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

The mechanisms are studied for enhanced formation of C54-TiSi2 at about 700 degrees C when rapid thermal annealing at 3 degrees C/s in N-2 is performe d on 32-nm-thick codeposited Ti-5.9 at.% Ta on Si(100) single-crystal subst rates. The enhancement is related to an increased C54-TiSi2 nucleation rate due to the development of a multilayered microstructure. The multilayer mi crostructure forms at temperatures below 600 degrees C with the formation o f an amorphous disilicide adjacent to the Si substrate and a M5Si3 (M = Ti, Ta) capping layer. This amorphous disilicide crystallizes at higher temper atures to C49-TiSi2. The multilayer microstructure introduces an additional interface that increases the area available for the heterogeneous nucleati on of C54. The capping layer is identified as hexagonal Ti5Si3 or its isomo rphous compound (Ti1-xTax)(5)Si-3. Crystal simulations demonstrate that C54 (040) has a lattice mismatch of 6-7% relative to Ti5Si3(300) suggesting tha t a pseudomorphic epitaxial relationship may lower the interfacial energy b etween 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 pha se does not play a major role in catalyzing C54 formation.