Effects of high-κ gate dielectric materials on metal and silicon gate workfunctions

The dependence of metal and polysilicon gate work-functions on the underlying gate dielectric in advanced MOS gate stacks is explored. We observe that the metal workfunctions on high-kappa dielectrics differ appreciably from their values on SiO2 or in a vacuum. We also show the first application of the interface dipole theory on the metal-dielectric interface and obtained excellent agreement with experimental data. Important parameters such as the slope parameters for SiO2, Si3N4, ZrO2, and HfO2 are extracted. In addition, we also explain the weaker dependence of n+ and p+ polysilicon gate workfunctions on the gate dielectric. Challenges for gate workfunction engineering are highlighted. This work provides additional guidelines on the choice of gate materials for future CMOS technology incorporating high-kappa gate dielectrics.