Unconventional thin film pattern relaxation via direct solvent immersion annealing in a solvent mixture

Direct immersion annealing (DIA) of polymer thin films in a solvent mixture has been found highly effective in block-copolymer ordering, reducing annealing time scales by an order of magnitude. The amount of each solvent in the 'solvent-mixture' is carefully chosen to increase polymer dynamics (with a good solvent) while preventing dewetting (with a non-solvent). We explore the time-scale of selective-solvent diffusion into topographically nanoimprinted films via DIA, by studying the film swelling and the onset of polymer relaxation. Pattern relaxation ("slumping") of PMMA thin films of varying molecular weights (15k - 600k) via DIA is strikingly different from thermal annealing based pattern-relaxation. We observed an "incubation time" corresponding to the diffusion of selective-solvent into the films in presence of a non-solvent. This incubation time changed with the solvent ratio in a non-linear fashion. Surprisingly, the pattern decay dynamics remained unaffected as compared to thermal annealing where the dynamics have been found to couple very well with the slumping temperature. The dependence of solvent diffusion time-scales, film surface tension, as well as the pattern decay dynamics will also be discussed.