Polishing method and polishing apparatus

A polishing method comprising:

• preparing a plurality of spectrum groups each containing a plurality of reference spectra corresponding to different film thicknesses;
• directing light to a substrate and receiving reflected light from the substrate;
• producing, from the reflected light, a sampling spectrum for selecting a spectrum group;
• selecting a spectrum group containing a reference spectrum which is closest in shape to the sampling spectrum;
• producing a measurement spectrum for obtaining a film thickness while polishing the substrate;
• selecting, from the selected spectrum group, a reference spectrum which is closest in shape to the measurement spectrum that has been produced when the substrate is being polished;
• obtaining a film thickness corresponding to the selected reference spectrum;
• and
• excluding in advance, from the plurality of spectrum groups, one of spectrum groups containing reference spectra which are close in shape to each other.

A polishing method comprising:

• obtaining at least one spectrum group containing a plurality of reference spectra by polishing a reference substrate;
• correcting the plurality of reference spectra such that a polishing rate of the reference substrate is regarded as constant, thereby obtaining a plurality of corrected reference spectra corresponding to different film thicknesses;
• directing light to a substrate and receiving reflected light from the substrate;
• producing a measurement spectrum for obtaining a film thickness while polishing the substrate;
• selecting, from the at least one spectrum group, a corrected reference spectrum which is closest in shape to the measurement spectrum that has been produced when the substrate is being polished;
• and
• obtaining a film thickness corresponding to the corrected reference spectrum selected.