A chemical mechanical polishing apparatus and method can use an eddy current monitoring system and an optical monitoring system. Signals from the monitoring systems can be combined on an output line and extracted by a computer. A thickness of a polishing pad can be calculated. The eddy current monitoring...http://www.google.com/patents/US7195536?utm_source=gb-gplus-sharePatent US7195536 - Integrated endpoint detection system with optical and eddy current monitoring
