Patent ID: 7385697

Claim:
A method of determining the optical constants of a sample system comprising a substrate with at least one thin film on a surface thereof, utilizing a spectroscopic beam of electromagnetic radiation, comprising the steps of: a) obtaining ellipsometric data over a spectroscopic range between FIR and VUV wavelengths and displaying said data as an ellipsometric parameter vs. a parameter which varies with wavelength, said plot being characterized by a range corresponding to longer wavelengths in which said sample system is substantially transparent and typically demonstrates effects of interference resulting from reflections from the surface and at least one thin layer interface therebelow, and a range corresponding to shorter wavelengths in which said plot demonstrates dominant absorption effects; b) proposing a mathematical model of said sample system, said mathematical model comprising parameters which allow determining a selection from the group consisting of: refractive index and extinction coefficient, and real and imaginary parts of the dielectric function; and generating data corresponding to the data in step a and effectively displaying said generated data from said mathematical model; c) selecting a range in said plots in which absorption effects are not dominant, and simultaneously performing regression over said range to set parameter values in said mathematical model to values such that the plots of the obtained and generated data are substantially the same; d) setting the range of wavelengths to a selection from the group consisting of: the entire obtained spectroscopic range; and a portion of the spectroscopic range including the range in which absorbtion effects are dominant and a portion of the spectroscopic range in which absorption effects are not dominant; then performing a selection from the group consisting of: a point by point fit begining in the range in which absorption effects are not dominant, such that refractive index and extinction coefficients or real and imaginary parts of the dielectric function are determined over said selected spectroscopic range; and a simultaneous global regression using wavelengths both inside and outside the spectroscopic range in which absorption effects are not dominant, such that refractive index and extinction coefficients or real and imaginary parts of the dielectric function are determined over said selected spectroscopic range; and e) diplaying at least some determined optical constant data over at least a portion of said spectroscopic range.