Reactively magnetron sputtered Hf-N films. II. Hardness and electrical resistivity

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Abstract
The microhardness and electrical resistivity have been measured on thin Hf-N films, covering the entire composition range from pure Hf to overstoichiometric HfN. Influence of substrate bias on the properties of stoichiometric HfN films has also been studied. All films have been prepared by high-rate reactive magnetron sputtering at a substrate temperature of 400 °C. Both hardness and resistivity increase as nitrogen is added to the α-Hf phase. For the cubic HfN phase the hardness has a maximum, ≊3500 HV, and the resistivity a minimum, 225 μΩ cm, at a composition close to stoichiometry. However, both values are considerably higher than those reported for bulk samples. This is explained in terms of nonequilibrium growth conditions, giving rise to high densities of dislocations and interstitially incorporated nitrogen atoms. For films with a nitrogen content above 50 at. % a very high-resistivity value is found, 2.0 Ω cm at maximum. By applying a low substrate bias voltage the resistivity of stoichiometric HfN was decreased with a factor of about 3, and simultaneously a grain growth and/or reduced defect concentration was observed. At higher bias voltages the resistivity increases and the grain sizes decrease.