MINIMIZATION OF ERRORS IN ELLIPSOMETRIC MEASUREMENTS

Ellipsometry allows a very accurate determination of thickness and refractive indices of transparent films. These quantities, however, are not measured directly but must be extracted from the ellipsometric angles-PSI and DELTA. Correlation between sample parameters and PSI and DELTA is nonlinear, so an error analysis is absolutely necessary. The two sources of errors and errors of the instrument and uncertainties in the sample model used for data reduction. For the most common types of automatic ellipsometers these instrument errors are discussed quantitatively with emphasis on measurements of very-thin films. Verification of the proper performance of ellipsometers with special checksamples is shown. By means of several examples the optimization of measuring parameters as well as sample parameters in order to minimize errors is shown.