US Patent 10079154 Atomic layer etching of silicon nitride

A method for selectively etching SiN with respect to SiO or SiGe or Si of a structure is provided comprising providing a plurality of cycles of atomic layer etching. Each cycle comprises a fluorinated polymer deposition phase comprising flowing a fluorinated polymer deposition gas comprising a hydrofluorocarbon gas into the plasma processing chamber, forming the fluorinated polymer deposition gas into a plasma, which deposits a hydrofluorocarbon polymer layer on the structure, and stopping the flow of the fluorinated polymer deposition gas into the plasma processing chamber and an activation phase comprising flowing an activation gas comprising at least one of NH3 or H2 into the plasma processing chamber, forming the activation gas into a plasma, wherein plasma components from NH3 or H2 cause SiN to be selectively etched with respect to SiO or SiGe or Si, and stopping the flow of the activation gas into the plasma processing chamber.