Modeling of boron diffusion in polysilicon-on-silicon structures using a rapid thermal anneal step for ultra-shallow junction formation

The diffusion of boron in polysilicon-on-silicon structures subjected to a rapid thermal anneal (RTA) step in investigated. The high temperature step (> 1000 °C) causes a breakdown of the interfacial oxide leading to increased dopant flux across the polysilicon-silicon interface. The effect of the break-up of the interfacial oxide is modeled as a temperature-dependent interface transport coefficient across the polysilicon-silicon interface. The enhanced boron diffusion is attributed to the interfacial oxide breakdown and the dissociation of boron defect complexes at the polysilicon-silicon interface. The enhanced concentration-dependent effective boron diffusivities in the single crystal silicon for polysilicon-on-silicon structures are extracted using Boltzmann-Matano analysis. A phenomenological model is implemented in SUPREM-III to accurately model the boron diffusion profiles in polysilicon-on-silicon structures subjected to a RTA step.