(521e) Formation, Stability, and Annihilation of a “Stitch” Morphology in Block Copolymer Thin Films

Authors: 
Bezik, C., University of Chicago
de Pablo, J. J., University of Chicago
Block copolymers are a candidate to be used for lithographic patterning to fabricate
semiconductor devices owing to their ability to spontaneously self-assemble into device
relevant morphologies. Of interest is the ability of symmetric linear diblock copolymers to self-
assemble into a repeating pattern of lines at nanoscale resolution. This process may be
directed using lithographic templates wherein a guiding stripe preferential to one component
of the block copolymer is introduced to guide the assembly over a scale much larger than that
at which the block copolymers would otherwise form regular, defect free structures. It has
been observed previously that when assembling thin films of block copolymers over such
patterns, defective morphologies not predicted by the equilibrium phase diagram may result,
hindering the defect free assembly necessary for industrial applications. In particular, a
“stitch” morphology has been elsewhere experimentally observed, consisting of two unique
domains. Over the guiding stripes are observed lamellae oriented orthogonally to the stripe,
while over the background regions are observed sheets of lamellae parallel to the substrate,
with a poly-styrene domain wetting the surface entirely. In this work, using a theoretically
informed coarse-grained model of block copolymers in conjunction with the string method, we
explore the energetics of the assembly of this stitch morphology. We compare its pathway of
formation to the formation of lamellae as well as its pathway of annihilation and compare to
experimental results. Ultimately, we elucidate the mechanism for the formation of such
structures, address why they arise experimentally, and suggest strategies for avoiding their
formation or accelerating their annihilation.