Patent ID: 7115858

Claim:
An apparatus for measuring one or more parameters of a diffracting structure and at least one underlying layer on a sample, said apparatus comprising: a radiation source that emits broadband radiation; a polarizing element, said radiation passing through said polarizing element toward said sample, said radiation being normally incident on and diffracted by said diffracting structure and at least one underlying layer on said sample, a zeroth order diffracted radiation passing through said polarizing element, at least one of said polarizing element and said sample are rotatable to produce a relative rotation between said polarizing element and said diffracting structure; a spectrograph that detects the intensity of spectral components of said zeroth order diffracted radiation after passing through said polarizing element at a plurality of polarization orientations between said polarizing element and said diffracting structure; wherein said spectrograph produces a spectrograph signal for said spectral components at a plurality of polarization orientations, said apparatus further comprising a computer system for analyzing said spectrograph signal to determine said one or more parameters of said diffracting structure and at least one underlying layer on said sample, said computer system comprising: at least one computer connected to said spectrograph to receive said spectrograph signal; and a computer program executed by said at least one computer, wherein said computer program includes instructions for: extracting spectral information from said spectrograph signal; obtaining an optical model simulating said diffracting structure and at least one underlying layer using at least one variable parameter; obtaining spectral information for said optical model; and curve fitting said spectral information for said optical model to the extracted spectral information to determine said one or more parameters of said diffracting structure and at least one underlying layer on said sample.