Dear Xiaodong,

SF6/O2 is a very isotropic process. I suggest you try SF6/Ar for starter.
Keep SF6 around 10% of gas flow. Yes, it will be somewhat reactive sputter
etching. Can you cool your substrate to cryogenic temperature in your RIE
system? You may not want polymerization using CxFy gases to form on the
sidewall for your small feature size because your etching may halt at some
trench depth as your polymer closes up the neck of the trench.


Yours sincerely,

Isaac Chan
University of Waterloo