Uniform magnetically enhanced reactive ion etching using nested electromagnetic coils

A magnetic field-enhanced plasma reactor is disclosed, comprising a reaction chamber for applying a plasma to a substrate, a plurality of primary electromagnets disposed about said reaction chamber, and a plurality of secondary electromagnets. At least two of the primary electromagnets are adjacent to each other, and each of these primary electromagnets has at least one secondary electromagnet disposed within a region defined by a right rectangular prism having the largest perimeter that fits within the outer perimeter of the primary magnet. Typically, at least one of the secondary electromagnets in one of the at least two adjacent primary electromagnets is itself adjacent to a secondary electromagnet disposed in the other of the at least two adjacent primary electromagnets. This arrangement is found to eliminate non-uniformities observed at regions of the substrate which are disposed closest to the vertices formed by the adjacent primary electromagnets.