Effect of nitrogen partial pressure on the structural and mechanical properties of (MoNbTaW)N thin films deposited by DC magnetron sputtering

This study investigates the influence of nitrogen partial pressure on the microstructure, crystal structure, chemical bonding, and mechanical properties of (MoNbTaW)N films deposited on silicon substrates via DC reactive sputtering. The depositions were carried out at room temperature from a MoNbTaW alloy target at 0.6 Pa by varying nitrogen partial pressure between 0% and 50%. The surface morphology, crystal structure, bonding characteristics, and mechanical properties were studied using scanning electron microscopy (SEM), atomic force microscopy (AFM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and nanoindentation. SEM and AFM findings reveal significant morphological changes from lenticularlike structures to fine-grain structures as nitrogen partial pressure increases from 0% to 50%, with feature size decreasing from 12 to 8 nm. XRD analysis confirms a crystalline structure in all films, transforming from body-centred cubic to face-centred cubic, occurring between 16% and 33% nitrogen partial pressure. XPS analysis confirms the formation of metal-nitrogen (Me-N) bonds through binding energy shifts. Despite these structural changes, no significant variations in hardness and film modulus were observed with changes in nitrogen partial pressure, which can be attributed to weaker p(N)-d(TM) interactions. The study underscores nitrogen's crucial role in altering microstructure and crystal structure, while the strength of the Me-N bond limits its effect on mechanical properties.