Plasma Etching of SiO₂ Contact Holes Using Hexafluoroisopropanol and C₄F₈

This study presents the feasibility of the use of hexafluoroisopropanol (HFIP) as a substitute to perfluorocarbon (PFC) for the plasma etching of SiO₂ to confront the continuous increase in demand for PFC emission reduction. SiO₂ etching is conducted in HFIP/Ar and C₄F₈/Ar plasmas, respectively, and its characteristics are compared. The SiO₂ etch rates in the HFIP/Ar plasma are higher compared with those in the C₄F₈/Ar plasma. The thickness of the steady-state fluorocarbon films formed on the surface of SiO₂ are lower in the HFIP/Ar plasma compared with in the C₄F₈/Ar plasma. Higher SiO₂ etch rates and thinner fluorocarbon films in the HFIP/Ar plasma are attributed to the oxygen atoms in HFIP, which generate oxygen radicals that react with the fluorocarbon films to turn into volatile products. Due to the higher dissociation of C-F bonds in CF₄ compared with in HFIP, the etch rates of SiO₂ in the C₄F₈/Ar plasma increase more rapidly with the magnitude of the bias voltage compared with those in the HFIP/Ar plasma. The etch profiles of the 200 nm diameter SiO₂ contact holes with an aspect ratio of 12 show that fairly anisotropic SiO₂ contact hole etching was achieved successfully using the HFIP/Ar plasma.