Noncontacting measurement of opaque thin films using a dual beam thermal wave probe

A dual beam thermal wave probe has been used to measure the thickness of opaque thin films in a noncontact, nondestructive manner. The method relies on the measurement of the differential phase of two interferometrically determined photodisplacement signals. The technique does not require calibration against standard samples and can be used to determine film thicknesses from a few tens of nanometers up to several micrometers. Alternatively, if the film thickness is known, thermal material properties like diffusivity or conductivity can be determined. The conditions under which the system is expected to give the most accurate results are analyzed.