Methods and apparatus for processing a substrate are provided. In some embodiments, a method of processing a substrate having a first layer may include disposing a substrate atop a substrate support in a lower processing volume of a process chamber beneath an ion shield having a bias power applied thereto, the ion shield comprising a substantially flat member supported parallel to the substrate support, and a plurality of apertures formed through the flat member, wherein the ratio of the aperture diameter to the thickness flat member ranges from about 10:1-1:10; flowing a process gas into an upper processing volume above the ion shield; forming a plasma from the process gas within the upper processing volume; treating the first layer with neutral radicals that pass through the ion shield; and heating the substrate to a temperature of up to about 550 degrees Celsius while treating the first layer.