Logic design for printability using OPC methods

The steps that create physical shape data in a typical logic device design-to-reticle flow are cell layout, place and route, tapeout, OPC or RET, data fracture, and reticle build. Here, we define OPC as the transformation of reticle data to compensate for lithographic and process distortions so that the final wafer pattern is as close to the target pattern-the designed layout-as possible. We define RETs as the general class of transformations for reticle data that aim to improve the patterning process window; therefore, OPC is a subset of RET. DFM is traditionally considered to be implemented at the cell layout or routing stages of this flow. Examples include the optimization of a layout based on critical-defect area, the addition of redundant contacts and vias, wire spreading, upsizing of metal landing pads, and the addition of dummy metal tiles to improve the planarity after chemical-mechanical planarization (CMP). We presented a detailed analysis of these techniques in an earlier work. In contrast, this article analyzes the possibility of extending these traditional methods into the OPC stage and introduces new post-tapeout RET methods for improving printability.