New variable-transmission illumination technique optimized with design rule criteria

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Abstract
We report on a novel technique for tuning the illumination of a lithography tool through the use of variable transmission apertures. In conjunction with this illumination technique, we have developed simulation software capable of identifying the optimum source plane coherence and intensity distribution to increase process latitude. This 'system' approach is capable of analyzing features specific to a given device level, or selected subsets of structure types within a given level. The fabrication of the aperture involves selectively depositing (alpha) -C onto a quartz plate that is inserted into the illuminator. Experimental testing has shown this film to be stable in its optical properties with extended exposure to DUV light. A description of the simulation software, aperture fabrication techniques, materials used, and experimental results for several aperture configurations are reported.

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