Thickness Control of Coatings by Means of Modulated IR Radiometry

Coatings prepared by reactive magnetron sputtering of approximately equal thermal transport properties but differing coating thicknesses are analyzed by means of non-contact non-destructive modulated IR radiometry. For the quantitative interpretation, the measured thermal wave signals are calibrated, using the signals measured for a homogenous opaque solid of smooth surface. The relative minima of the inverse calibrated phase lag signals are interpreted with respect to the effective thermal transport properties and to the coating thickness using an inverse solution of the two-layer thermal wave problem. Based on measurements of various coatings, the limitations of this thermal wave method and the errors of measurement for the coating thickness are discussed by comparing with microscopic measurements.