Phase transformation and morphological evolution of ion-beam sputtered tinoxide films on silicon substrate

Amorphous tin oxide films were deposited on a silicon substrate by ion-beam sputtering (IBS) using a SnO2 target. Phase transformation and morphologic al changes of deposited films at different annealing temperatures were stud ied by X-ray diffraction and scanning electron microscopy. Crystallization of the as-deposited film started at 350 degrees C and SnO and SnO2 phases f ormed at 400 degrees C. Disproportionation of SnO into Sn and SnO, was obse rved at 450 degrees C followed by the oxidation of metallic tin at 550 degr ees C. Large volume changes accompanying the oxidation of metallic tin at t his temperature caused the partial detachment and formation of heavy wrinkl es on the film. These results suggest that the oxygen deficiency of tin oxi de films should be avoided by optimizing the deposition process, since a dr astic morphological change at the phase transformation to SnO2 during annea ling may destroy the integrity of the thin films and degrade the long-term stability of tin oxide films used as gas sensors at high temperatures. (C) 1999 Elsevier Science Ltd.