Enhancement of silicon oxide etch rate and substrate selectivity with xenon addition

Abstract

A plasma etching process, particularly useful for selectively etching oxide over a feature having a non-oxide composition, such as silicon nitride and especially when that feature has a corner that is prone to faceting during the oxide etch. A primary fluorine-containing gas, preferably hexafluorobutadiene (C F ), is combined with a significantly larger amount of the diluent gas xenon (Xe) to enhance nitride selectivity without the occurrence of etch stop. The chemistry is also useful for etching oxides in a time oxide etch in which holes and corners have already been formed, for example counterbore vias in a dual damascene structure. In this case, the relative amount of xenon need not be so high, but xenon still reduces faceting of the oxide corners. The invention may be used with related heavy fluorocarbons and other fluorine-based etching gases. The plasma etching preferably includes striking the plasma with argon, switching to xenon and the fluorine-based gas but at reduced bias power to stabilize the plasma, and then increasing the bias to a full etching level.