Sub-resolution assist features (SRAFs), or scatter bars (SBs), have steadily proliferated through IC manufacturer data preparation flows as k1 is pushed lower with each technology node. The use of this technology is quite common for gate layer at 130 nm and below, with increasingly complex geometric rules being utilized to govern the placement of SBs in proximity to target layer features. Recently, model-based approaches for placement of SBs have arisen. In this work, the variety of rule-based and model-based SB options are explored for the gate layer by using new characterization and optimization functions available in the latest generation of correction and OPC verification tools. The analysis includes the effects of defocus, exposure, and misalignment, and it is shown that significant improvements to CD control through the full manufacturing variability window can be realized.

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