Annealing temperature effect on the mechanical and tribological properties of molybdenum nitride thin films

Mo thin films with 100-nm thickness were deposited on silicon substrates using DC magnetron sputtering method. Mo thin films were subsequently annealed at different temperatures (400°C to 900°C) with flow of nitrogen. The crystallographic structure of the samples was obtained using X-ray diffraction method. Atomic force microscopy and scanning electron microscopy were used for surface morphology investigation. Nano-indentation and scratch tests were performed to obtain the surface hardness and friction coefficient of the samples, respectively. Results show that the γ-Μο2Ν(111) phase of molybdenum nitride with face-centered cubic structure and higher hardness, elastic modulus, and lower coefficient of friction and scratch volume is formed when the sample is annealed at 650°C, while the Mo2N phase with tetragonal structure and lower hardness, elastic modulus, and higher scratch volume and friction coefficient is formed at higher temperatures of 775°C and 900°C. It is found that increasing the annealing temperature causes an increase of the grain size and film surface roughness. From the mechanical results, it may be deduced that 650°C is a critical temperature for variation of mechanical and tribological properties.