Flow-Induced Microdomain Alignment During Block Copolymer Graphoepitaxy

Block copolymer (BCP) graphoepitaxy provides a strategy for advanced nanofabrication based on self-assembly. However, the polymer flow processes that occur due to the topography of the substrates and their effects on the self-assembled microdomain patterns are not well understood. Here, by analyzing film thickness profiles and microdomain morphologies as a function of time during solvent vapor annealing, the time scale of the flow processes (capillary flow and dewetting) and how they determine the in-plane orientation of cylindrical microdomains with respect to the sidewalls of trenches etched in the substrate are revealed. Capillary flow in the first minute of annealing planarizes the film into an incommensurate thickness. The film then dewets through nucleation and growth of islands and holes, which extend either isotropically or anisotropically along the trench axis, depending on film thickness. Isotropic dewetting produces microdomains, which are primarily transverse to the trench sidewalls, whereas anisotropic dewetting promotes alignment parallel to the trench walls. This study demonstrates an intriguing connection between flow-induced microdomain alignment, film thickness, and trench depth during BCP graphoepitaxy, revealing general principles for controlling BCP microdomain orientation over topographical templates.