Correlation between plasma conditions and properties of (Ti,Al)N coatings deposited by PECVD

Metastable Ti1−xAlxN films have been deposited by PECVD from chloride precursors at a constant TiCl4/AlCl3 ratio in a pulsed DC glow discharge. Depending on the discharge voltage and on the distance between the specimen and gas inlet, the aluminum content of the film was significantly influenced. With increasing discharge voltage and increasing distance, the Al content of the films increased, leading to a decrease in the lattice parameter of the cubic films, and finally resulting in a two-phase mixture of cubic and hexagonal (Ti,Al)N. All single-phase films exhibited a cubic TiN structure with a strong {100} texture. These coatings had a columnar morphology, while coatings consisting of two phases showed a granular morphology with grain sizes between 100 and 200 nm. The microhardness of these granular coatings was above 4000 HV0.02, and thus significantly higher compared to coatings with a columnar morphology.