Structural and mechanical properties of titanium-aluminium-nitride films deposited by reactive close-field unbalanced magnetron sputtering

Titanium-aluminium-nitride (Ti1-xAlxN) films were deposited onto unheated silicon (100) substrates by reactive close-field unbalanced magnetron sputtering at a pulsed-bias voltage of -50 V in an Ar-N-2 gas mixture. The effects of aluminium content (x) on structural and mechanical properties of these films have been studied. The films were analyzed by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, X-ray diffraction (XRD), cross-sectional scanning electron spectroscopy (SEM), atomic force microscopy (AFM) and nanoindentation measurements. By XPS the stoichiometric composition of TiN and AlN was found as forming a ternary phase of Ti-Al-N, while no unbound Al and Ti atomic species were detected in films. The Raman scattering spectra of the films within the whole range of x values were investigated. Four peaks at 242, 320, 5 10 and 640 cm(-1), arisen from the transverse acoustic, longitudinal acoustic, second-order transverse acoustic and transverse optical modes of Ti-AI-N phase, respectively, were observed in Raman spectra. The XRD theta-2theta scans exhibited the structural changes in Ti1-xAlxN films with different Al contents. The films were essentially cubic Bl-NaCl TiN with (111) oriented grains in the range of x = 0 to 0.48. A two-phase structure consisting of B I -NaCl (TiN) and B4-wurtzite (AlN) was observed at x = 0.57, while at higher A] contents, a single-phase structure of B4-wurtzite AlN with (0002) and (1011) grains was formed. The films at x = 0.41 had hardness of approximately 31 GPa, Young's modulus of 315 GPa, and an excellent plasticity (32% in indentation deformation) at loads exceeding their elastic limit. Nanoindentation measurements combined with AFM and cross-sectional SEM revealed that the improved mechanical properties of Ti1-xAlxN films with the addition of Al into TiN compound were attributed to their densified microstructure with development of fine grains and reduced surface roughness. (C) 2004 Elsevier B.V. All rights reserved.