Ultrathin Random Copolymer-Grafted Layers for Block Copolymer Self-Assembly

Abstract

Hydroxyl-terminated P(S-r-MMA) random copolymers (RCPs) with molecular weights (Mn) from 1700 to 69000 and a styrene unit fraction of approximately 61% were grafted onto a silicon oxide surface and subsequently used to study the orientation of nanodomains with respect to the substrate, in cylinder-forming PS-b-PMMA block copolymer (BCP) thin films. When the thickness (H) of the grafted layer is greater than 5-6 nm, a perpendicular orientation is always observed because of the efficient decoupling of the BCP film from the polar SiO2 surface. Conversely, if H is less than 5 nm, the critical thickness of the grafted layer, which allows the neutralization of the substrate and promotion of the perpendicular orientation of the nanodomains in the BCP film, is found to depend on the Mn of the RCP. In particular, when Mn = 1700, a 2.0 nm thick grafted layer is sufficient to promote the perpendicular orientation of the PMMA cylinders in the PS-b-PMMA BCP film. A proximity shielding mechanism of the BCP molecules from the polar substrate surface, driven by chain stretching of the grafted RCP molecules, is proposed.

Thermal Approaches to Perpendicular Block Copolymer Microdomains in Thin Films: A Review and Appraisal

“…The OH terminal group was realized via random copolymerization of styrene and methyl methacrylate using a hydroxy‐functionalized 2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO) initiator, resulting in an α‐terminated OH group and ω‐terminated TEMPO group. More recently, a more thermally stable version of P(S‐ r ‐MMA)‐OH synthesized via Activator ReGenerated by Electron Transfer ATRP was reported by Sparnacci et al …”

“…SEM plan‐view images illustrating the evolution of the nanodomain orientation in BCP films deposited on top of P(S‐ r ‐MMA) layers with σ values of ≈0.15 chain nm −2 (top) and ≈0.37 chain nm −2 (bottom). Reproduced with permission . Copyright 2015, American Chemical Society.…”

“…[87] The OH terminal group was realized via random copolymerization of styrene and methyl methacrylate using a hydroxy-functionalized 2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) initiator, resulting in an α-terminated OH group and ω-terminated TEMPO group. More recently, a more thermally stable version of P(S-r-MMA)-OH synthesized via Activator ReGenerated by Electron Transfer ATRP was reported by Sparnacci et al [36] For end-grafted P(S-r-MMA)-OH, the total molecular weight and grafting density (proportional to thickness) are critical factors that influence the orientation of PS-b-PMMA. Insufficiently high molecular weight or grafting density (σ) results in insufficient shielding of the BCP from the polar substrate, usually resulting in parallel or mixed orientation.…”

“…Of these reports, reports that promote perpendicular microdomains via thermal annealing are highly promising because they are easily reproducible and industry friendly. These methods include substrate modification, [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] use of top coats, [24,[47][48][49][50][51][52][53][54][55][56][57] incorporation of additives, [58][59][60][61][62][63][64] exploitation of the architecture effect, [65][66][67][68] use of modified [42,43,[69][70][71] or newly synthesized BCPs, [72][73][74]…”

Technological strategies for self-assembly of PS-b-PDMS in cylindrical sub-10 nm nanostructures for lithographic applications

“…For this system, phase separation can be induced even by simple thermal treatments in a timescale compatible with the requirements of the microelectronics industry [35][36][37] and vertical orientation can be achieved by several techniques including the formation of a suitable random copolymer brush layer onto the silicon substrate prior to the deposition of the DBC thin film [38][39][40]. As the vertical orientation of the nanofeatures occurs for a wide range of DBC film thickness [33,[41][42][43] these DBCs represent interesting scaffolds for the synthesis of lithographic masks with stripes or vertical pillars having tailored characteristic dimensions and heights.…”