Reordering of Self-Assembled Nanostructures in Block Copolymer Thin Films

Abstract

Over the past decades, much attention has been focused on various attempts to effectively control the various self-assembled nanostructures formed by block copolymers (BCPs) in line with the continuously increasing industrial and academic demand for nanostructures. Despite these sublime efforts, the effective application of the nanostructure formed by the block copolymer has not been easily made in the meantime due to the problems of complete control of the structure. A representative example is formation of defects during the self-assembly process, which often hinders the successful leap of BCP nanopatterns into applications in various fields. To avoid the creation of unwanted structures inside BCP nanopatterns, we need to go back to the initial alignment step and resolve them, or selectively remove them from within the structure. Reordering of self-assembled nanostructures is the latter concept. Depending on the requirement of applications, it will sometimes be necessary to further enhance the structural order, change the shape and location, or change the orientation from the initially ordered structures through reordering process. In this thesis, I will describe all of my work during the PhD course on the reordering transition of BCP self-assembly nanopatterns. Firstly, Chapter 1 will briefly introduce nanopatterning with block copolymers, their related requirements, and how they can be met through the reordering process. Next, in Chapter 2, I will suggest a design of reordering strategies and overview of entire works. Chapter 3 introduces basic study of the shear alignment of BCP thin films, which is the initial alignment step in reordering processes. In the Chapter 3, we can easily find that many defective structures are created in shear aligned nanopatterns. Chapter 4 is a study of the reordering of the defect structures found in shear aligned patterns. It will be shown that through the proposed reordering process, the removal of defect structures can be carried out effectively within a large area. Chapter 5 is about creating a block copolymer 2D array through reordering of pattern morphology. This study will show that it is possible to fabricate a uniform crystalline 2D dot array within a large area. Chapter 6 introduces the study of the phenomenon of reordering through disordering from the crystalline 2D structure obtained from the results of Chapter 5. The result of study in Chapter 6 will give a great intuition on the related fields that utilize disordered materials. Such reordering studies within BCP are expected to help a basic understanding of rearrangement not only for BCP but also for various other self-assembled materials.