Polishing system with platen for substrate edge control

A polishing system, comprising:

• a platen having an annular top surface to support an annular main polishing pad, the platen having a circular aperture in the top surface of the platen in approximately a center of the platen, the platen rotatable about an axis of rotation that passes through approximately the center of the platen;
• an annular flange projecting radially inward from the platen into the circular aperture and having an annular top surface to support an annular inner polishing pad, the annular flange having an outer edge secured to and rotatable with the platen and vertically fixed relative to the top surface of the platen, wherein an outer perimeter of the annular top surface of the annular flange is coplanar with the top surface of the platen, and wherein the annular flange is deformable such that an inner edge of the annular flange is vertically movable relative to the outer edge;
• an actuator configured to apply pressure to an underside of the annular flange to deflect the flange to move the inner edge of the annular flange vertically relative to the outer edge of the annular flange and the platen;
• and
• a carrier head to hold a substrate in contact with the main polishing pad and movable to selectively position a portion of the substrate on the inner polishing pad.