Method for rapid, accurate measurement of step heights between dissimilar materials

A computerized phase shifting interferometer operates interactively with a user to correct surface profile data of a sample containing a film of material which is optically dissimilar to the material of a substrate. Profile data is measured, and optically dissimilar areas of the sample are identified by differences in measured height. The user is prompted to enter optical parameters for each identified area into the computer. Then the user is prompted to enter a best guess of the film thickness. A Newton approximation technique is performed by the computer to produce subsequent guesses of the film thickness until a computed thickness increment is below a predetermined value.