Patent ID: 7038850

Claim:
An apparatus for evaluating a semiconductor wafer comprising: a light source for generating a probe beam; a detector for monitoring the changes in the probe beam after reflection from the sample; and a processor operatively coupled to the detector for evaluating the wafer based on the monitored changes in the probe beam, said evaluation including modeling the diffraction resulting from the interaction of the probe beam with the wafer by defining a zero-th order structure for the wafer, the zero-th order structure including a perturbation domain to represent a scatterer associated with the wafer, the zero-th order structure also including a background material to representing the material within the wafer that is below the scatterer and solving a K space Lippmann-Schwinger equation including terms for a wave function for the zero-th order structure, a Green's function for the zero-th order structure and a perturbation function for the perturbation domain.