Thermodynamic analysis of solid-state metal/Si interfacial reactions

Abstract

An attempt has been made to interpret the experimentally reported transitions of layer sequences during the Co/Si, Ti/Si, and Ni/Si interfacial reactions in a consistent way, and to build a thermodynamic calculation scheme that enables it. The basic ideas are that the silicide with the highest driving force of formation under a metastable local equilibrium state at an interface would form first at the lowest temperature, and that when several silicides can nucleate simultaneously and compete for growth at an initial stage of a high temperature reaction, the one whose composition is closest to those of surrounding phases would form a continuous interfacial layer first and grow thicker. A critical review of literature information has also been made in order to clarify the first-forming silicide and silicide formation sequence in each metalySi interfacial reaction. The observed first-forming crystalline silicides, CoSi, Ti5Si3, and Ni2Si, in each metalySi interfacial reaction were in agreement with the present prediction based on the first idea. The reason why Co2Si and C49 TiSi2 have frequently been observed in high temperature Co/Si and TiySi reactions as if they were the first-forming crystalline silicides could also be explained based on the second idea. By combining both ideas, a general thermodynamic calculation scheme that can be applied for analysis, rationalization, and even prediction of interfacial reactions between different materials could be suggested.