Physics in Fermi level pinning at the polySi/Hf-based high-k oxide interface

First principles investigation of defect energy levels at semiconductor-oxide interfaces: Oxygen vacancies and hydrogen interstitials in the Si–SiO2–HfO2 stack

“…At variance, the amorphous components show pinning levels within the silicon band gap, which account for the position of measured levels. 55,56 Hence, our results for both the energetics and the Fermi-level pinning indicate that oxygen vacancies locate in the noncrystalline transition regions of the gate stack.…”

“…The oxygen vacancy has been the object of extensive studies in literature 41,53,54 because it is suspected to be at the origin of the Fermi-level pinning in p-type polysilicon gate stacks. 55,56 The hydrogen interstitial is ubiquitous at such interfaces. While it is known to play a beneficial role in passivating dangling bonds at the Si-SiO 2 interface, this impurity may be at the origin of the negative bias temperature instability 57 and the positive charging of the gate oxide.…”

“…60 According to the current understanding of Fermi-level pinning in these gate stacks, the oxygen vacancy formation is accompanied by a silicon oxidation reaction. 55,56 The vacancy generation proceeds as long as this reaction is exothermic ͑⌬G Ͻ 0͒, 55,56 thereby fixing the pinning level through the condition ⌬G = 0. Our results indicate that oxygen vacancies in monoclinic HfO 2 do not lead to Fermi-level pinning.…”

Anomalous VFB Shift in High-k Gate Stacks - Is its Origin at the Top or Bottom Interface ? -

“…This is actually the case for HfO 2 . Here, we should take account of the electron entropy effect caused by neutral oxygen vacancy (V o → V o 2+ ) (6). Since then, the significant role of this vacancy in high-k films has often been discussed.…”

Interstitial oxygen induced Fermi level pinning in the Al2O3-based high-k MISFET with heavy-doped n-type poly-Si gates

“…For Hf-based high-k dielectrics, it has proposed that oxygen vacancies (V O s) are the physical origin of substantial V th shifts (V O model), 12,13 which clearly explains substantial V th shifts observed in Hf-based high-k dielectrics. Based on this explanation, further investigations were performed to avoid formation of V O in HfO 2 and eventually succeeded in replacing SiO 2 by controlling the V O formation in HfO 2 .…”