Spin-on films deposited from solutions of tetraethylorthosilicate (Si(OC2H5)(4)), ethanol and/or butanol, water and nitric acid and annealed at temperatures ranging from 298 to 1173 K were analyzed by means of secondary ion mass spectrometry (SIMS), scanning electron microscopy, and infrared-absorption spectroscopy. The SIMS analyses show a non-uniform step-like distribution of carbon in as-deposited and annealed films except for the heating at 873 K. Annealing at 873 K leads to a relative uniform depletion of carbon over the whole thickness of the spin-on films. This carbon distribution may be the result of a competition between the elimination of organic groups and the sintering of the film porosity. The influence of striation in the spin-on films on the SIMS intensity at the interlayer is discussed in terms of interface widths and reduced adhesion of the films.