Abstract
Recently, we have investigated the effects of radially non-symmetric pupil filters and multiple-pupil exposure sequences in optical lithography [to appear in: Proc. SPIE 2726 (1996)]. Based on numerical simulations we predicted that extremely narrow lines could be delineated using the superposition of exposures with symmetric and anti-symmetric pupil functions. Here, we present experimental results verifying this prediction. Using conventional masks and a pupil filtering i-line stepper with a numerical aperture of 0.4, we were able to achieve linewidths of 0.18 µm in 1.0 µm thick positive photoresist, with a depth of focus of 1 µm.
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