Directed Self-Assembly (DSA) of Block Copolymer Films with Direct Immersion Annealing

The self-assembly of block copolymers into periodic nanostructures has long been studied for their potential use in integrated circuits, nanofiltration devices, metamaterials, energy and data storage devices, and many more applications. Their use, however, is limited by a number of structural and kinetics challenges. The present research describes how a recently developed annealing technique, Direct Immersion Annealing (DIA), can be used to address these challenges. The mechanism that leads to a reduction in domain size of up to as much as 60% for a range of molecular weights of block copolymer during DIA is examined for 1D, 2D, and 3D morphologies. We find that the chain orientation within a structure has a significant impact on the structural rearrangements that occur as the result of constrained swelling. This leads to a reduction of the domain size for out-of-plane structure and an increase in domain size for in-plane structure in the dry film. The non-equilibrium state of the morphology that leads to the reduced domain size leaves the chains in a non- equilibrium conformation that deviates from shape traditionally observed in block copolymers. SANS analysis confirms that the chains take on a flattened disc-like shape in this state. The solvent presence during DIA also presents the ability to tune the interaction parameter of the block, where it is shown that the interface width between domains can be reduced by almost 30% using a selective solvent. Finally, the kinetics of DIA are examined for its ability to rapidly order (30s in best case) neat and nanofilled block copolymer systems. The rapid ordering kinetics of direct immersion annealing are limited to the molecular weight regime where chains are unentangled. At higher molecular weights, the ordering diffusion coefficient scales as N^-2.9.