A Top Coat with Solvent Annealing Enables Perpendicular Orientation of Sub‐10 nm Microdomains in Si‐Containing Block Copolymer Thin Films

Abstract

Achieving sub‐10 nm high‐aspect‐ratio patterns from diblock copolymer self‐assembly requires both a high interaction parameter (χ, which is determined by the incompatibility between the two blocks) and a perpendicular orientation of microdomains. However, these two conditions are extremely difficult to achieve simultaneously because the blocks in a high‐χ copolymer typically have very different surface energies, favoring in‐plane microdomain orientations. A fully perpendicular orientation of a high‐χ block copolymer, poly(styrene‐block‐dimethylsiloxane) (PS‐b‐PDMS) is realized here using partially hydrolyzed polyvinyl alcohol (PVA) top coats with a solvent annealing process, despite the large surface energy differences between PS and PDMS. The PVA top coat on the block copolymer films under a solvent vapor atmosphere significantly reduces the interfacial energy difference between two blocks at the top surface and provides sufficient solvent concentration gradient in the through‐thickness direction and appropriate solvent evaporation rates within the film to promote a perpendicular microdomain orientation. The effects of interfacial energy differences and the swellability of PVA top coats controlled by the degree of hydrolysis on the orientation of micro­domains are examined. The thickness of the BCP film and top coats also affects the orientation of the BCP film.

Isoporous Block Copolymer Membranes

“…As self-assembled block copolymer fi lms are interesting for many different applications besides separation membranes, casting of block copolymer solutions onto solid substrates has been investigated by many groups. The alignment of the block copolymer's microdomains is infl uenced by parameters like the substrates' topography, [12][13][14] its selectivity of interactions towards the different blocks of a block copolymer, [ 15 ] the top surface, [ 16 ] the liquid treatment of a porous support prior to fi lm casting, [ 17 ] or the fi lm thickness, [ 18 ] and also epitaxial growth of crystalline domains has been studied. [ 19 ] Besides spin-coating or dipcoating also spraying or electrospraying of block copolymer solutions on a solid substrate have been demonstrated to yield well-aligned morphologies in thin fi lms.…”

Topcoat‐Assisted Perpendicular and Straightly Parallel Coexisting Orientations of Block Copolymer Films

“…However, a fully perpendicular orientation of PS-b -PDMS cylindrical microdomains was realized using partially hydrolyzed poly(vinyl alcohol) (PVA) as a topcoat on PS-b -PDMS fi lms and suitable solvent-annealing conditions. [ 27 ] The PVA topcoat signifi cantly reduces interfacial tension differences from ≈20.3 mN m −1 to ≈3.45 mN m −1 and the directional evaporation of solvent annealing also facilitates the formation of perpendicular PS-b -PDMS microdomains.…”

Directed Self‐Assembly of Poly(2‐vinylpyridine)‐b‐polystyrene‐b‐poly(2‐vinylpyridine) Triblock Copolymer with Sub‐15 nm Spacing Line Patterns Using a Nanoimprinted Photoresist Template

“…Russell et al reported the use of a surface‐anchored random copolymer to balance the interfacial interactions of the blocks with the substrates . Willson et al reported the concept of the removable top coating polymer layer, which is neutral to BCP segment blocks, to balance the domain surface energies to obtain sub‐20 nm spacing line patterns . However, the design and removal of topcoat layer is delicate and complicated.…”