LIFETIME PREDICTION METHODS FOR P-MOSFETS - A COMPARATIVE-STUDY OF STANDARD AND CHARGE-PUMPING LIFETIME CRITERIA

Lifetime prediction methods are compared for buried-channel p-MOSFET's DC-stressed under hot-electron injections. Experiments are achieved w ith current-voltage and charge-pumping measurements in order to find a reliable lifetime evaluation with regard to the time-dependent degrad ation. It is shown that a large difference appears whether one conside rs a logarithmic or a power time-dependent law for the degradation of the maximum of the transconductance. This arises from the difficulty t o extrapolate to the working voltage when the gradients vary with time . We used a modified charge-pumping technique in order to compare the hot-carrier immunity of different drain structures. The local increase in the negative trapped charge is compared to the degradations of the threshold-voltage shift, the relative changes of the drain current, a nd of the transconductance. A close correlation is found between the t ransconductance degradation and the oxide charge in conventional p-dev ices where the degradation is dominated by the channel shortening. In deep-submicrometer LDD p-devices, the increase in oxide charge and int erface traps in the graded-drain region plays a significant role in th e change in the channel shortening and series resistance. The local bu ild-up of the oxide charge is shown to grow logarithmically in time. C omparisons of a lifetime prediction method based on the trapping pheno mena with I-V lifetime criteria show that the maximum of the transcond uctance degradation is better correlated to the oxide charge than the other parameters.