Polishing monitoring method, polishing apparatus and monitoring apparatus

A monitoring method for monitoring a change in thickness of a conductive film brought into sliding contact with a polishing surface of a polishing pad using an eddy current sensor, the monitoring method comprising:

• acquiring an output signal of the eddy current sensor when the eddy current sensor is facing the conductive film, the output signal comprising two signals corresponding to a resistance component and an inductive reactance component of an impedance of an electric circuit including a coil of the eddy current sensor;
• defining the two signals as a data point on a coordinate system;
• repeating said acquiring of the output signal and said defining of the data point on the coordinate system until at least three data points are obtained;
• determining a center of curvature of an arc specified by the at least three data points;
• determining a reference angle of inclination of a line connecting the center of curvature and a newest data point of the at least three data points;
• after said determining of the reference angle of inclination, repeating said acquiring of the output signal and said defining of the data point on the coordinate system;
• determining a new center of curvature of an arc specified by a new set of at least three of the data points, including a newest data point, on the coordinate system each time a new data point is defined on the coordinate system;
• determining an angle of inclination of a line connecting the new center of curvature and the new data point of the new set of at least three data points;
• subtracting the reference angle of inclination from the angle of inclination to obtain an increase in the angle of inclination;
• and
• monitoring a change in thickness of the conductive film by monitoring a change in the increase in the angle of inclination.