TDDB and polarity-dependent reliability of high-quality, ultrathin CVD HfO2 gate stack with TaN gate electrode

In this letter, we present a comprehensive study on longterm reliability of ultrathin TaN-gated chemical vapor deposition gate stack with EOT=8.5-10.5. It is found that, due to the asymmetric band structure of HfO₂ gate stack with an interfacial layer, the HfO₂ gate stack shows polarity-dependent leakage current, critical defect density, and defect generation rate, under gate and substrate injection. However, no such polarity dependence of time-to-breakdown (T_BD) is observed when T_BD is plotted as a function of gate voltage. The 10-year lifetime of an HfO₂ gate stack is projected to be Vg=-1.63 V for the equivalent oxide thickness (EOT) =8.6 and Vg=-1.88 V for EOT=10.6 at 25°C. These excellent reliability characteristics are attributed to reduced leakage current of HfO₂ gate stack with physically thicker films that result in larger critical defect density and Weibull slope to that of SiO₂ for the same EOT. However, at 150°C, and with area scaling to 0.1 cm² and low percentile of 0.01%, the maximum allowed voltages are projected to Vg=-0.6 V and -0.75 V for EOT of 8.6, and 10.6, respectively.