Observation of thermal growth of silicide on titanium-deposited silicon surfaces

Titanium (Ti) silicide formed by evaporation of Ti onto Si surfaces is employed as a gate electrode for MOS devices. In order to elucidate the structure of Ti silicide grown at high-temperature at the atomic level, Ti was evaporated onto Si(0 0 1)-2 × 1 and Si(1 1 1)-7 × 7 surfaces at room temperature, and the thermal growth of Ti silicide on these surfaces was observed using a scanning tunnelling microscope (STM). When the Si(0 0 1) sample was annealed at temperatures of 650 °C or above, we observed a roughening of the surface associated with formation of silicide lumps with a height of ∼2.5 nm, around which the surface formed a stepped slope. High-temperature observation of the terraces indicated strong interaction between Si on the terrace and Ti. On the Si(1 1 1) surface, in contrast, heating at 700 and 900 °C left many agglomerated lumps distributed randomly on wide and flat terraces with dimer–adatom–stacking-fault structure, indicating that Si at the step edges may be easily removed to form silicide.