Formation of buried epitaxial CoSi, layer through diffusion mediated reaction

Interaction of Co with a Ge covered Si(ll1) surface is studied employing ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS), medium energy ion scattering spectroscopy (MEIS), cross sectional transmission electron microscopy (XTEM), low energy electron diffraction (LEED), reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM). 2 ML of Co is deposited on a Si(ll1) surface, which is covered with - 3 ML of Ge, both at room temperature. On annealing the sample at 46O”C, Co diffuses through the Ge layer and reacts with the Si atoms underneath. This results in the formation of a buried CoSi, layer. XTEM pictures as well as the blocking dip pattern in MEIS suggest that the CoSi, formed at the interface between Si and Ge, is a B-type epitaxial. The Co .layer undergoes agglomeration and forms Ge/CoSi,/Si dot structures and Ge/Si terraces. A mixture of 1 X 1 and 5 X 5 patterns originating, respectively, from Ge/CoSi,/Si and Ge/Si regions are observed in RHEED and LEED. The results open up a novel way of fabrication of buried epitaxial metallic layers and semiconductor/metal nanostructures.