VTH shift mechanism in dysprosium (Dy) incorporated HfO2 gate nMOS devices

Abstract

We discuss temperature-dependent Dy diffusion and the diffusion-driven Dy-silicate formation process in Dy incorporated HfO2. The Dy-induced dipoles are closely related to the Dy-silicate formation at the high-k/SiO2 interfaces since the VFB shift in Dy2O3 is caused by the dipole and coincides with the Dy-silicate formation. Dipole formation is a thermally activated process, and more dipoles are formed at a higher temperature with a given Dy content. The Dy-silicate related bonding structure at the interface is associated with the strength of the Dy dipole moment, and becomes dominant in controlling the VFB/VTH shift during the high temperature annealing in the Dy-Hf-O/SiO2 gate oxide system. Dy-induced dipole reduces the degradation of the electron mobility. Charge trapping characteristics in relation to the stress-induced flatband shift and SILC are discussed with a band diagram. The higher effective barrier height of Dy2O3, which is around 2.32 eV, calculated from the F-N plot, accounts for the reduced leakage current in Dy incorporated HfO2 nMOS devices. The lower trap generation rate by the reduced hole trap density and the reduced hole tunneling of the Dy-doped HfO2 dielectric demonstrate the high dielectric breakdown strength by weakening the charge trapping and defect generation during the stress.