Bob is definitely on the right track with his chrome
process. However, I might recommend less O2 (more like
a 3:1 Cl2:O2 ratio) and less RIE power. I guess it
depends on what type of machine your are using and how
well it keeps cool. If you have an ICP available it
definitely improves the rate and will allow you to run
a lower bias power. Count on an etch rate of
approximately 25 nm/min and a selectivity of 0.75:1.
Depending on the resist and the exposed area of
chromium, you might be able to get to 50 nm/min with a
selectivity of 2:1. This process will also take off
chromium oxide, which is typically the top layer on a
photo mask, but a slower rate than chromium.

Regards,

Michael Marrs