Abstract: A hollow cathode magnetron for sputtering target material from the inner surface of a target onto an off-spaced substrate. The magnetron is in the shape of a truncated cone, also known as a conical frustum. The target cone is backed by a conical cathode maintained at a predetermined voltage for attracting gas ions into the inner surface of the target cone to sputter material therefrom. The inner surface of the cone is bounded at its inner and outer edges by magnetic pole pieces orthogonal to and extending inwardly and outwardly of the cone surface. The magnetic path is completed by a conical magnet surrounding the target and conical electrode and magnetically connected to the pole pieces Lo form a magnetic cage. Lines of magnetic flux extending above the target surface between the pole pieces are substantially parallel the target surface, providing uniform erosion over the entire surface.