Formation of 10-30 nm SiO2/Si structure with a uniform thickness at ∼120 °C by nitric acid oxidation method

Silicon dioxide NOD layers with a thickness more than 10 nm can be formed at similar to 120 degrees C by direct Si oxidation with nitric acid (HNO3). Si is initially immersed in 40 wt.% HNO3 at the boiling temperature of 108 degrees C, which forms a similar to 1 nm SiO2 layer, and the immersion is continued after reaching the azeotropic point (i.e., 68 wt.% HNO3 at 121 degrees C), resulting in an increase in the SiO2 thickness. The nitric acid oxidation rates are the same for (111) and (10 0) orientations, and n-type and p-type Si wafers. The oxidation rate is constant at least up to 15 nm SiO2 thickness (i.e., 1.5 nm/h for single crystalline Si and 3.4 nm/h for polycrystalline Si (poly-Si)), indicating that the interfacial reaction is the rate-determining step. SiO2 layers with a uniform thickness are formed even on a rough surface of poly-Si thin film. (c) 2006 Elsevier B.V. All rights reserved.