GROWTH OF COBALT OVERLAYERS ONTO SI(100)

The growth of evaporated Co overlayers onto Si(100) at 350 K was studied using Auger electron spectroscopy. Cobalt 5N was evaporated at a rate of almost-equal-to 0.4 monolayers/min from a filament. The amount deposited was monitored with a quartz crystal microbalance with a resolution of 0.2 monolayers. The changes in the L23 VV Si as well as in the cobalt LMM and MVV Auger transitions were followed. The growth mode of Co and onto Si(100) surface depends strongly on the presence of oxygen. Without oxygen a diffusion front of Co is found after deposition of almost-equal-to 4 monolayers. In the presence of oxygen (5 x 10(-10) mbar), Si atoms diffuse to the surface, the adsorbed oxygen acting as the driving force with possible building of CoSi and Co2Si. The admitted oxygen does not cause detectable oxidation of the Si surface nor of the Co overlayer. A thin layer of SiO2 can be formed on the Si surface by O2+ bombardment, acting as a diffusion barrier to Co overlayers.