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Scatter Bar (SBAR) insertion is a computationally expensive operation. SBAR are usually generated rule-based. SBAR rule tables dictate the insertion of SBAR with different SBAR width dependent on the width of the printable main features and the spacing between the main features and SBAR. Optimization of the SBAR rules drives manufactures to ever more complex SBAR tables which increase the runtime. In advanced process nodes, SBAR printing issues, missing SBAR due to clean-up problems and joining SBAR of different width together remain challenging. On the other hand, pixelized inversion methods may yield optimized SBAR solutions, especially in terms of SBAR placement for contact layers, but comes at the expense of significant computational effort and increased mask writing and inspection time. Since OPC changes the spacing between SBAR and main features, an accurate and optimized SBAR solution requires OPC and SBAR optimization to run interactively.
This work focuses on both line/space and contact layers To ensure fast SBAR optimization, SBAR placement and SBAR width optimization are separated. SBAR of uniform width are placed fast driven by a simple rule-based table comprising only a single SBAR width. This intermediate SBAR layer is subject into a model-based approach, which fragments the SBAR layer based on proximity with respect to the main features or other SBAR, and assigns measurement sites to each SBAR fragment. A model is used to move each SBAR fragment inward or outward so that the image cut line shows a maximum SBAR intensity closer to a predefined SBAR printing threshold. While the main features are unchanged, several iterations are applied to converge the SBAR fragments. Keeping the SBAR fragments fixed, OPC is applied to the main features. Repeating these steps allows optimization of the SBAR width and the OPC simultaneously. Site based as well as contours based verification methods are applied to ensure that the SBAR printing margin has been significantly improved. The improved SBAR printing margin allows manufactures to apply more aggressive SBAR placement rules, which, in addition to the optimized SBAR width, helps to enlarge the depth of focus, therefore, widen the common process window of the lithography process.
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