Thickness And Temperature Depending Intermixing Of Siox/Sio2 And Sioxny/Sio2 Superlattices: Experimental Observation And Thermodynamic Modeling

Multilayered SiOx/SiO2 and SiOxNy/SiO2 thin films were fabricated using different techniques and subsequently annealed at high temperatures (>= 1100 degrees C) in order to form Si nanocrystals by means of the well-known superlattice approach. The thickness of the SiOx and SiOxNy layers was varied from 1.5 to 5 nm, while for the SiO2 layers it was fixed at 4 nm. Using transmission electron microscopy, we showed that the multilayered structure generally sustains the high temperature annealing for both types of films. However, for samples with ultrathin SiOx or SiOxNy layers a breakdown of the superlattice structure and a complete intermixing of layers were observed at high temperatures. On the contrary, annealing at lower temperature (900 degrees C) preserves the multilayered structure even of such samples. Theoretical calculations showed that the intermixing of SiOx/SiO2 and SiOxNy/SiO2 superlattices in the ultrathin layers thickness limit may be explained thermodynamically by the gain in the Gibbs free energy, which depends in turn on the annealing temperature. Published by AIP Publishing.