Abstract
High resolution synchrotron radiation photoemission has been used to investigate the interfacial reaction and phase formation at the ultra thin Ni/Si(100)-2x1 interface under ultrahigh vacuum. The curve-fit analysis of the Si 2p core-level spectra, based on the concept of inelastic mean-free-path, indicates that the interaction between adsorbates and Si(100)-2x1 reaches down to the third top layer. At Ni coverage less than 0.0375 ML, Ni atoms prefer to occupy the adamantane sites on the first subsurface layer, equivalent to form a NiSi2 bonding environment. The band bending has its maximum value of 0.16 eV. As Ni coverage is higher than 0.0375, Ni atoms begin to occupy the Pedestal sites on the dimmer rows. The band bending shifts decrease from 0.16 to 0.04 eV at 1 ML Ni coverage. Three amorphous NixSiy bonding environments, a-NiSi2, a-NiSi, and a-Ni2Si coexist at 1ML Ni coverage. As Ni coverage increases, a Ni-silicides mixed layer exists at the Ni/Si(100) interface. The amorphous mixed layer consists of a-NiSi2, a-NiSi, and a-Ni2Si. When Ni coverage reaches 7 ML, a new Ni-silicide start to form and the growth mode also switches from layer-by-layer-like to island growth. The whole growth mode at the Ni/Si(100) interface is thus treated as a modified Stranski-Krastanov type. Upon annealing a 7 ML Ni/Si(100) interface, four stable polycrystalline NixSiy alloys coexist at temperatures ranging from 400 to 700 oC, and the dominant phase is poly-NiSi. At 800 oC, epi-NiSi2 becomes dominant phase.