The growth of an intermediate CoSi phase during the formation of epitaxial CoSi 2 by solid phase reaction

Abstract

Among the epitaxial transition metal silicides CoSi 2 is of special interest for applications in ULSI technology due to its high thermal stability and low electrical resistivity. The solid phase reaction of metallic bilayers with Si in an N 2 ambient is a well-known process for growing epitaxial CoSi 2. However, the real function of the so-called diffusion barrier, which is arising during the annealing process, remains unclear. TEM studies revealed the intermediate growth of a CoSi phase with grains of preferred orientation to Si. The growth of this phase raises the temperature of CoSi 2 nucleation, which starts at the CoSi/Si interface. The nucleation temperature determines the quality of the growing epitaxial CoSi 2, which is better for Ti as a barrier forming material than for Hf, also used successfully. Whether an intermediate oriented growth of CoSi is promoting the epitaxial quality of CoSi 2 otherwise than by shifting the nucleation temperature, remains an open question.