"When a wafer, in particular, is processed as a workpiece, contaminants, such as particles and metals or organic impurities, adhered to an unusable peripheral area of the surface of the wafer when the wafer is chucked for carrying may flow together with the condensate of the dry vapor from the unusable peripheral area to an usable inner area, in which devices are formed, of the surface of the wafer" . . . . .