Nanopore Structure of Sputtered Silica Thin Films Probed by Spectroscopic Ellipsometry and Variable-Energy Positron Annihilation

Abstract

Nanopore structure of silica thin films prepared by magnetron sputtering under various conditions was investigated by spectroscopic ellipsometry and variable-energy positron annihilation. Film overall porosity, evaluated by ellipsometry, was found to decrease, asymptotically to zero, with decreasing argon pressure and film thickness. This result is in qualitative agreement with our oxygen gas permeability data of silica films on polymeric substrate. Positron annihilation showed that nanometer-size pores were present in films prepared at an argon pressure of 1.5 Pa, whereas subnanometer-size pores were present in films prepared at an argon pressure of 0.25 Pa. In both cases, the pore sizes were decreased with decreasing film thickness.