Multilayer thin film thickness measurement method
to measure thickness of liquid thin film within a layer stack
J.J. Bleeker (TU Delft - Mechanical Engineering)
J. Snieder – Coach (TU Delft - Mechatronic Systems Design)
R. A.J. van Ostayen – Mentor (TU Delft - Mechatronic Systems Design)
Nandini Bhattacharya – Graduation committee member (TU Delft - ImPhys/Medical Imaging)
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Abstract
The research objective of this research is to develop a measurement method that can measure thin film thicknesses through a multilayer that consists of both surrounding thick layers and in between thin films. An optical non-contact measurement method is researched and developed to non-destructively measure the thickness of a liquid thin film, which is situated between other layers. The measurement method used in this research is called spectral reflectance. The method works by analyzing the reflectance spectrum from a light beam which is directed perpendicularly and with a wide range of wavelengths on the surface of the layer. The reflectance spectrum that is measured with a spectrometer includes oscillations that result from the interference of light that reflects at the different interfaces in the multilayer. The oscillation contains frequency content which is used to determine the thickness of the layer. This research shows that the spectral reflectance technique can be used to measure the thickness of a stack of thin films with the condition that the thin films are all coherent. It is possible to determine the film thickness of a stack coherent thin films, which are surrounded by incoherently thick layers. The outer layers can be assumed to be incoherently thick based on a combination of factors such as the layer thickness of the thick layer, the measured wavelength range and the resolution of the spectrometer.