Hi Serena,

I suggest to try CF4/O2 (about 5% of O2). Make sure your pressure is below 50
mtorr.
This should work pretty well. And of course your RIE chamber should be well
descummed before the process of RIE etching.

Regards,

Dr. A.Yu. Rusanov
Institute of Solid State Physics, RAS,
Lab of Superconductivity/Lab of Nanolithography


} Hi,
} I'm trying to make 70nm wide (50nm deep) Nb trenches separated by about 100 nm
(edge-to-edge).  With Al2O3 as an etch mask, I've been using SF6/O2 RIE to try
to etch away the Nb.
} (20sccm SF6 and 0.6  sccm O2, 60 mtorr, 60W)
} I think my Nb is being completely undercut (all Nb under the 70nm wide Al2O3
etch mask is being etched away).
} How can I rid of the undercut?  Is it possible?  Is my pattern too small to
use RIE? I know I should reduce the pressure to less than 10mtorr, but what
else? Should I try CHF3/CF4?
} Thanks,
} Serena