REACTION-KINETICS IN THE TI SIO2 SYSTEM AND TI THICKNESS DEPENDENCE ON REACTION-RATE/

The reaction kinetics of Ti films on SiO2 were investigated using Ruth erford backscattering spectrometry, x-ray diffraction, Auger electron spectroscopy, and transmission electron microscopy. Consistent with ea rlier studies, the reaction results in the formation of a TiO(w)/Ti5Si 3/SiO2 stack at temperatures in the range 700-820-degrees-C. As the si licide layer grows, the concentration of O in TiO(w) increases, with t he reaction ceasing at w is similar to 1.2. In addition, the reaction rate depends on the initial Ti thickness, as thicker Ti films possess faster reaction rates. Applying current diffusion-controlled kinetic g rowth models, we find nominal agreement with our data at each thicknes s and predict activation energies in the range 3.0-3.4 eV. However, su ch a model is unable to account for either the Ti thickness dependence or the slowing and eventual cessation of silicide formation as the ox ide composition approaches its limiting value. We implement a model wh ich takes into account the reduction in the thermodynamic driving forc e for T5Si3 formation due to the incorporation of oxygen into the over lying Ti. This model predicts a silicide growth relationship of the fo rm kt=(1/2)x2+ax(f)2SIGMA(n=3)infinity(1/n)(x/x(f))n, with k independe nt of Ti thickness and given by k=k0 exp(-DELTAE/k(B)T). The final Ti5 Si3 thickness, x(f), is determined by the initial Ti thickness, the st oichiometries of each phase formed and the final oxide composition. Th is model yields a more accurate fit to our data than if we assume para bolic growth since it predicts the eventual cessation of the reaction as x approaches x(f). We find DELTAE=2.9+-0.1 eV Our model also seems to explain the dependence on initial Ti thickness.