Channel Hot-Carrier Degradation in Short-Channel Transistors With High- $k$ /Metal Gate Stacks

Channel hot-carrier (CHC) degradation in nMOS transistors is studied for different SiO₂/HfSiON dielectric stacks and compared to SiO₂. We show that, independent of the gate dielectric, in short-channel transistors, the substrate current peak (used as a measure for the highest degradation) is at V_G = V_D, whereas for longer channels, the maximum peak is near V_G = V_D/2. We demonstrate that this shift in the most damaging CHC condition is not caused by the presence of the high- k layer but by short-channel effects. Furthermore, the CHC lifetime of short-channel transistors was evaluated at the most damaging condition V_G = V_D, revealing sufficient reliability and even larger operating voltages for the high-k stacks than for the SiO₂ reference.