Effect of nitrogen flow ratios on the microstructure and properties of Ta-Al-N thin films by reactive cosputtering

Quasi-amorphous Ta-Al films were obtained at the TaAl atomic ratio of ∼1. The properties of quasi-amorphous films may be different from the polycrystalline ones. In this paper, the Ta-Al-N thin films were prepared by the nitridation of quasi-amorphous Ta-Al alloys using reactive magnetron cosputtering at various nitrogen flow ratios (F N2 %=F N2 (FAr+F N2) 100%). The mechanical and electrical properties of the Ta-Al-N thin films were related to the quasi-amorphous and polycrystalline microstructure. X-ray diffraction evidenced that the quasi-amorphous Ta-Al-N films were formed at 2-7.5 F N2 % while the polycrystalline ones were obtained at 10-20 F N2 %. The hardness of Ta-Al-N films was between 7.1 and 18.0 GPa by means of nanoindentation. A maximum hardness was found at 7.5 F N2 % due to the composite quasi-amorphous microstructure with nanocrystalline grains embedded in an amorphous matrix to enhance the mechanical properties. The resistivity of the polycrystalline Ta-Al-N films was much higher than that of the quasi-amorphous Ta-Al-N. The high resistivity of Ta-Al-N at 10-20 F N2 % was about 9130-25,400 μ cm in the nonconducting range.