Atomic-force-microscopy visualization of Si nanocrystals in SiO2 thermal oxide using selective etching

The topography and local hardness of the etched surfaces of layers of SiO₂ thermal oxide that contained Si nanocrystals in its bulk were studied using atomic-force microscopy. The Si nanocrystals were obtained by implanting Si⁺ ions into the oxide with subsequent high-temperature annealing. It is shown that the use of selective etching that removes the oxide material makes it possible to reveal Si nanocrystals that appear in the profile of etched surfaces in the form of nanohillocks with a height of up to 2–3 nm. These values are in satisfactory agreement with the average radius of Si nanocrystals in the SiO₂ oxide layer. Independent confirmation of the Si-nanocrystal observation was obtained by comparing the topography of etched surfaces with the local-hardness maps obtained for the same surfaces; in these maps, the hillocks appear as sites at the surface with a reduced hardness. The phase precipitation of implanted Si is also observed in the form of extended flat clusters oriented in the oxide bulk parallel to the oxide surface. The suggested method for revealing the Si nanocrystals and clusters incorporated into the oxide provides a convenient way to study the specific features of nucleation growth and spinodal decomposition in the Si solid solution in the SiO₂ oxide.