Formation of Nickel-Platinum Silicides on a Silicon Substrate: Structure, Phase Stability, and Diffusion from Ab initio Computations

TL;DR

This study uses ab initio calculations to explore the formation, phase stability, and diffusion mechanisms of nickel-platinum silicides on silicon, revealing atomistic insights into phase transformations and diffusion barriers.

Contribution

It provides new atomic-level understanding of Ni(Pt) silicide formation, phase stability, and diffusion processes on silicon surfaces using ab initio methods.

Findings

Ni atoms rapidly diffuse into Si forming Ni2Si

Pt stabilizes NiSi phase by low solubility and segregation

Pt diffusion is slower and acts as a diffusion barrier

Abstract

The formation of Ni(Pt)silicides on a Si(001) surface is investigated using an ab initio approach. After deposition of a Ni overlayer alloyed with Pt, the calculations reveal fast diffusion of Ni atoms into the Si lattice, which leads initially to the formation of Ni2Si. At the same time Si atoms are found to diffuse into the metallic overlayer. The transformation of Ni2Si into NiSi is likely to proceed via a vacancy-assisted diffusion mechanism. Silicon atoms are the main diffusing species in this transformation, migrating from the Si substrate through the growing NiSi layer into the Ni2Si. Pt atoms have a low solubility in Ni2Si and prefer Si-sites in the NiSi lattice, thereby stabilizing the NiSi phase. The diffusivity of Pt is lower than that of Ni. Furthermore, Pt atoms have a tendency to segregate to interfaces, thereby acting as diffusion barriers.