Mask assisted off‐axis illumination technique for random logic

While off‐axis illumination has been demonstrated to improve contrast and depth of focus for low k1, packed line–space (L/S) patterns [S. Asai, I. Hanyu, and K. Hikosaka, J. Vac. Sci. Technol. B 9, 2788 (1991); K. Kamon et al., Jpn. Appl. Phys. 30, 3021 (1991); K. Tounai et al., Proc. SPIE 1674, 753 (1992)], application of this approach to the more discordant patternings associated with random logic levels is suspect. We introduce a conventional mask ‘‘assist’’ feature technique that extends the off‐axis L/S enhancements to more isolated features (both spaces and lines). It will be shown that the effective process window is substantially improved and exhibited proximity effects are mitigated for this technique. Also, a comparison to a phase‐shifting mask solution for the patterning mix expected in random logic layouts is performed. Simulation results are verified on a 0.53 NA, DUV stepper.