A method of forming a semiconductor device that includes heating a wafer on which an Al—Cu sputtering thin film is formed before patterning the Al—Cu sputtering thin film. The heating is performed at a temperature no less than a solid solution temperature of copper or at a temperature between 300° C. and 600° C. The process temperature in heating the process wafer is not higher than the flow temperature of aluminum or is the temperature at which a reflow process can be performed.