Inhomogeneous refractive index of SiOXFY thin films prepared by ion beam assisted deposition

Silicon oxyfluoride thin films with refractive indices lower than SiO2 thin film were fabricated by a CF4 ion beam-assisted deposition and the optical, chemical and mechanical properties of them were investigated. Si or SiO2 as a source material was evaporated by an e-beam gun in the O2 backfilled chamber. When Si was evaporated, silicon oxyfluoride films turned out to be inhomogeneous in the refractive index and the average index of the SiOxFy films was varied from 1.41 to 1.44. When SiO2 was evaporated at a high oxygen partial pressure, they were homogeneous and the lowest index was 1.23. FTIR measurements showed the SiF2 bond at approximately 936 cm−1 and SiOphenyl bond at approximately 948 cm−1, respectively. SEM, XPS, and RBS measurements showed that the CF4 ion beam bombardment on growing SiO2 films induces an inclusion F as well as a porosity in the films and results in the low index of Silicon oxyfluoride films.