Structural and dielectric properties of Ru-based gate/Hf-doped Ta 2O 5 stacks

Abstract

Hf-doped Ta 2O 5 thin films are studied with respect to their composition, dielectric and electrical properties. The incorporation of Hf is performed by sputtering of a 0.7 nm thick Hf layer on top of Ta 2O 5 and subsequent annealing to stimulate diffusion of Hf into Ta 2O 5 and their intermixing. The elemental in-depth distribution of the films is investigated by the time of flight secondary ion mass spectroscopy (ToF-SIMS), which has revealed that Hf and Ta 2O 5 are intermixed throughout the whole thickness. Two sub-layers exist in all the samples – an upper homogeneous Hf-doped Ta 2O 5 sub-layer and a near interfacial region which is a mixture of Ta- and Si-oxides. The X-ray reflectivity (XRR) analysis shows existence of interfacial layer with a thickness of about 1.9–2 nm, irrespectively of the total thickness of the stacks. Metal–oxide–Si structures with Ru and RuO 2 metal electrodes have been prepared and investigated in terms of dielectric constant, effective work function (EWF) and interfacial layer parameters. The influence of post-metallization annealing steps on these parameters was also studied.