Methods and apparatus for inspection of a structure and associated apparatuses

A method for determining an overlay metric is disclosed including obtaining angle resolved distribution spectrum data relating to a measurement of a target structure including a symmetrical component. An overlay dependent contour of a feature of the target structure is determined from the angle resolved distribution spectrum data, from which an overlay metric is determined. The method includes exposing an exposed feature onto a masked layer including a mask which defines masked and unmasked areas of the layer, such that a first portion of the exposed feature is exposed on a masked area of the layer and a second portion of the exposed feature is exposed on a non-masked area of the layer, the size of the first portion with respect to the second portion being overlay dependent; and performing an etch step to define an etched feature, the etched feature corresponding to the second portion of the exposed feature.