Hot carrier degradation modes and optimization of LDD MOSFETs

The hot carrier instability and the related device characteristics of Leff= 1µm MOSFETs with Lightly Doped Drain (LDD) structure is evaluated in detail. For the n- dose below 1E13/cm2, a new type of IBB and IG increase was found when the gate bias, VG, was increased toward and over the drain bias, VD, and related new modes of hot carrier instability were confirmed. The instability for the lower VG stress is attributed to the charge build-up at the n- drain region, while the instability for the larger VG stress is attributed to the oxide degradation at both source and drain regions. The device characteristics and the mechanism of instability for n→= 1E13/cm2 are similar to those of conventional devices. It is shown that the instability inherent to the LDD structure can be suppressed by optimizing the n-dose. Thereby, it is important that the lateral electric field peak remains under the gate.