Eddy current monitoring to detect vibration in polishing

A non-transitory computer readable media having a computer program encoded thereon comprising instructions to cause one or more computers to:

• during polishing by a polishing pad of a substrate held by a carrier head of a polishing system, receive a signal from an in-situ eddy current monitoring system that includes a sensor that sweeps below the carrier head;
• detect mechanical vibrations in the polishing system based on a signal from the in-situ eddy current monitoring system;
• and
• generate an alert in response to detecting the mechanical vibrations.

A method, comprising:

• bringing a body into contact with a polishing pad of a polishing system;
• supplying a polishing liquid to the polishing pad;
• generating relative motion between the body and the polishing pad while the body contacts the polishing pad;
• during the relative motion while the body contacts the polishing pad, generating a signal from an in-situ eddy current monitoring system;
• and
• detecting mechanical vibrations in the polishing system based on a signal from the in-situ eddy current monitoring system.