Athermal Solid Phase Reaction in Pt/SiO x Thin Films Induced by Electron Irradiation

Abstract

Microelectronics based on Si requires metal silicide contacts. The ability to form platinum silicide (Pt₂Si) by electronic excitation instead of thermal processes would benefit the field. We studied the effects of electron irradiation on Pt₂Si formation in composite films-composed of Pt and amorphous silicon oxides (a-SiO _x )-by transmission electron microscopy and electron diffraction. Pt₂Si formed in Pt/a-SiO _x bilayer and a-SiO _x /Pt/a-SiO _x sandwiched films by 75 keV electron irradiation, at 298 and 90 K. The reaction is attributable to dissociation of SiO _x triggered by electronic excitation. In a-SiO _x /Pt/a-SiO _x sandwiched films, reflections of pure Pt were not present after irradiation, i.e., Pt was completely consumed in the reaction to form Pt₂Si at 298 K. However, in Pt/a-SiO _x bilayer films, unreacted Pt remained under the same irradiation conditions. Thus, it can be said that the extent of the interfacial area is the predominant factor in Pt₂Si formation. The morphology of Pt islands extensively changed during Pt₂Si formation even at 90 K. Coalescence and growth of metallic particles (Pt and Pt-Si) are not due to thermal effects during electron irradiation but to athermal processes accompanied by silicide formation. To maintain the reaction interface between metallic particles and the dissociation product (i.e., Si atoms) by electronic excitation, a considerable concomitant morphology change occurs. Elemental analysis indicates that the decrease in Si concentration near Pt is faster than the decrease in O concentration, suggesting formation of a Si depletion zone in the amorphous silicon oxide matrix associated with formation of Pt₂Si.