Forcing electrons to spiral near the target surface by placing magnets below the target has many benefits. First, the electron's path length in the 'magnetron' is increased, raising its ionization probability. Second, electrons trapped by space-charge effects and magnetic fields are less likely to escape and bombard the substrate. The resulting films are denser, with greater adhesion to the substrate. This design increases the density of the plasma and flattens it near the target surface, resulting in higher power dissipation for a given target size, greater sputtered area for the same power input, higher deposition rates, greater target utilization and further- improved film uniformity and adhesion.
Torus sources operate with DC or RF power without modification.
Torus targets are disc shaped and held to their water-cooled backing plate by a rim clamp. Powering a sputter source with a DC supply gives higher sputter and deposition rates and allows reactive sputtering. However, it can be used only with electrically conducting or semiconducting targets. RF will sputter any material, including insulators. Basically, a pulsed excimer laser capable of causing evaporation is directed through a viewport at a target mounted in a vacuum chamber.