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 configured to emit light;
• an illuminating fiber having a plurality of distal ends arranged at different locations in the polishing table, the illuminating fiber being coupled to the light source to direct the light, emitted by the light source, to a surface of the wafer;
• a spectrometer configured to break up reflected light from the wafer in accordance with wavelength and measure an intensity of the reflected light at each of wavelengths;
• a light-receiving fiber having a plurality of distal ends arranged at the different locations in the polishing table, the light-receiving fiber being coupled to the spectrometer to direct the reflected light from the wafer to the spectrometer;
• and
• a processor configured to generate a spectral waveform indicating a relationship between the intensity and wavelength of the reflected light and determine a film thickness based on the spectral waveform.