Structure and mechanical properties of TiAlTaN thin films deposited by dcMS, HiPIMS, and hybrid dcMS/HiPIMS

Abstract

The quaternary Ti1-x-yAlxTayN system exhibits superior thin film properties compared to Ti1-xAlxN. Apart from the Ta content, the sputtering method has a crucial effect on the structural and mechanical properties. High power impulse magnetron sputtering (HiPIMS) produces denser thin films with improved hardness compared to direct current magnetron sputtering (dcMS), but at lower deposition rates. However, a hybrid dcMS/HiPIMS process combines the advantages of dcMS and HiPIMS and is, therefore, a suitable method to synthetize Ti1-x-yAlxTayN thin films. To analyze the effect of the sputtering technique on the structural and mechanical properties, Ti1-x-yAlxTayN is sputtered from TiAlTa compound targets with Ta fractions up to 0.2 by dcMS, HiPIMS, and dcMS/HiPIMS.The Ta metal fraction within Ti1-x-yAlxTayN steadily increased up to y ≈ 0.25, while the Al content notably decreased at higher Ta levels. This reduction was most pronounced in HiPIMS, resulting in an order of decreasing Al content as dcMS, dcMS/HiPIMS, and HiPIMS. All thin films exhibit a Ti1-x-yAlxTayN substitutional solid solution with a linearly increasing lattice parameter corresponding to higher Ta contents. At similar Ta contents, HiPIMS-Ti1-x-yAlxTayN and dcMS/HiPIMS-Ti1-x-yAlxTayN show larger out-of-plane lattice parameters compared to dcMS/HiPIMS-Ti1-x-yAlxTayN, indicating elevated compressive stresses within the thin films. The Ti1-x-yAlxTayN thin films show a column-like structure, with HiPIMS promoting the formation of a denser morphology with less columns. The HiPIMS-Ti1-x-yAlxTayN with H = 41 GPa and dcMS/HiPIMS-Ti1-x-yAlxTayN with H = 40 GPa achieve their peak hardness at a lower Ta metal fraction of y ≈ 0.12–0.13, in contrast to dcMS-Ti1-x-yAlxTayN, which reaches H = 38 GPa at y ≈ 0.25. The shift to lower Ta contents for the maximum hardness in HiPIMS-Ti1-x-yAlxTayN and dcMS/HiPIMS-Ti1-x-yAlxTayN is due to higher compressive stresses and smaller crystallite sizes in these films at low Ta metal fractions. The H/E and H3/E2 ratios of the HiPIMS-Ti1-x-yAlxTayN and dcMS/HiPIMS-Ti1-x-yAlxTayN exhibited a similar trend of increasing values, reaching a maximum, and then decreasing with higher Ta content. Consequently, the hybrid dcMS/HiPIMS process produces Ti1-x-yAlxTayN thin films with mechanical properties comparable to pure HiPIMS, making it a suitable sputtering method for the synthesis of Ti1-x-yAlxTayN.