The etch rates of BCB film in a reactive ion etcher(RIE) were measured using Ar, O2, O2+CF4, and O2+SF6 gas mixtures. Faster etch rates were obtained when CF4 and SF6 were added to oxygen, since the presence of atomic fluorine enhances the etch rate of organics, while also etching Si and SiO2 formed by exposure to oxygen gas. Surface compositional changes on the BCB film were observed by XPS after plasma modification. Pure O2 and O2+CF4 plasma oxidized the carbo-siloxane linkage (C-Si-O) of the BCB, resulting in the formation of SiO2 on the surface. The O2 +SF6 plasma, however, did not produce the surface SiO2, because of its faster Si and SiO2 etch rates. Ar ion sputtering following the plasma modification, restored the surface chemical composition to a state similar to the initial BCB surface.