TEM and Spectroscopic Ellipsometry studies of multilayer gate dielectrics containing crystalline and amorphous Si nanoclusters

Gate dielectrics containing crystalline or amorphous silicon nanoclusters are fabricated by thermal oxidation, followed by deposition of SiOx films (x=1.15) using thermal evaporation of SiO in vacuum and a two-step N2/N2+O2 annealing process. Cross-sectional Transmission Electron Microscopy proves the formation of two regions in the SiOx film: a region free of nanoclusters close to the top surface and a second region with nanoclusters underneath the first one. Spectroscopic Ellipsometry was used to obtain the volume fraction of the pure Si phase in the oxide matrix, ∼31 and 28 vol% for the films with nanocrystals and amorphous nanoparticles, respectively. The dependencies of the index of refraction and extinction coefficient on wavelength obtained using Bruggeman Effective Medium Approximation are close to those of silicon monoxide. A correlation is found between the thicknesses of the three regions determined by Transmission Electron Microscopy and Spectroscopic Ellipsometry.