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Peening in ion-assisted thin-film deposition: a generalized model

A simple but generalized, ballistic collisional based, model of densification and stress evolution in ion-assisted deposition of thin films is developed. It is proposed that densification of voided films occurs by forward atomic recoil generation and, consequentially, modification of tensile stresses. The total recoil generation is believed to generate extended defects such as dislocations or amorphous layers, which result in compressive stress, the process that occurs in conventional peening. The role of thermal spikes is examined and found not to give rise, generally, to observed ion-energy-dependences of densification and stress evolution. Consequently, although such processes may mediate surface roughness and crystal grain behaviour, they are not considered to be dominant in the peening action.