Phase measurement interferometric microscopy of thin films: Analysis of topography, refractive index, and thickness of solvent swollen polystyrene films

An analysis of phase measurement interferometric microscopy (PMIM) images of optically transparent films is presented. Multiple reflections of light within thin films produce a non-linear relationship between the measured optical thickness h and the true film thickness d, introducing oscillatory surface features in uncorrected PMIM topographical images. A method for simultaneously determining the microtopography, thickness, and refractive index of thin films using optical maxima and minima observed in PMIM images is described. The analysis is used to characterize 100-200 nm thick polystyrene (PS) films deposited on silicon wafers. The refractive index and degree of swelling of a PS film immersed in a mixed solvent, 27%(by volume) toluene in acetonitrile, are reported.