The chlorine plasma/copper reaction that is the base of a new copper (Cu) dry etching process was studied. The reaction product is a rough and porous Cu chloride compound film. Influences of process parameters such as plasma exposure time, pressure, plasma power, and substrate temperature, on the copper chlorination process, were explored. In addition to variations of morphology and reaction rate, we also investigated the relationship between the structure of the reaction product and the process condition. The result shows that both the plasma phase chemistry and the ion bombardment energy are critical to the reaction mechanism and the reaction product's morphology. A simple model that describes the progress of the reaction through the Cu layer has been developed based on above results. This study result indicates that it is possible to etch Cu with a plasma process at room temperature.