Scan methods and apparatus for ion implantation

An ion implanter is provided having an ion beam generator for generating an ion beam, a platen for holding a workpiece, such as a semiconductor wafer, and a tilt mechanism for tilting the platen and the wafer with respect to the ion beam. A scan controller mechanically moves the wafer and the platen relative to the ion beam so that the motion of the wafer and the platen is tangential, i.e. parallel, to the wafer surface. As a result, the ion beam intersects the wafer surface at a fixed position along the beamline as the wafer is scanned. The size and shape of the ion beam are thereby constant over all areas of the wafer surface during the implant for increasing implant uniformity.