Properties of thick SiO2/Si structure formed at 120°C by use of two-step nitric acid oxidation method

Thick (i.e., ∼10 nm) SiΟ 2 /Si structure has been formed at 121 °C by immersion of Si in relatively low concentration HNO 3 followed by that in 68 wt.% HNO 3 (i.e., two-step nitric acid (HNO 3 ) oxidation method of Si, NAOS) and spectroscopic properties and electrical characteristics of the NAOS SiO 2 layers are investigated. The SiO 2 thickness strongly depends on the concentration of HNO 3 aqueous solutions employed in the initial oxidation, and it becomes the largest at the HNO 3 concentration of 40 wt.%. The MOS diodes with the ∼9 nm SiO 2 layer formed by the NAOS method possess a relatively low leakage current density (e.g., 10 -8 A/cm 2 at the forward bias of 1 V) and it is further decreased by more than one order of magnitude by post-metallization annealing (PMA) in hydrogen at 250 °C. The good leakage characteristic is attributable to atomically flat SiO 2 /Si interfaces and high atomic density of 2.30-2.32 x 10 22 atoms/cm 3 of the NAOS SiO 2 layers. High-density interface states are present in as-prepared SiO 2 layers and they are eliminated by PMA in hydrogen.