Embodiments of a plasma apparatus are provided. The plasma apparatus includes a processing chamber and a wafer chuck disposed in the processing chamber. The plasma apparatus also includes a target element located over the wafer chuck and an electromagnet array located over the target element and having a number of electromagnets. Some of the electromagnets in a magnetic-field zone of the electromagnet array are enabled to generate a magnetic field adjacent to the target element. The magnetic-field zone is moved during a semiconductor manufacturing process.