ArF resist has very weak plasma resistivity, so linewidth roughness (LWR) and line-edge roughness (LER) generally occur under the conventional etching conditions using perfluorocarbon gases. The main cause of the roughness generation has been thought to be high energy ions. However, decreasing the pressure to 0.4 Pa, the roughness was suppressed considerably. So, the origin of the roughness is not depend solely on ion energy, but on the amount of fluorine atoms. Therefore, iodoperfluorocarbon gas was used to decrease the flux density of fluorine atoms. Iodine atoms react with fluorine atoms and interhalogen compounds are formed. The resultant etched surface was very smooth without LWR and LER, even at 1.3 Pa. (C) 2008 American Vacuum Society.