Highly Selective Etching of SiO₂ over Si₃N₄ and Si in Capacitively Coupled Plasma Employing C₅HF₇ Gas

Abstract

In a dual-frequency-excited parallel plate capacitively coupled plasma employing a heptafluoro-cyclo-pentene (C 5 HF 7 ) gas with addition of O 2 and dilution in Ar gas, highly selective etching of SiO 2 at selectivities of 40 against Si 3 N 4 and 57 against polycrystalline Si was realized. Gas phase fluorocarbon species containing H atoms such as C x HF y ( x >2) played key roles in the selective deposition of thick hydrofluorocarbon films that covered the Si 3 N 4 and polycrystalline silicon (poly-Si) surfaces and in the selective etching of SiO 2 over the photoresist, SiN, and Si.