Characterizing the Interface Scaling of High χ Block Copolymers near the Order-Disorder Transition

Advancements in the directed self-assembly of block copolymers (BCPs) have prompted the development of new materials with larger effective interaction parameters (χ_e). This enables BCP systems with phase separation at increasingly small degrees of polymerization (N). Very often these systems reside near the order-disorder transition and fit between the weak and strong segregation limits where the behavior of BCP systems is not as thoroughly understood. Utilizing resonant soft X-ray reflectivity (RSoXR) enables both the BCP pitch (L₀) and interface width (w_M) to be determined simultaneously, through a direct characterization of the composition profile of BCP lamellae oriented parallel to a substrate. A series of high χ_e BCPs with χ_e ranging from ≈0.04 to 0.25 and χ_eN from 19 to 70 have been investigated. The L₀/w_m ratio serves as an important metric for the feasibility of a material for nanopatterning applications; the results of the RSoXR measurement are used to establish a relationship between χ_e and L₀/w_m. The results of this analysis are correlated with experimentally established limits for the functionality of BCPs in nanopatterning applications. These results also provide guidance for the magnitude of χ_e needed to achieve small interface width for samples with sub-10 nm L₀.