System for measuring a sample with a layer containing a periodic diffracting structure

Abstract

To measure the critical dimensions and other parameters of a one- or two-dimensional diffracting structure of a film, the calculation may be simplified by first performing a measurement of the thickness of the film, employing a film model that does not vary the critical dimension or parameters related to other characteristics of the structure. The thickness of the film may be estimated using the film model sufficiently accurately so that such estimate may be employed to simplify the structure model for deriving the critical dimension and other parameters related to the two-dimensional diffracting structure.

1 . A method for measuring a sample with a layer containing a periodic diffracting structure, said method comprising:
 directing a first beam of electromagnetic radiation of a plurality of wavelengths at said periodic diffracting structure;   detecting a diffraction of said first beam at said plurality of wavelengths from said diffracting structure;   finding a value for thickness of the layer using a film model of the layer; and   determining one or more parameters related to said diffracting structure using said thickness value and the diffraction detected.