Electrical measurements on ion-implanted LPCVD polycrystalline silicon films

The electrical conduction properties of ion implanted polycrystalline silicon films have been studied. The polysilicon films were deposited by pyrolysis of silane at 647°C in LPCVD system onto oxide-coated silicon wafers to a thickness of 0.6 μm. Dopants were itroducd by implanting with boron or phosphorus ions, accelerated to 145 keV; doses ranged from 1 × 10¹² cm^?2 to 1 × 10¹⁵ cm^?2. Film resistivities spanning 8 orders of magnitude were obtained using this doping range. Current-voltage characteristics of polysilicon resistors were measured at temperatures ranging from 24 to 140°C. The associated barrier heights and activation energies were derived. The grain-boundary trapping states density was estimated to be 5 × 10¹² cm^?2. We found that both dopant atom segregation and carrier trapping at the grain boundaries play important roles in polysilicon electrical conduction properties. However, within the dose range studies, the dopant atom segragation is most detrimental to the film conductivity for doses < 1 × 10¹³ cm^?2; as the dose is increased, carrier trapping effects become more pronounced for doses up to 5 × 10¹⁴ cm^?2. For doses ? 5 × 10¹⁴ cm^?2, conduction due to carriers tunneling through the potential barriers at grain boundaries has to be considered.