Resistivity-based calibration of in-situ electromagnetic inductive monitoring

A computer program product for calibrating an in-situ electromagnetic induction monitoring system, the computer program product tangibly encoded on a non-transitory computer readable media, comprising instructions to cause a computer system to:

• store a correlation function relating thicknesses of a conductive layer to signal values from the in-situ electromagnetic induction monitoring system and store a first value representing an electrical resistivity at which the correlation function applies;
• receive a sheet resistance measurement of a first conductive layer on a calibration substrate, the first conductive layer having an electrical resistivity at a second value;
• receive a first signal value measurement of the first conductive layer on the calibration substrate from the in-situ electromagnetic induction monitoring system;
• receive a second signal value measurement in the absence of a substrate having an outer conductive layer from the in-situ electromagnetic induction monitoring system;
• and
• calculate based on the first value representing the electrical resistivity at which the correlation function applies, the sheet resistance measurement, the first signal value measurement, and the second signal value measurement, an offset and a gain to apply to signals from the in-situ electromagnetic induction monitoring system to compensate for variation between the electrical resistivity at which the correlation function applies and the electrical resistivity of the first conductive layer.

A polishing system, comprising:

• a rotatable platen to support a polishing pad;
• a carrier head to hold a substrate against the polishing pad;
• an in-situ electromagnetic induction monitoring system including a sensor to generate a sequence of signal values that depend on a thickness of a conductive layer on the substrate;
• and
• a controller configured to
• store a correlation function relating thicknesses of a conductive layer to signal values from the in-situ electromagnetic induction monitoring system and store a first value representing an electrical resistivity at which the correlation function applies,
• receive a sheet resistance measurement of a first conductive layer on a calibration substrate, the first conductive layer having an electrical resistivity at a second value;
• receive a first signal value measurement of the first conductive layer on the calibration substrate from the in-situ electromagnetic induction monitoring system;
• receive a second signal value measurement in the absence of a substrate having an outer conductive layer from the in-situ electromagnetic induction monitoring system;
• and
• calculate based on the first value representing the electrical resistivity at which the correlation function applies, the sheet resistance measurement, the first signal value measurement, and the second signal value measurement, an offset and a gain to apply to signals from the in-situ electromagnetic induction monitoring system to compensate for variation between the electrical resistivity at which the correlation function applies and the electrical resistivity of the first conductive layer.