Patent ID: 7477405

Claim:
A measurement system configured to determine a critical dimension and a layer characteristic parameter of a structure during production, the system comprising: a stage configured to support the structure during measurements; a measuring unit comprising: an illumination system configured to direct incident light of substantially broad wavelengths band with a predetermined solid angle of light propagation, toward a surface of the structure during a measurement; and a detection system configured to detect light propagating from the surface of the structure during measurements, wherein the measuring unit is configured to generate one or more output signals in response to the detected light during measurements; and a computer system coupled to the measuring unit and configured and operable for receiving and analyzing said output signals to extract spectral information, and fitting said spectral information to reference data to determine said parameters of the patterned structure, wherein said reference data is indicative of weighted diffraction efficiency at plurality of angles of incidence around an average direction of said predetermined solid angle of light propagation toward a surface of the structure during measurement.