Abstract
As the channel length and the gate oxide thickness are scaled down, the off-state MOSFETs’ leakage current becomes more severe. The off-state leakage components are the sub-threshold current, surface/bulk thermal generation of carriers in the junction space-charge region, gate direct tunneling current etc. Furthermore, Many researchers have attributed the leakage current to the band-to-band tunneling occurring in the overlay region at negative gate bias and named the phenomenon “gate-induced drain leakage current (GIDL)”.According to the SIA roadmap, CMOS with gate length of 50-70 nm needs an oxide thickness of around 1.5-2.0 nm, which corresponds to 2-3 layers of atoms. With such a thin gate oxide, the gate direct tunneling current and the gate induced drain leakage current would become more apparent at low voltage due to the high electric field at low voltage. The exact oxide thickness and doping profiles in the gate-to-drain overlay region play important roles in the GIDL current. And this leakage current is very sensitive to the oxide thickness, drain concentration, and lateral drain doping gradient. In the gate-to-drain overlay region, since the gate work function and high drain concentration would serve to enhance the field strength. So, recently complete suppression of the GIDL current has been demonstrated for low-concentration LDD devices by suppressing the electric field. At somewhat higher field, the band-to-band tunneling in the gate-overlapped deep-depletion drain region has been proven to be the generation mechanism for Gate-Induced Drain Leakage (GIDL). In this thesis, we investigate GIDL models with n-MOSFETs oxide thickness of 20 Å, 26 Å, and 50 Å, respectively. We show that the published GIDL models are not well fitting to our measured data. Since the surface electric field in the gate-to-drain overlay region play important roles in the GIDL current. In order to observe the surface electric field, we generate tsuprem4 structures whose aspects are similar to the measured samples. Then, devices characteristic are simulated with Medici to observe the surface electric field in the gate-overlapped-drain region. Moreover, we derive a new GIDL model and fitting well with measured data.