The feasibility of patterning a cured polymeric film of benzocyclobutene (BCB) using silicon nitride (SiNx) as an etch mask was investigated. Due to the carbon- and silicon-containing composition of BCB, a gas mixture with oxygen- and fluorine-containing components is required, which unfortunately also etches SiNx. Therefore, a reactive ion etching process with high selectivity between the etch rates of the BCB, CYCLOTENE(TM) 3022-46, and the SiNx was developed. We have investigated the dependence of the etch rates as a function of the CF4 content in the O-2/CF4, gas mixture. The surface morphology and the angle of the etched BCB sidewall were determined using a scanning electron microscope. A process with 37.5% CF4 content was defined, exhibiting etch rates of 155 and 14 nm/min for the polymerized BCB and the SiNx, respectively. This yields a selectivity of 11:1. The morphology of the etched BCB surface is smooth. Depending on the shape of the SiNx etch mask, sidewall angles of the BCB structure between 70 degrees and 80 degrees were obtained. These inclinations allow an effective deposition of a contact metallization. For further technological processing, a residual dielectric SiNx film can be left on the structure when the BCB layer is etched.