Patent ID: 8078419

Claim:
A method of monitoring a change in thickness of a conductive film on a substrate brought into sliding contact with a polishing surface of a polishing pad using an eddy current sensor, said method comprising: acquiring an output signal of the eddy current sensor as a correction signal value during water-polishing of a substrate, during dressing of the polishing pad, or during replacement of the polishing pad; acquiring a characteristic signal value of the eddy current sensor; acquiring an output signal of the eddy current sensor as an initial signal value under the same conditions as those when the characteristic signal value is acquired; calculating an initial drift from a difference between the characteristic signal value and the initial signal value; correcting a predetermined correction reference value by subtracting the initial drift from the predetermined correction reference value to obtain a corrected correction reference value, the predetermined correction reference value comprising the output signal of the eddy current sensor obtained in advance under the same conditions as those when the correction signal value is acquired; calculating a correcting amount from a difference between the correction signal value and the corrected correction reference value; calculating an actual measurement signal value by subtracting the correcting amount from the output signal of the eddy current sensor when polishing a substrate having a conductive film; and monitoring a change in thickness of the conductive film during polishing by monitoring a change in the actual measurement signal value.