Three-zone carrier head and flexible membrane

A chemical mechanical polishing head, comprising:

• a base assembly;
• a retaining ring secured to the base assembly;
• and
• a flexible membrane secured to the base assembly, the flexible membrane including
• a main portion with a lower surface to provide a substrate-mounting surface, the substrate mounting surface having a radius R,
• an annular outer portion extending upwardly from an outer edge of the main portion, the annular outer portion having a lower edge connected to the main portion and an upper edge, and
• exactly three annular flaps to divide a volume above the main portion into a plurality of chambers when the flexible membrane is secured to a carrier head, the three annular flaps including
• a first annular flap joined to an inner surface of the main portion at a radial position between 75% and 95% of R,
• a second annular flap joined to the annular outer portion at a position between the lower edge and the upper edge, the second annular flap extending inwardly from the outer annular portion, and
• a third annular flap joined to the upper edge of the annular outer portion, the third annular flap extending inwardly from the outer annular portion.