Polishing monitoring method and polishing apparatus

1. 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.

2. The method according to claim 1 , 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.

3. 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.

4. 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.

5. The apparatus according to claim 4 , wherein the predetermined correction reference value comprises the output signal of said eddy current sensor obtained in advance under the same conditions as those when the correction signal value is acquired.