SCANNING TUNNELING MICROSCOPY OF THE INITIAL-STAGES OF METAL CONDENSATION ON SEMICONDUCTOR SURFACES - PROGRESS REPORT

After a brief description of the theoretical and experimental basis of scanning tunneling microscopy (STM) typical results from the initial stage of metal condensation on semiconductor surfaces will be presented. As substrates Si(111) and Si(100) are used. Their reconstruction is explained by the current atomic models and compared with STM images of the clean surfaces. While the 7 x 7 reconstruction of Si(111) can be prepared with a defect concentration in the order of 0.03% of a monolayer, Si(100) shows a higher density of imperfections by at least one order of magnitude. STM images from nonreactive systems (Ag/Si(111) and Ag/Si(100)) are described and from a reactive system (Fe/Si(111)), which forms well defined silicides. In case of Ag/Si and room temperature condensation the initial stage is characterized by a two-dimensional interface layer, which does not cover the substrates completely and the growth of rather regular three-dimensional Ag islands, whose shape is consistent with metallic character. After Fe deposition on Si(111) the surface is covered by islands, which due to their irregular size and shape indicate compound formation or intermixing with Si. After annealing Fe/Si(111) shows the development of well ordered Fe silicide layers.