Structural and dielectric properties of Ru-based gate/Hf-doped Ta2O5 stacks

Hf-doped Ta2O5 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 Ta2O5 and subsequent annealing to stimulate diffusion of Hf into Ta2O5 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 Ta2O5 are intermixed throughout the whole thickness. Two sub-layers exist in all the samples – an upper homogeneous Hf-doped Ta2O5 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 RuO2 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.