Patent ID: 8390823

Claim:
A method of determining an approximate structure of an object on a substrate, the method comprising: detecting a diffraction signal arising from illumination of a first region by a radiation beam; detecting an electromagnetic scattering property arising from illumination of a second region by another radiation beam; and determining an approximate structure of the object based on the detected diffraction signal and the detected electromagnetic scattering property, wherein the determining comprises: estimating at least one estimated object structure based on the detected electromagnetic scattering property, determining at least one model diffraction signal from the at least one estimated object structure, comparing the detected diffraction signal to the at least one model diffraction signal, and determining the structure of the object based on the result of the comparison of the detected diffraction signal to the at least one model diffraction signal, wherein the substrate comprises an upper layer and an underlying layer, the substrate comprises the first region, the first region comprising the object, the object comprising a patterned portion of the upper layer and a first portion of the underlying layer, and the substrate further comprising the second region where the upper layer is absent, the second region comprising a second portion of the underlying layer.