Hot Carrier Stress Sensing Bulk Current for 28 nm Stacked High-k nMOSFETs

This work primarily focuses on the degradation degree of bulk current (I-B) for 28 nm stacked high-k (HK) n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs), sensed and stressed with the channel-hot-carrier test and the drain-avalanche-hot-carrier test, and uses a lifetime model to extract the lifetime of the tested devices. The results show that when I-B reaches its maximum, the ratio of V-GS/V-DS values at this point, in the meanwhile, gradually increases in the tested devices from the long-channel to the short ones, not just located at one-third to one half. The possible ratiocination is due to the ON-current (I-DS), in which the short-channel devices provide larger I-DS impacting the drain junction and generating more hole carriers at the surface channel near the drain site. In addition, the decrease in I-B after hot-carrier stress is not only the increment in threshold voltage V-T inducing the decrease in I-DS, but also the increment in the recombination rate due to the mechanism of diffusion current. Ultimately, the device lifetime uses Berkley's model to extract the slope parameter m of the lifetime model. Previous studies have reported m-values ranging from 2.9 to 3.3, but in this case, approximately 1.1. This possibly means that the critical energy of the generated interface state becomes smaller, as is the barrier height of the HK dielectric to the conventional silicon dioxide as the gate oxide.