Rapid annealing and the anomalous diffusion of ion implanted boron into silicon

The anomalous diffusion of ion implanted boron into silicon is shown to be a transient effect with a decay time that decreases rapidly with increasing anneal temperature. The decay time is approximately 45 min at 800°C and decreases to the order of a second at 1000°C. The anomalous displacement in the low concentration region is greater at low temperatures but a larger fraction of the boron is redistributed at high temperature. Sheet resistance measurements agree with the idea that the moving fraction of the boron atoms is electrically active and limited to the intrinsic carrier concentration at the anneal temperature. The activation energy for the decay of the transient is greater than that for the diffusion coefficient, which makes an appropriate rapid thermal anneal cycle an important practical process in the fabrication of shallow p-n junctions.