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

Abstract

Advancements in the directed self-assembly of block copolymers (BCPs) have prompted the development of new materials with larger effective interaction parameters (<i>χ</i>_e). This enables BCP systems with phase separation at increasingly small degrees of polymerization (<i>N</i>). 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 (<i>L</i>₀) and interface width (<i>w</i>_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 <i>χ</i>_e BCPs with <i>χ</i>_e ranging from ≈0.04 to 0.25 and <i>χ</i>_e<i>N</i> from 19 to 70 have been investigated. The <i>L</i>₀/<i>w</i>_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 <i>χ</i>_e and <i>L</i>₀/<i>w</i>_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 <i>χ</i>_e needed to achieve small interface width for samples with sub-10 nm <i>L</i>₀.