Patent ID: 7198545

Claim:
A method for calibrating a chemical mechanical planarization tool using an eddy current probe and a plurality of calibration wafers, wherein each calibration wafer has a measurable predetermined property and a measurement of the measurable predetermined property of a first calibration wafer is different than a measurement of the measurable predetermined property of a second calibration wafer, the method comprising: determining a first set of impedance measurements of the calibration wafers while each calibration wafer is disposed in the tool and the tool has a tool parameter that is at a first condition; collecting a second set of impedance measurements of the calibration wafers while each calibration wafer is disposed in the tool and the tool parameter is at a second condition; and establishing a reference point, based upon a first and a second data point from the first set of impedance measurements and a first and a second data point from the second set of impedance measurements.