Effectiveness of Nitridation of Hafnium Silicate Dielectrics: A Comparison Between Thermal and Plasma Nitridation

The results of a systematic study on the effects of nitrogen incorporation into (60%Hf/40%Si) hafnium silicate/SiO₂ dielectric stacks are presented. Several nitridation methods and processes are compared as a function of the highest performing SiO₂ interlayer/high-k/post-deposition anneal combination on each wafer. It is shown that nitrogen incorporation results in a reduction in not only leakage current density but also maximum drive current, and carrier mobility. The relative increase in leakage current density with measurement temperature is independent of nitridation method or process, which indicates that phase separation may not be a problem for 2-nm hafnium silicate dielectrics. Depending on exact performance requirements, a nitridation step may not be necessary, as its benefits are limited (on ~2.0 nm equivalent oxide thickness films) to a factor of 2 reduction in leakage current density, with 4% and 7% reduction in mobility and drive current, respectively.