System for measuring film thickness

摘要

In apparatus and a method for measuring the thickness of a film (13), the film (13) is illuminated with a low coherence light signal that is preferably generated from a source (12, 100) including two or more LEDs (102, 103). The light reflected from the surfaces of the film (13) is collected and coupled to an interferometer (18). The slope of the Fourier transform of the output of the signal from the interferometer (18) is measured to provide a determination of the thickness of the film (13). In the preferred embodiment, the interferometer output is sampled at fewer than two points per cycle of the low coherence light signal. <IMAGE>