Fracture properties of hydrogenated amorphous silicon carbide thin films

The cohesive fracture properties of hydrogenated amorphous silicon carbide (a-SiC:H) thin films in moist environments are reported. Films with stoichiometric compositions (C/Si approximate to 1) exhibited a decreasing cohesive fracture energy with decreasing film density similar to other silica-based hybrid organic-inorganic films. However, lower density a-SiC:H films with non-stoichiometric compositions (C/Si approximate to 5) exhibited much higher cohesive fracture energy than the films with higher density stoichiometric compositions. One of the non-stoichiometric films exhibited fracture energy (similar to 9.5 J m(-2)) greater than that of dense silica glasses. The increased fracture energy was due to crack-tip plasticity, as demonstrated by significant pileup formation during nanoindentation and a fracture energy dependence on film thickness. The a-SiC:H films also exhibited a very low sensitivity to moisture-assisted cracking compared with other silica-based hybrid films. A new atomistic fracture model is presented to describe the observed moisture-assisted cracking in terms of the limited Si-O-Si suboxide bond formation that occurs in the films. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.