Computing a mask that takes into account the variation of exposure and focus [4] has clear economic value. As shown in this article, masks computed for good image fidelity at multiple exposure and focus points are not simple geometric combinations of masks that are computed to optimize print-ability at a single ED point. An approach that takes the entire process window into account can reveal which areas of the design are robust and which will present problems at the edges of the process window. With simple treatments, masks like those shown in Figs. 1 and 2 can be made manufacturable and yield the expected result in silicon [5, 6]. Adoption of this approach requires more extensive calibration of the semiconductor process [7] and new mask computation tooling.
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