A pair of magnets for producing a mirror magnetic field are disposed outside of an electrode structure carrying a target. Microwaves from a microwave source are introduced toward and into a space defined by the mirror magnetic field for generating high-density plasma. While maintaining this high-density plasma over a wide area of the surface of the target, an electric field substantially perpendicular to the surface of the target is applied for sputtering of the target material. The optimized conditions for plasma generation can be selected when the high-density plasma formed outside of a processing chamber is guided to migrate toward an area above the target in the processing chamber. Capability of sputtering of the material from the entire surface of the target increases the rate of film deposition on a substrate and improves the target utilization rate (the quantity of the material deposited on the substrate/the usable area of the target).