A report presents a study of the efficacy of shot shifting for reducing stitching errors in diffraction gratings made by electron-beam (E-beam) lithography. Stitching errors arise from fabricating a grating as a mosaic of smaller gratings by frequently translating the grating blank. (This is done because typically, the required size of a grating exceeds that of the field swept by the electron beam.) In shot shifting, each field is written at a fraction of the total electron dose and the stage is moved the same fraction of a field width before writing the next field, so that the averaging effect of shifted multiple passes will suppress errors that arise from miscalibration between beam and translation-stage motions. In the study, a simplified linear model was used to describe the grating-writing process in the spatial-frequency domain. The origin and magnitude of stitching-error spatial-frequency sidebands was demonstrated. The effect of the multipass writing was shown to be equivalent to that of a band-pass filter that selectively nulls nearby sidebands. It was shown that M-order multipass writing suppresses only the nearest M-1 sidebands, and that increasing M results in restrictions on the allowable grating periods.
This work was done by David Dougherty, Paul Maker, and Richard Muller of Caltech for NASA's Jet Propulsion Laboratory.
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Study of Stitching Errors in Shot-Shifted E-Beam Lithography
(reference NPO-21072-) is currently available for download from the TSP library.
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