Magnet for generating a magnetic field in an ion source

摘要

An ion source (10) for an ion implanter is provided, comprising (i) an ionization chamber (14) defined at least partially by chamber walls (12) and having an aperture (18) through which an ion beam (B) may be extracted along a path (P2); and (ii) a magnet assembly (45) entirely surrounding the ionization chamber (14), comprising a closed figure yoke (46) about which is wound a pair of coils (49, 51). The yoke (46) is preferably toroidal in shape and further comprises a pair of opposing poles (48a, 48b), wherein a substantial portion of magnetic flux (F) generated by the coils leaves a first of the opposing poles (48a), passes through the ionization chamber (14), and enters a second of the opposing poles (48b) during operation of the ion source. A non-magnetic shield (52) surrounds the magnet assembly (45) to shield the assembly from backstreaming electrons. Stray magnetic fields generated by the magnet assembly (45) are oriented in a direction perpendicular to and kept low within the path of an ion beam extracted from the aperture. The primary magnetic field output by the magnetic assembly (45) is relatively homogeneous within the ionization chamber (14). <IMAGE>