Key factors for maximizing yield in a modern semiconductor fab for Memory device manufacturing include wafer critical dimension uniformity and accuracy control. Resolution Enhancement Techniques (RET) solutions for the highly repetitive arrayed memory devices have been driven by the need for perfect geometric consistency without compromising the lithographic quality. Traditionally, both optical proximity correction (OPC) and sub-resolution assist features (SRAFs) insertion for these repetitive cell-array structures have been dealt by applying manual hand-crafted or rule-based methods. But these can be prone to iterative human intervention, long runtimes and sub-par lithographic quality. This work adopts a pattern/property aware approach (PA)2 and cell-array OPC technology that leverage the inherent repetitive and hierarchical structure of the cell-array to ensure the lithographic quality and perfect geometric consistency and symmetry down to the level of feature edges with model-based OPC and rule-based SRAF solutions. The flow also demonstrates a drastic reduction in runtime and turn-around-time to mask tapeouts for the full chip (core and periphery).
Traditionally, optical proximity correction (OPC) on cell array patterns in memory layout uses simple bias rules to correct hierarchically-placed features, but requires intensive, rigorous lithographic simulations to maximize the wafer process latitude. This process requires time-consuming procedures to be performed on the full chip (excluding the cell arrays) to handle unique cell features and layout placements before (and even sometimes after) OPC. The time required limits productivity for both mask tapeouts and the wafer process development. In this paper, a new cell array OPC flow is introduced that reduces turnaround-time for mask tapeouts from days to hours, while maintaining acceptable OPC quality and the perfect geometric consistency on the OPC output that is critical for memory manufacturing. The flow comprises an effective sub-resolution assist features (SRAFs) insertion and OPC for both the cell array and the peripheral pattern areas. Both simulation and experimental results from actual wafer verification are discussed.