Disclosed is a technique for embedding metal in a recess provided in the surface of a process object, such as a semiconductor wafer W, only by plasma sputtering. The metal is copper as a typical example. The recess has a microscopic hole or trench having a diameter or width of 100 nm or less as a typical example. A film forming step and a diffusion step are alternately performed a plurality of times. The film forming step deposits a small amount of a metal film in the recess. The diffusion step moves the deposited metal film toward the bottom portion of the recess. In the film forming step, bias power to be applied to a stage for supporting the wafer W is set to a value ensuring that, on the surface of the wafer W, the rate of metal deposition due to the drawing-in of metal particles is substantially equal to the rate of the sputter etching by plasma. In the diffusion step, the wafer W is maintained at a temperature which permits occurrence of surface diffusion of the metal film deposited in the recess.