Pt-Si reaction through interfacial native silicon oxide layers

High-resolution transmission electron microscopy (HRTEM) and selected-area electron diffraction (SAED) were used to study the formation of 20 nm thick platinum silicide films in the presence of an interfacial native silicon o xide layer. Pt films 10 nm thick were sputtered on Si[001] substrates cover ed by a native oxide layer 0-2.2 nm thick and annealed between 165 and 800 degreesC. HRTEM observations on cross-sections show that, when an interfaci al oxide layer is present, the reactants interdiffuse through the oxide pin holes. The pinholes influence the Pt-Si reaction over all the annealing tem perature range examined. Up to 250 degreesC their influence is observed by differences in the silicide phases formed and in the silicide-Si interface flatness. In the 350-550 degreesC annealing temperature range, films with o r without an interfacial oxide layer are continuous, polycrystalline and qu ite homogeneous in thickness, being equivalent for electrical uses. Silicid e films grown through an interfacial oxide layer consist of two adjacent Pt 2Si and PtSi layers in contrast with oxide-free wafers, which show only PtS i grains. The continuous PtSi film transforms to an epitaxial island-type f ilm after annealing at 650 degreesC. The Pt2Si layer, however, does not fol low the same evolution but remains unchanged up to 700 degreesC at least. B y these means, the continuity of silicide films obtained in presence of an interfacial oxide layer can be preserved even above 700 degreesC. These res ults explain the evolution of the resisitivity as a function of the tempera ture obtained for the same samples.