Study of Charge and Inversion Layer Mobility in Hafnium Oxide Stacks

Abstract

Charge in HfO2 gate stacks grown from various MOCVD sources has been studied. For these films, charge in the stack is mainly concentrated at the interfaces between the layers and is negative at the HfO2/interfacial layer (IL) interface and positive at the Si/IL interface. A forming gas anneal (FGA) can reduce interface charge, hysteresis, and interface state densities. The marked difference in the post deposition annealing (PDA) response of similar films deposited from different precursors, however, strongly suggests that charge in these stacks is related to the deposition chemistry and may be due to residual impurities or defects left in the film from the deposition. The study on the inversion layer mobility indicates that coulomb scattering due to interface trapped charge accounts mainly for the hole mobility degradation. Electron mobility experiences much more severe degradation than hole mobility, suggesting the existence of multiple scattering sources.