Structural and chemical analysis of a model Si–SiO₂ interface using spatially resolved electron-energy-loss spectroscopy

Abstract

This work reports an experimental electron-energy-loss spectroscopy study carried out on a model thermal Si–SiO₂ interface. Valence-loss spectra and core-loss spectra (Si L_2,3 and O K edges) were recorded across the interface in line-spectrum mode with a high spatial resolution in a field emission gun scanning transmission electron microscope. From the analysis of the line spectra and on the basis of high-resolution electron microscopy and high-angle annular dark-field experiments, it is concluded that the interface is not sharp but extends over about three atomic planes consisting of Si and O atoms arranged in a structure evolving between crystalline SiO and SiO₂ before growing as an amorphous SiO₂ layer. In addition, from the analysis of the valence-loss spectra in terms of energy-loss function or dielectric function ε, we show that valence-electron-energy-loss spectroscopy could be a relevant alternative method for determining the electron properties, for example the bandgap, and the dielectric constant of dielectric gates on a nanometre scale.

Acknowledgements

We wish to thank Pierre Mur and Anne-Marie Papon, Laboratoire d’Etude des Techniques de l’Information Commissariat à l’Energie Atomique, Grenoble, who determined the model structure and prepared the TEM samples, Roland Pantel and Stephane Jullian, ST Microelectronics, Crolles, for giving us access to their FET TECNAI G2 and for their technical support when using the microscope, and Gianluigi Botton (McMaster University, Ontario, Canada), Christian Colliex (Laboratoire de Physique des Solides (LPS), Université d’Orsay, France) and David Muller (Bell Laboratories, Murray Hill, USA) for useful discussions in the course of these studies.