Plasma Etching of SiON Films Using Liquefied C7F14 Gas as Perfluorocarbon Alternative

Abstract

In this study, we evaluated the possibility of replacing existing perfluorocarbon gas with C7F14, which can be recovered in its liquid state from room-temperature air. We performed plasma etching of SiON films using the CF4 + X + O2 mixed gas, where X = CHF3, C4F8, or C7F14, and examined the etching characteristics of the films (e.g., etching rate, etching profile, and selectivity over Si). Using contact angle goniometry, atomic force microscopy, and X-ray photoelectron spectroscopy, we analyzed the physicochemical changes in the etched SiON film surface. Moreover, optical emission spectroscopy and double Langmuir probe measurements were carried out for plasma diagnosis. Compared with the conventional CHF3 and C4F8 mixed plasma, the C7F14 mixed plasma exhibited a more perpendicular etching profile with higher SiON/Si selectivity and a smoother surface.