Temperature-dependent electron microscopy study of Au thin films on Si (100) with and without native oxide layer as barrier at the interface

TL;DR

This study investigates how temperature affects the morphological evolution of gold thin films on silicon surfaces with and without native oxide layers, revealing the oxide's role as a diffusion barrier and the formation of nanostructures at specific temperatures.

Contribution

It provides new insights into temperature-dependent nanostructure formation and the influence of native oxide layers on gold-silicon interfaces during annealing.

Findings

Nanogold silicide structures form at lower temperatures on reconstructed Si surfaces.

Native oxide acts as a barrier to inter-diffusion, delaying nanostructure formation.

Rectangular nanostructures appear at different temperatures depending on oxide presence.

Abstract

Real time electron microscopy observation on morphological changes in gold nano structures deposited on Si (100) surfaces as a function of annealing temperatures has been reported. Two types of interfaces with the substrate silicon were used prior to gold thin film deposition: (i) without native oxide and on ultra-clean reconstructed Si surfaces and (ii) with native oxide covered Si surfaces. For a \approx 2.0 nm thick Au films deposited on reconstructed Si(100) surfaces using molecular beam epitaxy method under ultra high vacuum conditions, aligned four-fold symmetric nanogold silicide structures formed at relatively lower temperatures (compared with the one with native oxide at the interface). For this system, 82% of the nanostructures were found to be nano rectangles like structures with an average length \approx 27 nm and aspect ratio of 1.13 at \approx 700{\deg}C. For \approx 5.0 nm thick Au films deposited on Si (100) surface with native oxide at the interface, formation of rectangular structures were observed at higher temperatures (\approx 850{\deg} C). At these high temperatures, desorption of the gold silicide followed the symmetry of the substrate. Native oxide at the interface was found to act like a barrier for the inter-diffusion phenomena. Structural characterization was carried out using advanced electron microscopy methods.