Investigation of fracture properties of magnetron-sputtered TiN films by means of a FIB-based cantilever bending technique

A cantilever bending technique for the determination of mode I fracture toughness and strength of thin films is presented. First, the depth profile of residual stresses in the film is determined in order to investigate the possible existence of pronounced stress gradients. Then cantilevers, about 70 μm in length and consisting of the film and the substrate, are fabricated by means of a focused ion beam workstation. The beams are loaded with an in situ microindenter until fracture, which allows the fracture toughness and the strength of the thin film to be calculated from the load-deflection curve and the residual stresses to be determined. The method is presented by investigating the fracture properties of a 1.1-μm thick magnetron-sputtered TiN film on Si, leading to a fracture toughness of 2.6±0.3MPam and a strength of σf=4.4±0.5GPa. Finally, the influence of the compressive residual stresses on the structural integrity and the role of the grain boundary strength are discussed.