Magnetron sputter gun target assembly with distributed magnetic field

A target assembly for use in a magnetron sputtering apparatus having a source of a magnetic field, the target assembly comprising:

• an annular sputtering target disposed around a central axis and having a generally planar sputtering surface extending transverse of the central axis, an inner surface proximal to the central axis, an outer surface distal from the central axis, the sputtering surface extending between the inner and outer surfaces, and a base surface opposite from the sputtering surface, the target further including an inner ring and an outer ring, both formed of substantially the same material as the target and extending from the sputtering surface, the inner ring being positioned adjacent the inner surface and the outer ring being positioned adjacent the outer surface;
• a ferromagnetic outer pole member surrounding the target against the outer surface and extending along the outer ring beyond the sputtering surface;
• a ferromagnetic inner pole member surrounded by the target against the inner surface and extending along the inner ring beyond the sputtering surface;
• and
• a ferromagnetic backing member positioned against the base surface and having an outer portion positioned against the outer pole member, and an inner portion positioned against the inner pole member, the inner and outer portions being positioned relative to the source of the magnetic field for conducting flux in a first path through the outer portion and the outer pole member, across the sputtering surface between the outer and inner rings, and through the inner pole member and inner portion, the backing member further including a shunt portion positioned between and magnetically spaced from the inner and outer portions and extending from the target toward the source of the magnetic field associated with the inner portion for conducting magnetic flux in a second path through a portion of the target intermediate the inner and outer surfaces, and across the sputtering surface toward the outer ring.