Ion implantation with charge neutralization

A plasma generator for generating plasma to neutralize an ion beam and a work piece surface, the plasma generator comprising

• a plasma generator chamber defined by walls,
• a relatively narrow outlet aperture for plasma produced in the chamber to leave the chamber to neutralize the beam and work piece surface,
• at least one cathode,
• at least one anode spaced from the cathode and from the walls of the chamber,
• magnets arranged within the walls to generate a magnetic field that deflects primary electrons emitted from the cathode from directly reaching the anode, and
• a conductive shield, positioned within the chamber between the anode and the magnets, the shield having an electric potential selected to deflect electrons, the magnetic field and the conductive shield effective during operation to cause electrons from the cathode to trace extended paths to ionize gas within the chamber to generate plasma before reaching the anode.

An ion implanter for implanting ions in a workpiece using a magnetically scanned ion beam, comprising

• apparatus for generating an ion beam and directing it toward a surface of a work piece,
• a plurality of magnets to focus and scan the ion beam in a first direction,
• a workpiece holder to hold the workpiece and to move the workpiece in a second direction substantially perpendicular to the first direction,
• a plasma generator for generating plasma to neutralize the ion beam and the work piece surface, the plasma generator comprising
• a chamber defined by walls,
• a relatively narrow outlet aperture for plasma produced in the chamber to leave the chamber to neutralize the beam and work piece surface,
• at least one cathode,
• at least one anode spaced from the cathode and from the walls of the chamber,
• magnets arranged within the plasma generator chamber, adjacent to the chamber walls to generate a magnetic field to deflect primary electrons emitted from the cathode from directly reaching the anode, and
• a conductive shield, positioned within the chamber between the anode and the magnets, the shield having an electric potential selected to deflect electrons, the magnetic field and the conductive shield effective during operation to cause electrons from the cathode to trace extended paths to ionize gas within the chamber to generate plasma before reaching the anode,
• a drift tube defined by walls through which the ion beam passes before reaching the workpiece, wherein the aperture opens into the tube, and
• a series of parallel, linear magnets positioned perpendicular to the general path of the ion beam, the magnets having a side facing the beam and an opposing side facing away from the beam, the two sides of the magnets having opposite polarity, the adjacent poles of adjacent magnets being of opposite polarity, the magnets sized and arranged in a pattern along the tube to create a magnetic field that prevents the plasma from reaching the walls of the drift tube and to enable any deflection of the ion beam produced by one magnet pole to be substantially neutralized by the successive magnet pole of the next adjacent downstream magnets.