Ion beam assisted deposition of AlN monolithic films and Al/AlN multilayers: a comparative study

Monolithic AlN films and Al/AlN multilayers with periodic thickness ranging from 6 to 24 nm were synthesized by ion beam assisted deposition (IBAD) from electron beam evaporated aluminum and a nitrogen ion beam. During deposition of the multilayers, the nitrogen ion beam was alternately switched on and off, corresponding to AlN and Al sublayer deposition periods, respectively. A comparative study, with respect to microstructure and mechanical properties, was conducted both between the monolithic AlN films prepared with varied IBAD process parameters, and between the Al/AlN multilayers and their constituent monolithic AlN films. Two fundamental IBAD parameters of ion energy (100-500 eV) and ion-to-atom arrival rate ratio (1.45-3.60) were found to play important roles in the properties of the monolithic AlN films, Some contradictions in this respect appearing in the literature are discussed. When comparing the Al/AlN multilayers with their constituting monolithic AlN films, a substantial improvement of the mechanical properties has been observed only at low ion energies and ion-to-atom arrival rate ratios. Possible reasons are discussed. (C) 1998 Elsevier Science S.A.