US Patent 11171011 Method for etching an etch layer

A method of forming a feature in a stack comprising a dielectric material on a substrate is provided. An etch plasma is generated from an etch gas, exposing the stack to the etch plasma and partially etching the feature in the stack. The stack is primed. A protective film is deposited on sidewalls of the feature by repeating for a plurality of cycles the steps of exposing the stack to a first reactant, allowing the first reactant to adsorb onto the stack, and exposing the stack to a second reactant, wherein the first and second reactants react with one another to form the protective film over the stack. The etching, priming, and depositing a protective film are repeated until the feature is etched to a final depth.