Pt-Si reaction through interfacial native silicon oxide layers

High-resolution transmission electron microscopy (HRTEM) and selectedarea electron diffraction (SAED) were used to study the formation of 20 nm thick platinum silicide films in the presence of an interfacial native silicon oxide layer. Pt films 10 nm thick were sputtered on Si[001] substrates covered by a native oxide layer 0-2.2nm thick and annealed between 165 and 800 C. HRTEM observations on cross-sections show that, when an interfacial oxide layer is present, the reactants interdiffuse through the oxide pinholes. The pinholes influence the Pt-Si reaction over all the annealing temperature range examined. Up to 250 C their influence is observed by differences in the silicide phases formed and in the silicide-Si interface flatness. In the 350-550°C annealing temperature range, films with or without an interfacial oxide layer are continuous, polycrystalline and quite homogeneous in thickness, being equivalent for electrical uses. Silicide films grown through an interfacial oxide layer consist of two adjacent Pt2Si and PtSi layers in contrast with oxide-free wafers, which show only PtSi grains. The continuous PtSi film transforms to an epitaxial island-type film after annealing at 650°C. The Pt2Si layer, however, does not follow the same evolution but remains unchanged up to 700°C at least. By these means, the continuity of silicide films obtained in presence of an interfacial oxide layer can be preserved even above 700°C. These results explain the evolution of the resisitivity as a function of the temperature obtained for the same samples.