Abstract: A method for processing a semiconductor wafer or similar article includes the step of spinning the wafer and applying a fluid to a first side of the wafer, while it is spinning. The fluid flows radially outwardly in all directions, over the first side of the wafer, via centrifugal force. As the fluid flows off of the circumferential edge of the wafer, it is contained in an annular reservoir, so that the fluid also flows onto an outer annular area of the second side of the wafer. An opening allows fluid to flow out of the reservoir. The opening defines the location of a parting line beyond which the fluid will not travel on the second side of the wafer. An apparatus for processing a semiconductor wafer or similar article includes a reactor having a processing chamber formed by upper and lower rotors. The wafer is supported between the rotors. The rotors are rotated by a spin motor. A processing fluid is introduced onto the top or bottom surface of the wafer, or onto both surfaces, at a central location.