Measurement of thin film thickness by electronic speckle pattern interferometry

The surface profile of an Al thin film and its thickness have been observed by electronic speckle pattern interterometry (ESPI). The Michelson interferometer was used as our basic interferometric system to obtain interference fringes on a CCD camera. These interference fringes, arising from the path differences due to the surface contours of the thin film, were analyzed with three different techniques: fast Fourier transform (FFT), phase shifting, and digital image subtraction, and the results were compared with each other. We also derived a new formula for the image subtraction method, which is only valid in one-dimensional calculations. An unwrapping procedure was used to obtain a continuous phase in the FFT and phase shifting methods. Results Oil thickness measurements are presented and are found to be in good agreement with each other. (C) 2004 Elsevier B.V. All rights reserved.