(382e) High ? Block Copolymers Based On Hydrogen Bonding Polymers

Directed self-assembly (DSA) of block copolymers (BCPs) is a promising technique for producing sub-30 nm pitch patterning by allowing for pitch multiplication of lithographically derived patterns. However, to achieve pattern pitches below 20 nm, materials with high χ (i.e. the Flory-Huggins interaction parameter) are required.  This is because materials with lower χ values, such as polystyrene-block-polymethylmethacrylate (PS-b-PMMA), phase mix at the low degrees of polymerization that would be required to obtain such a small dimension.  Our approach to designing high χ block copolymers is based on polystyrene blocks attached to blocks which contain strong hydrogen bonding moeties such as alcohols, phenols, and carboxylic acids.  This produces BCPs where each block has relatively strong cohesive interactions with itself, but which are orthogonal to the interactions the other block has with itself.  For example, in polystyrene-block-poly(acrylic acid) (PS-b-PAA), the PS block has strong aromatic and pi-pi interactions with itself, while the PAA block has strong hydrogen bonding, but little-to-none aromatic interactions.  Within this framework, three different polymers have been synthesized using either atom transfer radical polymerization (ATRP) or nitroxide-mediated radical polymerization (NMP): polystyrene-block-poly(acrylic acid) (PS-b-PAA), polystyrene-block- poly(2-hydroxyethyl-methacrylate) (PS-b-PHEMA), and polystyrene-block-poly(4-hydroxystyrene) (PS-b-PHOST).  PS-b-PHEMA and PS-b-PHOST have both shown sub-20 nm pitches with the possibility for sub-10 nm pitches.  The challenges of directed self-assembly of each system and their unique properties will be discussed.