Plasma etching processes using a plasma containing fluorine as well as bromine
and/or iodine are suited for high aspect ratio etching of trenches, contact holes
or other apertures in silicon oxide materials. The plasma is produced using at
least one fluorine-containing source gas and at least one bromine- or iodine-containing
source gas. Bromine/iodine components of the plasma protect the aperture sidewalls
from lateral attack by free fluorine, thus advantageously reducing a tendency for
bowing of the sidewalls. Ion bombardment suppresses absorption of bromine/iodine
components on the etch front, thus facilitating advancement of the etch front without
significantly impacting taper.
