Ultralow work function of scandium metal gate with tantalum nitride interface layer for n-channel metal oxide semiconductor application

The authors have investigated n-channel metal oxide semiconductor compatible metal gate with ultralow work function using tantalum nitride (TaNx)/scandium(Sc) stack layer. By adjusting the deposition condition, the effective work function as low as 4.0eV with improved thermal stability can be obtained. Without TaNx layer, work function of pure Sc gate on HfO2 was about 4.2eV and show thermal instability at high temperature which can be explained by reaction between Sc and HfO2. The authors found that control of TaNx layer is the critical process to maintain thermal stability and work function. The TaNx∕Sc stack process shows promise for future high-k metal gate applications.