Metal-dielectric band alignment and its implications for metal gate complementary metal-oxide-semiconductor technology

TLDR

Metal work functions on high‑κ dielectrics differ appreciably from their values on SiO₂ or in vacuum. The study explored how the metal gate work function depends on the underlying gate dielectric in advanced MOS stacks and applied interface dipole theory to the gate–dielectric interface, achieving excellent agreement with experimental data. The authors extracted slope parameters for several gate dielectrics, explained the weaker dependence of polysilicon gate work functions on dielectric material, highlighted challenges in gate work‑function engineering, and offered guidelines for selecting gate materials in future high‑κ MOS technology.

Abstract

The dependence of the metal gate work function on the underlying gate dielectric in advanced metal-oxide-semiconductor (MOS) gate stacks was explored. Metal work functions on high-κ dielectrics are observed to differ appreciably from their values on SiO2 or in vacuum. We applied the interface dipole theory to the interface between the gate and the gate dielectric of a MOS transistor and obtained excellent agreement with experimental data. Important parameters such as the slope parameters for gate dielectrics like SiO2, Al2O3, Si3N4, ZrO2, and HfO2 were extracted. In addition, we also explain the weaker dependence of n+ and p+ polysilicon gate work functions on the gate dielectric material. Challenges for gate work function engineering are highlighted. This work provides additional guidelines on the choice of gate materials for future MOS technology incorporating high-κ gate dielectrics.