US Patent 9779956 Hydrogen activated atomic layer etching

A method for selectively etching SiO and SiN with respect to SiGe or Si of a structure is provided. A plurality of cycles of atomic layer etching is provided, where each cycle comprises a fluorinated polymer deposition phase and an activation phase. The fluorinated polymer deposition phase comprises flowing a fluorinated polymer deposition gas comprising a fluorocarbon gas, forming the fluorinated polymer deposition gas into a plasma, which deposits a fluorocarbon polymer layer on the structure, and stopping the flow of the fluorinated polymer deposition gas. The activation phase comprises flowing an activation gas comprising an inert bombardment gas and H2, forming the activation gas into a plasma, wherein the inert bombardment gas activates fluorine in the fluorinated polymer which with the plasma components from H2 cause SiO and SiN to be selectively etched with respect to SiGe and Si, and stopping the flow of the activation gas.