Self-assembled block copolymer structures are useful in nanolithography applications, producing patterns with high resolution and throughput. We previously showed control over the direction of in-plane cylindrical microdomains formed by self-assembly of a block copolymer (BCP) using a variety of physical templates made from hydrogen silsesquioxane (HSQ) resist ^{[1] [2]} . The HSQ templates were fabricated by electron-beam lithography and then functionalized with a minority or majority block brush to interact with the BCP and direct the self-assembly (as shown in Figure 1). However, HSQ templates were not easily removed and remained as part of the final pattern. Remaining HSQ caused non-uniform pattern transfer due to dissimilar etch rates between the BCP and HSQ. In this study, we solved this issue by using a removable-resist template coated with an etchable-block brush. We fabricated two- and three-dimensional BCP patterns and then removed the templates. Examples (Figure 2) include three-dimensional bends, junctions and mesh-shaped structures, and the ability to change the BCP morphology through templating.

The negative-tone-post templates were made by electron-beam lithography of poly (methyl methacrylate) (PMMA) resist at high dose (100-600 pC/pixel). After development of patterns using methyl isobutyl ketone (MIBK) and acetone ultrasonication, the surface of the patterns was coated with hydroxyl-terminated polystyrene (PS) brush (1 kg mol^-1). Then poly(styrene-b-dimethylsiloxane) (PS-b-PDMS) BCP (MW=45.5 kg mol^-1, f_PDMS=0.32, period 35 nm) was spun and solvent annealed with a mixture of heptane and toluene. CF₄ and O₂ reactive ion etch (RIE) was used to remove the top PDMS layer and the PS matrix.  The O₂ RIE not only removed not only the PS matrix but also removed the PMMA template in the same step. The final results were in-plane oxidized-PDMS cylindrical microdomain patterns in the form of two- and three-dimensional structures devoid of templates. This study provides a path to complex pattern formation for nanolithography with feature sizes below 20 nm.

1. Yang, J. K. W. et al. Nature Nanotechnology 5, 256-260, 2010.
2. Duan H. et al. Journal of Vacuum Science and Technology B 28 C6C58-C6C62, 2010.