In situ cleaning effect on the electrical properties of Ge MOS devices by Ar gas anneal

An in situ surface-cleaning technique by annealing germanium substrates at 550 degC in Ar gas is investigated. Reduced equivalent oxide thickness confirms the effective removal of native oxides by this technique. Improved electrical characteristics in terms of reduced interface-state density and slow trap density are demonstrated in the Ge MOS devices, with surface-nitridation treatment and chemical vapor deposited HfO₂ high-kappa dielectric, suggesting the advantage of this technique. Significant elimination of GeO_xN _y interfacial layer is observed from cross-sectional transmission electron microscopy images after 600 degC postmetallization anneal, suggesting that an interface passivation technique having better thermal stability is required in order to suppress the severe interdiffusion across the interface between Ge substrate and the upper dielectric layer