The stability and degradation of PECVD fluoropolymer nanofilms

Abstract

Fluoropolymer films are frequently used in microfabrication and for producing hydrophobic and low-k dielectric layers in various applications. As the reliability of functional coatings is becoming a more pressing issue in industry, it is necessary to determine the physical stability and degradation properties of this important class of films. To this end, a study has been undertaken to ascertain the aging characteristics of fluoropolymer films under various environmental conditions that such a film may experience during its use. In particular, fluorocarbon films formed by plasma-enhanced chemical vapour deposition (PECVD) using octafluorocyclobutane, or c-C4F8, as a precursor gas have been exposed to abrasive wear, elevated temperatures, ultraviolet radiation, as well as oxygen plasma and SF6 plasma, the latter being commonly used in conjunction with these films in ion etching processes. The results show that sub-micron thick fluoropolymer films exhibit a significant amount of elastic recovery during nanoscratch tests, minimising the impact of wear. The films exhibit stability when exposed to 365 nm UV light in air, but not 254 nm light in air, which generated significant decreases in thickness. Exposure to temperatures up to 175 °C did not generate loss of material, whereas temperatures higher than 175 °C did. Etching rates upon exposure to oxygen and SF6 plasmas were also measured.