A substrate processing system includes a pedestal including a substrate supporting surface having a diameter that is greater than a diameter of a substrate to be processed by the substrate processing system. A first surface extends a first distance above the substrate supporting surface in a direction substantially perpendicular to the substrate supporting surface. The first distance is greater than or equal to one-half of a thickness of the substrate. A gap is defined between the first surface and an outer diameter of the substrate. A second surface extends a second distance from the first surface at an angle with respect to the first surface. The angle is greater than zero and less than ninety degrees. A third surface extends from the second surface and is substantially parallel to the substrate supporting surface. An etchant source directs etchant onto the substrate to etch the substrate.