Effect of thermal treatment on the hardness and fracture toughness of sputter deposited bi-layered thin films on silicon

Microhardness testing is widely used for characterizing the mechanical properties of both bulk materials and thin films. Although this technique is usually associated with hardness measurements, fracture properties of brittle materials can also be studied with cracking associated with microhardness indentations. It is well known that the length of radial cracks emanating from the corners of indents made with Vickers and Berkovich indenters is related to the fracture toughness of the material. In the present study, microhardness testing has been used to follow the evolution of the mechanical properties of a 10 nm. Cu/200 nm. Ni(V)/300 nm. Al(Cu) thin film deposited on a Si substrate. Composite hardness and fracture toughness have been followed as a function of heat treatment temperatures and times and were found to be dependent on both variables. The roles of residual stresses, interdiffusion, and intermediate phase formation in the observed variation in hardness and fracture toughness are discussed.