Quantitative Three-Dimensional Characterization of Block Copolymer Directed Self-Assembly on Combined Chemical and Topographical Prepatterned Templates

Characterization
of the three-dimensional (3D) structure in directed
self-assembly (DSA) of block copolymers is crucial for understanding
the complex relationships between the guiding template and the resulting
polymer structure so DSA could be successfully implemented for advanced
lithography applications. Here, we combined scanning transmission
electron microscopy (STEM) tomography and coarse-grain simulations
to probe the 3D structure of P2VP-b-PS-b-P2VP assembled on prepatterned templates using solvent vapor annealing.
The templates consisted of nonpreferential background and raised guiding
stripes that had PS-preferential top surfaces and P2VP-preferential
sidewalls. The full 3D characterization allowed us to quantify the
shape of the polymer domains and the interface between domains as
a function of depth in the film and template geometry and offered
important insights that were not accessible with 2D metrology. Sidewall
guiding was advantageous in promoting the alignment and lowering the
roughness of the P2VP domains over the sidewalls, but incommensurate
confinement from the increased topography could cause roughness and
intermittent dislocations in domains over the background region at
the bottom of the film. The 3D characterization of bridge structures
between domains over the background and breaks within domains on guiding
lines sheds light on possible origins of common DSA defects. The positional
fluctuations of the PS/P2VP interface between domains showed a depth-dependent
behavior, with high levels of fluctuations near both the free surface
of the film and the substrate and lower fluctuation levels in the
middle of the film. This research demonstrates how 3D characterization
offers a better understanding of DSA processes, leading to better
design and fabrication of directing templates.