Growth and characterization of ultrathin cobalt silicide films on Si(211) and (311)

Abstract

We have studied the structural and electrical properties of ultrathin cobalt silicide films deposited on Si(211) and (311) and annealed at a variety of temperatures. Transmission electron microscopy reveals two regimes of silicide growth. If more than 10 Å of Co is deposited, textured CoSi forms at low temperatures, which transforms to two epitaxial orientations of CoSi₂ at about 500°C. If less than 10 Å of Co is deposited, only one epitaxial CoSi₂ orientation is observed, which occurs in discontinuous islands or lines. The resistivities of the thinnest films reflect the degree of continuity of the silicide layers. In thicker films, where disorder is the major factor, the resistivity for intermediate annealing temperatures (∼500°C) depends dramatically on the orientation of the Si substrate, being an order of magnitude lower for Si(311) and (211) than for (111). The differences between these observations and those made on films grown under the same conditions on Si(111) can be understood by noting both the greater tendency of the film to form intermediate phases which are epitaxial on the high symmetry Si(111) surface and the faceting of the CoSi₂-Si(311) and (211) interfaces.