Microstructural characterization of thin SiOx films obtained by physical vapor deposition

X-ray diffraction and reflectivity. X-ray photoelectron spectroscopy and spectroscopic ellipsometry were applied to study the initial composition, thickness, lattice structure and refractive index of 'fresh' and annealed thin SiOx films (similar to 15 nm) on crystalline silicon substrates, prepared by thermal evaporation of SiO in vacuum. It has been ascertained that the film thickness and composition (x = 1.3) of the 'fresh' films are very close to the values set during the deposition. It has been shown that furnace annealing of the films at 1000 degrees C causes phase separation, film densification and small modification of the Si-SiOx interface. Transmission electron microscopy results have proven that a self-assembling process leads to formation of Si nanocrystals with a diameter of similar to 4-5 nm and to epitaxial overgrowth of the Si substrate, increasing the c-Si/SiOx interface transition region to 6-7 monolayers. The nanocrystals are randomly distributed in an amorphous SiO2 matrix being closer to the Si-SiOx interface. Formation of tunnel oxide layer with a thickness of 3-5 nm has been found upon annealing. Clockwise hysteresis has been observed in the capacitance-voltage characteristics measured which has been explained by assuming charging and discharging of the nanocrystals with holes, which tunnel from the Si substrate. (c) 2010 Elsevier B.V. All rights reserved.