Film-thickness measuring method, method of detecting notch portion, and polishing apparatus

A polishing method comprising:

• polishing a substrate while rotating the substrate on a polishing surface of a polishing pad by a polishing head;
• measuring a film thickness of the substrate by a film-thickness measuring device during the polishing of the substrate;
• stopping the polishing of the substrate;
• when a variation in film thickness of a periphery of the substrate is out of a reference range, measuring film thicknesses of the periphery of the substrate, while rotating the substrate on the polishing surface of the polishing pad by the polishing head and controlling a position of the film-thickness measuring device relative to the polishing head,
• wherein controlling the position of the film-thickness measuring device relative to the polishing head comprises controlling, in synchronization with the polishing head, at least one of an oscillating motor that oscillates the polishing head along the polishing surface and a table motor that rotates the polishing table;
• and
• re-polishing the substrate such that the variation of the film thicknesses of the periphery of the substrate is eliminated.