Hello all,

I need to etch ~7500A poly-Si patterned with S1813 resist and stop on Si3N4.
The etch tool is a batch process, non-loadlocked, parallel plate design with
13.5 MHz RF power to substrate electrode. Available process gases are CF4,
CHF3, and O2. I may be able to substitute SF6 for CF4, but cannot use
Cl-based chemistries due to safety concerns.

The literature indicates that CF4-O2 chemistry produces highest Si etch rate
at ~12% O2. I was thinking to run this mixture at low pressure and high RF
power to obtain a fast Si etch and some sidewall taper (need good metal step
coverage over the etched poly lines).

What is the typical Si/SiN selectivity under such conditions? Will
pressure/power significantly affect it? How does Si/SiN selectivity vary
with %O2 in a CF4-O2 process? SF6 will increase etch rate and reduce resist
loss, but are there other advantages to using it in this application?

I'd appreciate any recommendations and/or links to information. Thanks a
lot.

Boris