Primarily due to the inability to form volatile etch products for copper (Cu) plasma etching at temperatures < 200 degrees C, no effective subtractive etch process for Cu has been reported. We have developed a low temperature (< 20 degrees C), reactive plasma etch process for Cu films in an attempt to mitigate the size effect in electrical resistivity, a critical limitation to future integrated circuit device generations. As previously proposed by a thermochemical analysis of the Cu-Cl-H system, the plasma etch process is executed in two steps. In the first step, Cu films are exposed to a Cl-2 plasma to preferentially form CuCl2, which is believed to be volatilized as Cu3Cl3 by exposure to a H-2 plasma in the second step. Cu films (100 nm thick) with SiO2 as a mask have been patterned by this two-step etching process in an inductively coupled plasma system. Experimental parameters such as power applied to the substrate electrode, gas flow rate, and plasma treatment time have been investigated to assess their effect on pattern quality. The addition of argon to the H-2 plasma improved Cu pattern fidelity and gave reasonable etch rates. Possible etch mechanisms for this low temperature process are discussed.