Impact of the polysilicon doping level on the properties of the silicon/oxide interface in polysilicon/oxide/silicon capacitor structures

In this work, new observations noted in the capacitance-voltage (CV) behaviour of polysilicon/oxide/silicon capacitor structures are reported. As the doping concentration in the polysilicon layer is reduced, anomalous CV characteristics are observed, which are not related to depletion into the polysilicon layer. By examination of the temperature and frequency dependence of the CV characteristics, in conjunction with analysis and simulation, it is demonstrated that the anomalous CV behaviour is a result of a high density of near monoenergetic interface states located at the silicon/oxide interface. Furthermore, by an examination of the temperature and time of the final anneal (H₂ + N₂), a mechanism by which the polysilicon doping level can influence the silicon/oxide interface properties is proposed.