The effect of the copper film's microstructure on the Cl-2 plasma-based copper etch process has been studied. Copper films were sputter deposited and annealed at different temperatures. The film's grain size increased and the resistivity decreased with the annealing temperature. Under the same plasma exposure condition, the copper conversion rate and the CuClx reaction product formation rate increased monotonically with the grain size. At the same time, the Cl content and the porosity of CuClx increased with the grain size. The roughness of the etched Cu surface also increased with the original copper grain size. These observations were explained by diffusion mechanisms of Cl and Cu atoms in the plasma-copper reaction process as well as microstructures of CuClx and the original copper film. (c) 2008 The Electrochemical Society.