Determination of Interface Roughness Using A Wavelength Scanning TIS Instrument

Optical scattering from surface micro irregularities at a specific wavelength is directly related to the RMS-roughness value of the surface1. It is usually measured by a TIS (Total Integrated Scatter) instrument. In its’ conventional application this method can only be used to investigate the front surface of opaque samples. In the case of transparent samples or samples coated with a transparent film, one must handle two scattering interfaces as well as possible interference effects in the film. The resulting light scattering cannot be described by the standard TIS equation. By combining the scalar scattering theory with the Fresnel formalism we have obtained a model which predicts the scattering from a double layer as a function of wavelength. By fitting model calculations to experimental scattering spectra with the interface roughness values as parameters we can extract the rms-roughness values of the two interfaces. The model has been described elsewhere2. Using the scattering spectra and such fitting calculations we can conveniently, and non-destructively, determine the RMS-roughness of a "hidden" interface.