a split magnet ring , particularly useful in a magnetron plasma reactor sputter depositing tantalum or tungsten or other barrier metal into a via and also resputter etching the deposited material from the bottom of the via onto the via sidewalls . the magnet ring includes two annular magnet rings composed of the same axial polarity separated by a non - magnetic spacing of at least the axial length of one magnet and associated poles . a small unbalanced magnetrons rotates about the back of the target having an outer pole of the same polarity as the ring magnets surrounding a weaker inner pole of the opposite pole .