Uniformity of epitaxial nanostructures of CoSi2 via defect control of the Si (111) surface

The morphology and the size distribution of self-organized cobalt silicide nanostructures, grown on Si (111) substrates with controlled defects, have been investigated. An initial defect structure on the Si (111) surface is produced by quenching the substrate from just below the 7 × 7 ⇌ ‘1 × 1’ (disordered) phase transition temperature. This has produced predominantly the Si (111)-(7 × 7) reconstructed structure along with some disordered regions and defect lines on the substrate surface. The disordered regions contain randomly placed Si adatom ring clusters or a lattice gas of ring clusters and small patches of √7 × √7 R 19° structure. These substrates have been preannealed for different durations before 0.5 monolayer Co deposition on them for forming CoSi2 by reactive deposition epitaxy. With increasing duration of substrate annealing and consequent reduction of defect density and surface roughness, a change of island morphology, a transition from bimodal to monomodal size distribution and an increase of average island size have been observed. Reduction of surface defects via substrate preannealing appears to lead to the growth of homogeneous nanostructures.

► Si adatom ring clusters and √7 × √7 R 19° patches have been observed on Si(111). ► Epitaxial growth of CoSi2 on Si(111) with control of defects on substrates is studied. ► Defect reduction causes a bimodal to monomodal transformation of CoSi2 nanoislands. ► It also causes islands of different shapes to transform into triangular islands. ► Average size of the nanoislands increases with reduction of substrate surface defects.