Influence of spin casting solvent on the self‐assembly of silicon‐containing block copolymer thin films via high temperature thermal treatment

Abstract

The present paper focuses on the influence of different solvents (toluene, mesitylene, acetone, tetrahydrofuran, propylene glycol monomethyl ether acetate (PGMEA) and ethyl acetate) on the self‐assembly behaviour of cylinder‐forming polystyrene‐block‐poly(dimethylsiloxane‐random‐vinylmethylsiloxane) diblock copolymer films deposited on thin brush layers of polystyrene (PS) or polymethylmethacrylate (PMMA) polymers grafted to a silicon substrate. The morphology and the key metrics for all samples were determined from the analysis of the SEM images and their evolution was investigated, as a function of the annealing time at 310 °C, for each solvent and for both PS and PMMA brushes. In general, shorter correlation lengths ξ are observed on PS brushes than on PMMA brushes. In addition, SEM data analysis reveals that tetrahydrofuran, PGMEA and ethyl acetate solvents promote a morphological change from fingerprint‐like parallel cylinders to a hexagonally packed dot pattern for annealing time tA > 30 s. Finally, the line edge roughness and linewidth roughness values are weakly dependent on both the casting solvent and the nature of the grafted brush. The reported data reveal that the choice of the polymer brush nature and of the solvent employed during the spin coating of the diblock copolymer film could substantially affect the self‐assembly process and requires accurate optimization due to their subtle interplay. © 2021 Society of Industrial Chemistry.

Polymer Brushes by Grafting to Reaction in Melt: New Insights into the Mechanism

“…Similar reactions in melt require temperature at least higher than the glass/melting transition temperature of the polymer, although it was recently demonstrated that small amounts of solvent remain trapped in the polymer film after the spin-coating process thus increasing the chain mobility during the annealing. [31][32][33] On the other hand, higher grafting densities are obtained by the latter approach due to reduced excluded volume interactions, which are responsible for monomer-monomer repulsion and are predominant in solution. [26,34] An exhaustive investigation of this effect was provided by Auroy through the grafting on silica of a hydroxy-terminated poly(dimethylsiloxane) with molecular weight of 145 000 g mol −1 and solubilized in heptane at different concentrations.…”

Special issue: self‐assembly and bioapplications

“…These building blocks, including natural biomolecules, synthetic molecules, and polymeric micelles, can spontaneously assemble into ordered nanostructures that show promising potential applications in fields of catalysis, energy, optics, and biomedicine 1–6 . Various weaker interactions were employed in polymer self‐assembly systems, resulting in diverse/hierarchical nanomaterials 7–11 . In particular, the nanoassembles formed by synthetic biomacromolecules and amphiphilic copolymers are promising candidates in bio‐related applications 12–15 .…”

“…Perego et al . examined the influence of different solvents on the diblock copolymer films, guiding the precise control of ordered assembled nanostructures 7 . Qiang et al .…”