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

摘要

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. The invention uses one of three hydrogen-free fluorocarbons having a low F/C ratio, specifically hexafluorobutadiene (C₄F₆), hexafluorocyclobutene (C₄F₆), and hexafluorobenzene (C₆F₆). At least hexafluorobutadiene has a boiling point below 10 C. and is commercially available. The fluorocarbon together with a substantial amount of a noble gas such as argon 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 (CH₂F₂) 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.