An inverse ellipsometric problem for thin film characterization: comparison of different optimization methods

Ayşe Akbalık; Sébastien Soulan; Jean-Hervé Tortai; David Fuard; Issiaka Kone; Jérôme Hazart; Patrick Schiavone

doi:10.1117/12.814118

23 March 2009 An inverse ellipsometric problem for thin film characterization: comparison of different optimization methods

Ayşe Akbalık, Sébastien Soulan, Jean-Hervé Tortai, David Fuard, Issiaka Kone, Jérôme Hazart, Patrick Schiavone

Author Affiliations +

Proceedings Volume 7272, Metrology, Inspection, and Process Control for Microlithography XXIII; 72723S (2009) https://doi.org/10.1117/12.814118
Event: SPIE Advanced Lithography, 2009, San Jose, California, United States

Abstract

In this paper, an ill-posed inverse ellipsometric problem for thin film characterization is studied. The aim is to determine the thickness, the refractive index and the coefficient of extinction of homogeneous films deposited on a substrate without assuming any a priori knowledge of the dispersion law. Different methods are implemented for the benchmark. The first method considers the spectroscopic ellipsometer as an addition of single wavelength ellipsometers coupled only via the film thickness. The second is an improvement of the first one and uses Tikhonov regularization in order to smooth out the parameter curve. Cross-validation technique is used to determine the best regularization coefficient. The third method consists in a library searching. The aim is to choose the best combination of parameters inside a pre-computed library. In order to be more accurate, we also used multi-angle and multi-thickness measurements combined with the Tikhonov regularization method. This complementary approach is also part of the benchmark. The same polymer resist material is used as the thin film under test, with two different thicknesses and three angles of measurement. The paper discloses the results obtained with these different methods and provides elements for the choice of the most efficient strategy.

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Ayşe Akbalık, Sébastien Soulan, Jean-Hervé Tortai, David Fuard, Issiaka Kone, Jérôme Hazart, and Patrick Schiavone "An inverse ellipsometric problem for thin film characterization: comparison of different optimization methods", Proc. SPIE 7272, Metrology, Inspection, and Process Control for Microlithography XXIII, 72723S (23 March 2009); https://doi.org/10.1117/12.814118

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