Properties Of Thick Sio_2/si Structure Formed At 120 ℃ By Use Of Two-step Nitric Acid Oxidation Method

摘要

Thick (i.e., ～10nm) SiO_2/Si structure has been formed at 121 ℃ 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 ℃. The good leakage characteristic is attributable to atomically flat SiO_2/Si interfaces and high atomic density of 2.30-2.32 × 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.