The growth dynamics of oxygen assisted focused electron beam induced deposition of Si-containing materials (from SiOxCy to SiO2) were investigated as a function of relevant process parameters. The results obtained from organosilanes of different families (alkoxy, alkyl, and isocyanatosilanes) are compared. Residual water molecules in the SEM chamber were found to be responsible for side reactions leading to carbon etching and oxygen incorporation in focused electron beam induced deposition (FEBID) materials and ruled the deposition process during conventional FEBID. Depending on the precursor reactivity to oxygen, the material growth rate either increased or decreased with increasing additional O-2 until it remained constant from 1 SCCM. Accounting for the FEBID material density, oxygen always increased the deposition efficiency in terms of Si atoms deposited per second. Less carbon residues in the deposits were obtained at large replenishment times (above 50 mu s) and low dwell times (below 15 mu s), which hint to relatively slow process steps in the complex deposition mechanism in our deposition equipment. O-2 assisted FEBID showed to be insensitive to electron density variations, and secondary electrons were demonstrated to have sufficient energy to initiate the oxidation reaction and achieve 90% of the deposition process. (c) 2007 American Vacuum Society.