Controlled fabrication of Si nanocrystals embedded in thin SiON layers by PPECVD followed by oxidizing annealing

The controlled fabrication of Si nanocrystals embedded in thin silicon oxynitride films (<15 nm) on top of a silicon substrate has been realized by PPECVD with N2O–SiH4 precursors. The effect of inert and oxidizing annealing processes on the Si nanocrystal spatial and size distributions is studied by coupling ellipsometry measurements and cross-sectional transmission electron microscopy observations. This study gives an interesting insight into the physics underlying the Si nanocrystal nucleation, growth and oxidation mechanisms. In particular, it evidences the presence in the as-deposited films of a high density of small amorphous Si particles that crystallize after high temperature thermal annealing. Annealing under oxidizing conditions is shown to be a powerful way to create tunnel oxides of good quality and controlled thickness needed to design future memory devices.