FORMATION OF BURIED EPITAXIAL COSI2 LAYER THROUGH DIFFUSION MEDIATED REACTION

Interaction of Co with a Ge covered Si(111) surface is studied employi ng ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS), med ium energy ion scattering spectroscopy (MEIS), cross sectional transmi ssion electron microscopy (XTEM), low energy electron diffraction (LEE D), reflection high energy electron diffraction (RHEED) and atomic for ce microscopy (AFM). 2 ML of Co is deposited on a Si(111) surface, whi ch is covered with similar to 3 ML of Ge, both at room temperature. On annealing the sample at 460 degrees C, Co diffuses through the Ge lay er and reacts with the Si atoms underneath. This results in the format ion of a buried CoSi2 layer. XTEM pictures as well as the blocking dip pattern in MEIS suggest that the CoSi2 formed at the interface betwee n Si and Ge, is a B-type epitaxial. The Co layer undergoes agglomerati on and forms Ge/CoSi2/Si dot structures and Ge/Si terraces. A mixture of 1 x 1 and 5 x 5 patterns originating, respectively, from Ge/CoSi2/S i and Ge/Si regions are observed in RHEED and LEED. The results open u p a novel way of fabrication of buried epitaxial metallic layers and s emiconductor/metal nanostructures.