The shunt flattens the magnetic field lines above the target face. Configuration Standard magnetron and target configuration. Effect of the magnetic field is maximized where field lines are most parallel to target surface. Enhanced Configuration Steel shim shunts normal path of field lines causing the field to become more uniform near target surface resulting in improved sputtering performance. The purpose of the magnetic field in any magnetron arrangement is to intensify and confine electrons above the face of the target causing a high gas ionization rate.
Material removal is most efficient where the magnetic field lines run parallel to the target face.
See the diagram above. The ideal magnetic configuration would have parallel lines across the entire target face. This intensifies and confines the plasma into a small, confined space leading to narrow erosion grooves, low target utilization, and a lower yield. Voltage must be increased over the target lifetime to maintain a consistent product. The plasma is not confined to a small erosion area and voltage is more stable over the target lifetime.