Probing formation and epitaxy of ultrathin Titanium Silicide using low and medium energy ion scattering

TL;DR

This study investigates the formation and structure of ultrathin titanium silicide on silicon using ion scattering and electron microscopy, revealing epitaxial growth, compositional changes, and surface/interface characteristics relevant for semiconductor contacts.

Contribution

It provides detailed nanoscale insights into ultrathin Ti-silicide formation, combining ion scattering and TEM to reveal epitaxial interfaces and compositional evolution during annealing.

Findings

Epitaxial silicide layer approximately 1.5 nm thick confirmed by HR-TEM.

Surface layer is Ti-rich, while the interface is Si-rich with strong ordering.

Significant interface roughness observed without affecting surface smoothness.

Abstract

Titanium silicide is a key contact material in advanced three-dimensional semiconductor device architectures. Here, we examine the formation of ultrathin Ti-silicide on Si(100) using a combination of non-destructive in-situ and ex-situ ion scattering techniques capable of resolving composition and structure at the nanoscale. In-situ Time-of-Flight Low-Energy Ion Scattering (ToF-LEIS) indicates intermixing after annealing at 350 {\deg}C, with further compositional changes after annealing at 500 {\deg}C, including the emergence of a Si terminating layer at the surface. Consecutive ex-situ Time-of-Flight Medium-Energy Ion Scattering (ToF-MEIS) reveals a Ti-rich polycrystalline surface layer and a Si-rich interface layer exhibiting strong ordering along the Si [100] axis. High-Resolution Transmission Electron Microscopy (HR-TEM) images confirm these findings, revealing a $\approx$1.5 nm thick epitaxial silicide layer at the interface. The presence of an epitaxial interface is particularly promising for minimizing contact resistivity in ultrathin contact layers, where interfacial order can dominate electronic performance. In addition, both ToF-MEIS and HR-TEM unveil significant variations in the thickness of the silicide layer, with a substantial interface roughness but no translation of this roughness to the surface.