The rapid introduction of immersion lithography for NAND flash: challenges and experience

Immersion technology is definitely the mainstream lithography technology for NAND FLASH in recent years since hyper-NA immersion technology drives the resolution limit down to the 40-50 nm half pitch region. Immersion defectivity and overlay issues are key challenges before introducing immersion technology into mass production. In this work, both long term immersion defectivity and overlay data, as well as good photoresist performance, show the Nikon S610C immersion scanner plus LITHIUS i+ cluster is capable of 40-50 nm NAND FLASH mass production. Immersion defects are classified based on their causes, and no tool specific immersion defects, e.g. bubbles and water marks, were found in the Nikon S610C plus TEL LITHIUS i+ cluster. Materials-induced immersion defects require more attention to achieve production-worthy results.