Stress-induced defect generation in HfO2/SiO2 stacks observed by using charge pumping and low frequency noise measurements

The technique of combining the low frequency drain current noise and the frequency-dependent charge pumping techniques has been employed to extract the trap densities in both the interfacial SiO2 layer and high-k layer in the n-type MOSFETs with HfO2/SiO2 stacks. It is found that positive bias stress creates more traps in the gate dielectric stack near the gate electrode while negative stress increases the density of traps generated in the proximity of the Si substrate. The results show that under electrical stress new traps are predominantly created close to the anode side and the degree of asymmetry is surprisingly large.