Robust SMO methodology for exposure tool and mask variations in high volume production

A robust source mask optimization (RSMO) methodology has been developed for the first time to decrease variations of critical dimension (CD) and overlay displacement on wafer caused by extremely complex exposure tools and mask patterns. The RSMO methodology takes into account exposure tool variations of source shape, aberrations and mask as well as dose and focus to get source shapes and mask patterns robust to the exposure tool variations. A comparison between the conventional SMO and the new RSMO found that the RSMO improved the edge placement error (EPE) and displacement sensitivity to coma and astigmatism aberrations by 14% and 40%, respectively. Interestingly, even a greatly-simplified source from the RSMO provides totally smaller EPE than uselessly complex source shape from the conventional SMO. Thus, the RSMO methodology is much more effective for semiconductor products with high volume production.