Simple method for determination of the thickness of a nonabsorbing thin film using spectral reflectance measurement.

A method to determine the thickness of a nonabsorbing thin film on an absorbing substrate is presented. A linear relation between the thin-film thickness and the tangent wavelength of the reflectance spectrum for a specific interference order is revealed, which permits the calculation of the thickness provided that the wavelength-dependent optical parameters of the thin film and the substrate are known. The thickness can be calculated precisely from the reflectance spectrum by using one extreme only, as is demonstrated theoretically for SiO(2) thin film on a Si substrate. The application of this method is demonstrated experimentally for the same thin-film structure but with different Si substrates. The results are compared with those given by the algebraic fitting method, and very good agreement is confirmed.