Direct writing by locally induced chemical vapor deposition has been applied to direct-write tailor-made microstructures of siliconoxide for modification and repair of microelectronic circuits. Focused ion beam (FIB) tools are used for locally confined deposition of dielectric material in the deep sub-µm range. State-of-the-art procedures typically provide insufficient dielectrics with high leakage currents and low breakdown voltage. The detailed investigation of the deposition mechanisms in this study proposes an approach to significantly improve dielectric material properties. Siloxane and oxygen as volatile precursors introduced in a vacuum chamber are used to deposit siliconoxide at ambient temperatures on various substrates such as Si, GaAs, or metals. The deposition process was initiated by a focused Ga+-beam. As elementary electronic test vehicles for a systematic electrical investigation ion beam induced depositions in of capacitor architectures are applied. The chemical composition of the layers is investigated by secondary ion mass spectroscopy (SIMS) and reveals effects of atomic mixing at the interfaces. The variation of process parameters such as ion energy and ion dose, scan time and delay time lead to a better understanding of the mechanisms. The composition of the precursor gas mixture is of significant influence on insulating properties. The results demonstrate that optimized FIB-induced deposition of dielectrics offers a new window for in-situ post-processing of integrated circuits