Differences between interfacial and surface molybdenum in the formation of TiSi2

Abstract

Backscattering and diffraction results are presented for the effects of an interfacial or a surface Mo layer on the formation of Ti-silicides during solid-state interaction between Ti films and Si substrates. It is shown that the interfacial and surface Mo are fundamentally different in their involvement in the Ti-silicide formation. The interfacial Mo induces the formation of C40 (Mo,Ti)Si2 at the interface adjacent to the Si substrate already after annealing at 550 °C, in agreement with our previous results. Hence, the desired C54 TiSi2 can grow directly on top of the C40 (Mo,Ti)Si2 at relatively low temperatures as a result of the template effect. The surface Mo is, however, found in a metal-rich silicide presumably (Mo,Ti)5Si3 at 550–600 °C, which eventually converts to (Mo,Ti)Si2 upon annealing at higher temperatures. Underneath this metal-rich silicide lies a fully developed C49 TiSi2 layer. Consequently, the formation of C54 TiSi2 in the presence of surface Mo follows the usual path of the C49–C54 phase transition. This important difference in the participation of Mo in the silicide formation spreads doubts about the validity of using interfacial Mo versus surface Mo to study the dominant mechanism(s) responsible for the enhanced formation of C54 TiSi2.