The present invention relates to a method and apparatus for varying the cross-sectional shape (308a, 308b, 308c) of an ion beam, as the ion beam is scanned over the surface of a workpiece (304), to generate a time-averaged ion beam having an improved ion beam current profile uniformity. In one embodiment, the cross-sectional shape of an ion beam is varied as the ion beam moves across the surface of the workpiece. The different cross-sectional shapes of the ion beam respectively have different beam profiles (e.g., having peaks at different locations along the beam profile), so that rapidly changing the cross-sectional shape of the ion beam results in a smoothing of the beam current profile (e.g., reduction of peaks associated with individual beam profiles) that the workpiece is exposed to. The resulting smoothed beam current profile provides for improved uniformity of the beam current and improved workpiece dose uniformity.