SENSITIVITY OF VARIABLE-ANGLE SPECTROSCOPIC ELLIPSOMETRY TO ISOTROPICTHIN-FILM PROPERTIES

Ellipsometry involves the solution of complicated mathematical relatio ns between the measured data and the desired physical parameters. Deal ing with these equations remains a central issue in the method, especi ally in light of the increased measurement speed and data set size. He re the sensitivity of ellipsometry measurements to parameters of inter est for isotropic thin films is investigated as a first step to develo ping an ellipsometry expert system. A general approach to selecting in cidence angles and light wavelengths is demonstrated for the particula r case of ZrO2 films sputter deposited onto fused silica substrates. A t first the measurements must be sensitive to changes in the parameter of interest and, beyond that, the system of equations must be suffici ently well posed considering measurement error and computer truncation and roundoff. Simulations of the ZrO2 film show that the incidence an gles for best sensitivity do not correspond to those for the best equa tion conditions. This method can be applied to any reflecting surface to assist in the selection of angles and wavelengths. It is planned th at a very large number of such simulations covering an increasing numb er of reflecting surface materials and configurations will be performe d and stored in a high performance database for easy access. Such prog ress in the development of expert systems to make the equations work i n the background for all but the most inquisitive ellipsometrist is de scribed. (C) 1997 Elsevier Science S.A.