Effect of N2O nitridation on the electrical properties of MOS gate oxides

Furnace annealing in N₂O is a convenient technique for improving the reliability of thermal oxides without significant modifications of the process flow. We investigate the impact of N₂O nitridation on MOSFET device performance, assessing the various factors contributing to the observed degradation of electron mobility. Estimates based on low-frequency C-V and charge pumping measurements show that nitridation causes a significant increase of the interface trap density in the vicinity of the conduction band. Interface traps contribute a parasitic component to the gate-channel capacitance, thus leading to an overestimate of the inversion charge. This effect accounts for a substantial fraction of the mobility degradation which is observed for the nitrided devices. The remaining degradation can be ascribed to an enhancement of Coulomb scattering, maybe due to differences in dopant segregation, and to a change of the surface roughness characteristics.