Reactive deposition epitaxy of CoSi₂ nanostructures on Si(001): Nucleation and growth and evolution of dots during anneal

Nucleation dependence of reactively deposited CoSi₂/Si(001) morphology and structure were analyzed in situ by scanning tunneling microscopy and surface electron diffraction. On a flat surface, Volmer-Weber growth results in a mixture of faceted CoSi₂(221)-c(2×√3)– and flat-topped CoSi₂(001)-c(2×4)– reconstructed three-dimensional nanocrystals (dots). To test their stability, the dots were annealed at the growth temperature for prolonged periods of time. The initial dot shape was found to be metastable against elongation, as the mean size increased significantly with annealing time. However, eventually the dot arrays attained a state closer to equilibrium, as could be judged from the transition to a more laterally isotropic shape, simultaneously with a reduction of the mean dot size. This “inverse coarsening” is achieved by partial dissolution of the dots, with the excess material transferred onto the interdot silicon area, converting it into a silicide. Growth on a 3°-off vicinal surface results in two-dimensional p(2×2)+c(2×2)–reconstructed platelets. These observations may have important implications for the semiconductor industry.