An edge ring assembly surrounds a substrate support surface in a plasma etching chamber. The edge ring assembly comprises an edge ring and a dielectric spacer ring. The dielectric spacer ring, which surrounds the substrate support surface and which is surrounded by the edge ring in the radial direction, is configured to insulate the edge ring from the baseplate. Incorporation of the edge ring assembly around the substrate support surface can decrease the buildup of polymer at the underside and along the edge of a substrate and increase plasma etching uniformity of the substrate.