Synthesis of High Etch Contrast Poly(3-hydroxystyrene)-Based Triblock Copolymers and Self-Assembly of Sub-5 nm Features

We demonstrate the successful synthesis of a series of poly(3-hydroxystyrene)-block-poly(dimethylsiloxane)-block-poly(3-hydroxystyrene) (P3HS-b-PDMS-b-P3HS) triblock copolymers by atom transfer radical polymerization (ATRP). This system is a promising candidate for pattern transfer of single-digit nanometer features, due to its intrinsic high etch contrast, etch versatility, and the triblock architecture. Hydroxy-terminated PDMS polymers were directly functionalized to initiate the ATRP of an acetal-protected 3-hydroxystyrene monomer. The resulting triblocks have dispersity ranging from 1.10 to 1.26, and the synthesis provides robust control over molecular weights and volume fractions. The large chemical incompatibility between the blocks enabled the formation of ordered structures at low molecular weights, which yielded lamellar periodicities as small as 9.3 nm. This triblock hence permits access to sub-5 nm feature sizes. The phase diagram is asymmetric, with lamellar morphologies observed at lower volume fractions of the P3HS block, relative to the diblocks. This asymmetry is ascribed to the dispersity of the middle block relative to the end blocks.