Experimental comparison of off-axis illumination and imaging interferometric lithography

Imaging interferometric lithography (IIL) has been proposed recently to ext end optical lithography (OL) to the linear systems resolution limit of opti cs. In this work, a comparison of IIL and OL with off-axis illumination (OA I) is presented with both numerical simulations and experimental verificati on. In OAI, the optical modulation transfer function decreases at higher sp atial frequencies as a result of the inclusion of the same low frequencies in mope than one of the incoherently related offset exposures. Pupil plane filters avoid this multiple counting of the low frequency components and im prove the pattern fidelity. Different filters provide different tiling of s patial frequency space and result in significant differences in the final p atterns. Results of different tiling schemes for both OAI and IIL approache s are discussed. Overall, IIL provides the most robust imaging results. (C) 1999 American Vacuum Society.