Can ionic liquid additives be used to extend the scope of poly(styrene)-block-poly(methyl methacrylate) for directed self-assembly?

Abstract

Abstract. Directed self-assembly (DSA) is a promising approach for extending conventional lithographic techniques by being able to print features with critical dimensions under 10 nm. The most widely studied block copolymer system is polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA). This system is well understood in terms of its synthesis, properties, and performance in DSA. However, PS-b-PMMA also has a number of limitations that impact on its performance and hence scope of application. The primary limitation is the low Flory-Huggins polymer-polymer interaction parameter (χ), which limits the size of features that can be printed. Another issue with block copolymers in general is that specific molecular weights need to be synthesized to achieve desired morphologies and feature sizes. Here we explore blending ionic liquid (IL) additives with PS-b-PMMA to increase the χ parameter. ILs have a number of useful properties that include negligible vapor pressure, tunable solvent strength, thermal stability, and chemical stability. The blends of PS-b-PMMA with an IL selective for the PMMA block allowed the resolution of the block copolymer to be improved. Depending on the amount of additive, it is also possible to tune the domain size and the morphology of the systems. These findings may expand the scope of PS-b-PMMA for DSA.

Ionic Liquid for Directed Self-Assembly of PS-<i>b</i>-PMMA

“…It means that the effective χ (χ eff ) of PS-b-PMMA/IL blends system can be increased. The domain size and morphology of the system are depended on amount of IL additive [6][7][8]. Recently, we confirmed that decreasing of L 0 value (L 0 shrink) was caused after long time and/or high temperature annealing in this system.…”

Enhanced vertical ordering of block copolymer films by tuning molecular mass

“…56,57 This approach to increasing segregation strength and the 'quality' of block copolymer ordering has recently been demonstrated in a number of bock copolymer materials 58-62 and Bennett et al 63 have shown the applicability of this approach to ordering in the PS-PMMA block copolymer materials studied in the present paper where an ionic liquid that selectively complexes with the PMMA block was found to lead to large changes in c. 59,60 Of course, the practical use of high molecular mass polymers to enhance the perpendicular orientation of BCP materials is not without difficulties. 56,57 This approach to increasing segregation strength and the 'quality' of block copolymer ordering has recently been demonstrated in a number of bock copolymer materials 58-62 and Bennett et al 63 have shown the applicability of this approach to ordering in the PS-PMMA block copolymer materials studied in the present paper where an ionic liquid that selectively complexes with the PMMA block was found to lead to large changes in c. 59,60 Of course, the practical use of high molecular mass polymers to enhance the perpendicular orientation of BCP materials is not without difficulties.…”

“…56,57 This approach to increasing segregation strength and the 'quality' of block copolymer ordering has recently been demonstrated in a number of bock copolymer materials 58-62 and Bennett et al 63 have shown the applicability of this approach to ordering in the PS-PMMA block copolymer materials studied in the present paper where an ionic liquid that selectively complexes with the PMMA block was found to lead to large changes in c. 59,60 Of course, the practical use of high molecular mass polymers to enhance the perpendicular orientation of BCP materials is not without difficulties. Bennett et al 63 have already made progress in enhancing the ordering PS-PMMA block copolymer lms using ionic liquid additives. 64 However, there are other ways of increasing block copolymer cN besides increasing molecular mass and decreasing temperature.…”

“…The addition of small molecule additives with a selective affinity for one of the blocks provides another strategy for increasing cN to enhance block copolymer ordering in thin lms. 56,57 This approach to increasing segregation strength and the 'quality' of block copolymer ordering has recently been demonstrated in a number of bock copolymer materials [58][59][60][61][62] and Bennett et al 63 have shown the applicability of this approach to ordering in the PS-PMMA block copolymer materials studied in the present paper where an ionic liquid that selectively complexes with the PMMA block was found to lead to large changes in c. 59,60 Of course, the practical use of high molecular mass polymers to enhance the perpendicular orientation of BCP materials is not without difficulties. We inevitably run up against complications associated with the slow rate of BCP ordering associated with lm vitrication at low temperatures and the more serious problem of degradation of the quality of BCP ordering due to dynamic heterogeneity in glass-forming materials at low temperatures.…”

Nanomanufacturing: A Perspective

“…This latter effect is leading to the search for materials with higher Flory-Huggins interaction parameters (χ), 369,370,371 or for small-molecule additives that can be used to drive phase separation. 372,373,374,375,376,377 …”