Abstract: A plasma chamber includes a pedestal, an upper electrode, and an annular structure. The pedestal has a central region to support a wafer and a step region that circumscribes the central region. A sloped region circumscribes the step region, with the sloped region having a top surface that slopes downward from the step region such that a vertical distance between the inner boundary of the top surface and the central region is less than a vertical distance between the outer boundary of the top surface and the central region. The upper electrode is coupled to a radio frequency power supply. An inner perimeter of the annular structure is defined to circumscribe the central region of the pedestal when the annular structure is disposed over the pedestal, and a portion of the annular structure has a thickness that increases with a radius of the annular structure.