Effect of polysilicon gate doping concentration variation on MOSFET characteristics

Polysilicon gates have replaced the metal gates in CMOS technology. If the doping is not high enough in polysilicon then the flatband voltage should be corrected. Polysilicon gates are also depleted with the application of gate voltage. The dependence of MOSFET current (I_ds) on polysilicon gate concentration is studied using the results simulated by Sentaurus TCAD tool in case of N channel MOSFETs. With the decrease in polysilicon gate doping concentration (N_d), the drain current is more degraded. A theory is developed, in order to explain the simulation results that take into consideration the correction in flatband voltage and the voltage drop due to polysilicon depletion. From the analysis of simulated and theoretical curves, an inversion region is suspected to occur at the polysilicon gate for low doping concentration at high gate voltage.