Methods and apparatuses for determining thickness of a conductive layer

A method of determining a thickness of a conductive layer on a workpiece, the method comprising:

• measuring a magnetic flux density change when the conductive layer on the workpiece is in a magnetic field;
• and
• calculating the thickness of the conductive layer using a calibration curve formed by relating the magnetic flux density change to thickness of a conductive layer disposed in the magnetic field, wherein the calibration curve either fits a smooth function interpolation to a plurality of calibration points or connects the plurality of calibration points with a plurality of functions.

A method of determining a thickness of a conductive layer on a workpiece, the method comprising:

• using an eddy current sensor to measure a value when the conductive layer on the workpiece is in a magnetic field;
• and
• calculating the thickness of the conductive layer using a calibration curve that correlates thickness to the measured value, the calculated thickness being within 5% error over a range from about 1 kÅ to about 20 kÅ.

An apparatus for determining thickness, the apparatus comprising:

• an eddy current sensor calibrated to measure a magnetic flux density change when a conductive layer on a workpiece is in a magnetic field;
• and
• a processor configured to execute a program that transforms the measured magnetic flux density change into a calculated thickness of the conductive layer, wherein the program comprises a calibration curve fit to a plurality of calibration points, the calibration curve comprising either a smooth function interpolation or a piecewise function.