Charge-pumping characteristics of virgin and stressed lightly-doped drain MOSFETs

Abstract

Qualitative differences between the charge-pumping characteristics of lightly-doped drain (LDD) MOSFETs against the characteristics of conventional MOSFETs with abrupt junctions are analyzed and explained. The contribution of the particular interface regions in LDD devices to the charge-pumping characteristics is clarified by studying the spatial distributions of the charge-pumping threshold and flat-band voltages. A two-dimensional transient numerical model of the charge-pumping effect is also applied in the analysis. In order to understand the deep tail at the rising edge of the characteristics of LDD devices, an analytical model of the gate/LDD electrical-field fringing is derived. The accuracy of the analytical solution to the field-fringing problem is investigated regarding the self-induced lateral field in the semiconductor near the gate edge. The degradation of n-channel LDD MOSFETs under electrical stress is studied. The spatial distribution of stress-generated traps is extracted at different stress moments. Assuming these distributions as input the charge-pumping characteristics are calculated by employing the transient numerical model and compared with experimental data.