Matrix atomic losses and oxygen incorporation under ruby-laser irradiation of silicon in gaseous atmospheres

The present work provides information both on the loss and the incorporation mechanisms which occur in silicon during high-fluence pulsed-laser irradiation in different gas atmospheres. 〈100〉 silicon samples were irradiated with 20-ns single pulses from a Q-switched ruby laser in ${\mathrm{O}}_2$, ${\mathrm{CO}}_2$, ${\mathrm{N}}_2$, and Ar atmospheres at different ambient pressures. Under these conditions and at sufficiently high laser fluences, significant impurity incorporation may take place, competing with important material loss. Incorporation is observed only for those gaseous atmospheres which lead to a chemical reaction at the surface of the molten silicon. A comparison between heat-flow-model calculations and experimental results seems to indicate that the material-loss mechanism proceeds via a thermodynamical evaporation rather than via a boiling process. Moreover, the observed results exclude an incorporation mechanism taking place via a reaction of the evaporated atoms with the ambient gas, followed by deposition on the sample surface, and rather suggest the occurrence of a reaction at the molten surface. Convective transport is then assumed in order to explain the very quick and massive incorporation. Finally, a simple phenomenological model, which describes the material loss and the impurity-incorporation process, is presented. The model is successfully used to fit the experimental data concerning ${\mathrm{O}}_2$- and ${\mathrm{CO}}_2$-gas atmospheres.