Analysis of statistical variation in NBTI degradation of HfO2/SiO2 FETs

The variations in negative bias temperature instability (NBTI) degradation in transistors with HfO2/SiO2 gate dielectric in which thin HfO2 was deposited on SiO2 by atomic layer deposition (ALD) were investigated. The median value of NBTI degradation in the FET with HfO2/SiO2 is lower than that with SiON, but the NBTI variation is large and increases as HfO2 becomes thicker. We propose a model in which the NBTI variation is caused by the variations of the initial hydrogen density in the gate oxide and the small variation of the initial interface trap density. By using this model, the observed large NBTI variation in the high-k device can be well reproduced.