SiO2 layers with the reduced dielectric permittivity produced by the anodic oxidation of Si substrates containing ion beam-synthesized SiC nanoparticles

Abstract

The anodic oxidation of 90 keV CO + ion-implanted Si substrates was investigated as a function of the ion dose ranging from 2.5 × 10 15 to 5 × 10 16 cm −2 after the annealing at the temperature of 1100 °C. SRIM software calculations, spectral ellipsometry, Fourier transform infrared spectroscopy, high-resolution electron microscopy, scanning electron microscopy, energy-dispersive X-ray spectrometry and atomic force microscopy were employed to study the structural and optical properties of the oxidized layers. In the samples implanted with an ion dose higher than 1 × 10 16 cm −2 , the formation of SiC nanocrystals was observed at a depth of the projected CO + ion range. After the anodic oxidation, the pore formation in the anodic oxide layers was observed. The pore localization correlated with the SiC nanocrystal distribution. The anodic SiO 2 layer porosity increased as a function of thickness and reached its maximal value of 60-65 vol% at a thickness exceeding ∼250 nm. The refractive index and the dielectric permittivity of the porous SiO 2 films were extracted from the ellipsometry spectra using the Bruggemann effective medium approximation. Both the refractive index and the dielectric permittivity of the porous SiO 2 films decreased as the pre-implanted CO + ion dose grew. In the spectral range of 1-5 eV, the dielectric permittivity of the porous SiO 2 layer was 0.4-0.6 lower than in the thermally grown SiO 2 layer. The results obtained are discussed within the differences in the anodic oxidation of the silicon matrix and regions containing SiC nanocrystals.