Systems and methods for suppressing parasitic plasma and reducing within-wafer non-uniformity

A substrate processing system for depositing film on a substrate, comprising:

• a processing chamber defining a reaction volume;
• a showerhead including:
• a stem portion having one end connected adjacent to an upper surface of the processing chamber;
• and
• a base portion connected to an opposite end of the stem portion and extending radially outwardly from the stem portion,
• wherein the showerhead is configured to introduce at least one of process gas and purge gas into the reaction volume;
• a plasma generator configured to selectively generate RF plasma in the reaction volume;
• and
• an edge tuning system including:
• a collar arranged around the stem portion of the showerhead between the base portion of the showerhead and the upper surface of the processing chamber,
• wherein the collar includes:
• an inner collar arranged adjacent to the stem portion;
• an upper outer collar arranged around an upper portion of the inner collar;
• a lower outer collar arranged around a lower portion of the inner collar;
• and
• wherein the inner collar includes:
• one or more holes for supplying purge gas from an inner cavity of the collar to an area between the base portion of the showerhead and the upper surface of the processing chamber through a gap between the upper outer collar and the lower outer collar;
• and
• one or more openings along a showerhead-side end of the inner collar through which purge gas flows to locations between the showerhead and a lower most end of the lower outer collar;
• and
• a parasitic plasma reducing element located around the stem portion between the collar and an upper surface of the showerhead and configured to reduce parasitic plasma between the showerhead and the upper surface of the processing chamber,
• wherein the parasitic plasma reducing element includes a plurality of plates that are arranged in a spaced relationship between the upper surface of the showerhead and the collar.