A wafer stage for holding a wafer in a chamber of a plasma processing system, the wafer stage includes an electrode on which a wafer is placed, to which electrical current is supplied, a diameter of the electrode is larger than a diameter of said wafer, a plurality of magnets separately arranged on an outermost region of said electrode and said magnets are arranged such that alternate magnetic poles face towards the inside of the chamber, and an outer-ring placed around said wafer, the outer ring having a magnetic metal ring at a lower side.