Improving humidity-controlled solvent annealing processes for block copolymer poly(ethylene oxide)-b-polystyrene

Abstract

a b s t r a c tThis paper addresses two challenges in humidity-controlled solvent annealing of poly (ethylene oxide)-b-polystyrene thin films: (1) reduction in annealing time by nearly an order of magnitude for toluene under high humidity, which is achieved by decreasing the annealing chamber volume; (2) utilization of two industry-benign solvents, methyl ethyl ketone (MEK) and propylene glycol monomethyl ether acetate (PGMEA), to achieve ordered surface patterns under high humidity. When toluene is employed for annealing, the rate of block copolymer ordering is controlled by the time required to saturate the vapor phase, which depends on the chamber size in this study. The kinetics with MEK and PGMEA are more complex: While saturation time plays a role, these solvents reduce the incompatibility between PS and PEO, so longer annealing times are required to achieve good lateral order. We also present evidence that lateral ordering is faster than lattice swelling in the small chamber, so large grains are achieved without inflating the domain size and periodicity.

Correlating polymer structure, dynamics, and function with atomic force microscopy

“…The presence of solvent vapor plasticizes polymer films while also swelling the BCP domains and mediating block interactions. During SVA, polymer films therefore freely reorganize to adopt a new equilibrium morphology as defined under solvent swollen conditions 99–101 . However, measurements of the quenched state following SVA are complicated by chain collapse, gradients in solvent flow, and surface dewetting upon solvent removal.…”

“…During SVA, polymer films therefore freely reorganize to adopt a new equilibrium morphology as defined under solvent swollen conditions. [99][100][101] However, measurements of the quenched state following SVA are complicated by chain collapse, gradients in solvent flow, and surface dewetting upon solvent removal. For example, Zhang et al showed that thermally annealed PS-b-P2VP films with cylinders, initially oriented perpendicular to the substrate, exhibit dewetting after SVA, with parallel cylinders near the dewetted regions.…”

Solvent-assisted self-assembly of block copolymer thin films

“…[122][123][124] Notably, a suitable selection of the casting solvent and ambient atmosphere conditions can lead to vertically ordered BCP morphologies aligned by the solvent evaporation front. [125][126][127] BCP-evaporating solvent interactions can be leveraged to control macroscopic orientation of domains in deposited thin films. Kowalewski et al utilized the zone casting process, originally developed for obtaining large-area arrays of small molecule single-crystals 128 in which BCP solution is cast from a slit-shaped nozzle onto a slowly moving substrate (Fig.…”

Restructuring in block copolymer thin films: In situ GISAXS investigations during solvent vapor annealing

“…Long tubes may also hamper fast changes of conditions. Chambers with a very small volume and evacuation of the sample chamber before injection of liquid solvent [40,211] have been proposed. This way, the time needed for SVA may be reduced from several hours to several minutes.…”

“…Combining a nonselective with a selective solvent or two solvents being selective for either block and varying the mixing ratio may overcome these limitations and pave the way for a systematic variation of the degree of swelling of the different microdomains. Very detailed studies of the influence of the properties of solvent mixtures on the thin film structures have been reported; however, so far mostly ex-situ investigations have been carried out[92,211,[213][214][215][216][217][218][219].…”