Output signal processing apparatus for eddy current sensor

A polishing apparatus comprising:

• a polishing table configured to hold a polishing pad that polishes a workpiece;
• a holder that holds the workpiece and can press the workpiece against the polishing pad;
• an eddy current sensor that has an exciting coil configured to form eddy current in the workpiece and a detection coil that detects the eddy current formable in the workpiece, the eddy current sensor does not include a balance coil;
• and
• an output signal processing apparatus for an eddy current sensor, the output signal processing apparatus processing an output signal of the detection coil which is output from the eddy current sensor,
• wherein the output signal processing apparatus has
• a holding circuit that holds reference data indicating a characteristic of the output signal output from the detection coil at a reference state and outputs the reference data at a state other than the reference state;
• a pseudo signal generating circuit that generates, from the reference data output from the holding circuit, a pseudo signal corresponding to the output signal output from the detection coil at the reference state, and outputs the pseudo signal;
• a bridge circuit that, at the state other than the reference state, receives an output signal output from the detection coil and the pseudo signal and outputs a signal corresponding to a difference between the output signal and the pseudo signal, as a bridge output signal;
• and
• a bridge signal processing circuit that processes the bridge output signal output from the bridge circuit.

A polishing apparatus comprising:

• a polishing table configured to hold a polishing pad that polishes a workpiece;
• a holder that holds the workpiece and can press the workpiece against the polishing pad;
• an eddy current sensor that has an exciting coil configured to form eddy current in the workpiece and a detection coil that detects the eddy current formable in the workpiece, the eddy current sensor does not include a balance coil;
• and
• an output signal processing apparatus for an eddy current sensor, the output signal processing apparatus processing an output signal of the detection coil which is output from the eddy current sensor,
• wherein the output signal processing apparatus has
• a holding circuit that holds reference data indicating a characteristic of the output signal output from the detection coil at a reference state and outputs the reference data at a state other than the reference state;
• and
• a difference circuit that receives characteristic data indicating a characteristic of the output signal output from the detection coil at the state other than the reference state and the reference data output from the holding circuit and acquires a difference between the characteristic data and the reference data.

A polishing method that performs polishing by using a polishing apparatus having

• a polishing table configured to hold a polishing pad that polishes a workpiece;
• a holder that holds the workpiece and can press the workpiece against the polishing pad;
• and
• an eddy current sensor that includes an exciting coil configured to form eddy current in the workpiece and a detection coil that detects the eddy current formable in the workpiece, the eddy current sensor does not include a balance coil,
• the method comprising:
• by a holding circuit, holding reference data indicating a characteristic of the output signal output from the detection coil at a reference state and outputting the reference data at a state other than the reference state;
• by a pseudo signal generating circuit, generating, from the held reference data, a pseudo signal corresponding to the output signal output from the detection coil at the reference state and outputting the pseudo signal;
• by a bridge circuit, at the state other than the reference state, receiving the output signal output from the detection coil and the pseudo signal and outputting a signal corresponding to a difference between the output signal and the pseudo signal, as a bridge output signal;
• and
• by a bridge signal processing circuit, processing the bridge output signal.

A polishing method that performs polishing by using a polishing apparatus having

• a polishing table configured to hold a polishing pad that polishes a workpiece;
• a holder that holds the workpiece and can press the workpiece against the polishing pad;
• and
• an eddy current sensor that includes an exciting coil configured to form eddy current in the workpiece and a detection coil that detects the eddy current formable in the workpiece, the eddy current sensor does not include a balance coil,
• the method comprising:
• by a holding circuit, holding reference data indicating a characteristic of the output signal output from the detection coil at a reference state and outputting the reference data at a state other than the reference state;
• and
• by a difference circuit, receiving characteristic data indicating a characteristic of the output signal output from the detection coil at the state other than the reference state and the reference data output from the holding circuit and acquiring a difference between the characteristic data and the reference data.