Mechanisms for enhanced C54–TiSi₂ formation in Ti–Ta alloy films on single-crystal Si

Abstract

The mechanisms are studied for enhanced formation of C54–TiSi₂ at about 700 °C when rapid thermal annealing at 3 °C/s in N₂ is performed on 32-nm-thick codeposited Ti–5.9 at.% Ta on Si(100) single-crystal substrates. The enhancement is related to an increased C54–TiSi₂ nucleation rate due to the development of a multilayered microstructure. The multilayer microstructure forms at temperatures below 600 °C with the formation of an amorphous disilicide adjacent to the Si substrate and a M₅Si₃ (M = Ti, Ta) capping layer. This amorphous disilicide crystallizes at higher temperatures to C49–TiSi₂. The multilayer microstructure introduces an additional interface that increases the area available for the heterogeneous nucleation of C54. The capping layer is identified as hexagonal Ti ₅Si₃ or its isomorphous compound (Ti_1–xTa_x)₅Si₃. Crystal simulations demonstrate that C54(040) has a lattice mismatch of 6–7% relative to Ti₅Si₃(300) suggesting that a pseudomorphic epitaxial relationship may lower the interfacial energy between these two phases and reduce the energy barrier for C54 nucleation. A C40 disilicide phase was also observed at temperatures above that required to form C54–TiSi₂ suggesting that, in the present experiments, the C40 phase does not play a major role in catalyzing C54 formation.