Effect of doping concentration on the grain boundary trap density and threshold voltage of polycrystalline SOI MOSFETs

PolySOI MOSFETs have been fabricated on undoped and doped polycrystalline silicon films and characterized to study the effect of doping on grain boundary passivation. The grain boundary trap density (NST) and threshold voltages have been extracted experimentally to evaluate the extent of grain boundary passivation by the dopants. Charge sheet model based on the effective doping concentration has been employed to analytically estimate the threshold voltages using the experimentally determined grain boundary trap density and grain size (Lg) as model parameters. The variation of threshold voltages with increasing doping concentration for the range of NA ≪ (NST/Lg) has been studied both by simulation and experiments and the results are presented. Analytically estimated threshold voltages and experimental results show that the threshold voltage falls with increase in the dopant concentration and that this effect is indeed due to the reduction in NST as a result of the grain boundary passivation by the dopants.