Dominant Layer for Stress-Induced Positive Charges in Hf-Based Gate Stacks

Positive charges in Hf-based gate stacks play an important role in the negative bias temperature instability of pMOSFETs, and their suppression is a pressing issue. The location of positive charges is not clear, and central to this letter is determining which layer of the stack dominates positive charging. The results clearly show that positive charges are dominated by the interfacial layer (IL) and that they do not pile up at the HfSiON/IL interface. The results support the assumption that positive charges are located close to the IL/substrate interface. Unlike electron trapping that reduces rapidly for thinner Hf dielectric layer, positive charges cannot be reduced by using a thinner HfSiON film.