Hot carrier degradation in p-channel MOSFETs

The impact of scaling device channel length and thinning gate oxide for improved performance, and the effect of the gate conductor material and spacer process on p-channel hot-carrier degradation are described. p-channel devices with n⁺ polysilicon and WSi₂ (polycide) gates, with 100-Å and 150-Å gate oxides, and channel lengths ranging from 0.5 μm to 1.3 μm were stressed at V_ds=-5.0 to -6.0 V and room temperature for 1000 s. Positive shifts in threshold voltage as well as increased saturation drain current and transconductance are observed after stress. The degradation in device characteristics of a 1.0-μm device, biased over a range of voltage conditions, was found to be related to the measured gate current by a power-law dependence. As the device channel length is decreased, the observed degradation in threshold voltage increased exponentially. However, as the device gate oxide thickness is reduced, the threshold voltage degradation remained constant for a given bias and fixed channel length, even though the gate current increases significantly. Device degradation is also a strong function of the gate conductor material and the spacer dimension on the sidewall of the gate conductor