Mechanistic understanding of mobility degradation on gate-last ZrO2 with medium thermal budget annealing

In this paper, we provide a mechanistic understanding of mobility degradation of gate-last ZrO₂ subjected to medium thermal budget annealing. We find that high-k post deposition anneal (PDA) even at modest temperatures can improve the interfacial layer (IL) and bulk oxide, but mobility suffers. The mechanism for this mobility degradation is the enhanced remote Coulomb scattering from nonstoichiometric ZrO_x region near the IL. The high-k PDA, even at moderate temperature, enables oxygen gettering of the IL and deprives oxygen from ZrO₂ near the IL, which results in the accumulation of defects/traps in the region near ZrO₂/IL interface. This enhances remote Coulomb scattering due to the high concentration of oxide traps and their close proximity to the conductance channel. Consequently, mobility is degraded even though IL and bulk oxide are improved.