UV laser-induced oxidation of heavily doped silicon

In this work the authors have investigated the incorporation of oxygen into heavily doped silicon by laser treatment. Different dopants from groups III and V (such as As, Sb, and In) were implanted into (100) silicon to doses in the range 1-5 x 1016 cm-2. Laser annealing was carried out in air using repetitive UV pulses (approx. 1 Hz) provided by excimer lasers, XeCl (lambda = 0.308 μm), or KrF (lambda = 0.243 μm). The pulse durations were about 35 ns, and the energy density per pulse was in the range 1-1.3 J/cm2, sufficient to melt the silicon surface layer to a depth of several thousand angstroms, for a time period not exceeding approximately 150 ns. The authors observe in all cases, after one laser shot, incorporation of a small amount of oxygen localized in the surface as a thin silicon dioxide layer 50-60 A thick, as deduced from ellipsometry measurements (native oxide approx. 30 A). Below the oxide layer, ion-implanted Si is recrystallized, and the different dopants (As, Sb, and In) are incorporated in substitutional sites into silicon lattices at very high concentration levels when compared with their solubility limit at thermal equilibrium. By repetitive laser irradiation (50 to 500 shots) at the same energy density, they observe that the amount of oxygen incorporated depends markedly on the dopant