Infinitely high etch selectivity of Si₃N₄ layer to ArF photoresist in dual-frequency superimposed capacitively coupled plasmas

Etch rates of Si3 N4 and ArF photoresist (PR) in the C H2 F2 H2 Ar dual-frequency superimposed capacitively coupled plasmas are controlled by the hydrofluorocarbon layers that deposit on the Si3 N4 and PR surfaces. The thickness of the hydrofluorocarbon layers depends on C H2 F2 and H2 flow rates in the plasma chemistry. The differences in etching behaviors between Si3 N4 and PR at certain H2 flow regimes is due to the ability of Si3 N4 layer to consume the hydrofluorocarbon layer by forming HCN and Si F4 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 Si3 N4 PR etch selectivity exits at a certain process window.