Indentation fracture of a-C:H thin films from chemical vapour deposition

Abstract

Thin films of a-C:H were produced by chemical vapour deposition from butene and butadiene gases on silicon. Hardness, elastic modulus and residual stress of the films vary depending on the voltage bias and chamber pressure during deposition. Films obtained with voltage bias of −200 V and chamber pressure of 8 Pa for the two precursor gases were analyzed. Film thicknesses were about 900 nm and hardness was 6.6 GPa for film from butadiene gas and 7.9 GPa for butene gas. Cube-corner and Berkovich indenters were used to produce indentation fracture on these films. Crack initiation, delamination and chipping were correlated to modifications of load versus displacement curves. Fractography of cracks was made by scanning electron microscopy and atomic force microscopy. Cracks generated by indentation with cube-corner and Berkovich indenters were compared. Delamination could be analyzed from the derivative of load versus displacement curves. Samples that present higher hardness values do not show chipping. Indentation energy before and after chipping events, calculated from load versus displacement curves for cube-corner and Berkovich indenters are compared. A careful analysis of load versus displacement curve is a very powerful tool to analyze sequence of fracture events of indentation on a-C:H films.