Kinetics of defect annihilation in chemo-epitaxy directed self-assembly

Abstract

As a potential solution to next-generation nanolithography, directed self-assembly (DSA) of block copolymers (BCPs) is still restrained in high volume manufacturing primarily due to its defectivity issue. Though defects possess greater free energies than aligned morphologies and are highly energetically unfavorable, they can be kinetically trapped and persist for a long time during annealing. Understanding the kinetics of defect annihilation is crucial to revealing the mechanism of defect formation and to further reducing defectivity in DSA. In this work, we focus on two types of predominant defects in DSA——dislocation and bridge. Statistical analysis of experimental data reveals that dislocation annihilation follows power law, and dislocations are expected to be fully eliminated by long annealing time. On the other hand, bridge defects decrease exponentially with annealing time, and reach a plateau at long annealing time. We also study the impact of annealing temperature and film thickness on annihilation kinetics, and discover that thicker film shows lower bridge density yet significantly slower kinetics. Finally we discuss the impact of etching on bridge reduction. Though these findings are based on polystyrene-b-poly(methyl methacrylate) (PS-<i>b</i>-PMMA), we anticipate they could be applied to other BCP platforms as well.