TDDB and Polarity-Dependent Reliability of High-Quality, Ultrathin CVD HfO 2 Gate Stack with TaN Gate Electrode

Abstract

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 Å. It is found that, due to the asymmetric band structure of HfO 2 gate stack with an interfacial layer, the HfO 2 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 HfO 2 gate stack is projected to be Vg = -1.63 V for the equivalent oxide thickness (EOT) = 8.6 Å and Vg = -1.88 V for EOT = 10.6 Å at 25 °C. These excellent reliability characteristics are attributed to reduced leakage current of HfO 2 gate stack with physically thicker films that result in larger critical defect density and Weibull slope to that of SiO 2 for the same EOT. However, at 150 °C, and with area scaling to 0.1 cm 2 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 A, respectively.