Abstract : In this thesis, the deposition of silica films from silane and oxygen in a high-density plasma system is investigated. The influence of the process parameters and silane injection system design on the material properties is studied using spectroscopic ellipsometry (SE), Fourier transform infrared spectroscopy (FTIR), transmission spectroscopy and atomic force microscopy (AFM). The gas phase is analyzed using optical emission spectroscopy (OES) and differentially pumped quadrupole mass spectrometry (QMS). The creation of H2O in the system and its incorporation into the film during deposition is studied using capillary jet injection of the silane precursor and measuring the Si-OH absorption in the deposited film at various points on the substrate. Gas flow simulations, using the Direct Simulation Monte Carlo (DSMC) technique, are used to model the fluxes of the species ont! o the substrate plane. The simulation shows that the flux of H2O onto the substrate holder is uniform while the silane flux varies along the substrate holder, which explains the experimentally observed lower level of silanol in the deposited film in the regions that have a high deposition rate. A comparison between the experimental and simulation results leads to the conclusion that high-density plasma deposition systems can only be considered as well mixed when no rapid removal of the gas phase species, such as SiH4, is present.