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12 April 2013 SMO and NTD for robust single exposure solution on contact patterning for 40nm node flash memory devices
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Contact-hole patterning is even more challenging than line/space patterning because of the lower image contrast and smaller process window. To enable single exposure solution of 40-45nm half pitch contact-hole at this nearly resolvable limit of current 1.35NA ArF immersion lithography, negative tone development (NTD) process, source mask co-optimization (SMO) methodology and free-form source were explored in this study. The optimization of free form source and mask for NTD process was firstly carried out via Brion Tachyon SMOTM software. The wafer-level performance was then compared for different mask layout solutions and different mask types. A manufacture worthy process window was achieved for 40nm technology node Flash memory product through the combination of free-from source, SMO and NTD technologies. In the performance comparison for mask types, 6% HTPSM performed wider DoF and exposure latitude for all three pitch designs. But OMOG mask is superior to 6% HTPSM on mask and wafer CD uniformity. To further improve the overlapping process window, preserving the SMO layout solution as possible for the sparse environments and minimizing the SRAF writing errors were proposed as the two most critical tuning knobs.
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Chih-Chieh Yu, C. C. Yang, Elvis Yang, T. H. Yang, K. C. Chen, and Chih-Yuan Lu "SMO and NTD for robust single exposure solution on contact patterning for 40nm node flash memory devices", Proc. SPIE 8683, Optical Microlithography XXVI, 868322 (12 April 2013);

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