Device and process for liquid treatment of a wafer shaped article

A spin chuck in an apparatus for single wafer wet processing has structures at its periphery that, in combination with a supported wafer, form a series of annular nozzles that direct flowing gas from a chuck-facing surface of the wafer, around the edge of the wafer, and exhaust the gas away from the non-chuck-facing surface of the wafer, thereby preventing treatment fluid applied to the non-chuck-facing surface from contacting the edge region of the wafer. Retaining pins with enlarged heads engage the wafer edge and prevent it from being displaced upwardly when a high flow rate of gas is utilized.