Abstract: A substrate wafer processing method and apparatus is disclosed utilizing a bowl having a central axis, a baffle surface positioned above the inside bottom surface of the bowl and a chuck member having a top surface for supporting and spinning substrate and positionable coaxially within the bowl closely spaced from the baffle surface. Means and methods are described for directing a gas stream radially outwardly between the bottom surface of the chuck member and the baffle. The specific surface construction of the baffle is disclosed as part of a plenum member as well as a deflecting surface that projects to a level above the top surface of the substrate.