be done to improve that?
 Power reduction, gas reduction, or pressure reduction?  The current
conditions are Power=200W, P50 mtorr CHF3/O2 50/2 sccm.  I don't have much
samples to study the behavior and must try first shots...any suggestions are
highly appreciated.

Best regards

Leonardo Lesser

Ph.D. Student at Nanobioscience Lab
Institute of Physics
Academia Sinica, Taiwan R.O.C.