Polishing apparatus

A polishing apparatus comprising:

• a polishing table for supporting a polishing pad;
• a polishing head configured to press a wafer against the polishing pad;
• a light source;
• an illuminating fiber having distal ends arranged at different locations in the polishing table;
• a light-receiving fiber having distal ends arranged at the different locations in the polishing table;
• a spectrometer coupled to the light-receiving fiber, the spectrometer being configured to decompose reflected light, transmitted from the wafer through the light-receiving fiber, according to wavelength and measure intensity of the reflected light at each of wavelengths;
• a processor configured to determine a film thickness of the wafer based on a spectral waveform indicating a relationship between the intensity and the wavelength of the reflected light;
• and
• a first dimmer and a second dimmer attached to the illuminating fiber,
• wherein the illuminating fiber includes a first illuminating fiber and a second illuminating fiber,
• one ends of the first illuminating fiber and the second illuminating fiber are coupled to the light source,
• other ends of the first illuminating fiber and the second illuminating fiber constitute the distal ends of the illuminating fiber arranged at the different locations, and
• the first dimmer is attached to the first illuminating fiber and the second illuminating fiber, and the second dimmer is attached to at least one of the first illuminating fiber and the second illuminating fiber.