Large-area nanostructures manipulation : pattern generation, size modulation and pattern transfer

Abstract

Recently, nanostructures have become vitally crucial in a wide variety of emerging applications. The high-throughput structure generation, precise feature size control, and high-fidelity pattern transfer remain challenging because of various process limitations. Based on interference lithography, several strategies are theoretically and experimentally studied in this dissertation to achieve large-area, high-performance, and versatile nanopatterning. To achieve the nanopatterning of high-aspect-ratio structures, the interference pattern contrast is numerically and experimentally investigated on a home-built phase-locked interference lithography system. Enlarging the exposure latitude for the linewidth control, the sufficient interference pattern contrast is very crucial to achieving the desired feature sizes in the photoresist. Using high-contrast interference fringes for exposure, sub-50-nm, high-aspect-ratio, and wafer-scale nanopatterning can be fabricated in photoresist and the high-aspect-ratio attribute makes the resist pattern well suited for pattern transfer techniques used in nanoimprint mold fabrication. To achieve high-quality IL nanopatterning on diverse substrates, a process optimization strategy is devised to reduce the standing wave based on numerical modeling. Since the multi-layer substrates usually introduce the optical mismatch in the photoresist resulting in the standing wave phenomenon, which significantly affects the nanopattern quality. Using the tri-layer resist process for high-fidelity pattern transfer as an example, the condition of standing wave generation can be quantitatively characterized by calculating the interface reflectance and the electric field distribution of the photoresist. The standing wave reduction can be achieved by well-designing the multi-layer thicknesses before exposure. This systematic numerical analysis can also be extended in complex multi-layer substrates for the perfect nanopatterning using IL. To achieve the nanopatterning on unconventional substrates, a high-fidelity and clean nanotransfer lithography strategy is proposed. The water-soluble material is used as the transfer carrier to fully embed pre-fabricated nanostructures to well maintain the order and triboelectric charges on the carrier surface work as adhesive media to ensure high transfer yield. Based on this, we demonstrate the transfer of nanostructures of high resolution, high aspect ratio, three-dimensional profiles, and various materials. The pattern transfer can be also demonstrated on diverse receivers that can be rigid, soft, planar, or curved, even including a 125-μm-diameter single-mode optical fiber. To achieve the nanopatterning with spatially varying dimensions, a lithographic portfolio that enables precise local dimension tunability is invented. The modulation resolution can be down to the sub-wavelength scale and the modulation area can be up to the wafer scale. Using this novel, high-throughput nanopatterning strategy, 4-inch wafer-scale nanogratings with highly uniform linewidths and 3-inch wafer-scale high-resolution structural color painting are demonstrated. The methods studied in this dissertation can be combined with each other and compatible with most mature nanofabrication techniques, indicating applications in nanoscience and nanotechnology fields such as nanophotonics, meta-optics, biosciences, etc.