We report the atomic layer deposition (ALD) of silicon oxide films using a chlorine-free silylamine precursor and ozone (O3). Bis(dimethylaminomethylsilyl)trimethylsilylamine (DTDN-2H2) containing three Si atoms was used as the precursor, and a high growth rate of 1.34 Å per cycle at 400 °C was obtained, which is significantly higher than ∼0.55 Å per cycle using tris-DMAS at the same temperature. DFT calculations showed that a precursor fragment containing three Si atoms could be attached to the SiO2 substrate, which explains the higher growth rate of DTDN-2H2. The ALD temperature window was 350–400 °C with good step coverages. Stoichiometric SiO2 films were prepared with no carbon or nitrogen impurities detected by XPS. The genuine ALD film prepared at 400 °C showed a leakage current density of 26 nA cm−2 at 2 MV cm−1 and an oxide-trapped charge density of 4.7 × 1011 cm−2.