Microstructure, residual stress, and fracture of sputtered TiN films

Abstract

Morphology, structure, residual stress, hardness, and fracture toughness of magnetron sputtered titanium nitride (TiN) thin films, deposited at 300°C with a thickness in the 0.3- to 2-μm range, were characterized. Film microstructure, the origin of residual stress, and its effect on the fracture toughness and hardness were analyzed. The grain size increased with the film thickness, with 1- to 2-μm-thick films having high pore density. For the 2-μm film, subgrains appeared at grain boundaries. X-ray diffraction showed (200) to (111) preferred orientation transition. The stress in the TiN films changed from highly compressive (−1.1GPa) to tensile with the film thickness, reaching 0.68GPa. Larger grain size, initial porosity, and subgrain generation are reasons for significant changes in the residual stress. Average hardness measured by nanoindentation is 23.2±0.6GPa. The hardness of the films in compression is higher than in tension. Hardness variation with the film thickness is mainly due to the grain size and microstructure effects. The fracture toughness decreases with the film thickness, depending on the stress state and value. Compressive stress can significantly improve TiN film fracture toughness, while tensile stress seriously degrades it.