Investigation of oxygen penetration during UV nanosecond laser annealing of silicon at high energy densities

Highlights: • Oxygen and carbon impurities diffusion during melt laser annealing. • Identification and localization of optical defects signatures. • Impact of the surface oxide on the impurities diffusion. In this work, we present a comprehensive investigation of impurities contamination in silicon during UV Nanosecond Laser Annealing at high energy density. By investigating in detail the impact of the annealing ambient and of the surface preparation prior to UV-NLA (including the variation of the surface oxide thickness), we show that the observed oxygen penetration originates from the surface oxide layer. It is proposed that, at high energy UV-NLA, the prolonged contact of SiO₂ with high temperature liquid Si induces a partial degradation of the SiO₂/Si interface, leading to bond breaking and subsequent injection of O atoms into the substrate. A degradation involving less than 5% of the O atoms contained in the 1st SiO₂ mono-layer is sufficient to account for the measured amount of in-diffused O in all of the analysed samples.