Xps and sims analysis of gold silicide grown on a bromine passivated si(111) substrate

Abstract

When a thin film of Au (~100 nm) deposited under high vacuum conditions on a chemically prepared Br-passivated Si(111) substrate was annealed around 363°C, epitaxial layer-plus-island mode growth of gold silicide was observed along with some unreacted gold in stringy patterns. This unreacted gold was removed by etching the sample in aqua regia. X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) measurements were carried out on these samples. SIMS results reveal that the height of the islands is about 1.2 μm and the silicide/Si interface is abrupt. XPS measurements were made after sputtering the sample surface at constant intervals of time. Si 2p, Au 4f, C 1s and O 1s photoelectrons were detected. XPS spectra of Si 2p are resolved into three peaks corresponding to bulk Si, Si in silicide and Si in oxide. The Au 4f_7/2 peak in the silicide is shifted by 1-1.2 eV towards higher binding energy compared to metallic Au. The shift of Si 2p towards the higher binding energy in the silicide is understood from the higher electronegativity of Au, while the shift of Au 4f_7/2 peak towards higher binding energy is known to be due to d-electron depletion to form an sd hybrid. The XPS peak intensity profile with sputtering time indicates that the thin uniform layer (~5.5 nm) of gold silicide is sandwiched between a thin (~2.8 nm) SiO₂ layer and the Si(111) substrate.