Method for measuring thin-film thickness and step height on the surface of thin-film/substrate test samples by phase-shifting interferometry

摘要

The film thickness and surface profile of a test sample consisting of optically dissimilar regions are measured by phase-shifting interferometry. Conventional phase-shifting interferometry at a given wavelength is performed to measure the step height between two regions of the surface. The theoretical measured step height as a function of the film thickness is then calculated. A set of possible solutions corresponding to the experimentally measured-height are found numerically or graphically by searching the theoretically generated function at the measured height. If more than one solution exists, the phase-shifting procedure is repeated at a different wavelength and a new theoretical measured-height as a function of the film thickness is calculated for the optical parameters of the materials at the new wavelength, yielding another set of possible solutions that correspond to the newly measured height. The number of repetitions of the procedure depends on the number of unknowns of the test sample. The film thicknesses are obtained by comparing all possible solution sets and finding the single combination of thicknesses corresponding to the experimentally measured heights at different measurement wavelengths. The same method may also be used for reconstructing a 3-dimensional profile of the patterned film surface by measuring the film thickness variation point by point across the entire measurement field.