Low-temperature diffusion of high-concentration phosphorus in silicon, a preferential movement toward the surface

We demonstrate that ultrashallow high-concentration phosphorus profiles in silicon diffuse preferentially toward the surface during low-temperature annealing at 700°C after recrystallization of an amorphous layer. In this work, we observe the preferential diffusion following a preamorphizing germanium implant, and also after a self-amorphizing phosphorus implant. This phenomenon is driven by the presence and dissolution of silicon interstitial defects. The greater the distance between the defect band and the high-concentration phosphorus profile, the less the preferential diffusion for a fixed anneal time. The overall result of this effect is a phosphorus profile that is significantly shallower and steeper than after implant.