Interface trap density in amorphous La2Hf2O7/SiO2 high-κ gate stacks on Si

Abstract

The present paper investigates the interface trap density of a new high-κ gate dielectric stack, La2Hf2O7/SiO2 on Silicon. Amorphous La2Hf2O7 thin films are deposited by metal evaporation in the presence of atomic oxygen beams on an ultra-thin SiO2 layer (1.5 nm) grown by rapid thermal oxidation on a p-type Si substrate. A combination of electrical (C–V) and cross sectional TEM measurements indicates a value of the dielectric constant κ of about 19±2.2. The interface states density (Dit) was measured using the conductance method for different La2Hf2O7 thicknesses ranging from 3 nm to 14 nm. Dit ranges from 3.4×1010 eV-1 cm-2 to 4.8×1012 eV-1 cm-2 and shows a quasi-linear dependence on the La2Hf2O7 layer thickness. The interface state density increase with film thickness could have different explanations, such as oxygen de-passivation and/or defect generation at the Si-SiO2 interface, formation of a new Si-SiO2 interface by Si oxidation or alternatively, the SiO2 interfacial layer reduction by oxygen vacancies.