Influence of chemical composition and deposition conditions on microstructure evolution during annealing of arc evaporated ZrAlN thin films

The influence of substrate bias and chemical composition on the formed microstructure and resulting hardness of arc evaporated Zr1−xAlxN films in the compositional span 0.12≤ x ≤0.74 is investigated. A cubic ZrAlN phase is formed at low aluminum contents (x ≤ 0.38) whereas for a high Al-content, above x = 0.70, a single-phase hexagonal structure is obtained. For intermediate Al-contents, a two-phase structure is formed. The cubic structured films exhibit higher hardness than the hexagonal structured ones. A low bias results in N-rich films with a partly defect-rich microstructure while a higher substrate bias decreases the grain size and increases the residual stress in the cubic ZrAlN films. Recrystallization and out-diffusion of nitrogen from the lattice in the cubic ZrAlN films takes place during annealing at 800 °C, which results in an increased hardness. The cubic ZrAlN phase is stable to annealing temperatures of 1000 °C while annealing at higher temperature results in nucleation and growth of hexagonal AlN. In the high Al-content ZrAlN films, formation of ZrN- and AlN-rich domains within the hexagonal lattice during annealing at 1000 °C improves the mechanical properties.