The reactive etching of copper in BCl3 and SiCl4 based plasmas has been investigated and empirically modeled using statistically designed experimentation. Gas mixtures with N2 exhibit considerably higher etch rates than mixtures with Ar. In the temperature range of 225 to 275-degrees-C, the copper etch rate in BCl3/N2 can be as much as an order of magnitude larger than in BCl3/Ar. Plasma diagnostics [optical emission spectroscopy (OES) and Langmuir probe measurements] were used to study the effect of the diluent gas on the discharge characteristics and the resulting etch process. OES indicates that N2 does not act merely as a diluent but rather increases the concentration of Cl atoms. Langmuir probe data show very little difference in the ion densities between the various gas mixtures. These results suggest, in combination with the empirical model, that the etch rate is limited by the amount of available reactant rather than by product desorption in the temperature range investigated. High-resolution patterning is demonstrated, but the effectiveness of die etch is dependent on the processing conditions, especially on temperature and pressure.