A factorial analysis of the preparation and properties of a-C:H thin films

Abstract

A 2 3 factorial analysis was used to study the effects of rf input power, nitrogen added to the discharge, and post-deposition annealing on the optical properties of amorphous hydrogenated carbon (a-C:H) thin films. CH 4 , H 2 , and Ar, seeded with N 2 , were used as source gases to grow films using plasma enhanced chemical vapor deposition (PECVD). Multi-angle ellipsometry and spectrophotometry were used to derive information on film thickness, refractive index, extinction coefficient, and optical band gap. The factorial approach confirmed results from previous single-variable studies and permitted interaction effects to be quantified. Variable dependencies support the conclusion that a-C:H films are made up of graphite clusters in a matrix of highly crosslinked diamond-like phases and/or soft polymeric components. Medium range order introduced by the graphitic clusters determines the optical properties of a-C:H.