Techniques disclosed herein include an apparatus for treating substrates with plasma generated within a plasma processing chamber. In one embodiment, dielectric plates, of a plasma system can include structural features configured to assist in generating a uniform plasma. Such structural features define a surface shape, on a surface that faces the plasma. Such structural features can include a set of concentric rings having an approximately non-linear cross section, and protrude into the surface of the dielectric plate. Such structural features may include feature depth, width, and periodic patterns that may vary depth and width along the concentric rings.