Optical EngineeringFourier transform method for measurement of thin film thickness by speckle interferometry
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The surface profile of an Al thin film and its thickness are observed by electronic speckle pattern interferometry (ESPI). The Michelson interferometer is used as our basic interferometric system to obtain interference fringes on a CCD camera. These interference fringes depend on the path differences due to the surface contours of the thin film. The interference fringes are analyzed with the fast Fourier transform method and a wrapped phase is obtained. An unwrapping procedure is used to obtain a continuous phase. Results on thickness measurement are presented.