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Currently, one measures dielectric thin film thickness on a wafer surface by sampling a predetermined number of points across the wafer. Point measurements do not provide accurate information on the trend in thickness variation across the wafer surface. Such information could be quite useful while developing new coating, deposition, etching, or polishing processes. Hence, a system that can map single layer film thickness across the whole wafer or a large area of the wafer will be very useful to process developers. In this article, we will discuss a technique that can map film thickness across a large area in a relatively short amount of time. It takes about 4 s to determine about 23 000 thickness values across the wafer. The approach has been breadboarded and demonstrated. Using a single wavelength, this technique makes it possible to characterize single layer film thickness without having to know optical constants of the substrate material.