Physicochemical, structural, and mechanical properties of Si3N4 films annealed in O2

The physicochemical, structural, and mechanical properties of silicon nitride films deposited by radio frequency reactive magnetron sputtering were investigated before and after thermal annealing in 18O2. As-deposited films were essentially amorphous, stoichiometric, and free from contaminants for a wide range of deposition parameters, with hardness figures ranging from 16.5–22 GPa, depending mainly on the deposition temperature. After 18O2 annealing at 1000 °C, films hardness converged to 21 GPa, independently of the deposition temperature, which is explained based on the crystallization of the films at this annealing temperature. Moreover, oxygen is incorporated only in 7.5 nm of the Si3N4, forming silicon oxynitride at the top surface of the film, indicating a good oxidation resistance at high temperature. Finally, the elastic strain to failure (H³ /E²) , which mimics the wear resistance of the film, doubles after the 1000 °C annealing. These observations show the great potential of silicon nitride as a hard coating for high temperature applications