Interfacial reactions in ultrahigh vacuum deposited Y-Si multilayer thin films

Interfacial reactions of ultrahigh vacuum deposited Y-Si multilayer thin films have been studied by both conventional and high-resolution transmission electron microscopy, Auger electron spectroscopy, and x-ray diffraction. An amorphous Y-Si intermixing layer with a composition approximately equal to YSi2 was found to form in multilayer films with a composition ratio of 1Y:2Si at room temperature. Homogenization in atomic composition in the amorphous phase proceeded in samples annealed at 250–350 °C. In samples annealed at 400 °C for 30 min, the amorphous layer was completely transformed to crystalline YSi2. The formation of crystalline Y5Si3 and YSi was detected in as-deposited samples with concentration ratios 1Y:1Si and 5Y:3Si as well as in samples prepared with excess Y. Y5Si3 was the only silicide phase present in 5Y:3Si films after 400 °C annealing. The results indicated that the phase formation and stability in Y-Si multilayers depend critically on the composition. Based on the prediction of a growth control model, it was concluded that the formation of amorphous layer at room temperature is controlled by nucleation.