Determination of gain for eddy current sensor

A polishing system, comprising:

• a first polishing station including a first platen to support a first polishing pad, a first in-situ eddy current monitoring system including a first sensor to generate a first signal depending on a thickness of a conductive layer on a substrate, and a first temperature sensor;
• a second polishing station including a second platen to support a second polishing pad, a second in-situ eddy current monitoring system including a second sensor to generate a second signal depending on the thickness of the conductive layer on the substrate, and a second temperature sensor in the second polishing station;
• a carrier head to hold the substrate;
• and
• a controller configured to
• receive a second signal from a second eddy current monitoring system during polishing of the substrate at the second polishing station;
• determine a starting value of the second signal for a start of polishing of the substrate at the second polishing station;
• determine a gain for the second polishing station based on the starting value and a first temperature measured by the first temperature sensor, and wherein the controller is configured to determine the gain based on a second temperature measured by the second temperature sensor;
• for at least a portion of the second signal collected during polishing of at least one substrate at the second polishing station, calculate a third signal based on the second signal and the gain;
• determine at least one of a polishing endpoint or an adjustment to a polishing parameter for the at least one substrate based on the third signal;
• and
• at least one of cause the second polishing station to halt polishing at the polishing endpoint or adjust the polishing parameter at the second polishing station by the adjustment.

A polishing system, comprising:

• a rotatable platen to support a polishing pad;
• a carrier head to hold a first substrate against the polishing pad;
• an in-situ eddy current monitoring system including a sensor to generate a first signal depending on a thickness of a conductive layer on the first substrate;
• and
• a controller configured to
• receive a measurement of an initial thickness of the conductive layer before polishing,
• receive the first signal from the sensor,
• determine a starting value of the first signal for a portion of the first signal corresponding to the first substrate at a start of polishing of the first substrate,
• determine a gain based on the starting value and the measurement of the initial thickness of the conductive layer on the first substrate,
• for at least a portion of a signal collected during polishing of the first substrate or a subsequent substrate calculate a second signal based on the first signal and the gain,
• determine at least one of a polishing endpoint or an adjustment to a polishing parameter for the first substrate or the subsequent substrate based on the second signal, and
• at least one of cause the polishing system to halt polishing at the polishing endpoint or cause the polishing system to adjust the polishing parameter by the adjustment.