Determining the orientation of a substrate in-situ

A method of polishing a substrate, comprising:

• scanning an edge of a substrate using an orientation sensor located at a rotational center of a platen;
• analyzing data obtained by the orientation sensor to determine a location of a reference mark of the substrate in relation to a carrier head holding the substrate, wherein analyzing the signal to locate the reference mark includes identifying a reference mark signature;
• polishing a front surface of the substrate;
• and
• monitoring the front surface during polishing with an endpoint sensor embedded in the platen that scans the front surface, wherein monitoring the front surface includes identifying a portion of the front surface being scanned by the endpoint sensor using the determined location of the reference mark in relation to the carrier head.

A polishing system, comprising:

• a polishing station, including:
• a platen including a polishing pad;
• a carrier head configured to rotate a substrate;
• an isotropic electromagnetic sensor embedded in the platen at the rotational center of the platen, wherein the isotropic electromagnetic sensor is configured to scan an edge of a substrate that includes a reference mark;
• a plurality of endpoint sensors embedded in the platen around the isotropic electromagnetic sensor, each endpoint sensor configured to monitor a surface of the substrate being polished on the pad;
• and
• a controller in communication with the isotropic electromagnetic sensor and the endpoint sensors, wherein the controller is configured to analyze data obtained by the isotropic electromagnetic sensor to identify a location of the reference mark relative to the carrier head.