Kazuyuki Hirose

We demonstrate that CoSi<Sub>2</Sub> directly grows epitaxially on H-terminated Si(001) and the interface is atomically flat. The hydrogen present on the Si surface seems to suppress the direct reaction of Co with Si up to &sim;400<Sup>o</Sup>C. Thus, the hydrogen at the Co/Si interface hinders the formation of low temperature (metal-rich) phases such as Co<Sub>2</Sub>Si and CoSi. Upon thermal desorption of hydrogen at around &sim;460<Sup>o</Sup>C, the direct epitaxial growth of CoSi<Sub>2</Sub> on Si(001) occurs. However, with the increase of initial Co film thickness, cracks are formed partially due to a strong tensile stress. More detailed study is needed concerning the effects of such defects for the practical applications to VLSI.

By decreasing probing depth down to 0.41 nm, the energy loss of O ls photoelectrons with threshold energy of 3.5 eV, which was equivalent with excitation energy required for direct interband transition at Γ point in energy band structure of Si, was observed even through 1.12-nm-thick oxide film. It was found, considering penetration of electronic states from Si substrate into SiO_2 in the analysis of thickness dependence of energy loss of O ls photoelectron caused by the direct interband transition, that the top of valence band of compositional transition layer is almost equivalent to that of bulk Si. In other words, the SiO_2/Si interface defined by electronic structure exists in the oxide located effectively 0.61 nm away from nominal interface defined by chemical structure.