A SIMPLE METHOD TO QUALIFY THE LDD STRUCTURE AGAINST THE EARLY MODE OF HOT-CARRIER DEGRADATION

A simple combination of the heating gate technique and measurements of the forward and reverse (source and drain interchanged) saturation I- DS versus V-GS characteristics for an LDD NMOSFET is shown to reveal m ore information on the nature of an early hot-carrier degradation. Any susceptibility of the LDD structure to this type of degradation leads to an early evolution of the floating gate drain current, and a corre sponding evolution in the I-DS versus V-GS curves mentioned above, wit hout affecting the threshold voltage, Our method reveals that the earl y mode affects both forward and reverse saturation I-DS versus V-GS ch aracteristics, While the effect on the reverse characteristic can he a ttributed to an increase in the drain parasitic resistance, the effect on the forward characteristic apparently indicating source side activ ity, may be actually due to an increase in the effective channel lengt h, as suggested by simulations, an additional new observation of the d ecrease of the peak substrate current with the floating gate cycles, w hen coupled with simulations, allow us to locate and quantify the dama ge at the edge of the gate, We expect our observations to be useful in qualifying the LDD structure.