Structural and electrical properties of electron beam gun evaporated Er2O3 insulator thin films

Abstract

We present a detailed study of the evolution with annealing temperature (in an oxygen environment) of the morphological and structural properties of thin erbium oxide (Er2O3) films evaporated in an electron beam gun system. The electrical characteristics of metal-oxide-semiconductor structures are also described. Atomic force microscope and x-ray difractometry were used to map out the morphology and crystalline nature of films ranging in thickness from 4.5 to 100 nm. High-resolution cross-sectional transmission electron microscopy imaging and Auger electron spectroscopy reveal three sublayers: an outer dense nanocrystalline Er2O3 layer, a middle transition layer and amorphous SiO2 film placed close to the Si substrate. The effective dielectric constant depends on the thickness and the annealing temperature. A 1–2.8 nm interfacial SiO2 layer as well as an ErO inclusion with low polarizability are formed during the deposition and the annealing process has a profound effect on the dielectric constant and the leakages. The minimum effective oxide thickness is 2.4–2.8 nm and in the thinnest films we obtained a leakage current density as low as 1–5×10−8 A/cm2 at an electric field of 1 MV/cm. We observe a shift of the flatband voltage to the positive side and significant lowering of the positive charge down to ∼1×1010 cm−2. For a 4.5 nm film, the maximum total breakdown electric field was approximately 1×107 V/cm.