Ultrathin SiO2 layer on atomically flat Si(111) surfaces with excellent electrical characteristics formed by nitric acid oxidation method

We have developed a method of formation of atomically smooth Si∕SiO2 interfaces by oxidation of atomically flat Si(111) surfaces by use of azeotropic nitric acid (HNO3) aqueous solutions (i.e., 68wt% HNO3 at 121°C). For the SiO2 layer on the atomically smooth Si substrates, the concentration of suboxide species, Si2+, is ∼50% of that on the rough Si substrates, and the valence band discontinuity is higher by ∼0.1eV. In this case, the leakage current flowing through the ∼1.2nm SiO2 is low, and further decreased by postmetallization annealing at 250°C in hydrogen (e.g., 0.5A∕cm2 at VG=1V).