Low temperature formation of SiO2 thin films by nitric acid oxidation of Si (NAOS) and application to thin film transistor (TFT)

Nitric acid oxidation of Si (NAOS) can form 1.3-20 nm SiO2 films on Si(100) and poly-crystalline silicon (poly-Si) surfaces at low temperatures below 120 degrees C. The 1.3 nm SiO2 layer formed by immersion in 68 wt% HNO3 possesses a low leakage current density and it can be made lower by post-metallization annealing (PMA) in hydrogen than that for thermal oxide with the same thickness. A thicker SiO2 layer can be formed by immersion in 40 wt% HNO3 followed by 68 wt% HNO3, and its leakage current density becomes nearly the same after PMA as that of thermal oxide. The low leakage current density results from elimination of the interface states by hydrogen and the high atomic density of the NAOS-SiO2 layer as estimated from the vibrational frequencies of transverse and longitudinal optical phonons of the Si-O-Si asymmetric stretching mode. The thickness of the NAOS-SiO2 layer is uniform even on the rough poly-Si surfaces. The dispersion of the thickness of the NAOS-SiO2 layer is also found to be less than +/- 5% on the 32 cm x 40 cm poly-Si substrates. (C) 2009 Elsevier B.V. All rights reserved.