Abstract: An apparatus for processing a workpiece by delivering ions to the workpiece, which apparatus includes a processing chamber, a workpiece support having a workpiece support surface in the chamber, a sputtering target in the chamber and a coil for creating an inductively coupled plasma to sputter material from the target, ionize the sputtered material and direct the ionized, sputtered material at the workpiece. The coil is connected to receive an RF current for establishing in the coil an RF voltage having a peak-to-peak amplitude which varies between a minimum value at a first location along the circumference and a maximum value at a second location along the circumference, the first and second locations being substantially diametrically opposite one another, the RF voltage variation producing a corresponding variation in plasma density around the central axis.