Apparatus for CVD processing wherein a wafer (28) mounted in a chamber (24) of a reactor (20) on a vertically movable susceptor (26) beneath a showerhead (30). The susceptor extends beyond the outer perimeter of the wafer such that, when the susceptor is raised into contact with a shield ring (40) which normally rests on a ring support (42) in the chamber, the shield ring engages outer portion of the susceptor beyond the perimeter of the wafer, lifting the shield ring off its support. The shield ring (40) shields the edge of the top surface of the susceptor during the deposition, whereby unwanted deposition on the susceptor is prevented while, at the same time, allowing for deposition over the entire upper surface of the wafer. To center the shield ring and the susceptor with respect to each other, the shield ring may include a plurality of centering protrusions (60), at least some of which engage the susceptor as it moves upwards to lift the shield ring off its supports in the chamber.