Probing the behaviour of ultra thin Co layers on clean and hydrogen terminated Si(0 0 1) and Si(1 1 1) surfaces

In situ X-ray photoelectron spectroscopy (XPS) reveals that deposited Co atoms at room temperature react with Si at the growth front to form a thin “CoSi2-like” layer on both clean and hydrogen passivated Si(0 0 1) and Si(1 1 1) surfaces. Improvement in the silicides crystallinity upon annealing was characterised by an appreciable decrease in the full width at half maximum of the Co 2p3/2 XPS spectra and a shift in binding energy towards Co in the bulk CoSi2 crystal structure. Unlike the Si(0 0 1) substrate, the presence of hydrogen on the Si(1 1 1) surface appears to delay the decrease in the peak area ratio of Co 2p3/2/Si 2p as annealing temperatures increase. Ex situ surface morphology imaged by atomic force microscopy suggests a reduced adatom mobility on the Co/H-passivated Si surface compared to the Co/clean Si surface, as evidenced by a higher and smaller size CoSi2 islands density observed on Co deposited/H-terminated Si surfaces after annealing to 700 °C.