Fermi-Level Pinning at the Poly-Si/HfO2 Interface

The high threshold voltage in metal-oxide-semiconductor field effect transistor (MOSFET) devices adopting hafnia for the gate oxide material is a serious concern for alternative high-kappa gate oxides. The Fermi-level pinning at the highly-doped poly-Si/metal oxide interface has been reported as a cause because the interfacial metal-Si bonds can induce pinning of the Fermi level. In this work, the electronic structure and the chemical bonding states at the interface of n(+) type and p(+) type poly-Si/HfO2 were measured by using transmission electron microscopy (TEM) and X-ray photoemission spectroscopy (XPS) in order to find the reason for the high threshold voltage. The obtained Hf 4f core-level spectrum shows no Hf-Si state at the interface. Therefore, metallic Hf-Si bond formation at the interface may not be the reason for the high threshold voltage.