Time-dependent dielectric breakdown in poly-Si CVD HfO2 gate stack

In this paper, we present a comprehensive study on long-term reliability of CVD HfO2 gate stacks with n(+)-poly-Si gate electrodes. The area dependence and temperature acceleration (25-150degreesC) of TDDB, defect generation rate, and critical defect density of CVD HfO2 gate stacks are studied. Results show that 10 year lifetime of HfO2/n(+)-poly-Si gate stack (EOT=14.5Angstrom) is projected for Vg=-2.0V @25degreesC and Vg=-1.56V @150degreesC. This excellent reliability characteristics of HfO2 gate stack is mainly attributed to the thicker physical thickness of HfO2, resulting in significant reduction of tunneling leakage current by a factor of 10(3)similar to10(4) while maintaining comparable Weibull slope factor. In addition, the critical defect density of HfO2 gate stack is comparable to SiO2 with similar physical thickness. However, considering the cumulative impact of temperature acceleration at 150degreesC, scaling of an effective gate oxide area of 0.1cm(2) and a maximum allowed fraction of failures of 0.01%, the maximum allowed operating voltage is projected to be only similar to0.85V for HfO2/poly-Si gate stack with EOT=14.5Angstrom.