In-situ Nanoscale Characterization of Composition and Structure during Formation of Ultrathin Nickel Silicide

TL;DR

This study uses in-situ high-resolution techniques to analyze the formation process of ultrathin nickel silicide, revealing discrete phase transitions, intermediate compositions, and epitaxial growth characteristics.

Contribution

It provides detailed in-situ nanoscale insights into the phase evolution and structural changes during nickel silicide formation, which were previously uncharacterized.

Findings

Identification of a homogeneous NiSi intermediate phase.

Observation of epitaxial growth with lattice contraction.

Detection of off-stoichiometric final phase.

Abstract

We characterize composition and structure of ultrathin nickel silicide during formation from 3 nm Ni films on Si(100) using in-situ high resolution ion scattering and high resolution transmission electron microscopy. We show the transition to occur in discrete steps, in which an intermediate phase is observed within a narrow range of temperature from 230 oC to 290 oC. The film composition of this intermediate phase is found to be 50% Ni:50% Si, without evidence for long-range structure, indicating the film to be a homogeneous monosilicide NiSi phase. The final phase is resemblant of the cubic disilicide NiSi2, but with slightly off-stoichiometric composition of 38% Ni and 62% Si. Along the [100] axis, the lattices of the film and the substrate are found in perfect alignment. Due to the epitaxial growth of the silicide, a contraction of the c lattice constant of the film by 0.7-1% is detected.