RETRIEVAL OF OPTICAL-CONSTANTS AND THICKNESS OF THIN-FILMS FROM TRANSMISSION SPECTRA

We discuss a new method to estimate the absorption coefficient, the in dex of refraction, and the thickness of thin films using optical trans mission data only. To solve the problem we used a pointwise constraine d optimization approach, defining a nonlinear programming problem, the unknowns of which are the coefficients to be estimated, with linear c onstraints that represent prior knowledge about the physical solution. The method applies to all kinds of transmission spectra and does not rely on the existence of fringe patterns or transparency. Results on a morphous semiconductor thin films and gedanken films are reported. The y show that the new method is highly reliable. (C) 1997 Optical Societ y of America.