Silicide formation at the Ti/Si(111) interface: Room-temperature reaction and Schottky-barrier formation

High-resolution core-level synchrotron-radiation photoemission has been used to study the evolving Ti/Si(111)-2×1 interface at room temperature. Si 2p core-level results show extended intermixing and reaction following the Ti-induced disruption of the Si surface. Three reacted components are identified, shifted to lower binding energy relative to the substrate by 350, 625, and 1125 meV. These core-level results have been decomposed to obtain the intensity of each component as a function of coverage and determine the component-specific attenuation curves. Modeling of the attenuation curves shows that the first shifted species is associated with a bonding configuration of empirical formula ${\mathrm{TiSi}}_4$ and forms only during the deposition of the first angstrom of Ti. The second component is associated with TiSi, and this phase forms in the coverage range 0.5≤CTHETA≤8 Å. The final Si configuration reflects a phase of variable stoichiometry and binding energy, corresponding to a solution of Si in Ti. Titanium metal accumulates at coverages above ∼14 Å. The profile and morphology of this heterogeneous interface is controlled by Ti and Si diffusion through the reaction products and their grain boundaries. These chemical changes in the interface have been correlated with measurements of the variation in the Schottky-barrier height.