Chemical mechanical polishing using time share control

A polishing system, comprising:

• a platen rotatable about an axis;
• a polishing pad having a polishing-control groove that is concentric with the axis of rotation and a polishing surface having a plurality of slurry-supply grooves, wherein the slurry-supply grooves are narrower than the polishing-control groove, and wherein the polishing-control groove surrounds the slurry-supply grooves;
• a carrier head to hold a substrate against the polishing pad, the carrier head radially movable across the polishing pad;
• an actuator to move the carrier head;
• and
• a controller coupled to the actuator and configured to cause the carrier head to
• for a first duration, oscillate the substrate laterally across the polishing pad such that a central portion of the substrate and an edge portion of the substrate are positioned over the polishing surface of the polishing pad, and
• for a second duration, hold the substrate in a position such that the central portion of the substrate is positioned only over the polishing surface of the polishing pad and the polishing-control groove is positioned under only an arcuate region of the edge portion of the substrate for a second duration such that the central portion of the substrate is preferentially polished during the second duration.