Apparatus for reducing polymer deposition on substrate support

A substrate support for a plasma processing apparatus having a processing chamber and a power source which energizes process gas in an interior of the processing chamber into a plasma state for processing a substrate, the substrate support comprising:

• a substrate support surface which supports a substrate within the interior of the processing chamber, the substrate support having an outer surface;
• a substrate supported on the substrate support surface in overhanging relationship therewith;
• a focus ring supported on and surrounding the substrate support, the focus ring having an inner surface forming a gap between the outer surface of the substrate support and the focus ring, the gap being in fluid communication with the interior of the processing chamber when the substrate support is mounted in the processing chamber, the substrate extending over at least part of the focus ring such that the inner surface of the focus ring is located inwardly of an outer periphery of the substrate;
• and
• a clearance gas supply in fluid communication with the gap and adapted to supply clearance gas to the gap at a flow rate which is sufficient to block migration of process gas and volatile byproducts thereof into the gap during processing of a substrate supported on the substrate support surface, the clearance gas supply including a plurality of radially extending gas passages having outlets in the gap.