Etch rates of Si3N4 and ArF photoresist (PR) in the CH2F2/H-2/Ar dual-frequency superimposed capacitively coupled plasmas are controlled by the hydrofluorocarbon layers that deposit on the Si3N4 and PR surfaces. The thickness of the hydrofluorocarbon layers depends on CH2F2 and H-2 flow rates in the plasma chemistry. The differences in etching behaviors between Si3N4 and PR at certain H-2 flow regimes is due to the ability of Si3N4 layer to consume the hydrofluorocarbon layer by forming HCN and SiF4 etch by-products while the hydrofluorocarbon layer is deposited and not consumed on the PR surface. As a result, a process window for an infinite Si3N4/PR etch selectivity exits at a certain process window. (c) 2006 The Electrochemical Society.