We have characterized the step coverage and film quality of (tetraethoxysilane) TEOS-based silicon oxides which are directionally deposited on horizontal surfaces of trench features under oxygen-lean conditions in a high frequency (14 MHz) discharge. The film thickness on the sidewalls depends most strongly on the O2 :TEOS feed ratio. Water uptake after ambient exposure was used as a measure of film quality and the amount of water absorbed in the film correlated well with changes in the refractive index and stress. Oxide quality on horizontal surfaces could be improved by decreasing the TEOS feed or increasing the discharge power, but the sidewall oxide quality could not be improved by these methods. Small NF3 additions to the discharge markedly improved sidewall quality, altered the angle between the sidewall and the bottom of trench features from 90° to ˜115° (tapered profile) and increased the deposition rate, while preserving the directionality of deposition.