a resolving magnet having first polepieces separated by a first gap through which the ribbon ion beam passes. The second magnet assembly preferably comprises an angle corrector magnet having second polepieces separated by a second gap through which ions of the selected ion species in the ribbon ion beam pass. In a preferred embodiment, the first magnetic fields produced by the first magnet assembly are substantially horizontal and the second magnetic fields produced by the second magnet assembly are substantially vertical. The first magnet assembly preferably deflects ions of the selected ion species in the ribbon ion beam by an angle in a range of about 20xc2x0 to 90xc2x0 and more preferably by an angle of about 60xc2x0. The second magnet assembly preferably deflects ions of the selectedion species in the ribbon ion beam by an angle in a range of about 20xc2x0 to 90xc2x0 and more preferably by an angle of about 70xc2x0.
In one embodiment, the structure defining the resolving aperture comprises a mask positioned between the first and second magnet assemblies. In another embodiment, the structure defining the resolving aperture comprises the second polepieces of the second magnet assembly, and an entrance to the second gap constitutes the resolving aperture.
According to another aspect of the invention, a method is provided for producing an ion beam. The method comprises the steps of generating a ribbon ion beam in an ion source having an elongated extraction aperture, deflecting the ribbon ion beam perpendicular to the long dimension of the ribbon ion beam cross section, wherein