ERROR SOURCE IDENTIFICATION IN DOT ARRAYS

摘要

A method of error source identification in a dot array comprises the steps of generating a high-density grid pattern of nanoscale dots, for example dots of as little as 7 nanometres diameter at a pitch of 15 to 100 nanometres, on the surface of a substrate by an electron beam lithography machine in accordance with a design embodying a grid with the same dot pitch in two mutually orthogonal directions, i.e. a regular grid. Scanning electron micrographs (13) of individual sample areas of the generated array are then produced and the dot positions in each micrograph (13) and the displacements thereof from the dot positions in the design grid are determined, particularly with use of a fast Fourier transform and an estimated grid (12') representing the design grid, the estimated grid being recalculated as a best fit grid (12") in order to average the dot displacements. The determined displacements are evaluated to identify displacements indicative of systematic writing error and the source of the systematic writing error is identified by comparison of a frequency of the identified displacements with known or possible frequencies associated with errors occurring in machine operation.