Carrier ring wall for reduction of back-diffusion of reactive species and suppression of local parasitic plasma ignition

A carrier ring configured to support a substrate during transport to or from a pedestal of a process tool and surrounding the substrate during processing, the carrier ring comprising,

• an annular structure having an inner diameter and an outer diameter, the annular structure having a bottom surface that is substantially coplanar, and a top surface including a plurality of annular tiers;
• wherein the annular tiers include,
• a first annular tier extending from the inner diameter of the annular structure to a first intermediate diameter greater than the inner diameter, the first intermediate diameter being greater than a diameter of the substrate, the first annular tier having a first height above the bottom surface, the first annular tier defined to be adjacent a substrate support region of the pedestal that is configured to receive the substrate during processing,
• a second annular tier extending from the first intermediate diameter to a second intermediate diameter that is greater than the first intermediate diameter and less than the outer diameter of the annular structure, the second annular tier having a second height above the bottom surface, the second height being greater than the first height, and
• a third annular tier extending from the second intermediate diameter to the outer diameter of the annular structure, the third annular tier having a third height above the bottom surface, the third height being greater than the second height, wherein the third height is configured to establish a gap between a top surface of the third annular tier and a showerhead of the process tool during processing, wherein the third height is configured to suppress local ignition of plasma in the gap to define a plasma exclusion region below a peripheral region of the showerhead and over the top surface of the third annular tier, the plasma exclusion region surrounding a primary plasma region that is below a central region of the showerhead and over the substrate, the third height further being configured to establish a recirculation zone outside of the third annular tier that causes quenching of radicals on an external surface of the third annular tier;
• wherein the second annular tier is configured to be approximately aligned with a top surface of the substrate when present during processing in the process tool when the carrier ring is supported by a carrier support surface surrounding the substrate support region, wherein when the carrier ring is supported by the carrier support surface, the carrier ring does not support the substrate;
• wherein a process extension region is defined over the second annular tier during processing of the substrate in the process tool;
• wherein the carrier ring includes a base ring and an edge ring, the base ring having one or more recesses, the edge ring having one or more protrusions that respectively fit in the one or more recesses.