This invention provides a process for treating a workpiece having a front side, a back side, and an outer perimeter. In accordance with the process, a processing fluid is selectively applied or excluded from an outer peripheral margin of at least one of the front or back sides or the workpiece. Exclusion and/or application of the processing fluid occurs by applying one or more processing fluids to the workpiece as the workpiece and corresponding reactor are spinning about an axis of rotation that is generally orthogonal to the center of the face of the workpiece being processed. The flow rate of the one or more processing fluids, fluid pressure, and/or spin rate are used to control the extent to which the processing fluid is selectively applied or excluded from the outer peripheral margin.