Gate length dependent polysilicon depletion effects

Degradation of MOS gate capacitance in the inversion region becomes worse as the gate length is scaled down, according to a new experiment. Namely, the polysilicon depletion effect has gate length dependence. The origin of this gate length-dependent polydepletion effect has been modeled and verified by using device simulation. As a result, the gradient of dopant distribution resulting from ion implantation is shown to be an additional potential drop in the polygate. In addition, the enlarged depletion width at the gate sidewall can worsen the polydepletion effect for very-small MOSFETs.