Light-sheet Lithography for Generating Micro/Nano-Structures

Over the past few decades, the study of field distribution at the geometrical focus of a lens (PSF) has gained a huge research interest in field ranging from Nanolithography to microscopy. The central theme of this thesis is to study the intricate details of the field distribution through theoretical modelling, computational studies and experimentation. Specifically, spatial filtering techniques have been proposed to understand and manipulate the field distribution for demanding applications. Based on the findings during the theoretical modelling and computational studies we have proposed light sheet based optical lithography technique. Optical lithography (Photolithography) has emerged as an efficient tool for the fabrication of micro/Nanostructures. It uses photon energy to create patterns on the substrate coated with a photosensitive material. The photochemical reactions which are necessary for the fabrication are spatially confined by the 3D extent of the field distribution. Hence the knowledge of field distribution plays a very crucial role in photolithography. State of the art techniques in optical lithography such as, two photon direct laser writing lithography, interference-based lithography techniques and STED Nano-lithography have made optical lithography a highly sought-after technique for the fabrication of micro/Nanostructures. Specifically, two photon direct lithography is used for making complex 3D structures. Interference based lithography techniques are used for fabricating 1D, 2D and 3D periodic Nanostructures whereas, STED Nano-lithography is capable of fabricating diffraction unlimited structures. The first chapter provides an overview of all the keywords and concepts used in photolithography. A brief summary of the emergence of the field is provided along with the development of different optical lithography techniques. The discovery of photopolymerization process and invention of various photoresist systems has helped in the development of photolithography. These techniques have made physics, chemistry and biology accessible to Nano-scale level. An introduction to photoresist systems and them brief classification is given in this chapter. In addition, we have also provided a brief description to recent techniques in photolithography that is widely used for micro/nanofabrication. Understanding these techniques helps us in identifying the novelty of the proposed lithography technique. A brief introduction is given to understand the field distribution/ point spread function (PSF) that provides the foundation for the entire thesis. In the second chapter, we describe the vectoral model for theoretically understanding the PSF for a spherical lens geometry. This is predominantly since the existing lithography techniques relay on spherical lens geometry. In view of demanding applications, the illumination PSF is tailored by employing spatial filtering techniques. We intend to employ spatial filter in order to add new features to lithography and expand its reach. For example, introduction of spatial…