A method of processing a substrate includes polishing a front surface of a substrate on a first pad coupled to a first platen. The method further includes transferring the substrate from the first pad to a second pad coupled to a second platen with a carrier head. The method further includes moving the carrier head to a scan position to place an edge of the substrate above an orientation sensor disposed at a rotational center of the second pad. The method further includes scanning the edge of the substrate with the orientation sensor to produce a signal. The method further includes analyzing the signal to locate a reference mark of the substrate to determine a rotational orientation of the substrate relative to the carrier head.