CD bias and LER are the most critical factors to enable sub-90nm technology contact hole formation in terms of good Rs and barrier deposition. As pattern density increases, ARC (Anti-Reflective-Coating) layer is essential together with 193nm resist to print good contact holes. It, however, drives plasma contact etch much more challenging than before because ARC material is similar to PR(Photo Resist) and during the ARC plasma etch PR degradation is inevitable. In addition, oxide etch chemistry is evolving to create more carbon rich polymers for 193nm resist selectivity and is getting O2 gas dependant to control the amount of the polymer, which caused LER worse. In this study, impact of plasma polymerization during the plasma oxide etching on CD bias/LER was evaluated. Polymerization can be dominated by etching gas combination. Adding Freon 134(C2H2F4) into conventional ARCE chemistry such as CF4/CHF3 and oxide etch(C4F6/O2) enables to modulate CD bias/LER. Local non-uniformity of oxygen atoms in the contact hole is the root cause of LER. Etching sequence, adding dry CLN step at the end of oxide etch step is also play an important role on CD bias/LER as well. Furthermore, Impact of process parameters such as CF4/CHF3 ratio and etching time will be discussed.