Beam neutralization in low-energy high-current ribbon-beam implanters

Abstract

The fabrication of modern semiconducting integrated circuits often requires implantation steps that involve high currents of low-energy charged dopant atoms. When employing such beams, the addition of electrons or negative ions for neutralizing the effects of space charge is often crucial for achieving success. Without this supplement, ion beams can 'blow-up' causing loss of intensity and disruption of beam focusing. In the present disclosure, methods are presented for introducing and constraining neutralizing low-energy electrons and negative ions within the boundaries of ribbon beams within regions of magnetic field deflection. Apparatus is described for maintaining neutralization based upon a reduction of electron losses, plasma bridge connections and secondary electron production. As part of plasma introduction to the deflection region a novel cryogenic pumping apparatus selectively removes neutral atoms from a plasma stream.