Apparatus for processing substrates are provided herein. In some embodiments, an apparatus includes a process kit comprising a shield having one or more sidewalls configured to surround a first volume, the first volume disposed within an inner volume of a process chamber; and a first ring moveable between a first position, wherein the first ring rests on the shield, and a second position, wherein a gap is formed between an outer surface of the first ring and an inner surface of the one or more sidewalls, wherein a width of the gap is less than about two plasma sheath widths for a plasma formed at a frequency of about 40 MHz or higher and at a pressure of about 140 mTorr or lower.