Beyond its applications in silicon MOSFETs, cobalt disilicide is potentially useful for the formation of epitaxially overgrown quantum dots and quantum wires. We report the formation of cobalt silicide on Si (100) and its overgrowth by silicon. Cobalt films approximately 3.5 nm in thickness have been deposited on Si (100) using a cobalt carbonyl organometallic source. We observe by reflection high-energy electron diffraction (RHEED) that the deposited cobalt film is converted to epitaxial cobalt disilicide upon annealing at 850°C, considerably higher than the silicidation temperature typically observed for sputtered cobalt. We explain this behavior with the aid of secondary ion mass spectrometry (SIMS) profiling of the carbon and oxygen impurity concentrations. The cobalt disilicide layers have been overgrown with silicon at 625°C. We contrast the surface topology measured by atomic force microscopy (AFM) just after cobalt growth, after silicidation, and after overgrowth with silicon. The surface has been observed to be rough after growth of silicon by silane exposure for 15 min at 625°C at 0.55 mTorr of chamber pressure. The surface roughness prevails even after overgrowing with silicon for 60 min at same chamber temperature and pressure conditions.