A microwave electron cyclotron resonance ion source has been developed and studied for use in a reactive ion‐beam system. The system has been tested and fully characterized for thin film etching. The CF4reactive ion beam etching of W and Mo, have been investigated as a microfabrication technique for integrated semiconductor devices of submicron geometry. The etching rate has been characterized as a function of ion energy, ion‐beam current density, and angle of beam incidence. It has been found that the etching rate increase linearly with current density and pressure. The rate also increases with ion energy, but the rate of increase drops as the ion energy increases. The maximum etching occurs at a beam angle of 35°.