Dual function of precisely modified hydroxy-PS-b-PMMA as neutral layers and thin films for perpendicularly oriented lamella

Abstract

We propose a facile and fast control method to obtain perpendicularly oriented microphase-separated structures in block copolymer (BCP) thin films for nanopatterning with a BCP lithography technique. By synthesizing a derivative of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) with precisely introduced two hydroxy groups at the junction (PS-(OH)₂-PMMA) and by applying it onto silicon substrates, we investigated the lamellar orientations in PS-(OH)₂-PMMA thin films with respect to the annealing time of neutral layers (NLs) for modifying silicon substrates to neutralize the interfacial free energies between the substrate and each block component in the BCP thin films. Various NLs, including PS-(OH)₂-PMMA itself, were applied onto silicon substrates, and PS-(OH)₂-PMMA has turned out to take a dual role of BCP thin films for nanopatterning and NLs, which shows its supremacy over other methods. PS-(OH)₂-PMMA needs only 20 minutes of annealing to form NLs that sufficiently neutralize the substrates and induce perpendicular lamellae, which is a significant improvement over non-functionalized PS-b-PMMA. This result highlights the enhanced adsorbability of BCP neutral layers by the introduction of only a small amount of hydroxy groups.