Boron redistribution in strongly doped silicon thin Bi-layers gates

We have investigated and modeled the complex phenomenon of boron (B) redistribution process in strongly doped silicon (Si) bi-layers structure. A two stream transfer model well adapted to the particular structure of bi-layers and to the effects of strong-concentrations has been developed. This model takes into account the instantaneous kinetics of B transfer, trapping, clustering and segregation during the thermal B activation annealing. The used Si bi-layers have been obtained by low pressure chemical vapor deposition (LPCVD) method, using in-situ nitrogen-doped-silicon (NiDoS) layer and strongly B doped poly-Si (P⁺) layer. To avoid long redistributions, thermal annealing was carried out at relatively low-temperatures (700 and 850°C) for various times ranging between 15 minutes and 2 hours. The good adjustment of the simulated profiles with the experimental secondary ion mass spectroscopy (SIMS) profiles allowed a fundamental understanding about the instantaneous physical phenomena giving and disturbing the complex B redistribution profiles-shoulders kinetics.