Generation of isofocal target patterns using process modeling during optical proximity correction

Isofocal patterns produce the most ideal manufacturing conditions on a reticle, however, most semiconductor designs contain few isofocal features. A new way of looking at defocus conditions based on the change in intensity with respect to nominal focus [L. S. Melvin III et al. , J. Vac. Sci. Technol. B 23, 2631 (2005)]—referred to as I Δ —can be used to resize the target pattern to isofocal dimensions. The pattern is quantitatively analyzed using I Δ to find modified pattern shapes that give isofocal target patterns for optical proximity correction and/or resolution enhancement techniques. The target pattern is then made isofocal by resizing the pattern to the modified shape prior to the use of optical proximity correction and/or resolution enhancement techniques. Results of this concept demonstrate excellent improvement in the feature robustness of different features at various defocus conditions. The proposed isofocal targeting method can be applied to layers where trade-offs between pattern shape and final pattern fidelity may be manipulated to improve process depth of focus.