Interface properties of Hf-based high-k gate dielectrics —O vacancies and interface reaction—

We have investigated, theoretically the cause of the substantial threshold voltage (V
_th
) shifts observed in Hf-related high-k gate stacks with p+poly-Si and p-metal gates, by focusing on the ionic nature of HfO
₂
. The oxygen vacancy (Vo) level in ionic HfO
₂
is located in a relatively higher part of the band gap. This high position of the V
_O
results in a significant elevation of the Fermi level for p+poly-Si and p-metal gates, if Si can interact with high-k HfO
₂
. Vo formation in the HfO
₂
induces a subsequent electron transfer from HfO
₂
to gates, causing a substantial V
_th
shifts in MISFETs.