On the formation of erbium silicide in a-Si/Er/a-Si/c-Si structures

This work deals with the formation of a sputtered Er/amorphous Si (a-Si) interface and its behaviour when the a-Si/Er/a-Si/c-Si structures are annealed at high temperature. Er and a-Si layers were sequentially sputtered without breaking the vacuum and the interfaces were investigated by depth-profile XPS, grazing incidence X-ray diffraction (GIXD) and scanning electron microscopy (SEM). The evolution of the Er4d, Si2p and Si KLL spectra with abrasion time indicates a diffuse and reactive interface. GIXD reveals that the interfacial compound is Er5Si3. The formation of this compound is enhanced upon annealing at 400°C. Minute amount of ErSi2 is also detected at this temperature. At 600°C all the Er layer is consumed and GIXD detects aside Er5Si3 weak reflections of hexagonal ErSi2. At 800°C the only formed phase is ErSi2. SEM observations indicate that for small thicknesses of Er and a-Si the silicide layers are continuous, otherwise the films are rather granular. The results are compared to the ones obtained with Er films evaporated on Si.