The thickness of copper films prepared by the rf‐sputtering technique has been studied by changing the argon gas pressure and the distance between the target and the substrate. Glass disks with 110‐mm diameters were used as substrates. The relative thickness of a film was tested by using a laser beam. The distribution of copper was observed to be centralized as the argon gas pressure was lowered or the distance between the target and the substrate shortened. By using a proper arrangement, the film obtained was smooth enough for optical purposes.