Patent ID: 7821654

Claim:
A method for finding a value of one or more parameters of a diffracting structure wherein a measurement is carried out by directing a polychromatic beam of electromagnetic radiation at said diffracting structure and detecting corresponding intensities of a diffraction of said beam at a number of wavelengths from said structure, comprising: measuring intensities of a diffraction from the structure; providing a set of intensity data of the diffraction at the wavelengths corresponding to a first set of values of said one or more parameters; and performing an optimized estimation within a neighborhood of the set of intensity data using said measured intensities to arrive at a second set of values of the one or more parameters; wherein said providing comprises: generating a library of sets of intensity data of the diffraction at the wavelengths, wherein each set of data is generated assuming a corresponding set of values of the one or more parameters, said sets of values of the one or more parameters covering expected ranges of the one or more parameters; and comparing the measured intensities to the sets of data to find the set of intensity data that corresponds to the first set of values of said one or more parameters.