Effect of Coherence Factor σ and Shifter Arrangement for the Levenson-Type Phase-Shifting Mask

To apply the Levenson-type phase-shifting mask to actual ULSI devices, we have investigated the resolution limit and the depth of focus (DOF) for several shifter arrangements experimentally. Resist patterns were printed using a KrF excimer laser stepper of 0.42 NA. It was suggested that the σ value should be decreased for the various shifter arrangements to obtain higher resolution. Moreover, it was found that resolution capabilities of irregular shifter patterns were higher than those of conventional mask patterns under the condition σ=0.3. In addition, it was found that arrangements where the optical phases for both side apertures are equal should be avoided in the fabrication of 0.30 µm rule devices by a KrF excimer laser exposure with the Levenson-type phase-shifting mask.