DETERMINATION OF THE THICKNESS AND OPTICAL-CONSTANTS OF THIN-FILMS FROM TRANSMISSION SPECTRA

A method has been developed to determine the thickness and the wavelen gth-dependent refractive indices and absorption coefficients of thin o ptical films by fitting a five parameter function to measured transmis sion spectra. Initial values for the fitting parameter are obtained fr om the transmission values at the spectral maxima and minima of the in terference patterns created by the films. This is followed by a system atic variation of those parameters which can cause a failure of the ca lculation by reaching local minima of The residual sum of squares. The final fitting is performed with a Marquardt algorithm. A Monte Carlo simulation has indicated that the accuracy of this method is at least one order of magnitude better than that of the methods utilising only the interference extrema.