Interfacial Layers with Photoswitching Surface Energy for Block Copolymer Alignment and Directed Self-Assembly

Abstract

A photochemical process for controlling block copolymer (BCP) domain orientation in an area selected manner is described. Polymers with photoswitching surface energy, used as interfacial underlayers adjoining the BCP layer, were synthesized with photoacid labile monomers. The interfacial polymers were designed to be either inherently neutral or preferential to poly(styrene-block-4-trimethylsilylstyrene). Through patternwise exposure to 193nm light and subsequent reaction with photogenerated acid, the wetting characteristics of the underlayer material can be switched from neutral to preferential (N2P) or preferential to neutral (P2N). Thermal annealing of the BCP confined between a patterned N2P or P2N substrate and a neutral top coat results in alternating areas of perpendicular and parallel BCP domains within the same film. If adapted in tandem with directed self-assembly, this approach could enable new routes to customizable patterns for advanced microelectronics and memory devices.

Nanopatterning via Solvent Vapor Annealing of Block Copolymer Thin Films

“…The key to driving the self-assembly process is the annealing step of the thin film, during which the block copolymers undergo nanoscale phase segregation. , Thin films of the block copolymer of interest are typically spin-coated onto a substrate in order to produce smooth films of controlled thicknesses. The substrate surface should be cleaned beforehand in an appropriate manner, with perhaps additional functionalization with a brush layer, or other chemical means. − As-spun films are kinetically trapped in a disordered state due to fast evaporation of solvent and represent the starting point for self-assembly. By far, the two most widely used techniques for annealing of a block copolymer thin film are thermal and solvent vapor annealing, although other recently described and less-developed approaches deserve mention, including light- or laser-promoted photothermal annealing − and the use of shear forces, − electric fields, − solvent immersion, , and magnetic fields − to induce long-range alignment.…”

Self-Assembly of an Ultrahigh-χ Block Copolymer with Versatile Etch Selectivity

“…Studies of block copolymer (BCP) materials and their phase separation in bulk and thin-film form have exploded over the past few decades due to their multitude of applications in lithography − and drug delivery and as biomaterials, rheological modifiers, and mesoporous materials . This is partly because BCPs provide a flexible size and shape tunable platform to create nanostructures over large areas in the 3–200 nm length scale range, using inexpensive materials and processes.…”

Spatial Control of the Self-assembled Block Copolymer Domain Orientation and Alignment on Photopatterned Surfaces

“…Furthermore, pattern transfer blocking can be achieved in a single photolithographic exposure without involving additional processes. This similar concept of using directly patternable orientation layers was previously demonstrated with patterns created by photolithography, ,, electron beam, , and X-ray exposures, but successful DSA of silicon-containing BCPs using photopatternable surface treatments has not yet been demonstrated.…”

“…Previously, we reported photopatternable grafting surface treatments (pGSTs). These surfaces were used to control the orientation of poly­(styrene- block -4-trimethylsilylstyrene) (PS- b -PTMSS), − which has high etch selectivity and can be pattern-transferred . The pGSTs contained an acid-labile functional group and were designed to be either inherently neutral or preferential to one of the BCP domains.…”