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.