Selective Oxidation Behavior Of W/Wn/Polycrystalline-Si1-Xgex Gate Structure In H2o+H-2 Ambient

Selective oxidation behavior, i.e., oxidation of polycrystalline-Si1-xGex (poly-SiGe) without metal oxidation, of the W/WN/poly-SiGe structure was investigated for gate electrode applications. While the dry oxidized samples showed a dramatic increase of the oxidation rate with increasing Ge content, the oxidation rate in the selectively oxidized (in a H2O+H-2 ambient) samples was found to be very low irrespective of the Ge content. The oxides grown in a H2O+H-2 ambient are identified to be only SiO2 even up to 60% Ge, other than the dry oxidized samples that consist of nearly pure SiO2 underneath a mixed oxide alloy of (Si,Ge)O-x. Different oxidation mechanisms based on the competition between the oxidation rate and the Ge diffusion rate in Si are suggested to explain a remarkable difference in the oxide thickess and composition. For dependable applications of poly-SiGe in metal-shunted gate structures, this oxidation feature enables a very clean sidewall profile with an improved reliability of gate oxides after selective oxidation process. (C) 2003 American Institute of Physics.