A DOE nano-tribological study of thin amorphous carbon-based films

A design of experiment (DOE) matrix of 150 nm non-hydrogenated amorphous C and Cr doped amorphous C films was produced to investigate the effect of four key coating process parameters (use of an adhesion layer, Cr magnetron current, cathodic substrate bias voltage and Ar flow to the chamber) using a new rapid method of nano-scale wear test under conditions relevant to MEMS and similar devices. The condition of nano-wear was produced by controlled oscillation of the sample mounting within a nanoindentation system under ultra-low normal load. Specific wear rates were low, typically in the range 6–24×10−17 m3 N−1 m−1. The results were processed using an analysis of variance (ANOVA) procedure which showed that: hardness was reduced in the Cr containing films whilst specific wear rate and data scatter increased, increasing the cathodic substrate bias voltage reduced the specific wear rate due to increased coating hardness, the use of a Cr adhesion layer reduced the specific wear rate and scatter of results with Cr doped films but had no effect on pure a-C films, and Ar flow rate had no significant effect on specific wear rate but strongly interacted with the effect of the cathodic bias voltage.