Two-part retaining ring with interlock features

A carrier head, comprising:

• a housing;
• a substrate mounting surface supported by the housing;
• and
• a retaining ring having
• an annular lower portion surrounding the substrate mounting surface, the annular lower portion including a main body with a bottom surface for contacting a polishing pad during polishing, an inner rim projecting upward from the main body, an outer rim projecting upward from the main body and separated from the inner rim by a gap, and a plurality of azimuthally separated interlock features positioned between the inner rim and the outer rim, each interlock feature projecting upwardly from the main body, wherein the lower portion is a plastic, and wherein the lower portion comprises a plurality of threaded recesses formed in top surfaces of at least some of the interlock features, and
• an annular upper portion secured to the housing, the annular upper portion having a top surface and a bottom surface and a plurality of azimuthally separated recesses in the bottom surface, the recesses in the bottom surface of the annular upper portion defining thin portions of the upper portion and azimuthally separated thicker sections between the thin portions, wherein the plurality of interlock features fit into the plurality of recesses, wherein the upper portion includes a plurality of apertures formed through the thin portions and aligned with the plurality of threaded recesses, and wherein the upper portion includes a plurality of threaded holes located in at least some of the thicker sections, the plurality of threaded holes extending partially but not entirely through the thicker sections of the upper portion, and wherein the upper portion is a material that is more rigid than the plastic.