An apparatus may include a main chamber, a substrate holder, disposed in a lower region of the main chamber, and defining a substrate region, as well as an RF applicator, disposed adjacent an upper region of the main chamber, to generate an upper plasma within the upper region. The apparatus may further include a central chamber structure, disposed in a central portion of the main chamber, where the central chamber structure is disposed to shield at least a portion of the substrate position from the upper plasma. The apparatus may include a bias source, electrically coupled between the central chamber structure and the substrate holder, to generate a glow discharge plasma in the central portion of the main chamber, wherein the substrate region faces the glow discharge region.