1. A method of performing overlay metrology upon a sample including a substrate with at least two layers formed thereon, the method comprising: scanning an electron beam across a surface of the sample in a scan direction that is substantially collinear or parallel to a first set of linear pattern elements, the first set of linear pattern elements including at least two linear pattern elements corresponding to the at least two layers of the sample; detecting electrons from a scanned portion of the surface of the sample including the first set of linear pattern elements; and determining a spatial offset between the at least two linear pattern elements of the first set of linear pattern elements based upon the detected electrons.