Abstract
We present a combined analysis using cross-sectional transmission electron microscopy (X-TEM) and Raman spectroscopy to study the early formation dynamics of Si-nanocrystals, formed in SiO2 thin films after Si+ implantation and rapid thermal processing (RTP). We obtained values for the diffusion coefficient of Si in thermally grown SiO2 and the activation energy to precipitate formation in the first 100 seconds of high temperature annealing. These values indicate that the formation of Si-nanocrystals in implanted oxides proceeds much more efficiently than purely via a self diffusion process. We propose that the nanocrystal formation is assisted by the presence of both oxygen vacancies and SiO molecular species, presumably generated by the ion irradiation. Microscopy images reveal the ensemble nanocrystal population to be most accurately represented by a lognormal distribution function with characteristic values for the mean particle diameter, d and variance, σ. The evolution of the silicon nanocrystals with annealing was also investigated by measuring the Raman scattering signal associated with the TO phonon mode arising from Si-Si bonds in Si-rich oxides grown on transparent (Al2O3) substrates. This greatly simplifies the experimental observation of the Raman spectra from Si-nanocrystals as compared to previous studies of nanocrystals in oxide films on silicon substrates.