Film thickness measuring method, film thickness measuring apparatus, polishing method, and polishing apparatus

A film-thickness measuring apparatus comprising:

• a light emitter configured to direct light to a substrate having a film formed on a surface thereof;
• a light receiver configured to receive reflected light from the substrate;
• a spectrometer configured to measure an intensity of the reflected light at each of wavelengths;
• and
• a processor configured to produce a spectral waveform indicating a relationship between intensity and wavelength of the reflected light, the processor being configured to
• perform Fourier transform processing on the spectral waveform to determine strengths of frequency components and corresponding film thicknesses,
• determine a plurality of local maximum values of the strengths of the frequency components, and
• select, according to a preset selection rule, one film thickness from a plurality of film thicknesses corresponding respectively to the plurality of local maximum values,
• wherein the preset selection rule is either to select an N-th largest film thickness or to select an N-th smallest film thickness, N being a predetermined natural number, and
• the preset selection rule is predetermined based on a result of measuring a film thickness of a reference substrate having the same structure as said substrate, measuring of the film thickness of the reference substrate being performed with the same process as measuring of a film thickness of said substrate.

A polishing method comprising:

• directing light to a substrate having a film formed on a surface thereof while rubbing the substrate against a polishing surface;
• producing a spectral waveform indicating a relationship between intensity and wavelength of reflected light from the substrate;
• performing Fourier transform processing on the spectral waveform to determine strengths of frequency components and corresponding film thicknesses;
• determining a plurality of local maximum values of the strengths of the frequency components;
• and
• selecting, according to a preset selection rule, one film thickness from a plurality of film thicknesses corresponding respectively to the plurality of local maximum values,
• wherein the preset selection rule is either to select an N-th largest film thickness or to select an N-th smallest film thickness, N being a predetermined natural number and being variable depending on a structure of the substrate.

A polishing apparatus comprising:

• a polishing table configured to support a polishing pad having a polishing surface;
• a polishing head configured to press a substrate, having a film formed on a surface thereof, against the polishing surface;
• a light emitter configured to direct light to the substrate;
• a light receiver configured to receive reflected light from the substrate;
• a spectrometer configured to measure an intensity of the reflected light at each of wavelengths;
• a processor configured to produce a spectral waveform indicating a relationship between intensity and wavelength of the reflected light;
• and
• a polishing controller configured to control polishing of the substrate, the processor being configured to:
• perform Fourier transform processing on the spectral waveform to determine strengths of frequency components and corresponding film thicknesses,
• determine a plurality of local maximum values of the strengths of the frequency components, and
• select, according to a preset selection rule, one film thickness from a plurality of film thicknesses corresponding respectively to the plurality of local maximum values,
• wherein the preset selection rule is either to select an N-th largest film thickness or to select an N-th smallest film thickness, N being a predetermined natural number and being variable depending on a structure of the substrate.