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