DSA process optimization for low-NA EUV extreme pitch contact pattern rectification

As critical dimensions continue to shrink for next-generation devices, stochastic variation is becoming a major challenge for EUV lithography. Directed self-assembly (DSA) provides an opportunity to solve the issue by using block copolymers (BCPs) to self-assemble on top of lithographically defined guiding patterns. EUV-based DSA rectification process involves converting a topographic resist pattern into a chemical pattern via hydrophilic surface treatment of underlayer followed by resist removal, where the chemical pattern acts as a guide to create well-defined BCP structures. As a result, EUV patterns exposed using low dose can be rectified by DSA where CD variation is affected by the selfassembly process rather than EUV stochastics. In this work, we report DSA rectification process for low-NA EUV extreme pitch hexagonal contact holes using a new high-chi BCP, where chi is the Flory-Huggins interaction parameter. We discuss effects of different DSA process parameters such as film thickness, annealing temperature and time, and polar block removal conditions on the resulting local CD uniformity (LCDU), pattern placement error (PPE), and defectivity. After increasing the BCP film thickness, optimizing the thermal annealing conditions (temperature and time), and applying a hybrid develop process, we achieved 62.5% improvement in LCDU and 22.8% improvement in PPE for the high-chi DSA rectified patterns compared to the original low-dose EUV guide patterns.