Reduction of native oxides by annealing in reducing gas or plasma

Abstract

Native oxide growth on germanium, silicon germanium, and InGaAs undesirably affects CET (capacitive equivalent thickness) and EOT (effective oxide thickness) of high-k and low-k metal-oxide layers formed on these semiconductors. Even if pre-existing native oxide is initially removed from the bare semiconductor surface, some metal oxide layers are oxygen-permeable in thicknesses below about 25 Å thick. Oxygen-containing species used in the metal-oxide deposition process may diffuse through these permeable layers, react with the underlying semiconductor, and re-grow the native oxide. To eliminate or mitigate this re-growth, the substrate is exposed to a gas or plasma reductant (e.g., containing hydrogen). The reductant diffuses through the permeable layers to react with the re-grown native oxide, detaching the oxygen and leaving the un-oxidized semiconductor. The reduction product(s) resulting from the reaction may then be removed from the substrate (e.g., driven off by heat).