Transient diffusion of ion-implanted B in Si: Dose, time, and matrix dependence of atomic and electrical profiles

The time evolution of B diffusion and electrical activation after ion implantation and annealing at 800 and 900 °C is studied using secondary-ion mass spectrometry and spreading-resistance profiling. The time evolution at 800 °C is observed in both crystalline and post-amorphized samples. Amorphized samples show near-normal concentration enhanced diffusion. Crystalline samples show anomalous transient diffusion, with a rapidly diffusing low-concentration region and a static peak region above a critical concentration Cenh=3.5×1018 cm−3. The peak region above Cenh is shown to be electrically inactive. The static, inactive B is released over a period of many hours, compared with the transient diffusion enhancement which relaxes to near-normal within 30 min. The time evolution of B diffusion at 900 °C is observed as a function of implantation dose. A critical concentration for transient diffusion, Cenh=8×1018 cm−2, independent of dose, is observed at this temperature. The transient diffusion enhancement in the diffusing part of the B profile increases with dose, up to a dose of ∼5×1014 cm−3, and saturates at higher doses. A comparison with published data shows that Cenh∼ni within a factor 2 over the temperature range 550–900 °C. We interpret our observations in terms of a nonequilibrium point-defect model of diffusion and intermediate defect formation.