NUCLEATION AND GROWTH OF COSI2 ON SI(100) STUDIED BY SCANNING-TUNNELING-MICROSCOPY

The initial stages of CoSi2 formation on the Si(100) surface are inves tigated by scanning tunneling microscopy (STM). We find a quasi-period ical reconstruction of the Si surface for very low Co coverages of 0.0 1 ML which is similar to the Ni induced (2 x 8) structure. At higher C o coverage, in reactive deposition epitaxy, the formation of qualitati vely different two and three-dimensional islands is observed. We have evidence that the former are Si terminated, with Co probably being pos itioned in substitutional sites beneath the island. The growth of the 3D CoSi2 islands is connected with substantial mass transport from the substrate into the islands to enable the silicide formation. Their el ongated shape is attributed to strain and they occur in different epit axial relations to the substrate. CoSi2 islands in (100) orientation a re identified by the c(2 x 2) surface lattice with mixed Co and Si occ upation. Simultaneous deposition of Co and Si up to 30 ML results in t he formation of CoSi2 island clusters and a rough surface. The roughne ss exponent beta=0.66 is in agreement with an existing Monte-Carlo sim ulation.