Adsorption of tris (dimethylamino) silane {[(CH3)(2)N](3)SiH, TDMAS} and decomposition of the adsorbed TDMAS with an ozone ambient on Si (100) surfaces as an atomic layer deposition (ALD) process of SiO2 have been investigated using Fourier transform infrared absorption spectroscopy (IRAS) with a multiple internal reflection geometry. TDMAS dissociatively adsorbs on the Si (100) surface to produce adsorbates including hydroaminocarbons and Si hydrides even at room temperature. IRAS suggests that TDMAS adsorbs preferentially on OH sites on Si surfaces that are produced by an H2O adsorption. Ozone oxidizes TDMAS adsorbed on the Si surface and makes the surface active to further TDMAS adsorption to progress the ALD cycle. The mechanism of SiO2 ALD process with TDMAS and ozone is discussed in this paper. (C) 2007 The Electrochemical Society.