Defect-Free Perpendicular Diblock Copolymer Films: The Synergy Effect of Surface Topography and Chemistry

Abstract

We propose a direct self-assembly mechanism towards obtaining defect-free perpendicular lamellar phases of diblock copolymer (BCP) thin films. In our numerical study, a thin BCP film having a flat top surface is casted on a uni-directional corrugated solid substrate. The substrate is treated chemically and has a weak preference toward one of the two BCP components. Employing self-consistent field theory (SCFT), we find that there is an enhanced synergy between two substrate characteristics: its topography (geometrical roughness) combined with a weak surface preference. This synergy produces the desired perpendicular lamellar phase with perfect inplane ordering. Defect-free BCP lamellar phases are reproducible for several random initial states, and are obtained for a range of substrate roughness and chemical characteristics, even for a uni-directional multi-mode substrate roughness. Our theoretical study suggests possible experiments that will explore the interplay between uni-directional substrate corrugation and chemical surface treatment. It may lead to viable and economical ways of obtaining BCP films with defect-free lateral alignment.

Effect of Sinusoidal Surface Roughness and Energy on the Orientation of Cylinder-Forming Block Copolymer Thin Films

“…The C 1 is more stable for large u values. Similar effects of u were reported by Man et al 29,30 They showed that increasing u can cause a phase transition from perpendicular to parallel orientation of lamellar phases. This indeed indicates that for both cylinder and lamellae, the substrate preference u can cause a phase transition from perpendicular to parallel orientation.…”

“…This is consistent with the results shown in Figure 4, and also with previous studies. 21,29,30 B. The unidirectional substrate corrugation along the b-direction…”

“…Man et al 29,30 systematically studied the self-assembly of lamellar forming BCP thin film on a sinusoidal substrate, and showed an enhanced synergy between substrate topography combined with a weak surface preference to obtain defect-free perpendicular lamellar BCP thin films. Recently, Carpenter et al 31 presented a study combining SCFT calculations with experimental results, and found that the orientation of cylinders with respect to the trench depends on the commensurability of the BCP hexagonal packing with the substrate characteristic length and film thickness.…”

Metallic Nanomeshes Fabricated by Multimechanism Directed Self-Assembly

“…Similar orthogonal guidance has been reported from a corrugated surface formed from an underlying BCP, , shallow trenches, or steps or facets in the substrate surface, , comprising topographic modulations with comparable feature size to the BCP. An incommensurate domain spacing between the upper and lower layers is required to avoid alignment of the upper microdomains parallel to those in the lower layer. − …”

Defect Removal by Solvent Vapor Annealing in Thin Films of Lamellar Diblock Copolymers

“…In order to facilitate the fabrication of defect-free films, further treatments are needed. As examples to techniques that have been developed to tailor the self-assembly behavior of BCP thin films we mentioned electric field alignment 4,5 , shear alignment 6,7 , microwave annealing 8 , and thermal annealing 1,2,[9][10][11][12][13][14][15][16] . Besides these approaches, solvent vapor annealing (SVA) 1,3,[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] has been used to enhance the mobility of polymer chains, and to facilitate the annihilation of defects.…”