Extending the scope of poly(styrene)-block-poly(methyl methacrylate) for directed self-assembly

Abstract

Directed self-assembly (DSA) is a promising technique 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 polystyreneblock-polymethyl methacrylate (PS-b-PMMA). The 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 by DSA. Another issue with block copolymers in general is that specific molecular weights need to be synthesized to achieve desired morphologies and feature sizes. We are exploring blending ionic liquid additiveswithPS-b-PMMAto increase the χ parameter. This allows smaller feature sizes to be accessed by PS-b-PMMA. 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.

Solvent Processing and Ionic Liquid-Enabled Long-Range Vertical Ordering in Block Copolymer Films with Enhanced Film Stability

“…Apparently, the first use of an IL to process a BCP materials was Bennett et al, where it was shown that adding a small amount of IL such as 1-ethyl-3-methylimidazolium bis­(trifluoromethane sulfonyl)­amide (EMIM NTf 2 ) can enhance χ parameter, studied from the domain swelling of the PS-PMMA revealed by small-angle X-ray scattering (SAXS) ( L o ∼ χ 1/6 ), and enable order in a low N system that would not otherwise order. , Moreover, they also found that ILs can induce morphological transition in hexagonally ordered cylindrical films to lamellar morphology when used in excess due to domain swelling of the minority cylinder-forming block. More recently, Chen et al have demonstrated a similar effects in a low M w BCP material to attain nanopattern pitches below 20 nm .…”

“…24 Interestingly, they have also been shown to increase the Flory−Huggins interaction parameter, χ, in BCPs, thereby enabling ordering in low N BCP systems with smaller feature size. 24,25 Apparently, the first use of an IL to process a BCP materials was Bennett et al, where it was shown that adding a small amount of IL such as 1-ethyl-3-methylimidazolium bis-(trifluoromethane sulfonyl)amide (EMIM NTf 2 ) can enhance χ parameter, studied from the domain swelling of the PS-PMMA revealed by small-angle X-ray scattering (SAXS) (L o ∼ χ 1/6 ), and enable order in a low N system that would not otherwise order. 24,25 Moreover, they also found that ILs can induce morphological transition in hexagonally ordered cylindrical films to lamellar morphology when used in excess due to domain swelling of the minority cylinder-forming block.…”

“…In BCPs, such as PS-PMMA, certain ILs were found to associate with the PMMA block of the copolymer and enhance the mobility of the block like a plasticizer, reducing the glass-transition temperature of the BCP . Interestingly, they have also been shown to increase the Flory–Huggins interaction parameter, χ, in BCPs, thereby enabling ordering in low N BCP systems with smaller feature size. , …”

Coarse-Grained Modelling and Temperature Effect on the Morphology of PS-b-PI Copolymer

“…Theoretical and experimental phase diagrams can be used to predict these morphologies formations. The morphology of a copolymer can be influenced by solvents [10,11,12], composition [1,13,14,15], temperature [13,15,16,17,18], external forces [19,20], additives [17,21,22,23,24,25,26], etc. Morphology of copolymer can be useful for a broad range of applications.…”