Room temperature synthesis of HfO₂/HfO _x heterostructures by ion-implantation

Implantation of Hf films with oxygen ions is shown to be an effective means of fabricating high-quality HfO₂/HfO _x heterostructures at room temperature, with the layer composition and thicknesses determined by the ion energy and fluence. Implantation with 3 keV O⁺ ions to a fluence of 1 × 10¹⁷ ions cm^-2 produces a polycrystalline (monoclinic-) HfO₂ layer extending from the surface to a depth of ∼12 nm, and an underlying graded HfO _x layer extending an additional ∼7 nm, while implantation with 6 keV O to a similar fluence produces a near-stoichiometric surface layer of 7 nm thickness and a graded substoichiometric layer extending to depth of ∼30 nm. These structures are shown to be broadly consistent with oxygen range data but more detailed comparison with dynamic Monte Carlo simulations suggests that the near-surface region contains more oxygen than expected from collisional processes alone. The bandgap and dielectric strength of the HfO₂ layer produced by 3 keV; 1 × 10¹⁷ ions cm^-2 implant is shown to be indistinguishable from those of an amorphous film deposited by atomic layer deposition at 200 °C. The utility of these layers is demonstrated by studying the resistive switching properties of metal-oxide-metal test structures fabricated by depositing a top metal contact on the implanted film. These results demonstrate the suitability of ion-implantation for the synthesis of functional oxide layers at room temperature.