Control of overpolishing of multiple substrates on the same platen in chemical mechanical polishing

A polishing method, comprising:

• simultaneously polishing a first substrate and a second substrate using a single polishing pad;
• storing a default overpolishing time;
• monitoring the first substrate and the second substrate during polishing with an in-situ monitoring system;
• determining a first polishing endpoint time of the first substrate with the in-situ monitoring system;
• determining a second polishing endpoint time of the second substrate with the in-situ monitoring system, wherein the second polishing endpoint time is different from the first polishing endpoint time;
• calculating an overpolishing stop time, the overpolishing stop time being between the first polishing endpoint time plus the default overpolishing time and the second polishing endpoint time plus the default overpolishing time;
• continuing polishing of the first substrate past the first polishing endpoint time and continuing polishing of the second substrate past the second polishing endpoint time;
• and
• halting polishing of the first substrate and the second substrate simultaneously at the overpolishing stop time.