Thin film measurement system for moving objects based on a laterally distributed linear variable filter spectrometer

Instantaneous measurement of optical or geometrical parameters of thin layers is an ambitious aim in many industrial applications. These layers have a variety of use-cases, such as optical bandpassing, dielectric permittivity, or lubrication. Mostly, these layers are in motion due to the production process. In order to observe process parameters, the motion usually has to be disrupted. Thus, the increase of production time due to control purposes is an undesirable drawback of this otherwise suitable technique. In this publication, we present a solution to this particular drawback of most production process monitoring systems exemplarily for film thickness measurement. We show the realization of a measurement principle which has, to our knowledge, never been published before in this application. Therefore, we exploit the advantages of the combination of a linear variable filter with a complementary metal oxide semiconductor sensor array. By an apt readout sequence, this measurement system is able to measure transmission spectra while the target is in motion. We show that this measurement system is able to measure film thicknesses of objects in the range of several 100 nm thickness at up to a velocity of 4 m/s. A reproducibility below 2 nm was acquired. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3697750]