We have developed a model to predict the process-window length in SiOCH etching using fluorocarbon plasmas (C4F8/Ar/O-2 and C4F8/Ar/N-2). The amount of incident reactive particles such as CF2, O, and N radicals were estimated by calculating the partial pressure and dissociation degree of each parent molecule. We have evaluated the relationship between the incident flux and film properties and found that regardless of the film composition and density, the optimum etching condition (P-c) was determined based on the balance between the total C flux and the C removal ability by O and N. Lower concentration of O in SiOCH resulted in a narrow process window because a thick polymer layer formed on the etched surface even under lower CFx flux conditions. In the etching of porous SiOCH film, lower film density increased the etch rate. Because of the narrow process window in the SiOCH etching, the slight change in the incident flux (caused by the aspect ratio or nonuniformity and/or instability of the plasma reactor) induced a great change in the etching properties. In order to fabricate reliable interconnects for next-generation devices, a quantitatively controlled, uniform, and stable plasma system is needed. (c) 2005 American Vacuum Society.