Defect annihilation in block copolymer nanopatterning through solvent immersion annealing

Directed self-assembly (DSA) of block copolymer (BCP) thin films is a promising strategy for fabricating nanoscale patterns. However, defects and limited controllability during processing remain significant barriers to practical implementation. In this study, we introduce solvent immersion annealing (SIA) as a facile and effective approach to improving alignment quality and suppressing defect formation in shear-aligned polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) thin films. By immersing shear-aligned films in solvent mixtures, SIA provides enhanced control over polymer swelling and chain mobility, enabling rapid annihilation of defects and long-range ordering within minutes. Systematic analysis of immersion time, solvent composition, and swelling behavior reveals that the optimal SIA process is achieved by preserving a delicate balance between chain rearrangement and film stability during solvent immersion. Compared to solvent vapor annealing (SVA), SIA offers superior swelling controllability and reduced sensitivity to external factors such as ambient humidity. Furthermore, large-area SEM and GISAXS analyses confirm that SIA enables scalable fabrication of well-aligned nanopatterns across extended surfaces. Taken together, this work highlights SIA as a robust and efficient strategy for achieving BCP nanopatterns with substantially reduced defect density, therefore offering potential for future lithography applications.