A method of making a contact plug and a metallization line structure is disclosed in which a substrate is provided with at least one contact hole within an insulation layer situated on a semiconductor substrate of a semiconductor wafer. The cam groove includes a finite number of focal-length steps, so as to perform a focusing operation between infinite and closest photographing positions at each focal-length step. In a QAM modulation system, input signal strings, where p is an integer not less than 3, are converted into three string signals, which are then allocated to three phase planes, time-division multiplexed and multi-level modulated to realize QAM modulation in which the n-ary number may be set to approximately 2.