Gate Leakage Properties Of Small-Scaled High-k Gate Dielectric MOS Devices

As dimensions of MOSFET are scaling down, thickness of gate oxide is continuously decreased so that gate leakage will significantly be increased. For solving the problem, high-k gate dielectric currently becomes hot research topic to substitute traditional SiO2.Gate leakage properties of small-scaled MOSFET are studied. Based on device physics of MOSFET, the quantized energy levels and distribution of carrier concentration are calculated by self-consistently solving one-dimensional Schr?dinger equations and two-dimensional Poisson equation. The impact of quantum effects is considered and the full boundary conditions of two-dimensional Poisson equation are proposed in this model.Based on the above calculation, tunneling probability of electrons through the gate oxide is obtained by using modified WKB(MWKB) method. Thus a direct tunneling current model of the ultra-thin gate dielectric MOSFET is obtained for different gate voltages. A good agreement between 1-D simulated results and experimental data is obtained, indicating validly of the model. The 2-D simulated results indicate that for lower gate voltages, the direct tunneling current from the channel edges is much lager than that from the channel center, and the total direct tunneling current is larger than that calculated by 1-D model. For higher gate voltages, the tunneling current of different locations along the channel almost has the same values for 2-D and 1-D models.Analysis of interface properties and gate leakage mechanisms shows that the interface trapped charges and oxide charges are the most important reason of the gate leakage current. Interface properties are improved obviously by O₂+C₂HCl₃(TCE) pretreatment, and also the gate leakage current decrease and SILC effects are weakened.