[Granted] A method for treating a workpiece. The method includes directing a first ion beam to a first region of a workpiece, wherein the first ion beam has a first ion angular profile of first ions extracted through an aperture of an extraction plate. The method also includes directing a second ion beam to the first region of the workpiece, wherein the second ion beam has a second ion angular profile different than the first ion profile of second ions extracted through the aperture of the extraction plate.