Characterization of tantalum zirconium nitride sputter-deposited nanocrystalline coatings

The structural, chemical, optical and mechanical properties of nanocrystalline tantalum zirconium nitride films deposited by DC unbalanced magnetron sputtering were studied by means of X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, spectroscopic ellipsometry and nanoindentation. Coatings were deposited on silicon substrates with a growth temperature of 440 °C and RF bias voltages in the −40 to −130 V range. The concentration of zirconium and tantalum was regulated by controlling the power to the sputtering guns. The nitrogen concentration was controlled by varying the nitrogen flow rate and, hence, partial pressure. XRD revealed that these films formed a solid solution and that the grain size, deduced from the width of the XRD peaks using the Scherrer formula, did not vary with tantalum content. The elemental composition was determined from XPS measurements. The optical constants were measured using spectroscopic ellipsometry. A correlation between film structure/composition and optical constants was established using a Drude-Lorentz model. The mechanical properties of the coatings were evaluated using nanohardness testing and were found to depend on composition and deposition parameters. Optimum mechanical properties were achieved for a tantalum content of 10% and a substrate bias of −70 V.