MÉTROLOGIE DE FOCALISATION BASÉE SUR LA DIFFRACTION

摘要

Diffraction-based focus target cells, targets and design and measurement methods are provided, which enable sensitive focus measurements to be carried out by overlay measurement tools. Cells comprise a periodic structure having a coarse pitch and multiple elements arranged at a fine pitch. The coarse pitch is an integer multiple of the fine pitch, with the fine pitch being between one and two design rule pitches and smaller than a measurement resolution and the coarse pitch being larger than the measurement resolution. The elements are asymmetric to provide different amplitudes in +1st and −1st diffraction orders of scattered illumination, and a subset of the elements has a CD (critical dimension) larger than a printability threshold and the other elements have a CD smaller than the printability threshold.