Flexible adjustable return path magnet assembly and methods

A sputter deposition assembly comprising a sputtering chamber, a sputtering target, and a magnet assembly, the magnet assembly being mounted adjacent to a rear surface of the sputtering target, the magnet assembly comprising a magnetic backing plate and spaced-apart first and second permanent magnets, the first and second permanent magnets each having a proximal end and a distal end, the distal end being further from the sputtering target than is the proximal end, the magnet assembly creating a magnetic field comprising field lines that extend from the proximal end of the first permanent magnet, through the sputtering target, along an arc located in front of the sputtering target, back through the sputtering target, into the proximal end of the second permanent magnet, through the second permanent magnet, along a return path, and to the distal end of the first permanent magnet, the return path passing through the magnetic backing plate of the magnet assembly, the magnetic backing plate defining a gap, the magnet assembly further comprising an elongated flexible magnetic control body mounted so as to project into the gap, the elongated flexible magnetic control body having a length and being differentially bendable along the length so as to project further into the gap at one position along the length than at another position along the length.