Polishing monitoring method and polishing apparatus

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;
• calculating a correcting amount from a difference between the correction signal value and a predetermined 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, wherein:
• the output signal of the eddy current sensor comprises a resistance component and an inductive reactance component of an impedance of an electric circuit including a coil of the eddy current sensor;
• the resistance component and the inductive reactance component are defined as coordinates on a coordinate system;
• and
• the coordinates are rotated and moved on the coordinate system such that a distance between an origin of the coordinate system and a point specified by the coordinates decreases in accordance with a decrease in the thickness of the conductive film.

An apparatus for polishing a substrate, said apparatus comprising:

• a polishing pad having a polishing surface;
• an eddy current sensor;
• a top ring configured to press a substrate against said polishing surface;
• a dresser configured to dress said polishing surface;
• a mechanism configured to provide relative motion between the substrate and said polishing pad;
• and
• a monitoring unit configured to monitor a change in thickness of a conductive film on a substrate brought into sliding contact with said polishing surface using said eddy current sensor,
• wherein said monitoring unit is operable to
• acquire an output signal of said eddy current sensor as a correction signal value during water-polishing of a substrate, during dressing of said polishing pad, or during replacement of said polishing pad,
• calculate a correcting amount from a difference between the correction signal value and a predetermined correction reference value,
• calculate an actual measurement signal value by subtracting the correcting amount from the output signal of said eddy current sensor when polishing a substrate having a conductive film, and
• monitor a change in thickness of the conductive film during polishing by monitoring a change in the actual measurement signal value, and
• wherein:
• the output signal of said eddy current sensor comprises a resistance component and an inductive reactance component of an impedance of an electric circuit including a coil of said eddy current sensor;
• the resistance component and the inductive reactance component are defined as coordinates on a coordinate system;
• and
• the coordinates are rotated and moved on the coordinate system such that a distance between an origin of the coordinate system and a point specified by the coordinates decreases in accordance with a decrease in the thickness of the conductive film.