Characterization of oblique deposited nanostructured SiOx films by ellipsometric and IR spectroscopies

Studies of oblique deposited nanostructured SiOx films by ellipsometric and IR spectroscopies are presented, as additional information is obtained by scanning electron microscopy (SEM). The films were deposited onto Si substrates under a 75 degrees incidence vapor by vacuum evaporation of SiO and were annealed in Ar at 950 degrees C. The thickness and composition of the films were estimated from the ellipsometric data analysis applying the Bruggeman effective approximation theory. Three-layer optical model described satisfactory the annealed film structure and verified the formation of nanocrystalline Si clusters. SEM micrographs showed that evaporated films consisted of silicon oxide pillars separated by air space and tilted at an angle of similar to 57 degrees to Si substrate surface. The thin silica pillars were most probably free from Si-SiO2 interface leading to absence of strong absorption on LO vibrations in the IR spectrum. The estimated porosity factor was similar to 62 %. By annealing, the film oxidized to SiO2 but it remained columnar with a porosity factor of similar to 47 %.