Local crystal structure and mechanical properties of sputtered Ti-doped AlN thin films

In this article, we predominantly report the investigation of the local crystal structure around a Ti dopant by X-ray absorption spectroscopy (XAS) and the nano-mechanical properties of co-sputtered Al1-xTixN (x = 0 to 4%) thin films. Grazing incidence X-ray diffraction (GIXRD) results show that these films are crystallized with the hexagonal wurtzite structure of AlN. Surface chemical analysis and morphology analysis of Al1-xTixN films are executed using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques, respectively. X-ray absorption near-edge structure (XANES) shows that a Ti atom replaces Al in the AlN crystal and forms localized distorted tetrahedral TiN species, leading to a tensile strain. The bond lengths (Ti-N)ax and (Ti-N)bs are found to be moderately decreased with increasing Ti concentration, which is extracted from the extended X-ray absorption fine structure (EXAFS) analysis. However, the Ti-Al bond length in the second coordination sphere having Al vacancies is unaffected by Ti concentration. The hardness (H) and modulus (E) of Al1-xTixN films are measured by the nano-indentation technique, and increase from 17.5 to 27.6 GPa and 231 to 293 GPa, respectively with x = 0 to 4 at% because of the improvement of p-d hybridization between the Ti and N atoms.