Ion implantation apparatus includes an ion beam generator for generating an ion beam, a scanner for scanning the ion beam across a workpiece in a first direction, a mechanical translator for translating the workpiece in a second direction so that the ion beam is distributed over the workpiece, and a controller for controlling the translation velocity and beam scan width to limit the time that the ion beam is off the workpiece. In the case of a semiconductor wafer, the translation velocity in the beam scan width are controlled to produce an approximately circular scan pattern. |