X-RAY PHOTOEMISSION-STUDY OF THE BA SI(100) INTERFACE AND THE OXIDATION OF SI PROMOTED BY BA OVERLAYERS

The interaction of barium overlayers with the Si(100) surface and the subsequent interface formation have been studied by x-ray photoelectron spectroscopy. Also studied, were the effects of Ba overlayers and the Ba/Si interface on the oxidation of Si at different Ba coverage (0 less-than-or-equal-to theta less-than-or-equal-to 2.4 ML) and different oxygen exposures. It is found that the Ba/Si interface formation follows a two-step mechanism. At low Ba coverage (theta less-than-or-equal-to 2 ML), Ba deposits on top of, and strongly interacts with, silicon. This interaction is associated with charge transfer from the overlayer Ba atoms to silicon. Between 2 and 4 ML Ba coverage, the Ba/Si interface is unstable and silicon diffuses through the Ba overlayer. In addition, Ba overlayers on the Si(100) surface are found to significantly enhance the oxidation of silicon. At theta = 2.4 ML Ba coverage, the obtained SiO2 oxides are found to be a factor of 5 thicker than those obtained for the clean unpromoted Si(100) surface.