Challenges in Forming Sub-10 nm Nanowires via Directed Self-Assembly for Future Applications in Silicon Nanowire Biosensors

In this study, we developed a fabrication method for the formation of well-aligned sub-10 nm nanowire arrays by combining electron-beam lithography (EBL) with the directed self-assembly (DSA) of block copolymers, aimed at the realization of highly sensitive Si nanowire (SiNW) biosensors. Polystyrene-<i>block</i>-poly(dimethylsiloxane) (PS-<i>b</i>-PDMS) was employed to form sub-10 nm PDMS nanowires. The effects of the film thickness and reactive ion etching conditions were systematically investigated to determine the optimal fabrication parameters. To achieve well-aligned PDMS nanowires, hydrogen silsesquioxane (HSQ) guide lines were patterned between electrodes on a silicon-on-insulator (SOI) substrate to direct the orientation of the PDMS domains. Systematic investigations revealed that the morphology of the resulting PDMS nanostructures (dot, dot-and-line, or line) was strongly influenced by local variations in the effective film thickness. Furthermore, a quantitative linear relationship was established between the guide line spacing and the number of PDMS nanowires, demonstrating that the number of nanowires can be precisely controlled by geometric confinement. An incremental increase of approximately 15 nm in the guide line spacing was required for the formation of each additional nanowire. All PDMS nanowires exhibited uniform widths of 9-11 nm, achieving the sub-10 nm feature size required for next-generation biosensor applications. These studies provide a reliable and scalable route for fabricating ordered PDMS nanowire arrays and offer significant potential for the development of a nanoelectronic device with structural dimensions on the 10 nm scale.