High quality interfacial sulfur passivation via H2S pre-deposition annealing for an atomic-layer-deposited HfO2 film on a Ge substrate

Abstract

The effects of sulfur passivation of the Ge substrate were studied through (NH₄)₂S solution treatment and the rapid thermal annealing under an H₂S atmosphere prior to atomic-layer-deposition (ALD) of HfO₂. While a chemically unstable and uneven sulfur layer was formed by (NH₄)₂S solution treatment, a stable, highly uniform and dense sulfur layer with a thickness of ∼2 nm was formed by H₂S annealing on Ge substrates. The sulfur concentration at the interface increased with H₂S annealing temperature. Sulfur passivation suppressed the diffusion of Ge into the HfO₂ film and any interfacial layer growth during ALD, which resulted in a decreased equivalent oxide thickness of gate insulator. The interface properties, such as interface defect state density and hysteresis in capacitance–voltage behavior, were also improved by sulfur passivation through H₂S annealing. H₂S annealing is much more compatible with a mass-production process compared to the conventional (NH₄)₂S solution treatment process.