THE TEMPERATURE EVOLUTION OF ULTRA-THIN FILMS IN SOLID-PHASE REACTIONOF CO WITH SI(111) STUDIED BY SCANNING-TUNNELING-MICROSCOPY

The solid-phase reaction of 5 Angstrom of Co with the Si (111) surface is investigated by scanning tunneling microscopy (STM) in the range f rom room temperature to 700 degrees C. Room-temperature deposition lea ds to a granular film surface. The small grains transform upon anneali ng between 200 and 300 degrees C into triangular surface terraces with step heights of 1.5 and 3.1 Angstrom. Further annealing up to 500 deg rees C leads to their growth and a decrease of the relative number of 1.5 Angstrom steps. These observations are explained by the formation of a cobalt silicide with a CsCl-type lattice. Furthermore, apart from the known 2x2 reconstructions and the unreconstructed surface, variou s surface features like individual double-line-shaped defects and step s with a height of 0.4 Angstrom are resolved. Finally, the formation o f pinholes is observed after annealing: at 500 degrees C. They lead up on further annealing to a complicated pinhole-induced CoSi2 network th at breaks up into individual islands at similar to 700 degrees C. (C) 1998 Published by Elsevier Science B.V. All rights reserved.