This study examined the effects of different frequency combinations, 27.12/2 MHz and 60/2 MHz, and the gas flow ratio of dual-frequency capacitively coupled CH2F2/C4F8/O-2/Ar plasmas on the etch characteristics of silicon oxide. The etch rate of the SiO2 layer decreased and the etch selectivity increased with increasing flow ratio, Q(CH2F2), of CH2F2/(CH2F2 + C4F8). The etch rates of SiO2 and the chemical-vapor deposited amorphous carbon layer decreased with increasing Q(CH2F2) but the etch selectivity of SiO2 over the ACL increased. The etch rate of SiO2 at 60/2 MHz was faster than that at 27.12/2 MHz. In addition, the line edge roughness and critical dimension values tended to increase with increasing Q(CH2F2). (C) 2012 Elsevier B. V. All rights reserved.