Ultrathin SiO2 layer with a low leakage current density formed with approximately 100% nitric acid vapor.

An ultrathin silicon dioxide (SiO(2)) layer with 0.65-1.5 nm thickness has been formed by approximately 100% nitric acid (HNO(3)) vapor oxidation, and its electrical characteristics and physical properties are investigated. The oxidation kinetics follows a parabolic law except for the ultrathin (<or=0.8 nm) region, indicating that diffusion of oxidizing species (i.e. oxygen atoms generated by decomposition of approximately 100% HNO(3) vapor) through a growing SiO(2) layer is the rate-determining step. The diffusion activation energy for HNO(3) vapor oxidation is 0.14 eV, much lower than that of thermal oxidation of 1.24 eV. The leakage current density for the 0.65 nm SiO(2) layer formed by HNO(3) vapor oxidation is lower by approximately one order of magnitude than that for a thermal oxide layer with the same thickness. The low leakage current density is attributed to (i) the atomically flat SiO(2)/Si interface and uniform thickness of the ultrathin SiO(2) layer, (ii) the low concentration of suboxide species and the low interface state density and (iii) the high atomic density of the SiO(2) layer, which leads to a high band discontinuity energy at the SiO(2)/Si interface. The leakage current density is further decreased by PMA at 250 degrees C in 5 vol% H(2) atmosphere.