Thin films of symmetric block-copolymers (L-BCP) of polystyrene-b-polymethyl methacrylate (PS-b-PMMA) assume lamellar microstructure parallel to the Silicon substrate due to wetting of the Si oxide layer by the PMMA domain. We investigate the origins of drastically different domain spacing (Lo, predicted by equilibrium melt theory) achieved in dried L-BCP films after immersion in a mixture of controlled good/intermediate/poor solvents, termed direct immersion annealing (DIA), compared to thermal melt annealing. DIA has been shown to produce lameller microdomains (~L<sub>o</sub>/2) that are nearly 50% smaller in size compared to that produced by thermal annealing. We show it is possible to reversibly go from one domain size to the other by switching between these successive annealing techniques. However, there is large asymmetry in the reversible kinetics of the processes due to the different molecular mechanisms involved in the two different techniques. To explore this, neutron reflectivity and atomic force microscopy are used to characterize the surface and bulk film structure. The interesting structural crossover between the two distinct states, and the underlying kinetics of the process by thermal annealing/DIA will be discussed in terms of chain swelling, diffusion and in-plane vs out-of-plane chain junction density evolution.

Reversibility of large domain size change between direct solvent immersion annealing and thermal annealing in lamellar block copolymer films

ACS Spring Meeting 2021

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