Nonuniformity in void concentration between the initial and final growth stage of sputtereda-Ge films studied using spectroscopic ellipsometry

In this study $a$-Ge films were sputtered onto 60° vitreous silica prisms. The films were examined by spectroscopic ellipsometry at the prism-film and air-film interfaces. The void fraction was found to be significantly different near these two interfaces for an rf-sputtered film but almost the same for a dc-magnetron-sputtered film. This difference between depositions is related to a higher degree of energetic particle bombardment in the latter case. Previous studies of the thickness dependence of void fraction in the film were done on different films of various thickness, while the present measurements were performed on the same film and thus directly verify the nonuniformity in the void concentration in rf-sputtered films.