Tris(dimethylsilyl)amine (TDMSA) is used in the presence of O2 and NH3 for the atmospheric pressure chemical vapor deposition (CVD) of conformal, corrosion barrier silicon oxynitride (SiOxNy) films at moderate temperature. Plausible decomposition pathways taking place during the process, as well as resulting gas-phase by-products, are investigated by an innovative methodology, coupling solid-state films characteristics with gas phase analysis. Liquid NMR, gas chromatography coupled with mass spectrometry (GC-MS) and electron spin resonance (ESR) allow probing stable compounds and radical intermediate species in the gas phase. At least fifteen by-products are identified, including silanols, siloxanes, disilazanes, silanamines, and mixed siloxane-silanamine molecules, in addition to more usual compounds such as water. The radical dimethylsilane, Me2HSi˙, is noted across all experiments, hinting at the decomposition of the TDMSA precursor. Deposition of SiOxNy films occurs even in the absence of NH3, demonstrating the judicious choice of the silanamine TDMSA as a dual source of nitrogen and silicon. Additionally, the presence of Si-H bonds in the precursor structure allows formation of SiOxNy films at temperatures lower than those required by other conventional silazane/silanamine precursors. Addition of NH3 in the inlet gas supply results in lower carbon impurities in the films. The identified by-products and formulated decomposition and gas-phase reactions provide stimulating insight and understanding of the deposition mechanism of SiOxNy films by CVD, offering possibilities for the investigation of representative chemical models and process simulation.