US Patent 11841622 Method and apparatus for diffraction-based overlay measurement

A method of overlay error measurement includes disposing a reference pattern module over a substrate. The substrate includes first and second overlay measurement patterns in first and second locations. The reference pattern module includes first and second reference patterns. The method includes creating a first overlap of the first reference pattern with the first overlay measurement pattern and a second overlap of the second reference pattern with the second overlay measurement pattern. The method further includes determining a first overlay error between the first reference pattern of the reference pattern module and the first overlay measurement pattern of the substrate and determining a second overlay error between the second reference pattern and the second overlay measurement pattern. The method also includes determining a total overlay error between the first and second overlay measurement patterns of the substrate based on the first and second overlay errors.