A Thermal and Manufacturable Approach to Stabilized Diblock Copolymer Templates
Stabilization of the morphology in thin diblock copolymer films is critical for the generation of robust templates for subsequent device fabrication. Copolymers containing thermally cross-linkable groups, such as benzocyclobutene (BCB), can be annealed to induce an ordered microdomain morphology and then subsequently heated to cross-link the system, locking in the morphology and eliminating the need for multistep processing. Poly[(styrene-r-BCB)-b-lactic acid] (PSBCB-b-PLA) was synthesized by a combination of living free radical and ring-opening polymerizations. Thin films (30 nm) of PSBCB-b-PLA annealed at 170 °C, followed by cross-linking at 200 °C, showed that the ordered and oriented microdomain morphology was preserved. For PSBCB-b-PLA, with PLA volume fractions of 0.24 and 0.36, arrays of cylindrical microdomains of PLA oriented normal to the surface were produced in a cross-linked PS matrix. Washing these films with a weak base degraded and removed the PLA, producing a nanoporous cross-linked template.