Process for etching oxide using hexafluorobutadiene or related fluorocarbons and manifesting a wide process window

Abstract

An oxide 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. One aspect of the invention uses one of four hydrogen-free fluorocarbons having a low F/C ratio, specifically hexafluorobutadiene (C F ), octafluoropentadiene (C F ), hexafluorocyclobutene (C F ), and hexafluorobenzene (C F ). At least hexafluorobutadiene has a boiling point below 10° C. and is commercially available. Another aspect of the invention, uses an unsaturated fluorocarbon such as pentafluoropropylene (C HF ), and trifluoropropyne (C HF ), both of which have boiling points below 10° C. and are commercially available. The fluorocarbon together with a substantial amount of a noble gas such as argon or xenon is excited into a high-density plasma in a reactor which inductively couples plasma source power into the chamber and RF biases the pedestal electrode supporting the wafer. Preferably, one of two two-step etch process is used. In the first, the source and bias power are reduced towards the end of the etch. In the second, the fluorocarbon is used in the main step to provide a good vertical profile and a more strongly polymerizing fluorocarbon such as difluoromethane (CH F ) is added in the over etch to protect the nitride corner. The same chemistry can be used in a magnetically enhanced reactive ion etcher (MERIE), preferably with an even larger amount of argon.