Mechanical properties, bonding characteristics, and thermal stability of magnetron-sputtered HfNx films

Abstract HfNx (x = 0.81–2.07) films were fabricated through direct current magnetron sputtering by varying nitrogen flow ratio [N2/(Ar + N2)] from 0.1 to 1.0. The structural evolution, mechanical properties, and bonding characteristics of the as-deposited HfNx films were investigated for various values of the stoichiometric variable x. The results indicated that the films prepared using nitrogen flow ratios lower than 0.2 and higher than 0.4 exhibited crystalline and near-amorphous structures, respectively. The highest level of the nanoindentation hardness of the near-stoichiometric Hf51N49 films prepared using a nitrogen flow ratio of 0.2 was 26.0 GPa. Further increases to the x value of HfNx films decreased the hardness levels, which could be attributed to higher Hf3N4 content. The bonding constitutions comprised metallic Hf, Hf N bonds of HfN and Hf3N4, and Hf O bonds. The amounts of Hf N bonds in Hf3N4 structure increased as x increased. The thermal stability values of the HfNx films at 500 and 600 °C in a 15-ppm O2–N2 atmosphere were evaluated.