Hydrido-organo-siloxane-polymer (HOSP), a typical silsesquioxane-based low dielectric constant material, was etched with ions of different incident angles in CHF3 plasma. The etch rate normalized to the rate obtained with ions incident perpendicular to the surface deviated from the general cosine dependence on the ion incident angle. That is, the rate deviated to over-cosine values at low ion angles below 70°, due to the physical sputtering of the surface by energetic ions, and to under-cosine values at high angles, above 70°, due to the redeposition of particles emitted from the bottom. The roughness of the etched surface also varied with the ion incident angle as a result of the surface etching by energetic ions and the redeposition of particles emitted from the bottom. For example, when the bias voltage was –100V, the surface roughness was different according to three angle regions: i) ion bombardment dominant region below 70°, ii) intermediate region between 70° and 85o, and iii) redeposition dominant region above 85°. The surface composition and chemical structure after etching were also affected by the ion incident angle. The F/C atomic in the surface layer was much lower at ion angles higher than 70° than below 70° because cage-like Si-O bonds were more rapidly dissociated by F atoms from fluorocarbon polymer layer than network Si-O bonds at high angles. This information obtained in this study is useful for predicting the profile and surface characteristics of interconnection patterns in microelectronics fabrication.