The profile becomes more overpassivated (positive profile)
at larger features sizes due to excess oxygen at the sidewalls
and underpassivated (undercut/bowing) at smaller feature
sizes due to lack of oxygen at the side walls.
-> download poster (
2.6 MB PDF file)
By adding LF bias, the profile uniformity across different
trench sizes can be increased.
The bias by LF allows a broader energy range of ions to
bombard the surface and decrease ion focusing.
This allows overpassivated larger features to be etched
the same as smaller features.
However, the increase in ion bombardment results in
a loss in selectivity from 20:1 down to ~7:1.
This results have been obtained at
Lawrence Berkeley National laboratory
in cooperation with OPT
Y. Wu, D.L Olynick, A. Goodyear,
C. Peroz, S. Dhuey, X. Liang, S. Cabrini