Metal-dielectric band alignment and its implications for metal gate complementary metal-oxide-semiconductor 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 ${\mathrm{SiO}}_{\mathrm{2}}$ 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 ${\mathrm{SiO}}_{\mathrm{2}},$ ${\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}},$ ${\mathrm{Si}}_{\mathrm{3}}{\mathrm{N}}_{\mathrm{4}},$ ${\mathrm{ZrO}}_{\mathrm{2}},$ and ${\mathrm{HfO}}_{\mathrm{2}}$ 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.