Polishing apparatus

A polishing apparatus comprising:

• a top ring shaft;
• a housing fixed to the top ring shaft;
• a flexible membrane defining a pressure chamber configured to press a wafer against a polishing pad;
• a top ring body configured to hold the flexible membrane;
• a retaining ring coupled to the top ring body and disposed so as to surround the flexible membrane;
• a carrier ring that surrounds the retaining ring, the carrier ring being secured to the top ring body, the carrier ring having a lower surface arranged to contact the polishing pad;
• a gimbal mechanism configured to allow the top ring body, the flexible membrane, the carrier ring, and the retaining ring to tilt with respect to the housing;
• radial arms coupled to the retaining ring, the radial arms extending radially outwardly;
• and
• an outer ring secured to the radial arms;
• and
• no more than one local load exerting mechanism configured to adjustably tilt the retaining ring with respect to the housing while maintaining an attitude of the wafer by exerting a downward local load on a part of the outer ring.