A New Approach to First-order Scalar Rometry Overlays Based on the Introduction of Auxiliary Electromagnetic Fields

摘要

A metrology measuring method and a tool are provided which illuminate a diffraction target fixed by a fixed illumination source and measure a signal composed of a sum of a 0th order diffraction signal and a 1st order diffraction signal, The measuring step is repeated for a plurality of relations between the 0th order diffracted signal and the 1st order diffracted signal while keeping the circle fixed, and the first order diffracted signal is derived from the measured sum. The illumination may be coherent and the measurement may be in the pupil plane or the illumination may be incoherent and the measurement may be in the field plane and in either case a partial overlap of the zeroth and first order diffraction orders is measured . The illumination may be annular and the diffraction target may be a one-cell SCOL target having a periodic structure with a different pitch to separate overlap regions.