1. A method for determining overlay error in a semiconductor target, the method comprising: for illumination x-rays having at least one angle of incidence (AOI), obtaining a correlation model that correlates overlay error of a target with a modulation intensity parameter for each of one or more diffraction orders or a continuous diffraction intensity distribution for x-rays scattered from the target in response to the illumination x-rays; illuminating a first target with illumination x-rays having at least one AOI and collecting x-rays that are scattered from the first target in response to the illumination x-rays; and determining an overlay error of the first target based on the modulation intensity parameter of the x-rays collected from the first target for each of the one or more diffraction orders or the continuous diffraction intensity distribution and the correlation model.