Long-Term Stability and Oxidation of Ferroelectric AlScN Devices: An Operando Hard X-ray Photoelectron Spectroscopy Study

Aluminum scandium nitride (Al1-xScxN) is a promising material for ferroelectric devices due to its large remanent polarization, scalability, and compatibility with semiconductor technology. By doping AlN with Sc, the bonds in the polar AlN structure are weakened, which enables ferroelectric switching below the dielectric breakdown field. However, one disadvantage of Sc doping is that it increases the material's tendency toward oxidation. Herein, the oxidation process of tungsten-capped and uncapped Al0.83Sc0.17N thin films is investigated by hard X-ray photoelectron spectroscopy (HAXPES). The samples is exposed to air for either 2 weeks or 6 months. HAXPES spectra indicate the replacement of nitrogen by oxygen and the tendency of oxygen to favor oxidation with Sc rather than Al. The appearance of an N2 spectral feature thus can be directly related to the oxidation process. An oxidation model that mimics these spectroscopic results of the element-specific oxidation processes within Al1-xScxN is presented. Finally, in operando HAXPES data of uncapped and capped AlScN-capacitor stacks are interpreted using the proposed model.