In a message dated 12/26/2002 11:00:18 AM Central Standard Time,
[email protected] writes:

> forming gas in O2/CF4 etching (Joseph Chao)
>
Joseph,
Forming gas is used to reduce the oxide layer on these metals back to the
metal and this step then allows the metal to be etched.  The added benefit of
using a N2 plasma first prior to etching is that it heats up the wafers in
the chamber to a uniform temperature and you get much better etch uniformity
across the wafer.  Starting an etch cycle on cold wafer results in very high
etch rates at the edges and much slower in the center. This trick also works
for all other barrel etching of Nitride and oxide. I used this trick for
years to get great results.

Good Luck
Campman