Experimental comparison of off-axis illumination and imaging interferometric lithography

Abstract

Imaging interferometric lithography (IIL) has been proposed recently to extend optical lithography (OL) to the linear systems resolution limit of optics. In this work, a comparison of IIL and OL with off-axis illumination (OAI) is presented with both numerical simulations and experimental verification. In OAI, the optical modulation transfer function decreases at higher spatial frequencies as a result of the inclusion of the same low frequencies in more than one of the incoherently related offset exposures. Pupil plane filters avoid this multiple counting of the low frequency components and improve the pattern fidelity. Different filters provide different tiling of spatial frequency space and result in significant differences in the final patterns. Results of different tiling schemes for both OAI and IIL approaches are discussed. Overall, IIL provides the most robust imaging results.