PS-b-PAA as a High χ Polymer for Directed Self-assembly: A Study of Solvent and Thermal Annealing Processes for PS-b-PAA

Poly(styrene)-b-poly(acrylic acid) copolymers (PS-b-PAA) was shown to be one promising material for achieving substantially smaller pitch patterns than PS-b-PMMA while still retaining high etch contrast and application for chemoepitaxy. Phase separation of acetone vapor annealed PS-b-PAA (Mw=16,000 g/mol with 50:50 volume ratio of PS: PAA) on PS brush achieved a lamellar morphology with a pattern pitch size (L-0) of 30 nm. However the thermal annealing of the same PS-b-PAA generated a dramatically larger pitch size of 43 nm. SEM and GPC analysis revealed that the intermolecular crosslinking during thermal annealing process has increased the effective N (degree of polymerization), which suggests that even a small amount of crosslinking would lead to big pitch change. Thus, PS-b-PAA is not suitable for fast thermal annealing process as it loses pitch size control due to PAA crosslinking.