Improving local critical dimension uniformity (LCDU) is always significant for enlarging process windows and reducing defect rates in lithography, especially for more scaling sub-20nm nodes in DRAM devices. In this study, various strategies are evaluated to improve both ADI and AEI LCDU on one of multiple patterning processes, Litho-Etch-Litho-Etch (LELE) process. Firstly, different advanced photoresists and track recipe optimization methods are explored and evaluated. The best result shows ADI LCDU is improved by 10.0%, and AEI LCDU by 10.3%. Secondly, several source mask optimization (SMO) solutions are tested and ADI and AEI LCDU is improved by 5.5% and 5.7%. Thirdly, new type of photomask, 30% high transmission phase shift mask (HT PSM), is introduced to optimize NILS and MEEF performances. The result shows ADI and AEI LCDU are enhanced by 13.7% and 14.2%. Additionally, etch advanced vertical profile approach can further improve on-device AEI LCDU by 19.0%.
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