A Fast Fourier Transform Approach to Finding the Thickness of Single-Layer Thin Films with Slowly Varying Indices of Refraction and Negligible Absorption Coefficients
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A nonstandard photolithographic exposure tool motivates the search for a method to determine photoresist thickness in real time. Optical physics of two-interface thin film systems and the theory of Fourier series reveal a way to calculate photoresist thickness by applying an FFT (fast Fourier transform) algorithm to the reflectance spectrum of a light beam incident on the photoresist. Analyses of simulated data and preliminary measurements assess the speed and accuracy of the FFT algorithm and suggest further areas of research.
CitationMiller, G. F. (2012). A fast fourier transform approach to finding the thickness of single-layer thin films with slowly varying indices of refraction and negligible absorption coefficients (Unpublished thesis). Texas State University-San Marcos, San Marcos, Texas.