Polishing apparatus and polishing method

A polishing apparatus for polishing a workpiece, comprising:

• a polishing table configured to support a polishing pad;
• a polishing head configured to press the workpiece against the polishing pad to polish the workpiece;
• a light source configured to emit light;
• a light-emitting optical fiber cable coupled to the light source and configured to direct the light to the workpiece;
• a light-receiving optical fiber cable configured to receive reflected light from the workpiece;
• a first spectrometer coupled to the light-receiving optical fiber cable;
• a second spectrometer directly coupled to the light source;
• and
• a processing system including a memory storing a program and an arithmetic device configured to perform an arithmetic operation according to instructions included in the program,
• the memory storing therein first base intensity data indicating reference intensity of light measured by the first spectrometer before polishing of the workpiece,
• the memory storing therein second base intensity data indicating reference intensity of the light of the light source measured by the second spectrometer before polishing of the workpiece,
• the memory storing therein a calculation formula for calculating relative reflectance data,
• the processing system being configured to determine, during polishing of the workpiece, a film thickness of the workpiece based on the relative reflectance data,
• the calculation formula being expressed as
• the relative reflectance data=MD1/[BD1·k]
• where MD1 represents first intensity measurement data indicating intensity of the reflected light from the workpiece measured by the first spectrometer, BD1 represents the first base intensity data, and k represents a rate of change in second intensity measurement data with respect to the second base intensity data, and the second intensity measurement data is indicative of intensity of the light of the light source measured by the second spectrometer during polishing of the workpiece.