Apparatus and method for spin processing

Equipment for coating a wafer is disclosed, where the equipment includes a wafer holder configured to spin the wafer while holding the wafer; a rotary drive configured to spin the wafer holder; a nozzle configured to pour liquid onto a surface to be coated of the wafer; an annular duct disposed circumferentially around the wafer when the wafer is spun by the wafer holder, the duct configured to collect material ejected off an edge of the wafer; and an air knife disposed proximate a backside, the backside being opposite the side to be coated, where the air knife is configured to blow an air curtain through a slot onto an exposed edge region of the backside at a grazing angle of incidence to flow gas radially outward along the backside toward the annular duct.