Atomic layer deposition of SiO2 from tris(dimethylamino)silane (TDMAS) and ozone as precursors on Si(100) surfaces at near-room temperatures was studied by infrared absorption spectroscopy with a multiple internal reflection geometry. TDMAS can be adsorbed at OH sites on hydroxylated Si surfaces at room temperature. Ozone oxidation of the TDMAS-treated Si surface is effective in removing hydroaminocarbon adsorbates introduced during TDMAS adsorption at room temperature. After oxidation by ozone, treatment with H2O vapor at a substrate temperature of around 160AC causes regeneration of OH sites for TDMAS adsorption. Cycles involving TDMAS adsorption and ozonization at room temperature followed by H2O treatment at 160AC permit the buildup of layers of SiO2. The amount of residual hydroaminocarbon at the interface between the growing SiO2 film and the substrate can be reduced with the ozone treated Si surface as a starting surface.