Negative bias temperature instability in TIN/Hf-silicate based gate stacks

This work studies the effects of negative bias temperature instability (NBTI) on p-channel MOSFETS with TiN/HfSi_xO_y (20% SiO ₂) based high-κ gate stacks under different gate bias and elevated temperature conditions. For low bias conditions, threshold voltage shift (△V_T) is most probably due to the mixed degradation within the bulk high-κ. For moderately high bias conditions, H-species dissociation in the presence of holes and subsequent diffusion may be initially responsible for interface state and positively charged bulk trap generation. Initial time, temperature and oxide electric field dependence of △V _T in our devices shows an excellent match with that of SiO ₂ based devices, which is explained by reaction-diffusion (R-D) model of NBTI. Under high bias condition at elevated temperatures, due to higher Si-H bond-annealing/bond-breaking ratio, the experimentally observed absence of the impact ionization induced hot holes at the interfacial layer (IL)/Si interface probably limits the interface state generation and △V_T they quickly reach saturation.