Hi,

I'm trying to find a good RIE recipe for anisotropically etching Si
(crystalline and poly-Si) and SiN while maintaining straight and as smooth
as possible sidewall profile. I'm using a metal etch mask (have tried both
Cr and Ni) and would like some selectivity over SiO2, though high
selectivity is not crucial. I would like to be able to etch vertically as
much as possible, my current goal is 2um. I have a plasma therm RIE system
with the following gases

Channel1 Ar, CH4, He
Channel2 O2, H2
Channel3 SF6, CBrF3, CHF3, CF4
Channel4 Cl2

All combinations of gases I have tried with O2 seem to give poor sidewall
profile. My latest attempt was CF4/H2 with the hope of forming some polymer
passivation on the sidewalls though this the etch rate of crystalline Si
seems too slow in this process and my mask is not holding up to as deep an
etch as I want (also no selectivity to SiO2).

If anyone has any suggestions I would greatly appreciate it! I have read
that etching with Cl or Br may improve the process and give selectivity to
SiO2 though I have no experience myself with those gases.

Thanks!

Nate Lawrence
PhD Candidate
Department of Electrical and Computer Engineering,
Boston University