Aluminum nitride (AlN) thin films were prepared by ion-beam assisted
deposition method, and the influence of the nitrogen ion beam energy on
their microstructure and mechanical properties was studied by changing the
ion beam energy from 0.1 to 1.5 keV. Films prepared with a low-energy ion
beam show a columnar structure, while films prepared with a high-energy ion
beam show a granular structure. The film hardness is found to decrease with
increasing nitrogen ion beam energy. It is also found that the film hardness
does not change drastically after annealing in nitrogen atmosphere at 500
°C, yielding the residual stress relaxation. It is proposed that the film
hardness is dependent on the film microstructure, which can be controlled
with the nitrogen ion beam energy, rather than the residual stress in the
films.