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Proceedings Paper

Problems in thin film thickness measurement resolved: improvements of the fast Fourier transform analysis and consideration of the numerical aperture of microscope headers and collimators
Author(s): M. Quinten; F. Houta; T. Fries
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Paper Abstract

Thin film thickness determination with a reflectometer suffers from two problems. One problem is the leakage in the Fast Fourier Transform caused by the fact that the two variables wavenumber 1/λ and optical thickness n⋅d are not really independent, since the refractive index n of the film material itself depends upon the wavenumber. This causes uncertainties in the thickness determination in the order of up to 5% for highly refractive materials like semiconductors. We present a simple but effective improvement of this contribution of the leakage that reduces the uncertainty to less than 2% for highly refractive materials.

Another problem that mainly affects thin films below about 2 μm arises if one uses measuring heads collimators or even microscope headers to obtain high lateral resolutions in the thickness determination. The use of a header introduces angles of incidence different from the default angle α = 0° in reflectometry. Then, the measured reflectance becomes polarization-dependent and the angle must be explicitly considered in the evaluation algorithm. For a microscope header however, all angles between 0° and the angle of aperture must be considered. We will present a solution that allows to reduce the work for each header on taking into account the polarization of the reflected light and a corresponding effective angle αeff.

Paper Details

Date Published: 21 June 2015
PDF: 8 pages
Proc. SPIE 9526, Modeling Aspects in Optical Metrology V, 95260R (21 June 2015); doi: 10.1117/12.2184684
Show Author Affiliations
M. Quinten, FRT GmbH (Germany)
F. Houta, FRT GmbH (Germany)
T. Fries, FRT GmbH (Germany)

Published in SPIE Proceedings Vol. 9526:
Modeling Aspects in Optical Metrology V
Bernd Bodermann; Karsten Frenner; Richard M. Silver, Editor(s)

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