Measurement technique for characterizing odd aberration of lithographic projection optics based on dipole illumination

A dipole illumination based measurement technique for measuring odd aberration of lithographic projection optics is proposed. In the present technique, odd aberration is extracted from the image displacements at multiple illumination settings. Theoretical analysis of the impact of illumination profile on the measurement accuracy is presented. By use of dipole illumination, the image displacement variation range that determines the measurement accuracy is enlarged. Using lithographic simulator PROLITH, the measurement accuracies of odd aberration under conventional illumination and dipole illumination are compared. The simulation results show that the measurement accuracy of odd aberration increases significantly when dipole illumination is used.