Abstract : Facing patterns designs below the 0.25µm node, IC manufacturers must replace the historical SiO2 insulator (k~4.4) with new lower dielectric constant materials (“low-K”), such as SiLK™ (purely organic material with k=2.65), to allow lower interconnection delay time. The main issue is that oxygen-based plasma etching of SiLK™ induce a part of isotropic etching component (“bow” or “bowing” effect), proscribed for further integration scheme. To limit this effect, we need to deposit a passivation layer on the features sidewalls during the etching process. We show that this is strongly correlated with both SiLK™ graphitization and presence of low-volatile carbon-based etching by-products in the plasma. Others carbon sources enhance sidewalls passivation. On the origin of bowed profiles, we identify that the charging effects are mainly responsible for ions deflection towards the features sidewalls. Those results can be extended to all low-Ks with low reactive ion etching energy thresholds.