Selective etching of silicon nitride using remote plasmas of CF4 and SF6

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Abstract
Silicon nitride is etched using a remote plasma discharge of CF4 or SF6, diluted in a He or N2 carrier gas. By itself, this process chemistry does not etch silicon nitride selectively, a desirable property of a useful process; however, by including a source of abstractable hydrogen, e.g., H2 or CH4, in the process mix, the Si3N4 :Si and Si3N4 :SiO2 etch rate ratios can be considerably increased. The hydrogen source serves to consume atomic fluorine, enhancing the preferential deposition of a fluorocarbon layer on Si and SiO2 (in the case of CF4 ). This fluorocarbon film impedes Si and SiO2 etching by atomic F. For SF6 , some form of etch-impeding surface layer also may be formed.

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