Constant current stress of Ti-doped Ta2O5 on nitrided Si

Abstract

The response of Ti-doped Ta2O5 stacked films (4–6 nm) to constant current stress (CCS) under gate injection has been investigated. Two doping methods (‘surface’ and ‘bulk’ doping of Ta2O5) as well as two Si-surface nitridation processes (rapid thermal annealing in N2O and NH3) have been used to prepare the stacks. The effect of doping approach, Si-surface nitridation and the metal electrode (Al and W) on the dielectric degradation has been discussed in terms of stress-induced leakage current (SILC), stress-induced flat band voltage shifts, charge trapping and defect generation. CCS generates charges in the bulk dielectric and in slow states, whose sign and amount depend on both the nitridation process and the doping approach. The method of doping has the strongest impact on the SILC whose behaviour is found to be substantially different from that in SiO2. The method of doping plays a crucial role in the CCS degradation and can be used as an enabling tool for control of this degradation. The gate-deposition-induced defects are another key factor which controls the stress degradation. These defects are very susceptible to electrical stress and could lead to serious reliability concerns.