Selective in-situ carbon-based mask protection

Abstract

A method of etching an underlying layer includes performing a pretreatment step, a reaction step, and an etch step. The pretreatment step includes exposing surfaces of a patterned carbon-containing layer to oxygen to form C—O bonds at the surfaces with or without using plasma. The reaction step includes exposing the C—O bonds to an oxygen-reactive precursor to selectively form a mask protection layer on the surfaces of the patterned carbon-containing layer. The etch step is performed after the pretreatment step, and includes flowing an etchant gas and exciting plasma from the etchant gas to etch the underlying layer using the patterned carbon-containing layer as an etch mask. Any of the pretreatment step, the reaction step, and the etch step may be performed consecutively, concurrently, or repeated as a cycle.