Patent ID: 7321433

Claim:
An apparatus for measuring geometrical profiles of periodic microstructures of a sample, the apparatus comprising a light source for emission of a light beam, polarizing means for polarizing the emitted light beam, focusing means for focusing the polarized light beam on the microstructures of the sample so as to provide, at a number of microstructures, a plurality of illumination angles simultaneously, a collection means for collecting light diffracted from the illuminated microstructures, the collection means being adapted to collect both the 0'th and higher diffraction orders, resolving means for resolving the collected light into diffraction data relating to illumination angles, polarization angles, diffraction orders, and illumination wavelengths, and a reconstruction algorithm for determining the geometrical profile of the illuminated microstructures, the reconstruction algorithm being adapted to perform the following steps: comparing the resolved diffraction data with modeled diffraction data from a known geometrical profile, the comparison taking both the 0'th and higher diffraction orders into account, the known geometrical profile being selected from a database of pre-defined families of profiles, the selection being performed using minimum norm techniques, repeating adjusting the geometrical profile of the known selected geometrical profile until the modeled diffraction data matches the resolved diffraction data within predetermined tolerances.