An ion implantation system having a grid assembly. The system includes a plasma source configured to provide plasma in a plasma region; a first grid plate having a plurality of apertures configured to allow ions from the plasma region to pass therethrough, wherein the first grid plate is configured to be biased by a power supply; a second grid plate having a plurality of apertures configured to allow the ions to pass therethrough subsequent to the ions passing through the first grid plate, wherein the second grid plate is configured to be biased by a power supply; and a substrate holder configured to support a substrate in a position where the substrate is implanted with the ions subsequent to the ions passing through the second grid plate.