Methods and apparatus for improved metal ion filtering are provided herein. In some embodiments, a substrate processing apparatus includes: a chamber body and a chamber lid disposed on the chamber body defining a processing region within the chamber body beneath the lid; a collimator disposed in the processing region; a power source coupled to the collimator; and a first set of magnets disposed around the chamber body above the collimator and a second set of magnets disposed around the chamber body and below the collimator that together create a guidance magnetic field that is substantially orthogonal to the collimator.